EP2095069A2 - Optical computerized method for the 3d measurement of an object by fringe projection and use of a phase-shift method, corresponding system - Google Patents

Optical computerized method for the 3d measurement of an object by fringe projection and use of a phase-shift method, corresponding system

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Publication number
EP2095069A2
EP2095069A2 EP07871965A EP07871965A EP2095069A2 EP 2095069 A2 EP2095069 A2 EP 2095069A2 EP 07871965 A EP07871965 A EP 07871965A EP 07871965 A EP07871965 A EP 07871965A EP 2095069 A2 EP2095069 A2 EP 2095069A2
Authority
EP
European Patent Office
Prior art keywords
illumination
points
fringes
projection
shooting
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP07871965A
Other languages
German (de)
French (fr)
Inventor
Sylvain Fischer
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
PHOSYLAB
Original Assignee
PHOSYLAB
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by PHOSYLAB filed Critical PHOSYLAB
Publication of EP2095069A2 publication Critical patent/EP2095069A2/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
    • G01B11/25—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures by projecting a pattern, e.g. one or more lines, moiré fringes on the object

Definitions

  • the present invention relates to an opticocomputer method for 3D measurement of the complete or near-complete outer surface of a fringed projection object and use of a phase shift method and a corresponding measurement system.
  • the surface characterization and the relief measurement by optical methods are realized thanks to different techniques among which the triangulation, the photogrammetry, the Moiré technique, the interferometry, the holography and the technique of "Speckle".
  • photogrammetry is a widely used technique, but its use is often limited because of a certain complexity of the measurement process and its relatively high cost of implementation.
  • This projection principle is a contactless optical method that is widely recognized as having a high potential for the measurement and characterization of a wide variety of objects.
  • This method makes use of parallel or divergent luminous fringes projected onto the surface of an object by means of a conventional imaging system or a coherent light interference pattern and an image acquisition apparatus whose axis is distinct from that of the fringe projection system.
  • the resulting phase distribution of the bright fringes of the image acquired contains information on the relief of the illuminated surface of the analyzed object. This phase distribution is processed by calculation to reconstruct the relief of the surface of the object.
  • the Phase Shifting Method is a powerful method for reconstructing the phase distribution of a set of light fringes because of its high precision and accuracy. its speed of execution. It has been implemented with a piezoelectric transducer which makes it possible to obtain an offset of the light fringes, ie modulates their phase distribution. Another implementation consists in modulating the wavelength of a laser diode by driving its current, the diode being in a non-compensated interferometer to induce the phase shift of the light fringes. Another alternative for inducing this phase shift of the light fringes is to use a liquid crystal mask in the fringe projection system and to illuminate it in white light.
  • phase shift calibration algorithms using four or five image acquisitions of the light fringes have been developed. These algorithms are very useful for identifying and compensating for measurement error sources such as non-constant phase shift, higher order harmonics in light fringes, and very low signal-to-noise ratios.
  • Other phase shift calibration methods have been developed but they increase the amount of computation and therefore consume many more resources and processor time.
  • the one with two distinct points of view and / or two distinct points of illumination can be associated with an algorithm of stripping of the phase and, this, in order to recover the absolute value and not modulo 2 ⁇ of the phase, ie the value of the phase without ambiguity.
  • the PSM technique is robust, producing a very limited number of erroneous propagation effects.
  • this automatically solves the problems associated with discontinuities of the light fringes which could taint the accuracy of the results or even prevent a correct phase measurement.
  • the analysis algorithm is optimized in terms of time and memory consumption and is therefore easily executed on a personal computer for example.
  • the present invention proposes to improve the PSM technique.
  • the invention is based on a shape reconstruction system of an object by projection of light fringes using the phase shift method (FP-PSM system for "Fringe Projection - Phase Shifting Method") in which a set of illuminated fringes by illuminating a mask with light, which mask is a screen with opaque areas and light-transparent areas, which areas are distributed in a defined pattern, which pattern is produced by transmitting light through the mask wanted set of bright fringes and projected all these light fringes on the surface of an object to be treated.
  • phase shift method FP-PSM system for "Fringe Projection - Phase Shifting Method”
  • Images of the fringed object are acquired with a camera and repeats the acquisition operation several times by moving the set of light fringes in space and between each acquisition so that there is a phase shift of the distribution of the light fringes between each acquired image of the illuminated surface of the object.
  • the acquired images are processed by calculation in a computer, in particular the phase shift of the distribution of the light fringes between each image makes it possible to recover the distributed variations of the height (the relief) of the illuminated surface of the object, visible variations according to the projection axis pair (axis of the light beam projected on the object, also called illumination axis) versus acquisition axis (axis of the image acquisition camera, also called shooting axis).
  • the relief thus recovered is the partial relief of the illuminated surface of the object which includes all the visible details according to the pair projection and acquisition axes.
  • the invention relates to the integration in the FP-PSM system of four fringe projection paths and four image acquisition paths of the surface of an object illuminated by the fringes according to a particular tetrahedral geometry.
  • the projections of the fringes on the object are made according to four incidences from at least one device of illumination of the object by fringes associated (s) with possible means of switching and returning the luminous beam of fringes towards the object and whose illumination points are considered, an illumination point being a point from which emerges the light allowing the direct illumination of the surface of the object by fringes (each point of illumination is therefore along the corresponding incidence, that is to say along the projection axis), the illumination device as a physical entity that can correspond to the point of illumination or be physically shifted from the point of illumination and the illumination returned to the object or, more generally, the illumination device may be divided into several elements, one of which may correspond to the point of illumination as will be seen later.
  • the four points of illumination are placed substantially at the vertices of a tetrahedron (at or near the vertices) at the center of which the object is located.
  • the lines coming from the illumination points and passing through the center of the tetrahedron define the projection / illumination axes of the system (or "bearings" indicated above).
  • the four illumination points are at a sufficient distance from the object so that each pair of illumination points illuminates the surface delimited by the contour seen according to the pseudonormal at said surface which pseudo-normal is the median of the two projection axes in the plane that they define together.
  • the shooting there are four shooting points placed on the medians of the trihedrons formed by the triplets of projection axes or close to these medians, the straight lines from the shooting points and passing by the center of the tetrahedron thus define the axes of shooting.
  • the four points of view are at a sufficient distance from the object so that the fields of view of each pair of points of view include the area defined as previously by the pair of two common neighboring projection axes. to the two axes of shooting of the pair of shooting points.
  • each surface included in the contour defined above is visible by two points of view.
  • the four points of illumination project luminous fringes on the object, each according to its axis of projection, but not necessarily the same set of luminous fringes.
  • the invention relates first of all to an optico-computing method for 3D measurement of the external surface of an object in relief by projecting fringes on said object and using a phase shift method, the fringes being projected on the object by at least one illumination device, images of the fringed object being taken along several axes of shooting with at least one means of shooting, said images being transmitted to a computer equipment comprising a program relief calculation from the images.
  • each projection axis being considered as a point of illumination disposed substantially at each of the four vertices of a virtual tetrahedron, the object being placed substantially in the center of said tetrahedron, and the shots are taken from four points of capture substantially along four axes of view, each of the axes of view being the median (from the center of the tetrahedron) of one of the four trihedrons formed by the four triplets of projection axes, the four points of view being at a distance from the object such that at each point of view, each image includes at least a part of each of the three surfaces of the object that can be illuminated by the three points of illumination of the triplet of projection axes defining by its median the axis of view of said point of view a set of images of each of the six il
  • substantially mean that the points are on the corresponding axis or in its vicinity.
  • the measurement of the external surface must be understood as meaning the measurement of the surface on which the fringes appear projected for the optical acquisition means, any transparent thicknesses at the surface that can not be taken into account since the illumination fringes through.
  • the four illumination points come from at least one and up to four illumination devices by fringes, and in that said device is provided at the illumination points and / or the illuminations said means is redirected by at least one mirror and / or said means are physically movable,
  • the four illumination points come from four independent illumination devices, said devices being arranged at the points of illumination or the illuminations being redirected towards the object,
  • the illumination is redirected towards the object by at least one mirror
  • the four illumination points come from three independent illumination devices,
  • the four illumination points come from two independent illumination devices
  • the four illumination points come from a single illumination device
  • the four illumination points come from a single illumination device, and in that the illumination of said means is redirected along the corresponding projection axis by a set of mirrors,
  • the mirror (s) are active, (the mirrors act as a four-output beam switch) the mirror (s) are controlled by the computer equipment,
  • an illumination source a beam expander and a liquid crystal screen controlled by the computer equipment are used for each illumination device to form a fringe pattern
  • a light source, a beam expander and a liquid crystal screen controlled by the computer equipment are used for each illumination device, in order going towards the object, to form a fringe pattern therein ,
  • two independent and movable imaging means are used which can be moved for at least one of them
  • the shooting axis can be moved by physical displacement of the corresponding shooting means
  • the axis of shooting is movable by redirection by a set of mirrors
  • the means of shooting is of the camera or camera type and makes it possible to capture images that can be transmitted to the computer equipment,
  • the object is sequentially illuminated along the four projection axes, to acquire a set of images of each of the six surfaces that can be illuminated and defined by six pairs of illumination points,
  • the invention relates secondly to a 3D measurement system of the outer surface of a raised object for implementing the method of any one of the preceding claims, which is characterized in that it comprises at least one illumination device of the object with fringes and a part of image acquisition and relief calculation in a computer equipment comprising a program from said images acquired by at least one means of shooting, the illumination device (s) allowing projection on the object of fringes according to four projection axes (final optical path of the fringes towards the object), the origin (real or virtual according to the structure of the illumination device (s)) ) of each projection axis being considered as a point of illumination disposed substantially at each of the four vertices of a virtual tetrahedron, the object being placed substantially in the center of said tetrahedron, and the images are taken at four points of capture substantially along four axes of view, each of the axes of view being the median (from the center of the tetrahedron) of one of the four trihedrons formed by the four triplets
  • the illumination device comprises a light source, a beam expander and a liquid crystal screen controlled by the computer equipment to form a pattern of fringes.
  • the initial pattern of the phase distribution of the luminous fringes is determined in a software manner and can be modified in particular (without any material modification in the preferred version) by a trained operator or software which determines the optimal pattern for a particular object.
  • a trained operator or software which determines the optimal pattern for a particular object.
  • the phase shift is controlled by the processeu r and induced by the mask in an extremely fast time which allows to proceed more r acquisitions of images in milliseconds.
  • the speed of acquisition and processing places the system of the invention in the category of "real time" systems which allows its implementation on the production lines.
  • this non-contact system is well adapted to hostile environments (dirt, vibrations) and does not require any absolute positioning of the object.
  • FIG. 1 which is a known single-channel measurement system of the outer surface of an object
  • Figure 2 which is an example of an algorithm for a two-channel system with an illumination point and two taps
  • FIG. 3 which is an example of an algorithm for a two-channel system with two illumination points and a point of view (2PI / 1PV)
  • FIG. 4 which shows schematically, relative to an object, the illumination points and the projection axes with regard to the means of illumination of the object by fringes as well as the axes of shooting on which are placed the points of view in the case of the tetrahedral multi-channel system of the invention
  • FIG. 4 which shows schematically, relative to an object, the illumination points and the projection axes with regard to the means of illumination of the object by fringes as well as the axes of shooting on which are placed the points of view in the case of the tetrahedral multi-channel system of the invention
  • FIG. 5 which shows the three-dimensional tetrahedral system with, in its simplest version, four liquid crystal screens placed at the four illumination points and from which emerge the luminous fringes projected along each projection / illumination axis and four cameras placed at four points of view.
  • a set of light fringes distributed in the right section of a light beam (the "beam") according to a known initial pattern is generated.
  • the distribution of the fringes can be modeled by a two-dimensional distribution of the phase of the luminous intensity or phase of the luminous fringes in the cross section of the beam.
  • a mathematical function ⁇ then completely describes this phase distribution.
  • All luminous fringes are projected onto the surface of an object whose relief is to be reconstructed.
  • the set of luminous fringes forms on the surface illuminated by the object a distorted image of the initial pattern of all the luminous fringes.
  • the variations of the height, ie the relief of the illuminated surface, cause this deformation of the initial pattern.
  • the image thus formed on the surface is a distribution of the phase of the luminous fringes which results from the modulation of the distribution of the phase of the luminous fringes of the initial pattern by the relief of the illuminated surface.
  • FIG. 1 A known single-channel system for reconstituting the partial relief of the illuminated surface by a fringe pattern is shown in FIG. 1 and comprises for the illumination device of the object 6 by fringes:
  • a uniform light source 1 also called “source”
  • source the most homogeneous possible (homogeneity of the distribution of the light power in the cross section of the emitted beam)
  • beam expander 2 also called “expander” producing, here, a parallel beam 4
  • liquid crystal screen 3 also called a "mask”
  • a reflecting mirror 10 the illumination device thus making it possible to produce an illumination beam along an illumination axis 5, and for the acquisition and processing part:
  • a CCD type 8 camera making it possible to acquire images of the object 6 illuminated by the fringes along a shooting axis 7, a computer equipment 9 (computer / microcomputer) comprising a processor capable of performing calculations according to algorithms on data including the images acquired by the camera, as well as driving the mask to set the fringe pattern.
  • the light source generates the light necessary for illumination through the mask of the surface of the object whose system must reconstruct the relief of the illuminated surface.
  • the beam expander gives a parallel section of the light beam with the dimensions required to properly illuminate the mask and the surface to be illuminated of the object.
  • the position of the source 1 relative to the expander 2 determines the divergence or not of the light beam passing through the mask and illuminates the object.
  • the dimensions of the illuminated surface are not necessarily limited to the dimensions of the mask and may be larger or smaller than the latter.
  • a parallel illumination beam as shown in Figure 1, simplifies the calculations.
  • the axis of the optical system consisting of the source, the expander and the mask which is also the axis of propagation of the light beam is oriented so that the surface of the object is illuminated directly (direct illumination), no other components are needed between the mask and the object. If, in a variant, this axis is initially oriented in a direction that does not pass through the object, then a mirror is placed between the mask and the object and oriented to redirect the initial light beam towards the object in order to properly illuminate the surface with the fringes (indirect illumination).
  • the processor 9 controls the mask 3 to generate all the light fringes according to the desired pattern, controls the camera 8 and stores the images acquired by the camera and proceeds to the calculations necessary to determine the relief of the illuminated surface of the object for example 3D visual reconstruction on a screen.
  • This system is said to be a single channel because it has only a couple or duet of point of illumination and point of view.
  • a two-channel system comprises, for example, on the one hand, a uniform homogeneous light source possible, a beam expander, a liquid crystal display (the mask), an optical beam switch and several mirrors, and, on the other hand, two cameras and a processor.
  • This type of two-channel system has one illumination point and two cameras and is symbolized 1PI / 2PV.
  • the mirrors are distributed and distributed in space so that they can bend a light beam according to one or the other of two possible paths, each path being defined by a system of mirrors that illuminates the surface of the light. object along a projection axis specific to the path.
  • the optical beam switch is driven by the computer and directs the light beam from the mask to one or the other of the mirror systems.
  • the surface of the object is illuminated sequentially according to the two possible pairs of axes of projection and acquisition of the two-channel system.
  • the processor proceeds to the reconstruction of two distinct partial reliefs and thanks to these two reliefs to the reconstruction of the almost complete relief of the illuminated surface of the object.
  • the two partial reliefs reconstructed according to two, the choice, the four possible pairs of axes of projection and acquisition being distinct, it is possible to reconstruct without ambiguity the relief of the illuminated surface of the object through a stripping technique of the phase. This relief is then the quasi-integral relief of the illuminated surface of the object.
  • the mask shapes the initial pattern of the distribution of the object. phase of bright fringes.
  • the processor determines which pixels of the mask should be opaque or transparent to the light of the beam passing through it.
  • the initial pattern is preferably formed in a parallel section of the same beam (non-diverging and non-converging straight beam).
  • the illumination beam may be divergent, but this complicates the process because it is necessary to know the divergence to take it into account in order to correct the surface measurement calculations.
  • the beam illuminates the surface of the object and is either reflected from the surface (opaque surface to beam light, reflection operation) or transmitted to the beam. through the object (object transparent to the light of the beam, operation in transmission).
  • the transparent objects it is however necessary that a fringe pattern is deposited on a surface of the object and is visible
  • the transparent objects are measurable in transmission provided that one of the two faces crossed between the P1 and / the PV does not distort the pattern of the fringes that has formed on the other, otherwise the information is no longer reliable because it is not possible to distinguish between the deformations of the one or the other face of the object.
  • the images formed on the surface of the object and seen from both viewpoints of the two cameras are acquired and digitized by the two cameras that transmit them to the processor.
  • the processor acquires several images of the illuminated surfaces of the object. Between each acquisition, the processor controls the mask so that the initial pattern of the phase distribution of the luminous fringes is shifted in space, ie the distribution of the phase undergoes a desired phase shift and is therefore known. .
  • the processor can then proceed to the necessary calculations: it calculates the phase variations of the phase distribution of the light fringes and proceeds to the stripping of this phase thanks to the two points of view (that is to say that it determines the absolute value and not modulo 2 ⁇ ) which makes it possible to obtain the exact relief of the surface of the object, that is to say without ambiguity.
  • the parts of the surface not visible by one channel are visible by the other which allows to reconstruct almost all the surface illuminated by the two incidences of illumination.
  • FIG. 2 An example of an algorithm that can be used for such a 1 PI / 2PV two-channel system is given in FIG. 2.
  • a two-channel system may alternatively have two illumination points and a camera. It is then symbolized 2PI / 1PV.
  • An example of an algorithm that can be used for such a two-channel 2PI / 1PV system is given in FIG. 3.
  • the system comprises, for example, on the one hand, for the device for illuminating the object with fringes, preferably:
  • the illumination system may comprise other arrangements, in particular in number of sources, expanders, screens and switches whose type is adapted accordingly) and for the acquisition and processing part, preferably:
  • the mirrors are distributed between four mirror systems and distributed in space so that they can bend a light beam according to one or the other of four possible angles, each incidence being defined by a system of mirrors that enables illuminate the surface of the object along a clean projection / illumination axis.
  • the optical beam switch is driven by the computer and directs the light beam from the mask to one or the other of the mirror systems.
  • the surface of the object is sequentially illuminated along the four possible projection / incidence axes of the tetrahedral multi-channel system of the invention.
  • a projection / incidence axis is defined by the segment from the center of the last mirror of each possible path (which mirror reflects the light fringes directly onto the object to illuminate it with fringes) and the center of the illuminated surface.
  • Each last mirror defines an illumination point.
  • the four points of illumination are placed at the vertices of a tetrahedron (or near these vertices) at the center of which is the object to be illuminated. The edges coming from the points of illumination and passing through the center of the tetrahedron merge with the projection axes of the system.
  • the four points of illumination are at a sufficient distance from the object so that each pair of illumination points illuminates the surface delimited by the contour seen according to the pseudo-normal to said surface, which pseudo-normal is the median of the two projection axes in the plane that they define together.
  • Each of the four cameras (or mirror to a camera) is placed at a point on one of the four medians (from the center of the previously defined tetrahedron, with one camera per median) of the four trihedrons formed by the four triplets of projection axes or is placed close to one of these four medians.
  • Each camera is thus placed at a point of view.
  • the edges coming from the points of view and passing through the center of the tetrahedron define the axes of shooting of the system.
  • the four points of view are at a sufficient distance from the object so that the fields of view of each pair of shooting points includes the area defined as previously by the pair of two adjacent projection axes common to both shooting axes of the pair of shooting points.
  • FIG. 4 This arrangement is shown schematically in Figure 4 in which an object is placed in the center O of a tetrahedron whose four vertices PM, PI2, PI3 and PI4 form the four points of illumination. From these four points of illumination start along axes of projection / illumination PM-O, PI2-0, PI3-0 and PI4-0, the light beams bearing fringes and directed towards the center of the tetrahedron and, therefore, illuminating the object with fringes.
  • the four illumination axes make it possible to define four trihedrons formed by triplets of projection axes (triplets of which there are four).
  • the median of each trihedron is the support of a shooting axis and thus there are four shooting axes thus defined, PV1,2, PV2,3, PV3,4 and PV1,4.
  • the processor proceeds to the reconstruction of the distinct partial reliefs defined by each pair of projection and shooting axes and thanks to these reliefs to the unambiguous reconstruction of the almost-complete relief of the various illuminated surfaces of the object. Thanks to the unambiguous and almost integral reconstruction of these illuminated surfaces, the processor proceeds to the unambiguous reconstruction of the quasi-integral relief of the complete outer surface of the illuminated object.
  • the four projection axes make it possible to project fringes on the object but not necessarily the same set of luminous fringes for all the axes.
  • a set of images of each of the six illuminated surfaces defined by the six pairs of illumination points is acquired. These images make it possible to recover the partial reliefs (seen according to the two pairs of axes projection and acquisition defined by two axes of projection and an axis of acquisition or, again, a projection axis and two axes of acquisition or, finally, a projection axis and a shooting axis and another axis of projection and another axis of shooting all four neighbors together) of each of the six illuminated surfaces of the object.
  • quadsi quadsi-integral
  • the invention allowing, when the complete illumination and visualization of the surface are possible, to find the completeness surface details.
  • the luminous fringes used are "analog" in the sense that the transition between the minimum brightness and the maximum brightness is continuous, ie is a grayscale gradient and not an abrupt transition. which would be called “digital".
  • a mask / liquid crystal screen that can be controlled in gray levels is used. This makes it possible to improve the accuracy of the reconstruction of the relief of the illuminated surface of the object.
  • the pitch of the luminous fringes determines the accuracy / resolution of the relief measurement. The smaller this step, the better the measurement accuracy of the PSM method.
  • This accuracy is however also determined by the quality of the other components of the system such as the step of the gray levels that the acquisition camera can distinguish and the resolution of the acquisition camera, namely the periodicity of its pixels .
  • the quality of the image processing algorithm further determines the resolution and measurement accuracy of the PSM method.
  • Each triplet of partial reliefs makes it possible to recover the quasi-integral surface of a hemisphere of the sphere, each hemisphere being illuminated by an illumination point because this point is sufficiently far away from the sphere for this purpose.
  • This example of an object of the spherical type corresponds to an implementation intended more generally for the treatment of an object whose relief of the surface is a priori not known. This implementation requires a complex phasing and is relatively heavy.
  • each illumination axis illuminates a defined area of the surface of the object being treated, which area generally intersects a portion of the area illuminated by each of the other three axes of illumination except exceptionally unfavorable geometry of the object treated. It is understood that it is desirable that it be so to leave no extent of the surface of the treated object not illuminated and therefore not treated.
  • a first configuration called “trivial” includes four light sources, four beam expander, four LCD screens and four cameras.
  • the accuracy of the measurement is the best because the projection of the patterns and the acquisition by the cameras are direct and therefore without deformations of the image fringed by components intermediate.
  • this hardware configuration is relatively expensive.
  • a second configuration comprises a light source, a beam widener, a liquid crystal screen placed immediately after the beam expander, a camera, three optical switches at an input and two outputs (1 X2) and three switches with two inputs and one output (2X1).
  • the three switches 1 X2 are intended to switch the light emitted by the source to one of the four paths each leading to one of the four illumination points by placing a switch 1 X2 at each output of the switch 1 X2 whose input captures the light emitted by the source, the outputs of two downstream switches each feeding one of the paths leading to one of the four illumination points.
  • the three 2X1 switches are intended to switch light from each point of view to the camera by placing a 2X1 switch so that it captures light from two paths coming from two shooting points and a 2X1 switch. so that it captures the light from the other two paths from the other two points of view and placing the third switch 2X1 so that it captures the light from the outputs of the two previous 2X1 switches and its output illuminates the camera.
  • a set of mirrors (preferably "almost perfect") completes the configuration to guide the four paths bringing light to the four points of illumination and the four paths from the four points of view.
  • switches 1 X2 and 2X1 are used which are a switch with one input and four outputs (1 X4) and a switch with four inputs and one output (4X1). ).
  • the switch 1 X4 switches the light emitted by the source to one of the four paths each leading to one of the four illumination points and the switch 4X1 switches the light from each of the four paths from each of the four shooting points to the camera.
  • a set of mirrors completes this configuration in order to orient the four paths leading the light to the four points of illumination and the four paths coming from the four points of view.
  • a third hardware configuration is derived from the second configurations and has the same elements except that there are four liquid crystal screens instead of one, each screen being placed between one of the four illumination points and the object. treaty.
  • the accuracy of the measurement is better than that of the second configurations due to the absence of deformation of the projected patterns, absence due to the elimination of the intermediate components between the liquid crystal displays and the suface of the treated object.
  • the cost of this third hardware configuration is low but slightly higher than the cost of the second configurations.
  • a fourth hardware configuration is derived from the second configurations and provides a compromise between cost and accuracy.
  • This fourth configuration has the same elements as those of the second configurations but with four cameras each placed in one of the four points of view and only three switches 1 X2 or a switch 1 X4 which switch the light emitted by the source to one the four paths leading to the four points of illumination at a time.
  • the accuracy of the measurement obtained is better than that of the second and third configurations because the acquisition by the cameras is di rect and therefore without deformations of the image fringed by intermediate components.
  • the cost is a little higher than those of the second and third configurations but lower than that of the first configuration.
  • a fifth hardware configuration is derived from the fourth configuration and also provides a compromise between cost and accuracy.
  • This fifth configuration has the same elements as those of the fourth configuration but with four liquid crystal screens each placed between one of the four points of illumination and the surface of the object treated.
  • the accuracy of the measurement obtained is better than that of the fourth configuration because the projection of the patterns and the acquisition by the cameras are direct and therefore without deformations of the image fringed by intermediate components.
  • the cost is slightly higher than that of the fourth configuration but lower than that of the first configuration.
  • Each control mode includes different phases of illuminations / acquisitions, some examples of which are provided below.
  • a first modality consists of a complete control in which all the quadruplets defined by an illumination point and three points of view work and that, one after the other (an illumination and three sets of acquisitions).
  • an illumination and three sets of acquisitions For each projection axis, three sets of acquired images are available for processing, one set per axis of view.
  • the information obtained is as complete as possible, but the acquisition time is the least optimized and the use of computer resources is the heaviest.
  • the acquisition time per quadruplet is the same as for a single-channel system (an illumination point, a point of view) but, on the other hand, the Processing time is longer because there is more information to process.
  • the quadruplets may alternatively be defined by a point of view and three adjacent illumination points.
  • three sets of acquired images are available for processing, one set per projection axis.
  • quadruplets three points of illumination / a point of view forces the point of view to acquire all these points. images sequentially, each illumination point illuminating one after the other so as not to destroy the fringe patterns projected by each of the different points of illumination. This last mode of driving However, this is of little interest, especially as regards the acquisition time which is the longest for the tetrahedral multi-channel system of the invention (except colorimetric multiplexing).
  • a second modality consists of a semi-complete piloting.
  • This modality corresponds to the previous one except that some or all quadruplets are reduced to triplets (one point of illumination and only two adjacent points of view) and that only the quadruplets or triplets necessary for the recovery of the quasi-integral relief of the entire surface of the processed object work to avoid unnecessary redundant information.
  • the acquisition time and the use of IT resources are improved.
  • the degree of complexity of the relief of the surface of the object treated and the degree of complexity of the geometry of the same object determine the number of quadruplets and / or triplets necessary for the desired treatment.
  • a third modality consists of an optimized control in which an illumination channel and a camera of an adjacent shooting axis operate at the same time, the different pairs or duets of illumination points / shooting point operating at one and the same time. after others.
  • the duets illumination axis / shooting axis are chosen so that the information necessary for the treatment of the surface of the treated object is sufficient to cover the almost complete relief of this complete surface but is also reduced to minimum necessary for this.
  • two duets have a point of illumination in common and that this is necessary for the good quasi-integral relief coverage of the illuminated surface, it is clear that these two duets must function at the same time, ie constitute again a triplet.
  • three duets with a point of illumination in common they gather in a quadruplet. So the time acquisition is optimized and the use of computer resources also. This piloting procedure is only feasible if the relief and the geometry of the treated object are sufficiently simple.
  • the FP-PSM method is the most suitable for the tetrahedral multi-channel system of the invention, other methods can be implemented with such a system for resolving the integral (or almost integral) relief of the outer surface of an object in three dimensions.
  • the number of light sources, wideners and liquid crystal displays for generation of the fringes can be between one (as described above) and four, the system (s) switching of illumination beams by fringes and reflecting mirrors towards the object being provided accordingly. It may be the same for the number of cameras, between one and four, and with less than four cameras, means (s) switchable (s), displacement (s) camera (s) ...) to allow shooting from the four locations are provided to allow the geometric distribution described.
  • the illumination beam switching system (s) may, in certain embodiments, be combined with the mirrors, the mirror acting as a beam switching means.
  • many applications are possible, simple 3D visualization on 2 D screen, visualization in space by means of 3D visualization, control of a machine for photo-polymerization of 3D objects or a do machining machine ...
  • the invention can be applied to color fringes, several illumination devices, each of one color specific, being implemented for colorimetric multiplexing, the color camera (s) and the computer equipment can differentiate the illumination fringes according to the color during simultaneous illuminations of the object from several illumination points .
  • one or more calibration steps with standard objects can make it possible to take into account and correct various optical aberrations and / or slight shifts in the arrangement of the elements of the system during subsequent measurements on the objects to be measured.

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Abstract

The invention relates to a computerized optical method for the 3D measurement of the external surface of an relief object by fringe projection on said object and use of phase-shift method in which four fringe projection axis are implemented on the object, the origin of each projecting axis being considered as an illumination point located substantially on each summit of a virtual tetrahedron, the object being placed substantially in the centre of said tetrahedron, wherein the exposures are realized from four exposition points located substantially along four exposure axis, each exposure axis being the median of the of the four tetrahedron formed by the four projection axis triplets, the four exposure points being at a distance from the object such that at each exposure point, each image includes at least one part of each of the three surfaces of the object capable of being lighted by the three illumination points of the triple projection axis defining by its median the exposure axis of the said exposure point, and wherein a set of images is acquired in the computer system, of each of the six surfaces capable of being illuminated and defined by six pairs of illumination points. A corresponding system completes the invention.

Description

Procédé optico-informatique de mesure 3D d'un objet en relief par projection de franges et utilisation d'une méthode à décalage de phase, système correspondant Optico-computer method for 3D measurement of an object in relief by projection of fringes and use of a phase shift method, corresponding system
La présente invention concerne un procédé optico- informatique de mesure 3D de la surface extérieure complète ou quasi-complète d'un objet en relief par projection de franges et utilisation d'une méthode à décalage de phase ainsi qu'un système de mesure correspondant.The present invention relates to an opticocomputer method for 3D measurement of the complete or near-complete outer surface of a fringed projection object and use of a phase shift method and a corresponding measurement system.
Elle a des applications en métrologie et peut être associée à toute application aval utilisant des informations 3D comme par exemple la visualisation 3D ou la commande d'outillage.It has applications in metrology and can be associated with any downstream application using 3D information such as 3D visualization or tool control.
La caractérisation de surface et la mesure de relief par des procédés optiques sont réalisées grâce à différentes techniques parmi lesquels la triangulation, la photogrammétrie, la technique de Moiré, l'interférométrie, l'holographie et la technique du « Speckle ». A ce jour, la photogrammétrie est une technique largement employée, mais son utilisation est souvent limitée à cause d'une certaine complexité du processus de mesure et de son coût assez élevé de mise en oeuvre.The surface characterization and the relief measurement by optical methods are realized thanks to different techniques among which the triangulation, the photogrammetry, the Moiré technique, the interferometry, the holography and the technique of "Speckle". To date, photogrammetry is a widely used technique, but its use is often limited because of a certain complexity of the measurement process and its relatively high cost of implementation.
Une autre technique consiste à projeter des franges lumineuses sur les surfaces à analyser. Ce principe de projection est une méthode optique sans contact dont il est communément reconnu qu'elle possède un fort potentiel pour la mesure et la caractérisation d'objets très variés. Cette méthode fait usage de franges lumineuses parallèles ou divergentes projetées sur la surface d'un objet grâce à un système conventionnel d'imagerie ou par une figure d'interférence en lumière cohérente et un appareil d'acquisition d'image dont l'axe est distinct de celui du système de projection de franges. La distribution résultante de phase des franges lumineuses de l'image acquise contient l'information sur le relief de la surface illuminée de l'objet analysé. Cette distribution de phase est traitée par calcul afin de reconstrui re le relief de la surface de l'objet.Another technique is to project bright fringes on the surfaces to be analyzed. This projection principle is a contactless optical method that is widely recognized as having a high potential for the measurement and characterization of a wide variety of objects. This method makes use of parallel or divergent luminous fringes projected onto the surface of an object by means of a conventional imaging system or a coherent light interference pattern and an image acquisition apparatus whose axis is distinct from that of the fringe projection system. The resulting phase distribution of the bright fringes of the image acquired contains information on the relief of the illuminated surface of the analyzed object. This phase distribution is processed by calculation to reconstruct the relief of the surface of the object.
Dans le cadre des techniques utilisant des franges lumineuses, la méthode à décalage de phase (PSM pour « Phase Shifting Method ») est une méthode puissante pour reconstruire la distribution de phase d'un ensemble de franges lumineuses du fait de sa grande précision et de sa rapidité d'exécution. Elle a été mise en oeuvre avec un transducteu r piézo-électrique qui permet d'obtenir u n décalage des franges lumineuses c'est à dire module leur distribution de phase. Une autre mise en œuvre consiste à moduler la longueur d'onde d'une diode laser en pilotant son courant, la diode étant dans un interféromètre non- compensé pour induire le décalage de phase des franges lumineuses. Une autre alternative pour induire ce décalage de phase des franges lumineuses consiste à mettre en oeuvre un masque à cristaux liquide dans le système de projection de franges et à l'illuminer en lumière blanche.As part of light fringe techniques, the Phase Shifting Method (PSM) is a powerful method for reconstructing the phase distribution of a set of light fringes because of its high precision and accuracy. its speed of execution. It has been implemented with a piezoelectric transducer which makes it possible to obtain an offset of the light fringes, ie modulates their phase distribution. Another implementation consists in modulating the wavelength of a laser diode by driving its current, the diode being in a non-compensated interferometer to induce the phase shift of the light fringes. Another alternative for inducing this phase shift of the light fringes is to use a liquid crystal mask in the fringe projection system and to illuminate it in white light.
Toutefois, le calibrage du système qui induit le décalage de phase dans la technique PSM est une étape très critique. Des algorithmes de calibrage du décalage de phase utilisant quatre ou cinq acquisitions de l'image des franges lumineuses ont été développés. Ces algorithmes sont très utiles pour identifier et compenser les sources d'erreurs de mesu re comme le décalage de phase non constant, les harmoniques d'ordre supérieur contenues dans les franges lumineuses et des rapports signal sur bruit très faibles. D'autres méthodes de calibrage du décalage de phase ont été développées mais elles augmentent la quantité de calculs et consomment donc beaucoup plus de ressources et du temps des processeurs. Parmi les techniques PSM, celle à deux points distincts de prise de vue et/ou deux points distincts d'illumination (en fait, le dépouillement de phase peut être effectué avec un point d'illumination et deux points de prise de vue ou , encore, deux points d'illumination et un point de prise de vue ou, encore, deux points d'illumination et deux points de prise de vue) peut être associée à un algorithme de dépouillement de la phase et, ce, dans le but de recouvrer la valeur absolue et non modulo 2π de la phase, c'est à dire la valeur de la phase sans ambiguïté. Avec cette amélioration, la technique PSM est robuste, produit un nombre très limité d'effets de propagation des erreu rs. De plus, cela résout automatiquement les problèmes associés aux discontinuités des franges lumineuses qui pourrait entacher la précision des résultats ou même empêcher une mesure de phase correcte. L'algorithme de dépouillement est optimisé en terme de consommation de temps et de mémoire et est donc facilement exécuté su r un ordinateur personnel par exemple.However, the calibration of the system that induces phase shift in the PSM technique is a very critical step. Phase shift calibration algorithms using four or five image acquisitions of the light fringes have been developed. These algorithms are very useful for identifying and compensating for measurement error sources such as non-constant phase shift, higher order harmonics in light fringes, and very low signal-to-noise ratios. Other phase shift calibration methods have been developed but they increase the amount of computation and therefore consume many more resources and processor time. Among the PSM techniques, the one with two distinct points of view and / or two distinct points of illumination (in fact, the phase stripping can be carried out with one point of illumination and two points of view or again , two points of illumination and a point of view, or two points of illumination and two points of view) can be associated with an algorithm of stripping of the phase and, this, in order to recover the absolute value and not modulo 2π of the phase, ie the value of the phase without ambiguity. With this improvement, the PSM technique is robust, producing a very limited number of erroneous propagation effects. In addition, this automatically solves the problems associated with discontinuities of the light fringes which could taint the accuracy of the results or even prevent a correct phase measurement. The analysis algorithm is optimized in terms of time and memory consumption and is therefore easily executed on a personal computer for example.
La présente invention propose d'améliorer la technique PSM. L'invention est basée sur un système de reconstruction de forme d'un objet par projection de franges lumineuses utilisant la méthode du décalage de phase (système FP-PSM pour « Fringe Projection - Phase Shifting Method ») dans lequel on génère un ensemble de franges lumineuses en illuminant un masque avec de la lumière, lequel masque est un écran avec des zones opaques et des zones transparentes à la lumière, lesquelles zones sont distribuées selon un motif défini, lequel motif produit par transmission de la lumière à travers le masque l'ensemble voulu des franges lumineuses et on projeté l'ensemble de ces franges lumineuses sur la surface d'un objet à traiter. Des images de l'objet frangé sont acquises avec une caméra et on répète plusieurs fois l'opération d'acquisition en déplaçant dans l'espace et entre chaque acquisition l'ensemble des franges lumineuses de sorte qu'il existe un décalage de phase de la distribution des franges lumineuses entre chaque image acquise de la surface illuminée de l'objet. Les images acquises sont traitées par calcul dans un ordinateur, notamment le décalage de phase de la distribution des franges lumineuses entre chaque image permet de recouvrer les variations distribuées de la hauteur (le relief) de la surface illuminée de l'objet, variations visibles selon le couple axe de projection (axe du faisceau lumineux projeté sur l'objet, encore dit axe d'illumination) versus axe d'acquisition (axe de la caméra d'acquisition des images, encore dit axe de prise de vue). Le relief ainsi recouvré est le relief partiel de la surface illuminée de l'objet qui comporte tous les détails visibles selon le couple axes de projection et d'acquisition.The present invention proposes to improve the PSM technique. The invention is based on a shape reconstruction system of an object by projection of light fringes using the phase shift method (FP-PSM system for "Fringe Projection - Phase Shifting Method") in which a set of illuminated fringes by illuminating a mask with light, which mask is a screen with opaque areas and light-transparent areas, which areas are distributed in a defined pattern, which pattern is produced by transmitting light through the mask wanted set of bright fringes and projected all these light fringes on the surface of an object to be treated. Images of the fringed object are acquired with a camera and repeats the acquisition operation several times by moving the set of light fringes in space and between each acquisition so that there is a phase shift of the distribution of the light fringes between each acquired image of the illuminated surface of the object. The acquired images are processed by calculation in a computer, in particular the phase shift of the distribution of the light fringes between each image makes it possible to recover the distributed variations of the height (the relief) of the illuminated surface of the object, visible variations according to the projection axis pair (axis of the light beam projected on the object, also called illumination axis) versus acquisition axis (axis of the image acquisition camera, also called shooting axis). The relief thus recovered is the partial relief of the illuminated surface of the object which includes all the visible details according to the pair projection and acquisition axes.
L'invention porte plus particulièrement sur l'intégration dans le système FP-PSM de quatre voies de projection de franges et quatre voies d'acquisition d'images de la surface d'un objet illuminé par les franges selon une géométrie tétraédrique particulière. A cette fin, les projections des franges sur l'objet se font selon quatre incidences à partir d'au moins un dispositif d'illumination de l'objet par des franges associé(s) avec d'éventuels moyens de commutation et de renvoi du faisceau lumineux de franges vers l'objet et dont on considère les points d'illumination, un point d'illumination étant un point d'où apparaît émerger la lumière permettant l'illumination directe de la surface de l'objet par des franges (chaque point d'illumination est donc le long de l'incidence correspondante, c'est-à-dire le long de l'axe de projection), le dispositif d'illumination en tant qu'entité physique pouvant correspondre au point d'illumination ou être décalée physiquement du point d'illumination et l'illumination renvoyée vers l'objet ou, plus généralement, le dispositif d'illumination peut être réparti en plusieurs éléments dont un peut correspondre au point d'illumination comme on le verra ultérieurement. Dans tous les cas, les quatre points d'illumination sont placés sensiblement aux sommets d'un tétraèdre (aux sommets ou bien près de ces sommets) au centre duquel se trouve l'objet. Ainsi, les droites issues des points d'illumination et passant par le centre du tétraèdre définissent les axes de projection/d'illumination du système (ou « incidences » indiquées ci-dessus). De plus, les quatre points d'illumination sont à distance suffisante de l'objet de sorte que chaque couple de points d'illumination illumine la surface délimitée par le contour vu selon la pseudonormale à ladite surface laquelle pseudo-normale est la médiane des deux axes de projection dans le plan qu'ils définissent ensemble. Pour ce qui concerne la prise de vue, on dispose quatre points de prise de vue placés sur les médianes des trièdres formés par les triplets d'axes de projection ou bien proche de ces médianes, les droites issues des points de prise de vue et passant par le centre du tétraèdre définissent ainsi les axes de prise de vue. De plus, les quatre points de prise de vue sont à distance suffisante de l'objet en sorte que les champs de vision de chaque couple de points de prise de vue incluent la surface définie comme précédemment par le couple des deux axes de projection voisins communs aux deux axes de prise de vue du couple de points de prise de vue. Ainsi, chaque surface incluse dans le contour défini ci- dessus est visible par deux points de prise de vue. Les quatre points d'illumination projètent des franges lumineuses sur l'objet, chacun selon son axe de projection, mais pas obligatoirement le même ensemble de franges lumineuses. On peut acquérir un ensemble d'images de chacune des six surfaces illuminées et définies par les six couples de points d'illumination, lesquelles images permettent de recouvrer les reliefs partiels (vus selon les couples d'axes projection et acquisition définis chacun par un axe de projection et un axe d'acquisition) de chacune des six surfaces illuminées de l'objet, lesquels reliefs partiels permettent de recouvrer fidèlement la quasi-totalité des détails du relief (le relief quasi-intégral) et sans ambiguïté de chacune des six surfaces illuminées de l'objet, lesquels reliefs quasi- intégraux ainsi recouvrés des six surfaces illuminées de l'objet permettent de recouvrer la quasi-intégralité des détails et sans ambiguïté de la surface extérieure complète de l'objet.More particularly, the invention relates to the integration in the FP-PSM system of four fringe projection paths and four image acquisition paths of the surface of an object illuminated by the fringes according to a particular tetrahedral geometry. For this purpose, the projections of the fringes on the object are made according to four incidences from at least one device of illumination of the object by fringes associated (s) with possible means of switching and returning the luminous beam of fringes towards the object and whose illumination points are considered, an illumination point being a point from which emerges the light allowing the direct illumination of the surface of the object by fringes (each point of illumination is therefore along the corresponding incidence, that is to say along the projection axis), the illumination device as a physical entity that can correspond to the point of illumination or be physically shifted from the point of illumination and the illumination returned to the object or, more generally, the illumination device may be divided into several elements, one of which may correspond to the point of illumination as will be seen later. In all cases, the four points of illumination are placed substantially at the vertices of a tetrahedron (at or near the vertices) at the center of which the object is located. Thus, the lines coming from the illumination points and passing through the center of the tetrahedron define the projection / illumination axes of the system (or "bearings" indicated above). In addition, the four illumination points are at a sufficient distance from the object so that each pair of illumination points illuminates the surface delimited by the contour seen according to the pseudonormal at said surface which pseudo-normal is the median of the two projection axes in the plane that they define together. Regarding the shooting, there are four shooting points placed on the medians of the trihedrons formed by the triplets of projection axes or close to these medians, the straight lines from the shooting points and passing by the center of the tetrahedron thus define the axes of shooting. In addition, the four points of view are at a sufficient distance from the object so that the fields of view of each pair of points of view include the area defined as previously by the pair of two common neighboring projection axes. to the two axes of shooting of the pair of shooting points. Thus, each surface included in the contour defined above is visible by two points of view. The four points of illumination project luminous fringes on the object, each according to its axis of projection, but not necessarily the same set of luminous fringes. One can acquire a set of images from each of the six illuminated surfaces and defined by the six pairs of illumination points, which images make it possible to recover the partial reliefs (seen according to the pairs of projection and acquisition axes each defined by a projection axis and an acquisition axis) of each of the six illuminated surfaces of the object, which partial reliefs allow to recover faithfully almost all the details of the relief (the quasi-integral relief) and unambiguously of each of the six illuminated surfaces of the object, which quasi-integral reliefs thus recovered from the six Illuminated surfaces of the object allow to recover almost all the details and unambiguously from the complete outer surface of the object.
Plus précisément, l'invention concerne en premier lieu un procédé optico-informatique de mesure 3D de la surface extérieure d'un objet en relief par projection de franges sur ledit objet et utilisation d'une méthode à décalage de phase, les franges étant projetées sur l'objet par au moins un dispositif d'illumination, des images de l'objet frangé étant prises selon plusieurs axes de prise de vue avec au moins un moyen de prise de vue, lesdites images étant transmises à un équipement informatique comportant un programme de calcul de relief à partir des images.More specifically, the invention relates first of all to an optico-computing method for 3D measurement of the external surface of an object in relief by projecting fringes on said object and using a phase shift method, the fringes being projected on the object by at least one illumination device, images of the fringed object being taken along several axes of shooting with at least one means of shooting, said images being transmitted to a computer equipment comprising a program relief calculation from the images.
Selon l'invention, on met en œuvre quatre axes de projection (trajet optique final des franges vers l'objet) des franges sur l'objet, l'origine (réelle ou virtuelle selon la structure du/des dispositifs d'illumination) de chaque axe de projection étant considéré comme un point d'illumination disposé sensiblement à chacun des quatre sommets d'un tétraèdre virtuel, l'objet étant placé sensiblement au centre dudit tétraèdre, et on réalise les prises de vue à partir de quatre points de prise de vue disposés sensiblement le long de quatre axes de prise de vue, chacun des axes de prise de vue étant la médiane (issue du centre du tétraèdre) d'un des quatre trièdres formés par les quatre triplets d'axes de projection, les quatre points de prise de vue étant à une distance de l'objet telle qu'en chaque point de prise de vue, chaque image inclut au moins une partie de chacune des trois surfaces de l'objet pouvant être éclairée par les trois points d'illumination du triplet d'axes de projection définissant par sa médiane l'axe de prise de vue dudit point de prise de vue, on acquière dans l'équipement informatique un ensemble d'images de chacune des six surfaces pouvant être illuminées et définies par six couples de points d'illumination.According to the invention, four projection axes (final optical path of the fringes towards the object) of the fringes on the object, the origin (real or virtual according to the structure of the illumination device (s)) are used. each projection axis being considered as a point of illumination disposed substantially at each of the four vertices of a virtual tetrahedron, the object being placed substantially in the center of said tetrahedron, and the shots are taken from four points of capture substantially along four axes of view, each of the axes of view being the median (from the center of the tetrahedron) of one of the four trihedrons formed by the four triplets of projection axes, the four points of view being at a distance from the object such that at each point of view, each image includes at least a part of each of the three surfaces of the object that can be illuminated by the three points of illumination of the triplet of projection axes defining by its median the axis of view of said point of view a set of images of each of the six illuminable surfaces defined by six pairs of illumination points is acquired in the computer equipment.
Les termes « sensiblement » signifient que les points sont sur l'axe correspondant ou à son voisinage. La mesure de la surface extérieure doit être comprise comme signifiant la mesure de la surface sur laquelle les franges apparaissent projetées pour les moyens optiques d'acquisition, d'éventuelles épaisseurs transparentes en surface ne pouvant être prises en compte puisque les franges d'illumination les traversent.The terms "substantially" mean that the points are on the corresponding axis or in its vicinity. The measurement of the external surface must be understood as meaning the measurement of the surface on which the fringes appear projected for the optical acquisition means, any transparent thicknesses at the surface that can not be taken into account since the illumination fringes through.
Dans divers modes de mise en œuvre de l'invention, les moyens suivants pouvant être utilisés seuls ou selon toutes les combinaisons techniquement possibles, sont employés :In various embodiments of the invention, the following means can be used alone or in any technically possible combination, are employed:
- on répète les six possibilités d'éclairage avec des motifs de franges différents à chaque fois,- we repeat the six lighting possibilities with different fringe patterns each time,
- les quatre points d'illumination proviennent d'au moins un et jusqu'à quatre dispositifs d'illumination par des franges, et en ce que l'on dispose ledit/lesdits dispositif aux points d'illumination et/ou le/les illuminations dudit/desdits moyens sont redirigées par au moins un miroir et/ou ledit/lesdits moyens sont déplaçables physiquement,the four illumination points come from at least one and up to four illumination devices by fringes, and in that said device is provided at the illumination points and / or the illuminations said means is redirected by at least one mirror and / or said means are physically movable,
- les quatre points d'illumination proviennent de quatre dispositifs d'illumination indépendants, lesdits dispositifs étant disposés aux points d'illumination ou les illuminations étant redirigées vers l'objet,the four illumination points come from four independent illumination devices, said devices being arranged at the points of illumination or the illuminations being redirected towards the object,
- l'illumination est redirigée vers l'objet par au moins un miroir,the illumination is redirected towards the object by at least one mirror,
- les quatre points d'illumination proviennent de trois dispositifs d'illumination indépendants,the four illumination points come from three independent illumination devices,
- les quatre points d'illumination proviennent de deux dispositifs d'illumination indépendants,the four illumination points come from two independent illumination devices,
- les quatre points d'illumination proviennent d'un seul dispositif d'illumination,the four illumination points come from a single illumination device,
- les quatre points d'illumination proviennent d'un seul dispositif d'illumination, et en ce que l'on redirige l'illumination dudit moyen le long de l'axe de projection correspondant par un ensemble de miroirs,the four illumination points come from a single illumination device, and in that the illumination of said means is redirected along the corresponding projection axis by a set of mirrors,
- le/les miroirs sont actifs, (les miroirs font office de commutateur de faisceau à quatre sorties) le/les miroirs sont commandés par l'équipement informatique,the mirror (s) are active, (the mirrors act as a four-output beam switch) the mirror (s) are controlled by the computer equipment,
- on met en œuvre pour chaque dispositif d'illumination une source lumineuse, un élargisseur de faisceau et un écran à cristaux liquide commandé par l'équipement informatique pour y former un motif de franges,an illumination source, a beam expander and a liquid crystal screen controlled by the computer equipment are used for each illumination device to form a fringe pattern,
- on met en œuvre pour chaque dispositif d'illumination, dans l'ordre en allant vers l'objet, une source lumineuse, un élargisseur de faisceau et un écran à cristaux liquide commandé par l'équipement informatique pour y former un motif de franges,a light source, a beam expander and a liquid crystal screen controlled by the computer equipment are used for each illumination device, in order going towards the object, to form a fringe pattern therein ,
-on met en œuvre des franges lumineuses qui sont analogiques, (la transition entre une bande claire et une bande sombre est sensiblement continue par dégradé de niveau de gris)-on implements luminous fringes that are analog, (the transition between a light band and a dark band is substantially continuous by grayscale gradient)
- on met en œuvre quatre moyens de prise de vue indépendants et fixes, qui sont disposés aux points de prise de vue, - on met en œuvre quatre moyens de prise de vue indépendants et fixes, qui sont disposés en dehors des points de prise de vue, des moyens de renvoi de type miroirs étant placés aux points de prise de vue pour renvoyer les images vers le moyen de prise de vue correspondant,four independent and fixed means of shooting are used, which are arranged at the points of view, four independent and fixed shooting means, which are arranged outside the shooting points, are implemented, mirror-type return means being placed at the shooting points in order to send the images back to the recording means; matching shot,
- on met en œuvre trois moyens de prise de vue indépendants et d'axe de prise de vue déplaçable pour au moins l'un d'entre eux,three independent shooting means and a movable axis of view are used for at least one of them,
- on met en œuvre deux moyens de prise de vue indépendants et d'axe de prise de vue déplaçable pour au moins l'un d'entre eux,two independent and movable imaging means are used which can be moved for at least one of them,
- on met en œuvre un seul moyen de prise de vue et d'axe de prise de vue déplaçable,a single means of shooting and movable axis of shooting is implemented,
- l'axe de prise de vue est déplaçable par déplacement physique du moyen de prise de vue correspondant,the shooting axis can be moved by physical displacement of the corresponding shooting means,
- l'axe de prise de vue est déplaçable par redirection par un jeu de miroirs,- The axis of shooting is movable by redirection by a set of mirrors,
- le moyen de prise de vue est de type caméra ou appareil photo et permet de capter des images qui peut être transmises à l'équipement informatique,the means of shooting is of the camera or camera type and makes it possible to capture images that can be transmitted to the computer equipment,
- pour les prises de vue on illumine séquentiellement l'objet selon les quatre axes de projection, pour acquérir un ensemble d'images de chacune des six surfaces pouvant être illuminées et définies par six couples de points d'illumination,for the shots, the object is sequentially illuminated along the four projection axes, to acquire a set of images of each of the six surfaces that can be illuminated and defined by six pairs of illumination points,
L'invention concerne en second lieu un système de mesure 3D de la surface extérieure d'un objet en relief pour la mise en œuvre du procédé de l'une quelconque des revendications précédentes, qui est caractérisé en ce qu'il comporte au moins un dispositif d'illumination de l'objet par des franges et une partie d'acquisition d'images et de calcul de relief dans un équipement informatique comportant un programme à partir desdites images acquises par au moins un moyen de prise de vue, le/les dispositifs d'illumination permettant la projection sur l'objet de franges selon quatre axes de projection (trajet optique final des franges vers l'objet), l'origine (réelle ou virtuelle selon la structure du/des dispositifs d'illumination) de chaque axe de projection étant considéré comme un point d'illumination disposé sensiblement à chacun des quatre sommets d'un tétraèdre virtuel, l'objet étant placé sensiblement au centre dudit tétraèdre, et les prises de vue sont effectuées à quatre points de prise de vue disposés sensiblement le long de quatre axes de prise de vue, chacun des axes de prise de vue étant la médiane (issue du centre du tétraèdre) d'un des quatre trièdres formés par les quatre triplets d'axes de projection, les quatre points de prise de vue étant à une distance de l'objet telle qu'en chaque point de prise de vue, chaque image inclut au moins une partie de chacune des trois surfaces de l'objet pouvant être éclairée par les trois points d'illumination du triplet d'axes de projection définissant par sa médiane l'axe de prise de vue dudit point de prise de vue, et en ce que l'équipement informatique comporte des moyens pour acquérir un ensemble d'images de chacune des six surfaces pouvant être illuminées et définies par six couples de points d'illumination.The invention relates secondly to a 3D measurement system of the outer surface of a raised object for implementing the method of any one of the preceding claims, which is characterized in that it comprises at least one illumination device of the object with fringes and a part of image acquisition and relief calculation in a computer equipment comprising a program from said images acquired by at least one means of shooting, the illumination device (s) allowing projection on the object of fringes according to four projection axes (final optical path of the fringes towards the object), the origin (real or virtual according to the structure of the illumination device (s)) ) of each projection axis being considered as a point of illumination disposed substantially at each of the four vertices of a virtual tetrahedron, the object being placed substantially in the center of said tetrahedron, and the images are taken at four points of capture substantially along four axes of view, each of the axes of view being the median (from the center of the tetrahedron) of one of the four trihedrons formed by the four triplets of projection axes, the four shooting points being at a distance from the object such that at each point of view, each image includes at least a portion of each of the three surfaces of the object that can be illuminated by the three points s of illumination of the triplet of projection axes defining by its median axis of view of said point of view, and in that the computer equipment comprises means for acquiring a set of images of each of the six surfaces that can be illuminated and defined by six pairs of illumination points.
Dans une variante de mise en œuvre du système, le dispositif d'illumination comporte une source lumineuse, un élargisseur de faisceau et un écran à cristaux liquide commandé par l'équipement informatique pour y former un motif de franges.In an alternative embodiment of the system, the illumination device comprises a light source, a beam expander and a liquid crystal screen controlled by the computer equipment to form a pattern of fringes.
La combinaison d'une instrumentation rapide et facilement transportable et d'un logiciel robuste étend la possibilité de mise en oeuvre de la technique de projection de franges et de la méthode du décalage de phase pour la reconstruction du relief d'un objet jusqu'aux sites de production. Ainsi elle a l'avantage de pouvoir être utilisée dans des systèmes de tri rapide d'objets avec un taux d'erreur quasiment nul des industries de recyclage (par exemple tri par type et recyclage des cartouches d'encre d'imprimantes), des systèmes de contrôle-qualité en ligne et en temps réel des industries de la mécanique de précision (par exemple presses rapides de précision) ou pour répondre aux besoins en systèmes de contrôle- qualité rapide des industries produisant sur chaînes d'assemblage (par exemple contrôle de la justesse du montage des éléments à assembler dans le compartiment moteur ou l'habitacle d'un véhicule dans l'industrie automobile).The combination of fast and easily transportable instrumentation and robust software extends the possibility of fringe projection technique and phase shift method for reconstructing the relief of an object up to production sites. So it has the advantage of being able to be used in fast object sorting systems with almost zero error rate of recycling industries (eg sorting by type and recycling of printer ink cartridges), online quality control systems and real-time precision engineering industries (eg fast precision presses) or to meet the needs of fast quality control systems of industries producing on assembly lines (eg control of the correctness of assembly of the elements to be assembled in the engine compartment or the passenger compartment of a vehicle in the automotive industry).
Grâce à l'invention, le motif initial de la distribution de phase des franges lumineuses est déterminé de façon logicielle et peut être notamment modifié (sans modification matérielle dans la version préférée) par un opérateur formé ou un logiciel qui détermine le motif optimal pour un traitement donné moyennant quelques informations saisies par l'opérateur et portant sur la taille de l'objet, la nature de sa surface, les zones de sa surface à traiter etc, voi re modifié automatiquement par une série de mesures itératives d'adaptation. De plus, le décalage de phase est commandé par le processeu r et induit par le masque dans un délai extrêmement rapide ce qui permet de procéder à plusieu rs acquisitions d'images en quelques millisecondes. Ainsi, la rapidité d'acquisition et de traitement place le système de l'invention dans la catégorie des systèmes «temps réel » ce qui permet sa mise en oeuvre su r les chaînes de production. Enfin , ce système sans contact est bien adapté aux envi ronnements hostiles (saleté, vibrations) et ne nécessite aucun positionnement absolu de l'objet.Thanks to the invention, the initial pattern of the phase distribution of the luminous fringes is determined in a software manner and can be modified in particular (without any material modification in the preferred version) by a trained operator or software which determines the optimal pattern for a particular object. given treatment with some information entered by the operator and relating to the size of the object, the nature of its surface, the areas of its surface to be treated etc, it is modified automatically by a series of iterative adaptation measures. In addition, the phase shift is controlled by the processeu r and induced by the mask in an extremely fast time which allows to proceed more r acquisitions of images in milliseconds. Thus, the speed of acquisition and processing places the system of the invention in the category of "real time" systems which allows its implementation on the production lines. Finally, this non-contact system is well adapted to hostile environments (dirt, vibrations) and does not require any absolute positioning of the object.
La présente invention va maintenant être exemplifiée sans pour autant en être limitée avec la description qui suit en relation avec les figures suivantes: la Figure 1 qui est un système connu de mesure à un seul canal de la surface extérieure d'un objet, la Figure 2 qui est un exemple d'algorithme pour un système à deux canaux avec un point d'illumination et deux points de prise de vue (1PI/2PV), la Figure 3 qui est un exemple d'algorithme pour un système à deux canaux avec deux points d'illumination et un point de prise de vue (2PI/1PV), la Figure 4 qui représente schématiquement, par rapport à un objet, les points d'illumination et les axes de projection pour ce qui concerne les moyens d'illumination de l'objet par des franges ainsi que les axes de prise de vue sur lesquels sont placés les points de prise de vue dans le cas du système multi-canaux tétraédrique de l'invention, etThe present invention will now be exemplified without being limited thereto with the description which follows in relation to the following figures: Figure 1 which is a known single-channel measurement system of the outer surface of an object, Figure 2 which is an example of an algorithm for a two-channel system with an illumination point and two taps FIG. 3 which is an example of an algorithm for a two-channel system with two illumination points and a point of view (2PI / 1PV), FIG. 4 which shows schematically, relative to an object, the illumination points and the projection axes with regard to the means of illumination of the object by fringes as well as the axes of shooting on which are placed the points of view in the case of the tetrahedral multi-channel system of the invention, and
La figure 5 qui représente le système tétraédrique en trois dimensions avec, dans sa version la plus simple, quatre écrans à cristaux liquides placés aux quatre points d'illumination et d'où émergent les franges lumineuses projetées selon chaque axe de projection/illumination et quatre caméras placées aux quatre points de prise de vue.FIG. 5, which shows the three-dimensional tetrahedral system with, in its simplest version, four liquid crystal screens placed at the four illumination points and from which emerge the luminous fringes projected along each projection / illumination axis and four cameras placed at four points of view.
Le principe général à la base de l'invention va maintenant être présenté. Un ensemble de franges lumineuses distribuées dans la section droite d'un faisceau lumineux (le « faisceau ») selon un motif initial connu est généré. Le motif étant connu, la distribution des franges peut être modélisée par une distribution en deux dimensions de la phase de l'intensité lumineuse ou phase des franges lumineuses dans la section droite du faisceau. Une fonction mathématique φ décrit alors complètement cette distribution de phase.The general principle underlying the invention will now be presented. A set of light fringes distributed in the right section of a light beam (the "beam") according to a known initial pattern is generated. As the pattern is known, the distribution of the fringes can be modeled by a two-dimensional distribution of the phase of the luminous intensity or phase of the luminous fringes in the cross section of the beam. A mathematical function φ then completely describes this phase distribution.
L'ensemble des franges lumineuses est projeté sur la surface d'un objet dont on veut reconstruire le relief. L'ensemble des franges lumineuses forme sur la surface illuminée de l'objet une image déformée du motif initial de l'ensemble des franges lumineuses. Les variations de la hauteur, c'est à dire le relief de la surface illuminée, provoquent cette déformation du motif initial. L'image ainsi formée sur la surface est une distribution de la phase des franges lumineuses qui résulte de la modulation de la distribution de la phase des franges lumineuses du motif initial par le relief de la surface illuminée.All luminous fringes are projected onto the surface of an object whose relief is to be reconstructed. The set of luminous fringes forms on the surface illuminated by the object a distorted image of the initial pattern of all the luminous fringes. The variations of the height, ie the relief of the illuminated surface, cause this deformation of the initial pattern. The image thus formed on the surface is a distribution of the phase of the luminous fringes which results from the modulation of the distribution of the phase of the luminous fringes of the initial pattern by the relief of the illuminated surface.
Il est possible de déduire de plusieurs images formées sur la surface illuminée de l'objet et par le calcul, la distribution de la phase des franges lumineuses du motif déformé en prenant soin d'induire un décalage (dans l'espace) connu de la distribution de la phase des franges lumineuses entre chaque image formée sur la surface. A cette fin des méthodes de calcul connues peuvent être mises en œuvre. Parmi ces méthodes de dérivation de la distribution des franges lumineuses à partir de plusieurs images projetées avec un décalage induit de la phase de ces mêmes franges, on peut citer celles mentionnées dans :It is possible to deduce from several images formed on the illuminated surface of the object and by calculation, the distribution of the phase of the luminous fringes of the deformed pattern taking care to induce a shift (in space) known from the distribution of the phase of the light fringes between each image formed on the surface. For this purpose, known calculation methods can be implemented. Among these methods of deriving the distribution of light fringes from several images projected with an induced phase shift of these same fringes, mention may be made of those mentioned in:
- P. S Huang, C. Zhang and F. P. chiang, "High-speed 3-D shape measurement based on digital fringe projection", Opt. Eng.42(1), 163-168, 2003;- P. Huang S, C. Zhang and F. P. Chiang, "High-speed 3-D shape measurement based on digital fringe projection", Opt. Eng. 42 (1), 163-168, 2003;
- L. Salas, E. Luna, J. Salinas, V. Garcia and M. Servin, "Profilometry by fringe projection", Opt. Eng.42(11) 3307- 3314, 2003;L. Salas, E. Luna, J. Salinas, V. Garcia and M. Servin, "Profilometry by fringe projection", Opt. Eng. 42 (11) 3307-3314, 2003;
- I. Yamaguchi, S. Ohta, and J. Kato, "Surface contouring by phase-shifting digital holography", Optics and Lasers in Engineering 36, 417-428, 2001; etI. Yamaguchi, S. Ohta, and J. Kato, "Surface contouring by phase-shifting digital holography", Optics and Lasers in Engineering 36, 417-428, 2001; and
- G. S. Spagnolo, D. Ambrosinib, D. Paolettib and G. Accardo, "Fibre optic projected fringes for monitoring marble surface status", J. CuIt. Héritage 1 S337-S343, 2000. De cette distribution de phase du motif déformé, il est possible de déduire par une méthode de calcul connue, le relief de la surface illuminée de l'objet. Une telle méthode a notamment été mentionnées dans :- GS Spagnolo, D. Ambrosinib, D. Paolettib and G. Accardo, "Fiber Optic Projected Fringes for Monitoring Marble Surface Status", J. CuIt. Inheritance 1 S337-S343, 2000. From this phase distribution of the deformed pattern, it is possible to deduce by a known calculation method, the relief of the illuminated surface of the object. Such a method has been mentioned in particular in:
- Hu and al, "Calibration of a three dimensional shape measurement System", Opt. Eng.42(2), pp 487-493, 2003; et- Hu and al, "Calibration of a three dimensional shape measurement system", Opt. Eng.42 (2), pp 487-493, 2003; and
- H. Zhang, F. Wu, M. J. Lalor and D. R. Burton, "Spatiotemporal phase unwrapping and its application in fringe projection fiber optic phase-shifting profilometry", Opt. Eng.39(7) 1958-1964, 2000.- H. Zhang, Wu F., J. Lalor M. and D. R. Burton, "Spatiotemporal phase unwrapping and its application in fringe fiber optic projection phase-shifting profilometry", Opt. Eng.39 (7) 1958-1964, 2000.
Un système connu à un seul canal permettant une reconstitution du relief partiel de la surface illuminée par un motif de franges est représenté Figure 1 et comprend pour le dispositif d'illumination de l'objet 6 par des franges :A known single-channel system for reconstituting the partial relief of the illuminated surface by a fringe pattern is shown in FIG. 1 and comprises for the illumination device of the object 6 by fringes:
- une source 1 lumineuse uniforme, encore appelée « source», la plus homogène possible (homogénéité de la distribution de la puissance lumineuse dans la section droite du faisceau émis), un élargisseur 2 de faisceau encore appelé «élargisseur» produisant, ici, un faisceau parallèle 4,a uniform light source 1, also called "source", the most homogeneous possible (homogeneity of the distribution of the light power in the cross section of the emitted beam), a beam expander 2 also called "expander" producing, here, a parallel beam 4,
- un écran 3 à cristaux liquides encore appelé «masque»,a liquid crystal screen 3, also called a "mask",
- éventuellement un miroir de renvoi 10, le dispositif d'illumination permettant ainsi de produire un faisceau d'illumination selon un axe d'illumination 5, et pour la partie d'acquisition et de traitement :optionally, a reflecting mirror 10, the illumination device thus making it possible to produce an illumination beam along an illumination axis 5, and for the acquisition and processing part:
- une caméra 8 type CCD permettant d'acquérir des images de l'objet 6 illuminé par les franges selon un axe de prise de vue 7, un équipement informatique 9 (ordinateur/microordinateur) comportant un processeur capable d'effectuer des calculs selon des algorithmes sur des données dont les images acquises par la caméra, ainsi que de piloter le masque pour définir le motif de franges. La source lumineuse génère la lumière nécessaire à l'illumination à travers le masque de la surface de l'objet dont le système doit reconstituer le relief de la surface illuminée.a CCD type 8 camera making it possible to acquire images of the object 6 illuminated by the fringes along a shooting axis 7, a computer equipment 9 (computer / microcomputer) comprising a processor capable of performing calculations according to algorithms on data including the images acquired by the camera, as well as driving the mask to set the fringe pattern. The light source generates the light necessary for illumination through the mask of the surface of the object whose system must reconstruct the relief of the illuminated surface.
L'élargisseur de faisceau donne une section parallèle du faisceau lumineux avec les dimensions requises pour illuminer correctement le masque puis la surface à illuminer de l'objet.The beam expander gives a parallel section of the light beam with the dimensions required to properly illuminate the mask and the surface to be illuminated of the object.
La position de la source 1 par rapport à l'élargisseur 2 détermine la divergence ou non du faisceau lumineux qui traverse le masque et éclaire l'objet. Ainsi les dimensions de la surface illuminée ne sont pas forcement limitées aux dimensions du masque et peuvent être plus ou moins grandes que ces dernières. Toutefois, un faisceau d'illumination parallèle, comme représenté Figure 1, permet de simplifier les calculs.The position of the source 1 relative to the expander 2 determines the divergence or not of the light beam passing through the mask and illuminates the object. Thus, the dimensions of the illuminated surface are not necessarily limited to the dimensions of the mask and may be larger or smaller than the latter. However, a parallel illumination beam, as shown in Figure 1, simplifies the calculations.
Si l'axe du système optique constitué de la source, de l'élargisseur et du masque qui est également l'axe de propagation du faisceau lumineux est orienté de telle sorte que la surface de l'objet est illuminée directement (illumination directe), aucun autre composant n'est nécessaire entre le masque et l'objet. Si, dans une variante, cet axe est initialement orienté dans une direction qui ne passe pas par l'objet, alors un miroir est placé entre le masque et l'objet et orienté pour rediriger le faisceau lumineux initial vers l'objet afin d'illuminer correctement sa surface avec les franges (illumination indirecte). Cette double possibilité d'illumination explique l'introduction de la notion de point d'illumination pour qualifier une origine virtuelle du faisceau final d'illumination de l'objet par les franges, point d'illumination qui peut correspondre physiquement au dispositif d'illumination de l'objet par des franges si l'illumination est directe ou ne pas correspondre si l'illumination est indirecte. On comprend que cette notion d'illumination directe ou indirecte peut également s'appliquer par analogie à la partie d'acquisition, la caméra pouvant recevoir directement les images de l'objet (la caméra est sur l'axe de prise de vue 7 comme représenté Figure 1) ou indirectement, les images étant renvoyées par un miroir vers une caméra qui n'est pas sur l'axe de prise de vue 7. Ceci explique par analogie l'introduction de la notion de point de prise de vue qui est sur l'axe de prise de vue.If the axis of the optical system consisting of the source, the expander and the mask which is also the axis of propagation of the light beam is oriented so that the surface of the object is illuminated directly (direct illumination), no other components are needed between the mask and the object. If, in a variant, this axis is initially oriented in a direction that does not pass through the object, then a mirror is placed between the mask and the object and oriented to redirect the initial light beam towards the object in order to properly illuminate the surface with the fringes (indirect illumination). This double possibility of illumination explains the introduction of the notion of illumination point to qualify a virtual origin of the final illumination beam of the object by the fringes, point of illumination which can correspond physically to the illumination device of the object by fringes if the illumination is direct or not to correspond if the illumination is indirect. It is understood that this notion of direct or indirect illumination can also be applied by analogy to the acquisition part, the camera being able to directly receive the images of the object (the camera is on the shooting axis 7 as shown in Figure 1) or indirectly, the images being returned by a mirror to a camera that is not on the axis of shooting 7. This explains by analogy the introduction of the concept of point of view which is on the axis of shooting.
Le processeur 9 pilote le masque 3 pour générer l'ensemble des franges lumineuses selon le motif souhaité, pilote la caméra 8 et stocke les images acquises par la caméra et procède aux calculs nécessaires à la détermination du relief de la surface illuminée de l'objet pour par exemple reconstruction visuelle 3D sur un écran.The processor 9 controls the mask 3 to generate all the light fringes according to the desired pattern, controls the camera 8 and stores the images acquired by the camera and proceeds to the calculations necessary to determine the relief of the illuminated surface of the object for example 3D visual reconstruction on a screen.
Ce système est dit à un seul canal car il ne comporte qu'un couple ou duet de point d'illumination et de point de prise de vue.This system is said to be a single channel because it has only a couple or duet of point of illumination and point of view.
Pour une reconstitution du relief quasi-intégral de la surface illuminée par un motif de franges, on peut mettre en œuvre un système à deux canaux. Un système à deux canaux comprend, par exemple, d'une part, une source lumineuse uniforme la plus homogène possible, un élargisseur de faisceau, un écran à cristaux liquides (le masque), un commutateur de faisceau optique et plusieurs miroirs, et, d'autre part, deux caméras et un processeur. Ce type de système à deux canaux comporte un point d'illumination et deux caméras et est symbolisé 1PI/2PV.For a reconstruction of the quasi-integral relief of the surface illuminated by a pattern of fringes, it is possible to implement a two-channel system. A two-channel system comprises, for example, on the one hand, a uniform homogeneous light source possible, a beam expander, a liquid crystal display (the mask), an optical beam switch and several mirrors, and, on the other hand, two cameras and a processor. This type of two-channel system has one illumination point and two cameras and is symbolized 1PI / 2PV.
Les miroirs sont répartis et distribués dans l'espace de sorte qu'ils peuvent infléchir un faisceau lumineux selon l'un ou l'autre de deux chemins possibles chaque chemin étant défini par un système de miroirs qui permet d'illuminer la surface de l'objet selon un axe de projection propre au chemin. Le commutateur de faisceau optique est piloté par l'ordinateur et dirige le faisceau lumineux issu du masque vers l'un ou l'autre des systèmes de miroirs. Ainsi, la surface de l'objet est illuminée de façon séquentielle selon les deux couples possibles d'axes de projection et d'acquisition du système à deux canaux.The mirrors are distributed and distributed in space so that they can bend a light beam according to one or the other of two possible paths, each path being defined by a system of mirrors that illuminates the surface of the light. object along a projection axis specific to the path. The optical beam switch is driven by the computer and directs the light beam from the mask to one or the other of the mirror systems. Thus, the surface of the object is illuminated sequentially according to the two possible pairs of axes of projection and acquisition of the two-channel system.
Le processeur procède à la reconstitution de deux reliefs partiels distincts puis grâce à ces deux reliefs à la reconstitution du relief quasi-intégral de la surface illuminée de l'objet. En effet, les deux reliefs partiels reconstruits selon deux, au choix, des quatre couples possibles d'axes de projection et d'acquisition étant distincts, il est possible de reconstruire sans ambiguïté le relief de la surface illuminée de l'objet grâce à une technique de dépouillement de la phase. Ce relief est alors le relief quasi-intégral de la surface illuminée de l'objet.The processor proceeds to the reconstruction of two distinct partial reliefs and thanks to these two reliefs to the reconstruction of the almost complete relief of the illuminated surface of the object. Indeed, the two partial reliefs reconstructed according to two, the choice, the four possible pairs of axes of projection and acquisition being distinct, it is possible to reconstruct without ambiguity the relief of the illuminated surface of the object through a stripping technique of the phase. This relief is then the quasi-integral relief of the illuminated surface of the object.
Dans le système à deux canaux, une fois que le faisceau est généré par la source et mis, par l'élargisseur, aux dimensions requises par l'illumination de la surface de l'objet, le masque façonne le motif initial de la distribution de phase des franges lumineuses. Le processeur détermine quels pixels du masque doivent être opaques ou transparents à la lumière du faisceau qui le traverse. Après transmission par le masque du faisceau, le motif initial est formé, de préférence, dans une section parallèle de ce même faisceau (faisceau droit non divergent et non convergent). Dans une variante, le faisceau d'illumination peut être divergent mais cela complique le procédé puisqu'il faut connaître la divergence pour en tenir compte afin de corriger les calculs de mesure de surface.In the two-channel system, once the beam is generated by the source and set by the expander to the dimensions required by the illumination of the surface of the object, the mask shapes the initial pattern of the distribution of the object. phase of bright fringes. The processor determines which pixels of the mask should be opaque or transparent to the light of the beam passing through it. After transmission by the beam mask, the initial pattern is preferably formed in a parallel section of the same beam (non-diverging and non-converging straight beam). In a variant, the illumination beam may be divergent, but this complicates the process because it is necessary to know the divergence to take it into account in order to correct the surface measurement calculations.
Le faisceau illumine la surface de l'objet et est soit réfléchi par la surface (surface opaque à la lumière du faisceau, fonctionnement en réflexion) soit transmis à travers l'objet (objet transparent à la lumière du faisceau, fonctionnement en transmission). Dans ce dernier cas, on doit noter que les objets transparents (il faut toutefois qu'un motif de franges soit déposé sur une surface de l'objet et y soit visible) sont mesurables en transmission sous réserve qu'une des deux faces traversées entre le/les Pl et les/le PV ne déforme pas le motif des franges qui s'est formé sur l'autre, sinon, l'information n'est plus fiable car il n'est pas possible de distinguer entre les déformations de l'une ou de l'autre face de l'objet.The beam illuminates the surface of the object and is either reflected from the surface (opaque surface to beam light, reflection operation) or transmitted to the beam. through the object (object transparent to the light of the beam, operation in transmission). In the latter case, it should be noted that the transparent objects (it is however necessary that a fringe pattern is deposited on a surface of the object and is visible) are measurable in transmission provided that one of the two faces crossed between the P1 and / the PV does not distort the pattern of the fringes that has formed on the other, otherwise the information is no longer reliable because it is not possible to distinguish between the deformations of the one or the other face of the object.
Les images formées sur la surface de l'objet et vues selon les deux points de vue des deux caméras sont acquises et numérisées par les deux caméras qui les transmettent au processeur.The images formed on the surface of the object and seen from both viewpoints of the two cameras are acquired and digitized by the two cameras that transmit them to the processor.
Avant de procéder aux calculs, le processeur acquière plusieurs images des surfaces illuminées de l'objet. Entre chaque acquisition, le processeur pilote le masque de telle sorte que le motif initial de la distribution de phase des franges lumineuse soit décalé dans l'espace c'est à dire que la distribution de la phase subit un décalage de phase voulu et donc connu.Before proceeding with the calculations, the processor acquires several images of the illuminated surfaces of the object. Between each acquisition, the processor controls the mask so that the initial pattern of the phase distribution of the luminous fringes is shifted in space, ie the distribution of the phase undergoes a desired phase shift and is therefore known. .
Le processeur peut alors procéder aux calculs nécessaires: il calcule les variations de phase de la distribution de phase des franges lumineuse puis procède au dépouillement de cette phase grâce aux deux points de vues (c'est à dire qu'il en détermine la valeur absolue et non pas modulo 2π) ce qui permet d'obtenir le relief exact de la surface de l'objet c'est à dire sans ambiguïté. De plus, les parties de la surface non visibles par un canal sont visibles par l'autre ce qui permet de reconstituer la quasi-intégralité de la surface illuminée par les deux incidences d'illumination.The processor can then proceed to the necessary calculations: it calculates the phase variations of the phase distribution of the light fringes and proceeds to the stripping of this phase thanks to the two points of view (that is to say that it determines the absolute value and not modulo 2π) which makes it possible to obtain the exact relief of the surface of the object, that is to say without ambiguity. In addition, the parts of the surface not visible by one channel are visible by the other which allows to reconstruct almost all the surface illuminated by the two incidences of illumination.
Un exemple d'algorithme utilisable pour un tel système à deux canaux 1 PI/2PV est donné Figure 2. Un système à deux canaux peut, en variante, comporter deux points d'illumination et une caméra. Il est alors symbolisé 2PI/1PV. Un exemple d'algorithme utilisable pour un tel système à deux canaux 2PI/1PV est donné Figure 3.An example of an algorithm that can be used for such a 1 PI / 2PV two-channel system is given in FIG. 2. A two-channel system may alternatively have two illumination points and a camera. It is then symbolized 2PI / 1PV. An example of an algorithm that can be used for such a two-channel 2PI / 1PV system is given in FIG. 3.
Pour une reconstitution du relief quasi-intégral de la surface extérieure quasi-complète de l'objet on peut mettre en œuvre le système multi-canaux tétraédrique à quatre points d'illumination et quatre points de prise de vue de l'invention. Le système comprend par exemple, d'une part, pour le dispositif d'illumination de l'objet par des franges, de préférence :For a reconstruction of the near-integral relief of the almost complete external surface of the object, it is possible to implement the tetrahedral multi-channel system with four illumination points and four image points of the invention. The system comprises, for example, on the one hand, for the device for illuminating the object with fringes, preferably:
- une source lumineuse uniforme la plus homogène possible,- a uniform light source as homogeneous as possible,
- un élargisseur de faisceau,- a beam expander,
- un écran à cristaux liquides (le « masque»),- a liquid crystal display (the "mask"),
- un commutateur de faisceau optique à quatre sorties,a four-output optical beam switch,
- plusieurs miroirs de renvoi vers l'objet, (dans des variantes le système d'illumination peut comporter d'autres dispositions, notamment en nombre de sources, élargisseurs, écrans et commutateurs dont le type est adapté en conséquence) et, d'autre part, pour la partie d'acquisition et de traitement, de préférence :several mirrors for returning to the object, (in variants the illumination system may comprise other arrangements, in particular in number of sources, expanders, screens and switches whose type is adapted accordingly) and for the acquisition and processing part, preferably:
- quatre caméras, (dans des variantes le nombre de caméras peut être réduit)- four cameras, (in variants the number of cameras can be reduced)
- un processeur.- a processor.
Les miroirs sont répartis entre quatre systèmes de miroirs et distribués dans l'espace de sorte qu'ils peuvent infléchir un faisceau lumineux selon l'une ou l'autre de quatre incidences possibles, chaque incidence étant définie par un système de miroirs qui permet d'illuminer la surface de l'objet selon un axe de projection/d'illumination propre. Le commutateur de faisceau optique est piloté par l'ordinateur et dirige le faisceau lumineux issu du masque vers l'un ou l'autre des systèmes de miroirs. Ainsi, la surface de l'objet est illuminée de façon séquentielle selon les quatre axes de projection/d'incidence possibles du système multi-canaux tétraédrique de l'invention.The mirrors are distributed between four mirror systems and distributed in space so that they can bend a light beam according to one or the other of four possible angles, each incidence being defined by a system of mirrors that enables illuminate the surface of the object along a clean projection / illumination axis. The optical beam switch is driven by the computer and directs the light beam from the mask to one or the other of the mirror systems. Thus, the surface of the object is sequentially illuminated along the four possible projection / incidence axes of the tetrahedral multi-channel system of the invention.
Un axe de projection/d'incidence est défini par le segment issu du centre du dernier miroir de chaque chemin possible (lequel miroir réfléchit les franges lumineuses directement sur l'objet pour l'illuminer de franges) et le centre de la surface illuminée. Chaque dernier miroir définit un point d'illumination. Les quatre points d'illumination sont placés aux sommets d'un tétraèdre (ou bien près de ces sommets) au centre duquel se trouve l'objet à illuminer. Les arêtes issues des points d'illumination et passant par le centre du tétraèdre se confondent avec les axes de projection du système. Les quatre points d'illumination sont à distance suffisante de l'objet en sorte que chaque couple de points d'illumination illumine la surface délimitée par le contour vu selon la pseudo-normale à ladite surface, laquelle pseudo-normale est la médiane des deux axes de projection dans le plan qu'ils définissent ensemble.A projection / incidence axis is defined by the segment from the center of the last mirror of each possible path (which mirror reflects the light fringes directly onto the object to illuminate it with fringes) and the center of the illuminated surface. Each last mirror defines an illumination point. The four points of illumination are placed at the vertices of a tetrahedron (or near these vertices) at the center of which is the object to be illuminated. The edges coming from the points of illumination and passing through the center of the tetrahedron merge with the projection axes of the system. The four points of illumination are at a sufficient distance from the object so that each pair of illumination points illuminates the surface delimited by the contour seen according to the pseudo-normal to said surface, which pseudo-normal is the median of the two projection axes in the plane that they define together.
Chacune des quatre caméras (ou un miroir de renvoi vers une caméra) est placée en un point situé sur une des quatre médianes (issues du centre du tétraèdre précédemment défini, avec une caméra par médiane) des quatre trièdres formés par les quatre triplets d'axes de projection ou bien est placée proche d'une de ces quatre médianes. Chaque caméra est ainsi placée en un point de prise de vue. Les arêtes issues des points de prise de vue et passant par le centre du tétraèdre définissent les axes de prise de vue du système.Each of the four cameras (or mirror to a camera) is placed at a point on one of the four medians (from the center of the previously defined tetrahedron, with one camera per median) of the four trihedrons formed by the four triplets of projection axes or is placed close to one of these four medians. Each camera is thus placed at a point of view. The edges coming from the points of view and passing through the center of the tetrahedron define the axes of shooting of the system.
Les quatre points de prise de vue sont à distance suffisante de l'objet en sorte que les champs de vision de chaque couple de points de prise de vue incluent la surface définie comme précédemment par le couple des deux axes de projection voisins communs aux deux axes de prise de vue du couple de points de prise de vue.The four points of view are at a sufficient distance from the object so that the fields of view of each pair of shooting points includes the area defined as previously by the pair of two adjacent projection axes common to both shooting axes of the pair of shooting points.
Cette disposition est représentée schématiquement Figure 4 dans laquelle un objet est place au centre O d'un tétraèdre dont les quatre sommets PM, PI2, PI3 et PI4 forment les quatre points d'illumination. De ces quatre points d'illumination partent le long d'axes de projection/d'illumination PM-O, PI2-0, PI3-0 et PI4-0, les faisceaux lumineux porteurs de franges et dirigés vers le centre du tétraèdre et, donc, illuminant l'objet avec des franges. Les quatre axes d'illumination permettent de définir quatre trièdres formés par des triplets d'axes de projection (triplets au nombre de quatre). La médiane de chaque trièdre est le support d'un axe de prise de vue et on a donc quatre axes de prise de vue ainsi définis, PV1,2, PV2,3, PV3,4 et PV1,4.This arrangement is shown schematically in Figure 4 in which an object is placed in the center O of a tetrahedron whose four vertices PM, PI2, PI3 and PI4 form the four points of illumination. From these four points of illumination start along axes of projection / illumination PM-O, PI2-0, PI3-0 and PI4-0, the light beams bearing fringes and directed towards the center of the tetrahedron and, therefore, illuminating the object with fringes. The four illumination axes make it possible to define four trihedrons formed by triplets of projection axes (triplets of which there are four). The median of each trihedron is the support of a shooting axis and thus there are four shooting axes thus defined, PV1,2, PV2,3, PV3,4 and PV1,4.
Le processeur procède à la reconstitution des reliefs partiels distincts définit par chaque couple d'axes de projection et de prise de vue puis grâce à ces reliefs à la reconstitution sans ambiguïté du relief quasi-intégral des différentes surfaces illuminées de l'objet. Grâce à la reconstruction sans ambiguïté et quasi-intégrale de ces surfaces illuminées, le processeur procède à la reconstruction sans ambiguïté du relief quasi-intégral de la surface complète extérieure de l'objet illuminé.The processor proceeds to the reconstruction of the distinct partial reliefs defined by each pair of projection and shooting axes and thanks to these reliefs to the unambiguous reconstruction of the almost-complete relief of the various illuminated surfaces of the object. Thanks to the unambiguous and almost integral reconstruction of these illuminated surfaces, the processor proceeds to the unambiguous reconstruction of the quasi-integral relief of the complete outer surface of the illuminated object.
Les quatre axes de projection permettent de projeter des franges sur l'objet mais pas obligatoirement le même ensemble de franges lumineuses pour tous les axes. On acquière un ensemble d'images de chacune des six surfaces illuminées et définies par les six couples de points d'illumination. Ces images permettent de recouvrer les reliefs partiels (vus selon les deux couples d'axes projection et acquisition définis par deux axes de projection et un axe d'acquisition ou, encore, un axe de projection et deux axes d'acquisition ou, enfin, un axe de projection et un axe de prise de vue et un autre axe de projection et un autre axe de prise de vue tous les quatre voisins ensembles) de chacune des six surfaces illuminées de l'objet. Ces reliefs partiels permettent de recouvrer sans ambiguïtés la quasi-totalité des détails du relief, c'est-à-dire le relief quasi-intégral, de chacune des six surfaces illuminées de l'objet. Les reliefs quasi- intégraux ainsi recouvrés sans ambiguïté des six possibilités de surfaces illuminées de l'objet permettent de recouvrer sans ambiguïtés également la quasi- intégralité des détails de la surface extérieure complète de l'objet.The four projection axes make it possible to project fringes on the object but not necessarily the same set of luminous fringes for all the axes. A set of images of each of the six illuminated surfaces defined by the six pairs of illumination points is acquired. These images make it possible to recover the partial reliefs (seen according to the two pairs of axes projection and acquisition defined by two axes of projection and an axis of acquisition or, again, a projection axis and two axes of acquisition or, finally, a projection axis and a shooting axis and another axis of projection and another axis of shooting all four neighbors together) of each of the six illuminated surfaces of the object. These partial reliefs make it possible to recover without ambiguities almost all the details of the relief, that is to say the quasi-integral relief, of each of the six illuminated surfaces of the object. The quasi-integral reliefs thus unambiguously recovered from the six possibilities of illuminated surfaces of the object make it possible to recover unambiguously also almost all the details of the complete outer surface of the object.
Il faut noter que le terme « quasi » (quasi-intégral) est utilisé pour tenir compte des cas généralement exceptionnels où certaines petites parties de l'objet ne recevraient pas d'illumination ou seraient invisibles du fait d'un obstacle de surface comme par exemple un replis, une gorge profonde inclinée par rapport à l'axe d'illumination ou de prise de vue, etc., l'invention permettant, lorsque l'illumination et la visualisation complètes de la surface sont possibles, de retrouver l'intégralité des détails de surface.It should be noted that the term "quasi" (quasi-integral) is used to account for generally exceptional cases where some small parts of the object would not receive illumination or would be invisible due to a surface obstacle such as a fold, a deep groove inclined relative to the axis of illumination or shooting, etc., the invention allowing, when the complete illumination and visualization of the surface are possible, to find the completeness surface details.
On peut également noter que les franges lumineuses mises en œuvre sont «analogiques» au sens où la transition entre le minimum de luminosité et le maximum de luminosité est continue c'est à dire est un dégradé de niveaux de gris et non pas un transition abrupte qui serait appelée «numérique». Afin d'obtenir de telles franges « analogiques », on met en œuvre un masque/écran à cristaux liquides contrôlable en niveaux de gris. Ceci permet d'améliorer la précision de la reconstruction du relief de la surface illuminée de l'objet. On peut également noter que le pas des franges lumineuses détermine la précision/résolution de la mesure du relief. Plus ce pas est petit, meilleure peut être la précision de mesure de la méthode PSM. Cette précision est toutefois également déterminée par la qualité des autres composants du système comme par exemple le pas des niveaux de gris que la caméra d'acquisition peut distinguer et la résolution de la caméra d'acquisition, à savoir le pas de périodicité de ses pixels. Enfin, la qualité de l'algorithme de traitement des images détermine encore et la résolution et la précision de mesure de la méthode PSM.It can also be noted that the luminous fringes used are "analog" in the sense that the transition between the minimum brightness and the maximum brightness is continuous, ie is a grayscale gradient and not an abrupt transition. which would be called "digital". In order to obtain such "analog" fringes, a mask / liquid crystal screen that can be controlled in gray levels is used. This makes it possible to improve the accuracy of the reconstruction of the relief of the illuminated surface of the object. It can also be noted that the pitch of the luminous fringes determines the accuracy / resolution of the relief measurement. The smaller this step, the better the measurement accuracy of the PSM method. This accuracy is however also determined by the quality of the other components of the system such as the step of the gray levels that the acquisition camera can distinguish and the resolution of the acquisition camera, namely the periodicity of its pixels . Finally, the quality of the image processing algorithm further determines the resolution and measurement accuracy of the PSM method.
On va maintenant décrire plus concrètement des exemples de mise en œuvre de l'invention.We will now describe more concretely examples of implementation of the invention.
On considère tout d'abord un objet qui est sensiblement sphérique dont la surface est accidentée (relief complexe) et est illuminée par le système multi- canaux tétraédrique. Le recouvrement de sa surface est complet. Pour permettre l'illumination (et la visualisation) de l'objet au centre du tétraèdre, par le dessous, on peut le poser sur un support transparent (par exemple une lame transparente sur laquelle l'illumination ne peut se réaliser/déposer et qui laisse passer le motif de franges sans le déformer ou dont la déformation peut être prise en compte) ou le maintenir en l'air par un/des fils ou rubans ou, dans une alternative plus complexe, l'amener en rotation contrôlée par le processeur pour l'éclairer de frange et l'observer sur toutes ses faces. Pour le niveau de précision souhaité dans cet exemple, cinq systèmes de franges décalées par surface illuminée sont nécessaires. La succession des prises de vue est alors la suivante (en référence à la Figureδ):We first consider an object that is substantially spherical with a rugged surface (complex relief) and is illuminated by the tetrahedral multi-channel system. The covering of its surface is complete. To allow the illumination (and visualization) of the object in the center of the tetrahedron, from below, it can be placed on a transparent support (for example a transparent slide on which the illumination can not be realized / deposited and which let the pattern of fringes without deforming or whose deformation can be taken into account) or keep it in the air by a son or ribbons or, in a more complex alternative, bring it into rotation controlled by the processor to light it with bangs and to observe it on all its faces. For the desired level of precision in this example, five illuminated surface offset fringe systems are required. The succession of shots is then the following (with reference to Figureδ):
- PM illumine avec le système de franges F1, et PV123, PV124 PV134 acquièrent simultanément trois images de franges projetées {IMFi 123 û IMFi 124 r, IMFi 134 ι}ι = 1, , 3; les reliefs partiels R123, R124 et R134 de la surface illuminée sont recouvrés selon l'algorithme à deux canaux 1PI/2PV décrit précédemment pour chaque triplets un point d'illumination/deux points de prise de vue contenu dans le quadruplet (PM, PV123, PV124, PV134).PM illuminates with the fringe system F1, and PV123, PV124 PV134 simultaneously acquire three images of projected fringes {IM F i 123 û IM F i 124 r, IM F i 134 ι} ι = 1,, 3; the partial reliefs R123, R124 and R134 of the illuminated surface are recovered according to the two-channel algorithm 1PI / 2PV previously described for each triplet one point of illumination / two points of shooting contained in the quadruplet (PM, PV123, PV124, PV134).
- PI2 illumine avec le système de franges F2 et PV123, PV124, PV234 acquièrent simultanément trois images de franges projetées {IMF2123 û IMF2124 r, IMF2234 ι}ι = 1, , 3; les reliefs partiels R123, R124 et R234 de la surface illuminée sont recouvrés selon l'algorithme à deux canaux 1PI/2PV décrit précédemment pour chaque triplets un point d'illumination/deux points de prise de vue contenu dans le quadruplet (PI2, PV123, PV124, PV234).PI2 illuminates with the fringe system F2 and PV123, PV124, PV234 simultaneously acquire three images of projected fringes {IM F 2123 IM F2 124 r, IM F2 234 ι} ι = 1,, 3; the partial reliefs R123, R124 and R234 of the illuminated surface are recovered according to the two-channel 1PI / 2PV algorithm previously described for each triplet an illumination point / two shooting points contained in the quadruplet (PI2, PV123, PV124, PV234).
- PI3 illumine avec le système de franges F3 et PV123, PV134, PV234 acquièrent simultanément trois images de franges projetées {IMF3123 û IMF3134 r, IMF3234 ι}ι = 1, , 3; les reliefs partiels R123, R134 et R234 de la surface illuminée sont recouvrés selon l'algorithme à deux canaux 1PI/2PV décrit précédemment pour chaque triplets un point d'illumination/deux points de prise de vue contenu dans le quadruplet (PI3, PV123, PV134, PV234).PI3 illuminates with the fringe system F3 and PV123, PV134, PV234 simultaneously acquire three images of projected fringes {IM F 3123 - IM F3 134 r, IM F3 234 ι} ι = 1,, 3; the partial reliefs R123, R134 and R234 of the illuminated surface are recovered according to the two-channel 1PI / 2PV algorithm previously described for each triplet an illumination point / two shooting points contained in the quadruplet (PI3, PV123, PV134, PV234).
- PI4 illumine avec le système de franges F4 et PV124, PV134, PV234 acquièrent simultanément trois images de franges projetées {IMF4 124 ,; IMF4 134 ,; IMF4 234 ι}ι = 1, , 3; les reliefs partiels R124, R134 et R234 de la surface illuminée sont recouvrés selon l'algorithme à deux canaux 1PI/2PV décrit précédemment pour chaque triplets un point d'illumination/deux points de prise de vue contenu dans le quadruplet (PI4, PV124, PV134, PV234).PI4 illuminates with the fringe system F4 and PV124, PV134, PV234 simultaneously acquire three images of projected fringes {IM F4 124 ,; IM F4 134,; IM F4 23 4 ι} ι = 1,, 3; the partial reliefs R124, R134 and R234 of the illuminated surface are recovered according to the two-channel 1PI / 2PV algorithm previously described for each triplet an illumination point / two points of view contained in the quadruplet (PI4, PV124, PV134, PV234).
- Chaque triplet de reliefs partiels permet de recouvrer la surface quasi-intégrale d'un hémisphère de la sphère, chaque hémisphère étant illuminé par un point d'illumination car ce point est suffisamment éloigné de la sphère pour cela. Il y a quatre surfaces d'hémisphère orientées à 120° les unes de autres. Elles permettent le recouvrement de la surface quasi-intégrale et complète de la sphère. Cet exemple d'un objet de type sphérique correspond à une mise en œuvre destinée plus généralement au traitement d'un objet dont le relief de la surface n'est a priori pas connu. Cette mise en œuvre nécessite un phasage complexe et est relativement lourde.Each triplet of partial reliefs makes it possible to recover the quasi-integral surface of a hemisphere of the sphere, each hemisphere being illuminated by an illumination point because this point is sufficiently far away from the sphere for this purpose. There are four hemispherical surfaces oriented at 120 ° to each other. They allow the recovery of the almost complete and complete surface of the sphere. This example of an object of the spherical type corresponds to an implementation intended more generally for the treatment of an object whose relief of the surface is a priori not known. This implementation requires a complex phasing and is relatively heavy.
On considère maintenant un objet qui est une plaque lisse. Seuls les reliefs de sa surface supérieure et de sa surface inférieure font l'objet du traitement dans cet exemple de mise en œuvre. Cette plaque est perpendiculaire à l'axe de projection issu du point d'illumination PM. Cette mise en œuvre, plus simple que la précédente, ne requière que trois systèmes de franges décalées par surface illuminée. La succession des prises de vue est alors la suivante:We now consider an object that is a smooth plate. Only the reliefs of its upper surface and its lower surface are the subject of the treatment in this example of implementation. This plate is perpendicular to the projection axis from the illumination point PM. This implementation, simpler than the previous one, only requires three fringe systems offset by illuminated surface. The succession of shots is then the following:
- PM illumine avec le système de franges F1 et PV123, PV134 acquièrent simultanément trois images de franges projetées {I MFi 123 ι! IMFi 134 ι}ι = 1, ,3; le relief intégral (la surface est lisse, sans aspérité ni zone d'ombre) de la surface supérieure de la plaque est recouvré selon l'algorithme à deux canaux 1PI/2PV.- PM illuminates with fringe system F1 and PV123, PV134 simultaneously acquire three images of projected fringes {IM F i 123 ι! IM F i 134 ι} ι = 1,, 3; the integral relief (the surface is smooth, without roughness or shadow area) of the upper surface of the plate is recovered according to the two-channel 1PI / 2PV algorithm.
- PI2 illumine avec le système de franges F2 et PV234 acquière trois images de franges projetées {IMF2234 ι}ι = 1,PI2 illuminates with the fringe system F2 and PV234 acquires three images of projected fringes {IM F 2234 ι} ι = 1,
, 3; puis, 3; then
PI3 illumine avec le système de franges F3, PV234 acquière trois images de franges projetées {IMF3234 ι}ι = 1,PI3 illuminates with the fringe system F3, PV234 acquires three images of projected fringes {IM F 3234 ι} ι = 1,
, 3; avec l'ensemble d'images {IMF2234 ι; IMF3234 ι}ι = 1, 3 , le relief intégral de la surface inférieure de la plaque est recouvré selon l'algorithme à deux canaux 2PI/1PV., 3 ; with the set of images {IM F 2234 ι; IM F 3234 ι} ι = 1, 3 , the integral relief of the lower surface of the plate is recovered according to the two-channel algorithm 2PI / 1PV.
Cet exemple, dont le phasage est assez simple, est mis en œuvre lorsque l'application traite un objet dont le relief de la surface est a priori connu (identification d'un objet attendu ou mesure de la conformité du relief par rapport à un modèle donné). On considère maintenant un objet qui est une plaque lisse comportant un relief sur une de ses faces. Seuls les reliefs de sa surface supérieure et de sa surface inférieure font l'objet du traitement dans cet exemple de mise en oeuvre. Cette plaque est perpendiculaire à l'axe de projection issu du point d'illumination PM. La surface supérieure porte un petit promontoire (parallélépipède). Cette mise en œuvre est encore relativement simple et ne requière que trois systèmes de franges décalées par surface illuminée. La succession des prises de vue est alors la suivante:This example, whose phasing is quite simple, is implemented when the application processes an object whose surface relief is a priori known (identification of an expected object or measurement of conformity of the relief with respect to a model given). We now consider an object that is a smooth plate with a relief on one of its faces. Only the reliefs of its upper surface and its lower surface are the subject of the treatment in this example of implementation. This plate is perpendicular to the projection axis from the illumination point PM. The upper surface carries a small promontory (parallelepiped). This implementation is still relatively simple and requires only three fringe systems offset by illuminated surface. The succession of shots is then the following:
- PM illumine avec le système de franges F1 et PV123, PV124, PV134 acquièrent simultanément trois images de franges projetées {IMFi 123.; IMFi 124.; IMFi 134.}. = 1, , 3; les reliefs partiels R123, R124 et R134 de la surface illuminées sont recouvrés selon l'algorithme à deux canaux 1PI/2PV décrit précédemment pour chaque triplet un point d'illumination/deux points de prise de vue contenu dans le quadruplet (PM, PV123, PV124, PV134); puis, le relief intégral de la surface supérieure de la plaque est recouvré grâce aux trois reliefs partiels.PM illuminates with fringe system F1 and PV123, PV124, PV134 simultaneously acquire three images of projected fringes {IM F i 123 .; IM F 124; IM F i 134.}. = 1, 3 ; the partial reliefs R123, R124 and R134 of the illuminated surface are recovered according to the two-channel 1PI / 2PV algorithm previously described for each triplet an illumination point / two shooting points contained in the quadruplet (PM, PV123, PV124, PV134); then, the integral relief of the upper surface of the plate is recovered thanks to the three partial reliefs.
- PI2 illumine avec le système de franges F2, PV234 acquière trois images de franges projetées {IMF2234 ι}ι = 1,PI2 illuminates with the fringe system F2, PV234 acquires three images of projected fringes {IM F 2234 ι} ι = 1,
, 3; puis, 3; then
PI3 illumine avec le système de franges F3, PV234 acquière trois images de franges projetées {IMF3234 ι}ι = 1,PI3 illuminates with the fringe system F3, PV234 acquires three images of projected fringes {IM F 3234 ι} ι = 1,
, 3; avec l'ensemble d'images {IMF2234 ι; IMF3234 ι}ι = 1, 3 , le relief intégral de la surface inférieure de la plaque est recouvré selon l'algorithme à deux canaux 2PI/1PV., 3 ; with the set of images {IM F2 234 ι; IM F3 234 ι} ι = 1, 3 , the integral relief of the lower surface of the plate is recovered according to the two-channel algorithm 2PI / 1PV.
Cet exemple de mise en œuvre, dont le phasage est encore assez simple, a nécessité une acquisition supplémentaire par rapport à l'exemple précédent à cause de zones partiellement aveugles (c'est à dire aveugle pour un seul duet : point d'illumination / point de prise de vue) causées par le promontoire pour chaque triplet 1PI/2PV qui traite la surface supérieure. On voit donc que dans le système multi-canaux tétraédrique de l'invention, aucun ajustement matériel n'est nécessaire (pas de déplacement des points d'illumination/de prise de vue ou de l'objet). Seul un changement dans le traitement des images a été requis. Le système multi-canaux tétraédrique de l'invention est donc flexible et complet.This implementation example, whose phasing is still quite simple, required an additional acquisition compared to the previous example because of partially blind zones (that is to say blind for a single duet: illumination point / point of view) caused by the promontory for each triplet 1PI / 2PV which treats the upper surface. It can thus be seen that in the tetrahedral multi-channel system of the invention, no hardware adjustment is necessary (no displacement of the illumination / shooting points or the object). Only a change in image processing was required. The tetrahedral multi-channel system of the invention is therefore flexible and complete.
On doit remarquer que si les points d'illumination sont placés à distance suffisante de l'objet traité, chaque axe d'illumination illumine une étendue définie de la surface de l'objet traité laquelle étendue recoupe généralement une partie de l'étendue illuminée par chacun des trois autres axes d'illumination sauf géométrie exceptionnellement défavorable de l'objet traité. On comprend qu'il est souhaitable qu'il en soit ainsi afin de ne laisser aucune étendue de la surface de l'objet traité non illuminée et donc non traitée.It should be noted that if the illumination points are placed at a sufficient distance from the object being treated, each illumination axis illuminates a defined area of the surface of the object being treated, which area generally intersects a portion of the area illuminated by each of the other three axes of illumination except exceptionally unfavorable geometry of the object treated. It is understood that it is desirable that it be so to leave no extent of the surface of the treated object not illuminated and therefore not treated.
Il est également préférable de ne pas laisser plusieurs canaux illuminer en même temps une même surface de l'objet traité afin de ne pas détruire l'information portée par les images frangées de chaque canal d'illumination. Toutefois, il est possible de multiplexer ces différentes images par la couleur d'illumination des franges comme cela sera indiqué ultérieurement.It is also preferable not to let several channels illuminate the same surface of the treated object at the same time so as not to destroy the information carried by the fringed images of each illumination channel. However, it is possible to multiplex these different images by the illumination color of the fringes as will be indicated later.
On va maintenant donner quelques exemples de configurations matérielles du système multi-canaux tétraédrique de l'invention.We will now give some examples of hardware configurations of the tetrahedral multi-channel system of the invention.
Une première configuration, dite « triviale » comporte quatre sources de lumière, quatre élargisseurs de faisceau, quatre écrans à cristaux liquides et quatre caméras. Dans cette configuration « triviale », la précision de la mesure est la meilleure car la projection des motifs et l'acquisition par les caméras sont directes et donc sans déformations de l'image frangées par des composants intermédiaires. Toutefois, cette configuration matérielle est d'un coût relativement élevé.A first configuration, called "trivial" includes four light sources, four beam expander, four LCD screens and four cameras. In this "trivial" configuration, the accuracy of the measurement is the best because the projection of the patterns and the acquisition by the cameras are direct and therefore without deformations of the image fringed by components intermediate. However, this hardware configuration is relatively expensive.
Une deuxième configuration, dite « économique » comporte une source de lumière, un élargisseu r de faisceau, un écran à cristaux liquides placé immédiatement après l'élargisseur de faisceau, une caméra, trois commutateurs optiques à une entrée et deux sorties (1 X2) et trois commutateurs à deux entrées et une sortie (2X1 ). Les trois commutateurs 1 X2 sont destinés à commuter la lumière émise par la source vers un des quatre chemins menant chacun à un des quatre points d'illumination en plaçant un commutateur 1 X2 à chaque sortie du commutateur 1 X2 dont l'entrée capte la lumière émise par la sou rce, les sorties de deux commutateurs en aval alimentant chacune un des chemins menant à un des quatre points d'illu mination. Les trois commutateurs 2X1 sont destinés à commuter la lumière issue de chaque point de prise de vue vers la caméra en plaçant un commutateur 2X1 en sorte qu'il capte la lumière issue de deux chemins venant de deux points de prise de vue et u n commutateur 2X1 en sorte qu'il capte la lumière issue des deux autres chemins venant des deux autres points de prise de vue et en plaçant le troisième commutateur 2X1 en sorte qu'il capte la lumière issue des sorties des deux commutateurs 2X1 précédents et que sa sortie illumine la caméra. Enfin, un jeu de miroirs (de préférence « presque parfaits ») complète la configu ration pour orienter les quatre chemins amenant la lumière aux quatre points d'illumination et les quatre chemins venant des quatre points de prise de vue.A second configuration, called "economic" comprises a light source, a beam widener, a liquid crystal screen placed immediately after the beam expander, a camera, three optical switches at an input and two outputs (1 X2) and three switches with two inputs and one output (2X1). The three switches 1 X2 are intended to switch the light emitted by the source to one of the four paths each leading to one of the four illumination points by placing a switch 1 X2 at each output of the switch 1 X2 whose input captures the light emitted by the source, the outputs of two downstream switches each feeding one of the paths leading to one of the four illumination points. The three 2X1 switches are intended to switch light from each point of view to the camera by placing a 2X1 switch so that it captures light from two paths coming from two shooting points and a 2X1 switch. so that it captures the light from the other two paths from the other two points of view and placing the third switch 2X1 so that it captures the light from the outputs of the two previous 2X1 switches and its output illuminates the camera. Finally, a set of mirrors (preferably "almost perfect") completes the configuration to guide the four paths bringing light to the four points of illumination and the four paths from the four points of view.
Dans une variante de cette deuxième configuration, on utilise à la place des commutateurs 1 X2 et 2X1 précédemment indiqués, des commutateurs qui sont un commutateur à une entrée et quatre sorties (1 X4) et un commutateur à quatre entrées et u ne sortie (4X1 ). Le commutateur 1 X4 commute la lumière émise par la source vers l'un des quatre chemins menant chacun à un des quatre points d'illumination et le commutateur 4X1 commute la lumière issue de chacun des quatre chemins venant chacun des quatre points de prise de vue vers la caméra. De même que précédemment, un jeu de miroi rs complète cette configuration afin d'orienter les quatre chemins amenant la lumière aux quatre points d'illumination et les quatre chemins venant des quatre points de prise de vue.In a variant of this second configuration, instead of switches 1 X2 and 2X1 previously indicated, switches are used which are a switch with one input and four outputs (1 X4) and a switch with four inputs and one output (4X1). ). The switch 1 X4 switches the light emitted by the source to one of the four paths each leading to one of the four illumination points and the switch 4X1 switches the light from each of the four paths from each of the four shooting points to the camera. As before, a set of mirrors completes this configuration in order to orient the four paths leading the light to the four points of illumination and the four paths coming from the four points of view.
Ces deuxièmes configurations donnent une précision de mesure légèrement moindre que celle de la première configuration à cause des petites déformations des images introduites par l'imperfection des miroirs et c'est donc pour cela que, de préférence, on utilise des miroirs « presque parfaits » . On peut noter qu 'une étape d'étalonnage sur un objet étalon peut permettre de prendre en compte ces imperfections (et/ou d'autres) et d'effectuer des corrections lors des mesures sur les objets à mesurer. En contrepartie, le coût de ces deuxièmes configurations matérielles est moi ndre que pour la première.These second configurations give a measurement accuracy slightly less than that of the first configuration because of the small deformations of the images introduced by the imperfection of the mirrors and it is for this reason that preferably "nearly perfect" mirrors are used. . It may be noted that a calibration step on a standard object may make it possible to take into account these imperfections (and / or others) and to make corrections during measurements on the objects to be measured. In return, the cost of these second hardware configurations is me ndre only for the first.
Une troisième configuration matérielle est dérivée des deuxièmes configurations et comporte les mêmes éléments sauf qu 'il y a quatre écrans à cristaux liquides au lieu d'un seul, chaque écran étant placé entre l'un des quatre points d'illumination et l'objet traité. La précision de la mesure est meilleure que celle des deuxièmes configurations grâce à l'absence de déformations des motifs projetés, absence due à l'élimination des composants intermédiaires entre les écrans à cristaux liquides et la su rface de l'objet traité. Le coût de cette troisième configuration matérielle est bas mais un peu plus élevé que le coût des deuxièmes configurations. Une quatrième configuration matérielle est dérivée des deuxièmes configurations et permet d'obtenir un compromis entre le coût et la précision. Cette quatrième configuration comporte les mêmes éléments que ceux des deuxièmes configurations mais avec quatre caméras placées chacune en un des quatre points de prise de vue et seulement trois commutateurs 1 X2 ou un commutateur 1 X4 qui commutent la lumière émise par la source vers l'un des quatre chemins menant aux quatre points d'illumination à la fois. La précision de la mesure obtenue en est meilleure que celle des deuxièmes et troisième configurations car l'acquisition par les caméras est di recte et donc sans déformations de l'image frangées par des composants intermédiai res. Toutefois, le coût en est un peu plus élevé que ceux des deuxièmes et troisième configurations mais moins élevé que celui de la première configuration.A third hardware configuration is derived from the second configurations and has the same elements except that there are four liquid crystal screens instead of one, each screen being placed between one of the four illumination points and the object. treaty. The accuracy of the measurement is better than that of the second configurations due to the absence of deformation of the projected patterns, absence due to the elimination of the intermediate components between the liquid crystal displays and the suface of the treated object. The cost of this third hardware configuration is low but slightly higher than the cost of the second configurations. A fourth hardware configuration is derived from the second configurations and provides a compromise between cost and accuracy. This fourth configuration has the same elements as those of the second configurations but with four cameras each placed in one of the four points of view and only three switches 1 X2 or a switch 1 X4 which switch the light emitted by the source to one the four paths leading to the four points of illumination at a time. The accuracy of the measurement obtained is better than that of the second and third configurations because the acquisition by the cameras is di rect and therefore without deformations of the image fringed by intermediate components. However, the cost is a little higher than those of the second and third configurations but lower than that of the first configuration.
Une cinquième configuration matérielle est dérivée de la quatrième configu ration et permet d'obtenir également un compromis entre le coût et la précision. Cette cinquième configuration comporte les mêmes éléments que ceux de la quatrième configuration mais avec quatre écrans à cristaux liquides placés chacu n entre un des quatre points d'illumination et la surface de l'objet traité. La précision de la mesure obtenue en est meilleu re que celle de la quatrième configuration car la projection des motifs et l'acquisition par les caméras sont directes et donc sans déformations de l'image frangées par des composants intermédiaires. Toutefois, le coût en est un peu plus élevé que celui de la quatrième configuration mais moins élevé que celui de la première configuration.A fifth hardware configuration is derived from the fourth configuration and also provides a compromise between cost and accuracy. This fifth configuration has the same elements as those of the fourth configuration but with four liquid crystal screens each placed between one of the four points of illumination and the surface of the object treated. The accuracy of the measurement obtained is better than that of the fourth configuration because the projection of the patterns and the acquisition by the cameras are direct and therefore without deformations of the image fringed by intermediate components. However, the cost is slightly higher than that of the fourth configuration but lower than that of the first configuration.
On va maintenant décrire plus en détail les modalités de pilotage pour mise en œuvre de l'invention. II existe trois modalités de pilotages possibles pour le système multi-canaux tétraédrique de l'invention. Chaque modalité de pilotage comporte différentes phases d'illuminations / acquisitions dont quelques exemples sont fournis dans la suite.We will now describe in more detail the piloting arrangements for implementing the invention. There are three possible control modalities for the tetrahedral multi-channel system of the invention. Each control mode includes different phases of illuminations / acquisitions, some examples of which are provided below.
Une première modalité consiste en un pilotage complet dans lequel tous les quadruplets définis par un point d'illumination et trois points de prise de vue fonctionnent et, cela, les uns après les autres (une illumination et trois ensembles d'acquisitions). Ainsi, pour chaque axe de projection, trois ensembles d'images acquises sont disponibles pour traitement, un ensemble par axe de prise de vue. L'information obtenue est la plus complète possible mais le temps d'acquisition est le moins optimisé et l'utilisation des ressources informatiques est la plus lourde. Toutefois, les trois points de prise de vue fonctionnant simultanément, le temps d'acquisition par quadruplet est le même que pour un système à un canal simple (un point d'illumination, un point de prise de vue) mais, par contre, le temps de traitement est plus long car il y a plus d'information à traiter.A first modality consists of a complete control in which all the quadruplets defined by an illumination point and three points of view work and that, one after the other (an illumination and three sets of acquisitions). Thus, for each projection axis, three sets of acquired images are available for processing, one set per axis of view. The information obtained is as complete as possible, but the acquisition time is the least optimized and the use of computer resources is the heaviest. However, the three shooting points operating simultaneously, the acquisition time per quadruplet is the same as for a single-channel system (an illumination point, a point of view) but, on the other hand, the Processing time is longer because there is more information to process.
Il est à noter que les quadruplets peuvent être, dans une variante, définis par un point de prise de vue et trois points d'illumination adjacents. Ainsi, pour chaque axe de prise de vue, trois ensembles d'images acquises sont disponibles pour traitement, un ensemble par axe de projection. Toutefois et au contraire de l'exemple de quadruplets précédent où les trois points de prise de vue peuvent acquérir leurs images simultanément, les quadruplets trois points d'illumination / un point de prise de vue oblige le point de prise de vue à acquérir toutes ces images séquentiellement, chaque point d'illumination illuminant l'un après l'autre afin de ne pas détruire les motifs de franges projetés par chacun des différents points d'illumination. Ce dernier mode de pilotage présente toutefois peu d'intérêt notamment en ce qui concerne le temps d'acquisition qui est le plus long pour le système multi-canaux tétraédrique de l'invention, (sauf multiplexage colorimétrique).It should be noted that the quadruplets may alternatively be defined by a point of view and three adjacent illumination points. Thus, for each axis of view, three sets of acquired images are available for processing, one set per projection axis. However and contrary to the previous example of quadruplets where the three points of view can acquire their images simultaneously, quadruplets three points of illumination / a point of view forces the point of view to acquire all these points. images sequentially, each illumination point illuminating one after the other so as not to destroy the fringe patterns projected by each of the different points of illumination. This last mode of driving However, this is of little interest, especially as regards the acquisition time which is the longest for the tetrahedral multi-channel system of the invention (except colorimetric multiplexing).
Une deuxième modalité consiste en un pilotage semi-complet. Cette modalité correspond à la précédente sauf que certains ou tous les quadruplets sont réduits à des triplets (un point d'illumination et seulement deux points de prise de vue adjacents) et que seuls les quadruplets ou triplets nécessaires au recouvrement du relief quasi-intégral de la surface complète de l'objet traité fonctionnent afin d'éviter toute information redondante inutile. Le temps d'acquisition et l'utilisation des ressources informatiques sont améliorés. Le degré de complexité du relief de la surface de l'objet traité et le degré de complexité de la géométrie de ce même objet déterminent le nombre de quadruplets et/ou de triplets nécessaires au traitement voulu.A second modality consists of a semi-complete piloting. This modality corresponds to the previous one except that some or all quadruplets are reduced to triplets (one point of illumination and only two adjacent points of view) and that only the quadruplets or triplets necessary for the recovery of the quasi-integral relief of the entire surface of the processed object work to avoid unnecessary redundant information. The acquisition time and the use of IT resources are improved. The degree of complexity of the relief of the surface of the object treated and the degree of complexity of the geometry of the same object determine the number of quadruplets and / or triplets necessary for the desired treatment.
Une troisième modalité consiste en un pilotage optimisé dans lequel un canal d'illumination et une caméra d'un axe de prise de vue adjacent fonctionnent à la fois, les différents couples ou duets points d'illumination/point de prise de vue fonctionnant les uns après les autres. Les duets axe d'illumination/axe de prise de vue sont choisis de telle sorte que l'information nécessaire au traitement de la surface de l'objet traité soit suffisante pour recouvrir le relief quasi-intégral de cette surface complète mais soit aussi réduite au minimum nécessaire pour cela. Toutefois, si deux duets ont un point d'illumination en commun et que cela est nécessaire au bon recouvrement de relief quasi-intégral de la surface illuminée, il est clair que ces deux duets doivent fonctionner en même temps, c'est à dire constituer à nouveau un triplet. De même pour trois duets avec un point d'illumination en commun: ils se rassemblent en un quadruplet. Ainsi, le temps d'acquisition est optimisé et l'utilisation des ressources informatiques également. Cette procédure de pilotage n'est réalisable que si le relief et la géométrie de l'objet traité sont suffisamment simples.A third modality consists of an optimized control in which an illumination channel and a camera of an adjacent shooting axis operate at the same time, the different pairs or duets of illumination points / shooting point operating at one and the same time. after others. The duets illumination axis / shooting axis are chosen so that the information necessary for the treatment of the surface of the treated object is sufficient to cover the almost complete relief of this complete surface but is also reduced to minimum necessary for this. However, if two duets have a point of illumination in common and that this is necessary for the good quasi-integral relief coverage of the illuminated surface, it is clear that these two duets must function at the same time, ie constitute again a triplet. Similarly for three duets with a point of illumination in common: they gather in a quadruplet. So the time acquisition is optimized and the use of computer resources also. This piloting procedure is only feasible if the relief and the geometry of the treated object are sufficiently simple.
On comprend que l'invention peut être déclinée de nombreuses manières sans pour autant sortir du cadre défini par l 'objet de ses revendications.It is understood that the invention can be declined in many ways without departing from the scope defined by the subject of its claims.
Ainsi , bien que la méthode FP-PSM soit la plus adaptée pour le système multi-canaux tétraédrique de l'invention, d'autres méthodes peuvent être mises en œuvre avec un tel système pour résolution du relief intégral (ou quasi intégral) de la surface extérieu re complète d'un objet en trois dimensions. De même en ce qui concerne la structure du système, le nombre de sources lumineuses, d'élargisseurs et d'écrans à cristaux liquides pour génération des franges peut être compris entre un (comme décrit ci-dessus) et quatre, le/les systèmes de commutation de faisceaux d'illumination par franges et miroirs de renvoi vers l 'objet étant prévus en conséquence. Il peut en être de même pour le nombre de caméra(s), compris entre une et quatre, et avec moins de quatre caméras, des moyens (mi roir(s) commutable(s), déplacement(s) de caméra(s) ... ) pour permettre des prises de vues à parti r des quatre emplacements sont prévus pour permettre la répartition géométrique décrite. De plus le/les systèmes de commutation de faisceaux d'illumination peuvent, dans certaines variantes de réalisation, être combinés aux miroirs, le miroir jouant le rôle de moyen de commutation de faisceau. Enfin, en aval de la mesure, de nombreuses applications sont possibles, simple visualisation 3D sur écran 2 D, visualisation dans l'espace par moyens de visualisation 3D, pilotage d'une machine de photo-polymérisation d'objets 3D ou d'u ne machine d'usinage... Par ailleu rs, si, de préférence, les franges lumineuses sont noires et blanches avec niveaux de gris intermédiaire (franges analogiques), on peut appliquer l'invention à des franges de couleu rs, plusieurs dispositifs d'illumination, chacun d'une couleur spécifique, étant mis en œuvre pour multiplexage colorimétrique, la/les caméras couleu rs et l'équipement informatique pouvant différentier les franges d'illumination en fonction de la couleur lors d'illuminations simultanées de l'objet à partir de plusieurs points d'illumination. On peut également répéter les mesures avec des dispositions et structures de franges différentes (orientation et/ou fréquence du motif et/ou fréquence différente selon la position su r la surface de l'objet... suite à un processus itératif d'adaptation pour rechercher une amélioration de la précision notamment dans des zones de surface particulière de l'objet) notamment pour améliorer la qualité des résultats. Enfi n, une ou plusieu rs étapes d'étalonnage avec des objets étalon peuvent permettre de prendre en compte et corriger des aberrations optiques diverses et/ou de légers décalages dans la disposition des éléments du système lors des mesures ultérieures sur les objets à mesurer. Thus, although the FP-PSM method is the most suitable for the tetrahedral multi-channel system of the invention, other methods can be implemented with such a system for resolving the integral (or almost integral) relief of the outer surface of an object in three dimensions. Similarly with regard to the structure of the system, the number of light sources, wideners and liquid crystal displays for generation of the fringes can be between one (as described above) and four, the system (s) switching of illumination beams by fringes and reflecting mirrors towards the object being provided accordingly. It may be the same for the number of cameras, between one and four, and with less than four cameras, means (s) switchable (s), displacement (s) camera (s) ...) to allow shooting from the four locations are provided to allow the geometric distribution described. In addition, the illumination beam switching system (s) may, in certain embodiments, be combined with the mirrors, the mirror acting as a beam switching means. Finally, downstream of the measurement, many applications are possible, simple 3D visualization on 2 D screen, visualization in space by means of 3D visualization, control of a machine for photo-polymerization of 3D objects or a do machining machine ... On the other hand, if, preferably, the light fringes are black and white with intermediate gray levels (analog fringes), the invention can be applied to color fringes, several illumination devices, each of one color specific, being implemented for colorimetric multiplexing, the color camera (s) and the computer equipment can differentiate the illumination fringes according to the color during simultaneous illuminations of the object from several illumination points . It is also possible to repeat the measurements with different fringe arrangements and structures (orientation and / or frequency of the pattern and / or different frequency depending on the position on the surface of the object ... following an iterative adaptation process for to seek an improvement of the accuracy especially in particular surface areas of the object) in particular to improve the quality of the results. Finally, one or more calibration steps with standard objects can make it possible to take into account and correct various optical aberrations and / or slight shifts in the arrangement of the elements of the system during subsequent measurements on the objects to be measured.

Claims

REVENDICATIONS
1. Procédé optico-informatique de mesure 3D de la surface extérieure d'un objet en relief par projection de franges sur ledit objet et utilisation d'une méthode à décalage de phase, les franges étant projetées sur l'objet par au moins un dispositif d'illumination, des images de l'objet frangé étant prises selon plusieurs axes de prise de vue avec au moins un moyen de prise de vue, lesdites images étant transmises à un équipement informatique comportant un programme de calcul de relief à partir des images, caractérisé en ce que l'on met en œuvre quatre axes de projection des franges sur l'objet, l'origine de chaque axe de projection étant considéré comme un point d'illumination disposé sensiblement à chacun des quatre sommets d'un tétraèdre virtuel, l'objet étant placé sensiblement au centre dudit tétraèdre, et en ce que l'on réalise les prises de vue à partir de quatre points de prise de vue disposés sensiblement le long de quatre axes de prise de vue, chacun des axes de prise de vue étant la médiane d'un des quatre trièdres formés par les quatre triplets d'axes de projection, les quatre points de prise de vue étant à une distance de l'objet telle qu'en chaque point de prise de vue, chaque image inclut au moins une partie de chacune des trois surfaces de l'objet pouvant être éclairée par les trois points d'illumination du triplet d'axes de projection définissant par sa médiane l'axe de prise de vue dudit point de prise de vue, et en ce que l'on acquière dans l'équipement informatique un ensemble d'images de chacune des six surfaces pouvant être illuminées et définies par six couples de points d'illumination.An optico-computing method for 3D measurement of the external surface of an object in relief by projecting fringes on said object and using a phase shift method, the fringes being projected onto the object by at least one device illumination, images of the fringed object being taken along several axes of shooting with at least one means of shooting, said images being transmitted to a computer equipment comprising a program for calculating relief from the images, characterized in that four fringe projection axes are implemented on the object, the origin of each projection axis being considered as an illumination point disposed substantially at each of the four vertices of a virtual tetrahedron, the object being placed substantially in the center of said tetrahedron, and in that the shots are taken from four shooting points arranged substantially along four axes of view, ch each of the shooting axes being the median of one of the four trihedrons formed by the four triplets of projection axes, the four shooting points being at a distance from the object such that at each point of capture in view, each image includes at least a portion of each of the three surfaces of the object that can be illuminated by the three points of illumination of the triplet of projection axes defining by its median the axis of view of said point of and acquiring in the computer equipment a set of images of each of the six surfaces that can be illuminated and defined by six pairs of illumination points.
2. Procédé selon la revendication 1, caractérisé en ce que les quatre points d'illumination proviennent d'au moins un et jusqu'à quatre dispositifs d'illumination par des franges, et en ce que l'on dispose ledit/lesdits dispositif aux points d'illumination et/ou le/les illuminations dudit/desdits moyens sont redirigées par au moins un miroir et/ou ledit/lesdits moyens sont déplaçables physiquement.2. Method according to claim 1, characterized in that the four illumination points come from at at least one and up to four illumination devices with fringes, and in that said device (s) is provided at the illumination points and / or the illumination (s) of said at least one means are redirected by at least one mirror and / or said means / means are physically movable.
3. Procédé selon la revendication 2, caractérisé en ce que les quatre points d'illumination proviennent d'un seul dispositif d'illumination, et en ce que l'on redirige l'illumination dudit moyen le long de l'axe de projection correspondant par un ensemble de miroirs.3. Method according to claim 2, characterized in that the four illumination points come from a single illumination device, and in that the illumination of said means is redirected along the corresponding projection axis. by a set of mirrors.
4. Procédé selon la revendication 2 ou 3, caractérisé en ce que le/les miroirs sont commandés par l'équipement informatique.4. Method according to claim 2 or 3, characterized in that the mirror (s) are controlled by the computer equipment.
5. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que l'on met en œuvre pour chaque dispositif d'illumination une source lumineuse, un élargisseur de faisceau et un écran à cristaux liquide commandé par l'équipement informatique pour y former un motif de franges.5. Method according to any one of the preceding claims, characterized in that it implements for each illumination device a light source, a beam expander and a liquid crystal screen controlled by the computer equipment for therein. form a pattern of fringes.
6. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que l'on met en œuvre des franges lumineuses qui sont analogiques.6. Method according to any one of the preceding claims, characterized in that one implements light fringes which are analog.
7. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que l'on met en œuvre quatre moyens de prise de vue indépendants et fixes, qui sont disposés aux points de prise de vue.7. Method according to any one of the preceding claims, characterized in that it implements four independent and fixed shooting means, which are arranged at the shooting points.
8. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que pour les prises de vue on illumine séquentiellement l'objet selon les quatre axes de projection, pour acquérir un ensemble d'images de chacune des six surfaces pouvant être illuminées et définies par six couples de points d'illumination.8. Method according to any one of the preceding claims, characterized in that for the images sequentially illuminates the object along the four axes of projection, to acquire a set of images of each of the six surfaces that can be illuminated and defined by six pairs of points of illumination.
9. Système de mesure 3D de la surface extérieure d'un objet pour la mise en œuvre du procédé de l'une quelconque des revendications précédentes, caractérisé en ce qu'il comporte au moins un dispositif d'illumination de l'objet par des franges et une partie d'acquisition d'images et de calcul de relief dans un équipement informatique comportant un programme à partir desdites images acquises par au moins un moyen de prise de vue, le/les dispositifs d'illumination permettant la projection sur l'objet de franges selon quatre axes de projection, l'origine de chaque axe de projection étant considéré comme un point d'illumination disposé sensiblement à chacun des quatre sommets d'un tétraèdre virtuel, l'objet étant placé sensiblement au centre dudit tétraèdre, et les prises de vue sont effectuées à quatre points de prise de vue disposés sensiblement le long de quatre axes de prise de vue, chacun des axes de prise de vue étant la médiane d'un des quatre trièdres formés par les quatre triplets d'axes de projection, les quatre points de prise de vue étant à une distance de l'objet telle qu'en chaque point de prise de vue, chaque image inclut au moins une partie de chacune des trois surfaces de l'objet pouvant être éclairée par les trois points d'illumination du triplet d'axes de projection définissant par sa médiane l'axe de prise de vue dudit point de prise de vue, et en ce que l'équipement informatique comporte des moyens pour acquérir un ensemble d'images de chacune des six surfaces pouvant être illuminées et définies par six couples de points d'illumination.9. 3D measurement system of the outer surface of an object for implementing the method of any one of the preceding claims, characterized in that it comprises at least one device for illuminating the object by means of fringes and a part of image acquisition and relief calculation in a computer equipment comprising a program from said images acquired by at least one means of shooting, the illumination device (s) allowing the projection on the fringe object according to four axes of projection, the origin of each projection axis being considered as an illumination point disposed substantially at each of the four vertices of a virtual tetrahedron, the object being placed substantially in the center of said tetrahedron, and the shots are taken at four points of view arranged substantially along four axes of shooting, each of the axes of shooting being the median of one of the four forte by the four triplets of projection axes, the four shooting points being at a distance from the object such that at each point of view, each image includes at least a portion of each of the three surfaces of the object being able to be illuminated by the three points of illumination of the triplet of projection axes defining by its median the axis of view of said point of view, and in that the computer equipment comprises means for acquire a set of images of each of the six surfaces that can be illuminated and defined by six pairs of illumination points.
10. Système de mesure selon la revendication 9, caractérisé en ce que le dispositif d'illumination comporte une source lumineuse, un élargisseur de faisceau et un écran à cristaux liquide commandé par l'équipement informatique pour y former un motif de franges. Measuring system according to claim 9, characterized in that the illumination device comprises a light source, a beam expander and a liquid crystal screen controlled by the computer equipment to form a pattern of fringes.
EP07871965A 2006-12-19 2007-12-18 Optical computerized method for the 3d measurement of an object by fringe projection and use of a phase-shift method, corresponding system Withdrawn EP2095069A2 (en)

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FR0655661A FR2910123B1 (en) 2006-12-19 2006-12-19 OPTICAL-COMPUTING METHOD FOR 3D MEASUREMENT OF THE EXTERNAL SURFACE OF AN OBJECT IN RELIEF BY PROJECTION OF FRINGES AND USE OF A METHOD WITH A PHASE SHIFT, CORRESPONDING SYSTEM
PCT/FR2007/052551 WO2008081149A2 (en) 2006-12-19 2007-12-18 Optical computerized method for the 3d measurement of an object by fringe projection and use of a phase-shift method, corresponding system

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US20100092040A1 (en) 2010-04-15
FR2910123B1 (en) 2009-01-23

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