CN113031003B - Panoramic optical system, panoramic scanning system and imaging system based on MEMS (micro-electromechanical systems) micro-mirror - Google Patents
Panoramic optical system, panoramic scanning system and imaging system based on MEMS (micro-electromechanical systems) micro-mirror Download PDFInfo
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- CN113031003B CN113031003B CN202110333307.3A CN202110333307A CN113031003B CN 113031003 B CN113031003 B CN 113031003B CN 202110333307 A CN202110333307 A CN 202110333307A CN 113031003 B CN113031003 B CN 113031003B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/88—Lidar systems specially adapted for specific applications
- G01S17/89—Lidar systems specially adapted for specific applications for mapping or imaging
- G01S17/894—3D imaging with simultaneous measurement of time-of-flight at a 2D array of receiver pixels, e.g. time-of-flight cameras or flash lidar
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/481—Constructional features, e.g. arrangements of optical elements
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/483—Details of pulse systems
- G01S7/486—Receivers
- G01S7/4865—Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak
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Abstract
A panoramic optical system, a panoramic scanning system and an imaging system based on an MEMS (micro-electromechanical system) micromirror belong to the technical field of optical imaging. The scanning angle of the MEMS micro-mirror in the scanning type laser radar is small. The panoramic optical system based on the MEMS micro-mirror comprises a cylindrical refraction and reflection type panoramic prism, wherein a through hole is formed in the center of a cylinder, a conical space is arranged in the cylinder, the height of the conical space is smaller than that of the cylinder, the conical space is communicated with the through hole, the conical space is overlapped with the axis of the cylinder, and the maximum flaring surface of the conical space is an end surface of the cylinder when the conical space is not arranged; the base angle of the tangent plane of the conical space along the axis is 36.5 deg.. The panoramic optical system based on the MEMS micro-mirror also comprises an inclined truncated cone-shaped compensating prism; the frustum-shaped compensating prism is frustum-shaped, three side surfaces of the frustum-shaped compensating prism are planes, and one side surface of the frustum-shaped compensating prism is a curved surface. The MEMS micro-mirror is mainly used for scanning and imaging of the MEMS micro-mirror in the scanning type laser radar.
Description
Technical Field
The invention relates to a panoramic optical system, a panoramic scanning system and an imaging system, and belongs to the technical field of optical imaging.
Background
With the promotion of technologies such as artificial intelligence, optical communication technology, automation technology and the like, automatic driving and more unmanned transportation equipment are gradually becoming reality, so an environment perception system with good perception capability to the surrounding environment is urgently needed, so that the unmanned equipment can make an accurate decision, and a laser radar 3D vision system is one of the most effective means for solving high-precision perception of three-dimensional environment information at present, is always taken as a leading-edge problem in the world and is widely concerned.
The main technical routes of the current environment-aware lidar can be divided into two main categories: mechanical rotary lidar and solid state lidar. The mechanical rotary laser radar is used for realizing the scanning of a light beam by adopting a mechanical rotating part, the technology is developed at the earliest and is relatively mature, but the mechanical rotary laser radar has the defects of difficult assembly, low scanning frequency and high price. The main methods of the solid-state laser radar include micro-electro-mechanical system (MEMS) hybrid solid-state laser radar, Flash (Flash) laser radar, and Optical Phased Array (OPA) laser radar. Although the Flash technology is partially commercially available at present, the main defect of the route is that when the laser with large energy illuminates the whole target scene in a Flash mode at one time, only a small part of reflected light can be received by the detector, so that a large amount of laser energy is wasted, the signal-to-noise ratio of echo signals is low, the detection distance is limited, and the key factor for restricting the large-scale application of the technology is also realized; OPA scanning is a fully solid-state radar technique. However, the technology is essentially based on the diffraction effect of optics, and the problems of effective optical transmittance, side lobe effect and the like are key problems which need to be solved in further development of the technology, so far, the research on the OPA technology in the world has low maximum detection distance and is not mature, and many key problems are not solved well. The core technology of the MEMS hybrid solid-state laser radar is that a traditional one-dimensional mechanical rotating part is replaced by an MEMS micro-mirror, so that a certain integration level can be achieved, and the problem of solid stating is solved to a certain extent. But its main disadvantage is the small size of the MEMS micro-mirror and thus the limited scanning range. This disadvantage can however be overcome by configuring the respective optical system to be angle-broadened. Therefore, the MEMS lidar is one of the most promising technical routes due to its light weight, fast scanning speed and low cost, and is also the technical scheme of the most possible large-scale practical application.
In a conventional MEMS scanning lidar, the mechanical scanning angle of the MEMS micro-mirror is small (below 15 °), and even with the addition of the angle-expanding system, the scanning angle is still small (typically less than 60 °). However, the current demands for automatic driving and some application scenarios put higher demands on the environment sensing system, namely solid stating and panoramic imaging, which means that no cumbersome mechanical rotating device is needed, and the volume can be miniaturized so as to be integrated in the interior of the vehicle body, and simultaneously 360-degree panoramic scanning in the horizontal direction can be realized.
The traditional panoramic imaging technology comprises a fish-eye lens, a plurality of lenses are spliced to realize panoramic imaging and a catadioptric panoramic lens, and the methods are all used for imaging devices based on CCD or CMOS. A fisheye lens is essentially a super-wide angle lens with a very short focal length, which can reach a hemispherical field of view, named because its front portion is as prominent as a fisheye lens. However, when a large field of view is obtained, a large image distortion is generated, and the whole system is large and complex. The difficulty is very high in design processing and image correction at the later stage of assembly. The multi-lens splicing is to splice images of a plurality of lenses to form a panoramic image, but in the image splicing process, the cameras are not matched, the structural tolerance, the image edge overlapping and the color parameters of different cameras are not matched, so that the imaging distortion can be caused, the whole system is complex in structure, large in size, high in cost and high in consistency correction difficulty. In addition, the conventional catadioptric panoramic lens is generally combined by dozens of lenses and has no scanning component, so that the conventional catadioptric panoramic lens is not suitable for the MEMS scanning type laser radar.
Disclosure of Invention
The invention aims to solve the problem of small scanning angle of an MEMS (micro-electromechanical system) micro-mirror in the existing scanning type laser radar.
The panoramic optical system based on the MEMS micro-mirror comprises a catadioptric panoramic prism;
the catadioptric panoramic prism is a cylinder, a through hole is formed in the center of the cylinder, a conical space is arranged in the cylinder, the height of the conical space is smaller than that of the cylinder, the conical space is communicated with the through hole, the conical space is overlapped with the axis of the cylinder, and the maximum flaring surface of the conical space is an end surface of the cylinder when the conical space is not formed; the base angle of the tangent plane of the conical space along the axis is 36.5 deg..
Furthermore, the material of the refraction and reflection type panoramic prism is glass BK7, and the refractive index n is 1.52.
Furthermore, the panoramic optical system based on the MEMS micro-mirror also comprises an oblique circular truncated cone-shaped compensating prism;
the oblique circular truncated cone-shaped compensating prism is in an oblique circular truncated cone shape and is provided with four side faces and an upper bottom face and a lower bottom face, three side faces of the four side faces are planes, one side face is a curved face, two opposite side faces of the three side faces are trapezoidal and are parallel to each other, and the upper bottom face and the lower bottom face are parallel and are different in area.
Furthermore, the center radius corresponding to the curved surface of the truncated cone-shaped compensating prism is 160mm, and the center focal length of the truncated cone-shaped compensating prism is 300 mm.
The oblique truncated cone-shaped compensating prism is arranged at the front end of the light path of the catadioptric panoramic prism, namely after laser is emitted, the oblique truncated cone-shaped compensating prism firstly passes through the catadioptric panoramic prism, and then the catadioptric panoramic prism is catadioptric.
Further, the material of the truncated cone-shaped compensating prism is glass BK7, and n is 1.52.
A MEMS micro-mirror based panoramic scanning system, the MEMS micro-mirror based panoramic scanning system comprising: the system comprises a transmitting system, an optical isolator, a panoramic optical system based on an MEMS micro-mirror, the MEMS micro-mirror, an MEMS micro-mirror control system, a receiving system and a signal processing control system;
the transmitting system comprises a laser and a laser control system;
the receiving system comprises a high-speed APD photoelectric detector;
the signal processing control system comprises a timing and time measuring system;
the panoramic scanning system based on the MEMS micro-mirror adopts a receiving and sending combined mode, and when the panoramic scanning system based on the MEMS micro-mirror works, the laser control system, the MEMS micro-mirror control system and the time measuring system start to work simultaneously after receiving synchronous signals; the MEMS micro-mirror control system controls the MEMS micro-mirror to reflect the light beam to the catadioptric panoramic prism according to a scanning track, and the light beam is reflected to a target space through catadioptric panoramic prism;
the scattering signal reflected by the target is received by a high-speed APD photoelectric detector, the detector converts the optical signal into an electric signal, and then the processed electric signal is sent to a timing and time measuring system.
Furthermore, the laser adopts a high repetition frequency high-power 1550nm pulse optical fiber laser, and the repetition frequency is 100 KHz.
Further, the process of controlling the MEMS micro-mirror to scan by the MEMS micro-mirror control system includes the following steps:
the rotation angular velocity around the central axis of the MEMS micro-mirror is omega, and the linear velocity of the rising line is v z And if the projection curve of the spiral line on the xoy coordinate plane is an equidistant Archimedes spiral line, the motion and parameter equation is as follows:
wherein, delta is the polar angle of the scanning point on the scanning plane; r is the radius of the bottom surface of a cone in a conical space inside the catadioptric panoramic prism, and H is the height of the conical space; t is time;
the xoy coordinate plane is a plane where a conical bottom surface of a conical space inside the panoramic prism is located or a plane parallel to the conical bottom surface of the conical space inside the panoramic prism, and the z axis is a coordinate axis perpendicular to the xoy coordinate plane;
let H be H/n be the distance that each turn of the helix rises, then the length d of the radius extension of each turn of the helix is (H/R) × H; according to the equation of motion, the trajectory length L of the spiral line is:
in the formula, n is the number of turns of the spiral line and the polar diameter of the spiral line
δ min Is the initial polar angle, δ max To end the polar angle.
Further, an initial polar angle δ min ＝2πr min D, end polar angle delta max ＝2πr max D; wherein r is min Is the minimum helix diameter, r max Is the maximum helix diameter.
An imaging system comprises two sets of panoramic scanning systems based on MEMS micro-mirrors;
two catadioptric panoramic prisms of the two sets of panoramic scanning systems based on the MEMS micro-mirror are oppositely arranged, and the axes of the two catadioptric panoramic prisms which are oppositely arranged are superposed; the two MEMS micromirrors are arranged between the two catadioptric panoramic prisms, lasers of the two panoramic scanning systems based on the MEMS micromirrors respectively enter from through holes of the corresponding catadioptric panoramic prisms, are reflected by the MEMS micromirrors and then irradiate on the corresponding catadioptric panoramic prisms, and imaging is achieved after the catadioptric panoramic prisms are folded back.
Further, the two lasers of the two sets of MEMS micro-mirror based panoramic scanning systems alternately emit laser light.
Has the advantages that:
the invention utilizes the characteristics of the MEMS galvanometer spiral scanning form and the laser radar 3D imaging technology to design a catadioptric panoramic scanning optical system with simple structure and small volume, which is suitable for the laser radar of MEMS micromirror scanning, the MEMS micromirror is arranged in the optical system to carry out spiral scanning, and further the scanning of 360 degrees of horizontal view field and 15 degrees of vertical view field is realized, the horizontal resolution is 0.1 degree, and the vertical resolution is 0.5 degree. And simultaneously, the spiral scanning principle of the MEMS micro-mirror is researched, the optimal scanning parameters are determined, and the optimal scanning beam filling ratio is realized. And the Zemax optical design software is used for analyzing the design result, the spot sequence diagram shows that the emergent light spots are circular and are uniformly distributed, the divergence angle is smaller than 1mrad, the actual requirements can be well met, and the problems of laser radar solid state and 360-degree panoramic scanning imaging are solved.
Drawings
FIG. 1 is a view of a structure of a catadioptric panoramic prism;
FIG. 2 is a schematic view of an optical path of an axial section of a catadioptric panoramic prism;
FIG. 3 is a schematic diagram of a 360-degree MEMS micro-mirror panoramic scanning laser radar system;
FIG. 4 is a diagram of MEMS micro-mirror control command signals and MEMS micro-mirror scanning trajectories;
FIG. 5 is a spiral scanning trajectory of the MEMS micro-mirror;
FIG. 6 shows the actual scanning trajectory of the MEMS micro-mirror;
FIG. 7 is a view of a refractive panoramic prism;
FIG. 8 is an optical path diagram of a panoramic optical system in a meridian plane;
FIG. 9 is an optical path diagram of the panoramic optical system in the sagittal plane;
fig. 10 is a diagram of spot arrays of emergent light spots of different scanning fields, and α values in fig. 10(a) to 10(f) are 38 °, 39 °, 40 °, 41 °, 42 ° and 43 ° in sequence;
FIG. 11 is a schematic view of an oblique truncated cone-shaped compensating prism;
FIG. 12 is a schematic view of the corrected overall optical path;
FIGS. 13(a) and 13(b) are spot alignment diagrams for different scan fields at 100mm and 200mm from the exit surface;
FIG. 14 is a schematic view of the geometric relationship of a catadioptric panoramic optical system.
Detailed Description
The first embodiment is as follows:
the embodiment is a panoramic optical system based on an MEMS (micro-electromechanical system) micro-mirror, which comprises a refraction-reflection type panoramic prism and an inclined truncated cone-shaped compensating prism;
as shown in fig. 1, the catadioptric panoramic prism is a cylinder 1, a through hole 2 is arranged in the center of the cylinder, a conical space 3 is arranged in the cylinder, the height of the conical space is smaller than that of the cylinder, the conical space is communicated with the through hole, the conical space is actually a truncated cone space due to the fact that the cone tip of the conical space is actually coincident with the through hole, the conical space is coincident with the axis of the cylinder, and the maximum flaring surface (the bottom surface of the conical space) of the conical space is an end surface of the cylinder when the conical space is not arranged; the base angle of the section of the conical space along the axis (longitudinal section) is 36.5 °, i.e. in fig. 2 β is 36.5 °.
The real object image of the refraction-reflection type panoramic prism is shown in fig. 7, the structure is simple, the size is small, the refraction-reflection type panoramic prism can be obtained through integral injection molding, and mass production can be realized. The material is common glass BK7, and the refractive index n is 1.52.
The panoramic optical system of the half-folded panoramic prism and the MEMS micro-mirror is explained by combining the design principle and the design process as follows:
in order to realize 360-degree panoramic scanning imaging of the laser radar in the horizontal direction, the invention needs to design an anti-distortion catadioptric prism optical system, the geometric relation schematic diagram of the anti-distortion catadioptric panoramic optical system is shown in fig. 14, the z axis is coincident with the optical axis, the z axis is a symmetry axis, and the reflecting surface is rotationally symmetrical around the z axis. The angle between the incident light and the negative direction of the z axis is represented by an included angle theta; included angle for angle between reflected light and negative z-axis direction
Representing; point F is the principal point of the ideal mirror surface, placing the MEMS micro-mirror at point F.
In the figure, parameters of a rotationally symmetrical reflecting surface type under a polar coordinate system are (l, theta) and parameters under a plane rectangular coordinate system are (r, z), wherein l represents the distance from an original point to any point of the reflecting mirror, and theta represents an included angle between reflected light of the MEMS micro-mirror and the vertical direction; r represents a distance in the direction of the horizontal coordinate axis; z represents a distance in the z-axis direction. The reflecting surface type can be expressed as z ═ z (r) under the rectangular plane coordinate system parameter and l ═ l (θ) under the polar coordinate system parameter, and the relationship between the two is:
the included angle between the tangent T at the M point of the reflecting surface and the negative direction of the Z axis is beta, and the following can be obtained:
in the formula, l 'is a differential form of l (θ), i.e., l' ═ dl/d θ. After finishing, obtaining:
integrating the above equation to obtain:
in the formula, l (0) is a distance from the origin of coordinates to the reflection surface when the reflection angle θ is 0. Because the angle theta has a corresponding imaging relationship with the image point on the image plane, when theta is associated with theta
Having a linear proportional relationship, i.e.
Distortion can be eliminated. Wherein k is a linear proportionality coefficient. From the geometrical relationships in the above figures, it can be seen that:
further, a differential expression of the mirror surface profile can be obtained:
different linear proportionality coefficients k, the surface profile of the anti-distortion mirror will be different,
when k is 1, l (θ) is l (0)/cos θ, z is l (0), and the surface shape of the reflecting surface is a plane.
When k is 3, l 2 (θ)＝l 2 (0)/cos2θ，z 2 -r 2 ＝l 2 (0) The surface type of the reflecting surface is a hyperboloid.
When k is 5, l 3 (θ)＝l 3 (0)/cos3θ，z 3 -r 3 ＝l 3 (0) The surface of the reflecting surface is a 3-order rotationally symmetric aspheric surface.
Designing a refraction and reflection optical path as shown in fig. 2, and rotating the entity (half of the axial section of the refraction and reflection type panoramic prism) in the figure by 360 degrees to form the designed refraction and reflection type panoramic prism. The pulse laser emits laser beams with the spot diameter of 3mm through the collimating mirror, the laser beams are incident on the MEMS micro-mirror and are deflected to the catadioptric panoramic prism through the MEMS micro-mirror. The maximum scanning angle of the experimental MEMS micro-mirror is +/-7 degrees. According to the optical characteristics of the reflector, after MEMS reflection, spiral scanning is carried out in the range of a mechanical angle +/-14 degrees, scanning beams are emitted through the catadioptric panoramic scanning optical system, and a detection target area is irradiated by a light beam space lattice which forms 360 degrees multiplied by 7.5 degrees. In order to make the scanning beam line a scanning range of the same vertical field in the horizontal direction, the catadioptric optical path in the catadioptric panoramic lens is theoretically derived, and when α is 41 °, β is 36.5 °. The base angle of the catadioptric panoramic prism is designed to be 53.5 ° (the base angle of the prism is the complementary angle of β in fig. 2). And when α is 45 °, the reflected light cannot be refracted, and thus the catadioptric prism does not operate in a small range. Therefore, the effective scanning angle of the MEMS is set to be more than or equal to 38 degrees and less than or equal to 44 degrees, and the vertical scanning range formed by emergent scanning beams is +/-3.75 degrees.
And acquiring a three-dimensional image by using a panoramic scanning system or an imaging system based on the MEMS micro-mirror.
The designed catadioptric panoramic prism is subjected to simulation analysis by using optical system design software Zemax (an oblique truncated cone-shaped compensating prism is not arranged in the panoramic scanning system), and fig. 8 is an optical path diagram of the whole system in an optical axis meridian plane, and fig. 9 is an optical path diagram of the whole system in an optical axis sagittal plane. It can be seen that the system beam is not divergent in the meridional plane, but is largely divergent in the sagittal plane. The quality of light beams is seriously reduced after passing through the refraction and reflection type panoramic prism optical system, and the requirements of practical application cannot be met.
FIG. 10 is a diagram of the exit light spot arrays of different scanning fields of the system, and the values of α are 38 °, 39 °, 40 °, 41 ° and 42 ° 43 ° in sequence from top left to bottom right. It can be seen that the emergent spot is elliptical and the spot size becomes very large. The reason for this is that the divergence of the light beam in the sagittal plane occurs because the first transmission surface and the third reflection surface of the catadioptric prism are conical in shape and the fourth projection surface is cylindrical. This results in a beam that does not diverge in the meridian plane but diverges three times in the sagittal plane. In order to perform divergence correction on the sagittal light beam, for this purpose, an oblique truncated cone-shaped compensation prism is added in the panoramic optical system of the MEMS micromirror for divergence compensation, as shown in fig. 11, the oblique truncated cone-shaped compensation prism is in the shape of an oblique truncated cone and is provided with four side surfaces and upper and lower bottom surfaces, three side surfaces of the four side surfaces are flat surfaces, one side surface is a curved surface, two opposite side surfaces of the three side surfaces are trapezoidal and parallel to each other, and the upper and lower bottom surfaces are parallel and have different areas. The center radius corresponding to the curved surface of the oblique circular truncated cone-shaped compensating prism is 160mm, the center focal length of the oblique circular truncated cone-shaped compensating prism is 300mm, the material is BK7, and n is 1.52.
The oblique truncated cone-shaped compensating prism is added into the original system for divergence correction, and the sagittal divergence effect is well improved. But only the beam quality in one scanning direction can be corrected after the addition of the truncated cone prism, and the beams in other fields still have divergence. Therefore, the optimal positions of the correction prisms of the system in different scanning fields are obtained in Zemax software, as shown in FIG. 12, FIG. 12 shows the optimal positions of the inclined truncated cone compensation prisms corresponding to different deflection angles of the MEMS micro-mirror, then the mechanical structure and the MEMS scanning control are used for matching, and the truncated cone prisms are correspondingly moved to enable the sagittal light spot quality of the light beam at each scanning angle to be optimal.
Fig. 13(a) and 13(b) are point diagrams of emergent light spots at different scanning angles at positions 100mm and 200mm away from the emergent surface, and it can be seen that the light spots are uniformly distributed, the quality of the light spots is good, and the divergence problem is well corrected. The invention adopts a far field two-point method to calculate the divergence angles of the emergent light spots of different view fields, obtains the maximum divergence angle of the emergent light spots of different view fields to be less than 1mrad, and meets the requirement of practical application.
The second embodiment is as follows:
the present embodiment is a panoramic scanning system based on MEMS micro-mirrors.
In order to make the panoramic scanning system more compact, a right-angle prism is added in the panoramic scanning system based on the MEMS micro-mirror to perform the light path turning, as shown in fig. 3. The panoramic scanning system based on the MEMS micro-mirror comprises a transmitting system, a panoramic optical system based on the MEMS micro-mirror, an MEMS micro-mirror 103, an MEMS micro-mirror control system, a receiving system and a signal processing control system 106; the transmitting system comprises a high-repetition-frequency narrow-bandwidth 1550 laser 102 and a laser control system 101; the receiving system includes a high-speed APD photodetector 105; the signal processing control system comprises a timing and time measuring system; the MEMS micro-mirror based panoramic optical system includes an catadioptric panoramic prism 104, and in some embodiments, the MEMS micro-mirror panoramic optical system further includes a truncated cone-shaped compensating prism;
the whole system adopts a receiving and transmitting combined mode, an optical isolator 107 is added in the system, namely a high-reflection high-transmittance film system is plated in the polarization beam splitter. When the panoramic scanning system works, the control system generates three paths of synchronous signals which are respectively sent to the laser control system, the MEMS micro-mirror control system and the time measuring system. After the signals are sent out, the three work simultaneously. The laser control system receives signals and then controls the laser to generate pulse laser beams, a parallel light beam with the diameter of 3mm is formed after the pulse laser beams pass through the collimator, the light beams are incident to the optical isolator to be reflected and then are sent to the MEMS scanning micro-mirror through the through hole of the catadioptric panoramic prism, the MEMS micro-mirror control system controls the MEMS micro-mirror to reflect the light beams to the catadioptric panoramic prism according to a preset spiral scanning track, and the light beams are sent to a target space through catadioptric in the catadioptric panoramic prism. The system adopts a receiving and transmitting combination device, so that the transmitting optical system and the receiving optical system share a set of optical path, the strongest scattering signal reflected by the target is received by the high-speed APD photoelectric detector, the detector converts the optical signal into an electric signal, and then the processed electric signal is sent to the timing and time measuring system, so that the flight time of the pulse laser between the system and the target can be obtained, and the distance of the target can be calculated. And combining the target distance signal and the space scanning two-dimensional coordinate to obtain a three-dimensional coordinate of the target, and finally sending the three-dimensional coordinate information to a computer for point cloud imaging display.
The MEMS micro-mirror is arranged in the panoramic optical system to perform spiral line panoramic scanning, 360-degree panoramic scanning can be realized through single-circle spiral line scanning, and the number of scanning circles determines the vertical field of view. And meanwhile, two sets of panoramic scanning systems are used in a matched mode (namely imaging systems), so that the vertical field of view of the system is expanded, and panoramic scanning imaging in a range of 360 degrees x15 degrees can be realized. Meanwhile, the system adopts a customized high-repetition-frequency high-power 1550nm pulse optical fiber laser, the repetition frequency is 100KHz, and two lasers are used for alternately emitting, so that the data rate can be doubled, the point cloud image imaging quality is improved, and the frame frequency is improved. The scanning space light beam forms an echo signal through the reflection of the surrounding environment and a target, and the echo signal is converged on a photosensitive surface of an APD detector through a catadioptric panoramic scanning optical system and a non-imaging objective lens to form the echo signal. After timing and time-measuring signal processing, the distance information (Z axis) of the surrounding environment and the target is obtained and is matched with the (X-Y axis) space position information recorded by the MEMS micro-mirror to obtain a three-dimensional image.
The third concrete implementation mode: the present embodiment is described in connection with figure 3,
the embodiment is an imaging system, which comprises two sets of panoramic scanning systems based on MEMS micro-mirrors, wherein two catadioptric panoramic prisms are oppositely arranged (one end of a cylinder, which is provided with a conical space 3, is opposite), and the oppositely arranged axes of the two catadioptric panoramic prisms are superposed; the two MEMS micromirrors are arranged between the two catadioptric panoramic prisms, lasers of the two panoramic scanning systems based on the MEMS micromirrors respectively enter from through holes of the corresponding catadioptric panoramic prisms, are reflected by the MEMS micromirrors and then irradiate on the corresponding catadioptric panoramic prisms, and imaging is achieved after the catadioptric panoramic prisms are folded back.
The MEMS micro-mirror scanning laser radar becomes the best choice for realizing solid-state and miniaturization of the laser scanning 3D image sensor at present due to the advantages of miniaturization, high scanning speed, relatively low price and the like. But the scanning angle is limited due to the small size of the micromirror, thereby limiting the range of its use. The invention establishes the spiral motion and parameter equation of the MEMS micromirror, gives consideration to the design of a panoramic optical system, and explores the rules between the resonance frequency and the frame frequency, the field angle and the radial angular motion speed of the MEMS micromirror, thereby determining the optimal parameters and realizing that the high repetition frequency pulse laser emitted by the laser irradiates the interested surrounding environment with high frame frequency and high filling ratio.
The imaging system can realize 360-degree panoramic scanning imaging of a horizontal field of view, and the horizontal resolution is 0.1 degree; the vertical field of view is 15 deg., and the resolution is 0.5 deg.. The design result is analyzed by using Zemax, the spot diagrams show that the emergent light spots are circular, the emergent light spots are uniformly distributed, the divergence angle is smaller than 1mrad, the actual requirements can be well met, the problem of laser radar solid state is solved, and 360-degree panoramic scanning imaging is realized.
The fourth concrete implementation mode:
the present embodiment is a panoramic scanning system based on an MEMS micro-mirror or a scanning process of the MEMS micro-mirror controlled by an MEMS micro-mirror control system in an imaging system, that is, a scanning method of the MEMS micro-mirror.
With the continuous development of the current automatic driving technology and the surrounding environment sensing technology, the laser three-dimensional image sensing system is receiving wide attention, and the laser radar system based on the MEMS scanning micro-mirror is an important choice for solving the miniaturization and solid-stating of the technology. The MEMS micro-mirror in the scanning system has the advantages of small size, low price, fast scanning speed, and the like, and can implement two-dimensional scanning of two axes, so the MEMS micro-mirror becomes a key device for developing a new generation of miniaturized, light-weight, and low-cost laser three-dimensional image sensor system. For a biaxial rotation MEMS scanning micromirror, it can rotate in two mutually perpendicular directions simultaneously. The scanning points of different scanning tracks on corresponding scanning visual fields are different, and the different scanning tracks have respective advantages and disadvantages, so that the imaging quality of the system can be best by selecting different micromirror scanning tracks in different target scenes. Common scanning tracks comprise Lissajous scanning curves, helical scanning tracks, raster scanning tracks and the like, and the three scanning tracks are analyzed to find out a scanning control track suitable for imaging of the scanning system.
The command signals and the experimentally obtained scanning trajectories are shown in fig. 4. When the command signals are designed to rx (t) cos (n pi t) and ry (t) sin (m pi t), the scanning trajectory of the MEMS micromirror is lissajous diagram, see fig. 4(a) and (d), where fig. 4(a) is the simulated command signal scanning trajectory pattern and fig. 4(d) is the corresponding actual scanning result of (a). When the command signal is designed to be rx (t) nt + cos [ m pi (t-t) 0 )]And when ry (t) is about swing (p pi t, q), the scan trace is a linear retrace pattern, where fig. 4(b) is a simulated command signal scan trace pattern, and fig. 4(e) is a corresponding actual scan result of (b). When the command signal is designed as
Meanwhile, the scanning track is an equidistant spiral line, fig. 4(c) is a simulation instruction signal, and fig. 4(f) is a corresponding experimental result of (c). The experimental results show that: the scanning pattern obtained by the Lissajous figure command signal is most stable, namely a closed loop, the frame frequency is high, and the defect is that the spatial lattice has non-uniformity and needs to be corrected; the linear regression graph instruction signal can also obtain a closed-loop scanogram, the space uniformity is good, and the defect is that the frame frequency is low; the scanning image obtained by the spiral line command signal can cause the edge information to be lost, and is not suitable for two-dimensional plane scanning imaging, but the 360-degree panoramic scanning in the horizontal direction can be realized by matching with a catadioptric lens. The spiral scanning mode of the MEMS micro-mirror can be used herein.
Because the catadioptric panoramic prism does not work when the included angle between the MEMS micro-mirror and the horizontal plane is 45 degrees, the catadioptric panoramic prism does not start from the original position when the MEMS micro-mirror is controlled to carry out spiral scanning. And the vertical scan field of view is 15 deg. and the resolution is 0.5 deg., so that the number of scan turns of a single panoramic scanning system is 15, and thus the polar angle range is 30 pi. The range from the initial polar angle of 10 pi to the end polar angle of 40 pi is chosen in fig. 5 for clarity of presentation. After the MEMS equidistant spiral line scanning track is matched with the designed catadioptric panoramic optical system, the real track of the MEMS equidistant spiral line is a conical equidistant spiral line, as shown in figure 6, a single-circle spiral line can realize 360-degree panoramic scanning, the number of turns of the single-circle spiral line determines the vertical field resolution, and the radius of the spiral line is matched with that of the catadioptric prism.
Assuming that the radius of the bottom surface of the cone is R, the height of the space of the cone is H, the rotation angular velocity of the MEMS micro-mirror around the central axis is omega, and the linear velocity of the rising line is v z Delta is the polar angle of the scanning point on the scanning plane; the projection curve of the method on the xoy coordinate plane is an equidistant Archimedes spiral line, and then the motion and parameter equation is as follows:
if H is equal to H/n (n is the number of turns of the spiral line) is the ascending distance of each turn of the spiral line, the radial elongation length d of each turn of the spiral line is equal to (H/R) multiplied by H. According to the equation of motion, the trajectory length L of the spiral line is:
in the formula, the pole diameter of the spiral line
(in 2D scan, z is 0); initial polar angle delta min ＝2πr min D, end polar angle delta max ＝2πr max /d。
The matching relationship between the rotation angular velocity ω of the MEMS micromirror and the spiral parameters h and d can be derived:
the scanning indexes of the laser radar provided by the invention are as follows: horizontal field of view 360 °, angular resolution 0.1 °; the vertical field of view is 15 ° and the angular resolution is 0.5 °, which yields n 15. After the catadioptric optical system parameters are determined, the corresponding MEMS equidistant spiral control function can be obtained. The repetition frequency pulse of the laser is 100K, and the two lasers are adopted for alternate emission, so that the system data update rate, namely the frame frequency, can reach more than 10 Hz.
The present invention is capable of other embodiments and its several details are capable of modifications in various obvious respects, all without departing from the spirit and scope of the present invention.
Claims (7)
1. The panoramic optical system based on the MEMS micro-mirror is characterized by comprising a catadioptric panoramic prism;
the refraction and reflection type panoramic prism is a cylinder, a through hole is formed in the center of the cylinder, a conical space is arranged in the cylinder, the height of the conical space is smaller than that of the cylinder, the conical space is communicated with the through hole, the conical space is overlapped with the axis of the cylinder, and the maximum flaring surface of the conical space is an end surface of the cylinder without the conical space; the base angle of the tangent plane of the conical space along the axis is 36.5 degrees;
the refraction and reflection type panoramic prism is made of glass BK7, and the refractive index n is 1.52;
the MEMS micro-mirror based panoramic optical system also comprises a compensating prism;
the compensating prism is in an oblique platform shape and is provided with four side surfaces and an upper bottom surface and a lower bottom surface, three side surfaces of the four side surfaces are planes, one side surface is a curved surface, two opposite side surfaces of the three side surfaces are trapezoidal and are mutually parallel, and the upper bottom surface and the lower bottom surface are parallel and have different areas;
the center radius corresponding to the curved surface of the compensating prism is 160mm, and the center focal length of the compensating prism is 300 mm;
the compensating prism is arranged at the front end of the light path of the catadioptric panoramic prism, namely after laser is emitted, the laser firstly passes through the compensating prism and then is catadioptric through the catadioptric panoramic prism;
the material of the compensating prism is glass BK7, and n is 1.52.
2. A MEMS micro-mirror based panoramic scanning system, the MEMS micro-mirror based panoramic scanning system comprising: the system comprises a transmitting system, an optical isolator, a panoramic optical system based on an MEMS micro-mirror, the MEMS micro-mirror, an MEMS micro-mirror control system, a receiving system and a signal processing control system; the MEMS micro-mirror based panoramic optical system is the MEMS micro-mirror based panoramic optical system of claim 1;
the transmitting system comprises a laser and a laser control system;
the receiving system comprises a high-speed APD photoelectric detector;
the signal processing control system comprises a timing and time measuring system;
the panoramic scanning system based on the MEMS micro-mirror adopts a receiving and sending combined mode, and when the panoramic scanning system based on the MEMS micro-mirror works, the laser control system, the MEMS micro-mirror control system and the time measuring system start to work simultaneously after receiving synchronous signals; the MEMS micro-mirror control system controls the MEMS micro-mirror to reflect the light beam to the catadioptric panoramic prism according to a scanning track, and the light beam is reflected to a target space through catadioptric panoramic prism;
the scattering signal reflected by the target is received by a high-speed APD photoelectric detector, the detector converts the optical signal into an electric signal, and then the processed electric signal is sent to a timing and time measuring system.
3. The MEMS micro-mirror based panoramic scanning system of claim 2, wherein the laser is a high repetition frequency high power 1550nm pulsed fiber laser with repetition frequency of 100 KHz.
4. The MEMS micro-mirror based panoramic scanning system of claim 2, wherein the MEMS micro-mirror control system controls the MEMS micro-mirror to scan comprises the steps of:
the rotation angular velocity around the central axis of the MEMS micro-mirror is omega, and the linear velocity of the rising line is v z And if the projection curve of the spiral line on the xoy coordinate plane is an equidistant Archimedes spiral line, the motion and parameter equation is as follows:
wherein, delta is the polar angle of the scanning point on the scanning plane; r is the radius of the bottom surface of a cone in a conical space in the catadioptric panoramic prism, and H is the height of the conical space; t is time;
the xoy coordinate plane is a plane where a conical bottom surface of a conical space inside the panoramic prism is located or a plane parallel to the conical bottom surface of the conical space inside the panoramic prism, and the z axis is a coordinate axis perpendicular to the xoy coordinate plane;
let H/n be the ascending distance of each turn of the spiral line, and the radius elongation length d of each turn of the spiral line is (H/R) × H; according to the equation of motion, the trajectory length L of the spiral is:
in the formula, n is the number of turns of the spiral line and the polar diameter of the spiral line
δ min Is the initial polar angle, δ max To end the polar angle.
5. The MEMS micro-mirror based panoramic scanning system of claim 4, wherein the MEMS micro-mirror control system controls the initial polar angle δ during scanning of the MEMS micro-mirror min ＝2πr min D, end polar angle delta max ＝2πr max D; wherein r is min Is the minimum helix diameter, r max Is the maximum helix diameter.
6. An imaging system, characterized in that the imaging system comprises two sets of MEMS micro-mirror based panoramic scanning systems, the MEMS micro-mirror based panoramic scanning systems being the MEMS micro-mirror based panoramic scanning systems of one of claims 2 to 5;
two catadioptric panoramic prisms of the two sets of panoramic scanning systems based on the MEMS micro-mirror are oppositely arranged, and the axes of the two catadioptric panoramic prisms which are oppositely arranged are superposed; the two MEMS micromirrors are arranged between the two catadioptric panoramic prisms, lasers of the two panoramic scanning systems based on the MEMS micromirrors respectively enter from through holes of the corresponding catadioptric panoramic prisms, are reflected by the MEMS micromirrors and then irradiate on the corresponding catadioptric panoramic prisms, and imaging is achieved after the catadioptric panoramic prisms are folded back.
7. An imaging system according to claim 6, wherein the two lasers of the two sets of MEMS micro-mirror based panoramic scanning systems alternately emit laser light.
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