GB2075185A

GB2075185A - Dimensional checking apparatus

Info

Publication number: GB2075185A
Application number: GB8112343A
Authority: GB
Original assignee: Pharos AB
Current assignee: Pharos AB
Priority date: 1980-04-23
Filing date: 1981-04-21
Publication date: 1981-11-11
Also published as: NL8102015A; JPH0213722B2; NL191216B; SE448785B; IT1137149B; JPS56163976A; FR2481444B1; DE3116253A1; IT8121317A0; SE8102307L; GB2075185B; NL191216C; DE3116253C2; FR2481444A1

Abstract

Apparatus for checking the dimensional accuracy and/or measuring the dimensions of large objects (1), provided with checking points which serve as or carry suspended measuring scales (2-7) comprises at least one beam-projection unit 12, 20 movable along a guide 8, 9 to emit a narrow beam of light at an angle to the guide. The position of the projector unit is optically or magnetically readable automatically and is stored in the memory of a calculating unit into which measurement data of an undistorted object can also be entered. The projection units 12, 20 also comprise devices for determining beam angle. From measurements on one checking point the apparatus calculates the spatial location of that point and the correct apparatus setting for other points. When the apparatus is set on other points, the correctness of the position of the point is indicated optically or accoustically. <IMAGE>

Description

SPECIFICATION Dimensional checking apparatus The present invention relates to dimensional checking apparatus for measuring the dimensions of large heavy objects, such as car bodies.

Modern cars with a monocoque body are manufactured on production lines in large numbers with accurate precision. The engine, power transmission, front assembly and rear assembly are fitted directly or indirectly to the body on reinforcements and/or brackets welded to the body. The function of the car is highly dependent on certain attachment points, e.g. for the steering units, the front and the rear assemblies, which should occupy the precise positions intended by the manufacturer.

In the event of a collision, impact forces are frequently propagated into the body shell to produce residual deformations. Without thorough inspection and measurement, it may be difficult to identify any such deformations, and this may have a detrimental effect on the driving characteristics of the car.

Compensation for minor deformations in the chassis is possible by utilising the adjustment facilities normally incorporated in the front assembly. However, under no circumstances is it acceptable for the attachment positions for the front assembly suspension to be effectively repositioned by enlarging bolt holes, etc.

The Swedish Patent Specification No. 7103780-8 discloses an arrangement for a car hoisted in a device such as a jig or an alignment bench for checking whether the car retains the correct dimen sionsforthe particular car model concerned, for instance after a collision.

The points in a car which are used to check the measurements of the chassis normally consist of selected fixture holes and attachment holes for bolts and bolted joints under the car. In order to be able to define these measuring points, use is made of so-called measuring-point units which are attached to all relevant checking points in the car chassis.

Suspended in each unit is a scale which is marked in millimetres and has a travelling cursor which may be preset at a nominal height level. By reading where a beam of light impinges on the scales, it is possible to directly determine any deviations of the chassis.

Reflecting colour markings make it easy to check the position of the beam of light on the scales at a range of several metres.

The light in this instance comes from a laser which emits a virtually parallel beam of red light on a path parallel to a girder that forms a guide track. The beam of light strikes a beam-deflection unit that is movable on the guide, and is divided into two mutually perpendicular beam components. One light beam continues on a path parallel to the guide, while the other is deflected at right angles out from the guide in this instance. When the beam-deflection unit is moved along the guide, the deflected light beam will also be displaced along the guide and can be directed to be incident on one scale at a time. The distance between the scales can then be directly read off from a measuring tape of roll-up type which is located on the guide.

In this manner, all the longitudinal and vertical dimensions of the car chassis can be measured. In order to measure the width dimensions, the beamdeflection unit may be moved to the extreme end of its guide, to emit a beam of light along a transverse guide on which there is a further beam-deflection unit, so that measurements are made in the same manner as with the first guide.

if the car needs to be re-shaped or re-aligned, the operator sets the beam-deflection units on the respective guides consecutively in those positions in which they are to be placed according to the data for the car model concerned in order for the light beam normally to impinge on the scales. If, in any position, the light beam does not then impinge on the scale concerned, the car shape is adjusted until it is correctly aligned, and the scale will indicate this.

According to the above-mentioned Swedish Patent, measurement checking thus takes place in that in a starting position for the movement, an indicating device movable along the measurement guide path is mechanically attached to the guide path. The measuring tape line, which is capable of being rolled up, is attached to the indicating unit, and is read off at the beam-deflection unit. Among the disadvantages of this design is that the measuring tape must be attached to a roller, pulley or the like. In addition, the measuring line tape may become worn and/or stretched with the passage of time. A further disadvantage is that such a measuring tape does not facilitate electronic registration.

One object of the present invention is to provide an improved apparatus comprising a measuring arrangement which avoids some of these listed problems and facilitates the use of an electronic reader, so that more reliable readings can be obtained without mechanical wear with the passage of time, and so that measuring values can be transmitted electronically to a central processing unit or the like.

The invention consists in dimensional checking apparatus in which an object is provided with predetermined checking points, which serve as, or carry measuring scales, and a guide is provided on which is mounted at least one movable beamprojection unit, which emits a narrow light beam at an angle to the guide, the position of the beamprojection unit along the guide or the distance between a reference point on the guide and the beam-projection unit being automatically readable by means of a reading unit, information concerning the location of the beam-projection unit on, or its movement along the guide being stored in a calculating unit equipped with memories, and means are provided to enter measurement data of an undistorted object into the memories prior to a measuring operation, the calculating unit being arranged to calculate from one or several measuring operations against at least one checking point the location of the measurement object in relation to the guide and those locations in space where other checking points should be located, as well as the location on and angular setting of the beam-projection unit or units in relation to the guide or guides for impingement on other checking points, and to indicate for each checking point, optically or acoustically, an intended value depending on the calculated locations and the settings of the beam-projection unit or units.

Each beam-projection unit may have an associated data processor and visual display unit, or a central unit may be employed, with an associated keyboard for the entry of data from record manuals, and a central display unit or data printer can be provided.

Electronic reading can take place in different ways.

Reading of movement of a beam-projector unit along a guide can take place by means of magnetically recorded information on a steel tape located alongside the guide. It is also possible to record information directly on the guide. Optical markings may be used on the guide, with alternately white and black fields, and using several scanning diodes for fine resolution. The beam-projection units can be fitted with gearwheels and an electronic or electrooptical reading of the rotation of the said gearwheel can be made either directly or via a code disc. It is also possible to combine these methods. A particularly accurate and reliable distance indication is obtained with magnetic information disposed along the guide in combination with optical markings at relatively large distances from each other, for example, at a distance of 1 dm from each other.These optical markings are used for updating of the counter which counts each magnetic marking passed by a beam-projection unit.

In a preferred embodiment, a common light source projects a beam on a path parallel to the guide, and the or each beam-projection unit is in the form of a beam-deflection unit designed to emit a beam component from the incident light beam at an angle to the associated guide.

The electronic reading of the distance between a beam-projection unit or beam-deflection unit and a reference point on the guide may, for example, utilise a laser whose emitted light is deflected by the or each beam-deflection unit can also be accomplished in other ways than those described heretofore. According to one method, the distance can be measured by ultrasonic-acoustic distance measuring towards an acoustic plane. Eitherthe reference point or the beam-projection unit or beam-deflection unit can then be provided with data defining the acoustic plane and the distance. It is also possible to use a laser beam, if provided, to itself serve for measurement of the distance by interferrometric distance measuring. It is also possible to use for distance measuring a wound-up tape or tread or wheel which runs along the guide and is read off.The distance measurement is then converted into electric signals, and the signal data processed.

Each processing unit, regardless of whether it is arranged in each separate beam-projection or beamdeflection unit, or in a central unit, can be provided with a memory into which an operator can enter standard data for the car model concerned prior to a measurement of an object to be measured, such as a motor vehicle. This memory can be so organized that points in a coordinate system, such as a Cartesian system with x, y and z coordinates are specified for the measuring points which are critical for the measurement of the object being measured.

Measurements of the length and width of the object concerned are also fed into the memory, for instance by the operator pressing a key at the correct setting.

The measurement is presented in x, y and z coordinates and compared with the input reference values.

Deviations are presented on a visual "deviation indicator", showing the set-point value, actual value and differential value, for example.

Input of reference values into the memory can take place, for example, by means of magnetic cards of the type used in programmable computers, by means of punched tape, by means of an optical code reader, etc. If a central processing unit is used, input can also take place via a keyboard, a cassette tape, a floppy disc, etc.

When a central unit is used, this is appropriately connected to the measurement path (the guide) via a flex or cord for the purpose of transmission of data, but it is also possible to have acoustic or optical transmission. Optical transmission takes place pre ferablywith infrared light in order to avoid the transmission being subjected to interference from the light prevailing in the premises in which the measurement is taking place. The central unit is provided with a keyboard by means of which the operator can control the measuring procedure. If the beam-projection units or beam deflection units are provided with drive motors and electronic means for angular setting in the horizontal and vertical directions, an operator can control the entire measuring procedure standing at the keyboard.One advantage of using a central unit is that the beam-projection or beam-deflection unit will be less complicated if it merely needs to be provided with movement indicators and transmitters to transmit the information, i.e.

if it does not need to be equipped with a calculating unit.

In the design according to Swedish Patent 7103780-8, two measuring guides are used, one for measurement in the y direction and one for measurement in the x direction. The present invention is exceedingly well applicable to this design. However, a measurement of an object to be measured can also take place using only a straight measuring path. In this case, one or more deflection units may be used and one or more deflection angles in relation to the measuring path. If resetting can take place between perpendicular deflection and a deflection at an angle of 45" in relation to the light beam along the measuring guide, both the distance in the x direction and the distance in the y direction of the object being measured can be obtained with the same deflection unit. If two deflection units are used, the light can be deflected simultaneously towards the same measuring point by both units, and if the light is modulated in different phases of a common frequency from the two units, with such a frequency and phase difference that an impingement point is seen to be flashing if only one light beam is incident thereon, but as steady light if illuminated by the light beams from two or more units. By this means, very accurate alignment towards a measuring point from two or several directions can be accomplished. An operator can easily perform the setting whilst standing or seated at a keyboard, if the units are equipped with drive motors operable from this keyboard.It is naturally also possible to use this feature even in the case of units which are moved manually along the measuring path by an operator and each of which unit is provided with its own calculation unit.

The units can also be provided to direct a beam at an adjustable angle, and in this case, a mirror incorporated in the unit can be turned and the turning thereof be indicated by reading of a micrometer screw in a manner known per se, for example via a code disc, a differential transformer, a resolver orthe like.

The obtainable information, such as movement along the measuring path, turning of the mirror and basic data for the position and angular position of the mirror are sufficient for calculation of the distance and width between the measuring points of the object being measured.

Particularly if the separate units are provided with respective calculators, they can additionally by supplied with acoustic information, so that for example a sound signal is heard when the set-point value has been reached within a predetermined tolerance level. The sound signal can also be made pulsated or frequency modulated in order to indicate the deviation from the set-point value more graduated.

The invention will now be described with reference to the drawings, in which: Figure 1 schematically illustrates a first embodiment of an arrangement constructed in accordance with the invention; Figure 2 schematically illustrates a second embodiment of the arrangement according to the invention; and Figure 3 is a block schematic circuit diagram of means to determine the movement along the guide.

An embodiment for checking measurements and giving correct indication in the case of correct measurements of a car is shown in Figure 1. The car is hoisted by means of a lifting device (not shown).

Scales 2-7 are attached to suitable measuring points beneath the car 1. These measuring points have different positions for different car models. Measuring points and dimensions for a standard vehicle of each car model are specified in special measuring records, such as service manuals.

Two mutually transverse guides 8 and 9 are formed by respective girders placed obliquely below the hoisted car at a suitable working height for an operator who is to perform the measurement check.

The lengthwise guide 8 is parallel to the longitudinal axis of the car. A light source 10 is fixedly placed at one end of the guide 8. The light source emits a narrow collimated light beam on a path parallel to the guide, for deflection on to one of the scales to be clearly readable by the operator where he stands. A He-Ne laser can satisfy these requirements.

Shown on the guide 8 are two beam-deflection units, 12 and 13, each of which is designed to deflect light from the laser in a direction at right angles to the guide 8. The unit 12 is movable along the girder 8, and the unit 13 in this embodiment is permanently placed at that end of the guide 8 which lies adjacent a guide 9.

The unit 12 projects a deflected light beam component and allows a light beam component to pass straight ahead. The unit 13 deflects the light beam received along a path parallel to the guide 8 so that it passes along the guide 9 and is then deflected towards the same point of impingement on the measuring scale 2 as the deflected light beam from the unit 12 by means of a further deflection unit 14.

It is possible to use only one beam-deflection unit 12 on the guide 8, and to perform the measurement of the car in the x and y directions separately in two different stages, in which case, during measurement in the y direction the beam-deflection unit 12 is placed in the position shown for the unit 13.

The movement path along the guide 8, and the guide 9, if present, is provided with electronically detectable markings along the whole of its length, which markings are usable for measurement, and the movable beam-deflection units are fitted with detectors to detect the markings. These markings and detectors may be of various types, as known per se. For example, it may be mentioned that a guide can be fitted along its length with a steel tape line containing magnetically recorded information, in which case any beam-deflection unit or units is provided with a detecting head to pick up information. The steel tape line may be excluded, and the guide itself provided with recorded information.It is also possible to provide the guide with optical markings having alternate white and black fields, for example, each of a length of 1 cm, and to provide any beam-deflection unit or units with a plurality, of scanning diodes for millimeter interpolation, for example, ten. The scanning units can also be furnished with gearwheels with electro-optic reading, either directly or via a code disc, and combinations of these indicating devices are possible.

A suitable indication can be provided by means of magnetically recorded information spaced along a guide together with optical markings placed at relatively long intervals, such as, for example, every tenth cm., such as a well dimmed light-emitting diode whose emission is dectected by a well dimmed light indicator such as a photo diode. By this means the indicator unit can be updated at sparse intervals, and an extra indication be obtained that the magnetic markings have been correctly indicated.

The markings are suitably detected in the form of pulses which are fed to an up/down counter, i.e. a counter which counts upwards when a beamdeflection unit is moved in one direction, and downwards when it is moved in the other direction.

Indication of the direction in which the unit is moved takes place in a manner known perse, such as, for example, the use of an extra detector displaced in relation to the ordinary detector in order to determine the markings phase-displaced with, for example, 1/4 of a wave length in relation to the responses of said ordinary detector.

Distance measuring can also take place between a beam-projection or beam-deflection unit and a reference point, such as the laser, for example by means of ultrasonic-acoustic distance measuring towards an acoustic plane, or by means of interferometric distance measuring, according to which the distance is read off from an already present laser beam, or by means of wound-up tape or thread or wheels, which run alongside the guide and provide data to be read off.

In Figure 1 an operator 15 is shown at a beamdeflection unit 12. In one hand he is holding a magnetic card 16, which is to be inserted into an aperture 17, which can be seen in the other unit 14, which is of the same design as the unit 12. Recorded on the magnetic card is information concerning standard data for the car model that is to be measured. The units 12 and 14 are provided with three indication windows, a window 18 indicating the standard distance, a window 19 indicating the measured distance, and a window 20 indicating any deviation between the standard distance and the actually measured distance.

The measuring commences when the operator ensures that a light beam 21 deflected by the beam-deflection unit 12 passes to a respective marking point on both rear scales 2 and 3. The movement path, i.e. the guide 8, is thus parallel with the longitudinal axis of the car. Using a key on the guide unit 12 (not shown), the operator marks that this position is the starting position for movement of the beam-deflection unit along the guide. The distance along the guide which the beam-deflection unit has moved in order for the deflected light beam to impinge on scales 4 and 5 is now shown in window 18. The operator moves the unit 12, and when he sees the light beam impinge on at least one of the scales 4 or 5, he marks this by depressing another key (not shown) on the unit 12.Shown in the windows 19 and 20 are the true distance and the distance between the standard distance and the true distance respectively.

The unit 12 can also be provided with an acoustic indication, which sounds when the set-point value is obtained within a certain given tolerance level. This signal can be pulsed or frequency modulated, in order to indicate the deviation from the set-point value in a more graduated manner. For example, the signal can sound with a highertonetheclosertothe set-point value the beam-deflection unit is set. This feature is particularly suitable in those cases in which the car being measured is to be aligned to comply with certain given dimensions. The operator then moves the beam-delfection unit 12 until he hears the acoustic tone, and finely adjusts the unit to the position where the tone sounds lightest. If the light beam does not then pass through the two scales at the preset points of impingement, the car is processed to produce realignment until this is so.

After having performed the measuring operation on the scales 4 and 5, the operator depresses a key (not shown) to mark that the distance to the scales 6 and 7 is now being measured, and the measurement is performed for these in an analogous manner to thatforthe scales 4 and 5.

In a likewise manner, measurements are performed in the y direction by moving the beamdeflection unit 14 along the guide 9. Particularly when aligning a car, it is appropriate to mark the x and y directions at the same time against the same measuring point. To accomplish this, the beamdeflection unit 12 is so elaborated that it emits both a deflected light beam towards the scales and passes a light beam component along the guide in the same direction as the incident light beam. The light beam passing along the guide is deflected to pass along the guide 9 by a stationary beam-deflection unit 13 at the point of intersection between the guides 8 and 9, and is subsequently deflected by the deflection unit 14 to that one of the scales 2,3 which is also in the path of the deflected light beam from the beamdeflection unit 12.In the Figure, the light beam from the unit 14 is shown to impinge on the scale 2.

The two beams of light emitted from the beamdeflection unit 12 can be obtained by a semitransparent mirror placed in the beam path from the light source 10, whereby two fixed light beam components of roughly the same intensity are obtained.

However, an essential advantage is gained if the two emanating light beams are modulated with a frequency which causes the light on a point of impingement to appear to be flashing to an observator when only one beam is incident between. A suitable frequency lies between 3 and 13 Hz. The two modulated light beams from the unit 12 are so out of phase in relation to each other that when both are incident upon a common point the light beams will appear as a steady light. Appropriately, the modulation of the two light beams may be in counter-phase.

Modulation can be accomplished in a simple manner by using a mirror placed in the unit 12 in the beam path from the light source 10 which is made of a liquid crystal cell of the type which is reflecting when a first voltage level over a specific value is applied and transparent when a second voltage level below the specific value is applied. The liquid crystal cell is excited with a voltage which varies cyclically between these levels at the modulation frequency.

Another method of accomplishing modulation is to place a polarisation means 11 in front of the light source and to polarise the light alternately in two mutually perpendicular directions. This polarisator may be a Pockel's cell excited by an alternating voltage waveform, or a rotating disc with polarisers having mutually alternate intersection-polarisation, which polarisers are arranged on a ring passing through the beam path. In the beam path for the incident light beam from the light source 10 in the unit 12 a polarised mirror is provided, appropriately with a dichroic coating, which mirror reflects light polarised in one direction, and permits light polarised in a direction perpendiculartheretoto pass through. The polarisation of the light from the light source 10 is changed at the said flashing frequency of from 3 to 13 Hz.

Figure 2 shows a second embodiment in which only one guide 17 is placed by the side of the car that is to be checked. A light source 18, and possibly a modulation unit 19, are stationarily located at one end of the guide 17.

On the guide are two beam-deflection units, 20 and 21, each of which deflects a light beam emanating from the light source in the horizontal plane in mutually different directions, so that any selected scale, e.g. the scale 2, is impinged on from two directions. The position of the point of impingement in a beam-oriented coordinate system is unambiguously determined by the location along the guide of the two beam-deflection units, 20 and 21, and the two angles between the deflected light beam from each beam-deflection unit, and the distance.In the Figure, the deflected light beams are shown to lie in a common horizontal plane, and to impinge on a point on the scale in this plane, but it is also possible to omit suspended scales at the measuring points on the vehicle, and to deflect the light beams with the beam-deflecting units at an angle in the vertical plane, so that they impinge directly on the different selected measuring points. It should be observed that this modification is naturally applicable to the embodiment shown in Figure 1.

In the embodiment shown in Figure 2, the beamdeflection units are provided with detectors to indicate the markings on the guide, and with transmission means to transmit data to a central processing unit 22 representing the detected information concerning the moved distance. In the Figure, this transmission is shown to take place via a cable between the guide and the central unit, but the data transmission can also take place without wireconductors, for example via acoustic transmission, or via modulated infrared light.

The information in respect of the car model concerned can be fed into memories in the central unit 22 priorto a measurement for example by means of a magnetic card, punched tape, cassette tape recorder, floppy disc etc. The two beamdeflection units, 20 and 21, can either be moved manually by the operator, as described for the embodiment shown in Figure 1, in which case the central unit is appreciably smaller than that of the embodiment shown in the Figure, and can easily be carried by the operator. It may, for example, be of the same size as a pocket calculator. This central unit displays for the beam-deflection unit with which the operator is working at that time the standard distance, the true distance and the difference between these values, in the same manner and for the same working operations as described for the embodiment shown in Figure 1.It should be observed that the beam-deflection unit 20 may have 90 deflection, and the movement thereof along the guide indicates the distances in thex direction (along the longitudinal axis of the car) between the scales. The beamdeflection unit 21 has a deflection other than 90 , and the distance in the y direction between the rulers with the samex coordinate as for each pair of scales, 2 and 3, or 4 and 5, or 6 and 7, is given by the distance along the girder for the unit 21 between impingements on each ruler in a pair divided by the tangent of the angle between the guide and the deflected light beam. If this angle is 45 , the moved distance will be the same as the distance in the y direction.

It is also possible, however, to equip the beamdeflection units 20 and 21 with controllable drive motors, and in such a case the operator can perform the entire measuring operation whilst standing or remaining seated at the central unit, as shown in the Figure. It is possible to permit the central unit to guide the drive motors automatically to suitable settings along the guide depending on input data for the car model concerned. When aligning a car, the aligning process work is continued until the deflected light beam correctly impinges on each scale.

When a car is to be only measured, the beamdeflection units can be run automatically to positions along the guide adapted to the car model concerned, and then moved through key control by the operator to a position in which a deflected light beam actually impinges on an impingement point, or the operator can move the beam-deflection unit from the starting position by pressing the appropriate keys on the keyboard of the central unit 22.

As in the embodiment shown in Figure 1, it is the distance between different positions along the guide for each deflection unit that is of importance. The operator marks with a special key or a special code that the position of the unit constitutes the starting position for a measurement.

The deflections for the respective beam-deflection units, 20 and 21, do not need to be fixed, but instead the angular position for deflection may also be adjustable, either continuously or in stages, by turning one of the mirrors incorporated in the unit. In the beam-deflection units, it is appropriate to perform the deflection with the aid of two reflecting surfaces set at an angle in relation to each other that is similar to the reflecting surfaces in a pentagonal prism, and to adjust the angle between these mirrors. This gives an insensitivity to any inadvertent turning of the actual beam-deflection unit about the guide. Turning of one of the mirrors can be read off on a micrometer screw, or may take place in such a manner that the mirror may be connected to a resolver, in which case the turning of the mirror can be remote-controlled from the central unit.

In the above description, it has been assumed that deflection takes place in one plane, appropriately the horizontal plane, and that the deflected light beam impinges on preset points of impingement on scales suspended at special measuring points. In that the beam-deflection units or the central units have been equipped with calculating units, there is no work inconvenience in also deflecting the light beam in the vertical direction, to impinge directly on the measuring points, since each calculating unit can easily be programmed to calculate the height of the measuring point above the horizontal plane on the basis of the set angles. The beam-deflection units can be proivded with a turning means and a vertical angle transducer, for instance of pendulum accelerometer type, for height adjustment and vertical angle indication of the deflected light beam. When two mirrors set in a manner similar to that of the reflecting surfaces of a pentagonal prism are used for the deflection, it is suitable to place these height adjustment and height-indicating means so that the bisector between the reflecting surfaces is tilted, appropriately around a turning point on the optical axis of the incident light beam. The calculating unit performs the geometrical calculation of the height angle of the bisector and also of the deviation of the deflection angle in the horizontal plane on account of the height adjustment of the light beam.Another variant for vertical adjustment of the light beam is to ensure, for example by means of a level or an angle transducer servo-controlled to the zero positions, that the said bisector between the reflecting surfaces is kept horizontal and to deflect the light beam then deflected in the horizontal plane by the mirrors in the vertical direction by means of a turnable deflection means, such as a mirror or the like, placed in the beam path.

Shown schematically in Figure 3 is a block schematic circuit diagram of the electrical control arrangement of an embodiment constructed in accordance with the invention. A light source 30 is stationarily located at one end of a guide, to emit a narrow collimated light beam in orderforimpinge- ment on one of the scales to be clearly discernible by the operator where he stands at the guide. A laser of He-Ne type satisfies these requirements. A modulator unit may be placed in front of the light source in order to accomplish modulation of the light. This is shown here to comprise a rotating disc 31 which is driven by a drive motor 32 and is provided with a ring 33 of polarisers alternately disposed with mutually intersecting polarisation planes.

Two beam-deflection units are provided on the beam path. Both have the mirrors arranged in a manner similar to that of the reflecting surfaces of a pentagonal prism. The unit 34 has to accomplish perpendicular deflection of the radiation from the laser 30, and the angle between the mirrors 36 and 37 is then 45". The unit 35 has to accomplish an obtuse deflection of the radiation from the laser 30 and if this angle is 45 , the angle 6 between the mirrors 38 and 39 is 67.5 . By arranging the mirrors in the units in a manner similar to the reflecting surfaces of a pentagonal prism, insensitivity to any turning of the unit about the guide is obtained.

If, now the mirror 37 is a polarised mirror, for example with a dichroic coating, which mirror reflects light polarised in one direction and permits light polarised in another direction to pass through, the radiation is reflected by the mirror during half the revolution of the rotating disc 31, and transmitted to the other deflection unit 35 during the other half thereof. As mentioned above, instead of the unit formed by the elements 31 to 33, and a polarised mirror 37, a mirror in the form of a liquid crystal cell may be used, in which case a pulse-shaped alternating voltage waveform is applied to the cell electrodes.

The beam-deflection unit 34 has an indicator 40 and the beam-deflection unit 35 an indicator41 to read off markings 42 provided on the guide. The indicators 40 and 41 each comprises an up/down counter connected to a data-processing unit 43, which reads the counter setting at specific points of time. A memory 44 is connected to the unit 43. Prior to measurement, information concerning the object to be measured can be read into the memory via the data input. Data concerning the actual object are presented on a visual display unit 45 and acoustic indication 46 can be arranged in the manner described heretofore.Using the keyboard 47, the operator states which functions are required to be presented at the time. the elements 43 to 48 can naturally by arranged in each beam-deflection unit separately, as described with reference to Figure 1, instead of to a central unit, common to both units 34 and 35.

In the case when the units 34 and 35 are to be controlled from a central unit, as described with reference to Figure 2, data is fed to a control unit 48 which in turn supplies drive to the respective drive motors 49 and 50 in the beam-deflection units 34 and 35 in orderto run these to intended locations along the guide in accordance with the data fed into the memory 44 upon commencement of measurement.

Control unit 48 can also take care of the setting of the angle between the mirrors for the purposes of modification of the deflection angle by control of a respective resetting unit, 51 and 52, one in each unit, 34 and 35. A horizontal indicating means, 53 and 54 respectively, is placed to sense the deviation from the horizontal position for the bisector of the angle between the mirrors in the beam-deflection units.

The units may either be provided with adjusting means which automatically turn the units 34 and 35 so that the means 53 and 54 respectively are always in the horizontal position, and possible height alignment of the deflective light beam can be accomplished with some common type of adjustable scanning device (not shown), or else the setting in the vertical direction can be accomplished by rotation of the means 53 and 54 respectively to special inclinations calculated by the data processing unit.

The means may, for example, be pendulum accelerometers of the type described in the Swedish Patent Specification No. 7806294-0.

The data processing unit 43 appropriately calculates the positions for the check points in coordinates in an object-fixed coordinate system, which is determined in relation to the guide through measurement against reference points upon commencement of the measurement. When a central data processing unit is used, upon completion of a series of measurements, this can calculate special data for the object being measured, such as diagonal measurement and/or if the measuring points within prdetermined tolerances lie on a specific curved line or the like, can read into the memory of the processing unit prior to commencement of measurement, and on the basis of these criteria indicate in a display window if the measuring object is approved or not.

Several modifications are possible within the scope of the invention. Thus, for example, the units 12 and 14 or 20 and 21 do not have to be units which deflect a light beam projected along the guide, but each unit may be provided with its own light source projectable in different angular positions in relation to the guide.

Further details of such apparatus are given in our three co-pending United Kingdom PatentApplications of even date: Application No. 8112339 (Our reference V392) Application No. 8112341 (Our reference V393) Application No.8112342 (Our reference V456)

Claims

1. Dimensional checking apparatus in which an object is provided with predetermined checking points, which serve as, or carry measuring scales, and a guide is provided on which is mounted at least one movable beam-projection on which is mounted at least one movable beam-projection unit, which emits a narrow light beam at an angle to the guide, the position of the beam-projection unit along the guide or the distance between a reference point on the guide and the beam-projection unit being automatically readable by means of a reading unit, information concerning the location of the beamprojection unit on, or its movement along the guide being stored in a calculating unit equipped with memories, and means are provided to enter measurement data of an undistorted object into the memories prior to a measuring operation, the calculating unit being arranged to calculate from one or several measuring operations against at least one checking point the location of the measurement object in relation to the guide and those locations in space where other checking points should be located, as well as the location on and angular setting of the beam-projection unit or units in relation to the guide or guides for impingement on other checking.

points, and to indicate for each checking point, optically or acoustically, an intended value depending on the calculated locations and the settings of the beam-projection unit or units.

2. Apparatus as claimed in Claim 1, in which means for storing tolerance deviations for the positions of the checking points of the standard model are provided in the memory of the calculating unit, and that an indication is given as soon as a beam-projection unit is so set within the tolerance range that the transmitted light beam should impinge on a checking point.

3. Apparatus as claimed in Claim 2, in which said indication is an acoustic signal.

4. Apparatus as claimed in any preceding Claim, in which said beam-projection unit or each of said units emits a light beam in one common plane, the dimensions for the object of reference character are stated in a two-dimensional coordinate system in this plane, and the calculating unit compares the two dimensional system data for the object being measured with data for the object of reference character and displays any deviations from relevant set point values.

5. Apparatus as claimed in any preceding Claim, in which scales are fitted at checking points, at which the projected light beam or beams are to be incident.

6. Apparatus as claimed in Claim 1 or Claim 2, in which the light beam from the or each said beamprojection unit is variable in two dimensions in relation to its movement path on its guide, and the calculation unit is adapted to perform calculations and comparisons for measured and stored data stated in three dimensions, and visually displays and/or signals acoustically if the positions of the measured checking points lie within predetermined tolerance limits.

7. Apparatus as claimed in any preceding Claim, in which each said beam-projection unit is provided with its own calculation unit and associated visual display unit.

8. Apparatus as claimed in any one of Claims 1 to 6, in which a plurality of said beam-projection units cooperate with a common calculating unit.

9. Apparatus as claimed in any preceding Claim, in which means are provided for the calculating unit, upon completion of a measurement series towards several measuring points, to perform special calculations on the basis of calculated positions for the checking points, such as calculation of diagonal measurements or the shape of a curved line with plotted checking points, and in that the calculating unit, on the basis of the special calculations, indicates visually or acoustically if the object is acceptable or not.

10. Apparatus as claimed in any preceding Claim, in which the or each said beam-projection unit comprises a respective light source.

11. Apparatus as claimed in any one of Claims 1 to 9, in which the or each said beam-projection unit comprises a beam-deflection unit co-operating with a light source projecting a light beam parallel to said guide.

12. Dimensional checking apparatus substantially as described with reference to Figure 1, Figure 2 or Figure 3.