Method and apparatus for electro-optically determining the dimension, location and attitude of objects

Claims

What is claimed is:

1. A method for determining the dimension, location or attitude of an object surface, comprising projecting a zone of light onto the surface of said object, said zone comprising at least two bright portions with at least one dark portion therebetween,

forming an image of said zone on said surface onto a photodiode array with lens means whose axis is angularly spaced from the axis of said projected light, said image comprising said two bright portions and said dark portion therebetween;

determining from the position of the dark portion of said image on said array relative to said lens axis the location of said surface illuminated by said zone, and

determining from said location of said surface the location, attitude or dimension of said object.

2. A method according to claim 1, wherein said zone of light is provided by a laser operating in the TEM.sub.01 or higher mode.

3. A method according to claim 1 wherein said position of said image comprises said dark portion.

4. A method for determining the dimension, location, or attitude of an object surface, said object being in motion, comprising projecting onto the surface of said object a zone of light,

forming an image of said zone on said surface onto a photodiode array with a lens system whose axis is angularly spaced from the axis of the projected light, said projection of said light zone being provided within a short time interval sufficient to effectively freeze the image on said array,

scanning said photodiode array between successive light projection intervals,

determining from the position of said image on said diode array the location of said surface illuminated by said zone, and

determining from said location of said surface the location, attitude, or dimension of said object.

5. A method according to claim 4 wherein said object comprises a gear.

6. A method according to claim 5 wherein said gear is rotated about its axis and wherein said pulse of light is initiated by a gear position sensor.

7. A method according to claim 6 wherein said gear portion sensor comprises a rotational encoder connected to said gear.

8. A method according to claim 6 wherein said gear position sensor comprises means for detecting the presence of a gear tooth surface.

9. A method according to claim 5 wherein a plurality of said zones of light are projected onto a surface of a single gear tooth and wherein the images of said zones are formed on at least one diode array.

10. A method according to claim 9 wherein the positions of said images on said at least one diode array are compared to determine the involute form or lead of said gear tooth.

11. A method according to claim 4 wherein said time interval is controlled as a function of the light energy reflected from said surface.

12. A method according to claim 4 wherein the output of the diode array is momentarily stored in a temporary memory means.

13. A method for determining the angular tilt of an object surface which is inclined relative to a plane of measurement, comprising projecting onto the surface of said object at least two zones of light, the direction of light projection being normal to a plane of measurement,

forming an image of said zones on said surface onto at least one photodiode array with a lens means whose axis is angularly spaced from the axis of said projected light, and

determining from the separation of said image on said diode array the angular tilt of said surface, relative to said plane of measurement.

14. A method according to claim 13 wherein four zones in a rectilinear pattern are projected, wherein said diode array comprises a matrix array, and wherein said angular tilt of said surface is determined by comparing image separation in two planes.

15. A method according to claim 13 further comprising determining the location of said object surface from the position of one or more of said images on said diode array.

16. A method according to claim 13 wherein a second lens and diode array are placed at an equal and opposite angular spacing from said axis of said projection of said zones, whereby, when said surface is normal to the projected light, the separation of said images on said first and second diode arrays is equal.

17. A method for determining the dimension, location, or attitude of an object surface, comprising:

projecting a zone of light onto a surface of an object;

forming an image of said zone of light on a photodiode array with lens means having an optical axis which is angularly spaced from the optical axis of the projected light, said image being sufficiently small such that it is not incident upon all of the photodiodes in said array whereby the position on said photodiode array on which said image is formed is dependent upon the location of said object surface;

determining the position of said image on said photodiode array;

determining from the position of said image on said photodiode array the location of said surface illuminated by said zone of light;

utilizing a broad light source to illuminate said surface;

forming an image of said object surface on a two axis scanning array means; and

determining from the location of said surface and from the image on said two axis scanning array means, the dimension, location, or attitude of said object surface.

18. A method according to claim 17 wherein said two axes scanning array means comprises a matrix photodiode array.

19. A method according to claim 18 wherein said matrix array comprises said photodiode array.

20. A method according to claim 18 wherein said matrix array and photodiode array are distinct.

21. A method according to claim 17 further comprising illuminating the surface of said object to facilitate forming said surface image.

22. A method according to claim 17 further comprising analyzing said surface image to determine a physical characteristic of said surface.

23. A method according to claim 17 further comprising analyzing said surface image to determine the location of a portion thereof and determining the location of said zone of light relative to said surface image portion.

24. A method according to claim 18 wherein said projected light is flashed.

25. A method according to claim 18 wherein said zone is a spot.

26. A method according to claim 17 further comprising illuminating said surface for forming said surface image, and wherein said projection of said light and illumination of said surface are effected sequentially.

27. A method according to claim 18 further comprising projecting an additional zone of light into said object surface, forming an image of said additional zone of light onto a photodiode array with lens means having an optical axis angularly spaced from the axis of the projected light, and determining, from the locations of the photodiode array images, the attitude of the object surface.

28. A method according to claim 18 wherein said light zone is projected from a light source, and wherein said light source, lens means and photodiode array are mounted on a robot arm.

29. Apparatus for determining the dimension, location, or attitude of an object surface, comprising means for projecting onto the surface of said object a zone of light, said zone comprised of at least two bright portions with at least one dark portion therebetween,

a photodiode array,

lens means for forming an image of said zone on said surface onto said photodiode array, said lens means having an optical axis which is angularly spaced from the axis of said projected light, said image comprising said two bright portions and said dark portion therebetween,

means for determining from the position of the dark portion of said image on said diode array relative to said lens axis, the location of said surface illuminated by said zone, and

means for determining from said location of said surface the location, attitude or dimension of said object.

30. Apparatus according to claim 29, wherein said projecting means comprises a laser operating in the TEM.sub.01 or higher mode.

31. Apparatus according to claim 29 wherein said image position determining means comprises means for determining the position of said dark portion of said image.

32. Apparatus for determining dimension, location, or attitude of an object surface, comprising:

means for projecting a zone of light onto the surface of an object;

a photodiode array;

means for moving said object;

lens means for forming an image of said zone onto said photodiode array, said lens means having an optical axis which is angularly spaced from the axis of the projected light, said projection of said light zone being provided within a time interval sufficiently short to effectively freeze the image on said array during relative motion thereof;

means for scanning said photodiode array between successive light projection intervals;

means for determining from the position of said image on said diode array the location of said surface illuminated by said zone; and

means for determining from said location of said surface the location, attitude, or dimension of said object.

33. Apparatus according to claim 32 wherein said object comprises a gear.

34. Apparatus according to claim 33 further comprising means for rotating said gear about its axis and gear position sensor means for initiating said projection of light.

35. Apparatus according to claim 34 wherein said gear position sensor comprises a rotational encoder connected to said gear.

36. Apparatus according to claim 34 wherein said gear position sensor comprises means for detecting the presence of a gear tooth surface.

37. Apparatus according to claim 33 further comprising means for projecting a plurality of said zones of light onto a surface of a single gear tooth and means for forming the images of said zones on at least one diode array.

38. Apparatus according to claim 37 further comprising means for comparing the positions of said images on said at least one diode array to determine the involute form or lead of said gear tooth.

39. Apparatus according to claim 32 further comprising means for controlling said time interval as a function of the light energy reflected from said surface.

40. Apparatus according to claim 32 further comprising temporary memory means for momentarily storing the output of the diode array.

41. Apparatus for determining the angular tilt of an object surface which is inclined relative to a plane of measurement, comprising:

means for projecting onto the surface of said object at least two zones of light, the direction of light projection being normal to a plane of measurement,

lens means for forming an image of said zones on said surface onto at least one photodiode array, said lens means having an axis which is angularly spaced from the axis of said projected light, and

means for determining from the separation of said images on said diode array the angular tilt of said surface relative to said plane of measurement.

42. Apparatus according to claim 41 wherein said light zone projecting means comprises means for projecting four light zones in a rectilinear pattern, wherein said diode array comprises a matrix array, and said surface angular tilt determining means comprises means for comparing image separation in two planes.

43. Apparatus according to claim 41 further comprising means for determining the location of said object surface from the position of one or more of said images on said diode array.

44. Apparatus according to claim 41 further comprising a second lens and diode array placed at an equal and opposite angular spacing from said axis of said projection of said zones, whereby, when said surface is normal to the projected light, the separation of said images on said first and second diode arrays is equal.

45. Apparatus for determining the dimension, location or attitude of an object surface, comprising:

means for projecting a zone of light onto a surface of an object;

lens means for forming an image of said zone of light on a photodiode array, said lens means having an optical axis which is angularly spaced from the optical axis of the projected light, said image being sufficiently small such that it is not incident upon all of the photodiodes in said array whereby the position on said photodiode array on which said image is formed is dependent upon the location of said object surface;

means for determining the position of said image on said photodiode array;

means for determining from the position of said image on said photodiode array the location of said surface illuminated by said zone of light;

means comprising a broad light source to illuminate said surface;

means for forming an image of said object surface on a two axis scanning array means; and

means for determining from the location of said surface and from the image on said two axis scanning array means, the dimension, location, or attitude of said object surface.

46. Apparatus according to claim 45 wherein said two axis scanning array means comprises a matrix photodiode array.

47. Apparatus according to claim 45 wherein said matrix array comprises said photodiode array.

48. Apparatus according to claim 45 wherein said matrix array and photodiode array are distinct.

49. Apparatus according to claim 45 further comprising means for illuminating the surface of said object to facilitate forming said surface image.

50. Apparatus according to claim 45 further comprising means for analyzing said surface image to determine a physical characteristic of said surface.

51. Apparatus according to claim 45 further comprising means for analyzing said surface image to determine the location of a portion thereof and means for determining the location of said zone of light relative to said surface image portion.

52. Apparatus according to claim 45 wherein said light projecting means comprises means for flashing said projected light.

53. Apparatus according to claim 45 wherein said zone is a spot.

54. Apparatus according to claim 47 further comprising means for illuminating said surface for forming said surface image, and means for sequentially projecting said light and illuminating said surface.

55. Apparatus according to claim 45 further comprising means for projecting an additional zone of light onto said object surface, means for forming an image of said additional zone of light onto a photodiode array with lens means having an optical axis angularly spaced from the axis of the projected light, and means for determining, from the locations of the photodiode array images, the attitude of the object surface.

56. Apparatus according to claim 45 wherein said light projecting means, said lens means and said photodiode array are mounted on a robot arm.

57. A method for determining the dimension, location, or attitude of an object surface, comprising:

projecting a pulsed zone of light onto a surface of an object;

forming an image of said pulsed zone of light on a photodiode array with lens means having an optical axis which is angularly spaced from the optical axis of the projected light, said image being sufficiently small such that it is not incident upon all of the photodiodes in said array whereby the position on said photodiode array on which said image is formed is dependent upon the location of said object surface,

storing the output of said diode array in temporary delay means;

amplifying said stored diode array output, and controlling the amplification of said stored output in inverse proportion to the light energy reflected from said zone;

determining, from the amplified stored array outputs, the position of said image on said photodiode array, said determination being effected in the interval between successive light pulses;

determining from the position of said image on said array the location of said surface illuminated by said zone of light; and

determining from said location of said surface, the dimension location, or attitude of said object.

58. A method for determining the dimension, location, or attitude of an object surface, comprising:

projecting a pulsed zone of light onto a surface of an object;

forming an image of said pulsed zone of light on a photodiode array with lens means having an optical axis which is angularly spaced from the optical axis of the projected light, said image being sufficiently small such that it is not incident upon all of the photodiodes in said array whereby the position on said photodiode array on which said image is formed is dependent upon the location of said object surface,

storing the output of said diode array in temporary delay means;

applying a threshold voltage to said stored diode array output, and controlling said voltage in dependence upon the amount of light reflected from said zone;

determining, from the stored array outputs, the position of said image on said photodiode array, said determination being effected in the interval between successive light pulses;

determining from the position of said image on said array the location of said surface illuminated by said zone of light; and

determining from said location of said surface, the dimension, location, or attitude of said object.

59. A method according to claim 58 further comprising controlling the light pulse length in dependence upon the amount of light reflected from said zone.

60. Apparatus for determining the dimension, location or attitude of an object surface, comprising:

means for projecting a pulsed zone of light onto a surface of an object;

lens means for forming an image of said pulsed zone of light on a photodiode array, said lens means having an optical axis which is angularly spaced from the optical axis of the projected light, said image being sufficiently small such that it is not incident upon all of the photodiodes in said array whereby the position on said photodiode array on which said image is formed is dependent upon the location of said object surface,

means for storing the output of said diode array in temporary delay means,

means for amplifying said stored diode array output, and means for controlling the amplification of said stored output in inverse proportion to the light energy reflected from said zone;

means for determining, in the interval between successive pulses of light, from the amplified stored diode array output, the position of said image on said photodiode array;

means for determining from the position of said image on said photodiode array the location of said surface illuminated by said zone of light; and

means for determining from said location of said surface, the dimension, location, or attitude of said object.

61. Apparatus for determining the dimension, location or attitude of an object surface, comprising:

means for projecting a pulsed zone of light onto a surface of an object;

lens means for forming an image of said pulsed zone of light on a photodiode array, said lens means having an optical axis which is angularly spaced from the optical axis of the projected light, said image being sufficiently small such that it is not incident upon all of the photodiodes in said array whereby the position on said photodiode array on which said image is formed is dependent upon the location on said object surface,

means for storing the output of said diode array in temporary delay means,

means for applying a threshold voltage in dependence upon the amount of light reflected from said zone;

means for determining, in the interval between successive pulses of light, from the stored diode array output, the position of said image on said photodiode array;

means for determining from the position of said image on said photodiode array the location of said surface illuminated by said zone of light; and

means for determining from said location of said surface, the dimension, location, or attitude of said object.

62. A method according to claim 61 further comprising means for controlling the light pulse length in dependence upon the amount of light reflected from said zone.

FIELD OF THE INVENTION

This invention discloses method and apparatus for optically determining the dimension, location and attitude of part surfaces. Particular embodiments describe optical triangulation based co-ordinate measurement machines capable of accurate measurement of complex surfaces, such as gear teeth and turbine blades.

The invention also discloses means for accurately sensing in up to 5 axes the xy location, range and attitude in two planes of an object or object feature, as well as the measurement of angular and size variables on the object.

There are many triangulation sensors in the present art, but none is known to have achieved what this one discloses, namely 0.0001" or even 50 millionths of an inch accuracy on complex surfaces, in a manner capable of high speed analysis of surface form.

To be truly accurate on surfaces of widely varying form, the sensor must have an ability to operte with huge (eg. 10.sup.4) variations in returned light intensity from the part, without giving an apparent change in dimension. And too, the sensor must provide high resolution, drift free digital readout of part dimension. These and other features are present in the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a diagrammatic view of an embodiment of the invention;

FIG. 2 is a block diagram of the basic elements of a system for moving the rotary table of FIG. 1;

FIG. 3 is a diagrammatic view of a further embodiment of the invention;

FIGS. 3A and 3B are electrical schematic diagrams of printed circuits useful in the embodiment of FIG. 3;

FIG. 4 is a graphical representation of a video output signal generated by the diode array of FIG. 3;

FIGS. 5 and 6 are graphical representations of a scan of a diode array illustrating a technique for finding the optical center of a spot of light which falls on the array;

FIG. 7 is a diagrammatic view of a further embodiment of the invention particularly adapted to the measurement of the pitch circle runout of gears;

FIG. 8 is a diagrammatic view of a portion of the embodiment of FIG. 7;

FIG. 9 is a graphical representation of data generated by the embodiment of FIG. 7;

FIG. 10 is a diagrammatic view of a portion of a further embodiment of the invention adapted to the measurement of gear involute or helix angle;

FIG. 11 is a diagrammatic view of a portion of a further embodiment of the invention adapted to the measurement of the thickness of a small flat pump vane;

FIG. 12 is a block diagram of an electronic system for performing the measuring function in the embodiment of FIG. 11;

FIG. 13 is a graphical representation of a system in accordance with the invention wherein a line image, as opposed to a spot image, is projected onto the object under examination;

FIG. 14 is a diagrammatic view of a further embodiment of the invention adapted to sense yaw and pitch;

FIG. 16 is a diagrammatic view of a further embodiment of the invention having capability of five axis sensing; and

FIGS. 17 and 18 are block diagrams of electronic systems particularly useful for sensing moving parts in accordance with the invention.

FIG. 1 illustrates apparatus useful for the contouring of three dimensional objects (for example, turbine blades and gears). This system can be operated in two distinct modes. In one of these modes, the theoretical part shape is stored in a computer which moves the sensor under its control through the theoretical shape of the part and any signal from sensor indicates a part deviation from nominal size. A second mode is useful in scanning part surfaces to digitize the surface shape. In this second mode the sensor itself is used as a null seeking device and any movement of the sensor necessary to keep the system nulled is recorded by the computer as the part shape.

One primary advantage of this type of system is that it is noncontacting. The optical means of measurement allows one to measure parts that are either too soft to be touched by mechanical probes, or too brittle or fragile. In addition, even though the sensor itself may have a very small measurement range in the order of several tenths of an inch, the overall system can have measurement ranges in the order of 6 to 10 inches because of the ability of high resolution precision table to move the sensor over these large areas. Also, there are no contact points to wear or get caught in holes, and the system can also check the presence of holes. Thus there is provided a very accurate, local sensor reference that does not touch the part and additionally a highly accurate frame of reference capable of containing a measurement volume of several cubic feet.

The system consists of three basic parts: a sensor; a moveable table system; and a control computer.

The sensor (8) consists of an illuminating light source (1), in this case a laser, whose power output is controlled by a pockels cell (2). The light energy after passing through the pockels cell is focused to a spot 2A on the surface of the object being measured, via a focussing lens (3). The light scattered from the object 4 is picked up by an imaging lens (5) at angle .gamma. and imaged onto a linear photo diode array (7). The function of the mirror (6) is to reduce the overall package size. The linear photo diode array then is used to sense the position of the imaged light spot. For optimum accuracy .gamma. should be in the range 30.degree.-50.degree.. Current systems operate at 45.degree..

The optical system is aligned so that the image light spot is at the center of the linear photo diode array (7) when the surface of the object is in its nominal position. As the object (4) is moved either towards or away from the sensor (8) the imaged light spot moves across the photo diode array (7). The movement of the object (4) and the movement of the imaged light spot in the linear photo diode array (7) are related by similar triangles centered about the imaging lens (5). This technique is referred to as optical triangulation.

It is sometimes desirable, depending on the shape of the object, to have a duplicate light receiving system on the opposite side of the illumination spot. This would then consist of an additional imaging lens (12), an additional mirror (13) and an additional photo diode array (14).

It is important to note that it is desirable for highest accuracy to keep the laser spot or light spot very small on the surface of the object. A spot in the order of two to five thousandths of an inch is most generally desirable.

This is desirable for two reasons. First, any surface reflectivity variations across the light spot will result in centroid determination errors at the array. It has been observed that keeping the spot small reduces these types of errors dramatically. Secondly, since the spot on the object surface is magnified by the lens on the array, a small spot on the surface is needed to keep a reasonably small spot on the array. The small spot also allows tight curves to be gaged accurately.

In the case where a laser is used as the illumination source, there is, of course, the problem of speckle in the resultant image due to the coherence of the illuminating light. The means used to avoid this problem are, first to use as large an aperture imaging lens as possible, and second to use a wide photo diode array. This wide array will tend to average in a transverse direction the speckle in the laser sport. To illustrate, system accuracy was notably improved when, at a magnification of 3:1, a 0.017" wide diode array was used instead of the 0.001" wide version previously employed.

A very important design consideration in the sensor is the amount of light that is reflected from the object surface. In the normal course of events, an object surface can vary from very dull to very bright and from very rough to very smooth. These variations do modify the amount of light that is reflected from the surface of the object and, therefore, the resultant light on the photo diode array. Since a certain minimum amount of light is necessary for detection of the spot, and since the presence of too much light causes uncertainty in the location of the center of the spot, it is necessary to control the amount of light falling on the array or correspondingly, to control the integration time of the array to allow more light gathering time. For this reason, a micro computer (19) is used to control both the voltage on the pockels cell which, therefore, controls the amount of light striking the surface of the object, and also to control the operating speed or integration time of the linear photo diode array. Under normal operating mode, it is desirable to keep the photo diode array running with as high a speed as possible in order to maximize the speed of operation. Therefore, the primary control mode is to vary the power arriving at the surface by sampling the array and, in a feedback loop, via the micro computer, to control the photo diode array speed. If such a point is reached where the pockels cell is allowing the maximum amount of light from the laser to pass through it, then it is necessary to slow down the speed of operation of the photo diode array in order to work with surfaces that are even duller than those with which it is possible to work by controlling only the laser power. In this case, the overall speed of the gage is reduced. However, it is still possible to make measurements from dull surfaces. It is possible via this technique to work with surfaces whose reflectivity varies by up to 5 orders of magnitude (10.sup.5 X).

Another important point in the design of the sensor is the magnification used in the system. It is desirable to have an optical magnification ranging between three times and five times in order to take the greatest advantage of the spot movement in relation to the diode array size. In addition, it is possible to tilt the photo diode array at an angle to the direction of normal light incidence. This serves two functions. It helps maintain the focus of the system over a large range of movement, and, it also results in a higher effective magnification.

The moving table system allows the sensor head to have effectively larger range. For example, if the x-y tables (9) have a movement range of 6 inches each and resolution of 50 millionths of an inch, this, in conjunction with the sensor resolution being extremely high, allows one to have a very large high accuracy measuring volume. It is also possible for the z axis table (11) to have a movement of 12 to 14 inches. This, coupled with the ability to rotate the part a full 360.degree., allows one to fully contour a part by moving in turn the x, the y, the z or the .theta. axis. The control computer allows the design data for an object stored in its memory to be converted into movements of the sensor via the table system. The basic elements of the system are shown in FIG. 2 where there is shown a control computer (15), an input terminal (16), which is used to enter commands as well as additional data into computer, a x-y plotter (17), which is used to plot out contours or deviations from desired contour, a 4 axis table controller (18), which accepts commands from the control computer and thereby moves the sensor head to various locations in space, and the sensor control micro computer (19), which controls the scanning speed of the arrays as well as the voltage applied to the pockels cell for light control. It also accepts information from the arrays or arrays (20) and (21), which will allow the micro computer to vary the array integration time.

Conversely, polar coordinate based systems can be used when the sensor is moved in r and .theta., and possibly .theta. as well. Polar arrangements are advantageous when contours of concave surfaces, for example, are desired. Such a system is also of interest if rapidly varying curvatures are encountered. Another advantage of a polar system is that the angular scan (.theta. or .theta.) can be mechanically very fast and smooth as it is provided by a high grade bearing motor and shaft encoder combination.

A further embodiment of the invention is shown in FIG. 3. The electro-optical system within the optical head consists of the laser (33), pockels cells (32), analyzer (34), beam focussing lens (31), part being measured (25), imaging lenses (26)(35), each linear diode arrays (29)(38), and each diode array control cards (30)(39). Printed circuit diagrams PC 7807 (FIG. 3A) and PC 7808 (FIG. 3B) are incorporated by reference.

The video signal produced by the diode array is sampled and held between clock pulses to produce a boxcar type video output similar to FIG. 4. The array control boards work with external clock and start signals supplied by the light level compensation board P.C. 7808 (40). The video signals are fed to the programmable filters (low pass) (41) and the four video filter outputs per side are fed to their respective multi-level spot centroid finder (42) where one of the signals is selected. The video signal is then level detected, the resulting count pulse sequences are counted and displayed for visual indication, and also sent to the A/D and Data Distribution card PC 7903 (43) where they are counted in binary. The resulting binary number is then sent to the micro computer (44) where the data is scaled and linearized.

In operation, the external control computer signals the internal micro-computer to initiate a reading. The micro-computer in turn signals the pockels cell controller (45) to take a light power reading. On completion of this, the pockels cell is set by the controller to a certain illumination level. After this operation, the light level compensation circuit is signaled to initiate a sequence of diode array scans.

Once the left and optional right channel readings are obtained the data is sent to the micro-computer for processing, after which data is put on the computer bus.

The linear diode arrays are set to operate from an external clock and each scan is initiated by an external start command. The image of the laser spot formed on the diode array by lens (26) produces a voltage pulse on the video output of the diode array giving indication where the spot is located on the array. The shape of this video pulse follows the Gaussian power distribution of the laser: its magnitude depends on the intensity of the reflected light and the time delay between two subsequent scans. To accommodate the changes in intensity of the illuminating beam and a secondary system which is based on generating increasing time delays between subsequent scans.

When a new reading is initiated by the computer or an external control device, the primary light level compensation is activated. The pockels cell controller takes a voltage measurement of the video pulse through a peak hold circuit and based on this measurement, it either reduces or increases the intensity of the illuminating beam. The pockels cell voltage, and therefore the light output, is held constant for the duration of the upcoming dimensional measurement.

The dimensional measurement is initiated by the micro-computer (44) after the pockels cell has settled down to a new intensity level. The linear diode arrays are operated at a constant clock rate put out by the light level compensation board. The same board (PC 7808) also generates the array start pulses.

The amplitude of the signal generated by the photo diode arrays is proportional to the light integration time for a given optical power level. The light integration time is the elapsed time between the start of two subsequent scans. Thus controlling the integration time allows one to control the diode array output voltage: meanwhile the clock-rate can be kept constant. The constant clock-rate permits the use of constant bandwidth video filters (41) as the frequency content of the video signals remains unchanged from scan to scan. These filters are requred to overcome the problem of multiple triggering on speckle effect-induced high frequencies in the video signals.

The system used in this gage generates start pulses to the diode arrays by a geometric sequence of T=t, T=2t, T=4t, T=8t etc. where t is the unit integration time. Thus the video output voltage varies as 1, 2, 4, 8 etc. with the increasing integration time on each subsequent scan. Each integrating time period consists of two parts, namely a wait period and a scan period. In this design, it equals the array scan time. Thus, during T=t, the wait period equals zero, in T=4t, T=8t, etc. the wait period is greater than the scan period.

The above binary sequence is generated on PC 7/7808 by the binary counter chain formed by D6, D5, D4, D11 and D10. The sequence number is generated by counter D9 and selected by multiplexer D12. At the end of each diode array scan D9 is incremented and a longer integration time gets selected by D12. When the wait period is over, a start pulse is generated, which initiates a diode array scan. The sequence is terminated, when either both video signals reach a fixed threshold level, or a scan cycle finished signal is generated by comparator D15, which limits the binary sequences to a number preset by a thumbwheel.

The optical triangulation method utilized in this design derives the dimensional information about the part by computing the position of the centroid of the light spots falling on the diode arrays. Rather than going through a complex computing method, a simple counting technique was devised to find the optical center or centroid of the spot as shown on FIG. 5.

Each diode array element is counted as 2 in zone A and when the video signal goes over the threshold in zone B, each element is counted as one. When video falls below the