WO2001001072A1

WO2001001072A1 - Apparatus and method for determining dimensional geometries for an object

Info

Publication number: WO2001001072A1
Application number: PCT/US2000/017795
Authority: WO
Inventors: Glen Castore
Original assignee: M & M Precision Systems Corporation
Priority date: 1999-06-30
Filing date: 2000-06-28
Publication date: 2001-01-04
Also published as: AU5897400A

Abstract

A high speed optical measurement apparatus (10) and method for measuring the surface geometry of an object. The optical measurement apparatus includes a stationary light source (12) for focusing a light signal through an extended sensing zone (34), a fixture for rotating an object of interest through the sensing zone, a detector (44) for monitoring a reflected light signal from a surface of the object and a programmable controller (45) for analyzing data received from the detector (44). The detector (44) generates data in response to the reflected light and transfers the data to the programmable controller (45).

Description

APPARATUS AND METHOD FOR DETERMINING DIMENSIONAL GEOMETRIES FOR AN

OBJECT

Field of Invention The invention relates to measuring the surface geometry of an object and, more specifically, to non-contact optical measurement systems for determining the dimensional values of the object.

Background of the Invention Dimensional inspection of complex forms such as gears, screw threads, cutting tools used m metal working, and compressor scrolls is commonly performed during modem manufacturing operations. Traditional inspection methods are time consuming and require considerable skill on the part of the inspector to reach acceptable levels of measurement certainty. Screw threads, for example, have a number of dimensions or characteristics which are useful for both manufacturing process control and for determining performance of the fastener under load. Typically only two or three of these characteristics are regularly checked, m large part because of the time, skill, and equipment required to measure all these characteristics. Likewise, during the manufacture of gears, characteristics, such as the lead, involute or index of the gear, are measured to determine the control of the process . There are two primary methods m use for determining the acceptability of these complex forms as manufactured: functional testing and analytical testing. Functional testing compares the measurements of an object being manufactured against a master. The dimensional variation between the object and the master is measured and from this a determination can be made as to whether the object is within specifications. For example, a functional test of a gear may involve running an object gear against a master gear and determining the relative rate of rotation of the two gears. One of the gears may be mounted on a fixed axis and the other mounted on a floating axis. A measure of linear displacement can be made as the gears are rotated against each other. Consequently, it is often difficult to determine the specific aspect of the gear form which is incorrect. Additional testing and expert interpretation are generally required to obtain enough information to correct the manufacturing process .

Analytical testing provides a quantitative method for determining the geometrical features of an object. Analytical testing generally includes a large computer controlled apparatus which may include a high resolution contact sensor or stylus to measure various characteristics of the object. M & M Precision, assignee of the present invention, sells analytical testing apparatuses of this type under model designation QC 1000 Gear Analyzer. For a gear, measurement characteristics of interest may include the straightness of a gear tooth (lead) , the form of the curved cross section of a tooth (involute) or the tooth to tooth distance (index) can be accurately measured The measurement process using a contact sensor requires several measurements to fully characterize one gear. Analytical testing is not generally performed on every gear being manufactured.

High speed, high precision, non-contact measurement methods have been 15 proposed for inspection of mechanical components such as gears, screw threads, turbine blades, camshafts and similar parts. Such sensors need a resolution on the order of 0.1 to 1 micron. Ideally this resolution can be maintained m a normal manufacturing environment so the sensor can be used for m-line inspection and used to compensate for inaccuracies as the parts are made. Additionally, it would be preferred that the measurement methods are capable of simultaneously measuring multiple dimensional characteristics so that the manufacturing process is uninterrupted by the quality control process.

There are a variety of optical devices used for high precision measurement of surface profiles. For example, tπangulation sensors as described m United States Patent 4,547,674 to Pryor, report the location of an object along a line m the direction of a laser beam and within the field of view of receiving optics. The best laser tπangulation sensors have a resolution of 0.25 microns which is believed to be close to the theoretical limit for this technology. Speckle noise is the limiting factor in the performance of current designs of tπangulation sensors. In measuring an object such as a gear or an object having a screw thread, secondary reflections are also a significant source of optical noise. Light from secondary reflections incident upon the photodetector can cause the data to be m error by as much as 3 microns. Moreover, the sensors are generally moved about the stationary object using a precision motion system similar to that which is used for current analytical gear checkers and computer controlled coordinate measuring systems. Still further, these systems generally acquire a single data point at a time and thus, are somewhat slow and difficult to integrate with the manufacturing process without affecting output. Triangulation sensors are sold by a number of companies including CyberOptics, Keyence, and Omron.

United States Patent No. 4,983,043, to Harding, describes a method for determining the position of an object along a line projected m space, wherein the line is perpendicular to the direction of the laser beam. A cylindrical lens and focusing optics are used to create a focused line segment which is also m the focal plane of the receiving optics. A translation mechanism is provided which moves the focused line segment into the object along the plane of the cross section of interest. Location along the line is typically determined by the centroid of an image on a linear pixel array detector. This type of sensor is capable of recording multiple data points at one

United States Patents 4,796,997 and 5,024,529 to Svetkoff et al . , incorporate a describe a scanning spot laser sensor. This type of scanning laser sensor uses much the same principle as a tπangulation sensor for determining the position of a target from the light distribution on a photodetector. The beam is moved using either a spinning polygonal mirror, a galvanometer minor, or an acousto-optic cell. This type of device is used for inspecting printed circuit boards. It cannot be used for measuring objects such as screw threads or gears because of its inability to filter secondary reflections.

Summary of the Invention

The present invention is directed to a high speed optical measurement apparatus for measuring the surface geometry of an object. The optical measurement apparatus constructed m accordance with the present invention includes a stationary light source for focusing a light signal through an extended sensing zone, a fixture for rotating an object of interest through the sensing zone, a detector for monitoring a reflected light signal from a surface of the object and a programmable controller for analyzing data received from the detector.

The object whose exterior measurements are to be measured is rotated by the fixture so that light impinges upon the object through an extended YD

sensing zone. The extended sensing zone is generally rectangularly shaped. More preferably, the light source emits a focused line of light onto the object surface. A rotary encoder is used to determine a rotation rate and an angular orientation of the object. The rotary encoder triggers the detector at fixed angular positions to record and transfer the data to the programmable controller. The detector monitors the reflected light signal caused by reflection of the line of light from the object surface as the light signal scans across the surface and provides data m response to receipt of the reflected light signal . Preferably, the detector includes a field programmable gate array or a digital signal processor for data analysis and data reductionl . The data generated by the field programmable gate array or digital signal processor is used by the programmable controller for determining the location of the object surface.

In accordance with a preferred embodiment of the present invention, a method for determining a position of a surface of an object includes generating a coherent light signal and transmitting a line of light in a specified direction; rotating an object in a position relative to the light signal; monitoring a reflected light signal caused by a reflection of the light signal from the object surface as the line of light scans through a region; producing data in response to receipt of the reflected light signal; and determining a location of the object surface from the data produced by the reflected light signal and rotation of the object. The step of determining the location is performed by monitoring an intersection point of the light signal with the object surface and determining a vertical and angular position of the point. The intersection point is defined by an intersection of two focusing planes, a first focusing plane of a transmit optics and a second focusing plane of a receive optics system.

The dimensional characteristics of interest of an object can be measured quickly and accurately. For example, if the object of interest is a gear, all of the teeth can be measured for such characteristics as index, lead or involute and a determination can be made whether the gear is m specification. Moreover, multiple sensors which include the light source and the detector can be circumferentially positioned about the object of interest to simultaneously generate data for different object surfaces. For example, three sensors could be appropriately positioned to determine the involute, lead and index characteristics of a gear with only one 3600 rotation of the gear. Moreover, multiple sensors could be used to measure the same object surface and depending on the positioning of the sensors would require less than 3600 rotation of the object to determine the dimensional characteristics for all of the object surfaces of interest. As a result, a high speed optical measurement system can 2 be used during the manufacturing process to quantitatively measure the desired characteristics of interest for every object produced. This, m turn, will allow compensation of errors m the manufacturing process to occur at a much faster rate .

The invention has utility m determining the dimensional characteristics of a variety of different parts including but not limited to gears, screw threads, cutting tools, compressor scrolls and impeller blades. These and other objects, advantages and features of the invention will become better understood from the detailed description of the invention which is described m conjunction with the accompanying drawings. Brief Description of the Drawings

Figure 1 is a perspective schematic of components of a laser position sensor constructed m accordance with a preferred embodiment of the invention;

Figure 2 is a block diagram of a circuit for measuring a location of a surface of an object;

Figure 3 is a perspective view of the invention for use m measuring the physical characteristics of a gear;

Figures 4A - 4C show application of the invention for use m measuring physical characteristics of a gear tooth on a gear;

Figure 5 is a perspective view of a test gear mated with a master gear constructed m accordance with another embodiment of the invention; ?

Figure 6 is a depiction of use of the invention on a screw thread such as a thread for use on an impeller blade of a large volume air compressor;

Figure 7 is a depiction of use of the invention on a tap or similar cutting tool;

Figures 8A and 8B are top and side views depicting use of the invention on a compressor scroll .

Detailed Description

Figure 1 illustrates the components of a preferred embodiment of a laser scanning sensor 10 that forms part of an optical sensing system which includes projection optics P and receive optics R for use m determining a location of a surface on a object 0 (Figure 2) . Preferably the projection and receive optics are housed within a sensor housing. A laser diode 12 serves as a point light source for emitting light that passes through a collimating lens 14. A preferred laser diode 12 emits light m the visible light spectrum. The collimating lens transforms the spherically expanding rays emitted from the laser into generally parallel light rays. Although not shown m Figure 1, the light beam could be bent or folded using mirrors or prisms m a region between the source and the collimating lens 14 m a way to accommodate a particular geometry of the scanning system 10.

After passing through the lens 14 a collimated light beam 15 from the lens is directed through a cylindrical lens 20. The cylindrical lens 20 forms the incoming collimated beam into an outgoing line of light 22. The line of light 22 passes through through a focusing lens 32 that focuses the beam of light on a plane 34 of the object of interest. As the object rotates, the focused beam scans along a line 36 m the projection optics focal plane 34.

The receive optics R includes a focusing lens 40, and a high speed photodetector 44. It should be apparent m view of this disclosure that there may be additional focussing lenses depending on the particular receive optics configuration. As is known to those skilled m the art, the focussing lens 40 may also be referred to as a telecentric optical train. An example of an appropriate photodetector is an avalanche photodiode series C5331 photodetector manufactured by Hamamatsu. The focusing lens 40 defines a receive optics plane 46 that intersects the projection optics plane 34 along the line 36 traversed by the focused beam 30. Preferably, the receive optics R includes a field programmable gate array 45 or a digital signal processor (not shown) . The field programmable gate array or the digital signal processor receives the electronic signal data generated by the photodetector and compresses the data for analysis by a microcomputer (not shown) .

The length of the line 36ιs primarily dependent upon the diameter of the optical components used. When the focused light encounters a surface on a rotating object 0, light is reflected into the lens 40 and triggers an output //

from the high speed photodetector 44. A variation of the preferred embodiment is to include a CCD array m the receive optics. Such a variation would not only generate a timing signal when the CCD array was struck but would also give a spatial co-ordinate for the reflection point on the surface .

A block diagram of a circuit for measuring a location of a surface of an object is depicted m Figure 2. The circuit includes a power supply 50 for applying power to circuit components that require electric power for their operation. One such component is a motor 52 used to rotate the object of interest. The motor can be any motor as is known to one of ordinary skill m the art, for example, a DC servo motor could be used. The motor rotates a shaft 54 upon which the object 0 is mounted. The rotation rate of the object determines the speed m which the location of an object surface can be calculated. For example, a surface of an object rotated at about 10 rpm can be inspected analytically m about 15 seconds with a sensor capable of a data rate of about 1600 points per second. A higher rotation rate or the use of multiple sensors measuring the same object surface will lower the analytical inspection time. The motor is powered through an amplifier 56. Optionally, the motor, and shaft are mounted to a table 58.

A rotary encoder 60 is mounted to the same shaft 54 that rotates the object. As the shaft \

rotates the encoder triggers the photodetectors 44 housed m the sensors 10 to take a reading at fixed angular orientations. Each reading by the sensor along with the angular orientation of the object based on the encoder generated signals is transmitted to a controller 70. A motion controller 62 controls the shaft rotation speed through a feedback loop with the rotary encoder 60 and the motor amplifier 56. The controller is used to send instructions to the motion controller and receive the data generated by the encoder and the sensor shown m Figure 1.

A preferred embodiment of the invention incorporates a plurality of sensors 10 spaced about an object region. Each sensor includes the projection P and receive R optics shown m figure 1. The sensors are stationary during operation. Preferably, each sensor contains one set of projection and receive optics. More preferably, the receive optics includes the field programmable gate array or the digital signal processor. Optionally, the controller may include the field programmable gate array (not shown) . The field programmable gate array or the digital signal processor, as discussed above m figure 1, processes the data received from the photodetector housed within the sensor and compresses the data for analysis by a microcomputer system. The angle of the sensor relative to the object surface is dependent on the geometry of the object. The laser diodes 12 used m the sensors are powered by an external power supply. An output from each sensor is connected by a serial communications line 64 to a serial port 66 connected to the microprocessor. The sensors are triggered by direct input from the rotary encoder and record a exact position of an intersection point from the line of light with the object surface. The controller also includes a microprocessor based microcomputer and a monitor and keyboard 72. Other peripherals to the microcomputer will be known to those skilled m the art and may include a network interface 74 for linkage to other microcomputers, and relays and LED displays 76 useful for monitoring system operation and performance .

Once data has been acquired the calculation of geometric characteristics using mathematical formulas known to those skilled m the art are applied. The data from the encoder and the sensors are coupled to the microprocessor that calculates the position of the intersection point on the object 0 from which the laser beam or beams is reflected and transmits that data to the serial communications port of the controller and to the microcomputer that logs data and uses the data to calculate object profiles and other characteristics .

Gear Teeth

Turning now to Figures 3 and 4A-C, one sees an object such as a gear 80 having a gear tooth 82 and an exposed tooth surface 84 mounted on the shaft 54. One use of the invention is to measure the involute, lead or index form of the gear tooth as the gear rotates at a reasonably high speed (approx. 10 RPM) . A laser light beam 90 from the sensor 10 scans a line of light produced by the sensor 10 projection optics P that impinges the tooth surface 84 approximately perpendicularly. As the gear rotates, the photodetector 44 m the sensor 10 images the intersection of the line with the tooth. Since the angular orientation of each image is recorded, as well as its location on the detector, the controller 70 can reconstruct the geometry of the slice of the tooth at the location the laser contacts the gear, knowing the rotational velocity of the gear. The rotational velocity of the gear is determined by the motion controller 62.

As the gear rotates, sensor 10 senses a sequence of pixel locations and the encoder records the angular orientations for those locations. In the preferred embodiment, the pixel locations are processed using the field programmable gate array which forms part of the sensor or the controller as discussed above. Optionally, the digital signal processor may be used. The field programmable gate array or the digital signal processor compresses the amount of data that flows from the sensor to the microcomputer executing the software to calculate the gear measurement values.

The processing of the output data is done m three steps. A first step is to apply a window which localizes the relevant pixel data. The second step is to process the relevant pixel data to find the spot center. The algorithm to find the spot center uses a weighted Gaussian function rather than a standard centroid algorithm. The weighted Gaussian function reduces the effect of some spurious reflections from the surface which generate noise for this type of sensor. The third step takes the sequence of spot center and angular orientation data values and determines the straightness (lead) of the line on the gear surface .

In a second application of the method for measuring gear shape, a laser line could be tangent to the tooth surface and perpendicular to the involute curve, as shown m Figure 4B . In this instance all pixels of the CCD array are excited as the tooth is rotated through the line. The angular orientation history of pixel excitation can again be analyzed, m this instance providing a measure of the tooth lead.

A high speed inspection device could include multiple sensors (typically at least 3 sensors) to simultaneously measure multiple characteristics of the gear. These characteristics include index, tooth spacing, tooth width, lead, and involute forms of the gear. Measurement accuracy is on the order of 0.0001 inches. Each of the three sensors generates a line which intersects the gear surface at a unique angle. The three laser lines form a 3- D coordinate frame which each tooth passes through as the gear is rotated. The intersection curve of the gear tooth surface and the laser lines determines which gear characteristic is measured by the sensor. One line of light intersects the gear tooth m two points and is used to measure index, tooth width, and tooth spacing (Figure 4C) . A second line of light intersects the gear as the gear rotates. This line measures gear involute (Figure 4A) . A third line of light intersects the gear m a path as the gear rotates and measures the lead of the tooth (Figure 4B) .

Alternatively, as shown m Figure 5, a master gear form 100 is compared directly to a test gear 108 The test gear is mounted on a freely rotating shaft 102 wherein the angular orientation is monitored by a rotary encoder 104. The master gear is mounted on a shaft 110 connected to a motor 106 and the master gear engages the test gear to rotate the test gear. The angular position of the master gear is monitored by a similar encoder 105. During operation, the motor rotates the master gear which m turn rotates the test gear. The rotation rate of the gears is monitored and controlled by a motion controller (not shown) . Sensors 10 positioned about the test gear are triggered by the rotary encoder on the shaft of the test gear at fixed angular positions as the gears rotate. The data is transmitted to a controller that includes a microprocessor 112 and subsequently analyzed by a microcomputer software program similar to that discussed above m regard to figure 2. Comparison of the data generated at the fixed angular orientations with known readings from the master π are made and a measure of the transmission error can be made m exactly the same way as is done with a single flank tester. Thus, transmission errors can be exactly correlated with the master gear as measured by the sensors .

Screw Threads

A device constructed m accordance with the present invention can be used for rapidly inspecting screw thread geometry. Screw thread characteristics that can be determined from a laser scan of the screw thread include: a) major diameter, b) minor diameter, c) pitch diameter, d) functional diameter, e) circularity, f) taper, g) pitch, h) lead variation, 1) flank half angles, j) root radius, and k) root to crest height.

One or more laser line sensors 10 are used to generate multiple profiles of the thread form. Once the profile data is obtained, it is analyzed using techniques known m the prior art to generate values for thread characteristics such as pitch diameter, major diameter, minor diameter, flank half angle, and root radius.

The structure is also used to measure lead and helical deviation. These measurements take advantage of the fact that m the case when the thread is rotated as the data is gathered the time sequence of data values can be known very precisely. As shown m the diagram of Figure 6, the screw thread is fixed m space and the laser line 120 moves parallel to the thread axis. The screw thread depicted m Figure 6 is an impeller blade 124 that is used on a large volume air compressor. It has a screw-like form which must be manufactured to close tolerances. The sensing system 10 shown m Figure us capable of rapidly and accurately measuring both sides of the wall 122 of the impeller blade. The microcomputer generates a detailed digital profile of the impeller blade which can be analyzed to determine curvature, thickness, height, and distance from one wall to the next at different distances from the centerlme of the impeller blade.

In accordance with another embodiment, the laser line 120 is fixed m space, at approximately the pitch diameter of the thread, and the thread is rotated using a high precision spindle.

A basic form of a compressor scroll 140 is shown m Figures SA and SB. The sensing system 10 projects a line 150 which simultaneously intersects several walls of the scroll . Consequently it can simultaneously measure the width of several walls and the distance between them. By attaching the sensing system 10 and the compressor scroll 140 to precision motion stages which move the scroll vertically and rotate it with respect to the system 10 the part can be rapidly measured with great precision. Such measuring can include measuring wall profiles, wall thicknesses, wall height and the distance between walls as a function of distance from the top of the scroll. Cutting tools such as taps, drills, and milling cutters are difficult to measure because their form includes a ft number of compound angles and rapid changes of form. Forms m which the surface slope changes rapidly are very difficult to measure with contact type probes. Figure 6 shows a tap 160 monitoring setup with two laser systems that sweep outlines of light orthogonal to one another. By rotating the sensor, all the form characteristics of the tap can be measured. These characteristics include thread pitch, rake angle of the cutting surface and pitch diameter at various axial locations.

The foregoing description of the preferred embodiments of the invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible m light of the above teachings. The embodiments were chosen and described to provide the best illustration of the principles of the invention and its practical applications to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled.

Claims

What is claimed is:

1. A high speed optical measurement apparatus for determining the dimensional geometry of an object comprising : a) a stationary light source for focusing a light signal through an extended sensing zone; b) a fixture for rotating an object surface of interest through the sensing zone; c) a detector for monitoring a reflected light signal from the object surface and generating data caused by reflection of the light signal; and d) a programmable controller for analyzing data received from the detector for determining a location of the object surface.

2. The high speed optical measurement apparatus of claim 1 wherein said sensing zone is generally rectangularly shaped.

3. The high speed optical measurement apparatus of claim 1 further comprising a rotary encoder for determining a rotation rate and an angular orientation of the object.

4. The high speed optical measurement apparatus of claim 1 wherein the rotary encoder triggers the detector at fixed angular positions to record and transfer the data to said programmable controller.

5. The high speed optical measurement apparatus of claim 1 further comprising at least one additional detector and at least one additional stationary light source scanning a light signal through an extended sensing zone for providing additional data to the programmable controller in determining a location of a different object surface from which the light is reflected.

6. The high speed optical measurement apparatus of claim 5 wherein the locations of the object surfaces are simultaneously calculated by the programmable controller in response to a signal from a rotary encoder.

7. The high speed optical measurement apparatus of claim 1 wherein the detector comprises a field programmable gate array for data analysis and data compression.

8. The high speed optical measurement apparatus of claim 1 wherein the detector comprises a digital signal processor for data analysis and data compression.

9. The apparatus of claim 1 wherein said object is a gear.

10. A high speed optical measurement apparatus for determining the dimensional geometry of an object comprising : a) a sensor comprising a light source for projecting a focused line of light onto an object surface and a detector for monitoring a reflected light signal wherein the detector generates data caused by reflection of the line of light from the surface of the object; b) a fixture for rotating the object surface relative to the light source; and c) a programmable controller for analyzing data received from said detector.

11. Position sensing apparatus comprising: a) at least one stationary light source for projecting a focused line of light onto an object surface such as a compressor scroll, object having a screw thread, cutting tool, gear or impeller blade; b) a fixture for rotating the object surface relative to the line of light; c) optics for monitoring a reflected light signal caused by reflection of the line of light from the object surface, the optics including a light responsive detector for generating a response signal based on receipt of the reflected light signal; and d) position determining circuitry for determining a location of the object surface based upon the reflected light signal.

12. A method for determining a position of a surface of an object comprising the steps of: a) generating a coherent light signal and transmitting a line of light m a specified direction; b) rotating an object m a position relative to the light signal; c) monitoring a reflected light signal caused by a reflection of the light signal from the object surface as the line of light scans through a region; d) producing data m response to receipt of the reflected light signal; and e) determining a location of the object surface from the data produced by the reflected light signal and rotation of the object.

13. The method of claim 12 wherein the step of determining the location is performed by monitoring an intersection point of the light signal with the object surface and determining a vertical and an angular position of the point.

14. The method of claim 12 wherein the light beam scans along a line defined by an intersection of two focusing planes, a first focusing plane of a transmit optics system and a second plane of a receive optics system.

15. The method of claim 12 wherein the object comprises a gear having gear teeth and wherein the gear is mounted for rotation with respect to the coherent light signal.

16. The method of claim 15 wherein the data is used for determining involute, index and lead locations m the gear.

17. The method of claim 12 wherein the object comprises a cutting tool and wherein the cutting tool is mounted for rotation with respect to the coherent light signal.

18. The method of claim 12 wherein the object comprises a compressor scroll and wherein the compressor scroll is mounted with respect to the coherent light signal.

19. The method of claim 12 wherein the object comprises an object having a screw thread that is mounted with respect to the coherent light signal. v

20. The method of claim 12 wherein the object comprises an impeller blade and wherein the impeller blade is mounted with respect to the coherent light signal.

21. A method for determining a position of a surface of a compressor scroll comprising the steps of: a) generating a coherent light signal and transmitting a line of light m a specified direction onto an object surface; b) rotating the object and causing the coherent light signal to scan through a region; c) monitoring a reflected light signal caused by reflection of the light signal from the surface of the object as the line of light scans through the region and producing a response signal m response to receipt of the reflected light signal; and d) determining a location of the surface of the compressor scroll from which the light signal reflected based upon the response signal derived from the scanning of the light through the region and a relative rate of rotation of the object.

22. A method for determining a position of a surface of a cutting tool comprising the steps of: a) generating a coherent light signal and transmitting a line of light m a specified direction onto an object surface; b) rotating the object and causing the coherent light signal to scan through a region; c) monitoring a reflected light signal caused by reflection of the light signal from a surface of an object as the line of light scans through the region and producing data m response to receipt of the reflected light signal; and d) determining a location of the surface of said cutting tool from which the light signal reflected based upon the response signal derived from the scanning of the light through said region and a relative rate of rotation of the object.

23. A method for determining a position of a surface of a object having a screw thread comprising the steps of: a) generating a coherent light signal and transmitting a line of light m a specified direction onto an object surface; b) rotating the object and causing the coherent light signal to scan through a region; c) monitoring a reflected light signal caused by reflection of the light signal from a surface of an object as the line of light scans through the region and producing data m response to receipt of the reflected light signal; and d) determining a location of the surface of the object from which the light signal reflected based upon the response signal derived from the scanning of the light through said region and a relative rate of rotation of the object.

24. A method for determining a position of a surface of an impeller blade comprising the steps of: He a) generating a coherent light signal and transmitting a line of light m a specified direction onto an object surface; b) rotating the object and causing the coherent light signal to scan through a region; c) monitoring a reflected light signal caused by reflection of the light signal from a surface of an object as the line of light scans through the region and producing data m response to receipt of the reflected light signal; and d) determining a location of the surface of said impeller blade from which the light signal reflected based upon the response signal derived from the scanning of the light through said region and a relative rate of rotation of the object.