Calibration method for optical rotation probe

Abstract

To provide an optical rotary probe calibration method for accurately calibrating an emitting direction of measurement light to be emitted from an optical rotary probe.SOLUTION: An optical rotary probe calibration method includes: a change step of changing an emitting direction of measurement light to be emitted from an optical rotary probe by a minute angle Δs from a pre-set reference direction; an acquisition step of acquiring a shape error of a reference object by emitting the measurement light toward the reference object from the optical rotary probe while rotating the emitting direction of the measurement light around an S-axis and while changing a relative position between the optical rotary probe and the reference object after performing the change step; and an adjustment error calculation step of calculating an adjustment error of the emitting direction of the measurement light with respect to the reference direction based on a theoretical value of the shape error of the reference object to be obtained when the emitting direction of the measurement light coincides with the reference direction and also based on a measurement value of the shape error of the reference object to be obtained in the acquisition step.SELECTED DRAWING: Figure 14

Description

[Technical field]

[0001] The present invention relates to a technique for calibrating the emission direction of measurement light emitted from an optical rotary probe. [Background technology]

[0002] As a shape measuring device for measuring the shape of a measurement object, for example, a three-dimensional coordinate measuring device is known that obtains the shape of the measurement object by non-contactly detecting the three-dimensional coordinate values ​​of various measurement points of the measurement object using an optical probe. The optical probe irradiates measurement light from a light source toward the measurement point of the measurement object and receives the reflected light of the measurement light reflected at the measurement point. The shape measuring device measures the shape of the measurement object based on the result of detecting the distance from the optical probe to the measurement point by a known measurement method using an interferometer.

[0003] Known examples of such optical probes include an optical rotary probe capable of performing rotational scanning around the longitudinal axis of the probe, as described in Patent Document 1. In a three-dimensional coordinate measuring device equipped with an optical rotary probe, the optical rotary probe is rotated and scanned to measure, for example, the inner shape of a cylindrical measurement target and simultaneously measure the surface shape. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-098180 A Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, there has been a need to measure shapes with large local curvatures in shape measurements of measurement objects. However, in the three-dimensional measuring device described in Patent Document 1, it is difficult to accurately set the emission direction of the measurement light of the optical rotary probe relative to the reference direction during calibration, and there is a problem that measurement errors become large when measuring shapes with large local curvatures.

[0006] The present invention has been made in view of the above circumstances, and has an object to provide a method for calibrating an optical rotary probe, which is capable of calibrating the emission direction of measurement light emitted from an optical rotary probe with high accuracy. [Means for solving the problem]

[0007] In order to solve the above problem, one aspect of the present invention provides a method for calibrating an optical rotary probe capable of emitting measurement light in a direction perpendicular to a probe axis and in which the emission direction of the measurement light can be freely rotated around the probe axis, the method including: a change step for changing the emission direction of the measurement light by a small angle from a preset reference direction; an acquisition step for acquiring a shape error of the reference object by emitting measurement light from the optical rotary probe toward the reference object while rotating the emission direction of the measurement light around the probe axis after the change step is performed, and changing the relative position between the optical rotary probe and the reference object; and an adjustment error calculation step for calculating an adjustment error of the emission direction of the measurement light relative to the reference direction based on a theoretical value of the shape error of the reference object obtained when the emission direction of the measurement light matches the reference direction and a measured value of the shape error of the reference object obtained in the acquisition step.

[0008] According to the method for calibrating an optical rotary probe according to the above aspect, since it is possible to calculate an adjustment error of the emission direction of the measurement light with respect to the reference direction, even if an adjustment error remains after calibration of the emission direction, it is possible to recalibrate the emission direction based on the calculated adjustment error. This makes it possible to improve the calibration accuracy of the emission direction of the optical rotary probe, and in turn to reduce the measurement error of a three-dimensional coordinate measuring device equipped with the optical rotary probe.

[0009] Preferably, the changing step and the obtaining step are each performed a plurality of times by changing the minute angle, and the adjustment error calculating step calculates an adjustment error of the emission direction of the measurement light relative to the reference direction based on the shape error of the reference object obtained for each minute angle.

[0010] Preferably, the acquiring step changes the relative position between the optical rotating probe and the reference object so that the distance between the optical rotating probe and the reference object is constant.

[0011] Preferably, the acquiring step includes acquiring a reference object within a range of a focal position of the measurement light ± a focal depth. covered The relative position between the optical rotary probe and the reference object is changed so that the measurement surface is located.

[0012] Preferably, the reference is a pin gauge arranged parallel to the probe axis.

[0013] Preferably, the obtaining step obtains a radial error of a pin gauge as the form error of the reference object. Effect of the Invention

[0014] According to the present invention, since it is possible to calculate an adjustment error of the emission direction of measurement light emitted from an optical rotary probe with respect to a reference direction, it is possible to calibrate the optical rotary probe with high accuracy. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram of a three-dimensional coordinate measuring device. [Diagram 2] FIG. 2 is a cross-sectional view of an example of an optical rotary probe. [Diagram 3] FIG. 11 is an explanatory diagram for explaining shape measurement of a measurement surface of a workpiece using an optical rotary probe. [Figure 4] 10 is a flowchart showing an outline of a method for calibrating the emission direction of measurement light of an optical rotary probe. [Diagram 5] 13 is a flowchart showing a procedure for setting a reference direction. [Figure 6]FIG. 13 is a diagram for explaining setting of a reference direction using a beam profiler. [Figure 7] FIG. 13 is a diagram for explaining setting of the optical path length using a ring gauge. [Figure 8] 13 is a flowchart showing a procedure for calibrating a relative angle. [Figure 9] 13A and 13B are diagrams showing the positional relationship between an optical rotary probe and a calibration sphere when the rotation angles are 0° and 90° in calibration of a relative angle using a calibration sphere. [Figure 10] 11 is a graph showing an S-angle error versus rotation angle and a graph showing an elevation angle error versus rotation angle, calculated in calibration of a relative angle using a calibration sphere. [Figure 11] 11 is a perspective view showing the positional relationship between an optical rotary probe and a pin gauge when measuring an adjustment error in the emission direction. FIG. [Figure 12] 11 is a diagram showing the positional relationship between an optical rotary probe and a pin gauge on the XY plane when measuring an adjustment error in the emission direction. FIG. [Figure 13] 13 is a graph showing theoretical values ​​of the measurement error of the radius of a pin gauge relative to the reference angle error of the S-angle of an optical rotary probe. [Figure 14] 5 is a flowchart showing a method for recalibrating an emission direction according to the first embodiment. [Figure 15] 4 is a graph showing theoretical values ​​of error and measured values ​​of error for small angles of rotation of the optical rotary probe in the first embodiment. [Figure 16] 10A and 10B are diagrams illustrating differences in intensity distribution of measurement light caused by differences in beam diameter. [Figure 17] 10 is a flowchart showing a method for recalibrating an emission direction according to a second embodiment. [Figure 18] 13A to 13C are diagrams illustrating a method for calibrating an adjustment error according to the second embodiment. [Figure 19] 13 is a graph showing a shape error with respect to a small angle of rotation of the optical rotary probe in the second embodiment. [Figure 20] FIG. 11 is a perspective view of a jig according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to the accompanying drawings. Prior to describing a method for calibrating an optical rotary probe, a configuration of a three-dimensional coordinate measuring device will be described.

[0017] [Configuration of 3D coordinate measuring device] 1 is a schematic diagram of a three-dimensional coordinate measuring apparatus 10. The X-axis, Y-axis, and Z-axis in FIG.

[0018] 1, the three-dimensional coordinate measuring device 10 uses an optical rotary probe 26 to measure the shape of a workpiece W, for example, the shape of the inner peripheral surface of a cylindrical workpiece W. Note that the shape of the workpiece W here includes the three-dimensional shape, two-dimensional shape, surface shape, contour shape, and various dimensional shapes such as length and diameter of the workpiece W. In addition, the shape and type of the workpiece W to be measured are not particularly limited.

[0019] The three-dimensional coordinate measuring device 10 includes a stand 12, a table 14 (base plate) provided on the stand 12, a right Y-carriage 16R and a left Y-carriage 16L provided upright at both ends of the table 14, and an X-guide 18 connecting the upper parts of the right Y-carriage 16R and the left Y-carriage 16L. A gate-shaped frame 19 is formed by the right Y-carriage 16R, the left Y-carriage 16L, and the X-guide 18.

[0020] Sliding surfaces along which the right Y carriage 16R and the left Y carriage 16L slide along the Y axis direction are formed on the upper surface and side surfaces of both ends in the X axis direction of the table 14. The right Y carriage 16R and the left Y carriage 16L are provided with air bearings (not shown) at positions facing the sliding surfaces of the table 14. This allows the right Y carriage 16R and the left Y carriage 16L to move freely in the Y axis direction together with the X guide 18.

[0021] An X-carriage 20 is attached to X-guide 18. A sliding surface along the X-axis direction along which X-carriage 20 slides is formed on this X-guide 18. Also, an air bearing (not shown) is provided on X-carriage 20 at a position facing the sliding surface of X-guide 18. This allows X-carriage 20 to move freely in the X-axis direction.

[0022] A Z carriage 22 (also called a Z spindle) is attached to the X carriage 20. In addition, a Z-axis guiding air bearing (not shown) is provided on the X carriage 20 to guide the Z carriage 22 in the Z-axis direction. This allows the Z carriage 22 to be held by the X carriage 20 so as to be movable in the Z-axis direction. A measurement head 24 is provided at the lower end of the Z carriage 22, which selectively and detachably holds various known probes including an optical rotary probe 26.

[0023] Although not shown, the three-dimensional coordinate measuring device 10 is provided with a Y-axis drive section that moves the gate-shaped frame 19 in the Y-axis direction, an X-axis drive section that moves the X-carriage 20 in the X-axis direction, and a Z-axis drive section that moves the Z-carriage 22 in the Z-axis direction. This allows the measuring head 24 (optical rotary probe 26) to move in three mutually orthogonal axis directions (X, Y, and Z axis directions).

[0024] A Y-axis linear scale (not shown) is provided at the end of table 14 on the right Y carriage 16R side. In addition, an X-axis linear scale (not shown) is provided on X guide 18, and a Z-axis linear scale (not shown) is provided on Z carriage 22.

[0025] On the other hand, the right Y-carriage 16R is provided with a Y-axis detector (not shown) that reads the Y-axis linear scale. Also, the X-carriage 20 is provided with an X-axis detector (not shown) and a Z-axis detector (not shown) that read the X-axis linear scale and the Z-axis linear scale, respectively. The detection results of each detector are output to the control device 72 via the controller 70.

[0026] The measurement head 24 is provided with a head drive unit (not shown) such as a motor that rotates the optical rotary probe 26 around a rotation axis parallel to the Z-axis direction and around a rotation axis perpendicular to the Z-axis. This allows the measurement head 24 to continuously adjust the rotation angle of the optical rotary probe 26 around the two rotation axes. As a result, the attitude of the optical rotary probe 26 can be displaced (rotated) as desired.

[0027] The measurement head 24 is provided with a probe rotation angle detection unit (not shown) such as a rotary encoder that detects the rotation angle of the optical rotary probe 26. The detection result by the probe rotation angle detection unit is output to the control device 72 via the controller 70.

[0028] The optical rotary probe 26 is detachably attached to the measurement head 24. The optical rotary probe 26 emits measurement light LA ​​input from a wavelength swept light source 28 via an optical fiber cable 30 and a fiber circulator 32 toward the measurement surface (here, the inner peripheral surface) of the workpiece W. The optical rotary probe 26 also receives reflected light LB reflected by the measurement surface of the workpiece W, and outputs this reflected light LB and reference light LC (see FIG. 3), which will be described later, to a photodetector 36 via the fiber circulator 32 and the optical fiber cable 34.

[0029] In addition, although details will be described later, the optical rotary probe 26 is configured such that its tip portion (the rotational optical system 42, see FIG. 2) can rotate around a longitudinal axis 62a (corresponding to the probe axis of the present invention, see FIG. 2) described later. This allows the optical rotary probe 26 to perform rotational scanning of the measurement light LA ​​along the measurement surface of the workpiece W by rotating its tip portion.

[0030] Fig. 2 is a cross-sectional view of the optical rotary probe 26. As shown in Fig. 2, the optical rotary probe 26 includes a fixed optical system 40 that is fixed to the measurement head 24, and a rotary optical system 42 that is rotated around the longitudinal axis 62a of the optical rotary probe 26 by the fixed optical system 40.

[0031] The fixed optical system 40 includes a fiber optic cable 44 , a head mounting portion 46 , a collimator lens 48 , and a hollow motor 50 .

[0032] As this optical fiber cable 44 (as well as the other optical fiber cables 30, 34), various known optical fiber cables such as a single mode optical fiber cable and a polarization maintaining optical fiber cable are used.

[0033] One end of the optical fiber cable 44 is inserted through the measurement head 24 and the Z carriage 22, etc., and is connected to the fiber circulator 32. The other end of the optical fiber cable 44 is connected to a head mounting portion 46. The end face on the other end of the optical fiber cable 44 serves as an input / output end 44a, which emits measurement light LA ​​input from the wavelength swept light source 28 via the optical fiber cable 30, etc., and into which reflected light LB reflected by the measurement surface of the workpiece W, etc., enters. The symbol P in the figure indicates the optical path of the measurement light LA ​​and reflected light LB.

[0034] Furthermore, a portion of the measurement light LA ​​input from the wavelength sweep light source 28 or the like to the optical fiber cable 44 is reflected at the input / output end 44a as reference light LC (see FIG. 3).

[0035] The head mounting part 46 is a hollow cylinder extending in a direction parallel to the optical path P (longitudinal axis 62a). One end of the head mounting part 46 is detachably attached to the measurement head 24 described above. A hollow motor 50 is fixed to the other end of the head mounting part 46. A cable connection part 46a to which the other end of the optical fiber cable 44 is connected is provided at one end of the head mounting part 46. The cable connection part 46a holds the input / output end 44a of the optical fiber cable 44 inside the head mounting part 46 at a position that coincides (including approximately coincidence, the same applies below) with the central axis of the head mounting part 46.

[0036] The collimator lens 48 is provided inside the head mounting portion 46 at a position between the input / output end 44a and the hollow motor 50. The optical axis of the collimator lens 48 coincides with the center line of the optical path P. The collimator lens 48 converts the measurement light LA ​​output from the input / output end 44a into parallel light, and then outputs the measurement light LA ​​toward an imaging lens 64 in a shaft 62 described below. This makes it possible to prevent a decrease in the light receiving sensitivity of the reflected light LB caused by misalignment between the fixed optical system 40 and the rotating optical system 42. The collimator lens 48 also outputs the reflected light LB incident from the imaging lens 64 toward the input / output end 44a.

[0037] The hollow motor 50 rotates a shaft 62 (described later) in an axial direction (hereinafter, simply referred to as the axial direction) centered on a longitudinal axis 62a. The hollow motor 50 includes a hollow stator 52 (also referred to as a stator) formed by winding a coil (not shown), and a hollow rotor 54 (also referred to as a rotor) that rotates in the axial direction inside the stator 52. Note that the detailed structure of the hollow motor 50 is a known technique, and therefore detailed description thereof will be omitted.

[0038] The rotor 54 is formed with a hollow portion 54a through which the optical path P passes and which extends in a direction parallel to the optical path P (longitudinal axis 62a). As a result, the measurement light LA ​​emitted from the collimator lens 48 passes through the hollow portion 54a and enters an imaging lens 64, which will be described later, and the reflected light LB emitted from the imaging lens 64 passes through the hollow portion 54a and enters the collimator lens 48.

[0039] The rotor 54 rotates about the longitudinal axis 62a in response to application of a drive signal (voltage) to the stator 52 from the controller 70. The hollow motor 50 is provided with a rotor rotation angle detection unit (not shown) such as a rotary encoder that detects the rotation angle of the rotor 54. The detection result by the rotor rotation angle detection unit is output to the control device 72 via the controller 70. Instead of using the rotor rotation angle detection unit, the rotation angle of the rotor 54 may be detected by controlling the rotation angle of the rotor 54 by known servo control, for example.

[0040] A shaft holding plate 60 (to be described later) that constitutes the rotational optical system is fixed to an annular tip surface b of the rotor on the side facing the rotational optical system .

[0041] The hollow motor 50 is not limited to the configuration (structure) shown in FIG. 2, and various known hollow motors may be used instead.

[0042] The rotation optical system 42 rotates about the longitudinal axis in response to the rotation of the rotor 54. The rotation optical system 42 includes a shaft holding plate 60, a shaft 62, an imaging lens 64, and a right-angle prism mirror 66.

[0043] The shaft holding plate 60 is formed in substantially the same shape (annular) as the tip surface 54b of the rotor 54, and is fixed onto the tip surface 54b in a position parallel to the tip surface 54b. The shaft holding plate 60 is formed with a fitting hole through which the optical path P passes and which extends in a direction parallel to the optical path P (longitudinal axis 62a). One end of the shaft 62 fits into this fitting hole. As a result, the shaft holding plate 60 holds the shaft 62 with its longitudinal axis 62a aligned with the center line of the optical path P.

[0044] The shaft 62 is a hollow cylinder extending in a direction parallel to the optical path P, and has a longitudinal axis 62a parallel to the optical path P. When one end of the shaft 62 is fixed to the shaft holding plate 60, the longitudinal axis 62a coincides (substantially coincides) with the center line of the optical path P, and an inner surface 62b of the shaft 62 surrounds the optical path P.

[0045] An imaging lens 64 is provided inside the shaft 62 at the other end opposite to the one end described above of the shaft 62. A right-angle prism mirror 66 is provided at the other end of the shaft 62 so as to cover an opening on the other end side of the shaft 62.

[0046] The imaging lens 64 is disposed at a position where its optical axis coincides with the center line of the optical path P. The imaging lens 64 images the measurement light LA ​​incident from the collimator lens 48 on the measurement surface of the workpiece W through a right-angle prism mirror 66. The imaging lens 64 also emits the reflected light LB incident through the right-angle prism mirror 66 toward the collimator lens 48.

[0047] The right-angle prism mirror 66 reflects the measurement light LA ​​incident through the inside of the shaft 62 and the imaging lens 64 toward the measurement surface of the workpiece W. Specifically, the right-angle prism mirror 66 refracts the measurement light LA ​​incident from the imaging lens 64 by 90° (including approximately 90°) to make it a light beam parallel to the rotation plane [plane perpendicular to the longitudinal axis 62a (rotation axis)] of the right-angle prism mirror 66, etc., and then emits it toward the measurement surface of the workpiece W.

[0048] Further, the right-angle prism mirror 66 reflects the reflected light LB reflected by the measurement surface of the workpiece W toward the imaging lens 64. As a result, the reflected light LB passes from the right-angle prism mirror 66 through the collimator lens 48 and enters the input / output end 44a of the optical fiber cable 44.

[0049] The shaft holding plate 60, the shaft 62, the imaging lens 64, and the right-angle prism mirror 66 that constitute the rotational optical system 42 rotate integrally around the longitudinal axis in response to the rotation of the rotor 54. Then, as the right-angle prism mirror 66 is rotated around the longitudinal axis, the measurement light LA ​​is rotationally scanned along the measurement surface of the workpiece W.

[0050] 1, when the three-dimensional coordinate measuring device 10 is in the manual measurement mode, the controller 70 drives each driving unit (XYZ driving unit and head driving unit) (not shown) in response to an operation input to an operation unit (not shown) to displace the position and posture of the optical rotary probe 26, and drives the hollow motor 50 to rotate the right-angle prism mirror 66, etc., in the direction around the longitudinal axis. When the three-dimensional coordinate measuring device 10 is in the automatic measurement mode, the controller 70, under the control of the control device 72, drives each driving unit and the hollow motor 50 to displace the position and posture of the optical rotary probe 26, and rotate the right-angle prism mirror 66, etc., in the direction around the longitudinal axis.

[0051] In addition, the controller 70 is connected to the aforementioned detection units (XYZ axis detection unit, probe rotation angle detection unit, and rotor rotation angle detection unit) not shown, and outputs signals etc. output from each of these units to the control device 72.

[0052] Fig. 3 is an explanatory diagram for explaining shape measurement of the measurement surface of the workpiece W using the optical rotary probe 26. As shown in Fig. 3 and the already described Figs. 1 and 2, the wavelength swept light source 28 emits measurement light LA ​​to a fiber circulator 32 via an optical fiber cable 30. This measurement light LA ​​is wavelength swept light whose wavelength changes sinusoidally in a fixed wavelength band at a fixed wavelength sweep period (fixed wavelength sweep frequency).

[0053] The fiber circulator 32 connects to the swept-wavelength light source 28 via a fiber optic cable 30 , to the photodetector 36 via a fiber optic cable 34 , and to a fiber optic cable 44 of the optical rotation probe 26 .

[0054] The fiber circulator 32 is, for example, a non-reciprocating, one-way device having three ports, and outputs the measurement light LA ​​input from the wavelength swept light source 28 via the optical fiber cable 30 to the optical fiber cable 44. This causes the measurement light LA ​​from the wavelength swept light source 28 to be input to the optical rotary probe 26. As a result, the reflected light LB reflected from the measurement surface of the workpiece W and the reference light LC reflected at the input / output end 44a are input to the fiber circulator 32 via the optical fiber cable 44.

[0055] Furthermore, the fiber circulator 32 outputs an interference signal SG of the reflected light LB and the reference light LC input from the optical rotary probe 26 to a photodetector 36 via an optical fiber cable 34 .

[0056] The photodetector 36 may be, for example, a silicon photodiode, an InGaAs (indium gallium arsenide) photodiode, a phototube, a photomultiplier tube, etc. Under the control of the control device 72, the photodetector 36 converts the interference signal SG input from the fiber circulator 32 via the optical fiber cable 34 into an electric signal, amplifies the signal, and outputs the signal to the control device 72.

[0057] The control device 72 is configured by a calculation device such as a personal computer, and includes a calculation circuit configured by various processors and memories, etc. The various processors include a central processing unit (CPU), a graphics processing unit (GPU), an application specific integrated circuit (ASIC), and a programmable logic device (e.g., simple programmable logic devices (SPLD), complex programmable logic devices (CPLD), and field programmable gate arrays (FPGA)). The various functions of the control device 72 may be realized by one processor, or may be realized by multiple processors of the same type or different types.

[0058] For example, in the automatic measurement mode, the control device 72 drives each of the driving units (not shown) and the hollow motor 50 according to a predetermined measurement program to perform displacement of the position and posture of the optical rotary probe 26 and rotation of the right-angle prism mirror 66 and the like around the longitudinal axis. This causes the measurement light LA ​​of the optical rotary probe 26 to rotate on the measurement surface of the workpiece W, and the interference signal SG for each of the multiple measurement points on the measurement surface is detected by the photodetector 36. As a result, the detection result of the interference signal SG for each measurement point is input from the photodetector 36 to the control device 72. In the manual measurement mode, the control device 72 causes the above-mentioned rotational scanning of the measurement light LA ​​to be performed in response to an operation input to an operation unit (not shown).

[0059] In addition, in both the automatic measurement mode and the manual measurement mode, the control device 72 calculates the distance L2 from the right-angle prism mirror 66 to the measurement point on the measurement surface of the workpiece W for each measurement point based on the detection results of the interference signal SG for each measurement point detected by the photodetector 36.

[0060] Specifically, the control device 72 calculates, for each measurement point, a total distance value (L1+L2) of the distance L1 from the input / output end 44a to the right-angle prism mirror 66 and the distance L2 for each measurement point described above, based on the detection result of the interference signal SG for each measurement point. Note that since the method of calculating the total distance value is a publicly known technique (for example, JP 2016-024086 A and JP 2018-084434 A), a detailed description thereof will be omitted here.

[0061] Next, the control device 72 calculates the distance L2 for each measurement point based on the calculation result of the total distance value for each measurement point and the known distance L1. Then, the control device 72 calculates three-dimensional coordinates for each measurement point based on the position and attitude of the optical rotary probe 26 for each measurement point, the rotation angle around the longitudinal axis of the right-angle prism mirror 66 etc. for each measurement point, and the calculation result of the distance L2 for each measurement point. This allows the control device 72 to calculate the shape of the measurement surface of the workpiece W scanned with the measurement light LA.

[0062] It should be noted that the optical rotary probe shown in FIG. 2 and FIG. 3 is merely an example, and is not intended to limit the configuration of the optical rotary probe.

[0063] [Method of Calibrating the Optical Rotary Probe According to the First Embodiment] Next, a method for calibrating the optical rotary probe 26 according to the first embodiment will be described with reference to Fig. 4 to Fig. 16. Fig. 4 is a flowchart showing an outline of a method for calibrating the emission direction of the measurement light LA. Below, a case will be described in which the X-axis direction is the reference direction serving as the reference for emission, but this is not intended to limit the reference direction.

[0064] First, a reference direction for the emission of the measurement light LA ​​is set as shown in Fig. 4. Here, a reference direction for the emission of the measurement light LA ​​with respect to the X-axis direction in the XY plane, in other words, a direction in which the rotation angle s of the optical rotary probe 26 with respect to the X-axis direction becomes s = 0°, is set (step S10).

[0065] <Setting the reference direction of emission> The reference direction of emission of the measurement light LA ​​is preferably set by using, for example, a beam profiler 80. This allows the emission direction of the measurement light LA ​​to be set with high accuracy. Hereinafter, a method for setting the reference direction of emission in the XY plane using the beam profiler 80 will be described with reference to Fig. 5. Fig. 6 shows how the position of the intensity peak of the measurement light LA ​​is detected by using the beam profiler 80.

[0066] First, the control device 72 drives each driving unit (XYZ driving unit and head driving unit) not shown in the figure to set the attitude of the optical rotary probe 26 so that the shaft 62 of the optical rotary probe 26 is parallel to the Z-axis direction (step S110). Next, as shown in FIG. 6, the optical rotary probe 26 emits the measurement light LA ​​in the X-axis direction toward the beam profiler 80 (step S112). The control device 72 measures the intensity distribution of the measurement light LA ​​using the beam profiler 80 while moving the optical rotary probe 26 relatively to the beam profiler 80 by a distance L in the X-axis direction (the direction of the arrow in FIG. 6), and detects the amount of displacement of the position (coordinate) of the intensity peak of the measurement light LA ​​(step S114). Step S1 14 Based on the detection result, the angle (deviation angle) at which the measurement light LA ​​is deviated from the X-axis direction on the XY plane is calculated by the following formula (1) (step S116).

[0067] θ = atan(Ly / L) (1) Here, the meanings of each symbol are as follows:

[0068] θ: Angle of deviation of the emission direction of the measurement light LA ​​with respect to the X-axis direction L: Relative movement amount of the optical rotary probe 26 in the X-axis direction Ly: Displacement of the peak position of the measurement light LA ​​in the Y-axis direction The control device 72 updates the numerical value of the control software in the memory based on the deviation angle from the X-axis direction calculated in step S114, and sets a reference direction in which the rotation angle s of the optical rotary probe 26 becomes s=0° (step S118). This completes the setting of the reference direction for the XY plane. The angle (deviation angle) at which the measurement light LA ​​is deviation from the X-axis direction in the XZ plane is adjusted by the user, for example, using a mechanical adjustment mechanism (gauge, etc.). A description of this setting will be omitted.

[0069] In the above description, the method of setting the reference direction of emission of the measurement light LA ​​using the beam profiler 80 has been described, but the reference direction of emission of the measurement light LA ​​may also be set visually.

[0070] <Optical path length calibration> Returning to Fig. 4, after setting the reference direction of emission of the measurement light LA ​​in this way (step S10), the optical path length of the measurement light LA ​​of the optical rotary probe 26 is calibrated (step S20). The optical path length of the measurement light LA ​​is calibrated, for example, by setting the length LS of the shaft 62 of the optical rotary probe 26 to a predetermined length. Here, if the intersection point between the reflecting surface of the prism mirror 66 and the optical path P in Fig. 2 is taken as PX, the length LS of the shaft 62 corresponds to the distance from the input / output end 44a of the optical fiber cable 44 to the intersection point PX.

[0071] Hereinafter, with reference to Fig. 7, calibration of the optical path length of the measurement light LA ​​using a ring gauge 81 as an example will be described. As shown in Fig. 7, the control device 72 rotates the optical rotary probe 26 around the longitudinal axis 62a to measure the inner diameter of the ring gauge 81, which has a known inner diameter D. The diameter of the ring gauge 81 used for calibration is preferably about twice the distance from the longitudinal axis 62a of the optical rotary probe 26 to the focal point of the measurement light LA.

[0072] Next, the length LS of the shaft 62 of the optical rotary probe 26 is set based on the following equation (2) so that the measured value of the inner diameter of the ring gauge 81 matches the known inner diameter D of the ring gauge 81. This calibrates the optical path length of the measurement light LA.

[0073] Length LS = actual length measured by the optical rotary probe 26 - D / 2 (2) <Relative angle calibration procedure> 4, after calibrating the optical path length of the measurement light LA ​​(step S20), calibrate the relative angle from the reference angle (step S30). Here, the rotation angle s of the optical rotary probe 26 refers to the rotation angle in the rotation direction around the longitudinal axis 62a (hereinafter sometimes referred to as the S-axis) of the optical rotary probe 26 (i.e., the rotation angle around the longitudinal axis 62a in the emission direction of the measurement light LA). In addition, the state when the emission direction of the measurement light LA ​​of the optical rotary probe 26 is aligned with the reference direction (X direction) in step S10 is set as a reference angle (s=0°), and the rotation angle when the optical rotary probe 26 rotates around the longitudinal axis 62a from the reference angle (i.e., the relative angle from the reference angle) is represented as the "rotation angle s of the optical rotary probe". Hereinafter, a method of calibrating the relative angle using a calibration sphere 82 will be described as an example with reference to FIGS. 8 and 9. FIG. 8 is a flowchart showing the procedure for calibrating the relative angle, and FIG. 9 is a diagram showing the positional relationship between the optical rotary probe 26 and the calibration sphere 82 when the rotation angles s=0° and s=90° in calibrating the relative angle using the calibration sphere 82.

[0074] As shown in Fig. 9, the control device 72 rotates the optical rotary probe 26 around the longitudinal axis 62a of the optical rotary probe by a predetermined rotation angle s, and at that position, the focus of the measurement light LA ​​is aligned as close as possible to the surface of the calibration sphere 82 (step S210). For example, when measuring the calibration sphere 82 at a position where the rotation angle s is 90.0°, the control device 72 rotates the optical rotary probe 26 around the longitudinal axis 62a by 90.0° (rotation, described later), and further rotates the optical rotary probe 26 around the calibration sphere 82 by 90.0° (revolution, described later). As a result, the optical rotary probe 26 with the rotation angle s = 90° and the calibration sphere 82 have a positional relationship as shown in Fig. 9. Here, preferably, the surface of the calibration sphere 82 is located at a position about ±focal depth / 2 from the focal position of the measurement light LA.

[0075] Next, the control device 72 drives the X-axis drive unit, the Y-axis drive unit, and the Z-axis drive unit of the three-dimensional coordinate measuring device 10 without changing the emission direction of the measurement light LA ​​(i.e., with the optical rotary probe 26 fixed and not rotated around the longitudinal axis 62a), to scan the surface of the calibration sphere 82 with the measurement light LA, and measures the three-dimensional coordinates of a plurality of measurement points on the surface of the calibration sphere 82 at the rotation angle s (step S212). Fig. 9 shows, as an example, measurement points M on the calibration sphere 82 at rotation angles s = 0° and s = 90°.

[0076] Next, the control device 72 calculates the three-dimensional coordinates of the center of the calibration sphere 82 for that rotation angle s from the three-dimensional coordinate values ​​of the measurement points on the surface of the calibration sphere 82 (step S214). In this calculation, for example, the least squares method may be used using the known spherical diameter of the calibration sphere 82.

[0077] The control device 72 repeats steps S210 to S214 for a plurality of rotation angles s. For example, the rotation angle s of the optical rotary probe 26 is changed at intervals of 7.5°, such as s=0°, 7.5°, 15.0°, . . . 352.5°, and steps S210 to S214 are repeated for each rotation angle s (step S216: YES It should be noted that the intervals of the rotation angle s of the optical rotary probe 26 during measurement are not limited to 7.5 degrees.

[0078] After steps S210 to S214 are performed for all rotation angles s (step S216: NO ), and further, the control device 72 corrects the numerical values ​​of the control program in the memory so that the three-dimensional coordinates of the center of the calibration sphere 82 calculated for each rotation angle s coincide with the three-dimensional coordinates of the center of the calibration sphere 82 calculated for the rotation angle s = 0° (step S218). As examples, two correction methods will be described below.

[0079] The first method is a method of performing correction using the measurement values ​​obtained in step S210. For example, in an ideal case, the three-dimensional coordinates of the center of the calibration sphere 82 calculated for a rotation angle s = 90° coincide with the three-dimensional coordinates of the center of the calibration sphere 82 calculated for a rotation angle s = 0°, and therefore the vector components of the measurement light LA ​​are (x, y, z) = (0, 1, 0).

[0080] When the rotation angle s is not correctly 90° due to an error, for example, the control device 72 corrects the vector components of the measurement light LA ​​to (x, y, z) = (0.055, 0.992, 0.110) so that the three-dimensional coordinates of the center of the calibration sphere 82 calculated for a rotation angle s = 90° coincide with the three-dimensional coordinates of the center of the calibration sphere 82 calculated for a rotation angle s = 0°. For a rotation angle s for which there is no measured value, linear interpolation is performed for multiple rotation angles s for which there is a measured value to calculate the corrected values ​​of the vector components of the measurement light LA.

[0081] The second method is a correction method using trigonometric functions, in which the rotation angle error Δs of the emission direction of the measurement light LA ​​relative to the X-axis direction in the XY plane (hereinafter simply referred to as the S angle error) and the error angle Δφ of the emission direction of the measurement light LA ​​relative to the XY plane (hereinafter simply referred to as the elevation angle error) are calculated from the following formulas (3) and (4).

[0082]

number

[0083]

number

[0084] s: Rotation angle (°) when measuring the calibration sphere Δs: S angle error (°), (Error angle of the emission direction of the measurement light LA ​​relative to the X-axis direction in the XY plane) Δφ: Elevation angle error (°) (Error angle of emission direction of measurement light LA ​​relative to XY plane) F0: Distance from the longitudinal axis 62a of the optical rotary probe 26 to the focal point (x i , y i , z i ): The center coordinates of the calibration sphere 82 measured at each rotation angle s i: Rotation angle during measurement in step S210 (7.5°,15°,…,352.5°) 10, reference numeral 10A is a graph of the S-angle error Δs calculated for each rotation angle s based on the above formula (3), and reference numeral 10B is a graph of the elevation angle error Δφ calculated for each rotation angle s based on the above formula (4). The control device 72 updates the values ​​of the control software stored in the memory based on the calculated S-angle error Δs and elevation angle error Δφ.

[0085] <Recalibration of optical path length> 4, after the relative angle is calibrated in step S30, the optical path length of the measurement light LA ​​is recalibrated (step S40). The procedure for recalibrating the optical path length is the same as that in step S20, and therefore will not be described.

[0086] <Recalibration of the reference direction of emission> Furthermore, the reference direction of emission set in step S10 is recalibrated (step S50). The reference direction is set in step S10, but as described later with reference to FIG. 16, this setting may cause deviation from the intended reference direction of emission (X-axis direction in this example) depending on the precision of the setting, resulting in an error in the reference angle of the S angle. This recalibration of the emission direction is one of the features of the present invention. Here, the S angle means the rotation angle of the emission direction of the measurement light LA ​​relative to the X-axis direction (reference direction) in the XY plane.

[0087] Hereinafter, the principle of recalibration of the emission direction in step S50 will be described. In this embodiment, as an example, a cylindrical pin gauge 83 (corresponding to a reference object of the present invention) having a known radius R is used to measure the adjustment error of the emission direction, and the emission direction is recalibrated based on the measured adjustment error. FIGS. 11 and 12 are a perspective view and an XY plan view, respectively, showing the positional relationship between the optical rotary probe 26 and the pin gauge 83 when measuring the adjustment error of the emission direction (described in detail later). As shown in FIG. 11, the longitudinal axis of the pin gauge 83 is arranged parallel to the longitudinal axis 62a of the optical rotary probe 26. Then, as shown in FIG. 12, when the emission direction of the measurement light LA ​​has a reference angle error Δs0 of the S angle with respect to the reference direction (the X-axis direction in this example) in the XY plane, an error ΔR occurs in the measurement value. This error ΔR can be expressed as a function of the reference angle error Δs0 of the S angle by the following formula (5).

[0088]

number

[0089]

number

[0090]

number

[0091] In the present invention, the emission direction of the measurement light LA ​​of the optical rotary probe 26 after calibration is intentionally shifted by a small angle Δs1 from the reference direction set in step S10. in, the numerical value of the control software in the memory is updated to provisionally change the angle of the reference direction. The radius R of the pin gauge 83 is measured in a state where the reference angle is shifted by a minute angle Δs1 from the setting in step S10, and the error ΔR of the radius R is calculated. If there is no reference angle error Δs0 of the S angle in the emission direction of the measurement light LA ​​of the optical rotary probe 26, the calculated error ΔR should match the theoretical ΔR. Therefore, in the present invention, based on the difference between this calculated error ΔR and the theoretical ΔR, the reference angle error Δs0 of the S angle of the emission direction of the optical rotary probe 26 after calibration with respect to the reference direction is calculated as an adjustment error. By recalibrating the emission direction based on the calculated adjustment error, the calibration accuracy of the optical rotary probe 26 is improved, and the measurement error by the optical rotary probe 26 is reduced.

[0092] Hereinafter, a method for recalibrating the emission direction will be described with reference to Figs. 11 to 16. Fig. 14 is a flow chart showing the procedure for recalibrating the emission direction. As shown in Fig. 14, first, the pin gauge 83 is arranged so as to have a predetermined positional relationship with the optical rotary probe 26 (step S310). The radius R of the pin gauge 83 is preferably about ten to several tens of times the beam diameter of the measurement light LA. Figs. 11 and 12 are diagrams showing the positional relationship between the optical rotary probe 26 and the pin gauge 83 when measuring the adjustment error of the emission direction. As shown in Fig. 11, the pin gauge 83 is arranged parallel to the longitudinal axis 62a of the optical rotary probe 26. Here, preferably, the distance between the optical rotary probe 26 and the pin gauge 83 is constant, and the distance between the optical rotary probe 26 and the pin gauge 83 is set so that the surface of the pin gauge 83 is located as close as possible to the focal length of the measurement light LA.

[0093] More specifically, it is preferable to set the distance between the optical rotary probe 26 and the pin gauge 83 so that the surface of the pin gauge 83 is located at a position approximately ±focal depth / 2 from the focal position of the measurement light LA. In the example shown in Figures 11 and 12, the distance between the longitudinal axis 62a of the optical rotary probe 26 and the measurement surface of the pin gauge 83 is equal to the focal length F.

[0094] In the example of FIG. 12, the longitudinal axis 62a of the optical rotary probe 26 is placed at the origin on the XY plane, and the center C of the cross-sectional circle of the pin gauge 83 is placed on the X-axis.

[0095] By the calibration procedure from step S10 to step S40 described above, the optical rotary probe 26 is ideally adjusted so that the emission direction of the measurement light LA ​​coincides with the X-axis direction, which is the reference direction, at a rotation angle s = 0°. Therefore, ideally, at the rotation angle s = 0° of the optical rotary probe 26, the measurement light LA ​​should be emitted perpendicular to the axial direction of the pin gauge 83 and toward the apex of the pin gauge 83.

[0096] After arranging the optical rotary probe 26 and the pin gauge 83 in such a positional relationship, the control device 72 changes the optical rotary probe 26 around the longitudinal axis 62a (S-axis) by a predetermined minute angle Δs1 from the reference angle set in step S10 by the head drive unit (not shown) of the measurement head 24, and sets the angle as a tentative reference angle (step S312). The change in the optical rotary probe 26 at this time corresponds to the movement indicated by the dashed arrow A in FIG.

[0097] Next, the control device 72 controls the XYZ drive unit of the three-dimensional coordinate measuring device 10 to move the optical rotary probe 26 along a rotational trajectory centered on the pin gauge 83 (in the direction of arrow B shown by a solid line in Figure 12), while continuously rotating the optical rotary probe 26 around the longitudinal axis (rotation axis) 62a (i.e., while continuously changing the rotation angle s of the optical rotary probe 26), and emits measurement light LA ​​from the optical rotary probe 26 toward the pin gauge 83 to measure the radius R of the pin gauge 83 (step S314).

[0098] That is, the control device 72 synchronizes the rotational movement (revolutionary movement) of the optical rotary probe 26 around the pin gauge 83 with the rotational movement (rotational movement) around the longitudinal axis (rotation axis) 62a of the optical rotary probe 26, and emits the measurement light LA ​​from the optical rotary probe 26 toward the pin gauge 83 perpendicular to the longitudinal axis direction of the pin gauge 83 and while keeping the distance between the optical rotary probe 26 and the pin gauge 83 constant. In this case, it is desirable to perform the measurement by rotating the optical rotary probe 26 around the pin gauge 83 one revolution or more (360° or more). In addition, it is desirable to irradiate the measurement light LA ​​emitted from the optical rotary probe 26 onto the apex of the pin gauge 83.

[0099] Next, the control device 72 calculates the error ΔR of the radius R of the pin gauge 83 at the predetermined small angle Δs1 based on the measurement result obtained in step S314 (step S316). Note that since the radius R of the pin gauge 83 is known and the calculation of the error ΔR is a simple difference calculation, a description thereof will be omitted.

[0100] The control device 72 changes the reference angle of rotation of the optical rotary probe 26 about the longitudinal axis 62a by a small angle Δs1, and repeats the measurement of the radius R of the pin gauge 83 and the calculation of the error ΔR (step S318: YES After steps S312 to S316 are repeated a sufficient number of times to obtain an approximation formula (step S318: NO ), and further, the control device 72 obtains an approximation equation indicating the relationship between the infinitesimal angle Δs1 and the error ΔR (step S320). Preferably, the control device 72 obtains a quadratic polynomial using the least squares method.

[0101] Fig. 15 shows an example of a graph in which the error ΔR calculated from the measured values ​​in step S314 is plotted on the graph in Fig. 13 with the infinitesimal angle Δs1 on the horizontal axis and the error ΔR on the vertical axis. In Fig. 15, the error ΔR calculated from the measured values ​​is shown as a diamond, and the thin solid line shows an approximation formula obtained by the least squares method. The approximation formula shown in Fig. 15 is as follows.

[0102] ΔR=-76.044Δs1 2+35.86Δs1+4.4608 Moreover, the thick solid line indicates the theoretical error ΔR. As shown in Fig. 15, compared with the graph of the theoretical error ΔR, the graph of the error ΔR calculated from the measured values ​​is shifted in the vertical axis direction and is wider in the horizontal axis direction. Here, the shift in the vertical axis direction is mainly due to a uniform measurement error in the wavelength swept light source 28 of the measurement light LA. The wider width in the horizontal axis direction is mainly due to the broadening of the beam diameter of the measurement light LA ​​caused by the measurement position being shifted from the focal position of the measurement light LA.

[0103] Next, the control device 72 calculates the adjustment error of the emission direction of the measurement light LA ​​from the approximation equation obtained in step S320 (step S322). For example, the following quadratic polynomial (8) can be transformed into equation (9) by the least squares method.

[0104] ΔR==AΔs1 2 +BΔs1+C (8)

[0105]

number

[0106] Specifically, in the case of the graph shown in FIG. 15, the control device 72 calculates the approximate formula "ΔR=-76.044Δs1 2 From "Δs1+4.4608", the reference angle error Δs0 (adjustment error) can be obtained as 35.86 / (2×76.044)=0.236°. Based on the calculated adjustment error, the control device 72 re-updates the values ​​of the control software stored in the memory, thereby recalibrating the emission direction (step S324).

[0107] As described above, according to the method for calibrating the optical rotary probe 26 in this embodiment, the emission direction of the measurement light LA ​​emitted from the optical rotary probe 26 can be calibrated with high accuracy. Therefore, the measurement error of the optical rotary probe 26 can be reduced. In turn, the measurement error of the three-dimensional coordinate measuring device 10 equipped with the optical rotary probe 26 can be reduced. This makes it possible to accurately measure the shape of a large curvature of a local portion of the measurement target.

[0108] <Advantages of recalibrating the emission direction according to this embodiment> As described above, the calibration method of this embodiment can improve the calibration accuracy of the optical rotary probe 26, but the calibration method of this embodiment also has the following advantages.

[0109] First, in order to measure a microscopic shape, it is necessary to narrow the beam diameter of the measurement light LA. At the focal position of the measurement light LA, a beam diameter of several μm to several tens of μm can be obtained, but if the measurement light deviates from the focal position, the beam diameter of the measurement light LA ​​becomes larger. In addition, the beam diameter of the measurement light LA ​​may become larger due to the influence of white noise, etc.

[0110] In Fig. 16, reference numeral 16A shows the intensity distribution of the measurement light LA ​​obtained when the beam diameter is small, and reference numeral 16B shows the intensity distribution of the measurement light LA ​​obtained when the beam diameter is large. When calibrating the measurement light LA, the intensity distribution of the measurement light LA ​​is measured, but when the beam diameter of the measurement light LA ​​is large as shown by reference numeral 16B in Fig. 16, the gradient of the intensity near the peak becomes small, making it difficult to accurately detect the position of the intensity peak of the measurement light LA. For this reason, there has been a problem in the past that it is not possible to accurately set the reference direction of emission of the measurement light LA ​​of the optical rotary probe 26 (reference for the rotation angle of the optical rotary probe).

[0111] For example, if the focal length of the imaging lens 64 of the optical rotary probe 26 is 18 mm and the beam diameter of the measurement light LA ​​is 13 μm, a deviation of 0.5 mm from the focal length will result in a beam diameter of 150 μm. In this case, the setting accuracy of the position of the intensity peak of the measurement light LA ​​is about 3 μm, and the calibration accuracy of the emission direction is about 0.3°. If the distance from the longitudinal axis 62a (optical axis of the measurement light LA) of the optical rotary probe 26 to the focal length is 10 mm, the error in the measurement position will be as much as 50 μm.

[0112] Conventionally, there was a problem that such a large error made it impossible to accurately measure the shape of a large curvature of a local portion of a measurement target. On the other hand, in this embodiment, the radius R of the pin gauge 83 is measured in a state where the emission direction of the measurement light LA ​​of the calibrated optical rotary probe 26 is intentionally shifted by a small angle Δs1 from the reference angle set in step S10, and the error ΔR of the radius R is calculated.

[0113] As shown in Fig. 15, when the beam diameter of the measurement light LA ​​is expanded due to the measurement position being shifted from the focal position of the measurement light LA, the graph of the calculated error ΔR expands in the horizontal direction, but the graph maintains symmetry in the horizontal direction. Therefore, the expansion of the width of the graph in the horizontal direction does not affect the calculation result of the adjustment error based on the approximation formula of the calculated error ΔR. Therefore, in this embodiment, even if the beam diameter of the measurement light LA ​​is expanded, the emission direction of the measurement light LA ​​can be accurately calibrated based on the calculation result of the adjustment error.

[0114] Similarly, even if a uniform measurement error remains in the wavelength swept light source 28 of the measurement light LA ​​after calibration, as shown in Fig. 15, the graph of the error ΔR calculated from the measured values ​​is merely shifted in the vertical axis direction compared to the graph of the theoretical error ΔR, and does not affect the calculation result of the adjustment error based on the approximation formula of the calculated error ΔR. Therefore, in this embodiment, even if there is a uniform measurement error in the wavelength swept light source 28 of the measurement light LA, it is possible to calibrate the emission direction of the measurement light LA ​​with high accuracy.

[0115] [Method for recalibrating emission direction according to the second embodiment] In the above explanation, the reference angle error Δs0 of the S angle is calculated by measuring the radius R of the pin gauge 83 having a known radius. However, instead of measuring the radius R of the pin gauge 83, the surface shape of the pin gauge 83 may be measured. FIG. 17 shows a method for recalibrating the emission direction of the measurement light LA ​​according to the second embodiment. As shown in FIG. 17, the method for recalibrating the emission direction in the second embodiment is almost the same as the flowchart shown in FIG. 14, except that steps S410 and S412 are performed instead of steps S314 and S316. The differences will be explained below.

[0116] In the second embodiment, in step S410, the optical rotary probe 26 of The reference angle of the S angle around the longitudinal axis 62a (S axis) is set by a small angle Δ s1 With the angle changed by only this amount, the surface shape of the pin gauge 83 is measured instead of the radius R of the pin gauge 83. Reference numeral 18A in Fig. 18 shows a graph in which the measurement results of the surface shape at a certain minute angle Δs1 are plotted on the XY coordinates.

[0117] Next, in step S412, the control device 72 calculates the standard deviation σ (ΔR) of the error ΔR of the radius R of the pin gauge 83 based on the measurement value at each minute angle Δs1. Hereinafter, an example of a method for calculating the standard deviation σ (ΔR) for a certain minute angle Δs1 will be specifically described with reference to the graph shown in FIG. 18. First, the control device 72 calculates an approximation value of the radius R of the pin gauge 83 by approximating the measurement result of the surface shape by the least squares method. In the graph shown by reference numeral 18A, the approximation value of the radius R is indicated by a thick solid circle. Reference numeral 18B is a graph obtained by converting the graph of the XY coordinates of each measurement point shown by reference numeral 18A into the measurement value of the radius R (vertical axis) relative to the rotation angle (horizontal axis) centered on the center C of the pin gauge 83. Next, the control device 72 calculates the error ΔR, which is the difference between the approximation value of the radius R and the measurement value of the radius R. Reference numeral 18C shows a graph of the error ΔR (vertical axis) relative to the rotation angle s (horizontal axis) with the center C of the pin gauge 83 as the center. Furthermore, the control device 72 calculates the standard deviation σ (ΔR) of the error ΔR from the variation of the obtained error ΔR, and further calculates ±2σ, which is a range that includes about 95% of all measurement points in the normal distribution of the error ΔR, as the shape error. In the case of the graphs shown by reference numerals 18A to 18C in Fig. 18, the shape error (±2σ) is 60 μm. The control device 72 performs such calculation of the shape error for a plurality of different minute angles Δs1.

[0118] The subsequent steps are the same as those in the first embodiment. Fig. 19 shows a graph in which the small angle Δs1 of rotation around the longitudinal axis 62a of the optical rotary probe 26 is plotted on the horizontal axis and the shape error (±2σ) calculated in step S314 is plotted on the vertical axis. For example, when the graph in Fig. 19 is approximated to a quadratic polynomial by the least squares method, "±2σ=-76.508Δs1 2 +36.141Δs1+4.6607" (see the solid line graph in Figure 19).

[0119] Thus, it can be seen that the second embodiment, which measures the surface shape, also provides results that are almost the same as those of the first embodiment, which measures the radius R. Note that by changing the reference angle of the optical rotary probe 26 by a small angle Δs1 from the setting in step S10, the width of the interference signal between the measurement light LA ​​and the reflected light LB becomes wider when the measurement light LA ​​does not hit the pin gauge 83 perpendicularly to the measurement point. In the second embodiment, which measures the shape, this becomes a cause of error, resulting in a difference between the approximation formula of the first embodiment and the approximation formula of the second embodiment.

[0120] In the second embodiment, similarly to the first embodiment, it is possible to improve the calibration accuracy and reduce the measurement error of the optical rotary probe 26. In turn, it is possible to reduce the measurement error of the three-dimensional coordinate measuring device 10 equipped with the optical rotary probe 26.

[0121] [Method for recalibrating emission direction according to the third embodiment] In the first and second embodiments described above, the emission direction was recalibrated using the radius R of the cylindrical pin gauge 83. Here, the radius R of the pin gauge 83 is, for example, about ten to several tens of times the beam diameter of the measurement light LA. For example, when the beam diameter is 13 μm, the radius R of the pin gauge 83 is about 130 μm to several mm. It is not easy to manually perform alignment for measuring a pin gauge 83 with such a small radius R.

[0122] Therefore, instead of the pin gauge 83, a jig 84 may be used in which a pin gauge 86 is set up vertically (in the Z-axis direction) on a rectangular block 85 as shown in Fig. 20. The perpendicularity of the pin gauge 86 is not required to be very strict. For example, in the case of a pin gauge 86 with a radius R of 0.25 mm, if the inclination angle with respect to the XY plane is less than 1°, the effect of the inclination angle on the measurement error of the radius R is 0.03 µm, which is sufficient for use in calibration.

[0123] Below, we will explain the recalibration method when using this jig 84. First, before performing the recalibration shown in Fig. 14, measure the position of the pin gauge 86 on the block 85 of the jig 84. Usually, it is sufficient to perform this measurement once for the jig 84, and thereafter, the value obtained from this measurement is repeatedly used in recalibration.

[0124] First, the coordinates (x0, y0, z0) of the center (longitudinal axis) of the pin gauge 86 in the design are assumed. Next, the three faces B1, B2, and B3 of the block 85 of the jig 84 are measured, a work coordinate system (XYZ Cartesian coordinate system) of the block 85 of the jig 84 is created, and the diameter of the pin gauge 86 is measured to measure the position of the center of the pin gauge 86. Since the position measurement result may be shifted due to the positional tolerance of the pin gauge, the measurement result often differs from the designed position. In addition, a measurement error may occur because the measurement light LA ​​does not hit the apex of the pin gauge 86 perpendicularly. Here, the measurement result is assumed to be (x1, y1, z1 ≒ z0). If this measurement result differs from the designed position, the jig 84 is used for recalibration shown in FIG. 14 in the first and second embodiments, assuming that the center of the pin gauge 86 is located at (x1, y1, z0) of the measurement result in the work coordinate system.

[0125] According to the third embodiment, since the coordinates of the center of the pin gauge 86 have already been specified on the workpiece coordinate system before performing the recalibration method shown in Fig. 14, the pin gauge 86 can be positioned simply by placing the jig 84 on the table 14 of the three-dimensional coordinate measuring device 10. This provides the effect of facilitating the alignment of the pin gauge 83 in addition to the effects of the above embodiments.

[0126] As described above, according to the first to third embodiments, the emission direction of the measurement light LA ​​emitted from the optical rotary probe 26 can be calibrated with high accuracy. Therefore, the measurement error of the optical rotary probe 26 can be reduced. In turn, the measurement error of the three-dimensional coordinate measuring device 10 equipped with the optical rotary probe 26 can be reduced. This makes it possible to accurately measure, for example, a shape with a large curvature of a local portion of a measurement target.

[0127] Although the present invention has been described above with reference to examples, it goes without saying that the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention. [Explanation of symbols]

[0128] 10...three-dimensional coordinate measuring device, 26...optical rotary probe, 28...wavelength sweep light source, 36...photodetector, 40...fixed optical system, 42...rotating optical system, 44...optical fiber cable, 44a...inlet / outlet end, 48...collimator lens, 50...hollow motor, 52...stator ,5 4... rotor, 54a... hollow portion, 62... shaft, 62a... longitudinal axis, 62b... inner surface, 64... imaging lens, 66... ​​right-angle prism mirror ,7 0...controller, 72...control device, 80...beam profiler, 81...ring gauge, 82...calibration sphere, 83, 86...pin gauge, 84...jig, 85...block

Claims

1. A method for calibrating an optical rotary probe capable of emitting measurement light in a direction perpendicular to a probe axis and capable of freely rotating an emission direction of the measurement light around the probe axis, comprising the steps of: a changing step of changing the emission direction of the measurement light by a small angle from a preset reference direction; an acquisition step of acquiring a shape error of the reference object by emitting the measurement light from the optical rotary probe toward the reference object while rotating the emission direction of the measurement light around the probe axis and changing the relative position between the optical rotary probe and the reference object after the change step is performed; an adjustment error calculation step of calculating an adjustment error of the emission direction of the measurement light with respect to the reference direction based on a theoretical value of a shape error of the reference object obtained when the emission direction of the measurement light coincides with the reference direction and a measured value of the shape error of the reference object obtained in the acquisition step; A method for calibrating an optical rotation probe, comprising:

2. The minute angle is changed and the changing step and the acquiring step are each performed a plurality of times; The adjustment error calculation step calculates an adjustment error of an emission direction of the measurement light with respect to the reference direction based on a shape error of the reference object acquired for each minute angle.

2. A method for calibrating an optical rotary probe according to claim 1.

3. the acquiring step includes changing a relative position between the optical rotary probe and the reference object so that a distance between the optical rotary probe and the reference object is constant; 3. A method for calibrating an optical rotary probe according to claim 1 or 2.

4. the acquiring step changes a relative position between the optical rotary probe and the reference object so that a surface to be measured of the reference object is located within a range of a focal position of the measurement light ± a focal depth; A method for calibrating an optical rotary probe according to any one of claims 1 to 3.

5. The reference object is a pin gauge arranged parallel to the probe axis. A method for calibrating an optical rotary probe according to any one of claims 1 to 4.

6. The obtaining step obtains a radial error of the pin gauge as the shape error of the reference object.

6. A method for calibrating an optical rotary probe according to claim 5.

Images