Optical rotary probe calibration method

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 rotation probe.

Background Art

[0002] As a shape measurement device for measuring the shape of a measurement object, for example, a three-dimensional coordinate measurement device that obtains the shape of a measurement object by non-contact detection of the three-dimensional coordinate values of various measurement points of the measurement object using an optical probe is known. The optical probe irradiates measurement light from a light source toward a measurement point of the measurement object and receives the reflected light of the measurement light reflected at this measurement point. Then, the shape measurement 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] As such an optical probe, an optical rotation probe capable of performing rotational scanning around the axis of the longitudinal axis of the probe as in Patent Document 1 is known. In a three-dimensional coordinate measurement device equipped with an optical rotation probe, by performing rotational scanning of the optical rotation probe, for example, the inner surface shape of a cylindrical measurement object can be measured, or the surface shape can be measured simultaneously.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, there has been a need to measure the shape of objects with large curvature in localized areas. However, with the three-dimensional measuring device described in Patent Document 1, it is difficult to accurately set the direction of the measurement light emitted by the optical rotation probe relative to the reference direction during calibration, which leads to a problem of large measurement errors when measuring shapes with large curvature in localized areas.

[0006] This invention has been made in view of these circumstances, and aims to provide a calibration method for an optical rotating probe that can calibrate the direction of emission of measurement light emitted from the optical rotating probe with high precision. [Means for solving the problem]

[0007] To solve the above problems, a calibration method for an optical rotating probe that can emit measuring light in a direction perpendicular to the probe axis and whose direction of emission of measuring light is rotatable about the probe axis, according to one aspect of the present invention, includes: a modification step of changing the direction of emission of measuring light by a small angle from a pre-set reference direction; an acquisition step of acquiring the shape error of a reference object by emitting measuring light from the optical rotating probe toward the reference object while changing the relative position between the optical rotating probe and the reference object while rotating the direction of emission of measuring light about the probe axis after the modification step has been performed; and an adjustment error calculation step of calculating the adjustment error of the direction of emission of measuring light with respect to the reference direction based on a theoretical value of the shape error of the reference object obtained when the direction of emission of measuring light coincides with the reference direction and a measured value of the shape error of the reference object obtained in the acquisition step.

[0008] According to the calibration method for the optical rotating probe described above, the adjustment error of the emission direction of the measurement light relative to the reference direction can be calculated. Therefore, even if there is an adjustment error remaining after calibration of the emission direction, the emission direction can be recalibrated based on the calculated adjustment error. This improves the calibration accuracy of the emission direction of the optical rotating probe and, consequently, reduces the measurement error of a three-dimensional coordinate measuring device equipped with an optical rotating probe.

[0009] Preferably, the modification step and acquisition step are performed multiple times by changing a small angle, and the adjustment error calculation step calculates the adjustment error of the emission direction of the measurement light relative to the reference direction based on the shape error of the reference object acquired for each small angle.

[0010] Preferably, the acquisition step involves changing 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 remains constant.

[0011] Preferably, the acquisition step involves changing the relative position of the optical rotation probe and the reference object so that the measurement surface of the reference object is located within the range of the focal position ± depth of focus of the measurement light.

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

[0013] Preferably, the acquisition step involves acquiring the radius error of the pin gauge as the shape error of the reference object. [Effects of the Invention]

[0014] According to the present invention, it is possible to calculate the adjustment error with respect to the reference direction of the emission direction of the measurement light emitted from the optical rotating probe, thereby enabling high-precision calibration of the optical rotating probe. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic diagram of a three-dimensional coordinate measuring device. [Figure 2] This is an example of a cross-sectional view of a rotating optical probe. [Figure 3] This is an explanatory diagram illustrating the measurement of the shape of a workpiece surface using a rotating optical probe. [Figure 4] This flowchart outlines the calibration method for the emission direction of the measurement light of a rotating optical probe. [Figure 5] This flowchart shows the procedure for setting the reference direction. [Figure 6]It is a diagram for explaining the setting of the reference direction using a beam profiler. [Figure 7] It is a diagram for explaining the setting of the optical path length using a ring gauge. [Figure 8] It is a flowchart showing the procedure for calibrating the relative angle. [Figure 9] It is a diagram showing the positional relationship between the optical rotation probe and the calibration sphere when the rotation angle is 0° and 90° in the calibration of the relative angle using the calibration sphere. [Figure 10] It is a graph showing the S-angle error with respect to the rotation angle and a graph showing the elevation angle error with respect to the rotation angle, which are calculated in the calibration of the relative angle using the calibration sphere. [Figure 11] It is a perspective view showing the positional relationship between the optical rotation probe and the pin gauge when measuring the adjustment error of the emission direction. [Figure 12] It is a diagram showing the positional relationship between the optical rotation probe and the pin gauge on the XY plane when measuring the adjustment error of the emission direction. [Figure 13] It is a graph showing the theoretical value of the measurement error of the radius of the pin gauge with respect to the reference angle error of the S-angle of the optical rotation probe. [Figure 14] It is a flowchart showing the re-calibration method of the emission direction according to the first embodiment. [Figure 15] It is a graph showing the theoretical value and the measured value of the error with respect to the minute angle of rotation of the optical rotation probe in the first embodiment. [Figure 16] It is a diagram for explaining the difference in the intensity distribution of the measurement light caused by the difference in the beam diameter. [Figure 17] It is a flowchart showing the re-calibration method of the emission direction according to the second embodiment. [Figure 18] It is a diagram for explaining the calibration method of the adjustment error according to the second embodiment. [Figure 19] It is a graph showing the shape error with respect to the minute angle of rotation of the optical rotation probe in the second embodiment. [Figure 20] It is a perspective view of the jig according to the third embodiment. [Modes for carrying out the invention]

[0016] Embodiments of the present invention will be described below with reference to the attached drawings. Prior to describing the calibration method for the optical rotation probe, the configuration of the three-dimensional coordinate measuring device will be described.

[0017] [Configuration of a three-dimensional coordinate measuring device] Figure 1 is a schematic diagram of the three-dimensional coordinate measuring device 10. The X, Y, and Z axes in Figure 1 represent a mechanical coordinate system defined based on the mechanical coordinate origin unique to the three-dimensional coordinate measuring device 10.

[0018] As shown in Figure 1, the three-dimensional coordinate measuring device 10 uses an optical rotating probe 26 to measure the shape of a workpiece W, for example, the shape of the inner surface of a cylindrical workpiece W. The shape of the workpiece W as referred to here includes the three-dimensional shape, two-dimensional shape, surface shape, contour shape, and various dimensional shapes such as length or diameter. Furthermore, the shape and type of the workpiece W to be measured are not particularly limited.

[0019] The three-dimensional coordinate measuring device 10 comprises a frame 12, a table 14 (surface plate) mounted on the frame 12, a right Y carriage 16R and a left Y carriage 16L erected 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. The right Y carriage 16R, the left Y carriage 16L, and the X guide 18 constitute a gantry frame 19.

[0020] Sliding surfaces are formed on the upper and side surfaces of both ends of the table 14 in the X-axis direction, on which the right Y carriage 16R and the left Y carriage 16L slide along the Y-axis direction. Air bearings (not shown) are provided on the right Y carriage 16R and the left Y carriage 16L at positions facing the sliding surfaces of the table 14. As a result, the right Y carriage 16R and the left Y carriage 16L can move freely in the Y-axis direction together with the X guide 18.

[0021] An X-carriage 20 is attached to the X-guide 18. The X-guide 18 has a sliding surface formed along the X-axis direction on which the X-carriage 20 slides. In addition, an air bearing (not shown) is provided on the X-carriage 20 at a position opposite to the sliding surface of the X-guide 18. This allows the 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. The X carriage 20 is also provided with an air bearing (not shown) for Z-axis direction guidance, which guides the Z carriage 22 in the Z-axis direction. As a result, the Z carriage 22 is held by the X carriage 20 so as to be movable in the Z-axis direction. A measuring head 24 is provided at the lower end of the Z carriage 22, which selectively and detachably holds various known probes, including an optical rotating probe 26.

[0023] The three-dimensional coordinate measuring device 10 is also provided with a Y-axis drive unit for moving the gantry frame 19 in the Y-axis direction, an X-axis drive unit for moving the X carriage 20 in the X-axis direction, and a Z-axis drive unit for moving the Z carriage 22 in the Z-axis direction, although these are not shown in the diagram. This allows the measuring head 24 (optical rotating probe 26) to be moved in three mutually orthogonal axis directions (XYZ axis directions).

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

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

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

[0027] The measuring head 24 is equipped with a probe rotation angle detection unit (not shown), such as a rotary encoder, which detects the rotation angle of each optical rotating probe 26. The detection results from this probe rotation angle detection unit are output to the control device 72 via the controller 70.

[0028] The optical rotating probe 26 is detachably attached to the measurement head 24. The optical rotating probe 26 emits measurement light LA, which is input from the wavelength-swept light source 28 via the optical fiber cable 30 and fiber circulator 32, toward the measurement surface (in this case, the inner surface) of the workpiece W. The optical rotating probe 26 also receives reflected light LB reflected from the measurement surface of the workpiece W, and outputs this reflected light LB and the reference light LC (see Figure 3) described later to the photodetector 36 via the fiber circulator 32 and optical fiber cable 34.

[0029] Furthermore, as will be described in more detail later, the optical rotating probe 26 is configured so that its tip portion (rotating optical system 42, see Figure 2) can rotate around the longitudinal axis 62a (corresponding to the probe axis of the present invention, see Figure 2), which will be described later. As a result, by rotating its tip portion, the optical rotating probe 26 can rotate and scan the measurement light LA ​​along the measurement surface of the workpiece W.

[0030] Figure 2 is a cross-sectional view of the optical rotating probe 26. As shown in Figure 2, the optical rotating probe 26 comprises a fixed optical system 40 fixed to the measuring head 24 and a rotating optical system 42 that is rotated by the fixed optical system 40 in the direction of the longitudinal axis 62a of the optical rotating probe 26.

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

[0032] Various known optical fiber cables, such as single-mode optical fiber cables and polarization-maintaining optical fiber cables, can be used as the optical fiber cable 44 (and the other optical fiber cables 30 and 34).

[0033] One end of the optical fiber cable 44 is connected to the fiber circulator 32 by passing through the measuring head 24 and the Z carriage 22. The other end of the optical fiber cable 44 is connected to the head mounting section 46. The end face of the other end of the optical fiber cable 44 is the input / output end 44a, where the measurement light LA ​​input from the wavelength-swept light source 28 via the optical fiber cable 30 etc. is emitted, and the reflected light LB etc. reflected from the measuring surface of the workpiece W is incident. In the figure, the symbol P represents the optical path of the measurement light LA ​​and the reflected light LB.

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

[0035] The head mounting portion 46 is a hollow cylindrical body extending in a direction parallel to the optical path P (longitudinal axis 62a). One end of the head mounting portion 46 is detachably attached to the measuring head 24 described above. A hollow motor 50 is fixed to the other end of the head mounting portion 46. Furthermore, a cable connection portion 46a is provided at one end of the head mounting portion 46 to which the other end of the optical fiber cable 44 is connected. The cable connection portion 46a holds the inlet and outlet ends 44a of the optical fiber cable 44 inside the head mounting portion 46 and in a position that coincides with (approximately coincides with, the same applies hereinafter) the central axis of the head mounting portion 46.

[0036] The collimator lens 48 is located inside the head mounting portion 46 and 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 ​​emitted from the input / output end 44a into parallel light, and then emits this measurement light LA ​​toward the imaging lens 64 in the shaft 62, which will be described later. This prevents a decrease in the light receiving sensitivity of reflected light LB caused by misalignment between the fixed optical system 40 and the rotating optical system 42. The collimator lens 48 also emits the reflected light LB incident from the imaging lens 64 toward the input / output end 44a.

[0037] The hollow motor 50 rotates the shaft 62, described later, in a direction about its longitudinal axis 62a (hereinafter simply referred to as the direction about the longitudinal axis). This hollow motor 50 comprises a hollow stator 52 (also called a stationary element) made by winding a coil (not shown), and a hollow rotor 54 (also called a rotor) that rotates inside the stator 52 in a direction about the longitudinal axis. The detailed structure of the hollow motor 50 is publicly known, so a detailed explanation will be omitted.

[0038] The rotor 54 has a hollow section 54a through which the optical path P passes, and this hollow section 54a 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 section 54a and enters the imaging lens 64 described later, and the reflected light LB emitted from the imaging lens 64 passes through the hollow section 54a and enters the collimator lens 48.

[0039] The rotor 54 rotates around the longitudinal axis 62a in response to the application of a drive signal (voltage) from the controller 70 to the stator 52. The hollow motor 50 is equipped with a rotor rotation angle detection unit (not shown), such as a rotary encoder, which detects the rotation angle of the rotor 54. The detection results from this rotor rotation angle detection unit are output to the control device 72 via the controller 70. Alternatively, instead of using a rotor rotation angle detection unit, the rotation angle of the rotor 54 may be controlled by, for example, known servo control, to enable detection of the rotor 54's rotation angle.

[0040] Furthermore, a shaft holding plate 60, which constitutes the rotating optical system 42 and will be described later, is fixed to the annular tip surface 54b of the rotor 54 on the side facing the rotating optical system 42.

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

[0042] The rotating optical system 42 rotates in the longitudinal direction in accordance with the rotation of the rotor 54. This rotating optical system 42 comprises a shaft holding plate 60, a shaft 62, an imaging lens 64, and a right-angle prism mirror 66.

[0043] The shaft retaining plate 60 is formed in substantially the same shape (annular) as the tip surface 54b of the rotor 54 and is fixed on the tip surface 54b in a position parallel to the tip surface 54b. The shaft retaining plate 60 has 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 is fitted into this fitting hole. As a result, the shaft retaining 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 parallel to the optical path P, and has a longitudinal axis 62a parallel to the optical path P. With one end of the shaft 62 fixed to the shaft holding plate 60, the longitudinal axis 62a coincides (approximately coincides) with the center line of the optical path P, and the inner surface 62b of the shaft 62 surrounds the optical path P.

[0045] Furthermore, an imaging lens 64 is provided inside the shaft 62 and at the other end of the shaft 62 opposite to the aforementioned end. Also, a right-angle prism mirror 66 is provided at the other end of the shaft 62 so as to cover the opening on the other end side of the shaft 62.

[0046] The imaging lens 64 is positioned so that 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 onto the measurement surface of the workpiece W through the right-angle prism mirror 66. The imaging lens 64 also emits the reflected light LB incident from the right-angle prism mirror 66 towards the collimator lens 48.

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

[0048] Furthermore, the right-angle prism mirror 66 reflects the reflected light LB, which has been reflected from the measuring surface of the workpiece W, toward the imaging lens 64. As a result, the reflected light LB is incident on the inlet / outlet end 44a of the optical fiber cable 44 via the collimator lens 48 from the right-angle prism mirror 66.

[0049] The shaft holding plate 60, shaft 62, imaging lens 64, and right-angle prism mirror 66 that constitute the rotating optical system 42 rotate integrally around the longitudinal axis in accordance with the rotation of the rotor 54. As the right-angle prism mirror 66 rotates around the longitudinal axis, the measuring light LA ​​is rotated and scanned along the measuring surface of the workpiece W.

[0050] Returning to Figure 1, when the three-dimensional coordinate measuring device 10 is in manual measurement mode, the controller 70 drives the various drive units (XYZ drive unit and head drive unit), which are not shown, in response to the operation input to the operation unit (not shown) to displace the position and orientation of the optical rotating probe 26, and also drives the hollow motor 50 to rotate the right-angle prism mirror 66, etc., around the longitudinal axis. When the three-dimensional coordinate measuring device 10 is in automatic measurement mode, the controller 70 drives the various drive units and the hollow motor 50 under the control of the control device 72 to displace the position and orientation of the optical rotating probe 26, and also rotates the right-angle prism mirror 66, etc., around the longitudinal axis.

[0051] Furthermore, 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), and outputs signals etc. from these units to the control device 72.

[0052] Figure 3 is an explanatory diagram illustrating the measurement of the shape of the measurement surface of the workpiece W using the optical rotating probe 26. As shown in Figure 3 and the previously described Figures 1 and 2, the wavelength-swept light source 28 emits measurement light LA ​​to the fiber circulator 32 via the optical fiber cable 30. This measurement light LA ​​is wavelength-swept light in which the wavelength changes sinusoidally in a certain wavelength band at a certain wavelength-swept period (a certain wavelength-swept frequency).

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

[0054] The fiber circulator 32 is, for example, a non-reciprocating and unidirectional device with 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. As a result, the measurement light LA ​​from the wavelength-swept light source 28 is input to the optical rotating probe 26. Consequently, 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 the interference signal SG of the reflected light LB and reference light LC input from the optical rotating probe 26 to the photodetector 36 via the optical fiber cable 34.

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

[0057] The control device 72 is composed of an arithmetic unit such as a personal computer, and includes an arithmetic circuit composed of various processors and memory. These various processors include CPUs (Central Processing Units), GPUs (Graphics Processing Units), ASICs (Application Specific Integrated Circuits), and programmable logic devices [e.g., SPLDs (Simple Programmable Logic Devices), CPLDs (Complex Programmable Logic Devices), and FPGAs (Field Programmable Gate Arrays)]. The various functions of the control device 72 may be implemented by a single processor, or by multiple processors of the same or different types.

[0058] In automatic measurement mode, for example, the control device 72 drives the aforementioned drive units (not shown) and the hollow motor 50 according to a predetermined measurement program to perform displacement of the position and orientation of the optical rotating probe 26 and rotation of the right-angle prism mirror 66, etc., around its longitudinal axis. This performs rotational scanning of the measurement light LA ​​of the optical rotating probe 26 with respect to the measurement surface of the workpiece W, and interference signals SG for each of the multiple measurement points on this measurement surface are detected by the photodetector 36. As a result, the detection results of the interference signals SG for each measurement point are input from the photodetector 36 to the control device 72. In manual measurement mode, the control device 72 performs the rotational scanning of the measurement light LA ​​as described above in response to operation input to the operation unit (not shown).

[0059] Furthermore, in both automatic and manual measurement modes, 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 result of the interference signal SG detected by the photodetector 36.

[0060] Specifically, the control device 72 calculates the sum of the distances (L1+L2) for each measurement point, based on the detection results of the interference signal SG for each measurement point. This sum is calculated by adding the distance L1 from the input / output end 44a to the right-angle prism mirror 66 and the distance L2 for each measurement point as described above. The method for calculating the sum of distances is known from publicly available technology (for example, Japanese Patent Publication No. 2016-024086 and Japanese Patent Publication No. 2018-084434), so a detailed explanation is 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 for each measurement point and the known distance L1. Then, the control device 72 calculates the three-dimensional coordinates for each measurement point based on the position and orientation of the optical rotating probe 26 for each measurement point, the rotation angle of the right-angle prism mirror 66 etc. around the longitudinal axis for each measurement point, and the calculation result of the distance L2 for each measurement point. As a result, the control device 72 can calculate the shape of the measurement surface of the workpiece W scanned by the measurement light LA.

[0062] It should be noted that the optical rotating probes shown in Figures 2 and 3 are merely examples and are not intended to limit the configuration of optical rotating probes.

[0063] [Calibration method for the optical rotary probe according to the first embodiment] Next, a calibration method for the optical rotation probe 26 according to the first embodiment will be described using Figures 4 to 16. Figure 4 is a flowchart outlining the calibration method for the emission direction of the measurement light LA. The following description will focus on the case where the X-axis direction is used as the reference direction for emission, but this is not intended to limit the reference direction.

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

[0065] <Setting the reference direction for ejection> The reference direction of the emission of the measurement light LA ​​is preferably set using, for example, a beam profiler 80. This allows for accurate setting of the emission direction of the measurement light LA. The method for setting the reference direction of emission in the XY plane using the beam profiler 80 will be described below with reference to Figure 5. Figure 6 shows how the beam profiler 80 is used to detect the position of the peak intensity of the measurement light LA.

[0066] First, the control device 72 drives each drive unit (XYZ drive unit and head drive unit), which are not shown, to set the orientation 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 Figure 6, the optical rotary probe 26 emits the measurement light LA ​​toward the beam profiler 80 in the X axis direction (step S112). While moving the optical rotary probe 26 relative to the beam profiler 80 by a distance L in the X axis direction (direction of the arrow in Figure 6), the control device 72 uses the beam profiler 80 to measure the intensity distribution of the measurement light LA ​​and detects the displacement amount of the peak position (coordinate) of the intensity of the measurement light LA ​​(step S114). Based on the detection result in step S130, the angle at which the measurement light LA ​​is deviated from the X axis direction in the XY plane (deviation angle) is calculated using the following equation (1) (step S116).

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

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

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

[0070] <Calibration of optical path length> Returning to Figure 4, after setting the reference direction of the emission of the measurement light LA ​​in this manner (step S10), the optical path length of the measurement light LA ​​of the optical rotating 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 rotating probe 26 to a predetermined length. Here, if PX is the intersection point between the reflective surface of the prism mirror 66 and the optical path P in Figure 2, then the length LS of the shaft 62 corresponds to the distance from the inlet / outlet end 44a of the optical fiber cable 44 to the intersection point PX.

[0071] The calibration of the optical path length of the measurement light LA ​​using a ring gauge 81 will be described below as an example, with reference to Figure 7. As shown in Figure 7, the control device 72 rotates the optical rotation probe 26 around the longitudinal axis 62a to measure the inner diameter of a ring gauge 81 having 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 rotation probe 26 to the focal point of the measurement light LA.

[0072] Next, the length LS of the shaft 62 of the optical rotating probe 26 is set based on the following equation (2) so that the measured 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 measuring light LA.

[0073] Length LS = Actual length measured by optical rotating probe 26 - D / 2 ... (2) <Calibration procedure for relative angles> Next, returning to Figure 4, after calibrating the optical path length of the measurement light LA ​​(step S20), the relative angle from the reference angle is calibrated (step S30). Here, the rotation angle s of the optical rotating probe 26 refers to the rotation angle in the direction of rotation around the longitudinal axis 62a (hereinafter sometimes referred to as the S axis) of the optical rotating probe 26 (i.e., the rotation angle around the longitudinal axis 62a in the direction of emission of the measurement light LA). Furthermore, the state when the emission direction of the measurement light LA ​​of the optical rotating probe 26 is aligned with the reference direction (X direction) in step S10 is defined as the reference angle (s=0°), and the rotation angle when the optical rotating probe 26 rotates around the longitudinal axis 62a from that reference angle (i.e., the relative angle from the reference angle) is expressed as "rotation angle s of the optical rotating probe". Below, with reference to Figures 8 and 9, a method for calibrating the relative angle using a calibration sphere 82 will be described as an example. Figure 8 is a flowchart showing the procedure for calibrating relative angles, and Figure 9 is a diagram showing the positional relationship between the optical rotation probe 26 and the calibration sphere 82 when the rotation angles s=0° and s=90° during relative angle calibration using the calibration sphere 82.

[0074] As shown in Figure 9, the control device 72 rotates the optical rotary probe 26 around its longitudinal axis 62a by a predetermined rotation angle s, and at that position, aligns the focus of the measurement light LA ​​with the surface of the calibration sphere 82 as closely as possible (step S210). For example, when measuring the calibration sphere 82 at a rotation angle s of 90.0°, the control device 72 rotates the optical rotary probe 26 by 90.0° around its longitudinal axis 62a (rotation described later), and then rotates the optical rotary probe 26 by 90.0° around the calibration sphere 82 (revolution described later). As a result, the optical rotary probe 26 and the calibration sphere 82 at a rotation angle s = 90° are in the positional relationship shown in Figure 9. Preferably, the surface of the calibration sphere 82 is located at a position approximately ± depth of field / 2 from the focal position of the measurement light LA.

[0075] Next, the control device 72 drives the X-axis drive unit, Y-axis drive unit, and Z-axis drive unit of the three-dimensional coordinate measuring device 10 without changing the direction of emission of the measurement light LA ​​(i.e., with the optical rotation probe 26 fixed without rotating 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 multiple measurement points on the surface of the calibration sphere 82 at the rotation angle s (step S212). Figure 9 shows, as an example, the 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 from the three-dimensional coordinate values ​​of the measurement points on the surface of the calibration sphere 82, with respect to its rotation angle s (step S214). In this calculation, for example, the least squares method may be used using the known diameter of the calibration sphere 82.

[0077] The control device 72 repeats steps S210 to S214 for multiple rotation angles s. For example, the rotation angle s of the optical rotating probe 26 is changed at 7.5° intervals, such as s = 0°, 7.5°, 15.0°, ... 352.5°, and steps S210 to S214 are repeated for each rotation angle s (step S216: NO). Of course, the interval of the rotation angle s of the optical rotating probe 26 during measurement is not limited to 7.5° intervals.

[0078] After performing steps S210 to S214 for all rotation angles s (step S216: YES), the control device 72 further corrects the values ​​of the control program in memory so that the three-dimensional coordinates of the center of the calibration sphere 82 calculated for each rotation angle s match the three-dimensional coordinates of the center of the calibration sphere 82 calculated for rotation angle s = 0° (step S218). Two correction methods are described below as examples.

[0079] The first method is to correct 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°, so the vector components of the measurement light LA ​​are (x,y,z)=(0,1,0).

[0080] If the rotation angle s is not exactly 90° due to an error, 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° match the three-dimensional coordinates of the center of the calibration sphere 82 calculated for a rotation angle s=0°. For rotation angles s for which there are no measured values, the correction value of the vector components of the measurement light LA ​​is calculated by performing linear interpolation using multiple rotation angles s for which there are measured values.

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

[0082]

number

[0083]

number

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

[0085] <Recalibration of optical path length> Returning to Figure 4, after calibrating the relative angle 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 in step S20, so the explanation is omitted.

[0086] <Recalibration of the reference direction of the ejection> Furthermore, the reference direction of emission set in step S10 is recalibrated (step S50). In step S10, the reference direction is set, but as explained later using Figure 16, this setting, depending on its accuracy, can cause a deviation from the intended reference direction of emission (in this example, the X-axis direction), 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 refers to the rotation angle of the emission direction of the measurement light LA ​​with respect to the X-axis direction (reference direction) in the XY plane.

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

[0088]

number

[0089]

number

[0090]

number

[0091] In this invention, the angle of the reference direction is temporarily changed by updating the value in the control software in memory, by intentionally shifting the emission direction of the measurement light LA ​​of the optical rotary probe 26 after calibration by a small angle Δs1 relative to the reference direction set in step S10. The radius R of the pin gauge 83 is measured with the reference angle shifted by a small 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 this invention, based on the difference between this calculated error ΔR and the theoretical ΔR, the reference angle error Δs0 of the S angle in the emission direction of the optical rotary probe 26 after calibration relative 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 consequently, the measurement error by the optical rotary probe 26 is reduced.

[0092] The method for recalibrating the emission direction will be described below using Figures 11 to 16. Figure 14 is a flowchart showing the procedure for recalibrating the emission direction. As shown in Figure 14, first, the pin gauge 83 is positioned so that it is in a predetermined positional relationship with the optical rotating 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. Figures 11 and 12 show the positional relationship between the optical rotating probe 26 and the pin gauge 83 when measuring the adjustment error of the emission direction, respectively. As shown in Figure 11, the pin gauge 83 is positioned parallel to the longitudinal axis 62a of the optical rotating probe 26. Here, preferably, the distance between the optical rotating probe 26 and the pin gauge 83 is constant, and the distance between the optical rotating probe 26 and the pin gauge 83 is set so that the surface of the pin gauge 83 is 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 rotating probe 26 and the pin gauge 83 such that the surface of the pin gauge 83 is located approximately ± depth of field / 2 from the focal position of the measurement light LA. In the examples shown in Figures 11 and 12, the distance between the longitudinal axis 62a of the optical rotating probe 26 and the measurement surface of the pin gauge 83 is equal to the focal length F.

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

[0095] Through the calibration procedure described in steps S10 to S40 above, the optical rotating probe 26 is ideally adjusted so that at a rotation angle s=0°, the emission direction of the measurement light LA ​​coincides with the X-axis direction, which is the reference direction. Therefore, ideally, at a rotation angle s=0° of the optical rotating 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 positioning the optical rotating probe 26 and pin gauge 83 in this relative position, the control device 72 uses the head drive unit (not shown) of the measuring head 24 to rotate the optical rotating probe 26 around the longitudinal axis 62a (S axis) by a predetermined small angle Δs1 from the reference angle set in step S10, and sets this angle as a temporary reference angle (step S312). The change in the optical rotating probe 26 at this time corresponds to the movement shown by the dashed arrow A in Figure 12.

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

[0098] In other words, the control device 72 synchronizes the rotational movement (revolution) of the optical rotary probe 26 around the pin gauge 83 with the rotational movement (spinning) of the optical rotary probe 26 around its longitudinal axis (rotation axis) 62a, so that the measurement light LA ​​is emitted from the optical rotary probe 26 toward the pin gauge 83 perpendicular to the longitudinal axis of the pin gauge 83, while maintaining a constant distance between the optical rotary probe 26 and the pin gauge 83. In this case, it is desirable that the measurement be performed by rotating the optical rotary probe 26 around the pin gauge 83 by more than one full rotation (more than 360°). Furthermore, it is desirable that the measurement light LA ​​emitted from the optical rotary probe 26 irradiates 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 a predetermined small angle Δs1 based on the measurement result obtained in step S314 (step S316). Since the radius R of the pin gauge 83 is known and the calculation of the error ΔR is a simple difference calculation, the explanation is omitted.

[0100] The control device 72 changes the reference angle of rotation of the optical rotating probe 26 around the longitudinal axis 62a by a small angle Δs1 and repeatedly measures the radius R of the pin gauge 83 and calculates the error ΔR (step S318: NO). After repeating steps S312 to S316 a sufficient number of times to obtain an approximate formula (step S318: YES), the control device 72 further obtains an approximate formula showing the relationship between the small angle Δs1 and the error ΔR (step S320). Preferably, the control device 72 obtains a quadratic polynomial using the least squares method.

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

[0102] ΔR = -76.044Δs1 2 +35.86Δs1+4.4608 Furthermore, the thick solid line represents the theoretical error ΔR. As shown in Figure 15, the graph of the error ΔR calculated from the measured values ​​is shifted vertically and wider horizontally compared to the graph of the theoretical error ΔR. Here, the shift in the vertical axis is mainly due to a uniform measurement error in the wavelength-swept light source 28 of the measurement light LA. The widening in the horizontal axis is mainly due to the beam diameter of the measurement light LA ​​being broadened because the measurement position is 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 approximate formula obtained in step S320 (step S322). For example, the following quadratic polynomial (8) obtained by the least squares method can be transformed as shown in formula (9).

[0104] ΔR==AΔs1 2 +BΔs1+C ···(8)

[0105]

number

[0106] Specifically, in the case of the graph shown in Figure 15, the control device 72 uses the approximation formula "ΔR = -76.044Δs1 2 From "+35.86Δs1+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 recalibrates the ejection direction by updating the numerical values ​​of the control software stored in memory (step S324).

[0107] As described above, the calibration method for the optical rotary probe 26 in this embodiment allows for highly accurate calibration of the emission direction of the measurement light LA ​​emitted from the optical rotary probe 26. Therefore, the measurement error of the optical rotary probe 26 can be reduced. Consequently, 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 localized portion of the object being measured with large curvature.

[0108] <Advantages of recalibrating the exit 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 has the following further advantages.

[0109] First, in order to measure fine shapes, it is necessary to narrow the beam diameter of the measurement light LA. At the focal point of the measurement light LA, a beam diameter of several micrometers to tens of micrometers can be obtained, but the beam diameter of the measurement light LA ​​increases when it moves away from the focal point. In addition, the beam diameter of the measurement light LA ​​may also increase due to the effects of white noise, etc.

[0110] In Figure 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 as shown by reference numeral 16B in Figure 16, when the beam diameter of the measurement light LA ​​is large, the intensity gradient near the peak becomes small, making it difficult to accurately detect the position of the peak of the intensity of the measurement light LA. For this reason, conventionally, there has been a problem in that the reference direction of the emission of the measurement light LA ​​from the optical rotating probe 26 (the reference for the rotation angle of the optical rotating probe) cannot be set accurately.

[0111] For example, if the focal length of the imaging lens 64 of the optical rotating 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 peak position of the intensity 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 rotating probe 26 to the focal length is 10 mm, the measurement position error can reach 50 μm.

[0112] Conventionally, such large errors have made it difficult to accurately measure the shape of localized areas with large curvatures of the object being measured. In contrast, in this embodiment, the radius R of the pin gauge 83 is measured with the emission direction of the measurement light LA ​​of the calibrated optical rotation probe 26 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 Figure 15, if the beam diameter of the measurement light LA ​​is broadened due to the measurement position being shifted from the focal point of the measurement light LA, the calculated error ΔR graph will broaden in the horizontal direction, but the graph will maintain symmetry in the horizontal direction. Therefore, the width of the horizontal broadening of the graph does not affect the calculation result of the adjustment error based on the calculated error ΔR approximation formula. Accordingly, in this embodiment, even if the beam diameter of the measurement light LA ​​is broadened, the emission direction of the measurement light LA ​​can be calibrated accurately based on the calculation result of the adjustment error.

[0114] Similarly, even if a uniform length measurement error remains in the wavelength-swept light source 28 of the measurement light LA ​​after calibration, as shown in Figure 15, the graph of the error ΔR calculated from the measured values ​​is only shifted vertically compared to the graph of the theoretical error ΔR, and does not affect the calculation result of the adjustment error based on the calculated approximation formula for the error ΔR. Therefore, in this embodiment, even if there is a uniform length measurement error in the wavelength-swept light source 28 of the measurement light LA, the emission direction of the measurement light LA ​​can be calibrated with high accuracy.

[0115] [Method for recalibrating the exit direction according to the second embodiment] In the above description, the reference angle error Δs0 of the S angle was calculated by measuring the radius R of a pin gauge 83 with 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. Figure 17 shows a method for recalibrating the emission direction of the measurement light LA ​​according to the second embodiment. As shown in Figure 17, the method for recalibrating the emission direction in the second embodiment is almost the same as the flowchart shown in Figure 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 rotating probe 26 is rotated around the longitudinal axis 62a (S axis) with the reference angle of the S angle changed by a small angle Δ1s from the setting in step S10, and the surface shape of the pin gauge 83 is measured instead of the radius R of the pin gauge 83. Reference numeral 18A in Figure 18 shows a graph plotting the measurement results of the surface shape at a certain small angle Δs1 on an XY coordinate system.

[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 measured values ​​at each small angle Δs1. Below, an example of how to calculate the standard deviation σ(ΔR) for a certain small angle Δs1 will be specifically explained with reference to the graph shown in Figure 18. First, the control device 72 calculates an approximate value of the radius R of the pin gauge 83 by approximating the surface shape measurement results using the least squares method. In the graph shown by reference numeral 18A, the approximate value of the radius R is shown 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 to the measured value of the radius R (vertical axis) with respect 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 approximate value of the radius R and the measured value of the radius R. Reference numeral 18C shows a graph of the error ΔR (vertical axis) with respect to the rotation angle s (horizontal axis) with respect to the center C of the pin gauge 83. 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 as the shape error, which is the range that includes approximately 95% of all measurement points in the normal distribution of the error ΔR. In the case of the graphs shown by labels 18A to 18C in Figure 18, the shape error (±2σ) is 60 μm. The control device 72 performs such shape error calculations for multiple different small angles Δs1.

[0118] The subsequent procedure is the same as in the first embodiment. Figure 19 shows a graph plotted with the small angle Δs1 of rotation of the optical rotating probe 26 around the longitudinal axis 62a on the horizontal axis and the shape error (±2σ) calculated in step S314 on the vertical axis. For example, if we approximate the graph in Figure 19 with a quadratic polynomial using the least squares method, we get "±2σ = -76.508Δs1 2 This results in "+36.141Δs1+4.6607" (see the solid line graph in Figure 19).

[0119] Thus, it can be seen that in the second embodiment, which measures surface shape, results almost the same as those obtained in the first embodiment, which measures radius R, can be obtained. Note that by changing the reference angle of the optical rotation 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 widens when the measurement light LA ​​does not strike the pin gauge 83 perpendicularly to the measurement point. In the case of the second embodiment, which measures 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, as in the first embodiment, it is possible to improve calibration accuracy and reduce the measurement error of the optical rotary probe 26. Consequently, 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 the exit direction according to the third embodiment] In the first and second embodiments described above, the emission direction was recalibrated using the radius R of a 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, if the beam diameter is 13 μm, the radius R of the pin gauge 83 is about 130 μm to several millimeters. It is not easy to manually align a pin gauge 83 with such a small radius R for measurement.

[0122] Therefore, instead of the pin gauge 83, a jig 84 may be used in which the pin gauge 86 is erected vertically (in the Z-axis direction) on a rectangular block 85 as shown in Figure 20. The perpendicularity of the pin gauge 86 is not required to be particularly 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 that inclination angle on the measurement error of radius R is 0.03 μm, and it can be used for calibration.

[0123] The following describes the recalibration method when using this jig 84. First, before performing the recalibration shown in Figure 14, measure the position of the pin gauge 86 on the block 85 of the jig 84. Usually, this measurement only needs to be performed 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 block 85 of jig 84 are measured to create the work coordinate system (XYZ Cartesian coordinate system) of block 85 of jig 84, and the position of the center of the pin gauge 86 is measured by further measuring the diameter of the pin gauge 86. Due to tolerances in the positional accuracy of the pin gauge, deviations in the position measurement results may occur, and the measurement results often differ from the design position. In addition, measurement errors may occur if the measurement light LA ​​does not strike the vertex 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 design position, the jig 84 is used for recalibration as shown in Figure 14 in the first and second embodiments, assuming that the center of the pin gauge 86 is located at (x1, y1, z0) 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 determined on the work coordinate system before performing the recalibration method shown in Figure 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. As a result, in addition to the effects of the above embodiments, the pin gauge 83 can be easily aligned.

[0126] As described above, according to the first to third embodiments, the emission direction of the measurement light LA ​​emitted from the optical rotating probe 26 can be calibrated with high precision. Therefore, the measurement error of the optical rotating probe 26 can be reduced. Consequently, the measurement error of the three-dimensional coordinate measuring device 10 equipped with the optical rotating probe 26 can be reduced. This makes it possible, for example, to accurately measure the shape of a localized part of the object to be measured with a large curvature.

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

[0128] 10... Three-dimensional coordinate measuring device, 26... Optical rotating 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, 52a... Shaft holder, 54... Rotor, 54a... Hollow section, 62... Shaft, 62a... Longitudinal axis, 62b... Inner surface, 64... Imaging lens, 66... ​​Right-angle prism mirror, 66a... Inlet / outlet surface, 70... Controller, 72... Control device, 80... Beam profiler, 81... Ring gauge, 82... Calibration sphere, 83, 86... Pin gauge, 84... Jig, 85... Block

Claims

1. 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 the emission direction of the measurement light around the probe axis, comprising: 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; an adjustment error calculation step of 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 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 obtaining step are each performed a plurality of times; the adjustment error calculation step calculates an adjustment error of the emission direction of the measurement light with respect to the reference direction based on the shape error of the reference object acquired for each minute angle. The method for calibrating an optical rotary probe according to claim 1 .

3. the acquiring step changes 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 obtaining step changes a relative position between the optical rotary probe and the reference object so that the measurement surface of the reference object is positioned 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. The method for calibrating an optical rotary probe according to claim 5.

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