Distance measurement device and distance measurement method

Abstract

To enable high-precision measurement of a distance to an object while suppressing stray light inside a probe tip.SOLUTION: A distance measurement device is provided, comprising a probe tip having therein a light path switching element for switching a light path of measurement light incident from an optical element, where at least a portion of the probe tip located to face a fifth surface thereof is made of a material that absorbs the measurement light.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a distance measurement device and a distance measurement method. [Background technology]

[0002] As a technology for measuring the shape of the bottom or side of a hole in an object, for example, Patent Document 1 describes "a distance measurement device comprising a measurement probe and a probe tip, wherein the measurement probe comprises a polarization state control unit that controls the polarization of measurement light emitted to the probe tip, and a rotation mechanism that rotates the probe tip, and the probe tip comprises an optical path switching element, which switches the direction in which the measurement light is irradiated outside the probe tip based on the polarization of the measurement light, and the measurement light captures light reflected or scattered by the object." [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6730483 Summary of the Invention [Problem to be solved by the invention]

[0004] According to the invention described in Cited Document 1, the irradiation direction of the measurement light is switched by the optical path switching element at the tip of the probe, thereby making it possible to measure the side direction and the depth direction of the measurement probe.

[0005] However, when the measurement light captures light reflected or scattered by the object, the light is reflected inside the tip of the probe and becomes stray light, which can cause incorrect measurement of the distance to the object or reduced measurement accuracy.

[0006] The present invention has been made in view of the above points, and has as its object to suppress stray light inside the tip of a probe and measure the distance to an object with high accuracy. [Means for solving the problem]

[0007] The present application includes a number of means for solving at least part of the above problems, examples of which are as follows.

[0008] In order to solve the above problem, a shape measurement device according to one aspect of the present invention is a distance measurement device equipped with a measurement probe, the measurement probe having a cylindrical probe tip portion engaged with a tip of the measurement probe, a rotating portion that rotates the engaged probe tip portion, and an optical element that emits measurement light to the probe tip portion, the probe tip portion having an optical path switching element at the tip of the probe tip portion that switches the optical path of the measurement light incident from the optical element, the optical path switching element having a first surface onto which the measurement light incident from the optical element is incident, a second surface that reflects or transmits the measurement light depending on the polarization state of the measurement light incident from the first surface, a third surface that emits the measurement light reflected by the second surface onto an object, a fourth surface that emits the measurement light that has passed through the second surface onto the object, and a fifth surface opposite the third surface, and a material of at least a portion of the probe tip portion arranged at a position opposite the fifth surface absorbs the measurement light. [Effects of the Invention]

[0009] According to the present invention, it is possible to suppress stray light inside the tip of the probe and measure the distance to the object with high accuracy.

[0010] Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing an example of the configuration of a distance measurement device according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a diagram illustrating an example of the configuration of the distance measurement unit. [Figure 3] FIG. 3 is a diagram for explaining an example of distance calculation based on a measurement beat signal in the FMCW (Frequency Modulated Continuous Wave) system. [Figure 4] FIG. 4 is a diagram for explaining an example of distance calculation based on a measurement beat signal in the FMCW system. [Figure 5] FIG. 5 is a diagram for explaining the principle of switching the emission direction of measurement light by the optical path switching element. [Figure 6] Figures 6(A) and (B) show examples of stray light generated inside the measurement probe, where Figure 6(A) shows the case where the measurement light is emitted in a lateral direction, and Figure 6(B) shows the case where the measurement light is emitted in a straight direction. [Figure 7] FIG. 7 is a diagram showing an example of a reflection intensity profile detected during multiple reflections. [Figure 8] FIG. 8 is a schematic diagram showing an example of the configuration of a shape measurement device including a distance measurement device. [Figure 9] FIG. 9 is a diagram illustrating an example of the functional block configuration of the shape measurement device. [Figure 10] FIG. 10 is a diagram showing an example of the configuration of a distance measurement device according to the second embodiment of the present invention. [Figure 11] FIG. 11 is a diagram showing an example of the inclination angle of the absorbing wall in the second embodiment. [Figure 12] FIG. 12 is a diagram showing an example of the configuration of a distance measurement device according to the third embodiment of the present invention. [Figure 13] FIG. 13 is a diagram showing an example of the configuration of a distance measurement device according to the fourth embodiment of the present invention. [Figure 14] FIG. 14 is a diagram for explaining a method for calculating the distance from the correction origin to the object. [Figure 15] FIG. 15 is a flowchart illustrating an example of a shape measurement process performed by the shape measurement device. [Figure 16]FIG. 16 is a diagram showing an example of the configuration of a distance measurement device according to the fifth embodiment of the present invention. [Figure 17] FIG. 17 is a diagram showing an example of the configuration of a distance measurement device according to the sixth embodiment of the present invention. [Figure 18] FIG. 18 is a diagram showing an example of the configuration of the cap. [Figure 19] FIG. 19 is a diagram showing an example of the positional relationship between the optical window on the side surface of the cap and the absorbing wall. [Figure 20] FIG. 20 is a diagram showing an example of the positional relationship between the optical window on the bottom side of the cap and the absorbing wall. [Figure 21] FIG. 21 is a diagram showing an example of a method for assembling the optical path switching element and the cap to the tip of the probe. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, several embodiments of the present invention will be described with reference to the drawings. In all drawings used to explain each embodiment, the same components are generally designated by the same reference numerals, and repeated explanations will be omitted. Furthermore, in the following embodiments, the components (including element steps, etc.) are not necessarily essential unless otherwise specified or considered to be clearly essential in principle. Furthermore, when the terms "consisting of A," "composed of A," "having A," and "including A" are used, other elements are not excluded unless otherwise specified to include only the element. Similarly, in the following embodiments, when referring to the shape, positional relationship, etc. of components, etc., these terms include those that are substantially similar or similar to the shape, etc., unless otherwise specified or considered to be clearly essential in principle.

[0013] <Distance measurement device 1001 according to the first embodiment of the present invention> FIG. 1 is a schematic diagram showing an example of the configuration of a distance measurement device 1001 according to a first embodiment of the present invention.

[0014] The distance measurement device 1001 includes a distance measurement unit 111 and a measurement probe 115 .

[0015] The distance measurement unit 111 generates measurement light and outputs it to the measurement probe 115 via the connection cable 113. The distance measurement unit 111 also calculates the distance to the object T based on the reflected light input from the measurement probe 115 via the connection cable 113. The connection cable 113 is made of, for example, an optical fiber. do.

[0016] The measurement probe 115 is made up of a head 101 and a probe tip 106. The measurement probe 115 irradiates the object T with measurement light, receives the light reflected by the object T, and outputs it to the distance measurement unit 111 via a connection cable 113.

[0017] The head 101 of the measurement probe 115 has therein a lens unit 102, a first polarization state control unit 103, and a rotation unit 104.

[0018] The lens unit 102 is made of an optical fiber focuser. The lens unit 102 focuses the measurement light input from the distance measurement unit 111 and emits it into the space within the head 101 toward the first polarization state control unit 103. The first polarization state control unit 103 is made of, for example, a quarter-wave plate and controls the polarization state of the measurement light. The rotation unit 104 is made of a motor or the like. Under the control of the distance measurement unit 111, the rotation unit 104 drives the motor or the like to rotate the probe tip 106 around a rotation axis parallel to the measurement light output from the lens unit 102.

[0019] The probe tip 106 of the measurement probe 115 is formed, for example, in a hollow cylindrical shape so that the measurement light and reflected light can pass through. The probe tip 106 has an opening 109 in a first direction D1, which is the lateral direction, and an opening 110 in a second direction D2, which is the longitudinal direction. The probe tip 106 engages the second polarization state control unit 105 on the head 101 side inside the hollow cylindrical shape. The probe tip 106 also engages the optical path switching element 107 on the tip side inside the hollow cylindrical shape. The second polarization state control unit 105 and the optical path switching element 107 are rotated simultaneously as the probe tip 106 is rotated by the rotation unit 104. By disposing the optical path switching element 107 inside the probe tip 106, it is possible to prevent the optical path switching element 107 from coming into contact with the object T and being damaged.

[0020] The second polarization state controller 105 is made of, for example, a quarter-wave plate, and controls the polarization state of the measurement light.

[0021] The optical path switching element 107 is composed of, for example, a cubic polarizing beam splitter. The optical path switching element 107 reflects or transmits the measurement light incident from the first surface P1 at the second surface P2 depending on the direction of linear polarization of the measurement light. Specifically, the optical path switching element 107 reflects the measurement light in a first direction D1 substantially perpendicular to the rotation axis and emits it from the third surface P3. The optical path switching element 107 also transmits the measurement light in a second direction D2 substantially parallel to the rotation axis of the probe tip 106 and emits it from the fourth surface P4. The relationship between the control of the polarization state of the measurement light and the emission direction of the measurement light from the optical path switching element 107 will be described later with reference to FIG. 5.

[0022] Furthermore, an absorbing wall 108 is provided on the inner wall surface of the probe tip portion 106 at a position facing the fifth surface P5 of the optical path switching element 107. The normal of the absorbing wall 108 is approximately perpendicular to, but not strictly perpendicular to, the rotation axis of the probe tip portion 106. The absorbing wall 108 is made of, for example, an ND (Neutral Density) filter. The absorbing wall 108 has a higher absorption rate for light of a wavelength corresponding to the measurement light than the inner wall surface of the probe tip portion 106, and absorbs the light of the wavelength corresponding to the measurement light. The ND filter used for the absorbing wall 108 is preferably one that can reduce the amount of reflected light to approximately 1 / 100,000. Instead of an ND filter, a light-absorbing paint may be applied. Alternatively, for example, black paint, such as that applied to the edge of a lens, may be used. This reduces stray light inside the probe tip portion 106 and prevents a decrease in the accuracy of distance measurement. Instead of providing the absorbing wall 108, or in addition to the absorbing wall 108, the probe tip 106 may be formed of a material that absorbs light of a wavelength corresponding to the measurement light. Alternatively, the probe tip 106 may be coated with paint made of a material that absorbs light.

[0023] Instead of controlling the polarization state of the measurement light to change the emission direction of the measurement light, for example, a galvanometer mirror may be used to scan the measurement light. Using one galvanometer mirror allows the measurement light to be scanned one-dimensionally, and using two galvanometer mirrors allows the measurement light to be scanned two-dimensionally. Furthermore, a MEMS (Micro Electro Mechanical Systems) mirror, a polygon mirror, or the like may be used as the scanning mechanism for the measurement light.

[0024] Next, Fig. 2 shows an example of the configuration of the distance measurement unit 111. This figure shows an example of the configuration when the distance measurement unit 111 employs the FMCW method as the distance measurement method, which calculates the distance to the target object based on the propagation time of light.

[0025] In the distance measurement unit 111, the distance measurement control unit 216 transmits a sweep waveform signal to the oscillator 202. The oscillator 202 injects a triangular wave current into the laser light source 201 to modulate the drive current. As a result, the laser light source 201 generates FM (Frequency Modulated) light whose frequency is swept over time at a constant modulation speed. Note that the laser light source 201 may be configured as a semiconductor laser device with an external resonator, and the resonant wavelength of the laser light source 201 may be changed by a triangular wave control signal from the oscillator 202. In this case as well, the laser light source 201 generates FM light whose frequency is swept over time.

[0026] The generated FM light is split into two by the optical fiber coupler 203. The optical fiber coupler 203 may be a beam splitter. The same applies to the optical fiber couplers 204, 206, and 210 described later.

[0027] One of the FM lights split into two by optical fiber coupler 203 is guided to the reference optical system, and is further split into two by optical fiber coupler 204. One of the FM lights split into two by optical fiber coupler 204 is provided with a fixed optical path difference by optical fiber 205, and then multiplexed with the other of the FM lights by optical fiber coupler 206 and received by photodetector 207. This is configured as a Mach-Zehnder interferometer, and photodetector 207 detects a fixed reference beat signal proportional to the optical path difference. The reference beat signal is output to distance measurement control unit 216.

[0028] The other of the FM lights split by the optical fiber coupler 203 is switched to a polarization direction along the slow axis or fast axis of the optical fiber by the polarization switcher 217. After this, the FM light with its polarization direction switched passes through the circulator 208 and is split by the optical fiber coupler 210, one of the FM lights is reflected by the reference mirror 211 to become reference light, and the other FM light is output to the measurement probe 115 and emitted from the probe tip 106 to the object T.

[0029] The light reflected by the object T returns in this order to the probe tip 106, head 101, and distance measurement unit 111, where it is combined with the reference light reflected by the reference mirror 211 in the optical fiber coupler 210 and guided to the light receiver 209 by the circulator 208. The light receiver 209 detects a measurement beat signal generated by interference between the reference light and the measurement light, and outputs the signal to the distance measurement control unit 216.

[0030] The distance measurement control unit 216 performs A / D conversion on the measurement beat signal from the photoreceiver 209 using the reference beat signal from the photoreceiver 207 as a sampling clock. Alternatively, the reference beat signal and the measurement beat signal are sampled at a constant sampling clock. More specifically, the reference beat signal can be transformed into a signal with a phase shift of 90 degrees by performing a Hilbert transform. Since the local phase of the signal can be determined from the reference signal before and after the Hilbert transform, the timing at which the reference signal has a constant phase can be determined by interpolating this phase. By performing interpolated sampling on the measurement beat signal in accordance with this timing, it is possible to resample the measurement beat signal using the reference beat signal as a reference. Alternatively, the same results can be obtained by sampling and A / D converting the measurement signal using the reference beat signal as a sampling clock using the AD / DA conversion function of the distance measurement control unit 216.

[0031] Furthermore, the distance measurement control unit 216 outputs the sampled measurement beat signal to the control device 214. The control device 214 calculates the distance to the target object T from the sampled measurement beat signal. Note that a method for calculating the distance based on the sampled measurement beat signal will be described later with reference to FIGS. 3 and 4.

[0032] As a modification of the distance measurement unit 111, the circulator 208, the optical fiber coupler 210, the reference mirror 211, and the photodetector 209 may be disposed in the head 101 of the measurement probe 115. In this case, the measurement bead signal output by the photodetector 209 is output to the distance measurement control unit 216 via the connection cable 113.

[0033] 3 is a diagram for explaining an example of distance calculation based on a measurement beat signal using the FMCW method. In this diagram, the horizontal axis represents time and the vertical axis represents the frequency of the measurement light, and the diagram shows the relationship between reference light 301 reflected by the reference mirror 211 and reflected light 302 reflected by the object T.

[0034] There is a time difference Δt between the time when the reference light 301 and the reflected light 302 reach the photodetector 209. During this time difference Δt, the frequency of the FM light from the laser light source 201 changes, and therefore, at the photodetector 209, a beat frequency f equal to this frequency difference is detected. b If the time required to modulate the frequency by the frequency sweep width Δν is T, the time difference Δt can be expressed by the following equation (1): Δt=T f b / 2Δν (1)

[0035] The distance L to the target object T is half the distance that light travels during the time difference Δt. Therefore, the distance L can be calculated using the following equation (2) using the speed of light c in the atmosphere. L=cT·f b / 2Δν (2)

[0036] As is clear from equation (2), the distance L and the beat frequency f b Therefore, if the measurement beat signal detected by the light receiver 209 is subjected to FFT (First Fourier Transform) to determine the peak position and magnitude, the reflection position of the object T and the amount of reflected light can be determined.

[0037] 4 is a diagram for explaining an example of distance calculation based on a measurement beat signal using the FMCW method. The diagram shows an example of a reflection intensity profile, with the horizontal axis representing the FFT frequency and the vertical axis representing the reflection intensity.

[0038] The reflection intensity profile has data that is more discrete near its peak than the rest. The peak width w is calculated using the distance resolution c / 2Δν. Therefore, by fitting a function such as a quadratic function or Gaussian function with an upward convex shape to data from three or more points near the peak point 401 and using the peak of the fitted function, it is possible to determine the position of the target T with an accuracy greater than the distance resolution.

[0039] Although FFT has been used as an example of beat frequency analysis, the maximum entropy method may also be used, which can detect peak positions with higher resolution than FFT.

[0040] Next, FIG. 5 is a diagram for explaining the principle of switching the emission direction by the optical path switching element 107 according to the polarization direction of the measurement light.

[0041] The optical path switching element 107 engaged with the probe tip 106 has the property of transmitting the measurement light in the second direction D2 when the polarization direction of the measurement light oscillates parallel to the incident plane, and also has the property of reflecting the measurement light in the first direction D1 when the polarization direction of the measurement light oscillates perpendicular to the incident plane.

[0042] Therefore, by electrically switching the polarization direction of the measurement light by turning on and off the polarization switcher 217 (FIG. 2), the emission direction of the measurement light can be switched to the second direction D2 or the first direction D1. To rotate the emission direction of the measurement light while keeping it in the first direction D1, it is necessary to rotate the polarization direction of the measurement light in accordance with the rotation of the optical path switching element 107 and keep the polarization state relative to the optical path switching element 107 constant. For this purpose, the first polarization state controller 103 and the second polarization state controller 105 are used.

[0043] The first polarization state controller 103 is disposed with its axis tilted 45 degrees with respect to the polarization direction of the incident light, thereby converting linearly polarized light into circularly polarized light. The second polarization state controller 105 converts the measurement light converted into circularly polarized light by the first polarization state controller 103 back into linearly polarized light. Note that the second polarization state controller 105 and the light path switching element 107 are simultaneously rotated by the rotation unit 104, so that a constant polarized incident direction can always be maintained for the light path switching element 107, and the measurement light directed in the first direction D1 can be rotated.

[0044] <About stray light inside the measurement probe 115> Here, we will explain again the stray light inside the measurement probe 115. Figure 6 shows a configuration example in which the absorbing wall 108 is omitted from the measurement probe 115 shown in Figure 1, and shows an example of stray light generated inside the measurement probe 115.

[0045] As shown in FIG. 1A, when the measurement light is emitted sideways, it is reflected by the object T (first reflection), and the reflected light returns to the light path switching element 107 with its polarization disturbed. In this case, the polarization component of the reflected light that is orthogonal to the light path switching element 107 is reflected by the light path switching element 107 toward the lens unit 102. That is, the light path of the measurement light travels in the reverse direction. On the other hand, the polarization component of the reflected light that is parallel to the light path switching element 107 passes through the light path switching element 107 and is irradiated onto the opposing inner wall surface of the probe tip 106. Because this inner wall surface is directly opposite the inner wall surface that reflected the irradiated light, most of the irradiated reflected light passes through the light path switching element 107 again and is irradiated onto the object T. Then, it is reflected by the object T again (second reflection), and the reflected light returns to the light path switching element 107 with its polarization disturbed. The polarized component of the reflected light that is orthogonal to the optical path switching element 107 travels in the opposite direction along the optical path of the measurement light. When multiple reflections occur in this way, the detected reflection intensity profile will include two components: a component that is reflected once by the object T and a component that is reflected twice.

[0046] Similarly, as shown in FIG. 1B, when the emission direction of the measurement light is a straight direction, the measurement light is reflected by the object T (first reflection), and the reflected light returns to the light path switching element 107 with its polarization disturbed. In this case, the polarization component of the reflected light parallel to the light path switching element 107 passes through the light path switching element 107 and travels in the opposite direction along the optical path of the measurement light. On the other hand, the polarization component of the reflected light perpendicular to the light path switching element 107 is reflected laterally by the light path switching element 107 and irradiates the inner wall surface of the probe tip 106. Most of the reflected light irradiated onto the inner wall surface is then reflected again by the light path switching element 107 and irradiates the object T. The reflected light is then reflected again by the object T (second reflection), and returns to the light path switching element 107 with its polarization disturbed. Therefore, in this case as well, the detected reflection intensity profile includes both the component reflected the first time by the object T and the component reflected the second time.

[0047] Next, Figure 7 shows an example of a reflection intensity profile detected when multiple reflections occur. In this figure, the horizontal axis represents distance and the vertical axis represents detected reflection intensity.

[0048] Of the two distance peaks 700, 701 shown in the figure, distance peak 700 indicates the distance measured based on the first reflected light from object T, and distance peak 701 indicates the distance measured based on the second reflected light from object T. There is no problem if the distance to object T is known in advance, but if it is not known, it is impossible to determine which of distance peaks 700 and 701 indicates the distance to object T. Also, depending on the positional relationship of object T, the reflection intensity of distance peak 701 may be greater than the reflection intensity of distance peak 700, which may result in distance peak 701 being mistakenly detected as the distance to object T. Furthermore, if the reflection intensity of distance peak 701 is strong, shot noise increases, which may reduce the S / N ratio of the signal of distance peak 700, which is the signal that you actually want to measure.

[0049] In contrast to this, in this embodiment, the second reflection is suppressed by providing the absorbing wall 108. Therefore, stray light inside the measurement probe 115 can be suppressed, and erroneous detection of the distance to the object T and a decrease in measurement accuracy can be prevented.

[0050] <Configuration example of shape measurement device 1000 including distance measurement device 1001> Next, FIG. 8 is a schematic diagram showing an example of the configuration of a shape measurement device 1000 including a distance measurement device 1001.

[0051] The shape measuring apparatus 1000 has, as a stage mechanism 903, an X-axis stage 804 that moves the placed object T in the X direction, a Y-axis stage 805 that moves the X-axis stage 804 in the Y-axis direction, and a Z-axis stage 806 that holds the measurement probe 115 and moves it in the Z-axis direction. Furthermore, the shape measuring apparatus 1000 has a stage controller 808 that controls the stage mechanism 903.

[0052] When measuring the shape of object T, first, object T is placed on X-axis stage 804, and X-axis stage 804 and Y-axis stage 805 are moved to fix object T at a predetermined position on the XY plane. Next, the Z-axis stage 806 is used to move measurement probe 115 in the vertical direction to measure the three-dimensional shape of object T. Note that if the measurement range is narrow and the shape can be measured by movement only in the Z-axis direction, the X-axis stage 804 and Y-axis stage 805 may not be used, and object T may be positioned with a jig so that its position is uniquely determined, and only the Z-axis stage 806 may be moved to measure the three-dimensional shape of object T.

[0053] Note that the configuration example of the shape measuring device 1000 is not limited to the above-mentioned example. For example, if the measuring probe 115 is gripped instead of a tool in a three-axis machining center, on-machine measurement on the three-axis machining center can be realized.

[0054] Furthermore, if the measurement probe 115 is held by a multi-degree-of-freedom robot, a three-dimensional shape measuring device for measuring the shape of the object T can be realized.

[0055] Next, Fig. 9 shows an example of the functional block configuration of the shape measurement device 1000 shown in Fig. 8. The control device 214 has a distance calculation unit 901 and a shape calculation unit 902. The distance calculation unit 901 calculates the distance to the object T from the sampled measurement beat signal input from the distance measurement unit 111. The distance calculation unit 901 also performs tasks such as linking the calculated distance to the object T with a stage encoder signal that determines the XYZ coordinates of the stage mechanism 903. The shape calculation unit 902 measures the three-dimensional shape of the object T based on the linking result, by the distance calculation unit 901, between the distance to the object T and the stage encoder signal. The display unit 215 displays a three-dimensional image of the measured object T.

[0056] <Distance measurement device 1002 according to the second embodiment of the present invention> Next, FIG. 10 shows an example of the configuration of a distance measurement device 1002 according to a second embodiment of the present invention.

[0057] The distance measurement device 1002 is a device in which the orientation of the absorbing wall 108 in the distance measurement device 1001 ( FIG. 1 ) has been changed. That is, the absorbing wall 108 in the distance measurement device 1001 was arranged so that its normal was approximately perpendicular (not strictly perpendicular) to the rotation axis of the probe tip portion 106. In contrast, the absorbing wall 108 in the distance measurement device 1002 is arranged so that its normal and the rotation axis form an inclination angle θ that is greater than 0 degrees and less than 90 degrees. That is, the absorbing wall 108 in the distance measurement device 1002 is arranged at a clear incline compared to the distance measurement device 1001. Note that the components of the distance measurement device 1002 other than the absorbing wall 108 are common to the components of the distance measurement device 1001 and are denoted by the same reference numerals, and therefore description thereof will be omitted.

[0058] FIG. 11 shows an example of the inclination angle θ of the absorbing wall 108 in the distance measurement device 1002.

[0059] In the distance measurement device 1002, the measurement light that enters the first surface P1 of the optical path switching element 107, exits laterally at the second surface P2, and exits from the third surface P3 is reflected by the object T (first reflection), and the reflected light returns from the third surface P3 to the optical path switching element 107 with its polarization disturbed. Most of the reflected light is then reflected at the second surface P2 in the direction of the lens unit 102.

[0060] On the other hand, part of the reflected light that has passed through the second surface P2 is irradiated onto the absorbing wall 108. The absorbing wall 108 absorbs most of the irradiated light but reflects a portion of it. At this time, since the absorbing wall 108 is disposed at an inclination angle θ with respect to the rotation axis of the probe tip portion 106, the reflected light from the absorbing wall 108 is inclined by an inclination angle 2θ and returns to the light path switching element 107. Then, the reflected light is reflected again by the object T (second reflection), and returns to the light path switching element 107 with its polarization disturbed. Then, most of the reflected light is reflected by the second surface P2 in the direction of the lens unit 102, but since the second surface P2 has an inclination angle 2θ with respect to the rotation axis of the probe tip portion 106, it will not be condensed if 2θ is larger than the condensing angle of the lens unit 102.

[0061] Therefore, by determining the inclination angle θ based on the light collection angle of the lens portion 102 and arranging the absorbing wall 108, it is possible to prevent the occurrence of a distance peak 701 due to stray light in the reflection intensity profile (FIG. 7).

[0062] <Distance measurement device 1003 according to the third embodiment of the present invention> Next, a distance measurement device 1003 according to a third embodiment of the present invention will be described. Distance measurement device 1003 differs from distance measurement device 1001 (FIG. 1) in the shape of optical path switching element 107 engaged with probe tip 106.

[0063] FIG. 12 shows an example of the shape of the optical path switching element 107 engaged with the probe tip 106 of the exemplary configuration of the distance measurement device 1003.

[0064] The shape of the optical path switching element 107 in the distance measurement device 1001 is a rectangular parallelepiped. In contrast, the shape of the optical path switching element 107 in the distance measurement device 1003 is such that the fifth surface P5 opposite to the third surface P3 is inclined by an angle θ with respect to the rotation axis of the probe tip portion 106.

[0065] In the distance measurement device 1003, the measurement light emitted in a lateral direction from the third surface P3 of the optical path switching element 107 is reflected by the object T (first reflection), and the reflected light returns to the optical path switching element 107 with its polarization disturbed. Then, most of the reflected light is reflected by the second surface P2 in the direction of the lens unit 102.

[0066] On the other hand, the reflected light that has passed through the second surface P2 is irradiated from the fifth surface P5 onto the absorbing wall 108. However, since the fifth surface P5 has an inclination angle θ with respect to the rotation axis of the probe tip portion 106, the light emitted from the fifth surface P5 is refracted by θ' shown in the following formula (3). θ'=sin -1 (n sinθ) (3) Here, n is the refractive index of the optical path switching element 107.

[0067] The absorbing wall 108 absorbs most of the light from the fifth surface P5, but some of it is reflected. At this time, since the light from the fifth surface P5 is inclined by angle θ, the reflected light from the absorbing wall 108 is inclined by an inclination angle 2θ and returns to the light path switching element 107. It is then reflected again by the object T (second reflection), and the reflected light returns to the light path switching element 107 with its polarization disturbed. Most of the reflected light is then reflected by the second surface P2 in the direction of the lens unit 102, but because it has an inclination angle 2θ with respect to the rotation axis of the probe tip portion 106, it will not be focused if 2θ is larger than the focusing angle of the lens unit 102.

[0068] Therefore, if the inclination angle θ of the fifth surface P5 of the optical path switching element 107 is determined based on the light collection angle of the lens portion 102, it is possible to prevent the occurrence of a distance peak 701 due to stray light in the reflection intensity profile (FIG. 7).

[0069] <Distance measurement device 1004 according to the fourth embodiment of the present invention> Next, FIG. 13 shows an example of the configuration of a distance measurement device 1004 according to a fourth embodiment of the present invention.

[0070] In the distance measurement device 1004, a reflective coating 1300 that reflects part of the measurement light from the lens unit 102 is applied to a first surface P1 of the optical path switching element 107. In addition, AR coatings 1301 and 1302 that prevent reflection are provided on a third surface P3 in the lateral direction of the optical path switching element 107 and a fourth surface P4 in the straight direction.

[0071] In the distance measurement device 1004, by providing a reflective coating 1300 on the first surface P1 of the optical path switching element 107, the first surface P1 can be used as the origin for correction in distance measurement. This makes it possible to ignore distance measurement errors caused by changes in the optical path length due to the influence of heat, etc. in the optical path after the optical fiber coupler 210. In addition, by providing AR coatings 1301 and 1302 on the third surface P3 and the fourth surface P4 of the optical path switching element 107, stray light inside the optical path switching element 107, which causes noise, can be suppressed.

[0072] 14 is a diagram for explaining a distance measurement correction method using a correction origin corresponding to the distance measurement device 1004 (FIG. 13), and shows the FFT result of the detected beat signal obtained from the distance measurement device 1004. The horizontal axis of the diagram represents distance, and the vertical axis represents the detected intensity of the detected beat signal.

[0073] The distance based on the light reflected by the first surface P1 of the optical path switching element 107, which serves as the origin for correction, is detected as detection peak 1401. On the other hand, the distance based on the light that passes through the first surface P1 of the optical path switching element 107, is emitted from the third surface P3 or the fourth surface P4, is irradiated onto the object T, and is reflected is detected as detection peak 1402. Therefore, by subtracting the distance represented by detection peak 1401 from the distance represented by detection peak 1402, the distance from the first surface P1 of the optical path switching element 107, which serves as the origin for correction, to the object T can be obtained.

[0074] Next, FIG. 15 is a flowchart illustrating an example of distance measurement processing by the shape measurement device 100 including the distance measurement device 1004.

[0075] The distance measurement process is started, for example, in response to a predetermined start operation from the user. First, the control device 214 determines, based on the operation input from the user, whether the distance measurement of the object T (for example, a hole) is a side measurement in which the measurement light is emitted in a first direction D1, or a depth measurement in which the measurement light is emitted in a second direction D2 (step S1).

[0076] If it is determined in step S1 that side measurement is being performed, the control device 214 controls the distance measurement unit 111 to control the emission direction of the measurement light from the measurement probe 115 to the first direction D1, emits the measurement light, and rotates the probe tip 106 using the rotation unit 104. Then, the distance calculation unit 901 of the control device 214 acquires the sampled measurement beat signal from the distance measurement unit 111, and in synchronization with this, acquires from the stage controller 808 a stage encoder signal that determines the XYZ coordinates of the stage mechanism 903 and the rotation angle of the rotation unit 104, and links these together (step S2).

[0077] 14, the distance calculation unit 901 calculates the distance from the predetermined origin to the object T and the distance from the predetermined origin to the correction origin (the first surface P1 of the optical path switching element 107) based on the measurement beat signal (step S3). Next, the distance calculation unit 901 subtracts the distance from the predetermined origin to the correction origin from the distance from the predetermined origin to the object T to calculate the distance from the correction origin to the object T (step S4).

[0078] Next, the shape calculation unit 902 calculates the diameter of the object T (hole) based on the distance from the correction origin to the object T, the stage encoder signal, and the rotation angle of the rotation unit 104, which are linked by the distance calculation unit 901 (step S5). At this time, it is also possible to calculate the circularity of the object T (hole).

[0079] On the other hand, if it is determined in step S1 that the measurement is depth measurement, the control device 214 controls the distance measurement unit 111 to control the emission direction of the measurement light from the measurement probe 115 to the second direction D2, causing the measurement light to be emitted. Then, the distance calculation unit 901 of the control device 214 acquires a sampled measurement beat signal from the distance measurement unit 111, and in synchronization with this, acquires a stage encoder signal that determines the XYZ coordinates of the stage mechanism 903 from the stage controller 808, and links the two (step S6).

[0080] Next, similar to step S3, the distance calculation unit 901 calculates the distance from the predetermined origin to the object T and the distance from the predetermined origin to the correction origin (the first surface P1 of the optical path switching element 107) based on the measurement beat signal (step S7). Next, similar to step S4, the distance calculation unit 901 subtracts the distance from the predetermined origin to the correction origin from the distance from the predetermined origin to the object T to calculate the distance from the correction origin to the object T, that is, the depth (step S8). Note that the three-dimensional shape of the object T may be measured based on the calculation results of steps S5 and S8. This completes the distance measurement process.

[0081] <Distance measurement device 1005 according to the fifth embodiment of the present invention> Next, FIG. 16 shows an example of the configuration of a distance measurement device 1005 according to a fifth embodiment of the present invention.

[0082] The distance measurement device 1005 differs from the distance measurement device 1001 (FIG. 1) in the position of the optical path switching element 107. The optical path switching element 107 of the distance measurement device 1001 is locked inside the tip side of the probe tip portion 106. In contrast, the optical path switching element 107 of the distance measurement device 1005 is installed exposed outside the opening on the tip side of the probe tip portion 106.

[0083] This makes it easy to clean the optical path switching element 107 when it becomes soiled with dust or the like. Note that, similar to the distance measurement device 1004 (FIG. 13), AR coatings 1301 and 1302 may be provided on the third surface P3 and the fourth surface P4 of the optical path switching element 107. This makes it possible to suppress stray light inside the optical path switching element 107, which causes noise. Furthermore, a water-repellent coating may be provided on the third surface P3 and the fourth surface P4. This makes it possible to prevent the optical path switching element 107 from becoming soiled.

[0084] <Distance measurement device 1006 according to the sixth embodiment of the present invention> Next, FIG. 17 shows an example of the configuration of a distance measurement device 1006 according to a sixth embodiment of the present invention.

[0085] The distance measurement device 1006 is obtained by adding a cap 1700 that covers the exposed optical path switching element 107 to the distance measurement device 1005 (FIG. 16).

[0086] 18 shows an example configuration of a cap 1700. The cap 1700 has a first optical window 1701, a second optical window 1702, and an absorbing wall 108. The first optical window 1701 is disposed between the third surface P3 of the optical path switching element 107 and the object T, with an inclination angle greater than 0 degrees and less than 90 degrees so that the normal to the first optical window 1701 and the rotation axis of the probe tip portion 106 are not perpendicular to each other. The second optical window 1702 is disposed between the fourth surface P4 of the optical path switching element 107 and the object T, with an inclination angle greater than 0 degrees and less than 90 degrees so that the normal to the second optical window 1702 and the rotation axis of the probe tip portion 106 are not parallel to each other. The absorbing wall 108 is provided at a position facing the fifth surface P5 of the optical path switching element 107.

[0087] It is desirable to provide an AR coating and a water-repellent coating on the outer surface 1800 (FIG. 8) of the first optical window 1701. It is also desirable to provide an AR coating on the inner surface 1801 (FIG. 8) of the first optical window 1701. It is also desirable to chamfer the outer corners of the cap 1700. By chamfering the corners, it is possible to prevent the measurement probe 115 from shifting when the cap 1700 comes into contact with the object T, thereby preventing damage to the measurement probe 115.

[0088] FIG. 19 shows an example of the positional relationship between the first optical window 1701 on the side surface of the cap 1700 and the absorbing wall 108. As shown in FIG.

[0089] The tilt angle θ of the first optical window 1701 will now be described. A portion of the measurement light irradiated laterally from the third surface P3 of the optical path switching element 107 is reflected by the surface of the first optical window 1701. If the first optical window 1701 is made of glass, its reflectance is 4%. In this case, although depending on the sensitivity of the light receiver 209, the reflectance may be too high and the light receiver 209 may become saturated. Therefore, the first optical window 1701 is tilted by an angle θ with respect to the rotation axis of the probe tip 106. The light reflected by the first optical window 1701 returns to the second surface P2 at an angle 2θ and is reflected at an angle 2θ with respect to the rotation axis of the probe tip 106. Therefore, if the angle 2θ is made larger than the collection angle of the lens unit 102, the light reflected by the first optical window 1701 will not be collected by the lens unit 102. Therefore, the tilt angle θ can be determined based on the collection angle of the lens unit 102.

[0090] Note that the measurement light that is irradiated laterally from the third surface P3 of the optical path switching element 107 and passes through the first optical window 1701 experiences an optical axis shift due to the inclination θ and thickness d of the first optical window 1701. The amount of optical axis shift h is expressed by the following equation (4): d=h·sinθ(1-(cosθ / √(n 2 -sin 2 θ)) (4)

[0091] For example, if the thickness d of first optical window 1701 is 200 μm and the angle θ is 2 degrees, the optical axis shift amount h is about 4 μm. Although it depends on the beam diameter of the irradiated measurement light, if the beam diameter of the measurement light is about 100 μm, for example, an optical axis shift amount of about 4 μm does not affect the distance measurement and can be ignored.

[0092] Next, the relationship between the tilt angle θ of the first optical window 1701 and the absorbing wall 108 will be described. The tilt angle of the absorbing wall 108 is tilted only in the −θ direction with respect to the tilt angle θ of the first optical window 1701. Light that is reflected by the first optical window 1701 and incident on the absorbing wall 108 at an angle 2θ is tilted by 4θ when reflected by the absorbing wall 108, thereby preventing light from being collected by the lens unit 102.

[0093] FIG. 20 shows an example of the positional relationship between the second optical window 1702 on the bottom side of the cap 1700 and the absorbing wall 108.

[0094] First, the tilt angle θ of the second optical window 1702 will be described. A portion of the measurement light irradiated in a straight direction from the fourth surface P4 of the optical path switching element 107 is reflected by the surface of the second optical window 1702. If the second optical window 1702 is made of glass, its reflectance is 4%. In this case, although depending on the sensitivity of the light receiver 209, the reflectance may be too high and the light receiver 209 may become saturated. Therefore, the second optical window 1702 is tilted by an angle θ with respect to a line perpendicular to the rotation axis of the probe tip 106. The light reflected by the second optical window 1702 passes through the second surface P2 while being tilted by an angle 2θ. Therefore, if the angle 2θ is larger than the focusing angle of the lens unit 102, the light reflected by the second optical window 1702 will not be focused. Therefore, the tilt angle θ can be determined based on the focusing angle of the lens unit 102.

[0095] The measurement light that is irradiated in a straight direction from the fourth surface P4 of the optical path switching element 107 and passes through the second optical window 1702 experiences an optical axis shift, similar to the case of the first optical window 1701. However, if the optical axis shift h is about 4 μm, it can be ignored as it does not affect the distance measurement.

[0096] Next, we will explain the relationship between the tilt angle θ of the second optical window 1702 and the absorbing wall 108. As in the case of the first optical window 1701, light that is reflected by the second optical window 1702 and enters the absorbing wall 108 at an angle 2θ is tilted by 4θ when reflected by the absorbing wall 108, which prevents light from being collected by the lens unit 102.

[0097] Next, FIG. 21 shows an example of a method for assembling the optical path switching element 107 and the cap 1700 to the probe tip portion 106 in the distance measurement device 1006 (FIG. 17).

[0098] As shown in the figure, first, the optical path switching element 107 is adhered to the holder 2000. Next, the holder 2000 is inserted into and adhered to the probe tip portion 106. Finally, the cap 1700 is adhered to the holder 2000. By assembling the optical path switching element 107 and the cap 1700 to the probe tip portion 106 in this way, the optical path switching element 107 and the cap 1700 having the first optical window 1701, the second optical window 1702, and the absorbing wall 108 can be positioned with high precision.

[0099] The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with or add to the configuration of another embodiment.

[0100] Furthermore, the above-described configurations, functions, processing units, processing means, etc. may be partially or entirely implemented in hardware, for example, by designing them as integrated circuits. Furthermore, the above-described configurations, functions, etc. may be implemented in software by a processor interpreting and executing a program that implements each function. Information such as programs, tables, and files that implement each function can be stored in memory, a storage device such as a hard disk or SSD, or a storage medium such as an IC card, SD card, or DVD. Furthermore, the control lines and information lines shown are those considered necessary for explanation, and do not necessarily represent all control lines and information lines in the product. In reality, it can be assumed that almost all components are interconnected. [Explanation of symbols]

[0101] 1001~1006... distance Measurement device, 101...head, 102...lens unit, 103...first polarization state control unit, 104...rotation unit, 105...second polarization state control unit, 106...probe tip unit, 107...light path switching element, 108...absorbing wall, 109, 110...aperture, 111...distance measurement unit, 113...connection cable, 115...measurement probe, 808...stage controller, 901...distance calculation unit, 902...shape calculation unit, 903...stage mechanism, 1000...shape measurement device, 1300...reflective coating, 1301...AR coating, 1302...AR coating, 1700...cap, 1701...first optical window, 1702...second optical window, 2000...holder

Claims

1. A distance measurement device including a measurement probe, The measurement probe includes: a probe tip portion engaged with the tip of the measurement probe; a rotating part that rotates the locked probe tip; an optical element that emits measurement light to the probe tip, The probe tip has a tip end, an optical path switching element that switches the optical path of the measurement light incident from the optical element; The optical path switching element is a first surface onto which the measurement light incident from the optical element is incident; a second surface that reflects or transmits the measurement light depending on the polarization state of the measurement light incident on the first surface; a third surface that emits the measurement light reflected by the second surface to an object; a fourth surface that emits the measurement light that has passed through the second surface toward the object; a fifth surface corresponding to the third surface, a material of at least a portion of the probe tip disposed at a position facing the fifth surface absorbs the measurement light; The fifth surface is inclined at a predetermined angle with respect to the rotation axis of the probe tip. Distance measuring device.

2. 2. The distance measurement device according to claim 1, the probe tip has an absorption wall at a tip end of the probe tip that absorbs the measurement light, The absorption wall is the absorptance of the measurement light is higher than that of a material of a portion of the probe tip that is disposed at a position facing the fifth surface, disposed at a position facing the fifth surface of the optical path switching element Distance measuring device.

3. 3. The distance measurement device according to claim 2, The angle between the normal to the absorbing wall and the rotation axis of the probe tip is less than 90 degrees. Distance measuring device.

4. 3. The distance measurement device according to claim 2, The probe tip is a first optical window that transmits the measurement light emitted from the third surface of the optical path switching element and emits the measurement light to the object; a second optical window that transmits the measurement light emitted from the fourth surface of the optical path switching element and emits the measurement light to the object, an angle between a normal to the first optical window and a rotation axis of the probe tip portion is less than 90 degrees; The angle between the normal to the second optical window and the rotation axis of the probe tip is 0 degrees or more. Distance measuring device.

5. 5. The distance measurement device according to claim 4, The measurement probe includes: a cap for covering the optical path switching element engaged with the tip of the probe tip portion, The first optical window, the second optical window, and the absorbing wall are provided in the cap. Distance measuring device.

6. 3. The distance measurement device according to claim 2, The absorbing wall is made of an ND filter or a paint that absorbs the measurement light. Distance measuring device.

7. 2. The distance measurement device according to claim 1, The first surface of the optical path switching element is coated with a reflective coating that reflects a part of the measurement light incident from the optical element, and serves as a correction origin in distance measurement. Distance measuring device.

8. 2. The distance measurement device according to claim 1, a distance measurement unit that calculates a distance to the object; The distance measurement unit calculates the distance to the object based on a propagation time of light calculated based on reflected light from the object. Distance measuring device.

9. A distance measurement method using a distance measurement device including a distance measurement unit and a measurement probe, The measurement probe includes: a probe tip portion engaged with the tip of the measurement probe; a rotating part that rotates the locked probe tip; an optical element that emits measurement light to the probe tip, The probe tip has a tip end, an optical path switching element that switches the optical path of the measurement light incident from the optical element; The optical path switching element is a first surface onto which the measurement light incident from the optical element is incident; a second surface that reflects or transmits the measurement light depending on the polarization state of the measurement light incident on the first surface; a third surface that emits the measurement light reflected by the second surface to an object; a fourth surface that emits the measurement light that has passed through the second surface toward the object; a fifth surface opposite to the third surface, a material of at least a portion of the probe tip disposed at a position facing the fifth surface absorbs the measurement light; the fifth surface is inclined at a predetermined angle with respect to the rotation axis of the probe tip portion, switching the optical path of the measurement light incident from the optical element toward the third surface by the optical path switching element; scanning the object with the measurement light emitted from the third surface while rotating the probe tip by the rotating unit; calculating a distance to the object by the distance measurement unit based on the light reflected from the object; A distance measurement method including:

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