Distance measurement device, distance measurement method, and machining device

Abstract

A distance measurement device (42) is configured so as to be provided with: a frequency shift unit (61) that shifts the frequency of interference light between light which is received by a sensor head unit (21) and reflected by a processing surface (3a) and light which is emitted from the sensor head unit (21) to the processing surface (3a) of a workpiece (3); a band limiting unit (62) that limits the frequency band of the interference light which has undergone the frequency shift by the frequency shift unit (61); and a signal conversion unit (63) that converts the interference light, which has undergone the frequency band limitation by the band limiting unit (62), into a signal of a frequency domain. Further, the distance measurement device (42) is provided with: a shift amount changing unit (64) which changes the amount of the frequency shift of the interference light performed by the frequency shift unit (61), if a signal having a signal intensity equal to or greater than a threshold value is not included in the signal of the frequency domain, which has undergone conversion by the signal conversion unit (63); and a distance calculation unit (65) which calculates the distance from the sensor head unit (21) to the processing surface (3a) on the basis of the signal having the signal intensity equal to or greater than the threshold value, if a signal having the signal intensity equal to or greater than the threshold value is included in the signal of the frequency domain, which has undergone conversion by the signal conversion unit (63).

Description

Distance measuring device, ranging method and work equipment

[0001] The present disclosure relates to a distance measuring device, a distance measuring method, and a machining device.

[0002] There is a distance measuring device that irradiates light toward a workpiece surface and then calculates the distance from a sensor head that receives the light reflected from the workpiece surface to the workpiece surface. For example, Patent Document 1 discloses an example of such a distance measuring device that includes a sensor main body connected to the sensor head via an optical fiber. The sensor main body includes an optical interference unit and a distance calculation unit. The optical interference unit detects interference light between the light irradiated from the sensor head and the light received by the sensor head. The distance calculation unit converts the interference light into a frequency domain signal and calculates the distance from the sensor head to the workpiece surface based on the frequency domain signal.

[0003] International Publication No. 2020-070884

[0004] In a typical distance measuring device, for example, when implemented on an FPGA (Field-Programmable Gate Array), the frequency range of the frequency domain signal into which interference light can be converted (hereinafter referred to as the "convertible frequency range") may be limited in order to shorten distance measurement time or reduce memory capacity. The distance measuring device disclosed in Patent Document 1 may also have a limited convertible frequency range. Furthermore, the optical fiber connecting the sensor main body and the sensor head may be broken as the machining head mounting the sensor head moves. When the optical fiber is broken, it is necessary to replace the broken optical fiber with another optical fiber. If the optical path length of the broken optical fiber matches the optical path length of another optical fiber, the distance calculation unit of the distance measuring device can calculate the distance from the sensor head to the machining surface of the workpiece. However, it is rare for the optical path lengths to match, and depending on the difference between the optical path lengths, the frequency of the frequency domain signal may deviate from the convertible frequency range. In such a case, the distance calculation unit is unable to calculate the distance from the sensor head unit to the processing surface of the workpiece.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a distance measuring device that can calculate the distance from the sensor head unit to the processing surface of the workpiece even when a situation occurs in which the frequency of a signal in the frequency domain deviates from the convertible frequency range.

[0006] A distance measuring device according to the present disclosure includes a frequency shifter that shifts the frequency of interference light between light irradiated from a sensor head onto a workpiece surface and light received by the sensor head and reflected from the workpiece surface, a band limiter that limits the frequency band of the interference light after frequency shift by the frequency shifter, and a signal converter that converts the interference light after frequency band limiting by the band limiter into a frequency domain signal. The distance measuring device also includes a shift amount changer that changes the amount of frequency shift of the interference light by the frequency shifter if the frequency domain signal after conversion by the signal converter does not contain a signal whose signal strength is equal to or greater than a threshold, and a distance calculation unit that calculates the distance from the sensor head to the workpiece surface based on the signal whose signal strength is equal to or greater than the threshold if the frequency domain signal after conversion by the signal converter contains a signal whose signal strength is equal to or greater than the threshold.

[0007] According to the present disclosure, even if a situation arises in which the frequency of a signal in the frequency domain deviates from the convertible frequency range, the distance from the sensor head unit to the processing surface of the workpiece can be calculated.

[0008] 1 is a configuration diagram showing a machining device according to a first embodiment. FIG. 2 is a configuration diagram showing a sensor unit 20 of the machining device according to the first embodiment. FIG. 3 is an explanatory diagram showing a time waveform of frequency swept light. FIG. 4 is a configuration diagram showing a distance measuring device 42 according to the first embodiment. FIG. 5 is a hardware configuration diagram showing hardware of the distance measuring device 42 according to the first embodiment. FIG. 6 is a hardware configuration diagram of a computer when the distance measuring device 42 is realized by software, firmware, or the like. FIG. 7 is a flowchart showing a distance measuring method, which is a processing procedure of the distance measuring device 42. FIG. 8 is an explanatory diagram showing that the reflected light spectrum, which is a peak signal, is included in a convertible frequency band. FIG. 9 is an explanatory diagram showing an example of a reference workpiece. FIG. 10 is an explanatory diagram showing a state in which the reflected light spectrum comes to be included in a convertible frequency band by changing the frequency shift amount. FIG. 11 is a configuration diagram showing a machining device according to a second embodiment. FIG. 12 is a configuration diagram showing a sensor unit 20 of the machining device according to the second embodiment. FIG. 13 is an explanatory diagram showing an example of a reference workpiece having oil attached to its machining surface 3a. FIG. 14 is an explanatory diagram showing two peak signals output from a shift amount changing unit 64.

[0009] In order to explain the present disclosure in more detail, embodiments of the present disclosure will be described below with reference to the accompanying drawings.

[0010] Embodiment 1. Figure 1 is a configuration diagram showing a machining device according to embodiment 1. The machining device shown in Figure 1 includes a table 1, a vice 2, a processing unit 10, a sensor unit 20, and a control unit 50. The table 1 is a platform on which a workpiece 3 to be processed is placed. The vice 2 is a fixture that fixes the workpiece 3 so that it does not move when the workpiece 3 is processed. The workpiece 3 corresponds to a metal or the like whose processing surface 3a is processed by the processing unit 10.

[0011] The processing unit 10 includes a processing head 11, a processing tool 12, a head drive unit 13, and a cutting oil nozzle 14. The processing unit 10 supplies cutting oil to the processing surface 3a of the workpiece 3, and cuts the processing surface 3a of the workpiece 3.

[0012] The machining head 11 includes a head main body 11a and a spindle 11b. The head main body 11a is a metal structure that supports the spindle 11b and the sensor head 21. The spindle 11b incorporates a chuck device (not shown) that detachably holds the machining tool 12. The spindle 11b is a metal shaft-shaped component that rotates while holding the machining tool 12. The outer peripheral surface 11c is the outer peripheral surface that faces the table 1 among multiple outer peripheral surfaces of the head main body 11a.

[0013] The machining tool 12 is a metalworking cutting tool such as a milling cutter, end mill, drill, or tap. The machining tool 12 cuts the machining surface 3a of the workpiece 3 by rotating. The head driving unit 13 is a driving mechanism that changes the position of the head main body 11a relative to the machining surface 3a in accordance with a control signal output from the control unit 50. The direction in which the position of the head main body 11a is changed by the head driving unit 13 is the x-axis direction, y-axis direction, or z-axis direction shown in FIG. 1. The cutting oil nozzle 14 is a nozzle that applies cutting oil to the machining surface 3a of the workpiece 3 when a cutting oil supply command is received from the control unit 50.

[0014] The sensor unit 20 includes a sensor head unit 21, a sensor body unit 22, and an optical transmission unit 23. The sensor unit 20 calculates the distance from the tip 21a of the sensor head unit 21 to the processing surface 3a of the workpiece 3.

[0015] The sensor head 21 is attached to the outer peripheral surface 11c of the head main body 11a. The sensor head 21 irradiates the work surface 3a with irradiation light output from the sensor main body 22 and receives reflected light, which is the irradiation light reflected by the work surface 3a. The sensor head 21 outputs the reflected light to the sensor main body 22 via the optical transmission unit 23. Here, the sensor head 21 irradiates the work surface 3a with irradiation light and receives reflected light, which is the irradiation light reflected by the work surface 3a. However, this is merely an example, and the sensor head 21 may also irradiate light toward the surface of a reference workpiece as the work surface 3a of the workpiece 3 and receive reflected light, which is the irradiation light reflected by the surface of the reference workpiece. The reference workpiece is, for example, a metal or the like having a desired shape after cutting the workpiece 3.

[0016] The sensor main body 22 outputs the irradiated light to the sensor head 21 via the optical transmission unit 23. The sensor main body 22 acquires the reflected light from the sensor head 21 via the optical transmission unit 23. The sensor main body 22 detects the interference light between the irradiated light and the reflected light, and calculates the distance from the tip 21 a of the sensor head 21 to the processing surface 3 a based on the interference light. The sensor main body 22 outputs the distance from the tip 21 a of the sensor head 21 to the processing surface 3 a to the control unit 50.

[0017] The optical transmission unit 23 is realized by, for example, an optical fiber. The optical transmission unit 23 is a transmission path for light traveling from the sensor main body 22 to the sensor head 21 and for light traveling from the sensor head 21 to the sensor main body 22. The machining device shown in FIG. 1 is provided with the optical transmission unit 23. However, this is merely an example, and the machining device may not be provided with the optical transmission unit 23. In this case, light is transmitted between the sensor head 21 and the sensor main body 22 via space.

[0018] The control unit 50 outputs a control signal indicating the movement position of the head main body 11 a to the head drive unit 13 , and outputs a cutting oil supply command to the cutting oil nozzle 14 .

[0019] 2 is a configuration diagram showing the sensor unit 20 of the machining device according to embodiment 1. The sensor unit 20 includes a sensor head unit 21, a sensor main body unit 22, and an optical transmission unit 23, and the sensor head unit 21 includes a light-collecting optical element 35. The sensor main body unit 22 includes a frequency sweep optical output unit 31, an optical branching unit 32, an optical interference unit 36, an analog-to-digital converter (hereinafter referred to as "A / D converter") 39, an A / D converter 40, a register 41, and a distance measuring device 42.

[0020] The frequency swept light output unit 31 includes a frequency swept light source 31a that outputs frequency swept light whose frequency changes over time. The frequency swept light output unit 31 outputs the frequency swept light to the optical branching unit 32. The frequency swept light output unit 31 outputs a trigger signal indicating the timing at which the frequency swept light is output, or an amplitude signal indicating the amplitude of the frequency swept light, to the A / D converter 40.

[0021] 3 is an explanatory diagram showing the time waveform of the frequency swept light. The frequency of the frequency swept light is changed over time from the lowest frequency f ｍｉｎ to the highest frequency f ｍａｘ The frequency of the frequency-swept light is the light whose frequency changes from the highest frequency f ｍａｘ Once the frequency reaches the lowest frequency f ｍｉｎ Then, the frequency returns to the lowest frequency f ｍｉｎ to the highest frequency f ｍａｘ The frequency of the frequency-swept light varies from 100 to 1200 kHz. The frequency-swept light is sometimes called chirp signal light. In FIG. 3, the horizontal axis represents time and the vertical axis represents frequency. The solid line represents the reference light, and the dashed line represents the reflected light. The interference light is light having a frequency that is the difference between the frequency of the reference light and the frequency of the reflected light.

[0022] The optical branching unit 32 includes an optical coupler 33 and a circulator 34. The optical coupler 33 is an optical branching element that branches the frequency swept light output from the frequency swept light output unit 31 into reference light and irradiation light. The optical coupler 33 outputs the reference light to an optical interferometer 37 and outputs the irradiation light to the circulator 34.

[0023] The circulator 34 outputs the irradiation light output from the optical coupler 33 to the condensing optical element 35 of the sensor head unit 21 via the optical transmission unit 23. The circulator 34 outputs the reflected light output from the condensing optical element 35 to the optical interferometer 37.

[0024] The focusing optical element 35 focuses the irradiation light output from the circulator 34 onto the processing surface 3a. Specifically, the focusing optical element 35 includes two aspherical lenses. Of the two aspherical lenses, the aspherical lens on the circulator 34 side converts the irradiation light output from the circulator 34 into parallel light. The aspherical lens on the processing surface 3a side focuses the parallel light onto the processing surface 3a. The focusing optical element 35 also receives reflected light, which is the irradiation light reflected by the processing surface 3a, and outputs the reflected light to the circulator 34 via the optical transmission unit 23.

[0025] The optical interference unit 36 ​​includes an optical interferometer 37 and a photodetector 38. The optical interference unit 36 ​​generates interference light between the reference light and the reflected light output from the optical branching unit 32. The optical interference unit 36 ​​converts the interference light into an electrical signal and outputs the electrical signal to an A / D converter 39.

[0026] The optical interferometer 37 generates interference light between the reference light output from the optical coupler 33 and the reflected light output from the circulator 34, and outputs the interference light to the photodetector 38. The photodetector 38 detects the interference light output from the optical interferometer 37 and converts the interference light into an electrical signal. The photodetector 38 outputs the electrical signal to the A / D converter 39.

[0027] The A / D converter 39 converts the electrical signal output from the photodetector 38 from an analog signal to a digital signal and outputs the digital signal to the distance measuring device 42. The A / D converter 40 obtains a trigger signal indicating the timing at which the frequency swept light is output or an amplitude signal indicating the amplitude of the frequency swept light from the frequency swept light output unit 31. The A / D converter 40 converts the trigger signal or the amplitude signal from an analog signal to a digital signal and outputs the digital signal to the distance measuring device 42.

[0028] The register 41 is a recording medium that records, for example, the amount of frequency shift and the refractive index of cutting oil. The register 41 records the amount of frequency shift for each focal position of light irradiated from the sensor head unit 21 onto the machining surface 3a. The amount of frequency shift is a value determined by the optical path length of the optical fiber that realizes the optical transmission unit 23. The refractive index of cutting oil is a value determined by the type of cutting oil supplied from the cutting oil nozzle 14 to the machining surface 3a, the concentration of the cutting oil, the ambient temperature of the machining device, etc.

[0029] The distance measuring device 42 is a device that calculates the distance from the tip 21a of the sensor head unit 21 to the processing surface 3a of the workpiece 3. Fig. 4 is a configuration diagram showing the distance measuring device 42 according to embodiment 1. Fig. 5 is a hardware configuration diagram showing the hardware of the distance measuring device 42 according to embodiment 1. The distance measuring device 42 includes a frequency shift unit 61, a band limiting unit 62, a signal converting unit 63, a shift amount changing unit 64, and a distance calculating unit 65.

[0030] The frequency shift unit 61 is realized by, for example, a frequency shift circuit 71 shown in FIG. 5 . The frequency shift unit 61 acquires a digital signal related to the interference light (hereinafter referred to as “interference light data”) from the A / D converter 39, and acquires a digital signal related to the trigger signal (hereinafter referred to as “trigger data”) or a digital signal related to the amplitude signal (hereinafter referred to as “amplitude data”) from the A / D converter 40. For example, if the frequency shift unit 61 acquires the interference light data after acquiring the trigger data, it shifts the frequency of the interference light data by the frequency shift amount recorded in the register 41. The frequency shift unit 61 outputs the frequency-shifted interference light data to the band limiting unit 62.

[0031] The band limiting unit 62 is realized by, for example, a band limiting circuit 72 shown in FIG. 5 . The band limiting unit 62 includes, for example, a low-pass filter, a band-pass filter, or a high-pass filter. The band limiting unit 62 acquires the frequency-shifted interference light data from the frequency shifter 61. The band limiting unit 62 limits the frequency band of the frequency-shifted interference light data. The band limiting unit 62 outputs the frequency-band-limited interference light data to the signal converter 63.

[0032] The signal conversion unit 63 is realized by, for example, the signal conversion circuit 73 shown in FIG. 5 . The signal conversion unit 63 acquires the interference light data after frequency band limitation from the band limitation unit 62. The signal conversion unit 63 converts the interference light data after frequency band limitation into a frequency domain signal by, for example, FFT (Fast Fourier Transformation). The signal conversion unit 63 outputs the frequency domain signal to the shift amount change unit 64.

[0033] The shift amount changing unit 64 is realized by, for example, the shift amount changing circuit 74 shown in FIG. 5 . The shift amount changing unit 64 acquires the frequency domain signal from the signal converting unit 63. If the frequency domain signal does not contain a signal whose signal strength is equal to or greater than a threshold (hereinafter referred to as a “peak signal”), the shift amount changing unit 64 changes the amount of frequency shift performed by the frequency shifting unit 61. If the frequency domain signal contains a peak signal, the shift amount changing unit 64 outputs the peak signal to the distance calculating unit 65.

[0034] The distance calculation unit 65 is realized by, for example, a distance calculation circuit 75 shown in Fig. 5. Since a peak signal is included in the frequency domain signal, when the peak signal is output from the shift amount change unit 64, the distance calculation unit 65 calculates the distance from the tip 21a of the sensor head unit 21 to the processing surface 3a based on the peak signal. The distance calculation unit 65 outputs the calculated distance to the shape calculation unit 66.

[0035] The shape calculation unit 66 is built in, for example, the control unit 50. The shape calculation unit 66 acquires the distance calculated by the distance calculation unit 65 every time the position of the sensor head unit 21 is moved. The shape calculation unit 66 calculates the shape of the workpiece 3 based on a plurality of distances. Here, the shape calculation unit 66 is built in the control unit 50. However, this is merely an example, and the shape calculation unit 66 may be built in, for example, the distance measurement device 42.

[0036] 4, it is assumed that each of the components of the distance measuring device 42, namely, the frequency shift unit 61, the band limiting unit 62, the signal converting unit 63, the shift amount changing unit 64, and the distance calculating unit 65, is realized by dedicated hardware as shown in FIG. 5. That is, it is assumed that the distance measuring device 42 is realized by a frequency shift circuit 71, a band limiting circuit 72, a signal converting circuit 73, a shift amount changing circuit 74, and a distance calculating circuit 75. Each of the frequency shift circuit 71, the band limiting circuit 72, the signal converting circuit 73, the shift amount changing circuit 74, and the distance calculating circuit 75 corresponds to, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination thereof.

[0037] The components of the distance measuring device 42 are not limited to those realized by dedicated hardware, and the distance measuring device 42 may be realized by software, firmware, or a combination of software and firmware. Software or firmware is stored as a program in the memory of a computer. A computer refers to hardware that executes a program, and includes, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), a central processing unit, a processing unit, an arithmetic unit, a microprocessor, a microcomputer, a processor, or a DSP (Digital Signal Processor).

[0038] 6 is a hardware configuration diagram of a computer when the distance measuring device 42 is realized by software, firmware, etc. When the distance measuring device 42 is realized by software, firmware, etc., a program for causing the computer to execute the respective processing procedures of the frequency shifter 61, the band limiter 62, the signal converter 63, the shift amount changer 64, and the distance calculator 65 is stored in a memory 81. Then, a processor 82 of the computer executes the program stored in the memory 81.

[0039] 5 shows an example in which each of the components of the distance measuring device 42 is realized by dedicated hardware, while Fig. 6 shows an example in which the distance measuring device 42 is realized by software, firmware, etc. However, this is merely an example, and some of the components in the distance measuring device 42 may be realized by dedicated hardware, and the remaining components may be realized by software, firmware, etc.

[0040] Next, the operation of the machining device shown in Fig. 1 will be described. First, the operation of the machining device to calculate the shape of the workpiece 3 when the optical fiber that realizes the optical transmission section 23 is not broken will be described. In the machining device shown in Fig. 1, the workpiece 3 is assumed to be an object that has already been machined by the machining device. However, this is merely an example, and the workpiece 3 may be an object that has not yet been machined by the machining device, or an object that is in the middle of being machined.

[0041] The control unit 50 outputs a control signal indicating the movement position of the head main body 11a to the head driving unit 13. For simplicity of explanation, it is assumed here that the control unit 50 does not output a cutting oil supply command to the cutting oil nozzle 14. The head driving unit 13 changes the position of the head main body 11a relative to the machining surface 3a in accordance with the control signal output from the control unit 50.

[0042] 3 to the optical branching unit 32. The frequency sweep light output unit 31 outputs, to the A / D converter 40, a trigger signal indicating the timing at which the frequency sweep light is output, or an amplitude signal indicating the amplitude of the frequency sweep light, as frequency sweep light whose frequency changes over time every time the position of the head main body 11a relative to the processing surface 3a changes.

[0043] The optical coupler 33 acquires the frequency swept light from the frequency swept light output unit 31. The optical coupler 33 splits the frequency swept light into reference light and irradiation light. The optical coupler 33 outputs the reference light to the optical interferometer 37 and outputs the irradiation light to the circulator 34. The circulator 34 outputs the irradiation light output from the optical coupler 33 to the focusing optical element 35 via the optical transmission unit 23.

[0044] The focusing optical element 35 focuses the irradiation light output from the circulator 34 onto the processing surface 3 a. The focusing optical element 35 receives reflected light, which is the irradiation light reflected by the processing surface 3 a, and outputs the reflected light to the circulator 34 via the optical transmission unit 23. The circulator 34 outputs the reflected light output from the focusing optical element 35 to an optical interferometer 37.

[0045] The optical interferometer 37 receives the reference light from the optical coupler 33 and receives the reflected light from the circulator 34. As shown in FIG. 3 , the optical interferometer 37 generates light having a frequency difference between the frequency of the reference light and the frequency of the reflected light as interference light between the reference light and the reflected light. The optical interferometer 37 outputs the interference light to the photodetector 38. The photodetector 38 detects the interference light output from the optical interferometer 37 and converts the interference light into an electrical signal. The photodetector 38 outputs the electrical signal to the A / D converter 39.

[0046] The A / D converter 39 acquires an electrical signal indicative of the interference light from the photodetector 38. The A / D converter 39 converts the electrical signal indicative of the interference light from an analog signal to a digital signal and outputs the digital signal to the distance measuring device 42. The A / D converter 40 acquires, from the frequency swept light output unit 31, a trigger signal indicative of the timing at which the frequency swept light is output or an amplitude signal indicative of the amplitude of the frequency swept light. If the A / D converter 40 acquires the trigger signal, it converts the trigger signal from an analog signal to a digital signal and outputs the digital signal to the distance measuring device 42. If the A / D converter 40 acquires the amplitude signal, it converts the amplitude signal from an analog signal to a digital signal and outputs the digital signal to the distance measuring device 42.

[0047] FIG. 7 is a flowchart showing a distance measurement method, which is a processing procedure of the distance measurement device 42. The register 41 stores a frequency shift amount corresponding to the optical path length of the uncut optical transmission section 23. This frequency shift amount is a frequency shift amount used by the shift amount change unit 64 to shift the frequency of the interference light data so that a peak signal, which is a signal with a signal intensity equal to or greater than a threshold, among the frequency domain signals related to the interference light data after frequency band limitation by the band limiting unit 62 is included in a frequency band in which the peak signal can be detected. In other words, the register 41 stores a frequency shift amount such that the reflected light spectrum, which is the peak signal, is included in a convertible frequency band, as shown in FIG. 8. The convertible frequency band is a frequency band limited by the band limiting unit 62. FIG. 8 is an explanatory diagram showing that the reflected light spectrum, which is the peak signal, is included in the convertible frequency band. In FIG. 8, the horizontal axis represents frequency, and the vertical axis represents signal intensity.

[0048] The frequency shift unit 61 acquires from the register 41 a frequency shift amount corresponding to the focal position of light irradiated onto the processing surface 3 a from the sensor head unit 21. The frequency shift unit 61 acquires interference light data, which is a digital signal related to the interference light, from the A / D converter 39, and acquires trigger data, which is a digital signal related to the trigger signal, or amplitude data, which is a digital signal related to the amplitude signal, from the A / D converter 40. If the frequency shift unit 61 acquires the interference light data after acquiring the trigger data, it shifts the frequency of the interference light data by the frequency shift amount (step ST1 in FIG. 7 ).

[0049] When the frequency shifter 61 acquires the amplitude data, the frequency shifter 61 determines whether the frequency of the frequency sweep light is equal to or lower than the minimum frequency f based on the amplitude of the frequency sweep light indicated by the amplitude data. ｍｉｎ The frequency shifter 61 detects the timing when the frequency of the frequency sweep light returns to the lowest frequency f ｍｉｎ After detecting the timing when the frequency of the optical fiber 1 returns to the reference frequency, the frequency shifter 61 acquires the interference light data and shifts the frequency of the interference light data by the frequency shift amount (step ST1 in FIG. 7). The frequency shifter 61 outputs the frequency-shifted interference light data to the band limiter 62.

[0050] The band limiting unit 62 acquires the frequency-shifted interference light data from the frequency shifting unit 61. The band limiting unit 62 limits the frequency band of the frequency-shifted interference light data (step ST2 in FIG. 7 ). The frequency band limited by the band limiting unit 62 corresponds to the convertible frequency band shown in FIG. 8 . The band limiting unit 62 outputs the frequency-band-limited interference light data to the signal converting unit 63.

[0051] The signal conversion unit 63 acquires the interference light data after frequency band limitation from the band limitation unit 62. The signal conversion unit 63 converts the interference light data after frequency band limitation into a frequency domain signal by, for example, performing FFT on the interference light data (step ST3 in FIG. 7 ). The signal conversion unit 63 outputs the frequency domain signal to the shift amount change unit 64.

[0052] The shift amount change unit 64 acquires the frequency domain signal from the signal conversion unit 63. The shift amount change unit 64 determines whether the frequency domain signal includes a peak signal, which is a signal whose signal strength is equal to or greater than a threshold. When the optical transmission unit 23 is not disconnected, the frequency shift unit 61 shifts the frequency of the interference light data by the frequency shift amount recorded in the register 41. Therefore, as shown in FIG. 8 , the peak signal is included in the convertible frequency band. Therefore, when the optical transmission unit 23 is not disconnected, the peak signal is included in the frequency domain signal. If the peak signal is included in the frequency domain signal (step ST4: YES in FIG. 7 ), the shift amount change unit 64 outputs the peak signal to the distance calculation unit 65.

[0053] When a peak signal is output from the shift amount change unit 64, the distance calculation unit 65 calculates the distance from the tip 21a of the sensor head unit 21 to the machining surface 3a based on the peak signal (step ST5 in FIG. 7). The distance from the tip 21a of the sensor head unit 21 to the machining surface 3a can be obtained from the frequency of the peak signal. The process of calculating the distance from the frequency of the peak signal is a well-known technique, so a detailed description will be omitted. The distance calculation unit 65 outputs the calculated distance to the shape calculation unit 66.

[0054] If the position of the head main body 11a is changed by the control unit 50 outputting a control signal indicating the movement position of the head main body 11a to the head driving unit 13 (step ST6 in FIG. 7: YES), the processing of steps ST1 to ST5 is repeated. If the calculation of the distance is completed and the position of the head main body 11a is not changed (step ST6 in FIG. 7: NO), the machining device ends the series of processes.

[0055] The shape calculation unit 66 acquires the distance calculated by the distance calculation unit 65 each time the position of the sensor head unit 21 is moved. The shape calculation unit 66 calculates the shape of the workpiece 3 based on the multiple distances. The process of calculating the shape of the workpiece 3 based on the multiple distances is a known technique, and therefore a detailed description thereof will be omitted.

[0056] Next, the operation of the machining device when the optical fiber that realizes the optical transmission section 23 is broken and replaced with another optical fiber will be described. In this case, a reference workpiece is placed on the table 1 instead of the workpiece 3. Figure 9 is an explanatory diagram showing an example of the reference workpiece.

[0057] The control unit 50 outputs a control signal indicating the movement position of the head main body 11a to the head driving unit 13. The head driving unit 13 changes the position of the head main body 11a relative to the processing surface 3a in accordance with the control signal output from the control unit 50.

[0058] 3 to the optical branching unit 32. The frequency sweep light output unit 31 outputs, to the A / D converter 40, a trigger signal indicating the timing at which the frequency sweep light is output, or an amplitude signal indicating the amplitude of the frequency sweep light, as frequency sweep light whose frequency changes over time every time the position of the head main body 11a relative to the processing surface 3a changes.

[0059] The optical coupler 33 acquires the frequency swept light from the frequency swept light output unit 31. The optical coupler 33 splits the frequency swept light into reference light and irradiation light. The optical coupler 33 outputs the reference light to the optical interferometer 37 and outputs the irradiation light to the circulator 34. The circulator 34 outputs the irradiation light output from the optical coupler 33 to the focusing optical element 35 via the optical transmission unit 23.

[0060] The focusing optical element 35 focuses the irradiation light output from the circulator 34 onto the processing surface 3 a. The focusing optical element 35 receives reflected light, which is the irradiation light reflected by the processing surface 3 a, and outputs the reflected light to the circulator 34 via the optical transmission unit 23. The circulator 34 outputs the reflected light output from the focusing optical element 35 to an optical interferometer 37.

[0061] The optical interferometer 37 receives the reference light from the optical coupler 33 and receives the reflected light from the circulator 34. As shown in FIG. 3 , the optical interferometer 37 generates light having a frequency difference between the frequency of the reference light and the frequency of the reflected light as interference light between the reference light and the reflected light. The optical interferometer 37 outputs the interference light to the photodetector 38. The photodetector 38 detects the interference light output from the optical interferometer 37 and converts the interference light into an electrical signal. The photodetector 38 outputs the electrical signal to the A / D converter 39.

[0062] The A / D converter 39 acquires an electrical signal indicative of the interference light from the photodetector 38. The A / D converter 39 converts the electrical signal indicative of the interference light from an analog signal to a digital signal and outputs the digital signal to the distance measuring device 42. The A / D converter 40 acquires, from the frequency swept light output unit 31, a trigger signal indicative of the timing at which the frequency swept light is output or an amplitude signal indicative of the amplitude of the frequency swept light. If the A / D converter 40 acquires the trigger signal, it converts the trigger signal from an analog signal to a digital signal and outputs the digital signal to the distance measuring device 42. If the A / D converter 40 acquires the amplitude signal, it converts the amplitude signal from an analog signal to a digital signal and outputs the digital signal to the distance measuring device 42.

[0063] The frequency shifter 61 of the distance measuring device 42 obtains from the register 41 a frequency shift amount corresponding to the focal position of light irradiated onto the processing surface 3 a from the sensor head unit 21. The frequency shifter 61 obtains interference light data, which is a digital signal related to the interference light, from the A / D converter 39, and obtains trigger data, which is a digital signal related to the trigger signal, or amplitude data, which is a digital signal related to the amplitude signal, from the A / D converter 40. If the frequency shifter 61 obtains the interference light data after obtaining the trigger data, it shifts the frequency of the interference light data by the frequency shift amount (step ST1 in FIG. 7 ).

[0064] When the frequency shifter 61 acquires the amplitude data, the frequency shifter 61 determines whether the frequency of the frequency sweep light is equal to or lower than the minimum frequency f based on the amplitude of the frequency sweep light indicated by the amplitude data. ｍｉｎ The frequency shifter 61 detects the timing when the frequency of the frequency sweep light returns to the lowest frequency fｍｉｎ After detecting the timing when the frequency of the optical fiber 1 returns to the reference frequency, the frequency shifter 61 acquires the interference light data and shifts the frequency of the interference light data by the frequency shift amount (step ST1 in FIG. 7). The frequency shifter 61 outputs the frequency-shifted interference light data to the band limiter 62.

[0065] The band limiting unit 62 acquires the frequency-shifted interference light data from the frequency shifting unit 61. The band limiting unit 62 limits the frequency band of the frequency-shifted interference light data (step ST2 in FIG. 7 ). The band limiting unit 62 outputs the frequency-band-limited interference light data to the signal converting unit 63.

[0066] The signal conversion unit 63 acquires the interference light data after frequency band limitation from the band limitation unit 62. The signal conversion unit 63 converts the interference light data after frequency band limitation into a frequency domain signal by, for example, performing FFT on the interference light data (step ST3 in FIG. 7 ). The signal conversion unit 63 outputs the frequency domain signal to the shift amount change unit 64.

[0067] The shift amount change unit 64 acquires a frequency domain signal from the signal conversion unit 63. The shift amount change unit 64 determines whether the frequency domain signal contains a peak signal, which is a signal whose signal strength is equal to or greater than a threshold. The frequency shift amount recorded in the register 41 is the shift amount corresponding to the undisconnected optical transmission unit 23. Therefore, if the difference between the optical path length of the disconnected optical transmission unit 23 and the optical path length of the replaced optical fiber is large, the peak signal may not be included in the convertible frequency band. Therefore, if the disconnected optical transmission unit 23 is replaced with another optical transmission unit 23, the peak signal may no longer be included in the frequency domain signal. If the frequency domain signal does not contain a peak signal (step ST4 in FIG. 7: NO), the shift amount change unit 64 outputs a frequency shift amount change command to the frequency shift unit 61 (step ST7 in FIG. 7).

[0068] When the frequency shift unit 61 receives a command to change the frequency shift amount from the shift amount changing unit 64, it changes the frequency shift amount and shifts the frequency of the interference light data by the changed frequency shift amount (step ST8 in FIG. 7 ). The changed frequency shift amount is obtained by adding or subtracting, for example, a preset frequency from the frequency shift amount recorded in the register 41. The frequency shift unit 61 records the changed frequency shift amount in the register 41. The frequency shift unit 61 outputs the frequency-shifted interference light data to the band limiting unit 62.

[0069] The band limiting unit 62 acquires the frequency-shifted interference light data from the frequency shifting unit 61. The band limiting unit 62 limits the frequency band of the frequency-shifted interference light data (step ST2 in FIG. 7 ). The band limiting unit 62 outputs the frequency-band-limited interference light data to the signal converting unit 63.

[0070] The signal conversion unit 63 acquires the interference light data after frequency band limitation from the band limitation unit 62. The signal conversion unit 63 converts the interference light data after frequency band limitation into a frequency domain signal by, for example, performing FFT on the interference light data (step ST3 in FIG. 7 ). The signal conversion unit 63 outputs the frequency domain signal to the shift amount change unit 64.

[0071] The shift amount change unit 64 acquires a frequency domain signal from the signal conversion unit 63. The shift amount change unit 64 determines whether the frequency domain signal contains a peak signal, which is a signal whose signal strength is equal to or greater than a threshold. If the frequency domain signal does not contain a peak signal (step ST4 in FIG. 7 : NO), the shift amount change unit 64 outputs a frequency shift amount change command to the frequency shift unit 61, thereby further changing the frequency shift amount by the frequency shift unit 61 (step ST7 in FIG. 7 ). Upon receiving the frequency shift amount change command from the shift amount change unit 64, the frequency shift unit 61 further changes the frequency shift amount and shifts the frequency of the interference light data by the changed frequency shift amount (step ST8 in FIG. 7 ). The frequency shift unit 61 records the changed frequency shift amount in the register 41. The frequency shift unit 61 outputs the frequency-shifted interference light data to the band limiting unit 62.

[0072] The processing of steps ST2 to ST4, ST7, and ST8 is repeated until a peak signal is included in the frequency domain signal. As shown in FIG. 10 , if a peak signal is included in the frequency domain signal, the workpiece 3 is placed on the table 1 instead of the reference workpiece. FIG. 10 is an explanatory diagram showing how the reflected light spectrum is brought into the convertible frequency band by changing the frequency shift amount. In FIG. 10 , the horizontal axis represents frequency and the vertical axis represents signal intensity. After the workpiece 3 is placed on the table 1, the machining device calculates the shape of the workpiece 3 in the same manner as when the optical fiber realizing the optical transmission unit 23 is not broken. However, the frequency shift amount used by the frequency shift unit 61 is the frequency shift amount when a peak signal is included in the frequency domain signal.

[0073] Here, when the optical fiber that realizes the optical transmission unit 23 is broken and replaced with another optical fiber, a reference work is placed on the table 1 instead of the workpiece 3, and if a peak signal is subsequently included in the frequency domain signal, the workpiece 3 is placed on the table 1 instead of the reference work. However, this is merely an example, and even if the optical fiber is broken and replaced with another optical fiber, the processing of steps ST1 to ST8 in FIG. 7 may be performed with the workpiece 3 placed on the table 1.

[0074] In the first embodiment described above, the distance measuring device 42 is configured to include a frequency shifter 61 that shifts the frequency of interference light between light irradiated from the sensor head 21 onto the processing surface 3 a of the workpiece 3 and light received by the sensor head 21 and reflected by the processing surface 3 a, a band limiting unit 62 that limits the frequency band of the interference light after frequency shift by the frequency shifter 61, and a signal converter 63 that converts the interference light after frequency band limiting by the band limiting unit 62 into a frequency domain signal. The distance measuring device 42 also includes a shift amount changer 64 that changes the amount of shift of the frequency of the interference light by the frequency shifter 61 if the frequency domain signal after conversion by the signal converter 63 does not contain a signal whose signal strength is equal to or greater than a threshold, and a distance calculator 65 that calculates the distance from the sensor head 21 to the processing surface 3 a based on the signal whose signal strength is equal to or greater than the threshold if the frequency domain signal after conversion by the signal converter 63 contains a signal whose signal strength is equal to or greater than a threshold. Therefore, the distance measuring device 42 can calculate the distance from the sensor head portion 21 to the processing surface 3a of the workpiece 3 even if a situation occurs in which the frequency of the signal in the frequency domain deviates from the convertible frequency range.

[0075] In the distance measuring device 42 shown in FIG. 1 , when the frequency shifter 61 acquires interference light data from the A / D converter 39, it shifts the frequency of the interference light data by the frequency shift amount. When the frequency shifter 61 acquires the interference light data from the A / D converter 39 before shifting the frequency of the interference light data, the frequency shifter 61 may perform nonlinearity compensation of the frequency sweep light source 31 a on the interference light data based on the trigger data or amplitude data output from the A / D converter 40. The nonlinearity compensation process itself is a known technique, and therefore a detailed description thereof will be omitted. Furthermore, the frequency shifter 61 may perform downsampling, such as thinning out the signal by decimation, on the interference light data. The downsampling process itself is a known technique, and therefore a detailed description thereof will be omitted.

[0076] Second Embodiment In a second embodiment, a distance measuring device 42 including a distance calculation unit 67 that calculates the distance from the sensor head unit 21 to the processing surface 3a on which oil is attached will be described.

[0077] The configuration of the machining device other than the distance measuring device 42 is the same as that of the machining device shown in Figure 1. Figure 11 is a configuration diagram showing the distance measuring device 42 according to embodiment 2. In Figure 11, the same reference numerals as in Figure 4 indicate the same or corresponding parts, and detailed explanations will be omitted. Figure 12 is a hardware configuration diagram showing the hardware of the distance measuring device 42 according to embodiment 2. In Figure 12, the same reference numerals as in Figure 5 indicate the same or corresponding parts, and detailed explanations will be omitted. The distance measuring device 42 includes a frequency shift unit 61, a band limiting unit 62, a signal converting unit 63, a shift amount changing unit 64, and a distance calculating unit 67.

[0078] The distance calculation unit 67 is realized, for example, by a distance calculation circuit 77 shown in FIG. 12 . When a peak signal is included in the frequency domain signal and a peak signal is output from the shift amount change unit 64, the distance calculation unit 67 calculates the distance from the sensor head unit 21 to the machining surface 3 a based on the peak signal, similar to the distance calculation unit 65 shown in FIG. 4 . When two peak signals are included in the frequency domain signal converted by the signal conversion unit 63 because oil is attached to the machining surface 3 a, the distance calculation unit 67 calculates the oil film thickness attached to the machining surface 3 a and the distance from the sensor head unit 21 to the oil surface based on the two peak signals. The distance calculation unit 67 calculates the distance from the sensor head unit 21 to the machining surface 3 a from the film thickness and the distance to the oil surface. The distance calculation unit 67 outputs the calculated distance to the shape calculation unit 66.

[0079] 11, it is assumed that each of the components of the distance measuring device 42, namely, the frequency shifter 61, the band limiter 62, the signal converter 63, the shift amount changer 64, and the distance calculator 67, is realized by dedicated hardware as shown in Fig. 12. That is, it is assumed that the distance measuring device 42 is realized by a frequency shifter circuit 71, a band limiter circuit 72, a signal converter circuit 73, a shift amount changer circuit 74, and a distance calculator circuit 77. Each of the frequency shifter circuit 71, the band limiter circuit 72, the signal converter circuit 73, the shift amount changer circuit 74, and the distance calculator circuit 77 corresponds to, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC, an FPGA, or a combination thereof.

[0080] The components of the distance measuring device 42 are not limited to those realized by dedicated hardware, and the distance measuring device 42 may be realized by software, firmware, or a combination of software and firmware. When the distance measuring device 42 is realized by software, firmware, or the like, a program for causing a computer to execute the respective processing procedures of the frequency shifter 61, the band limiter 62, the signal converter 63, the shift amount changer 64, and the distance calculator 67 is stored in a memory 81 shown in Fig. 6. Then, a processor 82 shown in Fig. 6 executes the program stored in the memory 81.

[0081] 12 shows an example in which each of the components of the distance measuring device 42 is realized by dedicated hardware, while Fig. 6 shows an example in which the distance measuring device 42 is realized by software, firmware, etc. However, this is merely an example, and some of the components in the distance measuring device 42 may be realized by dedicated hardware, and the remaining components may be realized by software, firmware, etc.

[0082] Next, the operation of the distance measuring device 42 shown in Fig. 11 will be described. Except for the distance calculation unit 67, the distance measuring device 42 is the same as the distance measuring device 42 shown in Fig. 4. Therefore, only the operation of the distance calculation unit 67 will be described here.

[0083] The distance calculation unit 67 acquires a peak signal from the shift amount change unit 64. For example, as shown in FIG. 13 , when oil is attached to the machining surface 3 a, two peak signals may be output from the shift amount change unit 64 as shown in FIG. 14 . The machining surface 3 a is the surface of a reference workpiece or the machining surface of the workpiece 3. FIG. 13 is an explanatory diagram showing an example of a reference workpiece with oil attached to its machining surface 3 a. FIG. 14 is an explanatory diagram showing two peak signals output from the shift amount change unit 64. In FIG. 14 , the horizontal axis represents frequency and the vertical axis represents signal intensity. One of the two peak signals is a spectrum of light reflected by the oil surface. The other of the two peak signals is a spectrum of light reflected by the oil surface and reflected by the machining surface 3 a. The oil attached to the machining surface 3 a is cutting oil supplied from the cutting oil nozzle 14.

[0084] The distance calculation unit 67 calculates the distance L from the sensor head unit 21 to the oil surface based on one of the peak signals. １ Based on the peak signal, the distance L to the oil surface is calculated. １ The process of calculating the distance L from the sensor head 21 to the processing surface 3a is a known technique, and therefore a detailed description thereof will be omitted. ２ However, since the speed of light passing through oil changes depending on the refractive index of the oil, the distance L calculated based on the other peak signal is ２ may contain errors. As shown in the following formula (1), if the refractive index of light in a vacuum is "1", the higher the refractive index n of the oil, the slower the speed of light v, and the lower the refractive index of the oil, the faster the speed of light v. n = c / v (1) In formula (1), c is the speed of light in a vacuum. Note that the speed of light c' in air is 1.000292 at 0 degrees Celsius and 1 atmosphere. The relationship between the speed of light c' in air and the speed v of light passing through oil is expressed as in the following formula (2). n = c' / v (2)

[0085] The distance calculation unit 67 calculates the distance L ２To compensate for this, the refractive index n of the oil is calculated as shown in the following equation (3): n = {((FFT １２ -FFT １１ )-(FFT ０２ -FFT ０１ )) x L ｂｉｎ} / (d １ -d ０ ) (3) In formula (3), d ０ , d1 are distances to positions on the processing surface 3a whose distances to the processing surface 3a are known among a plurality of positions on the processing surface 3a. ０ Position and distance d １ The positions are different from each other. ０１ is the distance d ０ is the number of FFT Bin, which is the frequency axis showing the peak signal from the processing surface 3a at the position ０１ is the distance d ０ is the number of FFTBin from the oil surface at the position １１ is the distance d １ is the number of FFT Bin from the processing surface 3a at the position １２ is the distance d １ is the number of FFTBin from the oil surface at the position L ｂｉｎ is FFTBin and depends on, for example, the FFT size.

[0086] The distance calculation unit 67 calculates the speed v of light passing through the oil by substituting the refractive index n of the oil into equation (2). Then, the distance calculation unit 67 calculates the oil film thickness W based on the speed v of light passing through the oil. The film thickness W can be calculated based on the time difference between the time when light is irradiated from the sensor head unit 21 and the time when the reflected light is received by the sensor head unit 21, and the speed v. The distance calculation unit 67 calculates the distance L to the oil surface as shown in the following equation (4): １ and the oil film thickness W, the compensated distance L ２ ' is calculated. ２ '=L １ +W (4)

[0087] In the second embodiment described above, the distance measuring device 42 is configured so that, if two signals having a signal strength equal to or greater than a threshold are included in the frequency domain signals converted by the signal conversion unit 63 because oil is attached to the machining surface 3a, the distance calculation unit 67 calculates the thickness of the oil film attached to the machining surface 3a and the distance from the sensor head unit 21 to the oil surface based on the two signals having a signal strength equal to or greater than the threshold, and then calculates the distance from the sensor head unit 21 to the machining surface 3a from the film thickness and the distance to the oil surface. Therefore, even if a situation occurs in which the frequency of the frequency domain signal deviates from the convertible frequency range when oil is attached to the machining surface 3a, the distance measuring device 42 can calculate the distance from the sensor head unit 21 to the machining surface 3a of the workpiece 3.

[0088] In addition, the present disclosure allows for free combination of the respective embodiments, modification of any of the components of the respective embodiments, or omission of any of the components of the respective embodiments.

[0089] The present disclosure is suitable for a distance measuring device, a distance measuring method, and a machining device.

[0090] 1 table, 2 vice, 3 workpiece, 3a machining surface, 10 machining unit, 11 machining head, 11a head main body, 11b spindle, 11c outer peripheral surface, 12 machining tool, 13 head drive unit, 14 cutting oil nozzle, 20 sensor unit, 21 sensor head unit, 22 sensor main body, 23 optical transmission unit, 31 frequency sweep light output unit, 31a frequency sweep light source, 32 optical branching unit, 33 optical coupler, 34 circulator, 35 focusing optical element, 36 optical interference unit, 37 optical interferometer, 38 photodetector, 39, 40 A / D converter, 41 register, 42 distance measuring device, 50 control unit, 61 frequency shift unit, 62 band limiting unit, 63 signal conversion unit, 64 shift amount change unit, 65 distance calculation unit, 66 shape calculation unit, 67 Distance calculation unit, 71 frequency shift circuit, 72 band limiting circuit, 73 signal conversion circuit, 74 shift amount changing circuit, 75 distance calculation circuit, 77 distance calculation circuit, 81 memory, 82 processor.

Claims

1. A distance measuring device comprising: a frequency shift unit that shifts the frequency of interference light between light irradiated from a sensor head unit onto a processing surface of a workpiece and light received by the sensor head unit and reflected from the processing surface; a band limiting unit that limits the frequency band of the interference light after frequency shift by the frequency shift unit; a signal conversion unit that converts the interference light after frequency band limiting by the band limiting unit into a frequency domain signal; a shift amount changing unit that changes the amount of shift of the frequency of the interference light by the frequency shift unit if the frequency domain signal after conversion by the signal conversion unit does not contain a signal whose signal strength is equal to or greater than a threshold; and a distance calculation unit that calculates the distance from the sensor head unit to the processing surface based on the signal whose signal strength is equal to or greater than the threshold if the frequency domain signal after conversion by the signal conversion unit contains a signal whose signal strength is equal to or greater than a threshold.

2. A distance measuring device as described in claim 1, characterized in that light is irradiated from the sensor head unit onto the surface of a reference workpiece having a desired shape after processing of the workpiece as the processed surface of the workpiece, the frequency shift unit shifts the frequency of interference light between the light irradiated onto the surface of the reference workpiece and the light reflected by the surface of the reference workpiece, and the distance calculation unit calculates the distance from the sensor head unit to the surface of the reference workpiece as the distance from the sensor head unit to the processed surface.

3. The distance calculation unit of the distance measuring device described in claim 1 is characterized in that, if the frequency domain signals received by the sensor head unit after conversion by the signal conversion unit contain two signals whose signal strength is above a threshold because oil is attached to the machining surface, the distance calculation unit calculates the thickness of the oil film attached to the machining surface and the distance from the sensor head unit to the oil surface based on the two signals whose signal strength is above a threshold, and calculates the distance from the sensor head unit to the machining surface from the film thickness and the distance to the oil surface.

4. A distance measuring method in which a frequency shifting unit shifts the frequency of interference light between light irradiated from a sensor head unit onto a processing surface of a workpiece and light received by the sensor head unit and reflected from the processing surface, a band limiting unit limits the frequency band of the interference light after frequency shifting by the frequency shifting unit, a signal conversion unit converts the interference light after frequency band limiting by the band limiting unit into a frequency domain signal, a shift amount changing unit changes the amount of frequency shift of the interference light by the frequency shifting unit if the frequency domain signal after conversion by the signal conversion unit does not contain a signal whose signal strength is equal to or greater than a threshold, and a distance calculation unit calculates the distance from the sensor head unit to the processing surface based on the signal whose signal strength is equal to or greater than the threshold if the frequency domain signal after conversion by the signal conversion unit contains a signal whose signal strength is equal to or greater than a threshold.

5. A machining apparatus comprising: a sensor head unit that irradiates light onto a machining surface of a workpiece and receives light reflected from the machining surface; a light interference unit that detects interference light between the light irradiated from the sensor head unit and the light received by the sensor head unit; a frequency shift unit that shifts the frequency of the interference light detected by the light interference unit; a band limiting unit that limits the frequency band of the interference light after frequency shift by the frequency shift unit; a signal conversion unit that converts the interference light after frequency band limiting by the band limiting unit into a frequency domain signal; a shift amount changing unit that changes the amount of shift of the frequency of the interference light by the frequency shift unit if the frequency domain signal after conversion by the signal conversion unit does not include a signal whose signal strength is equal to or greater than a threshold; and a distance calculation unit that calculates a distance from the sensor head unit to the machining surface based on the signal whose signal strength is equal to or greater than the threshold if the frequency domain signal after conversion by the signal conversion unit includes a signal whose signal strength is equal to or greater than a threshold.

6. The machining device according to claim 5, characterized in that the distance calculation unit calculates the distance from the sensor head unit to the machining surface each time the position of the sensor head unit is moved, and is further characterized by having a shape calculation unit that calculates the shape of the workpiece based on the multiple distances calculated by the distance calculation unit.

Images