Straightness Measuring Device

Abstract

To provide a straightness measuring device that suppresses the influence of a spatial fluctuation and performs a stable measurement.SOLUTION: A straightness measuring device 10 comprises a laser source 12, a straightness mirror 24, a polarization beam splitter 14 that splits a laser beam L from the laser source 12 into a first laser beam L1 and a second laser beam L2, a piezoelectric element 16 that modulates only the frequency of the first laser beam L1 out of the first laser beam L1 and the second laser beam L2 to generate a modulated laser beam L3, a deflecting prism 22 that makes the second laser reflected light L5 and the modulated laser reflected light L4 reflected by the straightness mirror 24 to enter the polarization beam splitter 14 to generate interference light, a light receiving element 30 that outputs an interference signal S2 according to the interference fringe of the interference light, and a detector 33 that detects straightness based on the interference signal S2 and a driving signal S1.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a straightness measuring device, and more particularly to a straightness measuring device that measures the straightness in the moving direction of a movable body provided in a machine tool or measuring device. [Background technology]

[0002] 2. Description of the Related Art Conventionally, it is known to measure the straightness in the moving direction of a moving body provided in a machine tool or a measuring instrument by using a laser interferometer as disclosed in Patent Document 1, for example.

[0003] The above-mentioned laser interferometer has a laser oscillator, and in the optical path of the laser light from the laser oscillator, a straightness interferometer and a reflecting mirror attached to the moving body are arranged. The laser light from the laser oscillator is split into two polarized components of laser light by passing through the straightness interferometer and is emitted to the reflecting mirror, and the two laser lights reflected by the reflecting mirror are returned to the straightness interferometer and combined. The interference light of the two combined laser lights is received by a light receiving element to detect the relative change in the optical path length of the two laser lights, and the straightness of the moving direction of the moving body is measured based on the change. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-219350 A Summary of the Invention [Problem to be solved by the invention]

[0005] For example, in a straightness measuring device using a laser interferometer as in Patent Document 1, the laser light from the laser oscillator is expanded from the straightness interferometer toward the straightness reflector, so that the two expanded laser lights pass through spaces separated from each other. For example, when two laser lights pass through the same space, the effects of spatial fluctuations (e.g., disturbances) are reduced because they cancel each other out, but when they pass through spaces separated from each other as described above, they cannot cancel each other out and are affected by spatial fluctuations, resulting in a problem that stable measurement cannot be performed.

[0006] The present invention has been made in view of the above circumstances, and has an object to provide a straightness measuring device that can perform stable measurements by suppressing the effects of spatial fluctuations. [Means for solving the problem]

[0007] A straightness measuring device for achieving the object of the present invention is a straightness measuring device for detecting straightness in a moving direction of a moving body, and includes a laser light source that emits laser light of a single frequency, a straightness reflector arranged on the optical path of the laser light, a polarizing beam splitter that is arranged between the laser light source and the straightness reflector and splits the laser light emitted from the laser light source into a first laser light and a second laser light, a frequency modulation element that modulates the frequency of the first laser light to generate a modulated laser light, a λ / 4 plate that changes the phase of each of the second laser light and the modulated laser light, and a polarizing beam splitter that splits the first laser light into a first laser light and a second laser light. The optical fiber includes a deflection prism that spreads the second laser light and the modulated laser light in a direction away from each other and makes them incident on a straightness reflector, and a deflection prism that makes the reflected light of the second laser light and the reflected light of the modulated laser light reflected by the straightness reflector incident on a polarizing beam splitter via a λ / 4 plate, a light receiving element that outputs an interference signal of the interference light between the reflected light of the second laser light and the reflected light of the modulated laser light combined by the polarizing beam splitter, which is interference light output from the polarizing beam splitter, and a detection unit that detects straightness based on the interference signal and a drive signal that drives a frequency modulation element.

[0008] In one aspect of the present invention, the deflection prism is preferably attached to a movable body provided so as to be movable along an optical path of the laser light from the laser light source.

[0009] In one aspect of the present invention, the straightness reflecting mirror is preferably attached to a movable body provided so as to be movable along an optical path of the laser light from the laser light source.

[0010] In one form of the present invention, it is preferable that the detection unit includes a lock-in amplifier that extracts and outputs a detection signal in a high frequency band corresponding to the high frequency band of the drive signal from the interference signal, and a calculation unit that calculates straightness based on the detection signal output from the lock-in amplifier.

[0011] In one aspect of the present invention, the drive signal is preferably a signal in a high frequency band of 1 GHz or more. Effect of the Invention

[0012] According to the present invention, the influence of spatial fluctuations can be suppressed and stable measurements can be performed. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a block diagram showing a basic configuration of a straightness measuring device according to an embodiment. [Diagram 2] FIG. 1 is an explanatory diagram showing an example of a straightness measuring method using a straightness measuring device; [Diagram 3] An explanatory diagram showing how the optical path lengths of the two laser beams change when using the measurement method in Figure 2. [Figure 4] FIG. 13 is an explanatory diagram showing another example of a straightness measuring method using a straightness measuring device. [Diagram 5] An explanatory diagram showing how the optical path lengths of the two laser beams change in the measurement method of Figure 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the straightness measuring device of the present invention will be described with reference to the accompanying drawings.

[0015] FIG. 1 is a block diagram showing a basic configuration of a straightness measuring device 10 according to an embodiment of the present invention.

[0016] As shown in FIG. 1, the straightness measuring device 10 of the embodiment is a device that measures the straightness of a moving object in the moving direction by using a laser light L emitted from a laser light source 12, and is configured by sequentially arranging a polarizing beam splitter 14, a prism 18 equipped with a piezoelectric element 16, a λ / 4 plate 20, a deflection prism 22, and a straightness reflector 24 in the optical path of the laser light L from the laser light source 12.

[0017] As the laser light source 12, for example, a laser light source that emits a single-frequency laser light with a long interference distance, such as a He-Ne laser, is used. The laser light L emitted from this laser light source 12 is split into a first laser light L1 and a second laser light L2 by the above-mentioned polarizing beam splitter 14. At this time, the optical axis of the polarizing beam splitter 14 is adjusted to be at 45° with respect to the polarization plane of the incident laser light L. In this case, the first laser light L1 reflected by the polarizing beam splitter 14 is called S-polarized light, and the second laser light L2 transmitted through the polarizing beam splitter 14 is called P-polarized light, and their polarization directions are perpendicular to each other.

[0018] The first laser light L1 is incident on a prism 18 having a piezoelectric element 16 attached to a reflecting surface 18A. The piezoelectric element 16 is driven at a high frequency band based on a driving signal S1 in a high frequency band output from an oscillator 25, which is a frequency source. This vibrates the reflecting surface 18A, and the first laser light L1 reflected by this reflecting surface 18A is modulated in frequency to become a modulated laser light L3 having a frequency in the high frequency band. The optical axis of this modulated laser light L3 is set parallel to the optical axis of the second laser light L2.

[0019] With the above configuration, the first laser light L1 split by the polarizing beam splitter 14 is modulated into modulated laser light L3 by the piezoelectric element 16 which vibrates in response to a drive signal S1. The frequency of the modulated laser light L3 can be adjusted arbitrarily by the drive signal S1 in a high frequency band from the oscillator 25. In this embodiment, as described later, the frequency of the modulated laser light L3 is adjusted to a frequency in a high frequency band (for example, a high frequency band of 1 GHz or more) that is unlikely to be affected by air turbulence and has high linearity. Here, the piezoelectric element 16 is an example of a frequency modulation element of the present invention.

[0020] The second laser light L2 and the modulated laser light L3 are each converted into a circularly polarized light by changing the phase of each of them as they pass through the λ / 4 plate 20. Then, the second laser light L2 and the modulated laser light L3 that have passed through the λ / 4 plate 20 are expanded by a predetermined angle (θ) in the direction away from each other by the deflection prism 22, and are emitted toward the straightness reflector 24.

[0021] The straightness reflecting mirror 24 has a reflecting mirror 26 that reflects the modulated laser light L3 and a reflecting mirror 28 that reflects the second laser light L2. The reflecting mirror 26 is arranged so that the normal of the reflecting mirror 26 is parallel to the optical axis of the modulated laser light L3, and the reflecting mirror 28 is arranged so that the normal of the reflecting mirror 28 is parallel to the optical axis of the second laser light L2. As a result, the modulated laser light L3 incident on the reflecting mirror 26 is reflected by the reflecting mirror 26, and the reflected light (hereinafter referred to as the "modulated laser reflected light L4") is returned in the same direction as the modulated laser light L3. The modulated laser reflected light L4 then enters the deflection prism 22. The second laser light L2 incident on the reflecting mirror 28 is reflected by the reflecting mirror 28, and the reflected light (hereinafter referred to as the "second laser reflected light L5") is returned in the same direction as the second laser light L2. Then, the second reflected laser beam L5 enters the deflection prism 22.

[0022] The modulated reflected laser light L4 incident on the deflection prism 22 is converted from circularly polarized light to linearly polarized light by passing from the deflection prism 22 to the λ / 4 plate 20, and is then reflected by the reflecting surface 18A of the prism 18 and returned to the polarizing beam splitter 14. Similarly, the second reflected laser light L5 incident on the deflection prism 22 is converted from circularly polarized light to linearly polarized light by passing from the deflection prism 22 to the λ / 4 plate 20, and is then returned to the polarizing beam splitter 14.

[0023] The modulated laser reflected light L4 and the second laser reflected light L5 returned to the polarizing beam splitter 14 are combined and interfered with by the polarizing beam splitter 14. As a result, interference light L6 is generated by the polarizing beam splitter 14, and the interference light L6 is emitted from the polarizing beam splitter 14 and enters the light receiving element 30.

[0024] The light receiving element 30 receives the interference light L6 and outputs to the lock-in amplifier 32 an interference signal S2 corresponding to the interference fringes of the interference light L6.

[0025] In addition to the interference signal S2, the drive signal S1 is input to the lock-in amplifier 32 from the oscillator 25. The lock-in amplifier 32 extracts a detection signal S3 in a high frequency band corresponding to the high frequency band of the drive signal S1 from the interference signal S2, and outputs the detection signal S3 to the calculation unit .

[0026] The arithmetic unit 34 includes an amplifier 36, a counter 38 which is a frequency measuring unit, and a calculation unit 40. The detection signal S3 output from the lock-in amplifier 32 to the arithmetic unit 34 is amplified by the amplifier 36, and then the frequency of the detection signal S3 is counted by the counter 38. The calculation unit 40 calculates the optical path difference between the modulated laser light L3 and the second laser light L2 based on the count value of the counter 38, and calculates the straightness of the moving direction of the moving body based on a known angle (θ: see FIG. 1) which will be described later. Here, the lock-in amplifier 32 and the arithmetic unit 34 constitute a detection unit 33. The detection unit 33 is an example of a detection unit of the present invention which detects straightness.

[0027] Next, a straightness measuring method using the straightness measuring device 10 will be described.

[0028] FIG. 2 is an explanatory diagram showing a first measurement mode in which the straightness measuring device 10 is installed on a machine tool 50. As shown in FIG.

[0029] Fig. 2 shows an embodiment in which the straightness in the X-axis direction of a carriage 52 provided on a machine tool 50 is measured by a straightness measuring device 10. Also shown in the straightness measuring device 10 shown in Fig. 2 are a laser light emitting device 54, a deflection prism 22, and a straightness reflector 24. The laser light emitting device 54 is configured to include the laser light source 12 shown in Fig. 1, the polarizing beam splitter 14, the prism 18 having the piezoelectric element 16, and the λ / 4 plate 20. The carriage 52 is an example of a moving body of the present invention.

[0030] Carriage 52 of machine tool 50 is attached so as to be freely movable in the X-axis direction along X-table 56. When measuring the straightness in the X-axis direction of carriage 52 configured in this manner, laser light emitting device 54 is disposed on the front end side of the X-axis, and laser light emitting device 54 is fixed to tripod 58 so that modulated laser light L3 and second laser light L2 emitted from laser light emitting device 54 are parallel to the X-axis.

[0031] The straightness reflector 24 is disposed on the rear end side of the X-axis and fixed to a height-adjustable support base 60. The deflection prism 22 is disposed between the laser light emitting device 54 and the straightness reflector 24 on the axial path of the X-axis and attached to the carriage 52 via a height-adjustable support base 62. The heights of the deflection prism 22 and the straightness reflector 24 are adjusted by the support bases 60, 62, respectively, so that they are approximately the same height as the modulated laser light L3 and the second laser light L2.

[0032] Then, the frequency of the modulated laser light L3 is adjusted to a frequency in a high frequency band (for example, a high frequency band of 1 GHz or more) that is unlikely to be affected by air turbulence and has a high linearity, by the drive signal S1 from the oscillator 25. This completes the preparation for measurement.

[0033] Here, straightness refers to the amount of axial misalignment in a direction perpendicular to the movement direction (X-axis direction) of the deflection prism 22, and the direction of the axial misalignment is determined by the direction in which the modulated laser light L3 and the second laser light L2 are spread by the deflection prism 22.

[0034] 2, the modulated laser light L3 and the second laser light L2 are spread in the up-down direction in a vertical plane, so that it is possible to measure the straightness in the up-down direction (Z-axis direction) with respect to the X-axis. Note that, if the modulated laser light L3 and the second laser light L2 are spread in the left-right direction in a horizontal plane, it is possible to measure the straightness in the left-right direction (Y-axis direction) with respect to the X-axis.

[0035] When measuring the straightness of the carriage 52 in the X-axis direction by the straightness measuring device 10 configured as described above, the modulated laser light L3 modulated to a frequency in the high frequency band and the second laser light L2 are emitted from the laser light irradiator 54 toward the deflection prism 22, and the carriage 52 is moved along the X-axis direction to move the deflection prism 22 closer to or farther away from the straightness reflector 24.

[0036] At this time, for example, if the deflection prism 22 moves upward by a distance D in the process of moving along the X-axis as shown in Fig. 3, the optical path A of the modulated laser light L3 becomes A', and the optical path B of the second laser light L2 becomes B'. Since the relationships A=B, A'=AD×sin(θ), and B'=B+D×sin(θ) hold, the optical path difference between the modulated laser light L3 and the second laser light L2 is B'-A'=2×D×sin(θ). Therefore, if the optical path difference and θ are known, the straightness D can be found.

[0037] As described above, the optical path difference is calculated based on the detection signal S3 output from the lock-in amplifier 32 to the calculation unit 34. Moreover, θ is a known angle between the modulated laser light L3 and the second laser light L2 expanded by the deflection prism 22. Therefore, according to the straightness measuring device 10 of the embodiment, the straightness D can be obtained based on the calculated optical path difference and the known angle (θ).

[0038] Here, the modulated laser light L3 and the second laser light L2 traveling from the deflection prism 22 toward the straightness reflector 24 are expanded in a direction away from each other by the deflection prism 22 and pass through spaces separated from each other, and are therefore considered to be easily affected by spatial fluctuations. However, the modulated laser light L3 is modulated to a frequency in a high frequency band (e.g., 1 GHz or higher), and further, the detection unit 33 extracts a detection signal S3 in a high frequency band corresponding to the high frequency band of the drive signal S1 from an interference signal S2 generated by combining the reflected lights of the modulated laser light L3 and the second laser light L2, and detects the straightness based on this detection signal S3.

[0039] That is, the straightness measuring device 10 of the embodiment detects straightness based on the detection signal S3 in a high frequency band with high straightness and little effect from air turbulence, so that even if the modulated laser light L3 and the second laser light L2 pass through spaces separated from each other, the effect of spatial fluctuations can be suppressed and stable measurement can be performed. Also, the straightness measuring device 10 of the embodiment can measure straightness by simply making the modulated laser light L3 and the second laser light L2 go back and forth once between the deflection prism 22 and the straightness reflector 24, so that more stable measurement can be performed compared to, for example, an aspect in which the modulated laser light L3 and the second laser light L2 go back and forth twice.

[0040] In addition, the straightness measuring device 10 of the embodiment is a device that irradiates two laser beams (modulated laser beam L3 and second laser beam L2) with different frequencies from the deflection prism 22 toward the straightness reflector 24 and measures straightness based on the reflected beams, and is therefore configured as a straightness measuring device using a heterodyne detection method.

[0041] Conventionally, as a laser interferometer adopting a heterodyne detection method, for example, a laser light source (for example, Zeeman laser: see Japanese Patent Application Laid-Open No. 59-188511) that emits two high-frequency (for example, several hundred THz) laser lights is used, two laser lights with different frequencies are irradiated onto a measurement object, and the surface roughness and height shape of the measurement object are measured from the frequency difference (for example, 50 MHz) based on the optical path difference of the two laser lights reflected by the measurement object. However, the above-mentioned laser interferometer requires the use of a special laser light source such as a Zeeman laser, and the frequency of the laser light is very high, making it difficult to detect, and furthermore, since the above-mentioned frequency difference is small, it is easily affected by spatial fluctuations, and there is a problem that stable measurement cannot be performed.

[0042] In contrast, according to the straightness measuring device 10 of the embodiment, a laser light source 12 that emits a laser light of a single frequency is used, and the laser light L from the laser light source 12 is split into a first laser light L1 and a second laser light L2 by a polarizing beam splitter 14. Then, the first laser light L1 is modulated to a frequency in a high frequency band by a piezoelectric element 16, and the modulated modulated laser light L3 and the second laser light L2 are expanded and made to enter toward the straightness reflector 24, and the modulated laser reflected light L4 and the second laser reflected light L5 reflected by the straightness reflector 24 are synthesized and interfered by the polarizing beam splitter 14. Then, the interference light is received by the light receiving element 30, and the straightness is detected based on the interference signal S2 output from the light receiving element 30 and the drive signal S1 from the oscillator 25. As a result, the straightness measuring device 10 of the embodiment can perform measurement by the heterodyne detection method without using a special laser light source such as a Zeeman laser. Furthermore, by using the modulated laser light L3 modulated to a frequency in the high frequency band, the influence of spatial fluctuations can be suppressed, enabling stable measurement.

[0043] In the straightness measuring device 10 of the embodiment, the piezoelectric element 16 is exemplified as the frequency modulation element, but the present invention is not limited to this, and other frequency modulation elements such as an acousto-optical modulation element may also be used.

[0044] Fig. 4 is an explanatory diagram showing a second measurement mode in which the straightness measuring device 10 is installed in a machine tool 50. Note that the machine tool 50 shown in Fig. 4 has the same configuration as the machine tool 50 shown in Fig. 2, and therefore will be described using the same reference numerals.

[0045] The straightness measuring device 10 shown in FIG. 4 also measures the straightness of a carriage 52 provided on a machine tool 50 in the X-axis direction. The straightness measuring device 10 shown in FIG. 2 is different from the straightness measuring device 10 shown in FIG. 4 in that, while the deflection prism 22 is attached to the carriage 52 in FIG. 2, the straightness reflector 24 is attached to the carriage 52 in FIG. 4, and the deflection prism 22 shown in FIG. 2 is built into the laser beam emitting device 70 shown in FIG. 4. The laser beam emitting device 70 is configured to include the laser light source 12 shown in FIG. 1, the polarizing beam splitter 14, the prism 18 having the piezoelectric element 16, the λ / 4 plate 20, and the deflection prism 22. Thus, the straightness measuring device 10 in FIG. 4 is configured to emit the modulated laser beam L3 and the second laser beam L2 from the laser beam emitting device 70 toward the straightness reflector 24.

[0046] When measuring the straightness of the carriage 52 in the X-axis direction by the straightness measuring device 10 shown in Fig. 4, the modulated laser light L3 modulated to a frequency in the high frequency band and the second laser light L2 are emitted from the laser light emitting device 70 toward the straightness reflecting mirror 24, and the carriage 52 is moved along the X-axis direction to move the straightness reflecting mirror 24 along the X-axis direction. Then, for example, as shown in Fig. 5, if the straightness reflecting mirror 24 moves upward by a distance D during the process of moving along the X-axis, the optical path A of the modulated laser light L3 becomes longer and the optical path B of the second laser light L2 becomes shorter.

[0047] Hereinafter, similarly to the first measurement form described in Figures 2 and 3, the straightness D is calculated based on the optical path difference between the modulated laser light L3 and the second laser light L2 calculated by the calculation unit 34 and the known angle (θ).

[0048] In the second measurement form as well, straightness is detected based on the detection signal S3 in the high frequency band which has high linearity and is less susceptible to the effects of air turbulence. Therefore, even if the modulated laser light L3 and the second laser light L2 pass through spaces separated from each other, the effects of spatial fluctuations can be suppressed and stable measurement can be performed.

[0049] Although the embodiment of the present invention has been described above, the present invention is not limited to the embodiment, and various modifications can be made without departing from the gist of the present invention. [Explanation of symbols]

[0050] 10...straightness measuring device, 12...laser light source, 14...polarizing beam splitter, 16...piezo element, 18...prism, 20...lambda / 4 plate, 22...deflection prism, 24...straightness reflector, 25...oscillator, 26...reflector, 28...reflector, 30...light receiving element, 32...lock-in amplifier, 33...detection unit, 34...calculation unit, 36...amplifier, 38...counter, 40...calculation unit, 50...machine tool, 52...carriage, 54...laser light irradiation device, 56...X table, 58...tripod, 60...support, 62...support, 70...laser light emission device

Claims

[Claim 1] A straightness measuring device for detecting straightness in a moving direction of a moving body, comprising: a laser light source that emits laser light of a single frequency; a straightness reflector disposed on the optical path of the laser light; a polarizing beam splitter disposed between the laser light source and the straightness reflector, the polarizing beam splitter splitting the laser light emitted from the laser light source into a first laser light and a second laser light; a frequency modulation element that modulates only a frequency of the first laser light of the first laser light and the second laser light to generate a modulated laser light; a λ / 4 plate for changing the phases of the second laser light and the modulated laser light; a deflection prism that spreads the second laser light and the modulated laser light that have passed through the λ / 4 plate in a direction away from each other and causes them to enter the straightness reflector, and causes the reflected light of the second laser light and the reflected light of the modulated laser light reflected by the straightness reflector to enter the polarizing beam splitter via the λ / 4 plate; a light receiving element that outputs an interference signal of interference light between the reflected light of the second laser light and the reflected light of the modulated laser light, the interference light being output from the polarizing beam splitter; and a detection unit that detects the straightness based on the interference signal and a drive signal that drives the frequency modulation element; A straightness measuring device comprising:

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