JP7477755B2 - Straightness Measuring Device - Google Patents

Description

The present invention relates to a straightness measuring device, and in particular to a straightness measuring device that measures the straightness in the direction of movement of a moving body provided in a machine tool or measuring device.

Conventionally, it has been known to measure the straightness of a moving body in the direction of movement of a machine tool or measuring device using a laser interferometer, as disclosed in, for example, Patent Document 1.

The above-mentioned laser interferometer has a laser oscillator, and in the optical path of the laser light from this 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 that change.

JP 2004-219350 A

For example, in a straightness measurement device using a laser interferometer such as that 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 the problem that stable measurements cannot be performed.

The present invention was made in consideration of these circumstances, and aims to provide a straightness measuring device that can perform stable measurements by suppressing the effects of spatial fluctuations.

The straightness measuring device for achieving the object of the present invention is a straightness measuring device for detecting straightness in the 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 arranged between the laser light source and the straightness reflector that 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 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 second laser light that has passed through the λ/4 plate. The device is equipped with 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, 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 that are combined by the polarizing beam splitter, which is interference light emitted 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.

In one embodiment of the present invention, it is preferable that the deflection prism is attached to a movable body that is arranged to be movable along the optical path of the laser light from the laser light source.

In one embodiment of the present invention, it is preferable that the straightness reflector is attached to a movable body that is arranged to be movable along the optical path of the laser light from the laser light source.

In one embodiment of the present invention, the detection unit preferably 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 the straightness based on the detection signal output from the lock-in amplifier.

In one embodiment of the present invention, the drive signal is preferably a signal in a high frequency band of 1 GHz or more.

The present invention makes it possible to suppress the effects of spatial fluctuations and perform stable measurements.

FIG. 1 is a block diagram showing a basic configuration of a straightness measuring device according to an embodiment. FIG. 1 is an explanatory diagram showing an example of a straightness measuring method using a straightness measuring device. FIG. 3 is an explanatory diagram showing how the optical path lengths of the two laser beams change in the measurement method of FIG. FIG. 13 is an explanatory diagram showing another example of a straightness measuring method using a straightness measuring device. FIG. 5 is an explanatory diagram showing how the optical path lengths of the two laser beams change in the measurement method of FIG.

Below, an embodiment of the straightness measuring device of the present invention will be described with reference to the attached drawings.

Figure 1 is a block diagram showing the basic configuration of a straightness measuring device 10 according to an embodiment.

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.

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 polarizing beam splitter 14. At this time, the optical axis of the polarizing beam splitter 14 is adjusted to be 45° 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 that passes through the polarizing beam splitter 14 is called P-polarized light, and their polarization directions are perpendicular to each other.

The first laser light L1 is incident on a prism 18 having a piezoelectric element 16 attached to its reflecting surface 18A. The piezoelectric element 16 is driven at a high frequency band based on a high frequency band drive signal S1 output from an oscillator 25, which is a frequency source. This causes the reflecting surface 18A to vibrate, 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.

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 that vibrates in response to the drive signal S1. The frequency of the modulated laser light L3 can be adjusted as desired by the drive signal S1 in the high frequency band from the oscillator 25. In this embodiment, as described below, the frequency of the modulated laser light L3 is adjusted to a frequency in a high frequency band (e.g., a high frequency band of 1 GHz or more) that is highly linear and less susceptible to the effects of air turbulence. Here, the piezoelectric element 16 is an example of a frequency modulation element of the present invention.

The second laser light L2 and the modulated laser light L3 are each converted into circularly polarized light by changing the phase of each light as they pass through the λ/4 plate 20. The second laser light L2 and the modulated laser light L3 that have passed through the λ/4 plate 20 are then 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.

The straightness reflector 24 has a reflector 26 that reflects the modulated laser light L3 and a reflector 28 that reflects the second laser light L2. The reflector 26 is arranged so that the normal of the reflector 26 is parallel to the optical axis of the modulated laser light L3, and the reflector 28 is arranged so that the normal of the reflector 28 is parallel to the optical axis of the second laser light L2. As a result, the modulated laser light L3 incident on the reflector 26 is reflected by the reflector 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 reflector 28 is reflected by the reflector 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 light L5 enters the deflection prism 22.

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.

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. This generates interference light L6 in the polarizing beam splitter 14, which is then emitted from the polarizing beam splitter 14 and enters the light receiving element 30.

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

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 that corresponds to the high frequency band of the drive signal S1 from the interference signal S2 and outputs it to the calculation unit 34.

The calculation 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 calculation unit 34 is amplified by the amplifier 36, and 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) described later. Here, the lock-in amplifier 32 and the calculation unit 34 constitute the detection unit 33. The detection unit 33 is an example of a detection unit of the present invention that detects straightness.

Next, we will explain the straightness measurement method using the straightness measurement device 10.

Figure 2 is an explanatory diagram showing the first measurement mode when the straightness measuring device 10 is installed on a machine tool 50.

FIG. 2 shows how the straightness of a carriage 52 provided on a machine tool 50 in the X-axis direction is measured by the straightness measuring device 10. The straightness measuring device 10 shown in FIG. 2 also shows a laser light emitting device 54, a deflection prism 22, and a straightness reflector 24. The laser light emitting device 54 is configured with 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.

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

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

Then, the frequency of the modulated laser light L3 is adjusted to a high-frequency band (e.g., a high-frequency band of 1 GHz or more) that is less susceptible to the effects of air turbulence and has a high degree of linearity, by the drive signal S1 from the oscillator 25. This completes the measurement preparation.

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.

In other words, in the measurement mode shown in FIG. 2, the modulated laser light L3 and the second laser light L2 are spread in the up-down direction in a vertical plane, so it is possible to measure the straightness in the up-down direction (Z-axis direction) relative 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) relative to the X-axis.

When measuring the straightness of the carriage 52 in the X-axis direction using 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 irradiating device 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.

At this time, for example, as shown in FIG. 3, if the deflection prism 22 moves upward by a distance D in the process of moving along the X-axis, 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'. Here, since the relationships A=B, A'=A-D×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.

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. In addition, 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).

Here, the modulated laser light L3 and the second laser light L2 traveling from the deflection prism 22 toward the straightness reflector 24 are spread apart by the deflection prism 22 and pass through spaces separated from each other, so they are considered to be easily affected by spatial fluctuations. However, the modulated laser light L3 is modulated to a high-frequency band frequency (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 the interference signal S2 generated by combining the reflected lights of the modulated laser light L3 and the second laser light L2, and detects straightness based on this detection signal S3.

In other words, the straightness measuring device 10 of the embodiment detects straightness based on the detection signal S3 in a high frequency band that has high linearity and is less susceptible to the effects of air turbulence, so 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 measurements can be performed. In addition, 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 more stable measurements 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.

The straightness measuring device 10 of the embodiment is configured as a heterodyne detection type straightness measuring device, since it 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.

Conventionally, laser interferometers that use the heterodyne detection method use a laser light source (e.g., Zeeman laser: see JP 59-188511 A) that emits two high-frequency (e.g., several hundred THz) laser beams, irradiate the object to be measured with two laser beams of different frequencies, and measure the surface roughness and height shape of the object from the frequency difference (e.g., 50 MHz) based on the optical path difference between the two laser beams reflected by the object to be measured. However, the above-mentioned laser interferometers require the use of a special laser light source such as a Zeeman laser, and the frequency of the laser beam is very high, making detection difficult. Furthermore, since the frequency difference is small, it is easily affected by spatial fluctuations, making it difficult to perform stable measurements.

In contrast, according to the straightness measuring device 10 of the embodiment, a laser light source 12 that emits a single-frequency laser light 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. The first laser light L1 is then modulated to a high-frequency band frequency by a piezoelectric element 16, and the modulated modulated laser light L3 and the second laser light L2 are spread and made incident 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. The interference light is then 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 heterodyne detection type measurement without using a special laser light source such as a Zeeman laser. In addition, by using modulated laser light L3 modulated to a frequency in the high frequency band, the effects of spatial fluctuations can be suppressed and stable measurements can be performed.

In the embodiment of the straightness measuring device 10, a piezoelectric element 16 is used as an example of a frequency modulation element, but this is not limited thereto, and other frequency modulation elements such as an acousto-optical modulation element may also be used.

Figure 4 is an explanatory diagram showing a second measurement mode when the straightness measuring device 10 is installed on a machine tool 50. Note that the machine tool 50 shown in Figure 4 and the machine tool 50 shown in Figure 2 have the same configuration, so they will be described using the same reference numerals.

The straightness measuring device 10 shown in FIG. 4 also measures the straightness in the X-axis direction of the carriage 52 provided on the machine tool 50. The difference between the straightness measuring device 10 shown in FIG. 2 and the straightness measuring device 10 shown in FIG. 4 is 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 light emitting device 70 shown in FIG. 4. The laser light 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. Therefore, the straightness measuring device 10 in FIG. 4 is configured to emit the modulated laser light L3 and the second laser light L2 from the laser light emitting device 70 toward the straightness reflector 24.

When measuring the straightness of the carriage 52 in the X-axis direction using 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 reflector 24, and the carriage 52 is moved along the X-axis direction to move the straightness reflector 24 along the X-axis direction. Then, for example, as shown in FIG. 5, if the straightness reflector 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.

As in 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).

Even in the second measurement form, straightness is detected based on the detection signal S3 in the high frequency band, which has a 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 measurements can be performed.

Although an embodiment of the present invention has been described above, the present invention is not limited to the embodiment, and various modifications are possible without departing from the spirit of the present invention.

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, 52...carriage, 54...laser light irradiation device, 56...X table, 58...tripod, 60...support, 62...support, 70...laser light emission device

Claims (5)

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 the frequency of the first laser beam to generate a modulated laser beam;
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;
Equipped with
The detection unit includes a lock-in amplifier that extracts and outputs a detection signal of a high frequency band corresponding to a high frequency band of the drive signal from the interference signal;
a calculation unit that calculates straightness based on the detection signal output from the lock-in amplifier . 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 the frequency of the first laser beam to generate a modulated laser beam;
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;
Equipped with
A straightness measuring device , wherein the drive signal is a signal in a high frequency band of 1 GHz or more . The detection unit includes a lock-in amplifier that extracts and outputs a detection signal of a high frequency band corresponding to a high frequency band of the drive signal from the interference signal;
A calculation unit that calculates straightness based on the detection signal output from the lock-in amplifier.
3. The straightness measuring device according to claim 2. the deflection prism is attached to the movable body that is provided so as to be movable along the optical path of the laser light from the laser light source;
The straightness measuring device according to any one of claims 1 to 3 . The straightness reflector is attached to the movable body that is provided so as to be movable along the optical path of the laser light from the laser light source.
The straightness measuring device according to any one of claims 1 to 3 .

Images