JP7051480B2 - Relative position detection means - Google Patents

Description

The present invention relates to a relative position detecting means provided in a displacement detecting device for detecting a displacement of a moving part such as a machine tool or a semiconductor manufacturing apparatus.

Conventionally, a displacement detection device using light has been widely used as a device for measuring the displacement of an object to be measured in a non-contact manner. The displacement detection device changes the phase of the light from the light source based on the displacement of the object to be measured as a movable part, and detects the displacement amount of the object to be measured by detecting the changed state of the phase of the light. In recent years, there has been a demand for high-resolution displacement detection devices capable of measuring displacements of 1 nm or less, mainly for machine tools and semiconductor manufacturing equipment.

As the displacement detection device having such high resolution, for example, there are those described in Patent Documents 1 and 2. Patent Document 1 discloses a laser interferometer that enables highly accurate measurement by preventing a measurement error based on a deviation of the optical axis of two types of light waves having different wavelengths. On the other hand, Patent Document 2 discloses a displacement detection device capable of detecting a stable and highly accurate displacement amount by configuring a polarization-retaining fiber with an arbitrary length according to the oscillation characteristics of a light source.

Japanese Unexamined Patent Publication No. 2009-300263 Japanese Unexamined Patent Publication No. 2016-142552

However, in the displacement detection device described in Patent Documents 1 and 2, the incremental position information indicating the relative position information of the target to be measured provided on the object to be measured moving in the measurement direction is shown depending on the performance and shape of the parts provided in the device. The signal cycle is fixed. That is, in the laser interferometer described in Patent Document 1, the signal period is determined by the wavelength of the light source used, and in the displacement detection device described in Patent Document 2, the lattice spacing of the diffraction grating provided on the measured surface is determined. The signal cycle is determined by. For this reason, it has become difficult to handle a wide range of signal cycles without replacing the parts provided in the device. In order to detect a stable and highly accurate displacement amount, it is desired to be able to handle a wide range of incremental signal cycles when detecting the relative position information of the target.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a new and improved relative position detecting means capable of supporting a wide range of signal periods with a simple configuration.

One aspect of the present invention is a relative position detecting means for optically detecting the relative position of the displacement of the object to be measured in the measurement direction, and the target is placed on the object to be measured and is irradiated with light from a light source. Based on the change in the polarization state of the reflected light received by the relative position detection light receiving unit and the light receiving unit for relative position detection, the target receives light by changing the polarization state of the reflected light of the target with respect to the light. The target is provided with a relative position information output unit that outputs relative position information based on the displacement in the measurement direction, and the target includes a plate-shaped reflector placed on the object to be measured and a reflective object on the reflector. A double-reflecting member whose thickness changes from the tip to the proximal end along the measurement direction is provided in the double-reflecting member. It is characterized in that it is configured to be rotatable with respect to the relative.

According to one aspect of the present invention, the period of the incremental signal indicating the relative position information of the target is determined by the inclination and arrangement of the birefringent member, so that a wide range of signal periods can be supported with a simple configuration.

At this time, in one aspect of the present invention, the light receiving unit for relative position detection detects a change in the polarization state of the reflected light as the target moves in the measurement direction, and the relative position information output unit displays the relative position information output unit. The relative position information of the target may be output based on the signal obtained by photoelectric conversion of the change in the polarization state of the reflected light.

By doing so, it is possible to handle a wide range of signal cycles with a simple configuration, and it is possible to reliably and accurately output the relative position information of the target, so that stable and highly accurate displacement detection becomes possible.

Further, in one aspect of the present invention, the light receiving unit for relative position detection reflects the beam splitter that splits the reflected light into two and the S component of one of the reflected lights branched by the beam splitter to P. A first polarized beam splitter that transmits components, a first light receiving element that receives the transmitted light of the first polarized beam splitter, and a second light receiving element that receives the reflected light of the first polarized beam splitter. And a second polarized beam splitter that reflects the S component of the other reflected light branched by the beam splitter to transmit the P component, and is interposed between the beam splitter and the second polarized beam splitter. A 1/4 wavelength plate, a third light receiving element that receives the reflected light of the second polarized beam splitter, and a fourth light receiving element that receives the transmitted light of the second polarized beam splitter. It may be that.

By doing so, it is possible to reliably detect a change in the polarization state of the reflected light as the target moves in the measurement direction with a simple configuration.

Further, in one aspect of the present invention, the birefringence member is composed of a plurality of different members arranged in parallel along the measurement direction, or a plurality of different members are laminated along the incident direction of the light. It may be configured as such.

By doing so, it is possible to easily change the sensitivity and period of the signal output indicating the change in the polarization state of the reflected light as the target moves in the measurement direction with a simple configuration.

Further, in one aspect of the present invention, the birefringence member may be configured by laminating a plurality of members having different crystal axis directions along the incident direction of the light.

By doing so, it is possible to suppress the influence of thermal fluctuations and wavelength fluctuations of the light source when the crystal axial directions of the members constituting the birefringent member are orthogonal to each other.

Further, in one aspect of the present invention, the correction prism may be provided on either the front stage side or the rear stage side of the birefringence member with respect to the light source.

By doing so, the polarization state in the beam distribution transmitted through the birefringence member becomes uniform, so that stable and highly accurate displacement detection by the absolute position detecting means on the rear stage side becomes possible.

Further, in one aspect of the present invention, two light receiving units for relative position detection are provided along the measurement direction, and the phase variation of the polarization state of the reflected light detected by the light receiving units for relative position detection is provided. The wavelength fluctuation amount may be estimated and corrected based on the difference in the amount.

By doing so, the wavelength fluctuation amount can be easily estimated based on the difference in the phase fluctuation amount of the polarization state of the reflected light detected by each relative position detection light receiving unit, and the wavelength fluctuation amount is corrected based on such estimation. By doing so, more accurate displacement detection becomes possible.

Further, in one aspect of the present invention, a polarizing plate may be further provided between the light source and the birefringence member.

By doing so, the beam used for displacement detection can have a higher extinction ratio, so that more accurate displacement detection becomes possible.

Further, in one aspect of the present invention, the light receiving unit for relative position detection may be further provided with an azimuth correction unit that corrects azimuth with respect to the reflected light.

By doing so, the difference due to the angle difference of the reflected light transmitted through the polarizing plate is corrected, so that more accurate displacement detection becomes possible.

As described above, according to the present invention, the period of the incremental signal indicating the relative position information of the target is determined by the inclination and arrangement of the birefringent member, so that a wide range of signal periods can be supported with a simple configuration. In addition, since the relative position information of the target can be reliably and accurately output while being able to handle a wide range of signal cycles with a simple configuration, stable and highly accurate displacement detection becomes possible.

It is a front view which shows the outline of the structure of the displacement detection device which concerns on one Embodiment of this invention. It is a top view which shows the outline of the structure of the displacement detection device which concerns on one Embodiment of this invention. It is a side view which shows the outline of the structure of the relative position detecting means provided in the displacement detecting apparatus which concerns on one Embodiment of this invention. It is a block diagram which shows the structure of the relative position information output part provided in the relative position detection means which concerns on one Embodiment of this invention. (A) is an explanatory diagram showing the measurement principle of the relative position detecting means according to the embodiment of the present invention by the birefringent member, and (B) is an explanatory diagram relating to the crystal axis of the birefringent member. (A) is a side view showing the outline of the configuration of the absolute position detecting means provided in the displacement detecting device according to the embodiment of the present invention, and (B) is the configuration of the variable reflective film provided in the absolute position detecting means. (C) is a block diagram showing a configuration of an absolute position information output unit provided in the absolute position detecting means. It is a block diagram which shows the outline of the signal output by the displacement detection device which concerns on one Embodiment of this invention. It is explanatory drawing which shows the angle of the resage signal of the incremental signal generator provided in the relative position detection means which concerns on one Embodiment of this invention. It is a graph which shows the signal output of each component of the displacement detection apparatus which concerns on one Embodiment of this invention. (A) is an explanatory diagram showing an example of a modification of the birefringent member of the relative position detecting means according to the embodiment of the present invention, and (B) is an explanatory diagram of the movement amount and position information of the birefringent member. It is a graph which shows the relationship. (A) and (B) are explanatory views which show an example of another modification of the birefringent member of the relative position detecting means which concerns on one Embodiment of this invention. (A) to (C) are explanatory views showing an example of still another modification of the birefringent member of the relative position detecting means according to the embodiment of the present invention. It is explanatory drawing which shows an example of still another modification of the birefringent member of the relative position detection means which concerns on one Embodiment of this invention. It is a perspective view which shows the outline of the structure of the modification of the displacement detection device which concerns on one Embodiment of this invention. It is explanatory drawing which shows the outline of the structure and operation of another embodiment of the displacement detection device which concerns on one Embodiment of this invention. It is a side view which shows the outline of the structure of the prism with a reflective film provided in the modification of the displacement detection device which concerns on one Embodiment of this invention. It is a front view which shows the outline of the structure of the other modification of the displacement detection device which concerns on one Embodiment of this invention. It is a perspective view which shows the outline of the structure of one modification of the modification of the displacement detection device which concerns on one Embodiment of this invention. (A) and (B) are explanatory views showing an example of another installation mode of the correction prism provided in another modification of the relative position detecting means according to the embodiment of the present invention. It is a perspective view which shows the outline of the structure of the other modification of the modification of the displacement detection device which concerns on one Embodiment of this invention. It is a perspective view which shows the outline of the structure of the other modification of the displacement detection apparatus which concerns on one Embodiment of this invention.

Hereinafter, preferred embodiments of the present invention will be described in detail. It should be noted that the present embodiment described below does not unreasonably limit the content of the present invention described in the claims, and all the configurations described in the present embodiment are indispensable as the means for solving the present invention. It is not always the case. Further, the various lenses described in the following description may have any form as long as they have predetermined imaging performance, and may be a spherical or aspherical single lens, a lens group, or an imaging function. A diffraction grating having a lens may be used.

First, the configuration of the displacement detection device according to the embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a front view showing an outline of the configuration of a displacement detection device according to an embodiment of the present invention, and FIG. 2 is a plan view showing an outline of the configuration of a displacement detection device according to an embodiment of the present invention. be.

The displacement detection device 100 according to an embodiment of the present invention is a device that optically detects the absolute position and the relative position of the displacement of the object to be measured 10 in the measurement direction (X direction). The absolute position referred to here indicates the position information obtained by converting the change in the amount of light received by the displacement in the measurement direction (X direction) from the reference point of the object 10 into an absolute value such as voltage, and the relative position is defined as the relative position. It shows the position information in which the change in polarization is received and the periodic signal such as voltage is phase-converted.

As shown in FIGS. 1 and 2, the displacement detecting device 100 of the present embodiment includes a light source 102, a light source side beam splitter 108, a relative position detecting means 110, and an absolute position detecting means 140. The displacement detecting device 100 of the present embodiment is characterized in that the absolute position detecting means 140 and the relative position detecting means 110 are provided in-line with respect to the measuring direction (X direction) of the object to be measured 10.

The light source 102 may emit coherent light having a limited coherent distance. In the present embodiment, the light source 102 is a coherent light source such as a multimode semiconductor laser or a super luminescent diode, but a light source having a relatively short coherence distance is used. However, the light source 102 is not limited to these specific types of light sources.

Further, in the present embodiment, since polarized light is used as the light emitted from the light source 102, a first lens 104 made of a collimating lens and a polarizing element 106 are provided on the output stage side of the light source 102. In this way, the light emitted from the light source 102 is converted into collimated light through the first lens 104 and then converted into a certain linear polarization using the polarizing element 106.

The position of the light source 102 may be the position of the light source 102 shown in FIG. 1, or in order to avoid the influence of the heat generated by the light source 102, the light source 102 is installed at a distant place and an optical fiber is used. The light may be propagated so that the emission end of the optical fiber is placed at the position of the light source 102 shown in FIG. Also at this time, the diverging light beam emitted from the optical fiber is converted into a collimated beam by the collimating lens. When the beam from the light source is linearly polarized, an optical fiber such as a polarization-retaining fiber that can retain the plane of polarization is used.

The light source side beam splitter 108 is a polarization-independent beam splitter that splits the coherent light from the light source 102 into two. In the present embodiment, as shown in FIGS. 1 and 2, the light source side beam splitter 108 is directed toward the direction in which the light b1 from the light source 102 goes to the absolute position detecting means 140 and the target 112 provided in the relative position detecting means 110 as it is. It is divided in the direction of incidence.

The relative position detecting means 110 has a function of detecting the relative position of the displacement of the object 10 to be measured in the measurement direction based on the change in the polarization state of the reflected light b2 with respect to one of the light b1 branched by the light source side beam splitter 108. .. In the present embodiment, the relative position detecting means 110 includes a target 112, a light receiving unit 120 for relative position detection, and a relative position information output unit 130 (see FIG. 4).

The target 112 is placed on the object to be measured 10 and is irradiated with the light b1 from the light source 102. The target 112 is provided on the plate-shaped reflector 114 placed on the object to be measured 10 and the reflector 114, and the thickness from the tip 116a to the proximal end 116a'increases along the measurement direction. The birefringence member 116 that changes in this way is provided. The birefringent member 116 is configured such that the tip end side of the bottom surface 116b is rotatable with respect to the reflecting object 114 with the base end side of the bottom surface 116b as the center. That is, the birefringence member 116 may be able to adjust the angle θ ₂ between the bottom surface 116b of the birefringence member 116 whose tip 116a has an angle θ ₁ and the reflector 114.

The light receiving unit 120 for relative position detection changes the polarization state of the reflected light b2 at the target 112 with respect to the coherent light b1 and receives light. In the present embodiment, the relative position detection light receiving unit 120 includes a beam splitter 121, a first polarizing beam splitter 122, a first light receiving element 123, a second light receiving element 124, and a 1/4 wave plate 125 (see FIG. 3). ), A second polarizing beam splitter 126, a third light receiving element 127, and a fourth light receiving element 128. A signal indicating a change in the polarization state of the reflected light b2 received by the light receiving unit 120 for relative position detection is sent to the relative position information output unit 130 (see FIG. 4), and the relative position information output unit 130 sends the signal to the signal. Based on this, relative position information based on the displacement of the target 112 in the measurement direction is output. The details of the target 112, the light receiving unit 120 for relative position detection, and the relative position information output unit 130 provided in the relative position detecting means 110 will be described later.

The absolute position detecting means 140 detects the absolute position of the displacement of the object 10 to be measured in the measurement direction based on the change in the amount of reflected light b5 and b6 with respect to the other light b3 and b4 branched by the light source side beam splitter 108. Has a function. In the present embodiment, the absolute position detecting means 140 includes a prism 144 provided with a variable reflection film 146 on the top surface side and a mirror 142 that introduces the other light b3 branched by the light source side beam splitter 108 into the prism 144. , A light receiving unit 150 for absolute position detection, and an absolute position information output unit 160 (see FIG. 6C).

The light receiving unit 150 for absolute position detection receives light by changing the amount of light of the prism 144 and the reflected light b5 and b6 of the object 10 to be measured with respect to the light b4 reflected by the mirror 142. In the present embodiment, the light receiving unit 150 for absolute position detection includes a fifth light receiving element 152 and a sixth light receiving element 154. A signal indicating a change in the amount of reflected light b5 and b6 received by the light receiving unit 150 for absolute position detection is sent to the absolute position information output unit 160 (see FIG. 6C), and the absolute position information output unit 160 , Absolute position information based on the displacement of the prism 144 in the measurement direction is output based on the signal. The details of the prism 144, the light receiving unit 150 for absolute position detection, and the absolute position information output unit 160 provided in the absolute position detecting means 140 will be described later.

Next, the configuration of the relative position detecting means provided in the displacement detecting device according to the embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a side view showing an outline of the configuration of the relative position detecting means provided in the displacement detecting device according to the embodiment of the present invention, and FIG. 4 is a side view showing the outline of the relative position detecting means provided in the displacement detecting means according to the embodiment of the present invention. It is a block diagram which shows the structure of the relative position information output part.

As described above, the relative position detecting means 110 determines the relative position of the displacement of the object 10 to be measured in the measurement direction based on the change in the polarization state of the reflected light b2 with respect to one of the light b1 branched by the light source side beam splitter 108. It has a function to detect. In the present embodiment, the relative position detecting means 110 includes a target 112, a light receiving unit 120 for relative position detection, and a relative position information output unit 130.

In the present embodiment, the relative position detecting means 110 detects a change in the polarization state of the reflected light as the light receiving unit 120 for relative position detection moves in the measurement direction of the target 112, and the relative position information output unit 130 detects the reflected light. It is characterized in that the relative position information of the target 112 is output based on the signal obtained by photoelectric conversion of the change in the polarization state of the target 112.

The target 112 is placed on the object to be measured 10 and functions as a displacement detection target of the object to be measured 10. The target 112 is irradiated with the coherent light b1 from the light source 102 via the light source side beam splitter 108 after being converted into constant linear polarization via the first lens 104 and the splitter 106.

In the present embodiment, the target 112 is provided on the plate-shaped reflector 114 placed on the object to be measured 10 and the reflector 114, and is provided from the tip 116a to the proximal end 116a'along the measurement direction. A birefringent member 116 having a substantially triangular prism shape with an increasing thickness is provided. The birefringent member 116 is configured such that the tip end side of the bottom surface 116b is rotatable with respect to the reflecting object 114 with the base end side of the bottom surface 116b as the center. That is, the birefringence member 116 may be able to adjust the angle θ ₂ between the bottom surface 116b of the birefringence member 116 whose tip 116a has an angle θ ₁ and the reflector 114.

The light receiving unit 120 for relative position detection has a function of changing the polarization state of the reflected light b2 at the target 112 with respect to the light b1 and receiving light. In the present embodiment, the relative position detection light receiving unit 120 includes a beam splitter 121, a first polarizing beam splitter 122, a first light receiving element 123, a second light receiving element 124, a 1/4 wave plate 125, and a second. It includes a polarizing beam splitter 126, a third light receiving element 127, and a fourth light receiving element 128.

The beam splitter 121 is a polarization-independent unpolarizing beam splitter that splits the light b2 reflected by the reflector 114 into two. The first polarizing beam splitter 122 is a polarizing beam splitter that reflects the S component of one of the reflected light b7 branched by the beam splitter 121 and transmits the P component. The first light receiving element 123 is a light receiving element including a photodiode or the like that receives the transmitted light of the first polarizing beam splitter 122 and performs photoelectric conversion. The second light receiving element 124 is a light receiving element including a photodiode or the like that receives the reflected light b10 of the first polarizing beam splitter 122 and performs photoelectric conversion. The second polarization beam splitter 126 is a polarization beam splitter that reflects the S component of the other reflected light b8 branched by the beam splitter 121 and transmits the P component. The 1/4 wave plate 125 is interposed between the beam splitter 121 and the second polarizing beam splitter 126, and has a function of shifting the phase of the reflected light b8 by 1/4 wavelength. The third light receiving element 127 is a light receiving element including a photodiode or the like that receives the reflected light b11 of the second polarizing beam splitter 126 and performs photoelectric conversion. The fourth light receiving element 128 is a light receiving element including a photodiode or the like that receives the transmitted light b12 of the second polarizing beam splitter 126 and performs photoelectric conversion.

A signal indicating a change in the polarization state of the reflected light b2 received by the light receiving unit 120 for relative position detection is sent to the relative position information output unit 130, and the relative position information output unit 130 is based on the signal of the target 112. Outputs relative position information based on displacement in the measurement direction. As shown in FIG. 4, the relative position information output unit 130 includes a first differential amplifier 131, a second differential amplifier 132, a first A / D converter 133, and a second A / D. It includes a converter 134, a waveform correction processing unit 135, and an incremental signal generator 136.

In the first differential amplifier 131, the first light receiving element 123 and the second light receiving element 124 of the light receiving unit 120 for relative position detection are connected to the input end, and the first A / D converter 133 is connected to the output end. It is connected. Further, in the second differential amplifier 132, the third light receiving element 127 and the fourth light receiving element 128 of the light receiving unit 120 for relative position detection are connected to the input end, and the second A / D converter is connected to the output end. 134 is connected. The first A / D converter 133 and the second A / D converter 134 are connected to the waveform correction processing unit 135. The waveform correction processing unit 135 is connected to the incremental signal generator 136.

The relative position information output unit 130 has a function of outputting displacement information of the target 112 based on the intensity of the light received by the light receiving unit 120 for relative position detection. Specifically, in the relative position information output unit 130, first, the signal from the first light receiving element 123 made of a photodiode and the second light receiving element 124 is transmitted by the first differential amplifier 131 to the third light receiving element. The signals from 127 and the fourth light receiving element 128 are differentially amplified by the second differential amplifier 132 at predetermined amplification factors α and β, respectively. The Magnifications α and β are set so that the amplitudes of the two signals after amplification are equal to each other and according to the inputtable range of the A / D converters 133 and 134 in the subsequent stage.

The two signals obtained by differential amplification by the differential amplifiers 131 and 132 are digitized from analog sin and cos signals to digital signals by the A / D converters 133 and 134, and are digitized by the waveform correction processing unit 135. Arithmetic processing is performed. In the waveform correction processing unit 135 and the incremental signal generator 136, calculations are performed by a programmable logic device or the like incorporating a DSP, and the amplitude fluctuation, offset fluctuation, and phase fluctuation of the sinθ signal and cosθ signal caused by the disturbance of the analog signal are generated. Make corrections. By obtaining θ = Atan θ from the corrected signal, more accurate scale position information can be generated and an incremental signal of a required format can be generated.

In the present embodiment, the beam reflected from the target 112 is reflected by irradiating the target 112 having the birefringent member 116 whose thickness has changed along the measurement direction with a polarized beam and moving the target 112 in the measurement direction. The polarization state can be changed. Then, the relative position information output unit 130 detects the change in the polarization state by the four light receiving elements 123, 124, 127, 128, and the signal photoelectrically converted from the four light receiving elements 123, 124, 127, 128. The phase of the incremental signal is obtained based on the above, and the relative position information of the target 112 moving in the measurement direction is output from the incremental signal generator 136.

At that time, by adjusting the angle θ ₁ of the tip 116a of the birefringence member 116 and the angle θ ₂ between the bottom surface 116b of the birefringence member 116 and the reflector 114, the signal cycle of the incremental signal can be freely set to a predetermined magnitude. Can be decided. Therefore, since the relative position information of the target 112 can be reliably and accurately output while being able to handle a wide range of signal cycles with a simple configuration, stable and highly accurate displacement detection of the object to be measured 10 becomes possible.

Next, the operation of the relative position detecting means according to the embodiment of the present invention will be described with reference to the drawings. FIG. 5A is an explanatory diagram showing the measurement principle of the relative position detecting means according to the embodiment of the present invention by the birefringent member, and FIG. 5B is an explanatory diagram relating to the crystal axis of the birefringent member. Is.

The relative position detecting means 120 according to the embodiment of the present invention detects the movement amount L of the target 112 by observing the polarization state of the light beam. Specifically, as shown in FIG. 5A, light is transmitted through the birefringent member 116 having a different thickness depending on the transmission portion, and a phase difference is added between the P-polarization and the S-polarization. The phase difference is converted into a variation in the amount of light by a polarizing element (not shown), and the amount of movement L is detected.

At this time, if the optical path difference between P-polarization and S-polarization is represented by d, the refractive index difference between P-polarization and S-polarization is represented by Δn, and the wavelength of the light source is represented by λ, the phase difference Δφ can be represented by the following equation (1).
Δφ = 2π × d × Δn / λ ... (1)

As shown in FIG. 5A, the angle θ ₁ of the tip 116a of the birefringence member 116, the angle θ ₂ between the bottom surface 116b of the birefringence member 116 and the reflector 114, and the P polarization when the movement amount L is applied. The optical path difference d between S and S polarization can be expressed by the following equation (2).
d = L (tan θ ₁ -tan (θ ₁ -θ ₂ )) ... (2)

Since Δφ = 2π when the movement amount L is moved, the relational expression of the following equation (3) is established by rearranging the above-mentioned equation (1).
d = λ / Δn ... (3)

From the above-mentioned equations (1), (2), and equations (3), the relational expression of the following equation (4) is established.
L = λ / (Δn × (tan θ ₁ -tan (θ ₁ -θ ₂ ))) ... (4)

From the above equation (4), the movement amount L of the target 112 can be set to an arbitrary size at an angle θ ₁ of the tip 116a of the birefringence member 116 and an angle θ ₂ between the bottom surface 116b of the birefringence member 116 and the reflector 114. You can see that it can be changed. Further, since the dead path is 0, only the phase difference due to the movement of the target 112 can be detected.

For example, when the material of the birefringence member 116 is quartz, the wavelength λ of the light source is 790 nm, the movement amount L is 100 μm, and θ ₁ is 20 degrees, θ ₂ is 35.895 ... ≈ 35.9. It becomes a degree. That is, since the angles θ ₁ and θ ₂ of the birefringent member 116 can be adjusted according to the movement amount L of the target 112, the pitch of the movement amount L of the target 112 can be freely changed to a desired size. Therefore, the period of the incremental signal indicating the relative position information of the target 112 can be freely determined.

Further, the birefringent member 116 is made of a material having a different refractive index depending on the crystal axis (optical axis). Therefore, as shown in FIG. 5B, when the polarization direction of the incident light is tilted with respect to the crystal axis A1, the refractive index changes depending on the tilt angle θ ₃ . Specifically, the refractive index n _p of P polarization, the refractive index n _s of S polarization, the refractive index n _x in the X direction of the double refraction member, and the refractive index ny in the _Y direction of the double refraction member are expressed by the following equations, respectively. The relational expressions of (5) and (6) are established.
n _s = n _y ... (5)

If θ ₃ = 0 °, the P polarization of the incident light is aligned with the X-axis of the crystal, so that n _p = n _x , and similarly, the S polarization is n _s = n _y . That is, since the refractive index difference Δn can be changed by the incident light on the crystal axis A1, the relational expression of the following equation (7) is established.

Substituting the refractive index difference Δn represented by the above equation (7) into the equation (4) showing the relationship between the movement amount L of the target 112 and the angles θ ₁ and θ ₂ described above, the relationship of the following equation (8) The formula holds.

As shown in the above equation (8), the angle θ ₁ of the tip 116a of the birefringence member 116, the angle θ ₂ between the bottom surface 116b of the birefringence member 116 and the reflector 114, and the inclination angle of the incident light with respect to the crystal axis A1. The movement amount L of the target 112 can be changed by θ ₃ . That is, since the angles θ ₁ and θ ₂ of the birefringence member 116 and the inclination angle θ ₃ of the incident light with respect to the crystal axis A1 can be adjusted according to the movement amount L of the target 112, the pitch of the movement amount L of the target 112 is desired. You will be able to freely change the size.

Next, the configuration of the absolute position detecting means provided in the displacement detecting device according to the embodiment of the present invention will be described with reference to the drawings. FIG. 6A is a side view showing an outline of the configuration of an absolute position detecting means provided in the displacement detecting device according to the embodiment of the present invention, and FIG. 6B is a variable view provided in the absolute position detecting means. FIG. 6C is a plan view showing the configuration of the reflective film, and FIG. 6C is a block diagram showing the configuration of the absolute position information output unit provided in the absolute position detecting means.

The absolute position detecting means 140 measures the measurement direction of the object 10 to be measured (FIGS. 6A and 6B) based on the change in the amount of reflected light with respect to the light branched by the light source side beam splitter 108 (see FIG. 1). ) Has a function of detecting the absolute position of the displacement in the X direction). In the present embodiment, the absolute position detecting means 140 is placed on the object 10 to be measured, the prism 144 in which the light b4 from the light source 102 is irradiated through the mirror 142, and the reflected light b5 in the prism 144 with respect to the light b4. , Based on the displacement of the prism 144 in the measurement direction based on the change in the light amount of the reflected light b5 and b6 received by the light receiving unit 150 for absolute position detection and the light receiving unit 150 for absolute position detection that receives light by changing the light amount of b6. It includes an absolute position information output unit 160 (see FIG. 6C) that outputs absolute position information.

In the present embodiment, as shown in FIG. 6A, irradiation of light b4 placed on the object to be measured 10 is performed in order to optically detect the absolute position information of the displacement of the object to be measured 10 in the measurement direction. The object is a prism 144 having a predetermined thickness. Then, as shown in FIG. 6B, a variable reflective film 146 whose reflection characteristics change along the measurement direction (X direction shown in FIG. 6B) is provided on the top surface side of the prism 144.

As shown in FIG. 6A, the light receiving unit 150 for absolute position detection receives light through a second lens 151 that collects the reflected light b5 of the variable reflecting film 146 of the light b4 and exchanges photoelectrics. From a fifth light receiving element 152 made of a photodiode or the like and a photodiode or the like that receives light through a third lens 153 that collects the reflected light b6 of the interfering light b4 on the object 10 to be measured and exchanges photoelectric light. A sixth light receiving element 154 is provided. Then, the signal obtained by photoelectrically measured by the fifth light receiving element 152 and the sixth light receiving element 154 is sent to the absolute position information output unit 160 shown in FIG. 6 (C).

As shown in FIG. 6C, the absolute position information output unit 160 includes a first absolute position information calculator 161, a second absolute position information calculator 162, a comparator 163, an adder 164, and an absolute position conversion. It is equipped with a vessel 165. The first absolute position information calculator 161 converts the signal photoelectrically converted by the fifth light receiving element 152 into a voltage value. The second absolute position information calculator 162 converts the signal photoelectrically converted by the sixth light receiving element 154 into a voltage value. The comparator 163 calculates the difference in the position information between the first absolute position information calculator 161 and the second absolute position information calculator 162. The adder 164 adds the output signals of the first absolute position information calculator 161 and the second absolute position information calculator 162. The absolute position converter 165 outputs the displacement and the absolute position information of the measurement direction X of the prism 144 having the variable reflector 146 based on the information of the comparator 163 and the adder 164.

As described above, in the absolute position detecting means 140 of the present embodiment, the coherent light b4 incident through the mirror 142 passes through the variable reflective film 146, one is reflected by the variable reflective film 146, and the other is reflected. , Transmits through the variable reflective film 146. Then, the difference in the amount of light between the reflected light b5 reflected by the variable reflecting film 146 and the reflected light b6 transmitted by the variable reflecting film 146 and then reflected by the object 10 to be measured is the difference between the fifth light receiving element 152 and the sixth light receiving element 154. DC cancellation is performed by picking up with, taking a differential, and subtracting. For example, even if there is a fluctuation in the amount of light or noise, it can be eliminated by taking a differential. Therefore, by reading the changes in the transmittance and the reflectance more efficiently, the absolute position information of the target can be output reliably and accurately, so that stable and highly accurate displacement detection becomes possible.

Next, the operation of displacement detection by the displacement detection device according to the embodiment of the present invention will be described with reference to the drawings. FIG. 7 is a block diagram showing an outline of signal output by the displacement detection device according to the embodiment of the present invention, and FIG. 8 is an incremental signal generator provided in the relative position detection means according to the embodiment of the present invention. It is explanatory drawing which shows the angle of the resage signal, and FIG. 9 is a graph which shows the signal output of each component of the displacement detection apparatus which concerns on one Embodiment of this invention.

In the displacement detection device 100 according to the embodiment of the present invention, as shown in FIG. 7, an incremental signal indicating relative position information output from the incremental signal generator 136 and a prism 144 output from the absolute position converter 165. The absolute position signal generator 170 outputs the absolute position signal based on the displacement and the absolute position information of the measurement direction X of.

In the incremental signal generator 136 of the relative position information output unit 130 (see FIG. 4), the displacement of the target 112 is based on the signals supplied from the first differential amplifier 131 and the second differential amplifier 132 on the front stage side. The direction and the amount of displacement are obtained, and an incremental signal is generated. At that time, the angle θ of the resage signal shown in FIG. 8 is obtained based on the signals supplied from the first differential amplifier 131 (see FIG. 4) and the second differential amplifier 132 (see FIG. 4).

In the present embodiment, the SIN obtained by DC-cancelling the first light-receiving element 123 and the second light-receiving element 124, and the DC-cancellation of the third light-receiving element 127 and the fourth light-receiving element 128 are performed. After A / D conversion of each of the obtained COS, an angle calculation is performed to create a resage signal shown in FIG. Specifically, if SIN is written in x and COS is written in y, a circular Lissajous curve can be drawn, and when the incremental signal generator 136 moves the target 112 laterally in the measurement direction, the output is shown in FIG. Draw a circle to show. This is obtained by the angle of unit time and used as displacement information. Since such displacement information is output as the output of the incremental signal generator 136, the angle information of 360 degrees per lap is output, and the angle information is returned and repeated endlessly from 0 degrees to 360 degrees.

For example, in the case of 100 μm in one cycle of 360 degrees, it is 0 mm when θ is 0 degrees, 25 μm when θ is 90 degrees, and 50 μm when θ is 180 degrees. At that time, the incremental signal generator 136 can output the relative position with a resolution of 100 μm / 65536 = 1.53 nm by dividing by a 16-bit A / D converter. On the other hand, the absolute position converter 165 outputs the address information of 100 μm in one cycle of the incremental, and the absolute position signal generator 170 determines the absolute position of the upper 100 μm digit and synthesizes it with the incremental signal.

When the displacement detecting device 100 of the present embodiment is provided with the relative position detecting means 110 and the absolute position detecting means 140 as described above and is designed to have a cycle of 100 μm, the polarization state of the beam reflected from the target 112 can be changed. As shown in FIG. 9, what was vertical polarization changes to counterclockwise circular polarization, and when it goes further, it changes to horizontal linear polarization, and when it goes further, it changes to clockwise circular polarization. It returns to the original state and a signal of one cycle can be taken.

On the other hand, regarding the signal outputs of the first light receiving element 123 and the second light receiving element 124, when the output of the first light receiving element 123 through which the reflected light b2, b7, b9 passes as it is is MAX. , The output of the second light receiving element 124 that receives the reflected light b10 in the first polarizing beam splitter 122 becomes MIN. That is, when the output signal of the first light receiving element 123 has a sine curve, the output signal of the second light receiving element 124 has a −sin curve.

On the other hand, since the reflected light b8 in the beam splitter 121 passes through the λ / 4 wave plate 125, the signal outputs of the third light receiving element 127 and the fourth light receiving element 128 have a cos curve and a -cos curve, respectively. Become.

In the present embodiment, the first differential amplifier 131 takes the difference between the signal outputs of the first light receiving element 123 and the second light receiving element 124, and the second differential amplifier 132 and the third light receiving element 127. Since the signal output of the fourth light receiving element 128 is differential, the output signals of the first differential amplifier 131 and the second differential amplifier 132 have double amplitudes, respectively. At that time, the horizontal line in FIG. 9 indicates 0V, and DC cancellation is performed. As a result, even if the amount of light changes, it changes to the center of 0V, so that there is no error in phase detection. These differential amplification signals are converted into a sine curve and a cos curve, respectively, which are converted into angle information of 360 degrees per week by the incremental signal generator 136.

This angle information is obtained by the above-mentioned resage signal. For example, when the unit of absolute position information is 100 μm, the absolute information is 360 degrees within 100 μm. If it exceeds 100 μm, it will return to its original state, so a periodic signal will not be created and absolute position detection will not be possible. Therefore, this time, when the absolute position detecting means 140 simply transmits the light coming from the laser to the surface and takes a differential, one is reflected and the other is transmitted. For this reason, the balance of this changes linearly, and when subtracted, the signal becomes such that the voltage gradually increases. In the present embodiment, the output signals of the differential amplifiers 131 and 132 are digitally converted by the A / D converters 133 and 134, but the change in voltage is digitally converted and DC canceled by subtracting the digital conversion. A signal is obtained. Therefore, the digital angle value of the incremental signal created by the incremental signal generator 136 can be obtained as a graph in which a gentle gradient increase is repeated in one cycle, and the digital absolute value of the absolute position converter 165 is set at predetermined intervals. A graph is obtained that gradually increases the digital absolute value.

As described above, in the present embodiment, the birefringent member 116 of the target 112 of the relative position detecting means 100 has a wedge-shaped cross section whose thickness changes in the measurement direction, and is based on the tip 116a of the birefringent member 116. Since it is rotatable with respect to the end 116a', the period of the incremental signal can be changed to a desired magnitude depending on the inclination and arrangement of the birefringent member 116. In other words, as in the past, it is possible to change to the desired cycle without changing the parts according to the signal cycle of the incremental signal, so it is possible to handle a wide range of signal cycles with a simple configuration, and the relative position information of the target is reliably accurate. Since it can output well, stable and highly accurate displacement detection becomes possible.

Further, in the present embodiment, since the two light waves for detecting the displacement pass through the same optical path spatially, stable and highly accurate displacement detection is possible without being affected by the disturbance. Further, in the present embodiment, since the relative position detecting means 110 and the absolute position detecting means 140 are provided in-line with respect to the measurement direction of the object to be measured 10, it is possible to correspond to a wide range of incremental signal cycles with a simple configuration. Since the absolute position information based on the relative position information of the target can be output reliably and accurately, stable and highly accurate displacement detection becomes possible, which has extremely great industrial value.

The configuration of the birefringent member 116 of the target 112 of the relative position detecting means 100 according to the embodiment of the present invention is abbreviated that the cross section thereof is wedge-shaped if the thickness changes with respect to the measurement direction. It is not limited to the triangular prism shape. For example, as shown in FIG. 10 (A), the birefringent member 116c having a curved surface shape having an upward convex shape, the birefringent member 116d having a curved surface shape having a concave shape upward, and the birefringent member 116e having a sinusoidal curved surface shape may be used. By forming the birefringent member into a shape whose thickness changes with respect to the measurement direction in this way, as shown in FIG. 10B, the position information with respect to the movement amount in the measurement direction is accompanied by the change in the shape. Therefore, the period of the incremental signal can be changed to a desired magnitude depending on the inclination and arrangement of the birefringent member.

Further, the birefringence member 116 may be composed of a plurality of different members. For example, as shown in FIG. 11A, two birefringent members 116f and 116g may be configured in parallel along the measurement direction so that the sensitivity of the signal output can be changed depending on the measurement location. .. Further, as shown in FIG. 11B, the two birefringent members 116h and 116i are laminated along the incident direction of light, that is, the incident light direction, so that the signal period can be changed. May be. By configuring the birefringent member 116 from a plurality of different members in this way, the sensitivity and period of the signal output indicating the change in the polarization state of the reflected light as the target moves in the measurement direction can be easily achieved with a simple configuration. Can be changed to.

Further, the birefringence member 116 may be configured by laminating a plurality of members having different crystal axis directions along the incident direction of light in order to suppress the influence of thermal fluctuation and wavelength fluctuation of the light source. .. For example, as shown in FIG. 12A, another birefringent member 116k having the same effect on the crystal axis orthogonal to the birefringent member 116j may be superposed. As a result, since the crystal axis directions of the birefringent members 116j and 116k are orthogonal to each other, it is possible to suppress the influence of thermal fluctuations and wavelength fluctuations of the light source. Further, as shown in FIG. 12B, the cross section of the birefringence member 116l is formed into an isosceles triangle shape, and the in-line at the time of measurement is set to the position of the angle center of the isosceles triangle, thereby suppressing the abbe error. Will be able to. Further, as shown in FIG. 12 (C), the birefringent member 116o has the same effect on the crystal axis orthogonal to 90 °, and is emitted by superimposing another birefringent member 116n having the same shape. It is also possible to suppress the angular deviation of the light beam and reduce the thickness of the birefringent members 116n and 116o. It should be noted that these actions / effects can be obtained in the same manner with respect to the correction prisms 129 and 229 described later.

Further, the surface on which the incident light rays are incident on the birefringence member 116 is not limited to the slope surface, and may be another surface. For example, as shown in FIG. 13, when the double refraction member 116p has a plane 116p1 in addition to the slope 116p2, the apex side of the slope 116p2 is installed on the reflector 114 and is perpendicular to the plane 116p1 arranged on the upper side. When an incident light ray is incident on the surface, the refraction angle of the incident light ray can be suppressed, which is effective for high-precision measurement.

In the displacement detecting device 100 including the relative position detecting means 110 according to the embodiment of the present invention, the absolute position detecting means 140 and the relative position detecting means 110 are provided in-line with respect to the measurement direction of the object to be measured 10. As long as it has a configuration, it may be another configuration.

For example, as shown in FIG. 14, the reflecting object placed on the object to be measured may be a prism 244 with a reflective film common to the absolute position detecting means 240 and the relative position detecting means 210. As shown in FIG. 14, the prism with a reflective film 244 provided in the displacement detection device 200 according to this modification has a box shape, and prism surfaces 244a and 244b having a substantially V-shaped cross section are provided inside. .. A birefringent member 216 and a variable reflective film 246 are provided in-line (coaxially) along the measurement direction on the top surface side of the prism with a reflective film 244. The birefringence member 216 and the variable reflective film 246 do not have to be provided in-line, but in this case, an appe error may occur in absolute position detection and relative position detection due to a change in the attitude of the object to be measured. It is preferable to provide it on the top. Since the configuration and operation of the birefringence member 216 and the variable reflection film 246 are the same as those provided in the displacement detection device 100 according to the embodiment of the present invention, the description thereof will be omitted.

In this modification, in order to enable the light to be incident in the vertical direction at each light receiving element 223, 224, 227, 228, 252, 254, the relative position detecting means 210 has an input stage of the beam splitter 221. A fourth lens 217 for condensing the reflected light b'3 of the reflected light b'2 by the mirror 244 with a reflecting film of the light b'1 from the light source 202 is provided on the side, and a first polarized beam is provided. A mirror 218 is provided on the output stage of the splitter 222 on the first light receiving element 223 side, and a mirror 219 is provided on the output stage of the second polarized beam splitter 226 on the third light receiving element 227 side. On the other hand, in the absolute position detecting means 240, as shown in FIG. 14, a splitter 255, a polarizing beam splitter 256, and a 1/4 wave plate 257 are provided between the mirror 242 and the prism with a reflecting plate 244, and the absolute position detecting means 240 is provided. A mirror 258 is provided in the output stage on the fifth light receiving element 252 side of the polarizing beam splitter 256.

As described above, in the displacement detection device 200 of the present modification, the thickness of the birefringence member 216 of the target of the relative position detection means 200 changes in the measurement direction, similarly to the displacement detection device 100 according to the embodiment of the present invention. Since the cross section is wedge-shaped and the tip 216a of the birefringence member 216 is rotatable with respect to the base end 216b, the period of the incremental signal can be set to a desired size depending on the inclination and arrangement of the birefringence member 216. Can be changed to. Therefore, since the relative position information of the target can be reliably and accurately output while being able to handle a wide range of signal cycles with a simple configuration, stable and highly accurate displacement detection of the object to be measured becomes possible.

Further, the reflecting object to be placed on the object to be measured is a prism 244 with a reflecting film common to the absolute position detecting means 240 and the relative position detecting means 210, and each light receiving element 223, 224, 227, 228, 252, 254. Since the structure allows light to be incident in the vertical direction, the space of the device can be saved, and it has an extremely large industrial value.

In the present embodiment, as shown in FIG. 14, when the light source 202 is introduced by a fiber, the wavelength fluctuation may be estimated and corrected by measuring the temperature of the light source 202. On the other hand, when the light source 202 is not a fiber and the LD is included in the sensor head portion, the same wavelength fluctuation correction can be performed by arranging the thermometer near the LD and the sensor head portion.

Further, the optical axis of the birefringence member 216 does not necessarily have to be parallel or orthogonal to the measurement direction. For example, in the birefringence member 216 having an optical axis parallel to or perpendicular to the x-axis of FIG. 14, when the optical axis is rotated 45 degrees with the z-axis as the rotation axis with respect to the x-axis, the light source 202 is rotated. In the case of linearly polarized light, the light source 202 and the light receiving unit 220 for relative position detection may be tilted by 45 degrees with the z-axis as the rotation axis. On the other hand, when the light source 202 is circularly polarized, it is not necessary to rotate the light source 202. By increasing the degree of freedom of the optical axis in this way, flexible and highly accurate displacement detection becomes possible.

Further, in the present embodiment, the polarization state of the light incident on the target birefringence member 216 from the light source unit (sensor head) may be circularly polarized. When the polarization state of the incident light is circularly polarized light, the electric field component ratios of the normal light and the abnormal light in the birefringent medium can always be equal even if the azimuth of the sensor head shifts.

Further, in the present embodiment, as shown in FIG. 14, a 1/4 wave plate 225 is provided between the beam splitter 221 and the second polarizing beam splitter 226, but this is removed and the beam splitter 221 is used. A 1/4 wave plate 225 may be arranged immediately before. At this time, the optical axis of the 1/4 wave plate 225 is set at an angle of 45 degrees with respect to the optical axis of the birefringence member, and the azimuth angles of the P and S polarization axes of the PBS of the interference signal detection unit are set. It is preferable to adjust so that a +/- sin signal and a +/- cos signal can be obtained.

The relative position detection means 210 of the displacement detection device 200 shown in FIG. 14 is provided with one light receiving unit 220 for relative position detection that detects a change in the polarization state of the reflected light as the target moves in the measurement direction. However, two may be provided along the measurement direction. For example, as shown in FIG. 15, the first relative position detection light receiving unit 220a and the second relative position detection light receiving unit 220b are arranged side by side along the measurement direction, and the two relative position detection light receiving units 220a and 220b are arranged side by side. Is operated by the same light source 202 to obtain the amount of phase fluctuation at two points of the birefringent member 216, thereby estimating and correcting the amount of wavelength fluctuation based on the difference between the two points.

For example, the phase difference Φ between normal light and abnormal light due to wavelength fluctuation is the thickness d of the birefringent member 216 that gives a phase difference of Φ when the wavelength of light is λ and the wavelength λ, and the difference in refractive index between normal light and abnormal light is Δn. Then, it is expressed by the following equation (9).
Φ = Δn * d / λ ... (9)

The thickness d of the birefringent member 216 that gives a phase difference of Φ at the wavelength λ is as follows, where k is the inclination of the slope of the birefringence member 216 and x is the amount of movement of the birefringence member 216 in the measurement direction. It is represented by 10).
d = k * x ... (10)

Therefore, the phase difference ΔΦ1 between normal light and abnormal light detected by the first relative position detection light receiving unit 220a is the phase difference ΔΦ1 and ΔΦ'1 when the wavelengths of the light are λ, λ', wavelengths λ, and λ'. When the thickness d1 of the birefringent member 216 and the difference in the refractive index between the normal light and the abnormal light are Δn, they are represented by the following equations (11) to (13).
Φ1 = Δn * d1 / λ ... (11)
Φ'1 = Δn * d1 / λ'... (12)
ΔΦ1 = Φ'1-Φ1 ... (13)

On the other hand, the phase difference ΔΦ2 between normal light and abnormal light detected by the second relative position detection light receiving unit 220b has a phase difference of ΔΦ2 and ΔΦ'2 when the wavelengths of the light are λ, λ', wavelengths λ and λ'. Assuming that the thickness d2 of the birefringent member 216 and the difference in the refractive index between the normal light and the abnormal light are Δn, they are represented by the following equations (14) to (16).
Φ2 = Δn * d2 / λ ... (14)
Φ'2 = Δn * d2 / λ'... (15)
ΔΦ2 = Φ'2-Φ2 ... (16)

From the above equations (9) to (16), the phase difference ΔΦ12 between the normal light and the abnormal light detected by the first relative position detection light receiving unit 220a and the second relative position detection light receiving unit 220b is the following equation (17). ).
ΔΦ12 = Δn * k * {(λ-λ') / λλ'} * Δx ... (17)

Therefore, the wavelength λ'after modulation is represented by the following equation (18).
λ'= {Δn * k * λ * Δx} / {ΔΦ12 * λ + Δn * k * Δx} ... (18)

As described above, in the present embodiment, the phase difference between normal light and abnormal light due to wavelength fluctuation is proportional to the thickness d of the birefringent member 216. Therefore, if Δx and the slope k of the birefringent member 216 are known, the wavelength fluctuation You can estimate the amount. Therefore, the wavelength fluctuation amount can be easily estimated based on the difference in the phase fluctuation amount of the polarization state of the reflected light detected by the light receiving units 220a and 220b for relative position detection, and the wavelength fluctuation amount is corrected based on the estimation. By doing so, more accurate displacement detection becomes possible.

The shape of the prism with a reflective film 244 provided in the displacement detection device 200 according to the modified example of the embodiment of the present invention is not limited to the shape shown in FIG. For example, as shown in FIG. 16, the cross section of the prism with a reflective film 244'may be a hexagon whose cross section is symmetrical.

Specifically, as shown in FIG. 16, in the prism with a reflective film 244', the prism surfaces 244'a and 244'b are provided in the vicinity of the bottom surface side of the prism 244'with a reflective film, and the prism 244 with a reflective film is provided. A reflective film 248 is provided substantially in the center on the top surface side of the screen. Since the configuration and operation of the birefringence member 216 and the variable reflection film 246 are the same as those provided in the displacement detection device 100 according to the embodiment of the present invention, the description thereof will be omitted.

By configuring the reflecting film-equipped prism 244'in this way, the reflected light b'2a, b'11a on the prism surface 244'a of the incident light b'1 and b'10 on the reflecting film-equipped prism 244' Is reflected by the reflective film 248, and the reflected light b'2b and b'11b by the reflective film 248 are reflected by the prism surface 244'b. Therefore, even if the prism with a reflective film 244'moves in the Y direction, which is perpendicular to the measurement direction X, the incident light b'1 and b'10 and the reflected light b'b on the prism surface 244'b. 3. Since the interval I1 of b'12 becomes constant, the light reception by each light receiving element 223, 224, 227, 228, 252, 254 (see FIG. 14) provided in the absolute position detecting means 240 and the relative position detecting means 210 is stable. Will come to do. Therefore, stable and highly accurate displacement detection is possible by the absolute position detecting means 240 (see FIG. 14) and the relative position detecting means 210 (see FIG. 14).

Further, in the displacement detection devices 100 and 200, when it cannot be said that the diameter of the beam used for the measurement is sufficiently small with respect to the length of one cycle of the absolute position signals of the absolute position detection means 140 and 240, FIGS. 17 and 18 show. As shown in the above, the correction prisms 129 and 229 may be transmitted before the beam is incident on the birefringence members 116 and 216. At that time, the correction prisms 129 and 229 use members having the same function as the birefringent members 116 and 216, for example, members having the same material and shape. However, the optical axis of the crystal of the correction prisms 129 and 229 is orthogonal to the birefringent materials 116 and 216 by 90 °. Further, the installation location may be either before or after the incident on the birefringent members 116 and 216, but it is installed only on one of them.

By providing the correction prisms 129 and 229 having such a configuration on the birefringence members 116 and 216 either before or after the incident, the polarization state in the beam distribution transmitted through the birefringence members 116 and 216 becomes uniform. This enables stable and highly accurate displacement detection by the absolute position detecting means 140 and 240. As shown in FIG. 19A, the correction prisms 129a and 229a face each other using members having the same function as the birefringent members 116 and 216, for example, members having the same material and shape. It may be arranged. Further, as shown in FIG. 19B, even if the correction prisms 129b and 229b are arranged symmetrically with respect to the birefringent members 116 and 216, the same effect can be obtained.

Further, as shown in FIG. 20, the polarizing plate 230 may be mounted between the first lens 204 and the light source side beam splitter 208 with respect to the displacement detection device 200. By providing the polarizing plate 230 in this way, the beam used for displacement detection can have a higher extinction ratio. As a result, the displacement detection device 200 using polarization enables more accurate displacement detection. At this time, in the absolute position detecting means 240, as shown in FIG. 20, the installation of the splitter 255 (see FIGS. 14 and 18) between the mirror 242 and the polarizing beam splitter 256 may be omitted. .. The polarizing plate 230 may be arranged anywhere as long as it is between the light source 202 and the birefringence member 216, but the crystal axis of the polarizing plate 230 may be arranged immediately before the birefringence member 216 and the crystal axis of the birefringence member 216. It is most effective to displace it by 45 ° with respect to it. In that case, even if the object to be measured rotates in the Z-axis direction, its influence can be suppressed, which is preferable. Further, when the polarizing plate 230 is attached to the birefringence member 216, even if the object to be measured rotates in the Z-axis direction, the polarizing plate 230 also rotates, so that the influence can be suppressed.

Further, as shown in FIG. 21, the azimuth correction unit 380 for performing azimuth correction on the reflected light is further provided in the relative position detection light receiving unit 320 provided in the relative position detection means 310 of the displacement detection device 300 of the present embodiment. You may. In the present embodiment, as shown in FIG. 21, the azimuth correction unit 380 includes a beam splitter 381 for incident light, a reflection prism 382 for incident light, a polarizing plate 383 for azimuth correction, a lens 384 for azimuth rotation detection, and azimuth rotation detection. A beam splitter 385, a polarizing plate for detecting azimuth rotation 386, a reflection prism 387 for a power monitor, a light receiving element 388 for a power monitor, and a light receiving element 389 for angle measurement are provided. In this embodiment, in order to increase the azimuth detection angle sensitivity, a 1/2 wave plate, a dub prism, or the like is used immediately before the beam splitter 385 for azimuth rotation detection or immediately before the light receiving element 389 for angle measurement. An optical element that increases the change in the polarization azimuth may be provided.

By providing the azimuth correction unit 380 in this way, the incident light b "1 from the light source 302 is branched by the incident light beam splitter 381, and the branched light b" 15 is reflected by the incident light reflection prism 382. .. Then, the reflected light b "16 is reflected by the substantially V-shaped prism surfaces 344a and 344b of the prism 344 with a reflective film, and the reflected light b" 18 is the azimuth correction polarizing plate 383 and the azimuth rotation detection lens 384. Then, the light is incident on the beam splitter 385 for detecting the rotation of the azimuth.

In the reflected light b "18 incident on the beam splitter 385 for azimuth rotation detection, the branched light b" 19 is reflected by the reflecting prism 387 for the power monitor, and the reflected light b "20 is incident on the light receiving element 388 for the power monitor. On the other hand, the transmitted light b "21 of the reflected light b" 18 incident on the beam splitter 385 for detecting azimus rotation passes through the polarizing plate 386 for detecting azimus rotation and then incidents on the light receiving element 389 for angle measurement.

The light receiving element 389 for angle measurement reads the angle difference between the azimuth correction polarizing plate 383 and the azimuth rotation detecting polarizing plate 386, and measures the azimuth angle. When the azimuth rotates, the resage is distorted, and the distortion causes a measurement error, so it is necessary to correct it. At that time, if the amount of azimuth angle deviation is known in advance, correction can be performed, so a function for detecting the azimuth angle is required. Therefore, in the present embodiment, the light receiving unit 320 for relative position detection is provided with an azimuth correction unit 380 that corrects the azimuth of the reflected light. Therefore, the difference due to the angle difference of the reflected light transmitted through the polarizing plates 383 and 386 is corrected, and more accurate displacement detection becomes possible. The configuration and operation of the other components of the relative position detecting means 310 of the displacement detecting device 300 and the absolute position detecting means 340 in the present embodiment are the displacement detecting device 200 according to the modification of the embodiment of the present invention. Since it is the same as the above, the description thereof will be omitted.

Although each embodiment of the present invention has been described in detail as described above, those skilled in the art can easily understand that many modifications that do not substantially deviate from the new matters and effects of the present invention are possible. You can do it. Therefore, all such modifications are included in the scope of the present invention.

For example, a term described at least once in a specification or drawing with a different term in a broader or synonymous manner may be replaced by that different term anywhere in the specification or drawing. Further, the configuration and operation of the displacement detecting device and the relative position detecting means are not limited to those described in each embodiment of the present invention, and various modifications can be carried out.

10 Subject, 100, 200, 300 Displacement detector, 102, 202, 302 Light source, 104, 204 First lens, 106, 255 Polarizer, 108, 208 Light source side beam splitter, 110, 210, 310 Relative position Detection means, 112 target, 114, 244, 344 reflector, 116, 216, 316 double polarizing member, 116a tip, 116a'base end, 116b bottom surface, 120, 220, 320 light receiving part for relative position detection, 121, 221 321 beam splitter, 122, 222, 322 first polarized beam splitter, 123, 223, 323 first light receiving element, 124, 224, 324 second light receiving element, 125, 225, 325 1/4 wave plate, 126. , 226, 326 Second polarizing beam splitter, 127, 227, 327 Third light receiving element, 128, 228, 328 Fourth light receiving element, 129, 229 Correction prism, 130 Relative position information output unit, 131 First Differential amplifier, 132 2nd differential amplifier, 133 1st A / D converter, 134 2nd A / D converter, 135 waveform correction processing unit, 136 incremental signal generator, 140, 240, 340 absolute Position detecting means, 142, 242, 342 mirror, 144 prism, 146, 246, 346 variable reflecting film, 150 light receiving part for absolute position detection, 151, 251, 351 second lens, 152, 252, 352 fifth light receiving Element, 153, 253, 353, 3rd lens, 154, 254, 354, 6th light receiving element, 160 absolute position information output unit, 161 first absolute position information calculator, 162 second absolute position information calculator, 163 Comparer, 164 Adder, 165 Absolute Position Converter, 170 Absolute Position Signal Generator, 230 Polarizing Plate, 380 Azimas Correction Unit

Claims (9)

It is a relative position detecting means that optically detects the relative position of the displacement of the object to be measured in the measurement direction.
A target placed on the object to be measured and irradiated with light from a light source,
A light receiving unit for relative position detection that changes the polarization state of the reflected light at the target with respect to the light and receives light.
A relative position information output unit that outputs relative position information based on the displacement of the target in the measurement direction based on the change in the polarization state of the reflected light received by the light receiving unit for relative position detection is provided.
The target is
A reflective object placed on the object to be measured and
A birefringent member provided on the reflector and whose thickness changes from the tip end to the base end along the measurement direction is provided.
The birefringent member is a relative position detecting means, characterized in that the tip end side of the bottom surface is rotatably configured with respect to the reflecting object, with the base end side of the bottom surface as the center. The light receiving unit for relative position detection detects a change in the polarization state of the reflected light as the target moves in the measurement direction.
The relative position information output unit according to claim 1, wherein the relative position information output unit outputs the relative position information of the target based on a signal obtained by photoelectric conversion of a change in the polarization state of the reflected light. Position detection means. The light receiving unit for relative position detection is
A beam splitter that splits the reflected light into two, and
A first polarizing beam splitter that reflects the S component of one of the reflected lights branched by the beam splitter and transmits the P component,
A first light receiving element that receives the transmitted light of the first polarizing beam splitter, and
A second light receiving element that receives the reflected light of the first polarizing beam splitter, and
A second polarization beam splitter that reflects the S component of the other reflected light branched by the beam splitter and transmits the P component.
A quarter wave plate interposed between the beam splitter and the second polarization beam splitter,
A third light receiving element that receives the reflected light of the second polarizing beam splitter, and
The relative position detecting means according to claim 1 or 2, further comprising a fourth light receiving element that receives the transmitted light of the second polarizing beam splitter. The birefringent member is characterized in that a plurality of different members are configured in parallel along the measurement direction, or a plurality of different members are laminated along the incident direction of the light. The relative position detecting means according to any one of claims 1 to 3. The relative position detecting means according to claim 4, wherein the birefringent member is configured by laminating a plurality of members having different crystal axis directions along the incident direction of the light. The relative position detecting means according to any one of claims 1 to 5, wherein a correction prism is provided on either the front stage side or the rear stage side of the birefringence member with respect to the light source. Two light receiving units for relative position detection are provided along the measurement direction, and the wavelength fluctuation amount is based on the difference in the phase fluctuation amount of the polarization state of the reflected light detected by the light receiving units for relative position detection. The relative position detecting means according to any one of claims 1 to 6, wherein the relative position detecting means is estimated and corrected. The relative position detecting means according to any one of claims 1 to 7, wherein a polarizing plate is further provided between the light source and the birefringent member. The relative position detecting means according to any one of claims 1 to 8, wherein the light receiving unit for relative position detection is further provided with an azimuth correction unit that corrects azimuth with respect to the reflected light.

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