JP5235554B2 - Optical displacement measuring device - Google Patents

Description

  The present invention relates to an optical displacement measuring device that detects a relative movement position of a movable part such as a machine tool or a semiconductor manufacturing apparatus. Specifically, a micro-corner cube prism assembly mirror in which corner cube prisms are arranged in a reflective optical system that irradiates the diffraction grating again with two diffracted lights diffracted by the diffraction grating and returns the reflected light in the direction of the optical axis on which the reflected light is incident. By providing, it suppresses the light quantity fall when a foreign material etc. adhere to a scale part.

  2. Description of the Related Art Conventionally, an optical displacement measuring apparatus using a diffraction grating is known as an apparatus for detecting the relative movement position of a movable part such as a machine tool or a semiconductor manufacturing apparatus (see, for example, Patent Document 1).

  FIG. 10 is a block diagram showing an example of a conventional optical displacement measuring device. In the conventional optical displacement measuring apparatus 200, the coherent light La emitted from the coherent light source 201 is collected by the lens 202, divided into two coherent lights La1 and La2 by the polarization beam splitter 203, and the diffraction grating 204. Is irradiated. The two coherent lights irradiated on the diffraction grating 204 are diffracted by the diffraction grating 204 to generate two one-time diffracted lights Lb1 and Lb2. The two one-time diffracted beams Lb1 and Lb2 are reflected by the reflection optical system 205 having the plane mirror 205a and the quarter wavelength plate 205b, return the same optical path, the polarization direction is changed, and the diffraction grating 204 is irradiated again. The

  The two one-time diffracted beams Lb1 and Lb2 irradiated on the diffraction grating 204 are diffracted by the diffraction grating 204 to generate two two-time diffracted beams Lc1 and Lc2. The two two-time diffracted beams Lc1 and Lc2 return to the same optical path as the two coherent beams La1 and La2, and enter the polarization beam splitter 203. The two two-time diffracted lights Lc1 and Lc2 incident on the polarization beam splitter 203 are superimposed on each other by the polarization beam splitter 203, and the interference light Ld obtained by causing the two two-time diffracted lights Lc1 and Lc2 to interfere with each other is received by the light receiving unit 206. The

  In the optical displacement measuring apparatus 200 having such a configuration, the diffraction grating 204 moves in the grating vector direction in accordance with the movement of the movable part, thereby causing a phase difference between the two twice-diffracted lights. In the optical displacement measuring apparatus 200, two two-time diffracted lights are caused to interfere with each other, an interference signal is detected, a phase difference between the two two-time diffracted lights is obtained from the interference signal, and a moving position of the diffraction grating is detected.

  In the conventional optical displacement measuring apparatus 200, the reflection optical system 205 is constituted by a plane mirror 205a. Further, the optical system is configured so that the two coherent lights are focused on the surface of the plane mirror 205a.

In order to solve the above-described problem, the present invention has a diffraction grating that diffracts irradiated light, a scale section that relatively moves in the grating vector direction of the diffraction grating, a light emitting section that emits coherent light, and light emission The coherent light emitted by the unit is divided into two coherent lights, and each coherent light is irradiated to the diffraction grating of the scale unit to generate two one-time diffracted lights and two one-time diffracted lights Irradiates and receives two diffracted lights generated by diffracting the light by a diffraction grating and reflects two one-time diffracted lights generated by diffracting two coherent lights by the diffraction grating. A reflection optical system that irradiates the diffraction grating with two one-time diffracted lights, and a light receiving unit that receives the interference light obtained by interfering the two two-time diffracted lights with the irradiation light-receiving optical system and detects an interference signal. The reflective optical system has a vertex that combines three right angles. Cube-corner prisms formed of triangular pyramid prism has a micro-corner cube prisms collectively mirrors arranged side by side in rows and columns, to return in the direction of the optical axis of the incident light and reflects the incident light, the reflecting optical system Each of the corner cube prisms is an optical displacement measuring device having a size equivalent to a foreign substance that may adhere to the scale portion .

  FIG. 11 and FIG. 12 are operation explanatory views showing the problems of the conventional optical displacement measuring device. In the conventional optical displacement measuring apparatus 200, the optical path divided by the polarization beam splitter 203 is the same for the forward path and the return path, and the diffracted light diffracted by the diffraction grating 204 is returned to the polarization beam splitter 203 to generate interference light. Yes. For this reason, when the plane mirror 205a is used in the reflection optical system 205, if the mounting angle of the plane mirror 205a is shifted, light does not return as shown by a two-dot chain line in FIG. Further, if the mounting position of the flat mirror 205a is shifted along the optical axis, the focal position changes. Thereby, when attaching a plane mirror, a delicate angle and position adjustment are required.

  Further, in the conventional optical displacement measuring apparatus 200, the reflection optical system 205 is configured by the plane mirror 205a, and the optical system is configured such that the coherent light is focused on the surface of the plane mirror 205a. In the optical path of the optical system that focuses in this way, the incident light and the reflected light are inverted. For this reason, the influence of the foreign matter D or the like adhering to the diffraction grating 204 includes an irradiation area of light received when entering the diffraction grating 204 and an irradiation area of light received after being reflected by the flat mirror 205a. As a result, the amount of light detected by the light receiving unit 206 is generally about twice as large as the size of foreign matter, and the amount of light that can be acquired decreases when foreign matter or the like adheres to the diffraction grating 204. .

  The present invention has been made in order to solve such problems, and is an optical displacement that is easy to assemble and adjust the optical system and that can suppress a decrease in light quantity when foreign matter or the like adheres to the scale portion. It aims at providing a measuring device.

In order to solve the above-described problem, the present invention has a diffraction grating that diffracts irradiated light, a scale section that relatively moves in the grating vector direction of the diffraction grating, a light emitting section that emits coherent light, and light emission The coherent light emitted by the unit is divided into two coherent lights, and each coherent light is irradiated to the diffraction grating of the scale unit to generate two one-time diffracted lights and two one-time diffracted lights Irradiates and receives two diffracted lights generated by diffracting the light by a diffraction grating and reflects two one-time diffracted lights generated by diffracting two coherent lights by the diffraction grating. A reflection optical system that irradiates the diffraction grating with two one-time diffracted lights, and a light receiving unit that receives the interference light obtained by interfering the two two-time diffracted lights with the irradiation light-receiving optical system and detects an interference signal. The reflective optical system has a vertex that combines three right angles. Cube-corner prisms formed of triangular pyramid prism has a micro-corner cube prisms collectively mirrors arranged side by side vertically and horizontally reflects the incident light back in the direction of the optical axis of the incident light, irradiated light receiving optical system Is an optical displacement measuring device including an optical element that irradiates a diffraction grating with coherent light emitted from a light emitting unit at a radiation angle unique to a light source, with a narrowed radiation angle with a wide beam diameter .

  In the optical displacement measuring device of the present invention, the coherent light emitted from the light emitting unit is divided into two and irradiated to the diffraction grating of the scale unit. The two one-time diffracted lights diffracted by the diffraction grating are respectively reflected by the micro corner cube prism assembly mirror, and again irradiated to the diffraction grating. The two twice-diffracted lights diffracted by the diffraction grating are superimposed by the irradiation light receiving optical system to obtain interference light.

  The micro corner cube prism assembly mirror has a function of returning the reflected light in the direction of the optical axis on which the reflected light is incident, and the light returns to the incident direction even if the mounting angle is deviated. In addition, the micro-corner cube prism collective mirror receives and reflects light on each corner cube prism, and the influence of foreign matter adhering to the scale is only on each corner cube prism, affecting other areas. Does not reach.

  In the optical displacement measuring device of the present invention, since the reflecting optical system is provided with the micro corner cube prism assembly mirror, it is possible to receive the influence of the foreign matter adhered to the scale portion on an individual corner cube prism basis. A decrease in the amount of light can be suppressed.

  In addition, the micro corner cube prism assembly mirror returns to the direction of the optical axis on which the reflected light is incident, regardless of the mounting angle, so that the assembly adjustment and the mounting allowable value can be improved.

  Hereinafter, embodiments of the optical displacement measuring device of the present invention will be described with reference to the drawings.

<Principle of the optical displacement measuring device of the present invention>
FIG. 1 is a block diagram showing the principle of an optical displacement measuring device to which the present invention is applied. An optical displacement measuring apparatus 100A to which the present invention is applied includes a transmissive diffraction grating 101T that is attached to a movable part such as a machine tool and moves linearly, and a coherent light source 102 that emits coherent light such as laser light. Prepare.

  The optical displacement measuring apparatus 100A bisects the coherent light emitted from the coherent light source 102 and irradiates the diffraction grating 101T with the irradiation light receiving optical system 103 that interferes with the diffracted light diffracted by the diffraction grating 101T. Prepare.

  The irradiation light receiving optical system 103 includes a polarization beam splitter 104 that splits the coherent light emitted from the coherent light source 102 and combines the diffracted light diffracted by the diffraction grating 101T. The irradiation light receiving optical system 103 includes a lens 105 that narrows down the coherent light emitted from the coherent light source 102.

  The optical displacement measuring apparatus 100A includes a reflection optical system 106 that irradiates the diffraction grating 101T with the diffracted light that is irradiated onto the diffraction grating 101T by the irradiation light receiving optical system 103 and diffracted by the diffraction grating 101T.

  The reflection optical system 106 includes a corner cube prism 107 that reflects the diffracted light diffracted by the diffraction grating 101T in the light incident direction. Further, a quarter-wave plate 108 is provided in the optical path that is reflected by the corner cube prism 107 and reciprocates, and converts the polarization direction.

  The corner cube prism 107 is a triangular pyramid prism having apexes composed of three right angles. The incident light is folded back 180 ° in the incident direction by total internal reflection on three orthogonal surfaces, and the reflected light is always incident. It has the function of returning to the direction of the axis.

  The optical displacement measuring device 100A is a light receiving unit that receives interference light that is irradiated again by the reflection optical system 106 and diffracted by the diffraction grating 101T and interferes by the irradiation light receiving optical system 103, and generates an interference signal. 109.

  Next, the operation of the optical displacement measuring apparatus 100A to which the present invention is applied will be described. In the optical displacement measuring apparatus 100A, the coherent light La emitted from the coherent light source 102 is split into two coherent lights La1 and La2 by the polarization beam splitter 104. The coherent light La1 reflected by the polarizing beam splitter 104 is S-polarized light, and the transmitted coherent light La2 is P-polarized light. The two coherent lights La1 and La2 divided by the polarization beam splitter 104 are irradiated to the diffraction grating 101T.

  The coherent light La1 and La2 irradiated to the diffraction grating 101T are diffracted, and the one-time diffracted lights Lb1 and Lb2 diffracted by the diffraction grating 101T pass through the quarter wavelength plate 108 and enter the corner cube prism 107. The light incident on the corner cube prism 107 is reflected in the incident direction, returns to the direction of the optical axis on which the reflected light is incident, and passes through the quarter wavelength plate 108.

  The one-time diffracted light Lb1 reflected by the corner cube prism 107 passes through the quarter-wave plate 108 twice, so that S-polarized light is converted to P-polarized light. The once-diffracted light Lb2 reflected by the corner cube prism 107 passes through the quarter-wave plate 108 twice, so that P-polarized light is converted to S-polarized light.

  The one-time diffracted lights Lb1 and Lb2 reflected by the corner cube prism 107 are again irradiated to the diffraction grating 101T. The one-time diffracted lights Lb1 and Lb2 irradiated on the diffraction grating 101T are diffracted, and the two-time diffracted lights Lc1 and Lc2 diffracted by the diffraction grating 101T are incident on the polarization beam splitter 104.

  The S-polarized coherent light La1 reflected by the polarizing beam splitter 104 returns as P-polarized light, so that the twice-diffracted light Lc1 passes through the polarizing beam splitter 104. On the other hand, the P-polarized coherent light La2 transmitted through the polarizing beam splitter 104 returns as S-polarized light, so that the twice-diffracted light Lc2 is reflected by the polarizing beam splitter 104. Thereby, the twice-diffracted lights Lc1 and Lc2 are superimposed.

  The interference light Ld superimposed by the polarization beam splitter 104 is incident on the light receiving unit 109, and an interference signal is generated.

  In the conventional optical displacement measuring device, the reflection optical system that irradiates the diffraction grating with the diffracted light diffracted by the diffraction grating is constituted by a plane mirror, and the coherent light emitted from the light source is applied to the surface of the plane mirror. The irradiation optical system was configured to focus.

  In the optical displacement measuring device, the optical path divided by the polarization beam splitter is the same for the forward path and the return path, and the diffracted light diffracted by the diffraction grating is returned to the polarization beam splitter to generate interference light. For this reason, when a flat mirror is used in the reflective optical system, light does not return when the mounting angle of the flat mirror deviates, and the focal position changes when the mounting position deviates along the optical axis. Thereby, when attaching a plane mirror, a delicate angle and position adjustment are required.

  On the other hand, in the optical displacement measuring apparatus 100A to which the present invention is applied, the reflection optical system 106 includes a corner cube prism 107. Since the corner cube prism 107 always returns the reflected light in the direction of the incident optical axis, the light returns in a predetermined direction even if the mounting angle is shifted. In addition, since the light emitted from the coherent light source 102 is not collected, the focal position does not change due to the displacement of the mounting position.

  As described above, by using the corner cube prism in the reflecting optical system, it is possible to improve the assembly adjustment and the allowable mounting value.

  FIG. 2 is an explanatory diagram of an optical path showing the influence of foreign matter on the diffraction grating. In the optical displacement measuring apparatus 100A in which the reflection optical system 106 includes the corner cube prism 107, when the center of the optical axis of the incident light incident on the corner cube prism 107 is aligned with the center of the corner cube prism 107, the optical axis is on the coaxial optical path. Light is reflected. On the other hand, even when the center of the optical axis of the incident light and the center of the corner cube prism 107 do not match, the reflected light always returns to the direction of the incident optical axis. However, the optical axes of the incident light and the reflected light are shifted in parallel.

  For this reason, the influence of the foreign matter D or the like adhering to the diffraction grating 101T includes an irradiation area of light received when entering the diffraction grating 101T and an irradiation area of light received after being reflected by the corner cube prism 107. . As a result, the amount of light detected by the light receiving unit 109 is generally about twice as large as the size of the foreign matter, and the amount of light that can be acquired decreases when the foreign matter adheres to the diffraction grating 101T.

  Therefore, in the present invention, a micro corner cube prism assembly mirror in which minute corner cube prisms are arrayed is used in a reflection optical system to prevent a decrease in light amount due to the influence of foreign matter or the like.

<Configuration Example of Optical Displacement Measuring Device of First Embodiment>
FIG. 3 is a configuration diagram showing an example of the optical displacement measuring apparatus according to the first embodiment of the present invention. The optical displacement measuring apparatus 1A according to the first embodiment includes a scale unit 11A that is attached to a movable part such as a machine tool and linearly moves or rotates. In this example, the scale portion 11A includes a transmission type diffraction grating 11T and a protective layer 11G such as glass for protecting the diffraction grating 11T.

  In the diffraction grating 11T, a grating such as a narrow slit or groove is carved at a predetermined interval on a thin plate material. The light incident on the diffraction grating 11T is diffracted by a slit or the like carved on the surface. Diffracted light generated by diffraction is generated in a direction determined by the incident angle of light, the interval between gratings, the wavelength of light, and the like. Here, in the diffraction grating 11T, a direction perpendicular to a direction in which a grating (not shown) is formed is referred to as a grating vector direction. The scale unit 11A moves in the direction of the grating vector of the diffraction grating 11T as the movable part moves. In this example, a diffraction grating in which gratings are provided in parallel at a predetermined interval is used. However, in the present invention, it is not necessary to use a diffraction grating in which such gratings are provided in parallel. For example, a diffraction grating provided with radial gratings may be used. By using such a diffraction grating provided with a radial grating, it is possible to detect the position of a movable part or the like of a rotating machine tool as a so-called rotary encoder. In the present invention, an amplitude type diffraction grating in which brightness and darkness are recorded, and a phase type diffraction grating in which changes in refractive index and shape are recorded may be used, and the type of the diffraction grating is not limited.

  The optical displacement measuring apparatus 1A includes a coherent light source 12 that emits coherent light La such as laser light irradiated to the scale unit 11A. The coherent light source 12 is an example of a light emitting unit, and is configured by, for example, a semiconductor laser (LD), and the coherent light La is emitted at an emission angle unique to the light source.

  The optical displacement measuring apparatus 1A divides the coherent light La emitted from the coherent light source 12 into two parts and irradiates the scale part 11A, and also irradiates the diffracted light diffracted by the diffraction grating 11T of the scale part 11A. A light receiving optical system 13A is provided.

  The irradiation light receiving optical system 13A divides the coherent light La emitted from the coherent light source 12 into two lights having different polarization components, and superimposes two diffracted lights having different polarization components diffracted by the diffraction grating 11T. A polarizing beam splitter (PBS) 14 is provided. Further, the irradiation light receiving optical system 13A includes a lens 15a as an optical element that narrows down the coherent light emitted from the coherent light source 12 at a radiation angle unique to the light source. Further, the irradiation / light receiving optical system 13A includes a lens 15b that narrows down the interference light Ld superimposed by the polarization beam splitter.

  The polarization beam splitter 14 is output from the coherent light source 12 and receives coherent light La that is narrowed down by the lens 15a. The incident light from the coherent light source 12 is divided into a P component and an S component. Is reflected, and P-polarized light is transmitted. Here, if the light from the coherent light source 12 is linearly polarized light, the intensity of the divided light becomes equal if the polarization direction is inclined by 45 ° and is incident on the polarization beam splitter 14. The s-polarized diffracted light returned to the polarization beam splitter 14 is reflected, the p-polarized diffracted light is transmitted, and the two diffracted lights are superimposed.

  The optical displacement measuring device 1A includes a reflection optical system 16 that irradiates the scale unit 11A with the irradiation light receiving optical system 13A and irradiates the scale unit 11A again with the diffracted light diffracted by the diffraction grating 11T of the scale unit 11A.

  The reflective optical system 16 includes micro corner cube prism aggregate mirrors 17a and 17b that reflect the two diffracted lights diffracted by the diffraction grating 11T in the light incident direction, respectively. In addition, a quarter-wave plate 18a is provided in an optical path that is reflected by one microcorner cube prism assembly mirror 17a and reciprocates, and converts the polarization direction. Further, a quarter wavelength plate 18b is provided in the optical path that is reflected by the other micro corner cube prism assembly mirror 17b and reciprocates, and converts the polarization direction. In a configuration in which a diffraction grating having radial gratings is used as the diffraction grating 11T, the irradiation light receiving optical system 13A and the reflection optical system 16 emit light at a light irradiation angle so that light is emitted to the arcs arranged in an arc shape. The reflection angle may be changed along the arc.

  FIG. 4 is a plan view showing an example of a micro corner cube prism assembly mirror. The micro corner cube prism assembly mirrors 17a and 17b are aggregates of micro corner cube prisms 17p configured by triangular pyramid prisms having apexes obtained by combining three right angles. The micro corner cube prism assembly mirrors 17a and 17b are arranged with micro micro corner cube prisms 17p arranged vertically and horizontally at a predetermined ratio with respect to the beam region R of incident light. Each micro corner cube prism 17p has a function of returning incident light by 180 ° in the incident direction by total internal reflection of three orthogonal surfaces, and returning the reflected light to the incident optical axis direction without fail.

  Returning to FIG. 3, the ¼ wavelength plate 18a is disposed with its optical axis inclined at 45 ° with respect to the polarization direction of the light, reflected by the micro corner cube prism assembly mirror 17a, and returned to the scale unit 11A. Is converted to P-polarized light.

  Thereby, the S-polarized light emitted from the coherent light source 12 and reflected by the polarization beam splitter 14 is diffracted twice by the diffraction grating 11T by reciprocating along a predetermined optical path. Then, the light passes through the quarter-wave plate 18 a twice, is converted to P-polarized light, returns to the polarizing beam splitter 14, and passes through the polarizing beam splitter 14.

  Similarly, the quarter-wave plate 18b is disposed with the optical axis inclined by 45 ° with respect to the polarization direction of the light, and the P-polarized light reflected by the micro corner cube prism assembly mirror 17b and returning to the scale portion 11A is S. Converted to polarized light.

  Thereby, the P-polarized light emitted from the coherent light source 12 and transmitted through the polarization beam splitter 14 is diffracted twice by the diffraction grating 11T by reciprocating along a predetermined optical path. Then, the light passes through the quarter-wave plate 18 b twice, is converted to S-polarized light, returns to the polarizing beam splitter 14, and is reflected by the polarizing beam splitter 14.

  Accordingly, the S-polarized light and the P-polarized light emitted from the coherent light source 12 and split by the polarizing beam splitter 14 pass through predetermined optical paths, respectively, and are diffracted by the diffraction grating 11T of the scale portion 11A, and are then polarized by the polarizing beam splitter 14 Returned to and superimposed.

  The optical displacement measuring apparatus 1A is a light receiving unit that generates interference signals by receiving interference light that is irradiated again on the scale unit 11A by the reflection optical system 16, diffracted by the diffraction grating 11T, and interfered by the irradiation light receiving optical system 13A. 19 is provided.

  The light receiving unit 19 includes a beam splitter (BS) 20 that divides the interference light Ld superimposed by the polarization beam splitter 14 and focused by the lens 15b. The beam splitter 20 is composed of a half mirror or the like having a predetermined transmittance (reflectance), and the light superimposed by the polarization beam splitter 14 is divided into two.

  The light receiving unit 19 is inclined by 45 ° with respect to the polarization direction of incident light reflected by the beam splitter 20, and a polarized beam splitter (PBS) 21 that divides the incident light into two lights having different polarization components; A photoelectric converter (PD) 22a on which light reflected by the polarizing beam splitter 21 enters and a photoelectric converter (PD) 22b on which light transmitted through the polarizing beam splitter 21 enters are provided.

  The light receiving unit 19 includes a quarter wavelength plate 23 whose optical axis is inclined by 45 ° with respect to the polarization direction of the light transmitted through the beam splitter 20 and converts the polarization state of the incident light. The light receiving unit 19 is tilted by 45 ° with respect to the polarizing beam splitter 21, and is a polarized beam that splits the light that has been transmitted through the beam splitter 20 and whose polarization state has been converted by the quarter wavelength plate 23 into two light components having different polarization components. A splitter (PBS) 24 is provided. The light receiving unit 19 includes a photoelectric converter (PD) 25a on which the light reflected by the polarizing beam splitter 24 enters and a photoelectric converter (PD) 25b on which the light transmitted through the polarizing beam splitter 24 enters.

<Operation Example of Optical Displacement Measuring Device of First Embodiment>
Next, an example of the operation of the optical displacement measuring apparatus 1A according to the first embodiment will be described with reference to the drawings.

  The coherent light La emitted from the coherent light source 12 is narrowed down to an appropriate beam by the lens 15a, for example, converted into parallel light, incident on the polarizing beam splitter 14, and split into two lights by the polarizing beam splitter 14. The

  The coherent light La1 reflected by the polarizing beam splitter 14 is S-polarized light, and the transmitted coherent light La2 is P-polarized light. If the light from the coherent light source 12 is linearly polarized light, the intensity of the divided light becomes equal if the polarization direction is inclined 45 ° and is incident on the polarization beam splitter 14.

  The coherent light La1 reflected by the polarization beam splitter 14 enters the point P of the diffraction grating 11T in the scale portion 11A. The coherent light La2 that has passed through the polarization beam splitter 14 is incident on the Q point of the diffraction grating 11T in the scale portion 11A.

  The two coherent lights La1 and La2 incident on the diffraction grating 11T of the scale portion 11A are diffracted in the direction shown by the following equation (1).

sin θ ₁ + sin θ ₂ = n · λ / Λ (1)
θ ₁ : incident angle θ ₂ : diffraction angle Λ: grating pitch λ: wavelength of light n: diffraction order

In the diffraction grating 11T, assuming that the incident angle to the point P is θ _1P , the diffraction angle is θ _2P , the incident angle to the point Q is θ _1Q , and the diffraction angle is θ _2Q , in the example of FIG. 3, θ _1P = θ _2P = Θ _1Q = θ _2Q . The diffraction orders are the same at the P point and the Q point.

  The one-time diffracted beam Lb1 diffracted at the point P of the diffraction grating 11T passes through the quarter-wave plate 18a, is reflected by the micro corner cube prism assembly mirror 17a, passes through the quarter-wave plate 18a again, and again passes through the P of the diffraction grating 11T. It is diffracted back to the point. As described above, since the optical axis of the quarter-wave plate 18a is inclined by 45 ° with respect to the polarization direction of the light, the one-time diffracted light Lb1 returning to the point P of the diffraction grating 11T is P-polarized light. .

  Similarly, the one-time diffracted beam Lb2 diffracted at the Q point of the diffraction grating 11T passes through the quarter-wave plate 18b, is reflected by the micro corner cube prism assembly mirror 17b, and passes again through the quarter-wave plate 18b. Diffracted back to the Q point of 11T. The one-time diffracted light Lb2 returned to the Q point of the diffraction grating 11T is S-polarized light.

  The twice diffracted beams Lc1 and Lc2 diffracted again at the point P and the point Q of the diffraction grating 11T return to the polarization beam splitter 14. Since the twice-diffracted light Lc1 diffracted at the point P of the diffraction grating 11T is P-polarized light, it passes through the polarization beam splitter 14. Further, the twice-diffracted light Lc2 diffracted at the point Q of the diffraction grating 11T is S-polarized light and is reflected by the polarization beam splitter 14.

  As a result, the two two-time diffracted beams Lc1 and Lc2 are superimposed by the polarization beam splitter 14. The interference light Ld superimposed by the polarization beam splitter 14 is narrowed down to an appropriate beam by the lens 15 b and is divided into two by the beam splitter 20.

  The S-polarized light and P-polarized interference light Ld reflected by the beam splitter 20 is incident on the polarization beam splitter 21 inclined by 45 ° with respect to the polarization direction. The light reflected by the polarization beam splitter 21 enters the photoelectric converter 22a, and the transmitted light enters the photoelectric converter 22b.

  In the photoelectric converter 22a and the photoelectric converter 22b, an interference signal represented by the following equation (2) is obtained.

Acos (4 · K · x + δ) (2)
K = 2π / Λ
x: Movement amount of diffraction grating δ: Initial phase

  As a result, signals having a phase difference of 180 ° are obtained in the photoelectric converter 22a and the photoelectric converter 22b.

  The S-polarized and P-polarized interference light Ld transmitted through the beam splitter 20 passes through a quarter-wave plate 23 whose optical axis is inclined by 45 ° with respect to the polarization direction, and becomes circularly polarized light that is opposite to each other. The circularly polarized light beams that are opposite to each other are superposed to form linearly polarized light, which is incident on the polarization beam splitter 24, the reflected light is incident on the photoelectric converter 25a, and the transmitted light is incident on the photoelectric converter 25b. .

  The polarization direction of the linearly polarized light rotates once when the diffraction grating 11T moves by Λ / 2 in the X direction. Therefore, the photoelectric converters 25a and 25b can obtain an interference signal similar to the expression (2).

  The photoelectric converters 25a and 25b are different in phase by 180 °, and the polarization beam splitter 24 is inclined 45 ° with respect to the polarization beam splitter 21, so that the signals obtained by the photoelectric converters 25a and 25b are photoelectrically converted. The phases of the signals obtained by the devices 22a and 22b are different by 90 °.

  The differential amplifier 26 differentially amplifies the electric signals from the photoelectric converters 22a and 22b and outputs a signal in which the DC component of the interference signal is canceled. The differential amplifier 27 similarly outputs the electric signals from the photoelectric converters 25a and 25b. The signal is differentially amplified and a signal in which the DC component of the interference signal is canceled is output. Therefore, an A / B phase signal can be obtained from the differential amplifier 26 and the differential amplifier 27, and the A / B phase signal is input to the incremental signal generator 28.

<Examples of effects of the optical displacement measuring device according to the first embodiment>
In the optical displacement measuring apparatus 1A according to the first embodiment, since the optical system is symmetric with respect to the perpendicular L in FIG. 3, no position measurement error occurs even if the diffraction grating moves in the Y direction. . Further, by making the optical path lengths of the optical path incident on the point P and the optical path incident on the point Q equal, it is not affected by the wavelength variation of the light source.

  In the optical displacement measuring apparatus 1A according to the first embodiment, the reflecting optical system 16 includes micro corner cube prism assembly mirrors 17a and 17b. Since the micro-corner cube prism assembly mirrors 17a and 17b always return the reflected light in the direction of the incident optical axis, the light returns in a predetermined direction even if the mounting angle is shifted. In addition, since the light emitted from the coherent light source 12 is not collected, the focal position does not change due to the displacement of the mounting position.

  As described above, by using the micro corner cube prism assembly mirrors 17a and 17b in the reflection optical system 16, delicate angle adjustment is not required, and assembly adjustment of the reflection optical system 16 is facilitated. In addition, in the attachment of the scale portion 11A and the light receiving portion 19, the reflected light from the micro corner cube prism assembly mirrors 17a and 17b returns in the direction of the incident optical axis, thereby increasing the attachment allowable value.

  FIG. 5 is an explanatory diagram of the optical path showing the influence of the foreign matter on the scale portion, and FIG. 6 is a plan view showing the relationship between the micro corner cube prism assembly mirror and the size of the foreign matter. The micro corner cube prism 17p that constitutes the micro corner cube prism assembly mirrors 17a and 17b is very small at a predetermined ratio with respect to the beam region R of incident light, and the size of the foreign matter D or the like that is supposed to be attached thereto. The size is comparable.

  Thereby, in the micro corner cube prism assembly mirrors 17a and 17b, light is incident and reflected for each micro corner cube prism 17p. For this reason, the influence of the foreign matter D or the like adhering to the scale portion 11A is not limited to each of the individual micro-corner cube prisms 17p, and does not affect other regions, so that a decrease in the amount of light detected by the light receiving portion 19 is prevented. be able to. Therefore, it is possible to suppress the influence on foreign matters adhering to the scale portion 11A, partial defects of the diffraction grating 11T, bubbles such as protective layers and base materials constituting the scale portion 11A, and foreign matter contamination. .

<Modification of Optical Displacement Measuring Device of First Embodiment>
FIG. 7 is a configuration diagram illustrating a modification of the optical displacement measuring device according to the first embodiment. In the following description, the same components as those in the optical displacement measuring apparatus 1A according to the first embodiment will be described with the same reference numerals.

  The optical displacement measuring apparatus 1B according to the modification of the first embodiment includes a wavefront adjusting diffraction grating 30 as a wavefront adjusting optical element that maintains the wavefront state in the beam and makes the optical path length uniform. The wavefront adjusting diffraction grating 30 is installed between the scale portion 11A and the reflection optical system 16, and is diffracted by the diffraction grating 11T of the scale portion 11A and reflected by the reflection optical system 16 to reciprocate once diffracted beams Lb1 and Lb2. Diffraction in a predetermined direction.

  In this example, the wavefront adjusting diffraction grating 30 is configured to generate diffracted light in a direction opposite to the diffraction direction of the diffraction grating 11T, and the optical path L1 (A), the optical path L1 (B), the optical path L2 (A), and the optical path L2. (B) is made equal.

  FIG. 8 is a configuration diagram illustrating another modification of the optical displacement measuring apparatus according to the first embodiment. In the following description, the same components as those in the optical displacement measuring apparatus 1A according to the first embodiment will be described with the same reference numerals.

  An optical displacement measuring apparatus 1C according to another modification of the first embodiment includes a wavefront adjusting prism 31 as a wavefront adjusting optical element that maintains the wavefront state in the beam and makes the optical path length uniform. The wavefront adjusting prism 31 is installed between the scale unit 11A and the reflection optical system 16, is diffracted by the diffraction grating 11T of the scale unit 11A, is reflected by the reflection optical system 16, and travels back and forth. Is bent in a predetermined direction.

  In this example, the wavefront adjusting prism 31 is configured to bend the optical path in the direction opposite to the diffraction direction in the diffraction grating 11T, and the optical path L1 (A), the optical path L1 (B), the optical path L2 (A), and the optical path L2 (B). Are equal.

<Configuration Example of Optical Displacement Measuring Device of Second Embodiment>
FIG. 9 is a configuration diagram illustrating an example of the optical displacement measuring apparatus according to the second embodiment. In the following description, the same components as those in the optical displacement measuring apparatus 1A according to the first embodiment will be described with the same reference numerals.

  The optical displacement measuring device 1D of the second embodiment includes a scale unit 11B that is attached to a movable part such as a machine tool and moves linearly. In this example, the scale portion 11B includes a reflective diffraction grating 11R, a protective layer 11G made of glass or resin for protecting the diffraction grating 11R, a base 11H of the diffraction grating 11R made of glass, metal, or the like. .

  The optical displacement measuring device 1D includes a coherent light source 12 that emits coherent light La such as laser light irradiated to the scale unit 11B. The coherent light source 12 is composed of, for example, a semiconductor laser (LD), and coherent light La is emitted at a radiation angle unique to the light source. For example, the radiation angle of the semiconductor laser is about 8.5 ° in the horizontal direction and about 35 ° in the vertical direction.

  The optical displacement measuring device 1B divides the coherent light La emitted from the coherent light source 12 into two parts and irradiates the scale part 11B, and also irradiates the diffracted light diffracted by the diffraction grating 11R of the scale part 11B. A light receiving optical system 13B is provided.

  The irradiation light receiving optical system 13B divides the coherent light La emitted from the coherent light source 12 into two lights having different polarization components, and superimposes two diffracted lights having different polarization components diffracted by the diffraction grating 11R. A polarizing beam splitter (PBS) 14 is provided. Further, the irradiation light receiving optical system 13B includes a lens 15c as an optical element that narrows down the coherent light emitted from the coherent light source 12 at a radiation angle unique to the light source. The irradiation light receiving optical system 13B may include a lens 15b that narrows down the interference light Ld superimposed by the polarization beam splitter 14. The lens 15c reduces the coherent light emitted from the coherent light source 12 at a radiation angle unique to the light source to a predetermined radiation angle that can be incident on the polarization beam splitter 14 and the beam diameter is widened.

  The polarization beam splitter 14 emits linearly polarized coherent light La emitted from the coherent light source 12 and narrowed by the lens 15c, with the polarization direction inclined by 45 °, and the incident light from the coherent light source 12 is P component. The S-polarized light is reflected and the P-polarized light is transmitted. The s-polarized diffracted light returned to the polarization beam splitter 14 is reflected, the p-polarized diffracted light is transmitted, and the two diffracted lights are superimposed.

  The optical displacement measuring apparatus 1D includes a reflection optical system 16 that irradiates the scale unit 11B with the diffracted light that is irradiated to the scale unit 11B by the irradiation light receiving optical system 13B and diffracted by the diffraction grating 11R of the scale unit 11B.

  The reflection optical system 16 includes micro corner cube prism assembly mirrors 17a and 17b that reflect the two diffracted lights diffracted by the diffraction grating 11R toward the light incident direction, respectively. In addition, a quarter-wave plate 18a is provided in an optical path that is reflected by one microcorner cube prism assembly mirror 17a and reciprocates, and converts the polarization direction. Further, a quarter wavelength plate 18b is provided in the optical path that is reflected by the other micro corner cube prism assembly mirror 17b and reciprocates, and converts the polarization direction.

  The micro-corner cube prism assembly mirrors 17a and 17b have a size that allows the one-time diffracted beams Lb1 and Lb2 that are narrowed down by the lens 15c and have a predetermined radiation angle and the beam diameter to expand. As shown in FIG. 4, the micro corner cube prism assembly mirrors 17a and 17b are arranged with micro micro cube cube prisms 17p arranged vertically and horizontally at a predetermined ratio with respect to the beam region R of incident light. Each micro corner cube prism 17p has a function of returning incident light by 180 ° in the incident direction by total internal reflection of three orthogonal surfaces, and returning the reflected light to the incident optical axis direction without fail. As a result, when the one-time diffracted lights Lb1 and Lb2 whose beam diameter is widened with a predetermined radiation angle are incident, the reflected lights are collected because they return on the same optical path.

  The S-polarized light emitted from the coherent light source 12 and reflected by the polarization beam splitter 14 is reflected by the micro-corner cube prism assembly mirror 17a, and is diffracted twice by the diffraction grating 11R by reciprocating along a predetermined optical path. The Then, the light passes through the quarter-wave plate 18a disposed with the optical axis inclined at 45 ° with respect to the polarization direction of the light, and is converted to P-polarized light by returning twice, and returns to the polarization beam splitter 14, and the polarization beam splitter 14 is To Penetrate.

  Similarly, the P-polarized light emitted from the coherent light source 12 and transmitted through the polarization beam splitter 14 is reflected by the micro corner cube prism assembly mirror 17b so as to reciprocate in a predetermined optical path twice by the diffraction grating 11R. Diffracted. Then, the light passes through the quarter-wave plate 18 b disposed with the optical axis inclined by 45 ° with respect to the polarization direction of the light, and is converted into S-polarized light by returning twice to the polarization beam splitter 14. reflect.

  Thereby, the S-polarized light and the P-polarized light emitted from the coherent light source 12 and divided by the polarization beam splitter 14 pass through predetermined optical paths, respectively, and are diffracted by the diffraction grating 11R of the scale unit 11B. It returns to 14, and is overlaid.

  The optical displacement measuring apparatus 1B is a light receiving unit that generates interference signals by receiving interference light that is irradiated again on the scale unit 11B by the reflection optical system 16, diffracted by the diffraction grating 11R, and interfered by the irradiation light receiving optical system 13B. 19 is provided. The configuration of the light receiving unit 19 may be the same as that of the optical displacement measuring apparatus 1A of the first embodiment.

<Operation Example of Optical Displacement Measuring Device of Second Embodiment>
Next, an example of the operation of the optical displacement measuring apparatus 1D according to the second embodiment will be described with reference to the drawings.

  The coherent light La emitted from the coherent light source 12 is narrowed down to an appropriate beam by the lens 15c, enters the polarizing beam splitter 14 while spreading at a predetermined radiation angle, and is split into two lights by the polarizing beam splitter 14. Is done. The coherent light La1 reflected by the polarizing beam splitter 14 becomes S-polarized light, and the transmitted coherent light La2 becomes P-polarized light, and enters the diffraction grating 11R of the scale portion 11B.

  The one-time diffracted beam Lb1 diffracted by the diffraction grating 11R passes through the quarter-wave plate 18a, is reflected by the micro corner cube prism assembly mirror 17a, passes through the quarter-wave plate 18a, and returns to the diffraction grating 11R to be diffracted again. The By passing through the quarter-wave plate 18a twice, the one-time diffracted light Lb1 returned to the diffraction grating 11R is P-polarized light. Further, the micro corner cube prism assembly mirror 17a has a function of returning to the direction of the optical axis on which the reflected light is necessarily incident. Thus, when the one-time diffracted light Lb1 having a predetermined radiation angle and a widened beam diameter is incident, the reflected light is collected to return on the same optical path.

  Similarly, the one-time diffracted beam Lb2 diffracted by the diffraction grating 11R passes through the quarter-wave plate 18b, is reflected by the micro corner cube prism assembly mirror 17b, returns to the diffraction grating 11R again through the quarter-wave plate 18b. Is diffracted. By passing through the quarter-wave plate 18b twice, the one-time diffracted light Lb2 returned to the diffraction grating 11R is S-polarized light. Further, the micro corner cube prism assembly mirror 17b has a function of returning to the direction of the optical axis on which the reflected light is necessarily incident. As a result, when the one-time diffracted light Lb2 having a predetermined radiation angle and a widened beam diameter is incident, the reflected light is collected to return on the same optical path.

  The twice-diffracted lights Lc1 and Lc2 diffracted again by the diffraction grating 11R return to the polarization beam splitter 14. Since the twice-diffracted light Lc1 diffracted by the diffraction grating 11R is P-polarized light, it passes through the polarization beam splitter 14. Further, since the twice-diffracted light Lc2 diffracted by the diffraction grating 11R is S-polarized light, it is reflected by the polarization beam splitter 14.

  As a result, the two two-time diffracted beams Lc1 and Lc2 are superimposed by the polarization beam splitter 14. The interference light Ld superimposed by the polarization beam splitter 14 enters the light receiving unit 19, and an interference signal is obtained as described above.

<Examples of effects of the optical displacement measuring apparatus according to the second embodiment>
In the optical displacement measuring apparatus 1D of the second embodiment, the reflecting optical system 16 includes micro corner cube prism assembly mirrors 17a and 17b. In the micro corner cube prism assembly mirrors 17a and 17b, when light having a predetermined radiation angle and a beam diameter expanding is incident, the reflected light is collected because it returns on the same optical path.

  As a result, light having a larger beam diameter (coherent light La1 and La2) is irradiated onto the scale portion 11B, and return light (twice diffracted light Lc1 and Lc2) by the micro corner cube prism assembly mirrors 17a and 17b is condensed. Thus, the light can be incident on the light receiving unit 19.

  Therefore, the beam diameter of the light irradiated to the diffraction grating 11R of the scale portion 11B can be expanded with a simple optical system. By expanding the beam diameter of the light irradiated to the diffraction grating 11R, the area irradiated with light can be expanded with respect to the size of the foreign matter attached to the scale portion 11B, and the foreign matter attached to the scale portion 11B. Etc. can be further reduced to prevent the light quantity from decreasing.

  The present invention is applied to an apparatus for detecting the position of a movable part such as a machine tool.

It is a block diagram which shows the principle of the optical displacement measuring device with which this invention is applied. It is optical path explanatory drawing which shows the influence of the foreign material on a diffraction grating. It is a block diagram which shows an example of the optical displacement measuring device of the 1st Embodiment of this invention. It is a top view which shows an example of a micro corner cube prism assembly mirror. It is optical path explanatory drawing which shows the influence of the foreign material on a scale part. It is a top view which shows the relationship between the size of a micro corner cube prism assembly mirror and a foreign material. It is a block diagram which shows the modification of the optical displacement measuring device of 1st Embodiment. It is a block diagram which shows the other modification of the optical displacement measuring device of 1st Embodiment. It is a block diagram which shows an example of the optical displacement measuring device of the 2nd Embodiment of this invention. It is a block diagram which shows an example of the conventional optical displacement measuring device. It is operation | movement explanatory drawing which shows the subject of the conventional optical displacement measuring device. It is operation | movement explanatory drawing which shows the subject of the conventional optical displacement measuring device.

Explanation of symbols

  1A, 1B, 1C, 1D ... Optical displacement measuring device, 11A, 11B ... Scale section, 11T, 11R ... Diffraction grating, 12 ... Coherent light source, 13A, 13B ... Irradiation reception Optical system 14... Polarizing beam splitter, 15 a to 15 c... Lens, 16... Reflecting optical system, 17 a and 17 b. , 18b... Quarter-wave plate, 19.

Claims (3)

A scale part that has a diffraction grating that diffracts the irradiated light and moves relatively in the direction of the grating vector of the diffraction grating;
A light emitting unit for emitting coherent light;
The coherent light emitted from the light emitting unit is divided into two coherent lights, each coherent light is irradiated to the diffraction grating of the scale unit to generate two one-time diffracted lights, and two An irradiation light receiving optical system for causing interference between two two-time diffracted lights generated by diffracting one-time diffracted light by the diffraction grating;
A reflective optical system that reflects two one-time diffracted lights generated by diffracting two coherent lights by the diffraction grating, and irradiates the diffraction grating with two one-time diffracted lights;
A light receiving unit that receives interference light obtained by interfering two two-time diffracted lights by the irradiation light receiving optical system and detects an interference signal;
The reflection optical system has a micro-cube cube prism assembly mirror in which corner cube prisms composed of triangular pyramid prisms having apexes composed of three right angles are arranged side by side to reflect incident light. Return to the direction of the optical axis of the incident light,
The irradiation light receiving optical system includes an optical displacement measurement device including an optical element that irradiates the diffraction grating with a coherent light emitted from the light emitting unit at a radiation angle unique to a light source with a predetermined radiation angle with a wide beam diameter. apparatus. The diffraction grating is an optical displacement measuring apparatus according to claim 1, wherein a reflection type. Optical displacement measuring apparatus according to claim 1 or 2 including a wavefront adjusting optical element to uniform the optical path length while maintaining the wavefront state of the beam.

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