JP4154038B2 - Optical displacement measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
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.
[0002]
[Prior art]
Conventionally, an optical displacement measuring device using a diffraction grating is known as a device for detecting the relative movement position of a movable part such as a machine tool or a semiconductor manufacturing apparatus.
[0003]
For example, a conventional optical displacement measuring device proposed in Japanese Patent Laid-Open No. 60-98302 is shown in FIGS. FIG. 16 is a perspective view schematically showing this conventional optical displacement measuring apparatus 100, and FIG. 17 is a side view schematically showing this conventional optical displacement measuring apparatus 100. As shown in FIG.
[0004]
A conventional optical displacement measuring apparatus 100 includes a diffraction grating 101 that moves linearly in the directions of arrows X1 and X2 in the drawing as a movable part such as a machine tool moves, and a coherent light source 102 that emits laser light that is coherent light. And the half mirror 103 that splits the laser light emitted from the coherent light source 102 into two beams and interferes the two diffracted lights from the diffraction grating 101, and the diffracted light diffracted by the diffraction grating 101 It includes two mirrors 104a and 104b that reflect and a photodetector 105 that receives the two diffracted light beams that interfere with each other and generates an interference signal.
[0005]
The laser light emitted from the coherent light source 102 is split into two beams by the half mirror 103. These two beams are applied to the diffraction grating 101, respectively. The two beams irradiated on the diffraction grating 101 are each diffracted by the diffraction grating 101 to become diffracted light. The first-order diffracted light diffracted by the diffraction grating 101 is reflected by the mirrors 104a and 104b, respectively. The diffracted light reflected by the mirrors 104a and 104b is irradiated again on the diffraction grating 101, diffracted again by the diffraction grating 101, and returned to the half mirror 103 along the same optical path. The two diffracted lights returned to the half mirror 103 are superimposed and interfere with each other, and are irradiated to the photodetector 105.
[0006]
In such a conventional optical displacement measuring apparatus 100, the diffraction grating 101 moves in the directions of arrows X1 and X2 in the figure. In the optical displacement measuring apparatus 100, a phase difference occurs between the two diffracted lights generated by the diffraction grating 101 in accordance with the movement of the diffraction grating 101. Therefore, in this optical displacement measuring apparatus 100, the moving position of the movable part such as a machine tool can be measured by detecting the phase difference between the two diffracted lights from the interference signal obtained by the photodetector 105.
[0007]
FIG. 18 and FIG. 19 show another conventional optical displacement measuring device proposed in Japanese Patent Laid-Open No. 60-98302. FIG. 18 is a perspective view schematically showing a conventional optical displacement measuring apparatus 110, and FIG. 19 is a side view schematically showing the conventional optical displacement measuring apparatus 110. As shown in FIG.
[0008]
A conventional optical displacement measuring device 110 includes a diffraction grating 111 that moves linearly in the directions of arrows X1 and X2 in the drawing as a movable part such as a machine tool moves, and a coherent light source 112 that emits laser light that is coherent light. And the half mirror 113 that splits the laser light emitted from the coherent light source 112 into two beams and superimposes the two diffracted lights from the diffraction grating 111 to interfere with each other, and the two split by the half mirror 113 The two first mirrors 114a and 114b that irradiate the same position on the diffraction grating 111 and the two second mirrors 115a and 115b that reflect the first-order diffracted light diffracted by the diffraction grating 111 interfere with each other. And a photodetector 116 that receives two diffracted lights and generates an interference signal.
[0009]
The laser light emitted from the coherent light source 112 is divided into two beams by the half mirror 113. These two beams are reflected by the first mirrors 114a and 114b, respectively, and irradiated to the same position on the diffraction grating 111. The two beams irradiated on the diffraction grating 111 are each diffracted by the diffraction grating 111 to become diffracted light. The first-order diffracted light diffracted by the diffraction grating 111 is reflected by the second mirrors 115a and 115b, respectively. The diffracted light reflected by the second mirrors 115a and 115b is irradiated again on the diffraction grating 111, and is again diffracted by the diffraction grating 111. The diffracted light follows the same optical path and is returned to the half mirror 113. The two diffracted lights returned to the half mirror 113 are superimposed and interfere with each other, and are irradiated to the photodetector 116.
[0010]
In such a conventional optical displacement measuring apparatus 110, the diffraction grating 111 moves in the directions of arrows X1 and X2 in the figure. In the optical displacement measuring device 110, a phase difference occurs between the two diffracted lights generated by the diffraction grating 111 according to the movement of the diffraction grating 111. Therefore, in this optical displacement measuring device 110, the movement position of the movable part such as a machine tool can be measured by detecting the phase difference between the two diffracted lights from the interference signal obtained by the photodetector 116.
[0011]
[Problems to be solved by the invention]
By the way, in recent years, with the increase in accuracy of machine tools and industrial robots, there has been a demand for an optical displacement measuring apparatus capable of detecting a position with a high resolution of, for example, several tens of nm to several nm.
[0012]
An optical displacement measuring device capable of detecting a position with such a high resolution is proposed in Japanese Patent Application Laid-Open No. 1-185415. Here, a conventional optical displacement measuring device proposed in Japanese Patent Laid-Open No. 1-185415 is shown in FIG.
[0013]
An optical displacement measuring device 140 shown in FIG. 20 includes a transmission type diffraction grating 141 that linearly moves in the directions of arrows X1 and X2 in the figure as the movable part of a machine tool or the like moves, and a laser diode that emits laser light. 142, a collimator lens 143 that collimates the laser beam emitted from the laser diode 142, a first half mirror 144 that divides the collimated laser beam into two beams, and each of the divided beams And a pair of second mirrors 146a and 146b that respectively reflect diffracted lights generated by the two beams transmitted through the diffraction grating 141. And a pair of polarizers 14 that make the polarization directions of the diffracted lights reflected by the pair of second mirrors 146a and 146b orthogonal to each other. a, 147b, a second half mirror 148 that superimposes the two diffracted lights, a first light receiving element 149 that receives the two diffracted lights superimposed by the second half mirror 148, and a second half mirror A third half mirror 150 that further separates the diffracted light superimposed by the mirror 148 into two beams, a second light receiving element 151 that receives the beams separated by the third half mirror 150, and a third light receiving element 151, respectively. And a light receiving element 152.
[0014]
The two coherent lights divided by the first half mirror 144 have their incident angles adjusted by the first mirrors 145a and 145b, respectively, to θ. Further, the two coherent lights are incident on the same point on the grating surface of the diffraction grating 141. Diffracted light generated by coherent light irradiated at an incident angle θ has a diffraction angle of φ. In this optical displacement measuring device 140, since the incident angle and the diffraction angle are different, for example, the zero-order light generated by one coherent light or the other coherent light is diffracted by one coherent light. Primary light generated by light is not mixed. Therefore, the optical displacement measuring device 140 can stably detect diffracted light.
[0015]
However, in this optical displacement measuring device 140, two coherent lights are incident on the same point on the grating surface of the diffraction grating 141, and the incident angles of the two coherent lights are the same. For this reason, as shown in FIG. 21, the reflected light generated when one coherent light is irradiated onto the diffraction grating 141 travels backward through the incident path of the other coherent light and enters the laser diode 142.
[0016]
In general, a laser diode is sensitive to return light. If there is return light, oscillation becomes unstable, noise is generated, and the wavelength of emitted laser light becomes unstable. For this reason, in this optical displacement measuring device 140, the reflected light returns to the laser diode 142, which causes a decrease in the S / N ratio of the interference signal and a decrease in stability.
[0017]
When the diffraction grating is a reflection type, the reflected light = 0th order light. Therefore, when a diffraction grating with low diffraction efficiency is used, a large amount of laser light returns to the laser diode, making it difficult to obtain a stable interference signal.
[0018]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide an optical displacement measuring apparatus capable of stable position detection with high resolution.
[0019]
[Means for Solving the Problems]
  In order to solve the above-described problems, an optical displacement measuring apparatus according to the present invention is irradiated with coherent light, and moves relative to the coherent light in a direction parallel to the lattice vector. A diffraction grating that diffracts;the aboveAn illumination optical system that includes a light emitting unit that emits coherent light and a half mirror that divides the coherent light emitted by the light emitting unit into two coherent lights, and irradiates each coherent light to the diffraction grating. An interference optical system including a half mirror that overlaps and interferes with two diffracted lights obtained by diffracting each coherent light by the diffraction grating;the aboveA light receiving unit that receives two interfered diffracted lights and detects an interference signal, and obtains a phase difference between the two diffracted lights from the interference signal detected by the light receiving unit, and detects a relative movement position of the diffraction grating. Position detecting means, and the light emitting means calculates a difference in optical path length of the two coherent lights to the light receiving means.The interference signal in the light receiving meansEmitting coherent light having coherence that can be detected as a change in the modulation rate of the half mirror of the irradiation optical system and the half mirror of the interference optical system,Interference signalThe modulation rate is maximizedpositionThe irradiation optical system forms the optical paths of the two coherent lights on a plane inclined with respect to a plane perpendicular to the grating plane of the diffraction grating and parallel to the grating vector. The light is irradiated to the same point on the grating surface of the diffraction grating.
[0020]
In this optical displacement measuring device, two optical paths of coherent light are formed in a direction inclined with respect to a direction perpendicular to the grating surface of the diffraction grating, and the two coherent lights are formed on the grating surface of the diffraction grating. Irradiate the same point. In this optical displacement measuring device, the phase difference between the two diffracted lights generated by the two coherent lights is obtained, and the relative movement position of the diffraction grating is detected.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, as an embodiment to which the present invention is applied, an optical displacement measuring apparatus that detects the position of a movable part such as a machine tool using a diffraction grating will be described.
[0022]
First, in describing an optical displacement measuring apparatus according to an embodiment to which the present invention is applied, a diffraction grating used in the optical displacement measuring apparatus will be described.
[0023]
As shown in FIG. 1, the diffraction grating 11 has, for example, a thin plate shape, and a grating such as a narrow slit or groove is engraved on the surface at predetermined intervals. The light incident on the diffraction grating 11 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 interval between the gratings and the wavelength of the light.
[0024]
Here, the surface on which the grating of the diffraction grating 11 is formed is referred to as a grating surface 11a. When the diffraction grating 11 is a transmission type, both the surface on which coherent light is incident and the surface on which diffracted light is generated are referred to as a grating surface 11a. Also, it is perpendicular to the direction in which the grating of the diffraction grating 11 is formed (the directions of arrows C1 and C2 in FIG. 1), that is, the grating vector representing the direction of change in the grating transmittance, reflectance, groove depth, and the like. A direction that is parallel to the lattice plane 11a is called a lattice direction. The direction perpendicular to the direction in which the grating is formed and parallel to the grating surface 11a (the directions of arrows D1 and D2 in FIG. 1), that is, the direction parallel to the grating vector of the diffraction grating 11 is defined as the grating vector direction. Call it. Also, the direction perpendicular to the lattice plane 11a (the directions of arrows E1 and E2 in FIG. 1), that is, the direction perpendicular to the lattice direction and perpendicular to the lattice vector direction is referred to as a normal vector direction.
[0025]
Such a diffraction grating 11 is attached to a movable part of a machine tool or the like, and moves in the directions of arrows D1 and D2 in FIG. 1, that is, the grating vector direction as the movable part moves.
[0026]
In the present invention, the type of the diffraction grating is not limited, and the diffraction grating is not limited to those in which grooves or the like are mechanically formed, but may be prepared by baking interference fringes on a photosensitive resin, for example.
[0027]
Next, an optical displacement measuring apparatus according to a first embodiment to which the present invention is applied using a reflective diffraction grating 11 will be described.
[0028]
FIG. 2 is a schematic perspective view of the optical displacement measuring apparatus according to the first embodiment.
[0029]
Here, one virtual straight line parallel to the grating vector direction on the grating surface 11a of the diffraction grating 11 is defined as a straight line n. A virtual plane that includes the straight line n and is parallel to the normal vector is defined as a reference plane m1. Further, a virtual surface including the straight line n and having an angle γ with the reference surface m1 is defined as an inclined surface m2. Further, a virtual surface including the straight line n and having an angle δ with the reference surface m1 is defined as an inclined surface m3. Further, it is assumed that the inclined surface m2 and the inclined surface m3 are on the same plane side with respect to the grating surface 11a of the diffraction grating 11.
[0030]
FIG. 3 shows a side view of the components arranged on the inclined surface m2 as seen from a direction perpendicular to the inclined surface m2. FIG. 4 is a side view of coherent light incident on the diffraction grating 11 and diffracted light diffracted by the diffraction grating 11 as viewed from the grating vector direction. FIG. 5 shows a side view of components arranged on the inclined surface m3 as seen from a direction perpendicular to the inclined surface m3.
[0031]
As shown in FIGS. 2 and 3, the optical displacement measuring device 40 includes a coherent light source 12 that emits coherent light La and two coherent lights La1 that emit coherent light La emitted from the coherent light source 12. , La2 and an irradiation optical system 41 for irradiating the diffraction grating 11.
[0032]
The coherent light source 12 is an element that emits coherent light such as laser light. The coherent light source 12 is made of, for example, a multi-mode semiconductor laser that emits laser light having a coherent distance of about several hundred μm.
[0033]
The irradiation optical system 41 includes a first imaging element 21 that forms an image of the coherent light La emitted from the interference light source 12 on the grating surface 11 a of the diffraction grating 11, and the coherent light emitted from the coherent light source 12. A half mirror 22 that separates La into two coherent light beams La1 and La2, a reflector 23 that reflects one coherent light beam La1 separated by the half mirror 22, and the other coherent beam separated by the half mirror 22. And a reflector 24 that reflects the light La2.
[0034]
In the irradiation optical system 41, each member is arranged so that the optical path of the coherent light La (La1, La2) passing therethrough is formed on the inclined surface m2. Therefore, the coherent light La1 and La2 have an incident angle γ with respect to the diffraction grating 11 as seen from the grating vector direction, as shown in FIG.
[0035]
The first imaging element 21 is composed of an optical element such as a lens having a predetermined numerical aperture. The coherent light La emitted from the coherent light source 12 is incident on the first imaging element 21. The first imaging element 21 images the incident coherent light La on the grating surface 11a of the diffraction grating 11 with a predetermined beam diameter. The diameter of the imaged beam is desirably a size that includes a sufficient number of gratings for the diffraction grating 11 to generate diffracted light. The beam diameter is desirably large enough not to be affected by dust and scratches on the grating surface 11a. The beam diameter can be adjusted by changing the numerical aperture or the like of the first imaging element 21. For example, the beam diameter is preferably several tens of μm or more. Further, the image forming point does not necessarily need to be a point where the beam diameter is minimum, and the point where the difference in the optical path length in the beam image is minimum may be located on the lattice plane 11a.
[0036]
The coherent light La emitted from the coherent light source 12 is incident on the half mirror 22 via the first imaging element 21. The half mirror 22 transmits a part of the incident coherent light La to generate the coherent light La1, and reflects a part of the incident coherent light La to generate the coherent light La2.
[0037]
The reflector 23 reflects the coherent light La1 transmitted through the half mirror 22 and irradiates a predetermined position on the grating surface 11a of the diffraction grating 11. The reflector 24 reflects the coherent light La <b> 2 reflected by the half mirror 22 and irradiates a predetermined position on the grating surface 11 a of the diffraction grating 11.
[0038]
The reflector 23 and the reflector 24 irradiate the coherent light La1 and the coherent light La2 at predetermined positions on the grating surface 11a so that the incident angle on the inclined surface m2 is α. In addition, the reflector 23 and the reflector 24 are arrange | positioned so that the reflective surface may mutually face. Therefore, the coherent light La1 and the coherent light La2 have opposite incident directions in the lattice vector direction. Further, the reflector 23 and the reflector 24 irradiate the coherent light La1 and the coherent light La2 to the same position on the grating surface 11a.
[0039]
In the optical displacement measuring device 40, when the coherent light La1 is irradiated onto the diffraction grating 11, the coherent light La1 is diffracted, and diffracted light Lb1 reflected from the incident point is generated. Further, when the coherent light La2 is irradiated onto the diffraction grating 11, the coherent light La2 is diffracted, and diffracted light Lb2 reflected from the incident point is generated. The diffraction angles of the diffracted light Lb1 and the diffracted light Lb2 are δ as shown in FIG. 4 when viewed from the grating vector direction. That is, the diffracted lights Lb1 and Lb2 are generated along the inclined surface m3. The diffraction angle of the diffracted light Lb1 and the diffracted light Lb2 on the inclined surface m3 is β. The diffracted light Lb1 and the diffracted light Lb2 have opposite emission directions in the grating vector direction.
[0040]
As shown in FIGS. 2 and 5, the optical displacement measuring device 40 receives the two diffracted lights Lb1 and Lb2 that interfere with each other and generates an interference signal, and the diffracted light Lb1 and the diffracted light Lb2. And a light receiving optical system 42 for irradiating the light receiving element 13 with the interference.
[0041]
The light receiving optical system 42 includes a reflector 25 that reflects the diffracted light Lb1 generated by the coherent light La1, a reflector 26 that reflects the diffracted light Lb2 generated by the coherent light La2, and a diffracted light Lb1 reflected by the reflector 25. And the diffracted light Lb2 reflected by the reflector 26 are superimposed and interfere with each other, and the two diffracted lights Lb1 and Lb2 superimposed by the half mirror 27 are imaged on the light receiving surface 13a of the light receiving element 13. And a second imaging element 28.
[0042]
Since the light receiving optical system 42 has a diffraction angle δ as viewed from the grating vector direction of the two diffracted lights Lb1 and Lb2 as described above, the optical path of the diffracted lights Lb1 and Lb2 that pass through is formed on the inclined surface m3. Each member is arrange | positioned so that it may be. Further, the reflector 25 and the reflector 26 of the light receiving optical system 42 are disposed at positions where the diffracted lights Lb1 and Lb2 diffracted at the diffraction angle β on the inclined surface m3 can be reflected.
[0043]
The reflector 25 is irradiated with diffracted light Lb1 generated by irradiating the diffraction grating 11 with coherent light La1. The reflector 25 reflects the diffracted light Lb1 and irradiates the half mirror 27 with it. The reflector 26 is irradiated with diffracted light Lb2 generated by irradiating the diffraction grating 11 with coherent light La2. The reflector 26 reflects this diffracted light Lb2 and irradiates the half mirror 27 with it.
[0044]
The half mirror 27 transmits the diffracted light Lb1 reflected by the reflector 25 and reflects the diffracted light Lb2 reflected by the reflector 26, thereby superimposing the two diffracted lights Lb1 and Lb2.
[0045]
The second imaging element 28 includes an optical element such as a lens having a predetermined numerical aperture. Two diffracted beams Lb 1 and Lb 2 superimposed by the half mirror 27 are incident on the second imaging element 28. The second imaging element 28 images the two diffracted lights Lb1 and Lb2 on the light receiving surface 13a of the light receiving element 13 with a predetermined beam diameter. The image forming point does not necessarily need to be a point where the beam diameter is minimum, and the point where the difference in optical path length within the beam image is minimum may be located on the light receiving surface 13a.
[0046]
The light receiving element 13 is a photoelectric conversion element that converts the light irradiated to the light receiving surface 13a into an electric signal corresponding to the light amount, and includes, for example, a photodetector. The light receiving element 13 receives the interference light superimposed on the light receiving surface 13a and generates an interference signal corresponding to the light quantity.
[0047]
The optical displacement measuring device 40 includes a position detector (not shown) that detects the movement position of the diffraction grating 11 based on the interference signal from the light receiving element 13. This position detector obtains the phase difference between the two diffracted lights based on the interference signal generated by the light receiving element 13 and outputs a position signal indicating the relative movement position of the diffraction grating 11.
[0048]
In the optical displacement measuring device 40 having such a configuration, the diffraction grating 11 moves in the grating vector direction in accordance with the movement of the movable part, thereby causing a phase difference between the two diffracted beams Lb1 and Lb2. In the optical displacement measuring device 40, the interference signal is detected by causing the two diffracted lights Lb1 and Lb2 to interfere with each other, the phase difference between the two diffracted lights Lb1 and Lb2 is obtained from the interference signal, and the movement of the diffraction grating 11 is performed. Detect position.
[0049]
  Here, in the optical displacement measuring device 40, the case where the grating surface 11a of the diffraction grating 11 is inclined will be described with reference to FIG. In FIG. 6, the light receiving optical system 42 is shown on the opposite side of the irradiation optical system 41 with the diffraction grating 11 in between, but this is shown for convenience of explanation.TamaIt is. Actually, the reflection type diffraction grating 11 ismake use ofTherefore, the irradiation optical system 41 and the light receiving optical system 42 are arranged on the same surface side with respect to the detection surface 11 a of the diffraction grating 11.
[0050]
One end of the grating vector direction of the diffraction grating 11 moves in one direction of the normal vector direction (for example, the arrow X3 direction in FIG. 6), and the other end moves in the other direction of the normal vector direction (for example, the arrow X4 direction in FIG. 6). In this case, the diffraction angles of the diffracted light Lb1 and the diffracted light Lb2 change, and therefore the light of the two diffracted lights Lb1 and Lb2 after being superimposed by the half mirror 27. The axes do not match.
[0051]
However, in this optical displacement measuring device 40, the coherent light La emitted from the coherent light source 12 is imaged on the grating surface 11a of the diffraction grating 11 by the first imaging element 21, and the second The imaging element 28 focuses the two diffracted lights Lb1 and Lb2 on the light receiving surface 13a of the light receiving element 13. Therefore, in the optical displacement measuring device 40, the optical path lengths to the light receiving surfaces of the two diffracted lights Lb1 and Lb2 passing through the opening range of the second imaging element 28 are equal and imaged at the same point. Therefore, even when the optical axes of the two diffracted beams Lb1 and Lb2 are deviated, the imaging position of the light receiving surface 13a does not change and the optical path length does not change.
[0052]
As a result, in the optical displacement measuring device 40 according to the first embodiment of the present invention, the two diffracted beams Lb1 and Lb2 are overlapped without shifting from each other. Therefore, when the diffraction grating 11 is moved in a direction other than the direction parallel to the grating vector, for example, even when the diffraction grating 11 is tilted or the diffraction grating 11 is wavy, the light receiving element 13 detects. Interference signal does not decrease. Therefore, the optical displacement measuring device 40 can detect the moving position of the moving movable part with high resolution and high accuracy. Further, in the optical displacement measuring device 40, the degree of freedom of the attachment position to a movable part such as a machine tool is increased, and the position can be detected stably even if there is vibration or shaking in the movable part.
[0053]
Further, in the optical displacement measuring device 40, since the diffracted lights Lb1 and Lb2 are imaged at the same position on the light receiving surface 13a, beam vignetting does not occur and position detection can be performed with high accuracy.
[0054]
Further, in this optical displacement measuring device 40, the distance between the diffraction grating 11 and the irradiation optical system 41 or the light receiving optical system 42 is increased by increasing the aperture of the first imaging element 21 or the second imaging element 28. And a small light receiving element 13 can be used, and the design is simplified.
[0055]
Further, in the optical displacement measuring device 40, the optical path lengths of the coherent light La1 and the coherent light La2 are made equal, and the optical path lengths of the diffracted light Lb1 and the diffracted light Lb2 are made equal, thereby changing the wavelength. The resulting measurement error will not occur. Therefore, the optical displacement measuring device 10 emits coherent light having coherence capable of detecting the difference in optical path length as a change in the modulation rate of the interference fringes in order to adjust each optical path length. The coherent light source 12 may be used. For example, if a short multimode semiconductor laser having a coherence distance of about several hundred μm is used for the coherent light source 12, the positions of the half mirrors 22 and 27 are adjusted so that the modulation rate of the interference fringes is maximized. For example, the difference between the optical path lengths can be suppressed to several tens of μm or less.
[0056]
Further, in the optical displacement measuring apparatus 40 as described above, the irradiation optical system 41 is disposed on the inclined surface m2 having a predetermined inclination angle with respect to the reference surface m1, and the light receiving optical system 42 is disposed on the inclined surface m3. And irradiating the coherent light La1 and the coherent light La2 to the same point of the diffraction grating 11, the optical path formed by the coherent light and the diffracted light can be separated, and the design freedom of the apparatus is reduced. The degree increases. Further, the 0th-order diffracted light or reflected light from the grating surface 11a can be caused to interfere with the diffracted light Lb1 and Lb2 without being mixed into the irradiation optical system 41 or the light receiving optical system 42, and the position can be measured with high accuracy. Can do.
[0057]
By the way, in such an optical displacement measuring apparatus 40, even if the coherent light La1 and the coherent light La2 are incident at a predetermined distance, zero-order light and reflected light are applied to the irradiation optical system 41 and the light receiving optical system 42. It can be prevented from mixing. That is, in the optical displacement measuring device 40, the incident point of the coherent light La1 and the incident point of the coherent light La2 are set at different positions, so that the zero-order light and the reflected light are irradiated with the irradiation optical system 41 and the light receiving optical system. It can be prevented from being mixed into the system 42.
[0058]
However, when the incident points of the coherent light La1 and the coherent light La2 are separated from each other by a predetermined distance, if the diffraction grating 11 has uneven thickness or refractive index, the optical path lengths differ from each other, and the position is measured with high accuracy. It may be difficult to do.
[0059]
Hereinafter, the influence when the diffraction grating 11 has uneven thickness will be described in detail.
[0060]
The intensity of the two diffracted Lb1 and Lb2 lights to be superimposed₁, A₂Assuming that the amount of movement of the diffraction grating 11 in the grating vector direction is x and the initial phase is δ, the intensity I of the interference signal detected by the light receiving element 13 is expressed by the following equation (1).
I = A₁ ²+ A₂ ²+ 2A₁A₂cos (2Kx + δ) (1)
K = 2π / Λ (Λ is the lattice pitch)
The intensity I of this interference signal changes by one period as the diffraction grating 11 moves Λ / 2. δ is an amount that depends on the difference in optical path length between the two diffracted beams Lb1 and Lb2 superimposed. Therefore, if this δ fluctuates, the interference signal I fluctuates even if the diffraction grating 11 does not move, which causes an error.
[0061]
For example, let us consider a case where the transmission type diffraction grating provided with a grating inside glass has uneven thickness as shown in FIG. If the refractive index of the glass is n and the distance that the laser light Lx passes from one surface of the glass to the other is L, the optical path length when this laser light Lx passes through the diffraction grating is nL. Since the refractive index of air is approximately 1, the optical path length when the laser beam Lx passes through the diffraction grating is (n−1) compared to when the laser beam Lx passes through the air at the same distance. It becomes longer by L. Accordingly, if the glass thickness of the diffraction grating changes and the distance that the laser beam Lx passes from one surface of the glass to the other changes by L + ΔL, the optical path length changes by (n−1) ΔL. Will be.
[0062]
  Based on this, for example, as shown in FIG. 8, one laser beam Lx1 passes through a position where the thickness of the diffraction grating is not uneven, and the other laser beam Lx2 passes through a position where the thickness of the diffraction grating is uneven. About the laser beam of the bookThink. If the length of the laser beam Lx2 passing through the uneven thickness is + ΔL, the difference in optical path length between the two laser beams Lx1 and Lx2 is (n−1) ΔL. Therefore, δ shown in the above equation (1) changes by {(n−1) ΔL} · 2π / λ (λ is the wavelength of beams A and B), and an error occurs in the interference signal. The error amount of position detection at this time is (Λ / 2λ) (n−1). For example, if Λ = 0.55 μm, λ = 0.78 μm, n = 1.5, and ΔL = 1 μm, 0.18 μm. For example, this error is a considerably large value when the position is detected on the order of nanometers.
[0063]
Although the transmission type diffraction grating has been described above as an example, an error similarly occurs when the reflection type diffraction grating is covered with glass, and the grating is not covered with glass. If it is a thing, the change of the laser beam passing distance due to the unevenness becomes the change of the optical path length as it is, and an error occurs.
[0064]
As described above, when the diffraction grating 11 is uneven in thickness, an error occurs if the incident points of the coherent light La1 and the coherent light La2 are separated from each other by a predetermined distance. For example, the position of the nanometer order is detected. It becomes difficult.
[0065]
Therefore, in this optical displacement measuring device 40, the irradiation optical system 41 is disposed on the inclined surface m2 having a predetermined inclination angle with respect to the reference surface m1, and the light receiving optical system 42 is disposed on the inclined surface m3. The coherent light La1 and the coherent light La2 are incident on the same point on the diffraction grating 11. That is, the error due to the unevenness of the thickness and refractive index of the diffraction grating 11 occurs because the coherent light La1 and the coherent light La2 pass through different positions, and does not occur when the same point passes. For example, when the diffraction grating 11 is covered with glass or the like, it is difficult to pass the two coherent lights La1 and La2 through the same optical path. If the light enters the same position, the error can be minimized.
[0066]
In order to prevent the 0th-order diffracted light and reflected light from entering the irradiation optical system 41 and the light-receiving optical system 42, the 0th-order diffracted light enters the opening of the second imaging element 28 at the incident angle α and the diffraction angle β. Make it different to no extent. In addition, γ is an angle such that the reflected light from the diffraction grating 11 does not enter the opening of the first imaging element 21. That is, coherent light La1 and Lb2 are incident from directions other than perpendicular to the grating surface 11a.
[0067]
The relationship between the incident angles α and γ of the coherent light and the diffraction angles β and δ of the diffracted light is as shown in the following equations (2) and (3).
[0068]
Sinα + Sinβ = mλ / d (2)
d: Pitch of the diffraction grating
λ: Wavelength of light
m: diffraction order
Sinγ / Sinδ = Cosβ / Cosα (3)
Therefore, when α = β, γ = δ, and when α ≠ β, γ ≠ δ.
[0069]
Next, an optical displacement measuring apparatus according to a second embodiment to which the present invention is applied using a transmission type diffraction grating 11 will be described. In describing the optical displacement measuring apparatus according to the second embodiment, the same components as those in the first optical displacement measuring apparatus are denoted by the same reference numerals in the drawings, and the detailed description thereof will be omitted. Description is omitted. In the third and subsequent embodiments, the same components as those in the previous embodiments are denoted by the same reference numerals in the drawings, and detailed description thereof is omitted.
[0070]
FIG. 9 shows a schematic perspective view of the optical displacement measuring apparatus of the second embodiment.
[0071]
Here, the relationship among the straight line n, the reference plane m1, and the inclined plane m2 is the same as that in the first embodiment. In addition, an angle formed by the reference plane m1 including the straight line n is δ, and an imaginary plane on the opposite side of the inclined plane m2 across the lattice plane 11a is defined as an inclined plane m3 ′.
[0072]
FIG. 10 shows a side view of the components arranged on the inclined surface m2 as seen from a direction perpendicular to the inclined surface m2 and the inclined surface m3 ′. FIG. 11 is a side view of coherent light incident on the diffraction grating 11 and diffracted light diffracted by the diffraction grating 11 when viewed from the grating vector direction.
[0073]
The optical displacement measuring apparatus according to the second embodiment of the present invention is an apparatus that includes a transmissive diffraction grating 11 and detects the position of a movable part such as a machine tool.
[0074]
As shown in FIGS. 9 and 10, the optical displacement measuring apparatus 50 includes a coherent light source 12 that emits coherent light La and two coherent lights La1 that are emitted from the coherent light source 12. , La2 and an irradiation optical system 41 for irradiating the diffraction grating 11.
[0075]
In the irradiation optical system 41, each member is arranged so that the optical path of the coherent light La (La1, La2) passing therethrough is formed on the inclined surface m2. For this reason, the coherent lights La1 and La2 have an incident angle γ as seen from the grating vector direction as shown in FIG.
[0076]
The reflector 23 reflects the coherent light La1 transmitted through the half mirror 22 and irradiates a predetermined position on the grating surface 11a of the diffraction grating 11. The reflector 24 reflects the coherent light La <b> 2 reflected by the half mirror 22 and irradiates a predetermined position on the grating surface 11 a of the diffraction grating 11. The reflector 23 and the reflector 24 irradiate the coherent light La1 and the coherent light La2 at predetermined positions on the grating surface 11a so that the incident angle on the inclined surface m2 is α. The incident directions of the lattice vector directions of the coherent light La1 and the coherent light La2 are opposite to each other. The incident point of the coherent light La1 and the incident point of the coherent light La2 are the same point on the diffraction grating 11.
[0077]
In the optical displacement measuring device 50, when the coherent light La1 is irradiated onto the diffraction grating 11, the coherent light La1 is diffracted and diffracted light Lb1 transmitted through the incident point is generated. Further, when the coherent light La2 is irradiated onto the diffraction grating 11, the coherent light La2 is diffracted, and diffracted light Lb2 transmitted through the incident point is generated. When viewed from the grating vector direction, the diffraction angles of the diffracted light Lb1 and the diffracted light Lb2 are δ as shown in FIG. That is, diffracted lights Lb1 and Lb2 are generated along the inclined surface m3 ′. The diffraction angle of the diffracted light Lb1 and the diffracted light Lb2 on the inclined surface m3 ′ is β. The diffracted light Lb1 and the diffracted light Lb2 have opposite emission directions in the grating vector direction.
[0078]
Further, as shown in FIGS. 9 and 10, the optical displacement measuring device 50 receives the two diffracted lights Lb1 and Lb2 that interfere with each other and generates an interference signal, and the diffracted light Lb1 and the diffracted light Lb2. And a light receiving optical system 42 for irradiating the light receiving element 13 with the interference.
[0079]
Since the light receiving optical system 42 has a diffraction angle δ as viewed from the grating vector direction of the two diffracted lights Lb1 and Lb2 as described above, the optical path of the diffracted lights Lb1 and Lb2 that pass through is on the inclined plane m3 ′. Each member is arranged so as to be formed. Further, the reflector 25 and the reflector 26 of the light receiving optical system 42 are arranged at positions where the diffracted lights Lb1 and Lb2 diffracted at the diffraction angle β on the inclined surface m3 ′ can be reflected.
[0080]
The optical displacement measuring device 50 includes a position detector (not shown) that detects the movement position of the diffraction grating 11 based on the interference signal from the light receiving element 13.
[0081]
In the optical displacement measuring device 50 having such a configuration, the diffraction grating 11 moves in the grating vector direction in accordance with the movement of the movable part, thereby causing a phase difference between the two diffracted beams Lb1 and Lb2. In the optical displacement measuring device 50, interference signals are detected by causing the two diffracted lights Lb1 and Lb2 to interfere with each other, a phase difference between the two diffracted lights Lb1 and Lb2 is obtained from the interference signals, and the diffraction grating 11 is moved. Detect position.
[0082]
As described above, in the optical displacement measuring device 50, the irradiation optical system 41 is disposed on the inclined surface m2 having a predetermined inclination angle with respect to the reference surface m1, and the light receiving optical system 42 is disposed on the inclined surface m3 ′. By arranging and allowing the coherent light La1 and the coherent light La2 to enter the same point, the optical path formed by the coherent light and the diffracted light can be separated, and the degree of freedom in designing the apparatus is increased. Further, the 0th-order diffracted light or reflected light from the grating surface 11a can be caused to interfere with the diffracted light Lb1 and Lb2 without being mixed into the irradiation optical system 41 or the light receiving optical system 42, and the position can be measured with high accuracy. Can do.
[0083]
The relationship between the incident angles α and γ and the diffraction angles β and δ for preventing the 0th-order diffracted light and reflected light from being mixed into the irradiation optical system 41 and the light receiving optical system 42 is the same as in the first embodiment.
[0084]
Next, an optical displacement measuring apparatus according to a third embodiment to which the present invention is applied will be described with reference to FIG. The third embodiment is a partial modification of the components of the first embodiment and the second embodiment. Hereinafter, the first embodiment and the second embodiment will be described. The detailed description of the components that are not modified among the components of the embodiment is omitted.
[0085]
The optical displacement measuring device 60 of the third embodiment uses a polarization beam splitter as the half mirror 22 of the irradiation optical system 41. Hereinafter, in the description of the third embodiment, the half mirror 22 is described in other words as the polarization beam splitter 22.
[0086]
Further, this optical displacement measuring device 60 is replaced with the first polarizing beam splitter 61 and 1/4 as shown in FIG. 12 in place of the half mirror 27 and the second imaging element 28 of the light receiving optical system 42. A wave plate 62, a third imaging element 63, a non-polarizing beam splitter 64, a second polarizing beam splitter 65, and a third polarizing beam splitter 66 are used.
[0087]
The optical displacement measuring device 60 uses first light receiving elements 67a and 67b and second light receiving elements 68a and 68b instead of the light receiving element 13.
[0088]
The coherent light La emitted from the coherent light source 12 is incident on the polarizing beam splitter 22 of the irradiation optical system 41 with a polarization direction inclined by 45 degrees. The polarization beam splitter 22 of the irradiation optical system 41 splits the incident coherent light La into two coherent lights La1 and La2 whose polarization directions are orthogonal. The coherent light La1 transmitted through the polarization beam splitter 22 of the irradiation optical system 41 becomes P-polarized light, and the reflected coherent light La2 becomes S-polarized light.
[0089]
The diffracted light Lb 1 diffracted by the diffraction grating 11 and the diffracted light Lb 2 diffracted by the diffraction grating 11 are incident on the first polarizing beam splitter 61 of the light receiving optical system 42. The diffracted light Lb1 is P-polarized light, and the diffracted light Lb2 is S-polarized light. The polarization beam splitter 61 transmits the diffracted light Lb1 and reflects the diffracted light Lb2, thereby superimposing the two diffracted lights Lb1 and Lb2.
[0090]
The two superimposed diffracted beams Lb1 and Lb2 pass through the quarter-wave plate 62. The quarter wavelength plate 62 is disposed at a position where the optical axis is inclined by 45 degrees with respect to the polarization direction of each of the diffracted lights Lb1 and Lb2. Therefore, each of the diffracted lights Lb1 and Lb2 passes through the quarter wavelength plate 62 and becomes circularly polarized light in the opposite directions.
[0091]
The diffracted beams Lb1 and Lb2 that are reversely polarized circularly polarized light pass through the third imaging element 63.
[0092]
The third imaging element 63 is composed of an optical element such as a lens having a predetermined numerical aperture. The third imaging element 63 images the diffracted lights Lb1 and Lb2 on the light receiving surfaces of the first light receiving elements 67a and 67b and the second light receiving elements 68a and 68b with a predetermined beam diameter. The image forming point does not necessarily need to be a point where the beam diameter is minimum, and a point where the difference in optical path length within the beam image is minimum may be located on the light receiving surface.
[0093]
The two diffracted beams Lb1 and Lb2 that have passed through the third imaging element 63 are split into two beams by the non-polarizing beam splitter 64.
[0094]
One of the divided beams is further divided into two beams whose polarization directions are orthogonal by the second polarizing beam splitter 65, and are irradiated to the first light receiving elements 67a and 67b, respectively. The other split beam is further split into two beams whose polarization directions are orthogonal to each other by a third polarizing beam splitter 66 inclined by 45 degrees with respect to the second polarizing beam splitter 65. The light receiving elements 68a and 68b are irradiated.
[0095]
Here, light obtained by superimposing circularly polarized light rotating in opposite directions can be regarded as linearly polarized light rotating according to the phase difference between the two lights. Therefore, the diffracted light that has passed through the quarter-wave plate 62 becomes linearly polarized light that rotates as the diffraction grating 11 moves. In addition, when components having polarization directions different from each other by ω degrees are extracted from the linearly polarized light by a polarizing element such as a polarizing plate, signals obtained by detecting the intensity of the extracted light are signals having phases different from each other by 2ω degrees. For this reason, the first light receiving elements 67a and 67b detect the lights having the polarization directions different from each other by 90 degrees extracted by the second polarization beam splitter 65, and thus the phases of the detected signals are different from each other by 180 degrees. Therefore, the signal from which the DC component is removed can be detected by taking the difference between the signals detected by the first light receiving elements 67a and 67b. The same applies to the second light receiving elements 68a and 68b.
[0096]
The light extracted by the third polarizing beam splitter 66 is 45 degrees different from the light extracted by the second polarizing beam splitter 65. Therefore, the signals obtained from the second light receiving elements 68a and 68b are 90 degrees out of phase with the signals obtained from the first light receiving elements 67a and 67b. That is, the differential signal of the detection signal between the first light receiving element 67a and the first light receiving element 67b and the differential signal of the detection signal between the second light receiving element 68a and the second light receiving element 68b are mutually The 90 degree phase is different. Therefore, the optical displacement measuring device 60 can specify the moving direction of the diffraction grating 11 based on the position signal indicating the moving position of the diffraction grating 11 having a phase difference of 90 degrees.
[0097]
As described above, in the optical displacement measuring device 60 according to the third embodiment, the DC fluctuation due to the influence of the transmittance, reflectance, diffraction efficiency, etc. of the diffraction grating 11 can be removed from the detected interference signal. it can. Further, in the optical displacement measuring device 60, the moving direction of the diffraction grating 11 can be specified.
[0098]
Next, an optical displacement measuring apparatus according to a fourth embodiment to which the present invention is applied will be described with reference to FIG. The fourth embodiment is a partial modification of the constituent elements of the third embodiment. Hereinafter, the constituent elements of the third embodiment that are not modified. Detailed description of the elements is omitted.
[0099]
The optical displacement measuring apparatus 70 of the fourth embodiment uses a non-polarizing beam splitter for the half mirror 22 of the irradiation optical system 41. Hereinafter, in the description of the fourth embodiment, the half mirror 22 will be described as the non-polarizing beam splitter 22.
[0100]
Further, as shown in FIG. 13, the optical displacement measuring device 70 includes a half-wave plate 71 that rotates the polarization direction of one diffracted light incident on the first polarizing beam splitter 61 by 90 degrees. Yes.
[0101]
The coherent light La emitted from the coherent light source 12 is incident on the non-polarizing beam splitter 22 of the irradiation optical system 41 as S-polarized light. The non-polarizing beam splitter 22 of the irradiation optical system 41 divides the incident coherent light La into two coherent lights La1 and La2 having the same polarization direction.
[0102]
The diffracted light Lb1 and the diffracted light Lb2 diffracted by the diffraction grating 11 have the same polarization direction when diffracted. One diffracted light Lb1 passes through the half-wave plate 71 that rotates the polarization direction by 90 degrees, and enters the first polarizing beam splitter 61. The other diffracted light Lb2 is incident on the first polarization beam splitter 61 of the light receiving optical system 42 in the same polarization direction.
[0103]
For this reason, two diffracted lights Lb1 and Lb2 whose polarization directions are different by 90 degrees are incident on the first polarizing beam splitter 61 of the light receiving optical system. The diffracted light Lb1 is P-polarized light, and the diffracted light Lb2 is S-polarized light. The polarization beam splitter 61 transmits the diffracted light Lb1 and reflects the diffracted light Lb2, thereby superimposing the two diffracted lights Lb1 and Lb2. When P-polarized coherent light La is incident on the non-polarizing beam splitter 22, the half-wave plate 71 may be provided on the diffracted light Lb2 side.
[0104]
The two diffracted beams Lb1 and Lb2 that have interfered pass through the quarter-wave plate 62. The quarter-wave plate 62 is tilted by 45 degrees with respect to the polarization direction of the diffracted lights Lb1 and Lb2. Therefore, each of the diffracted lights Lb1 and Lb2 passes through the quarter wavelength plate 62 and becomes circularly polarized light in the opposite directions.
[0105]
The diffracted beams Lb1 and Lb2 that are reversely polarized circularly polarized light pass through the third imaging element 63. The third imaging element 63 images the diffracted lights Lb1 and Lb2 on the light receiving surfaces of the first light receiving elements 67a and 67b and the second light receiving elements 68a and 68b with a predetermined beam diameter.
[0106]
The two diffracted lights Lb1 and Lb2 that have passed through the third imaging element 63 are split into two beams by the non-polarizing beam splitter 64.
[0107]
One beam is further divided into two beams whose polarization directions are orthogonal to each other by the second polarization beam splitter 65, and are irradiated to the first light receiving elements 67a and 67b, respectively. The other beam is further divided into two beams whose polarization directions are orthogonal to each other by a third polarizing beam splitter 66 inclined by 45 degrees with respect to the second polarizing beam splitter 65, respectively. 68b is irradiated.
[0108]
As described above, in the optical displacement measuring device 70 according to the fourth embodiment, the DC fluctuation due to the influence of the transmittance, reflectance, diffraction efficiency, etc. of the diffraction grating 11 can be removed from the detected interference signal. it can. Further, in this optical displacement measuring device 70, the moving direction of the diffraction grating 11 can be specified.
[0109]
Next, an optical displacement measuring apparatus according to a fifth embodiment to which the present invention is applied will be described with reference to FIG. The fifth embodiment is a partial modification of the components of the fourth embodiment, and hereinafter, the configuration of the components of the fourth embodiment that are not modified. Detailed description of the elements is omitted.
[0110]
The optical displacement measuring device 80 according to the fifth embodiment uses a non-polarizing beam splitter for the half mirror 22 of the irradiation optical system 41. Hereinafter, in the description of the fifth embodiment, the half mirror 22 is described in other words as the polarization beam splitter 22.
[0111]
Further, as shown in FIG. 14, the optical displacement measuring device 80 includes a half-wave plate 71, a polarization beam splitter 61, a quarter-wave plate 62, and a third imaging element 63 of the light receiving optical system 42. Instead, a first quarter-wave plate 81, a second quarter-wave plate 82, a fourth imaging element 83, and a fifth imaging element 84 are used.
[0112]
The coherent light La emitted from the coherent light source 12 is incident on the non-polarizing beam splitter 22 of the irradiation optical system 41. The non-polarizing beam splitter 22 of the irradiation optical system 41 divides the incident coherent light La into coherent lights La1 and La2 having the same polarization direction.
[0113]
The diffracted light Lb1 and the diffracted light Lb2 diffracted by the diffraction grating 11 have the same polarization direction when diffracted. One diffracted light Lb1 passes through the first quarter-wave plate 81 of the light receiving optical system 42 with the polarization direction as it is. Here, the first quarter-wave plate 81 is disposed with the optical axis inclined by 45 degrees with respect to the polarization direction of the incident diffracted light Lb1. Therefore, this one diffracted light Lb1 becomes circularly polarized light in a predetermined rotation direction.
[0114]
The diffracted light Lb 1 that is circularly polarized light passes through the fourth imaging element 83. The fourth imaging element 83 is composed of an optical element such as a lens having a predetermined numerical aperture. The fourth imaging element 83 forms the diffracted light Lb1 on the light receiving surfaces of the first light receiving elements 67a and 67b and the second light receiving elements 68a and 68b with a predetermined beam diameter. The image forming point does not necessarily need to be a point where the beam diameter is minimum, and a point where the difference in optical path length within the beam image is minimum may be located on the light receiving surface.
[0115]
The other diffracted light Lb2 passes through the second quarter-wave plate 82 of the light receiving optical system 42 with the polarization direction as it is. Here, the second quarter-wave plate 82 is disposed with the optical axis inclined by 45 degrees with respect to the polarization direction of the incident diffracted light Lb2. In addition, the second quarter-wave plate 82 is disposed with the optical axis inclined so that the other diffracted light Lb2 that passes therethrough is circularly polarized in the reverse direction with respect to the one diffracted light Lb1.
[0116]
The diffracted light Lb 2 that is circularly polarized light passes through the fifth imaging element 84. The fifth imaging element 84 is composed of an optical element such as a lens having a predetermined numerical aperture. The fifth imaging element 84 forms an image of the diffracted light Lb2 on the light receiving surfaces of the first light receiving elements 67a and 67b and the second light receiving elements 68a and 68b with a predetermined beam diameter. The image forming point does not necessarily need to be a point where the beam diameter is minimum, and a point where the difference in optical path length within the beam image is minimum may be located on the light receiving surface.
[0117]
The diffracted beams Lb1 and Lb2 that are reversely polarized light beams pass through the fourth imaging element 83 and the fifth imaging element 84 and enter the non-polarizing beam splitter 64.
[0118]
The non-polarizing beam splitter 64 superimposes two incident diffracted lights Lb1 and Lb2 and splits them into two beams.
[0119]
One of the divided beams is further divided into two beams whose polarization directions are orthogonal by the second polarizing beam splitter 65, and are irradiated to the first light receiving elements 67a and 67b, respectively. The other split beam is further split into two beams whose polarization directions are orthogonal to each other by a third polarizing beam splitter 66 inclined by 45 degrees with respect to the second polarizing beam splitter 65. The light receiving elements 68a and 68b are irradiated.
[0120]
As described above, in the optical displacement measuring device 80 according to the fifth embodiment, the DC fluctuation due to the influence of the transmittance, reflectance, diffraction efficiency, etc. of the diffraction grating 11 can be removed from the detected interference signal. it can. Further, in this optical displacement measuring device 80, the moving direction of the diffraction grating 11 can be specified.
[0121]
The optical displacement measuring devices according to the first to fifth embodiments to which the present invention is applied have been described above. In the optical displacement measuring apparatus of each embodiment, the diffraction grating 11 in which the grating is provided in parallel at a predetermined interval is used. In the present invention, a diffraction grating in which such a grating is provided in parallel is used. It is not necessary. For example, as shown in FIG. 15, 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. 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.
[0122]
Moreover, in the optical displacement measuring device of each embodiment, although the diffraction grating 11 was attached to movable parts, such as a machine tool, and the case where this diffraction grating 11 moved according to the movement of a movable part was demonstrated, this invention Then, the irradiation optical system, the interference optical system, and the diffraction grating 11 may be moved relatively. For example, in the present invention, the diffraction grating may be fixed, and the irradiation optical system and the interference optical system may move according to the movement of a movable part such as a machine tool.
[0123]
In addition, the half mirror, the beam splitter, the imaging element, and the like used in the optical displacement measuring device of each embodiment are not limited to an element or a lens using a thin film, for example, using a diffractive optical element. Also good.
[0124]
In the optical displacement measuring device of each embodiment, the first imaging element 21 only needs to be disposed at a position where the coherent light La can be imaged with respect to the grating surface 11a of the diffraction grating 11. The position and the number of the arrangement are not limited. For example, the imaging elements may be arranged so as to image the coherent light La1 and La2 after being divided by the half mirror (polarization beam splitter or polarization beam splitter) 22.
[0125]
In the optical displacement measuring device of each embodiment, the second imaging element 28, the third imaging element 63, the fourth imaging element 83, and the fifth imaging element 84 are the light receiving element 13. Alternatively, the position and number of the dispositions are not limited because it is only necessary to be disposed at a position where the diffracted lights Lb1 and Lb2 can be imaged with respect to the light receiving surfaces of the light receiving elements 67 and 68. For example, an imaging element may be arranged so that the diffracted lights Lb1 and Lb2 before being superimposed by the half mirror 27 and the polarizing beam splitter 61 are imaged, and the diffracted light Lb1 after being split by the non-polarizing beam splitter 64 , Lb2 may be arranged to form an imaging element.
[0126]
【The invention's effect】
In the optical displacement measuring apparatus according to the present invention, the optical paths of the two coherent lights are formed in a direction inclined with respect to the direction perpendicular to the grating surface of the diffraction grating, and the two coherent lights are transmitted through the diffraction grating. Irradiate the same point on the lattice plane. In this optical displacement measuring device, the phase difference between the two diffracted lights generated by the two coherent lights is obtained, and the relative movement position of the diffraction grating is detected.
[0127]
  As a result, in the optical displacement measuring apparatus according to the present invention, the diffracted light can be superimposed without mixing the 0th-order diffracted light and reflected light from the diffraction grating into the irradiation optical system and the light receiving optical system. Position detection. Further, in the optical displacement measuring device according to the present invention, the position can be measured with high accuracy without causing an error due to the thickness of the diffraction grating and the uneven refractive index.
  In addition, half mirrors provided in each of the irradiation optical system and the interference optical system,Interference signalSince the modulation rate is adjusted so as to be maximum, it is possible to prevent a measurement error due to wavelength variation.
[Brief description of the drawings]
FIG. 1 is a perspective view of a diffraction grating used in an optical displacement measuring apparatus according to an embodiment of the present invention.
FIG. 2 is a perspective view of the optical displacement measuring apparatus according to the first embodiment of the present invention.
FIG. 3 is a side view of components arranged on an inclined surface m2 of the optical displacement measuring device according to the first embodiment of the present invention as seen from a direction perpendicular to the inclined surface m2. .
FIG. 4 is a side view of coherent light incident on the diffraction grating and the diffracted light diffracted by the diffraction grating of the optical displacement measuring apparatus according to the first embodiment of the present invention as seen from the grating vector direction. is there.
FIG. 5 is a side view of components arranged on an inclined surface m3 of the optical displacement measuring device according to the first embodiment of the present invention as seen from a direction perpendicular to the inclined surface m3. .
FIG. 6 is a diagram for explaining a case where the diffraction grating of the optical displacement measuring device according to the first embodiment of the present invention is tilted.
FIG. 7 is a diagram for explaining the optical path length of laser light passing through a diffraction grating.
FIG. 8 is a diagram for explaining a difference in optical path length of two laser beams passing through a diffraction grating when the diffraction grating has uneven thickness.
FIG. 9 is a perspective view of an optical displacement measuring device according to a second embodiment of the present invention.
FIG. 10 shows the components disposed on the inclined surface m2 and the inclined surface m3 ′ of the optical displacement measuring apparatus according to the second embodiment of the present invention with respect to the inclined surface m2 and the inclined surface m3 ′. It is the side view seen from the perpendicular direction.
FIG. 11 is a side view of coherent light incident on the diffraction grating of the optical displacement measuring device according to the second embodiment of the present invention and diffracted light diffracted by the diffraction grating when viewed from the grating vector direction. is there.
FIG. 12 is a perspective view of a main part of a light receiving optical system according to a third embodiment of the present invention.
FIG. 13 is a perspective view of essential parts of a light receiving optical system according to a fourth embodiment of the present invention.
FIG. 14 is a perspective view of essential parts of a light receiving optical system according to a fifth embodiment of the present invention.
FIG. 15 is a diagram for explaining another diffraction grating used in the optical displacement measuring apparatus according to the first to fifth embodiments of the present invention.
FIG. 16 is a perspective view of a conventional optical displacement measuring device.
FIG. 17 is a side view of a conventional optical displacement measuring device.
FIG. 18 is a perspective view of another conventional optical displacement measuring device.
FIG. 19 is a side view of another conventional optical displacement measuring device.
FIG. 20 is a diagram for explaining another conventional optical displacement measuring device.
FIG. 21 is a diagram for explaining reflected light returning to a coherent light source of still another conventional optical displacement measuring apparatus.
[Explanation of symbols]
11 diffraction grating, 40, 50, 60, 70, 80 optical displacement measuring device, 12 coherent light source, 13, 67, 68 light receiving element, 21, 28, 63, 83, 84 imaging element

Claims (1)

A diffraction grating that is irradiated with coherent light, moves relative to the coherent light in a direction parallel to the grating vector, and diffracts the coherent light;
Light emitting means for emitting said coherent light,
An irradiation optical system that includes a half mirror that divides coherent light emitted by the light emitting means into two coherent lights, and irradiates each coherent light to the diffraction grating;
An interference optical system including a half mirror that superimposes and interferes with two diffracted lights obtained by diffracting each coherent light by the diffraction grating;
Light receiving means for detecting an interference signal by receiving the two diffracted light the interference,
A position detecting means for obtaining a phase difference between the two diffracted lights from the interference signal detected by the light receiving means and detecting a relative movement position of the diffraction grating;
The light emitting means detects coherent light having coherence capable of detecting a difference in optical path length of the two coherent lights to the light receiving means as a change in the modulation rate of the interference signal in the light receiving means. Flash
The half mirror of the irradiation optical system and the half mirror of the interference optical system are adjusted to a position where the modulation rate of the interference signal is maximized,
The irradiation optical system forms an optical path of the two coherent lights on a plane inclined with respect to a plane perpendicular to the grating plane of the diffraction grating and parallel to the grating vector, and diffracts the two coherent lights. An optical displacement measuring device for irradiating the same point on a lattice surface of a lattice.

Images