JPH01301116A - Optical relative displacement detector - Google Patents

Abstract

PURPOSE:To prevent the detection result of relative displacement from having an error by operating a rotary mechanism according to the quantity of the deviation in the phase difference between 1st and 2nd intensity signals from a reference value when the phase difference deviates from the reference value. CONSTITUTION:In a normal state wherein a 1st diffraction grating and a 2nd diffraction grating are parallel to each other, the phase difference between the 1st intensity signal which is the intensity signal of light passed through both gratings 22 and 24 and the 2nd intensity signal which is the intensity signal of 2nd light passed through the grating 22 and a 3rd diffraction grating is set to the predetermined reference value. When the parallelism between both gratings is inferior, the phase difference between the 1st and 2nd intensity signals deviates from the reference value, so the rotary mechanism is operated according to the quantity of the deviation to set the gratings 22 and 24 parallel to each other. In this case, when the relative rotational positions of the gratings 22 and 24 are normal, both intensity signals become in phase with each other. Therefore, the detection result of the relative displacement is prevented from having an error owing to inferior parallelism between the gratings 22 and 24.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical relative displacement detection device that optically detects the relative displacement between a first member and a second member that are relatively movable along a straight line. In particular, the present invention relates to a technique for improving relative displacement detection accuracy.

[Conventional technology]

2. Optical linear encoders, mask inspection devices in the semiconductor manufacturing field, and the like are known as optical relative displacement detection devices. Optical relative displacement detection devices generally include (a)
a first diffraction grating and a second diffraction grating, each of which is disposed on the first member and the second member so as to be integrally displaceable therewith, extends parallel to the straight line and faces each other in a direction perpendicular to the straight line; , (b) a photodetector that receives the light that has passed through both the first diffraction grating and the second diffraction grating out of the light emitted by the light source and outputs an intensity signal according to the intensity of the light; and (C) the photodetector. It is configured to include relative displacement detection means for detecting relative displacement between the first member and the second member based on the intensity signal of the photodetector.

An example of an optical linear encoder is JP-A-59-1323.
It is disclosed in Publication No. 11. As shown in FIG. 8, light from a light source 100 is converted into a parallel beam by a collimator lens 102, and a main scale 104 and an index scale 106 are arranged at right angles to the parallel beam. The main scale 104 is arranged in the longitudinal direction (
It is represented by an arrow X in the figure. Hereinafter, it will be referred to as the X direction. ), the first diffraction grating 108 is movable integrally with a moving object (not shown) along the X direction, and a first diffraction grating 108 is formed with a large number of slits lined up at a constant pitch P in the X direction. On the other hand, the index scale 106 is attached to the frame of the encoder so that the light source 100 and the collimator lens 102 cannot move relative to each other, and two second diffraction gratings 110 and 112 are formed apart in a direction perpendicular to the X direction. ing. The two second diffraction gratings 110 and 112 also have slits lined up in the X direction with a constant bit P, but each slit of the diffraction grating 110 is separated from each slit of the diffraction grating 112 in the positive X direction (the front side and the front side in the figure). is shifted by one quarter of a pitch P (hereinafter expressed as P/4) in the X direction (toward the opposite side).

Among the parallel rays emitted from the collimator lens 102,
The first detection light that has passed through the first diffraction grating 10 and the second diffraction grating 110 reaches the first detection light detector 116, and a light intensity signal is output accordingly.
8 and the second detection light that has passed through the second diffraction grating 112 reaches the second detection light detector 118 12, and a light intensity signal is output. Therefore, if the main scale 104 moves, for example, in the positive X direction, the intensity signal 11 of the first detection light and the intensity signal I2 of the second detection light are graphed in FIGS. As shown, each intensity signal lI changes with a phase difference of P/4.

As shown in the graph in FIG. Index scale 10 of scale 104
6, that is, both scales 104. ，
The relative displacement of 106 in the X direction is known.

As is clear from the above explanation, in this conventional example,
The moving object and the members to which the index scale 106 is attached in a relatively immovable manner are a first member and a second member, respectively, and the first diffraction grating 1.
08 constitutes the first diffraction grating in the present invention, and two second diffraction gratings 110, 11 with index scale lO6
2 jointly constitute a second diffraction grating in the present invention, the first and second detection photodetectors 116 and 118 jointly constitute a photodetector, and the movement amount calculation means 120 functions as a relative displacement detection means. Configure.

[Problems to be Solved by the Invention] In the optical relative displacement detection device, the relative displacement between the first member and the second member is detected in a direction in which the first diffraction grating and the second diffraction grating are precisely parallel. In other words, the two straight lines along which the slits of both gratings are lined up are exactly parallel (in this state, the slits of both gratings are 6i
parallel to. ) is important. Therefore, prior to detecting the relative displacement, the first member and the second member are attached to the frame of the detection device so that the extending directions of the first diffraction grating and the second diffraction grating are precisely parallel. However, the first member and the second member may be attached with insufficient parallelism between both grids. In this case, a problem arises in that the intensity signal of the light that has passed through both the first diffraction grating and the second diffraction grating no longer changes normally, resulting in a decrease in relative displacement detection accuracy.

In particular, as in the aforementioned optical linear encoder, the second diffraction grating is comprised of a plurality of diffraction gratings (in the example, second diffraction gratings 110 and 112), which together face the first grating. In an aspect, the first member and the second member are improperly attached.

As a result, the phase of each of the plurality of diffraction gratings with respect to the first diffraction grating deviates from the normal phase, and the magnitude of the deviation,
And since the direction of the deviation is not the same for a plurality of diffraction gratings, whether the deviation occurs in a direction that advances the phase or a direction that delays the phase, the first diffraction grating and the second diffraction grating
A phase shift occurs in the intensity signal of the path light that has passed through each of the plurality of diffraction gratings of the diffraction grating, thereby reducing the detection accuracy of the relative displacement between the first member and the second member.

- To give a specific example, in the above-mentioned optical linear encoder, if the main scale 104 and index scale 106 are improperly attached, for example, the intensity signal l of the first detection light changes normally, but the second The intensity signal 2 of the detected light may not change normally, and in this case, the main scale 104 is constant for both intensity signals x, r, as shown in the graph of FIG. As the interval advances, the intermediate value is no longer taken, and the count of the intermediate value changes for a fixed amount of movement of the main scale 104, causing an error in the detection result of the amount of movement.

The present invention solves this problem, that is, in an optical relative displacement detection device, an error occurs in the relative displacement detection result due to poor parallelism between the first diffraction grating and the second diffraction grating. This was done with the goal of solving the problem.

[Means to solve the problem]

The gist of the present invention is the first diffraction grating.

An optical relative displacement detection device including a second diffraction grating, a light source, a photodetector, and a relative displacement detection means, which is movable integrally with the second member, faces the first diffraction grating, and is parallel to the second diffraction grating. a third diffraction grating extending from the second diffraction grating in a direction perpendicular to the direction in which the second diffraction grating extends;
(b) a second photodetector that receives the second light that has passed through both the first diffraction grating and the third diffraction grating out of the light emitted by the light source and outputs an intensity signal according to the intensity of the light; , (C) phase difference detection means for detecting a phase difference between the intensity signal of the photodetector and the intensity signal of the second photodetector, and (d) the phase difference detected by the phase difference detection means is predetermined. and a rotation mechanism for rotating at least one of the first member and the second member in a plane parallel to the planes of the first diffraction grating and the second diffraction grating so that the reference value is the same as that of the first diffraction grating.

[Effect]

In the optical relative displacement detection device according to the present invention, the first
In the normal case where the diffraction grating and the second diffraction grating are parallel to each other, the first intensity signal that is the intensity signal of the light that has passed through both gratings (hereinafter referred to as the first light), and the 3
The phase difference with the second intensity signal, which is the intensity signal of the second light that has passed through the diffraction grating, is set to a predetermined reference value.

If the parallelism of both gratings is poor, the phase difference between the first intensity signal and the second intensity signal will deviate from the reference value. If the diffraction gratings are operated as shown in FIG.

Note that two parts of one diffraction grating that are separated in a direction perpendicular to the direction in which the grating extends are defined as a second diffraction grating and a third diffraction grating, respectively, and the light from these two parts is used as the first light and the third diffraction grating, respectively. It can be made into two types of light. In this case, the reference value of the phase difference between the first intensity signal and the second intensity signal is 0,
That is, when the relative rotational positions of the first diffraction grating and the second diffraction grating are normal, the phases of both intensity signals become equal to each other.

Furthermore, since the first diffraction grating and the second diffraction grating are arranged in the direction of propagation of light from the light source, in order to obtain the first light that has passed through both gratings, the grating closer to the light source is of a transmission type. , the grating on the side far from the light source may be of a transmissive type or a reflective type. Further, when the third diffraction grating is provided on the member closer to the light source between the first member and the second member, it is considered to be a transmission type, but when it is provided on the member farther from the light source,
It may be of a transmissive type or a reflective type.

Furthermore, the detection of the phase difference between the first strong variation signal and the second strong variation signal is performed prior to the detection of the relative displacement between the first member and the second member, and is not performed after the start of the relative displacement detection. However, if there is a possibility that the relative rotational position of the first diffraction grating and the first diffraction grating 7 will change due to the relative displacement of the first member and the second member, the relative displacement detection This can also be done after the start.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to detect the relative displacement between the first member and the second member in a state where the first diffraction grating and the second diffraction grating extend in exactly parallel directions. hand,
This has the effect of improving detection accuracy.

Furthermore, according to the present invention, since the amount of deviation of the relative rotational position between the first diffraction grating and the second diffraction grating from the normal position is optically detected with high precision, the relative rotational position can be corrected with high precision. As a result, the first member and the second member
It is also possible to obtain the effect that the detection accuracy of relative displacement with the member is further improved.

Furthermore, according to the present invention, the light source is originally provided for detecting relative displacement between the first member and the second member.

The first diffraction grating, the second diffraction grating, and the photodetector can be used to correct the parallelism between the first diffraction grating and the second diffraction grating, and the newly required elements are the third diffraction grating, the second diffraction grating, and the second diffraction grating. Since only a photodetector and a rotation mechanism are required, there is also the effect that the increase in cost associated with implementation of the present invention can be suppressed as much as possible.

〔Example〕

An embodiment in which the present invention is applied to an optical linear encoder will be described in detail below with reference to the drawings.

FIG. 1 shows an optical linear encoder that is an embodiment of the present invention. This is basically the same as the conventional optical linear encoder shown in FIG. 8. In the figure, lO is the semiconductor laser as the light source, 12 is the collimator lens that converts the laser light emitted by the semiconductor laser 10 into parallel light, 14 is the main scale, and 16
is the index scale, and 17 is a laser driving device. The main scale 14 is moved integrally with a moving object O, which is moved in the X direction perpendicular to the plane of the paper in the figure, by a piezoelectric actuator 18 formed by laminating a large number of piezoelectric elements. In addition, piezoelectric actuator 1
8 is energized by a moving device 19.

As schematically shown in FIG. 2, the main scale 14 includes:
A diffraction grating 20 in which a large number of slits are arranged at a constant pitch P is provided. On the other hand, as schematically shown in FIG. 3, the index scale 16 both extends in the X direction, and
Three diffraction gratings 22 lined up in a direction perpendicular to its extending direction
, 24.26 are formed. Note that FIGS. 2 and 3 are front views of the main scale 14 and the index scale 16, respectively, viewed from the semiconductor laser IO side. Each diffraction grating 22, 2 of the index scale 16
4.26, fewer slits than the main scale 14 are arranged at a constant pitch P, and each slit position of the diffraction grating 22 and each slit position of the diffraction grating 26 are made equal to each other, and each slit position of the diffraction grating 24 is made equal to each other. The slit position is P in the negative X direction from each slit position of the diffraction grating 22°26.
It is shifted by /4.

The parallel light beam irradiated onto the main scale 14 undergoes zero-order diffraction at its diffraction grating 20, and then passes through the diffraction gratings 22, 24.
．． 26 again undergoes zero-order diffraction. The first . 2nd and 3rd
After the diffracted light passes through a magnifying lens 30, it is sent to three photodetectors 32.
．． 34 and 36 respectively. Photodetector 32,3
4.36 are fixed to a common support stand 38. Each photodetector 32, 34, 36 generates strongly variable signals 1+, Iz, r3 according to the intensity of each diffracted light, and sends them to the signal processing device 4.
Output to 0.

The signal processing device 40 generates intensity signals 11. of both the first diffracted light and the second diffracted light. The amount of movement of the main scale 14 is calculated based on I2, and this calculation is similar to that of the conventional optical linear encoder.

The signal processing device 40 also generates intensity signals 11. of both the first diffracted light and the third diffracted light. It has a function of detecting the phase difference of Is. Main scale 14 and index scale 1
6, the diffraction grating 20 and the diffraction gratings 22, 24, and 26 should be arranged so as to extend in exactly parallel directions, but this condition may not be met for some reason. The main scale 14 and the index scale 16 may be tilted at a relatively small angle in a plane parallel to the surfaces of the diffraction grating 20 and the diffraction gratings 22, 24, 26. At this time, the intensity signals It of the first and third diffracted lights, 1. For example, a phase difference ΔX shown in FIG. 4 occurs at +. The signal processing device 40 has a function of detecting this ΔX, and since the index scale 16 is rotatable within the above plane by the rotation mechanism 42, the signal processing device 40
The rotation mechanism 42 is operated so that the phase difference ΔX detected by
．． 26 are parallel to each other with high precision. A signal processing device 40 obtains a signal from the moving device 19 representing the height of the voltage applied by it to the piezoelectric actuator 18, and
and third diffracted light intensity signal 11. The difference between the voltages applied to the piezoelectric actuator 18 when Iz becomes the intermediate value between the two intensity signals 1. ．． The rotation mechanism 42 detects the phase difference between the index scale 1 and the index scale 1.
6 is supported by a stationary support member and the other end is supported by a piezoelectric element, and by controlling the voltage applied to the piezoelectric element, the index scale 16 is connected to the diffraction gratings 22, 24 .
This is to rotate a minute angle within a plane parallel to the plane of No. 26.

In this example, the intensity signals of the first and third diffracted lights! ,,1. Since the detection of the phase difference ΔX and the operation of the rotation mechanism 42 are performed prior to the detection of the amount of movement of the main scale 14, the effect that the amount of movement can be detected with high accuracy can be obtained.

Furthermore, in the index scale 16 of this embodiment, the diffraction grating 24 is arranged between the diffraction grating 22 and the diffraction grating 26, and the distance between the diffraction grating 22 and the diffraction grating 24 is the same as the distance between the diffraction grating 22 and the diffraction grating 26. is shorter than the distance of Therefore, the diffraction grating 22.2 for the diffraction grating 20
When the phase error of 6 is removed as described above, there is an advantage that the phase difference between the diffraction grating 24 and the diffraction grating 20 can be removed with higher accuracy.

As is clear from the above explanation, in this example,
The frames (not shown) to which the moving object 0 and the index scale 16 of the optical linear encoder are attached in a relatively immovable manner are the first member and the second part, respectively, and the diffraction grating 20 of the main scale 14 is of the transmission type. The first diffraction grating, the diffraction gratings 22 and 24 of the index scale 16, is a transmission type second diffraction grating, and the diffraction grating 26 is a transmission type third diffraction grating. Further, the part of the signal processing device 40 that calculates the movement amount of the main scale 14 is a relative displacement detection means, and the intensity signal 11 of the first diffracted light and the intensity signal of the third diffracted light! The part that calculates the phase difference with No. 3 is the phase difference detection means.

In the embodiment described in detail above, the detection resolution of the movement amount of the main scale 14 is set to one quarter of the slit pitch P of the diffraction grating 20. However, in order to increase the detection resolution, it is necessary to You can change it as follows.

That is, (1) the index scale 16 is arranged such that n+1 slit rows 60 in which a large number of slits are arranged in the X direction are arranged in the direction perpendicular to the X direction, such as 0th to nth slit rows, as shown in FIG. The n slit rows 60 from the 0th slit row 60 to the n−1 slit row 60 are sequentially shifted by P/n in the positive X direction, and the 0th slit row 60 and the The positions of the slit rows 60 and the slit rows 60 are equal to each other, and each slit of the main scale 14 is made long so that the n+1 slit rows 60 of the index scale 16 all face each other, as shown in FIG. ■An intensity signal corresponding to the intensity of each diffracted light by receiving each of the 0th to nth diffracted lights that have passed through both the diffraction grating 20 of the main scale 14 and each slit row 60! . nth to nth photodetectors (not shown) that output signals I7 to I7 are provided, and these photodetectors are connected to the signal processing device 40.

In this way, the main scale 14 can be set to, for example, positive
As it moves in the direction (rightward in the figure), the intensity signals 1° to 1 of the n-th to n-th diffracted lights, respectively,
As shown in FIG. 7(a), the phases of the slit arrays 60 change with a delay of P/n from each other in the direction of increasing numbers, and the signal processing device 40 generates intensity signals whose phases are opposite to each other. The combination of I, that is, the intensity signal I0 of the 0th diffracted light and the intensity signal I0 of the n/2nd diffracted light [
77□, intensity signal of first diffracted light 1. and the (n/2+1)th
If we calculate the value ΔI by subtracting the larger intensity signal I from the smaller number among the intensity signals 177□, 4, etc. of the diffracted light, we can obtain the main scale 1 as shown in FIG.
Every time 4 moves P/n, one of ΔI becomes 0, so if you count the number of times, main scale 14
The amount of movement of the slit pitch P of the diffraction grating 20 is n
It becomes possible to detect with a resolution of 1/2. Further, if the main scale 14 is positioned in sequence at the position where ΔI is 0, positioning can be performed in extremely fine steps called P/n steps. That is, in this embodiment, the n slit arrays 60 from the n-th slit array 60 to the n-1 slit array 60 constitute the second diffraction grating in the present invention, and the corresponding n slit arrays 60 constitute the second diffraction grating in the present invention. The detector is the first photodetector in the present invention.

Further, in this embodiment, the n-th slit array 60 constitutes the third diffraction grating of the present invention, and the intensity signal I0 of the 0th diffracted light and the intensity signal In of the n-th diffracted light are adjusted in phase. By doing this, the parallelism between the first diffraction grating and the second diffraction grating can be adjusted.The way the parallelism is adjusted is the same as in the previous embodiment, and in this embodiment, the nth photodetector is A second photodetector according to the present invention is configured.

Other various changes based on the knowledge of those skilled in the art.

The present invention can be implemented in a modified form.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of an optical linear encoder that is an embodiment of the present invention, Figs. 2 and 3 are front views of the main scale and index scale of the linear encoder, and Fig. 4 is an embodiment thereof. Intensity signal 1 of the first diffracted light when the parallelism between the main scale and the index scale is poor. 3 is a graph showing an example of the phase difference between the intensity signal 1.3 of the third diffracted light and the intensity signal 1.3 of the third diffracted light. 5 and 6 are respectively front views of an index scale and a main scale that are different in aspect from the above embodiment, and FIGS. 7(a) and 7(b) show movement amount detection of the main scale in the embodiment. This is a graph for explaining. FIG. 8 is a system diagram of a conventional optical linear encoder, and FIG. ) is a graph for explaining the reason why the detection accuracy of the movement amount of the main scale decreases when the parallelism between the main scale and the index scale is poor. 10: Semiconductor laser 14: Main scale 16: Index scale 20.22, 24, 26: Diffraction grating 32.34.36: Photodetector 40: Signal processing device 42: Rotating mechanism 60 Nislit row I11 people Toyota Automobile Co., Ltd. Loom Factory Figure 2 Figure 4 OF/2 P -''' 1!7 Figure 8 Figure 9

Claims (1)

[Scope of Claims] A device for detecting relative displacement between a first member and a second member that are relatively movable along a straight line, each of which is integrally attached to the first member and the second member, respectively. a first diffraction grating and a second diffraction grating that are displaceably provided and extend parallel to the straight line and face each other in a direction perpendicular to the straight line; and of the light emitted by the light source, the first diffraction grating and the second diffraction grating a photodetector that receives light that has passed through both the diffraction grating and outputs an intensity signal corresponding to the intensity of the light;
An optical relative displacement detection device including a relative displacement detection means for detecting relative displacement with a member, which is movable integrally with the second member, faces the first diffraction grating, and faces the second diffraction grating. a third diffraction grating that extends in parallel and is separated from the second diffraction grating in a direction perpendicular to the direction in which the second diffraction grating extends; and of the light emitted by the light source, the first diffraction grating and the third diffraction grating a second photodetector that receives the second light that has passed through both the light detector and outputs an intensity signal corresponding to the intensity of the light; and an intensity signal of the photodetector and the second photodetector. a phase difference detection means for detecting a phase difference; and at least one of the first member and the second member is subjected to the first diffraction so that the phase difference detected by the phase difference detection means becomes a predetermined reference value. An optical relative displacement detection device comprising: a rotation mechanism that rotates the grating and the second diffraction grating in a plane parallel to the plane thereof.