JP2005283357A - Photoelectric encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric encoder capable of preventing an origin from being position-shifted, even when a moving scale is inclined vertically. <P>SOLUTION: When a light beam 10 gets incident into an index 3, beams 10c, 10d for an origin signal are generated by slits 32a, 32. The beams 10c, 10d impinge respectively on diffraction gratings 42a, 42b formed in the moving scale 4. When each of the beams 10c, 10d impinge on a grating pattern part 420 corresponding to each of the diffraction gratings 42a, 42b, the each of the beams 10c, 10d is diffracted at ±1 degree of diffraction by the grating pattern part 420 to impinge on photoreception elements 7a-7d for the origin signal. On the other hand, when the each of the beams 10c, 10d impinge on a slit part 421, the the each of the beams 10c, 10d is transmitted through the slit part 421. The position of the origin is detected, as a result thereof, based on photoreception intensity changes of the photoreception elements 7a-7d for the origin signal generated in accompaniment to the moving of the moving scale 4. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photoelectric encoder that optically generates a main signal and an origin signal and uses these photoelectric conversion signals as displacement information and origin information.

  A diffraction grating whose grating pitch changes discontinuously (for example, two diffraction gratings having different grating pitches connected) is formed on the moving stage, and the diffraction light diffracted by irradiating the diffraction grating with laser light is used. A method of detecting a reference position (origin position) of a moving stage by detecting with a photodetector is known (for example, see Non-Patent Document 1).

Jun Meido and two others, “Reference position detection method using Fraunhofer diffraction”, Proceedings of the 1991 Spring Meeting of the Japan Society for Precision Engineering, p. 1139-1140

  However, when the reflective optical system is configured by the above-described conventional method, there is a problem that the origin position is shifted when the movable stage is tilted in the vertical direction.

A photoelectric encoder according to a first aspect of the present invention is formed in a light source, a moving scale fixed to a movable object, a main signal light beam generating unit that generates two main signal light beams from light from the light source, and a moving scale. The main signal diffracting unit that diffracts and emits the two main signal light beams from the signal light beam generating unit, respectively, and the interference light of the two main signal light beams emitted from the main signal diffracting unit are received. An origin that has a main signal detector that outputs a signal corresponding to the intensity of interference light and a slit pattern in which one or more slits are arranged in a predetermined pattern, and transmits a part of the light from the light source to form an origin signal beam A signal beam generator, a first origin signal diffractor formed on the moving scale and diffracting the origin signal beam from the origin signal beam generator in a predetermined direction, and a first origin signal Diffracted at the diffraction section An origin signal detector that receives a point signal light beam and outputs a signal corresponding to the received light intensity, and a moving scale so as to be adjacent to the moving direction of the moving scale with respect to the first origin signal diffractive portion or in the opposite direction. And a second origin signal diffracting unit that diffracts the origin signal beam from the origin signal beam generation unit in a direction different from the predetermined direction with a predetermined correlation with the slit pattern.
According to a second aspect of the present invention, in the photoelectric encoder according to the first aspect, the predetermined correlation is a correlation constituting a knife edge optical system.
According to a third aspect of the present invention, in the photoelectric encoder according to the first or second aspect, the main signal light beam generation unit and the origin signal light beam generation unit are formed on the same index scale.
According to a fourth aspect of the present invention, in the photoelectric encoder according to any one of the first to third aspects, an origin signal beam generation unit, a first origin signal diffracting unit, a second origin signal diffracting unit, and an origin signal detection are provided. It is equipped with multiple sets of vessels.
According to a fifth aspect of the present invention, in the photoelectric encoder according to the fourth aspect, two sets of the origin signal beam generation section, the first origin signal diffracting section, the second origin signal diffracting section, and the origin signal detector are provided. A first origin signal diffractive part and a second origin signal diffractive part are arranged so as to sandwich the main signal diffractive part in a direction orthogonal to the moving direction.

  According to the present invention, it is possible to prevent the deviation of the origin position even if the moving scale is inclined in the vertical direction.

Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.
-First embodiment-
FIG. 1 is a diagram showing a first embodiment of a photoelectric encoder according to the present invention, and shows a main configuration of the encoder. The encoder shown in FIG. 1 includes a light source 1, a collimating lens 2, an index 3, a moving scale 4, mirrors 5a and 5b, a main signal light receiving element 6, and origin signal light receiving elements 7a to 7d. Detection signals of the main signal light receiving element 6 and the origin signal light receiving elements 7a to 7d are output to an encoder processing circuit (not shown), where the displacement of the moving scale 4 in the x direction is calculated.

  As the light source 1, a laser light source, a light emitting diode (LED), or the like is used. In the index 3, a diffraction grating 31 for main signal and slits 32a and 32b for origin signals provided so as to sandwich the diffraction grating 31 are formed. For example, a diffraction grating 31 (for example, a phase grating) having a uniform grating pattern is formed on a transparent parallel plate made of optical glass or the like, and a metal thin film or the like is formed in the regions 3b and 3c across the band-like region 3a of the transparent parallel plate. Reflective coating is applied.

  A main signal diffraction grating 41 corresponding to the diffraction grating 31 of index 3 is formed on the moving scale 4. Further, origin signal diffraction gratings 42 a and 42 b on which origin signal light beams 10 c and 10 d described below are incident are formed on both sides of the diffraction grating 41 in the y direction. Each of the diffraction gratings 42a and 42b includes a grating pattern part 420 formed with a uniform grating pattern, a grating pattern part 420, and a slit grating part 421 having a different form. The slit grating portion 421 is formed in a slit shape corresponding to the slits 32 a and 32 b of the index 3.

  The slit grating part 421 of the diffraction grating 42a and the slit grating part 421 formed in the diffraction grating 42b are formed so as to be shifted by a distance D in the x direction. In the present embodiment, the grating pitch of the diffraction grating 31 and the grating pitch of the grating pattern portion 420 are set to the same pitch, but they are not necessarily the same pitch.

  The diffraction grating 41 of the moving scale 4 and the grating pattern portion 420 of the diffraction gratings 42a and 42b constitute a reflection type diffraction grating, such as a metal thin film on the surface of the transparent substrate on which the grating pattern constituting the phase grating is formed. Reflective coating is applied. Note that the substrate surface of the slit grating portion 421 is not subjected to a reflective coating and transmits light. The moving scale 4 is fixed to a movable object to be measured, and moves in the x direction integrally with the movable object.

  The light emitted from the light source 1 is converted into parallel light by the collimating lens 2 and irradiated to the index 3. The light beam 10 incident on the regions 3b and 3c to which the reflective coating of the index 3 is applied is reflected by the reflective coating, and only the light beam 10 incident on the band-shaped region 3a to which the reflective coating is not applied can pass through the index 3. . When the index 3 is irradiated with the light beam 10, the diffraction grating 31 forms the main signal light beams 10a and 10b, and the light beams 10c and 10d transmitted through the slits 32a and 32b are used as the origin signal light beams. .

(Main signal)
The light beam 10 applied to the diffraction grating 31 in the band-like region 3a of the index 3 is subjected to ± 1st order diffraction by the diffraction grating 31, and a light beam 10a which is + 1st order diffracted light is emitted in the direction of the mirror 5a. The light beam 10b which is -1st order diffracted light is emitted. The light beams 10a and 10b are reflected by the mirrors 5a and 5b, respectively, and enter the diffraction grating 41 formed on the moving scale 4, respectively. The light beams 10 a and 10 b that have entered the diffraction grating 41 are reflected by receiving ± first-order diffraction by the diffraction grating 41 and are incident on the main signal light receiving element 6. At this time, the phase of the diffracted light diffracted by ± 1st order changes depending on the moving state of the moving scale 4. Therefore, the movement information of the movement scale 4 is included in the phase information of the interference light received by the main signal light receiving element 6.

(Origin signal)
When the index 3 is irradiated with the light beam 10, the light beams 10 c and 10 d are transmitted through the slits 32 a and 32 b and vertically incident on the diffraction gratings 42 a and 42 b of the moving scale 4. As described above, the diffraction gratings 42a and 42b are composed of the grating pattern part 420 and the slit grating part 421. When the light beam 10c is incident on the grating pattern part 420, it undergoes ± 1st-order diffraction and is reflected. The light enters the origin signal light receiving elements 7a and 7b. At this time, the irradiation width of the diffracted light on the light receiving surface is substantially the same as the width of the slits 32a and 32b of the index 3. The widths of the slits 32a and 32b are set to be smaller than the light receiving surfaces of the origin signal light receiving elements 7a to 7d.

  On the other hand, when the light beam 10 c enters the slit grating part 421, the light beam 10 c passes through the slit grating part 421. This transmission ratio becomes the maximum when the slit 32a of the index 3 and the slit grating portion 421 of the moving scale 4 coincide (when the x position is the same), and the output signals of the origin signal light receiving elements 7a and 7b are reversed. To the minimum.

  When the light beam 10c is irradiated across both the slit grating part 421 and the grating pattern part 420, the light of the grating pattern part 420 is diffracted and the diffracted light enters the origin signal light receiving elements 7a and 7b. The light from the slit grating part 421 passes through the moving scale 4. Therefore, the magnitude of the output signal of the origin signal light receiving elements 7a and 7b at this time is such that the output signal when the entire light beam 10c is incident on the grating pattern part 420, and the slit 32a and the slit grating part 421. It takes a value between the output signals when they match.

  Similarly to the case of the light beam 10c, in the case of the light beam 10d, when the light beam 10d is incident on the grating pattern portion 420 of the diffraction grating 42b, the diffracted light generated at that time is detected by the origin signal light receiving elements 7c and 7d. The origin signal output is minimized when the slit 32b and the slit grating portion 421 of the diffraction grating 42b coincide.

  FIG. 2 schematically shows an output pattern of the origin signal output from the origin signal light receiving elements 7a to 7d. In FIG. 2, the vertical axis represents the origin signal output, and the horizontal axis represents the movement distance of the movement scale 4 in the x plus direction. A solid line A1 indicates the outputs of the origin signal light receiving elements 7a and 7b, and a broken line A2 indicates the outputs of the origin signal light receiving elements 7c and 7d.

  x1 indicates the moving distance of the moving scale 4 when the slit 32a and the slit grating portion 421 coincide with each other, and x2 indicates the moving distance when the slit 32b and the slit grating portion 421 coincide with each other. As shown in FIG. 1, since the slit 32a and the slit 32b are shifted by a distance D in the x direction, the position where the output is minimum is also shifted by the distance D. The output pattern A1 indicated by a solid line is symmetrical with respect to x1, and the output pattern A2 indicated with a broken line is symmetrical with respect to x2.

  In the encoder processing circuit to which the output signals of the origin signal light receiving elements 7c to 7d are inputted, it is possible to process the position x0 where the solid line and the broken line, which are the level coincidence points of the two outputs, as the origin position. This level matching point signal is referred to as an origin signal. When the light beams 10c and 10d pass over the slit grating portion 421, the output changes abruptly before and after the moving distances x1 and x2, and the slopes of the output patterns A1 and A2 become steep. Can be detected.

  By the way, when the moving scale 4 is tilted around the y-axis, the irradiation position of the diffracted light incident on the origin signal light receiving elements 7a to 7d changes. In the conventional photoelectric encoder, the origin information is formed by arranging a slit in front of the light receiving element, that is, the origin signal is formed based on the positional relationship where the diffracted light enters the light receiving element. For this reason, when the moving scale 4 is tilted, the irradiation position of the diffracted light may change and the origin position may be shifted. For example, when the moving scale 4 is tilted without moving in the x direction from a normal state where the diffracted light is received by the light receiving element, the diffracted light may be detached from the light receiving element. In such a case, the moving scale 4 may be measured if it is not at the origin position even though it is at the origin position.

  However, in the photoelectric encoder of the present embodiment, the origin position is detected based on the output intensity of the origin signal light receiving elements 7c to 7d, which is a change in the amount of light accompanying the movement of the movable scale 4. Therefore, since the light receiving surfaces of the origin signal light receiving elements 7a to 7d are larger than the widths of the slits 32a and 32b of the index 3, even if the moving scale 4 is slightly inclined, the diffracted light does not deviate from the light receiving surface and the output intensity does not change. . As described above, since the origin information is placed on the light amounts of the origin signal light beams 10c and 10d in the present invention, the origin position is not displaced even if the moving scale 4 is tilted up and down (around the y axis).

-Second Embodiment-
FIG. 3 is a diagram showing a second embodiment of the photoelectric encoder according to the present invention. FIG. 3 shows the main configuration of the encoder as in FIG. 1. The configuration of the index 13 and the moving scale 14 is different from that of the photoelectric encoder shown in FIG. 1, and the other configurations are the same. In the following, the description will focus on the parts different from the configuration of FIG. In FIG. 3, the encoder processing circuit is not shown.

  The index 13 is formed with a main signal diffraction grating 131 and origin signal random pattern slits 132a and 132b provided so as to sandwich the diffraction grating. The random pattern slits 132a and 132b are obtained by randomly arranging a reflection pattern and a transmission pattern. For example, a diffraction grating 131 (for example, a phase grating) having a uniform grating pattern is formed on a transparent parallel plate made of optical glass or the like, and a metal thin film or the like is formed in the regions 13b and 13c sandwiching the band-like region 13a of the transparent parallel plate. Reflective coating is applied. Also in the case of the second embodiment, the widths of the random pattern slits 132a and 132b are set smaller than the light receiving surfaces of the origin signal light receiving elements 7a to 7d.

  The moving scale 14 is formed with a main signal diffraction grating 141 corresponding to the diffraction grating 131 of the index 13. Further, origin signal diffraction gratings 142 a and 142 b on which origin signal light beams 10 c and 10 d to be described later enter are formed on both sides of the diffraction grating 141 in the y direction. Each of the diffraction gratings 142a and 142b includes a grating pattern portion 143 constituting a reflective diffraction grating in which a uniform grating pattern is formed, a random pattern portion 144 in which a reflection pattern and a transmission pattern are randomly arranged, and a transparent substrate. It is comprised with the transparent part 145 exposed.

  The pattern arrangement of the random pattern portion 144 of the diffraction grating 142a is formed in the same pattern arrangement so as to correlate with the pattern arrangement of the random pattern slit 132a. When the x positions of the random pattern portion 144 and the random pattern slit 132a coincide with each other, the mutual transmission patterns and the reflection patterns coincide with each other. That is, the random pattern portion 144 is disposed so as to function as a knife edge with respect to each slit formed by the transmission pattern of the random pattern slit 132a. There is a similar correlation between the random pattern portion 144 of the diffraction grating 142a and the random pattern slit 132a.

  In the diffraction grating 142a, the transparent portion 145, the random pattern portion 144, and the grating pattern portion 143 are provided in this order along the plus direction of the x-axis. On the contrary, in the diffraction grating 142b, the grating pattern portion 143, the random pattern portion 144, and the random pattern portion 144 are provided. The transparent portions 145 are provided in this order.

  The light emitted from the light source 1 is converted into parallel light by the collimating lens 2 and irradiated to the index 13. Also in the case of the index 13, only the light beam 10 incident on the band-like region 13 a not provided with the reflective coating can pass through the index 13. The diffraction grating 131 forms the main signal light beams 10a and 10b, and the light beams 10c and 10d transmitted through the random pattern slits 132a and 132b are used as the origin signal light beams.

(Main signal)
The light beams 10a and 10b emitted from the index 13 are incident on the diffraction grating 141 through the same process as in the first embodiment, and the diffracted light reflected by receiving the first-order diffraction by the diffraction grating 41 is reflected. The light enters the main signal light receiving element 6.

(Origin signal)
The light beams 10c and 10d transmitted through the random pattern slits 132a and 132b are perpendicularly incident on the diffraction gratings 142a and 142b of the moving scale 14. When the light beam 10c is incident on the grating pattern portion 143 of the diffraction grating 142a, it is reflected by receiving ± first-order diffraction, and the diffracted light is incident on the origin signal light receiving elements 7a and 7b.

  When the light beam 10c enters the transparent portion 145 of the diffraction grating 142a, the light beam 10c passes through the moving scale 14 and does not enter the origin signal light receiving elements 7a and 7b. When the light beam 10c is incident on the random pattern portion 144, when the position of the random pattern slit 132a and the position of the random pattern portion 144 completely coincide with each other, the light beam 10c is transmitted through the moving scale 14 to receive the origin signal light receiving element 7a, It does not enter 7b.

  Therefore, as the moving scale 14 moves in the positive x-axis direction, an origin signal output pattern B1 having a knife edge characteristic of a random pattern is obtained as shown by the solid line in FIG. The signal output of the portion indicated by the range C in FIG. 4 corresponds to the output signal when the light beam 10c passes through the random pattern portion 144, and the position of the random pattern slit 132a and the position of the random pattern portion 144 are completely The output drops rapidly when they match. On the other hand, the same applies to the case of the light beam 10d, but the diffraction grating 142b has an arrangement of the grating pattern portion 143, the random pattern portion 144, and the transparent portion 145 opposite to that of the diffraction grating 142a.

  That is, between the diffraction grating 142a and the diffraction grating 142b, the grating pattern part 143 and the random pattern part 144 which are grating parts having different modes are inverted with respect to the moving direction of the moving scale 14, so that the output pattern of a solid line An origin signal output pattern B2 as indicated by a broken line obtained by horizontally inverting B1 is obtained. As a result, the position x0 where the levels of the origin signal output pattern B1 and the origin signal output pattern B2 match can be processed as the origin position. The level coincidence point is in a region where the signal rapidly decreases.

  In the index 13 in the present embodiment, as shown in FIG. 5A, a main signal diffraction grating 131 and origin signal random pattern slits 132a and 132b are formed on the same substrate. However, they may be formed on different substrates as shown in FIG. In the example shown in FIG. 5B, the substrate 200 on which the diffraction grating 131 is formed and the substrate 201 on which the random pattern slits 132a and 132b are formed are arranged close to each other (for example, in contact with each other).

  Reflective coating is applied to the areas 201b and 201c of the substrate 201, and no reflective coating is applied to the central portion of the strip-shaped area 201a. In this case, the substrate 200 and the substrate 201 constitute an index optical system. The zero-order light emitted from the diffraction grating of the substrate 200 enters the random pattern slits 132a and 132b, and the transmitted light becomes the light beams 10c and 10d for the origin signal.

  Also in the second embodiment, since the origin position is detected by the output intensity of the origin signal light receiving elements 7c to 7d, which is a change in the amount of light accompanying the movement of the movement scale 14, the movement scale 14 moves up and down ( Even if it is tilted (around the y-axis), the origin position is not displaced.

  In the above-described embodiment, phase gratings are used for the diffraction gratings of indexes 3 and 13 and the diffraction gratings of moving scales 4 and 14, but light and dark gratings may be used. Further, a shielding object may be arranged instead of the slit portion 421 and the random pattern portion 144. In the above-described embodiment, two light receiving elements are used for each of the light beams 10c and 10d in order to increase the intensity of the origin signal. However, one light receiving element may be used.

  In the first embodiment described above, the diffraction gratings 42a and 42b are disposed so as to sandwich the diffraction grating 41, and in the second embodiment, the diffraction gratings 142a and 142b are disposed so as to sandwich the diffraction grating 141. By adopting such a configuration, it is possible to prevent occurrence of Abbe error when the moving scales 4 and 14 are tilted around the z axis. For this reason, in the above-described embodiment, two sets of combinations of slits and slit portions or combinations of random pattern slits and random pattern portions are used, but three or more sets may be used, and Abbe error is a problem. If it doesn't, one pair is acceptable.

  Further, in the first embodiment described above, the two slit portions 421 on the moving scale 4 are shifted in the scale moving direction, but they may not be shifted.

  In the correspondence between the embodiment described above and the elements of the claims, the diffraction gratings 31 and 131 are the main signal beam generation units, the diffraction gratings 41 and 141 are the main signal diffraction units, and the main signal light receiving element 6. Is a main signal detector, slits 32a and 32b and random pattern slits 132a and 132b are origin signal beam generation units, grating pattern units 143 and 420 are first origin signal diffraction units, slit grating unit 421 and random patterns. The unit 144 constitutes a second origin signal diffracting unit, and the origin signal light receiving elements 7a to 7d constitute an origin signal detector. In addition, the present invention is not limited to the above embodiment as long as the characteristics of the present invention are not impaired.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows 1st Embodiment of the photoelectric encoder by this invention, and shows the main structures of an encoder. The output pattern of the origin signal output from the light receiving elements 7a-7d for origin signals is typically shown. It is a figure which shows 2nd Embodiment of the photoelectric encoder by this invention. FIG. 10 schematically shows an origin signal output pattern in the second embodiment. It is a figure which shows the modification of the index 13, (a) is a perspective view of the index 13, (b) is a perspective view which shows the board | substrates 200 and 201 which are modifications.

Explanation of symbols

1 Light source 2 Collimating lens 3,13 Index 3
4,14 Moving scale 5a, 5b Mirror 6 Light receiving element for main signal 7a-7d Light receiving element for origin signal 10, 10a-10d Light beam 31, 41, 42a, 42b, 131, 141, 142a, 142b Diffraction grating 32a, 32b Slit 132a, 132b Random pattern slits 143, 420 Lattice pattern portion 144 Random pattern portion 145 Transparent portion 200, 201 Substrate 421 Slit lattice portion

Claims (5)

A light source;
A moving scale fixed to a movable object;
A main signal light beam generation unit for generating two main signal light beams from the light of the light source;
A main signal diffracting section formed on the moving scale and diffracting the two main signal light fluxes from the main signal light flux generating section and emitting them in substantially the same direction;
A main signal detector that receives the interference light of the two main signal light beams emitted from the main signal diffraction section and outputs a signal corresponding to the interference light intensity;
An origin signal beam generation unit that has a slit pattern in which one or more slits are arranged in a predetermined pattern, and transmits a part of the light of the light source to form an origin signal beam;
A first origin signal diffracting unit formed on the moving scale and diffracting the origin signal beam from the origin signal beam generating unit in a predetermined direction;
An origin signal detector arranged in the predetermined direction and receiving an origin signal light beam diffracted by the first origin signal diffracting section and outputting a signal corresponding to the received light intensity;
The origin signal beam generation is formed on the moving scale so as to be adjacent to the first origin signal diffracting portion in the moving direction of the moving scale or in the opposite direction, and has a predetermined correlation with the slit pattern. And a second origin signal diffracting section for diffracting the origin signal light beam from the section in a direction different from the predetermined direction. The photoelectric encoder according to claim 1,
The photoelectric encoder characterized in that the predetermined correlation is a correlation constituting a knife edge optical system. The photoelectric encoder according to claim 1 or 2,
The photoelectric encoder characterized in that the main signal beam generation unit and the origin signal beam generation unit are formed on the same index scale. The photoelectric encoder according to any one of claims 1 to 3,
A photoelectric encoder comprising a plurality of sets of the origin signal beam generation section, the first origin signal diffraction section, the second origin signal diffraction section, and the origin signal detector. The photoelectric encoder according to claim 4, wherein
Two sets of the origin signal beam generation section, the first origin signal diffraction section, the second origin signal diffraction section, and the origin signal detector are provided, and the first origin signal diffraction section and the first origin signal diffraction section, A photoelectric encoder, wherein the second origin signal diffractive portion is arranged so as to sandwich the main signal diffractive portion in a direction orthogonal to the moving direction.

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