JP2005055360A - Photoelectric type encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric type encoder reduced in an error between a generated main signal and an origin signal. <P>SOLUTION: An origin phase grating 4s is provided in one portion of a phase grating 4g for the main signal formed on a moving scale 4. Lights separated by an index 3 are diffracted respectively by the phase grating 4g on the moving scale 4, and both diffracted lights are advanced toward a main signal photoreceiving element 6. The both diffracted lights interfere each other, and the main signal photoreceiving element 6 outputs a sine wave signal repeated with strong and weak intensities in response to an interference fringe. Diffracted lights diffracted by the origin phase grating 4s are advanced toward origin signal photoreceiving elements 7a, 7b, when the origin phase grating 4s of the moving scale 4 is moved through the position where the lights separated by the index 3 are reflected respectively by mirrors 5a, 5b to be joined. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a photoelectric encoder.

  Conventionally, an interference type photoelectric encoder using a plurality of diffraction gratings is known (for example, see Patent Document 1). In the interference type photoelectric encoder, the light from the light source is separated into two light fluxes of + 1st order diffracted light and −1st order diffracted light by the first diffraction grating, and these two light fluxes are formed on the moving scale by a mirror or the like. The same position of the second diffraction grating is irradiated. The two light beams incident on the second diffraction grating are diffracted, emitted as parallel light, interfere with each other, and enter the photodetector. When the second diffraction grating moves, the intensity of the interference light detected by the photodetector changes. The amount of movement is detected based on the change in the intensity of the interference light.

  In addition to the second diffraction grating, an origin pattern for detecting the origin is also formed on the moving scale of the photoelectric encoder described above (see, for example, Patent Document 2). This origin pattern is formed by depositing a metal film beside the second diffraction grating and providing a part where the metal film is not deposited on a part thereof. A similar origin pattern is also formed beside the first diffraction grating. Light from the light source passes through the origin pattern provided beside the first diffraction grating and enters the second origin pattern. When light is incident on a portion where the metal film of the second origin pattern is not deposited, the light is transmitted through the second origin pattern and detected by the photodetector for origin detection, and becomes an origin signal.

  In addition, there is a method in which a metal film is deposited on only a part of the second origin pattern, and the light transmitted through the first origin pattern is reflected and detected. In this case, by irradiating the light from the light source to the first origin pattern from an oblique direction, the second origin pattern is irradiated from the oblique direction, and the origin is on the optical path of the reflected light of the second origin pattern. A light detector for detection is arranged to detect light.

JP 2002-81964 A JP 2002-286505 A

  Since the origin pattern described above is formed at a position different from the second diffraction grating for detecting the movement amount, there is a problem that an error occurs and the measurement accuracy is lowered.

A photoelectric encoder according to the present invention includes a moving scale fixed to a movable object, a diffraction grating formed on the moving scale, and a plurality of gratings for detecting the amount of movement of the movable object arranged in the moving direction of the movable object, The origin pattern formed in a part of the diffraction grating, the light beam forming means for forming two light beams from the light from the light source and irradiating the moving scale, and the first detecting the interference light of the light beam emitted from the diffraction grating And a second photodetector for detecting light emitted from the origin pattern.
According to a second aspect of the present invention, in the photoelectric encoder according to the first aspect, the origin scale is configured so that diffraction gratings having different grating spacings from the diffraction gratings are arranged.
According to a third aspect of the present invention, in the photoelectric encoder according to the first aspect of the present invention, the origin scale is constituted by a portion where no grating is formed.
According to a fourth aspect of the present invention, in the photoelectric encoder according to any one of the first to third aspects, a reflective film is formed on the surfaces of the diffraction grating and the origin pattern.
According to a fifth aspect of the present invention, in the photoelectric encoder according to any one of the first to third aspects, a reflective film is formed on the surface of either the diffraction grating or the origin pattern. And
A sixth aspect of the present invention is the photoelectric encoder according to any one of the first to fifth aspects, wherein a plurality of origin scales are formed in the diffraction grating.

  ADVANTAGE OF THE INVENTION According to this invention, the photoelectric encoder which reduces the error between the signal by a movement scale and the signal by an origin pattern can be provided.

The best mode for carrying out the present invention will be described below with reference to the drawings.
(First embodiment)
FIG. 1 is a diagram showing a main configuration of the photoelectric linear encoder according to the first embodiment of the present invention. The photoelectric encoder generates a signal for detecting the amount of movement (displacement) of an actuator (not shown) such as a linear motor, and sends the generated signal to a drive control circuit (not shown) of the actuator. The drive control circuit controls the moving speed and displacement amount of an actuator (not shown) using a signal from the photoelectric encoder.

  The photoelectric encoder of FIG. 1 has a light source 1, a condenser 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 and 7b. The light emitted from the light source 1 is converted into parallel light by the condenser lens 2 and then irradiated to the index 3. The index 3 is constituted by a transmissive phase grating 3g, for example. The direction in which the phase grating 3g of the index 3 is formed coincides with the grating forming direction in the moving scale 4 described later. The parallel light incident on the index 3 is ± 1st order diffracted by the phase grating 3g, the + 1st order light travels toward the mirror 5a, and the −1st order light travels toward the mirror 5b. The ± first-order diffracted light is further reflected by the mirrors 5a and 5b, respectively, and both diffracted lights enter the moving scale 4 as shown by the solid line in FIG.

(Main signal)
The moving scale 4 is fixed to a moving member (not shown) such as an actuator, and is configured to move integrally with the moving member. The moving scale 4 is constituted by, for example, a transmissive phase grating 4g. The transmissive phase grating 4g is, for example, one in which grooves (lattices) are formed at a predetermined interval on the surface of a glass substrate. The phase grating 4 g of the moving scale 4 is formed so as to coincide with the moving direction of the moving scale 4. The ± 1st-order diffracted light incident on the moving scale 4 is again diffracted by ± 1st-order by the moving scale 4. The diffracted light beam travels downward as indicated by the dotted line in FIG. 1 and enters the main signal light receiving element 6. At this time, the combined diffracted light interferes, so that the light received by the main signal light receiving element 6 repeats strength depending on the interference fringes passing through the light receiving surface of the light receiving element 6. As a result, the photoelectric conversion signal by the main signal light receiving element 6 becomes a sine wave signal.

(Origin signal)
In the phase grating 4g formed on the moving scale 4, an origin phase grating 4s having a grating pitch different from the grating pitch of the phase grating 4g is formed. When the origin phase grating 4s moves to a position where the ± first-order diffracted lights reflected by the mirrors 5a and 5b are incident and merged, the incident light is diffracted by the origin phase grating 4s and emitted. Since the grating pitch of the origin phase grating 4s is different from the grating pitch of the phase grating 4g, the light diffracted by the origin phase grating 4s is emitted in a direction different from that of the main signal light receiving element 6. Origin signal light receiving elements 7a and 7b are arranged in the traveling direction of the diffracted light emitted from the origin phase grating 4s. The light reflected by the mirror 5a and diffracted by the origin phase grating 4s is detected by the origin signal light receiving element 7a, and the light reflected by the mirror 5b and diffracted by the origin phase grating 4s is detected by the origin signal light receiving element 7b.

  When the origin pattern 4s of the moving scale 2 moves (passes) through the position where the light reflected by the mirror 3a and the mirror 3b is incident on the moving scale 2 and merges, it is received by the origin signal light receiving elements 7a and 7b, respectively. The light to be maximized. The photoelectric conversion signals by the origin signal light receiving elements 7a and 7b are called origin signals.

  The origin phase grating 4s functions as a slit having the width of the origin phase grating 4s. The origin signal light receiving elements 7a and 7b are provided with slits 7c and 7d having the same width as 4s, respectively. When the position of the origin phase grating 4s changes according to the movement of the moving scale 4, the origin phase grating 4s and the slits 7c and 7d function as a slit shutter, and the amount of light incident on the origin signal light receiving elements 7a and 7b changes, Strength is generated. In addition, the origin light receiving element is not provided with a slit, but instead, the width of the light receiving element may be narrowed, and the width of the light receiving element itself may serve as the slit.

  In the present embodiment, the phase grating pitch is 2.4 μm, and the width of the origin pattern 4 s is 100 μm. The width of the origin phase grating 4s may be any width as long as it is smaller than the diameter of the incident light. If the width of the origin phase grating 4s is smaller than the diameter of the incident light (for example, a circle having a diameter of 3 mm), a part of the light incident on the moving scale 4 enters the origin phase grating 4s and generates an origin signal. However, the remaining light can enter the phase grating 4g and generate a main signal. Therefore, even if the origin phase grating 4s is formed in the phase grating 4g, the interference light that generates the main signal is detected by the main signal light receiving element 6 without interruption, so that the main signal is not interrupted.

  In the present embodiment, an origin phase grating 4s having a locally different aspect is provided on the main signal phase grating 4g formed on the moving scale 4. As a result, the main signal optical system and the origin signal optical system can be configured with one incident optical system, the configuration of the encoder optical system is simplified, and the size can be easily reduced. Further, since the main signal phase grating 4g and the origin signal origin phase grating 4s can be formed on the same line on the moving scale 4, the occurrence of Abbe error can be suppressed and the measurement accuracy can be improved. .

  Note that the present embodiment is not limited to the one described above, and may be modified as follows. Although the phase grating is used for the index 3 and the moving scale 4, a light / dark grating may be used instead of the phase grating.

  Further, instead of the index 3, a beam splitter that separates the light from the light source 1 into two and guides them to the mirrors 5a and 5b, respectively, may be used.

  Furthermore, in the present embodiment, the origin phase grating 4s has a grating pitch different from that of the phase grating 4g. However, a part where no grating is formed may be provided as the origin phase grating 4s. When no grating is formed, the light incident on the origin phase grating 4s passes through the origin phase grating 4s as it is. The origin light receiving elements 7a and 7b are arranged in the optical path of the light transmitted through the origin phase grating 4s and emitted to receive the origin signal.

  In this embodiment, two origin signal light receiving elements are used, but it is not always necessary to arrange two, and either one may be used.

  The origin phase grating 4s does not have to be parallel to the phase grating 4g, and the orientation of the grating of the origin phase grating 4s may be orthogonal to the grating arrangement direction of the phase grating 4g. In this case, since the diffracted light that generates the origin signal is emitted in a direction orthogonal to the grating of the origin phase grating 4s, the origin light receiving elements 7a and 7b are arranged by being rotated 90 degrees from the direction shown in FIG. .

  Further, the origin phase grating 4s is not limited to one place, and a plurality of origin phase gratings 4s may be provided in the phase grating part 4g to increase the origin signal intensity. For example, when two origin phase gratings 4 s are provided in the moving scale 8, the origin phase grating 4 s is formed so that two origins simultaneously enter the incident light irradiation range. In this case, the origin light receiving elements 7a and 7b are each provided with two slits at intervals corresponding to the intervals between the two origin phase gratings 4s. In the case of such a configuration, the light intensity becomes maximum when the two slits of the two phase gratings 4s and the origin light receiving elements 7a and 7b coincide with each other, and an origin signal that is double that of a single origin is obtained. be able to.

(Second embodiment)
In the second embodiment, the moving scale is composed of a reflective phase grating. FIG. 2 is a configuration diagram of a main part in the case where the moving scale 8 is configured by a reflective phase grating. In FIG. 2, the photoelectric encoder has a light source 1, a condenser lens 2, an index 3, a moving scale 8, mirrors 5a and 5b, a main signal light receiving element 9, and origin signal light receiving elements 10a and 10b. The index 3 is composed of the same transmission type phase grating 3g as in the first embodiment, and the parallel light from the light source 1 is incident thereon. The direction in which the phase grating 3 g with the index 3 is formed coincides with the grating forming direction of the moving scale 8. The parallel light incident on the index 3 is ± 1st-order diffracted by the phase grating 3g, the + 1st-order light travels toward the mirror 5a, and the −1st-order light travels toward the mirror 5b. The ± first-order diffracted light is further reflected by the mirrors 5a and 5b, and both diffracted lights are incident on the moving scale 8 as shown by the solid line in FIG.

(Main signal)
Similar to the first embodiment, the moving scale 8 is configured to move together with a moving member (not shown). The phase grating 8g of the moving scale 8 is formed in a direction that matches the moving direction of the moving scale 4B. On the moving scale 8, an origin phase grating 8s having a pitch different from that of the phase grating 8g and the phase grating 8g is continuously formed at a predetermined pitch. The moving scale 8 is provided with a reflective coating by depositing metal (such as gold) or the like on the entire area of the lattice portion on the surface thereof. The reflective coating is not limited to metal, and any film that reflects light may be used.

  In FIG. 2, the ± first-order diffracted light incident on the phase grating 8 g of the moving scale 8 is diffracted and reflected by the moving scale 8 again at the ± first-order. The light beam after diffraction reflection travels upward in FIG. 2 and enters the main signal light receiving element 9 disposed above the moving scale 8. At this time, due to the interference between the two diffracted lights, a sine wave signal is observed in the main signal light receiving element 9 according to the movement of the moving scale 8.

(Origin signal)
When the origin phase grating 8s passes through the position where ± 1st order diffracted lights reflected by the mirrors 5a and 5b are incident and merged, the two diffracted lights are diffracted and reflected by the origin phase grating 8a, and the reflected diffracted lights are reflected. The light enters the origin signal light receiving elements 10a and 10b arranged in the traveling direction, and generates an origin signal.

  As in the first embodiment, the origin phase grating 8s functions as a slit. The origin signal light receiving elements 10a and 10b are provided with slits having the same width as the origin phase grating 8s (not shown). Thus, when the position of the origin phase grating 8s changes in accordance with the movement of the movable scale 8, it functions as a slit shutter, and the origin signal receiving elements 10a and 10b can confirm the strength of the signal.

  As described above, even when the diffracted light is reflected by the moving scale 8 and the main signal and the origin signal are detected, the same effects as the first embodiment can be obtained. In this embodiment, since the main signal light receiving element 9 and the origin signal light receiving elements 10a and 10b are arranged in the space between the index 3 and the moving scale 8, the encoder can be reduced in size.

  In the present embodiment, gold is deposited on the origin phase grating 8s and the reflective coating is applied thereto, but the gold coating may not be applied only to the region of the origin phase grating 8s. In this case, the origin signal light receiving elements 10a and 10b are arranged below the moving scale 8 as in the first embodiment. The origin signal has the maximum power at the origin position and the minimum power in other areas.

  In the above description, the linear encoder that detects the movement amount of the linear motor or the like has been described as an example. However, the present invention can also be applied to a rotary encoder that detects the rotation angle of the rotary motor. In this case, a disk may be provided on the rotary encoder, a main signal grid array may be formed on the outer peripheral portion of the disk, and an origin grid having a different aspect may be locally formed on a part of the grid array.

  Correspondence between each component in the claims and each component in the best mode for carrying out the invention will be described. The origin pattern is constituted by, for example, an origin phase grating 4s (8s). The light beam forming means includes, for example, an index 3 and mirrors 5a and 5b. The first photodetector is constituted by a main signal light receiving element 6 (9). The second photodetector is constituted by, for example, origin signal light receiving elements 7a and 7b (10a and 10b). In addition, unless the characteristic function of this invention is impaired, each component is not limited to the said structure.

It is a figure which shows the principal part structure of the photoelectric linear encoder by 1st embodiment of this invention. It is a figure which shows the principal part structure of the photoelectric type linear encoder by 2nd embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light source 3 ... Index 3g, 4g, 8g ... Phase grating 4, 8 ... Moving scale 4s, 8s ... Origin phase grating 5a, 5b ... Mirror 6, 9 ... Main signal light receiving element 7a, 7b, 10a, 10b ... Origin Signal receiving element 7c, 7d ... Slit

Claims (6)

A moving scale fixed to a movable object;
A diffraction grating formed on the moving scale and arranged in the moving direction of the movable object, wherein a plurality of gratings for detecting the amount of movement of the movable object;
An origin pattern formed in a part of the diffraction grating;
A light beam forming means for forming two light beams from light from a light source and irradiating the moving scale;
A first photodetector for detecting interference light of a light beam emitted from the diffraction grating;
A photoelectric encoder comprising: a second photodetector for detecting light emitted from the origin pattern. The photoelectric encoder according to claim 1,
The photoelectric encoder according to claim 1, wherein diffraction gratings having different grating intervals from the diffraction grating are arranged on the origin scale. The photoelectric encoder according to claim 1,
The origin scale is a portion where a lattice is not formed. The photoelectric encoder according to any one of claims 1 to 3,
A photoelectric encoder, wherein a reflection film is formed on surfaces of the diffraction grating and the origin pattern. The photoelectric encoder according to any one of claims 1 to 3,
A photoelectric encoder, wherein a reflective film is formed on a surface of either the diffraction grating or the origin pattern. The photoelectric encoder according to any one of claims 1 to 5,
The photoelectric encoder is characterized in that a plurality of the origin scales are formed in the diffraction grating.

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