JPH06341858A - Optical displacement detection apparatus - Google Patents

Abstract

PURPOSE:To correct the detection error of an optical displacement detection apparatus. CONSTITUTION:This optical displacement detection apparatus is provided with a disk 1 in which one pair of slits 3a, 3b have been formed and fixed light sources 4a, 4b which emit the incident light on the disk 1 are provided. In addition, one pair of fixed photodetectors 5a, 5b are contained so as to correspond to the pair of slits 3a, 3b. The photodetector 5a is provided with a long light-detecting face 6a arranged along the movement track of an optical spot 7a which has passed the slit 3a, and it outputs differential detection signals Xa, Ya corresponding to the light-receiving position of the optical spot 7a. In the same manner, the other photodetector 5b outputs one pair of differential detection signals Xb, Yb. The optical spot 7a from the slit 3a on one side and the optical spot 7b from the slit 3b on the other side are moved in mutually opposite directions along the respectively corresponding long light-receiving faces 6a, 6b. A processing circuit 8 processes the detection signals Xa, Ya, Xb, Yb which have been output from both fixed photodetectors 5a, 5b, it outputs displacement information on the disk 1, and it removes an error based on the displacement of the slits on basis of the displacement information.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical displacement detecting device. More specifically, the present invention relates to a structure for correcting a detection error due to a positional deviation of a slit formed on the surface of a moving body.

[0002]

2. Description of the Related Art Conventionally, various types of optical displacement detection devices have been known. For example, JP-A-60-225024
The publication discloses a structure using a rotating disk having spiral slits. As shown in FIG. 9, in the optical rotational displacement detection device having this structure, a disc 102 is attached so as to be rotatable around a rotary shaft 101. Disk 1
Reference numeral 02 denotes a light-shielding material such as metal, and a spiral slit 103 is formed on the surface thereof along the circumferential direction from the center of rotation. A light source (not shown) that radiates incident light is fixedly arranged on the upper surface of the disk 102. Also, the disc 102
The light receiving element 104 is fixedly arranged at a position directly facing the light source via. The light receiving element 104 has a longitudinal light receiving surface 105 arranged along the radial direction of the disc 102, and receives a transmitted light spot 106 from the spiral slit 103 that moves in the radial direction as the disc 102 rotates. , Outputs a rotational displacement detection signal.

FIG. 10 shows the relationship between the rotation angle of the disc 102 and the detection signal output. As the disc 102 rotates, the light spot 106 that passes through the spiral slit 103 moves along the light receiving surface 105 having a long shape. The light receiving element outputs a detection signal according to the light receiving position of the light spot. For example, when a one-dimensional position detecting element such as PSD is used as the light receiving element, a detection signal corresponding to the position of the center of gravity of the light spot on the light receiving surface is output. When no error factor is included, the rotation angle and the detection signal have a linear relationship.

An optical linear displacement detector based on the same principle is also known, and is disclosed in, for example, Japanese Patent Laid-Open No. 62-63816. As shown in FIG. 11, the optical linear displacement detection device uses a movable plate 201 capable of linear displacement. The moving plate 201 is made of a light-shielding material such as metal, and a linear slit 202 is formed on the surface thereof so as to be inclined in the displacement direction. A light source (not shown) that emits incident light is fixedly arranged on the upper surface side of the moving member 201. or,
A light receiving element 203 is fixedly arranged on the lower surface side of the moving plate 201 at a position facing the light source. The light receiving element 203 is provided with a long-shaped light receiving surface 204 arranged orthogonal to the displacement direction of the moving plate 201, and a transmitted light spot from the slit 202 that moves in the orthogonal direction along with the linear displacement of the moving plate 201. Is received, and a linear displacement detection signal is output. As is clear from the figure, the linear displacement amount and the detection signal output have a linear relationship.

[0005]

The above-mentioned optical displacement detection device, whether of the rotary type or the linear type, is basically composed of one slit and one corresponding light receiving element. . In order to improve the detection accuracy, it is necessary to precisely set the relative positional relationship between the slit and the light receiving element. However, it is difficult to completely remove the relative positional deviation due to various error factors. For example, in the case of the rotary type, it is difficult to completely remove the eccentricity of the spiral slit with respect to the rotation axis. Therefore, there is a problem that the eccentricity error is included in the detection signal if no measures are taken. In addition, even in the linear type, the relative positional relationship between the slit and the light receiving element is deviated. For example, when the movable plate is linearly displaced and rattling occurs in the orthogonal direction, a large error is included in the detection signal, which is a problem to be solved.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems of the prior art, it is an object of the present invention to provide a compensating structure capable of absorbing the eccentricity of a rotating disk and the displacement of a linear moving plate due to backlash. And The following measures have been taken in order to achieve this object. That is, the optical displacement detection device according to the present invention includes a moving member, a fixed light source, a fixed light receiving element, and a processing circuit as basic components. A predetermined slit is formed on the surface of the moving member. The fixed light source irradiates the moving member with incident light. The light receiving element is provided with a longitudinal light receiving surface arranged along the movement trajectory of the light spot that has passed through the slit, and outputs a detection signal according to the light receiving position of the light spot. The processing circuit processes the detection signal and outputs displacement information of the moving member. As a feature of the present invention,
The optical displacement detection device includes a pair of slits and a corresponding pair of fixed light receiving elements. The light spot from one slit and the light spot from the other slit move in mutually complementary directions along the corresponding longitudinal light receiving surfaces. The processing circuit includes correction means for processing the detection signals output from both fixed light receiving elements to remove an error based on the positional deviation of the slit from the displacement information of the moving body.

According to one aspect of the present invention, the moving member comprises a rotating disk. The pair of slits are formed along the circumferential direction. Further, each of the pair of fixed light receiving elements has a long light receiving surface arranged along the radial direction, and outputs the inner and outer detection signals which are differentially changed. The inside detection signal means a signal output from the inside of the longitudinal light receiving surface, and the outside detection signal conversely means a signal output from the outside of the longitudinal light receiving surface. Both detection signals change differentially according to the light receiving position of the light spot. in addition,
The correction means adds the inner detection signal and the outer detection signal output from the pair of fixed light receiving elements, respectively. Specifically, the pair of slits are spiral slits of the same shape that are symmetrically arranged with respect to the rotation axis of the disk. Alternatively, the pair of slits may be spiral slits having different curvatures that are partially overlapped with each other at symmetrical positions with respect to the rotation axis of the disk. Further, the pair of slits may be spiral slits having different curvatures arranged in parallel on one side with respect to the rotation axis of the disc. In this case, the fixed light source can irradiate the pair of slits in common.

[0008]

The optical displacement detecting device according to the present invention is characterized in that it has a pair of slits and a corresponding pair of fixed light receiving elements. The pair of slits have a complementary relationship to the positional deviation such as eccentricity or backlash, and the light spot from one slit and the light spot from the other slit are in opposite directions along the corresponding longitudinal light-receiving surface. Move to.
Therefore, the detection signals output from both fixed light receiving elements include error components in opposite directions. The error can be canceled by processing both detection signals, and the error based on the positional deviation of the slit can be removed from the displacement information.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic perspective view showing a first embodiment of an optical displacement detection device according to the present invention, which detects rotation. A disk 1 made of a light-shielding material such as metal is fixed to a rotary shaft 2 and can be rotationally displaced.
The rotary shaft 2 is connected to a detection target (not shown). A pair of spiral slits 3a, 3b is formed on the surface of the disk 1 and gradually expands from the center along the circumferential direction. These slits 3a and 3b can be formed by etching the disk 1 made of a light-shielding material such as metal.
Alternatively, instead of this, a light-shielding material such as metal may be vacuum-deposited on the surface of a disk made of a transparent glass plate through a mask to form a spiral slit pattern. Further, an optical resin material may be injection-molded to form the band-shaped slit pattern of the cylindrical lens.

A light source 4a made of, for example, an LED is fixedly arranged on one side of the upper side of the disk 1. The light source 4a emits substantially parallel light to one side of the surface of the disk 1 through a light projecting lens fixed to the surface thereof. On the other hand, below the disk 1, a light receiving element 5a is fixedly arranged in alignment with the light source 4a.
The light receiving surface 6a provided on the surface has a longitudinal shape along the radial direction of the disk 1. Along with the rotational displacement of the disk 1, the light spot 7a that has passed through the spiral slit 3a moves in the radial direction and is received by the light receiving surface 6a. The light receiving element 5a is composed of, for example, a one-dimensional position detecting element such as PSD, and outputs the detection signals Xa and Ya to a pair of output terminals. The inner detection signal Xa output from the radially inner terminal and the outer detection signal Ya output from the radially outer terminal differentially change according to the light receiving position of the light spot 7a. This detection signal Xa, Y
a is input to the processing circuit 8.

Similarly, the light source 4 is provided above the other side of the disk 1.
b is fixedly arranged. Below the disk 1, this light source 4
The light receiving element 5b is fixedly arranged so as to match with b. The light-receiving surface 6b provided on the surface has a longitudinal shape along the radial direction of the disk 1. Along with the rotational displacement of the disk 1, the light spot 7b from the spiral slit 3b moves in the radial direction and is received by the longitudinal light receiving surface 6b. This light receiving element 5b is also P
It is composed of a one-dimensional position detection element such as SD, and outputs an inner detection signal Xb and an outer detection signal Yb to a pair of output terminals.
The pair of detection signals Xb and Yb, which differentially change according to the light receiving position of the light spot 7b, are input to the processing circuit 8 described above. The processing circuit 8 receives the four input detection signals Xa, Y
By processing a, Xb and Yb, an output representing the displacement information of the disk 1 is obtained. The processing circuit 8 includes correction means for removing an error based on the positional deviation of the slits 3a and 3b from the rotational displacement information of the disk 1. Specifically, the correction means adds the inner detection signals Xa, Xb and the outer detection signals Ya, Yb output from the pair of fixed light receiving elements 5a, 5b to cancel the eccentricity error. There is.

FIG. 2 is a schematic plan view showing the pattern shape of the pair of spiral slits 3a and 3b shown in FIG. As shown in the figure, one slit 3a has R = aθ + R
It has a spiral shape represented by ₀ . It should be noted that the present invention is not limited to the strict spiral shape represented by this mathematical expression, but may be any spiral shape that gradually expands along the circumferential direction. In the above formula, θ is the disk 1
Represents a rotation angle of a, a is a coefficient representing curvature, and R ₀
Is a constant. The other slit 3b has R = a (θ−π)
It has a spiral shape represented by + R ₀ . Therefore, in this example, the pair of slits 3 a and 3 b are spiral slits of the same shape that are symmetrically arranged with respect to the center P of the rotation shaft 2.

When the disk 1 is rotated clockwise as shown by an arrow, for example, one light spot 7a moves radially outward along the longitudinal light receiving surface 6a. At this time, the other light spot 7
Similarly, b moves radially outward along the longitudinal light receiving surface 6b. In this way, the pair of light spots 7a and 7b move in opposite directions. Now, if there is an eccentricity error,
The value of R ₀ of the spiral slit 3a is different from that of the other spiral slits 3a.
Consider the case where it is larger than the value of R ₀ of b. At this time, a positive error appears in one outer detection signal Ya and a negative error appears in the other outer detection signal Yb. Therefore, by adding both outer detection signals Ya and Yb, the positive and negative errors cancel each other out. Similarly, both inside detection signals Xa and Xb
The eccentricity error is removed by adding the values to each other.
If these addition results are Y and X, it is possible to obtain the rotational displacement information from which the error is removed by taking the difference between the two. As is apparent from the figure, the detection range of the rotation angle is determined according to the draft angle φ of each spiral slit, and in this example, both spiral slits 3a and 3b have the same shape, and therefore overlapping is not possible. And is a relatively narrow detection angle range of 180 ° or less.

FIG. 3 is a schematic plan view showing another pattern example of the pair of spiral slits 3a and 3b. In this example, one of the spiral slits 3a is represented by R = aθ + R ₁ . The other spiral slit 3b has R = b (θ−π) + R
It is represented by ₂ . The coefficient a representing the curvature of the spiral slit 3a is larger than the coefficient b representing the curvature of the other spiral slits 3b. The constant R ₁ of the spiral slit 3a is larger than the constant R ₂ of the other spiral slits 3b. Therefore,
The pair of slits 3a and 3b can be partially overlapped with each other at symmetrical positions with respect to the rotation axis 2 of the disk 1, and the draft angle φ of each slit can be larger than 180 °. Therefore, the detection angle range can be set larger than that in the example of FIG.

FIG. 4 shows a pair of spiral slits 3a and 3b.
FIG. 11 is a schematic plan view showing still another pattern example of FIG. In this example, the pair of slits 3a and 3b have spiral shapes with different curvatures arranged in parallel on one side with respect to the rotation axis 2 of the disk 1. Therefore, the corresponding light-receiving surfaces 6a and 6b can also be arranged on one side, and there is an advantage that a pair of slits can be commonly irradiated by using a single fixed light source (not shown). On the other hand, in the previous examples shown in FIGS. 2 and 3, since the pair of light receiving elements are arranged on the opposite sides of the rotary shaft 2, the fixed light source has to be separated. In this example, one spiral slit 3a is represented by R = aθ + R ₁ ,
The other spiral slit 3b is represented by R = -bθ + R _2. The other spiral slit 3b has a small curvature and is opposite to the one spiral slit 3a.
For example, when the disk 1 rotates clockwise as indicated by the arrow, one light spot 7a moves radially outward along the light receiving surface 6a, and the other light spot 7b moves radially inward along the light receiving surface 6b. To do. The movement directions of the two light spots 7a and 7b are opposite to each other and are the same as in the previous example. However, with respect to the spiral slit 3b, since the spiral direction is opposite,
Correspondingly, the relationship between the inner detection signal Xb and the outer detection signal Yb is reversed in the radial direction. Also in this example, when the outside detection signal Ya of the one light receiving surface 6a includes a positive eccentricity error, a negative eccentricity error appears in the outside detection signal Yb of the other light receiving surface 6b. Therefore, both outside detection signals Y
Positive and negative eccentricity errors can be canceled by adding a and Yb. The same applies to the inside detection signals Xa and Xb.

FIG. 5 is a schematic plan view showing a second embodiment of the optical displacement detecting apparatus according to the present invention, which is applied to a linear type. As shown, the moving plate 11 is linearly displaced along a predetermined linear axis 20. On the surface of the movable plate 11, a pair of linear slits 13a and 13b that are oblique to the linear axis 20 and are symmetrical to each other are formed. In addition, the longitudinal light receiving surfaces 16a, 1a are arranged along the direction orthogonal to the linear axis 20.
A pair of light receiving elements having 6b are fixedly arranged. A fixed light source (not shown) to illuminate this pair of light receiving elements
Are arranged. When the linear moving plate 11 is linearly displaced rightward as shown by the arrow, one light spot 17a moves inward in the orthogonal direction. Similarly, the other light spot 17b also moves inward in the orthogonal direction. Therefore, both light spots 17
a and 17b move in opposite directions. Now, if backlash occurs in the orthogonal direction, for example, one light receiving surface 16
A positive error appears in the outer detection signal Ya of a, and a negative error appears in the outer detection signal Yb of the other light receiving surface 16b. By adding the two outer detection signals Ya and Yb to each other, the positive and negative error components are canceled out, and the net outer detection signal Y is obtained. The same applies to the inside detection signals Xa and Xb. By performing addition processing, a net inside detection signal X in which positive and negative error components are canceled out is obtained. The linear displacement information of the moving plate 11 can be obtained by calculating the difference Y-X of these detection signals.

FIG. 6 is a schematic circuit block diagram showing a specific configuration example of the processing circuit 8 shown in FIG. As shown in the figure, the inner detection signal Xa output from one light receiving element 5a and the inner detection signal Xb output from the other light receiving element 5b are summed and amplified by an amplifier A1 to obtain an inner detection signal X from which an error is removed. can get. Similarly, the outer detection signal Ya of the one light receiving element 5a and the outer detection signal Yb of the other light receiving element 5b are additively amplified by the amplifier A2 to obtain the outer detection signal Y from which the error is removed. The pair of detection signals X and Y are subjected to difference processing by the differential amplifier A3, and an output Y-X representing rotation information of the disc 1 is obtained. The addition result X + Y of the pair of detection signals X and Y is input to the automatic light amount controller APC, and the light emission amounts of the light sources 4a and 4b are controlled to be constant.

FIG. 7 is a geometrical diagram showing the relationship between the eccentricity and the detection error. As shown in the drawing, the spiral slit 3 has R = aθ +
It is represented by R ₀ . An eccentricity δ is included between the center S of the spiral and the rotation center P of the disk 1. As is apparent from the geometrical relationship in the figure, r ² = R ² + δ ² +2 between the radial distance r representing the position of the light spot 7 and the spiral distance R.
There is a relationship of Rδcosθ. Further, there is a relation of Rcos θ = rcos ω−δ between the radius vector angle ω of r and the radius vector angle θ of R. From the above three relational expressions, the relation between r and ω r = f (ω)
Can be derived analytically. The relational expression of r = f (ω) includes δ, and by analyzing this, the relation between the eccentricity δ and the position error can be clarified.

FIG. 8 shows the simulation result.
In this graph, the horizontal axis represents the rotation angle and the vertical axis represents the position error. This position error represents the difference between the actual output and the ideal output in%. The spiral slit used in this simulation is R = 3θ / π
It is represented by +9. The unit is mm, and the rotational displacement of 120 ° moves the light spot by about 2 mm. Curve A shows eccentricity δ when one spiral slit and one light receiving element are adopted.
Is a simulation of the error when is 0.2 mm.
As is clear from the graph, eccentricity causes an error of about 6%. The curve B is also the case where one spiral slit and one light receiving element are combined, and the eccentricity δ is 0.1 mm. At this time, an error of about 3% occurs. On the other hand, the curve C is a case where two spiral slits and two light receiving elements are used in combination, and the eccentricity δ which is a parameter is 0.
It is set to 2 mm. By performing the eccentricity correction according to the present invention, the error can be improved to 0.1% or less.

[0020]

As described above, according to the present invention, by combining a pair of slits and a corresponding pair of fixed light receiving elements, the detection signals output from both fixed light receiving elements are processed to obtain displacement information. It is possible to obtain an effect that it becomes possible to remove an error due to the positional deviation of the slit. Especially when applied to the rotational displacement detection, the error due to the eccentricity of the moving member can be eliminated. Further, when applied to linear displacement detection, it is possible to eliminate an error caused by the backlash of the moving member.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing a first embodiment of an optical displacement detection device according to the present invention.

FIG. 2 is a plan view showing an example of a pattern of a pair of slits.

FIG. 3 is a plan view showing another pattern example of a pair of slits.

FIG. 4 is a plan view showing still another pattern example of a pair of slits.

FIG. 5 is a plan view showing a second embodiment of the optical displacement detection device according to the present invention.

6 is a block diagram showing a specific configuration example of a processing circuit included in the optical displacement detection apparatus shown in FIG.

FIG. 7 is a geometric diagram showing the relationship between the eccentricity of the rotating disk and the position error.

FIG. 8 is a graph showing the relationship between eccentricity and position error.

FIG. 9 is a plan view showing an example of a conventional optical rotational displacement detection device.

10 is a graph showing the relationship between the rotation angle and the output of the optical rotary displacement detection device shown in FIG.

FIG. 11 is a plan view showing an example of a conventional optical linear displacement detection device.

[Explanation of symbols]

 1 disk 2 rotation axis 3a slit 3b slit 4a light source 4b light source 5a light receiving element 5b light receiving element 6a light receiving surface 6b light receiving surface 7a light spot 7b light spot 8 processing circuit

Claims (5)

[Claims] 1. A moving member having a predetermined slit formed therein, a fixed light source for irradiating the moving member with incident light, and a longitudinal light-receiving surface arranged along a moving locus of a light spot transmitted through the slit. An optical displacement detection device comprising a fixed light receiving element that outputs a detection signal according to the light receiving position of the light spot, and a processing circuit that processes the detection signal and outputs displacement information of the moving member. And a corresponding pair of fixed light receiving elements, the light spot from one slit and the light spot from the other slit move in complementary directions along the corresponding longitudinal light receiving surface, The optical displacement detection device is characterized in that it includes correction means for processing the detection signals output from both the fixed light receiving elements to remove the error based on the positional deviation of the slit from the displacement information of the moving body. Apparatus. 2. The moving member comprises a rotating disk,
Each of the pair of slits is formed along the circumferential direction, and each of the pair of fixed light receiving elements has a longitudinal light receiving surface arranged along the radial direction. 2. The optical displacement detection device according to claim 1, wherein the correction means adds the inner detection signal and the outer detection signal output from the pair of fixed light receiving elements. 3. The optical displacement detection device according to claim 2, wherein the pair of slits are spiral slits of the same shape that are symmetrically arranged with respect to the rotation axis of the disk. 4. The optical system according to claim 2, wherein the pair of slits are spiral slits having different curvatures, which are partially overlapped at symmetrical positions with respect to the rotation axis of the disk. Displacement detection device. 5. The pair of slits are spiral slits arranged in parallel on one side with respect to the rotation axis of the disc and having different curvatures, and the fixed light source irradiates the pair of slits in common. The optical displacement detection device according to claim 2, wherein