JPH08254442A - Optical encoder and manufacture thereof - Google Patents

Abstract

PURPOSE: To provide an optical encoder that is able to output a phase difference in a detection signal in an accurate manner. CONSTITUTION: One second slit 21 alone, serving as two functions of an illuminant slit and an index slit, is installed in a fixed scale 2, and light receiving elements 4 are disposed in a 2×2 row type each, thereby finding an azimuth angle ϕ and a roll angle θ of the fixed scale 2 where a phase difference in a detection signal is shifted as far as by 90 degrees at a time. At this time, the fixed scale 2 is tilted as far as the angle to a moving scale 1, whereby the index slit, where the phase difference in the detection signal is shifted as far as 90 degrees at a time, is thus set.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical encoder provided with an optical grating which is relatively movable, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, an optical linear encoder having an optical grating is provided, for example, as shown in FIG. 5, a moving scale 1 extending in a relative moving direction and a moving scale 1 opposed to each other with a gap therebetween. A fixed scale 2 is provided, and the movable scale 1 has a movable slit 1 at a predetermined pitch in the moving direction.
0 is provided, and the fixed scale 2 is provided with a light source slit 22 and an index slit 23 for obtaining detection signals each having a phase difference of 90 degrees. The index slit 23 is arranged such that the index slits 23b, 23c, and 23d are arranged by shifting the slit positions by 1/4 pitch with respect to one reference index slit 23a, and when the moving scale 1 moves, it is shown in FIG. As described above, a b-phase signal having a phase difference of 90 degrees with respect to an a-phase signal, and an a'phase signal and a b'phase signal having phases different by 180 degrees and 270 degrees from an a-phase signal are also disclosed. (For example, Japanese Patent Laid-Open No. 63-184013 and Shokai Sho 63
-175812).

[0003]

However, in the prior art, since the index slits are shifted by 1/4 pitch to obtain a 90-degree phase difference, when the slit pitch becomes several μm or less, the 1/4 pitch is obtained. It is difficult to obtain the positional accuracy of the slit to shift the slits one by one,
There was also the problem of high costs. . An object of the present invention is to provide an optical encoder that can accurately output a phase difference of a detection signal and can reduce the cost even if the slit pitch has a resolution of about several μm pitch. .

[0004]

In order to solve the above-mentioned problems, the present invention is directed to a moving scale having a first slit which is fixed to one of the members which move relative to each other and which is provided with a first slit.
A fixed scale that is fixed to the other member that relatively moves, faces the moving scale via a gap, and has a second slit that is aligned in the moving direction; and a light source that emits diffused light toward the fixed scale, The second slit is transmitted from the light source through the second slit and is reflected by the first slit,
And a light receiving element for detecting light transmitted through the slit of
In an optical encoder for detecting the relative displacement of both members that move relative to each other based on the periodic fluctuation of the detection signal of the light receiving element, a 4 × 2 matrix of the four light receiving elements on the same plane with the light source as the center. The fixed scale is arranged between the movable scale and the light receiving element, the slit pitch of the second slit is P _IT , and the effective light receiving center position and the light emitting center position on the fixed scale are set. The distance in the slit cutting direction is L ₁ , the distance in the relative movement direction between the effective light receiving center position and the light emitting center position on the fixed scale is L ₂ , and the first slit and the second slit are separated. When the gap length is L ₃ , the azimuth angle φ of the fixed scale and the movable scale in the direction of rotation around the light source position is φ = sin ⁻¹ (P _IT / 4), Scale and front Roll angle of the direction of rotation relative to the direction of movement and parallel lines moving scale theta ^{is, θ = sin -1 {(2L} 3 / L 1) - (P IT + 8L 2) / 8} become like the A fixed scale is fixed.

Further, the movable scale is fixed to one of the members that move relative to each other and has a first slit arranged in the moving direction, and the other scale that moves to the other is fixed to face the movable scale with a gap. A fixed scale having a second slit arranged in the moving direction, a light source for emitting diffused light toward the fixed scale, and the second scale from the light source.
A light-receiving element that detects light that passes through the slit, is reflected by the first slit, and is transmitted through the second slit. In a method of manufacturing an optical encoder that detects relative displacement of members, four light receiving elements are arranged in a 2 × 2 matrix type on the same plane with the light source as a center,
The fixed scale is arranged between the moving scale and the light receiving element, and two of the four light receiving elements on a diagonal line are arranged.
In order to make the phase difference between the pair of light receiving elements 180 degrees, the first
Of the four slits and the second slit are parallel to each other, the fixed scale is tilted about the light source position, and the phase difference between the two pairs of the four light receiving elements arranged in the moving direction is 90 degrees. The fixed scale is tilted with respect to the moving direction from a state parallel to the moving scale 1 so that

[0006]

By the above means, the fixed scale is provided with only one slit row which functions as a light source slit and an index slit, and the light receiving elements are arranged in a 2 × 2 row type, and the phase difference of the detection signals is 90 degrees each. By finding the azimuth angle and roll angle of the fixed scale that deviates, and tilting the fixed scale by that angle, you can set an index slit that shifts the phase difference of the detection signal by 90 degrees. A high-resolution encoder can be realized without the need for shifting.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a front view of an embodiment in which the present invention is applied to a linear encoder, and FIG. 2 is a perspective view showing a positional relationship among a moving scale, a fixed scale, a diffused light source, and a light receiving element. In the figure, 1 is a moving scale of a linear encoder, 11 is a first slit mounted on the moving scale surface by vapor deposition or the like, 2 is a fixed scale, and 21 is a fixed scale surface mounted on the fixed scale surface in the same manner as the moving scale 1. The second slits 3 are diffusion light sources. Reference numeral 4 denotes a light receiving element such as a photodiode, which is a light receiving element 4A for a phase, a light receiving element 4B for b phase,
It is composed of four light receiving elements 4a for the a'phase and 4D for the b'phase, and is arranged in a 2 × 2 matrix on a plane parallel to the moving scale 1 with the light source 3 at the center. There is. The second slit 21 provided in the fixed scale 2 has two functions of the light source slit and the index slit described in the conventional example, but these two are not distinguished,
There is only one slit row. Here, the light source slit functions as a point light source array, and the index slit changes the light intensity distribution accompanying the movement of the slit pattern of the reflected light from the moving scale into a sine wave signal.

With the above construction, when the moving scale moves, a pseudo sine wave signal is detected from each light receiving element. However, in order to make the phase difference of the detection signals from each light receiving element 90 degrees, the fixed scale A method of adjusting the value will be described below. The adjustment direction of the fixed scale for adjusting the phase difference is, as shown in FIG. 1, with the center of the second slit 21 as the origin and the first slit 11 and the second slit 11 of the moving scale 1
The slit 21 is twisted spatially, that is, the fixed scale 2 is rotated in parallel with the moving scale 1 with the center of the second slit 21 as the origin to change the azimuth angle φ. And the case where the fixed scale 2 is adjusted in the direction in which the fixed scale 2 is inclined with respect to the surface of the moving scale, that is, in the direction in which the roll angle θ changes, as shown in FIG. There are two adjustment directions. The phase difference between the detection signals is 90 degrees, but when the a phase is used as a reference, the phase difference between the a phase and the b phase is 90 degrees.
The fixed scale 2 is adjusted in two directions so that the phase difference between the a phase and the a ′ phase is 180 degrees and the phase difference between the a phase and the b ′ phase is 270 degrees.

First, when adjusting in the direction in which the azimuth angle φ changes, the phase difference of the detection signal changes between the pairs of light receiving elements arranged vertically and diagonally, that is,
Between light receiving elements 4A and 4C, between 4B and 4D, between 4A and 4D,
And the phase difference between 4B and 4C. This phase difference Φ ₁
Is approximately expressed by the following equation (1). Φ ₁ = (2L ₁ sin φ / P _IT ) × 360 (degrees) (1) where P _IT is the slit pitch of the second slit 21,
L ₁ is the distance between the effective light-receiving center position on the fixed scale 2 and the light-emitting center position in the direction in which the slit is cut, and φ is the first
Is an angle at which the slit 11 and the second slit 21 are twisted spatially, that is, an azimuth angle. Next, roll angle θ
In the case of adjusting in the changing direction, the phase difference of the detection signal changes between the pair of light receiving elements arranged in the vertical direction and the horizontal direction, that is, between the light receiving elements 4A and 4B, 4C and 4D.
Between 4A and 4D, and between 4B and 4C. The change Φ ₂ of the phase difference is expressed by the following equation (2). Φ ₂ = {(2L ₃ -L ₁ sin θ / 2L ₃ ) -1} × (2L ₂ / P _IT ) × 360 (degrees) (2) where θ is relative to the plane of the moving scale 1. The inclined angle, that is, the roll angle, L ₂ is the distance in the relative movement direction between the effective light receiving center position and the light emitting center position on the fixed scale 2.
L ₃ is the length of the gap between the first slit 11 and the second slit 21.

Therefore, when the position of the fixed scale 2 is adjusted, as shown in FIG.
The azimuth angle φ at which the phase difference between the b-phase and the b-b ′ phase is 180 degrees is obtained from the equation (1), and the azimuth angle φ is fixed scale from the state in which the first slit 11 and the second slit 21 are parallel to each other. Tilt 2 In this case, if azimuth angle φ is obtained from equation (1) with Φ ₁ = 180 degrees, the following equation (3)
It is represented by. φ = sin ⁻¹ (P _IT / 4) (3) Further, as shown in FIG. 4B, between the a phase and the b phase, a ′
The roll angle θ at which the phase difference between the phase and b ′ phase becomes 90 degrees is obtained from the equation (2), and the fixed scale 2 is tilted by the roll angle θ from the state parallel to the moving scale 1. In this case, Φ ₂ =
When the roll angle θ is calculated from the equation (2) with 90 degrees, it is represented by the following equation (4). θ = sin ⁻¹ {(2L ₃ / L ₁ )-(P _IT + 8L ₂ ) / 8} (4) Then, as shown in FIG. 4C, the phase difference between the a phase and the b phase is 90 degrees. , The phase difference between the a phase and the a ′ phase is 180 degrees, and the phase difference between the a phase and the b ′ phase is 270 degrees. In addition, although the example applied to the linear encoder has been described in the above embodiment, the application range of the present invention is not limited to this, and the present invention can be applied to a rotary encoder.

[0011]

As described above, according to the present invention, the fixed scale is provided with only one slit row which functions as a light source slit and an index slit, and the light receiving elements are arranged in a 2 × 2 row type. , The phase difference of the detection signal is deviated by 90 degrees, the azimuth angle and the roll angle of the fixed scale are obtained, and by tilting the fixed scale by that angle, the index slits by which the phase difference of the detection signal is deviated by 90 degrees are set. As described above, it is not necessary to shift the position of the index slit in units of μm, and a high resolution encoder can be realized. Also, since only one type of slit row is required for the fixed scale, it is possible to save the trouble of creating the fixed scale.
There is an effect that the cost can be reduced and an inexpensive and high-resolution optical encoder can be provided.

[Brief description of drawings]

FIG. 1 is a front view showing an embodiment of the present invention.

FIG. 2 is a perspective view showing an embodiment of the present invention.

FIG. 3 is a side view showing an embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a phase difference of detection signals according to the embodiment of the present invention.

FIG. 5 is a front view showing a conventional example.

FIG. 6 is an explanatory diagram showing an arrangement of index slits and a phase difference between detection signals in a conventional example.

[Explanation of symbols]

1 moving scale, 11 1st slit, 2 fixed scale, 21 2nd slit, 3 diffused light source, 4 light receiving element, 4A a phase light receiving element, 4B b phase light receiving element, 4C a'phase light receiving element, 4D b'phase light receiving element,

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Nakajima No.2-1 Kurosaki Shiroishi, Hachimannishi-ku, Kitakyushu, Fukuoka Prefecture Yasukawa Electric Co., Ltd.

Claims (2)

[Claims] 1. A moving scale, which is fixed to one of the members that move relative to each other, and has a first slit arranged in the moving direction,
A fixed scale that is fixed to the other member that relatively moves, faces the moving scale via a gap, and has a second slit that is aligned in the moving direction; and a light source that emits diffused light toward the fixed scale, The second slit is transmitted from the light source through the second slit and is reflected by the first slit,
And a light receiving element for detecting light transmitted through the slit of
In an optical encoder for detecting the relative displacement of both members that move relative to each other based on the periodic fluctuation of the detection signal of the light receiving element, a 4 × 2 matrix of the four light receiving elements on the same plane with the light source as the center. The fixed scale is arranged between the movable scale and the light receiving element, the slit pitch of the second slit is P _IT , and the effective light receiving center position and the light emitting center position on the fixed scale are set. The distance in the slit cutting direction is L ₁ , the distance in the relative movement direction between the effective light receiving center position and the light emitting center position on the fixed scale is L ₂ , and the first slit and the second slit are separated. When the gap length is L ₃ , the azimuth angle φ of the fixed scale and the movable scale in the direction of rotation around the light source position is φ = sin ⁻¹ (P _IT / 4), Scale and front Roll angle of the direction of rotation relative to the direction of movement and parallel lines moving scale theta ^{is, θ = sin -1 {(2L} 3 / L 1) - (P IT + 8L 2) / 8} become like the An optical encoder with a fixed scale fixed. 2. A moving scale having a first slit which is fixed to one of the members that move relative to each other, and has a first slit arranged in the moving direction.
A fixed scale that is fixed to the other member that relatively moves, faces the moving scale via a gap, and has a second slit that is aligned in the moving direction; and a light source that emits diffused light toward the fixed scale, The second slit is transmitted from the light source through the second slit and is reflected by the first slit,
And a light receiving element for detecting light transmitted through the slit of
In a method of manufacturing an optical encoder that detects a relative displacement of both members that move relative to each other based on a periodic fluctuation of a detection signal of the light receiving element, four light receiving elements are arranged on the same plane with the light source as a center. The fixed scale is arranged between the movable scale and the light receiving element, and the phase difference between two diagonal light receiving elements of the four light receiving elements is 180 degrees. As described above, the fixed scale is tilted about the light source position from the state in which the first slit and the second slit are parallel to each other, and further, of the four light receiving elements, two pairs of light receiving elements arranged in the moving direction are arranged. A method for manufacturing an optical encoder, characterized in that the fixed scale is tilted with respect to the moving direction from a state parallel to the moving scale 1 so that the phase difference becomes 90 degrees.