JPH07270121A - Position sensor - Google Patents

Abstract

(57) [Summary] [Object] The present invention uses a diffraction grating with a change in the grating pitch as a slit plate for high resolution, and does not require mechanical accuracy that can detect the amount of movement from the change in the diffraction angle due to the movement. It is an object to provide a position sensor having a simple structure. A light source or the diffracted light is detected by detecting a change in a diffraction angle due to a change in a position at which incident light is incident on the diffraction grating when light from a light source is incident on the diffraction grating having a different pitch depending on a location. A position sensor that detects changes in the position of the grid can detect positions with high resolution and high detection accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position sensor, and more particularly to a position sensor for measuring a rotation angle and the like with high accuracy.

[0002]

2. Description of the Related Art As shown in FIG. 9, a conventional position sensor is mainly composed of a light emitting element (light source) 8 such as an LED, a movable slit plate 9, a fixed slit plate 10 and a light receiving element 11. The light from the light source is collimated light and is applied to the moving slit plate. The projected image of the slit on the moving slit plate is formed on the fixed slit plate, and the light passing through the slit on the fixed slit plate is detected by the light receiving element. At this time, each time the moving slit moves by one pitch, the light receiving element obtains a change in the light amount for one cycle. The amount of movement of the moving slit is detected by detecting this change in the amount of light and counting the pulses. In this type of encoder and rotary position sensor, the resolution is determined by the slit pitch of each slit plate. However, even if the slit pitch is made small, there is an optical limit, and the projection image is blurred due to the diffraction phenomenon. Generally, the slit pitch is about 10
μm is the limit. Further, the obtained signal waveform is a pseudo sine wave, and accuracy cannot be obtained by increasing the resolution by dividing the signal.

[0003]

In such a conventional position sensor, it is difficult to achieve high resolution because a slit plate is used as a scale. Further, the positional accuracy of the two slits affects the measurement accuracy, so that mechanical accuracy is required. The present invention provides a position sensor with a simple structure that does not require mechanical precision that can detect the amount of movement from the change in the diffraction angle due to the movement of the slit plate in order to increase the resolution. Is intended.

[0004]

According to a first aspect of the present invention, light from a light source is incident on a diffraction grating having a different pitch depending on a location, and the light is incident on the diffraction grating at a different position. The change in position of the light source or the diffraction grating is detected by detecting the change in bending angle.

According to the second aspect of the invention, a diffraction grating is used in which the direction of the grating vector is substantially parallel to the displacement direction and the grating pitch changes in proportion to the position in the displacement direction.

According to the third aspect of the invention, a diffraction grating is used in which the direction of the grating vector is substantially perpendicular to the displacement direction and the grating pitch changes in proportion to the position in the displacement direction.

According to the fourth aspect of the invention, a diffraction grating whose grating pitch changes periodically is used.

According to the fifth aspect of the present invention, when the diffracted light is projected on the plane, a diffraction grating is used in which the grating pitch is changed so that the light moves in proportion to the displacement.

According to the sixth aspect of the invention, the position is detected by having one or more light receiving elements and arranging the light receiving element at a position for receiving the diffraction grating at a desired position.

According to the seventh aspect of the invention, the light receiving element has a light receiving surface covered with a shielding pattern, and a periodic displacement output is obtained by moving the diffracted light.

According to the eighth aspect of the invention, the diffracted light is received by the position detecting element, and the diffraction angle and the displacement amount are detected from the light receiving position.

According to the ninth aspect of the invention, the diffraction grating is of a reflection type.

[0013]

According to the first aspect of the invention, the change in the position of the light source or the diffraction grating is detected by detecting the change in the diffraction angle due to the change in the position of the incident light incident on the diffraction grating.

According to the second aspect of the invention, the direction of the lattice vector is substantially parallel to the displacement direction, and the lattice pitch changes in proportion to the position in the displacement direction.

According to the third aspect of the invention, the direction of the lattice vector is substantially perpendicular to the displacement direction, and the lattice pitch changes in proportion to the position in the displacement direction.

According to the fourth aspect of the present invention, since the diffraction grating in which the grating pitch is periodically changed is used, the displacement amount is enlarged, and the displacement amount is measured by counting.

According to the fifth aspect of the invention, when the diffracted light is projected on the plane, the diffraction grating is used in which the grating pitch is changed so that the light moves in proportion to the displacement. , A simple signal configuration can be made.

According to the sixth aspect of the invention, one or more light receiving elements are provided, and the light receiving element is arranged at a position for receiving the diffraction grating at a desired position to detect the position.

According to the seventh aspect of the present invention, the light receiving element having the light receiving surface covered with the shielding pattern is provided, and the periodic displacement output is obtained by the movement of the diffracted light.

According to the present invention, the diffracted light is received by the position detecting element, and the diffraction angle and the displacement amount are detected from the light receiving position.

According to the ninth aspect of the invention, the diffraction grating is of a reflection type and the light source and the detection section are integrated.

[0022]

EXAMPLES Examples of the present invention will be described below. The present invention uses a diffraction grating having a partially different pitch instead of the slit as a scale, and magnifies the displacement by using diffraction by the diffraction grating. Claim 1
The described invention will be described based on the embodiment of FIG. In the present embodiment, in order to simplify the description, the description will be given assuming that the diffraction grating is composed of two portions having different pitches. The respective pitches are indicated by P1 and P2. The light emitted from the light source 1 is collimated by the lens 2 and applied to the diffraction grating 3. As the light source 1, an LED, LD or the like is used. When accuracy is required, it is desirable to use collimated light with a small wavelength variation and a small beam diameter. Here, the case where the LD is used will be described.
The light illuminating the diffraction grating 3 does not necessarily need to be collimated. The present invention is applicable even in the case of focused light. The diffracted light diffracted by the diffraction grating 3 is detected by the light receiving element 4. Various means such as a photodiode (PD) and a position detection element (PSD) can be used as the means for detecting the light.

Next, the process in which the diffraction angle of light changes with the amount of displacement will be described. For simplicity of explanation, it is assumed that the light source and the lens do not move, but only the diffraction grating moves.
The present invention also applies to the case where the diffraction grating is fixed and the light source, the lens, and the detection means move. The collimated light A enters the diffraction grating 3 and is diffracted according to the pitch of the diffraction grating. The diffraction angle at this time is sin θ = λ / Λ
… Given in (1). However, light is incident on the diffraction grating vertically, where θ is the diffraction angle, λ is the wavelength of the light source, and Λ
Is the pitch of the diffraction grating. The light is the pitch of the diffraction grating, P
The diffraction angle when the portion 1 is irradiated is θ1.
When the diffraction grating moves in the x direction by an external force and the light is irradiated to the pitch P2 portion, the diffraction angle becomes θ2. The displacement of the diffraction grating can be detected by detecting this change. In the present invention, the detection of two positions has been described, but the resolution can be improved by further dividing.

The invention according to claim 2 will be described with reference to the embodiment shown in FIG. The difference from the invention described in claim 1 is that in the invention described in claim 2, the pitch of the diffraction grating does not change stepwise, and the pitch changes smoothly from PL to PS. By thus smoothing the pitch of the diffraction grating, the diffraction angle also changes smoothly, and the change can be expressed by the following expression (2) when Λ is a function of the displacement x in expression (1). . sin θ = λ / Λ (x) (2) The displacement x can be obtained from the diffraction angle θ by the equation (2). Since the direction of the lattice vector is the same as the displacement direction, the diffraction angle is inclined toward the displacement direction.

The invention according to claim 3 will be described based on the embodiment of FIG. The gist of the invention described in claim 3 is that of claim 2
Unlike the described invention and the like, the direction of the lattice vector is substantially perpendicular to the displacement direction. Therefore, the diffracted light is diffracted in the direction perpendicular to the displacement direction x, like the optical paths B and C. An advantage of the invention described in claim 3 is that the diffraction grating as shown in the detailed view of the diffraction grating of FIG. 3 can be easily manufactured by a general manufacturing method such as the two-beam interference method.

Next, the invention according to claim 4 will be described based on the embodiment of FIG. The difference from the invention described in claims 2 and 3 is that the pitch of the diffraction grating is periodically changed as shown in the detailed view of the diffraction grating in FIG. Figure 3
Even if the direction of the lattice vector is substantially perpendicular to the displacement direction, as in the embodiment shown in, the present invention is generally established. Figure 4
As described above, by using the diffraction grating having a periodical change, the diffracted light reciprocates due to the movement of the diffraction grating.
The amount of movement of the diffraction grating can be detected by counting this reciprocating period.

The invention according to claim 5 will be described based on the embodiment of FIG. In FIG. 2, the projection position y of the diffracted light on the plane perpendicular to the incident optical axis is the distance z from the diffraction grating to the projection surface.
Then, y = z · sin θ (3) Formula (2)
Therefore, the equation (3) becomes y = z · λ / Λ (x) (4). To move this in proportion to the amount of displacement, Λ (x)
= A / x (5), a diffraction grating having a pitch change may be used. However, A is a constant. By thus obtaining the projection of light in proportion to the displacement amount, it is possible to eliminate the need to calibrate the displacement amount and set the origin position. Similar effects can be obtained for the inventions according to claims 1, 3, and 4.

The invention according to claim 6 will be described with reference to the embodiment shown in FIG. The invention according to claim 6 is the light receiving of the present invention,
The present invention relates to a position detection method. When the diffracted light changes as indicated by B and C in the figure, light receiving elements (two-division PDs in this embodiment) are provided at positions b and c, and the position is detected by the presence or absence of a signal from each light receiving element. This method can be applied as a sensor of whether or not it has a displacement within a range.
For example, when detecting the type of PPC paper, the type B paper can be classified by setting the light receiving element b so as to output a signal.
Further, it is possible to perform high resolution measurement by using a two-division PD and obtain a difference signal between them, and it is also possible to perform wide range measurement using a PD array.

The invention according to claim 7 will be described with reference to FIG. The invention according to claim 7 relates to the light receiving and position detecting method of the present invention. As shown in FIG. 6, by covering the light receiving surface of the light receiving element with the shielding pattern 5, as the projection position of the diffracted light changes like B and C, a signal output as shown in FIG. 6B can be obtained. Thereby, a general encoder signal can be obtained.

The invention according to claim 8 will be described with reference to FIG. The invention according to claim 8 relates to the light receiving and position detecting method of the present invention. As shown in FIG. 7, a position detecting element (PSD) is arranged at the projection position of the diffracted light, and the displacement amount is detected by detecting the projection position of the light.
In this method, the light receiving unit is only one PSD element, the configuration is simple, and the moving distance can be easily calibrated by the voltage output of the PSD.

The ninth aspect of the invention will be described with reference to FIG. In the invention according to claim 9, the diffraction grating is of a reflective type. By using the reflection type diffraction grating as the diffraction grating, the light source unit and the detection unit can be installed on the same side of the reflection type diffraction grating. Therefore, since the light source unit and the detection unit can be integrated, the size of the sensor can be reduced.
The present invention is not limited to the above example, but can be widely applied to position sensors that measure a rotation angle and the like with high accuracy.

[0032]

According to the first aspect of the present invention, the displacement amount can be increased and the structure can be simplified by using not the slit scale but the diffraction grating having a partially different pitch.

According to the second aspect of the invention, analog displacement can be detected by smoothing the change in the grating pitch of the diffraction grating.

According to the third aspect of the invention, the diffraction grating can be easily manufactured by making the direction of the diffraction vector substantially perpendicular to the displacement direction.

According to the fourth aspect of the present invention, the displacement amount can be measured by counting signals of an encoder-like signal by making the grating pitch periodic.

According to the invention of claim 5, it is possible to easily calibrate the signal.

According to the invention described in claim 6, it is possible to detect the position range.

According to the invention described in claim 7, it is possible to obtain a periodic signal output by one light receiving element.

According to the invention as set forth in claim 8, displacement can be continuously detected by one element of the position detecting element (PSD), and the apparatus can also have a simple structure.

According to the ninth aspect of the present invention, the light source and the detection unit can be integrated by using the reflection type diffraction grating.

[0041]

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a position sensor of the invention according to claim 1;

FIG. 2 is a diagram showing an embodiment of the invention according to claim 2;

FIG. 3 is a diagram showing an embodiment of the invention according to claim 3;

FIG. 4 is a diagram showing an embodiment of the invention according to claim 4;

FIG. 5 is a diagram showing an embodiment of the invention according to claim 6;

FIG. 6 is a diagram showing an embodiment of the invention according to claim 7;

FIG. 7 is a diagram showing an embodiment of the invention according to claim 8;

FIG. 8 is a diagram showing an embodiment of the invention according to claim 9;

FIG. 9 is a diagram showing an example of a conventional rotary encoder.

[0042]

[Explanation of symbols]

 1 Light source 2 Lens 3 Diffraction grating 4 Light receiving element 5 Shielding pattern 6 Position detecting element (PSD) 7 Reflective diffraction grating 8 Light emitting element 9 Moving slit plate 10 Fixed slit plate 11 Light receiving element

Claims (9)

[Claims] 1. A light source or a light source is provided by detecting a change in a diffraction angle due to a change in a position at which incident light is incident on the diffraction grating when light from the light source is incident on the diffraction grating having a different pitch. A position sensor for detecting a change in position of the diffraction grating. 2. The position sensor according to claim 1, wherein a diffraction grating whose grating vector direction is substantially parallel to the displacement direction and whose grating pitch changes in proportion to the position in the displacement direction is used. 3. The position sensor according to claim 1, wherein a diffraction grating whose grating vector direction is substantially perpendicular to the displacement direction and whose grating pitch changes in proportion to the position in the displacement direction is used. 4. The position sensor according to claim 1, wherein a diffraction grating whose grating pitch changes periodically is used. 5. A diffraction grating having a grating pitch changed so that when diffracted light is projected on a plane, the light moves in proportion to displacement. Position sensor. 6. The method according to claim 1, further comprising at least one light receiving element, wherein the position is detected by disposing the light receiving element at a position for receiving a diffraction grating at a desired position. The described position sensor. 7. The position sensor according to claim 1, further comprising a light receiving element whose light receiving surface is covered with a shielding pattern, and which obtains a periodic displacement output by moving the diffracted light. 8. The position sensor according to claim 1, wherein the diffracted light is received by a position detecting element, and the diffraction angle and the displacement amount are detected from the light receiving position. 9. The position sensor according to claim 1, wherein the diffraction grating is a reflection type.