JP2610624B2 - Optical displacement detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical displacement detector that optically detects displacement of two members.

[Conventional technology]

A main scale for length measurement or angle measurement having an optical grating of a fixed pitch, and a reference scale having an optical grating corresponding to the optical grating of the main scale are disposed to face each other so as to be relatively displaceable. A light-emitting device is placed on one side, and a light-receiving device is placed on the other side. When both scales are displaced relative to each other, detection signals of multiple phases (for example, Asinθ, Acosθ) are obtained by the light-receiving device, and both scales are An optical displacement detector for detecting a displacement direction and a displacement amount of the optical displacement is known. Here, the detection signals of a plurality of phases are obtained in order to determine the relative displacement direction and to obtain an electrical interpolation pulse.

In recent years, as optical displacement detectors have been required to be smaller and more cost-effective, the optical receiver itself is composed of a light-receiving element array with a constant pitch, and has an optical structure that also serves as a reference scale. Various types of displacement detectors have been proposed.

As an example of such an optical displacement detector, an optical displacement detector previously proposed by the present applicant (JP-A-57-108621) is shown in FIGS.

This is a main scale 13 having an optical grating 12 in which light transmitting portions 12A and light shielding portions 12B having substantially the same width are arranged at regular intervals and alternately on a glass substrate 11, and
An illumination system 16 including a light emitter 14 provided on one side of 13 and a collimator lens 15 for irradiating light from the light emitter 14 to the main scale 13 as parallel rays;
The optical receiver 12 is arranged on a surface of the optical grating 12 on which an image is formed and converts light based on the image into an electric signal.

The light receiver 21 has an N-type semiconductor substrate 23 on the surface of a glass substrate 22.
And a photosensitive band 25 is formed by diffusing and forming a P-type semiconductor layer 24 at a constant pitch on the N-type semiconductor substrate 23, that is, a photosensitive member is formed on the bonding surface between the N-type semiconductor substrate 23 and the P-type semiconductor layer 24. 25, and furthermore, silicon oxide to prevent the reflection of the light transmitted through the main scale 13 on the surface to improve the light receiving efficiency and at the same time prevent the semiconductor layer from being deteriorated by the influence of the external environment. This is a configuration in which a protective film 26 is formed.

As shown in FIG. 4, the P-type semiconductor layer 24 forming the photosensitive band 25 is formed of a narrow band-like first band having a constant width and arranged at a constant pitch P.
Semiconductor pattern 24A and the first semiconductor pattern 24A
Semiconductor pattern having the same pitch and the same width as the first semiconductor pattern
The second semiconductor pattern 24B is shifted in the relative movement direction by δ (P / 4) with respect to 24A. Here, the pitch P between the semiconductor patterns 24A and 24B is the same as the pitch of the image of the optical grating 12 on the main scale 13 formed on the light receiver 21. The width s of the photosensitive zone 25 and the width t of the non-sensitive zone (the interval between the photosensitive zones 25) are both P / 2.

Light from the illumination system 16 passes through the light transmission section 12A of the main scale 23.
And reaches the P-type semiconductor layer 24. Here, when the main scale 13 and the light receiver 21 move relatively, for example, the light receiver
When the main scale 13 moves relative to 21, the junction between the N-type semiconductor substrate 23 and the P-type semiconductor layer 24, that is, the amount of light received by the photosensitive band 25 changes, so that it is obtained from the respective semiconductor patterns 24A and 24B. If the obtained signals are amplified by the preamplifiers 27A and 27B, two-phase detection signals Asinθ and Acosθ are obtained.
Therefore, the relative movement direction and the amount of displacement can be detected from the detection signal.

[Problems to be solved by the invention]

However, the optical displacement detector shown in FIGS. 3 and 4 has the following problems.

First, in order to obtain detection signals of a plurality of phases, a constant pitch P
In addition to the P-type semiconductor pattern 24A, the P-type semiconductor pattern 24B having a constant pitch P shifted by P / 4 with respect to the P-type semiconductor pattern 24A must be formed. Had become.

Secondly, since the width s and the interval t of the photosensitive zone 25 are approximately 1: 1, the light receiving efficiency is almost the same as that in the case of using the conventional reference scale, and the improvement of the light receiving efficiency cannot be expected.

Third, in order to obtain an interpolation pulse in which the pitch of the detection signal is divided into four or more, the electronic circuit must be complicated.

The above-mentioned problem is caused by the Japanese Patent Application Laid-Open
The same applies to JP-A-52-131489 and British Patent No. 1231029.

Here, an object of the present invention is to solve all of the conventional problems described above, and to obtain a detection signal of a plurality of phases with an inexpensive and simple configuration, and to improve the light receiving efficiency. It is to provide a detector.

[Means for solving the problem]

Therefore, according to the present invention, an optical scale having an optical grating in which a plurality of units are arranged at a constant pitch, with a light transmitting portion and a light shielding portion or a light reflecting portion and a light non-reflecting portion as units,
An optical displacement detector that includes an illumination system that irradiates light to the optical scale and generates a detection signal of a plurality of phases using an image of an optical grid of the optical scale; A plurality of photosensitive zones of P / 2, a photodetector arrayed at an interval of P / 4 in an array and at least a length range corresponding to a plurality of units of the optical grating is arranged on the surface on which the image is formed. In each of the units, outputs of photosensitive zones having the same phase positional relationship are synthesized.

[Action]

When light from the illumination system irradiates the optical scale, an image of the optical grating of the optical scale is formed on the light receiver. For example, in the case of a light transmission type optical grating in which light transmission parts and light shielding parts are arranged alternately at a constant pitch, light from the illumination system reaches the light receiver only through the light transmission parts. On the other hand, in the case of a reflective optical grating in which light reflecting portions and light non-reflecting portions are alternately arranged at a constant pitch, light from the illumination system is reflected by the light reflecting portion and reaches the light receiver.

Here, when the optical scale and the receiver move relative to each other,
Since the amount of light received by each photosensitive band of the photodetector changes according to the relative movement amount, a plurality of phase detection signals having different phases can be obtained from each photosensitive band.

In the present invention, when the pitch of the image of the optical grating is P, the width of each photosensitive zone is P / 2, and the interval is P / 4.
Multiple phase detection signals can be obtained. Thus, the relative movement direction and the displacement can be detected from the detection signal.

Therefore, since the detection signals of a plurality of phases can be obtained by one photosensitive band pattern, the manufacturing process of the photodetector is simplified and the cost is reduced, and the electronic circuit for obtaining the interpolation pulse is also complicated as in the conventional case. It is not necessary to convert. Further, since the interval between the photosensitive zones is narrower as P / 4 with respect to the width of the photosensitive zone, and the width of the photosensitive zone is set as P / 2, the width and the interval of the photosensitive zone are set to 1: 1 as in the related art. The light receiving efficiency can be further improved as compared with the reference scale method described above.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same or similar components as those in FIGS. 3 and 4 are denoted by the same reference numerals.
The explanation will be simplified.

This embodiment is shown in FIG. 1 and FIG. The displacement detector according to the embodiment has a light transmitting portion 12 having the same width on the surface of the glass substrate 11.
An optical scale 13 having an optical grating 12 in which A and light shielding portions 12B are alternately arranged at a constant pitch (for example, 20 μm).
And an illumination system 16 including a light emitter 14 and a collimator lens 15 for irradiating the optical scale 13 with light as parallel rays.
And a light receiver 31 that is arranged on the surface of the optical scale 13 on which the image of the optical grating 12 is formed and converts light based on the image into an electric signal.

The light receiver 31 is provided on the surface of the glass substrate 32 facing the optical scale 13 on the side opposite to the illumination system 16 with the optical scale 13 interposed therebetween.
A photosensitive band 35 is formed by forming a P-type semiconductor layer 34 in an array at a pitch Q (Q <P) smaller than the pitch P of the optical grating 12 on the N-type semiconductor substrate 33. That is, a photosensitive band 35 is formed on the junction surface between the N-type semiconductor substrate 33 and the P-type semiconductor layer 34, and further, a protective film 36 is formed on this surface.
Is formed.

As shown in detail in FIG. 2, a total of eight P-type semiconductor layers 34 forming the photosensitive zone 35 are formed at a pitch Q interval. In other words, when the light transmitting portion 12A and the light shielding portion 12B of the optical grating 12 are used as a unit, they are arranged in a length range corresponding to a plurality of units or more. The width of each P-type semiconductor layer 34 (that is, the width of the photosensitive zone 35) is w, and the adjacent interval (that is, the width of the non-sensitive zone) is v
Then, w = P / 2 v = P / 4 <w. Therefore, Q = w + v = 3P / 4 <P.

Therefore, since the phase difference between the detection signals obtained by the adjacent P-type semiconductor layers 34 is 90 °, when the respective P-type semiconductor layers 34 are connected for each phase, the phase differences are 0 °, 90 °, 180 °, 270 °. detection signals a ₁ ~a ₄ of 4 phase. In addition, these detection signals
If a _{1 to} a ₄ are amplified by the preamplifier 37 and the signals a ₁ , a ₃ , a ₂ , and a ₃ having different phases by 180 ° are differentially amplified by the differential amplifiers 38A and 38B, a two-phase detection signal b ₁ (Asinθ), b ₂ (Acos
θ) is obtained.

According to such an embodiment, the photosensitive zone 35 having a constant pitch Q
The only pattern, since it is possible to obtain the detection signal a ₁ ~a ₄ four-phase, step together with cost can be reduced to simplify manufacture of the light receiver 31, an electronic circuit in order to obtain a conventional manner the interpolation pulse Need not be complicated.

Also, since the width w of the photosensitive zone is larger than the width v of the non-sensitive zone, in other words, the interval between the photosensitive zones is greater than the width w of the photosensitive zone.
Since it is as narrow as P / 4 and the width w of the photosensitive zone is P / 2,
The light receiving efficiency can be further improved as compared with the conventional reference scale system in which the width and the interval of the photosensitive zone are set to 1: 1.

In the above embodiment, the P-type semiconductor layer 34 is formed on the N-type semiconductor substrate 33 to form the photosensitive band 35. However, the photosensitive band 35 may be any as long as it converts the amount of received light into an electric signal. N-type semiconductor layers may be formed on the type semiconductor substrate at a predetermined pitch, and furthermore, a photoconductive element (CdS)
And so on.

In the above embodiment, the light transmission type is described, but the invention can be applied to a reflection type. In this case, the optical grating 12 of the optical scale 13 is configured such that the light reflecting portions and the light non-reflecting portions are arranged alternately at a constant pitch and the optical grating 12 is irradiated with light from the illumination system 16. What is necessary is just to comprise so that the light reflected by the light reflection part may be made incident on a light receiver.

Further, the present invention can be applied not only to a linear displacement detector but also to a rotary encoder and the like. Further, the present invention can be naturally applied to not only a system using two optical gratings but also a so-called three-grading system using three optical gratings.

〔The invention's effect〕

As described above, according to the present invention, it is possible to provide an optical displacement detector that can obtain a detection signal of a plurality of phases and can improve the light receiving efficiency with an inexpensive and simple configuration. .

[Brief description of the drawings]

1 and 2 show an embodiment of the present invention. FIG. 1 is a schematic configuration diagram, and FIG. 2 is a diagram viewed from the direction of line II-II in FIG. 3 and 4 show a conventional displacement detector. FIG. 3 is a schematic configuration diagram, and FIG. 4 is a diagram of FIG.
It is the figure seen from the IV-IV direction. 11 ... Glass substrate, 12A ... Light transmitting part, 12B ... Light shielding part, 12 ... Optical grating, 13 ... Optical scale, 14 ... Light emitter, 15 ... Collimator lens, 16 ... Lighting system, 31 photodetector 32 glass substrate 33 N-type semiconductor base 34
... P-type semiconductor layer, 35 ... photosensitive zone, 36 ... protective film.

Claims (2)

(57) [Claims] 1. An optical scale having an optical grating in which a plurality of units are arranged at a fixed pitch in units of a light transmitting part and a light shielding part or a light reflecting part and a light non-reflecting part, and irradiating the optical scale with light. An optical displacement detector that generates a detection signal of a plurality of phases by using an image of an optical grid of an optical scale, wherein a pitch of the image is P, a plurality of widths of P / 2. Photosensitive bands are arranged on the surface on which the image is formed, and the photodetectors arranged in an array at intervals of P / 4 and in a length range corresponding to a plurality of units of the optical grating are arranged on the surface where the image is formed. An optical displacement detector characterized by combining outputs of photosensitive zones in a positional relationship. 2. An optical displacement detecting device according to claim 1, wherein said photodetector is formed by forming semiconductor layers having different polarities at a predetermined pitch on a semiconductor substrate. vessel.