JPS62135725A - Constitution of optical encoder - Google Patents

Abstract

PURPOSE:To prevent return light beams from being generated due to a reflection, and to improve an extinction ratio of an encoder by interposing a means for preventing return reflected light beams, in an air-gap between a fixed plate and a rotary reflecting plate. CONSTITUTION:In an air-gap of a fixed plate 6 and a rotary reflecting plate 5, a medium whose refractive index is equal to that of the fixed plate 6, namely, oil, etc. 18 being a medium whose refractive index is equal to that of a vitreous substance are interposed, since it is optimum that the fixed plate is formed by the vitreous substance. Also, a light beam B which has been made incident on the fixed plate 6 from an optical fiber 9 of its going path is not reflected by the boundary surface of the fixed plate 6 and air but becomes a linear light, reflected by the rotary reflecting plate 5, and reaches a light receiving element through an optical fiber 10 of its return path. Accordingly, deterioration of an extinction ratio caused by reflected light beams of the boundary surface can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to the structure of an optical encoder. More specifically, the present invention relates to a configuration for improving the extinction ratio of a light reflection type rotary encoder.

(B) Prior Art The structure and configuration of a conventionally used light reflection encoder will be explained with reference to the attached FIGS. 3 and 4. A rotating reflector 5 mounted on a rotary member 4t12 within the two outer shells 8, 11 is rotatably supported by a collar 14 and a bearing 13. A fixed plate 6 is provided in contact with the rotary reflecting plate 5, which is attached to a support 7 and has a plurality of slits 6' arranged at predetermined intervals and capable of transmitting 1% of the beam. The rotating reflecting plate 5 is provided with a plurality of slits 5' at predetermined intervals. As the zero rotation shaft 12 rotates, any of the slits 6' of the fixed plate 6 is synchronized with any of the slits 5' of the rotating reflecting plate 5. At this time, the light transmitted from the light receiving element via the outgoing optical fiber 9 passes through the slit 6' of the fixed plate 6, is reflected at the slit 5' of the rotating reflector 5, and then passes through the slit of the fixed plate 6 again. 6', the light is guided to the return optical fiber 10, and the light intensity is converted into an electrical signal at the light receiving element group H. FIG. 4 is a layout diagram of the constituent members of the encoder, and the symbols indicate the gaps between the fixed plate 6 and the rotating reflector plate 5.

(c) Problems to be Solved by the Invention The air, which is a medium interposed in the gap between the fixed plate 6 and the rotating reflecting plate 5, and the fixed plate 6 are different media and have different refractive indexes. That is, the fixed plate 6 is usually made of glass, and since air is a medium that naturally has a certain refractive index, the light B emitted from the outgoing optical fiber 9 is reflected between the fixed plate 6 and the air according to the law of reflection. Part of it is reflected at the boundary surface and becomes the returned light B', which is reflected at the same angle as the incident angle with respect to the normal perpendicular to the boundary surface. At the same time, incident light B becomes refracted light C and reaches the rotating reflector. However, this returning light B' has the extinction ratio of light, that is, the ratio I between the minimum value lll1° and the maximum value ■・ax of the output light intensity in the intensity modulation of the light wave.
There were problems such as increasing sin/I may. Especially in optical encoders where it is necessary to keep the code transmission error rate low, the performance depends on whether the extinction ratio is high or low.
This is a serious problem. The present invention was created in view of the above circumstances.

(d) Means for Solving the Problems 1 Effect Therefore, in the present invention, in order to solve the above problems and reduce the extinction ratio, a fixed plate is used instead of air in the gap between the fixed plate and the rotating reflector plate. To provide a configuration in which a hand or a step is interposed to prevent the light that is incident on the plate and reflected at the boundary surface from returning. As a prevention means, a medium, such as oil, which makes the refractive index equal to that of the fixing plate is interposed in the gap, or an antireflection film is formed on the measurement plate side of the gap.

By arranging the above-mentioned means in the gap between the fixed plate and the rotating reflector plate, it is possible to prevent the generation of returning light due to reflection, which in turn is useful for improving the extinction ratio.

(E) Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In FIG. 1, a medium having the same refractive index as the fixed plate 6 is interposed in the gap between the fixed plate 6 and the rotating reflecting plate 5.
Since the fixed plate 6 of this embodiment is optimally made of glass, an oil 18, which is a medium that makes the refractive index equal to that of the glass, is interposed between the fixed plate 6 and the rotating reflective plate 5. let The light B incident on the fixed plate 6 from the outgoing optical fiber 9 is reversed at the interface between the fixed plate 6 and the air, as in the conventional example.
The light travels straight, is reflected by the rotating reflector 5, passes through the return optical fiber 10, and reaches the light receiving element H. Therefore, it is possible to prevent deterioration of the extinction ratio due to light reflected from the boundary surface.

FIG. 2 shows another embodiment in which an antireflection film 20 is formed on the side of the fixed plate 6 facing the rotating reflector 5. The antireflection coating 20 is usually MgF? , Sb203 is formed on the fixing plate 6. - When a layer is applied, its thickness is d, the refractive index is n, and the light wave 14 is input, then nd = (
2m+1)λ/4 (m is an integer), the reflection becomes minimum. Therefore, it is possible to prevent the beam B entering the fixed plate 6 from the light emitting element through the outgoing fiber 9 from being reflected at the boundary surface of the medium and becoming returning light.

(f) Effects of the Invention In the present invention, the beam incident on the fixed plate is reflected at the interface between different media and the returned light is prevented by the means for preventing reflected return light provided in the gap between the fixed plate and the rotating reflector. This is useful for improving the extinction ratio of the optical encoder.

[Brief explanation of drawings]

FIG. 1 is a route layout diagram of an optical encoder according to the present invention. FIG. 2 is a route layout diagram of an optical encoder according to another embodiment, FIG. 3 is a sectional view of an optical encoder in which the configuration of the present invention is adopted, and FIG. 4 is a route diagram showing the arrangement of the optical paths in FIG. 3. , FIG. 5 is an explanatory diagram showing catadioptric refraction of a beam in a conventional example. 5 is a rotating reflector, 6 is a fixed plate, 9 is an outgoing optical fiber, 1
0 is the return optical fiber, 18 is the oil, 20 is the anti-reflective coating.

Claims (1)

[Claims] 1. A light emitting part and a light receiving part are provided, and a fixed plate and a rotating reflector are provided on the light path thereof, and the light from the light emitting part is synchronized with the rotation of the rotating reflector. In an optical encoder that transmits light through a slit in the fixed plate, is reflected on a rotating reflecting plate, passes through the fixed plate slit, is received by a light receiving section, and converts the light intensity into an electrical signal. A configuration of an optical encoder characterized in that a means for preventing reflected light from returning to a gap is provided. 2. The structure of the optical encoder according to claim 1, wherein a medium having the same refractive index as that of the fixed plate is interposed in the gap between the fixed plate and the rotating reflecting plate. 3. The structure of the optical encoder according to claim 2, wherein the medium having the same refractive index as that of the fixing plate is oil. 4. The structure of the optical encoder according to claim 1, wherein an anti-reflection film is formed on the side of the fixed plate in the gap between the fixed plate and the rotating reflective plate.