Reflection type sensor and optical encoder having the same

A reflection type sensor includes a light emitting element configured to emit light, a light receiving element configured to receive reflected light from a scale having a pattern, and a transparent member configured to cover the light emitting element and the light receiving element. A predetermined condition is satisfied.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a reflection type sensor and an optical encoder having the same.

Description of the Related Art

Conventionally, a reflection type sensor has been known in which a light receiving element receives reflected light from a measurement target irradiated with light from a light emitting element, and a displacement of the measurement target is detected by a change in the reflected light amount. The reflection type sensor has a problem in that, of the light emitted from the light emitting element, the light totally reflected on a transparent member covering the light emitting element and the light receiving element and incident on the light receiving element is superimposed as noise light on sensor signal light. Japanese Patent Laid-Open No. (“JP”) 2013-70078 discloses a reflection type sensor in which a light receiving area of a light receiving element is provided to a side closer to the light emitting element than the light totally reflected on the top surface of the transparent member.

However, in the reflection type sensor disclosed in JP 2013-70078, the light that is totally reflected on the top surface of the transparent member and then totally reflected by a side surface of the transparent member and enters the light receiving element may be superimposed as the noise light on the sensor signal light.

SUMMARY OF THE INVENTION

The present invention provides a compact reflection type sensor and an optical encoder having the same, each of which can reduce influence of internally reflected light.

A reflection type sensor according to one aspect of the present invention includes a light emitting element configured to emit light, a light receiving element configured to receive reflected light from a scale having a pattern, and a transparent member configured to cover the light emitting element and the light receiving element. The following conditional expression is satisfied:
D1(G+J)/tan θ
where G is a distance from a light emitter in the light emitting element to a top surface of the transparent member, J is a distance from a light receiver in the light receiving element to the top surface, θ is an angle at which light emitted from the light emitter is totally reflected on the transparent member, the light receiver is located between a first end of the light emitter and a position apart from the first end by a distance R defined as follows, and
R=(G+J)×tan θ
D1is a distance from a second end facing the first end of the light emitter to a side surface of the transparent member.

An optical encoder having the above reflection type sensor also constitutes another aspect of the present invention.

DESCRIPTION OF THE EMBODIMENTS

Referring now to the accompanying drawings, a detailed description will be given of embodiments according to the present invention. Corresponding elements in respective figures will be designated by the same reference numerals, and a duplicate description thereof will be omitted.

The optical encoder described in each of the embodiments is used for various devices such as an optical apparatus, and can detect a position of a movable member according to a relative movement between a scale and a reflection type sensor according to a movement of a movable member in the optical apparatus.

First Embodiment

FIG. 1is an external view of an optical encoder100according to this embodiment. The optical encoder100includes a reflection type sensor10and a scale50. The reflection type sensor10and the scale50are provided so as to face each other. The scale50is fixed to a movable member (not shown), and is movable in the X axis direction.

FIGS. 2 and 3are an external view and a side view of the reflection type sensor10according to this embodiment, respectively. The reflection type sensor10includes a light emitting element11, light receiving elements12and13, a transparent member14, and a nonreflective member15. The light emitting element11includes a light emitter11athat emits light. The light receiving elements12and13have the light receivers12aand13athat receive the light emitted from the light emitter11aand reflected by the scale50, respectively. The light emitting element11and the light receiving elements12and13are arranged on the nonreflective member15. In this embodiment, the reflection type sensor10has two light receiving elements12and13, but the number of light receiving elements is not limited to this embodiment. Only a single light receiving element may be provided, or three or more light receiving elements may be provided.

The transparent member14includes a transparent resin14aand a transparent glass14bdisposed on the transparent resin14a, and covers the light emitting element11and the light receiving elements12and13. Since the transparent resin14aand the transparent glass14bhave substantially equal refractive indexes, they can be regarded as optically substantially integrated members, and the boundary line between them can be ignored. The transparent member14may be made only of the transparent resin14a.

FIG. 4is a side view of the scale50. The scale50is a transparent member52having a pattern (lattice)51including reflectors (black parts in the drawing) and non-reflectors (white parts in the drawing) alternately arranged at a constant cycle (pitch), and a nonreflective member54are joined together by an adhesive53.

FIG. 5is a plan view of the light emitting element11and the light receiving element12, which are the principal parts of the reflection type sensor10. In the light receiver12a, light receiving cells a, b, c, d, . . . , iw, ix, iy, and iz are arranged at regular intervals along the horizontal direction of the drawing.

FIGS. 6 and 7are a top view and a side view of the reflection type sensor10, respectively.FIGS. 8 and 9are a sectional view taken along a line A-A and a sectional view taken along the line B-B inFIG. 6, respectively.

A light emitter11ain the light emitting element11is located apart from a top surface14cof the transparent member14by a distance G. A light receiver12a(13a) in the light receiving element12(13) is located apart from the top surface14cby a distance J. The distance G from the light emitter11ato the top surface14cmay be equal to the distance J from the light receiver12a(13a) to the top surface14c. Here, “equal” includes not only strictly equal but also approximately equal (substantially equal). In other words, this embodiment maintains sufficiently small a difference in height between the light emitting surface of the light emitter11aand the light receiving surface of the light receiver12a.

A description will now be given of light emitted from the light emitter11aincident on the top surface14cat an angle θ at which the transparent member14totally reflects the light. As illustrated inFIGS. 8 and 9, the light emitted from the light emitter11ais totally reflected on the top surface14cand propagates in the reflection type sensor10. At this time, the light totally reflected on the top surface14cdoes not enter an area inside a position apart from the end (first end) of the light emitter11aby a distance R determined by the following expression (1) (or an area within a circle having a distance (radius) R centered on the end of the light emitter11a):
R=(G+J)×tan θ  (1)

The light totally reflected on the top surface14cis noise light irrelevant to the sensor signal light. Accordingly, this embodiment disposes the light receivers12aand13abetween the end of the light emitter11aand the position separated from the end position by the distance R. This configuration can restrain the noise light totally reflected on the top surface14cfrom entering the light receivers12aand13a. The end (second end) facing the end (first end) of the light emitter11ais located between the end (first end) of the light emitter11aand the position separated from the first end by the distance R.

The transparent member14and the reflection type sensor10can be made compact by bringing the side surface14dof the transparent member14closer to the light emitter11aside. However, if the side surface14dis made too close to the light emitter11aside, the light totally reflected by the top surface14cand then totally reflected by the side surface14dmay enter the light receivers12aand13aas shown inFIG. 10. Accordingly, in this embodiment, a distance D1from the end (second end) of the light emitter11ato the side surface14dsatisfy the following conditional expression (2).
D1(G+J)/tan θ  (2)

Satisfying conditional expression (2) can restrain the light totally reflected from the top surface14cand the side surface14dfrom entering the light receivers12aand13a.

FIG. 11is an illuminance distribution diagram of the reflected light from the top surface14cin a section taken along a line PL-PL inFIG. 7where the scale50is removed when the conditional expression (2) is satisfied.FIG. 12is a graph of the received light amount in each light receiving cell in the light receiving element12inFIG. 11.FIG. 13is an illuminance distribution diagram of the reflected light from the top surface14cin the section taken along the line PL-PL inFIG. 7when the scale50is removed when the conditional expression (2) is not satisfied.FIG. 14is a graph of the received light amount in each light receiving cell in the light receiving element12inFIG. 13.

InFIGS. 11 and 13, the light emitting element11is located at the black square position at the center. Positions corresponding to the light receiving element12and the light receiver12aare indicated by dotted lines on the left side of the light emitting element11. Positions corresponding to the light receiving element13and the light receiver13aare indicated by dotted lines on the right side of the light emitting element11. The closer to white the color is, the higher the illuminance of the reflected light from the top surface14cis, and the closer to black the color is, the lower the illuminance is.

If the conditional expression (2) is not satisfied, the light totally reflected on the top surface14cand then totally reflected on the side surface14denters the light receivers12aand13aas described above. By satisfying the conditional expression (2), as compared with the case where the conditional expression (2) is not satisfied inFIG. 13, the illuminance in the light receivers12aand13acan be reduced as shown inFIG. 13. Therefore, as compared with the case where the conditional expression (2) is not satisfied inFIG. 14, as shown inFIG. 12, the received light amount for any of the light receiving cells can be reduced. In other words, the configuration according to this embodiment can restrain the internally reflected light from entering the light receivers12aand13a.

As described above, the configuration according to this embodiment can provide the compact reflection type sensor10and the optical encoder100having the same, each of which can reduce the influence of internally reflected light.

Second Embodiment

A basic configuration of the optical encoder100according to this embodiment is the same as that of the optical encoder100according to the first embodiment. This embodiment will discuss a configuration different from the optical encoder100of the first embodiment. The optical encoder100according to this embodiment has a reflection type sensor20having a configuration different from that of the first embodiment.

FIGS. 15 and 16are a top view and a side view of the reflection type sensor20according to this embodiment, respectively.FIG. 17is a sectional view taken along a line A-A inFIG. 15.

The reflection type sensor20has a light emitting element21, a light receiving element22, a transparent member23, and a nonreflective member24. In the first embodiment, the reflection type sensor10has a plurality of light receiving elements, but in this embodiment, the reflection type sensor20has a single light receiving element22. The light emitting element21includes a light emitter21athat emits light. The light receiving element22includes a light receiver22athat receives the reflected light from the scale50. The light emitting element21and the light receiving element22are disposed on the nonreflective member24.

Similar to the first embodiment, this embodiment disposes the light receiver22abetween the end (first end) of the light emitter21aand the position separated from the first end by the distance R. This configuration can restrain the noise light totally reflected by the top surface23aof the transparent member23from entering the light receiver22a. Similar to the first embodiment, the end (second end) facing the end (first end) of the light emitter21ais disposed between the end (first end) of the light emitter21aand a position separated from the first end by the distance R.

In this embodiment, similar to the first embodiment, the distance D1from the end (second end) of the light emitter21ato the side surface23bof the transparent member23around which the light receiving element22is disposed satisfies the conditional expression (2). This configuration can restrain the light totally reflected on the top surface23aand the side surface23bof the transparent member23from entering the light receiver22a.

Since this embodiment provides only the single light receiving element22, the side surface23con the side opposite to the side where the light receiving element22can be made closer to the light emitter21athan the other side surface23b. Thereby, the transparent member23can be made smaller than the transparent member14according to the first embodiment. However, if the side surface23cis brought too close to the light emitter21a, the light totally reflected on the side surface23cand then totally reflected on the top surface23amay enter the light receiver22aas shown inFIG. 18. According to this embodiment, the shortest distance D2from the end of the light emitter21ato the side surface23c(or the distance from the end of the light emitter21ato the side surface23cto which the end of the light emitter21is the closest) satisfies the following conditional expression (3).
D2>G/tan θ  (3)

Satisfying the conditional expression (3) can restrain the light totally reflected on the side surface23cclosest to the end of the light emitter21aand the top surface23afrom entering the light receiver22a.

FIG. 19is an illuminance distribution diagram of the reflected light from the top surface23ain the section taken along the line PL-PL inFIG. 16when the scale50is removed when the conditional expression (3) is satisfied.FIG. 20is a graph of the received light amount in each light receiving cell in the light receiving element22inFIG. 19.FIG. 21is an illuminance distribution diagram of the reflected light from the top surface23ain the section taken along the line PL-PL inFIG. 16where the scale50is removed when the conditional expression (3) is not satisfied.FIG. 22is a graph of the received light amount in each light receiving cell in the light receiving element22inFIG. 21.

InFIGS. 19 and 21, the light emitting element21is located at the black square position. Positions corresponding to the light receiving element22and the light receiver22aare indicated by dotted lines on the left side of the light emitting element21. Similar to the first embodiment, a color closer to white indicates a part with a higher illuminance due to the reflected light from the top surface23a, and a color closer to black indicates a part with a lower illuminance.

When the conditional expression (3) is not satisfied, as described above, the light totally reflected on the side surface23cclosest to the end of the light emitter21aand then totally reflected on the top surface23aenters the light receiver22a. By satisfying the conditional expression (3), the illuminance at the light receiver22acan be made lower as shown inFIG. 21than that in a case where the conditional expression (3) is not satisfied inFIG. 23. Therefore, the received light amount in any of the light receiving cells can be made smaller as shown inFIG. 22than that in a case where the conditional expression (3) inFIG. 24is not satisfied. That is, the configuration according to this embodiment can restrain the internally reflected light from entering the light receiver22a.

As described above, the configuration according to this embodiment provides the reflection type sensor20smaller than that of the first embodiment and an optical encoder100including the reflection type sensor20, each of which can reduce the influence of the internally reflected light.

Third Embodiment

A basic configuration of the optical encoder100according to this embodiment is the same as that of the optical encoder100of the first embodiment. This embodiment will discuss a configuration different from the optical encoder100of the first embodiment. The optical encoder100according to this embodiment has a reflection type sensor30having a configuration different from that of the first embodiment.

FIGS. 23 and 24are a top view and a side view of the reflection type sensor30according to this embodiment, respectively.

The reflection type sensor30has a light emitting element31, light receiving elements32,33, and34, a transparent member35, and a nonreflective member36. Unlike the first and second embodiments, the reflection type sensor30according to this embodiment has three light receiving elements32,33, and34. The light emitting element31includes a light emitter31athat emits light. The light receiving elements32,33, and34include light receivers32a,33a, and34afor receiving the reflected light from the scale50, respectively. The light emitting element31and the light receiving elements32,33, and34are disposed on the nonreflective member36.

In this embodiment, similar to the first and second embodiments, the light receivers32a,33a, and34aare disposed between the end (first end) of the light emitter31aand the position separated from the first end by the distance R. This configuration can restrain the noise light totally reflected by the top surface35aof the transparent member35from entering the light receivers32a,33a, and34a. Similar to the first and second embodiments, the end (second end) facing the end (first end) of the light emitter31ais located between the end (first end) of the light emitter31aand a position separated from the first end by the distance R.

In this embodiment, similar to the first and second embodiments, the distance D1from the end (second end) of the light emitter31ato the side surface35bof the transparent member35satisfies the conditional expression (2). This configuration can restrain the light totally reflected from the top surface35aand the side surface35bfrom entering the light receivers32a,33a, and34a.

FIG. 25is an illuminance distribution diagram of the reflected light from the top surface35ain the section taken along the line PL-PL inFIG. 24where the scale50is removed when the conditional expression (2) is satisfied.FIGS. 26 and 27are graphs of the received light amount in each light receiving cell in the light receiving elements32and34inFIG. 25, respectively.FIG. 28is an illuminance distribution diagram of the reflected light from the top surface35ain the section taken along the line PL-PL inFIG. 24where the scale50is removed when the conditional expression (2) is not satisfied.FIGS. 29 and 30are graphs of the received light amount in each light receiving cell in the light receiving elements32and34inFIG. 28, respectively.

InFIGS. 25 and 28, the light emitting element31is located at the black square position. The positions corresponding to the light receiving element32and the light receiver32aare indicated by dotted lines on the left side of the light emitting element31. The positions corresponding to the light receiving element33and the light receiver33aare indicated by dotted lines on the right side of the light emitting element31. The positions corresponding to the light receiving element34and the light receiver34aare shown below the light emitter31by dotted lines. Similar to the first and second embodiments, a color closer to white indicates a part with a higher illuminance due to the reflected light from the top surface35a, and a color closer to black indicates a part with a lower illuminance.

When the conditional expression (2) is not satisfied, the light totally reflected on the top surface35aand then totally reflected on the side surface35benter the light receivers32,33, and34. By satisfying the conditional expression (2), the illuminance at the light receiver22acan be made lower as shown inFIG. 25than that in a case where the conditional expression (2) is not satisfied inFIG. 28. Thus, the received light amount in any of the light receiving cells can be made smaller as shown inFIGS. 26 and 27than that in a case where the conditional expression (2) is not satisfied inFIGS. 29 and 30. That is, the configuration of this embodiment can restrain the internally reflected light from entering the light receivers32a,33a, and34a.

As described above, the configuration according to this embodiment can provide the compact reflection type sensor30and the optical encoder100having the reflection type sensor30, each of which can reduce the influence of the internally reflected light.

This application claims the benefit of Japanese Patent Application No. 2019-202624, filed on Nov. 7, 2019, which is hereby incorporated by reference herein in its entirety.