JP3195655B2 - Optical displacement detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact optical potentiometer or an optical displacement detecting device. More specifically, the present invention relates to an optical structure for deflecting an incident light beam according to a displacement.

[0002]

2. Description of the Related Art Conventionally, optical displacement detecting devices having various structures are known. For example, Japanese Unexamined Patent Publication No.
Japanese Patent Application Laid-Open Publication No. H11-139,086 discloses a structure using a rotary displacement plate having a spiral slit. As shown in FIG. 6, this conventional example includes a rotary displacement plate 102 fixed to a rotary shaft 101, and a spiral slit 103 is formed on the surface thereof along the circumferential direction. A fixed light source 104 is arranged above the rotational displacement plate 102, and a light receiving element 105 is fixedly arranged below the rotational displacement plate 102. A light receiving surface 106 is provided on the surface of the light receiving element 105 along the radial direction of the rotational displacement plate 102.

[0003] As the displacement plate 102 rotates, a parallel light beam passing through the slit 103 moves in the radial direction. The light receiving element 105 outputs a detection signal indicating a rotational displacement based on a light receiving position of the moving transmitted light beam.

[0004]

In order to improve the resolution of displacement detection and the linearity of a detection signal with respect to rotational displacement (linearity), the width of the spiral slit 103 must be reduced. However, the smaller the slit width, the smaller the amount of transmitted light. Therefore, there is a problem that the amount of received light decreases and the S / N ratio deteriorates. If the light emission amount of the light source is increased to compensate for the decrease in the light reception amount, a problem arises that the current consumption increases. If the slit width is increased to secure the amount of received light, the effective area of the light receiving surface is limited, the dynamic range is reduced, and the resolution is reduced as described above. In addition, the light emission distribution of the light source is easily affected by adverse effects such as unevenness and variation, and the linearity is deteriorated as described above.

[0005] The problems or problems of the above-described conventional structure will be described more specifically with reference to FIG. With this structure, the parallel incident light 107 from the light source is
Irradiate 03. The transmitted light 108 moves along the light receiving surface 106 as the spiral slit 103 moves. A detection signal is output according to this movement. As is clear from the figure, the opening width P of the slit 103 is unchanged from the light receiving surface 106.
Since the light is projected upward, both end portions of the light receiving surface 106 cannot be effectively used. That is, when the optical center of gravity 109 of the transmitted light 108 approaches the end of the light receiving surface 106, a part of the transmitted light 108 deviates from the light receiving surface. This limit is P / 2 from the end of the light receiving surface 106. Therefore, it cannot be used by the width of P at both ends, and the effective area of the light receiving surface 106 becomes LP. Here, L is the overall length of the light receiving surface 106. Since the size of the effective area is limited to LP with respect to the overall length L, the resolution also decreases at a rate of (LP) / L. When the intensity distribution of the parallel incident light 107 is not uniform, the center of gravity 109 of the transmitted light 108 is
03, which deviates from the center of the opening, and the linearity of the detection signal deteriorates. If the opening width P of the slit 103 is reduced, the above-described problems can be suppressed to some extent, but the amount of received light decreases and the S / N ratio deteriorates. If the light emission amount of the light source is increased to compensate for the decrease in the light reception amount, the current consumption increases and the life of the light source is shortened.

A conventional structure using a cylindrical lens instead of a slit in order to increase the efficiency of using incident light is disclosed in, for example, Japanese Patent Application Laid-Open No. 62-142223. As shown in FIG. 8, a displacement plate 201 that moves in a linear direction
Is provided with a cylindrical lens 202 disposed obliquely to the moving direction. A light source 203 is fixedly arranged above the displacement plate 201, and a light receiving element 204 is fixedly arranged below the displacement plate 201. The light receiving surface 205 has a longitudinal shape provided to be orthogonal to the moving direction of the displacement plate 201. The parallel incident light from the light source 203 is condensed by the cylindrical lens 202 and projects an image 206 on the light receiving surface 205.
An image 206 is formed on the light receiving surface 2 according to the linear displacement of the displacement plate 201.
05 in the longitudinal direction.

Unlike the conventional example shown in FIG. 6, the conventional example shown in FIG. 8 has an advantage that the amount of received light increases because parallel incident light is collected. However, in this conventional structure, a light-shielding film 207 must be formed to block incident light passing through a region other than the cylindrical lens 202. For this reason, there is a problem that the processing cost is increased and the light-shielding film is cracked or peeled off, resulting in poor reliability. further,
Since the light receiving surface is arranged at the focal position of the cylindrical lens 202, it is necessary to secure a certain amount of space between the displacement plate 201 and the light receiving element 204, which is disadvantageous in mounting.

[0008]

SUMMARY OF THE INVENTION In view of the above-mentioned problems in the prior art, the present invention provides a displacement plate structure which improves the utilization efficiency of incident light to increase the amount of received light and is easy to manufacture and process. For the purpose. The following measures were taken to achieve this purpose. That is, the optical displacement detection device according to the present invention includes a fixed light source that emits a light beam, a lens member that focuses the light beam on a spot, and a displacement in which a prism band having a continuously changing apex angle is extended. It comprises a member and a fixed light receiving element for receiving a spot via the prism band.

[0009]

The prism band formed on the displacement member is displaced so as to pass the light beam from the fixed light source. The apex angle of the prism band at the passing point continuously changes, refracting the light beam and deflecting the spot. For this reason, the light receiving position of the spot changes, and in response to this, the fixed light receiving element outputs a detection signal indicating displacement or position information of the displacement member. Preferably, the fixed light receiving element has a light receiving surface arranged along the moving direction of the deflected spot, and outputs a detection signal that changes differentially according to the light receiving position of the spot. The above-mentioned displacement member is constituted by a transparent displacement plate in which the prism band is integrally formed along the surface.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic perspective view showing one embodiment of the optical displacement detection device according to the present invention. A disk-shaped displacement plate 1 is fixed to a rotating shaft 2. On its surface, a prism band 3 is formed in an arc shape. In this example, the displacement plate 1 is made of a transparent material such as plastic, and the prism band 3 can be integrally formed by injection molding or the like. The prism band 3 has a continuously changing apex angle 4. In this example, the prism top surface 6 is inclined radially outward on one end 5 side of the prism band 3. As the distance from the one end 5 increases, the inclination of the apex angle 4 becomes gentler, and the top surface 6 becomes substantially flat in the central portion 7. Further, the vertex angle 4 inclines inward in the radial direction as it approaches the other end 8 side. In this embodiment, the prism band 3 is formed in an arc shape, but is not necessarily limited to this, and may be formed in a complete ring shape. Also, the change mode of the apex angle 4 is not limited to this example, and can be appropriately set according to the purpose of use of the optical displacement detection device.

A light source 9 is fixedly arranged above the displacement plate 1 so as to irradiate the prism band 3. The light source 9 is, for example, L
It can be composed of an ED or the like. A lens 10 is attached to the front of the light source 9, and focuses a light source light beam 11 as a spot 12. Unlike the related art, since the light from the light source is collected and used, the use efficiency can be improved. Further, the light source 9 has only to have a light source area enough to cover the movement trajectory of the prism band 3 and can be miniaturized. That is, prism band 3
Is formed in an arc shape, so that the movement trajectory is constant in the radial direction of the displacement plate 1. On the other hand, in the conventional example shown in FIG. 6, the slit 103 is formed in a spiral shape, and the light source needs a large light emitting area along the radial direction to cover the entire moving area.

A light receiving element 13 is fixedly arranged at a position facing the light source 9 via the prism band 3. Light receiving element 1
Reference numeral 3 denotes a light receiving surface 1 having a long shape along the radial direction of the displacement plate 1.
4 are provided. The light receiving surface 14 outputs a detection signal according to the spot 12. In this example, the light receiving element 13 is a two-terminal PSD, and outputs a pair of detection signals A and B that change differentially according to the light receiving position of the spot 12.
The pair of detection signals A and B are processed by the processing circuit 15 (A-B).
The arithmetic processing of / (A + B) is performed to generate an output signal representing the displacement or position of the displacement plate 1.

Next, the operation of the optical displacement detecting device shown in FIG. 1 will be described in detail with reference to FIG. This figure shows a cross-sectional structure in which the vicinity of the other end 8 of the prism band 3 is cut along the radial direction of the displacement plate 1. The optical axis 16 of the lens 10 attached to the light source 9 passes through the prism band 3 and
At the midpoint 17 of Condensed light beam 11 from light source 9
Is refracted by the prism band 3, and the spot 12 forms an image on the outer end side of the light receiving surface 14 in the longitudinal direction. Refraction angle δ at this time
Is represented by the following Equation 1.

(Equation 1) In Equation 1, n represents the relative refraction angle of the prism band 3, and φ represents the apex angle of the prism band 3. Equation 1 assumes that the vertex angle φ expressed in radians is much smaller than 1.

Next, assuming that the distance from the reference plane of the prism band 3 to the light receiving surface 14 is S, the distance Δ from the midpoint 17 of the light receiving surface 14 to the image forming position of the spot 12 is given by the following equation (2).
Is represented by

(Equation 2) Therefore, the relationship of the image forming position Δ of the spot 12 with respect to the vertex angle φ of the prism band 3 is expressed by the following Expression 3 using Expressions 1 and 2.

(Equation 3) As is apparent from Equation 3, the imaging position Δ of the spot 12 is substantially proportional to the apex angle φ, and a linear relationship is obtained. The relationship of Expression 3 approximately holds when the apex angle φ is small, and is not strictly linear as understood from Expressions 1 and 2. However, in practice, the vertex angle φ is set to a small value to some extent, and sufficient linearity of the detection signal can be guaranteed.

As described above, the apex angle φ of the prism band 3 is set so as to change in proportion to the rotation angle θ of the displacement plate 1. Therefore, the rotation angle θ and the imaging position of the spot 12 have a linear relationship. For example, FIG. 3 shows a state where the displacement plate 1 rotates counterclockwise and the intermediate portion of the prism band 3 is aligned with the optical axis 16. At this time, the vertex angle φ decreases with the rotation, and the prism top surface 6 is in a substantially horizontal state. Therefore, the condensed light beam 11 is not deflected, and the spot 12 is imaged at the midpoint 17 of the light receiving surface 14.

As shown in FIG. 4, when the displacement plate 1 further rotates counterclockwise, the top surface 6 of the prism band 3 is inclined inward toward the inside of the displacement plate 1 in the radial direction. In this state,
The condensed light beam 11 is refracted and deflected radially inward by the prism band 3, and the spot 12 is imaged on the radially inner end side of the light receiving surface 14. As described above, as the prism band 3 is displaced from the other end 8 to the one end 5, the spot 12 moves substantially linearly from the outer end to the inner end of the light receiving surface 14. The light receiving element outputs this movement amount as an electric signal to obtain displacement information or position information of the displacement plate 1.

FIG. 5 is a schematic sectional view showing another embodiment of the optical displacement detecting device according to the present invention. It has basically the same configuration as that of the embodiment shown in FIG. 1, and corresponding parts are denoted by corresponding reference numerals to facilitate understanding. The difference is that the light source 9 is not a convergent light beam but a parallel light beam 2.
1 along the optical axis 16. In connection with this, the condenser lens 20 is disposed between the displacement plate 1 and the light receiving surface 14.
Is interposed. After being refracted by the prism band 3, the parallel light beam 21 forms a spot on the light receiving surface 14 via the condenser lens 20. In this embodiment, since the parallel light beam 21 is deflected, the aberration of the prism band 3 can be suppressed as compared with the embodiment of FIG. 1, and the linearity of the detection signal is further improved.

[0018]

As described above, according to the present invention, by displacing the prism band so as to pass the light beam, the apex angle changes to deflect the spot and change the light receiving position of the condensed spot. The detection signal is output in accordance with. Compared to the conventional method using a spiral slit,
If the prism bands are used, they can be arranged in an arc shape, so that the irradiation position of the light source light can be limited, and the size of the light source can be reduced. Further, since the light reception is detected in a state where the light from the light source is condensed as a spot, there is an effect that the light reception amount can be increased and the S / N ratio of the detection signal can be improved as compared with the conventional structure using a slit. In addition, even if there is a local variation in the light emission distribution of the light source light, this is collected and used, so that, on average, the amount of received light can be made constant and the linearity can be improved. Further, since the image is formed as a spot, the entire length of the light receiving surface can be utilized as an effective light receiving area to the maximum and the resolution can be improved as compared with the conventional projection method using a slit. In addition, the prism band can be easily made by molding plastics, etc., it is a combination of flat surfaces instead of a special cylindrical curved surface processing like a cylindrical lens, and it does not become uneven thickness like a cylindrical lens, so There is no decrease in dimensional accuracy.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing one embodiment of an optical displacement detection device according to the present invention.

FIG. 2 is a cross-sectional view for explaining the operation of the embodiment shown in FIG.

FIG. 3 is a cross-sectional view for explaining the operation.

FIG. 4 is a cross-sectional view for explaining the operation.

FIG. 5 is a schematic sectional view showing another embodiment of the optical displacement detection device according to the present invention.

FIG. 6 is a perspective view showing an example of a conventional optical displacement detection device.

FIG. 7 is a schematic diagram for explaining a problem of the conventional example shown in FIG. 6;

FIG. 8 is a schematic perspective view showing another example of the conventional optical displacement detection device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Displacement plate 2 Rotating axis 3 Prism band 4 Apex angle 6 Top surface 9 Light source 10 Lens 11 Light flux 12 Spot 13 Light receiving element 14 Light receiving surface 15 Processing circuit

Continuation of the front page (56) References JP-A-62-142223 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01D 5/26-5/38 G01B 11/00-11 / 30

Claims (3)

(57) [Claims] 1. A fixed light source that emits a light beam, a lens member that focuses the light beam on a spot, a displacement member having a prism band having a continuously changing apex angle extended, and a prism member that passes through the prism band. And a fixed light receiving element for receiving the spot, and by displacing the prism band so as to pass the light beam, the apex angle changes to deflect the spot,
An optical displacement detection device that outputs a detection signal in accordance with a change in the light receiving position of a spot. 2. The optical system according to claim 1, wherein the light receiving element has a light receiving surface arranged along a moving direction of the spot and outputs a detection signal that changes differentially according to a light receiving position of the spot. Displacement detector. 3. The displacement member comprises a transparent displacement plate in which the prism band is integrally formed along a surface.
The optical displacement detection device according to claim 1.