JP2003344112A - Optical encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical encoder with few fluctuation of an output phase caused by decentering of a rotation slit, and a low price, and high resolution. <P>SOLUTION: The optical encoder comprises a rotation plate 1, a fixation plate 2, a light-emitting element 3 and a light-receiving elements 4A, 4B arranged to face with holding these plates 1, 2 between them. On the rotation plate 1, a slit 11 is formed along a circumference thereof, and light from the light-emitting element 3 is intermittently transmitted with rotation thereof. On the fixation plate 2 with openings 21A, 21B, light transmitting through the rotation plate 1 is separated into at least two fluxes with mutually shifted intermittent phases. The light-receiving elements 4A, 4B individually receive the flux to output at least two electric signals with cycles corresponding to intermittent states and shifted phases. Light guide members 5A, 5B guide from the fixation plate 2 to the light-receiving elements 4A, 4B with expanding the space between the adjacent fluxes. Consequently, the light-receiving elements 4A, 4B can be arranged at an expanded space. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an optical encoder in which a light emitting element and a light receiving element are combined. More specifically, the present invention relates to an optical encoder that uses a light guide member (light guide) on the light receiving element side.

[0002]

2. Description of the Related Art Generally, in an optical encoder, a rotary plate and a fixed plate are arranged close to each other in parallel, and a light emitting element and a light receiving element face each other with the rotary plate and the fixed plate sandwiched therebetween. An optical axis connecting the light emitting element and the light receiving element is arranged in a direction parallel to the rotation axis of the rotary plate. The rotary plate rotates about the rotary shaft, while the fixed plate is fixed to the body holding the rotary shaft. A predetermined number of slits are radially formed at equal intervals near the outer circumference of the rotary plate. Hereinafter, in this specification, the slit formed on the rotary plate may be referred to as a rotary slit. Since the number of rotary slits corresponds to the resolution, the number of rotary slits may be referred to as the resolution P in this specification. On the other hand, one or more slits are also formed in the fixed plate at substantially the same shape as the rotary slits at the same pitch. Hereinafter, in the present specification, the slit formed on the fixed plate is referred to as a fixed slit. In some cases, the fixed slit may be referred to as an opening in order to distinguish it from the slit formed on the rotary plate side. The rotary slit and the fixed slit are formed by hollowing out a light-shielding material such as metal or resin. Alternatively, a material in which a light-shielding film is formed on one surface of translucent glass or resin is used, and the light-shielding film may be selectively etched to form slits. The width dimension of the slits thus formed is about half the slit pitch. With the above configuration, when the rotary plate rotates, the relative positions of the rotary slit and the fixed slit change, and the light emitted from the light emitting element becomes a light beam that is interrupted by repeatedly blocking and transmitting light, and enters the light receiving element. The light receiving element converts the intermittent light flux into a periodic electric signal and outputs it. The rotation speed of the rotating plate can be detected by the cycle or frequency of the electric signal.

[0003]

In an optical encoder, a plurality of light beams having intermittent intermittent phase shifts are generated,
In some cases, the light receiving elements may output corresponding electrical signals that are out of phase with each other. For example, when the rotation direction is detected in addition to the rotation speed, two electric signals whose phases are shifted by 90 degrees from each other are output. The rotation direction of the rotary plate can be detected based on the relative phase relationship between the two-phase electric signals. When outputting electric signals having different phases, a plurality of fixed slits are arranged at predetermined angular intervals (n × Ap + Af) with respect to a row of rotating slits (which may be hereinafter referred to as tracks in the present specification) arranged along the circumferential direction. ) Only shift them. Here, n is a positive integer between 0 and the resolution P, Ap is the angular interval of the rotary slits, and Af is the angular difference corresponding to the required phase difference. Alternatively, the rotary plate may be provided with a plurality of concentric tracks, and the position of the rotary slit formed in each track may be relatively shifted by Af. In this case, the fixed slits corresponding to each track may be displaced from each other by n × Ap. In either case,
When n = 0, the plurality of fixed slits are arranged closest to each other, and when n = P / 2, the plurality of fixed slits are radially separated from each other and arranged at the farthest position.

Ideally, the rotary plate is attached eccentrically to the rotary shaft. However, in reality, due to various error factors, the rotary plate has some eccentricity with respect to the rotary shaft. Therefore, the circular track made up of rows of rotary slits formed on the rotary plate is also eccentric with respect to the rotary shaft. If there is this eccentricity, the phase difference appearing between the plurality of electric signals deviates from the set phase difference as the rotary plate rotates, and so-called phase fluctuation occurs. The phase variation of each light receiving element output due to the eccentricity of the rotary slit becomes maximum at n = P / 2, and n = P / 2.
The minimum is 0 or P. Further, when the rotary slit is provided with two tracks, the smaller the track spacing in the radial direction, the smaller the phase fluctuation. In short, the smaller the arrangement interval of the plurality of light receiving elements, the smaller the phase fluctuation of the output electric signal. As a means for narrowing the interval between the plurality of light receiving elements, for example, a method of integrally forming a plurality of light receiving regions on the same chip can be mentioned. However, when a plurality of light receiving regions are integrated and formed on one chip, the light receiving element becomes expensive. On the other hand, when an inexpensive general-purpose product having one light receiving area per chip is used, the chips cannot be arranged close to each other, and the phase variation becomes significant, which makes it difficult to achieve high resolution.

[0005]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, it is an object of the present invention to provide an optical encoder of low cost and high resolution in which the output phase fluctuation due to the eccentricity of the rotary slit is small. The following measures have been taken to achieve this purpose. That is, the rotating plate and the fixed plate are arranged in parallel to each other, and the light emitting element and the light receiving element are arranged to face each other with the rotating plate and the fixed plate interposed therebetween, and the rotating plate has slits formed at predetermined intervals along the circumferential direction. Has been done,
Light from the light emitting element is intermittently transmitted with rotation,
The fixed plate has an opening, and splits the intermittently transmitted light that has passed through the rotary plate into at least two light beams whose intermittent phases are shifted from each other, and at least two light receiving elements are arranged. , An optical encoder that receives each of the light fluxes and outputs at least two electrical signals that have a cycle corresponding to the interruption and are out of phase with each other, and is arranged between the fixed plate and the light receiving element. The light guide member is provided, and guides the light flux from the fixed plate to the corresponding light receiving element while expanding the distance between the light fluxes that are close to each other. It is characterized in that the light receiving elements can be arranged at an enlarged interval. Specifically, the light guide member is made of a transparent molded product including an incident surface that takes in the light flux and an emission surface that sends out the light flux to each light receiving element, and forms a reflection surface other than the incident surface and the emission surface. . Alternatively, the light guide member is composed of an optical fiber having an entrance for taking in the light flux and an exit for sending the light flux to each light receiving element.

According to the present invention, in the small-sized optical rotary encoder, the light guide member (light guide) is arranged between the fixed slit and the light receiving element. The light guide has a structure in which a plurality of light beams having different phases are received in a narrow region and then the light beams are guided to a plurality of light receiving elements arranged in a region wider than this. The fixed slits (openings) for each output phase are arranged in as narrow a region as possible, while the low cost light receiving elements are arranged in a wide region. A light guide is inserted between a fixed slit arranged in a narrow area and a light receiving element arranged in a wide area to guide a light beam to the light receiving element.
For example, the light guide has a shape and a structure in which an incident light beam is repeatedly totally reflected and emitted. A plurality of fixed slits with different spatial phases are arranged close to each other, and by using a light guide that guides the light flux to the light receiving elements that are spaced apart from this, without impairing the received light amount as much as possible, the phase difference accuracy of the output signal waveform can be improved. It is possible to obtain an inexpensive optical rotary encoder.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic perspective view showing an embodiment of an optical encoder according to the present invention. As shown in the figure, the present optical encoder includes a rotary plate 1 and a fixed plate 2 which are arranged in parallel to each other, and a light emitting element 3 and light receiving elements 4A and 4B which are opposed to each other with the rotary plate 1 and the fixed plate 2 interposed therebetween. The rotary plate 1 has rotary slits 11 formed at predetermined angular intervals Ap along the circumferential direction. The number of the rotary slits 11 is represented by the resolution P. With such a configuration, the rotary plate 1 rotates about the rotary shaft 12, and the light emitted from the light emitting element 3 is intermittently transmitted by the rotary slit 11.

On the other hand, the fixed plate 2 has an opening, and splits the light that has been intermittently transmitted through the rotary plate 1 into at least two light beams whose intermittent phases are shifted from each other. In this embodiment, the openings of the fixed plate 2 are fixed slits 21A and fixed slits 2A.
It is composed of 1B and is separated into two light fluxes which are out of phase with each other. In addition, in this embodiment, each fixed slit 21A, 2
Each of 1B is composed of two slits. The angular spacing of the two slits is the same as the angular spacing of the rotary slit 11. The fixed slit 21A and the fixed slit 21B are separated from each other by n × Ap + Af. Corresponding to these, two light receiving elements 4A and 4B are arranged, and each of the two light fluxes described above is received, and the two light beams having a phase corresponding to the interruption and having a phase shift from each other are provided. Output an electric signal.

As a feature of the present invention, a light guide member is arranged between the fixed plate 2 and the light receiving elements 4A and 4B. In the present embodiment, this light guide member includes two light guides 5A,
It is composed of 5B. A pair of light guides 5A, 5B
Is the two light receiving elements 4A corresponding to the two light beams from the fixed plate 2 while expanding the distance between the two light beams close to each other.
Light is guided to 4B. With such a configuration, it is possible to dispose the two light receiving elements 4A and 4B at an interval that is larger than the separation interval (n × Ap + Af) between the two light beams. In this embodiment, the light guide 5A has a corresponding fixed slit 21A.
The incident surface 51A that takes in the light flux that has passed through and the outgoing surface 52 that sends this taken light flux to the corresponding light receiving element 4A.
A side surface other than the entrance surface 51A and the exit surface 52A constitutes a reflection surface.
Similarly, the light guide 5B is also a molded product surrounded by a reflecting surface except for the incident surface 51B and the emitting surface 52B. In some cases, the light guide member may be replaced by an optical fiber having an entrance for taking in the two light beams and an exit for sending the two light beams to the respective light receiving elements.

As described above, the fixed plate 2 is assembled in parallel with the rotary plate 1. The fixed plate 2 is formed with a group of fixed slits 21A and 21B at two locations. The two fixed slits 21A and 21B are n × Ap + Af as described above.
Are separated from each other by an angular interval of. The light emitting element 3 and the light receiving elements 4A and 4B are assembled so as to face each other with the rotary plate 1 and the fixed plate 2 sandwiched therebetween. In other words, the optical axis 31 connecting the light emitting element 3 and the light receiving elements 4A and 4B is set parallel to the rotation axis 12. Here, the pair of light receiving elements 4A, 4A
The arrangement interval of B is larger than the arrangement interval of fixed slits 21A and 21B n × Ap + Af. Light receiving element 4A,
Light guides 5A and 5B are provided between 4B and the fixed plate 2 so that the light flux passing through the respective fixed slits 21A and 21B is incident on the corresponding light receiving elements 4A and 4B without loss of light quantity. The light guides 5A and 5B are mainly colorless and transparent, such as PC and P.
It is a molded product of MMA resin, and light incident from the incident surface is guided to the emission surface while repeating total reflection inside the resin, and emits a light beam toward the corresponding light receiving elements 4A and 4B.
The material of the light guides 5A and 5B may be glass, or the surfaces other than the incident surface and the emission surface may be plated or vapor-deposited with a reflective film. In some cases, an optical fiber may be used instead of the light guide. A plurality of light emitting elements 3 may be provided, but since the fixing plate 2 is close to each other, it is possible to reduce the cost as a single unit. Although the illustrated embodiment is a case where two light receiving elements are used to obtain a two-phase electric signal, the fluctuation of each phase can be suppressed by the same principle even in the case of three or more phases. For example, in the case of four phases, four corresponding fixed slits are required, but in this case, it is preferable to arrange the four fixed slits in a square shape in order to narrow the arrangement interval. Although the fixed plate 2 is arranged on the light guides 5A and 5B side in the illustrated embodiment, the fixed plate 2 may be arranged on the light emitting element 3 side instead. Alternatively, the fixed plate 2 may be provided on both sides of the light receiving element and the light emitting element so as to sandwich the rotating plate from above and below.

To facilitate understanding of the present invention, the relationship between the eccentricity of the rotating plate and the phase fluctuation of the electric signal will be briefly described. FIG. 2 shows a case where the pair of light receiving elements 1 and 2 are arranged apart from each other along the circumferential direction of the rotary plate. Here, the light receiving element 1
The distance between the light receiving element 2 and the light receiving element 2 is represented by ds, and the distance from the rotation axis to each of the light receiving elements 1 and 2 is represented by rs. As shown in the figure, when the rotary plate is eccentric, the center position of the rotary plate moves on a circular orbit as it rotates. Seen from the center of the rotating plate,
The angle from the light receiving element 1 to the light receiving element 2 becomes θ1 when the center of the rotating plate is closest to the intermediate position between the light receiving element 1 and the light receiving element 2, and becomes maximum when it is farthest, and becomes the minimum. . The angle per pitch is 2π / P
Therefore, the phase fluctuation of the electric signal output from each light receiving element is represented by (θ1−θ2) / (2π / P) × 100 (%). Therefore, the smaller θ1-θ2, the smaller the phase fluctuation. In order to reduce θ1-θ2, the eccentricity φ of the rotary plate is reduced and rs is increased while ds is increased.
Needs to be small. In the present invention, a light guide is used in order to reduce the distance ds between the pair of light receiving elements 1 and 2.

FIG. 3 shows a case where the pair of light receiving elements 1 and 2 are arranged in the radial direction. To facilitate understanding, the parts corresponding to those in FIG. 2 are designated by the corresponding reference numerals. When viewed from the center of the rotating plate, the angle from the light receiving element 1 to the light receiving element 2 is maximum when the center of the rotating plate is near the point where the light receiving element 1 and the light receiving element 2 are lined up in the direction most distant from the line. Becomes Also in this case, as is clear from the figure, the smaller the θ1-θ2, the smaller the phase fluctuation. θ1-
In order to reduce θ2, it is necessary to reduce the eccentricity φ of the rotary slit, increase rs, and reduce ds. The problem to be solved by the present invention is how to reduce ds.

As a means for solving the problem, a method of using a light receiving element (for example, a photodiode array) whose light receiving area is divided can be considered. This technique is shown in the reference diagram of FIG. As shown in (A), in the photodiode array forming the light receiving element 4, the light receiving regions 1 to 4 are integrated and formed on one chip, and the bare chip is mounted on the circuit board of the optical encoder for use. The illustrated photodiode array is an example in which a light receiving area 1 and a light receiving area 2 are arranged on a radially outer track, and a light receiving area 3 and a light receiving area 4 are arranged on a radially inner track. The light receiving area 1 and the light receiving area 2 separated along the circumferential direction are out of phase with each other by 180 degrees, for example. Similarly, the light receiving areas 3 and 4 which are separated from each other along the circumferential direction are also 180 degrees out of phase with each other. Further, the light receiving area 1 and the light receiving area 4 which are separated from each other along the radial direction are
For example, the phases are 90 degrees out of phase with each other. Similarly, light receiving area 2
Also, the phase of the light receiving area 3 is shifted by 90 degrees. However,
Since the photodiode array in which the four light receiving areas are compactly mounted in this way is expensive, it is difficult to incorporate it in a low-cost encoder. In some cases, instead of the photodiode array, the leads are wired to the individual diode chips, and the packaged one-piece resin is mounted on the circuit board for use. However, this package component is also more expensive than a single chip component.

FIG. 1B schematically shows a structure in which the light receiving areas 1 to 4 can be enlarged and arranged by using a light guide according to the present invention. As is clear from a comparison between the reference example of (A) and the example of (B), by using the light guide, the arrangement intervals of the light receiving regions adjacent to each other can be increased in both the radial direction and the circumferential direction. . As a result, the single photo chips 41 to 44 can be arranged, for example, in the shape of a square as shown in the figure, instead of the costly photodiode array. One-chip light receiving element 41, 42, 43,
Low cost general purpose phototransistors 44 can be used respectively. Also, regardless of the layout of the rice field,
Of course, various arrangements are possible by using the light guide.

[0015]

As described above, according to the present invention, even when a plurality of fixed slit groups are arranged close to each other, the light receiving elements can be arranged at intervals, and a low-priced general-purpose phototransistor chip can be used. Therefore, it is possible to obtain a low-cost, high-resolution optical encoder that suppresses deterioration of phase accuracy due to eccentricity of the rotary slit.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of an optical encoder according to the present invention.

FIG. 2 is a schematic diagram showing a relationship between eccentricity of a rotating plate and phase fluctuation.

FIG. 3 is a schematic diagram showing a relationship between eccentricity of a rotating plate and phase fluctuation.

FIG. 4 is a schematic plan view showing a reference example and an example of a layout of a light receiving element.

[Explanation of symbols]

1 ... Rotating plate, 2 ... Fixed plate, 3 ... Light emitting element,
4A ... Light receiving element, 4B ... Light receiving element, 5A ...
Light guide, 5B ... Light guide, 11 ... Rotating slit, 12 ... Rotating shaft, 21A ... Fixed slit, 21B ... Fixed slit, 31 ... Optical axis, 5
1A ... Incident surface, 51B ... Incident surface, 52A ...
Emitting surface, 52B ... Emitting surface

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Claims (3)

[Claims] 1. A rotary plate and a fixed plate, which are arranged in parallel with each other, and a light emitting element and a light receiving element, which are opposed to each other with the rotary plate and the fixed plate interposed therebetween, and the rotary plate is arranged at predetermined intervals along the circumferential direction. A slit is formed, and the light from the light emitting element is intermittently transmitted with rotation, and the fixed plate has an opening, and the light transmitted through the rotary plate intermittently is intermittently transmitted. The light is separated into at least two light beams whose phases are shifted from each other, and at least two light receiving elements are arranged, each of which receives the light beams, has a cycle corresponding to the intermittent, and is at least out of phase with each other. An optical encoder that outputs two electric signals has a light guide member arranged between the fixed plate and the light receiving element, and expands the distance between the light fluxes close to each other while The light receiving element corresponding to the fixed plate Guiding and optical encoder being characterized in that to allow placing the light receiving element in expanded intervals than the separation distance of the light beam I following. 2. The light guide member is made of a transparent molded product including an incident surface for taking in the light flux and an exit surface for sending the light flux to each light receiving element, and constitutes a reflecting surface except for the entrance surface and the exit surface. The optical encoder according to claim 1, wherein: 3. The optical encoder according to claim 1, wherein the light guide member comprises an optical fiber having an entrance for taking in each of the light beams and an exit for sending out the light beams to each light receiving element.