JP2002174536A - Encoder device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an encoder device which enables to measure a moving value with a higher accuracy by hindering possible change in the amplitude of a signal outputted from a photodetector even when an interval changes between a moving plate and a fixed plate. SOLUTION: The encoder device is provided with a moving plate 2 in which are formed rows of slits 2S arranged at a specified array pitch P along the specified direction of movement, a light emitting element 6 adapted to make a luminous flux incident into the rows of slits 2S passing with the movement of the moving plate 2 and a photodetector 5 for detecting the luminous flux emitted from the rows of slits 2S. It is also provided with an incoming side fixed plate 1F which is interposed between the photodetector 6 and the moving plate 2 and has a plurality of incident slits 1FS arranged so as to selectively pass the luminous flux and an outgoing side fixed plate 1R which is interposed between the photodetector 5 and the moving plate 2 and has a plurality of emission slits 1RS arranged so as to selectively pass the luminous flux. In such an arrangement, the array pitch of the incident slits 1FS and the array pitch of the emission slits 1RS are set so as to be twice or a larger integer multiple as much as the array pitch P of the rows of slits 2S formed on the moving plate 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an encoder device for optically detecting a rotational movement amount and a linear movement amount of a mechanical part. More specifically, the present invention relates to a slit structure of a fixed plate that is disposed to face a movable plate having a slit.

[0002]

2. Description of the Related Art A conventional encoder device basically comprises a moving plate, a light emitting element, a light receiving element, and a fixed plate, and various conventional structures are disclosed in, for example, JP-A-9-133552 and JP-A-11-183201. And JP-A-11-212505
And Japanese Patent Application Laid-Open No. 11-325973. The moving plate is arranged so as to be movable along a predetermined moving direction, and is formed with a row of slits arranged at a predetermined arrangement pitch along the moving direction. The light-emitting element makes a light beam incident on a row of slits that pass with the movement of the movable plate. The light receiving element receives a light beam emitted from the row of slits and outputs an electric signal according to the movement of the movable plate. The incident side fixed plate is provided between the light emitting element and the movable plate and has an incident slit for selectively transmitting the light flux. The emission-side fixed plate includes an emission slit that is interposed between the light receiving element and the movable plate and selectively transmits a light beam.

[0003]

Generally, a slit formed in a movable plate is of a transmission type or a reflection type. On the other hand, the slit formed in the fixed plate is of a transmission type, and the slit width is formed to be equal to or smaller than the width of the slit formed in the movable plate. Typically, a plurality of slits are formed in the movable plate in a row, whereas a single slit is formed in the fixed plate. The entrance-side fixed plate with one slit is placed between the moving plate and the light emitting element, and the emission-side fixed plate with one slit is placed between the moving plate and the light receiving element. Thus, an effective light beam can be formed from the light emitting element to the light receiving element. For the effective light flux, the row of slits engraved on the moving plate is transmitted /
By repeating blocking or reflection / absorption, a signal representing the moving amount of the moving plate is obtained. In an encoder device having a relatively low resolution, a sufficient signal can be obtained from the light receiving element with the amount of light obtained from the fixed plate having one slit.
In addition, even if the position of the movable plate is displaced between the incident-side fixed plate and the output-side fixed plate, a pair of the incident-side fixed plate and the output-side fixed plate on both sides of the movable plate form a single light flux. The output of the light receiving element does not fluctuate greatly.

[0004] However, when the resolution of the encoder device is increased, the arrangement pitch and slit width of the slits formed on the moving plate are necessarily reduced. Correspondingly, the width of the slit formed in the fixed plate becomes narrower, and it becomes impossible to guarantee a sufficient light receiving amount for the light receiving element with only one slit. To compensate for this, a plurality of slits are formed in the fixed plate at the same pitch as the arrangement pitch of the slits formed in the movable plate. However, when the number of slits of the fixed plate is increased, the ratio between the amount of light transmitted by the moving plate and the amount of light blocked by the movable plate is reduced, and there is a problem that the contrast is reduced. As the distance between the moving plate and the fixed plate increases, it becomes impossible to completely block the obliquely incident light, and the amount of light reaching the light receiving element increases even in the blocking state. Therefore, there is a problem that the light contrast is reduced and the amplitude of the signal output is reduced.

[0005]

The following means have been taken in order to solve the above-mentioned problems of the prior art. That is, the encoder device according to the present invention basically includes a moving plate, a light-emitting element, a light-receiving element, and a pair of fixed plates divided into an incident side and an emission side. The moving plate is arranged so as to be movable along a predetermined moving direction, and is formed with a row of slits arranged at a predetermined arrangement pitch along the moving direction. The light emitting element enters a light beam into the rows of the slits that pass with the movement of the moving plate. The light receiving element receives the light beam emitted from the row of slits and outputs an electric signal according to the movement of the moving plate. The entrance-side fixed plate has a plurality of entrance slits interposed between the light-emitting element and the movable plate and selectively transmitting the light beam. The emission-side fixed plate has a plurality of emission-side slits interposed between the light receiving element and the movable plate and selectively transmitting the light flux. As a feature, the arrangement pitch of the entrance slits and the arrangement pitch of the exit slits are set to twice or an integral multiple of the arrangement pitch of the rows of the slits formed on the moving plate.

[0006] Preferably, the moving plate comprises a rotatable disk, and the rows of slits are arranged along the circumferential direction of the disk. In one embodiment of the present invention, the moving plate has a row of transmission slits that transmit a light beam incident from the light emitting element and emit the light beam to the light receiving element located on the opposite side. In this case, the arrangement pitch of the entrance slits and the arrangement pitch of the exit slits are set to an even multiple of the arrangement pitch of the rows of slits formed in the moving plate, and the moving plates are located on opposite sides. It is arranged at a position where the interval between the fixed plate on the incident side and the fixed plate on the output side is approximately bisected. In another aspect, the moving plate has a row of reflective slits for reflecting a light beam incident from the light emitting element and emitting the light beam to the light receiving element located on the same side. In this case, the arrangement pitch of the entrance slits and the arrangement pitch of the exit slits are set to an even multiple of the arrangement pitch of the rows of slits formed on the moving plate. The light emitting element and the light receiving element are arranged in parallel along a direction orthogonal to the moving direction of the movable plate, and the incident side fixed plate and the emission side fixed plate are the parallel light emitting element and light receiving element. It is standardized in. Alternatively, the light emitting element and the light receiving element are arranged in parallel along a direction parallel to the moving direction of the moving plate, and the entrance slit and the exit slit are also arranged along a direction parallel to the moving direction. May be used.

According to the present invention, the arrangement pitch of the entrance slits and the arrangement pitch of the exit slits are set to an integer multiple (an integer of 2 or more) of the arrangement pitch of the slit rows formed on the movable plate. Can effectively block or absorb the luminous flux, thereby suppressing leakage of the luminous flux. It becomes difficult for an invalid light beam, which is transmitted or reflected at a timing to block or absorb the light beam incident from the light emitting element, to reach the light receiving element side. Therefore, even in the high-resolution encoder device, it is possible to sufficiently secure the interval between the movable plate and each fixed plate while suppressing the leakage of the invalid light flux. The design margin is increased in the space between the moving plate and the fixed plate, and the height of the moving plate and the fixed plate can be easily adjusted.
Further, even when the distance between the moving plate and each fixed plate changes with the movement of the moving plate, the amplitude of the signal output from the light receiving element hardly fluctuates, and the moving amount can be measured with high accuracy.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic perspective view showing a first embodiment of the encoder device according to the present invention.
This embodiment is a transmission type linear encoder device. As shown in the drawing, the present encoder device comprises a moving plate 2 and a light emitting element 6.
, Light receiving element 5, incident side fixed plate 1F, and output side fixed plate 1
R. The moving plate 2 is arranged so as to be able to move straight along a predetermined moving direction as indicated by an arrow, and is formed with a row of slits 2S arranged at a predetermined arrangement pitch P along the moving direction. Moving plate 2 having such a structure
Is made of, for example, a stainless steel thin plate, and the slit 2S is often formed by etching. Instead,
It is also possible to form a slit 2S by etching after forming a light-shielding film on the entire surface using a transparent glass plate or a resin plate. The light emitting element 6 is formed of, for example, an LED, and impinges a light beam on a row of slits 2 </ b> S that passes with the movement of the moving plate 2. The light receiving element includes, for example, a phototransistor, receives a light beam emitted from the slit 2S, and outputs an electric signal corresponding to the movement of the movable plate 2. The fixed plate 1F on the incident side is provided between the light emitting element 6 and the moving plate 2 and includes a plurality of incident slits 1FS for selectively transmitting a light beam emitted from the light emitting element 6. In this example, two entrance slits 1FS are formed. The width of the entrance slit 1FS is equal to or smaller than the width of the slit 2S formed in the movable plate 2. The fixed plate 1F having such a configuration can be produced by the same manufacturing method as that of the movable plate 2. The emission-side fixed plate 1R has basically the same configuration as the incident-side fixed plate 1F. The emission-side fixed plate 1R is interposed between the light receiving element 5 and the movable plate 2 and includes a plurality of emission slits 1RS that selectively transmit a light beam. As the features, the arrangement pitch of the entrance slit 1FS and the exit slit 1RS
Is set to twice or an integral multiple of the array pitch P of the rows of the slits 2S formed on the moving plate. In the present embodiment, the movable plate 2 has a row of transmissive slits 2 </ b> S, and transmits a light beam incident from the light emitting element 6 and emits it to the light receiving element 5 located on the opposite side.
In this case, the arrangement pitch of the entrance slits 1FS and the arrangement pitch of the exit slits 1RS are set to an even multiple of the arrangement pitch P of the rows of the slits 2S formed in the movable plate 2. In the present embodiment, particularly, the arrangement pitch of the entrance slit 1FS and the exit slit 1RS is set to twice (2P) the arrangement pitch P of the moving slits 2S. At this time, the movable plate 2 is disposed at a position that substantially divides the interval between the fixed plates 1F and 1R on the incident side and the output side located on the opposite sides from each other.

FIG. 2 is a schematic diagram for explaining the operation of the encoder device shown in FIG. (A) shows the transmission state of the encoder device, and the luminous flux emitted from the light emitting element is reflected by the incident-side fixed plate 1F, the moving plate 2, and the emission-side fixed plate 1 as shown by arrows.
After passing through R, the light reaches the light receiving element. In the transmission state, the slit 2S formed in the moving plate is
And the exit slit 1RS. However, the arrangement pitch of the entrance slit 1FS and the exit slit 1RS is 2
P, and the arrangement pitch of the moving slits 2S is P, which is half of the pitch. The distance between the incident-side fixed plate 1F and the output-side fixed plate 1R is substantially equal to 2P, and the moving plate 2 is disposed just halfway between the fixed plates 1F and 1R. In the illustrated transmission state, in addition to transmitting a light beam parallel to the optical axis connecting the light emitting element and the light receiving element, a light beam oblique from the optical axis is also transmitted. Accordingly, since the amount of light received by the light receiving element in the transmission state includes the parallel light and the skew light, the amplitude of the output signal increases, which is advantageous from the viewpoint of the contrast ratio.

FIG. 2B schematically shows a cut-off state of the encoder device shown in FIG. 1, and portions corresponding to the transmission state shown in FIG. 1A are denoted by corresponding reference numerals. When the movable plate 2 moves by P / 2 from the transmission state shown in (A), the state shown in (B) is reached. At this time, although not shown, the parallel light transmitted through the entrance slit 1FS is completely blocked by the moving plate 2. As shown in the figure, the oblique light transmitted through the entrance slit 1FS and the moving slit 2S is completely blocked by the stationary plate 1R on the exit side without passing through the exit slit 1RS. Accordingly, there is almost no leakage of the light beam in the cutoff state, and the ratio (contrast ratio) of the amount of received light in the transmission state and the cutoff state becomes extremely high. this is,
This is because the arrangement pitch of the entrance slit 1FS and the exit slit 1RS is set to twice the arrangement pitch of the moving slit 2S.

FIG. 3 shows a reference example of the encoder device, and portions corresponding to those in FIG. 2 are denoted by corresponding reference numerals to facilitate understanding. As shown in the drawing, in this reference example, the arrangement pitch of the entrance slit 1FS and the exit slit 1RS is the same as the arrangement pitch of the moving slit 2S.
It has become. In the transmission state shown in (A), the parallel light sequentially passes through the entrance slit 1FS, the moving slit 2S, and the exit slit 1RS, and reaches the light receiving element side. On the other hand, (B) shows a cutoff state. Although not shown, the parallel light from the light emitting element does not reach the light emitting element because it is blocked by the moving plate 2 after passing through the entrance slit 1FS. However, a part of the oblique light passing through the entrance slit 1FS is moved by the moving slit 2S and the exit slit 1RS.
To reach the light-emitting element side, causing a light flux leak. As a result, the light-blocking state is not completely dark but rather light, so that the contrast ratio deteriorates. This is because the arrangement pitch of the entrance slit 1FS and the exit slit 1RS is set to be the same as the arrangement pitch of the moving slit 2S.

FIG. 4 is a schematic diagram for explaining the operation of the encoder device according to the present invention shown in FIG. The difference from the schematic diagram shown in FIG. 2 is that the position of the moving plate 2 is not exactly between the fixed plate 1F on the incident side and the fixed plate 1R on the emitting side, but the moving plate 2 moves up and down and the fixed plate on the incident side. This shows a state approaching 1F. In the illustrated example, assuming that the interval between the fixed plate 1F on the incident side and the fixed plate 1R on the output side is 1, the moving plate 2 is located at a height of about ／. At this time, in the transmission state shown in (A), the parallel light passes through the entrance slit 1FS, the moving slit 2S, and the exit slit 1RS, and reaches the light receiving element side. On the other hand, in the cut-off state shown in FIG. 2B, unlike the cut-off state shown in FIG. 2B, a part of the oblique light radiated from the light emitting element passes through the entrance slit 1FS, the moving slit 2S, and the exit slit 1RS. It passes and reaches the light receiving element. As shown in FIG. 2A, in the cutoff state, unlike FIG. 2A, the oblique light is blocked by the fixed plate 1R on the emission side and does not reach the light emitting element. As described above, if the height of the moving plate 2 is shifted from the middle, light leakage occurs.
The contrast ratio tends to be lower than when the moving plate shown in FIG. 2 is located just in the middle.

FIG. 5 is a graph showing the relationship between the height position of the moving plate and the contrast. The moving plate height position divides the distance between the fixed plate on the incident side and the fixed plate on the output side into eight equal parts, and each equal part is represented by numerical values 0 to 8. The contrast represents the ratio of the amount of received light in the transmission state and the light reception state.
Is the minimum contrast. Also, the graph of FIG.
The arrangement pitch of the entrance slit and the exit slit is taken as a parameter, and the cases of 1P, 2P, 3P and 4P are graphed. As shown in the drawing, when the arrangement pitch of the slits formed in the fixed plate is 1P, the contrast increases when the moving plate is close to the fixed plate on the incident side or the output side. However, the contrast decreases as the moving plate is moved away from the fixed plate, and the contrast becomes minimum just in the middle between the fixed plate on the incident side and the fixed plate on the output side. Therefore, when the arrangement pitch of the fixed slits is 1P, it is preferable that the movable plate is disposed as close to the fixed plate as possible. However, if the distance is too close, the movable plate comes into contact with the fixed plate. Further, there is a possibility that the movable plate may come into contact with the fixed plate due to the vertical movement thereof, and it is very difficult to perform positioning. On the other hand, when the arrangement pitch of the fixed slits is 2P, the contrast is improved when the moving plate is close to the fixed plate and when the moving plate is located exactly in the middle of the pair of fixed plates. However, when the movable plate is located at a position 1/4 or 3/4 of the distance between the pair of fixed plates, the contrast is reduced. This is as described in FIG. Further, when the arrangement pitch of the fixed slits is 3P, the contrast is best when the movable plate is at 2/6, 4/6 of the distance between the pair of fixed plates.
The contrast becomes worse at the positions of 1/6, 3/6, and 5/6. Further, when the arrangement pitch of the fixed slits is 4P,
The moving plate is 2/8, 4/8, 6/8 of the distance between the pair of fixed plates.
, The contrast is best, but 1/8, 3 /
The contrast becomes low at the positions of 8, 5/8 and 7/8. As shown in the graph of FIG. 5, as the arrangement pitch of the fixed slits increases, the fluctuation of the contrast depending on the height position of the moving plate becomes more intense. Most preferably, it is set almost at the middle of the fixing plate. In some cases, the parallel pitch of the fixed slits may be an odd multiple of the pitch of the moving slits, such as 3P, while the moving plate may be arranged at 2/6 or 4/6 of the pair of upper and lower fixed plates. It is possible. Also, the arrangement pitch of the fixed slits may be an even multiple of the arrangement pitch of the moving slits, such as 4P, and the moving plate may be arranged substantially at the center of the pair of upper and lower fixed plates.

FIG. 6 is a schematic perspective view showing a second embodiment of the encoder device according to the present invention. Parts corresponding to those of the first embodiment shown in FIG. 1 are given the corresponding reference numerals to facilitate understanding. While the first embodiment is a linear encoder device, the present embodiment is a rotary encoder device. That is, the moving plate 2 is formed of a disk that is rotatable about a rotation axis indicated by a dashed line, and the rows of the slits 2S are arranged along the circumferential direction of the disk. Also in this case, the arrangement pitch of each of the entrance slit 1FS formed on the entrance-side fixed plate 1F and the exit slit 1RS formed on the exit-side fixed plate 1R is twice that of the moving slit 2S. However, in the case of a rotary encoder, the arrangement pitch of each slit is measured at angular intervals.

FIG. 7 is a schematic perspective view showing a third embodiment of the encoder device according to the present invention. Parts corresponding to those of the first embodiment shown in FIG. 1 are given the corresponding reference numerals to facilitate understanding. The first embodiment is a transmission type linear encoder device, while the present embodiment is a reflection type linear encoder device. That is, the moving plate 2
It has a row of reflective slits 2S that reflect a light beam incident from the light emitting element 6 and emit it to the light receiving element 5 located on the same side. The reflection type slit 2S is obtained by forming a reflection film at a predetermined arrangement pitch P on the surface of the movable plate 2 that absorbs or diffuses light. In the present embodiment, the light emitting element 6 and the light receiving element 5 are arranged in parallel along a direction orthogonal to the direction of linear movement of the moving plate 2 indicated by the arrow. In this case, the fixed plate 1 also serves as a fixed plate on the incident side and a fixed plate on the output side, and is shared by the parallel light emitting element 6 and light receiving element 5. The arrangement pitch of the fixed slits 1S formed on the fixed plate 1 is twice the pitch of the movable slits 2S formed on the movable plate 2. In the case of a reflective encoder device, the distance between the incident optical path from the fixed plate 1 to the movable plate 2 and the reflected optical path from the movable plate 2 to the fixed plate 1 is always equal. Therefore, even if the distance between the fixed plate 1 and the movable plate 2 changes,
In the transmission type encoder, the same effect as in the case where the position of the movable plate is located exactly in the middle between the incident side fixed plate and the emission side fixed plate is obtained, and an output with good contrast is always obtained.

FIG. 8 shows a fourth embodiment of the encoder device according to the present invention, in which parts corresponding to those of the third embodiment shown in FIG. ing. As in the third embodiment, this embodiment is also a reflective linear encoder device. The difference from the third embodiment is that the light emitting element 6 and the light receiving element 5 are arranged in parallel along a direction parallel to the moving direction of the moving plate 2. Correspondingly, the entrance side slit 1FS and the exit side slit 1RS are arranged on the fixed plate 1 along a direction parallel to the moving direction. In some cases, the light receiving elements 5 and the light emitting elements 6 can be arranged in a direction intersecting with the moving direction of the moving plate 2.

[0017]

As described above, according to the present invention, even in a high-resolution encoder device, in the case of the transmission type, the fixing plate provided on the light emitting element side and the fixed plate provided on the light receiving element side are located almost in the middle. By disposing the moving plate, an output with good contrast can be obtained. In the case of the reflection type, an output with good contrast can be obtained without being affected by the distance between the fixed plate and the movable plate. As a result, it is possible to obtain an encoder device that is easy to assemble and is less susceptible to the influence of the flatness and surface runout of the movable plate.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a first embodiment of an encoder device according to the present invention.

FIG. 2 is a schematic diagram for explaining the operation of the encoder device shown in FIG. 1;

FIG. 3 is a schematic diagram illustrating a reference example of an encoder device.

FIG. 4 is a schematic diagram for explaining the operation of the encoder device shown in FIG. 1;

FIG. 5 is a graph showing a relationship between a height of a moving plate and a contrast.

FIG. 6 is a perspective view showing a second embodiment of the encoder device according to the present invention.

FIG. 7 is a perspective view showing a third embodiment of the encoder device according to the present invention.

FIG. 8 is a perspective view showing a fourth embodiment of the encoder device according to the present invention.

[Explanation of symbols]

1F: fixed plate, 1R: fixed plate, 1FS: slit, 1RS: slit, 2: moving plate, 2S
... Slit, 5 ... Light receiving element, 6 ... Light emitting element

Claims (7)

[Claims] A moving plate provided with a row of slits arranged movably along a predetermined moving direction and arranged at a predetermined pitch along the moving direction; A light emitting element for incident a light beam on the row of slits passing therethrough; a light receiving element for receiving the light beam emitted from the row of slits and outputting an electric signal according to the movement of the moving plate; And a fixed plate on the incident side in which a plurality of entrance slits are arranged between the moving plate and the movable plate to selectively transmit the light beam; and the light beam is selectively interposed between the light receiving element and the moving plate. An emission side fixed plate in which a plurality of exit slits are arranged, the arrangement pitch of the entrance slits and the arrangement pitch of the exit slits are the same as those of the rows of the slits formed in the moving plate. Double the pitch or this The encoder apparatus characterized by is set to an integer multiple. 2. The encoder device according to claim 1, wherein the movable plate is formed of a rotatable disk, and the rows of the slits are arranged along a circumferential direction of the disk. 3. The moving plate according to claim 1, wherein the movable plate has a row of transmissive slits for transmitting a light beam incident from the light emitting element and emitting the light beam to the light receiving element located on the opposite side. Encoder device. 4. The arrangement pitch of the entrance slits and the arrangement pitch of the exit slits are set to an even multiple of the arrangement pitch of the rows of slits formed on the moving plate, and the moving plates are arranged on opposite sides. 4. The encoder device according to claim 3, wherein the distance between the incident-side fixed plate and the output-side fixed plate is approximately two. 5. The arrangement pitch of the entrance slits and the arrangement pitch of the exit slits are set to an even multiple of the arrangement pitch of the rows of slits formed on the moving plate, and the moving plate is arranged to be separated from the light emitting element. 2. The encoder device according to claim 1, further comprising a row of reflective slits for reflecting the incident light beam and emitting the light beam to the light receiving element located on the same side. 6. The light emitting element and the light receiving element are arranged in parallel along a direction orthogonal to the moving direction of the moving plate, and the fixed plate on the incident side and the fixed plate on the emitting side are arranged in parallel with each other. 6. The encoder device according to claim 5, wherein the encoder device is shared by the light receiving element and the light receiving element. 7. The light-emitting element and the light-receiving element are arranged in parallel along a direction parallel to a moving direction of the moving plate,
The encoder device according to claim 5, wherein the entrance slit and the exit slit are also arranged along a direction parallel to the moving direction.