JP2003344111A - Encoder device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an encoder device with fewer amplitude fluctuation of a signal output from a photodetector capable of measuring an amount of rotation with high accuracy, even when a space between a rotation plate and a fixing plate fluctuates. <P>SOLUTION: On a plate 1F at a center among three plates, a slit 1FS with a pitch P is notched radially with a rotating axis as a center and equally divided by resolution in a range contributing to the output of the photodetector 5 around a point crossing with an optical axis. On a plate 1R at one side, a slit 1RS with a pitch 2P twice as much as that of the slit 1FS on the central plate 1F is notched. On a plate 2 at another side, a slit 2S with a pitch 2P twice as much as that of the slit 1FS on the central plate 1F is notched radially with the rotating axis as the center extending over a circumference thereof. The plate 2 with the slit 2S notched extending over the circumference is rotated with the rotating axis, and the plates 1F, 1R are fixed where the remaining two slits 1FS, 1RS are notched. <P>COPYRIGHT: (C)2004,JPO

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a rotary encoder device for optically detecting a rotational movement amount of a mechanical part. More specifically, it relates to a slit structure of a rotating plate and a fixed plate constituting an encoder device. [0002] A conventional encoder device basically comprises a rotating plate, a light emitting element, a light receiving element and a fixed plate. Various conventional structures are disclosed in, for example, JP-A-9-133552, JP-A-11-183201, and JP-A-11-212505.
And Japanese Patent Application Laid-Open No. 11-325973. The rotating plate has a row of slits arranged at a predetermined arrangement pitch along the circumferential direction. The light-emitting element makes a light beam incident on a row of slits that pass with the rotation of the rotating plate. The light receiving element receives the light beam emitted from the row of slits and outputs an electric signal according to the rotation of the rotating plate. The fixed plate on the incident side is provided between the light emitting element and the rotating plate and has an incident slit for selectively transmitting a light beam. The emission-side fixed plate includes an emission slit that is interposed between the light receiving element and the rotating plate and selectively transmits a light beam. [0003] Generally, a slit formed in a rotating 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 equal to or smaller than the width of the slit formed in the rotating plate. Typically, a plurality of slits are formed in the rotating plate in a row, while a single slit is formed in the fixed plate. The incident side fixed plate with one slit is placed between the rotating plate and the light emitting element, and the emitting side fixed plate also with one slit is placed between the rotating plate and the light receiving element. Thus, an effective light beam can be formed from the light emitting element to the light receiving element. The rows of slits cut on the rotating plate transmit /
By repeating blocking or reflection / absorption, a signal representing the amount of movement of the rotating 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 rotary 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 rotary 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 rotating 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 rotating plate. However, when the number of slits in the fixed plate is increased, the ratio between the amount of light transmitted by the rotating plate and the amount of light blocked by the rotary plate is reduced, resulting in a problem that the contrast is reduced. As the distance between the rotating 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] To solve the above-mentioned problems of the prior art, the following means have been taken. That is, a pair of light receiving elements and a light emitting element are arranged facing each other on an optical axis parallel to a predetermined rotation axis, and three plates with slits are arranged between the light receiving element and the light emitting element. An optical mono-tally encoder device having a plate located at the center of the three plates has a resolution within a range contributing to the output of the light receiving element in the vicinity of the rotation axis and radially and intersecting the optical axis. A plurality of slits having a pitch equally divided by the above are engraved, and one of the plates located on both sides of the three contributes to the output of the light receiving element in the vicinity radially around the rotation axis and near the optical axis. In the range, the slit is cut at a pitch twice as large as the pitch of the slit cut on the center plate.
The other of the plates located on both sides of the sheet is radially centered on the rotation axis and over the entire circumference, slits are carved at twice the pitch of the slit carved on the central plate, and over the entire circumference The plate on which the slit is cut rotates with the rotation shaft, and the plate on which the remaining two slits are cut is fixed. According to the present invention, the arrangement pitch of the entrance slits formed on the plate located on the entrance side and the arrangement pitch of the exit slits formed on the plate located on the exit side are formed on the plate located at the center. It is set to twice the arrangement pitch of the slit rows. This makes it possible to effectively block or absorb the light beam by the rotating plate, thereby suppressing light beam leakage. It becomes difficult for an invalid light beam, which is transmitted or reflected at a timing at which the light beam incident from the light emitting element should be blocked or absorbed, to reach the light receiving element side. Therefore, even in a high-resolution rotary encoder device,
It is possible to sufficiently secure the interval between the three plates while suppressing the leakage of the invalid light flux. In particular, the plate located at the center is fixed, and one of the plates located on both sides is rotated to suppress signal fluctuation due to height fluctuation of the rotating plate. That is, even when the distance between the rotating plate and the fixed plate fluctuates due to the movement of the rotating plate, the amplitude of the signal output from the light receiving element hardly fluctuates, and the rotation amount can be measured with high accuracy. Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic perspective view showing an embodiment of the optical rotary encoder device according to the present invention. As shown in the figure, in the present optical rotary encoder device, a pair of light receiving elements 5 and light emitting elements 6 are arranged to face each other on an optical axis parallel to a predetermined rotation axis, and have an even resolution. Here, the resolution means the total number of rotational positions that can be identified by the rotary encoder device. Three plates having slits are arranged between the light receiving element 5 and the light emitting element 6. Plate 1F located at the center of the three
Is a plurality of slits 1FS (three in the illustrated example) having a pitch P equally divided with a resolution within a range contributing to the output of the light receiving element 5 in a vicinity radially intersecting the optical axis with respect to the rotation axis. Carved. One of the two plates 1R located on both sides is a slit 1FS cut in the central plate 1F in a range radially centering on the rotation axis and contributing to the output of the light receiving element 5 near the intersection with the optical axis. The slits 1R are formed at a pitch 2P that is twice as large as the pitch P. The other plate 2 of the two plates located on both sides is a slit 1FS cut in the center plate 1F radially around the rotation axis and over the entire circumference.
The slit 2S is carved at a pitch 2P twice as large as the pitch P of FIG. The plate 2 on which the slit 2S is engraved over the entire circumference rotates with the rotation axis, while the plates 1F and 1R on which the remaining two slits are engraved are fixed. Hereinafter, the rotating plate 2 is referred to as a rotating plate in this specification. In the present embodiment, since the slit 2S formed in the rotating plate 2 is located on the incident side facing the light emitting element 6, it may be referred to as an entrance slit. Further, since the plate 1F disposed at the center is fixed, it may be hereinafter referred to as a fixed plate. The pitch P of the slits 1FS formed in the fixed plate 1F corresponds to a value obtained by equally dividing 360 degrees with the resolution as described above. Remaining board 1
Since R is also fixed, it may be hereinafter referred to as a fixing plate in this specification. The slit 1 formed in this fixing plate 1R
The pitch of the RS is twice the pitch P of the slit 1FS formed in the fixed plate 1F as described above. Since the slit 1RS formed in the fixed plate 1R faces the light receiving element 5, it may be hereinafter referred to as an emission slit. The light receiving element 5 includes, for example, a phototransistor, receives a light beam emitted from the slit 1RS, and outputs an electric signal according to the movement of the rotating plate 2. On the other hand, the light emitting element 6 is, for example, L
The luminous flux is incident on a row of slits 2 </ b> S made of an ED and passing with the rotation of the rotating plate 2. The rotary plate 2 and the fixed plates 1F and 1R are often cut out by etching or pressing using a light-shielding plate mainly made of metal, resin, or the like. Alternatively, a light-shielding film may be formed to form a slit. FIG. 2 is a schematic view for explaining the operation of the optical rotary encoder device shown in FIG. (A)
Indicates a transmission state of the encoder device, and a light beam emitted from the light emitting element passes through the rotary plate 2, the fixed plate 1F, and the fixed plate 1R and reaches the light receiving element as shown by an arrow. In the transmission state, the entrance slit 2S formed in the rotating plate 2 is aligned with the intermediate slit 1FS and the exit slit 1RS. However, the arrangement pitch of the entrance slit 2S and the exit slit 1RS is 2P, and the arrangement pitch of the intermediate slits 1FS is P, which is half of that. Also, the rotating plate 2 and the fixed plate 1R
Of the rotation plate 2 and the fixed plate 1
Another fixing plate 1F is arranged in the middle of R. 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. Therefore, the amount of light received by the light receiving element in the transmission state is increased by the parallel light and the oblique light, so that the amplitude of the output signal increases,
This 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 rotating plate 2 moves by P from the transmission state shown in (A), the state shown in (B) is reached. At this time, the parallel light transmitted through the entrance slit 2S is completely blocked by the fixed plate 1R. Also, the entrance slit 2S and the intermediate slit 1
The oblique light transmitted through the FS is completely blocked by the fixed plate 1R on the output side without passing through the output 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 because the arrangement pitch of the entrance slit 2S and the exit slit 1RS is set to twice the arrangement pitch of the intermediate slits 1FS. FIG. 3 shows a conventional example of an optical rotary encoder device. Parts corresponding to those in FIG. 2 are denoted by corresponding reference numerals to facilitate understanding. As shown in the figure, in this conventional example, the arrangement pitch of the entrance slit 1FS and the exit slit 1RS is P, which is the same as the arrangement pitch of the rotary slit 2S. In the transmission state shown in (A), the parallel light passes through the entrance slit 1FS and the rotary slit 2
S, the light sequentially passes through 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 rotating plate 2 after passing through the entrance slit 1FS. However, the entrance slit 1F
Part of the oblique light passing through S passes through the rotation slit 2S and the emission slit 1RS, reaches the light emitting element side, and leaks a light beam. As a result, the light-blocking state is not completely dark but rather light, so that the contrast ratio deteriorates. This is because the entrance slit 1FS and the exit slit 1
This is because the arrangement pitch of the RS is set to be the same as the arrangement pitch of the rotary slit 2S. FIG. 4 is a schematic perspective view showing a reference example of the optical rotary encoder device. This reference example
This is an invention according to a prior application (Japanese Patent Application No. 2000-374016) of the same applicant. To facilitate understanding, parts corresponding to the embodiment of the present invention shown in FIG. 1 are denoted by corresponding reference numerals. The difference is that the plate 1F located on the incident side is not a rotating plate but a fixed plate as in the present invention. Instead, the plate 2 arranged in the center is a rotating plate. This is a normal structure in which the center rotating plate 2 is sandwiched between the fixed plates 1F and 1R on both sides. However, regarding the slit pitch, the present invention and the reference example are the same, and the pitch of the entrance slit 1FS and the exit slit 1RS on both sides is 2P, while the pitch of the intermediate slit 2S is P. This relationship is similar to that of the embodiment of the present invention shown in FIG. FIG. 5 is a schematic diagram for explaining the operation of the encoder device according to the reference example shown in FIG. (A) shows a transmission state of the encoder device, and a light beam emitted from the light emitting element passes through the incident-side fixed plate 1F, the rotating plate 2, and the emission-side fixed plate 1R and reaches the light receiving element as indicated by an arrow. In the transmission state, the slit 2S formed in the rotating plate is aligned with the entrance slit 1FS and the exit slit 1RS.
However, the arrangement pitch of the entrance slit 1FS and the exit slit 1RS is 2P, and the arrangement pitch of the rotary slit 2S is P, which is half of that. The distance between the incident side fixed plate 1F and the output side fixed plate 1R is substantially equal to 2P.
The rotary plate 2 is arranged just in the middle between F 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 rotary 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 rotating plate 2. As shown in the figure, the oblique light transmitted through the entrance slit 1FS and the rotation 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 rotary slit 2S. FIG. 6 is a schematic diagram for explaining the operation of the encoder device according to the reference example also shown in FIG. FIG.
Is that the position of the rotating 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 rotating plate 2 moves up and down to the fixed plate 1F on the incident side. It represents the approaching state. In the illustrated example, assuming that the distance between the fixed plate 1F on the incident side and the fixed plate 1R on the output side is 1, the rotating 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 rotation 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. 5B, unlike the cut-off state shown in FIG. 5B, a part of the oblique light emitted from the light emitting element passes through the entrance slit 1FS, the rotating slit 2S, and the exit slit 1RS. It passes and reaches the light receiving element. As shown in FIG. 5A, in the cutoff state, unlike FIG. 5A, 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, when the height of the rotating plate 2 is shifted from the middle, light leakage occurs. Therefore, the contrast ratio tends to be lower than when the rotating plate shown in FIG. 5 is located at the middle. . FIG. 7 is a graph showing the relationship between the height position of the rotating plate and the contrast in the reference example. The rotary plate height position is divided into eight equal parts between the fixed plate on the incident side and the fixed plate on the output side, 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 amount in the cutoff state, and 1.0 is set as the maximum contrast and 0.0 is set as the minimum contrast as a relative memory. Further, the graph of FIG. 7 takes the arrangement pitch of the entrance slit and the exit slit as a parameter and graphs the case of 1P and 2P. As shown in the drawing, when the arrangement pitch of the slits formed in the fixed plate is 1P, the contrast increases when the rotating plate is close to the fixed plate on the incident side or the output side. However, the contrast decreases as the rotating 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 rotating plate be disposed as close to the fixed plate as possible. However, if the distance is too close, the rotating plate comes into contact with the fixed plate. In addition, there is a possibility that the rotating plate may come into contact with the fixed plate due to the vertical movement, and it is very difficult to perform positioning. On the other hand, when the arrangement pitch of the fixed slits is 2P, when the rotating plate is close to the fixed plate and when the rotating plate is located exactly in the middle of the pair of fixed plates, the contrast is improved. However, when the rotating 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. As described above, in the reference example shown in FIG. 4, when the relative distance between the fixed plate and the rotary plate changes with the rotation of the rotary plate, the output amplitude changes. When the distance between the rotating plate and the fixed plate changes, the larger the distance between the fixed plates, the smaller the fluctuation in the output amplitude. However, when the distance between the two fixing plates increases, the distance between the light receiving and emitting elements substantially increases, and the output amplitude decreases. In view of this point, the present invention relates to a signal amplitude variation due to a change in the distance between the rotating plate and the fixed plate caused by rotation due to the assembling accuracy of the distance between the rotating plate and the fixed plate and the perpendicularity of the rotating plate to the rotation axis. Can be suppressed, and will be described below. In the reference example shown in FIG. 4, a fixed plate having slits of double pitch is formed on both sides of the light receiving element and the light emitting element, and the rotary plate is rotated at an intermediate position between the fixed plates. . On the other hand, in the encoder device of the present invention shown in FIG. 1, the rotating plate (the predetermined pitch P depending on the resolution) of the reference example is used.
Is formed as a fixed plate, and one of the plates having a double pitch slit is used as a rotating plate instead. In short, the structure in which the double-pitch slit is formed and the structure in which the single-pitch slit is sandwiched from both sides remains the same, but in the reference example, the single-pitch slit formed plate rotates. On the other hand, in the present invention, the plate on which the double pitch slits are formed is rotating. As a result, an optical rotary encoder device that is less susceptible to surface runout due to rotation of the rotating plate than the reference example can be obtained. Hereinafter, a quantitative explanation will be added to this point. As described above, the height of the surface of the rotary plate of the rotary encoder fluctuates with the rotation due to the distortion of the rotary encoder itself and the inclination of the assembly to the rotary shaft. If the height of the rotating plate does not fluctuate ideally, the distance between the double pitch slit on the light emitting element side and the double pitch slit on the light receiving element side is W, and 1
The height H of the double pitch slit is H = W / 2 based on the double pitch slit on the light receiving element side, and the ratio H
/ W is as follows. H / W = (W / 2) / W = 1/2 When the height of the rotating plate fluctuates ± dW / 2 in the structure of the reference example, Hmax / W and Hmin / W are Hmax / W = (W / 2 + dW). / 2) / W Hmin / W = (W / 2−dW / 2) / W, and the ratio change dR is as follows. dR = Hmax / W-Hmin / W = dW / W (1) In the present invention, since one of the double pitch slits rotates, for example, when the double pitch slit on the light emitting element side rotates, H = W / 2, so H / Wmax
And H / Wmin are H / Wmax = (W / 2) / (W−dW / 2) H / Wmin = (W / 2) / (W + dW / 2), and the ratio change dR is as follows. dR = H / Wmin-H / Wmax = (dW / W) /
^{(2-dW 2 / W 2} /2) where, smaller to the extent that dW can be ignored than the W,
Assuming that dW ² / W ² = 0, the following equation is obtained. dR = (dW / W) / 2 Equation 2 As is apparent from Equations 1 and 2, the change in the ratio due to the height fluctuation of the rotating plate is suppressed to about 1/2 compared to the reference example by the present invention. You. As described above, according to the present invention, a high-resolution output can be obtained even in a high-resolution optical rotary encoder device. Also, an optical rotary encoder device that is easy to assemble and is less susceptible to the effects of the flatness and surface runout of the rotating plate can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an embodiment of an optical rotary 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 showing a conventional example of an encoder device. FIG. 4 is a perspective view showing a reference example of the optical rotary encoder device. FIG. 5 is a schematic diagram for explaining the operation of the encoder device shown in FIG. 4; FIG. 6 is a schematic diagram for explaining the operation of the encoder device shown in FIG. 4; FIG. 7 is a graph showing the relationship between the height of the rotating plate and the contrast in the reference example. [Description of Signs] 1F: fixed plate, 1R: fixed plate, 1FS: slit, 1RS: slit, 2: rotating plate, 2S
... Slit, 5 ... Light receiving element, 6 ... Light emitting element

Claims (1)

Claims 1. A pair of light receiving elements and a light emitting element are opposed to each other on an optical axis parallel to a predetermined rotation axis, and a plate having a slit between the light receiving element and the light emitting element has a thickness of 3 mm. An optical mono-tally encoder device having an even number of resolutions, wherein a plate located at the center of the three is a light-receiving element in the vicinity of being radially centered on the rotation axis and intersecting the optical axis. In the range contributing to the output of the above, a plurality of slits having a pitch equally divided with the resolution are cut, and one of the plates located on both sides of the three is radially centered on the rotation axis and intersects the optical axis. Slits are cut at a pitch twice the pitch of the slit cut in the center plate in a range that contributes to the output of the light receiving element in the vicinity. The other of the plates located on both sides of the three plates is a rotating shaft. Radially around the center The slits are carved at twice the pitch of the slits carved on the board. The board on which the slits are carved around the entire circumference rotates with the rotation shaft, and the board with the remaining two slits is fixed. An optical mono-tally encoder device.