JP2005043327A - Absolute encoder and angle detecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an absolute encoder and an angle detecting method capable of detecting accurately an absolute value of a rotation angle of a rotary shaft. <P>SOLUTION: The first track 8a for correction is provided in the side most sided to a rotary shaft 2 of a track group 10, and the second track 8b for correction is provided in the side most distant from the rotary shaft 2, in a rotary disk 3 of the encoder 1. A charge reading-out part for a photodetecting part 6 of an optical sensor 5 reads out charges from a picture element within an area including the first incident position of light passed through the track 8a for the correction, and a picture element within an area including the second incident position of light passed through the second track 8b for the correction, as correction data, as to the incident positions of the light, and then reads out a charge from a picture element within an area including an incident position of light passed through tracks 9a-9i for angle detection, as a data for the angle detection. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an absolute encoder and an angle detection method for detecting an absolute value of a rotation angle of a measurement object.

  Conventionally, rotary encoders have been used for angle measurement of control ends (steering) of machine tools, FA devices, automobiles, and the like. Of the rotary encoders, in particular, an incremental method and an absolute method are widely known as an angle detection method of an optical rotary encoder. Absolute type rotary encoders (hereinafter referred to as absolute encoders) are generally highly accurate and have the advantage that errors do not accumulate.

  FIG. 15 is a perspective view showing a conventional absolute encoder. Referring to FIG. 15, a conventional absolute encoder 100 is attached to a rotating shaft 110 of a rotating body. The absolute encoder 100 includes a rotating plate 101 on which a gray code pattern 102 is provided, and a fixed plate 105 disposed to face the rotating plate 101 in the axial direction. The pattern 102 of the rotating plate 101 is composed of a plurality of tracks having predetermined slits, and the fixed plate 105 has a plurality of windows 104 corresponding to the plurality of tracks of the pattern 102. The light emitting element 103 and the light detecting element 106 are arranged to face each other with the rotating plate 101 and the fixed plate 105 interposed therebetween. The light detection element 106 includes a plurality of light detection units corresponding to a plurality of tracks of the rotating plate 101.

  When the slit of the rotating plate 101 and the window 104 of the fixed plate 105 overlap on a straight line connecting the light emitting element 103 and the light detecting unit of the light detecting element 106, the light from the light emitting element 103 passes through the rotating plate 101 and the fixed plate 105. The light passes through and enters the light detection portion of the light detection element 106. On the other hand, when the slit of the rotating plate 101 and the window 104 of the fixed plate 105 do not overlap, the light from the light emitting element 103 is blocked by the rotating plate 101 and does not enter the light detection unit of the light detecting element 106. Then, the light detection result in each light detection unit of the light detection element 106 is encoded and output as Gray codes G0 to G4 representing the absolute value of the rotation angle of the rotation shaft 110.

The technology related to the absolute encoder is also disclosed in the following Patent Document 1 and Patent Document 2.
Japanese Patent Application Laid-Open No. 07-311055 Japanese Patent Application Laid-Open No. 08-086667

  In the conventional absolute encoder 100 shown in FIG. 15, the light irradiated from the light emitting element 103 to the rotating plate 101 has a certain spread. Therefore, when the positional relationship between the rotating plate 101 and the light detecting element 106 changes as the rotating plate 101 rotates, the incident position of the light that has passed through the slit of the rotating plate 101 on the light detecting element 106 is It will shift | deviate with respect to the position of the light detection part of the corresponding light detection element 106. FIG. The same applies to the case where the rotating plate 101 is eccentrically attached to the rotating shaft 110. Therefore, in these cases, there is a possibility that the absolute value of the rotation angle of the rotating shaft 110 cannot be accurately detected.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an absolute encoder and an angle detection method capable of accurately detecting the absolute value of the rotation angle of the rotation shaft.

  In order to achieve such an object, an absolute encoder according to the present invention includes (1) a rotating shaft, and (2) a plurality of tracks attached to the rotating shaft and having slits of a predetermined pattern formed in the circumferential direction. And a plurality of tracks each including a rotation plate including a plurality of angle detection tracks and correction tracks, and (3) a light detection unit in which a plurality of pixels are arranged one-dimensionally, and the light detection unit has a diameter of the rotation plate. (4) a light sensor provided to face a plurality of tracks with the direction as a longitudinal direction, and (4) a light source provided to face a light detection unit of the light sensor across the plurality of tracks of the rotating plate, 5) Read-out means for reading out charges from each of the plurality of pixels constituting the light detection unit of the photosensor. (6) The plurality of tracks serve as correction tracks as light sources regardless of the rotation angle of the rotating plate. Including a first correction track and a second correction track in which a slit is arranged between the detection unit and (7) the reading unit is an incident position at which light that has passed through the plurality of tracks enters the light detection unit With respect to the pixels in the first pixel region including the first incident position where the light having passed through the slit of the first correction track is incident on the plurality of pixels constituting the light detection unit, the second correction A pixel in the second pixel region including a second incident position where light passing through the slit of the track enters, and a third pixel region including an incident position where light passing through the slits of the plurality of angle detection tracks are incident Charges are read in the order of pixels.

  In the absolute encoder described above, the light that has been irradiated from the light source and passed through the slit of the first correction track and the light that passed through the slit of the second correction track are detected by the light detection unit of the optical sensor. Detects regardless of the rotation angle. Therefore, according to this absolute encoder, out of the incident positions of the light that has passed through the plurality of tracks in the light detection unit of the optical sensor, the first incident position with respect to the first correction track and the second incident position with respect to the second correction track. 2 incident positions can always be obtained regardless of the rotation angle of the rotating plate. Therefore, even when the position of the rotating plate changes, the corrected incident positions for the plurality of angle detection tracks are estimated with reference to the first incident position and the second incident position. Thus, it is possible to accurately detect the presence or absence of the slit of each angle detection track on the light detection unit based on the incident state of the light at the incident position. Therefore, the absolute value of the rotation angle of the rotating shaft can be accurately measured.

  Furthermore, in the above-described encoder, for reading out the electric charges generated in each of the plurality of pixels of the photosensor, the area corresponding to the first correction track, which is correction data, and the second correction track are supported. The charge is read from each pixel in the area first, and subsequently, the charge is read from each pixel in the area corresponding to the angle detection track as the angle detection data. As a result, it is possible to efficiently read out charges from the light detection unit of the photosensor and measure the rotation angle. Here, it is preferable that the encoder measures the absolute value of the rotation angle of the rotation shaft by detecting light that has passed through the slits of the plurality of angle detection tracks at the light detection unit of the optical sensor. Or it is good also as a structure which calculates | requires the absolute value of a rotation angle in the external device using the data obtained by the encoder.

  In the encoder, the rotating plate has one of the first correction track and the second correction track positioned closest to the rotation axis among the plurality of tracks, and the other positioned closest to the rotation axis. In addition, the reading means uses, as a first pixel area and a second correction track, a predetermined area including a pixel at an end on the side where the first correction track is located, for a plurality of pixels constituting the light detection unit. It is preferable that the charge is read out by setting the predetermined region including the pixel at the end on the side of the second pixel region as the second pixel region and the region sandwiched between the first pixel region and the second pixel region as the third pixel region.

  As described above, by arranging the two correction tracks on both ends of the plurality of tracks, it is possible to accurately correct the incident position with respect to the angle detection track using the correction track. Furthermore, by applying the above-described charge readout method in such a configuration, charge readout and rotation angle measurement can be performed despite the fact that the angle detection track is disposed between the two correction tracks. It becomes possible to execute efficiently.

  In this case, the reading unit sequentially reads out the charges from the end pixel on the side where the first correction track is located for the first pixel region, and performs predetermined reading based on the obtained first incident position. The first pixel area is defined up to the pixels, and the second pixel area is sequentially read out of the pixels at the end on the side where the second correction track is located, and based on the obtained second incident position. It is preferable that a predetermined pixel is the second pixel region.

  The encoder may further include incident position estimating means for estimating a corrected incident position for each of the plurality of angle detection tracks based on the first incident position and the second incident position. good. As a result, even when the position of the rotating plate changes, the presence or absence of slits of each angle detection track on the light detection unit can be accurately detected based on the light incident state on the estimated incident position. Can do.

  In this case, it is preferable that the incident position estimation unit estimates the corrected incident position for each of the plurality of angle detection tracks based on the interval between the first incident position and the second incident position. Thereby, the corrected incident position with respect to each of the plurality of angle detection tracks can be suitably estimated.

  The encoder is estimated by the incident position estimation means based on the intensity of the light that has passed through the first correction track and the light that has passed through the second correction track, detected by the light detection unit of the optical sensor. Further, it may be characterized by further comprising level determining means for determining whether or not the light detected at the incident position is light that has passed through the slit. Thereby, since the presence or absence of the slit of each angle detection track on the light detection unit can be determined more accurately, the absolute value of the rotation angle of the rotation shaft can be detected more accurately.

  An angle detection method according to the present invention is an angle detection method using the above-described absolute encoder, and includes (1) an irradiation step of irradiating light from a light source to a plurality of tracks on a rotating plate, and (2) a light detection unit. A first detection step of reading out charge from each of the pixels in the first pixel region among the plurality of pixels to detect light passing through the slit of the first correction track; and (3) a second pixel. A second detection step of reading out the charge from each of the pixels in the region and detecting the light that has passed through the slit of the second correction track; and (4) reading out the charge from each of the pixels in the third pixel region. And a third detection step of detecting light that has passed through the slits of the plurality of angle detection tracks.

  In the angle detection method described above, a plurality of pixels constituting the light detection unit of the optical sensor corresponding to the first correction track, the second correction track, and the angle detection track provided on the rotating plate. The charge is read from the first pixel region, the second pixel region, and the third pixel region in this order. Accordingly, accurate detection of the absolute value of the rotation angle of the rotation shaft using the plurality of tracks having the above configuration can be efficiently performed. Here, the angle detection method preferably includes (5) a code generation step of generating a code indicating the absolute value of the rotation angle of the rotating plate and the rotating shaft based on the detection result in the third detecting step.

  In addition, the angle detection method includes (6) a first incident position with respect to the first correction track and a second correction track with respect to the second correction track based on the detection results in the first detection step and the second detection step. Correction data acquisition step for obtaining two incident positions, and (7) correction for each of the plurality of angle detection tracks based on the first incident position and the second incident position obtained in the correction data acquisition step. (8) In the third detection step, it is preferable to detect light incident on the incident position estimated by the incident position estimation step.

  By estimating the incident position corrected in this way, even if the position of the rotating plate has changed, each angle detection on the light detection unit is detected based on the incident state of light at the estimated incident position. The presence or absence of a slit in the track can be accurately detected. Accordingly, it is possible to accurately generate a code indicating the absolute value of the rotation angle of the rotating plate, and to accurately detect the absolute value of the rotation angle of the rotation shaft.

  Further, in the third detection step, a threshold is set based on the intensity of the light that has passed through the first correction track and the light that has passed through the second correction track, and the intensity of the light detected at the incident position. It is also possible to determine whether or not the light detected at the incident position is light that has passed through the slit. Thereby, since the presence or absence of the slit of each angle detection track on the light detection unit can be determined more accurately, the absolute value of the rotation angle of the rotation shaft can be detected more accurately.

  In the incident position estimation step, the corrected incident position for each of the plurality of angle detection tracks may be estimated based on the interval between the first incident position and the second incident position. Thereby, the corrected incident position with respect to each of the plurality of angle detection tracks can be suitably estimated.

  According to the absolute encoder and the angle detection method of the present invention, the absolute value of the rotation angle of the rotation shaft can be detected accurately and efficiently.

  Hereinafter, preferred embodiments of an absolute encoder and an angle detection method according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the dimensional ratios in the drawings do not necessarily match those described.

  FIG. 1 is a perspective view showing an embodiment of an absolute encoder according to the present invention. Referring to FIG. 1, the absolute encoder 1 of this embodiment includes a rotating shaft 2, a rotating plate 3, a light emitting element 4, and an optical sensor 5. The rotating shaft 2 is attached to an object for detecting a rotation angle, and is supported by a housing of an absolute encoder 1 (not shown). The rotating plate 3 is a disk-shaped member made of, for example, metal or resin, and its center is attached to the rotating shaft 2 and fixed. The rotating plate 3 has a track group 10 composed of a plurality of tracks provided in the circumferential direction of the rotating plate 3, and slits 7 a and 7 b having a predetermined pattern are formed in each track of the track group 10. ing.

  The optical sensor 5 is means for detecting the light emitted from the light emitting element 4 and passing through the slit 7a and the light passing through the slit 7b and generating a charge Q according to the intensity of these lights. The optical sensor 5 has a light detection unit 6 in which a plurality of pixels are arranged one-dimensionally, and generates a charge Q in each pixel. Then, the optical sensor 5 outputs the charge Q generated by each of the plurality of pixels constituting the light detection unit 6 to the conversion unit 20 in a predetermined order. A method for outputting charges from the light detection unit 6 will be described later.

  As this optical sensor 5, a line image sensor etc. can be used, for example. The optical sensor 5 is provided such that the light detection unit 6 crosses the track group 10 of the rotating plate 3 when viewed from the direction of the rotating shaft 2 with the radial direction of the rotating plate 3 as the longitudinal direction. The light emitting element 4 is a point light source, and is disposed so as to face the light detection unit 6 of the optical sensor 5 with the track group 10 of the rotating plate 3 interposed therebetween. As the light emitting element 4, for example, an LED or the like can be used.

  FIG. 2 is a plan view showing a part of the rotating plate 3 shown in FIG. 1 in an enlarged manner. Referring to FIG. 2, the track group 10 includes a correction track group 8 including at least two correction tracks, and an angle detection track group 9 including a plurality of angle detection tracks. For example, in this embodiment, the track group 10 has 11 tracks, and two of them (the correction track group 8) include the correction track 8a that is the first correction track, and the second track. This is a correction track 8b which is a correction track. The other nine (angle detection track group 9) are angle detection tracks 9a to 9i. These 11 tracks are arranged at a substantially constant interval from each other.

  In the present embodiment, the plurality of tracks included in the track group 10 are arranged in the order of the first correction track 8a, the angle detection tracks 9a to 9i, and the second correction track 8b from the rotating shaft 2 side. Is arranged in. That is, in the encoder 1 shown in FIGS. 1 and 2, one correction track 8a is positioned closest to the rotation axis 2 among the plurality of tracks, and the other correction track 8b is positioned closest to the rotation axis 2. positioned.

  Each of the correction tracks 8a and 8b is formed with a slit 7b having a predetermined pattern in the circumferential direction. The slits 7b are formed so as to penetrate the rotating plate 3 in the thickness direction, and a plurality of slits 7b are formed in the circumferential direction of the rotating plate 3 in each correction track. The slits 7b of the correction track 8a and the slits 7b of the correction track 8b are arranged so that their circumferential positions are alternately arranged. The slits 7b are arranged so that at least one slit 7b exists between the light emitting element 4 and the light detection unit 6 in each of the correction tracks 8a and 8b regardless of the rotation angle of the rotating plate 3.

  Further, slits 7a representing a predetermined pattern such as a gray code are formed in the circumferential direction in the angle detection tracks 9a to 9i between the correction tracks 8a and 8b. The slit 7a is formed so as to penetrate the rotating plate 3 in the thickness direction similarly to the slit 7b. In this embodiment, nine angle detection tracks are set because a maximum of 512 codes can be generated by a nine-digit gray code, and therefore the rotation angle (0 degree to 360) of the rotating plate 3 is generated by the gray code. This is because the resolution when the rotation angle of the rotary shaft 2 is detected is 1 degree or less.

  Here, FIG. 3A is a side sectional view showing a relative positional relationship among the light emitting element 4, the rotating plate 3, and the optical sensor 5. FIG. 3B is a diagram for explaining the positional relationship between the irradiation regions 16 and 17 of the light that has passed through the slit 7 a and the light that has passed through the slit 7 b, and the light detection unit 6 of the optical sensor 5. . Referring to FIG. 3A and FIG. 3B, a part of the light L irradiated to the rotating plate 3 from the light emitting element 4 passes through the slit 7a or 7b to the light detection unit 6 of the light sensor 5. Reach. At this time, the light that has passed through the slits 7a of the angle detection tracks 9a to 9i forms irradiation regions 16 having a shape similar to the shape of the slits 7a on the lines 19a to 19i corresponding to the angle detection tracks 9a to 9i. To do. The light that has passed through the slits 7b of the correction tracks 8a and 8b forms an irradiation region 17 having a shape similar to the shape of the slit 7b on the lines 18a and 18b corresponding to the correction tracks 8a and 8b.

  Here, the lines 19 a to 19 i and 18 a and 18 b are fictitious lines on the surface whose distance from the rotating plate 3 is substantially equal to that of the light detection unit 6, and the irradiation regions 16 and 17 are formed on the light detection unit 6. This is an imaginary region formed on a surface whose distance from the rotating plate 3 is substantially equal to that of the light detection unit 6 except for the region to be formed. The light detection unit 6 detects light incident on the irradiation regions 16 and 17 on the light detection unit 6. Further, in the present embodiment, each line is positioned in the order of the line 18a, the lines 19a to 19i, and the line 18b from the rotating shaft 2 side, corresponding to the arrangement of the plurality of tracks described above.

  As shown in FIG. 3A, a predetermined distance D exists between the rotating plate 3 and the optical sensor 5. For this reason, the light L from the light emitting element 4 which is a point light source passes through the slit 7 a or 7 b of the rotating plate 3 and then enters the light detection unit 6 with a certain spread. Therefore, the distance between the lines 18 a, 19 a to 19 i, and 18 b shown in FIG. 3B is larger than the distance between the tracks of the rotating plate 3. Further, the irradiation areas 16 and 17 are larger than the slits 7a and 7b formed in the rotating plate 3, respectively.

4 (a) and 4 (b), and FIGS. 5 (a) and 5 (b) are for explaining the case where the position of the rotating plate 3 is changed relative to the light detection unit 6, respectively. FIG. 4A and 4B show a case where the rotating plate 3 approaches the light detection unit 6 and the distance between the rotating plate 3 and the light detection unit 6 becomes D _min . Here, D _min is a minimum allowable value of the distance set in consideration of a change in the distance between the rotating plate 3 and the light detection unit 6 due to a manufacturing error or the like. Thus, when the distance between the rotating plate 3 and the light detection unit 6 is reduced, the intervals between the lines 18a, 19a to 19i, and 18b are reduced, and the widths and lengths of the irradiation regions 16 and 17 are also reduced.

On the other hand, in FIGS. 5A and 5B, the rotating plate 3 moves away from the light detection unit 6 and the distance between the rotating plate 3 and the light detection unit 6 becomes D _max. Is shown. Here, D _max is a maximum allowable value of the distance set in consideration of a change in the distance between the rotating plate 3 and the light detection unit 6 due to a manufacturing error or the like. Thus, when the distance between the rotating plate 3 and the light detection unit 6 increases, the distance between the lines 18a, 19a to 19i, and 18b increases, and the width and length of the irradiation regions 16 and 17 also increase. Further, the rotating plate 3 shown in FIG. 5A is displaced in a direction parallel to the rotating plate 3 relative to the light detection unit 6. Such a state mainly occurs when the rotating plate 3 is mounted eccentrically with respect to the rotating shaft 2.

The length of the light detection unit 6 in the longitudinal direction is a case where the distance between the rotation plate 3 and the light detection unit 6 is D _max , and the rotation plate 3 is relatively to the light detection unit 6. Even in the case of being eccentric in the direction parallel to the rotating plate 3, the length may be set so as to include all the irradiation regions 16 and 17 of the lines 18a, 19a to 19i, and 18b. In other words, the required length of the light detection unit 6 is {(width of the track group 10 of the rotating plate 3) + (maximum eccentricity of the rotating plate 3) × 2} × (the rotating plate 3 and the light detecting unit 6). The maximum magnification of the irradiation areas 16 and 17 due to the change in the distance between and. The width in the direction intersecting the longitudinal direction of the light detection unit 6 may be set so that the length in the circumferential direction of the slits 7a is shorter than the length of the irradiation region 16 by the shortest slits 7a. In other words, the maximum width of the light detection unit 6 is calculated as (the length of the shortest slit 7a) × (minimum magnification of the irradiation region 16 due to a change in the distance between the rotating plate 3 and the light detection unit 6).

Further, as shown in FIGS. 3B, 4B, and 5B, in the correction tracks 8a and 8b, the irradiation region 17 is within the light detection unit 6 regardless of the rotation angle of the rotating plate 3. The length of the slit 7b in the circumferential direction and the interval between the slits 7b are provided so that at least one is included. In particular, when the distance between the rotating plate 3 and the light detection unit 6 becomes D _max (see FIG. 5B), the irradiation region 17 expands, so that the distance between the rotating plate 3 and the light detection unit 6 is increased. The distance in the circumferential direction of the slit 7b and the interval between the slits 7b may be provided based on the case where the distance is D _max .

  Referring to FIG. 1 again, the absolute encoder 1 further includes a conversion unit 20, an incident position estimation unit 21, a level determination unit 22, and a code generation unit 23. Among these, the conversion unit 20 is mainly realized by an electric circuit electrically connected to the optical sensor 5. Moreover, the incident position estimation part 21, the level determination part 22, and the code generation part 23 are realizable with the computer which incorporated the central processing unit, for example. Alternatively, these means can be realized by an electric circuit.

  The conversion unit 20 is electrically connected to the light detection unit 6 of the optical sensor 5. The conversion unit 20 is conversion means for converting the charge Q extracted from each of the plurality of pixels of the light detection unit 6 into a voltage signal to generate the light intensity signals S1 and S3. FIG. 6 is a schematic diagram illustrating a configuration for reading the charge Q from the light detection unit 6 of the optical sensor 5 illustrated in FIG. 1. In the optical sensor 5 of the present embodiment, the charge readout unit 60 is provided for the plurality of pixels 6a constituting the light detection unit 6, and the charge Q from each of the plurality of pixels 6a of the light detection unit 6 is The data is output to the conversion unit 20 via the charge reading unit 60.

  The charge readout unit 60 is provided for each of the wiring 61 that electrically connects the conversion unit 20 and the charge readout unit 60 and the plurality of pixels 6 a of the light detection unit 6, and electrically connects the pixel 6 a and the wiring 61. A wiring 62 to be connected and a shift register 65 for controlling reading of the charge Q from each pixel 6a are provided. In addition, the wiring 62 from the pixel 6a is provided with a switch 63 for switching the connection between the pixel 6a and the wiring 61, and the shift register 65 reads out the charge Q by controlling opening and closing of the switch 63. Is controlling. The charge readout unit 60 having the above configuration reads out the charge Q from each of the plurality of pixels 6a of the light detection unit 6 in a predetermined order.

  The conversion unit 20 to which the charge Q from the light detection unit 6 is input amplifies the charge Q from the pixels near the first incident position 12a and the second incident position 12b (see FIG. 3B). A light intensity signal S1 indicating the intensity of light incident on the first incident position 12a and the second incident position 12b is generated, and the light intensity signal S1 is output to the incident position estimation unit 21 and the level determination unit 22. Further, the conversion unit 20 extracts the charge Q from the pixel near the incident position indicated by the instruction signal S2 from the incident position estimation unit 21, integrates the charge Q and converts it into a voltage signal, and converts the light intensity signal S3 into a voltage signal. The light intensity signal S 3 is generated and output to the level determination unit 22.

  The conversion unit 20 may further include a circuit that amplifies the light intensity signals S1 and S3 with an amplification factor corresponding to the distance between each pixel and the light emitting element 4. Specifically, in the conversion unit 20, the amplification factor of the light intensity signals S1 and S3 due to the charge Q from the pixel having a small distance from the light emitting element 4 is reduced, and the charge Q from the pixel having a large distance from the light emitting element 4 is obtained. It is preferable to increase the amplification factor of the light intensity signals S1 and S3. By amplifying the light intensity signals S1 and S3 in this manner, the difference in light intensity between the pixels due to the difference in distance between each pixel and the light emitting element 4 can be corrected.

  The incident position estimation unit 21 includes a first incident position 12a with respect to the correction track 8a and a second incident position with respect to the correction track 8b among the incident positions in the light detection unit 6 where light having passed through a plurality of tracks has entered. 12b, the incident position estimating means for estimating the corrected incident positions 13a to 13i for the angle detection tracks 9a to 9i (see FIG. 3B). Here, the position where the light detector 6 and the line 18a intersect is the first incident position 12a, and the position where the light detector 6 and the line 18b intersect is the second incident position 12b. The positions where the lines 19a to 19i intersect are the incident positions 13a to 13i. The estimation method in the incident position estimation part 21 is demonstrated below using FIG.3 (b) and FIG.

  Referring to FIG. 3B, the first incident position 12a, the incident positions 13a to 13i, and the second incident position 12b are spaced apart from each other by a distance P1. At this time, the incident positions 12a and 12b corresponding to the correction tracks 8a and 8b are spaced by a distance P1 × 10 with the incident positions 13a to 13i therebetween. The interval P1 is determined by the relative positions of the light emitting element 4, the rotating plate 3, and the light detection unit 6, and the track interval of the rotating plate 3 in the track group 10. Here, the slits 7b of the correction tracks 8a and 8b are at least between the light emitting element 4 and the light detection unit 6 in each of the correction tracks 8a and 8b regardless of the rotation angle of the rotating plate 3 as described above. It arrange | positions so that one slit 7b may exist. Therefore, light that has always passed through the correction track 8a and light that has passed through the correction track 8b are incident on the light detection unit 6 regardless of the rotation angle of the rotating plate 3.

  FIG. 7 is a diagram illustrating a plurality of pixels 6 a of the light detection unit 6 and an example of a light intensity distribution generated based on the electric charge Q read from each pixel 6 a by the reading circuit 60. In the encoder 1 of the present embodiment, the readout circuit 60 (see FIG. 6) first includes pixels at the end on the rotating shaft 2 side on which the first correction track 8a is located. The charge Q is read out for each of the pixels in the region (first pixel region) R1 including the first incident position 12a where the light having passed through the slit 7b enters. In the first pixel region R1, a light intensity signal S1 having a greater light intensity is obtained in the pixel 6a closer to the first incident position 12a. This is because the correction track 8a for allowing the light from the light emitting element 4 to pass is positioned on the first incident position 12a.

  The incident position estimation unit 21 detects the first incident position 12a corresponding to the correction track 8a based on the light intensity signal S1 obtained from the conversion unit 20. Specifically, as shown by an arrow in FIG. 7, the readout circuit 60 sequentially reads out charges from the pixel closest to the rotation axis 2 to the inner pixel with respect to the pixel 6a in the first pixel region R1. I do. At this time, in the signal sequence of the charge Q from the region R1 input to the conversion unit 20, the peak of the light intensity signal S1 detected first becomes a peak corresponding to the correction track 8a. Therefore, the first incident position 12a can be detected from the center position of this peak.

  Subsequently, the readout circuit 60 includes a pixel at an end portion on the side far from the rotation axis 2 on the side where the second correction track 8b is located, and the light that has passed through the slit 7b of the correction track 8b is incident thereon. The charge Q is read out for each of the pixels in the region (second pixel region) R2 including the second incident position 12b. In the second pixel region R2, a light intensity signal S1 having a greater light intensity is obtained in the pixel 6a closer to the second incident position 12b. This is because the correction track 8b is positioned on the second incident position 12b.

  The incident position estimation unit 21 detects the second incident position 12b corresponding to the correction track 8b based on the light intensity signal S1 obtained from the conversion unit 20. Specifically, as indicated by an arrow in FIG. 7, the readout circuit 60 sequentially charges the pixels 6a in the second pixel region R2 from the pixel farthest from the rotation axis 2 to the inner pixel. Is read out. At this time, in the signal sequence of the charge Q from the region R2 input to the conversion unit 20, the peak of the light intensity signal S1 detected first becomes a peak corresponding to the correction track 8b. Therefore, the second incident position 12b can be detected from the center position of this peak.

  Further, the incident position estimation unit 21 obtains an interval P1 × 10 between the first incident position 12a and the second incident position 12b, and based on the result, the position intervals at the incident positions 12a, 13a to 13i, 12b. Find P1. Then, the positions of the incident positions 13a to 13i are estimated with the interval P1, using one or both of the first incident position 12a and the second incident position 12b as a reference.

  The incident position estimation unit 21 outputs to the conversion unit 20 an instruction signal S2 for instructing to sequentially capture the charge Q from the pixels near the estimated incident positions 13a to 13i based on the above estimation result. Further, the readout circuit 60 is an area sandwiched between the first pixel area R1 and the second pixel area R2, and the incident positions 13a to 13i where the light that has passed through the slits 7a of the angle detection tracks 9a to 9i is incident. The charge Q is read out in the order indicated by the arrows in FIG. 7 for each of the pixels in the included region (third pixel region) R3. The signal sequence of the charge Q from the region R3 obtained in this way is used for detecting the rotation angle of the rotating shaft 2.

  The level determination unit 22 is light that has been detected at the incident positions 13a to 13i based on the intensity of the light that has passed through the correction tracks 8a and 8b detected by the light detection unit 6, and has passed through the slit 7a. It is a level determination means for determining whether or not. Specifically, the level determination unit 22 receives the light intensity signals S1 and S3 from the conversion unit 20. The level determination unit 22 adds the light intensity signal S1 corresponding to each pixel near the first incident position 12a and the light intensity signal S1 corresponding to each pixel near the second incident position 12b. The total value of the intensity of the light passing through the correction track 8a and the intensity of the light passing through the correction track 8b is obtained.

  Subsequently, the level determination unit 22 sets a threshold based on the total value of the intensity of the light that has passed through the correction tracks 8a and 8b. At this time, the threshold value may be, for example, one half of the total value of the light intensity, or may be any other ratio. Then, the level determination unit 22 compares the light intensity signal S3 input from the conversion unit 20 with a threshold value to determine whether or not the light intensity signal S3 is a signal due to light that has passed through the slit 7a. A result S4 is generated. The level determination unit 22 outputs the determination result S4 to the code generation unit 23.

  The code generation unit 23 is means for generating a Gray code S5 representing the absolute values of the rotation angles of the rotary shaft 2 and the rotary plate 3 based on the determination result S4 from the level determination unit 22. The code generator 23 knows from the determination result S4 whether or not the light intensity signal S3 related to the pixels near the incident positions 13a to 13i is due to the light that has passed through the slits 7a of the angle detection tracks 9a to 9i. it can. When the light intensity signal S3 is derived from the light that has passed through the slit 7a (that is, when the light intensity signal S3 is greater than the threshold value), the bit of the Gray code corresponding to the incident position is set to 1. When the light intensity signal S3 is not due to light that has passed through the slit 7a (that is, when the light intensity signal S3 is smaller than the threshold value), the bit of the Gray code corresponding to the incident position is set to 0. Thus, a nine-digit gray code S5 is generated. The code generation unit 23 outputs the generated gray code S5 to the outside of the absolute encoder 1.

  Next, an angle detection method using the absolute encoder 1 will be described as an operation of the absolute encoder 1 having the above configuration. In the method described below, the conversion unit 20, the incident position estimation unit 21, the level determination unit 22, and the code generation unit 23 included in the absolute encoder 1 are used, but these means are provided outside the absolute encoder 1. It may be.

  FIG. 8 is a flowchart illustrating an example of the angle detection method according to the present embodiment. In this angle detection method, first, light is emitted from the light emitting element 4 toward the track group 10 of the rotating plate 3 (irradiation step, S101). At this time, light that has passed through the slits 7a and 7b is incident on the plurality of pixels 6a constituting the light detection unit 6 of the optical sensor 5, and an amount of charge Q corresponding to the light intensity is generated. Then, the charge readout unit 60 and the conversion unit 20 sequentially read out the charge Q from each pixel 6a of the light detection unit 6 and generate a light intensity signal.

  First, the reading unit 60 reads the charge Q from each of the pixels 6a in the first pixel region R1 among the plurality of pixels 6a configuring the light detection unit 6. The read charge Q is converted into a voltage signal by the converter 20 and becomes a light intensity signal S1 (first detection step, S102). The light intensity signal S1 is output from the conversion unit 20 to the incident position estimation unit 21 and the level determination unit 22. Then, the incident position estimation unit 21 detects a position on the light detection unit 6 where the light intensity signal S1 first peaks in the region R1, and the first light on which the light that has passed through the correction track 8a has entered this position. (Correction data acquisition step, S103).

  Subsequently, the reading unit 60 reads the charge Q from each of the pixels 6a in the second pixel region R2. The read charge Q is converted into a voltage signal by the converter 20 and becomes a light intensity signal S1 (second detection step, S104). The light intensity signal S1 is output from the conversion unit 20 to the incident position estimation unit 21 and the level determination unit 22. Then, the incident position estimation unit 21 detects the position on the light detection unit 6 where the light intensity signal S1 first peaks in the region R2, and the second position where the light that has passed through the correction track 8b has entered this position. The incident position is 12b (correction data acquisition step, S105).

  Next, in the incident position estimation unit 21, incident positions 13 a to 13 i where light passing through each of the angle detection tracks 9 a to 9 i is incident based on the obtained first incident position 12 a and second incident position 12 b. Is estimated. That is, the incident position estimation unit 21 obtains the interval P1 × 10 between the first incident position 12a and the second incident position 12b, and further obtains the interval P1 between adjacent incident positions. Then, the positions of the incident positions 13a to 13i are estimated with the interval P1 using one or both of the first incident position 12a and the second incident position 12b as a reference (incidence position estimation step, S106). On the other hand, the level determination unit 22 determines a threshold based on the light intensity signal S1 from the conversion unit 20 (S107).

  Subsequently, the reading unit 60 reads the charge Q from each of the pixels 6a in the third pixel region R3. The conversion unit 20 takes out the charge Q from the pixel near the incident position 13a estimated by the incident position estimation unit 21, integrates it, and converts it into a voltage signal to generate the light intensity signal S3 (third detection step). , S108). The light intensity signal S3 is output to the level determining unit 22, and the level determining unit 22 compares the light intensity signal S3 with a threshold value. Thus, it is determined whether or not the light detected at the incident position 13a is light that has passed through the slit 7a (S109). The determination result S4 regarding the incident position 13a is output from the level determination unit 22 to the code generation unit 23. Thereafter, steps S108 and S109 are repeated for each of the incident positions 13b to 13i.

  In the code generation unit 23, a gray code S5 is generated based on the determination result S4 from the level determination unit 22 (code generation step, S110). Then, the generated gray code S5 is output to the outside of the absolute encoder 1. The gray code S5 reads the absolute values of the rotation angles of the rotating shaft 2 and the rotating plate 3.

  The effects of the absolute encoder and the angle detection method according to the above-described embodiment will be described.

  In the absolute encoder 1 shown in FIG. 1, in each of the correction tracks 8a and 8b, at least one slit 7b exists between the light emitting element 4 and the light detection unit 6 regardless of the rotation angle of the rotating plate 3. Has been placed. Therefore, the light that has been irradiated from the light emitting element 4 and has passed through the slit 7b of the correction track 8a and the light that has passed through the slit 7b of the correction track 8b are detected by the light detector 6 of the optical sensor 5 at the rotation angle of the rotary plate 3. Therefore, the first incident position 12 a and the second incident position 12 b can always be obtained regardless of the rotation angle of the rotating plate 3. Therefore, even if the position of the rotating plate 3 is changed, the corrected incident positions 13a to 13i are estimated by referring to the first incident position 12a and the second incident position 12b. The presence / absence of the slits 7a of the angle detection tracks 9a to 9i on the light detection unit 6 can be accurately detected based on the incident state of the light to the incident positions 13a to 13i. Therefore, according to the absolute encoder 1 according to the present embodiment, the absolute value of the rotation angle of the rotating shaft 2 can be accurately measured.

  In general, when the absolute encoder has only one light source, the incident position on the light detection unit deviates from the original position as shown in FIGS. 4 and 5 due to an error in attaching the rotating plate to the rotating shaft. There is. The same applies to the case where the rotating plate is mounted eccentrically with respect to the rotating shaft. According to this embodiment, since the absolute value of the rotation angle of the rotating shaft 2 can be accurately detected even when the position of the rotating plate 3 changes as described above, the light emitting element 4 that is a point light source. It is sufficient to provide only one, and a complicated optical system for enlarging the apparatus and a space with a long optical path length are not required. Therefore, it is possible to provide a small absolute encoder 1 having one light source.

  In the angle detection method according to the present embodiment, the absolute encoder 1 is used to estimate the corrected incident positions 13a to 13i with reference to the first incident position 12a and the second incident position 12b. Therefore, even when the position of the rotating plate 3 changes, the slits 7a of the angle detection tracks 9a to 9i on the light detection unit 6 are based on the incident state of light at the incident positions 13a to 13i. Presence or absence can be detected accurately. As a result, the Gray code S5 indicating the absolute value of the rotation angle of the rotating plate 3 can be accurately generated, and the absolute value of the rotation angle of the rotating shaft 2 can be accurately measured.

  Further, in the encoder 1 and the angle detection method described above, for the reading of the charges generated by each of the plurality of pixels 6a of the optical sensor 5, the region R1 corresponding to the first correction track 8a serving as correction data, and the first First, the charge from each pixel in the region R2 corresponding to the second correction track 8b is read out, and then in the region R3 corresponding to the angle detection tracks 9a to 9i serving as angle detection data. The charge is read from each pixel. Thereby, the reading of electric charges from the light detection unit 6 of the optical sensor 5 and the measurement of the rotation angle can be executed efficiently. As for the measurement of the absolute value of the rotation angle of the rotating shaft 2, the encoder 1 shown in FIG. 1 obtains the rotation angle within the device, but the rotation angle is rotated by an external device using the data obtained by the encoder 1. The absolute value of the corner may be obtained.

  Further, as in the above embodiment, the absolute encoder 1 has the circumferential length of the slit 7b so that at least one irradiation region 17 is included in the light detection unit 6 regardless of the rotation angle of the rotating plate 3. It is preferable that an interval between the slits 7b is provided. As a result, the intensity of the light that passes through the correction track 8a or 8b and enters the light detection unit 6 can be kept substantially constant regardless of the rotation angle of the rotating plate 3, so that the first incident position 12a and the first incident position 12a The second incident position 12b can be obtained more accurately. Further, since the intensity of the light that has passed through the correction tracks 8a and 8b can be obtained stably, the level determination unit 22 can obtain a stable threshold value.

  Moreover, it is preferable that the absolute encoder 1 is provided with the incident position estimation part 21 which estimates the incident positions 13a-13i based on the 1st incident position 12a and the 2nd incident position 12b. As a result, the presence or absence of the slits 7a of the angle detection tracks 9a to 9i on the light detection unit 6 can be accurately detected based on the estimated incident states of light at the incident positions 13a to 13i.

  Further, the incident position estimation unit 21 determines the incident positions 13a to 13i based on the first incident position 12a or the second incident position 12b and the interval between the first incident position 12a and the second incident position 12b. It is preferable to estimate. Thereby, the incident positions 13a to 13i can be estimated appropriately.

  Further, as in the above-described embodiment, the absolute encoder 1 includes the incident position estimation unit 21 based on the intensity of the light that has passed through the correction track 8a and the light that has passed through the correction track 8b detected by the light detection unit 6. It is preferable to include a level determination unit 22 that determines whether or not the light detected at the incident positions 13a to 13i estimated by the above is light that has passed through the slit 7a. This makes it possible to more accurately determine the presence or absence of the slits 7a of the angle detection tracks 9a to 9i on the light detection unit 6, so that the absolute value of the rotation angle of the rotary shaft 2 can be detected more accurately. it can.

  In the encoder 1, as shown in FIG. 2, the first correction track 8a is located closest to the rotation shaft 2 among the plurality of tracks of the track group 10, and the second correction track 8b is the most. The structure is located on the side far from the rotary shaft 2. As described above, by arranging the two correction tracks on both ends of the plurality of tracks, it is possible to accurately correct the incident position with respect to the angle detection track using the correction track.

  9 and 10 are diagrams illustrating estimation of the incident position of the light that has passed through the angle detection track when two correction tracks are used.

  FIG. 9 differs from the encoder 1 shown in FIG. 1 in that the correction tracks 8a and 8b on the rotating plate 3 and the light incident positions 12a and 12b on the light detection unit 6 of the optical sensor 5 corresponding thereto are shown. Both show the angle detection tracks 9a to 9i and the estimation of the incident position when the corresponding positions are located closer to the rotary shaft 2 than the incident positions 13a to 13i. In such a configuration, the interval between the incident positions 12a and 12b corresponding to the correction tracks 8a and 8b is the incident position interval P1 between the adjacent incident positions.

  In this configuration, as shown in FIG. 9, the slit 7b of the second correction track 8b is clogged with dust or the like, or dust adheres to the pixels in the region corresponding to the incident position 12b. Consider a case where a part of the light that has passed through the slit 7b of the correction track 8b is not detected. At this time, since the second incident position 12b is detected by being shifted by ΔP, the incident position interval P2 obtained from the incident positions 12a and 12b is P2 = P1 + ΔP with respect to the original interval P1. Furthermore, when the incident positions 13a to 13i are estimated using the interval P2, the interval estimation error ΔP is accumulated at the incident position 13i farthest from the rotation axis 2, and the estimated incident position becomes the original incident position. 13i greatly deviates from ΔP × 10.

  On the other hand, in FIG. 10, as in the encoder 1 shown in FIG. 1, light is incident on the correction tracks 8 a and 8 b on the rotating plate 3 and the corresponding light detection units 6 of the optical sensor 5. Positions 12a and 12b are incident positions when the angle detection tracks 9a to 9i and the corresponding incident positions 13a to 13i are positioned on the rotating shaft 2 side and on the far side from the rotating shaft 2, respectively. It shows the estimation. In such a configuration, the interval between the incident positions 12a and 12b corresponding to the correction tracks 8a and 8b is an interval P1 × 10 that is ten times the incident position interval.

  In this configuration, as shown in FIG. 10, the slit 7b of the second correction track 8b is clogged with dust or the like, or dust adheres to the pixels in the region corresponding to the incident position 12b. Consider a case where a part of the light that has passed through the slit 7b of the correction track 8b is not detected. At this time, the second incident position 12b is detected by being shifted by ΔP, but the incident position interval P2 obtained from the incident positions 12a and 12b is P2 = P1 + ΔP / 10 with respect to the original interval P1, and the shift is Small enough. Further, when the incident positions 13a to 13i are estimated using the interval P2, since the positions are all located on the first incident position 12a side as viewed from the second incident position 12b, the estimation error is smaller than ΔP. Become. As described above, by arranging the two correction tracks 8a and 8b on both ends of the plurality of tracks, the accuracy of correcting the incident position with respect to the angle detection track using the correction track is improved.

  Further, in the configuration in which the correction tracks are arranged on both ends in this way, the angle detection tracks 9a to 9i are arranged between the two correction tracks 8a and 8b by applying the above-described charge reading method. Nevertheless, it is possible to read out charges from each pixel in the order of correction data and angle detection data. As a result, it is possible to efficiently and accurately execute the reading of charges from the light detection unit of the optical sensor and the measurement of the rotation angle.

  However, the arrangement of the correction track is not limited to the configuration shown in FIG. 2, and for example, the first correction track may be arranged on the side far from the rotation axis and the second correction track may be arranged on the rotation axis side. good. Or it is good also as arrangement configurations other than these. Even in those configurations, as described above, the charge is first read out from each pixel in the first pixel area and the second pixel area as the correction data, and then the angle detection data is obtained. By reading the charge from each pixel in the third pixel region, it is possible to efficiently read the charge from the light detection unit of the photosensor and measure the rotation angle.

  In addition, the pixel regions R1 to R3 used for reading out charges from the pixels 6a of the light detection unit 6 may be fixed in advance. Alternatively, it may be set in real time according to the detection results of the incident positions 12a and 12b corresponding to the correction tracks 8a and 8b. As an example of such a method, in the charge reading method shown in FIG. 7, the charge is sequentially read from the end pixel on the side where the first correction track 8a is located in the first pixel region R1. At the time when the first peak is detected, the first incident position 12a is obtained, and the reading of the charges is ended with the region R1 up to a predetermined pixel based on the obtained incident position 12a. Subsequently, with respect to the second pixel region R2, the charge is sequentially read from the end pixel on the side where the second correction track 8b is located, and when the first peak is detected, the second incident position 12b is set. At the same time, the readout of the charge is finished with the region R2 up to a predetermined pixel based on the obtained incident position 12b. Then, there is a method of estimating the incident positions 13a to 13i corresponding to the angle detection tracks 9a to 9i from the incident positions 12a and 12b, and reading out the charge from the third pixel region R3. In addition to this, various methods can be used.

  Next, a modification of the absolute encoder 1 shown in FIG. 1 will be described.

  FIG. 11 is a plan view showing an optical sensor 50 as a first modification of the absolute encoder 1 according to the embodiment. This optical sensor 50 is an optical sensor that is arranged in place of the optical sensor 5 used in the above-described embodiment, and includes a light detection unit 51 in which a plurality of pixels 51a are arranged in a one-dimensional manner. In the light detection unit 51, the width W of each of the plurality of pixels 51 a in the direction intersecting with the longitudinal direction of the optical sensor 50 is provided based on the distance between the pixel 51 a and the light emitting element 4. Specifically, the width W of the pixel 51 a that is relatively close to the light emitting element 4 is short, and the width W of the pixel 51 a that is relatively far from the light emitting element 4 is long. Thus, the area of each pixel 51 a is an area that is inversely proportional to the incident intensity profile from the light emitting element 4 in the light detection unit 51.

  When a point light source is used as the light emitting element 4, a difference occurs in the intensity of light incident on each pixel 51 a due to a difference in distance from the light emitting element 4 of each of the plurality of pixels 51 a. According to the optical sensor 50 of the present modification, since the area of the pixel 51a is determined based on the distance between the pixel 51a and the light emitting element 4, it is possible to obtain a signal in which the difference in light intensity between the pixels 51a is corrected. In addition, the absolute encoder 1 can more accurately measure the absolute value of the rotation angle of the rotating shaft 2.

  FIG. 12 is an enlarged plan view showing a rotating plate 3a as a second modification of the absolute encoder 1 according to the embodiment. The rotating plate 3a is a rotating plate arranged in place of the rotating plate 3 used in the above embodiment. The difference between the rotating plate 3 a and the rotating plate 3 is that the slits 7 c of the correction tracks 8 a and 8 b are formed of a material that is transparent to the light from the light emitting element 4. The slit 7c is continuously formed over the entire circumference of the correction tracks 8a and 8b. In this modification, the rotating plate 3 is formed by performing non-transparent printing on a portion other than the slit 7c on the surface of the glass plate, for example. According to the rotating plate 3a of the present modification, the intensity of light that passes through the correction track 8a and enters the light detection unit 6 and the intensity of light that passes through the correction track 8b and enters the light detection unit 6 are set. The first incident position 12a and the second incident position 12b can be detected more accurately because they can be kept substantially constant regardless of the rotation angle of the rotating plate 3.

  FIG. 13 is an enlarged plan view showing a rotating plate 3b as a third modification of the absolute encoder 1 according to the above embodiment. The rotating plate 3b is a rotating plate arranged in place of the rotating plate 3 used in the above embodiment. The difference between the rotary plate 3b and the rotary plate 3 is that the correction track group 8 includes a correction track 8c in addition to the correction tracks 8a and 8b. As described above, the rotating plate may include three or more correction tracks. According to the rotating plate 3b of this modification, in the light detection unit 6 of the optical sensor 5, a third incident position can be obtained in addition to the first incident position 12a and the second incident position 12b. The estimation accuracy when the incident position estimation unit 21 estimates the incident positions 13a to 13i can be further increased. Furthermore, the accuracy of the threshold value in the level determination unit 22 can be increased.

  Next, a specific example of the configuration of the signal processing system used in the absolute encoder will be described.

  FIG. 14 is a circuit diagram showing a configuration example of a signal processing system in the encoder shown in FIG. This circuit diagram shows circuit configurations of the conversion unit 30, the incident position estimation unit 31, and the level determination unit 32. In this example, these means will be described as specific examples of the conversion unit 20, the incident position estimation unit 21, and the level determination unit 22 of the above-described embodiment.

  Referring to FIG. 14, the conversion unit 30 includes an integrator 30a, a differential amplifier 30b, and a memory 30c. The input of the integrator 30a is electrically connected to a charge readout unit 60 that reads out charges from each of the plurality of pixels 6a constituting the light detection unit 6 of the photosensor 5, and the output of the integrator 30a is the differential amplifier 30b. And electrically connected to the memory 30c. The integrator 30a is a circuit that integrates charges from each pixel of the optical sensor 5 and converts them into a voltage signal, and the integration operation is initialized by inputting an initialization signal φINT from a controller 31a described later.

  The memory 30c is a circuit for storing an output level (dark output level) from the integrator 30a when the integrator 30a does not receive charges from the photosensor 5. The input of the memory 30c is electrically connected to the integrator 30a, and the output of the memory 30c is electrically connected to the differential amplifier 30b. The memory 30c stores the output level from the integrator 30a before the light emitting element 4 is turned on with a storage signal φRM from the controller 31a described later as a trigger. Alternatively, a predetermined level may be stored in the memory 30c when the absolute encoder 1 is manufactured.

  The differential amplifier 30b is a circuit for generating a difference between the output level of the integrator 30a and the level stored in the memory 30c. One input of the differential amplifier 30b is electrically connected to the integrator 30a, and the other input of the differential amplifier 30b is electrically connected to the memory 30c. The output of the differential amplifier 30b is electrically connected to the level determination unit 32. The differential amplifier 30b subtracts the dark output level from the output level of the integrator 30a by subtracting the level stored in the memory 30c from the output level of the integrator 30a.

  The level determination unit 32 includes a comparator 32a and a memory 32b. The memory 32b is a circuit that obtains a threshold value based on the light intensity of the light that has passed through the correction tracks 8a and 8b and stores the threshold value. The input of the memory 32b is electrically connected to the output of the differential amplifier 30b, and the output of the memory 32b is electrically connected to the comparator 32a. The memory 32b calculates a threshold value based on a predetermined arithmetic expression using the storage signal φDM from the controller 31a as a trigger, and stores this.

  The comparator 32a is a circuit that compares the output level of the differential amplifier 30b with the threshold value stored in the memory 32b and outputs a comparison result. One input of the comparator 32a is electrically connected to the differential amplifier 30b, and the other output of the comparator 32a is electrically connected to the memory 32b. The output of the comparator 32a is electrically connected to code generation means (not shown) and the controller 31a. The comparator 32a outputs a voltage signal (logic 1) of a predetermined level when the output level of the differential amplifier 30b is larger than the threshold value, and outputs a voltage signal (logic 0) of another level otherwise.

  Further, the controller 31a controls the integrator 30a, the memory 30c, the memory 32b, and the charge reading unit 60, and obtains the order, interval, region, and the like of the pixels from which charges are extracted in the light detection unit 6 of the photosensor 5. This is a circuit for controlling the timing of taking out electric charges. The controller 31a is electrically connected to the comparator 32a, and based on the timing at which a signal related to the light that has passed through the correction tracks 8a and 8b is output from the comparator 32a, the first incident position 12a and the first incident position 12a. 2 incident positions 12b are stored. Then, the controller 31a calculates the interval between the incident positions based on the interval between the first incident position 12a and the second incident position 12b, and the timing at which the integrator 30a integrates the charge with this interval. The initialization signal φINT is sent to the integrator 30a. That is, the controller 31a constitutes an incident position estimation unit 31 that estimates the incident positions 13a to 13i based on the first incident position 12a and the second incident position 12b. Further, the controller 31a sends the storage signal φRM to the memory 30c and the storage signal φDM to the memory 32b at a predetermined timing. The charge reading operation in the charge reading unit 60 controlled by the controller 31a is as described above.

  Operations of the conversion unit 30, the incident position estimation unit 31, and the level determination unit 32 having the above-described configuration are as follows. First, when the light emitting element 4 is not irradiating light, a storage signal φRM is sent from the controller 31a to the memory 30c. Then, the dark output level of the integrator 30a is stored in the memory 30c. Next, when the light emitting element 4 emits light and the optical sensor 5 detects light, first, the charge from each pixel in the region R1 is read as the charge generated by the light that has passed through the correction track 8a and integrated. The light intensity signal is generated by integration by the device 30a. Then, after the dark output level is removed from the light intensity signal by the differential amplifier 30b, the level of this light intensity signal is stored in the memory 32b, and the light intensity signal is sent to the controller 31a via the comparator 32a. It is done.

  Subsequently, the charge from each pixel in the region R2 is read as the charge generated by the light that has passed through the correction track 8b and integrated by the integrator 30a to generate a light intensity signal. As in the case of the light that has passed through the correction track 8a, the level of the light intensity signal is stored in the memory 32b, and the light intensity signal is sent to the controller 31a. Thereafter, the storage signal φDM is sent from the controller 31a to the memory 32b. In the memory 32b, the threshold value is calculated based on the light intensity signals relating to the light passing through the correction track 8a and the light passing through the correction track 8b. Further, the controller 31a obtains the first incident position 12a and the second incident position 12b, and calculates an interval between them.

  Subsequently, the controller 31a instructs reading of charges from each pixel in the region R3, and sends an initialization signal φINT to the integrator 30a with reference to the calculated incident position interval. In the integrator 30a, the integration operation is initialized every time the initialization signal φINT is received. Therefore, the charges generated in the vicinity of the incident positions 13a to 13i are sequentially integrated. The light intensity signal generated by integrating the electric charge is input to the comparator 32a after the dark output level is removed by the differential amplifier 30b. Then, the light intensity signal is compared with a threshold value in the comparator 32a, and the comparison result is output to a code generation means (not shown). In the code generation means, a gray code is generated based on the comparison result.

  The absolute encoder and the angle detection method according to the present invention are not limited to the above-described embodiments and configuration examples, and various modifications are possible. For example, in the above configuration example, the conversion unit, the incident position estimation unit, and the level determination unit are realized by an electric circuit, but these units may be realized by a computer in which predetermined software is incorporated, You may implement | achieve combining an electric circuit and a computer suitably. In the above-described embodiment, the rotating plate has nine angle detection tracks. The number of tracks for detecting the angle of the rotating plate is not limited to this, and can be various according to the required resolution. Also, the number and arrangement of the correction tracks may be variously set in consideration of the corresponding charge reading method with the optical sensor.

  The present invention can be used as an absolute encoder and an angle detection method capable of accurately detecting the absolute value of the rotation angle of the rotating shaft.

It is a perspective view which shows the structure of one Embodiment of an absolute encoder. FIG. 2 is a plan view showing a part of the rotating plate shown in FIG. 1 in an enlarged manner. (A) Side surface sectional view showing the relative positional relationship of the light emitting element, the rotating plate, and the optical sensor, and (b) The positional relationship between the irradiation region of the light that has passed through the slit and the light detection unit of the optical sensor. FIG. It is a figure for demonstrating the case where the position of a rotating plate has changed relatively with respect to the photon detection part. It is a figure for demonstrating the case where the position of a rotating plate has changed relatively with respect to the photon detection part. It is a schematic diagram which shows the structure for reading an electric charge from the photon detection part of the photosensor shown in FIG. It is a figure which shows collectively the some pixel of a photon detection part, and the light intensity distribution produced | generated based on the electric charge read by the read-out circuit from each pixel. It is a flowchart which shows an example of the angle detection method using the encoder shown in FIG. It is a figure shown about estimation of the incident position of the light which passed the track for angle detections using the track for amendment. It is a figure shown about estimation of the incident position of the light which passed the track for angle detections using the track for amendment. It is a top view which shows the optical sensor used for the 1st modification of the absolute encoder shown in FIG. It is a top view which expands and partially shows the rotating plate used for the 2nd modification of the absolute encoder shown in FIG. It is a top view which expands and shows partially the rotating plate used for the 3rd modification of the absolute encoder shown in FIG. It is a circuit diagram which shows the structural example of the signal processing system in the absolute encoder shown in FIG. It is a perspective view which shows the structure of the conventional absolute encoder.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Absolute encoder, 2 ... Rotating shaft 3, 3a, 3b ... Rotating plate, 4 ... Light emitting element, 5 ... Optical sensor, 6 ... Light detection part, 6a ... Pixel, 7a-7c ... Slit, 8 ... Correction track Group, 8a to 8c ... correction track, 9 ... angle detection track group, 9a to 9i ... angle detection track, 10 ... track group, 12a ... first incident position, 12b ... second incident position, 13a- 13i ... incident position, 16, 17 ... irradiation area, 18a, 18b, 19a to 19i ... line, 20 ... conversion unit, 21 ... incident position estimation unit, 22 ... level determination unit, 23 ... code generation unit, 30 ... conversion unit , 30a ... integrator, 30b ... differential amplifier, 30c ... memory, 31 ... incident position estimation unit, 31a ... controller, 32 ... level determination unit, 32a ... comparator, 32b ... memory, 50 ... optical sensor, 51 ... Photodetector 51a ... pixel 60 ... charge reading section, 61, 62 ... wiring, 63 ... switch, 65 ... shift register.

Claims (12)

A rotation axis;
A rotating plate attached to the rotating shaft and having a plurality of tracks in which slits of a predetermined pattern are formed in the circumferential direction, and the plurality of tracks include a plurality of angle detection tracks and correction tracks,
A light sensor having a plurality of pixels arranged one-dimensionally, and the light detection unit is provided so as to face the plurality of tracks with the radial direction of the rotating plate as a longitudinal direction;
A light source provided to face the light detection unit of the photosensor across the plurality of tracks of the rotating plate;
Readout means for reading out charges from each of the plurality of pixels constituting the light detection unit of the photosensor,
The plurality of tracks are, as the correction tracks, a first correction track and a second correction track in which the slit is disposed between the light source and the light detection unit regardless of the rotation angle of the rotating plate. Including trucks,
The reading means relates to an incident position at which light that has passed through the plurality of tracks enters the light detection unit, and the slit of the first correction track with respect to the plurality of pixels constituting the light detection unit. A pixel in the first pixel area including a first incident position where light that has passed through the second incident area, and a second pixel area including a second incident position where light that has passed through the slit of the second correction track enters. An absolute encoder that reads out charges in the order of the pixels in the third pixel region including the incident position where the light that has passed through the slits of the plurality of angle detection tracks enters.   The absolute value of the rotation angle of the rotating shaft is measured by detecting light that has passed through the slits of the plurality of angle detection tracks in the light detection unit of the optical sensor. Absolute encoder. The rotary plate has one of the first correction track and the second correction track positioned closest to the rotation axis among the plurality of tracks, and the other positioned closest to the rotation axis. And
The reading means defines, for the plurality of pixels constituting the light detection unit, a predetermined region including an end pixel on the side where the first correction track is located, the first pixel region, the second pixel region, and the second pixel region. The predetermined area including the pixel at the end where the correction track is located is defined as the second pixel area, and the area sandwiched between the first pixel area and the second pixel area is defined as the third pixel area. 3. The absolute encoder according to claim 1, wherein reading is performed.   The readout means sequentially reads out charges from the end pixel on the side where the first correction track is located for the first pixel region, and is based on the determined first incident position. The first pixel region is defined as the first pixel region, and the second pixel region is obtained by sequentially reading out charges from the end pixel on the side where the second correction track is located. The absolute encoder according to claim 3, wherein the second pixel region includes a predetermined pixel based on an incident position.   2. An incident position estimating means for estimating a corrected incident position for each of the plurality of angle detection tracks based on the first incident position and the second incident position. Absolute encoder as described in any one of -4.   The incident position estimating means estimates a corrected incident position for each of the plurality of angle detection tracks based on an interval between the first incident position and the second incident position. The absolute encoder according to claim 5.   Estimated by the incident position estimating means based on the intensity of the light that has passed through the first correction track and the light that has passed through the second correction track, detected by the light detector of the optical sensor. 7. The absolute encoder according to claim 5, further comprising level determining means for determining whether or not the light detected at the incident position is light that has passed through the slit. An angle detection method using the absolute encoder according to any one of claims 1 to 7,
Irradiating light from the light source to the plurality of tracks of the rotating plate;
A first charge is read out from each of the pixels in the first pixel region among the plurality of pixels constituting the light detection unit, and light passing through the slit of the first correction track is detected. A detection step;
A second detection step of reading out charges from each of the pixels in the second pixel region and detecting light that has passed through the slit of the second correction track;
An angle detection method comprising: a third detection step of reading out charges from each of the pixels in the third pixel region and detecting light that has passed through the slits of the plurality of angle detection tracks.   9. The angle detection method according to claim 8, further comprising a code generation step for generating a code indicating an absolute value of a rotation angle of the rotary plate and the rotary shaft based on a detection result in the third detection step. . Based on detection results in the first detection step and the second detection step, the first incident position with respect to the first correction track and the second incident position with respect to the second correction track. A correction data acquisition step for obtaining
An incident position estimating step for estimating a corrected incident position for each of the plurality of angle detection tracks based on the first incident position and the second incident position obtained in the correction data acquiring step; With
The angle detection method according to claim 8 or 9, wherein, in the third detection step, light incident on the incident position estimated in the incident position estimation step is detected.   Light detected at the incident position by setting a threshold based on the intensity of the light that has passed through the first correction track and the light that has passed through the second correction track in the third detection step The angle detection method according to claim 10, wherein it is determined whether or not the light detected at the incident position is light that has passed through the slit by comparing the intensity of the light and the threshold. In the incident position estimating step, a corrected incident position for each of the plurality of angle detection tracks is estimated based on an interval between the first incident position and the second incident position. The angle detection method according to claim 10 or 11.

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