Encoder

Abstract

To provide an encoder that suppresses an influence of harmonic waves on a reception light waveform.SOLUTION: An optical encoder to detect a rotation position of a motor includes a light-emitting element, a slit plate that transmits or reflects light emitted from the light-emitting element and generates a bright and dark pattern, a light-receiving element that converts light from the slit plate into electric signals, and a signal processing unit that processes the electric signals from the light-receiving element. The slit plate includes a basic pattern in which bright parts and dark parts are disposed at equal intervals alternately with a first pitch on a circumference, and a harmonic suppressing pattern in which bright parts and dark parts are disposed at equal intervals alternately with a second pitch, which is 1 / N pitch of the first pitch (N is an integer of 2 or more) on the basic pattern.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to encoders. [Background technology]

[0002] Patent document 1 discloses an optical encoder that detects the speed and rotational position of a rotating disk by providing a code pattern on the rotating disk and receiving light from a light-emitting element that is transmitted through or reflected by the code pattern via a fixed slit with a light-receiving element. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-271453 A Summary of the Invention [Problem to be solved by the invention]

[0004] In optical encoders, errors in measurement may occur due to harmonics being superimposed on the received light waveform.

[0005] The present disclosure provides an encoder that suppresses the effects of harmonics in the received optical waveform. [Means for solving the problem]

[0006] According to one aspect of the present disclosure, there is provided an optical encoder for detecting the rotational position of a motor, the encoder comprising: a light-emitting element; a slit plate that transmits or reflects light emitted from the light-emitting element to generate a light and dark pattern; a light-receiving element that converts the light from the slit plate into an electrical signal; and a signal processing unit that processes the electrical signal from the light-receiving element, wherein the slit plate has a basic pattern in which light and dark are alternately arranged at equal intervals at a first pitch on a circumference, and a harmonic suppression pattern in which light and dark are alternately arranged at equal intervals at a second pitch that is 1 / Nth of the first pitch (where N is an integer greater than or equal to 2). Effect of the Invention

[0007] According to the encoder of the present disclosure, the influence of harmonics in the received light waveform can be suppressed. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing an overview of a servo system in which an encoder according to this embodiment is used. [Diagram 2] FIG. 2 is a diagram showing a schematic configuration of the encoder according to the first embodiment. [Diagram 3] FIG. 3 is a diagram for explaining the relationship between the light emitting diameter of the light emitting element and the light receiving pattern. [Figure 4] FIG. 4 is a diagram for explaining the relationship between the light emitting diameter of the light emitting element and the light receiving pattern. [Diagram 5] FIG. 5 is a diagram for explaining the relationship between the fundamental wave and the higher harmonics in the received light waveform. [Figure 6] FIG. 6 is a diagram illustrating a reflection pattern in the encoder according to the first embodiment. [Figure 7] FIG. 7 is a diagram illustrating a waveform of light received by the encoder according to the first embodiment. [Figure 8] FIG. 8 is a diagram illustrating a modification of the reflection pattern in the encoder according to the first embodiment. [Figure 9]FIG. 9 is a diagram illustrating a modification of the reflection pattern in the encoder according to the first embodiment. [Figure 10] FIG. 10 is a diagram illustrating a modification of the reflection pattern in the encoder according to the first embodiment. [Figure 11] FIG. 11 is a diagram illustrating a modified example of the reflection pattern in the encoder according to the first embodiment. [Figure 12] FIG. 12 is a diagram illustrating a modified example of the reflection pattern in the encoder according to the first embodiment. [Figure 13] FIG. 13 is a diagram illustrating a modified example of the reflection pattern in the encoder according to the first embodiment. [Figure 14] FIG. 14 is a diagram illustrating a modified example of the reflection pattern in the encoder according to the first embodiment. [Figure 15] FIG. 15 is a diagram illustrating a modified example of the reflection pattern in the encoder according to the first embodiment. [Figure 16] FIG. 16 is a diagram illustrating a modified example of the reflection pattern in the encoder according to the first embodiment. [Figure 17] FIG. 17 is a diagram illustrating a modified example of the reflection pattern in the encoder according to the first embodiment. [Figure 18] FIG. 18 is a diagram illustrating a modified example of the reflection pattern in the encoder according to the first embodiment. [Figure 19] FIG. 19 is a diagram illustrating a modified example of the reflection pattern in the encoder according to the first embodiment. [Figure 20] FIG. 20 is a diagram illustrating the arrangement of light receiving elements in the encoder according to the first embodiment. [Figure 21] FIG. 21 is a diagram illustrating a reflection pattern in the encoder according to the second embodiment. [Figure 22] FIG. 22 is a diagram illustrating the arrangement of light receiving elements in the encoder according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments will be described with reference to the accompanying drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0010] In addition, in the description of the specification and drawings of each embodiment, components having substantially the same or corresponding functional configurations may be denoted by the same reference numerals to avoid redundant explanation. In addition, in order to facilitate understanding, the scale of each part in the drawings may differ from the actual scale.

[0011] In the directions of parallel, right-angle, orthogonal, horizontal, vertical, up-down, left-right, front-back, etc., deviations are permitted to the extent that they do not impair the effects of the embodiment. The shape of the corners is not limited to right angles and may be rounded. Parallel, right-angle, orthogonal, horizontal, and vertical may include approximately parallel, approximately right-angle, approximately orthogonal, approximately horizontal, and approximately vertical, respectively.

[0012] For example, "approximately parallel" means that even if two lines or two surfaces are not completely parallel to each other, they can be treated as parallel to each other as long as it is within the range of manufacturing tolerance. As with "approximately parallel," "approximately right angle," "approximately perpendicular," "approximately horizontal," and "approximately vertical" are also intended to correspond to the respective terms as long as the relative positional relationship between the two lines or two surfaces is within the range of manufacturing tolerance.

[0013] First Embodiment <Servo system> A servo system using the encoder according to the present embodiment will be described below. Fig. 1 is a diagram showing an overview of a servo system 1 using an encoder 20 which is an example of the encoder according to the present embodiment.

[0014] The servo system 1 includes a servo motor 10, an encoder 20, and a servo amplifier 30. Although a servo system using the encoder according to the present embodiment will be described here, the motor using the encoder according to the present embodiment is not limited to a servo motor.

[0015] The servo motor 10 rotates the rotary shaft 11 in response to power from a servo amplifier 30 .

[0016] The encoder 20 detects the rotational position of the rotating shaft 11 of the servo motor 10. The encoder 20 is a so-called reflective optical encoder. The encoder 20 outputs the detected rotational position of the rotating shaft 11 to the servo amplifier 30.

[0017] The servo amplifier 30 controls the servo motor 10 by feeding back the detection result from the encoder 20 .

[0018] A detailed description will be given of the encoder 20. Fig. 2 is a diagram showing a schematic configuration of the encoder 20, which is an example of an encoder according to the first embodiment.

[0019] The encoder 20 includes a slit plate 21, a light emitting element 22, a light receiving element 23, and a signal processing unit 24.

[0020] The slit plate 21 is a circular plate having a reflection pattern that reflects the light emitted from the light emitting element 22 to the light receiving element 23. For example, the slit plate 21 has a strip-shaped reflection pattern that is equally divided in the circumferential direction. The slit plate 21 also has a light blocking pattern that blocks the light from the light emitting element 22 between the reflection patterns. In other words, the slit plate 21 has reflection patterns and light blocking patterns arranged alternately. The reflection patterns will be described in detail later.

[0021] The light emitting element 22 emits light toward the slit plate 21. The light emitting element 22 is, for example, a light emitting diode (LED).

[0022] The light receiving element 23 receives the light emitted from the light emitting element 22 and reflected by the slit plate 21, and converts the light into an electrical signal. The light receiving element 23 is, for example, a photodetector. When light strikes the light receiving element 23, a current flows.

[0023] The signal processing unit 24 processes the electrical signal from the light receiving element 23 and calculates the rotational position of the slit plate 21 .

[0024] A part of the light emitted from the light-emitting element 22 is reflected by the reflection pattern in the slit plate 21 and received by the light-receiving element 23. Also, a part of the light emitted from the light-emitting element 22 is blocked by the light-shielding pattern in the slit plate 21. When a part of the light emitted from the light-emitting element 22 is blocked by the light-shielding pattern in the slit plate 21, the light is not received by the light-receiving element 23.

[0025] Therefore, the electrical signal detected and output by the light receiving element 23 has a sinusoidal waveform according to the intensity of the light.

[0026] Here, a description will be given of the relationship between the light emission diameter of the light emitting element 22 and the width of the reflection pattern on the slit plate 21. Each of Figures 3 and 4 is a diagram for explaining the relationship between the light emission diameter of the light emitting element and the light reception pattern.

[0027] 3 and 4, LS1 and LS2 respectively indicate a light emitting element. WL1 and WL2 indicate a light emitting diameter of the light emitting element. RP indicates a reflection pattern. WR indicates a width of the reflection pattern. PD indicates a light receiving element.

[0028] 3, when the light-emitting diameter WL1 of the light-emitting element LS1 is large relative to the width WR of the reflection pattern RP, the image projected by the reflection pattern RP is blurred. Because the image projected by the reflection pattern RP is blurred, when the light-emitting diameter WL1 of the light-emitting element LS1 is large, the electrical signal SIG1 detected by the light-receiving element PD has a shape close to a sine wave.

[0029] 4, when the light-emitting diameter WL2 of the light-emitting element LS2 is small relative to the width WR of the reflection pattern RP, the image is clearly projected by the reflection pattern RP. Since the image is clearly projected by the reflection pattern RP, the electrical signal SIG2 detected by the light-receiving element PD has a shape close to a trapezoidal wave.

[0030] The influence of a sine wave superimposed with a harmonic is described below. Fig. 5 is a diagram for explaining the relationship between the fundamental wave and the harmonic in the received light waveform.

[0031] 5, line Lh1 indicates a sine wave, line Lh3 indicates the third harmonic of the sine wave indicated by line Lh1, and line Lc indicates a waveform in which the sine wave and the third harmonic are superimposed.

[0032] As shown in Figure 5, when examining the frequency components of the trapezoidal wave line Lc, it can be considered that a certain percentage of the third harmonic is superimposed on a sine wave. If the third harmonic is superimposed to form a trapezoidal wave, it will cause an error when detecting the rotation position.

[0033] Therefore, in order to suppress harmonics of a specific component, for example, the third harmonic, the encoder according to the first embodiment has a harmonic suppression pattern in the reflection pattern that suppresses harmonics of a specific component. The encoder according to the first embodiment is an optical encoder that detects the rotational position of a motor. The encoder according to the first embodiment has a light-emitting element, a slit plate that transmits or reflects light emitted from the light-emitting element to generate a light and dark pattern, a light-receiving element that converts the light from the slit plate into an electrical signal, and a signal processing unit that processes the electrical signal from the light-receiving element. The slit plate in the encoder according to the first embodiment has a basic pattern in which light and dark are alternately arranged at equal intervals at a first pitch on a circumference. Furthermore, when the harmonic component to be suppressed is the Nth harmonic, the slit plate in the encoder according to the first embodiment has a harmonic suppression pattern in which light and dark are alternately arranged at equal intervals at a second pitch that is 1 / Nth the first pitch (where N is an integer of 2 or more).

[0034] Fig. 6 is a diagram illustrating a reflection pattern PEx1 that suppresses the third harmonic in the encoder 20, which is an example of the encoder according to the first embodiment. In Fig. 6, a row EX shows a reflection pattern (PAT) and a signal waveform (WF) of the encoder according to the first embodiment. In Fig. 6, a row REF shows a general reflection pattern (PAT) and a signal waveform (WF) of an encoder of a reference example.

[0035] In the reflection pattern (PAT) in Fig. 6, the hatched areas indicate the reflective areas (light) and the non-hatched areas indicate the light-shielded areas (dark). The same applies to the following figures.

[0036] A method for forming the reflective pattern (PAT) will be described. For example, the slit plate 21 may be made of a material that does not reflect light, and a reflective film may be formed on the reflective portion to form the reflective pattern (PAT). Alternatively, the slit plate 21 may be made of a material that reflects light, and a slit may be formed on the light-shielding portion to form the reflective pattern (PAT).

[0037] In addition to the reflection pattern, the slit plate 21 may have another bright and dark pattern at different positions in the radial direction.

[0038] The reflection pattern PEx1 has a basic pattern BP1 in which light and dark are alternately arranged at equal intervals at a first pitch, and a harmonic suppression pattern HP1 in which light and dark are alternately arranged at equal intervals at a second pitch that is one-third the first pitch. In each of the basic pattern BP1 and the harmonic suppression pattern HP1, light and dark are alternately arranged at equal intervals along the circumferential direction of the slit plate 21.

[0039] Furthermore, the amount of influence of the harmonic suppression pattern HP1, i.e., the amplitude of the harmonics shown in Fig. 5, is determined by the radial width of the slit plate 21. That is, as the radial width increases, the influence (amplitude of the harmonics) increases, and as the width decreases, the influence decreases. In other words, the radial width of the harmonic suppression pattern HP1 is determined based on the amount of harmonics to be suppressed.

[0040] In the harmonic suppression pattern HP1, the bright and dark patterns are formed so that their phases are in opposite phase to the harmonics superimposed on the sine wave.

[0041] In this specification, when light and dark are alternately arranged at equal intervals with a predetermined pitch, this does not necessarily mean that light and dark are alternately arranged at mathematically strict equal intervals with a predetermined pitch. For example, when light and dark are alternately arranged at equal intervals with a predetermined pitch, this also includes the case where they are alternately arranged at equal intervals within the range of manufacturing tolerance in normal manufacturing.

[0042] On the other hand, the reflection pattern PRef of the encoder in the reference example has only the basic pattern BP.

[0043] The reflection pattern PEx1 has a waveform close to a sine wave as shown in the signal waveform WF due to the presence of the harmonic suppression pattern HP1. On the other hand, the reflection pattern PRef has a trapezoidal waveform.

[0044] 7 is a diagram for explaining the waveform of the received light by the encoder according to the first embodiment. The line Lex is the waveform of the received light obtained by the reflection pattern PEx1, and the line Lref is the waveform of the received light obtained by the reflection pattern PRef. The horizontal axis of FIG. 4 indicates the rotation angle, and the vertical axis of FIG. 4 indicates the signal intensity.

[0045] The reflection pattern PEx1 in the encoder according to the first embodiment was able to reduce harmonic components by 50% or more compared to the reflection pattern PRef of the encoder in the reference example.

[0046] According to the encoder of the first embodiment, the slit plate is provided with a harmonic suppression pattern, so that the influence of harmonics in the received light waveform can be suppressed.

[0047] As will be described below, the second pitch in the harmonic suppression pattern is not limited to one-third the first pitch in the basic pattern. For example, the second pitch may be one-Nth (where N is an integer equal to or greater than 2) of the first pitch in the basic pattern.

[0048] <Modification 1 (Phase inversion)> 8 shows a modified reflection pattern. Fig. 8 is a diagram for explaining a modified reflection pattern for suppressing the third harmonic in the encoder according to the first embodiment. The reflection pattern PEx11 has a harmonic suppression pattern HP11 instead of the harmonic suppression pattern HP1. The harmonic suppression pattern HP11 is a pattern with an inverted phase with respect to the harmonic suppression pattern HP1 in the reflection pattern PEx1 shown in Fig. 6.

[0049] Depending on the relationship between the phase of the third harmonic and the phase of the fundamental wave in the received light waveform, a harmonic suppression pattern HP11 with an inverted phase may be superimposed on the fundamental pattern BP.

[0050] <Modification 2 (second harmonic suppression pattern)> The harmonic suppression pattern is not limited to a pattern that suppresses the third harmonic. Figures 9 and 10 are diagrams for explaining a harmonic suppression pattern that suppresses the second harmonic as a modified example of the reflection pattern in the encoder according to the first embodiment. The reflection pattern PEx2 has a basic pattern BP2 and a harmonic suppression pattern HP2 that is half the pitch of the basic pattern BP2. In addition, the reflection pattern PEx21 has a harmonic suppression pattern HP21 that is inverted in phase with respect to the harmonic suppression pattern HP2, instead of the harmonic suppression pattern HP2.

[0051] According to the second modification, the second harmonic can be suppressed.

[0052] <Modification 3 (fourth harmonic suppression pattern)> 11 and 12 are diagrams illustrating a harmonic suppression pattern for suppressing the fourth harmonic as a modified example of the reflection pattern in the encoder according to the first embodiment. The reflection pattern PEx3 has a basic pattern BP3 and a harmonic suppression pattern HP3 that has a quarter pitch of the basic pattern BP3. Moreover, the reflection pattern PEx31 has a harmonic suppression pattern HP31 that is inverted in phase with respect to the harmonic suppression pattern HP3, instead of the harmonic suppression pattern HP3.

[0053] According to the third modification, the fourth harmonic can be suppressed.

[0054] <Modification 4 (5th harmonic suppression pattern)> 13 and 14 are diagrams illustrating a harmonic suppression pattern for suppressing the fifth harmonic as a modified example of the reflection pattern in the encoder according to the first embodiment. The reflection pattern PEx4 has a basic pattern BP4 and a harmonic suppression pattern HP4 having a pitch that is 1 / 5 of the pitch in the basic pattern BP4. Moreover, the reflection pattern PEx41 has a harmonic suppression pattern HP41, which is inverted in phase with respect to the harmonic suppression pattern HP4, instead of the harmonic suppression pattern HP4.

[0055] According to the fourth modification, the fifth harmonic can be suppressed.

[0056] <Modification 5 (Adjustment of the influence of the harmonic suppression pattern)> The amount of harmonics suppressed by the harmonic suppression pattern (amplitude of the harmonics) can be adjusted by adjusting the radial width of the reflection pattern. Fig. 15 is a diagram for explaining the amount of suppression of harmonics as a modification of the reflection pattern in the encoder according to the first embodiment.

[0057] The reflection pattern PEx5 has a basic pattern BP5 and a harmonic suppression pattern HP5 that suppresses the third harmonic component. By increasing the radial width H1, the amount of harmonics to be suppressed can be increased. Also, by decreasing the width H1, the amount of harmonics to be suppressed can be decreased.

[0058] <Modification 6 (Adjustment of the influence of the harmonic suppression pattern)> The amount of harmonics suppressed by the harmonic suppression pattern can be adjusted by adjusting the ratio of light and dark in the reflection pattern. Fig. 16 is a diagram for explaining the amount of suppression of harmonics as a modification of the reflection pattern in the encoder according to the first embodiment.

[0059] The reflection pattern PEx6 has a basic pattern BP6 and a harmonic suppression pattern HP6 that suppresses the third harmonic component. The pitch Pt1 is the same as that of the reflection pattern PEx1. On the other hand, the circumferential width Dt1 of the dark portion and the circumferential width Dt2 of the light portion in the harmonic suppression pattern HP6 are different. By adjusting the dark width Dt1 and the light width Dt2, the amount of harmonics to be suppressed can be adjusted.

[0060] <Modification 7 (Adjustment of the influence of the harmonic suppression pattern)> By adjusting the pitch in the reflection pattern, it is possible to adjust the amount of harmonics suppressed by the harmonic suppression pattern. Fig. 17 is a diagram illustrating the amount of suppression of harmonics as a modification of the reflection pattern in the encoder according to the first embodiment.

[0061] The reflection pattern PEx7 has a basic pattern BP7 and a harmonic suppression pattern HP7 that suppresses the third harmonic component. Pt21 indicates the first pitch, and Pt22 indicates the next pitch. By adjusting the pitch Pt21 and the pitch Pt22, the amount of harmonic suppression can be adjusted.

[0062] <Modification 8 (Suppression of multiple types of harmonics)> The harmonic suppression pattern is not limited to a pattern that suppresses one type of harmonic. Figures 18 and 19 are diagrams for explaining a harmonic suppression pattern that suppresses the third and fifth harmonics as a modified example of the reflection pattern in the encoder according to the first embodiment. The reflection pattern PEx8 has a basic pattern BP8 and a harmonic suppression pattern HP81 that is one-third the pitch of the basic pattern BP8. The reflection pattern PEx8 also has a basic pattern BP8 and a harmonic suppression pattern HP82 that is one-fifth the pitch of the basic pattern BP8.

[0063] The reflection pattern PEx81 has, in place of the harmonic suppression pattern HP81, a harmonic suppression pattern HP83 whose phase is inverted with respect to the harmonic suppression pattern HP81. Also, in place of the harmonic suppression pattern HP82, the reflection pattern PEx81 has, in place of the harmonic suppression pattern HP82, a harmonic suppression pattern HP84 whose phase is inverted with respect to the harmonic suppression pattern HP82.

[0064] According to the eighth modification, multiple types of harmonics can be suppressed.

[0065] The harmonics to be suppressed in the harmonic suppression pattern are not limited to the combination of the third harmonic and the fifth harmonic. For example, a combination of a plurality of odd harmonics may be suppressed as appropriate, such as the combination of the third harmonic and the seventh harmonic. Also, for example, a combination of an odd harmonic and an even harmonic may be suppressed, or a combination of a plurality of even harmonics may be suppressed. In other words, the slit plate has a first harmonic suppression pattern in which light and dark are alternately arranged at equal intervals at a second pitch that is 1 / Nth the first pitch (where N is an integer of 2 or more). The slit plate has a second harmonic suppression pattern in which light and dark are alternately arranged at equal intervals at a third pitch that is 1 / Mth the first pitch (where M is an integer different from N and is 2 or more). Furthermore, a combination of three or more harmonics may be suppressed.

[0066] <Photodetector> The light receiving element 23 will now be described. Fig. 20 is a diagram illustrating the arrangement of the light receiving elements in the encoder according to the first embodiment. The light receiving element 23 has unit light receiving elements 23a at a quarter pitch of the pitch of the basic pattern BP. The light receiving elements 23 are also provided across a plurality of light and dark patterns with respect to the basic pattern BP. For example, the light receiving element 23 has a plurality of unit light receiving elements 23a arranged in the circumferential direction on the slit plate.

[0067] The light receiving element 23 can detect the position with high accuracy by including a plurality of unit light receiving elements 23a. Also, the light receiving element 23 can detect the position with high accuracy and stability by including unit light receiving elements 23a across a plurality of light and dark patterns for the basic pattern BP, for example, by averaging across the plurality of light and dark patterns.

[0068] For example, when the light receiving elements 23 have unit light receiving elements 23a arranged at a quarter pitch of the pitch of the basic pattern BP, even multiple harmonic components can be suppressed by signal processing. Therefore, as a harmonic suppression pattern, light and dark may be alternately arranged at equal intervals at a second pitch that is 1 / K (where K is an odd number equal to or greater than 3) of the first pitch in the basic pattern BP.

[0069] Second Embodiment The encoder according to the second embodiment has a reflection pattern that suppresses high frequencies. The encoder according to the second embodiment is an optical encoder that detects the rotational position of a motor. The encoder according to the second embodiment has a light-emitting element, a slit plate that transmits or reflects light emitted from the light-emitting element to generate a light and dark pattern, a light-receiving element that converts the light from the slit plate into an electrical signal, and a signal processing unit that processes the electrical signal from the light-receiving element. The slit plate in the encoder according to the second embodiment has a pattern in which light and dark are alternately arranged at a predetermined pitch on the circumference, and the light parts are arranged at equal intervals. The pattern in the encoder according to the second embodiment has a shape in which the circumferential width gradually narrows from the central part in the radial direction toward both ends in the radial direction.

[0070] From another perspective, the slit plate in the encoder according to the second embodiment has a pattern in which light and dark are alternately arranged at an arbitrary pitch on the circumference. Also, in the pattern in the encoder according to the second embodiment, the shape of the light part is a hexagon having sides along the circumference at both radial ends.

[0071] The details of the encoder according to the second embodiment will be described with reference to the drawings. Fig. 21 is a diagram for explaining a reflection pattern PEy1 in the encoder according to the second embodiment. In Fig. 21, a column EX1 shows a reflection pattern (PAT) and a signal waveform (WF) of the encoder according to the second embodiment. In Fig. 21, a column REF shows a general reflection pattern (PAT) and a signal waveform (WF) in an encoder of a reference example.

[0072] In the reflection pattern (PAT) in FIG. 21, the hatched areas indicate the reflection areas (light), and the non-hatched areas indicate the light-shielding areas (dark).

[0073] The reflection pattern PEy1 has a pattern BP101 in which light and dark are alternately arranged at a predetermined pitch. In the pattern BP101, light and dark are alternately arranged along the circumferential direction of the slit plate, and the light portions are arranged at equal intervals. The light portions in the pattern BP101 have a shape in which the width in the circumferential direction (horizontal direction in FIG. 21) gradually narrows from the center portion in the radial direction (vertical direction in FIG. 21) toward the outer radial direction, and the width in the circumferential direction gradually narrows from the center portion in the radial direction toward the center. That is, the light portions in the pattern BP101 have a shape in which the width in the circumferential direction gradually narrows from the center portion in the radial direction toward both ends in the radial direction. More specifically, the light portions in the pattern BP101 have a hexagonal shape with sides along the circumferential direction at both ends in the radial direction (vertical direction in FIG. 21). It is preferable that the portion of the light portion in the pattern BP101 with the widest width in the circumferential direction coincides with the center portion in the radial direction of the light receiving element 23.

[0074] Next, the arrangement of the light receiving elements will be described. Fig. 22 is a diagram for explaining the arrangement of the light receiving elements in the encoder according to the second embodiment. The light receiving element 23 has unit light receiving elements 23a at a quarter pitch with respect to the pitch of the bright parts of the pattern BP101. Furthermore, the light receiving element 23 is provided across a plurality of bright and dark patterns with respect to the pattern BP101. For example, the light receiving element 23 has a plurality of unit light receiving elements 23a arranged in the circumferential direction on the slit plate.

[0075] The maximum width of the light in the radial direction after the pattern BP101 is projected onto the light receiving element 23 is wider than the width of the light receiving element 23 (unit light receiving element 23a) in the radial direction.

[0076] In unit light receiving element 23a, the amount of light reflected from pattern BP101 is related to the area of ​​overlap between unit light receiving element 23a and the bright portion of pattern BP101. Since pattern BP101 has a portion in which the bright width is widest in the radial center and the bright width in the circumferential direction gradually narrows from the radial center toward both ends, the amount of light received by unit light receiving element 23a gradually changes when pattern BP101 moves in the circumferential direction.

[0077] Therefore, a signal waveform close to a sine wave can be obtained as shown by the signal waveform WF in EX1 in Fig. 21. For example, according to the reflection pattern PEy1 in Fig. 21, the harmonic components can be suppressed to about one tenth compared to the reflection pattern PRef.

[0078] According to the encoder of the second embodiment, the slit plate has a pattern in which the bright portion has a gradually narrowing circumferential width from the radial center to both radial ends, thereby suppressing the effects of harmonics in the received light waveform. [Explanation of symbols]

[0079] 1 Servo System 10. Servo motor 11 Rotation axis 20 Encoder 21 Slit plate 22 Light emitting element 23 Photodetector 23a Unit light receiving element 24 Signal Processing Section 30 Servo Amplifier BP, BP1, BP2, BP3, BP4, BP5, BP6, BP7, BP8 Basic Pattern BP101 Pattern HP1, HP11, HP2, HP21, HP3, HP31, HP4, HP41, HP5, HP6, HP7, HP81, HP82, HP83, HP84 Harmonic suppression pattern PEx1, PEx11, PEx2, PEx21, PEx3, PEx31, PEx4, PEx41, PEx5, PEx6, PEx7, PEx8, PEx81, PEy1 Reflection pattern

Claims

1. An optical encoder for detecting a rotational position of a motor, A light-emitting element; a slit plate that transmits or reflects light emitted from the light-emitting element to generate a light and dark pattern; a light receiving element that converts the light from the slit plate into an electrical signal; A signal processing unit that processes an electrical signal from the light receiving element; Equipped with The slit plate is a basic pattern in which light and dark are alternately arranged at equal intervals on a circumference at a first pitch; a harmonic suppression pattern in which light and dark are alternately arranged at equal intervals at a second pitch that is 1 / Nth the first pitch (where N is an integer of 2 or more), in the basic pattern; Equipped with Encoder.

2. a light emitting diameter of the light emitting element is greater than a circumferential width of the harmonic suppression pattern; The encoder of claim 1 .

3. A radial width of the harmonic suppression pattern is determined based on an amount of suppression of harmonics. The encoder of claim 1 .

4. The second pitch is K times the first pitch (where K is an odd number equal to or greater than 3). The encoder of claim 1 .

5. An optical encoder for detecting a rotational position of a motor, A light-emitting element; a slit plate that transmits or reflects light emitted from the light-emitting element to generate a light and dark pattern; a light receiving element that converts the light from the slit plate into an electrical signal; A signal processing unit that processes an electrical signal from the light receiving element; Equipped with The slit plate is a basic pattern in which light and dark are alternately arranged at equal intervals on a circumference at a first pitch; a first harmonic suppression pattern in which light and dark are alternately arranged at equal intervals at a second pitch that is 1 / Nth the first pitch (where N is an integer of 2 or more), in the basic pattern; a second harmonic suppression pattern in which light and dark are alternately arranged at equal intervals at a third pitch that is 1 / Mth of the first pitch (where M is an integer greater than or equal to 2 and different from N), in the basic pattern; Equipped with Encoder.

6. a light emitting diameter of the light emitting element is larger than a circumferential width of each of the first harmonic suppression pattern and the second harmonic suppression pattern; The encoder of claim 5.

7. A radial width of each of the first harmonic suppression pattern and the second harmonic suppression pattern is determined based on an amount of suppression of harmonics. The encoder of claim 5.

8. The second pitch is one-third the first pitch, The third pitch is one-fifth the first pitch. The encoder of claim 5.

9. The light receiving element includes a plurality of unit light receiving elements arranged in a circumferential direction. An encoder according to any one of claims 1 to 8.

10. An optical encoder for detecting a rotational position of a motor, A light-emitting element; a slit plate that transmits or reflects light emitted from the light-emitting element to generate a light and dark pattern; a light receiving element that converts the light from the slit plate into an electrical signal; A signal processing unit that processes an electrical signal from the light receiving element; Equipped with the slit plate has a pattern in which light and dark are alternately arranged at a predetermined pitch on a circumference, The bright portion of the pattern has a shape in which the width in the circumferential direction gradually narrows from the radial center portion toward both ends in the radial direction. Encoder.

11. a maximum width of the light in the radial direction after the pattern is projected onto the light receiving element is wider than a width of the light receiving element in the radial direction; The encoder of claim 10.

12. An optical encoder for detecting a rotational position of a motor, A light-emitting element; a slit plate that transmits or reflects light emitted from the light-emitting element to generate a light and dark pattern; a light receiving element that converts the light from the slit plate into an electrical signal; A signal processing unit that processes an electrical signal from the light receiving element; Equipped with the slit plate has a pattern in which light and dark are alternately arranged at a predetermined pitch on a circumference, The pattern has a shape of a bright portion that is a hexagon having sides along the circumferential direction at both radial ends. Encoder.

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