Encoder

Abstract

The present invention provides an encoder that suppresses the influence of harmonics in a received light waveform. The encoder is an optical encoder that detects a rotational position of a motor, and includes: a light emitting element; a slit plate that transmits or reflects light emitted from the light-emitting element to generate a pattern of a bright portion and a dark portion; a light receiving element which converts light from the slit plate into an electric signal; and a signal processing unit that processes an electric signal from the light receiving element, the slit plate having: a basic pattern in which bright sections and dark sections are alternately arranged at equal intervals at a first pitch on the circumference; and a harmonic suppression pattern in which bright portions and dark portions are alternately arranged at equal intervals at a second pitch on the basic pattern, the second pitch being one-Nth of the first pitch, where N is an integer of 2 or more.

Description

Technical Field

[0001] The present invention relates to an encoder. Background Art

[0002] Patent Document 1 discloses an optical encoder that provides a code pattern on a rotating disk and detects the speed and rotational position of the rotating disk by receiving light from a light emitting element that has passed through or reflected the code pattern via a fixed gap with a light receiving element.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2004-271453 Summary of the invention

[0004] <Problems to be Solved by the Invention>

[0005] In optical encoders, since harmonics are superimposed on the received light waveform, errors may occur in measurement.

[0006] The present invention provides an encoder for suppressing the influence of harmonics in an optical waveform.

[0007] <Methods used to solve the problem>

[0008] According to one aspect of the present invention, there is provided an encoder, which is an optical encoder for detecting the rotational position of a motor, comprising: a light-emitting element; a slit plate for transmitting or reflecting light emitted from the light-emitting element to generate a pattern of bright and dark portions; a light-receiving element for converting the light from the slit plate into an electrical signal; and a signal processing unit for processing the electrical signal from the light-receiving element, wherein the slit plate has: a basic pattern in which bright portions and dark portions are alternately and evenly spaced at a first pitch on a circle; and a harmonic suppression pattern in which bright portions and dark portions are alternately and evenly spaced at a second pitch on the basic pattern, wherein the second pitch is one Nth of the first pitch, wherein N is an integer greater than 2.

[0009] <Effects of the Invention>

[0010] According to the encoder of the present invention, it is possible to suppress the influence of harmonics in the light waveform. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a diagram showing an overview of a servo system using the encoder according to the present embodiment.

[0012] Figure 2 It is a diagram showing a schematic structure of an encoder according to the first embodiment.

[0013] Figure 3 This is a diagram illustrating the relationship between the light emission diameter of a light emitting element and the light receiving pattern.

[0014] Figure 4 This is a diagram illustrating the relationship between the light emission diameter of a light emitting element and the light receiving pattern.

[0015] Figure 5 This is a diagram for explaining the relationship between the fundamental wave and the harmonics in the received light waveform.

[0016] Figure 6 It is a diagram showing a reflection pattern in the encoder according to the first embodiment.

[0017] Figure 7 It is a diagram for explaining the received light waveform generated by the encoder according to the first embodiment.

[0018] Figure 8 It is a diagram for explaining a modified example of the reflection pattern in the encoder according to the first embodiment.

[0019] Fig. 9 It is a diagram for explaining a modified example of the reflection pattern in the encoder according to the first embodiment.

[0020] Fig.10 It is a diagram for explaining a modified example of the reflection pattern in the encoder according to the first embodiment.

[0021] Fig.11 It is a diagram for explaining a modified example of the reflection pattern in the encoder according to the first embodiment.

[0022] Fig.12 It is a diagram for explaining a modified example of the reflection pattern in the encoder according to the first embodiment.

[0023] Fig.13 It is a diagram for explaining a modified example of the reflection pattern in the encoder according to the first embodiment.

[0024] Fig.14 It is a diagram for explaining a modified example of the reflection pattern in the encoder according to the first embodiment.

[0025] Fig.15 It is a diagram for explaining a modified example of the reflection pattern in the encoder according to the first embodiment.

[0026] Fig.16 It is a diagram for explaining a modified example of the reflection pattern in the encoder according to the first embodiment.

[0027] Fig.17 It is a diagram for explaining a modified example of the reflection pattern in the encoder according to the first embodiment.

[0028] Fig.18 It is a diagram for explaining a modified example of the reflection pattern in the encoder according to the first embodiment.

[0029] Fig.19It is a diagram for explaining a modified example of the reflection pattern in the encoder according to the first embodiment.

[0030] Fig. 20 It is a diagram for explaining the arrangement of light receiving elements in the encoder according to the first embodiment.

[0031] Fig.21 It is a diagram for explaining a reflection pattern in the encoder according to the second embodiment.

[0032] Fig. 22 It is a diagram for explaining the arrangement of light receiving elements in the encoder according to the second embodiment.

[0033] Description of Reference Numerals

[0034] 1 Servo system

[0035] 10 Servo motor

[0036] 11 Rotation axis

[0037] 20 Encoder

[0038] 21 Slit Plate

[0039] 22 Light-emitting element

[0040] 23 Light receiving element

[0041] 23a Unit light receiving element

[0042] 24 Signal Processing Unit

[0043] 30 Servo amplifier

[0044] BP, BP1, BP2, BP3, BP4, BP5, BP6, BP7, BP8 basic pattern

[0045] BP101 pattern

[0046] HP1, HP11, HP2, HP21, HP3, HP31, HP4, HP41, HP5, HP6, HP7, HP81, HP82, HP83, HP84 harmonic suppression patterns

[0047] PEx1, PEx11, PEx2, PEx21, PEx3, PEx31, PEx4, PEx41, PEx5, PEx6, PEx7, PEx8, PEx81, PEy1 reflection patterns. DETAILED DESCRIPTION

[0048] Hereinafter, embodiments will be described with reference to the drawings. Note that the present invention is not limited to these examples but is defined by the claims and includes all modifications within the meaning and scope equivalent to the claims.

[0049] In addition, in the descriptions and drawings of the various embodiments, for components having substantially the same or corresponding functional structures, repeated descriptions are sometimes omitted by marking the same reference numerals. In addition, for ease of understanding, the scales of the various parts in the drawings are sometimes different from the actual scales.

[0050] The deviations in parallel, right angle, orthogonal, horizontal, vertical, up and down, left and right, front and back directions are allowed to the extent that the effects of the embodiments are not impaired. The shape of the corner is not limited to a right angle, and may also be rounded. Parallel, right angle, orthogonal, horizontal, and vertical may include approximately parallel, approximately right angle, approximately orthogonal, approximately horizontal, and approximately vertical, respectively.

[0051] For example, approximately parallel means that even if two lines or two surfaces are not completely parallel to each other, they can be considered parallel to each other as long as they are within the acceptable range for manufacturing. Similar to approximately parallel, as long as the relative positional relationship between two lines or two surfaces is within the acceptable range for manufacturing, other situations such as approximately right angles, approximately vertical, approximately horizontal, and approximately vertical can also be considered.

[0052] 《First Implementation Mode》

[0053] <Servo System>

[0054] A servo system using the encoder of this embodiment will be described. Figure 1 1 is a diagram showing an overview of a servo system 1 using an encoder 20 as an example of an encoder according to the present embodiment.

[0055] The servo system 1 includes a servo motor 10, an encoder 20, and a servo amplifier 30. In addition, here, a servo system using the encoder of the present embodiment is described, but the motor using the encoder of the present embodiment is not limited to the servo motor.

[0056] The servo motor 10 rotates the rotary shaft 11 based on the power from the servo amplifier 30 .

[0057] The encoder 20 detects the rotation 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 rotation position of the rotating shaft 11 to the servo amplifier 30.

[0058] The servo amplifier 30 controls the servo motor 10 by feeding back the detection result from the encoder 20 .

[0059] The encoder 20 will be described in detail. Figure 2 This is a diagram showing a schematic configuration of an encoder 20 as an example of an encoder according to the first embodiment.

[0060] The encoder 20 includes a slit plate 21 , a light emitting element 22 , a light receiving element 23 , and a signal processing unit 24 .

[0061] The slot plate 21 is a circular plate having a reflection pattern that reflects light emitted from the light emitting element 22 onto the light receiving element 23. For example, the slot plate 21 has a reflection pattern that is equally divided into a rectangular shape in the circumferential direction. In addition, the slot plate 21 has a light shielding pattern that shields light from the light emitting element 22 between the reflection patterns. In other words, the reflection pattern and the light shielding pattern are alternately arranged on the slot plate 21. The details of the reflection pattern will be described later.

[0062] The light emitting element 22 irradiates light toward the slot plate 21. The light emitting element 22 is, for example, a light emitting diode (LED (Light Emitting Diode)).

[0063] The light receiving element 23 receives the light emitted from the light emitting element 22 and reflected by the slot plate 21, and converts it into an electric signal. The light receiving element 23 is, for example, a photodetector. When irradiated with light, current flows in the light receiving element 23.

[0064] The signal processing unit 24 calculates the rotational position of the slit plate 21 by processing the electric signal from the light receiving element 23 .

[0065] A portion of the light emitted from the light emitting element 22 is reflected by the reflection pattern in the slot plate 21 and is received by the light receiving element 23. In addition, a portion of the light emitted from the light emitting element 22 is shielded by the light shielding pattern in the slot plate 21. When a portion of the light emitted from the light emitting element 22 is shielded by the light shielding pattern in the slot plate 21, the light receiving element 23 does not receive the light.

[0066] Therefore, the electrical signal detected and output by the light receiving element 23 has a sinusoidal waveform according to the intensity of light.

[0067] Here, the relationship between the light emission diameter of the light emitting element 22 and the width of the reflection pattern in the slot plate 21 will be described. Figure 3 and Figure 4 Each of these is a diagram for explaining the relationship between the light emission diameter of a light emitting element and a light receiving pattern.

[0068] exist Figure 3 and Figure 4 In the figure, LS1 and LS2 represent light emitting elements, respectively. WL1 and WL2 represent the light emission diameters of the light emitting elements. RP represents the reflection pattern. WR represents the width of the reflection pattern. PD represents the light receiving element.

[0069] like Figure 3As shown, when the light emitting diameter WL1 of the light emitting element LS1 is larger than the width WR of the reflection pattern RP, the image projected by the reflection pattern RP becomes blurred. Since the image projected by the reflection pattern RP becomes 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.

[0070] On the other hand, Figure 4 As shown, when the light emission diameter WL2 of the light emitting element LS2 is smaller than the width WR of the reflection pattern RP, the reflection pattern RP projects an image clearly. Since the reflection pattern RP projects an image clearly, the electric signal SIG2 detected by the light receiving element PD has a shape close to a trapezoidal wave.

[0071] The following describes the influence of superimposing harmonics on a sine wave. Figure 5 This is a diagram for explaining the relationship between the fundamental wave and the harmonics in the received light waveform.

[0072] exist Figure 5 In FIG. 1 , line Lh1 represents a sine wave. Line Lh3 represents the third harmonic of the sine wave represented by line Lh1. Line Lc represents a waveform obtained by superimposing the sine wave and the third harmonic.

[0073] like Figure 5 As shown, if the frequency component of the trapezoidal line Lc is examined, it can be considered that a certain proportion of the third harmonic is superimposed on the sine wave. If the third harmonic is superimposed to form a trapezoidal wave, it will become an error when detecting the rotation position.

[0074] Therefore, in order to suppress harmonics of a specific component, such as the third harmonic, the encoder of the first embodiment has a harmonic suppression pattern in the reflection pattern that suppresses the harmonics of the specific component. The encoder of the first embodiment is an optical encoder that detects the rotational position of a motor. The encoder of the first embodiment includes 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. In addition, the slit plate in the encoder of the first embodiment has a basic pattern in which bright and dark parts are alternately and evenly spaced at a first pitch on the circumference. In addition, in the slit plate in the encoder of the first embodiment, when the harmonic component to be suppressed is the Nth harmonic, the basic pattern has a harmonic suppression pattern in which bright and dark parts are alternately and evenly spaced at a second pitch, wherein the second pitch is one-Nth of the first pitch (where N is an integer greater than 2).

[0075] Figure 6This is a diagram for explaining a reflection pattern PEx1 for suppressing a third harmonic in the encoder 20 as an example of the encoder according to the first embodiment. Figure 6 In FIG. 1 , column EX represents the reflection pattern (PAT) and signal waveform (WF) of the encoder of the first embodiment. Figure 6 Column REF shows a general reflection pattern (PAT) and a signal waveform (WF) in the encoder of the reference example.

[0076] In addition, Figure 6 In the reflection pattern (PAT) of FIG. 1 , the hatched area represents the reflection area (bright), and the non-hatched area represents the light-shielding area (dark). The same is true in the following figures.

[0077] The method for forming the reflection pattern (PAT) is described. For example, the reflection pattern (PAT) can be formed by forming the slit plate 21 with a component that does not reflect light and forming the reflection portion with a reflection film. For another example, the reflection pattern (PAT) can be formed by forming the slit plate 21 with a component that reflects light and forming slits in the light-shielding portion.

[0078] In addition, in addition to the reflection pattern, the slot plate 21 may also have other light and dark patterns at different positions in the radial direction.

[0079] The reflection pattern PEx1 includes a basic pattern BP1 in which bright portions and dark portions are alternately arranged at equal intervals at a first pitch, and a harmonic suppression pattern HP1 in which bright portions and dark portions are alternately arranged at equal intervals at a second pitch, wherein the second pitch is one third of the first pitch. In each of the basic pattern BP1 and the harmonic suppression pattern HP1, the bright portions and dark portions are alternately arranged at equal intervals along the circumferential direction of the slot plate 21.

[0080] In addition, the influence amount of the harmonic suppression pattern HP1, that is, Figure 5 The amplitude of the harmonics shown is determined by the radial width of the slot plate 21. That is, if the radial width is widened, the influence (amplitude of the harmonics) becomes larger, and if the width is narrowed, the influence becomes smaller. In other words, the radial width of the harmonic suppression pattern HP1 is determined based on the amount of harmonics to be suppressed.

[0081] In addition, the harmonic suppression pattern HP1 is formed so that the phase of the light and dark pattern becomes the opposite phase with respect to the harmonic superimposed on the sine wave.

[0082] In addition, in this specification, the case where the light parts and the dark parts are alternately arranged at equal intervals at a predetermined pitch is not limited to the case where the light parts and the dark parts are alternately arranged at equal intervals at a predetermined pitch in a mathematically strict manner. For example, the case where the light parts and the dark parts are alternately arranged at equal intervals at a predetermined pitch also includes the case where the light parts and the dark parts are alternately arranged at equal intervals within the range of manufacturing tolerance in normal manufacturing.

[0083] On the other hand, the reflection pattern PRef of the encoder of the reference example has only the basic pattern BP.

[0084] Since the reflection pattern PEx1 has the harmonic suppression pattern HP1, as shown in the signal waveform WF, a waveform close to a sine wave is obtained. On the other hand, in the case of the reflection pattern PRef, a waveform in a trapezoidal shape is obtained.

[0085] Figure 7 It is a diagram for explaining the received light waveform generated by the encoder of the first embodiment. The line Lex is the received light waveform obtained by the reflection pattern PEx1, and the line Lref is the received light waveform obtained by the reflection pattern PRef. Figure 7 The horizontal axis represents the rotation angle, Figure 7 The vertical axis represents signal strength.

[0086] The reflection pattern PEx1 of the encoder of the first embodiment can reduce the harmonic component by 50% or more compared to the reflection pattern PRef of the encoder of the reference example.

[0087] According to the encoder of the first embodiment, since the slot plate has the harmonic suppression pattern, it is possible to suppress the influence of harmonics in the light waveform.

[0088] In addition, as described below, the second pitch in the harmonic suppression pattern is not limited to being one third of the first pitch in the basic pattern. For example, the second pitch may be one Nth of the first pitch in the basic pattern (where N is an integer greater than 2).

[0089] <Variation 1 (Phase Inversion)>

[0090] Modifications of the reflection pattern will be shown. Figure 8 1 is a diagram for explaining a modified example of a reflection pattern for suppressing the third harmonic in the encoder of the first embodiment. The reflection pattern PEx11 includes a harmonic suppression pattern HP11 instead of the harmonic suppression pattern HP1. The harmonic suppression pattern HP11 is a pattern that suppresses the third harmonic. Figure 6 The harmonic suppression pattern HP1 in the reflected pattern PEx1 shown is a pattern obtained by phase inversion.

[0091] According to the relationship between the phase of the third harmonic and the phase of the fundamental wave in the received light waveform, the harmonic suppression pattern HP11 whose phase is inverted may be superimposed on the basic pattern BP.

[0092] <Modification 2 (second harmonic suppression pattern)>

[0093] The harmonic suppression pattern is not limited to a pattern that suppresses the third harmonic. Fig. 9 and Fig.10This is a diagram illustrating a harmonic suppression pattern for suppressing the second harmonic as a modified example of the reflection pattern in the encoder of the first embodiment. The reflection pattern PEx2 includes a basic pattern BP2 and a harmonic suppression pattern HP2, wherein the pitch in the harmonic suppression pattern HP2 is half the pitch in the basic pattern BP2. Furthermore, the reflection pattern PEx21 includes a harmonic suppression pattern HP21 obtained by inverting the phase of the harmonic suppression pattern HP2, instead of the harmonic suppression pattern HP2.

[0094] According to Modification 2, the second harmonic can be suppressed.

[0095] <Modification 3 (fourth harmonic suppression pattern)>

[0096] Fig.11 and Fig.12 This is a diagram illustrating a harmonic suppression pattern for suppressing the fourth harmonic as a modified example of the reflection pattern of the encoder of the first embodiment. The reflection pattern PEx3 includes a basic pattern BP3 and a harmonic suppression pattern HP3, wherein the spacing in the harmonic suppression pattern HP3 is one-fourth of the spacing in the basic pattern BP3. In addition, the reflection pattern PEx31 has a harmonic suppression pattern HP31 obtained by inverting the phase of the harmonic suppression pattern HP3, instead of the harmonic suppression pattern HP3.

[0097] According to Modification 3, the fourth harmonic can be suppressed.

[0098] <Modification 4 (Fifth harmonic suppression pattern)>

[0099] Fig.13 and Fig.14 This is a diagram illustrating a harmonic suppression pattern for suppressing the fifth harmonic as a modified example of the reflection pattern of the encoder of the first embodiment. The reflection pattern PEx4 includes a basic pattern BP4 and a harmonic suppression pattern HP4, wherein the pitch of the harmonic suppression pattern HP4 is one-fifth of the pitch of the basic pattern BP4. In addition, the reflection pattern PEx41 includes a harmonic suppression pattern HP41 obtained by inverting the phase of the harmonic suppression pattern HP4, instead of the harmonic suppression pattern HP4.

[0100] According to Modification 4, the fifth harmonic can be suppressed.

[0101] <Modification 5 (Adjustment of the influence of the harmonic suppression pattern)>

[0102] By adjusting the radial width of the reflection pattern, the amount of harmonics suppressed by the harmonic suppression pattern (the amplitude of the harmonics) can be adjusted. Fig.15 This is a diagram for explaining the amount of suppression of harmonics as a modification of the reflection pattern of the encoder according to the first embodiment.

[0103] The reflection pattern PEx5 has a basic pattern BP5 and a harmonic suppression pattern HP5 for suppressing a third harmonic component. When the width H1 in the radial direction is increased, the amount of suppressed harmonics can be increased. In addition, when the width H1 is narrowed, the amount of suppressed harmonics can be reduced.

[0104] <Modification 6 (Adjustment of the influence of the harmonic suppression pattern)>

[0105] By adjusting the ratio of light to dark in the reflection pattern, it is possible to adjust the amount of harmonics suppressed by the harmonic suppression pattern. Fig.16 This is a diagram for explaining the amount of suppression of harmonics as a modified example of the reflection pattern in the encoder according to the first embodiment.

[0106] The reflection pattern PEx6 has a basic pattern BP6 and a harmonic suppression pattern HP6 for suppressing the third harmonic component. The spacing Pt1 is the same as that of the reflection pattern PEx1. On the other hand, the circumferential width Dt1 of the dark portion in the harmonic suppression pattern HP6 is different from the circumferential width Dt2 of the bright portion. By adjusting the width Dt1 of the dark portion and the width Dt2 of the bright portion, the amount of harmonics suppressed can be adjusted.

[0107] <Modification 7 (Adjustment of the influence of the harmonic suppression pattern)>

[0108] By adjusting the pitch of the reflection patterns, the amount of harmonics suppressed by the harmonic suppression pattern can be adjusted. Fig.17 This is a diagram for explaining the amount of suppression of harmonics as a modification of the reflection pattern of the encoder according to the first embodiment.

[0109] The reflection pattern PEx7 includes a basic pattern BP7 and a harmonic suppression pattern HP7 for suppressing a third harmonic component. The pitch Pt21 indicates the first pitch, and the pitch Pt22 indicates the next pitch. By adjusting the pitch Pt21 and the pitch Pt22, the amount of suppressed harmonics can be adjusted.

[0110] <Variation 8 (Suppression of multiple harmonics)>

[0111] The harmonic suppression pattern is not limited to a pattern that suppresses one kind of harmonic. Fig.18 and Fig.19 This is a diagram illustrating a harmonic suppression pattern for suppressing third and fifth harmonics as a modified example of the reflection pattern of the encoder of the first embodiment. The reflection pattern PEx8 has a basic pattern BP8 and a harmonic suppression pattern HP81, wherein the spacing in the harmonic suppression pattern HP81 is one third of the spacing in the basic pattern BP8. The reflection pattern PEx8 has a basic pattern BP8 and a harmonic suppression pattern HP82, wherein the spacing in the harmonic suppression pattern HP82 is one fifth of the spacing in the basic pattern BP8.

[0112] The reflection pattern PEx81 includes a harmonic suppression pattern HP83 obtained by inverting the phase of the harmonic suppression pattern HP81 instead of the harmonic suppression pattern HP81. The reflection pattern PEx81 includes a harmonic suppression pattern HP84 obtained by inverting the phase of the harmonic suppression pattern HP82 instead of the harmonic suppression pattern HP82.

[0113] According to Modification 8, multiple types of harmonics can be suppressed.

[0114] In addition, the harmonics suppressed by the harmonic suppression pattern are not limited to the combination of the third harmonic and the fifth harmonic. For example, a combination of multiple odd-order harmonics, such as a combination of the third harmonic and the seventh harmonic, can also be appropriately suppressed. For another example, a combination of odd-order harmonics and even-order harmonics can also be suppressed, and a combination of multiple even-order harmonics can also be suppressed. In other words, the slot plate has a first harmonic suppression pattern in which bright and dark portions are alternately and evenly spaced at a second pitch, wherein the second pitch is one-Nth of the first pitch (where N is an integer greater than 2). Furthermore, the slot plate has a second harmonic suppression pattern in which bright and dark portions are alternately and evenly spaced at a third pitch, wherein the third pitch is one-Mth of the first pitch (where M is an integer greater than 2 and different from N). In addition, a combination of three or more harmonics can also be suppressed.

[0115] <Light-receiving element>

[0116] The light receiving element 23 will be described. Fig. 20 1 is a diagram illustrating the configuration of the light receiving element in the encoder of the first embodiment. The light receiving element 23 has unit light receiving elements 23a. The unit light receiving elements 23a are arranged at a pitch that is one-fourth of the pitch of the basic pattern BP. In addition, the light receiving element 23 is arranged across a plurality of light and dark patterns relative to the basic pattern BP. For example, the light receiving element 23 includes a plurality of unit light receiving elements 23a arranged in a circumferential direction on the slit plate.

[0117] Since the light receiving element 23 has a plurality of unit light receiving elements 23a, it is possible to detect the position with high precision. Furthermore, since the light receiving element 23 has unit light receiving elements 23a across a plurality of light and dark patterns relative to the basic pattern BP, it is possible to average between the plurality of light and dark patterns, thereby stably detecting the position with higher precision.

[0118] For example, when the light receiving element 23 has unit light receiving elements 23a arranged at a pitch of one quarter of the pitch of the basic pattern BP, it is possible to suppress harmonic components that are even multiples of the signal processing. Therefore, as a harmonic suppression pattern, it is also possible to alternately arrange bright parts and dark parts at equal intervals at a second pitch of one K (where K is an odd number greater than 3) that is one-third of the first pitch of the basic pattern BP.

[0119] Second Implementation Method

[0120] The encoder of the second embodiment has a reflection pattern for suppressing harmonics. The encoder of the second embodiment is an optical encoder for detecting the rotational position of a motor. The encoder of the second embodiment includes a light emitting element, a slit plate that transmits or reflects light emitted from the light emitting element to produce a pattern of light and dark parts, 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. In addition, the slit plate in the encoder of the second embodiment has a pattern in which light and dark parts are alternately arranged at a predetermined pitch on the circumference, and the light parts are arranged at equal intervals. In addition, the pattern in the encoder of the second embodiment has a shape in which the width in the circumferential direction gradually narrows from the radial center part toward the radial ends.

[0121] If described from another point of view, the slot plate in the encoder of the second embodiment has a pattern in which bright parts and dark parts are alternately arranged at an arbitrary pitch on the circumference. In addition, in the pattern of the encoder of the second embodiment, the shape of the bright part is a hexagon with edges along the circumferential direction at both ends in the radial direction.

[0122] The details of the encoder of the second embodiment will be described with reference to the drawings. Fig.21 1 is a diagram illustrating a reflection pattern PEy1 in the encoder according to the second embodiment. Fig.21 In FIG. 1 , column EX1 represents the reflection pattern (PAT) and signal waveform (WF) of the encoder of the second embodiment. Fig.21 Column REF shows a general reflection pattern (PAT) and a signal waveform (WF) in the encoder of the reference example.

[0123] In addition, Fig.21 In the reflection pattern (PAT), the hatched portion represents the reflection portion (bright portion), and the non-hatched portion represents the light-shielding portion (dark portion).

[0124] The reflection pattern PEy1 has a pattern BP101 in which bright portions and dark portions are alternately arranged at a predetermined pitch. In the pattern BP101, the bright portions and dark portions are alternately arranged along the circumferential direction of the slot plate, and the bright portions are arranged at equal intervals. The bright portions in the pattern BP101 have the following shape: Fig.21 The central part of the longitudinal direction of the circle is oriented toward the outer diameter, and the circumferential direction ( Fig.21 The width of the bright portion in the pattern BP101 gradually narrows in the lateral direction, and the width in the circumferential direction gradually narrows from the central part in the radial direction toward the center direction. That is, the bright portion in the pattern BP101 has a shape in which the width in the circumferential direction gradually narrows from the central part in the radial direction toward the two end parts in the radial direction. More specifically, the bright portion in the pattern BP101 has a shape in which the width in the circumferential direction gradually narrows from the central part in the radial direction toward the two end parts in the radial direction. Fig.21The two ends of the pattern BP101 (in the longitudinal direction) have a hexagonal shape with sides along the circumferential direction. In addition, in the bright part of the pattern BP101, the widest part in the circumferential direction coincides with the radial center of the light receiving element 23, which is more ideal.

[0125] Next, the arrangement of the light receiving elements will be described. Fig. 22 1 is a diagram illustrating the configuration of the light receiving element in the encoder of the second embodiment. The light receiving element 23 has unit light receiving elements 23a arranged at a pitch of one quarter of the pitch of the bright portion of the pattern BP101. In addition, the light receiving element 23 is arranged across a plurality of light and dark patterns relative to the pattern BP101. For example, the light receiving element 23 includes a plurality of unit light receiving elements 23a arranged in a circumferential direction on the slit plate.

[0126] In addition, the maximum width of the bright portion 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 23 a ) in the radial direction.

[0127] In the unit light receiving element 23a, the amount of light reflected from the pattern BP101 is related to the overlapping area of ​​the unit light receiving element 23a and the bright part of the pattern BP101. The pattern BP101 has a bright part with the widest width in the radial center and a bright part with a gradually narrowing width in the circumferential direction from the radial center to both ends. When the pattern BP101 moves in the circumferential direction, the amount of light received by the unit light receiving element 23a gradually changes.

[0128] Therefore, if Fig.21 As shown in the signal waveform WF of EX1 in the figure, a signal waveform close to a sine wave can be obtained. Fig.21 The reflection pattern PEy1 can suppress the harmonic component to about one tenth compared with the reflection pattern PRef.

[0129] According to the encoder of the second embodiment, since the slot plate has a pattern in which the bright portion has a shape in which the circumferential width gradually narrows from the radial center portion toward the radial end portions, it is possible to suppress the influence of harmonics in the light waveform.

Claims

1. An encoder, which is an optical encoder for detecting a rotational position of a motor, comprising: Light emitting element; a slit plate that transmits or reflects light emitted from the light emitting element to generate a pattern of bright and dark parts; A light receiving element converts the light from the slot plate into an electrical signal; as well as A signal processing unit processes the electrical signal from the light receiving element. The slot plate has: The basic pattern is formed by arranging light portions and dark portions alternately and evenly at a first pitch on a circumference; as well as The harmonic suppression pattern is formed by alternately arranging bright portions and dark portions at equal intervals on the basic pattern at a second pitch, wherein the second pitch is one Nth of the first pitch, where N is an integer greater than or equal to 2.

2. The encoder according to claim 1, wherein A light emission diameter of the light emitting element is larger than a circumferential width of the harmonic suppression pattern.

3. The encoder according to claim 1, wherein The radial width of the harmonic suppression pattern is determined based on the amount of harmonics to be suppressed.

4. The encoder according to claim 1, wherein: The second pitch is one K times the first pitch, where K is an odd number greater than or equal to 3.

5. An encoder, which is an optical encoder for detecting the rotational position of a motor, comprising: Light emitting element; a slit plate that transmits or reflects light emitted from the light emitting element to generate a pattern of bright and dark parts; A light receiving element converts the light from the slot plate into an electrical signal; as well as A signal processing unit processes the electrical signal from the light receiving element. The slot plate has: The basic pattern is formed by arranging light portions and dark portions alternately and evenly at a first pitch on a circumference; a first harmonic suppression pattern, in which bright portions and dark portions are alternately arranged at equal intervals on the basic pattern at a second pitch, wherein the second pitch is one Nth of the first pitch, wherein N is an integer greater than or equal to 2; and The second harmonic suppression pattern is formed by alternately arranging bright portions and dark portions at equal intervals on the basic pattern at a third pitch, wherein the third pitch is one-M of the first pitch, where M is an integer greater than 2 and different from N.

6. The encoder according to claim 5, wherein: A light emission 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.

7. The encoder according to claim 5, wherein: The radial widths of each of the first harmonic suppression pattern and the second harmonic suppression pattern are determined based on the amount of harmonics to be suppressed.

8. The encoder according to claim 5, wherein: The second spacing is one third of the first spacing, The third interval is one fifth of the first interval.

9. The encoder according to any one of claims 1 to 8, wherein: The light receiving element includes a plurality of unit light receiving elements arranged along a circumferential direction.

10. An encoder, which is an optical encoder for detecting a rotational position of a motor, comprising: Light emitting element; a slit plate that transmits or reflects light emitted from the light emitting element to generate a pattern of bright and dark parts; A light receiving element converts the light from the slot plate into an electrical signal; as well as A signal processing unit processes the electrical signal from the light receiving element. The slit plate has a pattern in which bright portions and dark portions are alternately arranged at predetermined intervals on the 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 the radial ends.

11. The encoder according to claim 10, wherein: The maximum width of the bright portion in the radial direction after the pattern is projected onto the light receiving element is wider than the width of the light receiving element in the radial direction.

12. An encoder, which is an optical encoder for detecting a rotational position of a motor, comprising: Light emitting element; a slit plate that transmits or reflects light emitted from the light emitting element to generate a pattern of bright and dark parts; A light receiving element converts the light from the slot plate into an electrical signal; as well as A signal processing unit processes the electrical signal from the light receiving element. The slit plate has a pattern in which bright portions and dark portions are alternately arranged at predetermined intervals on the circumference. In the pattern, the bright portion has a hexagonal shape having sides along the circumferential direction at both ends in the radial direction.

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