Optical encoder with partially blocked photodiode

Abstract

An optical encoder includes a photodiode array and an encoding disk arranged opposite to each other. The photodiode array includes at least three groups of position photodiodes and two index photodiodes arranged transversely. The two index photodiodes are adjacently arranged on the same side of the at least three groups of position photodiodes. The first group of position photodiodes and the last group of position photodiodes of the at least three groups of position photodiodes are partially shielded to reduce total harmonic distortion, and the position photodiodes other than the first group of position photodiodes and the last group of position photodiodes of the at least three groups of position photodiodes are not shielded.

Description

[0001] This application is a divisional application of the Chinese invention patent application with application number 201910932752.4, application date September 29, 2019, and name “Optical encoder with partially shielded photodiode”. Technical Field

[0002] The present invention relates to an optical encoder, and more particularly to an optical encoder capable of reducing total harmonic distortion and optical amplification mismatch and a photodiode array configuration thereof. Background Art

[0003] Optical rotary encoders can be used to detect the absolute or relative position of an infinitely rotating shaft, for example in a mouse device or printer.

[0004] The optical rotary encoder has a code disk and a photodiode array. The photodiode array is used to receive modulated light from the code disk to output differential quadrature signals with a phase difference of 90 degrees. However, the differential quadrature signals have problems of total harmonic distortion and phase difference not exactly equal to 90 degrees. In addition, in embodiments that include differential indexes to determine absolute position, there is also the problem of generating erroneous index signals due to optical magnification mismatch.

[0005] Therefore, an optical encoder that can mitigate or even eliminate the total harmonic distortion and optical amplification mismatch problems of differential quadrature signals is desirable. Summary of the invention

[0006] The present invention provides an optical encoder having a plurality of position photodiodes and a group of index photodiodes adjacently arranged to form a photodiode array extending along a first direction. The problem of total harmonic distortion is eliminated by partially shielding the two position photodiodes at both ends of the photodiode array.

[0007] The present invention also provides an optical encoder having a plurality of sets of position photodiodes and a set of index photodiodes arranged adjacent to each other, and partially shielding one of the index photodiodes to reduce the influence of optical magnification mismatch.

[0008] The present invention provides an optical encoder including a photodiode array and an opaque layer. The photodiode array includes at least three groups of position photodiodes arranged adjacently along a first direction, and each group of position photodiodes has a first photodiode, a second photodiode, a third photodiode and a fourth photodiode arranged in sequence along the first direction. The at least three groups of position photodiodes include a first group of position photodiodes and a last group of position photodiodes respectively arranged at both ends of the at least three groups of position photodiodes. The opaque layer shields the first group of position photodiodes and the last group of position photodiodes, but does not shield the position photodiodes other than the first group of position photodiodes and the last group of position photodiodes in the at least three groups of position photodiodes, wherein the shielding rate of the first photodiode, the second photodiode, the third photodiode and the fourth photodiode of the first group of position photodiodes by the opaque layer decreases in sequence, and the shielding rate of the first photodiode, the second photodiode, the third photodiode and the fourth photodiode of the last group of position photodiodes by the opaque layer increases in sequence.

[0009] The present invention also provides an optical encoder comprising a photodiode array, a first index photodiode, a second index photodiode and an opaque layer. The photodiode array comprises at least three groups of position photodiodes arranged adjacently along a first direction, and each group of position photodiodes has a first photodiode, a second photodiode, a third photodiode and a fourth photodiode arranged in sequence along the first direction. The first index photodiode is arranged adjacently at one of the two ends of the at least three groups of position photodiodes in the first direction. The second index photodiode is arranged adjacently to the first index photodiode in the first direction. The opaque layer shields a portion of one of the two edges of the second index photodiode in the first direction that extends inwardly and shields the first photodiode, the second photodiode, the third photodiode and the fourth photodiode of the first group of photodiodes and the last group of photodiodes at both ends of the at least three groups of position photodiodes.

[0010] The present invention also provides an optical encoder comprising a photodiode array, a first index photodiode, a second index photodiode and an opaque layer. The photodiode array comprises at least three groups of position photodiodes arranged adjacently along a first direction, and each group of position photodiodes comprises a first photodiode, a second photodiode, a third photodiode and a fourth photodiode arranged in sequence along the first direction. The at least three groups of position photodiodes comprise a first group of position photodiodes and a last group of position photodiodes respectively arranged at two ends of the at least three groups of position photodiodes. The first index photodiode is arranged adjacently at one of the two ends of the at least three groups of position photodiodes in the first direction. The second index photodiode is arranged adjacently to the first index photodiode in the first direction. The light-transmitting layer shields a portion of the first group of position photodiodes and the last group of position photodiodes and an inwardly extending portion of one of the two edges of the second index photodiode in the first direction, but does not shield position photodiodes other than the first group of position photodiodes and the last group of position photodiodes among the at least three groups of position photodiodes, wherein the shielding rates of the first photodiode, the second photodiode, the third photodiode and the fourth photodiode of the first group of position photodiodes by the light-impermeable layer decrease sequentially, and the shielding rates of the first photodiode, the second photodiode, the third photodiode and the fourth photodiode of the last group of position photodiodes by the light-impermeable layer increase sequentially.

[0011] In the embodiment of the present invention, the opaque layers above the photodiodes in the first group of positions and the photodiodes in the last group of positions are mirror-symmetrical or asymmetrical to each other.

[0012] In order to make the above and other purposes, features and advantages of the present invention more obvious, the following will be described in detail with reference to the accompanying drawings. In addition, in the description of the present invention, the same components are represented by the same symbols, which are hereby described together. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a schematic diagram of an optical encoder according to an embodiment of the present invention;

[0014] Figure 2 is a schematic diagram of a photodiode array and a coding slit of an optical encoder according to an embodiment of the present invention;

[0015] Figure 3 is a schematic diagram of the output current of the photodiode of the optical encoder according to an embodiment of the present invention;

[0016] Figure 4A Schematic diagram of the dimensions of the index photodiode and the encoding slit of the optical encoder according to an embodiment of the present invention;

[0017] Figure 4B is a schematic diagram of the output current and the difference of the index photodiode of the optical encoder according to an embodiment of the present invention;

[0018] Figure 5 is a schematic diagram of the output current and the difference of the index photodiode of the optical encoder according to an embodiment of the present invention when the light image profile is smaller than the diode;

[0019] Figure 6 is a schematic diagram of a photodiode array of an optical encoder according to another embodiment of the present invention;

[0020] Figure 7 is used Figure 6 Schematic diagram of an optical encoder configuration for eliminating erroneous index signals;

[0021] Figure 8 is a schematic diagram of the output current and the difference of the index photodiode of the optical encoder according to an embodiment of the present invention when the light image profile is larger than the diode;

[0022] Fig. 9 ; is a schematic diagram of a photodiode array of an optical encoder according to yet another embodiment of the present invention;

[0023] Fig.10 is used Fig. 9 Schematic diagram of an optical encoder configuration to eliminate erroneous index signals.

[0024] Description of Reference Numerals

[0025] 100 Optical encoder

[0026] 9 substrate

[0027] 10 Detection chip

[0028] 11 Light Source

[0029] 121, 122 Lens

[0030] 13 Photodiode Array

[0031] 15 Signal Processing Circuit

[0032] 20 Encoding disk

[0033] 30 Motor DETAILED DESCRIPTION

[0034] The present invention provides an optical encoder which reduces the influence of total harmonic distortion and optical amplification mismatch by partially shielding a photodiode array. The present invention can be applied to both a transmissive optical encoder and a reflective optical encoder.

[0035] Please refer to Figure 1 , which is a schematic diagram of an optical encoder 100 according to an embodiment of the present invention. The optical encoder 100 comprises a detection chip 10 disposed on a substrate 9 and a code disk 20 disposed relative to the detection chip 10, wherein the code disk 20 is provided with a plurality of code slits, including Figure 2 The position slit (AB Slit) and index slit (Index Slit) are shown. Figure 1 The code disk 20 is shown to be controlled by the motor 30 to rotate clockwise or counterclockwise, but the present invention is not limited thereto. According to different applications, the code disk 20 can be implemented as a code stripe to perform linear relative motion with the detection chip 10.

[0036] The detection chip 10 includes a light source 11 and a photodiode array 13. The light source 11 is, for example, a light emitting diode or a laser diode, which is used to emit a recognizable spectrum (for example, but not limited to, infrared light) to illuminate the encoding slit on the encoding disk 20 through a lens 121. In a reflective optical encoder, the encoding slit modulates the incident light and generates reflected light that is transmitted to the photodiode array 13 through another lens 122. In a transmissive optical encoder, the light source 11 and the photodiode array 13 may not be configured in the same packaging structure, but may be configured on two opposite sides of the encoding disk 20.

[0037] It must be pointed out that although Figure 1 The lenses 121 and 122 are shown separated from the detection chip 10, but this is only for illustration and not for limiting the present invention. In other embodiments, the lenses 121 and / or 122 may be disposed in the detection chip 10 to adjust (eg, guide and zoom) the light path.

[0038] Please refer to Figure 2 , which is a schematic diagram of the photodiode array 13 and the encoding slit of the optical encoder 100 according to an embodiment of the present invention. For illustration, Figure 2 Some encoding slits on the encoding disk 20 are shown. In different implementations, a full circle of encoding slits can be formed on the encoding disk 20, which includes multiple position slits (shown as AB Slit) and at least one index slit Index Slit. The Index Slit Index Slit can be used to indicate a starting angle, an ending angle or a specific angle.

[0039] The photodiode array 13 includes at least three groups of position photodiodes (eg Figure 1The at least three groups of position photodiodes are arranged adjacent to each other along a first direction (e.g., X direction), and each group of position photodiodes has a first photodiode I, a second photodiode II, a third photodiode III, and a fourth photodiode IV arranged in sequence along the first direction. The at least three groups of position photodiodes include a first group of position photodiodes (e.g., the leftmost group of photodiodes) and a last group of position photodiodes (e.g., the rightmost group of photodiodes), which are respectively arranged at both ends of the at least three groups of position photodiodes. In the present invention, the first direction is, for example, the arrangement direction of the plurality of photodiodes or the tangent direction of the encoding disk 20.

[0040] Please also refer to Figures 1 to 3 As shown, Figure 3 Schematic diagram of the output current of each photodiode of the optical encoder 100 of the embodiment of the present invention. In this embodiment, the phases of the output photocurrents of the first photodiode I and the second photodiode II are orthogonal. For example, the first photodiode I generates Figure 1 The signal A+ and Figure 3 Displayed as SINP; the second photodiode II produces Figure 1 The signal B+ and Figure 3 The output photocurrents of the first photodiode I and the third photodiode III are in phase with each other. For example, the third photodiode III generates Figure 1 The signal A- and Figure 3 The output photocurrents of the second photodiode II and the fourth photodiode IV are in phase with each other. For example, the fourth photodiode IV generates Figure 1 The signal B- and Figure 3 It is shown as COSM. It must be noted that the photocurrent signal can be a ramp signal, but is not limited to Figure 3 The sine wave signal is shown.

[0041] The optical encoder 100 further includes a signal processing circuit 15 for generating two channel signals CHA and CHB according to the signals A+, A-, B+ and B- for a downstream circuit (such as a processor) to determine the rotation angle of the encoder disk 20. The method of generating the two channel signals CHA and CHB is known and is not a main feature of the present invention, so it will not be described in detail here.

[0042] In this embodiment, the first photodiode I, the second photodiode II, the third photodiode III and the fourth photodiode IV of the at least three groups of position photodiodes have the same first width (e.g., D2 / 4) in the first direction and are perpendicular to the first direction (e.g., Figure 2 In the Y direction, the photodiodes have the same height H. In more detail, each photodiode has the same photosensitive area (or active area).

[0043] In this embodiment, the photodiode array 13 further includes two index photodiodes adjacently arranged in the first direction at one end of the two ends of the at least three groups of position photodiodes, for example, the first index photodiode INDEX_M- is adjacently arranged in the first direction at one end of the two ends of the at least three groups of position photodiodes, for example Figure 2 Displayed as left end to produce Figure 1 The signal I- and Figure 3 The second index photodiode INDEX_M+ is arranged adjacent to the first index photodiode INDEX_M- in the first direction, for example Figure 2 Displayed as left end to produce Figure 1 The signal I+ is Figure 3 The signal processing circuit 15 is further used to generate a channel signal CHI according to the signals I+ and I−, for example, by calculating a difference thereof, but the present invention is not limited thereto.

[0044] It is understood that when the first index photodiode INDEX_M- is disposed adjacent to the right end of the at least three sets of position photodiodes, the second index photodiode INDEX_M+ is disposed adjacent to the right end of the first index photodiode INDEX_M-. The present invention can reduce the area occupied by the photodiode array 13 and simplify the manufacturing by disposing all photodiodes on the same track.

[0045] In this embodiment, the second width (e.g., D2) of each of the two index photodiodes INDEX_M- and INDEX_M+ in the first direction is greater than the first width (e.g., D2 / 4) of the position photodiodes (photodiodes I to IV), for example, the second width is greater than or equal to 4 times the first width. The output currents INDEXM and INDEXP of the two index photodiodes INDEX_M- and INDEX_M+ are compared (examples are given below) to determine the absolute or reference angle of the encoder disk 20.

[0046] Relative to the position photodiode and the index photodiode, the encoding slit of the encoding disk 20 includes a plurality of position slits (shown as AB Slit) and at least one index slit Index Slit, the width of the index slit being greater than the position slit. In one embodiment, the encoding slits form a dark area (e.g., a non-reflective area or a non-transmissive area) and the area between the slits forms a bright area (e.g., a light reflecting area or a transmissive area). In another embodiment, the encoding slits form a bright area and the area between the slits forms a dark area, depending on different applications.

[0047] In a non-limiting embodiment, the slit width and slit spacing (i.e., the distance between adjacent position slits) D3 of the position slit are respectively equal to twice the first width of the position photodiode, for example D3 = (D2 / 2); and the slit width D1 of the index slit is equal to 1.5 times the second width of the index photodiode, for example D1 = (1.5×D2).

[0048] In other embodiments, regardless of whether the slit width D3 of the position slit is equal to twice the first width of the position photodiode, the light image profile projected by the position slit (reflected light or transmitted light, depending on the type of encoder) to the photodiode array 13 is equal to twice the first width of the position photodiode. Alternatively, regardless of whether the slit width D1 of the index slit is equal to 1.5 times the second width of the index photodiode, the light image profile projected by the index slit (reflected light or transmitted light, depending on the type of encoder) to the photodiode array 13 is equal to 1.5 times the second width of the index photodiode. In this embodiment, the size of the light image profile is determined by the magnification of the lenses 121 and 122 and the relative distance of the components. Preferably, the light image profile projected by the coding slit to the photodiode array 13 matches the size of the photodiode.

[0049] During operation, when the index slit passes over the position photodiodes, total harmonic distortion will be caused, especially the two groups of position photodiodes at the edge will contribute the most to the total harmonic distortion. Therefore, the present invention also provides an opaque layer, which can block the spectrum emitted by the light source 11, and is used to shield the first group of position photodiodes and the last group of position photodiodes. Figure 2 In the shaded area shown, the first group of position photodiodes (eg Figure 2 The shielding rates of the first photodiode I, the second photodiode II, the third photodiode III and the fourth photodiode IV of the leftmost photodiode group are shielded by the opaque layer in descending order; but the last group of photodiodes (e.g. Figure 2 The shielding rates of the first photodiode I, the second photodiode II, the third photodiode III and the fourth photodiode IV of the rightmost photodiode group being shielded by the opaque layer increase in sequence.

[0050] In a non-limiting embodiment, the first photodiode I, the second photodiode II, the third photodiode III and the fourth photodiode IV of the first group of position photodiodes are respectively shielded by the opaque layer by 85% to 95%, 65% to 75%, 45% to 55% and 25% to 35%; and the first photodiode I, the second photodiode II, the third photodiode III and the fourth photodiode IV of the last group of position photodiodes are respectively shielded by the opaque layer by 25% to 35%, 45% to 55%, 65% to 75% and 85% to 95%.

[0051] In addition, the position slit (shown as AB Slit) and the index slit are passed through the optical components (eg Figure 1 The optical image profile projected onto the photodiode array 13 by the lens 121 and / or 122 disposed between the encoder disk 20 and the photodiode array 13 can be magnified or reduced (for example, the magnification can be greater than or less than 1) through optical magnification adjustment, so that the optical image profile does not match the position photodiode and the index photodiode, and the photocurrent signal of the position photodiode interferes with the photocurrent signal of the index photodiode. As mentioned above, the projection mentioned here can be penetration or reflection.

[0052] Please refer to Figure 4A-4B As shown in FIG. 1 , if the light image profile is exactly equal to the size of the photodiode array 13, for example, the light image profile of the position slit and the slit spacing (shown as D3) is equal to twice the first width (D2 / 4) of the position photodiode and the light image profile of the index slit (shown as D1) is equal to 1.5 times the second width of the index photodiode, the Figure 4B The figure shows a single index output, for example, obtained by subtracting the output photocurrent M+ of the second index photodiode INDEX_M+ from the output photocurrent M- of the first index photodiode INDEX_M- (or vice versa). In this way, the correct reference position or angle can be obtained.

[0053] Figure 4A When the magnification of the optical component is exactly equal to 1, it means that the width of the position slit and the slit spacing is equal to twice the first width of the position photodiode, and the width of the index slit is equal to 1.5 times the second width of the index photodiode.

[0054] However, when the light image profile is not equal to the size of the photodiode array 13, interference may occur, such as Figure 5 and Figure 8 In the present invention, a light-proof layer (which can be made simultaneously with the light-proof layer shielding the position photodiode) is provided to shield a portion extending inwardly from one of the two edges of the second index photodiode INDEX_M+ in the first direction to eliminate crosstalk between photocurrents.

[0055] For example Figure 5 The interference situation is shown as follows: when the light image profile is smaller than the size of the photodiode array 13, the light image profile including the position slit and the slit spacing D3 is smaller than 2 times the first width of the position photodiode and / or the light image profile of the index slit D1 is smaller than 1.5 times the second width of the index photodiode. Figure 5It can be seen that there are two erroneous index signals. At this time, the opaque layer shields a portion of the second index photodiode INDEX_M+ extending inwardly away from the edge of the first index photodiode INDEX_M- in the first direction, such as Figure 6 After configuring this left opaque layer, Figure 7 It can be seen that originally Figure 5 The photocurrent M+ within the dotted line is suppressed and the erroneous index signal is eliminated.

[0056] For example Figure 8 The interference situation is shown when the light image profile is larger than the size of the photodiode array 13, wherein the light image profile including the position slit and the slit spacing D3 is larger than 2 times the first width of the position photodiode and / or the light image profile of the index slit D1 is larger than 1.5 times the second width of the index photodiode. Figure 8 It can be seen that there are two erroneous index signals. At this time, the opaque layer shields a portion of the second index photodiode INDEX_M+ extending inwardly from the edge of the first index photodiode INDEX_M- adjacent to the first index photodiode INDEX_M+ in the first direction, such as Fig. 9 After configuring this opaque layer on the right, Fig.10 It can be seen that originally Figure 8 The photocurrent M+ within the dotted line is suppressed and the erroneous index signal is eliminated.

[0057] It should be noted that the multiples (eg, 2 and 1.5) in the above embodiments are only for illustration and are not intended to limit the present invention. When the light image profile is larger or smaller than the size of the photodiode array 13, the photocurrent interference can be eliminated by shielding part of the second index photodiode INDEX_M+.

[0058] In the present invention, when the difference between the light image profile and the size of the photodiode array 13 is larger, the opaque layer (i.e. Figure 6 and Fig. 9 The larger the shielding area of ​​the shielding area II), the larger the shielding area of ​​the photosensitive surface or active area of ​​the index photodiode (under which one or more photodiodes are arranged) is. In the present invention, the opaque layer does not shield the first index photodiode INDEX_M- and the first group of position photodiodes and the last group of position photodiodes (i.e. Figure 6 and Fig. 9 The light-proof layer can be made by known processes such as sputtering or coating without any specific limitation.

[0059] It must be noted that, although in the above-mentioned embodiment, the shielding rates of the first photodiode, the second photodiode, the third photodiode and the fourth photodiode of the two-position photodiode group at both ends of the photodiode array are described as step-change, the present invention is not limited thereto. In other embodiments, the shielding rates of the two-position photodiode groups at both ends of the photodiode array are respectively reduced and increased in sequence with smooth changes, rather than step-changes between the photodiodes.

[0060] In summary, when an index slit with a larger area passes through a position photodiode, the output photocurrent will produce obvious total harmonic distortion. At the same time, if the size, shape, curvature and / or spacing of the light image profile projected from the coding slit to the photodiode array does not match the photodiode array, the photocurrent signal of the position photodiode will interfere with the photocurrent signal of the index photodiode, thereby generating an erroneous index signal (e.g. Figure 5 and Figure 8 ). Therefore, the present invention proposes a method of partially shielding the position light diode on both sides (for example Figure 2 , Figure 6 and Fig. 9 ) to reduce total harmonic distortion of optical encoders, and / or by shielding a portion of the indexing photodiodes (e.g. Figure 6 and Fig. 9 ) to eliminate erroneous index signals.

[0061] Although the present invention has been disclosed through the above examples, they are not intended to limit the present invention. Any person skilled in the art with ordinary knowledge in the art to which the present invention belongs can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the appended claims.

Claims

1. An optical encoder, comprising: A photodiode array, the photodiode array is used to receive the modulated light of the coded slit and comprises at least three groups of position photodiodes arranged adjacent to each other along a first direction, and each group of position photodiodes comprises a first photodiode, a second photodiode, a third photodiode and a fourth photodiode arranged in sequence along the first direction, the at least three groups of position photodiodes comprising a first group of position photodiodes and a last group of position photodiodes respectively arranged at two ends of the at least three groups of position photodiodes; and A light-proof layer, the light-proof layer is used to block the spectrum emitted by the light source and shield the first group of position photodiodes and the last group of position photodiodes, but does not shield the position photodiodes other than the first group of position photodiodes and the last group of position photodiodes in the at least three groups of position photodiodes, wherein: The shielding rates of the first photodiode, the second photodiode, the third photodiode and the fourth photodiode of the first group of position photodiodes by the light-impermeable layer decrease in sequence, and The shielding rates of the first photodiode, the second photodiode, the third photodiode, and the fourth photodiode of the last group of photodiodes by the light-impermeable layer increase in sequence.

2. The optical encoder according to claim 1, wherein The phases of the output photocurrents of the first photodiode and the second photodiode are orthogonal; The phases of the output photocurrents of the first photodiode and the third photodiode are in opposite phases; and The phases of output photocurrents of the second photodiode and the fourth photodiode are in opposite phases.

3. The optical encoder according to claim 2, wherein The shielding rates of the first photodiode, the second photodiode, the third photodiode and the fourth photodiode of the first group of position photodiodes by the light-impermeable layer are 90%, 70%, 50% and 30% respectively; and The shielding rates of the first photodiode, the second photodiode, the third photodiode and the fourth photodiode of the last group of photodiodes by the light-impermeable layer are 30%, 50%, 70% and 90% respectively.

4. The optical encoder according to claim 1, wherein the first photodiode, the second photodiode, the third photodiode and the fourth photodiode of the at least three groups of position photodiodes have a first width in the first direction and have the same height in a second direction perpendicular to the first direction.

5. The optical encoder according to claim 4, wherein The photodiode array further comprises two index photodiodes disposed adjacent to each other at one end of the two ends of the at least three groups of position photodiodes in the first direction, and A second width of each of the two index photodiodes in the first direction is greater than the first width. The optical encoder according to claim 5 , wherein the second width is greater than or equal to 4 times the first width.

7. The optical encoder according to claim 5, further comprising a code disk disposed relative to the photodiode array, wherein the code disk comprises: A plurality of slits at different positions, wherein the slit width and the slit spacing of the plurality of slits at different positions are equal to twice the first width; and An index slit, the slit width of which is equal to 1.5 times the second width, wherein, The plurality of position slits and the index slit serve as the encoding slits.

8. An optical encoder, comprising: A photodiode array, the photodiode array is used to receive the modulated light of the coded slit and comprises at least three groups of position photodiodes arranged adjacent to each other along a first direction, and each group of position photodiodes comprises a first photodiode, a second photodiode, a third photodiode and a fourth photodiode arranged in sequence along the first direction; A first index photodiode, the first index photodiode being adjacently arranged at one of the two ends of the at least three groups of position photodiodes in the first direction; a second index photodiode, the second index photodiode being arranged adjacent to the first index photodiode in the first direction; as well as A light-proof layer is used to block the spectrum emitted by the light source and shield a portion of the second index photodiode extending inwardly from one of the two edges in the first direction and shield the first photodiode, the second photodiode, the third photodiode and the fourth photodiode of the first group of photodiodes and the last group of photodiodes at both ends of the at least three groups of position photodiodes.

9. The optical encoder according to claim 8, wherein The first photodiode, the second photodiode, the third photodiode and the fourth photodiode of the at least three groups of position photodiodes have a first width in the first direction and have the same height in a second direction perpendicular to the first direction; and A second width of each of the first index photodiode and the second index photodiode in the first direction is greater than or equal to 4 times the first width.

10. The optical encoder according to claim 9, further comprising: an encoding disk, arranged relative to the photodiode array and comprising a plurality of position slits and at least one index slit as the encoding slit; and The optical element is disposed between the encoding disk and the photodiode array and is used for adjusting the light image profile projected from the position slit and the index slit to the photodiode array.

11. An optical encoder according to claim 10, wherein when the light image profile of the position slit is less than 2 times of the first width or the light image profile of the index slit is less than 1.5 times of the second width, the opaque layer shields a portion of the second index photodiode extending inward away from the edge of the first index photodiode.

12. An optical encoder according to claim 10, wherein when the light image profile of the position slit is greater than 2 times of the first width or the light image profile of the index slit is greater than 1.5 times of the second width, the opaque layer shields a portion of the second index photodiode extending inwardly from the edge of the first index photodiode adjacent to the second index photodiode. 13 . The optical encoder according to claim 10 , wherein the larger the difference between the size of the light image profile and the size of the photodiode array, the larger the shielding area of ​​the light-impermeable layer.

14. An optical encoder, comprising: A photodiode array, the photodiode array is used to receive the modulated light of the coded slit and comprises at least three groups of position photodiodes arranged adjacent to each other along a first direction, and each group of position photodiodes comprises a first photodiode, a second photodiode, a third photodiode and a fourth photodiode arranged in sequence along the first direction, and the at least three groups of position photodiodes comprise a first group of position photodiodes and a last group of position photodiodes respectively arranged at two ends of the at least three groups of position photodiodes; A first index photodiode, the first index photodiode being disposed adjacent to one of the two ends of the at least three groups of position photodiodes in the first direction; a second index photodiode, the second index photodiode being arranged adjacent to the first index photodiode in the first direction; as well as an opaque layer, the opaque layer being used to block the spectrum emitted by the light source and shielding a portion of the first group of position photodiodes and the last group of position photodiodes and one of the two edges of the second index photodiode in the first direction extending inwardly, but not shielding position photodiodes other than the first group of position photodiodes and the last group of position photodiodes among the at least three groups of position photodiodes, Among them, the shielding rates of the first photodiode, the second photodiode, the third photodiode and the fourth photodiode of the first group of position photodiodes by the opaque layer decrease sequentially, and the shielding rates of the first photodiode, the second photodiode, the third photodiode and the fourth photodiode of the last group of position photodiodes by the opaque layer increase sequentially.

15. The optical encoder according to claim 14, wherein The phases of the output photocurrents of the first photodiode and the second photodiode are orthogonal; The phases of the output photocurrents of the first photodiode and the third photodiode are in opposite phases; and The phases of output photocurrents of the second photodiode and the fourth photodiode are in opposite phases.

16. The optical encoder according to claim 15, wherein The shielding rates of the first photodiode, the second photodiode, the third photodiode and the fourth photodiode of the first group of position photodiodes by the light-impermeable layer are 90%, 70%, 50% and 30% respectively; and The shielding rates of the first photodiode, the second photodiode, the third photodiode and the fourth photodiode of the last group of photodiodes by the light-impermeable layer are 30%, 50%, 70% and 90% respectively.

17. The optical encoder according to claim 14, wherein The first photodiode, the second photodiode, the third photodiode and the fourth photodiode of the at least three groups of position photodiodes have a first width in the first direction and have the same height in a second direction perpendicular to the first direction; and A second width of each of the first index photodiode and the second index photodiode in the first direction is greater than the first width.

18. The optical encoder according to claim 17, further comprising: an encoding disk, arranged relative to the photodiode array and comprising a plurality of position slits and at least one index slit as the encoding slit; and The optical element is disposed between the encoding disk and the photodiode array and is used for adjusting the light image profile projected from the position slit and the index slit to the photodiode array.

19. The coding system according to claim 18, wherein When the light image profile is smaller than the size of the photodiode array, the light-proof layer shields a portion of the second index photodiode extending inwardly away from the edge of the first index photodiode; and When the light image profile is larger than the size of the photodiode array, the light-proof layer shields a portion of the second index photodiode extending inwardly from an edge adjacent to the first index photodiode.

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