Method for reducing encoder subdivision error and multi-reading-head photoelectric encoder

Abstract

The invention relates to the technical field of photoelectric encoders, in particular to a method for reducing encoder subdivision errors and a multi-reading-head photoelectric encoder, in a moire fringe signal period, SIN signals and COS signals which are collected are combined, a signal combination with the minimum orthogonality error is obtained through calculation, the signal combination is paired, and the signal combination with the minimum orthogonality error is obtained. The matching degree of the SIN signal and the COS signal is improved through an optimization matching mode, the higher the matching degree is, the smaller the subdivision error is, subdivision values of the paired SIN signal and COS signal are calculated, and the average value of the multiple subdivision values is used as a fine code angle signal of the encoder to be output. However, the traditional pairing method adopts a fixed pairing mode, the matching degree of the SIN signal and the COS signal is not the optimal signal combination, so that the subdivision value has a large error, and the precision of the encoder is directly low, and the SIN signal and the COS signal are subjected to optimization pairing, so that the reading precision of the encoder is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of photoelectric encoders, and in particular relates to a method for reducing encoder subdivision error and a multi-reader photoelectric encoder. Background Art

[0002] Photoelectric shaft angle encoder, also known as photoelectric angle position sensor, is a precision digital angle measuring device that integrates optics, mechanics and electronics. Photoelectric shaft angle encoder is generally composed of shaft system, light-emitting tube, code disk, slit, receiving tube and processing circuit. There are several concentric code tracks on the circular code disk of the encoder, and each code track is composed of light-transmitting and opaque fan-shaped ring sections. On one side of the code disk is a light-emitting element, and on the other side is a photosensitive element corresponding to each code track. Each light-emitting element and photosensitive element pair is called a reading head, and several reading heads are combined to form a group of reading heads. The code disk (moving grating) and the slit (static grating) are superimposed together to form moiré fringes. When the light emitted by the light-emitting element passes through the code disk and the slit and shines on the receiving element, a moiré fringe signal is formed. The moiré fringe signal contains the position information of the encoder code disk. When the code disk is in different positions, each photosensitive element outputs different moiré fringe current signals according to whether it is illuminated and the intensity of the light. The current signal is connected in series with the resistor, which converts the current signal into a voltage signal. This voltage signal is called the original moiré fringe input signal of the encoder.

[0003] A set of original moiré fringe signals of the precision code reading head of the photoelectric shaft encoder is generally divided into four channels, namely C0, C90, C180, and C270, which are four approximate sinusoidal signals with a phase difference of 90 degrees. Among them, the phase difference between C0 and C180 is 180 degrees. The sinusoidal signal obtained after the C0 and C180 signals enter the differential amplifier for amplification and shaping is recorded as the SIN signal; the phase difference between C90 and C270 is 180 degrees. The sinusoidal signal obtained after the C90 and C270 signals enter the differential amplifier for amplification and shaping is recorded as the COS signal. The phase difference between the SIN signal and the COS signal is 90 degrees. According to the values ​​of the SIN signal and the COS signal, the formula is: (1.1) The subdivision angle value θ of one fine code cycle of the encoder can be obtained. Since negative values ​​will appear in the actual calculation of formula (1.1), a certain angle will be added to the θ value according to the quadrant in the actual calculation to ensure that the subdivision value is positive and continuous within one moiré fringe signal cycle. For an absolute encoder, the subdivided fine code value is connected with the corrected coarse code value to form the encoder's angle value output.

[0004] When the displacement sensor has multiple sets of reading heads, each set of reading heads outputs four approximately sinusoidal Moiré fringe signals with a phase difference of 90 degrees. The subdivision method of each set of reading heads is the same, that is, the difference between C0 and C180 obtains the SIN signal, and the difference between C90 and C270 obtains the COS signal. Then, the SIN and COS of each set of reading heads are combined and subdivided using formula (1.1) to obtain the subdivision value of the group of reading heads. After all reading heads have completed the subdivision, the subdivision values ​​of multiple sets of reading heads are averaged, and the average value is used as the final precision code value output of the encoder.

[0005] Ideally, the moiré fringe signal output by the encoder reading head is a standard sine wave signal, and the SIN and COS signals after differentiation are also standard sine wave signals. When the formula (1.1) is used for subdivision, the subdivision error is zero. However, the moiré fringe signal output by the actual encoder is a non-ideal sine wave signal. When the formula (1.1) is used for subdivision, a subdivision error will be generated. The smaller the deviation between the SIN and COS signals and the ideal signal, the smaller the subdivision error and the higher the accuracy of the encoder.

[0006] When using formula (1.1) for subdivision, the higher the matching degree between the SIN signal and the COS signal, the smaller the subdivision error. When the matching degree between the SIN signal and the COS signal is low, such as when there is a large orthogonality error, the subdivision error will increase, resulting in low encoder accuracy. The existing technical solution is to match the SIN signal and the COS signal of each reading head. The matching degree between the SIN signal and the COS signal is not the best signal combination, resulting in a large error in the subdivision value, which directly leads to low encoder accuracy. Summary of the invention

[0007] In view of this, the invention aims to provide a method for reducing encoder subdivision error and a multi-reader photoelectric encoder. When pairing and subdividing SIN signals and COS signals, the traditional fixed pairing method is avoided, and the best signal is selected for combination pairing according to the characteristics of each signal, and then subdivided. The invention can reduce the subdivision error of the encoder and ultimately improve the accuracy of the encoder.

[0008] To achieve the above object, the technical solution created by the present invention is implemented as follows: The invention provides a method for reducing encoder subdivision error, wherein the encoder includes N precision code reading heads, N is greater than or equal to 8 and is an integer multiple of 4, the N precision code reading heads are evenly arranged on a precision code channel, and the N precision code reading heads output N / 4 SIN signals and N / 4 COS signals, specifically including the following steps: S1: In one moiré fringe signal cycle, N / 4 SIN signals and N / 4 COS signals are collected and normalized; S2: Select one normalized SIN signal and combine it with each normalized COS signal in turn, calculate the orthogonality error of the corresponding combination, compare and obtain the minimum orthogonality error, and pair the normalized SIN signal corresponding to the minimum orthogonality error with the COS signal; S3: Repeat S2 for the remaining normalized SIN signals and COS signals until each SIN signal finds a COS signal that is paired with it; S4: Calculate the subdivision values ​​of each pair of SIN and COS signals respectively, and take the average value of N / 4 subdivision values ​​as the encoder's precise angle signal output Preferably, the normalization process of the SIN signal and the COS signal is: Select the maximum voltage of each signal and voltage minimum , then the normalized voltage for: ; in, Represents the raw voltage acquired in real time before normalization.

[0009] Preferably, the orthogonality error is calculated as follows: The normalized SIN signal and COS signal are combined into a Lissajous figure, and the roundness error of the Lissajous figure is calculated and used as the orthogonality error; The minimum roundness error is obtained by comparison, and the normalized SIN signal corresponding to the minimum roundness error is paired with the COS signal.

[0010] Preferably, the circularity error of the Lissajous figure composed of the SIN signal and the COS signal is calculated by the least squares circle method.

[0011] Preferably, the roundness error The calculation formula is: ; Where n represents the number of sampling points in a moiré fringe signal period, m represents the mth sampling point, x m and y m Indicates the Lissajous figure m The horizontal and vertical coordinates corresponding to the sampling points, that is, the signal values ​​of the SIN signal and the COS signal at the time corresponding to the mth sampling point, Indicates the Lissajous figure m The distance between the sampling point and the standard circle.

[0012] Preferably, the orthogonality error is calculated as follows: The time difference between the normalized SIN signal peak moment and the normalized COS signal zero-crossing moment is taken as the orthogonality error; The minimum time difference is obtained by comparison, and the normalized SIN signal corresponding to the minimum time difference is paired with the COS signal.

[0013] Preferably, the subdivision values ​​of the SIN signal and the COS signal are The calculation formula is: ; Here, SIN and COS represent a paired SIN signal and COS signal.

[0014] On the other hand, the invention provides a multi-reader photoelectric encoder, which outputs a precise code angle signal by reducing the encoder subdivision error, and also includes: storing the numbers of the SIN signal and the COS signal, and directly using the stored SIN signal and COS signal numbers for pairing upon subsequent power-on.

[0015] Compared with the prior art, the invention can achieve the following beneficial effects:

[0016] The present invention optimizes the pairing process of SIN and COS signals, obtains the best orthogonality SIN and COS signal combination for pairing by one-by-one comparison, replaces the traditional fixed pairing method, and judges the orthogonality error of SIN and COS signals by the roundness error of Lissajous figure or the time difference between the peak value of SIN signal and the zero crossing of COS signal, realizes the optimal pairing of multi-channel signals, greatly improves the matching degree of SIN and COS signals, and further improves the original subdivision accuracy of encoder. On the basis of no structural optimization, higher-precision reading is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings: Figure 1 This is the schematic diagram of the signal acquisition principle of the reading head; Figure 2 This is a schematic diagram of the position of the reading heads when the number of reading heads N=64; Figure 3 is a flow chart of optimal pairing of SIN signal and COS signal provided in an embodiment of the present invention; Figure 4 is a schematic diagram of roundness error calculation provided according to an embodiment of the present invention; Figure 5 It is a program flow chart of the operation of the multi-reader photoelectric encoder provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and advantages of the invention clearer, the invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the invention and do not constitute a limitation to the invention. Similar components in different embodiments use associated similar component numbers. In the following embodiments, many detailed descriptions are to enable the invention to be better understood. However, those skilled in the art can easily recognize that some of the features can be omitted in different situations, or can be replaced by other components, materials, and methods. In some cases, some operations related to the invention are not shown or described in the specification, in order to avoid the core part of the invention being overwhelmed by too much description, and for those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations according to the description in the specification and the general technical knowledge in the art.

[0019] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other to form various implementation methods. At the same time, the steps or actions in the method description can also be interchanged or adjusted in a manner that is obvious to those skilled in the art. Therefore, the various sequences in the specification and the drawings are only for the purpose of clearly describing a certain embodiment and are not meant to be a necessary sequence, unless otherwise specified that a certain sequence must be followed.

[0020] In the description of the invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the invention, unless otherwise specified, the meaning of "multiple" is two or more.

[0021] In the description of the invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0022] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0023] In one embodiment of the present invention, a method for reducing encoder subdivision error is provided to solve the problem that when the traditional encoder reads, the SIN signal and the COS signal are fixedly paired, and the matching degree of the SIN signal and the COS signal is not the best signal combination, resulting in a large error in the subdivision value, which directly leads to a reduction in the accuracy of the encoder. For the reading principle of the multi-reader photoelectric encoder, please refer to Figure 1 The multi-reader encoder is mainly composed of a shaft system, a light-emitting tube, a code disc, a slit, a receiving tube and a processing circuit. During the rotation of the shaft system, the light emitted by the light-emitting tube passes through the code disc and the slit and shines on the receiving tube to form a moiré fringe signal. The original moiré fringe signal output by the encoder precision code reading head is divided into 4 channels. Correspondingly, the number of precision code reading heads is also a multiple of 4. Therefore, for the convenience of expression, the number of precision code reading heads of the encoder is represented by N, N≥8, and N is an integer multiple of 4. Each reading head outputs a moiré fringe signal that is approximately a sine wave, among which the phase of N / 4 precision code reading heads is 0°, the phase of N / 4 precision code reading heads is 90°, the phase of N / 4 precision code reading heads is 180°, and the phase of N / 4 precision code reading heads is 270°.

[0024] N precision code reading heads are evenly arranged at corresponding positions of the precision code channel. The reading phase difference between each precision code reading head and the precision code reading head installed opposite to it is 180°, and the reading phase difference between adjacent precision code reading heads is 90°. The signal after differential amplification of the signal with a phase of 0° and the signal with a phase of 180° is recorded as a SIN signal; the signal after differential amplification of the signal with a phase of 90° and the signal with a phase of 270° is recorded as a COS signal. The N reading heads generate a total of N / 4 SIN signals and N / 4 COS signals, which are recorded as the 1st to N / 4th SIN signals and the 1st to N / 4th COS signals, respectively. The traditional pairing method of SIN signals and COS signals is fixed, that is, the SIN signal of each precision code reading head itself is matched with its own COS signal, but the pairing method cannot obtain the best signal combination, which will cause the subdivision value to contain a large error. In order to eliminate this error, the embodiment of the present invention reduces the subdivision error and improves the encoder reading accuracy by optimizing the pairing process. Please refer to Figure 3 , the specific process is as follows: S1: First, the analog signal is collected through the precision code reading head, and the analog signal is converted into an AD digital signal, namely a SIN signal and a COS signal, through signal conversion. N precision code reading heads can collect N / 4 SIN signals and N / 4 COS signals in total. The signal collection process requires a complete moiré fringe signal cycle. Depending on the sampling frequency, each SIN signal and COS signal has multiple sampling points, that is, multiple voltages, within the moiré fringe signal cycle. .

[0025] Get the original voltage After that, the original voltages of the SIN and COS signals need to be normalized. Specifically, the maximum voltage of each SIN and COS signal within a complete moiré fringe signal cycle is obtained by comparison. and voltage minimum , according to the maximum voltage and voltage minimum Determine the normalization coefficient and perform normalization calculation using the following formula: (1.2) In addition, it is also important to note that due to the maximum voltage and voltage minimum It is only the voltage value collected within one week, and the normalization coefficient calculated by it will continue to be used in the subsequent power-on signal pairing process, so in some extreme cases, the real-time voltage The maximum value obtained when not in the pairing cycle and voltage minimum For example, in the actual measurement process, due to factors such as sensor accuracy, power supply voltage fluctuations, noise or interference, the voltage obtained in real time may be Beyond the expected range , ]. In addition, when collecting SIN and COS signals, the signal collection of the complete moiré fringe signal cycle may not be achieved. and It is not the maximum and minimum value of the complete cycle, because and was determined at an earlier point in time, while If the measurement is made at a later time point, the following two situations may also occur: when hour, ; when hour, .

[0026] S2: Randomly select a normalized SIN signal, record it as the first SIN signal, combine the first SIN signal with each normalized COS signal in turn, find the COS signal with the smallest orthogonality error obtained by combining with the first SIN signal through the traversal method, and pair the COS signal corresponding to the minimum orthogonality error after combination with the first SIN signal. In an embodiment of the present invention, a Lissajous figure is used to evaluate the degree of matching between the SIN signal and the COS signal during the encoder debugging process. By observing the degree to which the Lissajous figure deviates from the standard circle, the roundness error of the Lissajous figure is used as the orthogonality error, and the subdivision error of the moiré fringes is estimated by the size of the roundness error. For details, please refer to Figure 4 , combine the first SIN signal with each normalized COS signal in turn to form two composite trajectories of sinusoidal vibrations in mutually perpendicular directions. The Lissajous figure formed by two completely orthogonal SIN and COS signals is a standard circle, but due to the existence of errors, there will be a roundness error between the Lissajous figure formed by the SIN and COS signals and the standard circle. The roundness error of the Lissajous figure formed by any two SIN and COS signals can be calculated by the least squares circle method. The sampling points of the SIN and COS signals correspond to the points on the Lissajous figure. The sum of the squares of the distances from each point to the standard circle is calculated by the least squares circle method, which is considered to be the roundness error of the Lissajous figure formed by the SIN and COS signals. Roundness error The calculation formula is: (1.3) Where n represents the number of sampling points in a moiré fringe signal cycle. Usually, n ≥ 16. The larger the number of sampling points n, the greater the roundness error. The higher the calculation accuracy, the greater the roundness error The higher the matching degree between the SIN signal and COS signal, the better the result. m represents the mth sampling point. x m and y m Indicates the Lissajous figure m The horizontal and vertical coordinates corresponding to the sampling points, that is, the signal values ​​of the SIN signal and the COS signal at the time corresponding to the mth sampling point, Indicates the Lissajous figure m The distance between the sampling point and the standard circle.

[0027] S3: Repeat S2 for the remaining normalized SIN signals and the remaining COS signals, and pair the remaining SIN signals with the COS signals in sequence according to S2 until each SIN signal finds a COS signal that is paired with it, and a total of N / 4 pairing combinations are obtained.

[0028] S4: Record the paired SIN and COS signals, calculate the subdivision angle value of each pair of SIN and COS signals, perform electronic subdivision on the paired SIN and COS signals, and calculate the subdivision value. The calculation formula is: (1.1) A total of N / 4 subdivision values ​​are calculated, and the average value of the N / 4 subdivision values ​​is taken. The average value is used as the precision angle signal value of the encoder, and the subdivision value is transmitted to the host computer for output according to the communication protocol.

[0029] As an optional embodiment, other methods can also be used to pair the SIN signal and the COS signal. The only difference from the method of calculating the roundness error through the Lissajous graph is that the time difference between the peak moment of the normalized SIN signal and the zero-crossing moment of the normalized COS signal is used as the orthogonality error. In theory, if the two signals are completely orthogonal, this time difference should be 0. Specifically, for the normalized SIN signal, find its peak moment, which refers to the time point when the signal reaches the maximum or minimum value. For the normalized COS signal, find its zero-crossing moment, which refers to the time point when the signal changes from positive to negative or from negative to positive. Combine the SIN signal and the COS signal in sequence, find the pairing of the SIN signal and the COS signal with the smallest time difference, ensure that the orthogonality error between the signals is minimized, and thus improve the accuracy of signal processing.

[0030] In the embodiment of the present invention, a multi-reader photoelectric encoder is also designed based on the method of reducing the encoder subdivision error, and the above method of reducing the encoder subdivision error is used to output a precise code angle signal. For details, please refer to Figure 5 During the encoder debugging process, the SIN signal and COS signal of the encoder precision code reading head are paired by using the method of reducing the encoder subdivision error, and the numbers of the corresponding paired SIN signal and COS signal are recorded, and the maximum voltage of the SIN signal and COS signal is recorded. and voltage minimum The parameters used to calculate the normalization coefficient are stored in the non-volatile FLASH of the encoder data processor, and the pairing information and voltage parameters are directly obtained from the FLASH during subsequent power-on.

[0031] Before the encoder is powered on each time, the flag bit is first queried to confirm whether all the precision code reading heads have been paired, that is, the SIN signal and COS signal numbers of the encoder pairing can be read. If there are reading heads that have not been paired, the reading head pairing program is entered, and the pairing is performed using the method of reducing the encoder subdivision error. If all signals have been paired, the SIN signal and COS signal of each paired combination are electronically subdivided according to the pairing results, and the signal subdivision value is calculated using formula (1.1), and a total of N / 4 subdivision values ​​are calculated. The average of all subdivision values ​​is taken as the final encoder precision code signal value, and the subdivision value is transmitted to the host computer according to the communication protocol.

[0032] In short, the above description is only a preferred embodiment of this specification and is not intended to limit the protection scope of this specification. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this specification shall be included in the protection scope of this specification.

[0033] The systems, devices, modules or units described in one or more of the above embodiments may be implemented by a computer chip or entity, or by a product having a certain function. A typical implementation device is a computer. Specifically, the computer may be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.

[0034] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0035] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0036] The above is a description of a specific embodiment of the specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in an order different from that in the embodiments and still achieve the desired results. In addition, the processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

Claims

1. A method for reducing encoder subdivision error, the encoder includes N precision code reading heads, N is greater than or equal to 8 and is an integer multiple of 4, the N precision code reading heads are evenly arranged on the precision code channel, the N precision code reading heads output N / 4 SIN signals and N / 4 COS signals, characterized in that: The following steps are involved: S1: In one moiré fringe signal cycle, N / 4 SIN signals and N / 4 COS signals are collected and normalized; S2: Select one normalized SIN signal and combine it with each normalized COS signal in turn, calculate the orthogonality error of the corresponding combination, compare and obtain the minimum orthogonality error, and pair the normalized SIN signal corresponding to the minimum orthogonality error with the COS signal; S3: Repeat step S2 for the remaining normalized SIN signals and COS signals until each SIN signal finds a COS signal that is paired with it; S4: Calculate the subdivision values ​​of each pair of SIN signals and COS signals respectively, and output the average value of N / 4 subdivision values ​​as the encoder's precise angle signal.

2. The method for reducing encoder subdivision error according to claim 1, characterized in that: The normalization process of SIN signal and COS signal is: Select the maximum voltage of each signal and voltage minimum , then the normalized voltage for: ； in, Represents the raw voltage acquired in real time before normalization.

3. The method for reducing encoder subdivision error according to claim 1, characterized in that: The orthogonality error is calculated as follows: The normalized SIN signal and the COS signal are combined into a Lissajous figure, and the roundness error of the Lissajous figure is calculated and used as the orthogonality error; The minimum roundness error is obtained by comparison, and the normalized SIN signal corresponding to the minimum roundness error is paired with the COS signal.

4. The method for reducing encoder subdivision error as claimed in claim 3, characterized in that: The circularity error of the Lissajous figure composed of SIN signal and COS signal is calculated by the least square circle method.

5. The method for reducing encoder subdivision error as claimed in claim 4, characterized in that: Roundness error The calculation formula is: ； Where n represents the number of sampling points in a moiré fringe signal period, m represents the mth sampling point, x m and y m Indicates the Lissajous figure m The horizontal and vertical coordinates corresponding to the sampling points, that is, the signal values ​​of the SIN signal and the COS signal at the time corresponding to the mth sampling point, Indicates the Lissajous figure m The distance between the sampling point and the standard circle.

6. The method for reducing encoder subdivision error according to claim 1, characterized in that: The orthogonality error is calculated as follows: The time difference between the normalized SIN signal peak moment and the normalized COS signal zero-crossing moment is taken as the orthogonality error; The minimum time difference is obtained by comparison, and the normalized SIN signal corresponding to the minimum time difference is paired with the COS signal.

7. The method for reducing encoder subdivision error according to claim 1, characterized in that: Subdivision values ​​of SIN and COS signals The calculation formula is: ； Here, SIN and COS represent a paired SIN signal and COS signal.

8. A multi-reader photoelectric encoder, characterized in that: The method for reducing encoder subdivision error according to any one of claims 1 to 7 is used to output a precise code angle signal, further comprising: storing the numbers of the SIN signal and the COS signal, and directly using the stored numbers of the SIN signal and the COS signal for pairing upon subsequent power-on.

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