Method for reducing encoder subdivision error and multi-read head optical encoder

Abstract

The present application relates to the technical field of photoelectric encoder, and specifically provides a method for reducing the subdivision error of an encoder and a multi-reading head photoelectric encoder, wherein the collected SIN signal and COS signal are combined within a moire fringe signal period, the signal combination with the minimum orthogonality error is calculated and obtained, and the signal combination is paired, the matching degree of the SIN signal and the COS signal is improved through the pairing optimization, the higher the matching degree, the smaller the subdivision error, the subdivision values of the paired SIN signal and COS signal are calculated, and the average value of the plurality of subdivision values is taken as the fine code angle signal output of the encoder. The traditional pairing method is fixed pairing, 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 and directly leading to low accuracy of the encoder. The SIN signal and the COS signal are paired through optimization in the present application, which greatly improves the reading accuracy of the encoder.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of photoelectric encoder, and particularly relates to a method for reducing encoder subdivision error and a multi-reading head photoelectric encoder. BACKGROUND

[0002] Photoelectric shaft angle encoder, also known as photoelectric angle position sensor, is a kind of precision digital angle measuring device integrating light, machine and electricity. The photoelectric shaft angle encoder generally comprises a shaft system, a light-emitting tube, a code disc, a slit, a receiving tube and a processing circuit. The circular code disc of the encoder has a plurality of concentric code tracks. Each code track is composed of light-transmitting and non-light-transmitting sector-shaped intervals. On one side of the code disc is a light-emitting element, and on the other side corresponding to each code track is a photosensitive element. Each light-emitting element and photosensitive element are paired as a reading head, and several reading heads are combined to form a group of reading heads. The code disc (moving grating) and the slit (stationary grating) are superimposed together to form Moire fringes. When the light emitted by the light-emitting element passes through the code disc and the slit to irradiate the receiving element, Moire fringe signals are formed. The Moire fringe signals contain the position information of the code disc of the encoder. When the code disc is at different positions, the photosensitive elements output different Moire fringe current signals according to whether they are illuminated and the intensity of the illumination. The current signals are connected in series with a resistor, and the resistor converts the current signals into voltage signals. The voltage signals are called the original Moire fringe input signals of the encoder.

[0003] The original Moire fringe signals of a group of fine code reading heads of the photoelectric shaft angle encoder are generally divided into four paths, which are C0, C90, C180 and C270, and are four approximately sinusoidal wave signals with a phase difference of 90 degrees. C0 and C180 have a phase difference of 180 degrees, and the sinusoidal wave signal obtained after the C0 and C180 signals enter a differential amplifier for amplification and shaping is recorded as a SIN signal. C90 and C270 have a phase difference of 180 degrees, and the sinusoidal wave signal obtained after the C90 and C270 signals enter a differential amplifier for amplification and shaping is recorded as a 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 subdivision angle value θ of one fine code period of the encoder can be obtained through the formula:

[0004] (1.1)

[0005] That is, the subdivision angle value θ of one fine code period of the encoder can be obtained through the formula:

[0006] When the displacement sensor has multiple sets of reading heads, each set of reading heads outputs four-phase approximately sinusoidal Moiré fringe signals with a phase difference of 90 degrees. The subdivision method of each set of reading heads is consistent, that is, the SIN signal is obtained by differentiating C0 and C180, and the COS signal is obtained by differentiating C90 and C270, 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 set of reading heads. After all the reading heads are subdivided, the subdivision values of the multiple sets of reading heads are averaged, and the average value is output as the final precision code value of the encoder.

[0007] Ideally, the Moiré fringe signal output by the encoder reading head is a standard sinusoidal signal, the SIN and COS signals after differentiation are also standard sinusoidal signals, and the subdivision error is zero when formula (1.1) is used for subdivision. However, the Moiré fringe signal output by the actual encoder is a non-ideal sinusoidal signal, and the subdivision error will occur when formula (1.1) is used for subdivision. The smaller the deviation of the SIN signal and the COS signal from the ideal signal, the smaller the subdivision error, and the higher the precision of the encoder.

[0008] When formula (1.1) is used for subdivision, the higher the matching degree of the SIN signal and the COS signal, the smaller the subdivision error. When the matching degree of the SIN signal and the COS signal is low, such as having a large orthogonality error, the subdivision error will increase, resulting in low precision of the encoder. The existing technical solution matches the SIN signal and the COS signal of each reading head itself, 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 and directly leading to low precision of the encoder. SUMMARY

[0009] Therefore, the present application aims to provide a method for reducing the subdivision error of an encoder and a multi-reading head photoelectric encoder. When the SIN signal and the COS signal are paired and subdivided, the traditional fixed pairing method is avoided, and the best signal is selected for combination and pairing according to the characteristics of each signal. The present application can reduce the subdivision error of the encoder and ultimately improve the precision of the encoder.

[0010] To achieve the above-mentioned purpose, the technical solution of the present application is as follows:

[0011] The present application provides a method for reducing the subdivision error of an encoder, the encoder comprising N precision code reading heads, N being greater than or equal to 8 and being an integer multiple of 4, the N precision code reading heads being evenly arranged on a precision code track, the N precision code reading heads outputting N / 4 SIN signals and N / 4 COS signals, and the method comprising the following steps:

[0012] S1: Collect N / 4 SIN signals and N / 4 COS signals in one Moire fringe signal period, and normalize them;

[0013] S2: Optionally, combine one normalized SIN signal with each normalized COS signal, calculate the orthogonality error of each combination, compare to obtain the minimum orthogonality error, and pair the normalized SIN signal and COS signal corresponding to the minimum orthogonality error;

[0014] S3: Repeat S2 for the remaining normalized SIN signals and COS signals until each SIN signal finds its paired COS signal;

[0015] S4: Calculate the subdivision value of each paired SIN signal and COS signal, and take the average of the N / 4 subdivision values as the fine code angle signal output of the encoder

[0016] Preferably, the normalization process of the SIN signal and the COS signal is as follows:

[0017] Select the maximum voltage of each signal and the minimum voltage , then the normalized voltage is:

[0018] ;

[0019] Wherein, represents the original voltage collected in real time before normalization.

[0020] Preferably, the calculation method of the orthogonality error is as follows:

[0021] Synthesize the Lissajous figure of the normalized SIN signal and the COS signal, calculate the roundness error of the Lissajous figure, and take it as the orthogonality error;

[0022] Compare to obtain the minimum roundness error, and pair the normalized SIN signal and the COS signal corresponding to the minimum roundness error.

[0023] Preferably, the roundness error of the Lissajous figure composed of the SIN signal and the COS signal is calculated by the least square circle method.

[0024] Preferably, the calculation formula of the roundness error is:

[0025] ;

[0026] Wherein, n represents the number of sampling points in one Moire fringe signal period, and m represents the mth sampling point, xm and y m denotes the first m the horizontal and vertical coordinates of the sampling point, i.e. the signal values of the SIN signal and the COS signal at the time corresponding to the mth sampling point, denotes the first m the distance between the sampling point and the standard circle.

[0027] Preferably, the calculation method of the orthogonality error is:

[0028] the time difference between the normalized SIN signal peak time and the normalized COS signal zero-crossing time is taken as the orthogonality error;

[0029] the minimum time difference is compared and obtained, and the normalized SIN signal and the COS signal corresponding to the minimum time difference are paired.

[0030] Preferably, the subdivision value of the SIN signal and the COS signal is The calculation formula is:

[0031] ;

[0032] wherein, SIN and COS represent the paired SIN signal and the COS signal.

[0033] The present application provides another aspect of a multi-reading head photoelectric encoder, which utilizes the method for reducing the subdivision error of the encoder to output the fine code angle signal, and further comprises: storing the numbers of the SIN signal and the COS signal, and directly pairing the stored numbers of the SIN signal and the COS signal in subsequent power-on.

[0034] Compared with the prior art, the present application can achieve the following beneficial effects:

[0035] The pairing process of the SIN signal and the COS signal is optimized and designed in the present application, and the SIN signal and the COS signal combination with the best orthogonality is obtained through one-by-one comparison and pairing, which replaces the traditional fixed pairing method. The orthogonality error of the SIN signal and the COS signal is judged by the roundness error of the Lissajous figure or the time difference between the SIN signal peak and the COS signal zero-crossing, the optimal pairing of the multi-channel signal is realized, the matching degree of the SIN signal and the COS signal is greatly improved, and the original subdivision precision of the encoder is improved. Without structural optimization, higher precision reading is realized. BRIEF DESCRIPTION OF DRAWINGS

[0036] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments of the application illustrate the

[0037] Figure 1 is a schematic diagram of the signal acquisition principle of the reading head;

[0038] Figure 2 is a schematic diagram of the reading head position when the number of reading heads N = 64;

[0039] Figure 3 is a flow chart of the SIN signal and COS signal optimization pairing provided by the embodiment of the application;

[0040] Figure 4 is a schematic diagram of the roundness error calculation provided by the embodiment of the application;

[0041] Figure 5 is a program flow chart of the operation of the multi-reading head photoelectric encoder provided by the embodiment of the application. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical scheme and advantages of the application clearer, the application will be further described in detail below with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the application, and do not constitute a limitation on the application. Similar elements in different embodiments use associated similar element labels. In the following embodiments, many details are described in order to make the application better understood. However, those skilled in the art can easily recognize that some features can be omitted in different cases, or can be replaced by other elements, materials or methods. In some cases, some operations related to the application are not shown or described in the specification in order to avoid the core part of the application being overwhelmed by too much description, and it is not necessary for those skilled in the art to describe these related operations in detail based on the description in the specification and general technical knowledge in the art.

[0043] It should be noted that the embodiments in the application and the features in the embodiments can be combined with each other to form various embodiments without conflict. At the same time, each step or action in the method description can also be sequentially adjusted or adjusted in a manner obvious to those skilled in the art. Therefore, the various sequences in the specification and drawings are only for the purpose of clearly describing a certain embodiment, and do not mean a necessary sequence, unless otherwise stated that a certain sequence must be followed.

[0044] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application. In addition, the terms "first", "second" and the like are only for the purpose of description and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined with "first", "second" and the like can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0045] In the description of the present application, it should be noted that unless otherwise specified and limited, the terms "mounting", "connecting", "connecting" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be connected inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood through specific circumstances.

[0046] The present application will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0047] In one embodiment of the present application, a method for reducing the subdivision error of an encoder is provided to solve the problem that when the traditional encoder reads, the SIN signal and the COS signal adopt a fixed pairing mode, 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, directly leading to a decrease in the accuracy of the encoder. The reading principle of the multi-reading head photoelectric encoder is described in Figure 1A multi-readhead encoder mainly consists of a shaft system, LEDs, a code disk, a slit, a receiving tube, and a processing circuit. During the rotation of the shaft system, the light emitted by the LEDs passes through the code disk and the slit and illuminates the receiving tube, forming a moiré fringe signal. The original moiré fringe signal output by the encoder's precision readhead is divided into 4 channels. Correspondingly, the number of precision readheads is also a multiple of 4. Therefore, for ease of expression, the number of precision readheads of the encoder is represented by N, where N≥8 and N is an integer multiple of 4. Each readhead outputs one approximately sinusoidal moiré fringe signal, where the phase of N / 4 precision readheads is 0°, the phase of N / 4 precision readheads is 90°, the phase of N / 4 precision readheads is 180°, and the phase of N / 4 precision readheads is 270°.

[0048] N precision code reading heads are evenly distributed at corresponding positions on the precision code track. The phase difference between each precision code reading head and its corresponding counterpart is 180°, and the phase difference between adjacent precision code reading heads is 90°. The signal obtained by differentially amplifying the signal with a phase of 0° and the signal with a phase of 180° is denoted as the SIN signal; the signal obtained by differentially amplifying the signal with a phase of 90° and the signal with a phase of 270° is denoted as the COS signal. The N reading heads generate a total of N / 4 SIN signals and N / 4 COS signals, denoted as the 1st to N / 4th SIN signals and the 1st to N / 4th COS signals, respectively. Traditionally, the pairing method for SIN and COS signals is fixed, meaning each precision code reading head matches its own SIN signal with its own COS signal. However, this pairing method cannot obtain the optimal signal combination, leading to significant errors in the subdivision values. To eliminate this error, this embodiment of the invention optimizes the pairing process, reducing subdivision errors and improving encoder reading accuracy. Please refer to [link to relevant documentation]. Figure 3 The specific process is as follows:

[0049] S1: First, analog signals are acquired using precision code reading heads. The analog signals are then converted into digital (AD) signals, namely SIN and COS signals, through signal conversion. N precision code reading heads can acquire a total of N / 4 channels of SIN and N / 4 channels of COS signals. The signal acquisition process requires one complete moiré fringe signal cycle. Depending on the sampling frequency, each SIN and COS signal has multiple sampling points within the moiré fringe signal cycle, i.e., multiple voltage levels. .

[0050] Obtain the original voltage Next, the raw voltages of the SIN and COS signals need to be normalized. Specifically, the maximum voltage value of each SIN and COS signal within a complete moiré fringe signal period is obtained using a comparison method. and minimum voltage According to the maximum voltage and the voltage minimum value The normalization coefficient is determined and the normalization calculation is performed by the following formula:

[0051] (1.2)

[0052] In addition, it should also be noted that, since the voltage maximum value and the voltage minimum value is only a voltage value collected within one week, and the normalization coefficient calculated therefrom will continue to be used for subsequent signal pairing processes of power-on start, in some extreme cases, the voltage obtained in real time may not be between the maximum value and the voltage minimum value obtained in the pairing period, for example, in the actual measurement process, due to factors such as sensor accuracy, power supply voltage fluctuation, noise or interference, the voltage obtained in real time may exceed the expected range , In addition, there may also be a situation that, when the SIN signal and the COS signal are collected, the signal collection does not realize a complete Moiré fringe signal period, and the and in the collected signal are not the maximum value and the minimum value of a complete period, since and are determined at an earlier time point, and is measured at a later time point, the following two situations may also occur:

[0053] When , ;

[0054] When , .

[0055] S2: arbitrarily select one of the normalized SIN signals as a first SIN signal, combine the first SIN signal with each of the normalized COS signals in turn, find the COS signal with the minimum orthogonality error obtained by combining 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 the embodiment of the present application, the matching degree of the SIN signal and the COS signal in the encoder debugging process is evaluated by using a Lissajous figure. By observing the degree of deviation of the Lissajous figure from a standard circle, that is, taking the roundness error of the Lissajous figure as the orthogonality error, the subdivision error of the Moiré fringe is estimated by the size of the roundness error. For details, please refer to Figure 4The first SIN signal is combined with each normalized COS signal in sequence to form two synthetic tracks of sinusoidal vibration along perpendicular directions. The Lissajous figure formed by the two completely orthogonal SIN signals and COS signals is a standard circle, but due to errors, there is a roundness error between the Lissajous figure formed by the SIN signals and COS signals and the standard circle. The roundness error of the Lissajous figure formed by any two SIN signals and COS signals can be calculated by the least square circle method. The sampling points of the SIN signals and COS signals correspond to points on the Lissajous figure, and the sum of squares of the distances of each point to the standard circle is calculated by the least square circle method, which is considered as the roundness error of the Lissajous figure formed by the SIN signals and COS signals. The calculation formula of the roundness error is as follows:

[0056] (1.3)

[0057] wherein n represents the number of sampling points in one period of a moire fringe signal, and n≥16 in general, the greater the number of sampling points n, the higher the calculation precision of the roundness error , and the higher the matching degree of the obtained SIN signals and COS signals determined by the roundness error . m represents the mth sampling point, x m and y m represent the abscissa and ordinate of the mth sampling point on the Lissajous figure, i.e. the signal values of the SIN signals and COS signals at the time corresponding to the mth sampling point, m and represent the distance of the mth sampling point on the Lissajous figure to the standard circle. m

[0058] S3: The remaining normalized SIN signals are repeatedly paired with the remaining COS signals according to S2, and the remaining SIN signals are sequentially paired with the COS signals according to the mode of S2 until each SIN signal finds a paired COS signal, and N / 4 paired combinations are obtained.

[0059] S4: The paired SIN signals and COS signals are recorded, and the subdivision angle values of each pair of SIN signals and COS signals are calculated, and the paired SIN signals and COS signals are electronically subdivided, and the subdivision value is calculated by the formula:

[0060] (1.1)

[0061] ​The N / 4 subdivision values are obtained, the N / 4 subdivision values are averaged, and the average value is taken as the fine code angle signal value of the encoder; and the subdivision values are transmitted to the host computer according to a communication protocol.

[0062] As an optional embodiment, the SIN signal and the COS signal can also be paired by using other methods, and the difference from the method of calculating the roundness error by using the Lissajous figure is that the time difference between the peak time of the normalized SIN signal and the zero-crossing time of the normalized COS signal is taken as the orthogonality error. In theory, if the two signals are completely orthogonal, the time difference should be 0. Specifically, for the normalized SIN signal, the peak time is found, which refers to the time point at which the signal reaches the maximum or minimum. For the normalized COS signal, the zero-crossing time is found, which refers to the time point at which the signal changes from positive to negative or from negative to positive. The SIN signal and the COS signal are sequentially combined, the SIN signal and the COS signal with the minimum time difference are paired to ensure that the orthogonality error between the signals is minimized, thereby improving the accuracy of signal processing.

[0063] In the embodiment of the application, a multi-reading head photoelectric encoder is also designed based on the method for reducing the subdivision error of the encoder, and the fine code angle signal is output by using the above-mentioned method for reducing the subdivision error of the encoder. Specifically, please refer to Figure 5 In the debugging process of the encoder, the SIN signal and the COS signal of the fine code reading head of the encoder are paired by using the method for reducing the subdivision error of the encoder, and the numbers of the corresponding paired SIN signal and COS signal are recorded, and the maximum voltage and the minimum voltage of the SIN signal and the COS signal are stored in the non-volatile FLASH of the encoder data processor as parameters for calculating the normalization coefficient, and the pairing information and the voltage parameters are directly obtained from the FLASH after subsequent power-on.

[0064] Before each power-on of the encoder, the flag bit is first queried to confirm whether all the fine code reading heads have completed pairing, that is, the numbers of the paired SIN signal and COS signal of the encoder are readable. If there is a reading head that has not completed pairing, the reading head pairing program is entered, and the pairing is performed by using the method for reducing the subdivision error of the encoder. If all the signals have completed pairing, the SIN signal and the COS signal of each paired combination are electronically subdivided according to the pairing result, the subdivision value of the signal is calculated by using formula (1.1), and a total of N / 4 subdivision values are obtained. The average of all the subdivision values is taken as the final fine code signal value of the encoder, and the subdivision values are transmitted to the host computer according to the communication protocol.

[0065] In conclusion, the above merely describes preferred embodiments of the present specification, and is not intended to limit the protection scope of the present specification. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present specification shall be included in the protection scope of the present specification.

[0066] The systems, apparatuses, modules, or units illustrated in one or more embodiments above can be implemented by computer chips or entities, or by products with certain functions. A typical implementation device is a computer. Specifically, the computer may, for example, be 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.

[0067] It should also be noted that the terms "comprising", "containing", or any other variant thereof are intended to cover non-exclusive inclusion, such that processes, methods, articles, or devices that comprise a list of elements are not limited to those elements, but can also include other elements not expressly listed, or other elements inherent to such processes, methods, articles, or devices. Without more limitations, the element defined by the statement "comprising a" does not exclude the presence of additional identical elements in the process, method, article, or device that includes the element.

[0068] Each of the embodiments in the present specification is described in a progressive manner, and the same or similar parts between each embodiment can be referred to each other, and each embodiment focuses on the difference from other embodiments. In particular, for system embodiments, since they are basically similar to method embodiments, the description is relatively simple, and the relevant parts can be referred to the part of the method embodiment.

[0069] The above describes specific embodiments of the present specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims can be performed in an order different than the order in the embodiments and still achieve the desired result. In addition, the processes depicted in the figures do not necessarily require the particular order shown or sequential order to achieve the desired results. In certain implementations, multitasking and parallel processing can be advantageous or possible.

Claims

1. A method for reducing the encoder subdivision error, the encoder comprising N fine code readout heads, N being equal to or greater than 8 and being an integer multiple of 4, the N fine code readout heads being uniformly arranged on a fine code track, the N fine code readout heads outputting N / 4 SIN signals and N / 4 COS signals, characterized in that, The method comprises the following steps: ​ S1: collecting N / 4 SIN signals and N / 4 COS signals in one Moire fringe signal period, and performing normalization; S2: combining each normalized SIN signal with each normalized COS signal in turn, calculating the orthogonality error of each combination, comparing to obtain the minimum orthogonality error, and pairing the normalized SIN signal and the COS signal corresponding to the minimum orthogonality error; S3: repeating the S2 for the remaining normalized SIN signals and COS signals until each SIN signal finds a corresponding COS signal; S4: calculating the subdivision value of each pair of SIN signal and COS signal, and taking the average of the N / 4 subdivision values as the fine code angle signal output of the encoder.

2. The method of reducing encoder subdivision error of claim 1, wherein, The normalization process of the SIN signal and the COS signal is as follows: The voltage maximum of each signal is selected and the voltage minimum The normalized voltage is: ； wherein, represents the raw voltage collected in real time before normalization.

3. The method of reducing encoder subdivision error of claim 1, wherein, The calculation method of the orthogonality error is as follows: Synthesizing the normalized SIN signal and the COS signal into a Lissajous figure, calculating the roundness error of the Lissajous figure, and taking it as the orthogonality error; Comparing to obtain the minimum roundness error, and pairing the normalized SIN signal and the COS signal corresponding to the minimum roundness error.

4. The method of reducing encoder subdivision error of claim 3, wherein, The roundness error of the Lissajous figure composed of the SIN signal and the COS signal is calculated by the least square circle method.

5. The method of reducing encoder subdivision error of claim 4, wherein, Circularity error The calculation formula is: ； wherein n represents the number of sampling points in one period of the moire fringe signal, and m represents the mth sampling point, x m and y m represents the distance between the mth sampling point and the standard circle. m represents the horizontal coordinate and the vertical coordinate of the mth sampling point, i.e. the signal values of the SIN signal and the COS signal at the time corresponding to the mth sampling point, represents the distance between the mth sampling point and the standard circle. m represents the distance between the mth sampling point and the standard circle.

6. The method of reducing encoder subdivision error of claim 1, wherein, The calculation method of the orthogonality error is as follows: Taking the time difference between the peak time of the normalized SIN signal and the zero-crossing time of the normalized COS signal as the orthogonality error; Comparing to obtain the minimum time difference, and pairing the normalized SIN signal and the COS signal corresponding to the minimum time difference.

7. The method of reducing encoder subdivision error of claim 1, wherein, Subdivision values for SIN and COS signals The calculation is: ； Wherein, SIN and COS represent the paired SIN signal and the COS signal.

8. A multi-readhead optical encoder, characterized by, The method for reducing the subdivision error of the encoder according to any one of claims 1 to 7 outputs the fine code angle signal, further comprising: storing the numbers of the SIN signal and the COS signal, and directly pairing the stored numbers of the SIN signal and the COS signal in subsequent power-on.

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