CN104614002A - Subdivided signal error compensation method for photoelectric encoder of tracking control platform - Google Patents
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Abstract
The invention provides a subdivided signal error compensation method for a photoelectric encoder of a tracking control platform, which is suitable for the tracking control platform. The invention compensates the error of the subdivision signal of the encoder measuring module by tracking the position quantity of the controlled object of the control platform. The method has strong practicability and outfield adaptability, and does not need expensive error detection equipment and complex algorithm which causes large delay to the platform. Meanwhile, only shafting position information needs to be acquired, the tracking control platform, the encoder angle measurement module and a software and hardware structure of the lower layer of the platform do not need to be known, the transportability and the operability are strong, time and labor are saved, and a good solution idea is provided for solving the common encoder subdivision signal error problem of the photoelectric tracking control platform.
Description
Technical Field
The invention belongs to the technical field of precision tracking and control, and particularly relates to a method for compensating error of a subdivision signal of a photoelectric encoder of a tracking control platform.
Background
The tracking control platform has strict requirements on capturing, tracking and aiming, the precision needs to be in the order of arc-second, even the tracking control platform needs to work at ultra-low speed, and very high requirements on the shaft angle measurement precision and accuracy of the photoelectric encoder are provided. The period of the grating signal, the consistency and edge definition of the grating, the quality of the optical filter, the characteristics of the photoelectric detection element and the stability and dynamic performance of the output analog signal in the subsequent processing are main factors influencing the measurement accuracy of the photoelectric encoder. For the angle encoder without the built-in bearing, the influence of installation errors, bearing errors of a measured shaft, additional errors caused by adjustment errors of a reading head and the like on the measurement precision is also considered. For the built-in bearing angle encoder and the built-in stator coupler angle encoder, errors caused by couplers need to be considered. The influence of these factors on the encoder measurement is finally reflected on the subdivided signal error, and the subdivided signal error needs to be corrected or compensated for to improve the encoder precision. The influence of the subdivided signal errors on the encoder angle measurement accuracy is usually remedied from two aspects of error detection and error compensation. In the aspect of measuring errors of the subdivided signals, if the cause, the magnitude or the dynamic law of the subdivided errors can be detected, factors generating the errors can be avoided as much as possible or the subdivided errors can be directly compensated, so that the precision of the encoder is improved. The subdivision error measurement method has the problems that an encoder error detection device is complex, the detection process is complex, the requirement on the environment is strict, most of encoders can only be detected under the condition of a laboratory, and the subdivision error measurement method is not suitable for detecting the encoder on the working site. In addition, most of the detection devices can only detect the static error of the encoder, but cannot well detect the dynamic error of the encoder. The high price is also an important factor limiting its application in practical engineering. In the aspect of subdivision error compensation, multiple sides are based on researches of intelligent and self-adaptive algorithms such as a BP neural network and a radial basis function network. The encoder subdivision error compensation method has the problems that error correction needs to be carried out in a laboratory and other ideal environments, work content only corrects or compensates subdivision errors of an encoder angle measurement module, and influence of the subdivision errors on a whole platform is not considered when the encoder angle measurement module is applied to a complex large platform shafting. Therefore, it is difficult to adapt these methods for fine error compensation to the changes of the working site and working environment of the photoelectric encoder. Aiming at the defects of the existing encoder subdivided signal error compensation method, the invention provides a subdivided signal error compensation method of a photoelectric encoder of a tracking control platform. The method has strong practicability and outfield adaptability, and does not need expensive error detection equipment and complex algorithms which bring large delay to the platform. Meanwhile, the method only needs to acquire shafting position information, does not need to know the photoelectric control platform, the encoder angle measurement module and the software and hardware structure of the lower layer of the platform, has strong transplantable operability and is time-saving and labor-saving, and provides a good solution for solving the common encoder subdivision signal error problem of the photoelectric control platform. The method reduces the influence of the subdivided signal errors on the tracking control platform, and improves the angle measurement precision of the photoelectric encoder of the tracking control platform, so that the platform has wider bandwidth, higher rigidity, higher response speed, stronger load capacity and better stability.
The Chinese patent document library discloses an invention patent application technology named as a detection method for photoelectric signal subdivision errors of a high-precision encoder (patent application number 201210488003.5). The invention patent application technology discloses a method for measuring the straightness of an ultra-long guide rail, and relates to a method for measuring the straightness of the guide rail, in particular to the straightness of the ultra-long guide rail. The invention solves the problems of low measurement precision, large error and complex data processing and operation of the existing measurement method. According to the method, a plurality of data points on the ultra-long guide rail are measured and collected through the laser tracker, spatial straight line fitting is carried out on the data points, and the straightness of the guide rail can be obtained by calculating the straightness of the collected data information of N test sampling points through a least square fitting algorithm. The method has the advantages of simple and convenient data analysis and experiment operation, short test time, simple data processing, low test cost and high test efficiency. The laser tracking instrument is suitable for a linear encoder, is not suitable for an angle encoder, has high error detection equipment price, low practicability and external field adaptability, has high requirements on familiarity of photoelectric control platforms, encoder modules and software and hardware structures at the lower layers of the platforms, has poor transplantable operability, and is difficult to adapt to the conditions of the working site of the photoelectric encoder, the change of the working environment and the like.
Disclosure of Invention
The invention provides a subdivided signal error compensation method of a photoelectric encoder of a tracking control platform, aiming at solving the problem that the subdivided signal error of the encoder causes serious influence on the stability and the tracking control precision of the tracking control platform, and the conventional subdivided signal error compensation method cannot meet the requirements in the aspects of practicability, outfield adaptability, price, transplantable operability and instantaneity.
The technical scheme adopted by the invention is as follows: a tracking control platform photoelectric encoder subdivision signal error compensation method comprises a main processor module, a storage module, a display module, a power supply module, an execution module, a controlled module, a photoelectric encoder measuring module, a communication interface module and a human-computer interaction module. The tracking control platform uses a main processor module as a center, a controlled module is a tracking control platform control object, a photoelectric encoder measuring module is used for measuring the displacement of the controlled module, an execution module is used for driving and controlling the controlled module, a storage module is connected with the main processor module and used for storing real-time processing data, a curing program and the like, a display module connected to the main processor module is mainly used for displaying the dynamic state and the behavior of the controlled module, a communication module is used for information interaction among the modules, a human-computer interaction module is mainly convenient for an operator to operate the tracking control system, and a power supply module is used for supplying power for the whole hardware platform.
The method for compensating the error of the subdivided signal of the photoelectric encoder of the tracking control platform is realized according to the following steps:
step (1), controlling a platform photoelectric encoder to output two paths of orthogonal signals obtained by a moire fringe technology, wherein the waveform is a quasi sine wave, and the sine wave and the cosine wave are expressed as follows:
wherein the subdivision signals A and B are composed of four parts, A0And B0Representing the direct current component of the signal, which is a direct current error source; a. themAnd BmRepresenting the fundamental wave signal amplitude as a signal amplitude error source;represents the sum of the higher harmonics, which is the source of harmonic component error;erepresenting electrical noise as a source of noise; in addition, the conversion between the analog quantity and the digital quantity of the subdivided angle of the photoelectric encoder is a quantization error source, and the phase difference of the two paths of signals A and B is a phase error source;
for an encoder application platform with high precision requirement, an arc tangent subdivision method is adopted to achieve high subdivision multiple. The subdivision method and the subdivision error are shown in the following formula.
Wherein, thetarRepresenting true theoretical subdivision angle, θdFor measuring the obtained subdivision angle, delta theta is the subdivision signal error.
And judging the influence degree of the subdivision errors on the precision of the control platform, and if the influence degree is weak to be ignored, finishing the algorithm. Otherwise, judging the type of an error source through the mathematical analysis of the error of the subdivided signal;
step (2), calculating initial parameters of a subdivision error compensation method of a control platform:
a) encoder system resolution:
b) encoder raster angular resolution:
c) subdivision resolution of the subdivided signal:
the AllBit, CoarseBit and FineBit respectively represent the number of bits of the photoelectric encoder, the number of coarse code bits and the number of fine code bits. Wherein, the coarse code represents the number of single-circle gratings physically depicted by a code disc of the photoelectric encoder, and the fine code represents the periodic electronic subdivision number of the single subdivision signal;
step (3) solving the coarse code representation of the position of the actual measurement shaftingThe position quantity theta is represented by a coarse codeP_CoarseComprises the following steps: thetaP_Coarse＝CoarseCode*QC. The amount of positions for subdivision is represented by fine codes as thetaP_Fine＝θP-θP_Coarse；
Step (4) obtaining true real subdivision angle value
Step (5) judging whether the phase zero point of the subdivision angle is offset or not, if so, solving the subdivision angle quantity theta measured by taking the current subdivision angle zero point as a starting pointdRComprises the following steps: thetadR＝θd-InitialAngle。θdRepresenting the actually measured subdivision angle expressed by theta according to different subdivision error typesrAnd the expressions of A and B are used for solving, and InitialAngle represents the offset of the zero position of the subdivision angle. If the subdivision angular phase zero point is not offsetdR＝θd；
Step (6) of obtaining the corresponding thetadRFine code ofThe total code of the measured position is CodeAll 2FineBit+FineCode；
Step (7) of the formula CodeAll ═ CoarseCode · 2FineBit+ FineCode and ACoarseCode, the deducing step (6) obtaining the coarse code in the total code(the acoarseCode is different from CoarseCode in source, the acoarseCode is separated from the total code value input into the module, the acoarseCode is obtained from the measured position of the axis, and the acoarseCode and the CoarseCode are equivalent theoretically). The effect of this step is to further purify the crude code values to make them more accurate;
step (8), solving an uncorrected fine code NCFineCode which is codeAll-acoarseCode;
step (9) of obtaining the subdivision angle represented by the uncorrected subdivision precise code(FinePhaseOrigin and θ)dRThe sources are different, the former is from uncorrected fine codes, and the latter is from shafting position measurement values. The former value will typically be less than the latter for rounding reasons);
step (10), if there is zero drift, subdividing the angle measurement value thetadFine phaseorigin + initiala angle, otherwise θd＝FinePhaseOrigin；
Step (11), calculating a subdivision signal error quantity delta theta, namely a correction quantity according to different subdivision error types;
step (12) of obtaining the corrected subdivision angle thetadc＝θd+△θ；
Step (13) of solving the corrected precise codeThe corrected total code is then obtained by:
CodeAllCorrected＝ACoarseCode+FineCodeCorrected
step (14) of calculating a corrected shafting position value thetaPC：θPC＝CodeAllCorrected·Q
Step (15) of correcting the position amount thetaPCIs brought into the tracking control platform by feedback.
The main processor module of the subdivided signal error compensation method of the photoelectric encoder of the tracking control platform can be one or more of a PC (personal computer), an FPGA (field programmable gate array), a PowerPC (Power personal computer) and a DSP (digital signal processor).
The storage module of the subdivided signal error compensation method of the photoelectric encoder of the tracking control platform can be one or more of an electronic solid state disk, a TF, a CF or an SD card.
The display module of the subdivided signal error compensation method of the photoelectric encoder of the tracking control platform can be an OLED or an LCD.
The power module of the subdivided signal error compensation method of the photoelectric encoder of the tracking control platform adopts a specific power management chip and simultaneously comprises a battery and a battery charging circuit.
The execution module of the subdivided signal error compensation method of the photoelectric encoder of the tracking control platform is driven by the special power level of the controlled object.
The controlled module of the subdivided signal error compensation method of the photoelectric encoder of the tracking control platform is a control terminal and a control object of the tracking control platform.
The photoelectric encoder measuring module of the subdivided signal error compensation method of the photoelectric encoder of the tracking control platform is an encoder used by the platform and subdivided and digitized electronic circuit equipment matched with the encoder through a specific interface.
Compared with the prior art, the invention has the advantages that:
the invention can correct the subdivided signal error of the photoelectric encoder by using the actually measured position quantity of the tracking control system of the photoelectric encoder without changing the angle measuring system of the photoelectric encoder and adopting a complex intelligent algorithm influencing the tracking rapidity by theoretically analyzing the subdivided signal error of the photoelectric encoder and by means of a tracking control platform compared with the existing subdivided signal error compensation method. The method can be suitable for error compensation of the encoder output subdivision signal of large equipment with high precision, strong real-time performance and high complexity. Meanwhile, the invention has strong practicability and outfield adaptability, and does not need expensive error detection equipment and complex algorithm which brings larger time delay to the system. In addition, the invention only needs to acquire shafting position information, does not need to know the photoelectric control system, the encoder angle measurement system and the lower-layer software and hardware structure of the system, has strong transplantable operability and time and labor saving, and provides a good solution for solving the common encoder subdivision signal error problem of the photoelectric control system. The method reduces the influence of the subdivided signal errors on the tracking control platform, and improves the angle measurement precision of the photoelectric encoder of the tracking control platform, so that the platform has wider bandwidth, higher rigidity, higher response speed, stronger load capacity and better stability.
After the method is applied to a tracking control platform, the low-speed performance of the platform is obviously enhanced, which shows that the subdivided signal error compensation method provided by the invention is effective in inhibiting the tracking control error of the platform and improving the control precision of the platform, and particularly in the aspect of ensuring the low-speed stability of the control platform. Compared with the test results of only the speed loop subdivision error compensation correction and both the speed loop and the position loop correction of the tracking control platform, the latter control method has better effect, and particularly has a more stable operation stage after 0.05-0.3s of the platform starting stage and 0.8s of the platform. Meanwhile, the test result of the latter is closer to the test result of a reference platform with better performance. The subdivision error compensation method provided by the invention is simple and easy to implement, and the burden on the integral operation of the platform is small. Therefore, the tracking control platform selects to apply the subdivision error compensation algorithm provided by the invention to the speed loop and the position loop of the control platform at the same time. Tests show that compared with the performance of the tracking control platform, after error compensation and correction of the subdivided signals, the maximum value of the error of the tracking control position is reduced to 0.74 'from 1.42', the maximum value is reduced by 47.9%, the low-speed performance is obviously improved, and the overall performance of the control platform is enhanced.
Drawings
FIG. 1 is a block diagram of the overall structure of a tracking control platform;
FIG. 2 is a flow chart of a method for compensating error of a subdivided signal of a photoelectric encoder of a tracking control platform according to the present invention;
FIG. 3 is a diagram illustrating the effect of an error compensation method for a sub-divided signal of a photoelectric encoder applied to a tracking control platform according to an embodiment; wherein,indicating the low-speed tracking performance of the reference tracking control platform,indicating the low-speed tracking performance of the tracking control platform before error compensation of the non-subdivided signals,it shows that the error compensation method proposed by the present invention is only applied to the low-speed tracking performance of the tracking control platform after the speed loop of the tracking control platform,the error compensation method provided by the invention is simultaneously applied to the low-speed tracking performance of the tracking control platform after the speed loop and the position loop of the tracking control platform control system;
in fig. 1: 1. the system comprises a main processor module, 2, a storage module, 3, a display module, 4, a power supply module, 5, an execution module, 6, a controlled module, 7, a photoelectric encoder measuring module, 8, a communication interface module and 9, a human-computer interaction module.
Detailed Description
In order to better understand the error compensation method for the sub-divided signal proposed by the present invention, the present invention is further described below with reference to the accompanying drawings and embodiments.
Fig. 1 is a block diagram of the overall structure of a tracking control platform, and the tracking control platform includes a main processor module 1, a storage module 2, a display module 3, a power supply module 4, an execution module 5, a controlled module 6, a photoelectric encoder measurement module 7, a communication interface module 8, and a human-computer interaction module 9. The tracking control platform uses a main processor module 1 as a processing core, a controlled module 6 as a tracking control platform control object, a photoelectric encoder measuring module 7 mainly provides control and drive for an execution module 5 to measure the displacement of the controlled module 6 and measure the position of the controlled module 6, a storage module 2 is connected with the main processor module 1 and used for storing real-time processing data, a solidified program and the like, a display module 3 connected with the main processor module 1 is mainly used for displaying the dynamic and behavior of the controlled module, a communication module 8 is used for information interaction among the modules, a man-machine interaction module 9 is mainly convenient for an operator to operate the tracking control system, and a power supply module 4 is used for supplying power for the whole hardware platform.
The main processor module of the error compensation method for the subdivided signals of the photoelectric encoder of the tracking control platform can be one or more of a PC (personal computer), an FPGA (field programmable gate array), a PowerPC (personal computer) and a DSP (digital signal processor).
The storage module of the error compensation method for the subdivided signals of the photoelectric encoder of the tracking control platform can be one or more of an electronic solid state disk, a TF, a CF or an SD card.
The display module of the error compensation method for the subdivided signals of the photoelectric encoder of the tracking control platform can be an OLED or an LCD.
The power module of the subdivided signal error compensation method of the photoelectric encoder of the tracking control platform adopts a specific power management chip and simultaneously comprises a battery and a battery charging circuit.
The execution module of the error compensation method for the subdivided signals of the photoelectric encoder of the tracking control platform is driven by the special power level of the controlled object.
The controlled module of the error compensation method for the subdivided signal of the photoelectric encoder of the tracking control platform is a control terminal and a control object of the tracking control platform.
The photoelectric encoder measuring module of the subdivided signal error compensation method of the photoelectric encoder of the tracking control platform is an encoder used by the platform and subdivided and digitized electronic circuit equipment matched with the encoder through a specific interface.
Fig. 2 is a flowchart of a subdivided signal error compensation method for a photoelectric encoder of a tracking control platform according to the present invention, which is implemented according to the following steps:
step (1), controlling a platform photoelectric encoder to output two paths of orthogonal signals obtained by a moire fringe technology, wherein the waveform is a quasi sine wave, and the sine wave and the cosine wave are expressed as follows:
wherein the subdivision signals A and B are composed of four parts, A0And B0Representing the direct current component of the signal, which is a direct current error source; a. themAnd BmRepresenting the fundamental wave signal amplitude as a signal amplitude error source;andrepresents the sum of the higher harmonics, which is the source of harmonic component error;erepresenting electrical noise, as a source of noise. In addition, the conversion between the analog quantity and the digital quantity of the subdivided angle of the photoelectric encoder is a quantization error source, and the phase difference of the two paths of signals A and B is a phase error source.
For an encoder application platform with high precision requirement, an arc tangent subdivision method is adopted to achieve high subdivision multiple. The subdivision method and the principle of subdivision errors are shown in the following formula.
Wherein, thetarRepresenting true theoretical subdivision angle, θdFor measuring the obtained subdivision angle, delta theta is the subdivision signal error.
And judging the influence degree of the subdivision errors on the precision of the control platform, and if the influence degree is weak to be ignored, finishing the algorithm. Otherwise, judging the type of an error source through the mathematical analysis of the error of the subdivided signal;
step (2), calculating initial parameters of a subdivision error compensation method of a control platform:
a) encoder system resolution:
b) encoder raster angular resolution:
c) subdivision resolution of subdivided signalsRate:
the AllBit, CoarseBit and FineBit respectively represent the number of bits of the photoelectric encoder, the number of coarse code bits and the number of fine code bits. Wherein, the coarse code represents the number of single-circle gratings physically depicted by a code disc of the photoelectric encoder, and the fine code represents the periodic electronic subdivision number of the single subdivision signal;
step (3) solving the coarse code representation of the position of the actual measurement shaftingThe position quantity theta is represented by a coarse codeP_CoarseComprises the following steps: thetaP_Coarse＝CoarseCode*QC. The amount of positions for subdivision is represented by fine codes as thetaP_Fine＝θP-θP_Coarse；
Step (4) obtaining true real subdivision angle value
Step (5) judging whether the phase zero point of the subdivision angle is offset or not, if so, solving the subdivision angle quantity theta measured by taking the current subdivision angle zero point as a starting pointdRComprises the following steps: thetadR＝θd-InitialAngle。θdRepresenting the actually measured subdivision angle expressed by theta according to different subdivision error typesrAnd the expressions of A and B are used for solving, and InitialAngle represents the offset of the zero position of the subdivision angle. If the subdivision angular phase zero point is not offsetdR＝θd；
Step (6) of obtaining the corresponding thetadRFine code ofThe total code of the measured position is CodeAll 2FineBit+FineCode；
Step (7) of the formula CodeAll ═ CoarseCode · 2FineBit+FineCThe code and acoarseCode, deducing step 6 to obtain the coarse code in the total code(the acoarseCode is different from CoarseCode in source, the acoarseCode is separated from the total code value input into the module, the acoarseCode is obtained from the measured position of the axis, and the acoarseCode and the CoarseCode are equivalent theoretically). The effect of this step is to further purify the crude code values to make them more accurate;
step (8), solving an uncorrected fine code NCFineCode which is codeAll-acoarseCode;
step (9) of obtaining the subdivision angle represented by the uncorrected subdivision precise code(FinePhaseOrigin and θ)dRThe sources are different, the former is from uncorrected fine codes, and the latter is from shafting position measurement values. The former value will typically be less than the latter for rounding reasons);
step (10), if there is zero drift, subdividing the angle measurement value thetadFine phaseorigin + initiala angle, otherwise θd＝FinePhaseOrigin；
Step (11), calculating a subdivision signal error quantity delta theta, namely a correction quantity according to different subdivision error types;
step (12) of obtaining the corrected subdivision angle thetadc＝θd+△θ；
Step (13) of solving the corrected precise codeThe corrected total code is then obtained by:
CodeAllCorrected＝ACoarseCode+FineCodeCorrected
step (14) of calculating a corrected shafting position value thetaPC：θPC＝CodeAllCorrected·Q
Step (15) of correcting the position amount thetaPCBrought into the control platform by feedback.
Fig. 3 is an effect diagram of the method for compensating error of subdivided signals of an optical-electrical encoder applied to a tracking control platform in the embodiment. In actual engineering, the tracking control performance of an original tracking control platform and a reference tracking control platform with good performance are measured. The subdivided signal error compensation method of the photoelectric encoder of the tracking platform is applied to a speed loop of the tracking control platform, and the subdivided signal error compensation method is simultaneously applied to the speed loop and a position loop of the tracking control platform, so that the tracking control performance of the tracking control platform is respectively tested. The low-speed performance of the platform is obviously enhanced only after the speed loop compensation and the simultaneous compensation of the speed loop and the position loop, which shows that the subdivided signal error compensation method provided by the invention is effective in inhibiting the platform tracking control error and improving the platform control precision. Compared with the test results of only the speed loop subdivision error compensation correction and both the speed loop and the position loop correction of the tracking control platform, the latter control method has better effect, and particularly has a more stable operation stage after 0.05-0.3s of the platform starting stage and 0.8s of the platform. Meanwhile, the test result of the latter is closer to the test result of a reference platform with better performance. The subdivision error compensation method provided by the invention is simple and easy to implement, and the burden on the integral operation of the platform is small. Therefore, the tracking control platform selects to apply the subdivision error compensation algorithm provided by the invention to the speed loop and the position loop of the control platform at the same time. Tests show that compared with the performance of the tracking control platform, after error compensation and correction of the subdivided signals, the maximum value of the error of the tracking control position is reduced to 0.74 'from 1.42', the maximum value is reduced by 47.9%, the low-speed performance is obviously improved, and the overall performance of the control platform is enhanced.
The high-precision photoelectric tracking control system has strict requirements on capturing, tracking and aiming, the precision is in an order of arc seconds, and meanwhile, the high-precision photoelectric tracking control system usually works in a low-speed state, the tracking speed is even less than 1'/s, and the high requirements on the shaft angle measurement precision and accuracy of a photoelectric encoder are provided. The period of the grating signal, the consistency and edge definition of the grating, the quality of the optical filter, the characteristics of the photoelectric detection element and the stability and dynamic performance of the output analog signal in the subsequent processing are main factors influencing the measurement accuracy of the photoelectric encoder. The influence of these factors on the encoder measurement is finally reflected on the subdivided signal error, and the subdivided signal error needs to be corrected or compensated for to improve the encoder precision.
The influence of the subdivided signal errors on the measurement accuracy of the encoder is usually remedied from two aspects of error detection and error compensation. In the aspect of measuring errors of the subdivided signals, if the cause, the magnitude or the dynamic law of the subdivided errors can be detected, factors generating the errors can be avoided as much as possible or the subdivided errors can be directly compensated, so that the precision of the encoder is improved. In the aspect of research on the subdivision error compensation technology, the compensation of the angular measurement error of the photoelectric encoder including the subdivision error is usually realized by adopting a currently advanced artificial intelligence algorithm. The encoder subdivision error is subjected to mathematical analysis, and the encoder subdivision signal error is compensated by means of the position value of the tracking control platform measured by the tracking control platform where the encoder is located, so that the algorithm is simple and effective, and the encoder angle measurement system does not need to be modified like the conventional subdivision signal error correction or compensation method.
Claims (8)
1. A method for compensating error of subdivided signals of a photoelectric encoder of a tracking control platform is characterized by comprising the following steps: the tracking control platform comprises a main processor module (1), a storage module (2), a display module (3), a power supply module (4), an execution module (5), a controlled module (6), a photoelectric encoder measuring module (7), a communication interface module (8) and a human-computer interaction module (9); the tracking control platform takes a main processor module (1) as a processing core, a controlled module (6) as a tracking control platform control object, a photoelectric encoder measuring module (7) mainly provides control and drive for an execution module (5) to measure the displacement of the controlled module (6) and measure the position quantity of the controlled module (6), a storage module (2) is connected with the main processor module (1) and used for storing real-time processing data, a solidified program and the like, a display module (3) connected to the main processor module (1) is mainly used for displaying the dynamic state and the behavior of the controlled module, a communication module (8) is used for information interaction among the modules, a man-machine interaction module (9) is mainly convenient for an operator to operate the tracking control system, and a power supply module (4) is used for providing power supply for the whole hardware platform;
the method for compensating the error of the subdivided signal of the photoelectric encoder of the tracking control platform is realized according to the following steps:
step (1), controlling a platform photoelectric encoder to output two paths of orthogonal signals obtained by a moire fringe technology, wherein the waveform is a quasi sine wave, and the sine wave and the cosine wave are expressed as follows:
wherein the subdivision signals A and B are composed of four parts, A0And B0Representing the direct current component of the signal, which is a direct current error source; a. themAnd BmRepresenting the fundamental wave signal amplitude as a signal amplitude error source;represents the sum of the higher harmonics, which is the source of harmonic component error;erepresenting electrical noise as a source of noise; in addition, the conversion between the analog quantity and the digital quantity of the subdivided angle of the photoelectric encoder is a quantization error source, and the phase difference of the two paths of signals A and B is a phase error source;
an inverse tangent subdivision method is adopted for an encoder application platform with high precision requirement to achieve high subdivision multiple; the subdivision method and the subdivision error are shown as follows:
wherein, thetarRepresenting true theoretical subdivision angle, θdFor the subdivision angle obtained by measurement, the delta theta is the error of the subdivision signal;
judging the influence degree of the subdivision errors on the precision of the control platform, and if the influence degree is weak enough to be ignored, finishing the algorithm; otherwise, judging the type of an error source through the mathematical analysis of the error of the subdivided signal;
step (2), calculating initial parameters of a subdivision error compensation method of a control platform:
a) encoder system resolution:
b) encoder raster angular resolution:
c) subdivision resolution of the subdivided signal:
the AllBit, CoarseBit and FineBit respectively represent the number of bits of a photoelectric encoder, the number of coarse codes and the number of fine codes, wherein the coarse codes represent the number of single-circle gratings physically depicted on a code disc of the photoelectric encoder, and the fine codes represent the number of periodic electronic fine divisions of a single-fine division signal;
step (3) solving the coarse code representation of the position of the actual measurement shaftingThe position quantity theta is represented by a coarse codeP_CoarseComprises the following steps: thetaP_Coarse＝CoarseCode*QC. The amount of positions for subdivision is represented by fine codes as thetaP_Fine＝θP-θP_Coarse；
Step (4) obtaining true real subdivision angle value
Step (5) judging whether the phase zero point of the subdivision angle is offset or not, if so, solving the subdivision angle quantity theta measured by taking the current subdivision angle zero point as a starting pointdRComprises the following steps: thetadR＝θd-InitialAngle，θdRepresenting the actually measured subdivision angle expressed by theta according to different subdivision error typesrAnd the expressions of A and B, InitialAngle represents the offset of the zero point position of the subdivision angle, if the zero point of the subdivision angle phase has no offset, thetadR＝θd；
Step (6) of obtaining the corresponding thetadRFine code ofThe total code of the measured position is CodeAll 2FineBit+FineCode；
Step (7) of the formula CodeAll ═ CoarseCode · 2FineBit+ FineCode and ACoarseCode, the deducing step (6) obtaining the coarse code in the total codeThe ACoarseCode and the CoarseCode are different in source, the ACoarseCode is separated from the total code value input into the module, the CoarseCode is obtained from the measured position quantity of the shafting, and the ACoarseCode and the CoarseCode are equivalent theoretically; the effect of this step is to further purify the crude code values to make them more accurate;
step (8), solving an uncorrected fine code NCFineCode which is codeAll-acoarseCode;
step (9) of obtaining the subdivision angle represented by the uncorrected subdivision precise codeFinePhaseOrigin and θdRThe sources are different, the former comes from uncorrected fine codes, the latter comes from shafting position measurement values, and due to rounding,the former value will generally be less than the latter;
step (10), if there is zero drift, subdividing the angle measurement value thetadFine phaseorigin + initiala angle, otherwise θd＝FinePhaseOrigin；
Step (11), calculating a subdivision signal error quantity delta theta, namely a correction quantity according to different subdivision error types;
step (12) of obtaining the corrected subdivision angle thetadc＝θd+△θ；
Step (13) of solving the corrected precise codeThe corrected total code is then obtained by:
CodeAllCorrected＝ACoarseCode+FineCodeCorrected
step (14) of calculating a corrected shafting position value thetaPC：θPC＝CodeAllCorrected·Q；
Step (15) of correcting the position amount thetaPCAnd the feedback is carried into the tracking control platform.
2. The tracking control platform photoelectric encoder subdivision signal error compensation method of claim 1, characterized in that: the main processor module can be one or more of a PC, an FPGA, a PowerPC and a DSP.
3. The tracking control platform photoelectric encoder subdivision signal error compensation method of claim 1, characterized in that: the storage module can be one or more of an electronic solid state disk, a TF, a CF or an SD card.
4. The tracking control platform photoelectric encoder subdivision signal error compensation method of claim 1, characterized in that: the display module can be OLED or LCD.
5. The tracking control platform photoelectric encoder subdivision signal error compensation method of claim 1, characterized in that: the power module adopts a specific power management chip and simultaneously comprises a battery and a battery charging circuit.
6. The tracking control platform photoelectric encoder subdivision signal error compensation method of claim 1, characterized in that: the execution module is driven by the controlled object in a proprietary power level.
7. The tracking control platform photoelectric encoder subdivision signal error compensation method of claim 1, characterized in that: the controlled module is a tracking control platform control terminal and a control object.
8. The tracking control platform photoelectric encoder subdivision signal error compensation method of claim 1, characterized in that: the photoelectric encoder measuring module is an encoder used by the platform and subdivision and digital electronic circuit equipment matched with the encoder through a specific interface.
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