CN118293798A - High-robustness grating ruler absolute code channel system - Google Patents
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Abstract
The invention provides a high-robustness grating ruler absolute code channel system, which is characterized in that: the high-precision grating ruler reading head system consists of a light source (1), a scale grating (2), an indication grating (3), an incremental Photodiode (PD) (4), an absolute PD (5), an incremental PD detection circuit (6), an absolute PD detection circuit (7) and a calculation processing unit (8). The incremental PD (4) and the incremental PD detection circuit (6) form an incremental detection code channel together, and the incremental position information of the measurement system is output to the calculation processing unit (8); the absolute PD (5) and the absolute PD detection circuit (7) form an absolute detection code channel together, absolute position information of the measurement system is output to the calculation processing unit (8), and the calculation processing unit (8) corrects the system by error correction according to the incremental position information and the absolute position information and outputs high-precision absolute position information. The invention can be used for measuring high-precision micro displacement and can be widely used in the fields of precision semiconductor manufacture, precision displacement measurement, precision motion control, closed-loop feedback control of a numerical control machine tool and the like.
Description
Field of the art
The invention relates to a high-robustness grating scale absolute code channel system, which improves the measurement accuracy, robustness and robustness of a grating scale reading head system by using a specific system and an algorithm. The method can be used for high-precision micro-displacement measurement such as precision semiconductor manufacturing, precision displacement measurement, precision motion control, closed-loop feedback control of a numerical control machine tool and the like, and belongs to the technical field of photoelectric detection.
(II) background art
In modern industry, higher and higher requirements are put on the accuracy, speed, resolution and reliability of displacement measurement. As a high-precision linear displacement sensing device, the grating ruler has better performance on the indexes and lower manufacturing cost, so that the grating ruler has wide application in the fields of numerical control processing technology and the like. With the rapid development of numerical control processing technology, the improvement of the technical level of the grating ruler is greatly promoted.
The grating ruler takes a high-precision long grating (scale grating) as a measurement reference, and when the scale grating is overlapped with a grating (indication grating) on a reading head, moire fringes (moire patterns) are formed by a light field after passing through the two gratings. Fringe spacing W and direction of moire fringes according to the principle of geometrical shadingThe following equation is satisfied:
Wherein d 1、d2 and θ are the grating pitch and the angle between the two gratings respectively.
Formulas (1) and (2) represent a general pattern of moire (also referred to as oblique moire). The stripes will also exhibit different patterns depending on the d 1、d2 and θ values: when d 1 is equal to d 2 and θ approaches 0, the moire is almost perpendicular to the gate line direction, the fringe spacing w=d/θ, such fringes are called transverse moire; when d 1 is close to d 2 and θ is equal to 0, the moire is parallel to the direction of the grating, the fringe spacing w=d 2/Δd, such fringes being called longitudinal moire. In both of the above patterns, the fringe spacing W is much larger than the pitch d because the parameters on the denominator are small. When the relative displacement of the small grid distance d scale exists between the scale grating and the indication grating, the moire fringes will move in a larger fringe distance W scale, and the amplification of displacement signals is realized. And then, a special photoelectric detection device is utilized to convert moire fringes into an electric signal, and tiny displacement information is obtained by processing the electric signal.
The absolute grating ruler has a scale grating comprising an increment code track and an absolute code track, and the increment code track and the absolute code track are correspondingly arranged on the indication grating. When the system is started, the absolute position information with low precision can be quickly obtained by reading the unique position code on the scale grating through the absolute code channel on the indication grating. And then obtaining high-precision position information through moire fringes acquired by the incremental code channels on the indication grating. The absolute grating ruler has higher reliability and working efficiency because no reference zero position is required to be found. The scale grating of the reflective grating ruler is mostly made of steel materials, and the light source and the photoelectric detection device are positioned on the same side of the scale grating, so that the scale grating can be directly arranged on a base surface of a system to be tested. Thus, not only is the installation space saved, but also the device can be used for a wide-range test scene.
Early grating scales, the moire was typically a shutter moire (d 1＝d2 and θ=0 case). According to equation (1), the shutter moire pitch tends to be infinitely large, and therefore a four-field scan is required to obtain the light field information of the incremental track. The four-field scanning needs 4 collimation light sources, the increment code track of the indication grating needs to be provided with 4 windows aligned with the collimation light sources, the grating pitch of each window is the same as that of the scale grating, the grating lines of each window are sequentially different by 1/4 grating pitch, and the rear end of each window is respectively provided with a photoelectric detection device for receiving the 4-phase light intensity signals. Corresponding to four-field scanning, the increment window of the single-field scanning indication grating only needs to be opened by 1 window, and the formed fringes are longitudinal moire fringes or transverse moire fringes. The photoelectric detection device at the rear end of the window adopts a densely arranged photodiode array, and moire fringe signals with the phase difference of 1/4 are received between adjacent photodiodes. As the increment window of single-field scanning only needs to be opened by 1 window, the volume is smaller, and the integration is easy. And each phase of single-field scanning is provided with a plurality of photodiodes for detection, and the average effect among the photodiodes with the same phase can effectively reduce the influence caused by dirt or random errors. In addition, the failure rate and the debugging difficulty of single-field scanning are obviously reduced compared with those of four-field scanning.
Due to factors such as assembly, light source attenuation, light path pollution, random fluctuation and the like, a certain phase difference exists between the increment output and the absolute output. Under the condition of not considering the factor, the output accuracy of the whole is greatly influenced by the output judgment error of the increment code channel.
In order to solve the problems, the invention discloses an absolute code channel error correction technology in a high-precision grating ruler reading head system, which can be used for measuring high-precision micro displacement and can be widely used in the fields of precision semiconductor manufacturing, precision displacement measurement, precision motion control, closed-loop feedback control of a numerical control machine tool and the like. As shown in fig. 1, the invention realizes that the detection parameters can be adjusted in a feedback way according to the actual measurement condition through the special absolute PD detection circuit (7), and meanwhile, the output is judged and corrected through the logic and algorithm disclosed by the patent in the special calculation processing unit (8), so that the accuracy and the reliability of the grating ruler system are improved. .
(III) summary of the invention
The invention aims to provide an absolute code channel error correction technology in a high-precision grating ruler reading head system, which comprises a light source (1), a scale grating (2), an indication grating (3), an incremental PD (4), an absolute PD (5), an incremental PD detection circuit (6), an absolute PD detection circuit (7) and a calculation processing unit (8).
The purpose of the invention is realized in the following way:
After passing through the scale grating (2) and the indication grating (3), the light emitted by the light source (1) irradiates the increment PD (4) and the absolute PD (5). The marking ruler grating (2) is divided into an upper part and a lower part of stripes with different brightness and brightness intervals in the transmission type grating ruler, wherein one part of stripe intervals regularly correspond to the increment PD, and the other part of stripe intervals irregularly correspond to the absolute battery; the indication grating (3) is also divided into an upper part and a lower part, the stripe interval rule corresponds to the increment PD, and the other part is a transparent glass window corresponds to the increment PD. The overall system light routes the light source until the PD is accepted. The receiving PD generates different induced current signals according to the semiconductor characteristics and the illumination intensity, the induced current signals are converted into analog voltage signals and digital signals through corresponding detection circuits, and the analog voltage signals and the digital signals are input into a calculation processing unit and then parameter correction and output judgment are carried out on an absolute PD detection circuit (7) according to an algorithm and a measured condition. The invention aims at the absolute code channel error correction technology in a high-precision grating ruler reading head system, and the detection circuits corresponding to the absolute code channels are divided into two, so that code channel information M1 and M2 with 90-degree phase difference are generated, and the two code channel information are mutually redundant and error-corrected to improve the overall measurement precision.
The light source (1) is a quasi-straight light source, emits constant-wavelength continuous light with constant brightness, generates light spots to affect absolute PD and incremental PD output current after passing through two gratings, outputs corresponding analog signals and digital signals after passing through corresponding detection circuits and processes a processing unit, and the processing unit carries out algorithm correction and feedback correction on the circuits according to input signals. The receiving PD generates different induced current signals according to the semiconductor characteristics and the illumination intensity, the induced current signals are converted into analog voltage signals and digital signals through corresponding detection circuits, and the analog voltage signals and the digital signals are input into a calculation processing unit and then parameter correction and output judgment are carried out on an absolute PD detection circuit (7) according to an algorithm and a measured condition. The invention aims at the absolute code channel error correction technology in a high-precision grating ruler reading head system, and the detection circuits corresponding to the absolute code channels are divided into two, so that code channel information M1 and M2 with 90-degree phase difference are generated, and the two code channel information are mutually redundant and error-corrected to improve the overall measurement precision.
The corresponding incremental code track part and the absolute code track part in the scale grating (2) and the indication grating (3) are in corresponding relation. The collimating light source generates molar stripes through the incremental code tracks after passing through the two gratings, a molar stripe period W1 is correspondingly generated, the absolute code tracks generate light spots with alternate brightness, the absolute code tracks adopt an M-sequence coding mode, and the generated light spots output digital signals after passing through the incremental PD and the detection circuit thereof meet the M-sequence requirement.
The M sequence is a pseudo-random sequence, has the characteristics of easy generation, strong regularity, and very good autocorrelation and cross correlation, can be conveniently generated by using a shift register, and is suitable for a scene of mobile coding. Therefore, the M sequence is selected to be used for absolute code channel detection, wherein the absolute code channel stripes in the scale grating (2) accord with the M sequence rule. The M sequence is also called as the longest linear feedback shift register sequence, the recurrence relation is called as feedback logic function or recurrence equation, and the characteristic equation is that
Wherein f (x) is the generated data to be inserted into the least significant bit; c 0 to c n are feedback connections using shift registers of M-sequence, 0 when there is no feedback; x n is the corresponding original sequence.
The M sequences of the present claim take n=4, then their period p=2 4 -1=15, and 15M sequences can be generated. Each M-sequence is shifted by 1bit to correspond to one period of the incremental track, so the incremental track PD spacing is the same as the moire period W1. The incremental code is analyzed from principle to the initial phase of the absolute code channel is completely aligned with the initial phase of the absolute code channel so as to avoid error judgment, but the absolute code channel is output into a digital signal which is directly corresponding to brightness information because the incremental code channel is output into an analog signal, and the analog signal is converted into the digital signal to have a certain time delay, so that the absolute code channel can lead the incremental code channel by a certain phase physically and used for compensating time errors.
The incremental PD detection circuit (6) mainly comprises a trans-impedance amplifier (trans-IMPEDANCE AMPLIFIER, TIA) and is used for converting PD output current signals with different magnitudes caused by different brightness into voltage signals, and mainly comprises an operational amplifier, wherein the output delay is fixed delay, and errors cannot be introduced into the system. The absolute PD detection circuit (7) mainly comprises a TIA and a hysteresis comparator, wherein the TIA converts a current signal into a voltage signal, and the TIA converts the voltage signal into a digital signal according to input parameters VIH and VIL of a calculation processing unit (8). The output of the incremental PD detection circuit (6) and the output of the absolute PD detection circuit (7) are both sent to a calculation processing unit (8) to make logic judgment. At least 5 PDs with a W1 interval are included in the absolute track PD, and correspondingly 5 sets of processing circuits are included. The incremental code channel in the judgment logic is divided into two signals M1 and M2, according to the arrangement rule of the absolute code channel grating, M1 correspondingly outputs a periodic high level at the position with the phase being 0 degrees, and M2 outputs a periodic high level at the position with the phase being 90 degrees. Where M1 and M2 are required to perform mutual error correction if light smudge problems occur or environmental introduction disturbances lead to high level times greater than 1 incremental track period.
The error correction mode is to judge the phase positions of the corresponding increment code channels of the rising edge and the falling edge of the output of the M1 and the M2 respectively, if the corresponding phases are 0 degrees and 180 degrees, the M1 and the M2 are judged to be correct at the moment, if the misalignment condition occurs, the misalignment condition is judged, the minimum suspension angle deviation condition is the current calculation basis, and the VIH and the VIL are modified according to the deviation condition.
6. The absolute PD detection circuit (7) comprises a hysteresis comparator, wherein the reference voltage Vref in the hysteresis comparator needs to change along with the light spot brightness, and the reference voltage Vref is half of the maximum value of PD output voltage and is determined by the system. The logic of the output digital signal Vout is:
Wherein Vin is TIA output and input from hysteresis comparison, VIH is hysteresis voltage with high level, and VIL is hysteresis voltage with low level. VIH and VIL are controlled by a computing processing unit (8). In claim 4, if the rising edge and the falling edge are not aligned, the minimum phase error Δω is calculated. A calculation processing unit (8) corrects the phase alignment condition based on the calculated value, and changes VIH and VIL. If delta omega is larger than 0, the absolute code channel advance increment code channel can be described, so that the absolute code channel judgment delay is required to be increased; if Δω is smaller than 0, it indicates that the incremental code track leads the absolute code track, so it is necessary to reduce the absolute code track decision delay. Typically, VIH and VIL are adjusted simultaneously and have the following values:
This adjustment can be understood as a successive approximation strategy, the approximation of which is represented by the coefficient k. Too large a k may introduce too much measurement jitter. Too small k will result in too slow correction and large absolute errors in measurement.
The whole judging and correcting process is completed in a computing processing unit (8) and the correcting result is fed back to an absolute PD detection circuit (7). And meanwhile, calculating position information according to the existing data and the corrected data and outputting the position information.
(IV) description of the drawings
Fig. 1 is a schematic diagram of a high robustness grating scale absolute code track system. The high-precision grating ruler reading head system consists of a light source (1), a scale grating (2), an indication grating (3), an increment PD (4), an absolute PD (5), an increment PD detection circuit (6), an absolute PD detection circuit (7) and a calculation processing unit (8).
Fig. 2 is a schematic diagram of an incremental code track part in a high-precision grating ruler system, wherein light spots are formed on the surface of an incremental PD array after collimated light passes through a scale grating and an indication grating, the scale grating and the indication grating are regularly distributed stripes, certain angle errors can be generated due to installation relation, and finally molar stripe type light spots are formed after the light passes through the two gratings. The spot changes with the movement of the indication grating and the PD (both in the readhead system). Different PDs in the incremental PD array output different current values due to different surface light spot sizes, and sine and cosine signals are generated along with the movement of the grating ruler reading head after passing through the incremental PD detection circuit.
Fig. 3 is a schematic diagram of an incremental code track part in a high-precision grating ruler system, wherein collimated light passes through a scale grating and an indication grating to form light spots on the surface of an absolute PD array, the scale grating is stripes distributed according to an M-sequence, the indication grating is a transparent window, and the light passes through two gratings to form light spots corresponding to the M-sequence. The spot changes with the movement of the indication grating and the PD (both in the readhead system). The spot changes as the indicator grating moves. Different PDs in the absolute PD array output different current values due to different surface light spot sizes, and the digital square wave signals are output along with the movement of the grating ruler reading head after passing through the absolute PD detection circuit.
Fig. 4 is a schematic diagram of digital output of an incremental code track in a high-precision grating ruler system, a PD array is distributed in two types according to A, B, a 90-degree phase difference exists in output signal phases according to the distribution rule, a current absolute position can be definitely obtained according to an M-sequence specification, the digital output changes along with the change of light spots caused by movement of a grating ruler reading head, the current absolute position is calculated according to the digital output and the value of an M-sequence shift register in a calculation processing unit, the beginning of each sequence is calculated, and the current absolute position corresponds to the output sine wave of the incremental code track.
Fig. 5 is a logic of a calculation processing unit in the high-precision grating ruler system, wherein the logic integrally makes a judgment on the effectiveness of the output of the absolute code channel according to the output of the incremental code channel, and corrects the absolute PD detection circuit according to the judgment result so as to gradually approach the most accurate measurement value.
Fig. 6 is a waveform comparison of corrected and uncorrected outputs in a high precision grating scale system. The method can be used for judging that the unaligned edge exists before the uncorrectation, judging that the unaligned edge is 1 in the calculation processing unit, analyzing and finding that the phenomenon is caused by the fact that an indication grating or an identification grating which is caused by dirt, oil stains and the like blocks effective light, generating abnormal light spots and causing misjudgment, and correcting the abnormal light spots by adopting an increment signal when the situation occurs.
(Fifth) detailed description of the invention
Embodiment one:
Fig. 4 shows an embodiment of the absolute code track phase deviation redundancy output to increase the robustness of the system, and the high-precision grating scale reading head system consists of a light source (1), a scale grating (2), an indication grating (3), an incremental PD (4), an absolute PD (5), an incremental PD detection circuit (6), an absolute PD detection circuit (7) and a calculation processing unit (8). After passing through the scale grating (2) and the indication grating, the light irradiates on an absolute PD and an increment PD. The marking ruler grating (2) is divided into an upper part and a lower part of stripes with different brightness and brightness intervals in the transmission type grating ruler, wherein one part of stripe intervals regularly correspond to the increment PD, and the other part of stripe intervals irregularly correspond to the absolute battery; the indication grating is also divided into an upper part and a lower part, the stripe interval rule corresponds to the increment PD, and the other part is a transparent glass window corresponds to the increment PD. The overall system light routes the light source until the PD is accepted. The receiving PD generates different induced current signals according to the semiconductor characteristics and the illumination intensity, and the induced current signals are converted into voltage signals through a corresponding detection circuit. The invention aims at the absolute code channel error correction technology in a high-precision grating ruler reading head system, and the detection circuits corresponding to the absolute code channels are divided into two, so that code channel information M1 and M2 with 90-degree phase difference are generated, and the two code channel information are mutually redundant and error-corrected to improve the overall measurement precision.
The problem that the output precision is affected and the output waveform is destroyed due to the dirty grating or the system installation difference is needed to be divided into two solutions, the first problem is aimed at the non-alignment phenomenon caused by the system difference, and the problem is characterized in that more than two edges are not aligned, parameters in an absolute PD detection circuit are corrected at the moment, the alignment situation is gradually approximated, and finally the alignment situation is obtained to eliminate errors. The second is to correct the absolute code track by using the incremental code track for the error caused by the dirty grating, and the overall effect is shown in fig. 6. It can be seen that the output phases can be aligned completely, so as to eliminate the influence of the external environment on the high-precision grating ruler system, and improve the robustness of the whole system.
Embodiment two:
FIG. 5 is a diagram of the output and decision principle of the calculation processing unit logic, the base incremental code track and the absolute code track in the high precision grating ruler system; the method is characterized in that: the incremental PD detection circuit (6) mainly comprises a trans-impedance amplifier (trans-IMPEDANCE AMPLIFIER, TIA) and is used for converting PD output current signals with different magnitudes caused by different brightness into voltage signals, and mainly comprises an operational amplifier, wherein the output delay is fixed delay, and errors cannot be introduced into the system. The absolute PD detection circuit (7) mainly comprises a TIA and a hysteresis comparator, wherein the TIA converts a current signal into a voltage signal, and the TIA converts the voltage signal into a digital signal according to input parameters VIH and VIL of a calculation processing unit (8). The output of the incremental PD detection circuit (6) and the output of the absolute PD detection circuit (7) are both sent to a calculation processing unit (8) to make logic judgment. At least 5 PDs with a W1 interval are included in the absolute track PD, and correspondingly 5 sets of processing circuits are included. The incremental code channel in the judgment logic is divided into two signals M1 and M2, according to the arrangement rule of the absolute code channel grating, M1 correspondingly outputs a periodic high level at the position with the phase being 0 degrees, and M2 outputs a periodic high level at the position with the phase being 90 degrees. Where M1 and M2 are required to perform mutual error correction if light smudge problems occur or environmental introduction disturbances lead to high level times greater than 1 incremental track period.
The error correction mode is to judge the phase positions of the corresponding increment code channels of the rising edge and the falling edge of the output of the M1 and the M2 respectively, if the corresponding phases are 0 degrees and 180 degrees, the M1 and the M2 are judged to be correct at the moment, if the misalignment condition occurs, the misalignment condition is judged, the minimum suspension angle deviation condition is the current calculation basis, and the VIH and the VIL are modified according to the deviation condition.
Claims (5)
1. The utility model provides a high robustness grating chi absolute code way system which characterized in that: the high-precision grating ruler reading head system consists of a light source (1), a scale grating (2), an indication grating (3), an incremental Photodiode (PD) (4), an absolute PD (5), an incremental PD detection circuit (6), an absolute PD detection circuit (7) and a calculation processing unit (8); in the system, light emitted by a light source (1) respectively passes through a scale grating (2) and an indication grating (3) and forms specific light spots on the surfaces of an increment PD (4) and an absolute PD (5). The spot will have a specific shape depending on the position of the movement and the grating properties, which shape contains the current position information. The increment PD (4) and the increment PD detection circuit (6) form an increment detection code channel together, wherein the increment PD (4) converts a light spot reflecting current position information, which is irradiated on the surface of the light spot, into a current signal, the current signal is converted into an analog voltage signal after passing through the increment PD detection circuit (6), and the voltage signal containing the increment position information of the measurement system is input into a calculation processing unit (8) for further calculation. The absolute PD (5) and the absolute PD detection circuit (7) form an absolute detection code path together, wherein the absolute PD (5) converts a light spot reflecting current position information, which is irradiated on the surface of the absolute PD, into a current signal, the current signal is converted into a digital signal after passing through the absolute PD detection circuit (7), and the digital signal containing absolute information of a measurement system is input into a calculation processing unit (8) for further calculation. The calculation processing unit (8) judges the current position information state according to the input incremental position information and absolute position information, sends out correction instructions to the incremental PD detection circuit (6) and the absolute PD detection circuit (7), and calculates the current accurate absolute position according to the existing incremental position information and absolute position information.
2. The high robustness grating scale absolute track system of claim 1; the method is characterized in that: the light source 1 in the system is a collimated light source, and the light passes through the scale grating (2) and the indication grating and then irradiates the absolute PD and the increment PD. The marking ruler grating (2) is divided into an upper part and a lower part of stripes with different brightness and brightness intervals in the transmission type grating ruler, wherein one part of stripe intervals regularly correspond to the increment PD, and the other part of stripe intervals irregularly correspond to the absolute battery; the indication grating is also divided into an upper part and a lower part, the stripe interval rule corresponds to the increment PD, and the other part is a transparent glass window corresponds to the increment PD. The overall system light routes the light source until the PD is accepted. The receiving PD generates different induced current signals according to the semiconductor characteristics and the illumination intensity, and the induced current signals are converted into voltage signals through a corresponding detection circuit. The invention aims at the absolute code channel error correction technology in a high-precision grating ruler reading head system, and the detection circuits corresponding to the absolute code channels are divided into two, so that code channel information M1 and M2 with 90-degree phase difference are generated, and the two code channel information are mutually redundant and error-corrected to improve the overall measurement precision.
3. The high robustness grating scale absolute track system of claim 1; the method is characterized in that: corresponding relation between the corresponding incremental code track part and the absolute code track part in the scale grating (2) and the indication grating (3); the collimating light source generates molar stripes through the incremental code tracks after passing through the two gratings, a molar stripe period W1 is correspondingly generated, the absolute code tracks generate light spots with alternate brightness, the absolute code tracks adopt an M-sequence coding mode, and the generated light spots output digital signals after passing through the incremental PD and the detection circuit thereof meet the M-sequence requirement.
The M sequence is a pseudo-random sequence, has the characteristics of easy generation, strong regularity, and very good autocorrelation and cross correlation, can be conveniently generated by using a shift register, and is suitable for a scene of mobile coding; therefore, M sequences are selected to be used for absolute code channel detection, wherein absolute code channel stripes in the scale grating (2) accord with M sequence rules; the M sequence is also called as the longest linear feedback shift register sequence, the recurrence relation is called as feedback logic function or recurrence equation, and the characteristic equation is that
Wherein f (x) is the generated data to be inserted into the least significant bit; c 0 to c n are feedback connections using shift registers of M-sequence, 0 when there is no feedback; x n is the corresponding original sequence.
The M sequences of the present claim take n=4, then their period p=2 4 -1=15, and 15M sequences can be generated. Each M-sequence is shifted by 1bit to correspond to one period of the incremental track, so the incremental track PD spacing is the same as the moire period W1. The incremental code is analyzed from principle to the initial phase of the absolute code channel is completely aligned with the initial phase of the absolute code channel so as to avoid error judgment, but the absolute code channel is output into a digital signal which is directly corresponding to brightness information because the incremental code channel is output into an analog signal, and the analog signal is converted into the digital signal to have a certain time delay, so that the absolute code channel can lead the incremental code channel by a certain phase physically and used for compensating time errors.
4. The output of the incremental code channel and the absolute code channel according to claim 3 and the decision principle; the method is characterized in that: the incremental PD detection circuit (6) mainly comprises a trans-impedance amplifier (trans-IMPEDANCE AMPLIFIER, TIA) and is used for converting PD output current signals with different magnitudes caused by different brightness into voltage signals, and mainly comprises an operational amplifier, wherein the output delay is fixed delay, and errors cannot be introduced into the system. The absolute PD detection circuit (7) mainly comprises a TIA and a hysteresis comparator, wherein the TIA converts a current signal into a voltage signal, and the TIA converts the voltage signal into a digital signal according to input parameters VIH and VIL of a calculation processing unit (8). The output of the incremental PD detection circuit (6) and the output of the absolute PD detection circuit (7) are both sent to a calculation processing unit (8) to make logic judgment. At least 5 PDs with a W1 interval are included in the absolute track PD, and correspondingly 5 sets of processing circuits are included. The incremental code channel in the judgment logic is divided into two signals M1 and M2, according to the arrangement rule of the absolute code channel grating, M1 correspondingly outputs a periodic high level at the position with the phase being 0 degrees, and M2 outputs a periodic high level at the position with the phase being 90 degrees. Where M1 and M2 are required to perform mutual error correction if light smudge problems occur or environmental introduction disturbances lead to high level times greater than 1 incremental track period.
The error correction mode is to judge the phase positions of the corresponding increment code channels of the rising edge and the falling edge of the output of the M1 and the M2 respectively, if the corresponding phases are 0 degrees and 180 degrees, the M1 and the M2 are judged to be correct at the moment, if the misalignment condition occurs, the misalignment condition is judged, the minimum suspension angle deviation condition is the current calculation basis, and the VIH and the VIL are modified according to the deviation condition.
5. The correction principle of the absolute code channel in the output and judgment principle of the incremental code channel and the absolute code channel according to claim 3; the method is characterized in that: the absolute PD detection circuit (7) comprises a hysteresis comparator, wherein the reference voltage Vref in the hysteresis comparator needs to change along with the light spot brightness, and the reference voltage Vref is half of the maximum value of PD output voltage and is determined by the system. The logic of the output digital signal Vout is:
Wherein Vin is TIA output and input from hysteresis comparison, VIH is hysteresis voltage with high level, and VIL is hysteresis voltage with low level. The VIH and the VIL are controlled by a calculation processing unit (8); if the rising edge and the falling edge are not aligned in the condition of claim 4, calculating a minimum phase error delta omega; the calculation processing unit (8) corrects the phase alignment condition according to the calculated value and changes VIH and VIL; if delta omega is larger than 0, the absolute code channel advance increment code channel can be described, so that the absolute code channel judgment delay is required to be increased; if delta omega is smaller than 0, the incremental code channel leads the absolute code channel, so that the absolute code channel judgment delay needs to be reduced; typically, VIH and VIL are adjusted simultaneously and have the following values:
this adjustment can be understood as a successive approximation strategy, the approximation of which is represented by the coefficient k. Too large k may introduce too large measurement jitter, too small k may result in too slow correction, and large absolute measurement errors.
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