CN118274722A - High-precision grating size channel signal phase mutual correction algorithm and reading head system - Google Patents
High-precision grating size channel signal phase mutual correction algorithm and reading head system Download PDFInfo
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- G—PHYSICS
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Abstract
The invention provides a high-precision grating size channel signal phase mutual correction algorithm and a reading head system, which are characterized in that: the high-precision grating ruler reading head system consists of a collimation light source (1), a scale grating (2), an indication grating (3), a photodiode array (4) and a code channel signal phase mutual correction algorithm (5); through a code channel signal phase mutual correction algorithm (5), the photodiode array (4) can generate an output signal with correct phase information according to the relative displacement of the scale grating (2). 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-precision grating size channel signal phase mutual correction algorithm and a reading head system, which 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 (shown in figure 2) 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.
The invention adopts a system block diagram shown in fig. 1, and is a single-field scanning reflection type absolute grating ruler. Since moire fringes at the incremental code tracks (41) on the photodiode array (4) are periodic sinusoidal signals A, in use, the sinusoidal signals need to be converted into high-low level signals A 'through threshold comparison, and the displacement condition of the scale grating (2) relative to the indication grating (3) is judged according to the rising/falling of the signals A'.
The amplitude or background of moire fringe sine wave signals is weakened due to factors such as assembly, light source attenuation, light path dirt, random fluctuation and the like. In the case where the discrimination threshold is unchanged, a square wave signal with a low duty cycle is generated (as shown in the upper right of fig. 3). Or the amplitude or background of the moire fringe sine wave signal is enhanced due to factors such as assembly, light leakage, random fluctuation and the like. In the case where the discrimination threshold is unchanged, a square wave signal with a high duty ratio is generated (as shown in the upper right of fig. 4). Both cases cause the phase corresponding to the rising/falling edge of the signal a' to deviate from the design value, thereby obtaining erroneous displacement information.
In order to solve the problems, the invention discloses a high-precision grating size channel signal phase mutual correction algorithm and a 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 present invention can make the rising edge of the square wave output by the absolute code track (42) and the moire fringe signal zero phase alignment reference signal M of the increment code track (41) by the special design of the photodiode array (4). The signal A and the signal M are input into a code channel signal phase mutual correction algorithm (5) as input signals, each time the algorithm detects the rising edge of the signal M, the voltage value of the signal A is recorded as a discrimination threshold L ', the updated discrimination threshold L ' is fed back into a photodiode array (4), and the photodiode array (4) outputs a signal A with correct phase and duty ratio according to the updated discrimination threshold L '. Thereby improving the accuracy and reliability of the grating ruler system.
(III) summary of the invention
The invention aims to provide a high-precision grating ruler reading head system which consists of a collimation light source (1), a reflection type grating (2), a transmission type grating (3), a photodiode array (4) and a code channel signal phase intercorrelation algorithm (5).
The purpose of the invention is realized in the following way: the photodiode array (4) generates an output signal along with the relative displacement of the scale grating (2) in the light field irradiated on the light field, wherein the incremental code channel (41) generates an incremental sine wave signal A, the incremental sine wave signal A' is generated according to a set discrimination threshold L, and the absolute code channel (42) generates an absolute square wave signal M; the signal A and the signal M generated by the photodiode array (4) are input into a code channel signal phase mutual correction algorithm (5), the code channel signal phase mutual correction algorithm (5) can adjust a discrimination threshold L 'in real time according to the states of the signal A and the signal M, the discrimination threshold L' is fed back into the photodiode array (4), and the photodiode array (4) generates an increment square wave signal A 'with correct phase corresponding to the duty ratio and the rising/falling edge according to the updated discrimination threshold L', so that the real-time correction of the code channel signal phase is realized.
The collimation light source (1) in the system can be any one of a combination system of a Light Emitting Diode (LED) and a special lens or a light source system formed by collimating/expanding a laser. Characterized in that the collimated light source (1) has a small beam divergence angle, the beam divergence angle (full width at half maximum) of which is less than 10 °; preferably, the collimated light source (1) should also have a narrow spectral range, or be a monochromatic light source with a spectral width (full width at half maximum) of less than 35nm; preferably, the collimated light source (1) should also have a relatively large aperture, so that the incremental code tracks (21) and the absolute code tracks (22) on the scale grating (2) can be illuminated simultaneously; preferably, the direction of the beam of the collimated light source (1) forms an angle with the perpendicular to the plane of the scale grating (2), which angle is between 45 DEG and 10 DEG (acute angle).
The scale grating (2) in the system is a reflective grating which can generate one-dimensional relative displacement with the collimation light source (1) and the photodiode array (4), and can generate a changed light field along with the relative displacement and project the light field onto the indication grating (3); the scale grating (2) is characterized in that a metal material is used as a substrate, and periodic polished metal stripes are plated on the metal material, so that incident light beams can be reflected; the fringe period (pitch) in the region of the incremental track (21) on the scale grating (2) may be 20 μm, 30 μm, 40 μm, 50 μm etc.; correspondingly, the width of a single stripe may be 10 μm, 15 μm, 20 μm, 25 μm, etc.; the fringes in the absolute code track (22) areas of the scale grating (2) are distributed in random encoded form, the width of individual fringes can be 20 μm, 30 μm, 40 μm, 50 μm etc., the reflection fringes in each absolute code track (22) area must be aligned with one of the fringes in the incremental code track (21) area, and the individual fringe width must be greater than the pitch in the incremental code track (21) area; the stripe direction in the areas of the incremental track (21) and the absolute track (22) is consistent with the displacement direction of the scale grating (2).
The indication grating (3) in the system is a transmission grating which is relatively fixed with the positions of the collimation light source (1) and the photodiode array (4), and can carry out filtering treatment on the light field reflected by the scale grating (2); the light beam transmission device is characterized in that the indication grating (3) takes a glass material as a substrate, and periodic medium stripes are plated on the indication grating, so that the incident light beam can be transmitted; the stripes of the area of the incremental code track (31) on the indication grating (3) are inversely distributed relative to the stripe distribution of the area of the incremental code track (21) on the scale grating (2), namely, at the positions of the stripes in the area of the incremental code track (21), the corresponding positions in the area of the incremental code track (31) are free of stripes, and vice versa; the fringe period (pitch) in the area of the incremental track (31) on the index grating (3) may be 20 μm, 30 μm, 40 μm, 50 μm, etc.; correspondingly, the width of a single stripe may be 10 μm, 15 μm,20 μm, 25 μm, etc.; the stripe in the area of the increment code track (31) on the indication grating (3) is consistent with the cycle and the width of the stripe in the area of the increment code track (21) on the scale grating (2); the absolute code track (32) area on the indication grating (3) is a transparent window, and the window width is required to be an integral multiple of the stripe width in the absolute code track (22) area on the scale grating (2); the stripe direction in the areas of the incremental track (31) and the absolute track (32) on the indication grating (3) is consistent with the displacement direction of the scale grating (2).
The photodiode array (4) in the system is a one-dimensional photodiode array comprising a transimpedance amplifier (TIA) and a signal processing unit and can generate an output signal according to the change of an optical field irradiated on the photodiode array; an incremental track (41) area on the photodiode array (4) for generating an incremental sine wave signal a, an incremental square wave signal a'; when the photodiode array (4) does not receive a discrimination threshold L 'fed back by the code channel signal phase mutual correction algorithm (5), an incremental code channel (41) area generates an incremental square wave signal A' according to a preset discrimination threshold L; when the photodiode array (4) receives a discrimination threshold L ' fed back by the code channel signal phase mutual correction algorithm (5), an incremental code channel (41) area generates an incremental square wave signal A ' with a duty ratio of 50% according to the fed-back discrimination threshold L '; the pixel pitch in the region of the incremental track (41) on the photodiode array (4) is to be consistent with 1/4 of the moire pitch illuminated thereon; an absolute code track (42) area on the photodiode array (4) for generating an absolute square wave signal M; the rising/falling edges of the absolute square wave signal M generated by the absolute track (42) area on the photodiode array (4) must be aligned with the edges of the resulting image of the absolute track (22) area on the scale grating (2); the pixel spacing in the absolute code track (42) area on the photodiode array (4) is consistent with 1/2 of the imaging width of the grating stripes in the absolute code track (22) area on the scale grating (2); the stripe direction in the areas of the incremental track (31) and the absolute track (32) on the indication grating (3) is consistent with the displacement direction of the scale grating (2).
The photodiode array (4) and the code channel signal phase intercorrelation algorithm (5) in the system form a set of negative feedback regulation module, and the negative feedback regulation module can generate an increment square wave signal A' with the duty ratio of 50% along with the displacement of the scale grating (2); the signal processing unit in the photodiode array (4) comprises a single threshold comparator, and can convert an incremental sine wave signal A into an incremental square wave signal A ' or an incremental square wave signal A ' according to a preset discrimination threshold L or a discrimination threshold L ' fed back by a code channel signal phase intercorrection algorithm (5); after the system is started, when the photodiode array (4) does not receive a discrimination threshold L' fed back by the code channel signal phase intercorrection algorithm (5), the upper signal processing unit takes the preset discrimination threshold L as a reference voltage Vref, and the discrimination threshold L can be any one of a default value of the system or a last reference voltage recorded before the last system shutdown; When the photodiode array (4) receives the discrimination threshold L 'fed back by the code channel signal phase inter-correction algorithm (5), the upper signal processing unit takes the discrimination threshold L' fed back by the code channel signal phase inter-correction algorithm (5) as a reference voltage Vref; a single threshold comparator on the photodiode array (4) which outputs a high level when the voltage of the input signal is higher than the reference voltage Vref and outputs a low level when the voltage of the input signal is lower than the reference voltage Vref; the single threshold comparator on the photodiode array (4) can realize conversion from a sine wave signal to a square wave signal according to the reference voltage; The code channel signal phase intercorrelation algorithm (5) comprises a hysteresis comparator and a latch, and can record the voltage value of the increment sine wave signal A corresponding to the rising/falling edge of the absolute square wave signal M in real time to generate a discrimination threshold L'; a hysteresis comparator on a code channel signal phase intercorrelation algorithm (5), when the voltage of an input signal is higher than a set upper comparison threshold value VIH, the comparator outputs a high level, when the voltage of the input signal is lower than a set lower comparison threshold value VIL, the comparator outputs a low level, when the voltage of the input signal is between the set upper comparison threshold value VIH and the set lower comparison threshold value VIL, the level output by the comparator is kept unchanged, and the hysteresis comparator can effectively avoid unnecessary level turnover caused by noise of the input signal; An upper comparison threshold value VIH and a lower comparison threshold value VIL of a hysteresis comparator in the code channel signal phase intercorrelation algorithm (5) are determined from a high level VH and a low level VL of an input square wave signal, and are typically an upper comparison threshold value vih= (2/3) ×vh+ (1/3) ×vl, and a lower comparison threshold value vil= (1/3) ×vh+ (2/3) ×vl; the latch on the code channel signal phase mutual correction algorithm (5) can respond to the level inversion of the output signal of the hysteresis comparator in real time, and temporarily maintain the voltage value of the input signal during the level inversion; the latches on the code channel signal phase mutual correction algorithm (5) can record the voltage value of the maintained incremental sine wave signal A, generate a discrimination threshold L 'and feed back the discrimination threshold L' to the photodiode array (4) in real time; the negative feedback module formed by the photodiode array (4) and the code channel signal phase mutual correction algorithm (5) generates an incremental sine wave signal A with the duty ratio of 50% by recording the voltage value of the incremental sine wave signal A corresponding to the rising/falling edge of the absolute square wave signal M as a discrimination threshold L'.
When the system is influenced and the light intensity irradiated on the photodiode array (4) is weakened, the amplitude or background of an incremental sine wave signal A generated by an incremental code channel (41) on the system is reduced, the duty ratio of the generated incremental square wave signal A 'is less than 50% on the premise that the discrimination threshold L is unchanged, and the phase corresponding to the rising/falling edge of the incremental square wave signal A' is deviated from the design value; the method comprises the steps of inputting an incremental sine wave signal A generated by an incremental code channel (41) on a photodiode array (4) and an absolute square wave signal M generated by an absolute code channel (42) into a code channel signal phase mutual correction algorithm (5), wherein the code channel signal phase mutual correction algorithm (5) records the voltage value of the incremental sine wave signal A corresponding to the rising/falling edge of the absolute square wave signal M in real time; the code channel signal phase mutual correction algorithm (5) generates a discrimination threshold L 'which is equal to the voltage value of the recorded increment sine wave signal A and feeds the discrimination threshold L' back to the photodiode array (4); the photodiode array (4) generates an increment square wave signal A ' with the duty ratio of 50% according to the discrimination threshold L ', the phase corresponding to the rising/falling edge of the signal A ' is consistent with the design value, and the correction of the phase signal is realized.
When the system is influenced to enhance the light intensity irradiated on the photodiode array (4), the amplitude or background of an incremental sine wave signal A generated by an incremental code channel (41) on the system is increased, the duty ratio of the generated incremental square wave signal A 'is more than 50% on the premise that the discrimination threshold L is unchanged, and the phase corresponding to the rising/falling edge of the incremental square wave signal A' is deviated from the design value; inputting an incremental sine wave signal A generated by an incremental code channel (41) and an absolute square wave signal M generated by an absolute code channel (42) on a photodiode array (4) into a code channel signal phase mutual correction algorithm (5), wherein the code channel signal phase mutual correction algorithm (5) records the voltage value of the incremental sine wave signal A corresponding to the rising/falling edge of the absolute square wave signal M in real time, and the code channel signal phase mutual correction algorithm (5) generates a discrimination threshold L 'which is equal to the voltage value of the recorded incremental sine wave signal A and feeds back the discrimination threshold L' to the photodiode array (4); the photodiode array (4) generates an increment square wave signal A ' with the duty ratio of 50% according to the discrimination threshold L ', the phase corresponding to the rising/falling edge of the signal A ' is consistent with the design value, and the correction of the phase signal is realized.
(IV) description of the drawings
FIG. 1 is a block diagram of a high precision grating scale readhead system. The high-precision grating ruler reading head system consists of a collimation light source (1), a scale grating (2), an indication grating (3), a photodiode array (4) and a code channel signal phase mutual correction algorithm (5); wherein the scale grating (2), the indication grating (3) and the photodiode array (4) all comprise an increment code channel (X1) and an absolute code channel (X2); the photodiode array (4) can generate an incremental sine wave signal A and an absolute square wave signal M; the code channel signal phase mutual correction algorithm (5) can receive the increment sine wave signal A and the absolute square wave signal M output by the photodiode array (4) to generate a discrimination threshold L'; the photodiode array (4) can receive a preset discrimination threshold L and a discrimination threshold L ' output by a code channel signal phase mutual correction algorithm (5) to generate an increment square wave signal A ' and an increment square wave signal A '.
Fig. 2 shows moire patterns (moire) generated by overlapping two black and white gratings having different grating pitches and grating line directions. According to the principle of geometrical shading, the pitch W and direction of moire fringesThe equations shown in formulas (1) and (2) are satisfied, and moire patterns are classified into oblique moire patterns (d 1≠d2, θ+.0), transverse moire patterns (d 1＝d2, θ+.0), longitudinal moire patterns (d 1≠d2, θ=0), and shutter moire patterns (d 1＝d2, θ=0) according to the relationship between the pitch d 1、d2 and the angle θ. In the case of transverse moire and longitudinal moire, when θ or Δd is a small amount, the pitch W of moire is much larger than the pitch d, and amplification of displacement signals is achieved.
Fig. 3 shows the system output signal and correction means when the light intensity is reduced. When the system is influenced to weaken the light intensity, the generated increment square wave signal A' is an error signal with the duty ratio of less than 50% on the premise that the discrimination threshold L is unchanged. In the invention, a code channel signal phase mutual correction algorithm (5) records the voltage value of an increment sine wave signal A corresponding to the rising/falling edge of an absolute square wave signal M in real time, generates a discrimination threshold L ' equal to the recorded voltage value of the increment sine wave signal A, and generates an increment square wave signal A ' which is a correct signal with the duty ratio equal to 50% according to the discrimination threshold L '.
Fig. 4 is a graph of the system output signal condition and correction means as the intensity of the light increases. When the system is influenced to weaken the light intensity, the generated increment square wave signal A' is an error signal with the duty ratio of more than 50% on the premise that the discrimination threshold L is unchanged. In the invention, a code channel signal phase mutual correction algorithm (5) records the voltage value of an increment sine wave signal A corresponding to the rising/falling edge of an absolute square wave signal M in real time, generates a discrimination threshold L ' equal to the recorded voltage value of the increment sine wave signal A, and generates an increment square wave signal A ' which is a correct signal with the duty ratio equal to 50% according to the discrimination threshold L '.
(Fifth) detailed description of the invention
Embodiment one:
FIG. 3 shows an embodiment of a high precision grating scale channel signal phase cross-correction algorithm and readhead system. The high-precision grating reading head system consists of a collimation light source (1), a scale grating (2), an indication grating (3), a photodiode array (4) and a code channel signal phase mutual correction algorithm (5). The photodiode array (4) comprises an incremental code channel (41) and an absolute code channel (42), wherein the incremental code channel (41) can generate an incremental sine wave signal A along with the relative displacement of the scale grating (2), the incremental sine wave signal A' is generated according to a set discrimination threshold L, and the absolute code channel (42) can generate an absolute square wave signal M along with the relative displacement of the scale grating (2).
When the system is influenced and the light intensity irradiated on the photodiode array (4) is weakened, the amplitude or background of an incremental sine wave signal A generated by an incremental code channel (41) on the system is reduced, the duty ratio of the generated incremental square wave signal A 'is less than 50% on the premise that the discrimination threshold L is unchanged, and the phase corresponding to the rising/falling edge of the incremental square wave signal A' is deviated from the design value; the method comprises the steps of inputting an incremental sine wave signal A generated by an incremental code channel (41) on a photodiode array (4) and an absolute square wave signal M generated by an absolute code channel (42) into a code channel signal phase mutual correction algorithm (5), wherein the code channel signal phase mutual correction algorithm (5) records the voltage value of the incremental sine wave signal A corresponding to the rising/falling edge of the absolute square wave signal M in real time; the code channel signal phase mutual correction algorithm (5) generates a discrimination threshold L 'which is equal to the voltage value of the recorded increment sine wave signal A and feeds the discrimination threshold L' back to the photodiode array (4); the photodiode array (4) generates an increment square wave signal A ' with the duty ratio of 50% according to the discrimination threshold L ', the phase corresponding to the rising/falling edge of the signal A ' is consistent with the design value, and the correction of the phase signal is realized.
Embodiment two:
Fig. 4 shows an embodiment of a high precision grating scale channel signal phase cross-correction algorithm and readhead system. The high-precision grating reading head system consists of a collimation light source (1), a scale grating (2), an indication grating (3), a photodiode array (4) and a code channel signal phase mutual correction algorithm (5). The photodiode array (4) comprises an incremental code channel (41) and an absolute code channel (42), wherein the incremental code channel (41) can generate an incremental sine wave signal A along with the relative displacement of the scale grating (2), the incremental sine wave signal A' is generated according to a set discrimination threshold L, and the absolute code channel (42) can generate an absolute square wave signal M along with the relative displacement of the scale grating (2).
When the system is influenced to enhance the light intensity irradiated on the photodiode array (4), the amplitude or background of an incremental sine wave signal A generated by an incremental code channel (41) on the system is increased, the duty ratio of the generated incremental square wave signal A 'is more than 50% on the premise that the discrimination threshold L is unchanged, and the phase corresponding to the rising/falling edge of the incremental square wave signal A' is deviated from the design value; inputting an incremental sine wave signal A generated by an incremental code channel (41) and an absolute square wave signal M generated by an absolute code channel (42) on a photodiode array (4) into a code channel signal phase mutual correction algorithm (5), wherein the code channel signal phase mutual correction algorithm (5) records the voltage value of the incremental sine wave signal A corresponding to the rising/falling edge of the absolute square wave signal M in real time, and the code channel signal phase mutual correction algorithm (5) generates a discrimination threshold L 'which is equal to the voltage value of the recorded incremental sine wave signal A and feeds back the discrimination threshold L' to the photodiode array (4); the photodiode array (4) generates an increment square wave signal A ' with the duty ratio of 50% according to the discrimination threshold L ', the phase corresponding to the rising/falling edge of the signal A ' is consistent with the design value, and the correction of the phase signal is realized.
Claims (8)
1. A high-precision grating size channel signal phase mutual correction algorithm and a reading head system; the method is characterized in that: the high-precision grating ruler reading head system consists of a collimation light source (1), a scale grating (2), an indication grating (3), a photodiode array (4) and a code channel signal phase mutual correction algorithm (5), wherein: the scale grating (2) in the system comprises an incremental code channel (21) and an absolute code channel (22); the indication grating (3) in the system comprises an increment code channel (31) and an absolute code channel (32); the photodiode array (4) in the system comprises an incremental code track (41) and an absolute code track (41); in the system, a collimation light source (1) irradiates a collimation light beam to an increment code channel (21) and an absolute code channel (22) on a scale grating (2), the scale grating (2) reflects the light beam and forms special light field distribution, the light beam is overlapped on an increment code channel (31) and an absolute code channel (32) on an indication grating (3) and transmitted, and finally the light beam irradiates on an increment code channel (41) and an absolute code channel (42) of a photodiode array (4); the photodiode array (4) generates an output signal along with the relative displacement of the scale grating (2) in the light field irradiated on the light field, wherein the incremental code channel (41) generates an incremental sine wave signal A, the incremental sine wave signal A' is generated according to a set discrimination threshold L, and the absolute code channel (42) generates an absolute square wave signal M; the signal A and the signal M generated by the photodiode array (4) are input into a code channel signal phase mutual correction algorithm (5), the code channel signal phase mutual correction algorithm (5) can adjust a discrimination threshold L ' in real time according to the states of the signal A and the signal M, the discrimination threshold L ' is fed back into the photodiode array (4), and the photodiode array (4) generates an increment square wave signal A with correct phase corresponding to the duty ratio and the rising/falling edge according to the updated discrimination threshold L '.
2. The high precision grating scale channel signal phase intercorrelation algorithm and readhead system of claim 1; the method is characterized in that: the collimation light source (1) in the system can be any one of a combination system of a Light Emitting Diode (LED) and a special lens or a light source system formed by collimating/expanding a laser. Characterized in that the collimated light source (1) has a small beam divergence angle, the beam divergence angle (full width at half maximum) of which is less than 10 °; preferably, the collimated light source (1) should also have a narrow spectral range, or be a monochromatic light source with a spectral width (full width at half maximum) of less than 35nm; preferably, the collimated light source (1) should also have a relatively large aperture, so that the incremental code tracks (21) and the absolute code tracks (22) on the scale grating (2) can be illuminated simultaneously; preferably, the direction of the beam of the collimated light source (1) forms an angle with the perpendicular to the plane of the scale grating (2), which angle is between 45 DEG and 10 DEG (acute angle).
3. The high precision grating scale channel signal phase intercorrelation algorithm and readhead system of claim 1; the method is characterized in that: the scale grating (2) in the system is a reflective grating which can generate one-dimensional relative displacement with the collimation light source (1) and the photodiode array (4), and can generate a changed light field along with the relative displacement and project the light field onto the indication grating (3); the scale grating (2) is characterized in that a metal material is used as a substrate, and periodic polished metal stripes are plated on the metal material, so that incident light beams can be reflected; the fringe period (pitch) in the region of the incremental track (21) on the scale grating (2) may be 20 μm, 30 μm, 40 μm, 50 μm etc.; correspondingly, the width of a single stripe may be 10 μm, 15 μm, 20 μm, 25 μm, etc.; the fringes in the absolute code track (22) areas of the scale grating (2) are distributed in random encoded form, the width of individual fringes can be 20 μm, 30 μm, 40 μm, 50 μm etc., the reflection fringes in each absolute code track (22) area must be aligned with one of the fringes in the incremental code track (21) area, and the individual fringe width must be greater than the pitch in the incremental code track (21) area; the stripe direction in the areas of the incremental track (21) and the absolute track (22) is consistent with the displacement direction of the scale grating (2).
4. The high precision grating scale channel signal phase intercorrelation algorithm and readhead system of claim 1; the method is characterized in that: the indication grating (3) in the system is a transmission grating which is relatively fixed with the positions of the collimation light source (1) and the photodiode array (4), and can carry out filtering treatment on the light field reflected by the scale grating (2); the light beam transmission device is characterized in that the indication grating (3) takes a glass material as a substrate, and periodic medium stripes are plated on the indication grating, so that the incident light beam can be transmitted; the stripes of the area of the incremental code track (31) on the indication grating (3) are inversely distributed relative to the stripe distribution of the area of the incremental code track (21) on the scale grating (2), namely, at the positions of the stripes in the area of the incremental code track (21), the corresponding positions in the area of the incremental code track (31) are free of stripes, and vice versa; the fringe period (pitch) in the area of the incremental track (31) on the index grating (3) may be 20 μm, 30 μm, 40 μm, 50 μm, etc.; correspondingly, the width of a single stripe may be 10 μm, 15 μm, 20 μm, 25 μm, etc.; the stripe in the area of the increment code track (31) on the indication grating (3) is consistent with the cycle and the width of the stripe in the area of the increment code track (21) on the scale grating (2); the absolute code track (32) area on the indication grating (3) is a transparent window, and the window width is required to be an integral multiple of the stripe width in the absolute code track (22) area on the scale grating (2); the stripe direction in the areas of the incremental track (31) and the absolute track (32) on the indication grating (3) is consistent with the displacement direction of the scale grating (2).
5. The high precision grating scale channel signal phase intercorrelation algorithm and readhead system of claim 1; the method is characterized in that: the photodiode array (4) in the system is a one-dimensional photodiode array comprising a transimpedance amplifier (TIA) and a signal processing unit and can generate an output signal according to the change of an optical field irradiated on the photodiode array; an incremental code track (41) area on the photodiode array (4) can receive a judging threshold value L and a judging threshold value L ' and is used for generating an incremental sine wave signal A, an incremental square wave signal A ' and an incremental square wave signal A '; the pixel pitch in the region of the incremental track (41) on the photodiode array (4) is to be consistent with 1/4 of the moire pitch illuminated thereon; an absolute code track (42) area on the photodiode array (4) for generating an absolute square wave signal M; the rising/falling edges of the absolute square wave signal M generated by the absolute track (42) area on the photodiode array (4) must be aligned with the edges of the resulting image of the absolute track (22) area on the scale grating (2); the pixel spacing in the absolute code track (42) area on the photodiode array (4) is consistent with 1/2 of the imaging width of the grating stripes in the absolute code track (22) area on the scale grating (2); the stripe direction in the areas of the incremental track (31) and the absolute track (32) on the indication grating (3) is consistent with the displacement direction of the scale grating (2).
6. The high precision grating scale channel signal phase intercorrelation algorithm and readhead system of claim 1; the method is characterized in that: the photodiode array (4) and the code channel signal phase intercorrelation algorithm (5) in the system form a set of negative feedback regulation module, and the negative feedback regulation module can generate an increment square wave signal A' with the duty ratio of 50% along with the displacement of the scale grating (2); the signal processing unit in the photodiode array (4) comprises a single threshold comparator, and can convert an incremental sine wave signal A into an incremental square wave signal A ' or an incremental square wave signal A ' according to a preset discrimination threshold L or a discrimination threshold L ' fed back by a code channel signal phase intercorrection algorithm (5); After the system is started, when the photodiode array (4) does not receive a discrimination threshold L' fed back by the code channel signal phase intercorrection algorithm (5), the upper signal processing unit takes the preset discrimination threshold L as a reference voltage Vref, and the discrimination threshold L can be any one of a default value of the system or a last reference voltage recorded before the last system shutdown; when the photodiode array (4) receives the discrimination threshold L 'fed back by the code channel signal phase inter-correction algorithm (5), the upper signal processing unit takes the discrimination threshold L' fed back by the code channel signal phase inter-correction algorithm (5) as a reference voltage Vref; a single threshold comparator on the photodiode array (4) which outputs a high level when the voltage of the input signal is higher than the reference voltage Vref and outputs a low level when the voltage of the input signal is lower than the reference voltage Vref; The single threshold comparator on the photodiode array (4) can realize conversion from a sine wave signal to a square wave signal according to the reference voltage; the code channel signal phase intercorrelation algorithm (5) comprises a hysteresis comparator and a latch, and can record the voltage value of the increment sine wave signal A corresponding to the rising/falling edge of the absolute square wave signal M in real time to generate a discrimination threshold L'; a hysteresis comparator on a code channel signal phase intercorrelation algorithm (5), when the voltage of an input signal is higher than a set upper comparison threshold value VIH, the comparator outputs a high level, when the voltage of the input signal is lower than a set lower comparison threshold value VIL, the comparator outputs a low level, when the voltage of the input signal is between the set upper comparison threshold value VIH and the set lower comparison threshold value VIL, the level output by the comparator is kept unchanged, and the hysteresis comparator can effectively avoid unnecessary level turnover caused by noise of the input signal; an upper comparison threshold value VIH and a lower comparison threshold value VIL of a hysteresis comparator on the code channel signal phase intercorrelation algorithm (5) are determined according to a high level VH and a low level VL of the input square wave signal, and are typically vih= (2/3) ×vh+ (1/3) ×vl, vil= (1/3) ×vh+ (2/3) ×vl; the latch on the code channel signal phase mutual correction algorithm (5) can respond to the level inversion of the output signal of the hysteresis comparator in real time, and temporarily maintain the voltage value of the input signal during the level inversion; the latches on the code channel signal phase mutual correction algorithm (5) can record the voltage value of the maintained incremental sine wave signal A, generate a discrimination threshold L 'and feed back the discrimination threshold L' to the photodiode array (4) in real time; the negative feedback module formed by the photodiode array (4) and the code channel signal phase mutual correction algorithm (5) generates an incremental sine wave signal A with the duty ratio of 50% by recording the voltage value of the incremental sine wave signal A corresponding to the rising/falling edge of the absolute square wave signal M as a discrimination threshold L'.
7. The high precision grating scale channel signal phase intercorrelation algorithm and readhead system of claim 1; the method is characterized in that: when the system is influenced and the light intensity irradiated on the photodiode array (4) is weakened, the amplitude or background of an incremental sine wave signal A generated by an incremental code channel (41) on the system is reduced, the duty ratio of the generated incremental square wave signal A 'is less than 50% on the premise that the discrimination threshold L is unchanged, and the phase corresponding to the rising/falling edge of the incremental square wave signal A' is deviated from the design value; the method comprises the steps of inputting an incremental sine wave signal A generated by an incremental code channel (41) on a photodiode array (4) and an absolute square wave signal M generated by an absolute code channel (42) into a code channel signal phase mutual correction algorithm (5), wherein the code channel signal phase mutual correction algorithm (5) records the voltage value of the incremental sine wave signal A corresponding to the rising/falling edge of the absolute square wave signal M in real time; the code channel signal phase mutual correction algorithm (5) generates a discrimination threshold L 'which is equal to the voltage value of the recorded increment sine wave signal A and feeds the discrimination threshold L' back to the photodiode array (4); the photodiode array (4) generates an increment square wave signal A ' with the duty ratio of 50% according to the discrimination threshold L ', the phase corresponding to the rising/falling edge of the signal A ' is consistent with the design value, and the correction of the phase signal is realized.
8. The high precision grating scale channel signal phase intercorrelation algorithm and readhead system of claim 1; the method is characterized in that: when the system is influenced to enhance the light intensity irradiated on the photodiode array (4), the amplitude or background of an incremental sine wave signal A generated by an incremental code channel (41) on the system is increased, the duty ratio of the generated incremental square wave signal A 'is more than 50% on the premise that the discrimination threshold L is unchanged, and the phase corresponding to the rising/falling edge of the incremental square wave signal A' is deviated from the design value; inputting an incremental sine wave signal A generated by an incremental code channel (41) and an absolute square wave signal M generated by an absolute code channel (42) on a photodiode array (4) into a code channel signal phase mutual correction algorithm (5), wherein the code channel signal phase mutual correction algorithm (5) records the voltage value of the incremental sine wave signal A corresponding to the rising/falling edge of the absolute square wave signal M in real time, and the code channel signal phase mutual correction algorithm (5) generates a discrimination threshold L 'which is equal to the voltage value of the recorded incremental sine wave signal A and feeds back the discrimination threshold L' to the photodiode array (4); the photodiode array (4) generates an increment square wave signal A ' with the duty ratio of 50% according to the discrimination threshold L ', the phase corresponding to the rising/falling edge of the signal A ' is consistent with the design value, and the correction of the phase signal is realized.
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