Large-range absolute direction-distinguishing macro-micro cooperative grating displacement encoder and positioning method

Abstract

The application provides a large-range absolute direction discrimination macro-micro collaborative grating displacement encoder, which comprises a light source, a photoelectric detector, a grating and a mask, the grating is a hybrid grating, the hybrid grating comprises a grating area and an encoding area, a group of encoding one is arranged on the encoding area, and a group of encoding two is arranged on the mask; the group of encoding one comprises at least two layers, the first layer is nanoscale positioning encoding, the second layer and subsequent layers are direction discrimination positioning encoding, and the direction discrimination positioning encoding is used for increasing a direction discrimination range; the group of encoding two comprises encoding corresponding to the layers of the group of encoding one, and also comprises the same nanoscale positioning encoding arranged on the first layer and the direction discrimination positioning encoding arranged on the second layer and subsequent layers. The application can guide the motion direction in a large range to find an absolute mark, complete the design of an absolute measurement light path, and realize the pose monitoring and correction of a synthetic aperture optical system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of displacement encoders, in particular to a large-range absolute direction-distinguishing macro-micro collaborative grating displacement encoder and a positioning method. BACKGROUND

[0002] Scientific instrument telescope is one of the important means for human beings to explore the universe. No matter what kind of telescope, such as radio telescope, optical telescope, one of the main performance parameters is resolution. The resolution is related to the aperture size, but it is difficult to manufacture a single large-area telescope mirror. Currently, the sub-mirror assembly method is mainly used, and the observation performance is limited by the sub-mirror assembly accuracy. At the same time, due to the influence of environmental factors such as gravity load, temperature change, humidity change, the relative pose between the installed sub-mirrors will change slightly, which will directly lead to a large surface error of the main mirror. The current pose measurement scheme has high requirements for environmental stability. Long-term use and correction still have surface error, so there is an urgent need for a more stable and higher precision device that can absolutely measure the pose.

[0003] With the use of the telescope, error accumulation will cause a significant decline in its performance. For example, the observation performance of the South African Large Telescope has declined due to humidity, and the observation performance of the Hobby-Eberly Telescope has declined due to temperature. In the soon-to-be-built Large Magellanic Telescope, sub-mirror pose measurement is also of great concern. The 30m telescope, which is being researched by multiple countries including China, is expected to become the world's first extremely large telescope after completion in 2027. Therefore, the spatial pose detection of the sub-mirror is in urgent need. Not only the absolute pose needs to be detected during installation, but also it needs to be measured and fed back during subsequent use, so as to adjust the pose of the sub-mirror and actively control the sub-mirror to make the main mirror surface meet the requirements. How to measure the pose of the sub-mirror with high precision to provide a basis for realizing the adjustment of the sub-mirror co-focus and co-phase is the core technology for the research of large-aperture optical systems for astronomical observation.

[0004] There are electromagnetic displacement measurement and optical displacement measurement for pose measurement. In the electromagnetic measurement method, the precision of the capacitive sensor can reach nanometer level. The multi-degree-of-freedom measurement system composed of multiple capacitive sensors has been used for real-time detection of the pose of the sub-mirror of the Keck and Canary large telescopes. It has high accuracy and stability, but the measurement system composed of capacitive sensors is not only complex, but also sensitive to temperature and humidity, causing errors. The measurement reference of the grating encoder is the grating pitch, which is a physical structure, so it is relatively more stable.

[0005] The absolute positioning mode of the current grating displacement encoder generally only has a positioning signal in a range of 10 microns, which causes a long time to find the positioning signal in the range of 10 microns when correcting the zero position, and thus the zero position cannot be returned. SUMMARY

[0006] To solve the problems in the prior art, the present application provides a large-range absolute direction-distinguishing macro-micro collaborative grating displacement encoder, which can guide the movement direction in a large range to find the absolute mark, complete the design of the absolute measurement light path by means of the robustness of the grating encoder to the environment, and expand the multi-degree-of-freedom measurement to realize the pose monitoring and correction of the synthetic aperture optical system.

[0007] To achieve the above-mentioned purposes, the present application adopts the following solutions:

[0008] The present application provides a large-range absolute direction-distinguishing macro-micro collaborative grating displacement encoder, which comprises a light source, a photoelectric detector, a grating and a mask, the grating is a hybrid grating, the hybrid grating comprises a grating area and an encoding area, a group of encoding one is arranged on the encoding area, and a group of encoding two is arranged on the mask.

[0009] The group of encoding one comprises at least two layers, the first layer is a nanoscale positioning encoding, and the second layer and the subsequent layers are direction-distinguishing positioning encodings for increasing the direction-distinguishing range, the group of encoding two comprises encodings corresponding to the layers of the group of encoding one, and also comprises the same nanoscale positioning encoding arranged in the first layer and the direction-distinguishing positioning encodings arranged in the second layer and the subsequent layers; the direction-distinguishing positioning encoding comprises two encodings arranged in the same layer at a specific interval; the specific intervals of the hybrid grating and the mask are different, and the difference between the specific intervals of the highest layer of the direction-distinguishing positioning encodings of the group of encoding one and the group of encoding two is twice the range of the direction-distinguishing of the encoder.

[0010] In some embodiments, the direction-distinguishing positioning encoding is a transparent slit with a width of d; in the group of encoding one and the group of encoding two, the two encodings in one layer of the direction-distinguishing positioning encodings are encoding three and encoding four, respectively, wherein the nanoscale positioning encoding corresponds to the spatial position of the encoding three one by one; in the group of encoding one and the group of encoding two, the specific intervals between the encoding three and the encoding four are a first specific interval and a second specific interval, respectively, wherein the first specific interval is the distance between the two encodings on the hybrid grating, and the second specific interval is the distance between the two encodings on the mask, and the relationship between the two is second specific interval = first specific interval + d.

[0011] In some embodiments, an incremental signal module is further included, which uses the diffracted light of the grating area to perform interference measurement to form an incremental signal varying with the displacement in the X direction.

[0012] In some embodiments, the signals sequentially passing through the mask and the grating are received by the photodetector, wherein the signal width is 2d, and the wide-range direction-distinguishing interval is 2d.

[0013] In some embodiments, the waveform width of the absolute positioning encoding signal is 2a, and d / a>30.

[0014] In some embodiments, the grating is a transmission grating or a reflection grating.

[0015] The present application also provides a grating positioning method based on the above-mentioned wide-range absolute direction-distinguishing macro-micro collaborative grating displacement encoder, comprising the following steps:

[0016] S1: coarse positioning, determining the direction required for current correction according to the signals at the direction-distinguishing positioning encoding, and locking the absolute position within the wide-range direction-distinguishing interval;

[0017] S2: medium positioning, moving in the direction determined by the coarse positioning, finding the absolute mark of the nanoscale positioning encoding signal, and continuously reducing the interval of the absolute position, and the absolute positioning accuracy can reach the sub-grating period level;

[0018] S3: fine positioning, matching with the incremental signal by means of the absolute positioning accuracy of the sub-grating period level, positioning to the specific phase in the period of the incremental signal, and the positioning accuracy is nanoscale.

[0019] In some embodiments, in step S1, the signals of two encodings in the direction-distinguishing positioning encoding are used for judgment, and the signals of the two encodings are respectively the PD3 module signal and the PD4 module signal, and the judgment rules are as follows:

[0020] Taking the current time as 0, the time before as negative, and the time in the future as positive;

[0021] When the movement starting point is in the negative direction of the PD3 module signal peak zero point, and the movement speed is positive, only the PD3 module has signal change, and the signal change is monotonically increasing, it is judged that the movement direction continues to move forward to find the absolute zero position;

[0022] When the movement starting point is in the negative direction of the PD3 module signal peak zero point, and the movement speed is negative, only the PD3 module has signal change, and the signal change is monotonically decreasing, it is judged that the movement direction should be changed to positive movement to find the absolute zero position;

[0023] When the movement starting point is in the positive direction of the PD3 module signal peak zero point, and the movement speed is positive, the PD3 module signal monotonically decreases, and the PD4 module signal monotonically increases, it is judged that the movement direction should be changed to negative movement to find the absolute zero position;

[0024] When the motion starting point is in the positive direction of the zero point of the PD3 module signal peak value and the motion speed is negative, the PD3 module signal monotonically increases, the PD4 module signal monotonically decreases, and it is judged that the motion direction continues to move in the negative direction to find the absolute zero position.

[0025] In some embodiments, the application includes setting more layers of position encoding to realize a larger range of direction finding functions; meanwhile, X and Y axes can be simultaneously arranged on the hybrid grating to realize the expansion of multi-degree-of-freedom measurement functions.

[0026] The beneficial effects of the present application are:

[0027] The innovation points of the present application mainly include the design of the hybrid grating and the distribution scheme of the encoding thereon:

[0028] 1. The absolute encoding design of the asymmetric position on the double-layer or even n-layer hybrid grating, S2=S1+d, S1>d; S(n+1)=S(n)+d(n), S(n)>d, d(n)>d, n=3, 5, 7, 9…, so that the range of whether reaching the zero position can be observed in a larger range (2d(n)), and after calibrating the signal energy curve, even completely absolute direction finding and positioning measurement can be realized.

[0029] 2. The coarse-fine positioning method makes the final absolute positioning range and accuracy difference reach 10 6 times or more, and the positioning range of up to sub-millimeter or 2d(n) and the positioning accuracy of nanometer level can be realized simultaneously in the present application. Combined with the previous innovation point, this multiple can be made larger. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a three-dimensional optical path diagram of the grating displacement encoder in the embodiment of the present application.

[0031] Figure 2 It is a diagram of the change of the detector signal with the absolute position coordinates of the hybrid grating in the embodiment of the present application.

[0032] Figure 3 It is an encoding distribution diagram of the hybrid grating and the mask in the embodiment of the present application.

[0033] Figure 4 It is a schematic diagram when the motion starting point is in the negative direction of the zero point of the photoelectric detector PD3 signal peak value in the embodiment of the present application.

[0034] Figure 5 It is a schematic diagram when the motion starting point is in the negative direction of the zero point of the photoelectric detector PD3 signal peak value in the embodiment of the present application.

[0035] Figure 6The figure is a schematic diagram of the motion starting point in the positive direction of the peak value zero point of the photodetector PD3 signal in the embodiment of the present application.

[0036] Figure 7 The figure is a schematic diagram of the motion starting point in the positive direction of the peak value zero point of the photodetector PD3 signal in the embodiment of the present application.

[0037] Figure 8 The figure is a top view of the incremental signal module in the embodiment of the present application.

[0038] Figure 9 The figure is a top view of the absolute positioning module in the embodiment of the present application.

[0039] Figure 10 The figure is a top view of the incremental signal-reflection version module in the embodiment of the present application.

[0040] Figure 11 The figure is a top view of the absolute positioning module-reflection version in the embodiment of the present application.

[0041] Figure 12 The figure is a schematic diagram of the hybrid grating and mask plate with more layers of absolute coding in the embodiment of the present application.

[0042] In the figure, 1-rectangular light beam, 2-hybrid grating, 3-+1 level light beam, 4-1 level light beam, 5-right-angle prism, 6-BS, 7-PD1 module, 8-mask plate, 9-coding three, 10-coding four, 11-coding five, 12-PD2 module, 13-PD3 module, 14-PD4 module. DETAILED DESCRIPTION

[0043] In order to make the technical solutions and advantages of the present application clearer, the technical solutions of the embodiments of the present application will be described in detail below in combination with the drawings in the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0044] The embodiments of the present application will be described in detail below, and examples of the embodiments are shown in the drawings, in which the same or similar reference signs represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the present application, and cannot be understood as a limitation on the present application.

[0045] The present application provides a large-range absolute direction-distinguishing macro-micro collaborative grating displacement encoder, comprising a light source, a photodetector, a grating and a mask plate, the grating is a hybrid grating, the hybrid grating comprises a grating area and a coding area, a group of coding one is arranged on the coding area, and a group of coding two is arranged on the mask plate.

[0046] The group code one includes at least two layers of codes, the first layer is nanoscale positioning code three (Code 3), and the second layer is direction distinguishing positioning code four (Code 4) and direction distinguishing positioning code five (Code 5). The group code two includes codes corresponding to the layers of the group code one, and the spatial positions of the code three and the code four correspond to each other one by one, but the distance between the code four and the code five is S2 and S1 respectively, wherein S1 is the distance between the two codes on the hybrid grating, S2 is the distance between the two codes on the mask plate, and the relationship between them is S2 = S1 + d; if the number of code layers is continuously increased, a larger range of direction distinguishing correction and measurement can be achieved.

[0047] The specific interval of the direction distinguishing positioning code four and the code five of the hybrid grating in the same layer is different from the specific interval of the direction distinguishing positioning code four and the code five of the mask plate, and the double difference value is the direction distinguishing large range interval of the encoder.

[0048] In some embodiments, the group code one and the group code two further include a layer of the same absolute positioning code three.

[0049] In some embodiments, an incremental signal module is further included, which uses the diffracted light of the grating area for interference measurement to form an incremental signal varying with the displacement in the X direction.

[0050] In some embodiments, the signals sequentially passing through the mask plate and the grating are received by the photoelectric detector, wherein the waveform width of the direction distinguishing positioning code four and the code five signal is 2d, and the direction distinguishing large range interval is 2d.

[0051] In some embodiments, the waveform width of the signal at the absolute positioning code three is 2a, and generally d / a > 30.

[0052] In some embodiments, the grating is a transmissive grating or a reflective grating.

[0053] The application further provides a grating positioning method based on the above-mentioned large range absolute direction distinguishing grating displacement encoder, which includes the following steps:

[0054] S1: coarse positioning, determining the direction required for the current correction according to the signal at the direction distinguishing positioning code, and locking the absolute position in the direction distinguishing large range interval;

[0055] S2: medium positioning, moving in the direction determined by the coarse positioning, finding the absolute mark of the signal at the absolute positioning code, and continuously reducing the interval of the absolute position, and the absolute positioning accuracy can reach the sub-grating period level.

[0056] S3: fine positioning, with the help of sub-raster period level absolute positioning accuracy, matched with the incremental signal, positioned to the specific phase in the period of the incremental signal, the positioning accuracy is nanometer level.

[0057] In some embodiments, in step S1, two encoded signals in the direction discrimination positioning code are used for judgment, and the two encoded signals are PD3 module signal and PD4 module signal respectively.

[0058] In some embodiments, the grating positioning method is not only limited to more layers of positioning code to realize the larger range of direction discrimination function; at the same time, the X and Y axes can be arranged simultaneously on the hybrid grating, that is, the multi-degree-of-freedom measurement function is expanded.

[0059] The specific embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0060] As Figure 1 , the overall optical path structure of the present application is mainly divided into an incremental signal module and an absolute positioning module: in this embodiment, the light beam used is a rectangular light beam 1, and the remaining light beams can also be used as long as they can cover the grating and the mask plate; in this XYZ coordinate system, in the incremental signal module, the light beam directly irradiates the grating area of the hybrid grating 2 (moving), and due to the diffraction phenomenon, +1 order light beam 3 and -1 order light beam 4 are generated, under the action of the right-angle prism 5, finally the light is combined at the BS6 (Beam Splitter, beam splitter), and the PD1 module 7 (Photoelectric Detector, photoelectric detector) is detected to obtain the PD1 module signal. In the absolute positioning module, the light beam is modulated into a corresponding encoded light beam by the mask plate 8 (fixed), and then is blocked by the encoding three 9, the encoding four 10 and the encoding five 11, and the transmitted light beam is detected by the PD2 module 12, the PD3 module 13 and the PD4 module 14 to obtain the corresponding signals.

[0061] As Figure 8 , the incremental signal module uses the diffracted light of the grating for interference measurement, as Figure 2 , an incremental signal varying with X direction displacement is formed, as Figure 4 indicated by the photoelectric detector PD1 module signal, which is a sinusoidal signal. The absolute positioning module is the core content of the present application.

[0062] Here, a and d are both dimensionless values, only representing the proportional size relationship of a and d, and d / a is generally greater than 30.

[0063] As Figure 3 indicated, the encoding three is a normal absolute binary code, and the positioning accuracy is about sub-micron, but the encoding four and the encoding five are both Figure 3The binary code of the wide distance shown is a transparent slit with a width of d, but the distance between code four and code five is different on the hybrid grating and mask, wherein S2=S1+d, wherein d is a required large range interval for direction discrimination, so that when the codes on the mask and the hybrid grating are aligned, as the hybrid grating moves in the positive direction of the absolute coordinate, the signals of Figure 2 .

[0064] As Figure 9 the absolute positioning module, in the actual movement process, since the waveform width 2a of the pulse peak of the photodetector PD2 is about 10-30 microns, it is difficult to quickly find the pulse peak and calibrate the zero position, therefore, the use of code four and code five can realize two symmetrical signals with a waveform width of 2d microns, and the photodetectors PD3 and PD4 will exhibit different light intensity change characteristics at different positions.

[0065] The following will be specifically introduced, in the test, the current time is 0, the time before is negative, and the time in the future is positive.

[0066] As Figure 4 , when the motion starting point is in the negative direction of the photodetector PD3 signal peak zero point and the motion speed is positive, it is known that only the photodetector PD3 has signal change and monotonically increases, and it can be judged that the motion direction should continue to move positively, and the absolute zero position can be found.

[0067] As Figure 5 , when the motion starting point is in the negative direction of the photodetector PD3 signal peak zero point and the motion speed is negative, it is known that only the photodetector PD3 has signal change and monotonically decreases, and it can be judged that the motion direction should be changed to positive motion, and the absolute zero position can be found.

[0068] As Figure 6 , when the motion starting point is in the positive direction of the photodetector PD3 signal peak zero point and the motion speed is positive, it is known that the photodetector PD3 signal monotonically decreases and the photodetector PD4 signal monotonically increases, and it can be judged that the motion direction should be changed to negative movement, and the absolute zero position can be found.

[0069] As Figure 7 , when the motion starting point is in the positive direction of the photodetector PD3 signal peak zero point and the motion speed is negative, the photodetector PD3 signal monotonically increases and the photodetector PD4 signal monotonically decreases, and it can be judged that the motion direction should continue to move negatively, and the absolute zero position can be found

[0070] After the absolute zero position is found, further hybrid positioning is realized through phase matching of the photodetector PD1 signal, and the precision can be improved to the nanometer level.

[0071] Overall, the logic of the present application is:

[0072] First, with the help of the signals of photodetector PD3 and photodetector PD4, the current grating position is roughly positioned, and the direction required for current correction can be determined by combining the two signals. With the help of photodetector PD3 and photodetector PD4, the absolute position is locked in the range of 2d, forming rough positioning.

[0073] After rough positioning, continue to move in the direction and finally find the absolute mark of photodetector PD2. The range of this absolute mark is generally 2a, that is, 10-30 microns, so the absolute positioning interval continues to decrease, and the absolute positioning accuracy with the help of pulse peak value can reach the sub-grating period level, forming medium positioning.

[0074] Finally, with the help of the absolute positioning accuracy of the sub-grating period level, the grating diffraction interference incremental cosine signal of the photodetector PD1 module is matched, and the specific phase in an incremental signal cycle can be positioned. The positioning accuracy of this phase is generally about 4°, so the positioning accuracy can be as high as nanometer level. Thus, fine positioning is formed.

[0075] The current technical solution can avoid the situation that a large distance cannot find the zero position, and can analyze how to move to return to the zero position in a range of at least 300 microns (when d=150 microns) or even larger 2d(n), instead of searching the entire two-dimensional range.

[0076] The innovation points of the present application mainly include the design of hybrid gratings and the distribution scheme encoded thereon:

[0077] 1. The asymmetric position absolute coding design on the double-layer or even n-layer hybrid grating, S2=S1+d, S1>d, S(n+1)=S(n)+d(n), S(n)>d, d(n)>d, n=3,5,7,9…, so that the range of whether to reach the zero position can be observed in a larger range (2d(n)), and even complete absolute positioning measurement can be realized after calibration.

[0078] 2. The rough-fine positioning method makes the difference between the final absolute positioning range and the accuracy reach 10 6 times or more, and the positioning range of up to 2d(n) and the positioning accuracy of nanometer level can be realized at the same time in the present application. Combined with innovation point 1, this multiple can be larger.

[0079] In some embodiments, the transmissive grating in the present application is modified to a reflective grating, such as Figures 10-11For the reflective scheme, the core is still the asymmetric arrangement of absolute coding, and the combination of coarse and fine positioning accuracy at nanometer level. Two-by-two combination can form at least four schemes.

[0080] In some embodiments, if the hybrid grating is combined in X and Y directions, and the corresponding mask is matched, two-dimensional absolute direction measurement in a large range interval can be achieved.

[0081] In some embodiments, the scheme can be combined with a four-dimensional module to form a six-dimensional large-range absolute encoder.

[0082] In some embodiments, the energy signal is calibrated in the full interval. The expansion of the direction interval can make the grating encoder, which can only be made into a quasi-absolute device in a large range, have the potential to be a completely absolute device.

[0083] In some embodiments, as Figure 12 The application also provides a double-layer or even n-layer absolute coding distribution scheme: the asymmetric coding position of the hybrid grating and the mask, S2=S1+d, S1>d, S(n+1)=S(n)+d(n), S(n)>d, d(n)>d, n=3,5,7,9…, 2d(n) is the required large range interval, and the large range interval can be adjusted to be larger.

[0084] The existing absolute coding positioning can only find the absolute position mark during movement to obtain the absolute position, but cannot guide the driving mechanism to find the absolute zero position mark, so although the absolute position can be obtained, it needs to be moved to the zero point to find it. In some cases, it is obviously not feasible to search for absolute marks in all possible positions, and the mechanism needs to be guided to achieve pose correction, and the application can realize direction guidance during movement.

[0085] In the description of the present application, the terms "one embodiment" and "example" and the like mean that the specific features, structures or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms does not necessarily refer to the relative embodiment or example in a suitable manner.

[0086] It must be pointed out that the above description of the embodiments is not used for limitation but only for the purpose of helping to understand the core idea of the present application. Any improvement made by those skilled in the art without departing from the principles of the present application, and the equivalent alternatives of the product, also belong to the protection scope of the claims of the present application.

Claims

1. A large-range absolute direction-distinguishing macro-micro collaborative grating displacement encoder comprising a light source, a photodetector, a grating and a mask, characterized in that, The grating is a hybrid grating, the hybrid grating comprises a grating area and a coding area, a group of codes one is arranged on the coding area, and a group of codes two is arranged on the mask plate; The group of codes one comprises at least two layers, the first layer is a nanoscale positioning code, the second layer and subsequent layers are direction-distinguishing positioning codes, and the direction-distinguishing positioning codes are used for increasing a direction-distinguishing range; the group of codes two comprises codes corresponding to the number of layers of the group of codes one, and also comprises the same nanoscale positioning code arranged on the first layer and the direction-distinguishing positioning codes arranged on the second layer and subsequent layers; the direction-distinguishing positioning code is two codes arranged on the same layer at a specific interval; the specific interval of the highest layer of the direction-distinguishing positioning codes of the group of codes one and the group of codes two is twice the difference value of the specific interval of the encoder in the direction-distinguishing large range interval; The direction-distinguishing positioning code is a transparent slit with a width of d; in the group of codes one and the group of codes two, the two codes included in one layer of the direction-distinguishing positioning code are code three and code four respectively, wherein the nanoscale positioning code corresponds to the spatial position of the code three one by one; in the group of codes one and the group of codes two, the specific intervals between the code three and the code four are a first specific interval and a second specific interval respectively, wherein the first specific interval is the distance between the two codes on the hybrid grating, and the second specific interval is the distance between the two codes on the mask plate, and the relationship between the two is second specific interval = first specific interval + d.

2. The macro-micro cooperative grating displacement encoder of claim 1, wherein, An incremental signal module is further included, the incremental signal module uses the diffracted light of the grating area to perform interference measurement, and forms an incremental signal changing with X direction displacement.

3. The macro-micro cooperative grating displacement encoder of claim 2, wherein, The photoelectric detector receives signals sequentially passing through the mask plate and the hybrid grating, wherein the signal width is 2d, and the direction-distinguishing large range interval is 2d.

4. The macro-micro cooperative grating displacement encoder of claim 3, wherein, The waveform width of the signal at the nanoscale positioning code is 2a, and d / a>30.

5. The macro-micro cooperative grating displacement encoder of claim 2, wherein, The hybrid grating is a transmission grating or a reflection grating.

6. A method of positioning an optical grating, characterized by, Based on the large-range absolute direction-distinguishing macro-micro collaborative grating displacement encoder according to any one of claims 2-5, the following steps are included: S1: coarse positioning, determining the direction required for current correction according to the signal at the direction-distinguishing positioning code, and locking the absolute position in the direction-distinguishing large range interval; S2: medium positioning, moving in the direction determined by the coarse positioning, finding the absolute mark of the signal at the nanoscale positioning code, and continuing to reduce the interval of the absolute position, and the absolute positioning accuracy reaches the sub-grating period level; S3: fine positioning, matching the incremental signal by means of the absolute positioning accuracy of the sub-grating period level, positioning to the specific phase in the period of the incremental signal, and the positioning accuracy is the nanoscale level.

7. The grating positioning method of claim 6, wherein, In step S1, the signals of the two codes in the direction-distinguishing positioning code are used for judgment, and the signals of the two codes are PD3 module signal and PD4 module signal respectively, and the judgment rule is as follows: Taking the current time as 0, the time before is negative, and the time in the future is positive; When the motion starting point is in the negative direction of the PD3 module signal peak zero point, and the motion speed is positive, only the PD3 module has signal change, and monotonically increases, the motion direction is judged to continue positive movement to find the absolute zero position; When the motion starting point is in the negative direction of the PD3 module signal peak zero point, and the motion speed is negative, only the PD3 module has signal change, and monotonically decreases, the motion direction is judged to change to positive movement to find the absolute zero position; When the motion starting point is in the positive direction of the PD3 module signal peak zero point, and the motion speed is positive, the PD3 module signal monotonically decreases, and the PD4 module signal monotonically increases, the motion direction is judged to change to negative movement to find the absolute zero position; When the motion starting point is in the positive direction of the PD3 module signal peak zero point, and the motion speed is negative, the PD3 module signal monotonically increases, and the PD4 module signal monotonically decreases, the motion direction is judged to continue negative movement to find the absolute zero position.

8. The grating positioning method of claim 6, wherein, Its applications include setting more layers of positioning codes to realize larger range of direction discrimination functions; meanwhile, X-axis and Y-axis are simultaneously arranged on the hybrid grating to realize the expansion of multi-freedom measurement functions.

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