Single absolute code track grating displacement measurement system and method based on synthetic pitch

Abstract

The invention relates to the technical field of precise displacement measurement, and particularly provides a single absolute code channel grating displacement measurement system and method based on synthetic pitch, the system comprises a light source, a grating and a reading unit, the grating is provided with an absolute code channel and two increment code channels with different pitches, a reading unit is used for collecting absolute position coding signals on the absolute code channels and collecting phase information of the two incremental code channels. An absolute code channel in the system is used for obtaining displacement with the size of an absolute code channel coding unit as the resolution, then phase information of two incremental code channels is used for subdividing the absolute code channel coding unit in a synthetic pitch where a displacement end point is located, and subdivision displacement with any incremental code channel pitch as the resolution is obtained. According to the invention, interference displacement measurement is realized in an absolute grating measurement system, and the resolution and precision of displacement measurement are greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of precision displacement measurement, and in particular relates to a single absolute code channel grating displacement measurement system and method based on synthetic grating pitch. Background Art

[0002] The grating displacement measurement system uses a grating as a scale and a grating pitch as a measurement reference. Compared with laser measurement technology, grating measurement is less sensitive to environmental changes and has lower requirements for light source frequency stability, thereby effectively reducing costs. The optical path structure is relatively simple, easy to operate, and convenient to miniaturize, which makes up for the shortcomings of laser interferometry measurement and is becoming more and more widely used in the research and application of nanometer-level measurement.

[0003] Grating displacement measurement technology can be divided into incremental measurement and absolute measurement in terms of measurement methods, and it develops from incremental measurement to absolute measurement. Incremental grating displacement measurement technology obtains position information by calculating the number of increments starting from a certain point. Each time the machine is turned on, it is necessary to scan the reference point to correspond each position on the measuring grating to the absolute position; while absolute measurement technology obtains absolute position information by reading the absolute code position code. Each time the machine is turned on, the absolute position with a lower resolution is immediately obtained. Combined with the subdivision of the periodic grating lines of the incremental code, high-resolution absolute position information can be obtained. Therefore, absolute grating measurement technology can greatly improve the processing efficiency of machine tools. And because the position of the moving parts of the machine tool can be determined at any time, the safety of the machine tool during use is also improved. In recent years, especially in countries with a high level of industry, absolute grating measurement technology has been increasingly widely used due to its irreplaceable advantages.

[0004] In terms of measurement principle, grating measurement technology mainly includes moiré fringe method and grating interferometry method, and it develops from moiré fringe method to interferometry measurement using gratings with higher line density. Moiré fringes are fringes formed by the overlap of two gratings, but due to the large grating period, its measurement resolution and accuracy are low. In order to further improve the measurement accuracy, the grating interferometry method has obvious advantages. When the reading head and the measuring grating move relative to each other, the interference fringes generated will change periodically, and the displacement measurement is achieved by measuring the change of the interference fringes. Compared with the moiré fringe technology, this method has a smaller grating period, and the measurement resolution and measurement accuracy are significantly improved. It has become the mainstream technology for incremental grating measurement. Limited by the absolute code size, interferometry technology has not been fully developed in the direction of absolute grating measurement. In particular, domestic manufacturers and scientific research institutions that study absolute grating measurement still use the traditional moiré fringe method, and the measurement resolution and accuracy are generally low, while the interferometry method using gratings with higher line density has not been applied in absolute grating measurement systems.

[0005] In summary, grating measurement technology has developed from incremental measurement to absolute measurement in terms of measurement method, and from moiré fringe method to interferometric measurement using gratings with higher line density in terms of measurement principle, while the research on interferometric measurement method in absolute grating measurement technology has stagnated. In order to achieve higher resolution and accuracy of absolute grating displacement measurement, it is urgent to carry out research on absolute displacement measurement technology based on high line density gratings, analyze the main factors affecting its measurement accuracy and provide methods to improve it. The development of high-precision absolute grating measurement system has important scientific value and research significance. Summary of the invention

[0006] In view of this, the present invention aims to provide a single absolute code channel grating displacement measurement system and method based on synthetic grating pitch, which realizes high-precision absolute displacement measurement by combining absolute coding recognition and grating diffraction interference principle, greatly improves the displacement measurement accuracy, and realizes the application of interference measurement method in absolute grating measurement system.

[0007] To achieve the above object, the technical solution created by the present invention is implemented as follows: The invention provides a single absolute code channel grating displacement measurement system based on synthetic grating pitch, comprising: a light source, a grating and a reading unit; The grating has an absolute code channel and two incremental code channels with different pitches. The composite pitch of the two incremental code channels is: ; in, and Respectively represent the grating pitch of the two incremental code channels, Indicates the synthetic pitch; The synthetic grating pitch is an integer multiple of the absolute code channel encoding unit size; The reading unit includes a first reading head for obtaining absolute code channel readings, as well as a second reading head and a third reading head. The light source is used to provide polarized light incident on the two incremental code channels. The second reading head and the third reading head are used to respectively receive diffracted light from the two incremental code channels, and obtain phase information of the two incremental code channels through interference measurement.

[0008] Preferably, the absolute code channel is composed of an arrangement of light-transmitting coding units and light-impermeable coding units of fixed length.

[0009] Preferably, the first reading head is an image sensor.

[0010] Preferably, the light source is a laser for providing polarized light.

[0011] Preferably, polarized light is used to illuminate the two incremental code tracks, and diffracted light formed after the polarized light illuminates the two incremental code tracks is collected, and the phases of the two incremental code tracks are calculated from the diffracted light.

[0012] Preferably, it also includes a beam splitter and two single grating phase extraction optical paths, the beam splitter splits the polarized light into two beams which enter the two single grating phase extraction optical paths respectively, the two beams of polarized light are irradiated on two incremental code channels respectively, and the two incremental code channels diffract the corresponding polarized light into the second reading head and the third reading head respectively.

[0013] Preferably, it also includes a beam splitter and two single grating phase extraction optical paths. The polarized light enters the first single grating phase extraction optical path, and the polarized light is irradiated on any incremental code channel. The incremental code channel diffracts the polarized light, and the beam splitter divides the diffracted light into two beams. One beam of diffracted light enters the second reading head; the other beam of diffracted light enters the second single grating phase extraction optical path, and the diffracted light is irradiated on the remaining incremental code channel. The incremental code channel diffracts the diffracted light and enters the third reading head.

[0014] Another aspect of the invention provides a method for measuring displacement of a single absolute code track grating based on a synthetic grating pitch, and uses a single absolute code track grating displacement measurement system based on a synthetic grating pitch to perform displacement measurement, including: reading the displacement with the absolute code track encoding unit size as the resolution by a first reading head; The phase information of two incremental code channels is used to subdivide the absolute code channel encoding unit within the synthetic grating where the displacement end point is located, and the subdivided displacement with any incremental code channel grating as the resolution is obtained.

[0015] Preferably, the formula for subdividing the absolute code channel encoding unit within the synthetic grid pitch where the displacement end point is located using the phase information of the two incremental code channels is: ; in, Indicates the subdivision displacement of any incremental code channel pitch as resolution, Indicates the grating pitch of the incremental code channel, that is, or , Indicates the phase information of the incremental code channel, Indicates the distance from the zero point of the synthetic grating to the end point of the displacement within the synthetic grating distance where the displacement end point is located. Number.

[0016] Compared with the prior art, the invention can achieve the following beneficial effects:

[0017] The present invention reasonably selects two incremental code channel pitches, establishes a synthetic pitch through two incremental code channels with different pitches, and the size of the synthetic pitch can reach tens of microns, thereby removing the limitation of the incremental code channel grating period, so that the synthetic pitch can match the coding unit size of the absolute code channel, realizes absolute measurement with the incremental code channel pitch as the resolution at the synthetic pitch, performs coarse positioning of the displacement through the absolute code channel, performs fine positioning through the synthetic pitch and the incremental code channel, subdivides the absolute code channel coding unit where the displacement end point is located, obtains the displacement with the incremental code channel pitch as the resolution, realizes high-precision absolute displacement measurement by combining absolute coding recognition with the grating diffraction interference principle, and solves the contradiction between high-precision measurement and absolute positioning.

[0018] The measurement method proposed in the present invention uses two high-line density incremental code channels and adopts diffraction interference for high-precision measurement. Compared with the low-line density grating used in the traditional Moire fringe method, the resolution and accuracy of the measurement results of the present invention are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings: Figure 1 is a schematic diagram of code track lines on a grating provided in an embodiment of the present invention; Figure 2 is a schematic diagram of matching a synthetic grating pitch and a coding unit according to an embodiment of the present invention; Figure 3 is a schematic diagram of a phase extraction structure of an incremental code channel in a parallel mode provided by an embodiment of the present invention; Figure 4 4 is a schematic diagram of a phase extraction structure of an incremental code channel in a tandem mode provided according to an embodiment of the present invention.

[0020] Reference numerals include: Absolute code channel 1, encoding unit 11, incremental code channel 2, reference code channel 21, auxiliary code channel 22, synthetic grating distance 23; Laser 3, second reading head 4, third reading head 5, beam splitter 6, polarization beam splitter 7, quarter wave plate 8, reflector 9, half wave plate 10. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical scheme and advantages of the invention clearer, the invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the invention and do not constitute a limitation to the invention. Similar components in different embodiments use associated similar component numbers. In the following embodiments, many detailed descriptions are to enable the invention to be better understood. However, those skilled in the art can easily recognize that some of the features can be omitted in different situations, or can be replaced by other components, materials, and methods. In some cases, some operations related to the invention are not shown or described in the specification, in order to avoid the core part of the invention being overwhelmed by too much description, and for those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations according to the description in the specification and the general technical knowledge in the art.

[0022] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other to form various implementation methods. At the same time, the steps or actions in the method description can also be interchanged or adjusted in a manner that is obvious to those skilled in the art. Therefore, the various sequences in the specification and the drawings are only for the purpose of clearly describing a certain embodiment and are not meant to be a necessary sequence, unless otherwise specified that a certain sequence must be followed.

[0023] In the description of the invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the invention, unless otherwise specified, the meaning of "multiple" is two or more.

[0024] In the description of the invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0025] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0026] In one embodiment of the present invention, a single absolute code channel grating displacement measurement system based on synthetic grating pitch is provided, which combines absolute code recognition and grating diffraction interference principle, applies interference measurement in absolute displacement measurement, and realizes high-precision displacement measurement. Specifically, the system structure includes: a light source, a grating and a reading unit, wherein, see Figure 1 The grating includes an absolute code channel 1 and two incremental code channels 2 with different grating pitches, wherein the two incremental code channels 2 are respectively called a reference code channel 21 and an auxiliary code channel 22. The arrangement relationship of the above three code channels on the grating substrate is: the absolute code channel 1, the reference code channel 21 and the auxiliary code channel 22 are etched in sequence from top to bottom.

[0027] The absolute code channel 1 is composed of a fixed length of light-transmitting code and light-opaque code, which correspond to values ​​of 0 and 1 respectively, which can be called binary code. The light-transmitting code and the light-opaque code have the same size, collectively referred to as coding units 11. A fixed number of coding units 11 on the absolute code channel 1 constitute a code representing an absolute position. The arrangement of the code on the absolute code channel 1 is not periodic, and each code corresponds to an absolute position. Therefore, during the displacement measurement process, the position of the displacement end point can be determined based on the reading of the absolute code channel 1. However, the size of the coding unit 11 of the absolute code channel 1 is relatively large, and the absolute code channel 1 can ultimately only determine that the displacement end point is within a coding unit 11, and its specific position within the coding unit 11 cannot be accurately determined, so the displacement resolution obtained by the absolute code channel 1 is the size of the coding unit 11 of the absolute code channel 1.

[0028] The reading unit includes a first reading head for obtaining the reading of the absolute code track 1, a second reading head for obtaining the reading of the reference code track 21, and a third reading head for obtaining the reading of the auxiliary code track 22, wherein the first reading head is used to obtain the reading code of the absolute code track 1, and the first reading head is usually an image sensor, which can collect absolute position information with low resolution. The absolute position information obtained by the first reading head is a coded graphic signal, which needs to be identified by a subsequent signal processing system. After identification and decoding, an absolute position reading with a resolution of the size of the coding unit 11 can be obtained, and then a low-resolution displacement can be obtained to achieve coarse positioning of the absolute measurement system.

[0029] The displacement obtained by the first reading head has a low accuracy. Therefore, the embodiment of the present invention designs a reference code channel 21 and an auxiliary code channel 22 to subdivide the displacement end point encoding unit 11 to obtain a high-resolution displacement. For details, please refer to Figure 2 , both the reference code channel 21 and the auxiliary code channel 22 are grating code channels with high line density, and the grating pitch of both is much smaller than the size of the encoding unit 11. The reference code channel 21 and the auxiliary code channel 22 are prepared by holographic exposure or mechanical streaking technology. The reference code channel 21 and the auxiliary code channel 22 are incremental code channels composed of periodic lines, but the grating periods of the two code channels are different, and both use diffraction interference measurement methods. Specifically, polarized light is provided by a light source, and a two-layer optical structure is designed so that the polarized light is incident on the reference code channel 21 and the auxiliary code channel 22 at a specific incident angle, respectively. The reference code channel 21 and the auxiliary code channel 22 diffract the polarized light into the second reading head 4 and the third reading head 5, respectively, and the phase information is obtained by the diffracted light diffracted back by the reference code channel 21 and the auxiliary code channel 22, so as to realize the interference measurement of the displacement. Among them, an encoder is usually used as a light source.

[0030] In the embodiment of the present invention, the displacement measurement system is further provided with an optical structure for extracting the phase of the reference code channel 21 and the auxiliary code channel 22. Since the phase change of the synthetic grating 23 is the reverse superposition of the phase change of the reference grating 21 and the auxiliary grating 22, it is necessary to obtain and Two types of phase information, among which, represents the phase of the reference code channel 21 obtained by the diffracted light of the reference code channel 21, It represents the phase of the auxiliary code channel 22 obtained by the diffracted light of the auxiliary code channel 22. The optical structure specifically includes a beam splitter 6 and two single grating phase extraction optical paths, and two optical structures for extracting the phase are designed in the embodiment of the present invention.

[0031] As an alternative embodiment, see Figure 3The first structure is a parallel mode design. The polarized light emitted by the laser 3 first enters the beam splitter 6, which is a semi-transparent and semi-reflective mirror. The beam splitter 6 divides the polarized light into two beams and enters two single grating phase extraction optical paths respectively. The propagation process of the two polarized light beams in the two phase extraction optical paths and the structure of the two phase extraction optical paths are basically the same. Only the propagation process of one of the polarized light beams is described as an example: after splitting, the polarized light first enters a polarization beam splitter 7, and the polarized light is transmitted through the polarization beam splitter 7 at an angle of 45°. The polarized light continues to propagate and transmits through a quarter wave plate 8, and then passes through a reflector 9 to make the polarized light irradiate the reference code channel 21 of the grating at a specific angle. The obtained diffraction light passes through a quarter wave plate 8 again. At this time, the polarization state of the diffracted light changes, and the propagation direction of the diffracted light is changed by the reflector 9, so that the diffracted light after the polarization state is changed is transmitted through the polarization beam splitter 7 again at an angle of 135°, and enters the second reading head 4, and the phase information of the reference grating 21 is obtained by the second reading head 4. Similarly, the phase information of the auxiliary grating 22 is obtained through the third reading head 5.

[0032] As an alternative embodiment, see Figure 4 The second structure is a series mode design. The polarized light emitted by the laser 3 first enters the first single grating phase extraction optical path. The polarized light is transmitted through the polarization beam splitter 7 at an angle of 45°. The polarized light continues to propagate and transmits through a quarter wave plate 8. Then, the polarized light is irradiated on the reference code channel 21 of the grating at a specific angle through the reflector 9. The obtained diffraction light passes through a quarter wave plate 8 again. At this time, the polarization state of the diffraction light changes, and the propagation direction of the diffraction light is changed through the reflector 9, so that the diffraction light with the changed polarization state is transmitted through the polarization beam splitter 7 again at an angle of 135° and enters the beam splitter 6. The diffraction light is divided into two beams. Both diffraction lights carry the phase information of the reference grating 21. One of the diffraction lights is emitted into the second reading head 4, and the phase information of the reference grating 21 is obtained through the second reading head 4. Another beam of diffracted light is reflected by the beam splitter 6 and enters the second single grating phase extraction optical path. It first transmits through a half wave plate 10, and the polarization state of the diffracted light changes. It continues to propagate and transmits through the polarization beam splitter 7 at an angle of 45°. The diffracted light continues to propagate and transmits through a quarter wave plate 8. The diffracted light is then irradiated on the auxiliary code channel 22 of the grating at a specific angle through the reflector 9, and is diffracted twice by the auxiliary code channel 22. At this time, the diffracted light obtained is attached with the phase information of the auxiliary code channel 22. The diffracted light continues to propagate through a quarter wave plate 8, and the polarization state of the diffracted light changes. It transmits through the polarization beam splitter 7 again at an angle of 135° and enters the third reading head 5. The phase information of the reference grating 21 and the auxiliary grating 22 is obtained through the third reading head 5, that is, the phase information of the reference grating 21 and the auxiliary grating 22 is directly obtained. .

[0033] According to the grating diffraction characteristics and the grating phase shift theorem, it is necessary to analyze the influence of displacement change on the phase change of the diffracted light of the reference grating 21 and the auxiliary grating 22, and through the combination of different grating pitches of the reference code channel 21 and the auxiliary code channel 22, construct a synthetic pitch 23 absolute displacement measurement model, expand the benchmark of grating measurement, that is, expand the pitch of the incremental code channel 2 to a larger synthetic pitch, so that the synthetic pitch 23 matches the single encoding unit 11 of the absolute code channel 1. That is, through the influence of displacement change on the phase change of the diffracted light of the reference code channel 21 and the auxiliary code channel 22, a virtual synthetic pitch 23 is constructed, and the size of the synthetic pitch 23 corresponds to the size of the encoding unit 11 of the absolute code channel 1, and the size of the synthetic pitch 23 is an integer multiple of the encoding unit 11. The synthetic pitch 23 can be subdivided by the pitch of the reference code channel 21 or the auxiliary code channel 22 to achieve higher resolution displacement measurement. In the embodiment of the present invention, the pitch of the reference code channel 21 is expressed as , the grating pitch of auxiliary code channel 22 is expressed as , set the grating distance of reference code channel 21 Smaller than the grating pitch of auxiliary code channel 22 Therefore, the reference code 21 pitch should be used for subdivision. Subdividing the grid can obtain higher resolution displacement measurement. However, it should be noted that the grid pitch of auxiliary code channel 22 can also be used. Subdivided, in the subsequent description only the grid pitch The following description will be given by taking segmentation as an example.

[0034] It can be understood that the synthetic grating pitch 23 corresponds to one or more encoding units 11. When it is determined through the first reading head that the displacement end point is located in a certain encoding unit 11 on the absolute code channel 1, the synthetic grating pitch 23 corresponding to the encoding unit 11 is found. Since the synthetic grating pitch 23 is constructed based on the reference code channel 21 and the auxiliary code channel 22, the synthetic grating pitch 23 can be subdivided using the grating pitch of the reference code channel 21, which is equivalent to subdividing the encoding unit 11 where the displacement end point is located. The diffraction phase information of the reference code channel 21 obtained by the second reading head 4 can be used to calculate the high-precision position of the displacement end point in the encoding unit 11, and then the subdivided displacement amount with the grating pitch of the reference code channel 21 as the resolution is obtained.

[0035] Based on the above, the construction principle of the synthetic pitch 23 is as follows: See also Figure 2 First, the displacement is expressed as According to the fixed relationship between the displacement and the phase of incremental code channel 2, the displacement It can be expressed as: ; in, Indicates displacement Included in An integer multiple of Included in The number of Indicates displacement Included in An integer multiple of Included in The number of represents the phase of the reference code channel 21 obtained by the diffracted light of the reference code channel 21, represents the phase of the auxiliary code channel 22 obtained by diffracting the light of the auxiliary code channel 22.

[0036] because Therefore, the phase of the reference grating 21 is greater than the phase of the auxiliary grating 22, that is, , then the phase difference between the displacement measurement of the reference code channel 21 and the auxiliary code channel 22 is for: ; in, Indicates a synthetic pitch of 23.

[0037] The synthetic grating pitch 23 can be further expressed as: .

[0038] At this time, a synthetic grating distance 23 is constructed by the reference code track 21 and the auxiliary code track 22 to expand the absolute displacement measurable by the incremental code track 2 , so that the synthetic grating distance 23 is an integer multiple of the encoding unit 11 of the absolute code track 1 .

[0039] At this time, according to the synthetic grid pitch 23, the synthetic grid pitch 23 corresponding to the encoding unit 11 where the displacement end point is located can be obtained. The distance between the zero point of the synthetic grid pitch 23 and the displacement end point includes Number of , and then the subdivision displacement of this coding unit 11 can be obtained as: .

[0040] in, It is the subdivided displacement in the encoding unit 11. The result of the displacement measurement also needs to be added with the rough displacement obtained by measuring the absolute code channel 1, that is, the reading of the first reading head.

[0041] In addition, it should be noted that since errors are inevitable when collecting phase information through the reference code channel 21 and the auxiliary code channel 22, the size of the synthetic grating pitch 23 is limited. Factors causing phase measurement uncertainty include principle errors in the phase measurement method, phase measurement errors introduced by circuit noise due to limited signal-to-noise ratio, cosine errors, and other aspects. For the same phase measurement uncertainty, the larger the synthetic grating pitch 23 used, the greater the displacement measurement uncertainty caused, which brings great limitations to high-precision absolute displacement measurement; in addition, the line and surface errors during grating manufacturing, the errors during optical system adjustment, etc. will all cause errors in phase measurement. Therefore, according to the current interferometric displacement measurement design, when using the synthetic grating pitch 23 to subdivide the measurable absolute displacement, the uncertainty of the rough measurement of the absolute displacement should be less than one-fourth of the reference code channel 21 pitch, that is: ; in, represents the displacement obtained based on the synthetic grating pitch 23, that is, ,in Indicates the phase of the virtual synthesized code channel composed of the synthetic grating pitch 23.

[0042] The calculation formula for the uncertainty in the interferometric displacement measurement process is: ; The uncertainty in the interferometric displacement measurement process can be used to quantitatively analyze the grating manufacturing and measurement system assembly tolerance.

[0043] exist and When determining the specific numerical value, according to the measurement principle and engineering experience, the influence of the principle error, phase measurement error, cosine error, double grating misalignment error, line error of grating production, surface error and other factors on the synthetic grating measurement accuracy is studied, and the corresponding analysis program is written using Matlab and other software to analyze the sensitivity of each error factor, establish an error transfer model, determine the uncertainty synthesis rule, and clarify the boundary conditions of synthetic grating displacement measurement based on the principle that the coarse and fine measurement accuracy is better than one-quarter of the reference grating pitch, and complete the establishment of the synthetic grating absolute displacement measurement model. Specifically, based on the mathematical model of displacement measurement using synthetic grating pitch 23 and the size of the encoding unit 11 of the absolute code channel 1, the grating pitch of the reference grating 21 is selected. d 1 and the grating pitch of the auxiliary grating 22 d 2. Calculate D 12 The uncertainty of absolute displacement measurement is determined by allocating measurement error and adjustment tolerance according to the boundary condition model of synthetic pitch displacement measurement, and iterative optimization is performed. d 1. d 2, until the calculation meets the model requirements d1 and d 2. The above process is used to avoid the influence of measurement uncertainty on displacement measurement. The uncertainty analysis process does not belong to the displacement measurement process, but to the process of designing a displacement measurement system. In addition, when designing the system, it is also necessary to use optical software such as Zemax to carry out the optical design of the measurement structure by ray tracing based on the requirements of the measurement uncertainty of the synthetic grating pitch 23 on the grating posture, analyze the specific tolerances of parameters such as stray light and optical component processing accuracy in the structure, and conduct an integrated analysis of the tolerances of the system's optomechanical structure. Finite element analysis software such as ANSYS is used to analyze the stability and anti-interference ability of the measurement mechanical structure to ensure that the mechanical structure is easy to assemble and has good stability. The specific design processes are all existing design ideas, which are not within the scope of protection of the present invention and will not be elaborated here.

[0044] Based on the above displacement measurement system, a single absolute code channel grating displacement measurement method based on synthetic grating pitch is also proposed. The process of displacement measurement using the above system is as follows: First, the code of the absolute code channel 1 is read by the image sensor, and the displacement with the size of the coding unit 11 as the resolution is obtained by identification and decoding. At the same time, the second reading head 4 and the third reading head 5 respectively collect the phase information of the reference code channel 21 and the auxiliary code channel 22, and according to the subdivision formula , the coding unit 11 of the absolute code channel 1 within the synthetic grid pitch where the displacement end point is located is subdivided using the reference code channel 21, and the subdivided displacement amount obtained is: ; Combined with the coarse displacement obtained by measuring the absolute code channel 1, a high-precision displacement can be obtained, realizing the application of the interferometry method in the absolute grating measurement system.

[0045] In short, the above description is only a preferred embodiment of this specification and is not intended to limit the protection scope of this specification. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this specification shall be included in the protection scope of this specification.

[0046] The systems, devices, modules or units described in one or more of the above embodiments may be implemented by a computer chip or entity, or by a product having a certain function. A typical implementation device is a computer. Specifically, the computer may be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.

[0047] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0048] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0049] The above is a description of a specific embodiment of the specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in an order different from that in the embodiments and still achieve the desired results. In addition, the processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

Claims

1. A single absolute code channel grating displacement measurement system based on synthetic grating pitch, characterized in that: include: Light source, grating and reading unit; The grating is provided with an absolute code track and two incremental code tracks with different grating pitches; the composite grating pitch of the two incremental code tracks is: ； in, and Respectively represent the grating pitch of the two incremental code channels, Indicates the composite pitch; The synthetic grating pitch is an integer multiple of the absolute code channel encoding unit size; The reading unit includes a first reading head for obtaining the absolute code channel reading, as well as a second reading head and a third reading head. The light source is used to provide polarized light to be incident on the two incremental code channels. The second reading head and the third reading head are used to respectively receive the diffracted light of the two incremental code channels, and obtain the phase information of the two incremental code channels through interference measurement.

2. The single-channel absolute grating displacement measurement system based on synthetic grating pitch according to claim 1, characterized in that: The absolute code channel is composed of an arrangement of light-transmitting coding units and light-impermeable coding units of fixed length.

3. The single-channel absolute grating displacement measurement system based on synthetic grating pitch according to claim 2, characterized in that: The first reading head is an image sensor.

4. The single-channel absolute grating displacement measurement system based on synthetic grating pitch according to claim 1, characterized in that: The light source is a laser, which is used to provide polarized light.

5. The single-channel absolute grating displacement measurement system based on synthetic grating pitch according to claim 4, characterized in that: Polarized light is used to illuminate the two incremental code channels, and diffracted light formed after the polarized light illuminates the two incremental code channels is collected, and the phases of the two incremental code channels are calculated from the diffracted light.

6. The single-track absolute grating displacement measurement system based on synthetic grating pitch according to claim 5, characterized in that: It also includes a beam splitter and two single grating phase extraction optical paths. The beam splitter splits the polarized light into two beams which enter the two single grating phase extraction optical paths respectively. The two beams of polarized light are irradiated on two incremental code channels respectively. The two incremental code channels diffract the corresponding polarized light into the second reading head and the third reading head respectively.

7. The single-channel absolute grating displacement measurement system based on synthetic grating pitch according to claim 5, characterized in that: It also includes a beam splitter and two single grating phase extraction optical paths. Polarized light enters the first single grating phase extraction optical path and is irradiated on any incremental code channel. The incremental code channel diffracts the polarized light. The beam splitter divides the diffracted light into two beams. One beam of diffracted light enters the second reading head. The other beam of diffracted light enters the second single grating phase extraction optical path. The diffracted light is irradiated on the remaining incremental code channel. The incremental code channel diffracts the diffracted light and enters the third reading head.

8. A single absolute code channel grating displacement measurement method based on synthetic grating pitch, characterized in that: The method of performing displacement measurement using the single absolute code channel grating displacement measurement system based on synthetic grating pitch as claimed in any one of claims 1 to 7 comprises: Reading the displacement with the absolute code channel encoding unit size as the resolution by the first reading head; The absolute code channel encoding unit within the synthetic grating where the displacement end point is located is subdivided by using the phase information of the two incremental code channels to obtain the subdivided displacement amount with any incremental code channel grating as the resolution.

9. The single-channel absolute grating displacement measurement method based on synthetic grating pitch according to claim 8, characterized in that: The formula for subdividing the absolute code channel encoding unit within the synthetic grid pitch where the displacement end point is located using the phase information of the two incremental code channels is: ； in, Indicates the subdivision displacement of any incremental code channel pitch as resolution, Indicates the grating pitch of the incremental code channel, that is, or , Indicates the phase information of the incremental code channel, Indicates the distance from the zero point of the synthetic grating to the end point of the displacement within the synthetic grating distance where the displacement end point is located. Number.

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