An absolute six-degree-of-freedom pose sensor

Abstract

An absolute six-degree-of-freedom (DOF) pose sensor is disclosed. In this sensor, a parallel light incident module transmits a first beam of light through a first beam splitter to illuminate a one-dimensional grating, generating three diffracted beams of different orders. These diffracted beams then pass through the first beam splitter and illuminate a four-degree-of-freedom (DOF) detection module, thus obtaining the four-DOF absolute pose change of the detected target. A second beam of parallel light, split by the first beam splitter, enters a second beam splitter and is further split into two beams. One beam is reflected by two inclined surfaces of a Y-direction corner cube prism and is then detected by a Y-direction detector to measure the target's translation in the Y direction. The other beam enters a third beam splitter and is split into two beams. One beam is reflected by two inclined surfaces of an X-direction corner cube prism and is then detected by an X-direction detector to measure the target's translation in the X direction. This invention enables absolute six-degree-of-freedom pose detection. The optical path structure and backend algorithm are simple and compact, facilitating miniaturization and industrialization.

Description

Technical Field

[0001] This invention relates to pose measurement technology, and in particular to an absolute six-degree-of-freedom pose sensor. Background Technology

[0002] Scientific telescopes are one of the most important means for humankind to explore the universe. Regardless of the type of telescope, such as radio telescopes or optical telescopes, one of their main performance parameters is resolution, which is related to its aperture size. However, it is difficult to manufacture a single large-aperture telescope mirror. Currently, the main method used is to assemble sub-mirrors to create a large-aperture parabolic mirror. Therefore, its observation performance is limited by the assembly accuracy of its sub-mirrors. Furthermore, due to environmental factors such as gravity loads, temperature changes, and humidity variations, the relative poses of the assembled sub-mirrors will undergo slight changes, which will directly lead to significant surface shape errors in the primary mirror. Current pose measurement methods have high requirements for environmental stability, and surface shape errors still appear after long-term use and correction. Therefore, there is an urgent need for a more stable and higher-precision device capable of absolute pose measurement.

[0003] As telescopes are used, the accumulation of errors will lead to a significant decline in their observational performance. For example, the South African Large Telescope experienced a decline in observational performance due to humidity, while the Hobbies-Eberle Telescope suffered from performance degradation due to temperature effects. The soon-to-be-completed Large Magellanic Telescope also places great emphasis on sub-mirror attitude measurement. The 30m aperture telescope, a collaborative research project involving China and multiple countries, will have its primary mirror composed of 492 hexagonal sub-mirrors. Upon completion in 2027, it is expected to become the world's first extremely large telescope. Therefore, the need for sub-mirror spatial attitude detection is extremely urgent. Not only is absolute attitude detection required during installation, but it is also necessary to measure and provide feedback during subsequent use to adjust the sub-mirror's attitude and actively control it to ensure the primary mirror's surface shape meets requirements. How to perform high-precision measurement of sub-mirror attitude, providing a basis for adjusting sub-mirror confocality and phase co-occurrence, is a core technology in the research of large-aperture optical systems used for astronomical observation.

[0004] There are two main types of pose measurement: electromagnetic displacement measurement and optical displacement measurement. Among the electromagnetic measurement methods, capacitive sensors can achieve nanometer-level accuracy, and multi-degree-of-freedom measurement systems composed of multiple capacitive sensors are currently used for real-time detection of the pose of sub-mirrors in the Keck and Canary Islands large telescopes. They have high accuracy and stability. However, measurement systems composed of capacitive sensors are not only complex but also highly sensitive to temperature and humidity, affecting measurement accuracy.

[0005] Other optical measurement schemes for achieving absolute six-degree-of-freedom measurements are structurally complex. For example, they may use optical frequency combs, laser interferometers, or grating interferometers. These typically employ low-degree-of-freedom combinations to create data redundancy, thus achieving measurements from multiple degrees of freedom to the highest six degrees of freedom. However, these methods are prone to Abbe errors, resulting in complex and large systems that are difficult to debug and require a high level of prior knowledge, hindering on-site debugging and widespread adoption by workers. Furthermore, the cost and complexity of the backend algorithms and signal processing units are also high.

[0006] It should be noted that the information disclosed in the background section above is only for understanding the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0007] The main objective of this invention is to overcome the shortcomings of the aforementioned background technology and provide an absolute six-degree-of-freedom pose sensor.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] An absolute six-degree-of-freedom pose sensor includes a parallel light incident module, first to third beam-splitting prisms, a one-dimensional grating, a four-degree-of-freedom detection module, a Y-direction corner bevel prism, a Y-direction detector, an X-direction corner bevel prism, and an X-direction detector. The first beam of light from the parallel light incident module, passing through the first beam-splitting prism, illuminates the one-dimensional grating, generating three diffracted beams of different orders. These beams then pass through the first beam-splitting prism and illuminate the four-degree-of-freedom detection module, resulting in the four-degree-of-freedom absolute pose change of the detected target: translation in the Z-direction and rotation around the X-axis by an angle θ. x θ, the angle of rotation around the Y-axis y θ, the angle of rotation around the Z-axis z The parallel light, after being split into two beams by the second beam from the first beam splitter, enters the second beam splitter and is then split into two beams. One beam is reflected by the two inclined surfaces of the Y-direction corner cube prism and is detected by the Y-direction detector to measure the translation of the target in the Y-direction. The other beam enters the third beam splitter and is then split into two beams. One beam is reflected by the two inclined surfaces of the X-direction corner cube prism and is detected by the X-direction detector to measure the translation of the target in the X-direction.

[0010] Furthermore:

[0011] The three diffracted beams of different orders are 0th order, +1st order, and -1st order diffracted beams.

[0012] The four-degree-of-freedom detection module includes three sets of position detectors (PSDs), three sets of four-quadrant photodetectors (QPDs), or three sets of charge-coupled device detectors (CCDs).

[0013] The parallel light incident module includes a laser and a collimating lens group, wherein the laser light generated by the laser passes through the collimating lens group to form the parallel light.

[0014] The side of the Y-direction angle cone prism containing the triangular portion is perpendicular to the YOZ plane, and the side of the X-direction angle cone prism containing the triangular portion is perpendicular to the XOZ plane.

[0015] A focusing lens or beam expander with a corresponding focal length is provided in front of one or more of the four-degree-of-freedom detection module, the Y-direction detector, and the X-direction detector.

[0016] The position x of the light spot on each group of detectors in the four-degree-of-freedom detection module A y A x B y B x C y C It can be obtained by reading from the back-end circuit or by calculating from the back-end photocurrent information:

[0017]

[0018]

[0019] Where k1 and k2 are proportionality coefficients, and α = A, B, C;

[0020] The three diffraction spots of the grating are located at (x1, y1), (x0, y0), and (x0, y0) respectively on the three sets of detectors. -1 ,y -1 );

[0021] When one degree of freedom changes, the absolute pose of the grating is calculated as follows:

[0022] z = Δx A ·k z

[0023]

[0024]

[0025]

[0026] k in the formula z k θx k θy and k θz All are measured parameters, where f is the focal length of the convex lens of each group of detectors, and L is the equivalent distance between each group of detectors.

[0027] When all four degrees of freedom change simultaneously, the result of the grating absolute pose calculation is:

[0028]

[0029]

[0030]

[0031]

[0032] k in the formula θxz1 and k θxz-1 During the motion θ x The asymmetric influence coefficient, k, on the y-direction position of the +1 and -1 order light spots θydz1 and k θydz-1 During the motion θ y Asymmetric influence coefficients on the x-direction position of +1 and -1 order light spots.

[0033] A computer-readable storage medium storing a computer program, which, when executed by a processor, performs calculations of the position of the light spot on the detector of the absolute six-degree-of-freedom pose sensor and solves the absolute pose of the grating.

[0034] An absolute six-degree-of-freedom pose measurement device includes an absolute six-degree-of-freedom pose sensor, a processor, and a computer-readable storage medium. When the computer program stored in the computer-readable storage medium is executed by the processor, it calculates the position of the light spot on the detector of the absolute six-degree-of-freedom pose sensor and solves the absolute pose of the grating.

[0035] The present invention has the following beneficial effects:

[0036] This invention designs an absolute six-degree-of-freedom (DOF) pose sensor based on spot position monitoring. It utilizes a combination of a cornerstone prism and a diffraction grating to form a six-DOF pose measurement scheme. The grating enables four-DOF absolute pose monitoring, while the cornerstone prism facilitates absolute pose monitoring in the X and Y directions. The addition of the cornerstone prism simplifies the diffraction interference optical path, transforming it into simple spot position monitoring, reducing error sources, and allowing direct reading of X / Y displacement. Its structure is simple and compact, and its principle is straightforward, facilitating faster deployment and application. The absolute measurement optical path design of this invention's six-DOF pose sensor is robust to environmental conditions, enabling accurate and reliable pose monitoring of sub-mirrors in a synthetic aperture optical system.

[0037] This invention is simpler than existing six-degree-of-freedom electrical and optical measurement schemes. By measuring the position of the light spot, it can be converted into a six-degree-of-freedom absolute pose measurement, without the need for complex back-end processing circuits and signal processing algorithms. It is a simpler and more practical pose monitoring scheme. Due to the simple optical path structure and back-end algorithm of this invention, the structure is compact, which is conducive to miniaturization and industrialization. Attached Figure Description

[0038] Figure 1 This is a top view of an absolute six-degree-of-freedom pose sensor according to an embodiment of the present invention.

[0039] Figure 2 This is a three-dimensional schematic diagram of an absolute six-degree-of-freedom pose sensor according to an embodiment of the present invention.

[0040] Figure 3 This is a schematic diagram of a four-degree-of-freedom detection module according to an embodiment of the present invention.

[0041] Figure 4 This is a diagram showing the correspondence between the position and pose of the light spot in a four-degree-of-freedom detection module according to an embodiment of the present invention.

[0042] Figure 5 This is a three-dimensional schematic diagram of a cornerstone prism according to an embodiment of the present invention.

[0043] Figure 6 This is a top view of an absolute six-degree-of-freedom pose sensor according to another embodiment of the present invention.

[0044] Figure 7 This is a three-dimensional schematic diagram of an absolute six-degree-of-freedom pose sensor according to another embodiment of the present invention. Detailed Implementation

[0045] The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of the present invention.

[0046] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component. Furthermore, a connection can be used for fixing, coupling, or communication.

[0047] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0048] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of the present invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0049] See Figures 1 to 7 This invention provides an absolute six-degree-of-freedom pose sensor, comprising a parallel light incident module, first to third beam splitters BS1-BS3, a one-dimensional grating 3, a four-degree-of-freedom detection module, a Y-direction corner bevel prism 7, a Y-direction detector 5, an X-direction corner bevel prism 8, and an X-direction detector 6. The first beam of light passing through the first beam splitter BS1 in the parallel light incident module illuminates the one-dimensional grating 3, generating three diffracted beams of different orders. These beams then pass through the first beam splitter BS1 and illuminate the four-degree-of-freedom detection module, obtaining the four-degree-of-freedom absolute pose change of the detected target, namely, translation in the Z-direction and rotation around the X-axis by an angle θ. x θ, the angle of rotation around the Y-axis y θ, the angle of rotation around the Z-axis z The change, abbreviated as θ x θ y θ z Attitude change; the parallel light, after being split into two beams by the second beam from the first beam splitter BS1, enters the second beam splitter BS2 and is then split into two beams. One beam is reflected sequentially by the two inclined surfaces of the Y-direction corner cube prism 7 and is detected by the Y-direction detector 5 to measure the translation of the target in the Y direction. The other beam enters the third beam splitter BS3 and is split into two beams. One beam is reflected sequentially by the two inclined surfaces of the X-direction corner cube prism 8 and is detected by the X-direction detector 6 to measure the translation of the target in the X direction. This embodiment of the invention utilizes a combination of corner cube prisms and diffraction gratings to form a six-degree-of-freedom pose measurement scheme. Four-degree-of-freedom pose discrimination is performed using the positions of the three beam spots of the diffraction grating, and absolute X / Y axis positioning is achieved using the single-axis sensitive element of the corner cube prism.

[0050] In one embodiment, the aforementioned absolute six-degree-of-freedom pose sensor may include a base 9 on which the components are mounted.

[0051] In a preferred embodiment, the three diffracted beams of different orders are 0th order, +1st order, and -1st order diffracted beams.

[0052] In different embodiments, the four-degree-of-freedom detection module may include three sets of position detectors (PSDs), three sets of four-quadrant photodetectors (QPDs), or three sets of charge-coupled device detectors (CCDs).

[0053] See Figure 1 In a preferred embodiment, the parallel light incident module includes a laser LD and a collimating lens group, wherein the laser light generated by the laser LD passes through the collimating lens group to form the parallel light.

[0054] See Figure 1 and Figure 2 In a preferred embodiment, the side of the Y-direction angle cone prism 7 containing the triangular portion is perpendicular to the YOZ plane, and the side of the X-direction angle cone prism 8 containing the triangular portion is perpendicular to the XOZ plane.

[0055] See Figure 1 and Figure 2 In a preferred embodiment, a focusing lens or beam expander (2, 4) with a corresponding focal length is disposed in front of one or more of the four-degree-of-freedom detection module, the Y-direction detector 5, and the X-direction detector 6. See also Figure 6 and Figure 7 In other embodiments, focusing lenses and beam expanders may not be provided in front of each detector.

[0056] The following further describes specific embodiments of the present invention and their working principles.

[0057] The planar and 3D diagrams of the absolute six-degree-of-freedom grating encoder based on spot position detection are shown below. Figure 1 and 2 As shown, the principle is mainly as follows: The LD emits a laser beam, which enters the BS1 parallel to the collimating lens group. After illuminating the one-dimensional grating, diffraction occurs. The three diffracted beams (0th order, +1st order, and -1st order) are refracted by the BS1 and then illuminate the four-degree-of-freedom detection module. The four-degree-of-freedom detection module consists of three sets of position detectors (PSDs) or three sets of four-quadrant photodetectors (QPDs), which are collectively referred to here as the spot position monitoring module. Figure 3 As shown. The detectors in the X and Y directions are also composed of spot position monitoring modules. The four degrees of freedom poses of the grating correspond one-to-one, and their rules are as follows: Figure 4As shown, the four-degree-of-freedom absolute pose of the detected target can be obtained by decoupling the beam pose. Simultaneously, the second beam formed by the beam splitting at BS1 enters BS2, and after refraction, one beam enters the Y-direction corner cube prism. The three-dimensional diagram of the corner cube prism is shown below. Figure 5 As shown. A corner cube prism is sensitive to translation in one of the X or Y directions of parallel light, but insensitive to the other direction. Therefore, the corner cube prism probing the Y-direction light path is modified as follows... Figure 2 The setup shown allows for the detection of displacement in the Y direction without being affected by other directions. Similarly, the beam split by BS2, after entering BS3, can also detect displacement in the X direction without being affected by other directions. Thus, the absolute pose of all six degrees of freedom can be obtained.

[0058] In the QPD scheme, a focusing lens or beam expander with the corresponding focal length can be added in front of the detector. The focusing lens will reduce the light spot, thereby improving the measurement resolution and accuracy; the beam expander can increase the light spot, sacrificing some measurement accuracy to increase the measurement range.

[0059] The QPD (Quadrant-Based Photodetector) primarily calculates the absolute position of the light spot on the QPD by utilizing the different light intensity distributions in the four quadrants. The method is as follows:

[0060] The specific location of the light spot x A y A x B y B x C y C It is calculated based on the back-end photocurrent information, and the specific calculation formula can be expressed as follows:

[0061]

[0062]

[0063] Where k1 and k2 are proportionality coefficients, and α = A, B, C.

[0064] PSD and CCD can directly read the corresponding position information from the back-end circuitry, but their accuracy is generally low.

[0065] In different embodiments, position monitoring is performed using QPD / PSD / CCD or other photodetectors, requiring only the type of photodetector to be changed.

[0066] The measurement range, resolution, and accuracy can be adjusted by removing the focus or beam expander from the optical path.

[0067] Two-degree-of-freedom measurement principle

[0068] The measurement principles for X and Y are the same. When parallel light shines on one inclined plane of a cornerstone prism, it is reflected to another inclined plane, thus reflecting back to the original light path and leaving a spot position on the detector module, which is used as the zero position. When the cornerstone prism is displaced along the X or Y direction, the position where the beam contacts the inclined plane also changes. Therefore, the position of the spot reflected back to the detector module will also change along this direction, thereby obtaining the absolute change in pose.

[0069] Four-DOF absolute pose measurement principle

[0070] The diffracted light generated by the measurement grating is reflected back to BS1 and then illuminates the four-degree-of-freedom probe module, where QPD is used as the unit probe module.

[0071] QPD: The absolute position of the light spot on the QPD is mainly calculated by utilizing the different light intensity distributions in the four quadrants. The method is as follows:

[0072] As mentioned earlier, the specific location of the light spot x A y A x B y B x C y C It is calculated based on the back-end photocurrent information, and the specific calculation formula can be expressed as follows:

[0073]

[0074]

[0075] Where k1 and k2 are proportionality coefficients, and α = A, B, C.

[0076] PSD and CCD can directly read the corresponding position information from the back-end circuitry, but their accuracy is generally low.

[0077] First, the coordinates of the light spot positions are transformed into origin coordinates. That is, before measurement, the coordinate system is artificially defined, ensuring all diffracted beams are located at the predetermined origin. Assume a laser beam illuminates a grating, and the positions of the three diffracted light spots on the grating within the three four-quadrant detectors are (x1, y1), (x0, y0), (x...). -1 ,y -1 According to the geometric movement law, the final absolute pose calculation result of the grating is:

[0078]

[0079] k in the formula z k θx k θy and k θzAll of these are experimentally determined parameters, where f is the focal length of the convex lens of the photodetector, and L is the equivalent distance between photodetectors A and B (or C and B).

[0080] The above are the pose results when only one degree of freedom changes. The following analyzes the solution method when all four degrees of freedom change simultaneously. Assume that the positions of the three diffraction spots in the three four-quadrant photodetectors QPDA / B / C are (x1, y1) and (x0, y0), respectively. -1 ,y -1 Since the position of the zeroth-order ray has changed, and the position change of the zeroth-order ray is only related to θ. x θ y Since they are related, their values ​​can be directly derived.

[0081]

[0082] k in the formula θxz1 and k θxz-1 During the motion θ x The asymmetric influence coefficient, k, on the y-direction position of the +1 and -1 order light spots θydz1 and k θydz-1 During the motion θ y Asymmetric influence coefficients on the x-direction position of +1 and -1 order light spots.

[0083] At this moment, the positions of the light spots on the four-quadrant photodetector QPDA and four-quadrant photodetector QPDC are at θ. x θ y The attitude change also causes variations, which can be calculated using the asymmetric influence factor and then excluded. Within a small measurement range, θ... z Attitude changes only alter the y-direction spot positions of QPDA and QPDB, while z-direction attitude changes only alter the X-direction spot positions of QPDA and QPDB. Furthermore, utilizing ±1-order optical differential methods can reduce coupling errors between different degrees of freedom to some extent. Therefore, the conclusion is as follows:

[0084]

[0085] In the theoretical process, a zero-order diffraction beam and a set of ±1-order diffraction beams are all that is needed to complete the measurement.

[0086] The embodiments of the present invention can realize absolute pose measurement of all six degrees of freedom, and the measurement resolution / accuracy and measurement range of the six degrees of freedom can be adjusted.

[0087] Compared with the prior art, the advantages of the present invention are:

[0088] Existing products and methods achieve absolute six-degree-of-freedom (6DOF) measurement results by assembling single- or two-DOF sensors to create measurement redundancy, which is prone to Abbe error. Alternatively, they transform the measurement into a diffraction interference phenomenon through complex optical path structures, which, while offering higher accuracy, requires high installation precision. The entire system is complex and large, making debugging difficult. The cost and complexity of the backend algorithms and signal processing units are also high.

[0089] This invention proposes an absolute six-degree-of-freedom (DOF) pose sensor based on spot position monitoring. It utilizes a combination of a cornerstone prism and a diffraction grating to form a six-DOF pose measurement scheme. The grating enables four-DOF absolute pose monitoring, while the cornerstone prism facilitates absolute pose monitoring in the X and Y directions. The addition of the cornerstone prism simplifies the diffraction interference optical path, transforming it into a simple spot position monitoring system, reducing error sources, and allowing direct reading of X / Y displacement. Its structure is simple and compact, and its principle is straightforward, facilitating faster deployment and application. The absolute measurement optical path design of this invention's six-DOF pose sensor is robust to environmental conditions, enabling accurate and reliable pose monitoring of sub-mirrors in a synthetic aperture optical system.

[0090] This invention is simpler than existing six-degree-of-freedom electrical and optical measurement schemes. By measuring the position of the light spot, it can be converted into a six-degree-of-freedom absolute pose measurement, without the need for complex back-end processing circuits and signal processing algorithms. It is a simpler and more practical pose monitoring scheme. Due to the simple optical path structure and back-end algorithm of this invention, the structure is compact, which is conducive to miniaturization and industrialization.

[0091] This invention has promising applications in precision machine tool processing, sub-mirror assembly of synthetic aperture optical systems, and even in monitoring the deformation of certain key structures during fault diagnosis.

[0092] The background section of this invention may include background information about the problems or environment in which the invention is being developed, and is not necessarily a description of prior art. Therefore, the content included in the background section does not constitute an admission of prior art by the applicant.

[0093] The above description provides a further detailed explanation of the present invention in conjunction with specific / preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the concept of the present invention, and all such substitutions or modifications should be considered within the scope of protection of the present invention. In the description of this specification, the reference to terms such as "an embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples," etc., indicates that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. An absolute six-degree-of-freedom pose sensor, characterized in that, The diffraction interference optical path is simplified to a simple spot position monitoring. A six-degree-of-freedom pose measurement scheme is formed by combining a cornerstone prism and a diffraction grating. This scheme includes a parallel light incident module, first to third beam splitters, a one-dimensional grating, a four-degree-of-freedom detection module, a Y-direction cornerstone prism, a Y-direction detector, an X-direction cornerstone prism, and an X-direction detector. The first beam of light from the parallel light incident module, passing through the first beam splitter, illuminates the one-dimensional grating, generating three diffracted beams of different orders. These beams then pass through the first beam splitter and illuminate the four-degree-of-freedom detection module, respectively, to obtain the four-degree-of-freedom absolute pose change of the detected target, namely, the translation in the Z-direction and the angle of rotation around the X-axis. Angle of rotation around the Y-axis Angle of rotation around the Z-axis The parallel light, after being split into two beams by the second beam from the first beam splitter, enters the second beam splitter and is then split into two beams. One beam is reflected by the two inclined surfaces of the Y-direction corner cube prism and is detected by the Y-direction detector to measure the translation of the target in the Y-direction. The other beam enters the third beam splitter and is then split into two beams. One beam is reflected by the two inclined surfaces of the X-direction corner cube prism and is detected by the X-direction detector to measure the translation of the target in the X-direction. The position of the light spot on each group of detectors in the four-degree-of-freedom detection module x A , y A , x B , y B , x C , y C It can be obtained by reading from the back-end circuit or by calculating from the back-end photocurrent information: in k 1 and k 2 is the proportionality coefficient. α = A, B, C; The positions of the three diffraction spots of the grating on the three groups of detectors are (x1, y1), (x0, y0), and (x -1 ,y -1 ) respectively. When one degree of freedom changes, the absolute pose of the grating is calculated as follows: In the formula k z , k θx , k θy and k θz All are measured parameters. f The focal length of the convex lens for each group of detectors. L It is the equivalent distance between each group of detectors; When all four degrees of freedom change simultaneously, the result of the grating absolute pose calculation is: In the formula k θxz1 and k θxz-1 During exercise θ x The asymmetric influence coefficients on the y-direction positions of the +1 and -1 order light spots. k θydz1 and k θydz-1 During exercise θ y Asymmetric influence coefficients on the x-direction position of +1 and -1 order light spots.

2. The absolute six-degree-of-freedom pose sensor as described in claim 1, characterized in that, The three diffracted beams of different orders are 0th order, +1st order, and -1st order diffracted beams.

3. The absolute six-degree-of-freedom pose sensor as described in claim 1 or 2, characterized in that, The four-degree-of-freedom detection module includes three sets of position detectors (PSDs), three sets of four-quadrant photodetectors (QPDs), or three sets of charge-coupled device detectors (CCDs).

4. The absolute six-degree-of-freedom pose sensor as described in any one of claims 1 to 2, characterized in that, The parallel light incident module includes a laser and a collimating lens group, wherein the laser light generated by the laser passes through the collimating lens group to form the parallel light.

5. The absolute six-degree-of-freedom pose sensor as described in any one of claims 1 to 2, characterized in that, The side of the Y-direction angle cone prism containing the triangular portion is perpendicular to the YOZ plane, and the side of the X-direction angle cone prism containing the triangular portion is perpendicular to the XOZ plane.

6. The absolute six-degree-of-freedom pose sensor as described in any one of claims 1 to 2, characterized in that, A focusing lens or beam expander with a corresponding focal length is provided in front of one or more of the four-degree-of-freedom detection module, the Y-direction detector, and the X-direction detector.

7. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it calculates the position of the light spot on the detector of the absolute six-degree-of-freedom pose sensor as described in claim 1 and solves the absolute pose of the grating.

8. An absolute six-degree-of-freedom pose measurement device, characterized in that, The system includes an absolute six-degree-of-freedom pose sensor as described in any one of claims 1 to 6, a processor, and a computer-readable storage medium as described in claim 7, wherein the computer program stored in the computer-readable storage medium, when executed by the processor, performs calculations of the spot position on the detector of the absolute six-degree-of-freedom pose sensor and solves the absolute pose of the grating.

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