Laser Six-Degree-of-Freedom Geometric Error Measurement System and Method

Abstract

This invention provides a laser six-degree-of-freedom geometric error measurement system and method, belonging to the field of optical precision measurement technology. The system includes a beam splitter unit, a target mirror unit, and a measurement unit. Utilizing the beam splitter of the beam splitter unit, the second polarizing beam splitter of the target mirror unit, and the sixth and seventh photodetectors of the measurement unit, a single beam can be separated from the split beam L12 and directed as an independent path to the target mirror unit. The second polarizing beam splitter acts as a sensitive element for the roll angle. When the entire target mirror unit experiences a roll angle, the second polarizing beam splitter rotates accordingly, changing the polarization state of the passing split beam. This causes a change in the light intensity on the sixth and seventh photodetectors. The roll angle is directly calculated through this change in light intensity, reducing the influence of polarization-sensitive roll angle measurements and effectively solving the problem of inaccurate roll angle measurement in existing six-degree-of-freedom error measurement technologies.

Description

Technical Field

[0001] This invention relates to the field of optical precision measurement technology, and more specifically, to a laser six-degree-of-freedom geometric error measurement system and method. Background Technology

[0002] Linear motion guides (referred to as linear axes) and rotary axes both have six degrees of freedom geometric motion errors during movement. Three-axis CNC machine tools / coordinate measuring machines have 21 geometric errors that need to be measured, and five-axis CNC machine tools have 42 errors that need to be measured. Therefore, how to quickly measure the errors of CNC machine tools is a common problem that urgently needs to be solved. At the same time, measuring the six degrees of freedom errors of linear motion guides or rotary axes is an inevitable choice.

[0003] Among these, roll angle measurement is currently the most difficult quantity to measure in the six-degree-of-freedom error measurement of a linear axis, and it is also a parameter that is difficult to integrate with the other five degrees-of-freedom errors. Our previous patent CN114046732A provides a method and system for simultaneously measuring multi-degree-of-freedom geometric errors using lasers. It includes a measurement unit and a target mirror unit. The measurement unit includes a laser emission module, a polarizing beam splitter, a fixed reflector, first and second λ / 4 waveplates, a first polarizer, a first photodetector, an interferometric length measurement module, and a two-dimensional angle measurement module. The target mirror unit includes a beam splitter and a reflector. The laser emission module generates the emitted light L1. The polarizing beam splitter is used for ① beam splitting, ② beam combining, and ③ beam separation. The fixed reflector back-reflects the reference light L12, which propagates only within the measurement unit, so that the reference light L12 returns to the polarizing beam splitter. The system provided by this patent can achieve: simultaneous and rapid measurement of the five / six degrees-of-freedom geometric errors of a spatial object moving linearly along a linear axis; and long-term monitoring of the relative changes in the five / six degrees-of-freedom position and attitude of two objects in space.

[0004] However, when measuring the roll angle, the third λ / 4 waveplate 13 of the sensitive element returns to the first photodetector of the measurement unit. Fifth photodetector The roll angle is calculated from the changes in light intensity of both beams. The measurement accuracy is affected by the following factors: ① In addition to the polarization rotation of the polarization-sensitive device λ / 4 waveplate 13 being directly related to the measured roll angle, the polarization splitting defect of the polarizing beam splitter 2 prevents the complete separation of S-beams and P-beams. The polarization characteristics of the reflected light from the cornerstone prism 11 are related to the position and direction of the incident light. The polarization characteristics of both the λ / 4 waveplate 5 and the polarizer 6 affect the measured roll angle, reducing the accuracy of the measured roll angle. ② The distance between the target mirror unit and the measurement unit. If the distance is large, the light intensity will be attenuated to a certain extent. ③ The split beam L111″ passes through the second λ / 4 waveplate 5 and the polarizing beam splitter 2 before being detected by the fifth photodetector. The received beam L111′ passes through the second λ / 4 waveplate 5, the polarizing beam splitter 2, and the first polarizer 6 before being detected by the first photodetector. After being received, the light intensity will be attenuated to some extent after passing through these optical components; ④ First photodetector It also receives measurement light L12. Although the influence of measurement light L12 on the intensity of beam splitter L111′ has been reduced through algorithms, it cannot be completely eliminated. Summary of the Invention

[0005] In view of the above problems, the purpose of this invention is to provide a laser six-degree-of-freedom geometric error measurement system, a linear axis laser six-degree-of-freedom geometric error measurement method, and a rotating axis laser six-degree-of-freedom geometric error measurement method to overcome at least one technical problem existing in the prior art.

[0006] To address the aforementioned problems, this invention provides a laser six-degree-of-freedom geometric error measurement system, comprising a light distribution unit, a target mirror unit, and a measurement unit; wherein...

[0007] The light distribution unit includes: a laser emission module for generating outgoing light L1; a first polarizing beam splitter for splitting the outgoing light L1; a beam splitter for further splitting the split beam L12 separated from the outgoing light L1 by the first polarizing beam splitter; a fixed angle cone prism for back-reflecting the interference reference light L121 transmitted and split by the beam splitter from the split beam L12; and a λ / 4 waveplate for changing the polarization state of the split beam L11 separated from the outgoing light L1 by the first polarizing beam splitter.

[0008] The target mirror unit includes: a second polarizing beam splitter for re-splitting the beam splitter L122 that is split by the beam splitter L12 after being reflected by the beam splitter L12; a semi-transparent and semi-reflective element for reflecting and transmitting the beam splitter L11 that has passed through the λ / 4 waveplate; and a movable corner prism for back-reflecting the beam splitter L111 that is transmitted by the semi-transparent and semi-reflective element.

[0009] The beam splitter L111 is back-reflected by the moving corner prism and then re-split by the first polarizing beam splitter into interferometric measurement beam L111′ and beam splitter L111″. The beam splitter L11 is reflected by the semi-transparent and semi-reflective element to become beam splitter L112. The interference reference beam L121 is back-reflected by the fixed corner prism and then forms a combined beam L3 with the interferometric measurement beam L111′. The combined beam L3 interferes after passing through the first polarizer.

[0010] The measurement unit includes: a sixth photodetector and a seventh photodetector for receiving two reference rays of the split beam L122, which are split by the second polarizing beam splitter; a first photodetector for receiving the split beam L111″; a second photodetector for receiving the combined beam L3 after interference; and a third photodetector for receiving the split beam L112 focused by the focusing lens.

[0011] The sixth and seventh photodetectors are used to measure the angular error of the target mirror unit's rotation around the X-axis; the first photodetector is used to measure the linear error of the target mirror unit along the Y-axis and Z-axis; the second photodetector is used in conjunction with the interferometric length measurement module to measure the linear error of the target mirror unit along the X-axis; and the third photodetector is used to measure the angular error of the target mirror unit's rotation around the Y-axis and Z-axis.

[0012] To address the aforementioned problems, this invention also provides a method for measuring the six degrees of freedom geometric error of a linear axis using laser technology. This method employs the laser six-degree-of-freedom geometric error measurement system described above to simultaneously measure the six degrees of freedom geometric error of the linear axis under test using the same laser beam. The method includes the following steps:

[0013] The second polarizing beam splitter, the sixth photodetector, the seventh photodetector, and the target mirror unit are integrated and mounted on the linear axis to be measured; the light distribution unit, the first photodetector, the second photodetector, and the third photodetector are mounted on the photosensitive side of the target mirror unit;

[0014] The laser emission module emits emission light L1, and the measurement unit receives the light emitted by the light distribution unit that is distributed by the light distribution unit.

[0015] The roll angle of the straight axis to be measured is calculated based on the intensity changes of the two beams of light split by the second polarizing beam splitter, L122, received by the sixth and seventh photodetectors. The straightness error of the straight axis to be measured along the Y and Z axes is calculated based on the spot position change of the split beam L111″ received by the first photodetector. The positioning error of the straight axis to be measured along the X axis is measured based on the combined beam L3 received by the second photodetector in conjunction with the interferometric length measurement module. The pitch angle and yaw angle of the straight axis to be measured are measured based on the spot position change of the split beam L112 received by the third photodetector.

[0016] To address the aforementioned problems, this invention also provides a method for measuring the six-degree-of-freedom geometric error of a rotating shaft using a laser. This method employs the laser six-degree-of-freedom geometric error measurement system described above to measure the six-degree-of-freedom geometric error of the rotating shaft under test using the same laser beam. The method includes the following steps:

[0017] The second polarizing beam splitter, the sixth photodetector, the seventh photodetector, and the target mirror unit are integrated and mounted on the measuring shaft via a servo turntable; the light distribution unit, the first photodetector, the second photodetector, and the third photodetector are mounted on the photosensitive side of the target mirror unit;

[0018] The laser emission module emits emission light L1, and the measurement unit receives the light emitted by the light distribution unit that is distributed by the light distribution unit.

[0019] The angular error of the rotating shaft under test rotating around the Y-axis and Z-axis is measured based on the change in the position of the beam splitter L112 received by the third photodetector; the angular error of the rotating shaft under test rotating around the X-axis is calculated based on the change in the light intensity of the two beams of beam splitter L122 received by the sixth and seventh photodetectors and split by the second polarizing beam splitter; the radial runout error of the rotating shaft under test rotating around the Y-axis and the axial runout error along the Z-axis are calculated based on the change in the position of the beam splitter L111″ received by the first photodetector; and the radial runout error of the rotating shaft under test rotating around the X-axis is measured based on the beam combined L3 received by the second photodetector in conjunction with the interferometric length measuring module.

[0020] As can be seen from the above technical solution, the laser six-degree-of-freedom geometric error measurement system and method provided by the present invention can add the measurement of the roll angle of the measured object on the basis of measuring five degrees of freedom, thereby realizing the measurement of six degrees of freedom errors. Specifically, based on the beam splitter of the light distribution unit, combined with the design of the second polarizing beam splitter of the target mirror unit and the sixth and seventh photodetectors of the measurement unit, a beam L122 is separated from the split beam L12 by the beam splitter as an independent light path and directed to the target mirror unit. The second polarizing beam splitter acts as the sensitive element of the roll angle. When the entire target mirror unit has a roll angle, the second polarizing beam splitter rotates accordingly, and the incident direction of the split beam L122 relative to the second polarizing beam splitter changes, causing the light intensity on the sixth and seventh photodetectors to change. The roll angle is directly calculated by the change in light intensity, reducing the influence factors of measuring the roll angle based on polarization sensitivity, effectively solving the problem of the difficulty in accurately measuring the roll angle, so as to realize the simultaneous high-precision measurement of six degrees of freedom errors and significantly improve the accuracy of measuring six degrees of freedom errors.

[0021] To achieve the foregoing and related objectives, one or more aspects of the invention include the features that will be described in detail below. The following description and accompanying drawings illustrate certain exemplary aspects of the invention. However, these aspects indicate only a few of the various ways in which the principles of the invention can be used. Furthermore, the invention is intended to encompass all such aspects and their equivalents. Attached Figure Description

[0022] Other objects and results of the invention will become more apparent and readily understood with reference to the following description taken in conjunction with the accompanying drawings. In the drawings:

[0023] Figure 1 This is a schematic diagram of a linear six-degree-of-freedom geometric error measurement system based on a transmission dual-frequency laser according to an embodiment of the present invention;

[0024] Figure 2 This is a schematic diagram of a linear six-degree-of-freedom geometric error measurement system based on a reflective dual-frequency laser according to an embodiment of the present invention;

[0025] Figure 3 This is a schematic diagram of a linear six-degree-of-freedom geometric error measurement system based on a transmission dual-frequency laser according to another embodiment of the present invention;

[0026] Figure 4 This is a schematic diagram of a linear six-degree-of-freedom geometric error measurement system based on a transmission-type single-frequency laser according to an embodiment of the present invention;

[0027] Figure 5 This is a schematic diagram of a linear six-degree-of-freedom geometric error measurement system based on a reflective single-frequency laser according to an embodiment of the present invention;

[0028] Figure 6 This is a schematic diagram of a linear six-degree-of-freedom geometric error measurement system based on a transmission-type single-frequency laser according to another embodiment of the present invention;

[0029] Figure 7 This is a flowchart of a laser linear six-degree-of-freedom geometric error measurement method according to an embodiment of the present invention;

[0030] Figure 8 This is a schematic diagram of a six-degree-of-freedom geometric error measurement system for a rotating shaft based on a transmission dual-frequency laser, according to an embodiment of the present invention.

[0031] Figure 9 This is a flowchart of a six-degree-of-freedom geometric error measurement method for a laser rotating axis according to an embodiment of the present invention.

[0032] In the attached diagram, 11-laser emission module, 12-first polarizing beam splitter, 13-beam splitter, 14-fixed corner cube prism, 15-λ / 4 waveplate, 16-first polarizer, 17-second λ / 4 waveplate, 21-second polarizing beam splitter, 22-semi-transparent and semi-reflective element, 23-moving corner cube prism, 31-sixth photodetector, 32-seventh photodetector, 33-first photodetector, 34-second photodetector, 35-third photodetector, 36-focusing lens, 4-interferometric length measurement module, 41-first unpolarized beam splitter, 42-second polarizer, 43-fourth photodetector, 44-second unpolarized beam splitter, 45-first λ / 2 waveplate, 46-fifth photodetector, 5-servo turntable.

[0033] In all the accompanying drawings, the same reference numerals indicate similar or corresponding features or functions. Detailed Implementation

[0034] In the following description, numerous specific details are set forth for illustrative purposes and to provide a thorough understanding of one or more embodiments. However, it will be apparent that these embodiments may also be implemented without these specific details.

[0035] To address the problem that existing six-degree-of-freedom error simultaneous measurement schemes have complex optical path structures and mutual crosstalk, which affect the accuracy of six-degree-of-freedom error measurement, a laser six-degree-of-freedom geometric error measurement system and method are proposed.

[0036] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0037] To illustrate the laser six-degree-of-freedom geometric error measurement system and method provided by this invention Figure 1 The structure of a linear six-degree-of-freedom geometric error measurement system based on a transmission dual-frequency laser according to an embodiment of the present invention is shown; Figure 2 The structure of a linear six-degree-of-freedom geometric error measurement system based on a reflective dual-frequency laser according to an embodiment of the present invention is shown; Figure 3 The structure of a linear six-degree-of-freedom geometric error measurement system based on a transmission dual-frequency laser according to another embodiment of the present invention is shown; Figure 4 The structure of a linear six-degree-of-freedom geometric error measurement system based on a transmission single-frequency laser according to an embodiment of the present invention is shown; Figure 5 The structure of a linear six-degree-of-freedom geometric error measurement system based on a reflective single-frequency laser according to an embodiment of the present invention is shown; Figure 6 The structure of a linear six-degree-of-freedom geometric error measurement system based on a transmission single-frequency laser according to another embodiment of the present invention is shown; Figure 7The flowchart of a laser linear six-degree-of-freedom geometric error measurement method according to an embodiment of the present invention is shown; Figure 8 The structure of a six-degree-of-freedom geometric error measurement system for a rotating shaft based on a transmission dual-frequency laser, according to an embodiment of the present invention, is shown. Figure 9 The flowchart of a six-degree-of-freedom geometric error measurement method for a laser rotating shaft according to an embodiment of the present invention is shown.

[0038] like Figures 1 to 6 As shown in the figure, the laser six-degree-of-freedom geometric error measurement system provided by the present invention includes a light distribution unit, a target mirror unit, and a measurement unit; wherein,

[0039] The light distribution unit includes: a laser emission module 11 for generating outgoing light L1; a first polarizing beam splitter 12 for splitting outgoing light L1; a beam splitter 13 for further splitting the split beam L12 separated by the first polarizing beam splitter 12; a fixed angle cone prism 14 for back-reflecting the interference reference light L121 transmitted and split by the beam splitter 13; and a λ / 4 waveplate 15 for changing the polarization state of the split beam L11 separated by the first polarizing beam splitter 12.

[0040] The target mirror unit includes: a second polarizing beam splitter 21 for re-splitting the beam splitter L122 that is split by the beam splitter 12; a semi-transparent and semi-reflective element 22 for reflecting and transmitting the beam splitter L11 that has passed through the λ / 4 waveplate 15; and a movable corner prism 23 for back-reflecting the beam splitter L111 that is transmitted by the semi-transparent and semi-reflective element 22.

[0041] The beam splitter L111 is back-reflected by the moving corner prism 23 and then passed through the first polarizing beam splitter 12 again, where it is split into the interferometric measurement beam L111′ and the beam splitter L111″. The beam splitter L11 is reflected by the semi-transparent and semi-reflective element 22 to become the beam splitter L112. The interference reference beam L121 is back-reflected by the fixed corner prism 14 and then forms a combined beam L3 with the interferometric measurement beam L111′. The combined beam L3 interferes after passing through the first polarizer 16.

[0042] The measurement unit includes: a sixth photodetector 31 and a seventh photodetector 32 for receiving two reference rays of the split beam L122, which are split by the second polarizing beam splitter; a first photodetector 33 for receiving the split beam L111″; a second photodetector 34 for receiving the combined beam L3 after interference; and a third photodetector 35 for receiving the split beam L112 focused by the focusing lens 36; wherein,

[0043] The sixth photodetector 31 and the seventh photodetector 32 are used to measure the angular error of the target mirror unit's rotation around the X-axis; the first photodetector 33 is used to measure the linear error of the target mirror unit along the Y-axis and Z-axis; the second photodetector 34 is used in conjunction with the interferometric length measuring module 4 to measure the linear error of the target mirror unit along the X-axis; and the third photodetector 35 is used to measure the angular error of the target mirror unit's rotation around the Y-axis and Z-axis.

[0044] The function of the λ / 4 waveplate is as follows: light originally reflected by the polarizing beam splitter will be transmitted after passing through two λ / 4 waveplates and returning to the polarizing beam splitter; light originally transmitted by the polarizing beam splitter will be reflected after passing through two λ / 4 waveplates and returning to the polarizing beam splitter; light originally transmitted or transmitted by the polarizing beam splitter will be both reflected and transmitted after passing through one λ / 4 waveplate and returning to the polarizing beam splitter. Therefore, the combination of the λ / 4 waveplate and the polarizing beam splitter can change the optical path.

[0045] It should be noted that the terms "first", "second", "third", "fourth", "fifth", "sixth", and "seventh" in the technical solution of this invention are for distinguishing different positions of the same component and do not have any substantial meaning.

[0046] The sixth photodetector 31 and the seventh photodetector 32 are preferably light intensity detectors. The beam splitter 13 is a non-polarizing beam splitter. Through the structural design of the light distribution unit, the target mirror unit, and the measurement unit, it is possible to add the roll angle measurement of the measured object to the five degrees of freedom measurement, thereby realizing six degrees of freedom error measurement. Specifically, based on the beam splitter 13 of the light distribution unit, combined with the second polarizing beam splitter 21 of the target mirror unit and the sixth photodetector 31 and the seventh photodetector 32 of the measurement unit, a beam L122 is separately separated from the split beam L12 by the beam splitter 13 and directed as an independent light path to the target mirror unit. The second polarizing beam splitter 21 acts as a sensitive element for the roll angle. When the entire target mirror unit has a roll angle, the second polarizing beam splitter 21 rotates accordingly, and the incident direction of the split beam L122 relative to the second polarizing beam splitter 21 changes, causing a change in the light intensity on the sixth photodetector 31 and the seventh photodetector 32. The roll angle is directly calculated through the change in light intensity, reducing the influence factors of measuring the roll angle based on polarization sensitivity, effectively solving the problem of the difficulty in accurately measuring the roll angle, so as to achieve high-precision measurement of six degrees of freedom errors at the same time and significantly improve the accuracy of measuring six degrees of freedom errors.

[0047] As a preferred embodiment of the present invention, the laser emission module 11 is a dual-frequency laser;

[0048] The interferometric length measurement module 4 is disposed between the laser emission module 11 and the first polarizing beam splitter 12. The interferometric length measurement module 4 includes a first unpolarized beam splitter 41 for splitting the emitted light L1 into a laser L2, a second polarizer 42 for causing interference of the laser L2, and a fourth photodetector 43 for receiving the interference spot formed after the laser L2 passes through the second polarizer 42.

[0049] As a preferred embodiment of the present invention, the first photodetector 33, the second photodetector 34, and the third photodetector 35 are all any one of QD, PSD, CCD, and CMOS; and / or, the fourth photodetector 43 is any one of QD, PSD, CCD, CMOS, and pin.

[0050] As a preferred embodiment of the present invention, the laser emission module 11 is a single-frequency laser;

[0051] The interferometric length measurement module 4 is disposed between the first polarizing beam splitter 12 and the second photodetector 34. The interferometric length measurement module 4 includes a second unpolarized beam splitter 44 for splitting the transmitted light L31 and the reflected light L32 from the combined light L3, a first λ / 2 waveplate 45 for delaying the reflected light L32 by 90°, and a fifth photodetector 46 for receiving the interference spot light formed by the reflected light L32 after passing through the first λ / 2 waveplate 45.

[0052] As a preferred embodiment of the present invention, the sixth photodetector 31 and the seventh photodetector 32 are both any one of QD, PSD, CCD, CMOS and pin; and / or, the fifth photodetector 46 is any one of QD, PSD, CCD and CMOS.

[0053] In summary, it should be noted that in the technical solution provided by this invention, the laser emission module 11 can be either a dual-frequency laser or a single-frequency laser. The installation position of the interferometric length measuring module 4 differs depending on whether a dual-frequency or single-frequency laser is used. When the laser emission module 11 is a dual-frequency laser, such as... Figures 1 to 3 As shown. When the laser emission module 11 is a single-frequency laser, as... Figures 4 to 6 As shown.

[0054] In a preferred embodiment of the present invention, beam splitter L11 is light transmitted by the first polarizing beam splitter 12, and beam splitter L12 is light reflected by the first polarizing beam splitter 12; or...

[0055] Beam splitter L11 is the light reflected by the first polarizing beam splitter 12, and beam splitter L12 is the light transmitted by the first polarizing beam splitter 12.

[0056] In the technical solution of the present invention, such as Figure 1As shown, beam splitting L11 is the light transmitted by the first polarizing beam splitter 12, and beam splitting L12 is the light reflected by the first polarizing beam splitter 12. After being reflected back by the moving corner bevel prism 23, beam splitting L111 passes through the first polarizing beam splitter 12 again and is split into interferometric measurement light L111′ and beam splitting L111″. At this time, beam splitting L111″ is the light reflected by the first polarizing beam splitter 12 and is received by the first photodetector 33 alone; while interferometric measurement light L111′ is the light transmitted by the first polarizing beam splitter 12, and after being reflected back by the fixed corner bevel prism 14 with the interference reference light L121, it forms a combined beam L3. After interfering through the first polarizer 16, the combined beam L3 is received by the second photodetector 34.

[0057] like Figure 2 As shown, the beam splitter L11 is the light reflected by the first polarizing beam splitter 12, and the reference light L12 is the light transmitted by the first polarizing beam splitter 12. At this time, the beam splitter L111″, transmitted by the first polarizing beam splitter 12, is received solely by the first photodetector 33; while the interferometric measurement light L111′, reflected by the first polarizing beam splitter 12, and the interferometric reference light L121, are back-reflected by the fixed-angle pyramid prism 14 to form a combined beam L3. The combined beam L3, after interference by the first polarizer 16, is received by the second photodetector 34. Apart from this, the measurement principles of the transmission type (using the light transmitted by the first polarizing beam splitter 12 as the measurement light) and the reflection type (using the light reflected by the first polarizing beam splitter 12 as the measurement light) are the same.

[0058] As a preferred embodiment of the present invention, the semi-transparent and semi-reflective element 22 is a semi-transparent and semi-reflective mirror or a semi-transparent and semi-reflective film coated on the surface of the movable corner prism 23; and / or,

[0059] The first polarizing beam splitter 12 is a cubic polarizing beam splitter; and / or,

[0060] The second polarizing beam splitter 21 can be any one of a cubic polarizing beam splitter, a Wollaston prism, a Lochon polarizer, or a Glan polarizing prism.

[0061] For different polarization beam splitters, the placement of the sixth photodetector 31 and the seventh photodetector may differ, but the measurement principle remains the same.

[0062] As a preferred embodiment of the present invention, a second λ / 4 waveplate 17 is disposed between the first polarizing beam splitter 12 and the fixed-angle cone prism 14. Figure 3 and Figure 6As shown. By adding a second λ / 4 waveplate 17, the path of the interference reference light L121 after being reflected backward by the fixed-angle pyramid prism 14 and passing through the first polarizing beam splitter 12 is changed. However, after passing through the first polarizing beam splitter 12, the interference reference light L121 still forms a combined beam L3 with the interferometric measurement light L111′. The combined beam L3 is then received by the second photodetector 34 after interference by the first polarizer 16, and the measurement principle remains unchanged. However, for the transmission type, the interferometric measurement light L111′ is the reflected light from the first polarizing beam splitter 12; for the reflection type, the interferometric measurement light L111′ is the transmitted light from the first polarizing beam splitter 12.

[0063] The laser six-degree-of-freedom geometric error measurement system provided by this invention allows for the direct integration of the second polarizing beam splitter 21, the sixth photodetector 31, the seventh photodetector 32, and the target mirror unit onto the workpiece when the measured object is a linear axis. When the workpiece is a rotating axis, a servo rotary stage can be added, integrating the second polarizing beam splitter 21, the sixth photodetector 31, the seventh photodetector 32, and the target mirror unit, and then mounting them together with the servo rotary stage onto the rotating axis (workpiece) to achieve six-degree-of-freedom measurement of the rotating axis. The servo rotary stage is used to control the rotation of the target mirror unit to restore the light-receiving state of the aforementioned components when the second polarizing beam splitter 21, the sixth photodetector 31, the seventh photodetector 32, and the target mirror unit do not receive light.

[0064] This invention directly adds a sixth photodetector 31 and a seventh photodetector 32 to the target mirror unit. When measuring the roll angle, the roll angle is calculated by measuring the change in light intensity measured by the sixth photodetector 31 and the seventh photodetector 32 after the light is split by the second polarizing beam splitter 21, which is the sensitive element. Compared with existing solutions, the advantages of this invention are: ① There are no other optical elements between the two light intensity detectors (sixth photodetector 31 and seventh photodetector 32) and the polarizing beam splitter 21, so the polarization characteristics of the light will not be affected by other optical elements, thus affecting the measurement accuracy; ② The two light intensity detectors and the sensitive element, the second polarizing beam splitter 21, are mounted on the target mirror unit at a close and fixed distance, unaffected by the distance between the target mirror unit and the measurement unit. Compared with other six-degree-of-freedom measurement methods, the solution provided by this invention simplifies the optical path structure, reduces the complexity of the measurement system, and the volume of the measurement unit and the target mirror unit, making it convenient for practical applications.

[0065] like Figure 7 As shown, the linear axis laser six-degree-of-freedom geometric error measurement method provided by the present invention uses the laser six-degree-of-freedom geometric error measurement system of the present invention described above to simultaneously measure the six-degree-of-freedom geometric error of the workpiece under test based on the same laser beam, and includes the following steps:

[0066] Step S110: The second polarizing beam splitter 21, the sixth photodetector 31, the seventh photodetector 32 and the target mirror unit are integrated and installed on the linear axis to be measured; the light distribution unit, the first photodetector 33, the second photodetector 34 and the third photodetector 35 are installed on the photosensitive side of the target mirror unit;

[0067] Step S120: The laser emission module 11 emits emission light L1, and the measurement unit receives the light distributed by the light distribution unit from the emission light L1.

[0068] Step S130: Calculate the roll angle of the linear axis to be measured based on the intensity changes of the two beams of light split by the second polarizing beam splitter 21, which are received by the sixth photodetector 31 and the seventh photodetector 32 and received by the split beam L122. Calculate the straightness error of the linear axis to be measured along the Y-axis and Z-axis based on the spot position change of the split beam L111″ received by the first photodetector 33. Measure the positioning error of the device to be measured along the X-axis using the combined beam L3 received by the second photodetector 34 in conjunction with the interference length measuring module 4. Measure the pitch angle and yaw angle of the linear axis to be measured based on the spot position change of the split beam L112 received by the third photodetector 35.

[0069] Specifically, the second polarizing beam splitter 21, the sixth photodetector 31, and the seventh photodetector 32 are integrated with the target mirror unit and mounted on the workpiece to be measured. The workpiece to be measured is generally a linear or rotating axis of a machine tool. The light distribution unit is installed on the photosensitive side of the target mirror unit. By measuring the changes in light intensity, spot position, and frequency of the light distributed by the light distribution unit, which are received by the measurement unit, the six-degree-of-freedom geometric error of the workpiece to be measured based on the same laser beam is measured.

[0070] As a preferred embodiment of the present invention, the method for calculating the roll angle of the linear axis to be measured includes:

[0071] The light intensities of the two beams of light split by the second polarizing beam splitter 21, received by the sixth photodetector 31 and the seventh photodetector 32 respectively, are denoted as Ia(γ) and Ib(γ). The functional relationship between Ia(γ) and Ib(γ) is denoted as f(γ)=[Ia(γ)-Ib(γ)] / [Ia(γ)+Ib(γ)], where γ is the roll angle of the target mirror unit.

[0072] The target mirror unit is rotated around the X-axis by several specific angles γ1, γ2, ..., and the corresponding f(γ1), f(γ2), ... are measured, and the function curves of f(γ) and γ are calibrated.

[0073] The light intensities Ia(γ) and Ib(γ) are measured in real time. Based on the functional relationship between Ia(γ) and Ib(γ) and the function curve of f(γ) and γ, the rotation angle γ of the target mirror unit around the X-axis is calculated to obtain the roll angle of the straight axis to be measured.

[0074] As a preferred embodiment of the present invention, the method for calculating the straightness error of the straight axis to be measured along the Y-axis and Z-axis based on the change in the position of the beam splitting light L111″ received by the first photodetector 33 includes:

[0075] Based on the change between the real-time position (y1t, z1t) of the beam splitter L111″ received by the first photodetector 33 and the initial position (y10, z10) of the beam splitter L111″ recorded in the first photodetector 33, the change in the position of the beam splitter L111″ is determined, and the straightness errors of the measured part along the Y-axis and Z-axis are calculated as Δy = 2(y 1t -y 10 ) and Δz=2(z 1t -z 10 ).

[0076] As a preferred embodiment of the present invention, the method for measuring the pitch angle and yaw angle of the linear axis to be measured based on the intensity change of the beam splitter L112 received by the third photodetector 35 includes:

[0077] According to the real-time position (y) of the beam splitter L112 received by the third photodetector 35 t ,z t The change in the position of the beam splitter L112 is determined by comparing the initial position (y0, z0) of the beam splitter L112 with the change recorded in the third photodetector 35.

[0078] Based on the change in the position of the beam splitter L112, the pitch angle and yaw angle of the linear axis to be measured around the Y-axis and Z-axis are calculated as Δα=(y t -y0) / 2f and Δβ=(z-z0) / 2f, where f is the focal length of the focusing lens 36.

[0079] As a preferred embodiment of the present invention, the method for measuring the positioning error of the straight line axis to be measured along the X-axis based on the combined beam L3 received by the second photodetector 34 in conjunction with the interferometric length measuring module 4 includes:

[0080] When the laser emitted by the laser emission module 11 is a dual-frequency laser, an interference length measurement module 4 is installed between the laser emission module 11 and the first polarizing beam splitter 12; wherein, the interference length measurement module 4 includes a first non-polarizing beam splitter 41 for splitting the emitted light L1 into a reflected laser L2, a second polarizer 42 for interfering with the reflected laser L2, and a fourth photodetector 43 for receiving the interference spot formed by the interference of the reflected laser L2 by the second polarizer 42;

[0081] Let the frequencies of the two polarized beams with a frequency difference contained in the outgoing light L1 be f1 and f2, respectively. Then, when the outgoing light L1 is split by the first polarizing beam splitter 12, the frequency of the split beam L11 is f1 and the frequency of the split beam L12 is f2. Let the displacement of the split beam L111 along the X-axis with the target mirror unit be Δx, and the frequency change caused by the Doppler effect be f(Δx). Then the frequency of the split beam L111 is f1 + f(Δx). The combined beam L3 received by the second photodetector 34 is used as the measurement signal for heterodyne interferometry length measurement. The frequency of the measurement signal is f1 + f2. 测 =f1+f(Δx)-f2, the interference spot received by the fourth photodetector 43 is used as the standard signal for heterodyne interferometry length measurement, and the frequency of the standard signal is f. 标 =f1-f2;

[0082] Make the frequency f of the measurement signal 测 =f1+f(Δx)-f2 and the frequency f of the standard signal 标 Subtracting f1 from f2, we get f(Δx) = f 测 -f 标 Let N(Δx) be the number of times the interference fringes change in brightness caused by f(Δx), and let λ be the laser wavelength output by the laser emission module 11. Then the linearity error of the target mirror unit along the X-axis is Δx=N(Δx)·λ / 2, so as to obtain the positioning error of the measured part along the X-axis.

[0083] When the laser emitted by the laser emission module 11 is a single-frequency laser, an interferometric length measuring module 4 is installed between the first polarizing beam splitter 12 and the second photodetector 34. The interferometric length measuring module 4 includes a second non-polarizing beam splitter 44 for splitting the combined beam L3 into transmitted light L31 and reflected light L32, a first λ / 2 waveplate 45 for delaying the reflected light L32 by 90°, and a fifth photodetector 46 for receiving the interference spot light formed by the reflected light L32 after passing through the first λ / 2 waveplate 45.

[0084] The transmitted light L31 is received by the second photodetector 34. The intensity of the interference spot of the transmitted light L31 received by the second photodetector 34 is recorded as I2. The intensity of the interference spot of the reflected light L32 received by the fifth photodetector 46 is recorded as I5. The interference reference light L121 reflected back by the fixed corner bevel prism is used as the reference light for the interference length measurement signal. The interference measurement light L111′ is used as the measurement light for the heterodyne interference length measurement signal.

[0085] By processing I2 and I5, the number of changes in the brightness of the interference fringes caused by the phase difference φ(Δx) between the reference light of the interference length measurement signal and the measurement light of the heterodyne interference length measurement signal is N(Δx). The laser wavelength output by the laser emission module 11 is λ. Then, the linearity error of the target mirror unit along the X-axis is Δx=N(Δx)·λ / 2, so as to obtain the positioning error of the straight line axis to be measured along the X-axis.

[0086] like Figure 8 and Figure 9 As shown, the six-degree-of-freedom geometric error measurement method for shaft lasers provided by the present invention uses the six-degree-of-freedom geometric error measurement system of the present invention described above to measure the six-degree-of-freedom geometric error of the shaft under test based on the same laser beam, and includes the following steps:

[0087] Step A110: The second polarizing beam splitter 21, the sixth photodetector 31, the seventh photodetector 32 and the target mirror unit are integrated and mounted on the rotating shaft to be measured via the servo turntable 5; the light distribution unit, the first photodetector 33, the second photodetector 34 and the third photodetector 35 are installed on the photosensitive side of the target mirror unit;

[0088] Step A120: The laser emission module 11 emits emission light L1, and the measurement unit receives the light distributed by the light distribution unit from the emission light L1.

[0089] Step A130: Measure the angular error of the rotating shaft under test rotating around the Y-axis and Z-axis based on the change in the position of the beam splitter L112 received by the third photodetector 35; calculate the angular error of the rotating shaft under test rotating around the X-axis based on the intensity change of the two beams of beam splitter L122 received by the sixth photodetector 31 and the seventh photodetector 32 and split by the second polarizing beam splitter 21; calculate the radial runout error of the rotating shaft under test along the Y-axis and the axial runout error along the Z-axis based on the change in the position of the beam splitter L111″ received by the first photodetector 33; and measure the radial runout error of the rotating shaft under test along the X-axis based on the combined beam L3 received by the second photodetector 34 in conjunction with the interference length measuring module 4.

[0090] As a preferred embodiment of the present invention, in the process of measuring the angular error of the rotation of the shaft under test around the Y-axis and Z-axis based on the change in the position of the beam-splitting light L112 received by the third photodetector 35,

[0091] Based on the angular error of the rotating shaft under test around the Z-axis, the servo turntable 5 is controlled to rotate in the opposite direction of the rotating shaft under test, so that the spot of the beam splitter L112 returns to the center of the third photodetector 35 in the horizontal direction, so as to achieve servo tracking; wherein, the difference between the rotation angle of the rotating shaft under test and the rotation angle of the servo turntable 5 is the angular positioning error.

[0092] As a preferred embodiment of the present invention, a method for measuring the angular error of the rotation of the shaft under test around the Y-axis and Z-axis based on the change in the position of the beam splitter L112 received by the third photodetector 35 includes:

[0093] According to the real-time position (y) of the beam splitter L112 received by the third photodetector 35 t ′,z t The change in the position of the beam splitter L112 is determined by comparing the initial position (y0′, z0′) with the change in the beam splitter L112 spot position recorded in the third photodetector 35.

[0094] Based on the change in the position of the beam splitter L112, the angular errors of the rotation of the shaft under test around the Y and Z axes are calculated as Δα′=(y t Δβ′=(z′-z0′) / 2f and Δβ′=(z′-z0′) / 2f, where f is the focal length of the focusing lens.

[0095] As a preferred embodiment of the present invention, a method for calculating the radial runout error along the Y-axis and the axial runout error along the Z-axis of the shaft to be measured based on the change in the position of the beam splitter L111″ received by the first photodetector 33 includes:

[0096] Based on the real-time position (y) of the beam splitter L111″ received by the first photodetector 33 1t ′,z 1t The initial position (y′) of the beam splitter L111″ recorded in the first photodetector 33. 10 ′,z 10 The change in the beam position of the split beam L111″ is determined by the change in the beam position of the split beam L111″. The radial runout error along the Y-axis and the axial runout error along the Z-axis of the shaft to be measured are calculated to be Δy′=2(y′). 1t ′-y 10 ′) and Δz′=2(z 1t ′-z 10 ′).

[0097] As a preferred embodiment of the present invention, a method for calculating the angular error of the rotation of the shaft under test about the X-axis based on the intensity change of the two beams of light L122 received by the sixth photodetector 31 and the seventh photodetector 32 and split by the second polarizing beam splitter 21 includes:

[0098] The light intensities of the two reference rays of the beam splitting L122 received by the sixth photodetector 31 and the seventh photodetector 32 respectively and split by the second polarizing beam splitter 21 are denoted as Ia(γ′) and Ib(γ′). The functional relationship between Ia(γ′) and Ib(γ′) is denoted as f(γ′)=[Ia(γ′)-Ib(γ′)] / [Ia(γ′)+Ib(γ′)], where γ′ is the angular error of the target mirror unit around the X-axis.

[0099] The target mirror unit is rotated around the X-axis by several specific angles γ1′, γ2′, ..., and the corresponding f(γ1′), f(γ2′), ... are measured, and the function curves of f(γ′) and γ′ are calibrated.

[0100] The light intensities Ia(γ′) and Ib(γ′) are measured in real time. Based on the functional relationship between Ia(γ′) and Ib(γ′) and the function curve of f(γ′) and γ′, the rotation angle γ′ of the target mirror unit around the X-axis is calculated to obtain the angular error of the rotation of the shaft to be measured around the X-axis.

[0101] As a preferred embodiment of the present invention, the method for measuring the radial runout error of the shaft under test along the X-axis based on the combined beam L3 received by the second photodetector in conjunction with the interferometric length measuring module 4 includes:

[0102] When the laser emitted by the laser emission module 11 is a dual-frequency laser, an interference length measurement module 4 is installed between the laser emission module 11 and the first polarizing beam splitter 12; wherein, the interference length measurement module 4 includes a first non-polarizing beam splitter 41 for splitting the emitted light L1 into a reflected laser L2, a second polarizer 42 for interfering with the reflected laser L2, and a fourth photodetector 43 for receiving the interference spot formed by the interference of the reflected laser L2 by the second polarizer 42;

[0103] Let the frequencies of the two polarized beams with a frequency difference contained in the outgoing light L1 be f1′ and f2′, respectively. Then, when the outgoing light L1 is split by the first polarizing beam splitter 12, the frequency of the split beam L11 is f1′ and the frequency of the split beam L12 is f2′. Let the displacement of the split beam L111 along the X-axis with the target mirror unit be Δx′, and the frequency change caused by the Doppler effect be f(Δx′). Then, the frequency of the split beam L111 is f1′ + f(Δx′). The combined beam L3 received by the second photodetector 34 is used as the measurement signal for heterodyne interferometry length measurement. The frequency of the measurement signal is f. 测f' = f1' + f(Δx') - f2', using the interference spot received by the fourth photodetector 43 as the standard signal for heterodyne interferometry length measurement, with the frequency of the standard signal being f'. 标 ′=f1′-f2′;

[0104] Make the frequency f of the measurement signal 测 =f1′+f(Δx′)-f2′ and the frequency f of the standard signal 标 Subtracting f' = f1' - f2', we get f(Δx') = f 测 ′-f 标 Let f(Δx′) cause the number of changes in the brightness of the interference fringes to be N(Δx′), and let the laser wavelength output by the laser emission module 11 be λ. Then the linearity error of the target mirror unit along the X-axis is Δx′=N(Δx′)·λ / 2, so as to obtain the radial runout error of the shaft to be measured along the X-axis.

[0105] When the laser emitted by the laser emission module 11 is a single-frequency laser, an interferometric length measuring module 4 is installed between the first polarizing beam splitter 12 and the second photodetector 34. The interferometric length measuring module 4 includes a second non-polarizing beam splitter 44 for splitting the combined beam L3 into transmitted light L31 and reflected light L32, a first λ / 2 waveplate 45 for delaying the reflected light L32 by 90°, and a fifth photodetector 46 for receiving the interference spot light formed by the reflected light L32 after passing through the first λ / 2 waveplate 45.

[0106] The transmitted light L31 is received by the second photodetector 34. The intensity of the interference spot of the transmitted light L31 received by the second photodetector 34 is recorded as I2′. The intensity of the interference spot of the reflected light L32 received by the fifth photodetector 46 is recorded as I5′. The interference reference light L121 reflected back by the fixed corner prism 14 is used as the reference light for the interference length measurement signal. The interference measurement light L111′ is used as the measurement light for the heterodyne interference length measurement signal.

[0107] By processing I2′ and I5′, the number of changes in the brightness of the interference fringes caused by the phase difference φ(Δx′) between the reference light of the interference length measurement signal and the measurement light of the heterodyne interference length measurement signal is N(Δx′). The output laser wavelength of the laser emission module is λ. Then, the linearity error of the target mirror unit along the X-axis is Δ′x=N(Δx′)·λ / 2, so as to obtain the radial runout error of the shaft to be measured along the X-axis.

[0108] It should be noted that in the XYZ spatial coordinate system of the present invention, the term "six-degree-of-freedom geometric error" includes three linear errors Δx, Δy, and Δz for translation along the X, Y, and Z directions, and three angular errors Δγ, Δα, and Δβ for rotation around the X, Y, and Z coordinate axes.

[0109] For a linear motion guide rail (referred to as a linear axis) that translates along the X-axis, Δx is the positioning error, Δy and Δz are the straightness errors, and Δγ, Δα, and Δβ are the roll angle, pitch angle, and yaw angle, respectively.

[0110] For a rotating shaft that rotates around the Z-axis, Δx and Δy are radial runout errors, Δz is axial runout error, Δβ is angular positioning error, and Δγ and Δα are angular errors of rotation around the X-axis and Y-axis, respectively.

[0111] The embodiments of this invention are described in terms of translation along the X-axis and rotation around the Z-axis. In fact, translation along the Y-axis and Z-axis, as well as rotation around the X-axis and Y-axis, can be achieved simply by changing the installation method of the instrument, and this invention does not impose any particular limitation on this.

[0112] As can be seen from the above specific embodiments, the laser six-degree-of-freedom geometric error measurement system and method provided by the present invention can add the measurement of the roll angle of the measured object on the basis of measuring five degrees of freedom, thereby realizing the measurement of six degrees of freedom errors. Specifically, based on the beam splitter in the beam distribution unit, combined with the design of the second polarizing beam splitter in the target mirror unit and the sixth and seventh photodetectors in the measurement unit, a beam L122 is separately separated from the split beam L12 by the beam splitter as an independent light path and directed to the target mirror unit. The second polarizing beam splitter acts as a sensitive element for the roll angle. When the entire target mirror unit has a roll angle, the second polarizing beam splitter rotates accordingly, and the incident direction of the split beam L122 relative to the second polarizing beam splitter changes, causing the light intensity on the sixth and seventh photodetectors to change. The roll angle is directly calculated through the change in light intensity, reducing the influence factors of measuring the roll angle based on polarization sensitivity, effectively solving the problem of the difficulty in accurately measuring the roll angle, so as to realize the simultaneous high-precision measurement of six degrees of freedom errors and significantly improve the accuracy of measuring six degrees of freedom errors.

[0113] The laser six-degree-of-freedom geometric error measurement system and method according to the present invention have been described above by way of example with reference to the accompanying drawings. However, those skilled in the art should understand that various modifications can be made to the laser six-degree-of-freedom geometric error measurement system and method proposed in the present invention without departing from the scope of the invention. Therefore, the scope of protection of the present invention should be determined by the contents of the appended claims.

Claims

1. A laser six-degree-of-freedom geometric error measurement system, characterized in that, It includes a light distribution unit, a target mirror unit, and a measurement unit; among which, The light distribution unit includes: a laser emission module for generating outgoing light L1; a first polarizing beam splitter for splitting the outgoing light L1; a beam splitter for further splitting the split beam L12 separated from the outgoing light L1 by the first polarizing beam splitter; a fixed angle cone prism for back-reflecting the interference reference light L121 transmitted and split by the beam splitter from the split beam L12; and a λ / 4 waveplate for changing the polarization state of the split beam L11 separated from the outgoing light L1 by the first polarizing beam splitter. The target mirror unit includes: a second polarizing beam splitter for re-splitting the beam splitter L122 that is split by the beam splitter L12 after being reflected by the beam splitter L12; a semi-transparent and semi-reflective element for reflecting and transmitting the beam splitter L11 that has passed through the λ / 4 waveplate; and a movable corner prism for back-reflecting the beam splitter L111 that is transmitted by the semi-transparent and semi-reflective element. The beam splitter L111 is back-reflected by the moving corner prism and then re-split by the first polarizing beam splitter into interferometric measurement beam L111′ and beam splitter L111″. The beam splitter L11 is reflected by the semi-transparent and semi-reflective element to become beam splitter L112. The interference reference beam L121 is back-reflected by the fixed corner prism and then forms a combined beam L3 with the interferometric measurement beam L111′. The combined beam L3 interferes after passing through the first polarizer. The measurement unit includes: a sixth photodetector and a seventh photodetector for receiving two reference rays of the split beam L122, which are split by the second polarizing beam splitter; a first photodetector for receiving the split beam L111″; a second photodetector for receiving the combined beam L3 after interference; and a third photodetector for receiving the split beam L112 focused by the focusing lens. The sixth and seventh photodetectors are used to measure the angular error of the target mirror unit's rotation around the X-axis; the first photodetector is used to measure the linear error of the target mirror unit along the Y-axis and Z-axis; the second photodetector is used in conjunction with the interferometric length measurement module to measure the linear error of the target mirror unit along the X-axis; and the third photodetector is used to measure the angular error of the target mirror unit's rotation around the Y-axis and Z-axis.

2. The laser six-degree-of-freedom geometric error measurement system according to claim 1, characterized in that, The laser emission module is a dual-frequency laser; The interference length measurement module is disposed between the laser emission module and the first polarizing beam splitter; the interference length measurement module includes a first unpolarized beam splitter for splitting the emitted light L1 into laser L2, a second polarizer for causing interference of the laser L2, and a fourth photodetector for receiving the interference spot formed after the laser L2 passes through the second polarizer.

3. The laser six-degree-of-freedom geometric error measurement system according to claim 2, characterized in that, The first photodetector, the second photodetector, and the third photodetector are all any one of QD, PSD, CCD, and CMOS; and / or, The fourth photodetector can be any one of QD, PSD, CCD, CMOS, and pin.

4. The laser six-degree-of-freedom geometric error measurement system according to claim 1, characterized in that, The laser emission module is a single-frequency laser; The interferometric length measurement module is disposed between the first polarizing beam splitter and the second photodetector; the interferometric length measurement module includes a second unpolarized beam splitter for splitting the combined beam L3 into transmitted light L31 and reflected light L32, a first λ / 2 waveplate for delaying the reflected light L32 by 90°, and a fifth photodetector for receiving the interference spot light formed by the reflected light L32 after passing through the first λ / 2 waveplate.

5. The laser six-degree-of-freedom geometric error measurement system according to claim 4, characterized in that, The sixth and seventh photodetectors are both of any one of QD, PSD, CCD, CMOS and pin; and / or the fifth photodetector is any one of QD, PSD, CCD and CMOS.

6. The laser six-degree-of-freedom geometric error measurement system according to claim 1, characterized in that, The split beam L11 is the light transmitted by the first polarizing beam splitter, and the split beam L12 is the light reflected by the first polarizing beam splitter; or... The split beam L11 is the light reflected by the first polarizing beam splitter, and the split beam L12 is the light transmitted by the first polarizing beam splitter.

7. The laser six-degree-of-freedom geometric error measurement system according to claim 1, characterized in that, The semi-transparent and semi-reflective component is a semi-transparent and semi-reflective mirror or a semi-transparent and semi-reflective film coated on the surface of the movable corner prism; and / or, The first polarizing beam splitter is a cubic polarizing beam splitter; and / or, The second polarizing beam splitter is any one of a cubic polarizing beam splitter, a Wollaston prism, a Lochon polarizer, or a Glan polarizing prism.

8. A method for measuring the geometric error of a six-degree-of-freedom linear axis laser, characterized in that, The laser six-degree-of-freedom geometric error measurement system as described in any one of claims 1-7 simultaneously measures the six-degree-of-freedom geometric error of the linear axis under test using the same laser beam, comprising the following steps: The second polarizing beam splitter, the sixth photodetector, the seventh photodetector, and the target mirror unit are integrated and mounted on the linear axis to be measured; the light distribution unit, the first photodetector, the second photodetector, and the third photodetector are mounted on the photosensitive side of the target mirror unit; The laser emission module emits emission light L1, and the measurement unit receives the light emitted by the light distribution unit that is distributed by the light distribution unit. The roll angle of the straight axis to be measured is calculated based on the intensity changes of the two beams of light split by the second polarizing beam splitter, L122, received by the sixth and seventh photodetectors. The straightness error of the straight axis to be measured along the Y and Z axes is calculated based on the spot position change of the split beam L111″ received by the first photodetector. The positioning error of the straight axis to be measured along the X axis is measured based on the combined beam L3 received by the second photodetector in conjunction with the interferometric length measurement module. The pitch angle and yaw angle of the straight axis to be measured are measured based on the spot position change of the split beam L112 received by the third photodetector.

9. The linear axis laser six-degree-of-freedom geometric error measurement method according to claim 8, characterized in that, The method for calculating the roll angle of the linear axis to be measured includes: The light intensities of the two beams of light split by the second polarizing beam splitter, which are received by the sixth photodetector and the seventh photodetector respectively, are denoted as Ia(γ) and Ib(γ). The functional relationship between Ia(γ) and Ib(γ) is denoted as f(γ)=[Ia(γ)-Ib(γ)] / [Ia(γ)+Ib(γ)], where γ is the roll angle of the target mirror unit. The target mirror unit is rotated around the X-axis by several specific angles γ1, γ2, ..., and the corresponding f(γ1), f(γ2), ... are measured, and the function curves of f(γ) and γ are calibrated. The light intensities Ia(γ) and Ib(γ) are measured in real time. Based on the functional relationship between Ia(γ) and Ib(γ) and the function curve of f(γ) versus γ, the rotation angle γ of the target mirror unit around the X-axis is calculated to obtain the roll angle of the linear axis to be measured; and / or, The method for calculating the straightness error of the measured straight axis along the Y-axis and Z-axis based on the change in the position of the beam splitting light L111″ received by the first photodetector includes: Based on the real-time position (y) of the beam splitter L111″ received by the first photodetector 1t ,z 1t) The initial position (y) of the beam splitter L111″ recorded in the first photodetector 10 ,z 10 The change in the beam splitter L111″ is used to determine the change in the spot position of the beam splitter L111″. The straightness errors of the measured straight axis along the Y-axis and Z-axis are calculated as Δy = 2(y 1t -y 10 ) and Δz=2(z 1t -z 10 ); and / or, The method for measuring the pitch angle and yaw angle of the linear axis to be measured based on the change in the position of the beam splitter L112 received by the third photodetector includes: According to the real-time position (y) of the beam splitter L112 received by the third photodetector t ,z t The change in the position of the beam splitter L112 is determined by comparing the initial position (y0, z0) of the beam splitter L112 with the change in the position of the beam splitter L112 recorded in the third photodetector. Based on the change in the position of the beam splitter L112, the pitch angle and yaw angle of the linear axis to be measured rotating around the Y-axis and Z-axis are calculated as Δα=(y t -y0) / 2f and Δβ=(z-z0) / 2f, where f is the focal length of the focusing lens.

10. The linear axis laser six-degree-of-freedom geometric error measurement method according to claim 8, characterized in that, The method for measuring the positioning error of the straight line axis to be measured along the X-axis based on the combined beam L3 received by the second photodetector in conjunction with the interferometric length measuring module includes: When the laser emitted by the laser emission module is a dual-frequency laser, the interference length measurement module is installed between the laser emission module and the first polarizing beam splitter; wherein, the interference length measurement module includes a first non-polarizing beam splitter for splitting the emitted light L1 into a reflected laser L2, a second polarizer for interfering with the reflected laser L2, and a fourth photodetector for receiving the interference spot formed by the interference of the reflected laser L2 by the second polarizer; Let f1 and f2 be the frequencies of the two polarized beams with a frequency difference contained in the outgoing light L1. Then, when the outgoing light L1 is split by the first polarizing beam splitter, the frequency of the split beam L11 is f1, and the frequency of the split beam L12 is f2. Let Δx be the displacement of the split beam L111 along the X-axis with the target mirror unit, and f(Δx) be the frequency change caused by the Doppler effect. Then, the frequency of the split beam L111 is f1 + f(Δx). The combined beam L3 received by the second photodetector is used as the measurement signal for heterodyne interferometry length measurement. The frequency of the measurement signal is f1 + f(Δx). 测 =f1+f(Δx)-f2, the interference spot received by the fourth photodetector is used as the standard signal for heterodyne interferometry length measurement, and the frequency of the standard signal is f. 标 =f1-f2; The frequency f of the measurement signal 测 =f1+f(Δx)-f2 and the frequency f of the standard signal 标 Subtracting f1 from f2, we get f(Δx) = f 测 -f 标 Let N(Δx) be the number of times the interference fringes change in brightness caused by f(Δx), and let λ be the laser wavelength output by the laser emission module. Then, the linearity error of the target mirror unit along the X-axis is Δx = N(Δx)·λ / 2, so as to obtain the positioning error of the straight line axis to be measured along the X-axis. When the laser emitted by the laser emission module is a single-frequency laser, the interferometric length measurement module is installed between the first polarizing beam splitter and the second photodetector; wherein, the interferometric length measurement module includes a second non-polarizing beam splitter for splitting the combined beam L3 into transmitted light L31 and reflected light L32, a first λ / 2 waveplate for delaying the reflected light L32 by 90°, and a fifth photodetector for receiving the interference spot light formed by the reflected light L32 after passing through the first λ / 2 waveplate; The transmitted light L31 is received by the second photodetector. The intensity of the interference spot of the transmitted light L31 received by the second photodetector is recorded as I2. The intensity of the interference spot of the reflected light L32 received by the fifth photodetector is recorded as I5. The interference reference light L121 reflected back by the fixed corner prism is used as the reference light for the interference length measurement signal. The interference measurement light L111′ is used as the measurement light for the heterodyne interference length measurement signal. By processing I2 and I5, the number of changes in the brightness of the interference fringes caused by the phase difference φ(Δx) between the reference light of the interference length measurement signal and the measurement light of the heterodyne interference length measurement signal is N(Δx). The laser wavelength output by the laser emission module is λ. Then, the linearity error of the target mirror unit along the X-axis is Δx=N(Δx)·λ / 2, so as to obtain the positioning error of the straight line axis to be measured along the X-axis.

11. A method for measuring the geometric error of a six-degree-of-freedom rotating laser, characterized in that, The laser six-degree-of-freedom geometric error measurement system as described in any one of claims 1-7 measures the six-degree-of-freedom geometric error of the shaft under test using the same laser beam, comprising the following steps: The second polarizing beam splitter, the sixth photodetector, the seventh photodetector, and the target mirror unit are integrated and mounted on the measuring shaft via a servo turntable; the light distribution unit, the first photodetector, the second photodetector, and the third photodetector are mounted on the photosensitive side of the target mirror unit; The laser emission module emits emission light L1, and the measurement unit receives the light emitted by the light distribution unit that is distributed by the light distribution unit. The angular error of the rotating shaft under test rotating around the Y-axis and Z-axis is measured based on the change in the position of the beam splitter L112 received by the third photodetector; the angular error of the rotating shaft under test rotating around the X-axis is calculated based on the change in the light intensity of the two beams of beam splitter L122 received by the sixth and seventh photodetectors and split by the second polarizing beam splitter; the radial runout error of the rotating shaft under test rotating around the Y-axis and the axial runout error along the Z-axis are calculated based on the change in the position of the beam splitter L111″ received by the first photodetector; and the radial runout error of the rotating shaft under test rotating around the X-axis is measured based on the beam combined L3 received by the second photodetector in conjunction with the interferometric length measuring module.

12. The method for measuring the geometric error of a rotating laser six-degree-of-freedom axis according to claim 11, characterized in that, During the process of measuring the angular error of the rotation of the shaft under test around the Y-axis and Z-axis based on the change in the position of the beam splitter L112 received by the third photodetector, Based on the angular error of the rotation of the shaft to be measured around the Z-axis, the servo turntable is controlled to rotate in the opposite direction of the rotation of the shaft to be measured, so that the spot of the beam splitter L112 returns to the center of the third photodetector in the horizontal direction, thereby realizing the servo tracking; wherein, the difference between the rotation angle of the shaft to be measured and the rotation angle of the servo turntable is the angular positioning error.

13. The method for measuring the geometric error of a rotating laser six-degree-of-freedom axis according to claim 11, characterized in that, The method for measuring the angular error of the rotation of the shaft under test around the Y and Z axes based on the change in the position of the beam splitter L112 received by the third photodetector includes: According to the real-time position (y) of the beam splitter L112 received by the third photodetector t ′,z t The amount of change in the position of the beam splitter L112 is determined by comparing the change in the initial position (y0′, z0′) of the beam splitter L112 recorded in the third photodetector with the change in the position of the beam splitter L112 spot. Based on the change in the position of the beam splitter L112, the angular errors of the rotation of the shaft to be measured around the Y-axis and Z-axis are calculated as Δα′=(y t Δβ′=(z′-z0′) / 2f and Δβ′=(z′-z0′) / 2f, where f is the focal length of the focusing lens; and / or, The method for calculating the radial runout error along the Y-axis and the axial runout error along the Z-axis of the shaft under test based on the change in the position of the beam splitter L111″ received by the first photodetector includes: Based on the real-time position (y) of the beam splitter L111″ received by the first photodetector 1t ′,z 1t The initial position (y′) of the beam splitter L111″ recorded in the first photodetector and the initial position (y′) of the beam splitter L111″ recorded in the first photodetector. 10 ′,z 10 The change in the beam position of the split beam L111″ is determined by the change in the beam position of the split beam L111″. The radial runout error along the Y-axis and the axial runout error along the Z-axis of the shaft to be measured are calculated to be Δy′=2(y′). 1t ′-y 10 ′) and Δz′=2(z 1t ′-z 10 ′); and / or, The method for calculating the angular error of the rotation of the shaft under test around the X-axis based on the intensity change of the two beams of light split by the second polarizing beam splitter, received by the sixth and seventh photodetectors L122, includes: The light intensities of the two reference rays of the beam splitting L122 received by the sixth photodetector and the seventh photodetector respectively and split by the second polarizing beam splitter are denoted as Ia(γ′) and Ib(γ′). The functional relationship between Ia(γ′) and Ib(γ′) is denoted as f(γ′)=[Ia(γ′)-Ib(γ′)] / [Ia(γ′)+Ib(γ′)], where γ′ is the angular error of the target mirror unit rotating around the X-axis. The target mirror unit is rotated around the X-axis by several specific angles γ1′, γ2′, ..., and the corresponding f(γ1′), f(γ2′), ... are measured, and the function curves of f(γ′) and γ′ are calibrated. The light intensities Ia(γ′) and Ib(γ′) are measured in real time. Based on the functional relationship between Ia(γ′) and Ib(γ′) and the function curve of f(γ′) and γ′, the rotation angle γ′ of the target mirror unit around the X-axis is calculated to obtain the angular error of the rotation of the measured axis around the X-axis.

14. The method for measuring the six-degree-of-freedom geometric error of a rotating laser as described in claim 11, characterized in that, The method for measuring the radial runout error of the shaft under test along the X-axis based on the combined beam L3 received by the second photodetector in conjunction with the interferometric length measuring module includes: When the laser emitted by the laser emission module is a dual-frequency laser, the interference length measurement module is installed between the laser emission module and the first polarizing beam splitter; wherein, the interference length measurement module includes a first non-polarizing beam splitter for splitting the emitted light L1 into a reflected laser L2, a second polarizer for interfering with the reflected laser L2, and a fourth photodetector for receiving the interference spot formed by the interference of the reflected laser L2 by the second polarizer; Let the frequencies of the two polarized beams with a frequency difference contained in the outgoing light L1 be f1′ and f2′, respectively. Then, when the outgoing light L1 is split by the first polarizing beam splitter, the frequency of the split beam L11 is f1′ and the frequency of the split beam L12 is f2′. Let the displacement of the split beam L111 along the X-axis with the target mirror unit be Δx′, and the frequency change caused by the Doppler effect be f(Δx′). Then, the frequency of the split beam L111 is f1′ + f(Δx′). The combined beam L3 received by the second photodetector is used as the measurement signal for heterodyne interferometry. The frequency of the measurement signal is f. 测 f' = f1' + f(Δx') - f2', and the interference spot received by the fourth photodetector is used as the standard signal for heterodyne interferometry length measurement, wherein the frequency of the standard signal is f'. 标 ′=f1′-f2′; Make the frequency f of the measurement signal 测 =f1′+f(Δx′)-f2′ and the frequency f of the standard signal 标 Subtracting f' = f1' - f2', we get f(Δx') = f 测 ′-f 标 Let f(Δx′) cause the number of changes in the brightness of the interference fringes to be N(Δx′), and let the laser wavelength output by the laser emission module be λ. Then the linearity error of the target mirror unit along the X-axis is Δx′=N(Δx′)·λ / 2, so as to obtain the radial runout error of the shaft to be measured along the X-axis. When the laser emitted by the laser emission module is a single-frequency laser, the interferometric length measurement module is installed between the first polarizing beam splitter and the second photodetector; wherein, the interferometric length measurement module includes a second non-polarizing beam splitter for splitting the combined beam L3 into transmitted light L31 and reflected light L32, a first λ / 2 waveplate for delaying the reflected light L32 by 90°, and a fifth photodetector for receiving the interference spot light formed by the reflected light L32 after passing through the first λ / 2 waveplate; The transmitted light L31 is received by the second photodetector. The intensity of the interference spot of the transmitted light L31 received by the second photodetector is recorded as I2′. The intensity of the interference spot of the reflected light L32 received by the fifth photodetector is recorded as I5′. The interference reference light L121 reflected back by the fixed corner prism is used as the reference light for the interference length measurement signal. The interference measurement light L111′ is used as the measurement light for the heterodyne interference length measurement signal. By processing I2′ and I5′, the number of changes in the brightness of the interference fringes caused by the phase difference φ(Δx′) between the reference light of the interference length measurement signal and the measurement light of the heterodyne interference length measurement signal is N(Δx′). The laser wavelength output by the laser emission module is λ. Then, the linearity error of the target mirror unit along the X-axis is Δ′x=N(Δx′)·λ / 2, so as to obtain the radial runout error of the shaft to be measured along the X-axis.

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