Laser six-degree-of-freedom geometric error measurement system and method

Abstract

The invention provides a laser six-degree-of-freedom geometric error measurement system and method, and belongs to the technical field of optical precision measurement, and the system comprises a light distribution unit, a target lens unit and a measurement unit. According to the scheme design of a spectroscope of a light distribution unit, a second polarization spectroscope of a target mirror unit and a sixth photoelectric detector and a seventh photoelectric detector of a measurement unit, a beam of light can be independently split from beam splitting light L12 to serve as an independent path of light to be emitted to the target mirror unit, and the second polarization spectroscope serves as a sensitive element of a roll angle; when the whole target lens unit has a roll angle, the second polarizing beam splitter rotates along with the target lens unit, the polarization state of the passing split light is changed, the light intensity on the sixth photoelectric detector and the seventh photoelectric detector is changed, the roll angle is directly calculated through the light intensity change, influence factors for measuring the roll angle based on polarization sensitivity are reduced, and the measurement accuracy is improved. The problem that the roll angle is difficult to accurately measure during six-degree-of-freedom error measurement in the prior art is effectively solved.

Description

Technical Field

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

[0002] There are six degrees of freedom geometric motion errors in linear motion guides (linear axes for short) and rotating shafts when they move. There are 21 geometric errors that need to be measured for three-axis CNC machine tools / three-coordinate measuring machines, and 42 errors that need to be measured for five-axis CNC machine tools. Therefore, how to quickly measure the errors of CNC machine tools is a common problem that needs to be solved urgently. At the same time, measuring the six degrees of freedom errors of linear motion guides or rotating shafts is an inevitable choice.

[0003] Among them, the roll angle measurement is the most difficult quantity to measure in the current six-degree-of-freedom error measurement of the linear axis, and it is also a parameter that is difficult to integrate with the other five degrees of freedom errors. The existing patent CN114046732A developed by our unit previously provides a method and system for simultaneously measuring multi-degree-of-freedom geometric errors using lasers, which includes a measurement unit and a target mirror unit. The measurement unit includes a laser output module, a polarization beam splitter, a fixed reflector, the first to second λ / 4 wave plates, a first polarizer, a first photodetector, an interference length measurement module and a two-dimensional angle measurement module; the target mirror unit includes a beam splitter and a reflector; the laser output module is used to generate output light L1; the polarization beam splitter is used for ① beam splitting, ② beam combining and ③ separation; the fixed reflector is used to back-reflect the reference light L12 that propagates only inside the measurement unit, so that the reference light L12 returns to the polarization beam splitter. The system provided by this patent can realize: simultaneous rapid measurement of five / six-degree-of-freedom geometric errors of spatial objects moving in a straight line along a linear axis; long-term monitoring of the relative changes in the five / six-degree-of-freedom position and posture of two objects in space.

[0004] However, when measuring the roll angle, the third λ / 4 wave plate 13 of the sensitive element returns to the first photodetector of the measuring unit. , the fifth photodetector The roll angle is calculated by the change of light intensity of the two. The measurement accuracy will be affected by the following factors: ① In addition to the polarization rotation of the polarization sensitive device λ / 4 wave plate 13, which is directly related to the measured roll angle, the polarization splitting defect of the polarization beam splitter 2 causes the S light and the P light to be unable to be completely separated. The polarization characteristics of the reflected light of the corner cube prism 11 are related to the position and direction of the incident light. The polarization characteristics of the λ / 4 wave plate 5 and the polarizer 6 both affect the measured roll angle, reducing the accuracy of the measured roll angle; ② The distance between the target mirror unit and the measuring unit. If the distance is far, the light intensity will be attenuated to a certain extent; ③ The split light L111″ passes through the second λ / 4 wave plate 5 and the polarization beam splitter 2 and is detected by the fifth photodetector After receiving, the split light L111′ passes through the second λ / 4 wave plate 5, the polarization beam splitter 2, and the first polarizer 6, and then is received by the first photodetector After receiving, the light intensity will also be attenuated to a certain extent after passing through these optical elements; ④ The first photodetector At the same time, the measuring light L12 is also received. Although the influence of the measuring light L12 on the intensity of the split light L111 ′ has been reduced through an algorithm, it cannot be completely eliminated. Summary of the invention

[0005] In view of the above problems, the purpose of the present 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, so as to overcome at least one technical problem existing in the prior art.

[0006] In order to solve the above problems, the present invention provides a laser six-degree-of-freedom geometric error measurement system, including a light distribution unit, a target mirror unit and a measurement unit; wherein,

[0007] The light distribution unit includes: a laser output module for generating an output light L1, a first polarization beam splitter for splitting the output light L1, a beam splitter for re-splitting the split light L12 of the output light L1 split by the first polarization beam splitter, a fixed corner cube prism for back-reflecting the interference reference light L121 of the split light L12 transmitted and split by the beam splitter, and a λ / 4 wave plate for changing the polarization state of the split light L11 of the output light L1 split by the first polarization beam splitter;

[0008] The target mirror unit comprises: a second polarization beam splitter for re-splitting the split light L122 split by the beam splitter, a semi-transmissive and semi-reflective element for reflecting and transmitting the split light L11 passing through the λ / 4 wave plate, and a movable corner cube prism for back-reflecting the split light L111 transmitted by the semi-transmissive and semi-reflective element;

[0009] The split light L111 is reflected back by the movable corner cube and passes through the first polarization beam splitter again to be split into interference measurement light L111′ and split light L111″; the split light L11 is reflected by the semi-transparent and semi-reflective element to be split light L112; the interference reference light L121 is reflected back by the fixed corner cube and forms a combined light L3 with the interference measurement light L111′; the combined light L3 interferes after passing through the first polarizer;

[0010] The measuring unit comprises: a sixth photodetector and a seventh photodetector for respectively receiving two reference beams of the split light L122 split by the second polarization beam splitter, a first photodetector for receiving the split light L111″, a second photodetector for receiving the combined light L3 after interference, and a third photodetector for receiving the split light L112 focused by the focusing lens; wherein,

[0011] The sixth photodetector and the seventh photodetector are used to measure the angular error of the target mirror unit rotating around the X-axis; the first photodetector is used to measure the linear error of the target mirror unit along the Y-axis and the Z-axis; the second photodetector is used to cooperate with the interference length measurement module to measure the linear error of the target mirror unit along the X-axis; the third photodetector is used to measure the angular error of the target mirror unit rotating around the Y-axis and the Z-axis.

[0012] In order to solve the above problems, the present invention also provides a linear axis laser six-degree-of-freedom geometric error measurement method, which uses the above-mentioned laser six-degree-of-freedom geometric error measurement system to simultaneously measure the six-degree-of-freedom geometric errors of the linear axis to be measured based on the same laser beam, including the following steps:

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

[0014] The laser emission module emits an emission light L1, and the measuring unit receives the light of the emission light L1 distributed by the light distribution unit;

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

[0016] In order to solve the above problems, the present invention also provides a method for measuring the six-degree-of-freedom geometric error of a rotating shaft by laser, which uses the above-mentioned laser six-degree-of-freedom geometric error measurement system to measure the six-degree-of-freedom geometric error of the rotating shaft to be measured based on the same laser beam, including the following steps:

[0017] The second polarization beam splitter, the sixth photodetector, the seventh photodetector and the target mirror unit are integrated and installed on the rotating shaft to be measured through a servo turntable; the light distribution unit, the first photodetector, the second photodetector and the third photodetector are installed on the light sensitive side of the target mirror unit;

[0018] The laser emission module emits an emission light L1, and the measuring unit receives the light of the emission light L1 distributed by the light distribution unit;

[0019] The angular error of the rotation of the rotating shaft to be measured around the Y-axis and the Z-axis is measured according to the change in the spot position of the split light L112 received by the third photodetector, the angular error of the rotation of the rotating shaft to be measured around the X-axis is calculated according to the change in the light intensity of the two beams of light split by the second polarization beam splitter of the split light L122 received by the sixth photodetector and the seventh photodetector, the radial run-out error of the rotating shaft to be measured along the Y-axis and the axial run-out error along the Z-axis are calculated according to the change in the spot position of the split light L111″ received by the first photodetector, and the radial run-out error of the rotating shaft to be measured along the X-axis is measured according to the combined light L3 received by the second photodetector in cooperation with the interference length measurement module.

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

[0021] In order to achieve the above and related purposes, one or more aspects of the present invention include the features that will be described in detail later. The following description and the accompanying drawings describe some exemplary aspects of the present invention in detail. However, these aspects indicate only some of the various ways in which the principles of the present invention can be used. In addition, the present invention is intended to include all these aspects and their equivalents. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] By referring to the following description in conjunction with the accompanying drawings, and with a more comprehensive understanding of the present invention, other objects and results of the present invention will become more apparent and easy to understand. In the accompanying drawings:

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

[0024] Figure 2 It is a schematic diagram of the structure of a linear axis 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 It is a schematic structural diagram of a linear axis six-degree-of-freedom geometric error measurement system based on a transmission-type dual-frequency laser according to another embodiment of the present invention;

[0026] Figure 4 Schematic diagram of the structure of a linear axis 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 It is a schematic structural diagram of a linear axis 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 It is a schematic structural diagram of a linear axis 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 is a flow chart of a method for measuring six-degree-of-freedom geometric errors of a laser linear axis according to an embodiment of the present invention;

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

[0031] Fig. 9 Flow chart of a method for measuring six-DOF geometric errors of a laser rotating axis according to an embodiment of the present invention.

[0032] In the accompanying drawings, 11-laser output module, 12-first polarization beam splitter, 13-beam splitter, 14-fixed corner cube prism, 15-λ / 4 wave plate, 16-first polarizer, 17-second λ / 4 wave plate, 21-second polarization beam splitter, 22-semi-transparent and semi-reflective element, 23-movable corner cube prism, 31-sixth photodetector, 32-seventh photodetector, 33-first photodetector, 34-second photodetector, 35-third photodetector, 36-focusing lens, 4-interference length measurement module, 41-first non-polarization beam splitter, 42-second polarizer, 43-fourth photodetector, 44-second non-polarization beam splitter, 45-first λ / 2 wave plate, 46-fifth photodetector, 5-servo turntable.

[0033] The same reference numerals throughout the drawings indicate similar or corresponding features or functions. DETAILED DESCRIPTION

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

[0035] In view of the problem that the existing six-degree-of-freedom error simultaneous measurement scheme in the above-mentioned prior art has complex optical path structure and mutual crosstalk, which affects 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 be described in detail below with reference to the accompanying drawings.

[0037] In order to illustrate the laser six-degree-of-freedom geometric error measurement system and method provided by the present invention, Figure 1 The structure of a linear axis six-degree-of-freedom geometric error measurement system based on a transmission-type dual-frequency laser according to an embodiment of the present invention is shown; Figure 2 The structure of a linear axis 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 axis six-degree-of-freedom geometric error measurement system based on a transmission-type dual-frequency laser according to another embodiment of the present invention is shown; Figure 4 The structure of a linear axis six-degree-of-freedom geometric error measurement system based on a transmission-type single-frequency laser according to an embodiment of the present invention is shown; Figure 5 The structure of a linear axis 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 axis six-degree-of-freedom geometric error measurement system based on a transmission-type single-frequency laser according to another embodiment of the present invention is shown; Figure 7The flow chart of the method for measuring six-degree-of-freedom geometric errors of a laser linear axis according to an embodiment of the present invention is shown; Figure 8 The structure of the six-degree-of-freedom geometric error measurement system of the rotating shaft based on the transmission dual-frequency laser according to an embodiment of the present invention is shown; Fig. 9 The flowchart of the method for measuring the six-degree-of-freedom geometric error of a laser rotating axis according to an embodiment of the present invention is shown.

[0038] like Figures 1 to 6 As shown together, 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 output module 11 for generating an output light L1, a first polarization beam splitter 12 for splitting the output light L1, a beam splitter 13 for re-splitting the split light L12 of the output light L1 split by the first polarization beam splitter 12, a fixed corner cube 14 for back-reflecting the interference reference light L121 of the split light L12 transmitted and split by the beam splitter 13, and a λ / 4 wave plate 15 for changing the polarization state of the split light L11 of the output light L1 split by the first polarization beam splitter 12;

[0040] The target mirror unit includes: a second polarization beam splitter 21 for re-splitting the split light L122 reflected and split by the beam splitter 12, a semi-transparent and semi-reflective element 22 for reflecting and transmitting the split light L11 passing through the λ / 4 wave plate 15, and a movable corner cube prism 23 for back-reflecting the split light L111 transmitted by the semi-transparent and semi-reflective element 22;

[0041] The split light L111 is reflected back by the movable corner cube prism 23 and passes through the first polarization beam splitter 12 again to be split into the interference measurement light L111′ and the split light L111″; the split light L11 is reflected by the semi-transparent and semi-reflective element 22 to be the split light L112; the interference reference light L121 is reflected back by the fixed corner cube prism 14 to form a combined light L3 with the interference measurement light L111′; the combined light L3 interferes after passing through the first polarizer 16;

[0042] The measuring unit includes: a sixth photodetector 31 and a seventh photodetector 32 for respectively receiving two reference beams of the split light L122 split by the second polarization beam splitter, a first photodetector 33 for receiving the split light L111″, a second photodetector 34 for receiving the combined light L3 after interference, and a third photodetector 35 for receiving the split light 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 rotating 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 directions; the second photodetector 34 is used to cooperate with the interference length measurement module 4 to measure the linear error of the target mirror unit along the X-axis; the third photodetector 35 is used to measure the angular error of the target mirror unit rotating around the Y-axis and Z-axis.

[0044] The function of the λ / 4 wave plate is as follows: the light originally reflected by the polarization beam splitter will be transmitted after passing through the λ / 4 wave plate twice and then returning to the polarization beam splitter; the light originally transmitted by the polarization beam splitter will be reflected after passing through the λ / 4 wave plate twice and then returning to the polarization beam splitter; the light originally transmitted or transmitted by the polarization beam splitter will have both reflected light and transmitted light after passing through the λ / 4 wave plate once and then returning to the polarization beam splitter. Therefore, the light path can be changed by combining the λ / 4 wave plate and the polarization beam splitter.

[0045] It should be noted that the “first”, “second”, “third”, “fourth”, “fifth”, “sixth”, “seventh”, etc. in the technical solution of the present invention are for distinguishing different positions of the same components and do not have substantial meanings.

[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 lens unit and the measurement unit, the roll angle measurement of the measured object can be added on the basis of the five-degree-of-freedom measurement, thereby realizing the six-degree-of-freedom error measurement. Specifically, based on the beam splitter 13 of the light distribution unit, combined with the design of the second polarization beam splitter 21 of the target mirror unit and the sixth photodetector 31 and the seventh photodetector 32 of the measuring unit, a beam of light L122 is separately separated from the split light L12 through the beam splitter 13 as an independent light path to the target mirror unit, and the second polarization beam splitter 21 serves as a sensitive element for the roll angle. When the entire target mirror unit has a roll angle, the second polarization beam splitter 21 rotates accordingly, and the incident direction of the split light L122 relative to the second polarization beam splitter 21 changes, so that the light intensity on the sixth photodetector 31 and the seventh photodetector 32 changes, and the roll angle is directly calculated through the change in light intensity, thereby reducing the influencing factors of the roll angle measurement based on polarization sensitivity, and effectively solving the problem of the difficulty in accurately measuring the roll angle, so as to achieve simultaneous high-precision measurement of six-degree-of-freedom errors and significantly improve the accuracy of measuring six-degree-of-freedom errors.

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

[0048] The interference length measurement module 4 is arranged between the laser output module 11 and the first polarization beam splitter 12; the interference length measurement module 4 includes a first non-polarization beam splitter 41 for splitting the laser L2 from the output light L1, 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 solution of the present invention, the laser output module 11 is a single-frequency laser;

[0051] The interference length measurement module 4 is arranged between the first polarization beam splitter 12 and the second photodetector 34; the interference length measurement module 4 includes a second non-polarization beam splitter 44 for splitting the transmitted light L31 and the reflected light L32 from the combined light L3, a first λ / 2 wave plate 45 for delaying the phase of 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 wave plate 45.

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

[0053] In summary, it should be noted that: in the technical solution provided by the present invention, the laser emission module 11 can be a dual-frequency laser or a single-frequency laser. When a dual-frequency laser or a single-frequency laser is used, the installation position of the interferometric length measurement module 4 is different. When the laser emission module 11 is a dual-frequency laser, such as Figures 1 to 3 When the laser output module 11 is a single-frequency laser, as shown in Figures 4 to 6 shown.

[0054] As a preferred solution of the present invention, the split light L11 is the light transmitted by the first polarization beam splitter 12, and the split light L12 is the light reflected by the first polarization beam splitter 12; or,

[0055] The split light L11 is light reflected by the first polarization beam splitter 12 , and the split light L12 is light transmitted by the first polarization beam splitter 12 .

[0056] In the technical solution of the present invention, Figure 1As shown, the split light L11 is the light transmitted by the first polarization beam splitter 12, and the split light L12 is the light reflected by the first polarization beam splitter 12. The split light L111 is reflected back by the movable corner cube prism 23 and passes through the first polarization beam splitter 12 again, and is split again into the interference measurement light L111′ and the split light L111″. At this time, the split light L111″ is the light reflected by the first polarization beam splitter 12, and is received by the first photodetector 33 alone; while the interference measurement light L111′ is the light transmitted by the first polarization beam splitter 12, and is reflected back by the fixed corner cube prism 14 with the interference reference light L121 to form a combined light L3, and the combined light L3 is received by the second photodetector 34 after interference through the first polarizer 16.

[0057] like Figure 2 As shown, the split light L11 is the light reflected by the first polarization beam splitter 12, and the reference light L12 is the light transmitted by the first polarization beam splitter 12. At this time, the split light L111″ is the light transmitted by the first polarization beam splitter 12, and is received by the first photodetector 33 alone; while the interference measurement light L111′ is the light reflected by the first polarization beam splitter 12, and is back-reflected with the interference reference light L121 by the fixed corner cube prism 14 to form a combined light L3, and the combined light L3 is received by the second photodetector 34 after interference through the first polarizer 16. In addition, the measurement principles of the transmission type (the light transmitted by the first polarization beam splitter 12 is used as the measurement light) and the reflection type (the light reflected by the first polarization beam splitter 12 is used as the measurement light) are the same.

[0058] As a preferred solution 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 cube prism 23; and / or,

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

[0060] The second polarization beam splitter 21 is any one of a cubic polarization beam splitter, a Wollaston prism, a Rochon polarizer, and a Glan polarization prism.

[0061] For different polarization beam splitters, the locations of the sixth photodetector 31 and the seventh photodetector may be different, but the measurement principle remains unchanged.

[0062] As a preferred solution of the present invention, a second λ / 4 wave plate 17 is provided between the first polarization beam splitter 12 and the fixed corner cube prism 14. Figure 3 and Figure 6As shown. By adding the second λ / 4 wave plate 17, the route of the interference reference light L121 after being back-reflected by the fixed corner cube prism 14 and passing through the first polarization beam splitter 12 is changed. However, after passing through the first polarization beam splitter 12, the interference reference light L121 still forms a combined light beam L3 with the interference measurement light L111′. After the combined light beam L3 interferes with the first polarizer 16, it is received by the second photodetector 34, and its measurement principle remains unchanged. However, for the transmission type, the interference measurement light L111′ is the reflected light of the first polarization beam splitter 12; for the reflection type, the interference measurement light L111′ is the transmitted light of the first polarization beam splitter 12.

[0063] The laser six-degree-of-freedom geometric error measurement system provided by the present invention can directly integrate the second polarization beam splitter 21, the sixth photodetector 31, the seventh photodetector 32 and the target mirror unit and install them on the part to be measured when the part to be measured is a linear axis. When the part to be measured is a rotating axis, the second polarization beam splitter 21, the sixth photodetector 31, the seventh photodetector 32 and the target mirror unit can be integrated and then installed on the rotating axis (part to be measured) together with the servo rotating table by adding a servo rotating table to realize the six-degree-of-freedom measurement of the rotating axis. The servo rotating table is used to control the rotation of the target mirror unit to restore the state of the above-mentioned components receiving light when the second polarization beam splitter 21, the sixth photodetector 31, the seventh photodetector 32 and the target mirror unit cannot receive light.

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

[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 as described above to simultaneously measure the six-degree-of-freedom geometric errors of the measured part based on the same laser beam, including the following steps:

[0066] Step S110, the second polarization 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 light sensitive side of the target mirror unit;

[0067] Step S120, enabling the laser emitting module 11 to emit an emitted light L1, and enabling the measuring unit to receive the light of the emitted light L1 distributed by the light distribution unit;

[0068] Step S130, calculate the roll angle of the linear axis to be measured of the part to be measured according to the change in the light intensity of the two beams of light split by the second polarization beam splitter 21 of the split light L122 received by the sixth photodetector 31 and the seventh photodetector 32, calculate the straightness error of the linear axis to be measured along the Y-axis and the Z-axis according to the change in the spot position of the split light L111″ received by the first photodetector 33, measure the positioning error of the part to be measured along the X-axis according to the combined light L3 received by the second photodetector 34 in cooperation with the interference length measurement module 4, and measure the pitch angle and yaw angle of the linear axis to be measured according to the change in the spot position of the split light L112 received by the third photodetector 35.

[0069] Specifically, the second polarization beam splitter 21, the sixth photodetector 31, the seventh photodetector 32 and the target lens unit are integrated and installed on the object to be measured, which is generally a linear axis or a rotating axis of a machine tool, and the light distribution unit is installed on the light sensitive side of the target lens unit. The six-degree-of-freedom geometric error of the object to be measured based on the same laser beam is measured by the change of light intensity, spot position, frequency, etc. of the light distributed by the light distribution unit received by the measuring unit.

[0070] As a preferred solution 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 L122 received by the sixth photodetector 31 and the seventh photodetector 32 respectively and split by the second polarizing beam splitter 21 are recorded as Ia(γ) and Ib(γ), and the functional relationship between Ia(γ) and Ib(γ) is recorded 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, ..., the corresponding f(γ1), f(γ2), ... are measured, and the function curve of f(γ) and γ is calibrated;

[0073] The light intensities Ia(γ) and Ib(γ) are measured in real time. According to 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 linear axis to be measured.

[0074] As a preferred solution of the present invention, a method for calculating the straightness error of the linear axis to be measured along the Y-axis and the Z-axis according to the spot position change of the split light L111″ received by the first photodetector 33 includes:

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

[0076] As a preferred solution of the present invention, the method for measuring the pitch angle and the yaw angle of the linear axis to be measured according to the light intensity change of the split light L112 received by the third photodetector 35 includes:

[0077] According to the real-time position (y) of the spot of the split light L112 received by the third photodetector 35 t ,z t ) and the change of the initial position (y0, z0) of the spot of the split light L112 recorded in the third photodetector 35, to determine the change amount of the spot position of the split light L112;

[0078] According to the change in the spot position of the split light L112, the pitch angle and the yaw angle of the linear axis to be measured around the Y axis and the Z axis are calculated to be 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 solution of the present invention, a method for measuring the positioning error of the linear axis to be measured along the X-axis in cooperation with the interferometric length measurement module 4 according to the combined light beam L3 received by the second photodetector 34 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 polarization beam splitter 12; wherein the interference length measurement module 4 includes a first non-polarization beam splitter 41 for splitting the reflected laser L2 from the emitted light L1, 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] The frequencies of the two polarized lights with frequency difference contained in the outgoing light L1 are recorded as f1 and f2 respectively. Then, when the outgoing light L1 is split by the first polarization beam splitter 12, the frequency of the split light L11 is f1, and the frequency of the split light L12 is f2. The displacement of the split light L111 along the X-axis with the target mirror unit is Δx, and the frequency change caused by the Doppler effect is f(Δx). Then the frequency of the split light L111 is f1+f(Δx). The combined light L3 received by the second photodetector 34 is used as the measurement signal of heterodyne interference length measurement, and the frequency of the measurement signal is f 测 =f1+f(Δx)-f2, the interference spot received by the fourth photodetector 43 is used as the standard signal of heterodyne interferometry, and the frequency of the standard signal is f 标 =f1-f2;

[0082] Let the frequency of the measured signal f 测 =f1+f(Δx)-f2 and the frequency f of the standard signal 标 = f1-f2 subtracted, we get f(Δx)=f 测 -f 标 , let the number of light and dark changes of the interference fringes caused by f(Δx) be N(Δx), and the laser wavelength output by the laser output module 11 be λ, then the linear 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 object to be measured along the X-axis;

[0083] When the laser emitted by the laser output module 11 is a single-frequency laser, an interference length measurement module 4 is installed between the first polarization beam splitter 12 and the second photodetector 34; wherein the interference length measurement module 4 includes a second non-polarization beam splitter 44 for splitting the transmitted light L31 and the reflected light L32 from the combined light L3, a first λ / 2 wave plate 45 for delaying the phase of 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 wave plate 45;

[0084] The transmitted light L31 is received by the second photodetector 34, and the interference spot intensity of the transmitted light L31 received by the second photodetector 34 is recorded as I2, and the interference spot intensity 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 cube prism is used as the reference light of the interference length measurement signal, and the interference measurement light L111′ is used as the measurement light of the heterodyne interference length measurement signal;

[0085] By processing I2 and I5, the number of light and dark changes 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), and the laser wavelength output by the laser output module 11 is λ. Then, the linear 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 linear axis to be measured along the X-axis.

[0086] like Figure 8 and Fig. 9 As shown, the 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 as described above to measure the six-degree-of-freedom geometric error of the measured rotating axis based on the same laser beam, including the following steps:

[0087] Step A110, the second polarization beam splitter 21, the sixth photodetector 31, the seventh photodetector 32 and the target mirror unit are integrated and installed on the rotating shaft to be measured through 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 light sensitive side of the target mirror unit;

[0088] Step A120, enabling the laser output module 11 to emit output light L1, and enabling the measuring unit to receive the light of the output light L1 distributed by the light distribution unit;

[0089] Step A130, measure the angular error of the rotation of the measured shaft around the Y-axis and the Z-axis according to the change in the spot position of the split light L112 received by the third photodetector 35, calculate the angular error of the rotation of the measured shaft around the X-axis according to the change in the light intensity of the two beams of light split by the second polarization beam splitter 21 of the split light L122 received by the sixth photodetector 31 and the seventh photodetector 32, calculate the radial runout error of the measured shaft along the Y-axis and the axial runout error along the Z-axis according to the change in the spot position of the split light L111″ received by the first photodetector 33, and measure the radial runout error of the measured shaft along the X-axis according to the combined light L3 received by the second photodetector 34 in cooperation with the interference length measurement module 4.

[0090] As a preferred solution of the present invention, in the process of measuring the angular error of the rotation of the measured shaft around the Y axis and the Z axis according to the change of the spot position of the split light L112 received by the third photodetector 35,

[0091] According to the angular error of the measured shaft rotating around the Z axis, the servo turntable 5 is controlled to rotate in the opposite direction of the measured shaft, so that the spot of the split light L112 returns to the center of the third photodetector 35 in the horizontal direction to realize servo tracking; wherein, the difference between the rotation angle of the measured shaft and the rotation angle of the servo turntable 5 is the angular positioning error.

[0092] As a preferred solution of the present invention, a method for measuring the angular error of the rotation of the measured rotating shaft around the Y axis and the Z axis according to the change of the spot position of the split light L112 received by the third photodetector 35 includes:

[0093] According to the real-time position (y) of the spot of the split light L112 received by the third photodetector 35 t ′,z t ′) and the change of the initial position (y0′, z0′) of the spot of the split light L112 recorded in the third photodetector 35, to determine the change amount of the spot position of the split light L112;

[0094] According to the change in the spot position of the split light L112, the angular errors of the rotation of the axis to be measured around the Y axis and the Z axis are calculated to be Δα′=(y t ′-y0′) / 2f and Δβ′=(z′-z0′) / 2f, where f is the focal length of the focusing lens.

[0095] As a preferred solution of the present invention, a method for calculating the radial runout error of the rotating shaft to be measured along the Y axis and the axial runout error along the Z axis according to the spot position change of the split light L111″ received by the first photodetector 33 includes:

[0096] According to the real-time position (y 1t ′,z 1t ′) and the initial position (y 10 ′,z 10 ′), determine the change in the spot position of the split light L111″, and calculate the radial runout error of the shaft to be measured along the Y axis and the axial runout error along the Z axis, respectively, Δy′=2(y 1t ′-y 10 ′) and Δz′=2(z 1t ′-z 10 ′).

[0097] As a preferred solution of the present invention, a method for calculating the angular error of the rotation of the rotating shaft to be measured around the X-axis according to the intensity change of the two beams of light split by the second polarization beam splitter 21 and the split light L122 received by the sixth photodetector 31 and the seventh photodetector 32, comprises:

[0098] The light intensities of the two reference light beams split by the second polarizing beam splitter 21 and the split light L122 received by the sixth photodetector 31 and the seventh photodetector 32 are recorded as Ia(γ′) and Ib(γ′), and the functional relationship between Ia(γ′) and Ib(γ′) is recorded as f(γ′)=[Ia(γ′)-Ib(γ′)] / [Ia(γ′)+Ib(γ′)], wherein γ′ is the angular error of the target mirror unit rotating 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 curve of f(γ′) and γ′ is calibrated;

[0100] The light intensities Ia(γ′) and Ib(γ′) are measured in real time. According to 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 axis to be measured around the X-axis.

[0101] As a preferred solution of the present invention, a method for measuring the radial runout error of the rotating shaft to be measured along the X-axis according to the combined light beam L3 received by the second photodetector in cooperation with the interferometric length measurement 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 polarization beam splitter 12; wherein the interference length measurement module 4 includes a first non-polarization beam splitter 41 for splitting the reflected laser L2 from the emitted light L1, 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] The frequencies of the two polarized lights with frequency difference contained in the outgoing light L1 are recorded as f1′ and f2′ respectively. Then, when the outgoing light L1 is split by the first polarization beam splitter 12, the frequency of the split light L11 is f1′, and the frequency of the split light L12 is f2′. The displacement of the split light L111 along the X-axis with the target mirror unit is Δx′, and the frequency change caused by the Doppler effect is f(Δx′). Then the frequency of the split light L111 is f1′+f(Δx′). The combined light L3 received by the second photodetector 34 is used as the measurement signal of heterodyne interference length measurement, and the frequency of the measurement signal is f 测′=f1′+f(Δx′)-f2′, the interference spot received by the fourth photodetector 43 is used as the standard signal of heterodyne interference length measurement, and the frequency of the standard signal is f 标 ′=f1′-f2′;

[0104] Let the frequency of the measured signal f 测 ′=f1′+f(Δx′)-f2′ and the frequency f of the standard signal 标 ′=f1′-f2′, and we get f(Δx′)=f 测 ′-f 标 ′, let the number of light and dark changes of the interference fringes caused by f(Δx′) be N(Δx′), and the laser wavelength output by the laser output module 11 be λ, then the linear 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 rotating shaft to be measured along the X-axis;

[0105] When the laser emitted by the laser output module 11 is a single-frequency laser, an interference length measurement module 4 is installed between the first polarization beam splitter 12 and the second photodetector 34; wherein the interference length measurement module 4 includes a second non-polarization beam splitter 44 for splitting the transmitted light L31 and the reflected light L32 from the combined light L3, a first λ / 2 wave plate 45 for delaying the phase of 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 wave plate 45;

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

[0107] By processing I2′ and I5′, the number of light and dark changes 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′), and the laser wavelength output by the laser output module is λ. Then, the linear 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 rotating shaft to be measured along the X-axis.

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

[0109] For the linear motion guide rail with X-axis translation (linear axis for short), Δx is the positioning error, Δy and Δz are the straightness errors, Δγ, Δα, and Δβ are the roll angle, pitch angle, and yaw angle respectively.

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

[0111] The embodiment of the present invention is described as translation along the X axis and rotation around the Z axis. In fact, translation along the Y axis and Z axis and rotation around the X axis and Y axis can be achieved by simply changing the installation method of the instrument, and the present invention does not specifically limit this.

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

[0113] As described above with reference to the accompanying drawings, the laser six-degree-of-freedom geometric error measurement system and method proposed in the present invention are described by way of example. However, those skilled in the art should understand that various improvements 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 content of the present invention. Therefore, the protection scope of the present invention should be determined by the content of the attached claims.

Claims

1. A laser six-degree-of-freedom geometric error measurement system, characterized in that: It includes a light distribution unit, a target lens unit and a measurement unit; wherein, The light distribution unit includes: a laser output module for generating an output light L1, a first polarization beam splitter for splitting the output light L1, a beam splitter for re-splitting the split light L12 of the output light L1 split by the first polarization beam splitter, a fixed corner cube prism for back-reflecting the interference reference light L121 of the split light L12 transmitted and split by the beam splitter, and a λ / 4 wave plate for changing the polarization state of the split light L11 of the output light L1 split by the first polarization beam splitter; The target mirror unit comprises: a second polarization beam splitter for re-splitting the split light L122 split by the beam splitter, a semi-transmissive and semi-reflective element for reflecting and transmitting the split light L11 passing through the λ / 4 wave plate, and a movable corner cube prism for back-reflecting the split light L111 transmitted by the semi-transmissive and semi-reflective element; The split light L111 is reflected back by the movable corner cube and passes through the first polarization beam splitter again to be split into interference measurement light L111′ and split light L111″; the split light L11 is reflected by the semi-transparent and semi-reflective element to be split light L112; the interference reference light L121 is reflected back by the fixed corner cube and forms a combined light L3 with the interference measurement light L111′; the combined light L3 interferes after passing through the first polarizer; The measuring unit comprises: a sixth photodetector and a seventh photodetector for respectively receiving two reference beams of the split light L122 split by the second polarization beam splitter, a first photodetector for receiving the split light L111″, a second photodetector for receiving the combined light L3 after interference, and a third photodetector for receiving the split light L112 focused by the focusing lens; wherein, The sixth photodetector and the seventh photodetector are used to measure the angular error of the target mirror unit rotating around the X-axis; the first photodetector is used to measure the linear error of the target mirror unit along the Y-axis and the Z-axis; the second photodetector is used to cooperate with the interference length measurement module to measure the linear error of the target mirror unit along the X-axis; the third photodetector is used to measure the angular error of the target mirror unit rotating around the Y-axis and the Z-axis.

2. The laser six-degree-of-freedom geometric error measurement system according to claim 1, characterized in that: The laser output module is a dual-frequency laser; The interference length measurement module is arranged between the laser output module and the first polarization beam splitter; the interference length measurement module includes a first non-polarization beam splitter for splitting the laser L2 from the output light L1, 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 any one of QD, PSD, CCD, and CMOS; and / or, The fourth photodetector is 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 output module is a single-frequency laser; The interference length measurement module is arranged between the first polarization beam splitter and the second photodetector; the interference length measurement module includes a second non-polarization beam splitter for splitting the transmitted light L31 and the reflected light L32 from the combined light L3, a first λ / 2 wave plate for delaying the phase of 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 wave plate.

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

6. The laser six-degree-of-freedom geometric error measurement system according to claim 1, characterized in that: The split light L11 is light transmitted by the first polarization beam splitter, and the split light L12 is light reflected by the first polarization beam splitter; or, The split light L11 is light reflected by the first polarization beam splitter, and the split light L12 is light transmitted by the first polarization 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 element is a semi-transparent and semi-reflective mirror or a semi-transparent and semi-reflective film coated on the surface of the movable corner cube prism; and / or, The first polarization beam splitter is a cubic polarization beam splitter; and / or, The second polarization beam splitter is any one of a cubic polarization beam splitter, a Wollaston prism, a Rochon polarizer, and a Glan polarization prism.

8. A linear axis laser six-degree-of-freedom geometric error measurement method, characterized in that: The laser six-degree-of-freedom geometric error measurement system according to any one of claims 1 to 7 is used to simultaneously measure the six-degree-of-freedom geometric errors of the linear axis to be measured based on the same laser beam, comprising the following steps: The second polarization beam splitter, the sixth photodetector, the seventh photodetector and the target mirror unit are integrated and installed on the linear axis to be measured; the light distribution unit, the first photodetector, the second photodetector and the third photodetector are installed on the light sensitive side of the target mirror unit; The laser emission module emits an emission light L1, and the measuring unit receives the light of the emission light L1 distributed by the light distribution unit; The roll angle of the linear axis to be measured is calculated according to the change in the intensity of the two beams of light split by the second polarization beam splitter based on the split light L122 received by the sixth photodetector and the seventh photodetector, the straightness error of the linear axis to be measured along the Y-axis and the Z-axis is calculated according to the change in the spot position of the split light L111″ received by the first photodetector, the positioning error of the linear axis to be measured along the X-axis is measured according to the combined light L3 received by the second photodetector in cooperation with the interference length measurement module, and the pitch angle and yaw angle of the linear axis to be measured are measured according to the change in the spot position of the split light 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 comprises: The light intensities of the two beams of light L122 received by the sixth photodetector and the seventh photodetector respectively and split by the second polarizing beam splitter are recorded as Ia(γ) and Ib(γ), and the functional relationship between Ia(γ) and Ib(γ) is recorded 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, ..., the corresponding f(γ1), f(γ2), ... are measured, and the function curve of f(γ) and γ is calibrated; The light intensities Ia(γ) and Ib(γ) are measured in real time, and according to the functional relationship between the Ia(γ) and the Ib(γ) and the function curve between 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 linear axis to be measured; and / or, The method for calculating the straightness error of the linear axis to be measured along the Y axis and the Z axis according to the spot position change of the split light L111″ received by the first photodetector comprises: According to the real-time position (y 1t ,z 1t) and the initial position (y 10 ,z 10 ) changes, determine the spot position change of the split light L111″, and calculate the straightness errors of the linear axis to be measured along the Y axis and the Z axis respectively. 1t -y 10 ) and Δz=2(z 1t -z 10 ); and / or, The method for measuring the pitch angle and the yaw angle of the linear axis to be measured according to the change in the spot position of the split light L112 received by the third photodetector comprises: According to the real-time position (y) of the spot of the split light L112 received by the third photodetector t ,z t ) and the change of the initial position (y0, z0) of the spot of the split light L112 recorded in the third photodetector, to determine the change amount of the spot position of the split light L112; According to the change in the spot position of the split light L112, the pitch angle and the yaw angle of the linear axis to be measured rotating around the Y axis and the Z axis are calculated to be 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 linear axis to be measured along the X-axis according to the combined light L3 received by the second photodetector in cooperation with the interferometric length measurement 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 polarization beam splitter; wherein the interference length measurement module includes a first non-polarization beam splitter for splitting the reflected laser L2 from the emitted light L1, a second polarizer for interfering with the reflected laser L2, and a fourth photodetector for receiving an interference spot formed by the interference of the reflected laser L2 by the second polarizer; The frequencies of the two polarized lights with frequency difference contained in the outgoing light L1 are recorded as f1 and f2 respectively. Then, when the outgoing light L1 is split by the first polarization beam splitter, the frequency of the split light L11 is f1, and the frequency of the split light L12 is f2. The displacement of the split light L111 along the X-axis with the target mirror unit is Δx, and the frequency change caused by the Doppler effect is f(Δx). Then the frequency of the split light L111 is f1+f(Δx). The combined light L3 received by the second photodetector is used as the measurement signal of heterodyne interference length measurement, and the frequency of the measurement signal is f 测 =f1+f(Δx)-f2, the interference spot received by the fourth photodetector is used as the standard signal of heterodyne interferometry, and the frequency of the standard signal is f 标 =f1-f2; Let the frequency f of the measurement signal 测 =f1+f(Δx)-f2 and the frequency f of the standard signal 标 = f1-f2 subtracted, we get f(Δx)=f 测 -f 标 , let the number of light and dark changes of the interference fringes caused by f(Δx) be N(Δx), the laser wavelength output by the laser emission module be λ, then the linear 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 linear axis to be measured along the X-axis; When the laser emitted by the laser emission module is a single-frequency laser, the interference length measurement module is installed between the first polarization beam splitter and the second photodetector; wherein the interference length measurement module includes a second non-polarization beam splitter for splitting the transmitted light L31 and the reflected light L32 from the combined light beam L3, a first λ / 2 wave plate 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 wave plate; The transmitted light L31 is received by the second photodetector, and the interference spot intensity of the transmitted light L31 received by the second photodetector is recorded as I2, and the interference spot intensity of the reflected light L32 received by the fifth photodetector is recorded as I5. The interference reference light L121 back-reflected by the fixed corner cube prism is used as the reference light of the interference length measurement signal, and the interference measurement light L111′ is used as the measurement light of the heterodyne interference length measurement signal; By processing I2 and I5, the number of light and dark changes 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), and the laser wavelength output by the laser output module is λ. Then, the linear 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 linear axis to be measured along the X-axis.

11. A method for measuring the six-degree-of-freedom geometric error of a rotating shaft by laser, characterized in that: The laser six-degree-of-freedom geometric error measurement system according to any one of claims 1 to 7 is used to measure the six-degree-of-freedom geometric error of the rotating shaft to be measured based on the same laser beam, comprising the following steps: The second polarization beam splitter, the sixth photodetector, the seventh photodetector and the target mirror unit are integrated and installed on the rotating shaft to be measured through a servo turntable; the light distribution unit, the first photodetector, the second photodetector and the third photodetector are installed on the light sensitive side of the target mirror unit; The laser emission module emits an emission light L1, and the measuring unit receives the light of the emission light L1 distributed by the light distribution unit; The angular error of the rotation of the rotating shaft to be measured around the Y-axis and the Z-axis is measured according to the change in the spot position of the split light L112 received by the third photodetector, the angular error of the rotation of the rotating shaft to be measured around the X-axis is calculated according to the change in the light intensity of the two beams of light split by the second polarization beam splitter of the split light L122 received by the sixth photodetector and the seventh photodetector, the radial run-out error of the rotating shaft to be measured along the Y-axis and the axial run-out error along the Z-axis are calculated according to the change in the spot position of the split light L111″ received by the first photodetector, and the radial run-out error of the rotating shaft to be measured along the X-axis is measured according to the combined light L3 received by the second photodetector in cooperation with the interference length measurement module.

12. The method for measuring the six-degree-of-freedom geometric error of a rotating shaft by laser according to claim 11, characterized in that: In the process of measuring the angular error of the rotation of the measured rotating shaft around the Y axis and the Z axis according to the change in the spot position of the split light L112 received by the third photodetector, According to the angular error of the rotating shaft to be measured around the Z axis, the servo turntable is controlled to rotate in the opposite direction of the rotation of the rotating shaft to be measured, so that the spot of the split light L112 returns to the center of the third photodetector in the horizontal direction to realize the servo tracking; wherein the difference between the rotation angle of the rotating shaft to be measured and the rotation angle of the servo turntable is the angular positioning error.

13. The method for measuring the six-degree-of-freedom geometric error of a rotating shaft by laser according to claim 11, characterized in that: The method for measuring the angular error of the rotation of the measured rotating shaft around the Y axis and the Z axis according to the change in the spot position of the split light L112 received by the third photodetector comprises: According to the real-time position (y) of the spot of the split light L112 received by the third photodetector t ′,z t ′) and the change of the initial position (y0′, z0′) of the spot of the split light L112 recorded in the third photodetector, to determine the change amount of the spot position of the split light L112; According to the change in the spot position of the split light L112, the angular errors of the rotation of the measured shaft around the Y axis and the Z axis are calculated to be Δα′=(y t ′-y0′) / 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 of the rotating shaft to be measured along the Y axis and the axial runout error along the Z axis according to the spot position change of the split light L111″ received by the first photodetector comprises: According to the real-time position (y 1t ′,z 1t ′) and the initial position (y 10 ′,z 10 ′), determine the change in the spot position of the split light L111″, and calculate the radial runout error of the measured shaft along the Y axis and the axial runout error along the Z axis 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 rotating shaft to be measured around the X-axis according to the light intensity change of the two beams of light split by the second polarization beam splitter, the split light L122 received by the sixth photodetector and the seventh photodetector, comprises: The light intensities of the two reference light beams of the split light L122 received by the sixth photodetector and the seventh photodetector respectively and split by the second polarizing beam splitter are recorded as Ia(γ′) and Ib(γ′), and the functional relationship between Ia(γ′) and Ib(γ′) is recorded as f(γ′)=[Ia(γ′)-Ib(γ′)] / [Ia(γ′)+Ib(γ′)], wherein 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′, ..., the corresponding f(γ1′), f(γ2′), ... are measured, and the function curve of f(γ′) and γ′ is calibrated; The light intensities Ia(γ′) and Ib(γ′) are measured in real time, and the rotation angle γ′ of the target mirror unit around the X-axis is calculated according to the functional relationship between the Ia(γ′) and the Ib(γ′) and the function curve of f(γ′) and γ′, so as to obtain the angular error of the rotation of the axis to be measured around the X-axis.

14. The method for measuring the six-degree-of-freedom geometric error of a rotating shaft by laser according to claim 11, characterized in that: The method for measuring the radial runout error of the rotating shaft to be measured along the X-axis according to the combined light beam L3 received by the second photodetector in cooperation with the interferometric length measurement module comprises: 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 polarization beam splitter; wherein the interference length measurement module includes a first non-polarization beam splitter for splitting the reflected laser L2 from the emitted light L1, a second polarizer for interfering with the reflected laser L2, and a fourth photodetector for receiving an interference spot formed by the interference of the reflected laser L2 by the second polarizer; The frequencies of the two polarized lights with frequency difference contained in the outgoing light L1 are recorded as f1′ and f2′ respectively. Then, when the outgoing light L1 is split by the first polarization beam splitter, the frequency of the split light L11 is f1′, and the frequency of the split light L12 is f2′. The displacement of the split light L111 along the X-axis with the target mirror unit is Δx′, and the frequency change caused by the Doppler effect is f(Δx′). Then the frequency of the split light L111 is f1′+f(Δx′). The combined light L3 received by the second photodetector is used as the measurement signal of heterodyne interference length measurement, and the frequency of the measurement signal is f 测 ′=f1′+f(Δx′)-f2′, the interference spot received by the fourth photodetector is used as the standard signal of heterodyne interferometry length measurement, and the frequency of the standard signal is f 标 ′=f1′-f2′; Let the frequency f of the measurement signal 测 ′=f1′+f(Δx′)-f2′ and the frequency f of the standard signal 标 ′=f1′-f2′, and we get f(Δx′)=f 测 ′-f 标 ′, let the number of light and dark changes of the interference fringes caused by f(Δx′) be N(Δx′), the laser wavelength output by the laser emission module is λ, then the linear 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 rotating shaft to be measured along the X-axis; When the laser emitted by the laser emission module is a single-frequency laser, the interference length measurement module is installed between the first polarization beam splitter and the second photodetector; wherein the interference length measurement module includes a second non-polarization beam splitter for splitting the transmitted light L31 and the reflected light L32 from the combined light beam L3, a first λ / 2 wave plate 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 wave plate; The transmitted light L31 is received by the second photodetector, and the interference spot intensity of the transmitted light L31 received by the second photodetector is recorded as I2′, and the interference spot intensity of the reflected light L32 received by the fifth photodetector is recorded as I5′, and the interference reference light L121 back-reflected by the fixed corner cube prism is used as the reference light of the interference length measurement signal, and the interference measurement light L111′ is used as the measurement light of the heterodyne interference length measurement signal; By processing I2′ and I5′, the number of light and dark changes 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′), and the laser wavelength output by the laser output module is λ. Then, the linear 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 rotating shaft to be measured along the X-axis.

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