Multi-axis large-angle three-degree-of-freedom ultra-precision heterodyne interferometric measuring device and method

Abstract

A multi-axis large-angle three-degree-of-freedom heterodyne interferometer measuring device and method belong to the field of laser interferometry, and solve the problems of beam mismatch and limited angle range in the existing multi-beam interferometer large-angle measurement. The device comprises a heterodyne light source, a multi-axis heterodyne interference mirror group, a multi-channel joint control target mirror and a signal processing unit. The target mirror is composed of three lenses arranged in a triangle shape and a shared mirror, and can jointly control three return measurement lights. When the measured object tilts or deviates, the three return measurement lights can still be kept within the effective receiving range of the multi-axis heterodyne interference mirror group and form a demodulable interference signal. The light source outputs three groups of frequency difference reference light beams, which form reference and measurement light paths after being split, are coupled and interfered, are photoelectrically converted, and are used to calculate the axial displacement, tilt angle and deviation angle of the measured object according to a three-point geometric series formula. The present application greatly widens the angle measurement range and improves the three-degree-of-freedom calculation stability by relying on the target mirror to cooperatively control the wavefront.

Description

Technical Field

[0001] This invention belongs to the field of laser interferometry technology, and particularly relates to a multi-axis, large-angle, three-degree-of-freedom ultra-precision heterodyne interferometry device and method. Background Technology

[0002] Laser interferometry is a fundamental core technology in precision engineering, playing a crucial role in precision metrology, high-end equipment manufacturing, and ultra-precision motion platform position measurement. With the rapid development of these fields in recent years, displacement measurement methods are expanding from traditional single-axis displacement measurement to multi-axis displacement and angular displacement composite measurement. Three-degree-of-freedom laser interferometry systems, capable of simultaneously acquiring one displacement degree of freedom and two angular degrees of freedom, have become an important development direction for precision measurement systems.

[0003] Among existing three-degree-of-freedom laser interferometry techniques, the most widely used approach is the multi-beam parallel beam measurement method. This method typically employs three or more parallel measurement beams to measure the displacement at different positions of the measured object, and then calculates the three-degree-of-freedom information of the measured object, such as displacement, pitch angle, and yaw angle, based on the geometric relationships between the measured displacements. This method has advantages such as a clear measurement principle, high displacement measurement accuracy, and traceable measurement results, thus becoming an important technical route in the current field of three-degree-of-freedom laser interferometry.

[0004] However, multi-beam parallel beam measurement methods still have significant limitations in terms of the three-degree-of-freedom angle measurement range. Firstly, these methods typically require multiple measurement beams to maintain high parallelism and stable spatial relationships. When the object under test undergoes a large angular deflection, the propagation direction of the returning measurement light from each measurement channel changes simultaneously. This can lead to problems such as increased angle between the returning measurement light and the corresponding reference light, decreased spatial overlap, and exacerbated wavefront mismatch, resulting in decreased interference contrast and, in severe cases, difficulty in forming a stable, demodulated interference signal. Secondly, multi-beam three-degree-of-freedom measurements usually rely on the stable acquisition of multiple displacement quantities. If the interference signal quality of a certain measurement channel deteriorates under large-angle conditions, it directly affects the accuracy of acquiring the corresponding displacement quantity, thus limiting the angle measurement range and joint calculation stability obtained from multiple displacement quantities. At a deeper level, multi-beam three-degree-of-freedom measurements are not simply a parallel arrangement of single displacement measurement channels. The three measurement channels act on different spatial positions of the object under test, and the propagation state of their returning measurement light is simultaneously affected by the axial displacement, pitch, and yaw motion of the object under test. If the three measurement channels each employ independent target-end reflection structures, it is difficult to guarantee that all three channels maintain a demodulated interferometric state simultaneously under the same target attitude change conditions. Once the quality of the interferometric signal of any measurement channel deteriorates under large-angle attitude changes, the geometric solution relationship between the three measured displacements will be disrupted, thereby affecting the stability of the three-degree-of-freedom solution.

[0005] Looking at the common structures of existing multi-beam three-degree-of-freedom interferometry systems, improvements typically focus on the heterodyne interferometer mirror assembly itself, the multi-channel beam layout, and signal processing and solution methods. The target end generally still uses ordinary mirrors as the reflection structure for the measurement light. The main function of this type of target-end structure is to achieve the return of the measurement light, lacking the ability to actively control the propagation state of the returned light from multiple measurement channels. Therefore, while existing technologies can improve the overall system performance by optimizing the multi-channel optical path structure, there is still a lack of direct and effective solutions for improving interference preservation capabilities under large-angle conditions and expanding the angle measurement range in multi-beam three-degree-of-freedom structures through target-end optical structures.

[0006] Therefore, it is necessary to propose a new multi-axis, large-angle, three-degree-of-freedom ultra-precision heterodyne interferometry device based on a multi-channel, wavefront-controlled target mirror. Building upon a multi-beam heterodyne interferometry system, this device introduces a target mirror structure with predetermined relative positional relationships, channel correspondences, and joint wavefront control capabilities at the target end. This allows the three measurement channels to maintain a demodulated interferometric state simultaneously even with large attitude changes in the measured object, stably obtaining three measured displacements. Furthermore, one displacement degree of freedom and two angular degrees of freedom are calculated from these three displacements, thereby improving the angle measurement range and calculation stability in multi-beam three-degree-of-freedom measurements. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a multi-axis large-angle three-degree-of-freedom ultra-precision heterodyne interferometry device and method based on a multi-channel joint wavefront-controlled target mirror. The purpose is to: in a multi-beam heterodyne interferometry system, by setting a multi-channel joint wavefront-controlled target mirror with a predetermined relative position relationship and channel correspondence at the target end, jointly control the propagation state of the return measurement light of the three spatially distributed measurement channels, so that the three measurement channels can simultaneously maintain a demodulated interferometric state when the measured object undergoes a large angular attitude change.

[0008] A further objective of this invention is to enable three measurement channels to stably obtain three measurement displacements respectively, and to calculate one displacement degree of freedom and two angular degrees of freedom of the measured object based on the predetermined geometric relationship between the three measurement positions, thereby improving the angular measurement range and calculation stability in multi-beam three-degree-of-freedom heterodyne interferometry.

[0009] The key technical focus of this invention is not on simply superimposing the number of single-axis heterodyne interferometry channels, but rather on achieving synchronous and stable acquisition of three measured displacements under large-angle attitude changes by using a multi-channel combined wavefront-controlled target mirror, the spatial interaction position relationship of the three measurement channels, and the joint calculation relationship of the three displacements. For three-degree-of-freedom measurements, the three measurement channels need to simultaneously satisfy the effective interference condition under the same attitude change condition of the measured object; failure of any measurement channel will disrupt the geometric calculation relationship between the three measured displacements. The technical solution adopted in this invention is as follows:

[0010] A multi-axis, large-angle, three-degree-of-freedom ultra-precision heterodyne interferometry device includes:

[0011] The heterodyne light source is used to emit three pairs of reference beams. The two beams in the first pair of reference beams are defined as the first input beam and the second input beam, the two beams in the second pair of reference beams are defined as the third input beam and the fourth input beam, and the two beams in the third pair of reference beams are defined as the fifth input beam and the sixth input beam. The first and second input beams have different frequencies, the third and fourth input beams have different frequencies, and the fifth and sixth input beams have different frequencies.

[0012] A multi-axis heterodyne interferometer group is used to separate a first input beam into a first measurement beam and a first reference beam, a second input beam into a second measurement beam and a second reference beam, a third input beam into a third measurement beam and a third reference beam, a fourth input beam into a fourth measurement beam and a fourth reference beam, a fifth input beam into a fifth measurement beam and a fifth reference beam, and a sixth input beam into a sixth measurement beam and a sixth reference beam.

[0013] A multi-channel joint control target mirror is used to be installed on the object under test. It reflects the second, fourth, and sixth measurement beams, which are parallel to each other, to form corresponding second, fourth, and sixth return measurement beams. The second, fourth, and sixth return measurement beams are always returned to the multi-axis heterodyne interferometer group. When the object under test undergoes axial displacement, pitch rotation, or yaw rotation during movement, the multi-channel joint control target mirror moves synchronously with the object under test, keeping the second return measurement beam parallel to the second measurement beam, the fourth return measurement beam parallel to the fourth measurement beam, and the sixth return measurement beam parallel to the sixth measurement beam.

[0014] The multi-axis heterodyne interferometer array couples the second returning measurement beam with the first reference beam to form a first measurement interference optical signal, couples the fourth returning measurement beam with the third reference beam to form a second measurement interference optical signal, couples the sixth returning measurement beam with the fifth reference beam to form a third measurement interference optical signal, couples the first measurement beam with the second reference beam to form a first reference interference optical signal, couples the third measurement beam with the fourth reference beam to form a second reference interference optical signal, and couples the fifth measurement beam with the sixth reference beam to form a third reference interference optical signal.

[0015] The photoelectric conversion unit is used to receive the first measurement interference optical signal, the second measurement interference optical signal and the third measurement interference optical signal, and couple them into a measurement interference electrical signal; and to receive the first reference interference optical signal, the second reference interference optical signal and the third reference interference optical signal, and convert them into a reference interference electrical signal.

[0016] The electronic signal processing unit is used to demodulate and process the measurement interference signal and the reference interference signal to obtain the displacement, pitch, and yaw information of the multi-channel joint control target mirror.

[0017] Furthermore, the heterodyne light source includes a single-frequency laser, an optical isolator, and a Wollaston prism arranged in sequence. An optical isolator is provided between the emitting end of the single-frequency laser and the incident end of the Wollaston prism. The two refractive ends of the Wollaston prism are respectively oriented towards the input ends of two acousto-optic frequency shifters. The output end of each acousto-optic frequency shifter is connected to one end of three main fiber couplers through optical fibers and fiber beam splitters.

[0018] Furthermore, the multi-axis heterodyne interferometer group includes a base body, and a first fiber collimator, a second fiber collimator, a third fiber collimator, a fourth fiber collimator, a fifth fiber collimator, a sixth fiber collimator, a first polarization beam splitter prism, a second polarization beam splitter prism, a first fiber coupler, a second fiber coupler, a third fiber coupler, a fourth fiber coupler, a fifth fiber coupler and a sixth fiber coupler fixed on the base body. The reflection ends of the first polarization beam splitter prism and the second polarization beam splitter prism are arranged oppositely. A half-wave plate is provided between the first polarization beam splitter prism and the second polarization beam splitter prism. The incident ends of the first polarization beam splitter prism and the second polarization beam splitter prism are arranged in the same direction. The first fiber collimator, the third fiber collimator and the fifth fiber collimator are arranged in a "pin" shape. It is set that the first fiber collimator is located at the upper end, and the third fiber collimator and the fifth fiber collimator are respectively arranged on the left and right sides of the lower end, and the output ends all face the incident end of the first polarization beam splitter prism. The second fiber collimator, the fourth fiber collimator and the sixth fiber collimator are arranged in a "pin" shape. It is set that the second fiber collimator is located at the upper end, and the fourth fiber collimator and the sixth fiber collimator are respectively arranged on the left and right sides of the lower end, and the output ends all face the incident end of the second polarization beam splitter prism. The input ends of the second fiber coupler, the fourth fiber coupler and the sixth fiber coupler face the reflection end of the second polarization beam splitter prism. The input ends of the first fiber coupler, the third fiber coupler and the fifth fiber coupler face the reflection end of the first polarization beam splitter prism;

[0019] A first reflector is provided at the transmission end of the first polarization beam splitter prism. A fifth quarter-wave plate, a first quarter-wave plate and a third quarter-wave plate arranged in a "pin" shape are provided between the first reflector and the first polarization beam splitter prism. A fourth quarter-wave plate, a second quarter-wave plate and a sixth quarter-wave plate arranged in a "pin" shape are provided at the transmission end of the second polarization beam splitter prism;

[0020] The multi-channel joint control target mirror is arranged on the transmission end path of the second polarization beam splitter prism. The output ends of the first fiber coupler, the third fiber coupler and the fifth fiber coupler are respectively connected to the electronic signal processing unit through an optoelectronic conversion unit. The output ends of the second fiber coupler, the fourth fiber coupler and the sixth fiber coupler are respectively connected to the electronic signal processing unit through another optoelectronic conversion unit.

[0021] Further, a first polarizing beam splitter prism has a first polarizer, a third polarizer, and a fifth polarizer arranged in a "pin" shape at its incident end. On the side of the first polarizing beam splitter prism facing the second fiber coupler, there are a fourteenth quarter-wave plate, an eleventh quarter-wave plate, and a twelfth quarter-wave plate arranged in a "pin" shape. A tenth polarizer is provided between the fourteenth quarter-wave plate and the first polarizing beam splitter prism, a twelfth polarizer is provided between the eleventh quarter-wave plate and the first polarizing beam splitter prism, and an eleventh polarizer is provided between the twelfth quarter-wave plate and the first polarizing beam splitter prism;

[0022] A second polarizing beam splitter prism has a sixth polarizer, a second polarizer, and a fourth polarizer arranged in a "pin" shape at its incident end. On the side of the second polarizing beam splitter prism facing the first fiber coupler, there are a seventh quarter-wave plate, an eighth quarter-wave plate, and a ninth quarter-wave plate arranged in a "pin" shape. A seventh polarizer is provided between the seventh quarter-wave plate and the second polarizing beam splitter prism, a ninth polarizer is provided between the eighth quarter-wave plate and the second polarizing beam splitter prism, and an eighth polarizer is provided between the ninth quarter-wave plate and the second polarizing beam splitter prism.

[0023] Further, the multi-channel joint control objective lens includes a second reflector and a first lens, a second lens, and a third lens arranged in a "pin" shape. The first lens, the second lens, and the third lens are closer to the second polarizing beam splitter prism than the second reflector.

[0024] The present invention also provides a multi-axis large-angle three-degree-of-freedom ultra-precision heterodyne interference measurement method, which is realized based on the above-mentioned multi-axis large-angle three-degree-of-freedom ultra-precision heterodyne interference measurement device, and includes the following steps:

[0025] Step 1: Determine the relative position relationship between the first lens, the second lens, the third lens and the second reflector, and determine the installation position of the multi-channel joint control objective lens relative to the multi-axis heterodyne interference lens group, so that when the measured object moves within a predetermined axial displacement, pitch, and yaw range, the return measurement beams of the three measurement channels can all be kept within the effective reception range of the multi-axis heterodyne interference lens group;

[0026] Step 2: Install the multi-channel joint control objective lens on the measured object, use the three positions on the measured object corresponding to the first lens, the second lens, and the third lens one by one as measurement positions, and use the midpoint of the connection line of the two lower measurement positions as a reference point, so that the multi-channel joint control objective lens moves synchronously along the measurement direction with the measured object, and rotates synchronously with the measured object when the measured object undergoes pitch or yaw motion;

[0027] Step 3: The single-frequency light emitted by the single-frequency laser enters the Wollaston prism after passing through an optical isolator and is split into o-beams and e-beams. The o-beams and e-beams are then frequency-shifted by corresponding acousto-optic frequency shifters. The o-beams are split into first, third, and fifth input beams of the same frequency by corresponding fiber beam splitters. The e-beams are split into second, fourth, and sixth input beams of the same frequency by corresponding fiber beam splitters. The first and second input beams form a pair of reference beams, the third and fourth input beams form a pair of reference beams, and the fifth and sixth input beams form a pair of reference beams. The first, third, fifth, second, fourth, and sixth input beams are then transmitted to the multi-axis heterodyne interferometer group via corresponding main fiber couplers.

[0028] Step 4: The first input beam is transmitted through an optical fiber to the first fiber collimator, and then separated by the first polarizing beam splitter into a first measurement beam emitted from the transmission end of the first polarizing beam splitter and a first reference beam emitted from the refraction end of the first polarizing beam splitter. The first reference beam is directed toward the first fiber coupler, and the first measurement beam is directed toward the first reflector. The beam is then reflected back to the first polarizing beam splitter by the first reflector and refracted before being directed toward the second fiber coupler.

[0029] The second input beam is transmitted through an optical fiber to the second fiber collimator, and then split by the second polarization beam splitter into a second measurement beam emitted from the transmission end of the second polarization beam splitter and a second reference beam emitted from the refraction end of the second polarization beam splitter. The second reference beam is directed toward the second fiber coupler. The second measurement beam is directed toward the multi-channel joint control target mirror, and then reflected to form a second return measurement beam that returns to the second polarization beam splitter and is refracted toward the first fiber coupler.

[0030] The third input beam is transmitted through an optical fiber to the third fiber collimator, and then split by the first polarizing beam splitter into a third measurement beam emitted from the transmission end of the first polarizing beam splitter and a third reference beam emitted from the refraction end of the first polarizing beam splitter. The third reference beam is directed toward the third fiber coupler, and the third measurement beam is directed toward the first reflector. The beam is then reflected back to the first polarizing beam splitter by the first reflector and refracted toward the fourth fiber coupler.

[0031] The fourth input beam is transmitted through an optical fiber to the fourth fiber collimator, and then split by the second polarization beam splitter into a fourth measurement beam emitted from the transmission end of the second polarization beam splitter and a fourth reference beam emitted from the refraction end of the second polarization beam splitter. The fourth reference beam is directed toward the fourth fiber coupler. The fourth measurement beam is directed toward the multi-channel joint control target mirror, and then reflected to form a fourth return measurement beam that returns to the second polarization beam splitter and is refracted toward the third fiber coupler.

[0032] The fifth input beam is transmitted through an optical fiber to the fifth fiber collimator, and then split by the first polarizing beam splitter into a fifth measurement beam emitted from the transmission end of the first polarizing beam splitter and a fifth reference beam emitted from the refraction end of the first polarizing beam splitter. The fifth reference beam is directed toward the fifth fiber coupler, and the fifth measurement beam is directed toward the first reflector. The beam is then reflected back to the first polarizing beam splitter by the first reflector and refracted toward the sixth fiber coupler.

[0033] The sixth input beam is transmitted through an optical fiber to the sixth fiber collimator, and then split by the second polarization beam splitter into a sixth measurement beam emitted from the transmission end of the second polarization beam splitter and a sixth reference beam emitted from the refraction end of the second polarization beam splitter. The sixth reference beam is directed toward the sixth fiber coupler. The sixth measurement beam is directed toward the multi-channel joint control target mirror, and then reflected to form the sixth return measurement beam, which returns to the second polarization beam splitter and is refracted toward the fifth fiber coupler.

[0034] Step 5: The first fiber coupler couples the first reference beam and the second return measurement beam to form the first measurement interference optical signal; the second fiber coupler couples the second reference beam and the first measurement beam to form the first reference interference optical signal; the third fiber coupler couples the third reference beam and the fourth return measurement beam to form the second measurement interference optical signal; the fourth fiber coupler couples the fourth reference beam and the third measurement beam to form the second reference interference optical signal; the fifth fiber coupler couples the fifth reference beam and the sixth return measurement beam to form the third measurement interference optical signal; and the sixth fiber coupler couples the sixth reference beam and the fifth measurement beam to form the third reference interference optical signal.

[0035] Step 6: The photoelectric conversion unit converts the first measurement interference optical signal, the second measurement interference optical signal, and the third measurement interference optical signal into measurement interference electrical signals, and converts the first reference interference optical signal, the second reference interference optical signal, and the third reference interference optical signal into reference interference electrical signals;

[0036] Step 7: Let the displacement of the reference point along the measurement direction be Z, the pitch angle of the object being measured be denoted as α, and the yaw angle of the object being measured be denoted as ψ. When the object being measured performs one or more of the following actions along the measurement direction: displacement, pitch, and yaw, let the displacement of the upper measurement position along the measurement direction be L1, and the displacements of the two lower measurement positions along the measurement direction be L2 and L3, respectively. Then L1, L2, and L3 satisfy equations (1)-(3):

[0037] (1)

[0038] (2)

[0039] (3)

[0040] In the formula, s is the distance between the measurement position above and the reference point;

[0041] q is the distance between the two measurement locations below;

[0042] Solving from equations (1) to (3) yields:

[0043] (4)

[0044] (5)

[0045] (6)

[0046] The electronic signal processing unit demodulates and processes the measured interference signal and the reference interference signal to obtain the displacement Z, pitch angle α, and yaw angle ψ of the multi-channel joint control target mirror.

[0047] Furthermore, the first input beam is incident on the first polarizing beam splitter through the first polarizer, the second input beam is incident on the second polarizing beam splitter through the second polarizer, the third input beam is incident on the first polarizing beam splitter through the third polarizer, the fourth input beam is incident on the second polarizing beam splitter through the fourth polarizer, the fifth input beam is incident on the first polarizing beam splitter through the fifth polarizer, and the sixth input beam is incident on the second polarizing beam splitter through the sixth polarizer. The first measurement beam exits and returns after passing through the first quarter-wave plate, and after refraction, passes through the eleventh and twelfth quarter-wave plates before being directed towards the second fiber coupler. The second measurement beam passes through the second quarter-wave plate before being directed towards the second fiber coupler. The second returning measurement beam returns to the second polarizing beam splitter through the second quarter-wave plate, and after refraction, passes through the eighth and ninth quarter-wave plates. The third measurement beam is emitted and returned through the third quarter-wave plate, then refracted and emitted through the twelfth and eleventh quarter-wave plates to the fourth fiber coupler. The fourth measurement beam is emitted through the fourth quarter-wave plate, and the fourth returned measurement beam returns to the second polarizing beam splitter through the fourth quarter-wave plate. After refraction, it is emitted and emitted through the seventh and seventh quarter-wave plates to the third fiber coupler. The fifth measurement beam is emitted and returned through the fifth quarter-wave plate, then refracted and emitted through the tenth and eleventh quarter-wave plates to the sixth fiber coupler. The sixth measurement beam is emitted through the sixth quarter-wave plate, and the sixth returned measurement beam returns to the second polarizing beam splitter through the sixth quarter-wave plate. After refraction, it is emitted and emitted through the ninth and eighth quarter-wave plates to the fifth fiber coupler.

[0048] The first reference beam is directed to the first fiber coupler via the eighth polarizer and the ninth quarter-wave plate; the second reference beam is directed to the second fiber coupler via the second quarter-wave plate; the third reference beam is directed to the third fiber coupler via the seventh polarizer and the seventh quarter-wave plate; the fourth reference beam is directed to the fourth fiber coupler via the twelfth polarizer and the eleventh quarter-wave plate; the fifth reference beam is directed to the fifth fiber coupler via the ninth polarizer and the eighth quarter-wave plate; and the sixth reference beam is directed to the sixth fiber coupler via the tenth polarizer and the eleventh quarter-wave plate. All beams propagating between the second polarizing beam splitter and the first polarizing beam splitter pass through a half-wave plate.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0050] 1. This invention sets up a multi-channel joint wavefront-controlled target mirror at the target end of a multi-axis three-degree-of-freedom heterodyne interferometry system, so that the three measurement channels are respectively controlled at the channel level by corresponding lenses and the same reflector. This structure is different from the simple parallel arrangement of multiple single-axis target end structures, but is a joint target end control structure formed to meet the requirement of simultaneous stable return of the three measurement channels in three-degree-of-freedom measurement.

[0051] 2. This invention can jointly control the propagation state of the return measurement light of the three measurement channels when the object under test undergoes large pitch or yaw motion, so that the three measurement channels can simultaneously maintain a demodulated interference state, thereby stably obtaining the three measurement displacements L1, L2 and L3, and avoiding the instability of the three-degree-of-freedom solution caused by the deterioration of the interference signal quality of any measurement channel.

[0052] 3. Based on the synchronous and stable acquisition of three measured displacements, this invention calculates one displacement degree of freedom and two angular degrees of freedom of the measured object according to the predetermined geometric relationship between the three measurement positions. Therefore, it can improve the angle measurement range and calculation stability of the multi-beam three-degree-of-freedom heterodyne interferometry system under large angle attitude change conditions. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the structure of the device of the present invention;

[0054] Figure 2 This is a schematic diagram of the heterodyne light source.

[0055] Figure 3 This is a schematic diagram of the structure of a multi-axis heterodyne interference mirror group;

[0056] Figure 4 A schematic diagram showing the placement of polarizers and waveplates on the second polarizing beam splitter and the first polarizing beam splitter;

[0057] Figure 5 A schematic diagram showing the polarizer and waveplate on the second polarizing beam splitter and the first polarizing beam splitter from another perspective;

[0058] Figure 6 This is a schematic diagram of the structure of a multi-channel jointly controlled target mirror;

[0059] Figure 7 A schematic diagram showing the second, fourth, and sixth measurement beams directed onto the multi-channel joint control target mirror;

[0060] Figure 8 This is a schematic diagram showing the three measurement locations and their geometric parameters s and q.

[0061] In the diagram, 1. Heterodyne light source, 11. Single-frequency laser, 12. Optical isolator, 13. Wollaston prism, 14. Acousto-optic frequency shifter, 15. Fiber beam splitter, 16. Main fiber coupler, 2. Multi-axis heterodyne interferometer group, 21. Third fiber collimator, 22. First fiber collimator, 23. Fifth fiber collimator, 24. Sixth fiber collimator, 25. Second fiber collimator, 26. Fourth fiber collimator, 27. Third fiber coupler, 28. First fiber coupler, 29. Fifth fiber coupler, 210. Second polarizing beam splitter, 211. First polarizing beam splitter, 212. Sixth fiber coupler, 213. Second fiber coupler, 214. Fourth fiber coupler, 215. Third polarizer, 216. First polarizer, 217. Fifth polarizer, 218. 219. Sixth polarizer, 220. Second polarizer, 221. Fourth polarizer, 222. Seventh quarter-wave plate, 223. Eighth polarizer, 224. Ninth polarizer, 225. Eighth quarter-wave plate, 226. Ninth quarter-wave plate, 227. Fourth quarter-wave plate, 228. Second quarter-wave plate, 229. Sixth quarter-wave plate, 230. Fifth quarter-wave plate, 231. First quarter-wave plate, 232. Third quarter-wave plate, 233. Tenth polarizer, 234. Eleventh quarter-wave plate, 235. Eleventh polarizer, 236. Twelfth polarizer, 237. Eleventh quarter-wave plate, 238. Twelfth quarter-wave plate, 239. Half-wave plate, 3. Multi-channel joint control target mirror, 31. First lens, 32. Second lens, 33. Third lens, 34. Second reflecting mirror, 4. 5. Photoelectric conversion unit, 61. Electronic signal processing unit, 62. Second measuring beam, 63. Fourth measuring beam, 64. Sixth measuring beam. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described below with reference to specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0063] The connections mentioned in this invention are divided into fixed connections and detachable connections. Fixed connections, also known as non-detachable connections, include but are not limited to conventional fixed connection methods such as folded connections, riveted connections, adhesive connections, and welded connections. Detachable connections include but are not limited to conventional disassembly methods such as bolted connections, snap-fit ​​connections, pin connections, and hinged connections. When a specific connection method is not explicitly defined, it is assumed that at least one existing connection method can be found to achieve this function, and those skilled in the art can choose according to their needs. For example, a welded connection can be chosen for fixed connections, and a bolted connection can be chosen for detachable connections.

[0064] The present invention will be further described in detail below with reference to the accompanying drawings. The following embodiments are explanations of the present invention, but the present invention is not limited to the following embodiments.

[0065] Example 1: As Figures 1 to 7 As shown, a multi-axis, large-angle, three-degree-of-freedom ultra-precision heterodyne interferometry device includes:

[0066] Heterodyne light source 1 is used to emit three pairs of reference beams. The two beams in the first pair of reference beams are defined as the first input beam and the second input beam, the two beams in the second pair of reference beams are defined as the third input beam and the fourth input beam, and the two beams in the third pair of reference beams are defined as the fifth input beam and the sixth input beam. The first input beam and the second input beam have different frequencies, the third input beam and the fourth input beam have different frequencies, and the fifth input beam and the sixth input beam have different frequencies.

[0067] The multi-axis heterodyne interferometer group 2 is used to separate the first input beam into a first measurement beam and a first reference beam, the second input beam into a second measurement beam 61 and a second reference beam, the third input beam into a third measurement beam and a third reference beam, the fourth input beam into a fourth measurement beam 62 and a fourth reference beam, the fifth input beam into a fifth measurement beam and a fifth reference beam, and the sixth input beam into a sixth measurement beam 63 and a sixth reference beam.

[0068] The multi-channel joint control target mirror 3 is used to be installed on the object under test. It reflects the second measurement beam 61, the fourth measurement beam 62, and the sixth measurement beam 63, which are parallel to each other, to form corresponding second return measurement beams, fourth return measurement beams, and sixth return measurement beams. The second return measurement beam, the fourth return measurement beam, and the sixth return measurement beam always return to the multi-axis heterodyne interferometer group 2. When the object under test undergoes axial displacement, pitch rotation, or yaw rotation during movement, the multi-channel joint control target mirror 3 moves synchronously with the object under test, so that the second return measurement beam remains parallel to the second measurement beam 61, the fourth return measurement beam remains parallel to the fourth measurement beam 62, and the sixth return measurement beam remains parallel to the sixth measurement beam 63.

[0069] The multi-axis heterodyne interferometer group 2 couples the second returning measurement beam with the first reference beam to form a first measurement interference optical signal, couples the fourth returning measurement beam with the third reference beam to form a second measurement interference optical signal, couples the sixth returning measurement beam with the fifth reference beam to form a third measurement interference optical signal, couples the first measurement beam with the second reference beam to form a first reference interference optical signal, couples the third measurement beam with the fourth reference beam to form a second reference interference optical signal, and couples the fifth measurement beam with the sixth reference beam to form a third reference interference optical signal.

[0070] The photoelectric conversion unit 4 is used to receive the first measurement interference optical signal, the second measurement interference optical signal and the third measurement interference optical signal, and couple them into a measurement interference electrical signal; and to receive the first reference interference optical signal, the second reference interference optical signal and the third reference interference optical signal, and convert them into a reference interference electrical signal.

[0071] The electronic signal processing unit 5 is used to demodulate and process the measurement interference signal and the reference interference signal to obtain the displacement information, pitch angle information and yaw angle information of the multi-channel joint control target mirror 3.

[0072] Since the second measurement beam 61, the fourth measurement beam 62, and the sixth measurement beam 63 all undergo two-way propagation after being incident on the multi-channel joint control target mirror 3 and then reflected, the multi-channel joint control target mirror 3 can jointly control the propagation state of the second, fourth, and sixth return measurement beams, so that when the measured object undergoes a large pitch or yaw motion, the second, fourth, and sixth return measurement beams can simultaneously maintain a demodulated interference state.

[0073] The heterodyne light source 1 includes a single-frequency laser 11, an optical isolator 12, and a Wollaston prism 13 arranged in sequence. An optical isolator 12 is provided between the emission end of the single-frequency laser 11 and the incident end of the Wollaston prism 13. The two refraction ends of the Wollaston prism 13 respectively face the input ends of two acousto-optic frequency shifters 14. The output end of each acousto-optic frequency shifter 14 is connected to one end of three main fiber couplers 16 through an optical fiber and an optical fiber splitter 15.

[0074] The multi-axis heterodyne interferometer group 2 includes a base body, and a first fiber collimator 22, a second fiber collimator 25, a third fiber collimator 21, a fourth fiber collimator 26, a fifth fiber collimator 23, a sixth fiber collimator 24, a first polarization beam splitter prism 211, a second polarization beam splitter prism 210, a first fiber coupler 28, a second fiber coupler 213, a third fiber coupler 27, a fourth fiber coupler 214, a fifth fiber coupler 29, and a sixth fiber coupler 212 fixed on the base body. The reflection ends of the first polarization beam splitter prism 211 and the second polarization beam splitter prism 210 are arranged oppositely. A half-wave plate 239 is provided between the first polarization beam splitter prism 211 and the second polarization beam splitter prism 210. The incident ends of the first polarization beam splitter prism 211 and the second polarization beam splitter prism 210 are arranged in the same direction. The first fiber collimator 22, the third fiber collimator 21, and the fifth fiber collimator 23 are arranged in a "pin" shape. It is set that the first fiber collimator 22 is located at the upper end, and the third fiber collimator 21 and the fifth fiber collimator 23 are respectively arranged on the left and right sides at the lower end, and the output ends all face the incident end of the first polarization beam splitter prism 211. The second fiber collimator 25, the fourth fiber collimator 26, and the sixth fiber collimator 24 are arranged in a "pin" shape. It is set that the second fiber collimator 25 is located at the upper end, and the fourth fiber collimator 26 and the sixth fiber collimator 24 are respectively arranged on the left and right sides at the lower end, and the output ends all face the incident end of the second polarization beam splitter prism 210. The input ends of the second fiber coupler 213, the fourth fiber coupler 214, and the sixth fiber coupler 212 arranged in a "pin" shape face the reflection end of the second polarization beam splitter prism 210. The input ends of the first fiber coupler 28, the third fiber coupler 27, and the fifth fiber coupler 29 arranged in a "pin" shape face the reflection end of the first polarization beam splitter prism 211;

[0075] A first mirror is provided at the transmission end of the first polarization beam splitter prism 211. A fifth quarter-wave plate 230, a first quarter-wave plate 231, and a third quarter-wave plate 232 arranged in a "pin" shape are provided between the first mirror and the first polarization beam splitter prism 211. A fourth quarter-wave plate 227, a second quarter-wave plate 228, and a sixth quarter-wave plate 229 arranged in a "pin" shape are provided at the transmission end of the second polarization beam splitter prism 210;

[0076] The multi-channel joint regulation target mirror 3 is arranged on the transmission end path of the second polarization beam splitter prism 210. The output ends of the first fiber coupler 28, the third fiber coupler 27 and the fifth fiber coupler 29 are respectively connected to the electronic signal processing unit 5 through an optoelectronic conversion unit 4, and the output ends of the second fiber coupler 213, the fourth fiber coupler 214 and the sixth fiber coupler 212 are respectively connected to the electronic signal processing unit 5 through another optoelectronic conversion unit 4.

[0077] The incident end of the first polarization beam splitter prism 211 is arranged with a first polarizer 216, a third polarizer 215 and a fifth polarizer 217 in a "pin" shape. On the side of the first polarization beam splitter prism 211 facing the second fiber coupler 213, there are a fourteenth quarter-wave plate 234, an eleventh quarter-wave plate 237 and a twelfth quarter-wave plate 238 arranged in a "pin" shape. There is a tenth polarizer 233 between the fourteenth quarter-wave plate 234 and the first polarization beam splitter prism 211, a twelfth polarizer 236 between the eleventh quarter-wave plate 237 and the first polarization beam splitter prism 211, and an eleventh polarizer 235 between the twelfth quarter-wave plate 238 and the first polarization beam splitter prism 211;

[0078] The incident end of the second polarization beam splitter prism 210 is arranged with a sixth polarizer 218, a second polarizer 219 and a fourth polarizer 220 in a "pin" shape. On the side of the second polarization beam splitter prism 210 facing the first fiber coupler 28, there are a seventh quarter-wave plate 222, an eighth quarter-wave plate 225 and a ninth quarter-wave plate 226 arranged in a "pin" shape. There is a seventh polarizer 221 between the seventh quarter-wave plate 222 and the second polarization beam splitter prism 210, a ninth polarizer 224 between the eighth quarter-wave plate 225 and the second polarization beam splitter prism 210, and an eighth polarizer 223 between the ninth quarter-wave plate 226 and the second polarization beam splitter prism 210.

[0079] The multi-channel joint regulation target mirror 3 includes a second reflector 34 and a first lens 31, a second lens 32 and a third lens 33 arranged in a "pin" shape. The first lens 31, the second lens 32 and the third lens 33 are closer to the second polarization beam splitter prism 210 than the second reflector 34. The second measurement beam 61 passes through the first lens 31 and then shoots to the second reflector 34, and is reflected to form a second return beam passing through the first lens 31. The fourth measurement beam 62 passes through the second lens 32 and then shoots to the second reflector 34, and is reflected to form a fourth return measurement beam passing through the third lens 33. The sixth measurement beam 63 passes through the third lens 33 and then shoots to the second reflector 34, and is reflected to form a sixth return measurement beam passing through the second lens 32.

[0080] The three components arranged in a "pin" shape in each group have corresponding positions, that is, they are all set according to the propagation paths corresponding to the first measurement beam, the first reference beam, the second measurement beam 61, the second reference beam, the third measurement beam, the third reference beam, the fourth measurement beam 62, the fourth reference beam, the fifth measurement beam, the fifth reference beam, the sixth measurement beam 63 and the sixth reference beam, ensuring that each beam can pass through the corresponding optical element.

[0081] Embodiment 2: As Figures 1 to 8 shown, a multi-axis large-angle three-degree-of-freedom ultra-precision heterodyne interference measurement method is realized based on the multi-axis large-angle three-degree-of-freedom ultra-precision heterodyne interference measurement device described in Embodiment 1, and includes the following steps:

[0082] Step 1: Determine the relative position relationship between the first lens 31, the second lens 32, the third lens 33 and the second mirror 34, and determine the installation position of the multi-channel joint control target mirror 3 relative to the multi-axis heterodyne interferometer group 2, so that when the measured object moves within the predetermined axial displacement, pitch and yaw ranges, the return measurement beams of the three measurement channels where the second measurement beam 61, the fourth measurement beam 62 and the sixth measurement beam 63 are located can all remain within the effective reception range of the multi-axis heterodyne interferometer group 2;

[0083] Specifically, first, according to the spatial positions of the second measurement beam 61, the fourth measurement beam 62 and the sixth measurement beam 63 at the output of the multi-axis heterodyne interferometer group 2, determine the central positions of the first lens 31, the second lens 32 and the third lens 33, so that the first lens 31, the second lens 32 and the third lens 33 are respectively arranged on the corresponding optical paths of the second measurement beam 61, the fourth measurement beam 62 and the sixth measurement beam 63, and make the optical axes of the first lens 31, the second lens 32 and the third lens 33 coincide with the central optical axes of the corresponding second measurement beam 61, the fourth measurement beam 62 and the sixth measurement beam 63;

[0084] According to the three measurement position relationships required for three-degree-of-freedom calculation, determine the "pin" shape arrangement dimensions of the first lens 31, the second lens 32 and the third lens 33. Let the midpoint of the connection line between the two lower measurement positions be used as the reference point, and the distance from the upper measurement position to the reference point be s, and the distance between the two lower measurement positions be q. Among them, s is determined according to the predetermined pitch angle measurement range of the measured object, the pitch angle resolution requirement and the installable area of the measured object; q is determined according to the predetermined yaw angle measurement range of the measured object, the yaw angle resolution requirement and the installable area of the measured object. After determining s and q, make the first lens 31, the second lens 32 and the third lens 33 respectively correspond to the above three measurement positions one by one to ensure that the three-degree-of-freedom information can be calculated subsequently.

[0085] Secondly, the axial spacing between the first lens 31, the second lens 32, the third lens 33 and the second reflector 34 is determined. The first lens 31, the second lens 32 and the third lens 33 are arranged in the same lens mounting plane, and the reflecting surface of the second reflector 34 is arranged on the image side of the mounting plane of the first lens 31, the second lens 32 and the third lens 33. The axial spacing between the first lens 31, the second lens 32, the third lens 33 and the reflecting surface of the second reflector 34 is d. When the focal length of the first lens 31, the second lens 32 and the third lens 33 is f, the axial spacing d is set to be close to the focal length f. When it is necessary to take into account the beam center position, the receiving aperture or the installation space, d is allowed to be adjusted near f so that when the multi-channel joint control target mirror 3 moves within a predetermined pitch or yaw range, the residual exit tilt angle of the second return measurement beam, the fourth return measurement beam and the sixth return measurement beam relative to the corresponding second measurement beam 61, the fourth measurement beam 62 and the sixth measurement beam 63 is limited to the effective receiving range of the multi-axis heterodyne interferometer group 2.

[0086] Next, based on the maximum permissible pitch angle and maximum permissible yaw angle of the object under test, and the effective receiving range of the multi-axis heterodyne interferometer group 2, the installation distance of the multi-channel joint control target mirror 3 relative to the multi-axis heterodyne interferometer group 2 is determined. When determining the installation position, the predetermined optical paths of the second measurement beam 61, the fourth measurement beam 62, and the sixth measurement beam 63 are respectively passed through the corresponding lenses and incident on the effective reflection area of ​​the second reflecting mirror 34; at the same time, the second, fourth, and sixth returning measurement beams are ensured to return to the corresponding receiving areas of the multi-axis heterodyne interferometer group 2 when the object under test is within the predetermined axial displacement range, predetermined pitch range, and predetermined yaw range, respectively.

[0087] Based on the beam dimensions of the second measuring beam 61, the fourth measuring beam 62, and the sixth measuring beam 63, the effective light-passing areas of the first lens 31, the second lens 32, and the third lens 33 are determined, ensuring that the effective light-passing areas of each lens cover the passage areas of the corresponding incident and return measuring beams under maximum attitude change conditions. Based on the action areas of the three measuring channels on the second reflector 34, the effective reflection area of ​​the second reflector 34 is determined, ensuring that the effective reflection area of ​​the second reflector 34 covers the spot positions of the three measuring channels under maximum axial displacement, maximum pitch, and maximum yaw conditions, with predetermined margins reserved for installation and use.

[0088] If, during the above determination process, the return measurement beam of any measurement channel cannot be kept within the effective receiving range of the multi-axis heterodyne interferometer group 2, the installation distance of the multi-channel joint control target mirror 3 relative to the multi-axis heterodyne interferometer group 2 shall be adjusted first, or the axial distance d between the first lens 31, the second lens 32, the third lens 33 and the second reflector 34 shall be adjusted; if the requirements are still not met, the effective light transmission size of the three lenses and the effective reflection area of ​​the second reflector 34 shall be adjusted, or the spatial arrangement relationship between the three measurement positions shall be redefined, until the second, fourth, and sixth return measurement beams are all within the effective receiving range of the multi-axis heterodyne interferometer group 2 within the predetermined motion range of the measured object, and can form a demodulated interference signal.

[0089] Step 2: Install the multi-channel joint control target mirror 3 on the object under test. Take the three positions on the object under test that correspond one-to-one with the first lens 31, the second lens 32 and the third lens 33 as the measurement positions. Take the midpoint of the line connecting the two measurement positions below as the reference point. Make the multi-channel joint control target mirror 3 move synchronously with the object under test along the measurement direction, and rotate synchronously with the object under test when the object under test pitches or yaws.

[0090] Step 3: The single-frequency light emitted by the single-frequency laser 11 enters the Wollaston prism 13 after passing through the optical isolator 12, and is split into o-beam and e-beam. The o-beam and e-beam are respectively frequency-shifted by the corresponding acousto-optic frequency shifter 14. The o-beam is split into the first input beam, the third input beam and the fifth input beam with the same frequency by the corresponding fiber beam splitter 15. The e-beam is split into the second input beam, the fourth input beam and the sixth input beam with the same frequency by the corresponding fiber beam splitter 15. The first input beam and the second input beam form a pair of reference beams, the third input beam and the fourth input beam form a pair of reference beams, and the fifth input beam and the sixth input beam form a pair of reference beams. The first input beam, the third input beam, the fifth input beam, the second input beam, the fourth input beam and the sixth input beam are respectively transmitted to the multi-axis heterodyne interferometer group 2 through the corresponding main fiber coupler 16.

[0091] Step 4: The first input beam is transmitted through an optical fiber to the first fiber collimator 22, and then separated by the first polarizing beam splitter 211 into a first measurement beam emitted from the transmission end of the first polarizing beam splitter 211 and a first reference beam emitted from the refraction end of the first polarizing beam splitter 211. The first reference beam is directed toward the first fiber coupler 28, and the first measurement beam is directed toward the first reflector. The beam is then reflected back to the first polarizing beam splitter 211 by the first reflector and refracted toward the second fiber coupler 213.

[0092] The second input beam is transmitted through an optical fiber to the second fiber collimator 25, and then split by the second polarization beam splitter 210 into a second measurement beam 61 emitted from the transmission end of the second polarization beam splitter 210 and a second reference beam emitted from the refraction end of the second polarization beam splitter 210. The second reference beam is directed toward the second fiber coupler 213. The second measurement beam 61 is directed toward the multi-channel joint control target mirror 3, and then reflected to form a second return measurement beam that returns to the second polarization beam splitter 210 and is refracted toward the first fiber coupler 28.

[0093] The third input beam is transmitted through an optical fiber to the third fiber collimator 21, and is split by the first polarizing beam splitter 211 into a third measurement beam emitted from the transmission end of the first polarizing beam splitter 211 and a third reference beam emitted from the refraction end of the first polarizing beam splitter 211. The third reference beam is directed toward the third fiber coupler 27, and the second measurement beam 61 is directed toward the first reflector, and then reflected back to the first polarizing beam splitter 211 by the first reflector, and refracted toward the fourth fiber coupler 214.

[0094] The fourth input beam is transmitted through an optical fiber to the fourth fiber collimator 26, and is split by the second polarization beam splitter 210 into a fourth measurement beam 62 emitted from the transmission end of the second polarization beam splitter 210 and a fourth reference beam emitted from the refraction end of the second polarization beam splitter 210. The fourth reference beam is directed toward the fourth fiber coupler 214. The fourth measurement beam 62 is directed toward the multi-channel joint control target mirror 3, and then reflected to form a fourth return measurement beam that returns to the second polarization beam splitter 210 and is refracted toward the third fiber coupler 27.

[0095] The fifth input beam is transmitted through an optical fiber to the fifth fiber collimator 23, and is split by the first polarizing beam splitter 211 into a fifth measurement beam emitted from the transmission end of the first polarizing beam splitter 211 and a fifth reference beam emitted from the refraction end of the first polarizing beam splitter 211. The fifth reference beam is directed toward the fifth fiber coupler 29, and the fifth measurement beam is directed toward the first reflector, and then reflected back to the first polarizing beam splitter 211 by the first reflector, and refracted toward the sixth fiber coupler 212.

[0096] The sixth input beam is transmitted through an optical fiber to the sixth fiber collimator 24, and then split by the second polarization beam splitter 210 into a sixth measurement beam 63 emitted from the transmission end of the second polarization beam splitter 210 and a sixth reference beam emitted from the refraction end of the second polarization beam splitter 210. The sixth reference beam is directed toward the sixth fiber coupler 212. The sixth measurement beam 63 is directed toward the multi-channel joint control target mirror 3, and then reflected to form the sixth return measurement beam, which returns to the second polarization beam splitter 210 and is refracted toward the fifth fiber coupler 29.

[0097] Step 5: The first fiber coupler 28 couples the first reference beam and the second return measurement beam to form the first measurement interference optical signal; the second fiber coupler 213 couples the second reference beam and the first measurement beam to form the first reference interference optical signal; the third fiber coupler 27 couples the third reference beam and the fourth return measurement beam to form the second measurement interference optical signal; the fourth fiber coupler 214 couples the fourth reference beam and the third measurement beam to form the second reference interference optical signal; the fifth fiber coupler 29 couples the fifth reference beam and the sixth return measurement beam to form the third measurement interference optical signal; and the sixth fiber coupler 212 couples the sixth reference beam and the fifth measurement beam to form the third reference interference optical signal.

[0098] Step 6: The photoelectric conversion unit 4 converts the first measurement interference optical signal, the second measurement interference optical signal, and the third measurement interference optical signal into measurement interference electrical signals, and converts the first reference interference optical signal, the second reference interference optical signal, and the third reference interference optical signal into measurement interference electrical signals.

[0099] Step 7: Let the displacement of the reference point along the measurement direction be Z. The measurement direction refers to the direction from the transmission end of the second polarizing beam splitter 210 toward the multi-channel joint control target mirror 3. Let the pitch angle of the object under test be α, and the yaw angle of the object under test be ψ. Pitch refers to the up-and-down rotation of the optical element around the horizontal axis, and pitch angle refers to the angle change produced when the optical element performs pitch motion. Yaw refers to the horizontal rotation of the optical element around the vertical axis, and yaw angle refers to the angle change produced when the optical element performs yaw motion. Under the small angle approximation condition, when the object under test performs one or more of the actions of displacement, pitch, and yaw along the measurement direction, let the displacement of the upper measurement position along the measurement direction be L1, and the displacements of the two lower measurement positions along the measurement direction be L2 and L3, respectively. Then L1, L2, and L3 satisfy equations (1)-(3):

[0100] (1)

[0101] (2)

[0102] (3)

[0103] In the formula, s is the distance between the measurement position above and the reference point;

[0104] q is the distance between the two measurement locations below;

[0105] Solving from equations (1) to (3) yields:

[0106] (4)

[0107] (5)

[0108] (6)

[0109] The electronic signal processing unit 5 demodulates and processes the measured interference signal and the reference interference signal to obtain the displacement Z, pitch angle α and yaw angle ψ of the multi-channel joint control target mirror 3.

[0110] The first input beam is incident on the first polarizing beam splitter 211 through the first polarizer 216; the second input beam is incident on the second polarizer 210 through the second polarizer 219; the third input beam is incident on the first polarizing beam splitter 211 through the third polarizer 215; the fourth input beam is incident on the second polarizing beam splitter 210 through the fourth polarizer 220; the fifth input beam is incident on the first polarizing beam splitter 211 through the fifth polarizer 217; and the sixth input beam is incident on the second polarizing beam splitter 210 through the sixth polarizer 218. The first measurement beam exits and returns through the first quarter-wave plate 231, and after refraction, passes through the eleventh polarizer 235 and the twelfth quarter-wave plate 238 before being directed to the second fiber coupler 213. The second measurement beam 61 passes through the second quarter-wave plate 228 before being directed to the second fiber coupler 213. The second returning measurement beam returns to the second polarizing beam splitter 210 through the second quarter-wave plate 228, and after refraction, passes through the eighth polarizer 223 and the ninth quarter-wave plate 238. Wave plate 226 is directed toward the first fiber coupler 28. The third measurement beam is emitted and returned after passing through the third quarter-wave plate 232, and after refraction, it is directed toward the fourth fiber coupler 214 after passing through the twelfth polarizer 236 and the eleventh quarter-wave plate 237. The fourth measurement beam 62 is emitted through the fourth quarter-wave plate 227. The fourth returning measurement beam returns to the second polarizing beam splitter 210 after passing through the fourth quarter-wave plate 227, and after refraction, it is directed toward the third fiber coupler 27 after passing through the seventh polarizer 221 and the seventh quarter-wave plate 222. The fifth measurement beam is emitted and returned after passing through the fifth quarter-wave plate 230, and after refraction, it is directed toward the sixth fiber coupler 212 after passing through the tenth polarizer 233 and the eleventh quarter-wave plate 234. The sixth measurement beam is emitted through the sixth quarter-wave plate 229. The sixth returning measurement beam returns to the second polarizing beam splitter 210 after passing through the sixth quarter-wave plate 229, and after refraction, it is directed toward the fifth fiber coupler 29 after passing through the ninth polarizer 224 and the eighth quarter-wave plate 225.

[0111] The first reference beam is directed to the first fiber coupler 28 via the eighth polarizer 223 and the ninth quarter-wave plate 226; the second reference beam is directed to the second fiber coupler 213 via the second quarter-wave plate 228; the third reference beam is directed to the third fiber coupler 27 via the seventh polarizer 221 and the seventh quarter-wave plate 222; the fourth reference beam is directed to the fourth fiber coupler 214 via the twelfth polarizer 236 and the eleventh quarter-wave plate 237; the fifth reference beam is directed to the fifth fiber coupler 29 via the ninth polarizer 224 and the eighth quarter-wave plate 225; and the sixth reference beam is directed to the sixth fiber coupler 212 via the tenth polarizer 233 and the eleventh quarter-wave plate 234. All beams propagating between the second polarizing beam splitter 210 and the first polarizing beam splitter 211 pass through the half-wave plate 239.

[0112] The above embodiments are merely illustrative examples of the present invention and do not limit its scope of protection. Those skilled in the art can make partial changes to them, as long as they do not exceed the spirit and essence of the present invention, they are all within the scope of protection of the present invention.

Claims

1. A multi-axis, large-angle, three-degree-of-freedom ultra-precision heterodyne interferometry measuring device, characterized in that, include: Heterodyne light source (1) is used to emit three pairs of reference beams. The first pair of reference beams is defined as the first input beam and the second input beam, the second pair of reference beams is defined as the third input beam and the fourth input beam, and the third pair of reference beams is defined as the fifth input beam and the sixth input beam. The first and second input beams have different frequencies, the third and fourth input beams have different frequencies, and the fifth and sixth input beams have different frequencies. A multi-axis heterodyne interferometer group (2) is used to separate the first input beam into a first measurement beam and a first reference beam, separate the second input beam into a second measurement beam (61) and a second reference beam, separate the third input beam into a third measurement beam and a third reference beam, separate the fourth input beam into a fourth measurement beam (62) and a fourth reference beam, separate the fifth input beam into a fifth measurement beam and a fifth reference beam, and separate the sixth input beam into a sixth measurement beam (63) and a sixth reference beam. The multi-channel joint control target mirror (3) is used to be installed on the object under test. It reflects the second measurement beam (61), the fourth measurement beam (62) and the sixth measurement beam (63) that are parallel to each other to form the corresponding second return measurement beam, the fourth return measurement beam and the sixth return measurement beam. The second return measurement beam, the fourth return measurement beam and the sixth return measurement beam always return to the multi-axis heterodyne interferometer group (2). When the object under test undergoes axial displacement, pitch rotation or yaw rotation during the movement, the multi-channel joint control target mirror (3) moves synchronously with the object under test, so that the second return measurement beam remains parallel to the second measurement beam (61), the fourth return measurement beam remains parallel to the fourth measurement beam (62), and the sixth return measurement beam remains parallel to the sixth measurement beam (63). The multi-axis heterodyne interferometer group (2) couples the second return measurement beam with the first reference beam to form a first measurement interference light signal, couples the fourth return measurement beam with the third reference beam to form a second measurement interference light signal, couples the sixth return measurement beam with the fifth reference beam to form a third measurement interference light signal, couples the first measurement beam with the second reference beam to form a first reference interference light signal, couples the third measurement beam with the fourth reference beam to form a second reference interference light signal, and couples the fifth measurement beam with the sixth reference beam to form a third reference interference light signal; The photoelectric conversion unit (4) is used to receive the first measurement interference optical signal, the second measurement interference optical signal and the third measurement interference optical signal, and convert them into measurement interference electrical signals; and to receive the first reference interference optical signal, the second reference interference optical signal and the third reference interference optical signal, and convert them into reference interference electrical signals. The electronic signal processing unit (5) is used to demodulate and process the measurement interference signal and the reference interference signal to obtain the displacement information, pitch angle information and yaw angle information of the multi-channel joint control target mirror (3).

2. The multi-axis, large-angle, three-degree-of-freedom ultra-precision heterodyne interferometry measuring device according to claim 1, characterized in that: The heterodyne light source (1) includes a single-frequency laser (11), an optical isolator (12), and a Wollaston prism (13) arranged in sequence. An optical isolator (12) is provided between the emission end of the single-frequency laser (11) and the incident end of the Wollaston prism (13). The two refraction ends of the Wollaston prism (13) respectively face the input ends of two acousto-optic frequency shifters (14). The output end of each acousto-optic frequency shifter (14) is connected to one end of three main fiber couplers (16) through an optical fiber and an optical fiber splitter (15).

3. The multi-axis, large-angle, three-degree-of-freedom ultra-precision heterodyne interferometry measuring device according to claim 2, characterized in that: The multi-axis heterodyne interferometer group (2) includes a base body and a first fiber collimator (22), a second fiber collimator (25), a third fiber collimator (21), a fourth fiber collimator (26), a fifth fiber collimator (23), a sixth fiber collimator (24), a first polarization beam splitter prism (211), a second polarization beam splitter prism (210), a first fiber coupler (28), a second fiber coupler (213), a third fiber coupler (27), a fourth fiber coupler (214), a fifth fiber coupler (29), and a sixth fiber coupler (212) fixed on the base body. The reflection ends of the first polarization beam splitter prism (211) and the second polarization beam splitter prism (210) are arranged opposite to each other. A half-wave plate (239) is provided between the first polarization beam splitter prism (211) and the second polarization beam splitter prism (210). The incident ends of the first polarization beam splitter prism (211) and the second polarization beam splitter prism (210) are arranged in the same direction. The first fiber collimator (22), the third fiber collimator (21), and the fifth fiber collimator (23) are arranged in a "pin" shape. It is set that the first fiber collimator (22) is located at the upper end, and the third fiber collimator (21) and the fifth fiber collimator (23) are respectively arranged on the left and right sides at the lower end, and the output ends all face the incident end of the first polarization beam splitter prism (211). The second fiber collimator (25), the fourth fiber collimator (26), and the sixth fiber collimator (24) are arranged in a "pin" shape. It is set that the second fiber collimator (25) is located at the upper end, and the fourth fiber collimator (26) and the sixth fiber collimator (24) are respectively arranged on the left and right sides at the lower end, and the output ends all face the incident end of the second polarization beam splitter prism (210). The input ends of the second fiber coupler (213), the fourth fiber coupler (214), and the sixth fiber coupler (212) face the reflection end of the second polarization beam splitter prism (210). The input ends of the first fiber coupler (28), the third fiber coupler (27), and the fifth fiber coupler (29) face the reflection end of the first polarization beam splitter prism (211); A first reflecting mirror is provided at the transmission end of the first polarization beam splitter prism (211). Between the first reflecting mirror and the first polarization beam splitter prism (211), there are a fifth quarter-wave plate (230), a first quarter-wave plate (231), and a third quarter-wave plate (232) arranged in a "pin" shape. At the transmission end of the second polarization beam splitter prism (210), there are a fourth quarter-wave plate (227), a second quarter-wave plate (228), and a sixth quarter-wave plate (229) arranged in a "pin" shape. The multi-channel joint control objective lens (3) is arranged on the transmission end path of the second polarization beam splitter prism (210). The output ends of the first fiber coupler (28), the third fiber coupler (27), and the fifth fiber coupler (29) are respectively connected to the electronic signal processing unit (5) through an optoelectronic conversion unit (4). The output ends of the second fiber coupler (213), the fourth fiber coupler (214), and the sixth fiber coupler (212) are respectively connected to the electronic signal processing unit (5) through another optoelectronic conversion unit (4).

4. The multi-axis, large-angle, three-degree-of-freedom ultra-precision heterodyne interferometry measuring device according to claim 3, characterized in that: At the incident end of the first polarization beam splitter prism (211), there are a first polarizer (216), a third polarizer (215), and a fifth polarizer (217) arranged in a "pin" shape. On the side of the first polarization beam splitter prism (211) facing the second fiber coupler (213), there are a fourteenth quarter-wave plate (234), an eleventh quarter-wave plate (237), and a twelfth quarter-wave plate (238) arranged in a "pin" shape. Between the fourteenth quarter-wave plate (234) and the first polarization beam splitter prism (211), there is a tenth polarizer (233). Between the eleventh quarter-wave plate (237) and the first polarization beam splitter prism (211), there is a twelfth polarizer (236). Between the twelfth quarter-wave plate (238) and the first polarization beam splitter prism (211), there is an eleventh polarizer (235). At the incident end of the second polarization beam splitter prism (210), there are a sixth polarizer (218), a second polarizer (219), and a fourth polarizer (220) arranged in a "pin" shape. On the side of the second polarization beam splitter prism (210) facing the first fiber coupler (28), there are a seventh quarter-wave plate (222), an eighth quarter-wave plate (225), and a ninth quarter-wave plate (226) arranged in a "pin" shape. Between the seventh quarter-wave plate (222) and the second polarization beam splitter prism (210), there is a seventh polarizer (221). Between the eighth quarter-wave plate (225) and the second polarization beam splitter prism (210), there is a ninth polarizer (224). Between the ninth quarter-wave plate (226) and the second polarization beam splitter prism (210), there is an eighth polarizer (223).

5. The multi-axis, large-angle, three-degree-of-freedom ultra-precision heterodyne interferometry measuring device according to claim 4, characterized in that: The multi-channel joint control target mirror (3) includes a second reflecting mirror (34) and a first lens (31), a second lens (32) and a third lens (33) arranged in a "pin" shape. The first lens (31), the second lens (32) and the third lens (33) are closer to the second polarization beam splitter prism (210) than the second reflecting mirror (34).

6. A multi-axis, large-angle, three-degree-of-freedom ultra-precision heterodyne interferometry method, implemented based on the multi-axis, large-angle, three-degree-of-freedom ultra-precision heterodyne interferometry device described in claim 5, characterized in that... It includes the following steps: Step 1: Determine the relative positional relationship between the first lens (31), the second lens (32), the third lens (33) and the second reflecting mirror (34), and determine the installation position of the multi-channel joint control target mirror (3) relative to the multi-axis heterodyne interferometer group (2), so that when the measured object moves within a predetermined axial displacement, pitch and yaw range, the return measurement beams of the three measurement channels can all remain within the effective reception range of the multi-axis heterodyne interferometer group (2); Step 2: Install the multi-channel joint control target mirror (3) on the measured object, and use the three positions on the measured object corresponding to the first lens (31), the second lens (32) and the third lens (33) one by one as measurement positions, and use the midpoint of the connection line of the two lower measurement positions as the reference point, so that the multi-channel joint control target mirror (3) moves synchronously along the measurement direction with the measured object, and rotates synchronously with the measured object when the measured object undergoes pitch or yaw movement; Step 3: The single-frequency light emitted by the single-frequency laser (11) enters the Wollaston prism (13) after passing through the optical isolator (12) and is divided into o-light and e-light. After the o-light and e-light are frequency-shifted by the corresponding acousto-optic frequency shifters (14) respectively, the o-light forms the first input beam, the third input beam and the fifth input beam with the same frequency through the corresponding fiber optic beam splitters (15), and the e-light forms the second input beam, the fourth input beam and the sixth input beam with the same frequency through the corresponding fiber optic beam splitters (15). The first input beam and the second input beam form a pair of reference beams, the third input beam and the fourth input beam form a pair of reference beams, the fifth input beam and the sixth input beam form a pair of reference beams. The first input beam, the third input beam, the fifth input beam, the second input beam, the fourth input beam and the sixth input beam are respectively transmitted to the multi-axis heterodyne interferometer group (2) through the corresponding main fiber optic couplers (16); Step 4: The first input beam is transmitted to the first fiber optic collimator (22) through the optical fiber, and is separated by the first polarization beam splitter prism (211) into a first measurement beam emitted from the transmission end of the first polarization beam splitter prism (211) and a first reference beam emitted from the refraction end of the first polarization beam splitter prism (211). The first reference beam is directed to the first fiber optic coupler (28), and the first measurement beam is directed to the first reflecting mirror, and then reflected back to the first polarization beam splitter prism (211) by the first reflecting mirror and refracted to the second fiber optic coupler (213); The second input beam is transmitted through an optical fiber to the second fiber collimator (25), and is separated by the second polarization beam splitter (210) into a second measurement beam (61) emitted from the transmission end of the second polarization beam splitter (210) and a second reference beam emitted from the refraction end of the second polarization beam splitter (210). The second reference beam is directed toward the second fiber coupler (213). The second measurement beam (61) is directed toward the multi-channel joint control target mirror (3), and then reflected to form a second return measurement beam that returns to the second polarization beam splitter (210) and is refracted toward the first fiber coupler (28). The third input beam is transmitted through an optical fiber to the third fiber collimator (21), and is separated by the first polarization beam splitter (211) into a third measurement beam emitted from the transmission end of the first polarization beam splitter (211) and a third reference beam emitted from the refraction end of the first polarization beam splitter (211). The third reference beam is directed toward the third fiber coupler (27), and the third measurement beam is directed toward the first reflector. It is then reflected back to the first polarization beam splitter (211) by the first reflector and output to the fourth fiber coupler (214) by the first polarization beam splitter (211). The fourth input beam is transmitted through an optical fiber to the fourth fiber collimator (26), and is separated by the second polarization beam splitter (210) into a fourth measurement beam (62) emitted from the transmission end of the second polarization beam splitter (210) and a fourth reference beam emitted from the refraction end of the second polarization beam splitter (210). The fourth reference beam is directed toward the fourth fiber coupler (214). The fourth measurement beam (62) is directed toward the multi-channel joint control target mirror (3), and then reflected to form the fourth return measurement beam, which returns to the second polarization beam splitter (210) and is refracted toward the third fiber coupler (27). The fifth input beam is transmitted through an optical fiber to the fifth fiber collimator (23), and is separated by the first polarization beam splitter (211) into a fifth measurement beam emitted from the transmission end of the first polarization beam splitter (211) and a fifth reference beam emitted from the refraction end of the first polarization beam splitter (211). The fifth reference beam is directed toward the fifth fiber coupler (29), and the fifth measurement beam is directed toward the first reflector. It is then reflected back to the first polarization beam splitter (211) by the first reflector and refracted toward the sixth fiber coupler (212). The sixth input beam is transmitted through an optical fiber to the sixth fiber collimator (24), and is separated by the second polarization beam splitter (210) into the sixth measurement beam (63) emitted from the transmission end of the second polarization beam splitter (210) and the sixth reference beam emitted from the refraction end of the second polarization beam splitter (210). The sixth reference beam is directed toward the sixth fiber coupler (212). The sixth measurement beam (63) is directed toward the multi-channel joint control target mirror (3), and then reflected to form the sixth return measurement beam, which returns to the second polarization beam splitter (210) and is refracted toward the fifth fiber coupler (29). Step 5: The first fiber coupler (28) couples the first reference beam and the second return measurement beam to form the first measurement interference optical signal; the second fiber coupler (213) couples the second reference beam and the first measurement beam to form the first reference interference optical signal; the third fiber coupler (27) couples the third reference beam and the fourth return measurement beam to form the second measurement interference optical signal; the fourth fiber coupler (214) couples the fourth reference beam and the third measurement beam to form the second reference interference optical signal; the fifth fiber coupler (29) couples the fifth reference beam and the sixth return measurement beam to form the third measurement interference optical signal; and the sixth fiber coupler (212) couples the sixth reference beam and the fifth measurement beam to form the third reference interference optical signal. Step 6: The photoelectric conversion unit (4) converts the first measurement interference optical signal, the second measurement interference optical signal, and the third measurement interference optical signal into measurement interference electrical signals, and converts the first reference interference optical signal, the second reference interference optical signal, and the third reference interference optical signal into reference interference electrical signals; Step 7: Let the displacement of the reference point along the measurement direction be Z, the pitch angle of the object under test be denoted as α, and the yaw angle of the object under test be denoted as ψ. Under the condition that the pitch angle and yaw angle of the object under test are within the predetermined measurement angle range, and the displacement error introduced by the angle is less than the system allowable error, when the object under test undergoes displacement, pitch and yaw attitude changes along the measurement direction, let the displacement of the upper measurement position along the measurement direction be L1, and the displacements of the two lower measurement positions along the measurement direction be L2 and L3 respectively. Then L1, L2 and L3 satisfy equations (1)-(3): ；(1) ；(2) ；(3) In the formula, s is the distance between the measurement position above and the reference point; q is the distance between the two measurement locations below; Solving from equations (1) to (3) yields: ；(4) ；(5) ； (6) The electronic signal processing unit (5) demodulates the measured interference signal and the reference interference signal to obtain the displacement Z, pitch angle α and yaw angle ψ of the multi-channel joint control target mirror (3).

7. The multi-axis, large-angle, three-degree-of-freedom ultra-precision heterodyne interferometry method according to claim 6, characterized in that: The first input beam is incident on the first polarizing beam splitter (211) through the first polarizer (216), the second input beam is incident on the second polarizing beam splitter (210) through the second polarizer (219), the third input beam is incident on the first polarizing beam splitter (211) through the third polarizer (215), the fourth input beam is incident on the second polarizing beam splitter (210) through the fourth polarizer (220), the fifth input beam is incident on the first polarizing beam splitter (211) through the fifth polarizer (217), and the sixth input beam is incident on the sixth polarizer (218). The first measurement beam passes through the first quarter-wave plate (231) and returns, then is refracted and passed through the eleventh polarizer (235) and the twelfth quarter-wave plate (238) to the second fiber coupler (213). The second measurement beam (61) passes through the second quarter-wave plate (228) to the second fiber coupler (213). The second returning measurement beam returns to the second polarizing beam splitter (210) through the second quarter-wave plate (228), then is refracted and passed through the eighth polarizer (223) and the ninth quarter-wave plate. The third measurement beam (62) is emitted from the third quarter-wave plate (232) and returns, then refracted and emitted through the twelfth polarizer (236) and the eleventh quarter-wave plate (237) to the fourth fiber coupler (214). The fourth measurement beam (62) is emitted through the fourth quarter-wave plate (227). The fourth returning measurement beam returns to the second polarizing beam splitter (210) through the fourth quarter-wave plate (227), then refracted and emitted through the seventh polarizer (221) and the seventh quarter-wave plate (222) to the fourth fiber coupler (214). The fifth measurement beam is emitted and returned through the fifth quarter-wave plate (230) to the third fiber coupler (27), and after refraction, it is emitted through the tenth polarizer (233) and the eleventh quarter-wave plate (234) to the sixth fiber coupler (212). The sixth measurement beam is emitted through the sixth quarter-wave plate (229), and the sixth returning measurement beam returns to the second polarizing beam splitter (210) through the sixth quarter-wave plate (229), and after refraction, it is emitted through the ninth polarizer (224) and the eighth quarter-wave plate (225) to the fifth fiber coupler (29). The first reference beam is directed to the first fiber coupler (28) via the eighth polarizer (223) and the ninth quarter-wave plate (226). The second reference beam is directed to the second fiber coupler (213) via the second quarter-wave plate (228). The third reference beam is directed to the third fiber coupler (27) via the seventh polarizer (221) and the seventh quarter-wave plate (222). The fourth reference beam is directed to the fourth fiber coupler (214) via the twelfth polarizer (236) and the eleventh quarter-wave plate (237). The fifth reference beam is directed to the fifth fiber coupler (29) via the ninth polarizer (224) and the eighth quarter-wave plate (225). The sixth reference beam is directed to the sixth fiber coupler (212) via the tenth polarizer (233) and the eleventh quarter-wave plate (234). All beams propagating between the second polarizing beam splitter (210) and the first polarizing beam splitter (211) pass through the half-wave plate (239).

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