WO2023070757A1

WO2023070757A1 - Three-axis high-optical subdivision grating ruler

Info

Publication number: WO2023070757A1
Application number: PCT/CN2021/130686
Authority: WO
Inventors: 韦春龙; 周常河
Original assignee: 中国科学院上海光学精密机械研究所
Priority date: 2021-11-01
Filing date: 2021-11-15
Publication date: 2023-05-04
Also published as: CN114111587B; CN114111587A

Abstract

A three-axis high-optical subdivision grating ruler, which comprises: a dual-frequency polarized parallel light and reference light generation module, non-polarizing beam splitter prisms (2, 5), a combined grating (6), a two-dimensional subdivision prism assembly (10), a two-dimensional grating (11), a heterodyne photoelectric conversion unit module (2000), and a light source driving and signal detection and processing device (30). The dual-frequency polarized parallel light and reference light generation module generates three beams of dual-frequency polarized parallel light. After passing through the non-polarizing beam splitter prism (2) and the combined grating (6), the three beams of dual-frequency polarized parallel light are incident to the two-dimensional subdivision prism assembly (10), are diffracted and reflected back and forth approximately at a Littrow angle between the two-dimensional grating (11) and the two-dimensional subdivision prism assembly (10), are finally subjected to auto-collimation and reflected back, are respectively subjected to beam combination by the combined grating (6), coincide with respective incident light beams, are then reflected by the non-polarizing beam splitter prism (5), are received by the heterodyne photoelectric conversion unit module (2000), and are further detected and processed by the light source driving and signal detection and processing device (30), so as to obtain eight-or-more-times optically subdivided displacement and angle measurements of three axes X/Y/θz of relative motion of the two-dimensional grating (11).

Description

A Three-axis High Optical Subdivision Grating Scale

technical field

The invention belongs to the field of precision optical measuring instruments, in particular to a three-axis high optical subdivision grating ruler for three-degree-of-freedom displacement and angle measurement.

Background technique

Dual-frequency heterodyne laser interferometers are widely used in displacement and angle measurement in precision motion tables, precision optical machinery, and precision measuring instruments, but they are easily affected by the environment such as temperature, humidity, and air pressure. The single-frequency laser interferometer developed in recent years also has corresponding problems. Grating scales are also called optical encoders. Among them, the grating scales based on high-density diffraction gratings have higher precision and resolution than those based on low-density ordinary geometric gratings, and can reach sub-nanometer levels. The well-designed high-density diffraction grating has the unique advantage of being free from the influence of the environment such as temperature, humidity, air pressure, etc., and is more and more favored by the industry, especially the most sophisticated equipment in the world - the lithography machine has been Use these instruments for high-precision displacement and angle measurements.

HEIDENHAIN of Germany is the first company to introduce the grating ruler based on diffraction grating, and has developed a two-axis grating ruler for two-degree-of-freedom displacement measurement. Its principle is based on its patent US4776701. The optical optical path given in this patent and its actual product use effect show that, compared with the measurement diffraction grating fixed on the surface of the measured object, the installation distance of the reading head is strictly required, and a slight movement back and forth will cause the detector on the The spot moves laterally, resulting in an error. In addition, it is difficult to expand the three-free displacement measurement of the single reading head, and the corresponding single-reading head three-axis grating scale has not been designed yet.

The two-degree-of-freedom measuring grating ruler proposed by Kao et al. (C.F.KAO, S.H.LU, et.al., Diffractive Laser Encoder with a Grating in Littrow Configuration, Jpn.J.Appl.Phys.47.1833-1837) adopts the Littrow self-collimation angle The incident measurement grating makes the installation tolerance of the grating scale reading head larger, but it is essentially two independent one-dimensional optical path structures, which are complex, difficult to manufacture, and prone to Abbe errors. In addition, the three-degree-of-freedom measurement extension is more complex.

Gao research group proposed three degrees of freedom (A.Kimura, Wei Gao, W.Kim et.al, A sub-nanometric three-axis surface encoder with short-period planar gratings for stage motion measurement, Precision Engineering 36(2013), 771-781), six degrees of freedom (X.Li, Wei Gao, et.al., A six-degree-of-freedom surface encoder for precision positioning of a planar motion stage, Precision Engineering 37(2012), 576-585 ) measurement of three-axis, six-axis grating ruler. Chinese patents CN103307986A and CN103322927B respectively provide a two-axis grating ruler for two-degree-of-freedom measurement and a three-axis grating ruler for three-degree-of-freedom measurement.

Although the above-mentioned patents have effectively expanded the degree of freedom measurement, they all have the disadvantage of low optical subdivision.

Canon of Japan proposed US5038032, US5146085, US4912320 and other patents, IBM of the United States proposed patent US5442172, and ZYGO of the United States also applied for many novel grating interferometer patents, such as US8300233B2, US0194824A1, US0114061A1, in order to obtain higher precision and resolution. Germany's Heidenhain and Japan's Sony have also introduced high-resolution grating ruler measurement systems. However, in the technical scheme represented by the above, the optical subdivision number of the grating interferometer is generally 2 or 4. High electronic subdivision is often used, such as 14bit, 16bit. Further high-bit electronic subdivision is achievable, but limited by the optical 4 subdivision resolution of the grating interferometer, it is meaningless. Therefore, further improving the optical subdivision number of the grating interferometer is of great value for actually improving the optical resolution of the grating interferometer and even the overall resolution and accuracy of the grating ruler measurement system.

As the number of measurement axes, precision and resolution requirements of high-precision equipment represented by lithography machines continue to increase, multi-axis high-optical subdivision grating scales have become a research hotspot.

Chinese patent CN104613865B proposes a prism-based high optical subdivision grating scale, which can achieve more than 8 times of optical subdivision, but it is difficult to expand to two axes and above for one axis. Cunbai Lin et al. realized two-dimensional diagonal-based heterodyne grating interferometer with enhanced signal-to-noise ratio and optical subdivision, Optical Engineering, 57(6), 064102), its structure is huge, the grid line density is not high enough, and it is difficult to realize three-axis.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the prior art by carefully designing the grating interferometer, the core component of the grating ruler. Mainly reflected in: (1) make it reach zero optical path difference, so as to avoid being affected by the environment such as temperature, humidity, air pressure, etc.; (2) can realize three-axis measurement with three degrees of freedom based on a single reading head, and the structure is compact ; (3) It is suitable for high-density two-dimensional gratings and optical subdivision of 8 times or more in three axes; (4) The grating is incident on the near-Littrow self-collimation angle, which makes the installation tolerance of the grating ruler reading head larger.

Technical solution of the present invention is as follows:

A three-axis high optical subdivision grating scale, characterized in that it includes: a dual-frequency orthogonally polarized parallel light and reference light generation module, a non-polarizing beam splitter, a combined grating, a two-dimensional subdivision prism assembly, a two-dimensional grating, Heterodyne photoelectric conversion unit module, light source drive, signal detection and processor;

The dual-frequency orthogonally polarized parallel light and reference light generation module is used to generate at least three dual-frequency orthogonally polarized parallel light beams as incident light and one dual-frequency polarized light beam as reference light, which is generated by the heterodyne photoelectric The conversion unit module receives, and after photoelectric conversion, it is driven by the light source, signal detected and processed by the processor;

The three dual-frequency orthogonally polarized parallel beams are transmitted or reflected by the non-polarizing beam splitting prism, and then split into three groups of beams by the combined grating, each group of beams is composed of two beams, and the second group The exit surfaces of the light beam and the third group of light beams are parallel to each other, and the exit surfaces of the first group of light beams are respectively perpendicular to the exit surfaces of the second group of light beams and the exit surfaces of the third group of light beams;

The grid line directions of the two dimensions of the two-dimensional grating are orthogonal and are respectively set as the X axis and the Y axis in the three axes, and the plane formed by the grid line directions of the two dimensions of the two-dimensional grating is at a right angle to the corresponding The Z axis of the coordinate system is vertical, and the central symmetry axis of the two-dimensional subdivision prism is set as the Z axis, and the rotation angle θz around the Z axis is the third axis in the three axes;

The two beams divided into each group of light beams are diffracted-reflected back and forth near the Littrow angle between the two-dimensional grating and the two-dimensional subdivision prism assembly, and finally self-collimated back into the combined grating, and the The incident light beams of each group of light beams overlap, and after being reflected or transmitted by the non-polarizing beam splitting prism, they are received by the heterodyne photoelectric conversion unit module, after photoelectric conversion, and then driven by the light source and signal detection and processor Detection processing, to obtain the displacement and angle measurement of 8 times or more optical subdivision of the X/Y/θz three-axis of the relative motion of the two-dimensional grating.

The specific principle of three-axis high optical subdivision grating ruler is as follows:

The dual-frequency orthogonally polarized light source is driven by the light source and signal detection and processor, and then emits a dual-frequency orthogonally polarized beam (including two polarization states of P light and S light), which is divided into two beams by the first non-polarizing beam splitter prism , one beam is focused on the first detector through the polarizer and lens placed at 45 degrees to the P light, and then is detected and processed by the light source drive, signal detection and processor as a heterodyne reference light signal; the other beam passes through the first One-dimensional grating diffraction is divided into three beams of 0th order and ±1st order. After the three beams are collimated by the second lens, they are respectively incident on the combined grating through the second non-polarizing beam splitting prism; the combined grating is composed of three gratings Adjacent to the composition, the middle grating line is along the Y-axis direction, and the 0th-order beam is diffracted by it to form ±1-order two beams in the X/Z plane (the 0th order is set to block the diaphragm), respectively through the two-dimensional Diffraction-reflection near the Littrow angle back and forth between the grating and the two-dimensional subdivision prism assembly, and finally after self-collimation and retroreflection, two light spots are formed on the surface of the two-dimensional grating; the self-collimation on the two-dimensional subdivision prism assembly On the transmission surface (the light beam is perpendicular to its surface), a quarter-wave plate and an optical path compensation plate are respectively provided to realize self-collimation reflection; the quarter-wave plate is used to rotate the reflected P light and S light simultaneously 90°; the self-collimated light beam is diffracted again by the intermediate grating and coincides with the incident light beam, reflected by the second non-polarizing beam splitting prism and incident on the heterodyne photoelectric conversion unit module, and then driven by the light source and Signal detection and processor detection and processing; with the help of the 4-fold Doppler frequency shift of the two-dimensional subdivision prism assembly, combined with the 2-fold Doppler frequency shift of the dual-frequency heterodyne detection principle, an 8-fold Doppler frequency shift can be obtained Le frequency shift, realize X-axis 8 times optical subdivision function. Similarly, the left grating line of the combined grating is along the X-axis direction, and the -1-order beam diffracted by the first one-dimensional grating forms ±1-order two beams in the Y/Z plane after being diffracted by the left grating. The light beam (level 0 is set to block the diaphragm) is diffracted-reflected back and forth near the Littrow angle between the two-dimensional grating and the two-dimensional subdivided prism component, and finally after self-collimation and retroreflection, two light beams are formed on the surface of the two-dimensional grating point; on the self-collimation transmission surface on the two-dimensional subdivision prism assembly, a quarter-wave plate and an optical path compensation plate are respectively arranged to realize self-collimation reflection; the quarter-wave plate is used for After reflecting the P light and the S light, they are rotated by 90° at the same time; the self-collimated beam is diffracted again by the left grating and coincides with the incident beam, reflected by the second non-polarizing beam splitter and incident on the three The axial heterodyne photoelectric conversion unit module is driven by the light source and signal detection and processor detection and processing; with the help of the 4 times Doppler frequency shift of the two-dimensional subdivision prism assembly, combined with the 2 times of the dual-frequency heterodyne detection principle Doppler frequency shift, and then 8 times Doppler frequency shift can be obtained, realizing the first Y-axis 8 times optical subdivision function.

Similarly, the grating lines on the right side of the combined grating are along the Y-axis direction, and the +1-order light beam diffracted by the first one-dimensional grating forms ± The two beams of level 1 (level 0 is set to block the diaphragm), respectively pass through the two-dimensional grating and the two-dimensional subdivision prism component to diffract-reflect back and forth near the Littrow angle, and finally after self-collimation and retroreflection, form on the surface of the two-dimensional grating 2 light points; on the self-collimation transmission surface on the two-dimensional subdivision prism assembly, a quarter-wave plate and an optical path compensation plate are respectively arranged to realize self-collimation reflection; the quarter-wave plate is used for After reflecting the P light and the S light, they are rotated by 90° at the same time; the self-collimated beam is again combined through the diffraction and combination of the right grating of the combined grating and coincides with the incident beam, and is reflected by the second non-polarizing beam splitter prism And incident on the heterodyne photoelectric conversion unit module, and then driven by the light source and signal detection and processor detection and processing, with the help of the 4 times Doppler frequency shift of the two-dimensional subdivision prism component, combined with the principle of dual-frequency heterodyne detection 2 times Doppler frequency shift, and then 8 times Doppler frequency shift of the second Y axis can be obtained, realizing 8 times optical subdivision function.

Divide by the distance of the corresponding light spot on the two-dimensional grating by the difference between the displacement of the first Y axis and the second Y axis measured after the beam splitting and self-collimation of the left and right gratings in the Y/Z plane , the relative rotation angle θz of the two-dimensional grating around the Z axis can be obtained, which also has the function of 8 times optical subdivision.

The two-dimensional subdivided prism is composed of at least two quadrangular prisms with different angles from each other, the four sides of the bottom quadrangular prism are reflective surfaces, and the top four sides of the quadrangular prism are self-collimating transmission perpendicular to the light beam. surface, the top surface of the top quadrangular prism and the bottom surface of the bottom quadrangular prism are beam transmission surfaces, which are perpendicular to the Z axis and form a quadrilateral, and its adjacent two sides are respectively parallel to the X axis and the Y axis; in the two-dimensional subdivision prism On the self-collimating transmission surface, a quarter-wave plate and an optical path compensation plate are respectively arranged at the symmetrical position of the beam to realize self-collimating reflection; each set of quarter-wave plates and optical path compensation plates, one side Symmetrically glued on the beam self-collimating transmission surface, the other side is coated with a total reflection film, and each group of exit surfaces where the combined grating is split into three groups of beams and the beam self-collimation At the midpoint of the intersection line of the transmissive surface to achieve self-collimating reflection. In order to realize the measurement of the angle θz around the Z axis, two sets of quarter-wave plates and optical path compensation plates are set in the direction of the X-axis or Y-axis to realize self-collimation reflection; the quarter-wave plates are used to reflect P light and S light to rotate it 90° at the same time.

By increasing the number of quadrangular prisms in the middle of the two-dimensional subdivision prism, thereby increasing the number of its four sides as reflecting surfaces, and optimizing the angles of the four sides of each quadrangular prism, the two-dimensional grating and the two-dimensional detail can be effectively increased. The number of diffraction-reflection times near the Littrow angle between the split prism components can further improve the optical subdivision number. Le frequency shift, combined with the 2-fold Doppler frequency shift of the dual-frequency heterodyne detection principle, can achieve 16 times the optical subdivision number; using four four-sided prisms with different angles from each other to form a two-dimensional subdivision prism, then 12 times Doppler frequency shift can be obtained, combined with the 2 times Doppler frequency shift of the dual-frequency heterodyne detection principle, 24 times optical subdivision can be achieved; and so on.

The first non-polarizing beam splitting prism is divided into two beams, one of which is used as a reference beam, which can be reflected by the second non-polarizing beam splitting prism. The polarizer and the first lens placed at 45 degrees to the P light are replaced.

The heterodyne photoelectric conversion unit module, except one unit includes a polarizer placed at 45 degrees with the P light, the first lens and the first detector, as a reference light heterodyne photoelectric conversion unit; the other three units include three groups of the same The photoelectric conversion unit of the element. Each group of photoelectric conversion units includes: a polarizing prism, a focusing lens and a detector for detecting P light, and a focusing lens and a detector for detecting S light.

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

The three-axis high optical subdivision grating ruler optical system proposed by the present invention has a symmetrical optical path, a quasi-common optical path, and zero optical path difference, which eliminates the common problems of laser dual-frequency heterodyne interferometers on temperature, humidity and Pressure-sensitive dead-range error; and, it can realize three-axis measurement with three degrees of freedom based on high-density two-dimensional grating and a single reading head, and the structure is compact; further, the optical path passes through the two-dimensional subdivision prism assembly and the close The effective combination of Littrow angle diffraction-reflection self-collimation optical path can obtain the high optical subdivision function of three-axis 8 times and above that has not been reported in domestic and foreign literature.

Description of drawings

Fig. 1 is a schematic structural view of an embodiment of a three-axis high optical subdivision grating ruler of the present invention;

Fig. 2 is the Y direction projection schematic diagram of Fig. 1 of the present invention;

Fig. 3 is the X-direction projection schematic diagram of Fig. 1 of the present invention;

4 is a schematic diagram of a two-dimensional subdivision prism assembly of the present invention;

Fig. 5 is a schematic diagram of the combined grating of the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments It is a part of embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

In the description of the present application, it should be understood that the terms "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", " The orientation or positional relationship indicated by "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, It is only for the purpose of describing the present application and simplifying the description, but does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present application. The X, Y, Z, θz, P, and S referred to in the present invention are not specific references, but relative physical meanings.

Please refer to Fig. 1. Fig. 1 is a schematic structural diagram of an embodiment of a three-axis highly optically subdivided grating ruler of the present invention. As shown in the figure, a three-axis highly optically subdivided grating ruler includes: a dual-frequency orthogonally polarized light source 1, The first non-polarizing beam splitting prism 2, the polarizer 12 placed at 45 degrees to the P light, the first lens 13, the first detector 14, the first one-dimensional grating 3, the second lens 4, the second non-polarizing beam splitting Prism 5 , combined grating 6 , two-dimensional subdivision prism assembly 10 , two-dimensional grating 11 , heterodyne photoelectric conversion unit module 2000 , light source drive and signal detection and processor 30 .

The two-dimensional grid line directions of the two-dimensional grating 11 are respectively set as the X and Y axes in the three axes, and the two-dimensional grid line directions of the two-dimensional grating 11 are orthogonal and form a plane It is perpendicular to the Z axis of the corresponding Cartesian coordinate system, and the central symmetry axis of the two-dimensional subdivision prism 1000 is set as the Z axis, and the rotation angle θz around the Z axis is the third axis in the three axes;

The two-dimensional subdivision prism assembly 10 is a core device, consisting of a two-dimensional subdivision prism 1000, three quarter wave plates 7-1, 8-1, 9-1 and corresponding three optical path compensation plates 7- 2, 8-2, 9-2 composition. The two-dimensional subdivision prism 1000 is formed by superimposing three prisms with different four side angles, the four sides 1031, 1032, 1033, 1034 of the bottom prism and the four sides 1021, 1022, 1023 of the middle prism , 1024 are reflective surfaces, the four sides 1011, 1012, 1013, and 1014 of the top quadrangular pedestal are beam self-collimating transmission surfaces (the light beam is perpendicular to its surface), and the upper top surface 100 of the top quadrangular pedestal and the lower bottom surface 104 of the bottom quadrangular pedestal are The light beam transmission surface is perpendicular to the Z axis and is in the shape of a quadrilateral, and its adjacent two sides are respectively parallel to the X axis and the Y axis; The symmetrical positions of the light beam are respectively provided with quarter-wave plates 7-1, 8-1, 9-1 and optical path compensation plates 7-2, 8-2, 9-2 to realize self-collimation reflection; Quarter-wave plates 7-1, 8-1, 9-1 and optical path compensation plates 7-2, 8-2, 9-2, one side of each plate is symmetrically glued to the beam self-collimating transmission surface The other side is coated with a total reflection film, and is located at the midpoint of the intersection of each group of exit surfaces of the combined grating 6 into three groups of beams and the self-collimating transmission surface of the beams, so as to realize self-collimation reflection.

In order to realize the measurement of the angle θ _z around the Z axis, two groups of quarter-wave plates 8-1, 9-1 and optical path compensation plates 8-2, 9-2 are arranged in the direction of the Y axis (it can also be arranged in the direction of the X axis). , not specific) to realize self-collimating reflection; the quarter-wave plates 7-1, 8-1, 9-1 are used to reflect the P light and the S light while rotating them by 90°.

The heterodyne photoelectric conversion unit module 2000 includes a first polarizing prism (27) along the X axis, a third lens 28, a second detector 29, a fourth lens 26, and a third detector 25, and includes a first polarization prism (27) along the first Y axis. Two polarizing prisms 20, a fifth lens 21, a fourth detector 22, a sixth lens 23, and a fifth detector 24. A third polarizing prism 17, a seventh lens 18, a sixth detector 19, an eighth lens 16, and a seventh detector 15 are included along the second Y axis.

The specific implementation of the three-axis highly optical subdivision grating ruler of the present invention is shown in Figure 1, and further details are as follows.

The dual-frequency orthogonally polarized light source 1 is driven by the light source and the signal detection and processor 30 to emit a dual-frequency orthogonally polarized light beam (containing two polarization states of P light and S light, and the frequencies are slightly different), and passes through the first non-polarized The beam-splitting prism 2 is divided into two beams, one of which passes through the polarizer 12 placed at 45 degrees to the P light and the first lens 13 as a reference beam, focuses on the first detector 14, and is driven by the light source and detected by the signal. The processor 30 detects and processes it as a heterodyne reference light signal; the other beam is diffracted by the one-dimensional grating 3 and is divided into three beams of 0th order and ±1st order, and the three beams are collimated by the second lens 4 and passed through the first Two non-polarizing beam-splitting prisms 5 are respectively incident on the combination grating 6; the combination grating 6 is composed of 3 gratings (as shown in Fig. Along the Y-axis direction, after the 0th-order light beam is diffracted by it, as shown in Figure 2, two beams of ±1st order are formed in the X/Z plane (0th order is set to block the diaphragm, not shown), and are respectively passed through the two beams. The two-dimensional grating 11 and the two-dimensional subdivision prism 10 are back and forth near the Littrow angle diffraction-reflection, and after the final self-collimation and retroreflection, four light spots are formed on the two-dimensional grating surface 11; the self-collimation on the two-dimensional subdivision prism 10 On the straight transmission surfaces 1011, 1012, as shown in Figure 4, a quarter-wave plate 7-1 and an optical path compensation plate 7-2 are respectively arranged to realize self-collimation reflection; the quarter-wave plate 7 -1 is used to rotate the reflected P light and S light by 90° at the same time; the self-collimated beam is again combined with the incident beam of the intermediate grating 6-2 through the diffraction of the intermediate grating 6-2, and passes through the second non-polarized The beam splitting prism 5 is reflected and incident on the first polarizing prism 27, the P light is focused on the second detector 29 through the third lens (28), the S light is focused on the third detector 25 through the fourth lens 26, and then driven by the light source and signal detection and processor 30 detection and processing; by means of the 8 times Doppler frequency shift of the above-mentioned two-dimensional subdivision prism 10, combined with the 2 times Doppler frequency shift of the dual-frequency heterodyne detection principle, more than 16 times can be obtained Puller frequency shift to achieve 16 times optical subdivision function.

In the same way, the grating 6-1 on the left is along the X-axis direction, and after the -1-order light beam is diffracted by it, as shown in Figure 3, two beams of ±1-order are formed in the Y/Z plane (0-order is set stopper, not shown), through the two-dimensional grating 11 and the two-dimensional subdivision prism 10, respectively, to and fro near Littrow angle diffraction-reflection, and finally after self-collimation retroreflection, 4 light spots are formed on the two-dimensional grating surface 11; On the self-collimation transmission surfaces 1013, 1014 on the two-dimensional subdivision prism 10, as shown in Figure 4, a quarter-wave plate 8-1 and an optical path compensation plate 8-2 are respectively arranged to realize self-collimation Reflection; the quarter-wave plate 8-1 is used to rotate the P light and the S light by 90° at the same time; the self-collimated beam is combined with the intermediate grating 6-1 through the diffraction of the intermediate grating 6-1 again The incident light beams are coincident, reflected by the second non-polarizing beam splitter prism 5 and incident on the second polarizing prism 20, the P light is focused on the fifth detector 24 through the sixth lens 23, and the S light is focused on the fourth detector through the fifth lens 21 Device 22, driven by the light source and signal detection and processor 30 detection and processing; by means of the 8 times Doppler frequency shift of the above-mentioned two-dimensional subdivision prism 10, combined with the 2 times Doppler frequency shift of the dual-frequency heterodyne detection principle , and then can obtain 16 times Doppler frequency shift, realize 16 times optical subdivision function.

The grating 6-3 grid line on the right is along the X-axis direction, and after the +1-order light beam is diffracted by it, as shown in Figure 3, two beams of ±1 order are formed in the Y/Z plane (the 0-order is to set the diaphragm to block , not shown), through the two-dimensional grating 11 and the two-dimensional subdivided prism 10 to and fro near Littrow angle diffraction-reflection, and finally after self-collimation retroreflection, 4 light spots are formed on the two-dimensional grating surface 11; On the self-collimating transmission surfaces 1013 and 1014 on the subdivision prism 10, as shown in Figure 4, a quarter-wave plate 9-1 and an optical path compensation plate 9-2 are respectively arranged to realize self-collimating reflection; The quarter-wave plate 9-1 is used to rotate the P light and the S light by 90° at the same time; the self-collimated beam is again combined with the incident beam of the intermediate grating 6-3 through the diffraction of the intermediate grating 6-3 , reflected by the second non-polarizing beam splitting prism 5 and incident on the third polarizing prism 17, the P light is focused on the sixth detector 19 through the seventh lens 18, and the S light is focused on the seventh detector 15 through the eighth lens 16, Then by light source drive and signal detection and processor 30 detection and processing; By means of the 8 times Doppler frequency shift of the two-dimensional subdivision prism 10, combined with the 2 times Doppler frequency shift of the dual-frequency heterodyne detection principle, In turn, a 16-fold Doppler frequency shift can be obtained to achieve a 16-fold optical subdivision function.

The two-dimensional grating can be obtained by dividing the difference in the Y-axis displacement measured by the left and right gratings 6-1, 6-3 after beam splitting in the Y/Z plane by the distance of the corresponding light spot on the two-dimensional grating 11 11 The relative rotation angle θz around the Z axis also has the function of 16 times optical subdivision.

In this embodiment, by increasing the number of quadrangular prisms in the middle of the two-dimensional subdivision prism 1000, thereby increasing the number of its four sides as reflecting surfaces, and optimizing the angles of the four sides of each quadrangular prism, it can effectively increase the two-dimensional grating 11 and The number of times of diffraction-reflection near the Littrow angle between the two-dimensional subdivision prism components 10 can further improve the optical subdivision number. 12 times Doppler frequency shift, combined with the 2 times Doppler frequency shift of the dual-frequency heterodyne detection principle, can obtain 24 times Doppler frequency shift and realize 24 times optical subdivision. Similarly, by reducing the number of quadrangular prisms of the two-dimensional subdivision prism 1000 to 2, and optimizing the angles of the four sides of each quadrangular prism, it is easy to obtain a 4-fold Doppler frequency shift, combined with dual-frequency heterodyne detection The principle of 2 times Doppler frequency shift, to achieve 8 times the number of optical subdivisions.

In addition, when the two-dimensional grating 11 is rotated 45° around the Z axis, the incident beam is still diffracted-reflected back and forth between the two-dimensional grating 11 and the two-dimensional subdivided prism assembly 10 at a near Littrow angle, and finally self-collimated and retroreflected into the combined grating 6, coincide with the respective incident light beams of each group of light beams, and then after being reflected or transmitted by the non-polarizing beam splitting prism 5, it is received by the heterodyne photoelectric conversion unit module 2000 and passed through the photoelectric After the conversion, the light source is driven, the signal is detected, and the processor 30 detects and processes, then the displacement and angle measurement of twice the original optical subdivision number can be obtained when the two-dimensional grating 11 is not rotated by 45° around the Z axis. In this implementation An example is 32 times optical subdivision, and so on.

The first non-polarizing beam splitting prism 2 is divided into two beams, wherein a beam of reference light can be reflected by the second non-polarizing beam splitting prism 5 and does not lead to any one beam of the three beams of the combined grating, through The polarizer 12 and the first lens 13 placed at 45 degrees to the P light are replaced.

The three-axis high optical subdivision grating ruler optical system proposed by the present invention has a symmetrical optical path, a quasi-common optical path, and zero optical path difference, which eliminates the common problems of laser dual-frequency heterodyne interferometers on temperature, humidity and Pressure-sensitive dead-range error; and, it can realize three-axis measurement based on high-density two-dimensional grating and three degrees of freedom of a single reading head, and the structure is compact; further, the optical path passes through the two-dimensional subdivision prism 10 and the two-dimensional grating The effective combination of 11 near-autocollimation optical paths can obtain the ultra-high optical subdivision function of three-axis 8 times and above that has not been reported in domestic and foreign literature.

Claims

A three-axis high optical subdivision grating scale, characterized in that it includes: a dual-frequency orthogonally polarized parallel light and reference light generation module, a non-polarizing beam splitter, a combined grating, a two-dimensional subdivision prism assembly, a two-dimensional grating, Heterodyne photoelectric conversion unit module, light source drive, signal detection and processor;

The dual-frequency orthogonally polarized parallel light and reference light generation module is used to generate at least three dual-frequency orthogonally polarized parallel light beams as incident light and one dual-frequency polarized light beam as reference light, which is generated by the heterodyne photoelectric The conversion unit module receives, and after photoelectric conversion, it is driven by the light source, signal detected and processed by the processor;

The three dual-frequency orthogonally polarized parallel beams are transmitted or reflected by the non-polarizing beam splitting prism, and then split into three groups of beams by the combined grating, each group of beams is composed of two beams, and the second group The exit surfaces of the light beam and the third group of light beams are parallel to each other, and the exit surfaces of the first group of light beams are respectively perpendicular to the exit surfaces of the second group of light beams and the exit surfaces of the third group of light beams;

The grid line directions of the two dimensions of the two-dimensional grating are orthogonal and are respectively set as the X axis and the Y axis in the three axes, and the plane formed by the grid line directions of the two dimensions of the two-dimensional grating is at a right angle to the corresponding The Z axis of the coordinate system is vertical, and the central symmetry axis of the two-dimensional subdivision prism is set as the Z axis, and the rotation angle θz around the Z axis is the third axis in the three axes;

The two beams divided into each group of light beams are diffracted-reflected back and forth near the Littrow angle between the two-dimensional grating and the two-dimensional subdivision prism assembly, and finally self-collimated back into the combined grating, and the The incident light beams of each group of light beams overlap, and after being reflected or transmitted by the non-polarizing beam splitting prism, they are received by the heterodyne photoelectric conversion unit module, after photoelectric conversion, and then driven by the light source and signal detection and processor Detection processing, to obtain the displacement and angle measurement of 8 times or more optical subdivision of the X/Y/θz three-axis of the relative motion of the two-dimensional grating.
The three-axis high optical subdivision grating ruler according to claim 1, wherein the combined grating is composed of at least two groups of one-dimensional gratings, and the grating lines of each group of gratings are perpendicular to each other, and one group of gratings can be divided into Two parts, on either side of the other set.
The three-axis high optical subdivision grating ruler according to claim 1, wherein the two-dimensional subdivision prism assembly comprises a two-dimensional subdivision prism, at least three quarter-wave plates and at least three light range compensation sheet, the two-dimensional subdivided prism is formed by stacking up and down at least two groups of quadrangular prisms, one group is a top quadrangular prism, and the four sides are beam self-collimating transmission surfaces perpendicular to the beam; the other group It is at least one quadrangular prism, the four sides of which are not perpendicular to the light beam, and the top surface of the top quadrangular prism and the bottom surface of the bottom quadrangular prism are beam transmission surfaces, perpendicular to the Z axis, in a quadrilateral shape, and the two adjacent sides parallel to the X-axis and Y-axis, respectively;

Each set of quarter-wave plates and optical path compensation plates is symmetrically glued on the self-collimating transmission surface of the beam on one side, and coated with a total reflection film on the other side, and is located at the beam splitting center of the combined grating. Each of the three groups of light beams is on the midpoint of the intersection line between the outgoing surfaces of the three groups of beams and the self-collimating transmission surface of the light beams, so as to realize self-collimating reflection.
The three-axis high optical subdivision grating ruler according to claim 1 or 3, characterized in that the combined grating and the two-dimensional subdivision prism assembly can be directly glued together, or in the two-dimensional The top surface of the quadrangular truss on the top of the subdivision prism assembly directly produces the combined grating.
The three-axis high optical subdivision grating ruler according to claim 1, wherein the two-dimensional grating is reflective.
The three-axis high optical subdivision grating ruler according to claim 1, wherein the two-dimensional grating is a transmission type, and a reflector is added on the transmission light path to coincide with the light path of the reflection type two-dimensional grating of retroreflection.
The three-axis high optical subdivision grating ruler according to claim 1, wherein the heterodyne photoelectric conversion unit module includes four groups of photoelectric conversion units, one of which consists of polarizers placed at 45 degrees to the P light Composed of a lens and a photodetector as a reference light heterodyne photoelectric conversion unit; the other three groups, each of which includes a polarizing prism, a P light focusing lens and a P light detector for detecting P light, and a P light detector for detecting S Light S-light focusing lens and S-light detector.
The three-axis high optical subdivision grating ruler according to claim 1, characterized in that, the reference light in the dual-frequency orthogonally polarized parallel light and reference light generating module can also be transmitted or reflected by a non-polarizing beam splitting prism Any beam that does not pass to the combined grating is produced.
The three-axis high optical subdivision grating ruler according to claim 1, wherein the two-dimensional grating is rotated 45° around the Z axis, and the incident beam is still in the two-dimensional grating and two-dimensional subdivision prism assembly Diffraction-reflection back and forth near the Littrow angle, and finally self-collimated back into the combined grating, coincides with the respective incident beams of each group of beams, and then reflected or transmitted by the non-polarizing beam splitter prism, by the Received by the heterodyne photoelectric conversion unit module described above, after photoelectric conversion, and then driven by the light source and signal detection and processor detection processing, the two-dimensional grating can obtain twice the original optical detail when the two-dimensional grating is not rotated by 45° around the Z axis. Fractional displacement and angle measurements.