CN114111587A - Three-axis high-optical subdivision grating ruler - Google Patents
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
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Abstract
A three-axis high optical subdivision grating scale, comprising: the device comprises a dual-frequency polarization parallel light and reference light generation module, a non-polarization beam splitter prism, a combined grating, a two-dimensional subdivision prism assembly, a two-dimensional grating, a heterodyne photoelectric conversion unit module and a light source driving and signal detecting and processing device. The device is characterized in that the dual-frequency polarization parallel light and reference light generation module generates three beams of dual-frequency polarization parallel light, the three beams of dual-frequency polarization parallel light enter the two-dimensional subdivision prism assembly after passing through the non-polarization beam splitter prism and the combined grating, are diffracted and reflected by a back-and-forth near Littrow angle between the two-dimensional grating and the two-dimensional subdivision prism assembly, are finally reflected by auto-collimation, are respectively combined by the combined grating, are superposed with respective incident beams, are reflected by the non-polarization beam splitter prism, are received by the heterodyne photoelectric conversion unit module, and are further driven by a light source and are detected and processed by the signal detection and processor, so that the displacement and angle measurement of optical subdivision of 8 times of three axes of X/Y/theta z of the relative movement of the two-dimensional grating and more than 8 times of three axes of X/Y/theta z can be obtained.
Description
Technical Field
The invention belongs to the field of precision optical measuring instruments, and particularly relates to a three-axis high optical subdivision grating ruler for three-degree-of-freedom displacement and angle measurement.
Background
The dual-frequency heterodyne laser interferometer is widely applied to displacement and angle measurement in the fields of precision motion stages, precision optical machinery, precision measurement instruments and the like, but is easily affected by the environment such as temperature, humidity, air pressure and the like. The single-frequency laser interferometer developed in recent years also has corresponding problems. The grating ruler is also called an optical encoder, wherein, compared with the grating ruler based on low-density common geometric grating, the grating ruler based on high-density diffraction grating has higher precision and resolution, and can reach sub-nanometer level. The well-designed high-density diffraction grating ruler has the unique advantage of being free from the influence of environment such as temperature, humidity, air pressure and the like, and is more and more favored by the industry, particularly the most precise equipment in the world, namely a photoetching machine, which adopts the instrument to carry out high-precision displacement and angle measurement.
Germany heidham was the earliest introduced grating scale based on diffraction gratings, and has developed a two-axis grating scale for two-degree-of-freedom displacement measurement. The principle is based on its patent US 4776701. The optical path and the practical product using effect thereof disclosed in the patent show that, compared with a measuring diffraction grating fixed on the surface of an object to be measured, the installation distance of a reading head is strict, and a light spot on a detector can transversely move and generate errors due to slight forward and backward movement. In addition, the three-free displacement measurement of the single reading head is difficult to expand, and a corresponding three-axis grating ruler with the single reading head is not designed.
The two-degree-of-freedom measurement Grating ruler (C.F.KAO, S.H.LU, et al., differential Laser Encoder with a grading in Littrow Configuration, Jpn.J.Appl.Phys.47.1833-1837) proposed by Kao et al adopts Littrow self-collimation angle incidence measurement Grating, so that the installation tolerance of the reading head of the Grating ruler becomes larger, but the two-degree-of-freedom measurement Grating ruler is essentially two independent one-dimensional optical path structures, is complex, is not easy to manufacture and is easy to generate Abbe error. In addition, the three-degree-of-freedom measurement extension is more complex.
The Gao research group proposed three-axis, six-axis grating scales for three-degree-of-freedom (A.Kimura, Wei Gao, W.Kim et. al, A-nanometric three-axis surface encoder with short-period-planar grating for stage movement measurement 36(2013), 771-doping 781), six-degree-of-freedom (X.Li, Wei Gao, et. al, A six-degree-of-freedom surface encoder for prediction of a planar movement stage, prediction Engineering 37(2012), 576-585). Chinese patents CN103307986A and CN103322927B respectively show a two-axis grating ruler for two-degree-of-freedom measurement and a three-axis grating ruler for three-degree-of-freedom measurement.
The above patents, although effectively extended in terms of measurement of degrees of freedom, all suffer from the disadvantage of a low number of optical subdivisions.
US5038032, US5146085, US4912320 and so on by canon, US5442172 by IBM and US ZYGO also apply for a number of novel grating interferometer patents, such as US8300233B2, US0194824a1, US0114061a1, to obtain higher accuracy and resolution. High-resolution grating ruler measurement systems have also been introduced in Heidenhain, Japan. However, in the above-described typical embodiments, the number of optical divisions of the grating interferometer is generally 2 or 4. High electron subdivision is often used, such as 14bit, 16 bit. Further high bit electronic subdivision is achievable but is meaningless limited by the grating interferometer optics 4 subdivision resolution. Therefore, the further improvement of the optical subdivision number of the grating interferometer has important value for actually improving the optical resolution of the grating interferometer and the overall resolution and precision of the grating ruler measurement system.
With the increasing requirements on the number of measurement axes, the precision and the resolution of high-precision equipment represented by a photoetching machine, a multi-axis high-optical subdivision grating ruler becomes a research hotspot.
Chinese patent CN 104613865B proposes a prism-based high optical subdivision grating ruler, which can realize optical subdivision of more than 8 times, but one axis is difficult to expand into two axes or more. Cunbai Lin, et al, Two-dimensional directional-based heterodyne grating interferometer used diagonally realizes a Two-axis 8 subdivision function (Cunbai Lin, et al, Two-dimensional directional-based coherent grating interferometer with enhanced signal-to-noise ratio and Optical sub-division, Optical Engineering,57(6),064102), which has a huge structure, a low grating line density, and a difficulty in realizing three axes.
Disclosure of Invention
The invention aims to overcome the defects of the prior art by elaborately designing a core component in a grating ruler, namely a grating interferometer. The main body is as follows: (1) the optical path difference is zero, so that the optical path difference is prevented from being influenced by the environment such as temperature, humidity, air pressure and the like; (2) three-degree-of-freedom three-axis measurement based on a single reading head can be realized, and the structure is compact; (3) the method is suitable for the situation of high-density two-dimensional grating and can achieve optical subdivision of three axes by 8 times or more; (4) the measurement grating is incident at a near Littrow auto-collimation angle, so that the installation tolerance of a reading head of the grating ruler is larger.
The technical solution of the invention is as follows:
a three-axis high optical subdivision grating scale, comprising: the device comprises a dual-frequency orthogonal polarization parallel light and reference light generation module, a non-polarization beam splitter prism, a combined grating, a two-dimensional subdivision prism assembly, a two-dimensional grating, a heterodyne photoelectric conversion unit module and a light source driving and signal detecting and processing unit;
the double-frequency orthogonal polarization parallel light and reference light generating module is used for generating at least three beams of double-frequency orthogonal polarization parallel light beams as incident light and one beam of double-frequency polarization light beam as reference light, and the reference light is received by the heterodyne photoelectric conversion unit module, subjected to photoelectric conversion and then driven by a light source and detected and processed by the signal detection and processor;
the three beams of dual-frequency orthogonal polarization parallel beams are transmitted or reflected by the non-polarization beam splitter prism, and split into three groups of beams by the combined grating, each group of beams consists of two beams, the emergent surfaces of the second group of beams and the third group of beams are parallel to each other, and the emergent surface of the first group of beams is respectively vertical to the emergent surfaces of the second group of beams and the third group of beams;
the grid line directions of the two dimensions of the two-dimensional grating are orthogonal and are respectively set as an X axis and a Y axis in three axes, a plane formed by the grid line directions of the two dimensions of the two-dimensional grating is vertical to a Z axis of a corresponding rectangular coordinate system, the central symmetry axis of the two-dimensional subdivision prism is set as the Z axis, and a corner theta Z surrounding the Z axis is the third axis in the three axes;
two light beams divided by each group of light beams are diffracted and reflected back and forth at a near Littrow angle between the two-dimensional grating and the two-dimensional subdivision prism assembly, are finally reflected back into the combined grating from collimation, are superposed with the respective incident light beams of each group of light beams, are reflected or transmitted by the non-polarization beam splitting prism, are received by the heterodyne photoelectric conversion unit module, are subjected to photoelectric conversion, and are further subjected to light source driving and signal detection and processor detection processing, so that the displacement and angle measurement of optical subdivision of 8 times and more than three axes of X/Y/theta z of the relative movement of the two-dimensional grating is obtained.
The specific principle of the three-axis high-optical subdivision grating ruler is as follows:
the dual-frequency orthogonal polarization light source is driven by the light source and the signal detection and processor to emit dual-frequency orthogonal polarization light beams (containing two polarization states of P light and S light), the dual-frequency orthogonal polarization light beams are divided into two light beams through the first non-polarization beam splitter prism, one light beam is focused on the first detector through a polaroid and a lens which are arranged at an angle of 45 degrees with the P light, and then the dual-frequency orthogonal polarization light beam is detected and processed by the light source drive and signal detection and processor to be used as a heterodyne reference light signal; the other beam is diffracted and divided into three beams of 0 grade and +/-1 grade through the first one-dimensional grating, and the three beams are collimated by the second lens and then respectively incident on the combined grating through the second non-polarization beam splitter prism; the combined grating is formed by 3 adjacent gratings, the grating lines of the middle grating are along the Y-axis direction, two beams of +/-1 grade (0 grade is set for the barrier of the diaphragm) are formed in an X/Z plane after the 0 grade beam is diffracted by the combined grating, the beams are respectively diffracted and reflected by a near Littrow angle back and forth between the two-dimensional grating and the two-dimensional subdivision prism assembly, and finally 2 light spots are formed on the surface of the two-dimensional grating after the beams are self-collimated and retroreflected; on the auto-collimation transmission surface (the light beam is vertical to the surface) of the two-dimensional subdivision prism assembly, a quarter-wave plate and an optical path compensation plate are respectively arranged to realize auto-collimation reflection; the quarter-wave plate is used for rotating the reflected P light and S light by 90 degrees simultaneously; the auto-collimated light beam is diffracted and combined by the middle grating again and is superposed with an incident light beam, reflected by the second non-polarizing beam splitter prism and incident on the heterodyne photoelectric conversion unit module, and then is driven by the light source, detected by the signal detection and processor and processed; by means of 4 times of Doppler frequency shift of the two-dimensional subdivision prism assembly and 2 times of Doppler frequency shift of a double-frequency heterodyne detection principle, 8 times of Doppler frequency shift can be obtained, and an X-axis 8-time optical subdivision function is achieved. Similarly, the grating line on the left side of the combined grating is along the X-axis direction, the-1-level light beam diffracted by the first one-dimensional grating is diffracted by the grating on the left side, two beams of +/-1-level light beam (0 level is blocked by a diaphragm) are formed in the Y/Z plane, and are respectively diffracted and reflected by a near Littrow angle back and forth between the two-dimensional grating and the two-dimensional subdivision prism assembly, and finally after auto-collimation and retro-reflection, 2 light spots are formed on the surface of the two-dimensional grating; a quarter-wave plate and an optical path compensation plate are respectively arranged on an auto-collimation transmission surface on the two-dimensional subdivision prism assembly to realize auto-collimation reflection; the quarter-wave plate is used for reflecting the P light and the S light and simultaneously rotating the P light and the S light by 90 degrees; the auto-collimated light beam is diffracted and combined by the left grating again and is superposed with an incident light beam, reflected by a second non-polarizing beam splitter prism and incident on a triaxial heterodyne photoelectric conversion unit module, and then is driven by a light source and detected and processed by a signal detection and processor; by means of the 4-time Doppler frequency shift of the two-dimensional subdivision prism assembly and the 2-time Doppler frequency shift of the double-frequency heterodyne detection principle, the 8-time Doppler frequency shift can be obtained, and the 8-time optical subdivision function of the first Y axis is achieved.
Similarly, the grating grid line on the right side of the combined grating is along the Y-axis direction, the + 1-level light beam diffracted by the first one-dimensional grating is diffracted by the grating on the right side of the combined grating, two +/-1-level light beams (0 level is set for diaphragm blocking) are formed in the Y/Z plane, and are respectively diffracted and reflected by a near Littrow angle back and forth between the two-dimensional grating and the two-dimensional subdivision prism assembly, and finally, 2 light spots are formed on the surface of the two-dimensional grating after self-collimation and retroreflection; a quarter-wave plate and an optical path compensation plate are respectively arranged on an auto-collimation transmission surface on the two-dimensional subdivision prism assembly to realize auto-collimation reflection; the quarter-wave plate is used for reflecting the P light and the S light and simultaneously rotating the P light and the S light by 90 degrees; the light beam after auto-collimation is diffracted and combined by the right grating of the combined grating again and is superposed with an incident light beam, the light beam is reflected by the second non-polarizing beam splitter prism and enters the heterodyne photoelectric conversion unit module, and then is driven by the light source, detected and processed by the signal detection and processor, and by means of the 4-time Doppler frequency shift of the two-dimensional subdivision prism assembly and the 2-time Doppler frequency shift of the dual-frequency heterodyne detection principle, the 8-time Doppler frequency shift of the second Y axis can be obtained, and the 8-time optical subdivision function is realized.
The relative rotation angle theta Z of the two-dimensional grating around the Z axis can be obtained by dividing the difference of the displacement quantity of the first Y axis and the second Y axis measured after the beam splitting and the auto-collimation combination of the left grating and the right grating in the Y/Z plane by the distance of the corresponding light spot on the two-dimensional grating, and the optical subdivision function of 8 times is also achieved.
The two-dimensional subdivision prism is formed by superposing at least 2 quadrangular tables with different angles of four side surfaces, the four side surfaces of the bottom quadrangular table are reflecting surfaces, the four side surfaces of the top quadrangular table are auto-collimation transmission surfaces vertical to light beams, the upper top surface of the top quadrangular table and the lower bottom surface of the bottom quadrangular table are light beam transmission surfaces vertical to a Z axis and are quadrangular, and the adjacent two sides of the two-dimensional subdivision prism are respectively parallel to the X axis and the Y axis; on the auto-collimation transmission surface of the two-dimensional subdivision prism, a quarter-wave plate and an optical path compensation plate are respectively arranged at the symmetrical positions of the light beam to realize auto-collimation reflection; one surface of each group of quarter-wave plates and optical path compensation plates is symmetrically glued on the light beam auto-collimation transmission surface, the other surface is plated with a total reflection film, and the quarter-wave plates and the optical path compensation plates are respectively positioned on the middle point of the intersection line of each group of emergent surfaces of the three groups of light beams split by the combined grating and the light beam auto-collimation transmission surface so as to realize auto-collimation reflection. In order to realize the measurement of an angle theta Z around a Z axis, two groups of quarter-wave plates and optical path compensation plates are arranged in the X axis or Y axis direction to realize self-collimation reflection; the quarter-wave plate is used for reflecting the P light and the S light and simultaneously rotating the P light and the S light by 90 degrees.
The number of the four-edge tables is increased in the middle of the two-dimensional subdivision prism, so that the number of the four side surfaces of the two-dimensional subdivision prism as reflecting surfaces is increased, the four-edge table four-edge angle is optimized, the frequency of diffraction-reflection of a back-and-forth near Littrow angle between the two-dimensional grating and the two-dimensional subdivision prism assembly can be effectively increased, and the optical subdivision number is further increased, for example, by adopting the two-dimensional subdivision prism formed by overlapping 3 four-edge tables with different four-edge angles, 8 times of Doppler frequency shift can be obtained, and by combining 2 times of Doppler frequency shift of a double-frequency heterodyne detection principle, 16 times of optical subdivision number can be realized; the two-dimensional subdivision prism is formed by overlapping 4 quadrangular frustums with different four side surface angles, 12 times of Doppler frequency shift can be obtained, and 24 times of optical subdivision can be realized by combining 2 times of Doppler frequency shift of a double-frequency heterodyne detection principle; and so on.
The beam is divided into two beams by the first non-polarization beam splitter prism, wherein one beam is used as reference light, any one beam of the three beams which are reflected by the second non-polarization beam splitter prism and do not go to the combined grating is replaced by a polarizing plate and a first lens which are arranged at an angle of 45 degrees with the P light.
The heterodyne photoelectric conversion unit module is characterized in that one unit except the heterodyne photoelectric conversion unit module comprises a polaroid, a first lens and a first detector which are arranged at an angle of 45 degrees with the P light and are used as a reference light heterodyne photoelectric conversion unit; the other three cells comprise three sets of photoelectric conversion cells of the same element. Each group of photoelectric conversion units includes: and the polarizing prism is used for detecting 1 focusing lens and detector of the P light respectively, and 1 focusing lens and detector of the S light respectively.
Compared with the prior art, the invention has the following beneficial effects:
the optical system of the three-axis high-optical subdivision grating ruler has symmetrical optical paths, quasi-common optical paths and zero optical path difference, and eliminates the ubiquitous dead path error sensitive to temperature, humidity and pressure intensity of a laser double-frequency heterodyne interferometer in principle; in addition, three-degree-of-freedom three-axis measurement based on the high-density two-dimensional grating and a single reading head can be realized, and the structure is compact; furthermore, the optical path can obtain the high optical subdivision function of three axes 8 times and above which is not reported in domestic and foreign documents through the effective combination of the two-dimensional subdivision prism assembly and the near Littrow angle diffraction-reflection auto-collimation optical path of the two-dimensional grating.
Drawings
FIG. 1 is a schematic structural diagram of an embodiment of a three-axis high optical subdivision grating ruler according to the present invention;
FIG. 2 is a schematic view of the Y-direction projection of FIG. 1 according to the present invention;
FIG. 3 is a schematic view of the X-direction projection of FIG. 1 according to the present invention;
FIG. 4 is a schematic view of a two-dimensional subdivided prism assembly according to the present invention;
FIG. 5 is a schematic diagram of a combined grating according to the present invention.
Detailed Description
In order to make the objects, 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 with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
In the description of the present application, it is to be understood that the terms "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like are used in the indicated orientations and positional relationships based on the orientation shown in the drawings for convenience in describing the application and for simplicity in description, and are not intended to indicate or imply that the referenced devices or elements must have a particular orientation, be constructed in a particular orientation, and be operated, and are not to be considered limiting of the application. The X, Y, Z, thetaz, P and S are not specifically referred to but are referred to in relative physical sense.
Referring to fig. 1, fig. 1 is a schematic structural diagram of an embodiment of a three-axis high optical subdivision grating ruler of the present invention, and as shown in the figure, a three-axis high optical subdivision grating ruler includes: the device comprises a double-frequency orthogonal polarization light source 1, a first non-polarization beam splitter prism 2, a polarizing film 12 placed at 45 degrees with P light, a first lens 13, a first detector 14, a first one-dimensional grating 3, a second lens 4, a second non-polarization beam splitter prism 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 detecting and processing unit 30.
The grid line directions of the two dimensions of the two-dimensional grating 11 are set as the X and Y axes of the three axes respectively, the grid line directions of the two dimensions of the two-dimensional grating 11 are orthogonal, the plane formed by the two dimensions of the two-dimensional grating is perpendicular to the Z axis of the corresponding rectangular coordinate system, the central symmetry axis of the two-dimensional subdivision prism 1000 is set as the Z axis, and the corner θ Z around the Z axis is the third axis of the three axes;
the two-dimensional subdivision prism assembly 10 is a core device and consists of a two- dimensional subdivision prism 1000, 3 quarter-wave plates 7-1, 8-1 and 9-1 and 3 corresponding optical path compensation plates 7-2, 8-2 and 9-2. The two-dimensional subdivision prism 1000 is formed by overlapping 3 rectangular tables with different angles of four side surfaces, the four side surfaces 1031, 1032, 1033, 1034 of the bottom rectangular table and the four side surfaces 1021, 1022, 1023, 1024 of the middle rectangular table are reflecting surfaces, the four side surfaces 1011, 1012, 1013, 1014 of the top rectangular table are light beam auto-collimation transmission surfaces (the light beams are vertical to the surfaces thereof), the top surface 100 of the top rectangular table and the bottom surface 104 of the bottom rectangular table are light beam transmission surfaces, are vertical to the Z axis and are quadrilateral, and the adjacent two sides of the top rectangular table are respectively parallel to the X axis and the Y axis; on the auto- collimation transmission surfaces 1011, 1012, 1013 and 1014 of the two-dimensional subdivision prism 1000, quarter-wave plates 7-1, 8-1 and 9-1 and optical path compensation plates 7-2, 8-2 and 9-2 are respectively arranged at the positions where the light beams are symmetrical, so as to realize auto-collimation reflection; the light path compensation device comprises quarter-wave plates 7-1, 8-1 and 9-1 and optical path compensation plates 7-2, 8-2 and 9-2, wherein one surface of each plate is symmetrically glued on the light beam auto-collimation transmission surface, the other surface of each plate is plated with a total reflection film, and the light path compensation plates are positioned on the middle point of the intersection line of each group of emergent surfaces of the three groups of light beams split by the combined grating 6 and the light beam auto-collimation transmission surface so as to realize auto-collimation reflection.
To achieve an angle theta around the Z-axiszMeasuring, namely arranging two groups of quarter-wave plates 8-1 and 9-1 and optical path compensation plates 8-2 and 9-2 in the Y-axis direction (the arrangement in the X-axis direction is optional and not specific) to realize auto-collimation reflection; the quarter-wave plates 7-1, 8-1, 9-1 are used for reflecting the P light and the S light and simultaneously rotating the P light and the S light by 90 degrees.
The heterodyne photoelectric conversion unit module 2000 includes a first polarizing prism (27), a third lens 28, a second detector 29, a fourth lens 26, and a third detector 25 along the X axis, and includes a second polarizing prism 20, a fifth lens 21, a fourth detector 22, a sixth lens 23, and a fifth detector 24 along the first Y axis. And 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 three-axis high optical subdivision grating scale of the present invention is embodied as shown in fig. 1, and is further detailed as follows.
The dual-frequency orthogonal polarization light source 1 is driven by the light source drive and signal detection and processor 30 to emit dual-frequency orthogonal polarization light beams (containing two polarization states of P light and S light, and the frequencies are slightly different), and the dual-frequency orthogonal polarization light beams are divided into two light beams by the first non-polarization beam splitter prism 2, wherein one light beam is focused on the first detector 14 through the polarizing film 12 and the first lens 13 which are arranged at 45 degrees with the P light as reference light, and then is detected and processed by the light source drive and signal detection and processor 30 to be used as heterodyne reference light signals; the other beam is diffracted and divided into three beams of 0-level and +/-1-level beams by the one-dimensional grating 3, and the three beams are collimated by the second lens 4 and then respectively incident on the combined grating 6 through the second non-polarization beam splitter prism 5; the combined grating 6 is composed of 3 gratings (6-1, 6-2,6-3 are adjacent as shown in figure 5, the middle grating 6-2 is along the Y-axis direction, after the 0-order light beam is diffracted, two beams of +/-1-order light beam (0 order is set light bar block, not shown) are formed in the X/Z plane as shown in figure 2, the beams are respectively diffracted and reflected by the back and forth near Littrow angle between the two-dimensional grating 11 and the two-dimensional subdivision prism 10, finally, after the beams are reflected by self-collimation, 4 light spots are formed on the two-dimensional grating surface 11, quarter wave plates 7-1 and optical path compensating plates 7-2 are respectively arranged on the self-collimation transmission surfaces 1011 and 1012 on the two-dimensional subdivision prism 10 as shown in figure 4 to realize self-collimation reflection, the quarter wave plates 7-1 are used for simultaneously rotating the P light and the S light by 90 degrees after the P light and the S light are reflected, the beams after the self-collimation are combined with the middle grating 6-2 again, the beams are diffracted and combined with the middle grating 6-2 6-2, incident light beams are superposed, reflected by the second non-polarizing beam splitter prism 5 and incident on the first polarizing prism 27, P light is focused on the second detector 29 through the third lens (28), S light is focused on the third detector 25 through the fourth lens 26, and then is detected and processed by the light source driving and signal detecting and processing unit 30; by means of the 8-time Doppler shift of the two-dimensional subdivision prism 10 and the 2-time Doppler shift of the double-frequency heterodyne detection principle, the 16-time Doppler shift can be obtained, and the 16-time optical subdivision function is achieved.
Similarly, the grating line of the left grating 6-1 is along the X-axis direction, after the-1 st order light beam is diffracted by the grating line, as shown in fig. 3, two beams of light beams of ± 1 st order (0 st order is set to be blocked by a diaphragm, not shown) are formed in the Y/Z plane, and are respectively diffracted and reflected by near Littrow angles back and forth between the two-dimensional grating 11 and the two-dimensional subdivision prism 10, and after the light beams are finally reflected by auto-collimation, 4 light spots are formed on the surface 11 of the two-dimensional grating; on the auto-collimation transmission surfaces 1013 and 1014 on the two-dimensional subdivision prism 10, as shown in fig. 4, a quarter-wave plate 8-1 and an optical path compensation plate 8-2 are respectively arranged to realize auto-collimation reflection; the quarter-wave plate 8-1 is used for simultaneously rotating the P light and the S light by 90 degrees; the auto-collimated light beam is diffracted and combined again through the middle grating 6-1 to coincide with the incident light beam of the middle grating 6-1, is reflected by the second non-polarizing beam splitter prism 5 and is incident on the second polarizing prism 20, the P light is focused on the fifth detector 24 through the sixth lens 23, the S light is focused on the fourth detector 22 through the fifth lens 21, and is driven by the light source and detected and processed by the signal detection and processing unit 30; by means of the 8-time Doppler shift of the two-dimensional subdivision prism 10 and the 2-time Doppler shift of the double-frequency heterodyne detection principle, the 16-time Doppler shift can be obtained, and the 16-time optical subdivision function is achieved.
The grating lines of the right grating 6-3 are along the X-axis direction, after the + 1-order light beam is diffracted by the grating lines, as shown in FIG. 3, two beams of +/-1-order light beams (0-order is set to be blocked by a diaphragm and is not shown) are formed in a Y/Z plane, and are respectively diffracted and reflected by near Littrow angles back and forth between the two-dimensional grating 11 and the two-dimensional subdivision prism 10, and finally, after the light beams are self-collimated and retroreflected, 4 light spots are formed on the surface 11 of the two-dimensional grating; on the auto-collimation transmission surfaces 1013 and 1014 on the two-dimensional subdivision prism 10, as shown in fig. 4, a quarter-wave plate 9-1 and an optical path compensation plate 9-2 are respectively arranged to realize auto-collimation reflection; the quarter-wave plate 9-1 is used for simultaneously rotating the P light and the S light by 90 degrees; the auto-collimated light beam is diffracted and combined again through the middle grating 6-3 to coincide with the incident light beam of the middle grating 6-3, is reflected by the second non-polarizing beam splitter prism 5 and enters the third polarizing prism 17, the P light is focused on the sixth detector 19 through the seventh lens 18, the S light is focused on the seventh detector 15 through the eighth lens 16, and is then detected and processed by the light source drive and signal detection and processor 30; by means of the 8-time Doppler frequency shift of the two-dimensional subdivision prism 10 and the 2-time Doppler frequency shift of the double-frequency heterodyne detection principle, the 16-time Doppler frequency shift can be obtained, and the 16-time optical subdivision function is achieved.
The relative rotation angle theta Z of the two-dimensional grating 11 around the Z axis can be obtained by dividing the difference of Y-axis displacement measured by splitting the left and right gratings 6-1 and 6-3 in the Y/Z plane by the distance of the corresponding light spot on the two-dimensional grating 11, and the optical subdivision function of 16 times is also achieved.
In this embodiment, the number of the four-sided tables in the middle of the two-dimensional subdivision prism 1000 is increased, so that the number of the four sides of the two-dimensional subdivision prism 1000 as the reflecting surfaces is increased, the angle of the four sides of each four-sided table is optimized, the frequency of diffraction-reflection of the back-and-forth near Littrow angle between the two-dimensional grating 11 and the two-dimensional subdivision prism assembly 10 can be effectively increased, and the optical subdivision number is further increased, for example, by adopting the two-dimensional subdivision prism 1000 formed by overlapping 4 four-sided tables with different angles, 12-fold doppler shift can be obtained, and by combining 2-fold doppler shift based on the dual-frequency heterodyne detection principle, 24-fold doppler shift can be obtained, and 24-fold optical subdivision number can be realized. Similarly, by reducing the number of the four-edge tables of the two-dimensional subdivision prism 1000 to 2, and optimizing the four-side angle of each four-edge table, 4 times of doppler frequency shift can be easily obtained, and 8 times of optical subdivision number can be realized by combining 2 times of doppler frequency shift of the double-frequency heterodyne detection principle.
In addition, the two-dimensional grating 11 is rotated by 45 degrees around the Z axis, the incident light beams are still diffracted and reflected back and forth by a near Littrow angle between the two-dimensional grating 11 and the two-dimensional subdivision prism assembly 10, and finally are reflected back and forth into the combined grating 6 from collimation, are overlapped with the respective incident light beams of each group of light beams, are reflected or transmitted by the non-polarizing beam splitter prism 5, are received by the heterodyne photoelectric conversion unit module 2000, are subjected to photoelectric conversion, and are further subjected to detection processing by the light source driver and the signal detection and processor 30, so that 2 times of displacement and angle measurement of the original optical subdivision number can be obtained when the two-dimensional grating 11 is not rotated by 45 degrees around the Z axis, which is 32 times of the optical subdivision number in this embodiment, and so on.
The beam is split into two beams by the first non-polarizing beam splitter prism 2, wherein one of the reference beams can be replaced by any one of the three beams which are reflected by the second non-polarizing beam splitter prism 5 and do not go to the combination grating by a polarizing plate 12 and a first lens 13 which are placed at 45 degrees with respect to the P-beam.
The optical system of the three-axis high-optical subdivision grating ruler has symmetrical optical paths, quasi-common optical paths and zero optical path difference, and eliminates the ubiquitous dead path error sensitive to temperature, humidity and pressure intensity of a laser double-frequency heterodyne interferometer in principle; in addition, three-degree-of-freedom three-axis measurement based on the high-density two-dimensional grating and a single reading head can be realized, and the structure is compact; furthermore, the optical path can obtain the ultrahigh optical subdivision function of three axes 8 times and above which is not reported in domestic and foreign documents through the effective combination of the near auto-collimation optical path of the two-dimensional subdivision prism 10 and the two-dimensional grating 11.
Claims (9)
1. A three-axis high optical subdivision grating scale, comprising: the device comprises a dual-frequency orthogonal polarization parallel light and reference light generation module, a non-polarization beam splitter prism, a combined grating, a two-dimensional subdivision prism assembly, a two-dimensional grating, a heterodyne photoelectric conversion unit module and a light source driving and signal detecting and processing unit;
the double-frequency orthogonal polarization parallel light and reference light generating module is used for generating at least three beams of double-frequency orthogonal polarization parallel light beams as incident light and one beam of double-frequency polarization light beam as reference light, and the reference light is received by the heterodyne photoelectric conversion unit module, subjected to photoelectric conversion and then driven by a light source and detected and processed by the signal detection and processor;
the three beams of dual-frequency orthogonal polarization parallel beams are transmitted or reflected by the non-polarization beam splitter prism, and split into three groups of beams by the combined grating, each group of beams consists of two beams, the emergent surfaces of the second group of beams and the third group of beams are parallel to each other, and the emergent surface of the first group of beams is respectively vertical to the emergent surfaces of the second group of beams and the third group of beams;
the grid line directions of the two dimensions of the two-dimensional grating are orthogonal and are respectively set as an X axis and a Y axis in three axes, a plane formed by the grid line directions of the two dimensions of the two-dimensional grating is vertical to a Z axis of a corresponding rectangular coordinate system, the central symmetry axis of the two-dimensional subdivision prism is set as the Z axis, and a corner theta Z surrounding the Z axis is the third axis in the three axes;
two light beams divided by each group of light beams are diffracted and reflected back and forth at a near Littrow angle between the two-dimensional grating and the two-dimensional subdivision prism assembly, are finally reflected back into the combined grating from collimation, are superposed with the respective incident light beams of each group of light beams, are reflected or transmitted by the non-polarization beam splitting prism, are received by the heterodyne photoelectric conversion unit module, are subjected to photoelectric conversion, and are further subjected to light source driving and signal detection and processor detection processing, so that the displacement and angle measurement of optical subdivision of 8 times and more than three axes of X/Y/theta z of the relative movement of the two-dimensional grating is obtained.
2. The three-axis high optical subdivision grating ruler of claim 1, wherein the combined grating is composed of at least two sets of one-dimensional gratings, and the grating lines of each set are perpendicular to each other, wherein one set of gratings can be divided into two parts and located on both sides of the other set.
3. The three-axis high optical subdivision grating ruler of 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 optical path compensators, the two-dimensional subdivision prism is formed by at least two sets of four-edge tables which are overlapped up and down, one set is a top four-edge table, and the four side surfaces are light beam auto-collimation transmission surfaces perpendicular to light beams; the other group is at least one quadrangular frustum pyramid, the four side surfaces of the quadrangular frustum pyramid are reflecting surfaces which are not vertical to the light beams, the top surfaces of the quadrangular frustum pyramid tops and the bottom surfaces of the quadrangular frustum pyramid tops are light beam transmission surfaces which are vertical to the Z axis and are quadrangular, and the adjacent two sides of the quadrangular frustum pyramid are respectively parallel to the X axis and the Y axis;
one surface of each group of quarter-wave plates and optical path compensation plates is symmetrically glued on the light beam auto-collimation transmission surface, the other surface is plated with a total reflection film, and the quarter-wave plates and the optical path compensation plates are positioned on the middle point of the intersection line of each group of emergent surfaces of the three groups of light beams split by the combined grating and the light beam auto-collimation transmission surface so as to realize auto-collimation reflection.
4. The three-axis high optical subdivision grating ruler of claim 1 or 3, wherein the combined grating and the two-dimensional subdivision prism assembly can be directly glued together, or the combined grating is directly fabricated on the top surface of a quadrangular frustum at the top of the two-dimensional subdivision prism assembly.
5. The three-axis high optical subdivision grating scale of claim 1, wherein the two-dimensional grating is reflective.
6. The three-axis high optical subdivision grating ruler of claim 1, wherein the two-dimensional grating is transmissive, and a mirror is added to the transmitted light path to reflect light back in alignment with the light path of the reflective two-dimensional grating.
7. The three-axis high-optical subdivision grating scale of claim 1, wherein the heterodyne photoelectric conversion unit module comprises four sets of photoelectric conversion units, one of which is composed of a polarizer and a lens placed at 45 degrees to P light and a photodetector, and serves as a reference light heterodyne photoelectric conversion unit; and three other groups, each group including a polarizing prism, a P-light focusing lens and a P-light detector for detecting P-light, and an S-light focusing lens and an S-light detector for detecting S-light.
8. The three-axis high optical subdivision grating ruler of claim 1, wherein the dual-frequency orthogonal polarization parallel light and the reference light in the reference light generation module can also be generated by any beam of light which is transmitted or reflected by the non-polarization beam splitter prism and does not go to the combined grating.
9. The three-axis high optical subdivision grating ruler of claim 1, wherein the two-dimensional grating is rotated 45 ° around the Z axis, the incident beam is diffracted and reflected back and forth between the two-dimensional grating and the two-dimensional subdivision prism assembly at a near Littrow angle, and finally reflected back into the combined grating from collimation, and the combined grating is superposed with the respective incident beam of each group of beams, and then reflected or transmitted by the non-polarization beam splitter prism, and then received by the heterodyne photoelectric conversion unit module, and after photoelectric conversion, further processed by light source driving and signal detection and processor detection, the displacement and angle measurement of 2 times of the original optical subdivision number can be obtained when the two-dimensional grating is not rotated 45 ° around the Z axis.
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