MEASURING DEVICE WITH HETERODYNEMIC GRID AND MEASURING METHOD

Abstract

Measuring device with a heterodyne one-dimensional grating, comprising a light source used to generate two beams of linearly polarized lights that overlap each other and have orthogonal polarizations and a fixed frequency difference, wherein the linearly polarized lights each have a first polarized light with a frequency f A and a second polarized light with a frequency f B are, wherein the first polarized light is an S-polarized light and the second polarized light is a P-polarized light; further comprising a read head, a photoelectric receiver module and a signal processing system; wherein the reading head is used to receive the first polarized light and the second polarized light, each incident on a surface of the moving one-dimensional measuring grating, to generate a diffracted +1 order light and a diffracted -1 order light, each containing a first polarized light component and a second polarized light component, and wherein the diffracted +1 order light and the diffracted -1 order light each enter the photoelectric receiving module via the reading head; wherein the photoelectric receiving module is used to receive the diffracted light of the +1 order and the diffracted light of the -1 order to form two paths of beat frequency signals; and wherein one path consists of the second polarized light component of the diffracted light of the -1 order and the first polarized light component of the diffracted light of the +1 order interfering with each other to produce a beat frequency signal with a frequency f B -f A to form, while the other way involves the first polarized light component of the diffracted light of the -1st order and the second polarized light component of the diffracted light of the +1st order interfering with each other to form another beat frequency signal with a frequency f B -f A to form; where the signal processing system is used to perform a difference calculation for the two paths of beat frequency signals in order to realize the displacement measurement of the 4-fold optical subdivision by single diffraction of the one-dimensional measuring grid, characterized in that the reading head comprises a reflector, a polarizing beam splitter prism, a first quarter-wave plate, a second quarter-wave plate, a compensation mirror coated with a reflective film, a gyro prism and a refractive element; wherein the reflector is arranged on a falling light path of the light source to reflect the first polarized light and the second polarized light vertically onto the surface of the one-dimensional measuring grating, thereby producing a diffracted light of +1 order and a diffracted light of -1 order; and wherein the refractive element is arranged on a diffraction light path of the one-dimensional measuring grating to refract the diffracted light of the +1 order and the diffracted light of the -1 order, so that the diffracted light of the +1 order and the diffracted light of the -1 order are aligned parallel to each other and enter the polarizing beam splitter prism vertically; wherein the polarizing beam splitter prism is arranged on a transmission light path of the refractive element to reflect the first polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order each onto the first quarter-wave plate and to transmit the second polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order each onto the second quarter-wave plate; wherein the first quarter-wave plate is arranged on a reflection light path of the polarizing beam splitter prism in order to convert the first polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order into left-handed polarized light and to shine these into the gyro prism; wherein the gyroscopic prism is arranged on a transmission light path of the first quarter-wave plate to reflect the first polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order twice each, so that the first polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order are converted into P-polarized light by the first quarter-wave plate and then enter the polarizing beam splitter prism; wherein the second quarter-wave plate is arranged on a transmission light path of the polarizing beam splitter prism, so that the second polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order are each converted into a right-rotating polarized light and then enter the compensation mirror; wherein the compensation mirror is arranged on a transmission light path of the second quarter-wave plate to reflect the second polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order respectively, so that the second polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order are converted into S-polarized light by the second quarter-wave plate and then enter the polarizing beam splitter prism; wherein the polarizing beam splitter prism is further used to transmit the first polarized light components of the diffracted +1-order and -1-order light, which are converted into P-polarized light, to the photoelectric receiver module, and to reflect the second polarized light components of the diffracted +1-order and -1-order light, which are converted into S-polarized light, to the photoelectric receiver module, and wherein, when the one-dimensional measuring grating moves along a grating vector direction, the diffracted -1-order light undergoes a backward frequency shift Δf and the diffracted +1-order light undergoes a forward frequency shift +Δf, the frequency of the beat frequency signal output by the first receiver becoming f B -f A-2Δf and the frequency of the beat frequency signal output by the second receiver to f B -f A +2Δf changes.

Description

[0001] The present application claims the priorities of the Chinese patent application with application number 202010953637.8 and the invention title "Displacement measurement method with heterodyne grating", application number 202010953635.9 and the invention title "Optical displacement measurement system with heterodyne grating", application number 202010953595.8 and the invention title "Displacement measuring device with heterodyne grating", and application number 202010953663.0 and the invention title "Displacement measurement system with heterodyne two-dimensional grating and measurement method", which were filed with the Chinese Patent Office on September 11, 2020, in full, which are incorporated by reference into this application. TECHNICAL AREA

[0002] The present invention relates to the field of measurement technology for precision displacement, in particular a measuring device with a heterodyne grating for realizing a 4-fold optical subdivision based on single diffraction and a measuring method. STATE OF THE ART

[0003] The grating displacement measurement system uses the grating as a measuring ruler and the grating spacing as a measurement benchmark. Compared to laser measurement technology, grating measurement is less sensitive to environmental changes, and the beam incident on the grating covers many grooves, resulting in an average effect. The structure of the read head in the grating displacement measurement system is simple and compact; the distance between the grating and the read head is very small and does not increase with increasing measurement distance, which can significantly reduce the influence of the environment on the system's measurement accuracy and measurement costs. As the grating manufacturing quality improves, the measurement accuracy and resolution of the grating displacement measurement system also gradually improve, and its range of applications continues to expand.

[0004] The measurement resolution of grating displacement measurement technology is directly related to the grating period. Displacement measurement technology based on the principle of diffraction interference utilizes a high-density diffraction grating to achieve high-resolution and high-precision displacement measurements. Optical and electronic subdivision represent the primary means of further improving measurement resolution. Compared to electronic subdivision, optical subdivision offers superior reliability. Traditional grating displacement measurement systems employ single diffraction to achieve a 2x optical subdivision. To further enhance optical subdivision, existing technology typically utilizes secondary diffraction to achieve a 4x optical subdivision, or multiple diffraction to achieve even higher subdivisions.However, both secondary diffraction and multiple diffraction make the optical structure of the measuring system more complicated, and multiple diffraction uses the diffracted light at different positions of the grating, thus the shape accuracy of the grating surface and the alignment error between the grating and the reading head have a major influence on the measurement accuracy.

[0005] CN 103 604 375 A describes a two-dimensional measurement method and system for dual-frequency laser grating interference with optical alias suppression. It belongs to the field of grating metrology. The system comprises a laser system, a grating interference mirror set, and a photoelectric detection and signal processing unit.

[0006] CN 103 644 848 A describes a three-dimensional grating displacement measurement system with a dual-frequency laser. The measurement system comprises a dual-frequency laser whose output side is connected to a fiber optic cable, a light slit component, a polarizing light splitter prism, a quarter-wave plate for the measuring / reference arm, a light refraction element for the measuring / reference arm, a two-dimensional reflective reference / measuring grating, and a photoelectric detection and signal processing unit.

[0007] US 2015 / 0338205 A1 describes a displacement measurement system of a heterodyne grating interferometer comprising a read head, a measuring grating, and an electronic signal processing component. Laser light emitted from the laser tube is collimated, passes through the first polarization spectrometer, and then emits two light beams with orthogonal polarization and propagation directions.

[0008] US 2018 / 0202842 A1 describes an encoder that measures the relative motion of a second element with respect to a first element and comprises: a diffraction grating attached to the first element; an incident optical element that emits measurement light generally perpendicular to the grating pattern surface of the diffraction grating; a first reflection element attached to the second element that reflects the diffracting light produced by the diffraction grating; a first direction change element that changes the direction of the diffracting light; and a first photoelectric detector that detects the interference light.

[0009] US 2022 / 0214193 A1 describes a displacement measuring device, a displacement measuring method, and a photolithography device. The displacement measuring device comprises a light source module (300), a diffraction element (200), a scanning head assembly (100), light detection modules (410, 411, 412, 413), and a signal analysis module (500). The scanning head assembly (100) is used to receive two input beams (610, 611) generated by the light source module (300) and to direct the two input beams (610, 611) parallel to the diffraction element (200) to produce diffraction, and then to guide and combine the diffracted input beams to form at least one output beam (612, 613, 614). Each output beam (612, 613, 614) comprises diffracted light signals emitted from the same light point position of the diffraction element (200) in the same direction and corresponding to the two input beams (610, 611).

[0010] CN 106 813 578 A describes a two-dimensional grating measurement system. Four pyramidal glass elements are used. A vertical and an inclined incidence method are combined. Interference occurs between first-order and first-order diffracted light at vertical incidence, while interference also occurs between first-order and first-order diffracted light at inclined incidence. Two-dimensional displacement signals of a grating under measurement are determined from the two channels of the interference signals. With a suitable arrangement of several measuring probes on a motion stage, highly precise and highly stable six-degree-of-freedom data of the motion stage can be obtained. CONTENT OF THE PRESENT INVENTION

[0011] To overcome the shortcomings of the prior art, the present invention uses the following technical solution: The present invention provides a measuring instrument with a heterodyne one-dimensional grating, comprising a light source used to generate two beams of linearly polarized lights that overlap each other and have orthogonal polarizations and a fixed frequency difference, wherein the linearly polarized lights each emit a first polarized light with a frequency f A and a second polarized light with a frequency f Bare, and wherein the first polarized light is an S-polarized light and the second polarized light is a P-polarized light; characterized in that it further comprises a read head, a photoelectric receiver module and a signal processing system; wherein the read head is used to receive the first polarized light and the second polarized light, each incident on a surface of the moving one-dimensional measuring grating, in order to generate a diffracted +1-order light and a diffracted -1-order light, each containing a first polarized light component and a second polarized light component, and wherein the diffracted +1-order light and the diffracted -1-order light each incident into the photoelectric receiver module via the read head;and wherein the photoelectric receiving module is used to receive the diffracted light of the +1 order and the diffracted light of the -1 order to form two paths of beat frequency signals; and wherein one path of these is such that the second polarized light component of the diffracted light of the -1 order and the first polarized light component of the diffracted light of the +1 order interfere with each other to produce a beat frequency signal with a frequency f; B -f A to form, while the other way involves the first polarized light component of the diffracted light of the -1st order and the second polarized light component of the diffracted light of the +1st order interfering with each other to form another beat frequency signal with a frequency f B -f Ato form; and wherein the signal processing system is used to perform a difference calculation for the two paths of beat frequency signals in order to realize the displacement measurement of the 4-fold optical subdivision by single diffraction of the one-dimensional measuring grid.

[0012] Preferably, the reading head comprises a reflector, a polarizing beam splitter prism, a first quarter-wave plate, a second quarter-wave plate, a compensation mirror coated with a reflective film, a deflecting prism, and a deflecting element; wherein the reflector is arranged on a falling light path of the light source to reflect the first polarized light and the second polarized light vertically onto the surface of the one-dimensional measuring grating, thereby generating a diffracted light of the +1st order and a diffracted light of the -1st order; and wherein the deflecting element is arranged on a diffracted light path of the one-dimensional measuring grating to refract the diffracted light of the +1st order and the diffracted light of the -1st order, so that the diffracted light of the +1st order and the diffracted light of the -1st order are aligned parallel to each other and are incident vertically into the polarizing beam splitter prism;and wherein the polarizing beam splitter prism is arranged on a transmission light path of the deflecting element to reflect the first polarized light components of the diffracted +1 order light and the diffracted -1 order light each onto the first quarter-wave plate and to transmit the second polarized light components of the diffracted +1 order light and the diffracted -1 order light each onto the second quarter-wave plate; and wherein the first quarter-wave plate is arranged on a reflection light path of the polarizing beam splitter prism to convert the first polarized light components of the diffracted +1 order light and the diffracted -1 order light each into left-handed polarized light and to radiate these into the deflecting prism;and wherein the deflecting prism is arranged on a transmission path of the first quarter-wave plate to reflect the first polarized light components of the diffracted +1 order light and the diffracted -1 order light twice each, so that the first polarized light components of the diffracted +1 order light and the diffracted -1 order light are converted into P-polarized light by the first quarter-wave plate and then enter the polarizing beam splitter prism; and wherein the second quarter-wave plate is arranged on a transmission path of the polarizing beam splitter prism, so that the second polarized light components of the diffracted +1 order light and the diffracted -1 order light are each converted into right-handed polarized light and then enter the compensation mirror;and wherein the compensation mirror is arranged on a transmission light path of the second quarter-wave plate to reflect the second polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order respectively, so that the second polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order are converted into S-polarized light by the second quarter-wave plate and then enter the polarizing beam splitter prism;and wherein the polarizing beam splitter prism is further used to transmit the first polarized light components of the diffracted +1 order light and the diffracted -1 order light, which are converted into P-polarized light, to the photoelectric receiving module and to reflect the second polarized light components of the diffracted +1 order light and the diffracted -1 order light, which are converted into S-polarized light, to the photoelectric receiving module.

[0013] Preferably, the photoelectric receiving module comprises a first receiver and a second receiver; wherein the first receiver is used to receive the second polarized light component of the diffracted light of the -1st order and the first polarized light component of the diffracted light of the +1st order, as well as the beat frequency signal with a frequency f B -f Ato generate and transmit this to the signal processing system; and wherein the second receiver is used to receive the first polarized light component of the diffracted light of the -1st order and the second polarized light component of the diffracted light of the +1st order, as well as the other beat frequency signal with a frequency f B -f A to generate and transmit this to the signal processing system.

[0014] Preferably, it is provided that when the one-dimensional measuring grid moves along a grid vector direction, the diffracted light of the -1st order undergoes a backward frequency shift -Δf and the diffracted light of the +1st order undergoes a forward frequency shift +Δf, whereby the frequency of the beat frequency signal output by the first receiver becomes f B -f A -2Δf and the frequency of the beat frequency signal output by the second receiver to f B -fA +2Δf changes.

[0015] Preferably, the thickness of the compensation mirror corresponds to half the length of the deflecting prism in order to compensate for the light path of the second polarized light components of the diffracted +1 order light and the diffracted -1 order light, so that the light path of the second polarized light components of the diffracted +1 order light and the diffracted -1 order light is the same as the light path of the first polarized light components of the diffracted +1 order light and the diffracted -1 order light.

[0016] Preferably, the reading head further comprises a first rectangular prism and a second rectangular prism, each arranged on the diffraction light path of the one-dimensional measuring grating, wherein the first rectangular prism and the second rectangular prism each reflect the diffracted light of the +1st order and the diffracted light of the -1st order twice, which again incident on the surface of the one-dimensional measuring grating with a diffraction exit angle, and wherein two beams of new diffracted lights incident vertically on the polarizing beam splitter prism.

[0017] Preferably, the reading head comprises a polarizing beam splitter prism, a first quarter-wave plate, a second quarter-wave plate coated with a reflective film, and a deflecting prism; wherein the polarizing beam splitter prism is arranged on a dropout light path of the light source and is used to receive the first polarized light and the second polarized light, to transmit the second polarized light to the first quarter-wave plate, and to reflect the first polarized light to the second quarter-wave plate; and wherein the first quarter-wave plate is arranged on a transmission light path of the polarizing beam splitter prism to convert the second polarized light into right-handed polarized light and to radiate this into the deflecting prism;and wherein the deflecting prism is arranged on a transmission light path of the first quarter-wave plate to reflect the second polarized light back, so that the second polarized light passes through the first quarter-wave plate and is converted into S-polarized light and then returns to the polarizing beam splitter prism; and wherein the second quarter-wave plate is arranged on a reflection light path of the polarizing beam splitter prism to convert the first polarized light into left-hand polarized light, which is reflected by the reflection film, passes again through the second quarter-wave plate and is converted into P-polarized light and then returns to the polarizing beam splitter prism;and wherein the polarizing beam splitter prism is further used to transmit the first polarized light converted into P-polarized light and to reflect the second polarized light converted into S-polarized light, so that the first polarized light and the second polarized light are combined and then incident on the surface of the one-dimensional measuring grating to produce, by diffraction, the diffracted light of the -1st order and the diffracted light of the +1st order.

[0018] Preferably, the reading head further comprises a deflecting element and a third quarter-wave plate; wherein the deflecting element is arranged on a diffraction light path of the one-dimensional measuring grating to refract the diffracted light of the -1st order and the diffracted light of the +1st order, so that the diffracted light of the -1st order and the diffracted light of the +1st order are aligned parallel to each other and are incident vertically into the third quarter-wave plate;and wherein the third quarter-wave plate is arranged on a transmission light path of the deflecting element to convert the first polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order into S-polarized light and to shine this vertically onto the polarizing beam splitter prism, as well as to convert the second polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order into P-polarized light and to shine this vertically onto the polarizing beam splitter prism; and wherein the polarizing beam splitter prism is used to reflect the first polarized light components of the diffracted +1 order light and the diffracted -1 order light onto the first quarter-wave plate and to transmit the second polarized light components of the diffracted +1 order light and the diffracted -1 order light onto the second quarter-wave plate;and wherein the first quarter-wave plate is used to convert the first polarized light components of the diffracted +1 order light and the diffracted -1 order light into left-hand polarized light and to shine it into the deflecting prism; and wherein the deflecting prism is used such that the first polarized light components of the diffracted +1 order light and the diffracted -1 order light are reflected twice back onto the first quarter-wave plate and converted into P-polarized light, then again incident on the polarizing beam splitter prism and transmitted through the polarizing beam splitter prism to the photoelectric receiving module;and wherein the second quarter-wave plate is used such that the second polarized light components of the diffracted +1 order light and the diffracted -1 order light are converted into right-handed polarized light and reflected through the reflection film, pass through the second quarter-wave plate again and are converted into S-polarized light and then enter the polarizing beam splitter prism and are reflected by the polarizing beam splitter prism onto the photoelectric receiving module.;

[0019] Preferably, the photoelectric receiving module comprises a first receiver and a second receiver; wherein the first receiver is used to receive the first polarized light component of the diffracted +1 order light and the second polarized light component of the diffracted -1 order light, as well as the beat frequency signal with a frequency f B -fA to generate and transmit this to the signal processing system; and wherein the second receiver is used to receive the first polarized light component of the diffracted light of the -1st order and the second polarized light component of the diffracted light of the +1st order, as well as the other beat frequency signal with a frequency f B -f A to generate and transmit this to the signal processing system.

[0020] Preferably, it is provided that when the one-dimensional measuring grid moves along a grid vector direction, the diffracted light of the -1st order undergoes a backward frequency shift -Δf and the diffracted light of the +1st order undergoes a forward frequency shift +Δf, whereby the frequency of the beat frequency signal output by the first receiver becomes f B -f A -2Δf and the frequency of the beat frequency signal output by the second receiver to fB -f A +2Δf changes.

[0021] Preferably, the optical paths of the first polarized light component of the diffracted light of the -1 order and the second polarized light component of the diffracted light of the -1 order are the same, and the optical paths of the first polarized light component of the diffracted light of the +1 order and the second polarized light component of the diffracted light of the +1 order are the same.

[0022] Preferably, the reading head further comprises a first rectangular prism and a second rectangular prism, each arranged on the diffraction light path of the one-dimensional measuring grating, wherein the first rectangular prism and the second rectangular prism each reflect the diffracted light of the +1st order and the diffracted light of the -1st order twice, which again incident on the surface of the one-dimensional measuring grating with a diffraction exit angle, and wherein two beams of new diffracted lights incident vertically on the polarizing beam splitter prism.

[0023] The present invention further provides a measurement method with a heterodyne one-dimensional lattice, comprising the following steps: S1: Generating two beams of linearly polarized lights that overlap each other and have orthogonal polarizations and a fixed frequency difference, by means of a light source, wherein the linearly polarized lights each emit a first polarized light with a frequency f A and a second polarized light with a frequency f B are, and where the first polarized light is an S-polarized light and the second polarized light is a P-polarized light; S2: Entry of the first polarized light and the second polarized light each into a reading head and, after refraction through the reading head, incident on a surface of the one-dimensional measuring grating to generate a diffracted light of the +1 order and a diffracted light of the -1 order, each containing a first polarized light component and a second polarized light component, wherein the diffracted light of the +1 order and the diffracted light of the -1 order again incident via the reading head each into a photoelectric receiving module; S3: Receiving the diffracted light of the +1 order and the diffracted light of the -1 order by the photoelectric receiving module; wherein the second polarized light component of the diffracted light of the -1 order and the first polarized light component of the diffracted light of the +1 order interfere with each other to produce a beat frequency signal with a frequency f B -f Ato form, while the first polarized light component of the diffracted light of the -1st order and the second polarized light component of the diffracted light of the +1st order interfere with each other to form another beat frequency signal with a frequency f B -f A to form; S4: Performing a respective difference calculation for the two paths of beat frequency signals by a signal processing system in order to realize the displacement measurement of the 4-fold optical subdivision by single diffraction of the one-dimensional measuring grid.

[0024] Preferably, step S2 is intended to include in particular the following steps: S201: Reflecting the first polarized light and the second polarized light vertically onto the surface of the one-dimensional measuring grating through a reflector of the read head to produce a diffracted light of the +1 order and a diffracted light of the -1 order; S202: Refraction of the diffracted light of the +1 order and the diffracted light of the -1 order by a deflecting element of the reading head, so that the diffracted light of the +1 order and the diffracted light of the -1 order are aligned parallel to each other and enter a polarizing beam splitter prism of the reading head vertically; S203: respective reflection of the first polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order onto a first quarter-wave plate of the reading head through the polarizing beam splitter prism and respective transmission of the second polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order onto a second quarter-wave plate of the reading head; S204: conversion of the first polarized light components of the diffracted +1 order light and the diffracted -1 order light into left-handed polarized light by the first quarter-wave plate and shining this light into a deflecting prism of the reading head; subsequent reflection of the first polarized light components of the diffracted +1 order light and the diffracted -1 order light twice by the deflecting prism, so that the first polarized light components of the diffracted +1 order light and the diffracted -1 order light are converted into P-polarized light by the first quarter-wave plate and then enter the polarizing beam splitter prism;and respective conversion of the second polarized light components of the diffracted +1 order light and the diffracted -1 order light into right-handed polarized light by the second quarter-wave plate and shining this light into a compensation mirror of the reading head; subsequent reflection of the second polarized light components of the diffracted +1 order light and the diffracted -1 order light by the compensation mirror, so that the second polarized light components of the diffracted +1 order light and the diffracted -1 order light are converted into S-polarized light by the second quarter-wave plate and then enter the polarizing beam splitter prism; S205: Transmitting the first polarized light components of the diffracted +1 order light and the diffracted -1 order light, which are converted into P-polarized light, to the photoelectric receiving module through the polarizing beam splitter prism and reflecting the second polarized light components of the diffracted +1 order light and the diffracted -1 order light, which are converted into S-polarized light, to the photoelectric receiving module.

[0025] Preferably, the thickness of the compensation mirror corresponds to half the length of the deflecting prism in order to compensate for the light path of the second polarized light components of the diffracted +1 order light and the diffracted -1 order light, so that the light path of the second polarized light components of the diffracted +1 order light and the diffracted -1 order light is the same as the light path of the first polarized light components of the diffracted +1 order light and the diffracted -1 order light.

[0026] Preferably, step S2 is intended to include in particular the following steps: S201': Incident of the first polarized light and the second polarized light into a polarizing beam splitter prism of the reading head, transmission of the second polarized light onto a first quarter-wave plate of the reading head through the polarizing beam splitter prism and reflection of the first polarized light onto a second quarter-wave plate of the reading head; S202': Converting the second polarized light into right-handed polarized light by the first quarter-wave plate and shining this light into a deflecting prism; reflecting the second polarized light back through the deflecting prism so that the second polarized light passes through the first quarter-wave plate and is converted into S-polarized light and then returns to the polarizing beam splitter prism; and converting the first polarized light through the second quarter-wave plate into left-handed polarized light, which is reflected by a reflective film, passes through the second quarter-wave plate again and is converted into P-polarized light and then returns to the polarizing beam splitter prism; S203': Transmitting the first polarized light, converted into P-polarized light, through the polarizing beam splitter prism and reflecting the second polarized light, converted into S-polarized light, so that the first polarized light and the second polarized light are combined and then incident on the surface of the one-dimensional measuring grating to produce, by diffraction, the diffracted light of the -1 order and the diffracted light of the +1 order; S204' : Refraction of the diffracted light of the -1 order and the diffracted light of the +1 order by a deflecting element of the reading head, so that the diffracted light of the -1 order and the diffracted light of the +1 order are aligned parallel to each other and occur vertically in a third quarter-wave plate of the reading head; S205': Conversion of the first polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order into S-polarized light by the third quarter-wave plate and radiating this vertically onto the polarizing beam splitter prism, as well as conversion of the second polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order into P-polarized light and radiating this vertically onto the polarizing beam splitter prism; S206': Reflecting the first polarized light components of the diffracted +1 order light and the diffracted -1 order light onto the first quarter-wave plate through the polarizing beam splitter prism and transmitting the second polarized light components of the diffracted +1 order light and the diffracted -1 order light onto the second quarter-wave plate; S207': Conversion of the first polarized light components of the diffracted +1 order light and the diffracted -1 order light by the first quarter-wave plate into left-hand polarized light and radiating this into the deflecting prism; after the first polarized light components of the diffracted +1 order light and the diffracted -1 order light have been reflected twice back onto the first quarter-wave plate by the deflecting prism and converted into P-polarized light, they are radiated once more into the polarizing beam splitter prism and transmitted through the polarizing beam splitter prism to the photoelectric receiving module;and wherein the second polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order are converted by the second quarter-wave plate into right-handed polarized light and reflected by the reflection film, pass through the second quarter-wave plate again and are converted into S-polarized light and then enter the polarizing beam splitter prism and are reflected by the polarizing beam splitter prism onto the photoelectric receiving module.

[0027] Preferably, the optical paths of the first polarized light component of the diffracted light of the -1 order and the second polarized light component of the diffracted light of the -1 order are the same, and the optical paths of the first polarized light component of the diffracted light of the +1 order and the second polarized light component of the diffracted light of the +1 order are the same.

[0028] Preferably, the photoelectric receiving module comprises a first receiver and a second receiver; wherein the first receiver receives the second polarized light component of the diffracted light of the -1st order and the first polarized light component of the diffracted light of the +1st order, as well as the beat frequency signal with a frequency f B -f A generated and transmits this to the signal processing system; and wherein the second receiver receives the first polarized light component of the diffracted light of the -1 order and the second polarized light component of the diffracted light of the +1 order as well as the other beat frequency signal with a frequency f B -f A generated and transmitted to the signal processing system.

[0029] Preferably, it is provided that when the one-dimensional measuring grid moves along a grid vector direction, the diffracted light of the -1st order undergoes a backward frequency shift -Δf and the diffracted light of the +1st order undergoes a forward frequency shift +Δf, whereby the frequency of the beat frequency signal output by the first receiver becomes f B -f A -2Δf and the frequency of the beat frequency signal output by the second receiver to f B -f A +2Δf changes.

[0030] Preferably, it is provided that the diffracted +1 order light and diffracted -1 order light produced by diffracting the one-dimensional measuring grating each enter a first rectangular prism and a second rectangular prism, wherein the first rectangular prism and the second rectangular prism each reflect the diffracted +1 order light and the diffracted -1 order light twice, which again enter the surface of the one-dimensional measuring grating at a diffraction exit angle, and wherein two beams of new diffracted light enter the polarizing beam splitter prism vertically.

[0031] The present invention provides a measuring device with a heterodyne two-dimensional grating, a light source used to generate two beams of linearly polarized lights that overlap each other and have orthogonal polarizations and a fixed frequency difference, wherein the linearly polarized lights are a first polarized light and a second polarized light; characterized in that it further comprises a reading head, a photoelectric receiving module and a signal processing system;wherein the read head is used to receive the first polarized light and the second polarized light, each incident on a surface of the moving two-dimensional measuring grating, to generate a diffracted ±1-order light in a first dimension and a diffracted ±1-order light in a second dimension, and wherein the diffracted ±1-order light in the first dimension and the diffracted ±1-order light in the second dimension then each enter the photoelectric receiving module via the read head; and wherein the photoelectric receiving module is used to generate a corresponding beat frequency signal in accordance with each of the diffracted ±1-order light in the first dimension and the diffracted ±1-order light in the second dimension, and to send this signal to the signal processing system;and wherein the signal processing system is used to perform a difference calculation for the beat frequency signals generated by the diffracted light of ±1 order in the first dimension and the beat frequency signals generated by the diffracted light of ±1 order in the second dimension, in order to realize the displacement measurement of the 4-fold optical subdivision by the single diffraction of the two-dimensional measuring grid in the first dimension and the second dimension.

[0032] Preferably, the first polarized light is an S-polarized light with a frequency f. A and the second polarized light is a P-polarized light with a frequency f Bis; wherein the reading head comprises a polarizing beam splitter prism, a first quarter-wave plate, a second quarter-wave plate coated with a reflective film, a third quarter-wave plate, a deflecting prism, and a deflecting element; wherein the polarizing beam splitter prism is used to receive the first polarized light and the second polarized light, to transmit the second polarized light to the first quarter-wave plate, and to reflect the first polarized light to the second quarter-wave plate; and wherein the first quarter-wave plate is arranged on a transmission light path of the polarizing beam splitter prism to convert the second polarized light into right-handed polarized light and then to radiate this into the deflecting prism;and wherein the deflecting prism is arranged on a transmission path of the first quarter-wave plate to reflect the second polarized light back, after the second polarized light has passed through the first quarter-wave plate again and been converted into S-polarized light, it returns to the polarizing beam splitter prism; and wherein the second quarter-wave plate is arranged on a reflection path of the polarizing beam splitter prism to convert the first polarized light into left-hand polarized light and then reflect it back, after it has passed through the second quarter-wave plate again and been converted into P-polarized light, it returns to the polarizing beam splitter prism;and wherein the polarizing beam splitter prism is further used to transmit the first polarized light and to reflect the second polarized light, so that the first polarized light and the second polarized light are combined and then enter the third quarter-wave plate;and wherein the third quarter-wave plate is arranged on a light path through which the polarizing beam splitter prism transmits the first polarized light, and is used to convert the first polarized light into right-handed polarized light and then shine it vertically onto the surface of the two-dimensional measuring grating, and to convert the second polarized light into left-handed polarized light and then shine it vertically onto the surface of the two-dimensional measuring grating, and wherein the first polarized light and the second polarized light are each diffracted to produce a diffracted light of ±1 order in the first dimension and a diffracted light of ±1 order in the second dimension.

[0033] Preferably, the diffracted ±1-order light in the first dimension comprises a diffracted -1-order light in the first dimension and a diffracted +1-order light in the first dimension, wherein the diffracted ±1-order light in the second dimension comprises a diffracted -1-order light in the second dimension and a diffracted +1-order light in the second dimension, and wherein the diffracted -1-order light in the first dimension, the diffracted +1-order light in the first dimension, the diffracted -1-order light in the second dimension, and the diffracted +1-order light in the second dimension each contain a first polarized light component and a second polarized light component.

[0034] Preferably, the reading head further comprises a deflecting element arranged on a diffraction light path of the two-dimensional measuring grating to refract the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension and the diffracted light of the +1 order in the second dimension, so that the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension and the diffracted light of the +1 order in the second dimension are aligned parallel to each other and enter the third quarter-wave plate;wherein the third quarter-wave plate is used to convert the first polarized light component in the diffracted -1 order light in the first dimension, the diffracted +1 order light in the first dimension, the diffracted -1 order light in the second dimension and the diffracted +1 order light in the second dimension into S-polarized light and to shine this vertically into the polarizing beam splitter prism, as well as to convert the second polarized light component in the diffracted -1 order light in the first dimension, the diffracted +1 order light in the first dimension, the diffracted -1 order light in the second dimension and the diffracted +1 order light in the second dimension into P-polarized light and to shine this vertically into the polarizing beam splitter prism;and wherein the polarizing beam splitter prism is used to reflect the first polarized light component in the diffracted -1 order light in the first dimension, the diffracted +1 order light in the first dimension, the diffracted -1 order light in the second dimension and the diffracted +1 order light in the second dimension onto the first quarter-wave plate and to transmit the second polarized light component in the diffracted -1 order light in the first dimension, the diffracted +1 order light in the first dimension, the diffracted -1 order light in the second dimension and the diffracted +1 order light in the second dimension onto the second quarter-wave plate;and wherein the first quarter-wave plate is used to convert the first polarized light component in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension and the diffracted light of the +1 order in the second dimension into a left-handed polarized light and to shine this light again into the deflecting prism;and wherein the deflecting prism is used to reflect the first polarized light component twice in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension and the diffracted light of the +1 order in the second dimension and to radiate it onto the first quarter-wave plate, after it has been converted into P-polarized light, it is again radiated into the polarizing beam splitter prism and transmitted through the polarizing beam splitter prism into the photoelectric receiving module;and wherein the second quarter-wave plate is used to convert the second polarized light component in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension and the diffracted light of the +1 order in the second dimension into right-handed polarized light and then to reflect this, after it has been passed through the second quarter-wave plate again and converted into S-polarized light, it is directed into the polarizing beam splitter prism and reflected by the polarizing beam splitter prism into the photoelectric receiving module.

[0035] Preferably, the photoelectric receiving module comprises a first receiver, a second receiver, a third receiver, and a fourth receiver; wherein the first receiver is used to receive the first polarized light component in the diffracted +1-order light in the first dimension and the second polarized light component in the diffracted -1-order light in the first dimension, as well as a beat frequency signal with a frequency f B -f A to generate and send this to the signal processing system; wherein the second receiver is used to receive the first polarized light component in the diffracted light of the -1 order in the first dimension and the second polarized light component in the diffracted light of the +1 order in the first dimension, as well as a beat frequency signal with a frequency f B -f Ato generate and send this to the signal processing system; wherein the third receiver is used to receive the first polarized light component in the diffracted +1 order light in the second dimension and the second polarized light component in the diffracted -1 order light in the second dimension, as well as a beat frequency signal with a frequency f B -f A to generate and send this to the signal processing system; wherein the fourth receiver is used to receive the first polarized light component in the diffracted light of the -1 order in the second dimension and the second polarized light component in the diffracted light of the +1 order in the second dimension, as well as a beat frequency signal with a frequency f B- f a to generate and send this to the signal processing system;

[0036] Preferably, it is provided that the first polarized light components and second polarized light components received by the first receiver, the second receiver, the third receiver and the fourth receiver each pass through the deflecting prism once, their light paths in the reading head being the same.

[0037] Preferably, it is provided that when the two-dimensional measuring grid moves along a grid vector direction in the first dimension, the diffracted light of the -1st order undergoes a backward frequency shift -Δf in the first dimension and the diffracted light of the +1st order undergoes a forward frequency shift +Δf in the first dimension, whereby the frequency of the beat frequency signal output by the first receiver becomes f B -f A -2Δf and the frequency of the beat frequency signal output by the second receiver to f B -f A+2Δf changes; that when the two-dimensional measuring grid moves along the grid vector direction in the second dimension, the diffracted light of the -1st order undergoes a backward frequency shift -Δf in the second dimension, and the diffracted light of the +1st order undergoes a forward frequency shift +Δf in the second dimension, whereby the frequency of the beat frequency signal output by the third receiver changes to f B -f A -2Δf and the frequency of the beat frequency signal output by the fourth receiver to f B -f A +2Δf changes.

[0038] Preferably, the signal processing system is used to perform a differential calculation for the beat frequency signal output by the first receiver and the beat frequency signal output by the second receiver in order to realize the displacement measurement of the 4-fold optical subdivision by single diffraction of the two-dimensional measuring grid in the first dimension, and to perform a differential calculation for the beat frequency signal output by the third receiver and the beat frequency signal output by the fourth receiver in order to realize the displacement measurement of the 4-fold optical subdivision by single diffraction of the two-dimensional measuring grid in the second dimension.

[0039] The present invention further provides a measurement method with a heterodyne two-dimensional grid, comprising the following steps: S1: Generating two beams of linearly polarized lights that overlap each other and have orthogonal polarizations and a fixed frequency difference, using a light source, wherein the linearly polarized lights each have a first polarized light with a frequency f A and a second polarized light with a frequency f B are, and where the first polarized light is an S-polarized light and the second polarized light is a P-polarized light; S2: Entry of the first polarized light and the second polarized light each into a reading head and, after reflection and transmission by the reading head, incident on a surface of the moving two-dimensional measuring grid to generate a diffracted light of ±1 order in a first dimension and a diffracted light of ±1 order in a second dimension, wherein the diffracted light of ±1 order in the first dimension and the diffracted light of ±1 order in the second dimension again incident via the reading head each into a photoelectric receiving module; S3: Generating a corresponding beat frequency signal by the photoelectric receiving module in accordance with the diffracted light of the ±1 order in the first dimension and the diffracted light of the ±1 order in the second dimension and sending this to a signal processing system; S4: Performing a difference calculation by the signal processing system for the beat frequency signals generated by the diffracted light of ±1 order in the first dimension and the beat frequency signals generated by the diffracted light of ±1 order in the second dimension, in order to realize the displacement measurement of the 4-fold optical subdivision by the single diffraction of the two-dimensional measuring grid in the first dimension and the second dimension.

[0040] Preferably, step S2 is intended to include in particular the following steps: S201: The first polarized light is reflected by a polarizing beam splitter prism onto a second quarter-wave plate, whereby the first polarized light is converted into left-handed polarized light and then reflected. After passing through the second quarter-wave plate again and being converted into P-polarized light, it returns to the polarizing beam splitter prism; and the second polarized light is transmitted by the polarizing beam splitter prism onto a first quarter-wave plate. After the second polarized light is converted into right-handed polarized light, it enters a deflecting prism, and the second polarized light is reflected back through the deflecting prism. After passing through the first quarter-wave plate again and being converted into S-polarized light, it returns to the polarizing beam splitter prism; S202: The polarizing beam splitter prism transmits the first polarized light and reflects the second polarized light, so that the first polarized light and the second polarized light are combined and then incident into a third quarter-wave plate; wherein the third quarter-wave plate converts the first polarized light into right-handed polarized light and then shines vertically onto the surface of the two-dimensional measuring grating, and converts the second polarized light into left-handed polarized light and then shines vertically onto the surface of the two-dimensional measuring grating, and wherein the first polarized light and the second polarized light are each diffracted to produce a diffracted light of ±1 order in the first dimension and a diffracted light of ±1 order in the second dimension.

[0041] Preferably, the diffracted ±1-order light in the first dimension comprises a diffracted -1-order light in the first dimension and a diffracted +1-order light in the first dimension, wherein the diffracted ±1-order light in the second dimension comprises a diffracted -1-order light in the second dimension and a diffracted +1-order light in the second dimension, and wherein the diffracted -1-order light in the first dimension, the diffracted +1-order light in the first dimension, the diffracted -1-order light in the second dimension, and the diffracted +1-order light in the second dimension each contain a first polarized light component and a second polarized light component.

[0042] Preferably, it is intended that after step S202 it will further include the following steps: S203: after the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension and the diffracted light of the +1 order in the second dimension have been refracted by a deflecting element, they are aligned parallel to each other and enter the third quarter-wave plate vertically; S204: The third quarter-wave plate converts the first polarized light component in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension, and the diffracted light of the +1 order in the second dimension into S-polarized light and shines this vertically into the polarizing beam splitter prism; it also converts the second polarized light component in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension, and the diffracted light of the +1 order in the second dimension into P-polarized light and shines this vertically into the polarizing beam splitter prism; S205: the polarizing beam splitter prism reflects the first polarized light component in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension and the diffracted light of the +1 order in the second dimension onto the first quarter-wave plate and transmits the second polarized light component in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension and the diffracted light of the +1 order in the second dimension onto the second quarter-wave plate; S206: The second quarter-wave plate converts the second polarized light component in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension and the diffracted light of the +1 order in the second dimension into right-hand polarized light and then reflects this, after it has been passed through the second quarter-wave plate again and converted into S-polarized light, it is radiated into the polarizing beam splitter prism and reflected by the polarizing beam splitter prism into the photoelectric receiving module;and the first quarter-wave plate converts the first polarized light component in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension and the diffracted light of the +1 order in the second dimension into a left-rotating polarized light and shines this again into the deflecting prism;The deflecting prism reflects the first polarized light component twice in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension, and the diffracted light of the +1 order in the second dimension, and emits this onto the first quarter-wave plate. After it has been converted into P-polarized light, it is again radiated into the polarizing beam splitter prism and transmitted through the polarizing beam splitter prism into the photoelectric receiving module.

[0043] Preferably, the photoelectric receiving module comprises a first receiver, a second receiver, a third receiver, and a fourth receiver; wherein the first receiver is used to receive the first polarized light component in the diffracted +1-order light in the first dimension and the second polarized light component in the diffracted -1-order light in the first dimension, as well as a beat frequency signal with a frequency f B -f A to generate and send this to the signal processing system; wherein the second receiver is used to receive the first polarized light component in the diffracted light of the -1 order in the first dimension and the second polarized light component in the diffracted light of the +1 order in the first dimension, as well as a beat frequency signal with a frequency f B -f Ato generate and send this to the signal processing system; wherein the third receiver is used to receive the first polarized light component in the diffracted +1 order light in the second dimension and the second polarized light component in the diffracted -1 order light in the second dimension, as well as a beat frequency signal with a frequency f B -f A to generate and send this to the signal processing system; wherein the fourth receiver is used to receive the first polarized light component in the diffracted light of the -1 order in the second dimension and the second polarized light component in the diffracted light of the +1 order in the second dimension, as well as a beat frequency signal with a frequency f B -f A to generate and send this to the signal processing system.

[0044] Preferably, it is provided that the first polarized light components and second polarized light components received by the first receiver, the second receiver, the third receiver and the fourth receiver each pass through the deflecting prism once, their light paths in the reading head being the same.

[0045] Preferably, it is provided that when the two-dimensional measuring grid moves along a grid vector direction in the first dimension, the diffracted light of the -1st order undergoes a backward frequency shift -Δf in the first dimension and the diffracted light of the +1st order undergoes a forward frequency shift +Δf in the first dimension, whereby the frequency of the beat frequency signal output by the first receiver becomes f B -f A -2Δf and the frequency of the beat frequency signal output by the second receiver to f B -f A+2Δf changes; that when the two-dimensional measuring grid moves along the grid vector direction in the second dimension, the diffracted light of the -1st order undergoes a backward frequency shift of -Δf in the second dimension and the diffracted light of the +1st order undergoes a forward frequency shift of +Δf in the second dimension, whereby the frequency of the beat frequency signal output by the third receiver becomes f B -f A -2Δf and the frequency of the beat frequency signal output by the fourth receiver to f B -f A +2Af changes.

[0046] Preferably, the signal processing system performs a differential calculation for the beat frequency signal output by the first receiver and the beat frequency signal output by the second receiver in order to realize the displacement measurement of the 4-fold optical subdivision by single diffraction of the two-dimensional measuring grid in the first dimension, and performs a differential calculation for the beat frequency signal output by the third receiver and the beat frequency signal output by the fourth receiver in order to realize the displacement measurement of the 4-fold optical subdivision by single diffraction of the two-dimensional measuring grid in the second dimension.

[0047] In contrast to the prior art, a 4-fold optical subdivision can be achieved in the present invention by single diffraction at the surface of the one-dimensional measuring grid and the two-dimensional measuring grid, thereby effectively avoiding the influence of the grid surface shape accuracy and grid holding error on the measurement accuracy. Furthermore, the advantages of a simple structure, small size, low weight, easy installation and convenient application, etc., are achieved. At the same time, the method of secondary diffraction or multiple diffraction can also be combined to achieve a higher multiple of the optical subdivision. BRIEF DESCRIPTION OF THE DRAWING Fig. Figure 1 shows a schematic structural view of a measuring device with a heterodyne one-dimensional grid in a first embodiment of the present invention. Fig. Figure 2 shows a schematic diagram of the principle of a measuring device with a heterodyne one-dimensional grid in the first embodiment of the present invention. Fig. Figure 3 shows a schematic diagram of the generation principle of a first beat frequency signal in the first embodiment of the present invention. Fig. Figure 4 shows a schematic diagram of the generation principle of a second beat frequency signal in the first embodiment of the present invention. Fig. Figure 5 shows a schematic diagram of the principle for realizing an 8-fold optical subdivision in combination with secondary diffraction in the first embodiment of the present invention. Fig. Figure 6 shows a flowchart of a measurement method with a heterodyne one-dimensional grid in a second embodiment of the present invention. Fig. Figure 7 shows a schematic diagram of the principle of a measuring device with a heterodyne one-dimensional grid in a third embodiment of the present invention. Fig. Figure 8 shows a schematic diagram of the generation principle of a first beat frequency signal in the third embodiment of the present invention. Fig. Figure 9 shows a schematic diagram of the generation principle of a second beat frequency signal in the third embodiment of the present invention. Fig. Figure 10 shows a flowchart of a measurement method with a heterodyne one-dimensional grid in a fourth embodiment of the present invention. Fig. Figure 11 shows a schematic diagram of the principle for realizing a 4-fold optical subdivision by single diffraction of a measuring device with a heterodyne two-dimensional grating in a fifth embodiment of the present invention. Fig. Figure 12 shows a schematic diagram of the transmission principle of the optical beam before beam diffraction in the fifth embodiment of the present invention. Fig. Figure 13 shows a schematic diagram of the generation principle of a first beat frequency signal in the first dimension in the fifth embodiment of the present invention. Fig. Figure 14 shows a schematic diagram of the generation principle of a second beat frequency signal in the first dimension in the fifth embodiment of the present invention. Fig. Figure 15 shows a schematic diagram of the generation principle of a first beat frequency signal in the second dimension in the fifth embodiment of the present invention. Fig. Figure 16 shows a schematic diagram of the generation principle of a second beat frequency signal in the second dimension in the fifth embodiment of the present invention. Fig. Figure 17 shows a flowchart of a displacement measurement method with a heterodyne two-dimensional grid in a sixth embodiment of the present invention.

[0048] Reference numeral list in the first embodiment: 1 Light source; 2 Read head; 201 Reflector; 202 Polarizing beam splitter prism; 203 First quarter-wave plate; 204 Second quarter-wave plate; 205 Deflection prism; 206 Deflection element; 207 Compensation mirror; 208 First rectangular prism; 209 Second rectangular prism; 301 First receiver; 302 Second receiver; 4 Signal processing system; 5 Measuring grid.

[0049] Reference numeral list in the third embodiment: 1' Light source; 2' Read head; 201' Polarizing beam splitter prism; 202' First quarter-wave plate; 203' Second quarter-wave plate; 204' Third quarter-wave plate; 205' Deflection prism; 206' Deflection element; 207' First right-angled prism; 208' Second right-angled prism; 301' First receiver; 302' Second receiver; 4' Signal processing system; 5' Measuring grid.

[0050] Reference numeral list in the fifth embodiment: 1 Light source; 201 Polarizing beam splitter prism; 202 First quarter-wave plate; 203 Second quarter-wave plate; 204 Third quarter-wave plate; 205 Deflection prism; 206 Deflection element; 301 First receiver; 302 Second receiver; 303 Third receiver; 304 Fourth receiver; 4 Signal processing system; 5 Two-dimensional measuring grid. DETAILED DESCRIPTION

[0051] The present invention is explained in more detail below in combination with the accompanying drawings and specific embodiments to clarify the objective, the technical solutions, and the advantages of the present invention. It is understood that the specific embodiments described here serve only to illustrate the present invention and do not constitute a limitation of the present invention.

[0052] In the measuring instrument with heterodyne grid according to the present invention, a measuring grid is attached to a measuring object and used as a ruler for displacement measurement; when the measuring grid moves with the measuring object, the displacement measurement of the measuring object is realized by the displacement measurement of the measuring grid.

[0053] In the prior art, 4-fold or higher optical subdivision is achieved through secondary diffraction or multiple diffraction, which complicates the optical structure of the measuring system, and multiple diffraction uses the diffracted light at different positions of the grating, whereby the shape accuracy of the grating surface and the grating alignment errors have a major influence on the measuring accuracy.In the measuring instrument with a heterodyne one-dimensional grating according to the present invention, the reading head has a special design such that when the two beams of polarized light emitted from the light source with a fixed frequency difference are incident on the surface of the measuring grating through the reading head, a 4-fold optical subdivision can be achieved by single diffraction. This avoids the influence of the grating surface shape accuracy and the grating alignment error on the measurement accuracy. Furthermore, the reading head of the present invention has a simple structure, small size, and low weight, which simplifies the complexity of the optical structure in the measuring system. The present invention can also achieve higher multiples of the optical subdivision in combination with secondary diffraction or multiple diffraction.

[0054] The measuring grid can be a one-dimensional measuring grid or a two-dimensional measuring grid; corresponding to the one-dimensional measuring grid, the measuring instrument with a heterodyne grid is a measuring instrument with a heterodyne one-dimensional grid, and corresponding to the two-dimensional measuring grid, the measuring instrument with a heterodyne grid is a measuring instrument with a heterodyne two-dimensional grid.

[0055] Using the example of achieving a 4-fold optical subdivision through single diffraction, the measuring device with heterodyne grating according to the present invention will be explained in more detail below in combination with the accompanying drawings. Example 1

[0056] As in Fig. Figures 1 to 4 show a measuring instrument with a heterodyne one-dimensional grating in a first embodiment of the present invention, comprising a light source 1, a read head 2, a photoelectric receiver module, and a signal processing system 4; wherein the light source 1 is used to generate two beams of linearly polarized lights that overlap each other and have orthogonal polarizations and a fixed frequency difference, and are used as measuring beams, and wherein the linearly polarized lights are each a first polarized light and a second polarized light, and wherein the first polarized light is an S-polarized light with a frequency f A and the second polarized light is a P-polarized light with a frequency f Bis, and wherein the light source 1 can be a dual-frequency laser device 1 or two laser devices with a fixed emitted frequency difference;and wherein the read head 2 is used such that two beams of polarized lights are incident on a surface of the moving one-dimensional measuring grating 5, and wherein, after diffraction through the surface of the one-dimensional measuring grating 5, the two beams of polarized lights produce a diffracted light of the +1 order and a diffracted light of the -1 order, which carry the measurement information, and wherein the diffracted light of the +1 order and the diffracted light of the -1 order each contain a first polarized light component and a second polarized light component, and wherein the first polarized light component and the second polarized light component of the diffracted light of the +1 order, as well as the first polarized light component and the second polarized light component of the diffracted light of the -1 order, each enter the photoelectric receiving module via the read head 2.

[0057] The reading head 2 comprises a reflector 201, a polarizing beam splitter prism 202, a first quarter-wave plate 203, a second quarter-wave plate 204, a deflecting prism 205, a deflecting element 206, and a compensation mirror 207 coated with a reflective film, wherein the reflector 201 is on the emitted light path of the light source 1, the deflecting element 206 is on the diffraction light path of the one-dimensional measuring grating 5, the polarizing beam splitter prism 202 is on the transmission light path of the deflecting element 206, the first quarter-wave plate 203 is on the reflection light path of the polarizing beam splitter prism 202, the second quarter-wave plate 204 is on the transmission light path of the polarizing beam splitter prism 202, and the deflecting prism 205 is on the transmission light path of the The first quarter-wave plate 203 and the compensation mirror 207 are arranged on the transmission light path of the second quarter-wave plate 204.

[0058] The reflector 201 reflects the first polarized light and the second polarized light vertically onto the surface of the one-dimensional measuring grating 5. The diffracted light of the +1 order and the diffracted light of the -1 order produced after diffraction are aligned parallel to each other after refraction by the deflecting element 206 and enter the polarizing beam splitter prism 202 vertically. The polarizing beam splitter prism 202 reflects the first polarized light component of the diffracted light of the +1 order and the first polarized light component of the diffracted light of the -1 order onto the first quarter-wave plate 203 and transmits the second polarized light component of the diffracted light of the +1 order and the second polarized light component of the diffracted light of the -1 order onto the second quarter-wave plate 204.

[0059] The first quarter-wave plate 203 converts the first polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order into left-handed polarized light and shines these into the deflecting prism 205;wherein the deflecting prism 205 reflects twice each the first polarized light component of the diffracted light of the +1 order and the first polarized light component of the diffracted light of the -1 order, so that the first polarized light component of the diffracted light of the +1 order and the first polarized light component of the diffracted light of the -1 order are again converted into P-polarized light by the first quarter-wave plate 203 and then again incident on the polarizing beam splitter prism 202, and wherein the polarizing beam splitter prism 202 transmits the first polarized light component of the diffracted light of the +1 order, converted into P-polarized light, to the first receiver 301 and transmits the first polarized light component of the diffracted light of the -1 order, converted into P-polarized light, to the second receiver 302.

[0060] The second quarter-wave plate 204 converts the second polarized light component of the diffracted light of the +1 order and the second polarized light component of the diffracted light of the -1 order into right-handed polarized light and shines these into the compensation mirror 207;wherein the second polarized light component of the diffracted +1 order light and the second polarized light component of the diffracted -1 order light, after reflection by the compensation mirror 207, return to the second quarter-wave plate 204, so that the second polarized light component of the diffracted +1 order light and the second polarized light component of the diffracted -1 order light are converted into S-polarized light and then again incident on the polarizing beam splitter prism 202, and wherein the polarizing beam splitter prism 202 reflects the second polarized light component of the diffracted +1 order light, converted into S-polarized light, to the second receiver 302 and reflects the second polarized light component of the diffracted -1 order light, converted into S-polarized light, to the first receiver 301.

[0061] Since the first polarized light component of the diffracted +1 order light and the first polarized light component of the diffracted -1 order light pass through the deflecting prism 205, while the second polarized light component of the diffracted +1 order light and the second polarized light component of the diffracted -1 order light do not pass through the deflecting prism 205, the light paths of the first polarized light component and the second polarized light component of the diffracted +1 order light are different, as are the light paths of the first polarized light component and the second polarized light component of the diffracted -1 order light. Therefore, the compensation mirror 207 compensates for the light paths of the second polarized light component of the diffracted +1 order light and the second polarized light component of the diffracted -1 order light.

[0062] In a specific embodiment of the present invention, the thickness (h / 2) of the compensating mirror 207 corresponds to half the length (h) of the deflecting prism 205, such that the path of the second polarized light component of the diffracted +1 order light, which enters the second receiver 302 after passing through the compensating mirror 207 twice, is the same as the path of the first polarized light component of the diffracted +1 order light, which enters the first receiver 301 through the deflecting prism 205, and the path of the second polarized light component of the diffracted -1 order light, which enters the first receiver 301 after passing through the compensating mirror 207 twice, is the same as the path of the first polarized light component of the diffracted -1 order light, which enters the second receiver through the deflecting prism 205. 302 comes to mind, isto achieve compensation for the light path of the second polarized light component of the diffracted +1 order light and the second polarized light component of the diffracted -1 order light.

[0063] There are two purposes for compensating the light path: First purpose: To ensure that the optical path difference has a constant value when the measuring beams enter the first receiver 301 and the second receiver 302; Second purpose: if the ambient temperature of the optical displacement measurement system with heterodyne grating changes, the optical path difference of the measuring beams changes in the same way, which is not affected by the thermal expansion and contraction of the optical elements of the read head 2, thus introducing no measurement error.

[0064] The photoelectric receiving module comprises a first receiver 301 and a second receiver 302, the first receiver 301 being used (as shown in Fig. 3 shown), to receive the second polarized light component of the diffracted light of the -1 order and the first polarized light component of the diffracted light of the +1 order, after the second polarized light component of the diffracted light of the -1 order and the first polarized light component of the diffracted light of the +1 order interfered with each other and a first beat frequency signal with a frequency f B -f A formed, the first receiver 301 transmits the first beat frequency signal to the signal processing system 4; and the second receiver 302 is used (as in Fig. 4 shown), to receive the first polarized light component of the diffracted light of the -1 order and the second polarized light component of the diffracted light of the +1 order, after the first polarized light component of the diffracted light of the -1 order and the second polarized light component of the diffracted light of the +1 order interfered with each other and a second beat frequency signal with a frequency f B -f A Once formed, the second receiver 302 transmits the second beat frequency signal to the signal processing system 4.

[0065] When the one-dimensional measuring grid 5 moves along the grid vector direction, due to the Doppler frequency shift effect of the grid, the diffracted light of the -1st order undergoes a backward frequency shift -Δf and the diffracted light of the +1st order undergoes a forward frequency shift +Δf, so that the frequency of the first beat frequency signal output by the first receiver 301 changes to f B -f A -2Δf and the frequency of the second beat frequency signal output by the second receiver 302 to f B -f A +2Δf changes.

[0066] The signal processing system 4 is used to receive the first and second beat frequency signals transmitted by the first receiver 301 and the second receiver 302, and to perform a differential calculation for the first and second beat frequency signals in order to realize the displacement measurement of the 4-fold optical subdivision by single diffraction of the one-dimensional measuring grid 5. Since the differential calculation is state of the art, it is not repeated here.

[0067] The present invention can also achieve an 8-fold optical subdivision in combination with secondary diffraction. As in Fig. As shown in Figure 5, the reading head 2 further comprises a first right-angled prism 208 and a second right-angled prism 209, wherein the first right-angled prism 208 and the second right-angled prism 209 are each arranged on the diffraction light path of the one-dimensional measuring grating 5, and wherein the diffracted light of the +1st order and the diffracted light of the -1st order are reflected twice and are again directed at the surface of the one-dimensional measuring grating 5 at the diffraction exit angle to realize a secondary diffraction, thereby generating two beams of new diffracted lights, and wherein the two beams of new diffracted lights emerge vertically from the surface of the one-dimensional measuring grating 5 and are incident vertically into the polarizing beam splitter prism 202.Secondary diffraction of the diffracted +1 order light and the diffracted -1 order light doubles the optical subdivision multiple, thereby improving the measurement resolution. Example 2

[0068] The first embodiment shows the structure of a measuring device with a heterodyne one-dimensional grid. Corresponding to the measuring device with a heterodyne one-dimensional grid in the first embodiment, the second embodiment provides a method for grid displacement measurement using the measuring device with a heterodyne one-dimensional grid in the first embodiment.

[0069] Fig. Figure 6 shows a measurement procedure with a heterodyne one-dimensional grid in the second embodiment of the present invention.

[0070] As in Fig. As shown in Figure 6, the measurement method with a heterodyne one-dimensional grid in the second embodiment of the present invention comprises the following steps: S1: Generating two beams of linearly polarized lights that overlap each other and have orthogonal polarizations and a fixed frequency difference, using a light source, wherein the linearly polarized lights each have a first polarized light with a frequency f A and a second polarized light with a frequency f B are, and where the first polarized light is an S-polarized light and the second polarized light is a P-polarized light; S2: the first polarized light and the second polarized light each enter a read head and, after being refracted by the read head, each strike a surface of the one-dimensional measuring grating to generate a diffracted +1-order light and a diffracted -1-order light, each containing a first polarized light component and a second polarized light component, wherein the diffracted +1-order light and the diffracted -1-order light again pass through the read head into a photoelectric receiving module; and wherein step S2 in particular comprises the following steps: S201: Reflecting the first polarized light and the second polarized light vertically onto the surface of the one-dimensional measuring grating through a reflector of the read head to produce a diffracted light of the +1 order and a diffracted light of the -1 order; S202: Refraction of the diffracted light of the +1 order and the diffracted light of the -1 order by a deflecting element of the reading head, so that the diffracted light of the +1 order and the diffracted light of the -1 order are aligned parallel to each other and enter a polarizing beam splitter prism of the reading head vertically; S203: respective reflection of the first polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order onto a first quarter-wave plate of the reading head through the polarizing beam splitter prism and respective transmission of the second polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order onto a second quarter-wave plate of the reading head; S204: conversion of the first polarized light components of the diffracted +1 order light and the diffracted -1 order light into left-handed polarized light by the first quarter-wave plate and shining this light into a deflecting prism of the reading head; subsequent reflection of the first polarized light components of the diffracted +1 order light and the diffracted -1 order light twice by the deflecting prism, so that the first polarized light components of the diffracted +1 order light and the diffracted -1 order light are converted into P-polarized light by the first quarter-wave plate and then enter the polarizing beam splitter prism;and respective conversion of the second polarized light components of the diffracted +1 order light and the diffracted -1 order light into right-handed polarized light by the second quarter-wave plate and shining this light into a compensation mirror of the reading head; subsequent reflection of the second polarized light components of the diffracted +1 order light and the diffracted -1 order light by the compensation mirror, so that the second polarized light components of the diffracted +1 order light and the diffracted -1 order light are converted into S-polarized light by the second quarter-wave plate and then enter the polarizing beam splitter prism; wherein the thickness of the compensation mirror corresponds to half the length of the deflecting prism in order to compensate the light path of the second polarized light components of the diffracted +1 order light and the diffracted -1 order light, so that the light path of the second polarized light components of the diffracted +1 order light and the diffracted -1 order light is the same as the light path of the first polarized light components of the diffracted +1 order light and the diffracted -1 order light; S205: Transmitting the first polarized light components of the diffracted +1 order light and the diffracted -1 order light, which are converted into P-polarized light, to the photoelectric receiving module through the polarizing beam splitter prism, and reflecting the second polarized light components of the diffracted +1 order light and the diffracted -1 order light, which are converted into S-polarized light, to the photoelectric receiving module; S3: Receiving the diffracted light of the +1 order and the diffracted light of the -1 order by the photoelectric receiving module; wherein the second polarized light component of the diffracted light of the -1 order and the first polarized light component of the diffracted light of the +1 order interfere with each other to produce a beat frequency signal with a frequency f B -f Ato form, while the first polarized light component of the diffracted light of the -1st order and the second polarized light component of the diffracted light of the +1st order interfere with each other to form another beat frequency signal with a frequency f B -f A to form; The photoelectric receiving module comprises a first receiver and a second receiver; wherein the second polarized light component of the diffracted light of the -1 order and the first polarized light component of the diffracted light of the +1 order are received by the first receiver, and the two interfere with each other to produce a first beat frequency signal with a frequency f B -f Ato generate and transmit this to a signal processing system; and wherein the second receiver receives the first polarized light component of the diffracted light of the -1 order and the second polarized light component of the diffracted light of the +1 order, and the two interfere with each other to generate a second beat frequency signal with a frequency f B -f A to generate and transmit this to the signal processing system; When the one-dimensional measuring grid moves along the grid vector direction, the diffracted light of the -1st order undergoes a backward frequency shift -Δf and the diffracted light of the +1st order undergoes a forward frequency shift +Δf, whereby the frequency of the first beat frequency signal emitted by the first receiver becomes f B -f A -2Δf and the frequency of the second beat frequency signal output by the second receiver to f B -f A+2Δf changes; S4: Performing a respective difference calculation for the two paths of beat frequency signals by a signal processing system in order to realize the displacement measurement of the 4-fold optical subdivision by single diffraction of the one-dimensional measuring grid.

[0071] The signal processing system performs a differential calculation between the first beat frequency signal output by the first receiver and the second beat frequency signal output by the second receiver in order to achieve the displacement measurement of the 4-fold optical subdivision by single diffraction of the one-dimensional measuring grid. Since differential calculation is state of the art, it is not repeated here.

[0072] To achieve a higher multiple of the optical division, the diffracted +1-order and -1-order light generated by diffracting the one-dimensional measuring grating can each be incident into a first rectangular prism and a second rectangular prism, respectively. The first rectangular prism and the second rectangular prism each reflect the diffracted +1-order and -1-order light twice, respectively. These two reflections are then incident a second time at the diffraction angle onto the surface of the one-dimensional measuring grating. Two beams of newly diffracted light then incident vertically onto the polarizing beam splitter prism. A secondary diffraction of the diffracted +1-order and -1-order light doubles the multiple of the optical division, thereby improving the measurement resolution. Example 3

[0073] As in Fig. Figures 7 to 9 show a measuring instrument with a heterodyne one-dimensional grating in a third embodiment of the present invention, comprising a light source 1', a read head 2', a photoelectric receiver module, and a signal processing system 4'; wherein the light source 1' is used to generate two beams of linearly polarized lights that overlap each other and have orthogonal polarizations and a fixed frequency difference and are used as measuring beams, and wherein the linearly polarized lights are each a first polarized light and a second polarized light, and wherein the first polarized light is an S-polarized light with a frequency f A and the second polarized light is a P-polarized light with a frequency f Bis, and wherein the light source 1' can be a dual-frequency laser device or two laser devices with a fixed emitted frequency difference;and wherein the read head 2' is used such that two beams of polarized lights are incident on a surface of the moving one-dimensional measuring grating 5', and wherein, after diffraction by the surface of the one-dimensional measuring grating 5', the two beams of polarized lights produce a diffracted light of the +1 order and a diffracted light of the -1 order, which carry the measurement information, and wherein the diffracted light of the +1 order and the diffracted light of the -1 order each contain a first polarized light component and a second polarized light component, and wherein the first polarized light component and the second polarized light component of the diffracted light of the +1 order, as well as the first polarized light component and the second polarized light component of the diffracted light of the -1 order, each enter the photoelectric receiving module via the read head 2'.;

[0074] The reading head 2' comprises a polarizing beam splitter prism 201', a first quarter-wave plate 202', a second quarter-wave plate 203' coated with a reflective film, a third quarter-wave plate 204', a deflecting prism 205' and a deflecting element 206', wherein the polarizing beam splitter prism 201' is on the emitted light path of the light source 1', the deflecting element 206' is on the diffraction light path of the one-dimensional measuring grating 5', the first quarter-wave plate 202' is on the transmission light path of the polarizing beam splitter prism 201', the second quarter-wave plate 203' is on the reflection light path of the polarizing beam splitter prism 201', the third quarter-wave plate 204' is on the transmission light path of the deflecting element 206' and the deflecting prism 205' is arranged on the transmission light path of the first quarter-wave plate 202'.

[0075] The polarizing beam splitter prism 201' receives the first polarized light and the second polarized light, transmits the second polarized light to the first quarter-wave plate 202' and reflects the first polarized light to the second quarter-wave plate 203'; the first quarter-wave plate 202' converts the second polarized light into right-hand polarized light and shines this into the deflecting prism 205'; and the deflecting prism 205' reflects the second polarized light back, so that the second polarized light passes through the first quarter-wave plate 202' and is converted into S-polarized light and then returns to the polarizing beam splitter prism 201';and wherein the second quarter-wave plate 203' converts the first polarized light into left-hand polarized light, which is reflected by the reflection film, passes again through the second quarter-wave plate 203' and is converted into P-polarized light, and then returns to the polarizing beam splitter prism 201'; and wherein the polarizing beam splitter prism 201' transmits the first polarized light converted into P-polarized light and reflects the second polarized light converted into S-polarized light, so that the first polarized light and the second polarized light are combined and then incident on the surface of the one-dimensional measuring grating 5' to produce, by diffraction, the diffracted light of the -1 order and the diffracted light of the +1 order;and wherein the deflecting element 206' refracts the diffracted light of the -1 order and the diffracted light of the +1 order, such that the diffracted light of the -1 order and the diffracted light of the +1 order are aligned parallel to each other and are incident vertically into the third quarter-wave plate 204'; and wherein the third quarter-wave plate 204' converts the first polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order into S-polarized light and shines this vertically onto the polarizing beam splitter prism 201', and converts the second polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order into P-polarized light and shines this vertically onto the polarizing beam splitter prism 201';and wherein the polarizing beam splitter prism 201' reflects the first polarized light components of the diffracted +1 order light and the diffracted -1 order light onto the first quarter-wave plate 202' and transmits the second polarized light components of the diffracted +1 order light and the diffracted -1 order light onto the second quarter-wave plate 203'; and wherein the first quarter-wave plate 202' converts the first polarized light components of the diffracted +1 order light and the diffracted -1 order light into left-handed polarized light and shines these into the deflecting prism 205';and wherein the deflecting prism 205' reflects the first polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order twice back onto the first quarter-wave plate 202', after they have been converted into P-polarized light, they are again radiated into the polarizing beam splitter prism 201' and transmitted through the polarizing beam splitter prism 201' to the photoelectric receiving module;and wherein the second quarter-wave plate 203' converts the second polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order into right-handed polarized light, and wherein they are reflected by the reflection film after passing through the second quarter-wave plate 203' again and being converted into S-polarized light, they are directed into the polarizing beam splitter prism 201' and reflected by the polarizing beam splitter prism 201' onto the photoelectric receiving module.;

[0076] Since the first polarized light component of the diffracted light of the -1 order and the second polarized light component of the diffracted light of the -1 order, as well as the first polarized light component of the diffracted light of the +1 order and the second polarized light component of the diffracted light of the +1 order, each pass through the deflecting prism 205' once, the light paths of the first polarized light component of the diffracted light of the -1 order and the second polarized light component of the diffracted light of the -1 order are equal in the reading head 2', and the light paths of the first polarized light component of the diffracted light of the +1 order and the second polarized light component of the diffracted light of the +1 order are equal in the reading head 2', the functions are achieved at two aspects: The first aspect ensures that the optical path difference has a constant value when the measuring beams enter the photoelectric receiving module; On the other side, when the ambient temperature of the measuring instrument with heterodyne one-dimensional grating changes, the optical path difference of the measuring beams changes in the same way, which is not affected by the thermal expansion and contraction of the optical elements of the read head 2', thus introducing no measurement error.

[0077] The photoelectric receiving module comprises a first receiver 301' and a second receiver 302', wherein the first receiver 301' is used to receive the second polarized light component of the diffracted -1 order light and the first polarized light component of the diffracted +1 order light after the second polarized light component of the diffracted -1 order light and the first polarized light component of the diffracted +1 order light have interfered with each other and produced a first beat frequency signal with a frequency f B -f Aformed, the first receiver 301' transmits the first beat frequency signal to the signal processing system 4'; and wherein the second receiver 302' is used to receive the first polarized light component of the diffracted light of the -1 order and the second polarized light component of the diffracted light of the +1 order, after the first polarized light component of the diffracted light of the -1 order and the second polarized light component of the diffracted light of the +1 order have interfered with each other and formed a second beat frequency signal with a frequency f B -f A Once formed, the second receiver 302' transmits the second beat frequency signal to the signal processing system 4'.

[0078] When the one-dimensional measuring grid 5 moves along the grid vector direction, due to the Doppler frequency shift effect of the grid, the diffracted light of the -1st order undergoes a backward frequency shift -Δf and the diffracted light of the +1st order undergoes a forward frequency shift +Δf, so that the frequency of the first beat frequency signal output by the first receiver 301' becomes f B -f A -2Δf and the frequency of the second beat frequency signal output by the second receiver 302' to f B -f A +2Δf changes.

[0079] The signal processing system 4' is used to receive the beat frequency signals transmitted by the first receiver 301' and the second receiver 302', and to perform a differential calculation for two paths of beat frequency signals in order to realize the displacement measurement of the 4-fold optical subdivision by single diffraction of the one-dimensional measuring grid 5'. Since the differential calculation is state of the art, it is not repeated here. Example 4

[0080] The third embodiment shows the structure of another measuring device with a heterodyne one-dimensional grid; corresponding to the measuring device with a heterodyne one-dimensional grid in the third embodiment, the fourth embodiment provides a method for grid displacement measurement using the measuring device with a heterodyne one-dimensional grid in the third embodiment.

[0081] Fig. Figure 10 shows a sequence of a measurement procedure with a heterodyne one-dimensional grid in the fourth embodiment of the present invention.

[0082] As in Fig. As shown in 10, the measurement method with a heterodyne one-dimensional grid in the fourth embodiment of the present invention comprises the following steps: S1: Generating two beams of linearly polarized lights that overlap each other and have orthogonal polarizations and a fixed frequency difference, using a light source, wherein the linearly polarized lights each have a first polarized light with a frequency f A and a second polarized light with a frequency f B are, and where the first polarized light is an S-polarized light and the second polarized light is a P-polarized light; S2: the first polarized light and the second polarized light each enter a read head and, after being refracted by the read head, each strike a surface of the one-dimensional measuring grating to generate a diffracted +1-order light and a diffracted -1-order light, each containing a first polarized light component and a second polarized light component, wherein the diffracted +1-order light and the diffracted -1-order light again pass through the read head into a photoelectric receiving module; wherein step S2 in particular comprises the following steps: S201': the first polarized light and the second polarized light enter a polarizing beam splitter prism of the reading head, transmitting the second polarized light onto a first quarter-wave plate of the reading head through the polarizing beam splitter prism and reflecting the first polarized light onto a second quarter-wave plate of the reading head; S202': Converting the second polarized light into right-handed polarized light by the first quarter-wave plate and shining this light into a deflecting prism; reflecting the second polarized light back through the deflecting prism so that the second polarized light passes through the first quarter-wave plate and is converted into S-polarized light and then returns to the polarizing beam splitter prism; and converting the first polarized light through the second quarter-wave plate into left-handed polarized light, which is reflected by a reflective film, passes through the second quarter-wave plate again and is converted into P-polarized light and then returns to the polarizing beam splitter prism; S203': Transmitting the first polarized light, converted into P-polarized light, through the polarizing beam splitter prism and reflecting the second polarized light, converted into S-polarized light, so that the first polarized light and the second polarized light are combined and then incident on the surface of the one-dimensional measuring grating to produce, by diffraction, the diffracted light of the -1 order and the diffracted light of the +1 order; S204' : Refraction of the diffracted light of the -1 order and the diffracted light of the +1 order by a deflecting element of the reading head, so that the diffracted light of the -1 order and the diffracted light of the +1 order are aligned parallel to each other and occur vertically in a third quarter-wave plate of the reading head; S205': Conversion of the first polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order into S-polarized light by the third quarter-wave plate and radiating this vertically onto the polarizing beam splitter prism, as well as conversion of the second polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order into P-polarized light and radiating this vertically onto the polarizing beam splitter prism; S206': Reflecting the first polarized light components of the diffracted +1 order light and the diffracted -1 order light onto the first quarter-wave plate through the polarizing beam splitter prism and transmitting the second polarized light components of the diffracted +1 order light and the diffracted -1 order light onto the second quarter-wave plate; S207': Conversion of the first polarized light components of the diffracted +1 order light and the diffracted -1 order light by the first quarter-wave plate into left-hand polarized light and radiating this into the deflecting prism; after the first polarized light components of the diffracted +1 order light and the diffracted -1 order light have been reflected twice back onto the first quarter-wave plate by the deflecting prism and converted into P-polarized light, they are radiated once more into the polarizing beam splitter prism and transmitted through the polarizing beam splitter prism to the photoelectric receiving module;and wherein the second polarized light components of the diffracted light of the +1 order and the diffracted light of the -1 order are converted by the second quarter-wave plate into right-handed polarized light and reflected by the reflection film, pass through the second quarter-wave plate again and are converted into S-polarized light and then enter the polarizing beam splitter prism and are reflected by the polarizing beam splitter prism onto the photoelectric receiving module.

[0083] Since the first polarized component of the diffracted -1 order light and the second polarized component of the diffracted -1 order light, as well as the first polarized component of the diffracted +1 order light and the second polarized component of the diffracted +1 order light, each pass through the deflecting prism once, the light paths of the first polarized component of the diffracted -1 order light and the second polarized component of the diffracted -1 order light in the reading head are the same, and the light paths of the first polarized component of the diffracted +1 order light and the second polarized component of the diffracted +1 order light in the reading head are the same, the functions being reflected in two aspects: The first aspect ensures that the optical path difference has a constant value when the measuring beams enter the photoelectric receiving module; In the second aspect, when the ambient temperature of the measuring instrument with a heterodyne one-dimensional grating changes, the optical path difference of the measuring beams changes in the same way, which is not affected by the thermal expansion and contraction of the optical elements of the read head, thus introducing no measurement error; S3: Receiving the diffracted light of the +1 order and the diffracted light of the -1 order by the photoelectric receiving module; wherein the second polarized light component of the diffracted light of the -1 order and the first polarized light component of the diffracted light of the +1 order interfere with each other to produce a beat frequency signal with a frequency f B -f Ato form, while the first polarized light component of the diffracted light of the -1st order and the second polarized light component of the diffracted light of the +1st order interfere with each other to form another beat frequency signal with a frequency f B -f A to form; wherein the photoelectric receiving module comprises a first receiver and a second receiver; wherein the first receiver is used to receive the second polarized light component of the diffracted light of the -1st order and the first polarized light component of the diffracted light of the +1st order, as well as a beat frequency signal with a frequency f B -f Ato generate and transmit this to a signal processing system; and wherein the second receiver is used to receive the first polarized light component of the diffracted light of the -1st order and the second polarized light component of the diffracted light of the +1st order, as well as another beat frequency signal with a frequency f B -f A to generate and transmit this to the signal processing system; When the one-dimensional measuring grid moves along the grid vector direction, the diffracted light of the -1st order undergoes a backward frequency shift -Δf and the diffracted light of the +1st order undergoes a forward frequency shift +Δf, whereby the frequency of the beat frequency signal output by the first receiver becomes f B -f A -2Δf and the frequency of the beat frequency signal output by the second receiver to f B -f A +2Δf changes.

[0084] To achieve a higher multiple of the optical division, the diffracted +1-order and -1-order light generated by diffracting the one-dimensional measuring grating can each be incident into a first rectangular prism and a second rectangular prism, respectively. The first rectangular prism and the second rectangular prism each reflect the diffracted +1-order and -1-order light twice, respectively. These two reflections are then incident a second time at the diffraction angle onto the surface of the one-dimensional measuring grating. Two beams of newly diffracted light then incident vertically onto the polarizing beam splitter prism. A secondary diffraction of the diffracted +1-order and -1-order light doubles the multiple of the optical division, thereby improving the measurement resolution.

[0085] S4: Performing a respective difference calculation for the two paths of beat frequency signals by a signal processing system in order to realize the displacement measurement of the 4-fold optical subdivision by single diffraction of the one-dimensional measuring grid.

[0086] The signal processing system performs a differential calculation between the first beat frequency signal output by the first receiver and the second beat frequency signal output by the second receiver in order to achieve the displacement measurement of the 4-fold optical subdivision by single diffraction of the one-dimensional measuring grid. Since differential calculation is state of the art, it is not repeated here. Example 5

[0087] Fig. Figure 11 shows the structure of a measurement method with a heterodyne two-dimensional grid in the fifth embodiment of the present invention.

[0088] As in Fig. Figure 11 shows a measuring device with a heterodyne two-dimensional grating in the fifth embodiment of the present invention, comprising a light source 1, a read head, a photoelectric receiver module, and a signal processing system 4; wherein the light source 1 is used to generate two beams of linearly polarized lights that overlap each other and have orthogonal polarizations and a fixed frequency difference, and wherein the linearly polarized lights are each a first polarized light and a second polarized light, and wherein the first polarized light is an S-polarized light with a frequency f A and the second polarized light is a P-polarized light with a frequency f Bis, and wherein the light source 1 can be a dual-frequency laser device 1 or two laser devices with a fixed emitted frequency difference; and wherein the read head is used to shine two beams of linearly polarized light onto a surface of the moving two-dimensional measuring grid 5, after the two beams of linearly polarized light have been diffracted by the surface of the two-dimensional measuring grid 5, a diffracted light of ±1 order in a first dimension and a diffracted light of ±1 order in a second dimension are produced, wherein the diffracted light of ±1 order in the first dimension and the diffracted light of ±1 order in the second dimension are reflected back into the read head and finally exit the read head and enter the photoelectric receiving module; and wherein the photoelectric receiving module is used to,to receive the diffracted light of ±1 order in the first dimension and the diffracted light of ±1 order in the second dimension, to generate four paths of beat frequency signals and to implement a 4-fold optical subdivision, and wherein the photoelectric receiving module comprises a first receiver 301, a second receiver 302, a third receiver 303 and a fourth receiver 304; and wherein the first receiver 301 and the second receiver 302 are used to receive the diffracted light of ±1 order in the first dimension, to generate two paths of beat frequency signals and to send these to the signal processing system 4, and wherein the third receiver 303 and the fourth receiver 304 are used to receive the diffracted light of ±1 order in the second dimension, to generate two paths of beat frequency signals and to send these to the signal processing system 4,and wherein the signal processing system 4 is used to receive the beat frequency signals transmitted by the first receiver 301, the second receiver 302, the third receiver 303 and the fourth receiver 304, and to perform a differential calculation for the beat frequency signals transmitted by the first receiver 301 and the second receiver 302 in order to realize the displacement measurement of the 4-fold optical subdivision by the single diffraction of the two-dimensional measuring grid 5 in the first dimension, as well as to perform a differential calculation for the beat frequency signals transmitted by the third receiver 303 and the fourth receiver 304 in order to realize the displacement measurement of the 4-fold optical subdivision by the single diffraction of the two-dimensional measuring grid 5 in the second dimension.

[0089] The read head comprises a polarizing beam splitter prism 201, a first quarter-wave plate 202, a second quarter-wave plate 203, a third quarter-wave plate 204, a deflecting prism 205, and a deflecting element 206; wherein the polarizing beam splitter prism 201 is used to reflect the S-polarized light and transmit the P-polarized light; and wherein the first quarter-wave plate 202 is arranged on the transmission light path of the polarizing beam splitter prism 201 and the second quarter-wave plate 203 is arranged on the reflection light path of the polarizing beam splitter prism 201, and wherein a surface of the second quarter-wave plate 203 is coated with a reflective film to achieve reflection of the laser;and wherein the third quarter-wave plate 204 is arranged on an opposite side of the second quarter-wave plate 203, namely on the transmission light path of the polarizing beam splitter prism 201 in a different direction; and wherein the deflecting prism 205 is arranged on the transmission light path of the first quarter-wave plate 202 to reverse the laser; and wherein the deflecting element 206 is arranged on the diffraction light path of the two-dimensional measuring grating 5 to refract the laser.

[0090] Fig. Figure 12 shows the principle of light path transfer prior to beam diffraction in the fifth embodiment of the present invention.

[0091] As in Fig. As shown in Figure 12, the path of the first polarized light and the second polarized light before they enter the two-dimensional measuring grating 5 and are diffracted is as follows: the first polarized light emitted by the light source 1 enters the polarizing beam splitter prism 201, the first polarized light is reflected by the polarizing beam splitter prism 201 onto the second quarter-wave plate 203 and converted into left-hand polarized light, the first polarized light is reflected back onto the second quarter-wave plate 203 by the reflective film coated on the second quarter-wave plate 203, the second quarter-wave plate 203 converts the first polarized light into P-polarized light and the first polarized light returns to the polarizing beam splitter prism 201;The second polarized light emitted by the light source 1 enters the polarizing beam splitter prism 201, the second polarized light is transmitted by the polarizing beam splitter prism 201 onto the first quarter-wave plate 202 and converted into right-hand polarized light, then the second polarized light enters the deflecting prism 205, the deflecting prism 205 reflects the second polarized light back onto the first quarter-wave plate 202, the first quarter-wave plate 202 converts the second polarized light into S-polarized light, and the second polarized light returns to the polarizing beam splitter prism 201;The polarizing beam splitter prism 201 transmits the first polarized light (the P-polarized light) and reflects the second polarized light (the S-polarized light), so that the first polarized light and the second polarized light are combined and then enter the third quarter-wave plate 204; the third quarter-wave plate 204 converts the first polarized light into right-handed polarized light and shines this onto the surface of the two-dimensional measuring grid 5 and converts the second polarized light into left-handed polarized light and shines this onto the surface of the two-dimensional measuring grid 5.

[0092] After diffraction through the two-dimensional measuring grid 5, the first polarized light produces a diffracted light of -1 order in the first dimension and a diffracted light of +1 order in the first dimension; and after diffraction through the two-dimensional measuring grid 5, the second polarized light produces a diffracted light of -1 order in the second dimension and a diffracted light of +1 order in the second dimension.

[0093] The first dimension and the second dimension refer to the dimensional divisions according to the direction of the lines of the two-dimensional measuring grid 5, i.e., two directions of the lines on the surface of the two-dimensional measuring grid 5.

[0094] The diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension, and the diffracted light of the +1 order in the second dimension each contain a first polarized light component and a second polarized light component.

[0095] The first polarized light component in the diffracted +1 order light in the first dimension and the second polarized light component in the diffracted -1 order light in the first dimension generate a first beat frequency signal in the first dimension.

[0096] The first polarized light component in the diffracted light of the -1 order in the first dimension and the second polarized light component in the diffracted light of the +1 order in the first dimension generate a second beat frequency signal in the first dimension.

[0097] The first polarized light component in the diffracted +1 order light in the second dimension and the second polarized light component in the diffracted -1 order light in the second dimension generate a first beat frequency signal in the second dimension.

[0098] The first polarized light component in the diffracted light of the -1 order in the second dimension and the second polarized light component in the diffracted light of the +1 order in the second dimension generate a second beat frequency signal in the second dimension.

[0099] Fig. Figures 13 to 16 show the generation principle of the first beat frequency signal in the first dimension, the second beat frequency signal in the first dimension, the first beat frequency signal in the second dimension and the second beat frequency signal in the second dimension in the fifth embodiment of the present invention.

[0100] As in Fig. Figures 13 to 16 show that after the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension and the diffracted light of the +1 order in the second dimension have been refracted by the deflecting element 206, they are aligned parallel to each other and enter the third quarter-wave plate 204 vertically.

[0101] The third quarter-wave plate 204 converts the first polarized light component in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension and the diffracted light of the +1 order in the second dimension into S-polarized light and shines this vertically into the polarizing beam splitter prism 201, as well as converting the second polarized light component in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension and the diffracted light of the +1 order in the second dimension into P-polarized light and shines this vertically into the polarizing beam splitter prism 201.

[0102] The polarizing beam splitter prism 201 reflects the first polarized light component in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension and the diffracted light of the +1 order in the second dimension onto the first quarter-wave plate 202 and transmits the second polarized light component in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension and the diffracted light of the +1 order in the second dimension onto the second quarter-wave plate 203.

[0103] The second quarter-wave plate 203 converts the second polarized light component in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension and the diffracted light of the +1 order in the second dimension into a right-hand polarized light and then reflects this through the reflection film, after it has passed through the second quarter-wave plate 203 again and been converted into an S-polarized light, it is shone into the polarizing beam splitter prism 201 and reflected by the polarizing beam splitter prism 201 and shone into the first receiver 301, the second receiver 302, the third receiver 303 and the fourth receiver 304 respectively.

[0104] The first quarter-wave plate 202 converts the first polarized light component in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension, and the diffracted light of the +1 order in the second dimension into left-hand polarized light and shines this light again into the deflecting prism 205; the deflecting prism 205 reflects twice the first polarized light component in the diffracted light of the +1 order in the first dimension, which is emitted along the incident light path of the first polarized light component in the diffracted light of the -1 order in the first dimension and returns to the first quarter-wave plate 202;The deflecting prism 205 reflects twice the first polarized light component in the diffracted light of the -1 order in the first dimension, which precipitates along the incident light path of the first polarized light component in the diffracted light of the +1 order in the first dimension and returns to the first quarter-wave plate 202; the deflecting prism 205 reflects twice the first polarized light component in the diffracted light of the +1 order in the second dimension, which precipitates along the incident light path of the first polarized light component in the diffracted light of the -1 order in the second dimension and returns to the first quarter-wave plate 202;The deflecting prism 205 reflects twice the first polarized light component in the diffracted light of the -1 order in the second dimension, which falls along the incident light path of the first polarized light component in the diffracted light of the +1 order in the second dimension and returns to the first quarter-wave plate 202;The first polarized light components in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension, and the diffracted light of the +1 order in the second dimension pass through the first quarter-wave plate 202 again and are converted into P-polarized light. They enter the polarizing beam splitter prism 201 again and are transmitted through it. Then they enter the second receiver 302, the first receiver 301, the fourth receiver 304, and the third receiver 303, respectively.

[0105] It should be noted that the first polarized light components and the second polarized light components received by the first receiver 301, the second receiver 302, the third receiver 303 and the fourth receiver 304 each pass once through the deflecting prism 205, their light paths being the same in the reading head, thereby achieving the functions in two aspects: The first aspect ensures that the optical path difference has a constant value when the measurement signal enters the first receiver 301, the second receiver 302, the third receiver 303 and the fourth receiver 304; The second aspect is that when the ambient temperature of the measuring instrument with a heterodyne two-dimensional grating changes, the optical path difference of the measuring beams changes in the same way, which is not affected by the thermal expansion and contraction of the optical elements of the read head, thus introducing no measurement error.

[0106] The first receiver 301 is used to receive the first polarized light component in the diffracted +1-order light in the first dimension and the second polarized light component in the diffracted -1-order light in the first dimension, as well as a first beat frequency signal in the first dimension with a frequency (f B -f A ) to generate and transfer this to signal processing system 4.

[0107] The second receiver 302 is used to receive the first polarized light component in the diffracted light of the -1 order in the first dimension and the second polarized light component in the diffracted light of the +1 order in the first dimension, as well as a second beat frequency signal in the first dimension with a frequency (f B -f A ) to generate and transfer this to signal processing system 4.

[0108] The third receiver 303 is used to receive the first polarized light component in the diffracted +1 order light in the second dimension and the second polarized light component in the diffracted -1 order light in the second dimension, as well as a first beat frequency signal in the second dimension with a frequency (f B -f A ) to generate and transfer this to signal processing system 4.

[0109] The fourth receiver 304 is used to receive the first polarized light component in the diffracted light of the -1 order in the second dimension and the second polarized light component in the diffracted light of the +1 order in the second dimension, as well as a second beat frequency signal in the second dimension with a frequency (f B -f A ) to generate and transfer this to signal processing system 4.

[0110] When the two-dimensional measuring grid 5 moves along the grid vector direction in the first dimension, due to the Doppler frequency shift effect of the grid, the diffracted light of the -1st order in the first dimension undergoes a backward frequency shift -Δf and the diffracted light of the +1st order in the first dimension undergoes a forward frequency shift +Δf, so that the frequency of the first beat frequency signal output by the first receiver 301 in the first dimension becomes (f B -f A -2Δf) and the frequency of the second beat frequency signal output by the second receiver 302 in the first dimension to (f B -f A +2Δf) changes.

[0111] When the two-dimensional measuring grid 5 moves along the grid vector direction in the second dimension, due to the Doppler frequency shift effect of the grid, the diffracted light of the -1st order undergoes a backward frequency shift -Δf in the second dimension and the diffracted light of the +1st order undergoes a forward frequency shift +Δf in the second dimension, so that the frequency of the first beat frequency signal output by the third receiver 303 in the second dimension becomes (f B -f A -2Δf) and the frequency of the second beat frequency signal output by the fourth receiver 304 in the second dimension to (f B -f A +2Δf) changes.

[0112] The signal processing system 4 is used to perform a differential calculation for the first beat frequency signal in the first dimension output by the first receiver 301 and the second beat frequency signal in the first dimension output by the second receiver 302, in order to realize the displacement measurement with a heterodyne grating of 4-fold optical subdivision by single diffraction in the first dimension, and to perform a differential calculation for the first beat frequency signal in the second dimension output by the third receiver 303 and the second beat frequency signal in the second dimension output by the fourth receiver 304, in order to realize the displacement measurement with a heterodyne grating of 4-fold optical subdivision by single diffraction in the second dimension. Example 6

[0113] The fifth embodiment shows the structure of a measuring device with a heterodyne two-dimensional grid. Corresponding to the measuring device with a heterodyne two-dimensional grid in the fifth embodiment, the sixth embodiment provides a method for grid displacement measurement using the measuring device with a heterodyne two-dimensional grid in the fifth embodiment.

[0114] Fig. Figure 17 shows a measurement procedure with a heterodyne two-dimensional grid in the sixth embodiment of the present invention.

[0115] As in Fig. As shown in 17, the measurement method with a heterodyne two-dimensional grid in the embodiment of the present invention comprises the following steps: S1: Generating two beams of linearly polarized light, overlapping each other and exhibiting orthogonal polarizations and a fixed frequency difference, each consisting of a first polarized light in the S-polarization state and a second polarized light in the P-polarization state, using a light source; wherein the light source may be a dual-frequency laser device 1 or two laser devices with a fixed emitted frequency difference; and wherein the light source emits two beams of lasers with a fixed frequency difference, each consisting of a first polarized light and a second polarized light, and wherein the first polarized light is an S-polarized light with a frequency f A and the second polarized light is a P-polarized light with a frequency f B is; S2: the first polarized light and the second polarized light each enter a read head and, after reflection and transmission through the read head, each strike a surface of the two-dimensional measuring grating to generate a diffracted light of ±1 order in a first dimension and a diffracted light of ±1 order in a second dimension, wherein the diffracted light of ±1 order in the first dimension and the diffracted light of ±1 order in the second dimension again strike a photoelectric receiving module via the read head; and wherein step S2 in particular comprises the following steps: S201: The first polarized light is reflected by a polarizing beam splitter prism onto a second quarter-wave plate, whereby the first polarized light is converted into left-handed polarized light and then reflected. After passing through the second quarter-wave plate again and being converted into P-polarized light, it returns to the polarizing beam splitter prism; and the second polarized light is transmitted by the polarizing beam splitter prism onto a first quarter-wave plate. After the second polarized light is converted into right-handed polarized light, it enters a deflecting prism. The deflecting prism reflects the second polarized light back. When the second polarized light passes through the first quarter-wave plate again and is converted into S-polarized light, it returns to the polarizing beam splitter prism. S202: the polarizing beam splitter prism transmits the first polarized light and reflects the second polarized light, so that the first polarized light and the second polarized light are combined and then enter a third quarter-wave plate;wherein the third quarter-wave plate converts the first polarized light into right-handed polarized light and then shines vertically onto the surface of the two-dimensional measuring grid, and converts the second polarized light into left-handed polarized light and then shines vertically onto the surface of the two-dimensional measuring grid, the first polarized light is diffracted to produce a diffracted light of -1 order in the first dimension and a diffracted light of +1 order in the first dimension, the second polarized light is diffracted to produce a diffracted light of -1 order in the second dimension and a diffracted light of +1 order in the second dimension.

[0116] The diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension, and the diffracted light of the +1 order in the second dimension each contain a first polarized light component and a second polarized light component. S203: after the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension and the diffracted light of the +1 order in the second dimension have been refracted by a deflecting element, they are aligned parallel to each other and enter the third quarter-wave plate vertically; S204: The third quarter-wave plate converts the first polarized light component in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension, and the diffracted light of the +1 order in the second dimension into S-polarized light and shines this vertically into the polarizing beam splitter prism; it also converts the second polarized light component in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension, and the diffracted light of the +1 order in the second dimension into P-polarized light and shines this vertically into the polarizing beam splitter prism; S205: the polarizing beam splitter prism reflects the first polarized light component in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension and the diffracted light of the +1 order in the second dimension onto the first quarter-wave plate and transmits the second polarized light component in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension and the diffracted light of the +1 order in the second dimension onto the second quarter-wave plate; S206: The second quarter-wave plate converts the second polarized light component in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension and the diffracted light of the +1 order in the second dimension into right-hand polarized light and then reflects this, after it has been passed through the second quarter-wave plate again and converted into S-polarized light, it is radiated into the polarizing beam splitter prism and reflected by the polarizing beam splitter prism into the photoelectric receiving module;The first quarter-wave plate converts the first polarized light component in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension and the diffracted light of the +1 order in the second dimension into a left-rotating polarized light and shines this again into the deflecting prism;The deflecting prism reflects the first polarized light component twice in the diffracted light of the -1 order in the first dimension, the diffracted light of the +1 order in the first dimension, the diffracted light of the -1 order in the second dimension, and the diffracted light of the +1 order in the second dimension, and emits this onto the first quarter-wave plate. After it has been converted into P-polarized light, it is again radiated into the polarizing beam splitter prism and transmitted through the polarizing beam splitter prism into the photoelectric receiving module.

[0117] S3: the photoelectric receiving module generates a corresponding beat frequency signal in accordance with the diffracted light of the ±1 order in the first dimension and the diffracted light of the ±1 order in the second dimension and sends this to a signal processing system; and wherein the photoelectric receiving module comprises a first receiver, a second receiver, a third receiver and a fourth receiver; and wherein the first receiver is used to receive the first polarized light component in the diffracted +1-order light in the first dimension and the second polarized light component in the diffracted -1-order light in the first dimension, as well as a first beat frequency signal in the first dimension with a frequency (f B -f A ) to generate and send this to the signal processing system; and wherein the second receiver is used to receive the first polarized light component in the diffracted -1 order light in the first dimension and the second polarized light component in the diffracted +1 order light in the first dimension, as well as a second beat frequency signal in the first dimension with a frequency (f B -f A) to generate and send this to the signal processing system; and wherein the third receiver is used to receive the first polarized light component in the diffracted +1 order light in the second dimension and the second polarized light component in the diffracted -1 order light in the second dimension, as well as a first beat frequency signal in the second dimension with a frequency (f B -f A ) to generate and send this to the signal processing system; and wherein the fourth receiver is used to receive the first polarized light component in the diffracted -1 order light in the second dimension and the second polarized light component in the diffracted +1 order light in the second dimension, as well as a second beat frequency signal in the second dimension with a frequency (f B -f A ) to generate and send this to the signal processing system.

[0118] When the two-dimensional measuring grid moves along the grid vector direction in the first dimension, the diffracted light of the -1st order undergoes a backward frequency shift -Δf in the first dimension and the diffracted light of the +1st order undergoes a forward frequency shift +Δf in the first dimension, so that the frequency of the first beat frequency signal emitted by the first receiver in the first dimension becomes f B -f A -2Δf and the frequency of the second beat frequency signal output by the second receiver in the first dimension to f B -f A+2Δf changes; when the two-dimensional measuring grid moves along the grid vector direction in the second dimension, the diffracted light of the -1st order undergoes a backward frequency shift -Δf in the second dimension and the diffracted light of the +1st order undergoes a forward frequency shift +Δf in the second dimension, so that the frequency of the first beat frequency signal output by the third receiver changes to f in the second dimension B -f A -2Δf and the frequency of the second beat frequency signal output by the fourth receiver in the second dimension to f B -f A +2Δf changes.

[0119] S4: Performing a difference calculation by the signal processing system for the beat frequency signals generated by the diffracted light of ±1 order in the first dimension and the beat frequency signals generated by the diffracted light of ±1 order in the second dimension, in order to realize the displacement measurement of the 4-fold optical subdivision by the single diffraction of the two-dimensional measuring grid in the first dimension and the second dimension.

[0120] More precisely, the signal processing system is used to perform a differential calculation for the first beat frequency signal in the first dimension output by the first receiver and the second beat frequency signal in the first dimension output by the second receiver, in order to realize the displacement measurement of the 4-fold optical subdivision by single diffraction of the two-dimensional measuring grid in the first dimension, and a differential calculation for the first beat frequency signal in the second dimension output by the third receiver and the second beat frequency signal in the second dimension output by the fourth receiver, in order to realize the displacement measurement of the 4-fold optical subdivision by single diffraction of the two-dimensional measuring grid in the second dimension.

[0121] In this description, the explanations associated with the terms "an embodiment," "some embodiments," "an example," "a specific example," or "some examples" mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this description, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the described specific features, structures, materials, or characteristics may be combined appropriately in one or more embodiments or examples.In the absence of conflicts, experts in this field may additionally combine and connect the various embodiments or examples explained in this description, or the features in the various embodiments or examples.

[0122] Although the embodiments of the present invention are described and explained above, it is understood that these embodiments are exemplary and should not be interpreted as limiting the scope of the present invention. A person skilled in the art in this field can make the changes, modifications, substitutions, and variations to the embodiments within the scope of the present invention.

[0123] The specific embodiments of the present invention do not constitute a limitation on the scope of protection of the present invention. All other corresponding changes and modifications carried out in accordance with the technical concept of the present invention shall be considered to be covered by the scope of protection of the claims of the present invention.

Claims

[1] A heterodyne one-dimensional grating measuring device comprising a light source used to generate two beams of linearly polarized lights overlapping one another and having orthogonal polarizations and a fixed frequency difference, the linearly polarized lights each comprising a first polarized light having a frequency f A and a second polarized light with a frequency f B and wherein the first polarized light is S-polarized light and the second polarized light is P-polarized light; further comprising a read head, a photoelectric receiving module, and a signal processing system; wherein the read head is used to receive the first polarized light and the second polarized light, each incident on a surface of the moving one-dimensional measuring grating, to generate a +1-order diffracted light and a -1-order diffracted light, each containing a first polarized light component and a second polarized light component, and wherein the +1-order diffracted light and the -1-order diffracted light are each incident on the photoelectric receiving module via the read head; wherein the photoelectric receiving module is used to receive the +1-order diffracted light and the -1-order diffracted light to form two paths of beat frequency signals; and wherein one path thereof is that the second polarized light component of the -1-order diffracted light and the first polarized light component of the +1-order diffracted light interfere with each other to form a beat frequency signal having a frequency f B -f A to form, while the other way is that the first polarized light component of the -1-order diffracted light and the second polarized light component of the +1-order diffracted light interfere with each other to form another beat frequency signal with a frequency f B -f A to form; wherein the signal processing system is used to perform a difference calculation for the two paths of beat frequency signals in order to realize the displacement measurement of the 4-fold optical division by the single diffraction of the one-dimensional measuring grating, characterized by that the reading head comprises a reflector, a polarizing beam splitter prism, a first quarter-wave plate, a second quarter-wave plate, a compensation mirror coated with a reflective film, a gyro prism and a refractive element; wherein the reflector is arranged on an outgoing light path of the light source to vertically reflect the first polarized light and the second polarized light onto the surface of the one-dimensional measuring grating, thereby generating a +1-order diffracted light and a -1-order diffracted light; and wherein the refraction element is arranged on a diffraction light path of the one-dimensional measuring grating to refract the +1-order diffracted light and the -1-order diffracted light so that the +1-order diffracted light and the -1-order diffracted light are aligned parallel to each other and are vertically incident into the polarizing beam splitter prism; wherein the polarizing beam splitter prism is arranged on a transmission light path of the refraction element to reflect the first polarized light components of the +1-order diffracted light and the -1-order diffracted light onto the first quarter-wave plate, respectively, and to transmit the second polarized light components of the +1-order diffracted light and the -1-order diffracted light onto the second quarter-wave plate, respectively; wherein the first quarter-wave plate is arranged on a reflection light path of the polarizing beam splitter prism to convert the first polarized light components of the +1-order diffracted light and the -1-order diffracted light into a left-handed polarized light, respectively, and irradiate them into the gyro prism; wherein the gyro prism is arranged on a transmission light path of the first quarter-wave plate to reflect the first polarized light components of the +1-order diffracted light and the -1-order diffracted light twice each, so that the first polarized light components of the +1-order diffracted light and the -1-order diffracted light are converted into P-polarized light by the first quarter-wave plate and then incident into the polarizing beam splitter prism; wherein the second quarter-wave plate is arranged on a transmission light path of the polarizing beam splitter prism, so that the second polarized light components of the +1-order diffracted light and the -1-order diffracted light are each converted into a right-handed polarized light and then incident on the compensation mirror; wherein the compensation mirror is arranged on a transmission light path of the second quarter-wave plate to reflect the second polarized light components of the +1-order diffracted light and the -1-order diffracted light, respectively, so that the second polarized light components of the +1-order diffracted light and the -1-order diffracted light are converted into S-polarized light by the second quarter-wave plate and then incident into the polarizing beam splitter prism; wherein the polarizing beam splitter prism is further used to transmit the first polarized light components of the +1-order diffracted light and the -1-order diffracted light, which are converted into P-polarized light, to the photoelectric receiving module and to reflect the second polarized light components of the +1-order diffracted light and the -1-order diffracted light, which are converted into S-polarized light, to the photoelectric receiving module, and wherein when the one-dimensional measuring grating moves along a grating vector direction, the -1-order diffracted light undergoes a backward frequency shift -Δf and the +1-order diffracted light undergoes a forward frequency shift +Δf, whereby the frequency of the beat frequency signal output from the first receiver becomes f B -f A-2Δf and the frequency of the beat frequency signal output by the second receiver to f B -f A +2Δf changes. [2] Measuring device with heterodyne one-dimensional grating according to claim 1, characterized by that the photoelectric receiving module comprises a first receiver and a second receiver; wherein the first receiver is used to receive the second polarized light component of the -1-order diffracted light and the first polarized light component of the +1-order diffracted light, and the beat frequency signal having a frequency f B -f A and transmitting it to the signal processing system; and wherein the second receiver is used to receive the first polarized light component of the -1-order diffracted light and the second polarized light component of the +1-order diffracted light, as well as the other beat frequency signal having a frequency f B -fA and transmit it to the signal processing system. [3] Measuring device with heterodyne one-dimensional grating according to claim 1, characterized by that a thickness of the compensation mirror corresponds to half a length of the gyro prism to compensate a light path of the second polarized light components of the +1-order diffracted light and the -1-order diffracted light so that the light path of the second polarized light components of the +1-order diffracted light and the -1-order diffracted light is the same as the light path of the first polarized light components of the +1-order diffracted light and the -1-order diffracted light. [4] Measuring device with heterodyne one-dimensional grating according to claim 1, characterized bythat the reading head further comprises a first rectangular prism and a second rectangular prism, each arranged on the diffracted light path of the one-dimensional measuring grating, wherein the first rectangular prism and the second rectangular prism each reflect twice the +1-order diffracted light and the -1-order diffracted light, which are incident again at a diffraction exit angle on the surface of the one-dimensional measuring grating, and wherein two beams of new diffracted lights are vertically incident on the polarizing beam splitter prism. [5] A heterodyne one-dimensional grating measuring device comprising a light source used to generate two beams of linearly polarized lights overlapping one another and having orthogonal polarizations and a fixed frequency difference, the linearly polarized lights being a first polarized light having a frequency fA and a second polarized light having a frequency fB, respectively, and the first polarized light being an S-polarized light and the second polarized light being a P-polarized light; further comprising a reading head, a photoelectric receiving module, and a signal processing system; wherein the read head is used to receive the first polarized light and the second polarized light, each incident on a surface of the moving one-dimensional measuring grating, to generate a +1-order diffracted light and a -1-order diffracted light, each containing a first polarized light component and a second polarized light component, and wherein the +1-order diffracted light and the -1-order diffracted light are each incident on the photoelectric receiving module via the read head; wherein the photoelectric receiving module is used to receive the +1-order diffracted light and the -1-order diffracted light to form two paths of beat frequency signals; and wherein one path thereof is that the second polarized light component of the -1-order diffracted light and the first polarized light component of the +1-order diffracted light interfere with each other to form a beat frequency signal having a frequency fB - fA, while the other path is that the first polarized light component of the -1-order diffracted light and the second polarized light component of the +1-order diffracted light interfere with each other to form another beat frequency signal having a frequency fB - fA; wherein the signal processing system is used to perform a difference calculation for the two paths of beat frequency signals in order to realize the displacement measurement of the 4-fold optical division by the single diffraction of the one-dimensional measuring grating, characterized by that the read head comprises a polarizing beam splitter prism, a first quarter-wave plate, a second quarter-wave plate coated with a reflective film, and a gyroscopic prism; wherein the polarizing beam splitter prism is arranged on an outgoing light path of the light source and is used to receive the first polarized light and the second polarized light, transmit the second polarized light to the first quarter-wave plate, and reflect the first polarized light to the second quarter-wave plate; wherein the first quarter-wave plate is arranged on a transmission light path of the polarizing beam splitter prism to convert the second polarized light into a right-handed polarized light and irradiate it into the gyro prism; and wherein the gyro prism is arranged on a transmission light path of the first quarter-wave plate to reradiate the second polarized light, so that the second polarized light passes through the first quarter-wave plate and is converted into S-polarized light and then returns to the polarizing beam splitter prism; wherein the second quarter-wave plate is arranged on a reflection light path of the polarizing beam splitter prism to convert the first polarized light into a left-handed polarized light, which is reflected by the reflection film, passes through the second quarter-wave plate again and is converted into the P-polarized light, and then returns to the polarizing beam splitter prism; wherein the polarizing beam splitter prism is further used to transmit the first polarized light converted into P-polarized light and to reflect the second polarized light converted into S-polarized light, so that the first polarized light and the second polarized light are combined and then incident on the surface of the one-dimensional measuring grating to generate the -1-order diffracted light and the +1-order diffracted light by diffraction, and wherein when the one-dimensional measuring grating moves along a grating vector direction, the -1-order diffracted light undergoes a backward frequency shift -Δf and the +1-order diffracted light undergoes a forward frequency shift +Δf, the frequency of the beat frequency signal output from the first receiver becoming f B -f A -2Δf and the frequency of the beat frequency signal output by the second receiver to f B -f A +2Δf changes. [6] Measuring device with heterodyne one-dimensional grating according to claim 5, characterized by that the read head further comprises a refractive element and a third quarter-wave plate; wherein the refraction element is arranged on a diffraction light path of the one-dimensional measuring grating to refract the -1-order diffracted light and the +1-order diffracted light so that the -1-order diffracted light and the +1-order diffracted light are aligned parallel to each other and are vertically incident into the third quarter-wave plate; wherein the third quarter-wave plate is arranged on a transmission light path of the refraction element to convert the first polarized light components of the +1-order diffracted light and the -1-order diffracted light into S-polarized light and irradiate it vertically onto the polarizing beam splitter prism, and to convert the second polarized light components of the +1-order diffracted light and the -1-order diffracted light into P-polarized light and irradiate it vertically onto the polarizing beam splitter prism; wherein the polarizing beam splitter prism is used to reflect the first polarized light components of the +1-order diffracted light and the -1-order diffracted light onto the first quarter-wave plate and to transmit the second polarized light components of the +1-order diffracted light and the -1-order diffracted light onto the second quarter-wave plate; wherein the first quarter-wave plate is used to convert the first polarized light components of the +1-order diffracted light and the -1-order diffracted light into a left-handed polarized light and irradiate it into the gyro prism; wherein the gyro prism is used so that the first polarized light components of the +1-order diffracted light and the -1-order diffracted light are reflected back twice to the first quarter-wave plate and converted into P-polarized light, then incident again on the polarizing beam splitter prism and transmitted through the polarizing beam splitter prism to the photoelectric receiving module; and wherein the second quarter-wave plate is used so that the second polarized light components of the +1-order diffracted light and the -1-order diffracted light are converted into right-hand polarized light and reflected by the reflection film, pass through the second quarter-wave plate again and are converted into S-polarized light, and then are incident on the polarizing beam splitter prism and reflected by the polarizing beam splitter prism onto the photoelectric receiving module. [7] Measuring device with heterodyne one-dimensional grating according to claim 6, characterized bythat the photoelectric receiving module comprises a first receiver and a second receiver; wherein the first receiver is used to receive the first polarized light component of the +1-order diffracted light and the second polarized light component of the -1-order diffracted light, and the beat frequency signal having a frequency f B -f A and transmitting it to the signal processing system; and wherein the second receiver is used to receive the first polarized light component of the -1-order diffracted light and the second polarized light component of the +1-order diffracted light, as well as the other beat frequency signal having a frequency f B -f A and transmit it to the signal processing system. [8] Measuring device with heterodyne one-dimensional grating according to claim 5, characterized bythat the light paths of the first polarized light component of the -1-order diffracted light and the second polarized light component of the -1-order diffracted light are the same, and the light paths of the first polarized light component of the +1-order diffracted light and the second polarized light component of the +1-order diffracted light are the same. [9] Measuring device with heterodyne one-dimensional grating according to claim 5, characterized bythat the reading head further comprises a first rectangular prism and a second rectangular prism, each arranged on the diffracted light path of the one-dimensional measuring grating, wherein the first rectangular prism and the second rectangular prism each reflect twice the +1-order diffracted light and the -1-order diffracted light, which are incident again at a diffraction exit angle on the surface of the one-dimensional measuring grating, and wherein two beams of new diffracted lights are vertically incident on the polarizing beam splitter prism. [10] Heterodyne one-dimensional grating measurement method, comprising the following steps: S1: Generating two beams of linearly polarized lights which overlap each other and have orthogonal polarizations and a fixed frequency difference by means of a light source, wherein the linearly polarized lights each comprise a first polarized light with a frequency f A and a second polarized light with a frequency f B and wherein the first polarized light is an S-polarized light and the second polarized light is a P-polarized light; S2: The first polarized light and the second polarized light each enter a reading head and, after being refracted by the reading head, are incident on a surface of the one-dimensional measuring grating to generate a +1-order diffracted light and a -1-order diffracted light, each containing a first polarized light component and a second polarized light component, wherein the +1-order diffracted light and the -1-order diffracted light are again incident via the reading head into a photoelectric receiving module; S3: Receiving the +1-order diffracted light and the -1-order diffracted light by the photoelectric receiving module; wherein the second polarized light component of the -1-order diffracted light and the first polarized light component of the +1-order diffracted light interfere with each other to generate a beat frequency signal having a frequency f B -f Awhile the first polarized light component of the -1-order diffracted light and the second polarized light component of the +1-order diffracted light interfere with each other to form another beat frequency signal with a frequency f B -f A to form; S4: Performing a respective difference calculation for the two paths of beat frequency signals by a signal processing system to realize the displacement measurement of the 4-fold optical division by the single diffraction of the one-dimensional measuring grating, characterized by that step S2 comprises in particular the following steps: S201: Reflecting the first polarized light and the second polarized light vertically onto the surface of the one-dimensional measuring grating by a reflector of the reading head to generate a +1-order diffracted light and a -1-order diffracted light; S202: Refracting the +1-order diffracted light and the -1-order diffracted light by a refraction element of the read head so that the +1-order diffracted light and the -1-order diffracted light are aligned parallel to each other and are vertically incident on a polarizing beam splitter prism of the read head; S203: reflecting the first polarized light components of the +1-order diffracted light and the -1-order diffracted light onto a first quarter-wave plate of the read head through the polarizing beam splitter prism, and transmitting the second polarized light components of the +1-order diffracted light and the -1-order diffracted light onto a second quarter-wave plate of the read head; S204: converting the first polarized light components of the +1-order diffracted light and the -1-order diffracted light into left-hand polarized light by the first quarter-wave plate and irradiating them into a gyroscopic prism of the read head; then reflecting the first polarized light components of the +1-order diffracted light and the -1-order diffracted light twice by the gyroscopic prism, so that the first polarized light components of the +1-order diffracted light and the -1-order diffracted light are converted into P-polarized light by the first quarter-wave plate and then incident on the polarizing beam splitter prism;and converting the second polarized light components of the +1-order diffracted light and the -1-order diffracted light into right-hand polarized light by the second quarter-wave plate and irradiating them into a compensation mirror of the read head; then reflecting the second polarized light components of the +1-order diffracted light and the -1-order diffracted light by the compensation mirror, so that the second polarized light components of the +1-order diffracted light and the -1-order diffracted light are converted into S-polarized light by the second quarter-wave plate and thereafter incident on the polarizing beam splitter prism; ; S205: Transmitting the first polarized light components of the +1-order diffracted light and the -1-order diffracted light, which are converted into P-polarized light, to the photoelectric receiving module through the polarizing beam splitter prism, and reflecting the second polarized light components of the +1-order diffracted light and the -1-order diffracted light, which are converted into S-polarized light, to the photoelectric receiving module, wherein when the one-dimensional measuring grating moves along a grating vector direction, the -1-order diffracted light undergoes a backward frequency shift -Δf and the +1-order diffracted light undergoes a forward frequency shift +Δf, whereby the frequency of the beat frequency signal output from the first receiver becomes f B -f A -2Δf and the frequency of the beat frequency signal output by the second receiver to f B -fA +2Δf changes. [11] Heterodyne one-dimensional grating measuring method according to claim 10, characterized by that a thickness of the compensation mirror corresponds to half a length of the gyro prism to compensate a light path of the second polarized light components of the +1-order diffracted light and the -1-order diffracted light so that the light path of the second polarized light components of the +1-order diffracted light and the -1-order diffracted light is the same as the light path of the first polarized light components of the +1-order diffracted light and the -1-order diffracted light. [12] Heterodyne one-dimensional grating measurement method, comprising the following steps: S1: generating two beams of linearly polarized lights which overlap one another and have orthogonal polarizations and a fixed frequency difference, by means of a light source, wherein the linearly polarized lights are each a first polarized light with a frequency fA and a second polarized light with a frequency fB, and wherein the first polarized light is an S-polarized light and the second polarized light is a P-polarized light; S2: The first polarized light and the second polarized light each enter a reading head and, after being refracted by the reading head, are incident on a surface of the one-dimensional measuring grating to generate a +1-order diffracted light and a -1-order diffracted light, each containing a first polarized light component and a second polarized light component, wherein the +1-order diffracted light and the -1-order diffracted light are again incident via the reading head into a photoelectric receiving module; S3: Receiving the +1-order diffracted light and the -1-order diffracted light by the photoelectric receiving module; wherein the second polarized light component of the -1-order diffracted light and the first polarized light component of the +1-order diffracted light interfere with each other to form a beat frequency signal having a frequency fB - fA, while the first polarized light component of the -1-order diffracted light and the second polarized light component of the +1-order diffracted light interfere with each other to form another beat frequency signal having a frequency fB - fA; S4: Performing a respective difference calculation for the two paths of beat frequency signals by a signal processing system to realize the displacement measurement of the 4-fold optical division by the single diffraction of the one-dimensional measuring grating, characterized bythat step S2 comprises in particular the following steps: S201': Incident of the first polarized light and the second polarized light into a polarizing beam splitter prism of the read head, transmitting the second polarized light to a first quarter-wave plate of the read head through the polarizing beam splitter prism, and reflecting the first polarized light to a second quarter-wave plate of the read head; S202': Converting the second polarized light into right-handed polarized light through the first quarter-wave plate and irradiating it into a gyroscopic prism; re-radiating the second polarized light through the gyroscopic prism so that the second polarized light passes through the first quarter-wave plate and is converted into S-polarized light, and then returns to the polarizing beam splitter prism; and converting the first polarized light through the second quarter-wave plate into left-handed polarized light, which is reflected by a reflection film, passes through the second quarter-wave plate again, is converted into P-polarized light, and then returns to the polarizing beam splitter prism; S203': Transmitting the first polarized light converted into P-polarized light through the polarizing beam splitter prism and reflecting the second polarized light converted into S-polarized light, so that the first polarized light and the second polarized light are combined and then incident on the surface of the one-dimensional measuring grating to generate the -1-order diffracted light and the +1-order diffracted light by diffraction; S204' : Refracting the -1-order diffracted light and the +1-order diffracted light by a refraction element of the read head so that the -1-order diffracted light and the +1-order diffracted light are aligned parallel to each other and are vertically incident on a third quarter-wave plate of the read head; S205': converting the first polarized light components of the +1-order diffracted light and the -1-order diffracted light into S-polarized light by the third quarter-wave plate and irradiating it vertically onto the polarizing beam splitter prism, and converting the second polarized light components of the +1-order diffracted light and the -1-order diffracted light into P-polarized light and irradiating it vertically onto the polarizing beam splitter prism; S206': Reflecting the first polarized light components of the +1-order diffracted light and the -1-order diffracted light onto the first quarter-wave plate through the polarizing beam splitter prism, and transmitting the second polarized light components of the +1-order diffracted light and the -1-order diffracted light onto the second quarter-wave plate; S207': Converting the first polarized light components of the +1-order diffracted light and the -1-order diffracted light by the first quarter-wave plate into left-hand polarized light and irradiating it into the gyroscopic prism; after the first polarized light components of the +1-order diffracted light and the -1-order diffracted light are reflected twice by the gyroscopic prism back to the first quarter-wave plate and converted into P-polarized light, they are irradiated again into the polarizing beam splitter prism and transmitted through the polarizing beam splitter prism to the photoelectric receiving module;and wherein the second polarized light components of the +1-order diffracted light and the -1-order diffracted light are converted into right-hand polarized light by the second quarter-wave plate and reflected by the reflection film, pass through the second quarter-wave plate again and are converted into S-polarized light, and then are incident on the polarizing beam splitter prism and reflected by the polarizing beam splitter prism onto the photoelectric receiving module, and wherein when the one-dimensional measuring grating moves along a grating vector direction, the -1-order diffracted light undergoes a backward frequency shift -Δf and the +1-order diffracted light undergoes a forward frequency shift +Δf, whereby the frequency of the beat frequency signal output from the first receiver becomes f; B -f A-2Δf and the frequency of the beat frequency signal output by the second receiver to f B -f A +2Δf changes. [13] Heterodyne one-dimensional grating measuring method according to claim 12, characterized by that the light paths of the first polarized light component of the -1-order diffracted light and the second polarized light component of the -1-order diffracted light are the same, and the light paths of the first polarized light component of the +1-order diffracted light and the second polarized light component of the +1-order diffracted light are the same. [14] Heterodyne one-dimensional grating measuring method according to claim 10 or 12, characterized bythat the photoelectric receiving module comprises a first receiver and a second receiver; wherein the first receiver receives the second polarized light component of the -1-order diffracted light and the first polarized light component of the +1-order diffracted light, and the beat frequency signal having a frequency f B -f A and transmits it to the signal processing system; and wherein the second receiver receives the first polarized light component of the -1-order diffracted light and the second polarized light component of the +1-order diffracted light, as well as the other beat frequency signal having a frequency f B -f A and transmits this to the signal processing system. [15] Heterodyne one-dimensional grating measuring method according to claim 10 or 12, characterized bythat the +1-order diffracted light and the -1-order diffracted light generated by diffracting the one-dimensional measuring grating are respectively incident on a first rectangular prism and a second rectangular prism, wherein the first rectangular prism and the second rectangular prism each reflect the +1-order diffracted light and the -1-order diffracted light twice, which are again incident on the surface of the one-dimensional measuring grating at a diffraction exit angle, and wherein two beams of new diffracted lights are vertically incident on the polarizing beam splitter prism. [16] A heterodyne two-dimensional grating measuring device comprising a light source used to generate two beams of linearly polarized lights overlapping each other and having orthogonal polarizations and a fixed frequency difference, the linearly polarized lights being a first polarized light and a second polarized light, respectively; further comprising a reading head, a photoelectric receiving module, and a signal processing system; wherein the read head is used to receive the first polarized light and the second polarized light, each incident on a surface of the moving two-dimensional measuring grating, to generate a ±1-order diffracted light in a first dimension and a ±1-order diffracted light in a second dimension, and wherein the ±1-order diffracted light in the first dimension and the ±1-order diffracted light in the second dimension are then respectively incident on the photoelectric receiving module via the read head; wherein the photoelectric receiving module is used to generate a corresponding beat frequency signal in accordance with the ±1-order diffracted light in the first dimension and the ±1-order diffracted light in the second dimension, respectively, and send it to the signal processing system; wherein the signal processing system is used to perform a difference calculation for the beat frequency signals generated by the ±1-order diffracted light in the first dimension and the beat frequency signals generated by the ±1-order diffracted light in the second dimension, respectively, in order to realize the displacement measurement of the 4-fold optical division by the single diffraction of the two-dimensional measuring grating in the first dimension and the second dimension, characterized by that the first polarized light is an S-polarized light with a frequency f A and the second polarized light is a P-polarized light with a frequency f B wherein the read head comprises a polarizing beam splitter prism, a first quarter-wave plate, a second quarter-wave plate coated with a reflective film, a third quarter-wave plate, a gyroscopic prism, and a refractive element; wherein the polarizing beam splitter prism is used to receive the first polarized light and the second polarized light, transmit the second polarized light to the first quarter-wave plate, and reflect the first polarized light to the second quarter-wave plate; wherein the first quarter-wave plate is arranged on a transmission light path of the polarizing beam splitter prism to convert the second polarized light into a right-handed polarized light and then irradiate it into the gyro prism; wherein the gyro prism is arranged on a transmission light path of the first quarter-wave plate to reradiate the second polarized light, after the second polarized light passes through the first quarter-wave plate again and is converted into S-polarized light, it returns to the polarizing beam splitter prism; wherein the second quarter-wave plate is arranged on a reflection light path of the polarizing beam splitter prism to convert the first polarized light into a left-handed polarized light and then reflect it, after it passes through the second quarter-wave plate again and is converted into the P-polarized light, it returns to the polarizing beam splitter prism; wherein the polarizing beam splitter prism is further used to transmit the first polarized light and reflect the second polarized light, so that the first polarized light and the second polarized light are combined and thereafter incident into the third quarter-wave plate; wherein the third quarter-wave plate is arranged on a light path through which the polarizing beam splitter prism transmits the first polarized light, and is used to convert the first polarized light into right-handed polarized light and then irradiate it vertically onto the surface of the two-dimensional measuring grating, and to convert the second polarized light into left-handed polarized light and then irradiate it vertically onto the surface of the two-dimensional measuring grating, and wherein the first polarized light and the second polarized light are each diffracted to produce ±1-order diffracted light in the first dimension and ±1-order diffracted light in the second dimension, wherein when the two-dimensional measuring grating moves along a grating vector direction in the first dimension, the -1-order diffracted light in the first dimension undergoes a backward frequency shift -Δf and the +1-order diffracted light in the first dimension undergoes a forward frequency shift +Δf, the frequency of the beat frequency signal output from the first receiver becoming f B -f A -2Δf and the frequency of the beat frequency signal output by the second receiver to f B -f A +2Δf changes; and when the two-dimensional measuring grating moves along the grating vector direction in the second dimension, the -1-order diffracted light in the second dimension undergoes a backward frequency shift -Δf and the +1-order diffracted light in the second dimension undergoes a forward frequency shift +Δf, whereby the frequency of the beat frequency signal output from the third receiver becomes f B -f A -2Δf and the frequency of the beat frequency signal output by the fourth receiver to f B -f A +2Δf changes. [17] Measuring device with heterodyne two-dimensional grating according to claim 16, characterized bythat the ±1-order diffracted light in the first dimension comprises a -1-order diffracted light in the first dimension and a +1-order diffracted light in the first dimension, wherein the ±1-order diffracted light in the second dimension comprises a -1-order diffracted light in the second dimension and a +1-order diffracted light in the second dimension, and wherein the -1-order diffracted light in the first dimension, the +1-order diffracted light in the first dimension, the -1-order diffracted light in the second dimension and the +1-order diffracted light in the second dimension each contain a first polarized light component and a second polarized light component. [18] Measuring device with heterodyne two-dimensional grating according to claim 17, characterized bythat the reading head further comprises a refraction element arranged on a diffraction light path of the two-dimensional measuring grating for refracting the -1-order diffracted light in the first dimension, the +1-order diffracted light in the first dimension, the -1-order diffracted light in the second dimension, and the +1-order diffracted light in the second dimension, such that the -1-order diffracted light in the first dimension, the +1-order diffracted light in the first dimension, the -1-order diffracted light in the second dimension, and the +1-order diffracted light in the second dimension are aligned parallel to one another and are incident on the third quarter-wave plate; wherein the third quarter-wave plate is used to convert the first polarized light component in the -1-order diffracted light in the first dimension, the +1-order diffracted light in the first dimension, the -1-order diffracted light in the second dimension, and the +1-order diffracted light in the second dimension into S-polarized light and irradiate it vertically into the polarizing beam splitter prism, and to convert the second polarized light component in the -1-order diffracted light in the first dimension, the +1-order diffracted light in the first dimension, the -1-order diffracted light in the second dimension, and the +1-order diffracted light in the second dimension into P-polarized light and irradiate it vertically into the polarizing beam splitter prism; wherein the polarizing beam splitter prism is used to reflect the first polarized light component in the -1-order diffracted light in the first dimension, the +1-order diffracted light in the first dimension, the -1-order diffracted light in the second dimension, and the +1-order diffracted light in the second dimension onto the first quarter-wave plate, and to transmit the second polarized light component in the -1-order diffracted light in the first dimension, the +1-order diffracted light in the first dimension, the -1-order diffracted light in the second dimension, and the +1-order diffracted light in the second dimension onto the second quarter-wave plate; wherein the first quarter-wave plate is used to convert the first polarized light component in the -1-order diffracted light in the first dimension, the +1-order diffracted light in the first dimension, the -1-order diffracted light in the second dimension, and the +1-order diffracted light in the second dimension into a left-hand polarized light and to irradiate it again into the gyro prism; wherein the gyro prism is used to twice reflect the first polarized light component in the -1-order diffracted light in the first dimension, the +1-order diffracted light in the first dimension, the -1-order diffracted light in the second dimension, and the +1-order diffracted light in the second dimension and irradiate it onto the first quarter-wave plate, after being converted into P-polarized light, it is again irradiated into the polarizing beam splitter prism and transmitted through the polarizing beam splitter prism into the photoelectric receiving module; and wherein the second quarter-wave plate is used to convert the second polarized light component in the -1-order diffracted light in the first dimension, the +1-order diffracted light in the first dimension, the -1-order diffracted light in the second dimension, and the +1-order diffracted light in the second dimension into right-hand polarized light and then reflect it, after it has passed through the second quarter-wave plate again and been converted into S-polarized light, it is irradiated into the polarizing beam splitter prism and reflected by the polarizing beam splitter prism into the photoelectric receiving module, respectively. [19] Measuring device with heterodyne two-dimensional grating according to claim 18, characterized by that the photoelectric receiving module comprises a first receiver, a second receiver, a third receiver and a fourth receiver; wherein the first receiver is used to receive the first polarized light component in the +1-order diffracted light in the first dimension and the second polarized light component in the -1-order diffracted light in the first dimension, and a beat frequency signal having a frequency f B -f A to generate and send it to the signal processing system; wherein the second receiver is used to receive the first polarized light component in the -1-order diffracted light in the first dimension and the second polarized light component in the +1-order diffracted light in the first dimension, and a beat frequency signal having a frequency f B -f A to generate and send it to the signal processing system; wherein the third receiver is used to receive the first polarized light component in the +1-order diffracted light in the second dimension and the second polarized light component in the -1-order diffracted light in the second dimension, and a beat frequency signal having a frequency f B -f A to generate and send it to the signal processing system; wherein the fourth receiver is used to receive the first polarized light component in the -1-order diffracted light in the second dimension and the second polarized light component in the +1-order diffracted light in the second dimension, and a beat frequency signal having a frequency f B -f A and send it to the signal processing system. [20] Measuring device with heterodyne two-dimensional grating according to claim 19, characterized bythat the first polarized light components and second polarized light components received by the first receiver, the second receiver, the third receiver and the fourth receiver each pass through the gyro prism once, their light paths in the read head being the same. [21] Measuring device with heterodyne two-dimensional grating according to claim 19, characterized bythat the signal processing system is used to perform a difference calculation for the beat frequency signal output by the first receiver and the beat frequency signal output by the second receiver in order to realize the displacement measurement of the 4-fold optical subdivision by the single diffraction of the two-dimensional measuring grating in the first dimension, and to perform a difference calculation for the beat frequency signal output by the third receiver and the beat frequency signal output by the fourth receiver in order to realize the displacement measurement of the 4-fold optical subdivision by the single diffraction of the two-dimensional measuring grating in the second dimension. [22] Heterodyne two-dimensional grating measurement method, comprising the following steps: S1: Generating two beams of linearly polarized lights which overlap each other and have orthogonal polarizations and a fixed frequency difference by means of a light source, wherein the linearly polarized lights each comprise a first polarized light with a frequency f A and a second polarized light with a frequency f B and wherein the first polarized light is an S-polarized light and the second polarized light is a P-polarized light; S2: The first polarized light and the second polarized light each enter a reading head and, after being reflected and transmitted by the reading head, are incident on a surface of the moving two-dimensional measuring grating to generate a ±1-order diffracted light in a first dimension and a ±1-order diffracted light in a second dimension, and the ±1-order diffracted light in the first dimension and the ±1-order diffracted light in the second dimension are again incident via the reading head into a photoelectric receiving module; S3: generating a corresponding beat frequency signal by the photoelectric receiving module in accordance with the ±1-order diffracted light in the first dimension and the ±1-order diffracted light in the second dimension, respectively, and sending it to a signal processing system; S4: Performing a difference calculation by the signal processing system for the beat frequency signals generated by the ±1-order diffracted light in the first dimension and the beat frequency signals generated by the ±1-order diffracted light in the second dimension, in order to realize the displacement measurement of the 4-fold optical division by the single diffraction of the two-dimensional measuring grating in the first dimension and the second dimension, characterized by that step S2 comprises in particular the following steps: S201: the first polarized light is reflected by a polarizing beam splitter prism onto a second quarter-wave plate, the first polarized light being converted into left-handed polarized light and then reflected. After passing through the second quarter-wave plate again and being converted into P-polarized light, it returns to the polarizing beam splitter prism; and the second polarized light is transmitted through the polarizing beam splitter prism onto a first quarter-wave plate. After the second polarized light is converted into right-handed polarized light, it enters a gyroscopic prism, and the second polarized light is reflected by the gyroscopic prism. After the second polarized light is passed through the first quarter-wave plate again and being converted into S-polarized light, it returns to the polarizing beam splitter prism; S202: the polarizing beam splitter prism transmits the first polarized light and reflects the second polarized light, so that the first polarized light and the second polarized light are combined and then incident on a third quarter-wave plate; wherein the third quarter-wave plate converts the first polarized light into right-handed polarized light and then irradiates it vertically onto the surface of the two-dimensional measuring grating, and converts the second polarized light into left-handed polarized light and then irradiates it vertically onto the surface of the two-dimensional measuring grating, and wherein the first polarized light and the second polarized light are each diffracted to generate ±1-order diffracted light in the first dimension and ±1-order diffracted light in the second dimension, and wherein when the two-dimensional measuring grating moves along a grating vector direction in the first dimension, the -1-order diffracted light in the first dimension undergoes a backward frequency shift -Δf and the +1-order diffracted light in the first dimension undergoes a forward frequency shift +Δf, wherein the frequency of the beat frequency signal output from the first receiver becomes f B f A -2Δf and the frequency of the beat frequency signal output by the second receiver to f B -f A +2Δf changes; that when the two-dimensional measuring grating moves along the grating vector direction in the second dimension, the -1-order diffracted light in the second dimension undergoes a backward frequency shift -Δf and the +1-order diffracted light in the second dimension undergoes a forward frequency shift +Δf, whereby the frequency of the beat frequency signal output by the third receiver becomes f B -f A -2Δf and the frequency of the beat frequency signal output by the fourth receiver to f B -f A +2Δf changes. [23] Heterodyne two-dimensional grating measuring method according to claim 22, characterized bythat the ±1-order diffracted light in the first dimension comprises a -1-order diffracted light in the first dimension and a +1-order diffracted light in the first dimension, wherein the ±1-order diffracted light in the second dimension comprises a -1-order diffracted light in the second dimension and a +1-order diffracted light in the second dimension, and wherein the -1-order diffracted light in the first dimension, the +1-order diffracted light in the first dimension, the -1-order diffracted light in the second dimension and the +1-order diffracted light in the second dimension each contain a first polarized light component and a second polarized light component. [24] Heterodyne two-dimensional grating measuring method according to claim 23, characterized by that after step S202 it further comprises the following steps: S203: after the -1-order diffracted light in the first dimension, the +1-order diffracted light in the first dimension, the -1-order diffracted light in the second dimension, and the +1-order diffracted light in the second dimension are refracted by a refraction element, they are aligned parallel to each other and are vertically incident on the third quarter-wave plate; S204: the third quarter-wave plate converts the first polarized light component in the -1-order diffracted light in the first dimension, the +1-order diffracted light in the first dimension, the -1-order diffracted light in the second dimension, and the +1-order diffracted light in the second dimension into S-polarized light and irradiates it vertically into the polarizing beam splitter prism, and converts the second polarized light component in the -1-order diffracted light in the first dimension, the +1-order diffracted light in the first dimension, the -1-order diffracted light in the second dimension, and the +1-order diffracted light in the second dimension into P-polarized light and irradiates it vertically into the polarizing beam splitter prism; S205: the polarizing beam splitter prism reflects the first polarized light component in the -1-order diffracted light in the first dimension, the +1-order diffracted light in the first dimension, the -1-order diffracted light in the second dimension, and the +1-order diffracted light in the second dimension to the first quarter-wave plate, and transmits the second polarized light component in the -1-order diffracted light in the first dimension, the +1-order diffracted light in the first dimension, the -1-order diffracted light in the second dimension, and the +1-order diffracted light in the second dimension to the second quarter-wave plate; S206: the second quarter-wave plate converts the second polarized light component in the -1-order diffracted light in the first dimension, the +1-order diffracted light in the first dimension, the -1-order diffracted light in the second dimension, and the +1-order diffracted light in the second dimension into right-hand polarized light and then reflects it; after it passes through the second quarter-wave plate again and is converted into S-polarized light, it is irradiated into the polarizing beam splitter prism and reflected by the polarizing beam splitter prism into the photoelectric receiving module, respectively;and the first quarter-wave plate converts the first polarized light component in the -1-order diffracted light in the first dimension, the +1-order diffracted light in the first dimension, the -1-order diffracted light in the second dimension, and the +1-order diffracted light in the second dimension into a left-hand polarized light and irradiates it again into the gyro prism;The gyro prism reflects the first polarized light component in the -1-order diffracted light in the first dimension, the +1-order diffracted light in the first dimension, the -1-order diffracted light in the second dimension, and the +1-order diffracted light in the second dimension twice and radiates it onto the first quarter-wave plate. After being converted into P-polarized light, it is irradiated again into the polarizing beam splitter prism and transmitted through the polarizing beam splitter prism into the photoelectric receiving module. [25] Heterodyne two-dimensional grating measuring method according to claim 24, characterized by that the photoelectric receiving module comprises a first receiver, a second receiver, a third receiver and a fourth receiver; wherein the first receiver is used to receive the first polarized light component in the +1-order diffracted light in the first dimension and the second polarized light component in the -1-order diffracted light in the first dimension, and a beat frequency signal having a frequency f B -f A to generate and send it to the signal processing system; wherein the second receiver is used to receive the first polarized light component in the -1-order diffracted light in the first dimension and the second polarized light component in the +1-order diffracted light in the first dimension, and a beat frequency signal having a frequency f B -f A to generate and send it to the signal processing system; wherein the third receiver is used to receive the first polarized light component in the +1-order diffracted light in the second dimension and the second polarized light component in the -1-order diffracted light in the second dimension, and a beat frequency signal having a frequency f B -f A to generate and send it to the signal processing system; wherein the fourth receiver is used to receive the first polarized light component in the -1-order diffracted light in the second dimension and the second polarized light component in the +1-order diffracted light in the second dimension, and a beat frequency signal having a frequency f B -f A and send it to the signal processing system. [26] Heterodyne two-dimensional grating measuring method according to claim 25, characterized bythat the first polarized light components and second polarized light components received by the first receiver, the second receiver, the third receiver and the fourth receiver each pass through the gyro prism once, their light paths in the read head being the same. [27] Heterodyne two-dimensional grating measuring method according to claim 25, characterized bythat the signal processing system performs a difference calculation for the beat frequency signal output by the first receiver and the beat frequency signal output by the second receiver in order to realize the displacement measurement of the 4-fold optical subdivision by the single diffraction of the two-dimensional measuring grating in the first dimension, and performs a difference calculation for the beat frequency signal output by the third receiver and the beat frequency signal output by the fourth receiver in order to realize the displacement measurement of the 4-fold optical subdivision by the single diffraction of the two-dimensional measuring grating in the second dimension.

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