A precision displacement sensor with airfoil optical structure

Abstract

The present invention discloses a precision displacement sensor of an airfoil optical structure, which relates to the field of precision displacement measurement, and comprises: a first refraction device and a second refraction device are respectively located on the first side, the second side, the third side and the fourth side of a first polarization beam splitter; a laser is divided into a first polarization light and a second polarization light by the first polarization beam splitter; the first polarization light is incident on a biconvex lens through the first refraction device, and converges on an incident grating through the biconvex lens, and the obtained +1-order diffraction light beam passes through the first refraction device and the first polarization beam splitter to obtain a first reflected light; the first reflected light is incident on a detector device; the second polarization light is incident on a biconvex lens through the second refraction device, and converges on an incident grating through the biconvex lens, and the obtained -1-order diffraction light beam passes through the second refraction device and the first polarization beam splitter to obtain a second reflected light; the second reflected light is incident on a detector device; and the detector device realizes displacement measurement. The present invention improves the ability of the optical path structure to resist environmental interference.

Description

Technical Field

[0001] The invention relates to the field of precision displacement measurement, and in particular to a precision displacement sensor with an airfoil optical structure. Background Art

[0002] Due to the development of precision and high-end manufacturing process technology, the requirements for measurement accuracy are becoming increasingly higher. The traditional laser interferometer measurement system uses the wavelength of light as the measurement reference. The measurement accuracy is easily affected by the external environment and is not suitable for more complex industrial environments. The displacement measurement technology based on the principle of diffraction light interference has a measurement resolution that is directly related to the period of the grating and has strong resistance to environmental interference. A diffraction grating with a high line density can be used to achieve high-resolution and high-precision displacement measurement.

[0003] Although the displacement measurement system based on the principle of diffraction light interference has been widely used, there is still a lot of room for improvement in its optical structure design. General grating displacement sensors use reflectors to deflect light to meet the incident angle of grating diffraction, but the reflectors and their adjustment mechanisms not only occupy a large space in space, but the stability of the adjustment mechanism will also affect the final measurement results; at the same time, the small installation tolerance is also an important reason for limiting the actual use accuracy of grating sensors. Reducing the system's assembly tolerance and alignment tolerance requirements and improving the system's stability and reliability are also one of the important directions for designing high-precision grating displacement sensors. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a precision displacement sensor with an airfoil optical structure, which can improve the ability of the optical path structure to resist environmental interference and reduce the volume by removing the reflector and its adjustment mechanism in the prior art.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A precision displacement sensor of an airfoil optical structure, the displacement sensor comprising: a laser device, a first polarization beam splitter, a grating, a first refraction device, a biconvex lens, a second refraction device and a detector device;

[0007] The detector device is located on the second side of the first polarization beam splitter; the first refraction device is located on the third side of the first polarization beam splitter; the laser device is located on the first side of the first polarization beam splitter; the second refraction device is located on the fourth side of the first polarization beam splitter; the first side is opposite to the third side; the second side is opposite to the fourth side;

[0008] The laser device is used to emit a laser beam; the laser beam is vertically incident on the first side surface of the first polarization beam splitter, and is split by the first polarization beam splitter into a first polarized light and a second polarized light that are perpendicular to each other; the first polarized light is emitted from the third side surface of the first polarization beam splitter; and the second polarized light is emitted from the fourth side surface of the first polarization beam splitter;

[0009] The first polarized light is incident on the biconvex lens after being reflected twice by the first refraction device, and is incident on the grating at a Littrow angle after being converged by the biconvex lens to obtain a +1-order diffraction beam; the +1-order diffraction beam is reflected twice by the first refraction device and once by the first polarization beam splitter to obtain a first reflected light; the direction of the first reflected light is perpendicular to the direction of the first polarized light; the first reflected light is incident on the detector device;

[0010] After being reflected twice by the second refraction device, the second polarized light is incident on the biconvex lens, and after being converged by the biconvex lens, it is incident on the grating at a Littrow angle to obtain a -1 order diffraction beam; after being reflected twice by the second refraction device, the -1 order diffraction beam is incident on the first polarization beam splitter, and is emitted from the first polarization beam splitter to obtain a second reflected light; the direction of the second reflected light is consistent with the direction of the second polarized light; the second reflected light is incident on the detector device;

[0011] The first refraction device includes a first half pentagonal prism and a first quarter wave plate; the first polarized light is incident on the first quarter wave plate after being reflected twice by the first half pentagonal prism, and right-handed circularly polarized light is obtained after passing through the first quarter wave plate; the right-handed circularly polarized light is converged by the biconvex lens and incident on the grating at a Littrow angle;

[0012] The second refraction device includes a second half pentagonal prism and a second quarter wave plate; the second polarized light is incident on the second quarter wave plate after being reflected twice by the second half pentagonal prism, and left-handed circularly polarized light is obtained after passing through the second quarter wave plate; the left-handed circularly polarized light is converged by the biconvex lens and incident on the grating at a Littrow angle;

[0013] The first incident surface of the first half-penta prism is attached to the third side surface, and the first incident surface and the third side surface have the same size;

[0014] The second incident surface of the second semi-penta prism is attached to the fourth side surface, and the second incident surface and the fourth side surface have the same size;

[0015] In the detector device, the +1-order diffraction light beam interferes with the -1-order diffraction light beam to form an interference signal, and the interference signal is processed to achieve displacement measurement.

[0016] Optionally, the detector device includes a third quarter wave plate, a non-polarizing beam splitter, a second polarizing beam splitter, a first photodetector, a second photodetector, a third polarizing beam splitter, a third photodetector and a fourth photodetector;

[0017] The +1-order diffracted light beam is vertically incident on the third quarter-wave plate, and after passing through the third quarter-wave plate, left-handed circularly polarized light is obtained;

[0018] The -1 order diffraction beam is vertically incident on the third quarter wave plate, and after passing through the third quarter wave plate, right-handed circularly polarized light is obtained;

[0019] The left-handed circularly polarized light and the right-handed circularly polarized light are incident vertically on the non-polarizing beam splitter at the same time; the non-polarizing beam splitter splits the combined light of the left-handed circularly polarized light and the right-handed circularly polarized light into a third polarized light and a fourth polarized light of equal intensity;

[0020] The third polarized light is vertically incident on the second polarization beam splitter to interfere with the light, thereby obtaining a first interference light and a second interference light;

[0021] The fourth polarized light is vertically incident on the third polarization beam splitter to interfere, thereby obtaining third interference light and fourth interference light;

[0022] The first photodetector receives the first interference light to obtain a first signal; the second photodetector receives the second interference light to obtain a second signal; the third photodetector receives the third interference light to obtain a third signal; the fourth photodetector receives the fourth interference light to obtain a fourth signal; the first signal, the second signal, the third signal and the fourth signal are sine wave signals that are 90 degrees apart from each other.

[0023] Optionally, the polarization angle of the second polarization beam splitter is 0 degrees; and the polarization angle of the third polarization beam splitter is 45 degrees.

[0024] Optionally, the third spacing and the fourth spacing are consistent; the third spacing is the spacing between the second polarization beam splitter and the non-polarization beam splitter; the fourth spacing is the spacing between the third polarization beam splitter and the non-polarization beam splitter.

[0025] Optionally, the fifth spacing, the sixth spacing, the seventh spacing and the eighth spacing are all consistent; the fifth spacing is the spacing between the second polarization beam splitter and the first photodetector; the sixth spacing is the spacing between the second polarization beam splitter and the second photodetector; the seventh spacing is the spacing between the third polarization beam splitter and the third photodetector; the eighth spacing is the spacing between the third polarization beam splitter and the fourth photodetector.

[0026] Optionally, the laser device includes a laser and an optical isolator;

[0027] The optical isolator is arranged on the direct light path of the laser;

[0028] The laser light emitted by the laser device is passed through the optical isolator to obtain a laser beam.

[0029] Optionally, the laser is a single-frequency laser.

[0030] Optionally, the grating is a reflective holographic diffraction grating.

[0031] Optionally, the first spacing and the second spacing are consistent; the first spacing is the spacing between the first quarter wave plate and the first half pentagonal prism; the second spacing is the spacing between the second quarter wave plate and the second half pentagonal prism.

[0032] Optionally, the focal length of the biconvex lens is equal to the distance from the focal plane of the biconvex lens to the grating surface.

[0033] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0034] (1) A polarization beam splitter and two half-pentagonal prisms are combined to form a "wing-shaped" structure to achieve the splitting of two polarized light beams in the horizontal direction. The structure is compact and the space utilization rate is high. It not only shortens the optical path and improves the ability of the optical path structure to resist environmental interference, but also saves the space occupied by the reflector and its adjustment mechanism.

[0035] (2) The adjustment difficulty of the displacement sensor is reduced, and the stability of the measurement system is improved. The common method is to adjust the angle of the incident light incident grating by rotating the angle of the reflector. In the present invention, the angle of the incident grating can be adjusted only by translating the position of the incident light, which reduces the number of components that need to be adjusted in the optical path and reduces the difficulty of adjustment.

[0036] (3) Construct a single-power telescope system. Two laser beams are symmetrically and parallelly incident on the double convex lens and their focal points converge on the incident surface of the grating. This constitutes a single-power telescope system, which significantly improves the error tolerance of the grating and probe alignment and reduces the impact of the incomplete overlap of the two diffraction light spots caused by the yaw and pitch of the grating.

[0037] (4) By utilizing the characteristics of polarized optics, the light application efficiency is high, avoiding the light loss caused by the splitting of ordinary spectroscopes, and can effectively isolate undesired light beams, thereby reducing the interference of ambient stray light on the measurement signal and improving the reliability and stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0039] Figure 1 A schematic diagram of the three-dimensional structure optical path of a precision displacement sensor of an airfoil optical structure of the present invention;

[0040] Figure 2 It is a schematic diagram of the optical path of the two-dimensional structure of the present invention;

[0041] Figure 3 Schematic diagram of linear polarized P light of the two-dimensional structure of the present invention;

[0042] Figure 4 This is a schematic diagram of linearly polarized S light in the two-dimensional structure of the present invention.

[0043] Description of reference numerals:

[0044] 1-laser, 2-optical isolator, 301-first polarization beam splitter, 302-second polarization beam splitter, 303-third polarization beam splitter, 401-first half pentagonal prism, 402-second half pentagonal prism, 501-first quarter wave plate, 502-second quarter wave plate, 503-third quarter wave plate, 6-double convex lens, 7-grating, 8-non-polarization beam splitter, 901-first photodetector, 902-second photodetector, 903-third photodetector, 904-fourth photodetector. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] The purpose of the present invention is to provide a precision displacement sensor with an airfoil optical structure, which can improve the ability of the optical path structure to resist environmental interference and reduce the volume by removing the reflector and its adjustment mechanism in the prior art.

[0047] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0048] like Figure 1 As shown, the present invention provides a precision displacement sensor of an airfoil optical structure, the displacement sensor comprising: a laser device, a first polarization beam splitter 301, a grating 7, a first refraction device, a biconvex lens 6, a second refraction device and a detector device. The first polarization beam splitter 301 is a regular hexahedron, and has four surfaces that can receive and emit light, namely, a first side surface, a second side surface, a third side surface and a fourth side surface. Depending on the propagation direction of the light, each surface can be used as an incident surface or an exit surface.

[0049] The detector device is located on the second side of the first polarization beam splitter 301; the first refraction device is located on the third side of the first polarization beam splitter 301; the laser device is located on the first side of the first polarization beam splitter 301; the second refraction device is located on the fourth side of the first polarization beam splitter 301; the first side is opposite to the third side; and the second side is opposite to the fourth side.

[0050] The laser device is used to emit a laser beam; the laser beam is vertically incident on the first side of the first polarization beam splitter 301, and is divided by the first polarization beam splitter 301 into a first polarized light and a second polarized light perpendicular to each other; the first polarized light is emitted from the third side of the first polarization beam splitter 301; the second polarized light is emitted from the fourth side of the first polarization beam splitter 301. The first polarized light is consistent with the direction of the laser beam; the second polarized light is perpendicular to the direction of the laser beam; the angle of the linear polarized light emitted by the laser beam is 45°, that is, the angle between the linear polarized light and the horizontal plane is 45°.

[0051] The first polarized light is reflected twice by the first refractive device and is incident on the biconvex lens 6. After being converged by the biconvex lens 6, it is incident on the grating 7 at a Littrow angle to obtain a +1-order diffraction beam. The +1-order diffraction beam is reflected twice by the first refractive device and once by the first polarization beam splitter 301 to obtain a first reflected light. The direction of the first reflected light is perpendicular to the direction of the first polarized light. The first reflected light is incident on the detector device.

[0052] The second polarized light is incident on the biconvex lens 6 after being reflected twice by the second refractive device, and is incident on the grating 7 at a Littrow angle after being converged by the biconvex lens 6 to obtain a -1 order diffraction beam; the -1 order diffraction beam is incident on the first polarization beam splitter 301 after being reflected twice by the second refractive device, and is emitted from the first polarization beam splitter 301 to obtain a second reflected light; the direction of the second reflected light is consistent with the direction of the second polarized light; the second reflected light is incident on the detector device.

[0053] The first refractive device includes a first half pentagonal prism 401 and a first quarter wave plate 501; the first polarized light is reflected twice by the first half pentagonal prism 401 and is incident on the first quarter wave plate 501, and right-handed circularly polarized light is obtained after passing through the first quarter wave plate 501; the right-handed circularly polarized light is converged by the biconvex lens 6 and is incident on the grating 7 at a Littrow angle.

[0054] The second refractive device includes a second half-pentagonal prism 402 and a second quarter-wave plate 502; the second polarized light is reflected twice by the second half-pentagonal prism 402 and is incident on the second quarter-wave plate 502, and left-handed circularly polarized light is obtained after passing through the second quarter-wave plate 502; the left-handed circularly polarized light is converged by the biconvex lens 6 and is incident on the grating 7 at a Littrow angle.

[0055] The first incident surface of the first half-pentagonal prism 401 is attached to the third side surface of the first polarization beam splitter 301 , and the first incident surface and the third side surface have the same size.

[0056] The second incident surface of the second half-pentagonal prism 402 is attached to the fourth side surface of the first polarization beam splitter 301 , and the second incident surface and the fourth side surface have the same size.

[0057] In the detector device, the +1-order diffraction light beam interferes with the -1-order diffraction light beam to form an interference signal, and the interference signal is processed to achieve displacement measurement.

[0058] The detector device includes a third quarter wave plate 503 , a non-polarizing beam splitter 8 , a second polarizing beam splitter 302 , a first photodetector 901 , a second photodetector 902 , a third polarizing beam splitter 303 , a third photodetector 903 and a fourth photodetector 904 .

[0059] The +1-order diffracted light beam is vertically incident on the third quarter-wave plate 503 , and after passing through the third quarter-wave plate 503 , left-handed circularly polarized light is obtained.

[0060] The -1 order diffracted light beam is vertically incident on the third quarter wave plate 503, and after passing through the third quarter wave plate 503, right-handed circularly polarized light is obtained;

[0061] The left-handed circularly polarized light and the right-handed circularly polarized light are incident vertically on the non-polarizing beam splitter 8 at the same time; the non-polarizing beam splitter 8 splits the combined light of the left-handed circularly polarized light and the right-handed circularly polarized light into a third polarized light and a fourth polarized light of equal intensity.

[0062] The third polarized light is vertically incident on the second polarization beam splitter 302 to interfere with each other, thereby obtaining a first interference light and a second interference light.

[0063] The fourth polarized light is vertically incident on the third polarization beam splitter 303 to interfere, thereby obtaining third interference light and fourth interference light.

[0064] The first photodetector 901 receives the first interference light to obtain a first signal; the second photodetector 902 receives the second interference light to obtain a second signal; the third photodetector 903 receives the third interference light to obtain a third signal; the fourth photodetector 904 receives the fourth interference light to obtain a fourth signal; the first signal, the second signal, the third signal and the fourth signal are sine wave signals that differ by 90 degrees from each other.

[0065] Specifically, the polarization angle of the second polarization beam splitter 302 is 0 degrees; the polarization angle of the third polarization beam splitter 303 is 45 degrees.

[0066] Furthermore, the third spacing and the fourth spacing are consistent; the third spacing is the spacing between the second polarization beam splitter 302 and the non-polarization beam splitter 8 ; the fourth spacing is the spacing between the third polarization beam splitter 303 and the non-polarization beam splitter 8 .

[0067] Furthermore, the fifth spacing, the sixth spacing, the seventh spacing and the eighth spacing are all consistent; the fifth spacing is the spacing between the second polarization beam splitter 302 and the first photodetector 901; the sixth spacing is the spacing between the second polarization beam splitter 302 and the second photodetector 902; the seventh spacing is the spacing between the third polarization beam splitter 303 and the third photodetector 903; the eighth spacing is the spacing between the third polarization beam splitter 303 and the fourth photodetector 904.

[0068] As a specific implementation, the laser device includes a laser 1 and an optical isolator 2. The optical isolator 2 is arranged on the direct light path of the laser 1. The laser light emitted by the laser 1 passes through the optical isolator 2 to obtain a laser beam.

[0069] Specifically, the laser 1 is a single-frequency laser.

[0070] As a specific implementation, the grating 7 is a reflective holographic diffraction grating.

[0071] Specifically, the first spacing and the second spacing are consistent; the first spacing is the spacing between the first quarter wave plate 501 and the first half pentagonal prism 401; the second spacing is the spacing between the second quarter wave plate 502 and the second half pentagonal prism 402.

[0072] Furthermore, the focal length of the biconvex lens 6 is equal to the distance from the focal plane of the biconvex lens 6 to the surface of the grating 7 .

[0073] In practical applications, an optical isolator 2 and a first polarization beam splitter 301 are sequentially arranged on the direct light path of the laser 1; the optical isolator 2 prevents stray light from being reflected back to the laser 1, thereby affecting the stability of its output frequency; the laser light emitted by the laser 1 is split by the first polarization beam splitter 301 to form mutually perpendicular P polarized light and S polarized light, wherein the P polarized light is the first polarized light, and the S polarized light is the second polarized light.

[0074] After the P polarized light is reflected by the first semi-pentagonal prism 401, it is deflected by 45° and vertically incident on the first quarter wave plate 501 to become right-handed circularly polarized light; the right-handed circularly polarized light is vertically incident on the biconvex lens 6 and converges at a point on the grating 7; the incident angle of the right-handed circularly polarized light meets the Littrow condition to generate (+1) order diffracted light and returns along the original path; the (+1) order diffracted light is converted into parallel light after passing through the biconvex lens 6 and vertically incident on the first quarter wave plate 501 to become S polarized light; the S polarized light is reflected by the first semi-pentagonal prism 401, then vertically incident on the first polarization beam splitter 301 for reflection and then vertically incident on the third quarter wave plate 503 to become left-handed circularly polarized light.

[0075] After the S polarized light is reflected by the second semi-pentagonal prism 402, it is deflected by 45° and vertically incident on the second quarter-wave plate 502 to become left-handed circularly polarized light; the left-handed circularly polarized light is vertically incident on the biconvex lens 6 and converges at a point on the grating 7; the incident angle of the left-handed circularly polarized light meets the Littrow condition to generate (-1) order diffraction light and returns along the original path; the (-1) order diffraction light is converted into parallel light after passing through the biconvex lens 6 and vertically incident on the second quarter-wave plate 502 to become P polarized light; the P polarized light is reflected by the second semi-pentagonal prism 402, vertically incident on the first polarization beam splitter 301 to be transmitted, and then vertically incident on the third quarter-wave plate 503 to become right-handed circularly polarized light.

[0076] The left-handed circularly polarized light and the right-handed circularly polarized light are vertically incident on the non-polarizing beam splitter 8; the two overlapping circularly polarized light beams are divided into two beams of equal intensity by the non-polarizing beam splitter 8 and are incident on the second polarizing beam splitter 302 and the third polarizing beam splitter 303 for splitting and interference; the polarization angles of the second polarizing beam splitter 302 and the third polarizing beam splitter 303 are 0° and 45° respectively, so that four sine wave signals with a phase difference of 90° can be obtained at four photodetectors.

[0077] Furthermore, the laser 1 is a single-frequency laser; the grating 7 is a reflective holographic diffraction grating; the side lengths of the first half pentagonal prism 401 and the second half pentagonal prism 402 are consistent with and closely fit with the side lengths of the first polarization splitter; the first quarter-wave plate 501 and the second quarter-wave plate 502 are equidistant from the first half pentagonal prism 401 and the second half pentagonal prism 402; the focal length of the biconvex lens 6 is equal to the distance from the focal plane of the biconvex lens 6 to the surface of the grating 7; the second polarization beam splitter 302 and the non-polarization beam splitter 8 are equidistant from the third polarization beam splitter 303 and the non-polarization beam splitter 8; the four photoelectric receivers are equidistant from the corresponding polarization beam splitter surfaces.

[0078] As a specific implementation, the focal length of the biconvex lens 6 can be smaller than the distance from the focal plane of the biconvex lens 6 to the surface of the grating 7. At this time, the 0th order diffraction light generated by the first diffraction will not return along the original path of the opposite light path, and then reflect back into the laser to affect the stability of the laser output power. Specifically, when the light spot converges at the focus of the biconvex lens, the 0th order diffraction light will reflect back into the laser, so the optical isolator 2 is added to prevent the light beam from reflecting back to the laser and affecting the stability of the laser output power.

[0079] Furthermore, laser 1 is a single-frequency laser with a standard wavelength of 635nm, and the polarization state of the light beam is linear polarized mode light; grating 7 is a reflective holographic diffraction grating with a frequency of 1200 lines / mm; the polarization beam splitter is a standard size of 5×5×5mm; the side length of the half-pentagonal prism is 5mm; according to the grating equation d(sini+sinθ)=mλ, in which the grating pitch is 1200 lines / mm, the diffraction order m is ±1, the wavelength of the light source is 635nm, the littrow diffraction incident angle is equal to the diffraction angle, and the diffraction angle is 22.4°.

[0080] An optical isolator 2 and a first polarization beam splitter 301 are sequentially arranged on the direct light path of the laser 1; a first half pentagonal prism 401 is arranged on the right side of the first deflection beam splitter 301, and the left side surface of the first half pentagonal prism 401 and the right side surface of the first deflection beam splitter 301 are of the same size and overlap; a second half pentagonal prism 402 on the right side is arranged on the left side of the first deflection beam splitter 301, and the right side surface of the second half pentagonal prism 401 and the left side surface of the first deflection beam splitter 301 are of the same size and overlap; a first quarter wave plate 501 and a second quarter wave plate 502 are parallel to and equidistant from the two bottom surfaces of the first half pentagonal prism 401 and the second half pentagonal prism 402 respectively; a focal plane of the biconvex lens 6 is aligned with the first quarter wave plate 501 and the second quarter wave plate 502. The grating 7 is arranged directly below the biconvex lens 6 and the distance between the grating 7 and the biconvex lens 6 is equal to the focal length of the biconvex lens 6; the third quarter wave plate 503 is arranged on the upper right side of the first polarization beam splitter 301; the non-polarization beam splitter 8 is arranged on the transmission light path of the third quarter wave plate 503; the second polarization beam splitter 302 and the third polarization beam splitter 303 are respectively arranged at the transmission end and the reflection end of the non-polarization beam splitter 8 and the distance between the second polarization beam splitter 303 and the non-polarization beam splitter 8 is equal; the first photodetector 901 and the second photodetector 902 are respectively arranged on the two light output sides of the second polarization beam splitter 303, and the third photodetector 903 and the fourth photodetector 904 are respectively arranged on the two light output sides of the third polarization beam splitter 303.

[0081] The working principle of the displacement sensor provided by the present invention is as follows:

[0082] The linearly polarized light emitted by the laser 1 is incident on the first polarization beam splitter 301 through the optical isolator 2 to be split into P polarized light and S polarized light perpendicular to each other.

[0083] like Figure 3As shown, linearly polarized P light is vertically incident on the first half pentagonal prism 401, and after the light is deflected 45°, it is vertically incident on the first quarter wave plate 501 to become right-handed circularly polarized light. The right-handed circularly polarized light is vertically incident on the biconvex lens 6 and converges on the grating 7 to undergo the first diffraction. The +1-order diffraction light generated by the first diffraction satisfies the Littrow diffraction angle and returns to the biconvex lens 6 along the original path. After passing through the biconvex lens 6, it is vertically incident on the first quarter wave plate 501 to become S polarized light. After the S polarized light is vertically incident on the first half pentagonal prism 401, the light is deflected 45° and vertically incident on the first deflection beam splitter 301 and then reflected. The reflected S deflected light is vertically incident on the third quarter wave plate 503.

[0084] like Figure 4 As shown, the linearly polarized S light is vertically incident on the second half pentagonal prism 402, and the light is deflected 45° and vertically incident on the second quarter wave plate 502 to become left-handed circularly polarized light. The left-handed circularly polarized light is vertically incident on the biconvex lens 6 and converges on the grating 7 to undergo the first diffraction. The -1 order diffraction light generated by the first diffraction satisfies the Littrow diffraction angle and returns to the biconvex lens 6 along the original path. After passing through the biconvex lens 6, it is vertically incident on the second quarter wave plate 502 to become P polarized light. After the P polarized light is vertically incident on the second half pentagonal prism 402, the light is deflected 45° and vertically incident on the first deflection beam splitter 301 and then transmitted. The transmitted S deflected light is vertically incident on the third quarter wave plate 503.

[0085] like Figure 2 , Figure 3 , Figure 4 As shown, the linearly polarized P light and S light containing the first diffraction information are simultaneously incident on the third quarter wave plate 503 to become right-handed circularly polarized light and left-handed circularly polarized light, which are incident on the non-polarizing beam splitter 8. The two overlapping circularly polarized light beams are divided into two beams of equal intensity by the non-polarizing beam splitter 8 and are incident on the second polarizing beam splitter 302 with a polarization angle of 0° and the third polarizing beam splitter 503 with a polarization angle of 45° to cause interference. Four sine wave signals with a phase difference of 90° are obtained at four photodetectors. The photodetectors detect the intensity change of the interference fringes and convert them into electrical signals. Therefore, four electrical signals with a phase difference of 90° that follow the sine wave change rule are obtained. The grating displacement and direction information can be obtained through filtering, direction identification, counting and other circuit processing.

[0086] The incident surfaces of the first polarization beam splitter 301, the second polarization beam splitter 302 and the third polarization beam splitter 303 of the present invention are all surfaces of a cubic polarization beam splitter prism, and the diagonal surface of the cubic polarization beam splitter prism is a beam splitting surface. In the present invention, the propagation direction of all lasers when incident on the optical element is perpendicular to the incident surface.

[0087] The present invention realizes the first diffraction of the measuring beam, realizes the optical dichotomy, improves the measuring accuracy, has a symmetrical optical path structure and high space utilization, and uses a double convex lens to construct a single telescope system to improve the tolerance of the grating deflection and realize the self-compensation deflection angle when the grating moves. The entire displacement sensor has a compact structure, strong resistance to environmental interference, strong resistance to grating deflection, and high stability and measuring accuracy.

[0088] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0089] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A precision displacement sensor with an airfoil optical structure, characterized in that: The displacement sensor comprises: a laser device, a first polarization beam splitter, a grating, a first refraction device, a biconvex lens, a second refraction device and a detector device; The detector device is located on the second side of the first polarization beam splitter; the first refraction device is located on the third side of the first polarization beam splitter; the laser device is located on the first side of the first polarization beam splitter; the second refraction device is located on the fourth side of the first polarization beam splitter; the first side is opposite to the third side; the second side is opposite to the fourth side; The laser device is used to emit a laser beam; the laser beam is vertically incident on the first side surface of the first polarization beam splitter, and is split by the first polarization beam splitter into a first polarized light and a second polarized light that are perpendicular to each other; the first polarized light is emitted from the third side surface of the first polarization beam splitter; and the second polarized light is emitted from the fourth side surface of the first polarization beam splitter; The first polarized light is incident on the biconvex lens after being reflected twice by the first refraction device, and is incident on the grating at a Littrow angle after being converged by the biconvex lens to obtain a +1-order diffraction beam; the +1-order diffraction beam is reflected twice by the first refraction device and once by the first polarization beam splitter to obtain a first reflected light; the direction of the first reflected light is perpendicular to the direction of the first polarized light; the first reflected light is incident on the detector device; After being reflected twice by the second refraction device, the second polarized light is incident on the biconvex lens, and after being converged by the biconvex lens, it is incident on the grating at a Littrow angle to obtain a -1 order diffraction beam; after being reflected twice by the second refraction device, the -1 order diffraction beam is incident on the first polarization beam splitter, and is emitted from the first polarization beam splitter to obtain a second reflected light; the direction of the second reflected light is consistent with the direction of the second polarized light; the second reflected light is incident on the detector device; The first refraction device includes a first half pentagonal prism and a first quarter wave plate; the first polarized light is incident on the first quarter wave plate after being reflected twice by the first half pentagonal prism, and right-handed circularly polarized light is obtained after passing through the first quarter wave plate; the right-handed circularly polarized light is converged by the biconvex lens and incident on the grating at a Littrow angle; The second refraction device includes a second half pentagonal prism and a second quarter wave plate; the second polarized light is incident on the second quarter wave plate after being reflected twice by the second half pentagonal prism, and left-handed circularly polarized light is obtained after passing through the second quarter wave plate; the left-handed circularly polarized light is converged by the biconvex lens and incident on the grating at a Littrow angle; The first incident surface of the first half-penta prism is attached to the third side surface, and the first incident surface and the third side surface have the same size; The second incident surface of the second semi-penta prism is attached to the fourth side surface, and the second incident surface and the fourth side surface have the same size; In the detector device, the +1-order diffraction light beam interferes with the -1-order diffraction light beam to form an interference signal, and the interference signal is processed to achieve displacement measurement; The detector device includes a third quarter wave plate, a non-polarizing beam splitter, a second polarizing beam splitter, a first photodetector, a second photodetector, a third polarizing beam splitter, a third photodetector and a fourth photodetector; The +1-order diffracted light beam is vertically incident on the third quarter-wave plate, and after passing through the third quarter-wave plate, left-handed circularly polarized light is obtained; The -1 order diffraction beam is vertically incident on the third quarter wave plate, and after passing through the third quarter wave plate, right-handed circularly polarized light is obtained; The left-handed circularly polarized light and the right-handed circularly polarized light are incident vertically on the non-polarizing beam splitter at the same time; the non-polarizing beam splitter splits the combined light of the left-handed circularly polarized light and the right-handed circularly polarized light into a third polarized light and a fourth polarized light of equal intensity; The third polarized light is vertically incident on the second polarization beam splitter to interfere with the light, thereby obtaining a first interference light and a second interference light; The fourth polarized light is vertically incident on the third polarization beam splitter to interfere, thereby obtaining a third interference light and a fourth interference light; The first photodetector receives the first interference light to obtain a first signal; the second photodetector receives the second interference light to obtain a second signal; the third photodetector receives the third interference light to obtain a third signal; the fourth photodetector receives the fourth interference light to obtain a fourth signal; the first signal, the second signal, the third signal and the fourth signal are sine wave signals that are 90 degrees apart from each other.

2. The precision displacement sensor of the airfoil optical structure according to claim 1, characterized in that: The polarization angle of the second polarization beam splitter is 0 degrees; the polarization angle of the third polarization beam splitter is 45 degrees.

3. The precision displacement sensor of the airfoil optical structure according to claim 1, characterized in that: The third spacing is consistent with the fourth spacing; the third spacing is the spacing between the second polarization beam splitter and the non-polarization beam splitter; the fourth spacing is the spacing between the third polarization beam splitter and the non-polarization beam splitter.

4. The precision displacement sensor of the airfoil optical structure according to claim 1, characterized in that: The fifth spacing, the sixth spacing, the seventh spacing and the eighth spacing are all consistent; the fifth spacing is the spacing between the second polarization beam splitter and the first photodetector; The sixth spacing is the spacing between the second polarization beam splitter and the second photodetector; the seventh spacing is the spacing between the third polarization beam splitter and the third photodetector; and the eighth spacing is the spacing between the third polarization beam splitter and the fourth photodetector.

5. The precision displacement sensor of the airfoil optical structure according to claim 1, characterized in that: The laser device comprises a laser and an optical isolator; The optical isolator is arranged on the direct light path of the laser; The laser light emitted by the laser device passes through the optical isolator to obtain a laser beam.

6. The precision displacement sensor of the airfoil optical structure according to claim 5, characterized in that: The laser is a single-frequency laser.

7. The precision displacement sensor of the airfoil optical structure according to claim 1, characterized in that: The grating is a reflective holographic diffraction grating.

8. The precision displacement sensor of the airfoil optical structure according to claim 1, characterized in that: The first spacing and the second spacing are consistent; the first spacing is the spacing between the first quarter wave plate and the first half pentagonal prism; the second spacing is the spacing between the second quarter wave plate and the second half pentagonal prism.

9. The precision displacement sensor of the airfoil optical structure according to claim 1, characterized in that: The focal length of the biconvex lens is equal to the distance from the focal plane of the biconvex lens to the grating surface.

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