An optical system for a high-precision photoelectric angular displacement sensor and an angular displacement sensor

Abstract

The application discloses a high-precision photoelectric angular displacement sensor optical system and an angular displacement sensor, which comprises equivalent flat glass, a first lens, a second lens and a third lens; the equivalent flat glass, the first lens, the second lens and the third lens are sequentially arranged along an axial direction; the front of the equivalent flat glass is directed to the outer wall of an optical encoder disc; an aperture stop is arranged on the front surface of the first lens, and the first lens is used for converging the light energy passing through the aperture stop and then making the light energy incident on the second lens; the second lens is used for correcting the spherical aberration generated by the first lens and the third lens; and the third lens is used for correcting optical distortion and simultaneously correcting the residual aberration such as the residual spherical aberration and the coma of the first lens and the second lens. The application provides an angular displacement sensor optical system, which has the characteristics of miniaturization and high reliability and can meet the measurement requirements of a high-precision angular displacement sensor working in a severe temperature environment.

Description

Technical Field

[0001] This invention relates to an optical system and an angular displacement sensor for a high-precision photoelectric angular displacement sensor, which falls under the category of optical engineering. Background Technology

[0002] The photoelectric angular displacement sensor provides high-precision rotation angle information for a high-precision spatial pointing control demonstration and verification system. This system uses a motor-driven mechanical device to move the pointing mechanism. During this movement, it is crucial to acquire real-time, high-precision information such as the motor's rotation angle and speed. This information serves as the control input for the motor system and significantly impacts the overall system's accuracy and reliability. The primary function of the photoelectric angular displacement sensor is to provide the entire system with high-speed, high-precision, and high-reliability rotation angle information.

[0003] Existing conventional photoelectric angular displacement sensors typically use an optical encoder disk combined with multi-point detection for angle measurement. This type of sensor generally has an accuracy in the arcsecond range, essentially reaching the technical limit of this approach. Improving accuracy is extremely difficult, making it unsuitable for the technical requirements of high-precision spatial pointing control demonstration and verification systems. Furthermore, its setup and adjustment cycle is measured in weeks, resulting in long setup times and significant difficulty. Limited by inconsistent point detector responses and low reliability, this type of photoelectric angular displacement sensor has low reliability, generally requiring detector selection to meet reliability requirements, leading to extremely high product prices. Summary of the Invention

[0004] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide an optical system and angular displacement sensor for angular displacement sensors that meet the measurement requirements of high-precision angular displacement sensors working in harsh temperature environments.

[0005] The technical solution of this invention is:

[0006] An optical system for a high-precision photoelectric angular displacement sensor includes: an equivalent flat glass, a first lens, a second lens, and a third lens;

[0007] The equivalent flat glass, the first lens, the second lens, and the third lens are arranged sequentially along the axial direction;

[0008] The front of the equivalent flat glass faces the outer wall of the optical encoder disk;

[0009] An aperture stop is provided on the front surface of the first lens. The first lens is used to focus the light energy passing through the aperture stop and then incident it onto the second lens.

[0010] The second lens is used to correct the spherical aberration produced by the first and third lenses;

[0011] The third lens is used to correct optical distortion, and at the same time corrects residual aberrations such as spherical aberration and coma of the first and second lenses.

[0012] Preferably, the first lens is a positive lens, the optical material used for the first lens is LaK3, and the distance between the vertex of the equivalent flat glass rear surface and the front surface of the first lens ranges from 0.5 to 2 mm.

[0013] Preferably, the second lens is a positive lens, and the optical material used in the second lens is ZF4.

[0014] Preferably, the third lens is a negative lens, the optical material used in the third lens is ZF4, and the distance from the vertex of the rear surface of the third lens to the photosensitive surface of the photodetector ranges from 1.5 to 10 mm.

[0015] Preferably, the distance from the front surface of the equivalent flat glass to the outer wall of the optical encoder disk is in the range of 0.5 to 2 mm.

[0016] Secondly,

[0017] An angular displacement sensor using an optical system for a high-precision photoelectric angular displacement sensor as described in the first aspect includes: an optical encoder disk, an illumination source, a photodetector, a detector driving circuit, and an algorithm processing circuit;

[0018] The optical encoding disk has a thin-walled cylindrical structure. The encoding area on the side wall of the thin-walled cylindrical structure is processed with slits arranged in a circular pattern according to a certain rule to form an encoding pattern; the length direction of the slits is the same as the axial direction of the thin-walled cylindrical structure.

[0019] The illumination source is used to illuminate the optical encoder disc;

[0020] An optical system consisting of an equivalent flat glass plate, a first lens, a second lens, and a third lens images the coding area on the sidewall of the optical coding disk and transmits the optical signal to the photodetector.

[0021] The photodetector receives optical signals, performs photoelectric conversion to obtain electrical signals, and transmits them to the detector drive circuit.

[0022] The detector driving circuit receives the electrical signal sent by the detector, performs signal buffering processing, and transmits the buffered signal to the algorithm processing circuit.

[0023] The algorithm processing circuit receives the buffered signal transmitted by the detector driving circuit, performs image processing, and outputs the rotation angle information of the optical encoder disk.

[0024] Preferably, the coding pattern includes multiple adjacent coding units evenly distributed around the perimeter; the width of each coding unit ranges from 10um to 60um, and several coding units are hollowed out to form slits;

[0025] The number of uncut coded units in each image obtained by the photodetector is no less than 20.

[0026] Preferably, the slits are evenly distributed around the perimeter, and the width of the slits and the spacing between two adjacent slits are the same.

[0027] Preferably, different rotation angles of the optical encoder disk result in different encoded patterns in the images obtained by the photodetector.

[0028] Preferably, the length of the slit along the axial direction of the optical encoder disk is in the range of 5 to 10 mm.

[0029] The advantages of this invention compared to the prior art are:

[0030] 1) The optical system of the present invention can realize optical magnification of the observed target, improve the optical resolution of the system, and reduce the technical requirements and implementation difficulty of the detection system resolution.

[0031] 2) The first lens material of the optical system of this invention is fused silica, which can both correct optical system aberrations and protect the lenses in the optical system. This eliminates the need for a separate protective glass in the optical system, further reducing the weight of the optical system.

[0032] 3) The optical system of this invention can operate in a temperature environment of -50℃ to +70℃ by optimizing the selection of optical materials and air gaps, thereby increasing the operating temperature range of the system, reducing the requirements for the operating environment, and making the product easier to use. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the optical system composition of the present invention.

[0034] Figure 2 This is a schematic diagram of the angular displacement sensor used in the optical system of this invention. Detailed Implementation

[0035] This invention proposes an optical system and angular displacement sensor for a high-precision photoelectric angular displacement sensor based on machine vision. Belonging to the category of microscopic imaging objectives, the system simultaneously addresses various primary and higher-order aberrations, including spherical aberration, coma, and astigmatism. The optical system consists of three lenses and one equivalent flat glass plate. Based on primary aberration theory, the three-lens optical structure has six radii of curvature and two lens thicknesses, resulting in eight optimization variables, making it the simplest structure for correcting seven aberrations. The first lens 3 is a positive lens that converges the light energy emitted from the object side, preventing beam divergence and reducing the aperture of the subsequent optical system. The second lens 4 further converges the beam and partially corrects the aberrations of the first lens 3. The third lens 5 corrects distortion and the residual aberrations of the first two lenses. This system can be applied to a miniaturized, high-precision star sensor.

[0036] The optical system is constructed using materials suitable for aerospace applications, exhibiting excellent adaptability to the space environment. Furthermore, its simple structure reduces manufacturing and assembly complexity, thereby lowering development costs and meeting the demands for high reliability and low cost.

[0037] High-precision angular displacement sensors based on machine vision principles generally consist of an optical system, detector components and their circuits, data processing circuits, software, and a main structure.

[0038] The optical system converges the light energy of the coded lines, and the converged coded lines are imaged onto the detector for subsequent image processing and angular position data output. Therefore, the imaging quality, size and weight, and adaptability to the space environment are key indicators for evaluating the optical system.

[0039] like Figure 2 As shown, the angular displacement sensor using the optical system of the high-precision photoelectric angular displacement sensor includes: an optical encoder disk 1, an illumination source, a detector, a detector driving circuit, and an algorithm processing circuit.

[0040] The optical encoding disk 1 is a thin-walled cylindrical structure. The encoding area on the side wall of the thin-walled cylindrical structure is processed with slits arranged in a certain pattern to form an encoding pattern; the length direction of the slits is the same as the axial direction of the thin-walled cylindrical structure.

[0041] The illumination source is used to illuminate the optical encoder disk 1;

[0042] The optical system consisting of equivalent flat glass 2, first lens 3, second lens 4 and third lens 5 images the coding area on the side wall of optical coding disk 1 and transmits the light signal to the detector.

[0043] The detector receives optical signals, performs photoelectric conversion to obtain electrical signals, and transmits them to the detector drive circuit.

[0044] The detector driving circuit receives the electrical signal sent by the detector, performs signal buffering processing, and transmits the buffered signal to the algorithm processing circuit.

[0045] The algorithm processing circuit receives the buffer signal transmitted by the detector driving circuit, performs image processing, and outputs the rotation angle information of the optical encoder disk 1.

[0046] The coding pattern comprises multiple adjacent and evenly distributed coding units; the width of each coding unit ranges from 10µm to 60µm, and several coding units are hollowed out to form slits; the number of coding units without hollowing out in each image obtained by the detector is no less than 20. The slits are evenly distributed around the perimeter, and the slit width and the spacing between two adjacent slits are the same. Different rotation angles of the optical coding disk 1 result in different coding patterns in the images obtained by the detector. The length of the slits along the axial direction of the optical coding disk 1 ranges from 5 to 10 mm.

[0047] The optical system of this invention consists of an equivalent flat plate and three lenses, such as... Figure 1 As shown, from left to right, it includes: an optical encoder disk 1, an equivalent flat glass 2, a first lens 3, a second lens 4, a third lens 5, and a photodetector 6. The optical encoder disk 1 has a cylindrical structure; the radius of the optical encoder disk 1 is not less than 20 mm. The front of the equivalent flat glass 2 faces the outer wall of the optical encoder disk 1.

[0048] The optical system operates in the spectral range of 0.8μm to 0.9μm, has a focal length of 5.8mm, an entrance pupil diameter of 3mm, and an operating temperature range of -50℃ to +70℃.

[0049] Magnification and operating temperature are key technical requirements for optical systems. Since optical systems operate over a wide temperature range, anechoic design is necessary. Assuming the optical system consists of j optical elements, the following three conditions must be met to achieve the desired design: total optical power distribution, achromaticity, and anechoicity.

[0050] Total optical power The allocation must meet the following conditions:

[0051]

[0052] in, h represents the optical power of a single lens. i Let j be the radial height of the paraxial ray at the incident point of the i-th optical element (including: the first lens 3, the second lens 4, and the third lens 5). In this embodiment of the invention, j is 4.

[0053] Color difference coefficient Must meet:

[0054]

[0055] Where, ω i Let be the dispersion factor of the i-th optical element.

[0056] The thermal design ensures that the total optical length L satisfies:

[0057]

[0058] In the formula, α h Let x be the coefficient of linear expansion of the lens barrel, and L be the total optical length of the optical system. i h1 is the linear expansion coefficient of the i-th lens material; h1 is the radial height of the equivalent flat glass 2, that is, the radial height of the paraxial ray at the incident point of the equivalent flat glass 2.

[0059] Formula 3 provides the initial structure of the optical system. Optimizing the system based on this initial structure yields a design that meets the requirements.

[0060] To simplify the optical system design, the optical system consists of three lenses, with an overall "++-" structure. The distance from the front surface of the equivalent flat glass 2 to the outer wall of the optical encoder disk 1 ranges from 0.5 to 2 mm, preferably 1 mm. An aperture stop is provided on the front surface of the first lens 3. The first lens 3 is a positive lens used to collect the emitted light from the target after passing through the aperture stop and to converge the light energy emitted by the target onto the second lens 4. The first lens 3 uses LaK3 optical material. The distance between the rear surface of the equivalent flat glass 2 and the vertex of the front surface of the first lens 3 ranges from 0.5 to 2 mm, preferably 1 mm. The equivalent flat glass 2 is made of fused silica. The first lens 3 is made of fused silica. The second lens 4 is a positive lens used to correct the spherical aberration produced by the first lens 3 and the third lens 5. The second lens 4 uses ZF4 optical material. The third lens 5 is used to correct system distortion and also corrects residual aberrations such as residual spherical aberration and coma from the first lens 3 and the second lens 4. The third lens 5 is a negative lens. The optical material used in the third lens 5 is ZF4. The distance from the vertex of the rear surface of the third lens 5 to the photosensitive surface of the photodetector 6 is in the range of 1.5 to 10 mm, preferably 3 mm.

[0061] The spacers between the lenses and the lens barrel inside the optical system are made of titanium alloy, which makes the thermal expansion coefficients of the structural materials and glass materials similar, thus improving the environmental adaptability of the optical system.

[0062] Photodetector 6 is the system detector location, used to place the system detector.

[0063] The equivalent lens at the front of the optical system provides the optical path for my lighting source, and the outermost equivalent flat plate is made of fused silica. Using fused silica protects the lenses in the optical system and reduces the radiation dose to subsequent lenses from spatial radiation. This eliminates the need for a separate protective glass in the optical system, further reducing its weight.

[0064] Example

[0065] The front and back surfaces of the flat glass 2 are both flat, and the center thickness of the equivalent flat glass 2 is 5mm, and the outer contour diameter is 9mm.

[0066] The front surface of the first lens 3 is flat, the radius of curvature of the rear surface is -10.476mm, the center thickness of the lens is 4mm, and the outer diameter is 9mm.

[0067] The second lens 4 has a front surface curvature radius of 9.467 mm, a rear surface curvature radius of -60 mm, a center thickness of 3 mm, and an outer diameter of 9 mm. An aspherical surface with an aspherical coefficient of -850 is provided on the rear surface of the lens. An aperture stop with a diameter of 7.6 mm is provided at the apex of the front surface of the second lens 4. The third lens 5 has a front surface curvature radius of 9.467 mm, a rear surface curvature radius of 4.037 mm, a center thickness of 3 mm, and an outer diameter of 9 mm. The distance between the coding line surface of the optical encoder disk 1 and the front surface of the equivalent plate is 3.7 mm. The air gap between the rear surface of the equivalent plate and the first lens is 1 mm. The air gap between the first and second lenses is 1.8 mm. The air gap between the second and third lenses is 3 mm. The air gap between the third lens and the detector is 22.688 mm.

[0068] The optical system for an angular displacement sensor of this invention has a focal length of 5.8 mm, an entrance pupil diameter of 3 mm, an F-number of 1.9, an object-side target height of 1.5 mm, and a corresponding image-side height of 6 mm. The image-side height is four times the object-side height, enabling the photodetector 6 to perform high-resolution observation of the object side, thus improving the system's measurement accuracy. According to the paraxial optics principle, when the image-side height is four times the object-side height, the image distance is also four times the object distance. The paraxial imaging formula is as follows:

[0069]

[0070] In the formula: l is the object distance, l' is the image distance, and f' is the image-side focal length. At this point, l' = 4l. Substituting into the above formula, we get l = 7.25mm, l' = 29mm, and the theoretical total optical length is 36.25mm. In the design, factors such as the minimum thickness of the optical components, the minimum spacing between components during assembly, and the release of thermal stress need to be considered. Based on the comprehensive theoretical calculation results, the length of the optical system from the object side to the image plane is approximately 47.2mm.

[0071] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

[0072] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A high-precision photoelectric angular displacement sensor, characterized in that, include: Optical system, optical encoder disk (1), illumination source, photodetector (6), detector driving circuit and algorithm processing circuit; The optical system includes: equivalent flat glass (2), a first lens (3), a second lens (4) and a third lens (5); Equivalent flat glass (2), first lens (3), second lens (4), and third lens (5) are arranged sequentially along the axial direction; The front of the equivalent flat glass (2) faces the outer wall of the optical encoder disk (1); An aperture stop is provided on the front surface of the first lens (3). The first lens (3) is used to focus the light energy passing through the aperture stop and then incident it onto the second lens (4). The second lens (4) is used to correct the spherical aberration produced by the first lens (3) and the third lens (5); The third lens (5) is used to correct optical distortion, and at the same time corrects the residual spherical aberration and coma of the first lens (3) and the second lens (4); The first lens (3) is a positive lens. The optical material used in the first lens (3) is LaK3. The distance between the vertex of the back surface of the equivalent flat glass (2) and the front surface of the first lens (3) is 0.5~2mm. The second lens (4) is a positive lens, and the optical material used in the second lens (4) is ZF4. The third lens (5) is a negative lens. The optical material used in the third lens (5) is ZF4. The distance from the vertex of the rear surface of the third lens (5) to the photosensitive surface of the photodetector (6) is 1.5~10mm. The optical encoding disk (1) is a thin-walled cylindrical structure. The encoding area on the side wall of the thin-walled cylindrical structure is processed with slits arranged in a certain pattern to form an encoding pattern. The length direction of the slits is the same as the axial direction of the thin-walled cylindrical structure. The illumination source is used to illuminate the optical encoder disk (1); The optical system consisting of the equivalent flat glass (2), the first lens (3), the second lens (4) and the third lens (5) images the coding area on the side wall of the optical coding disk (1) and transmits the light signal to the photodetector (6). The photodetector (6) receives the optical signal, performs photoelectric conversion to obtain an electrical signal, and transmits it to the detector drive circuit; The detector driving circuit receives the electrical signal sent by the photodetector (6), performs signal buffering processing, and transmits the buffered signal to the algorithm processing circuit. The algorithm processing circuit receives the buffer signal transmitted by the detector driving circuit, performs image processing, and outputs the rotation angle information of the optical encoder disk (1) outward. The coding pattern consists of multiple adjacent coding units evenly distributed around the perimeter; the width of each coding unit ranges from 10um to 60um, and several coding units are hollowed out to form slits; The number of uncut coding units in each image obtained by the photodetector (6) is no less than 20.

2. The high-precision photoelectric angular displacement sensor according to claim 1, characterized in that, The slits are evenly distributed around the perimeter, and the width of the slits and the distance between two adjacent slits are the same.

3. A high-precision photoelectric angular displacement sensor according to claim 1, characterized in that, The optical encoder disk (1) rotates at different angles, resulting in different encoded patterns in the images obtained by the photodetector (6).

4. A high-precision photoelectric angular displacement sensor according to claim 1, characterized in that, The length of the slit along the axial direction of the optical encoder disk (1) ranges from 5 to 10 mm.

5. A high-precision photoelectric angular displacement sensor according to claim 1, characterized in that, The distance from the front surface of the equivalent flat glass (2) to the outer wall of the optical encoder disk (1) ranges from 0.5 to 2 mm.

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