Color confocal linear displacement sensor based on annular structured light and distance measuring method

Abstract

The invention relates to the technical field of high-precision linear displacement measurement, and particularly provides a color confocal linear displacement sensor based on annular structured light and a distance measuring method.The sensor comprises a light source, a spectrograph, and an axicon lens group, a binary lens and a polarization folded lens group which are sequentially arranged along an emergent light path, a light beam provided by a light source is shaped into annular structure light through an axicon lens group, then diffraction beam splitting is carried out on the annular structure light through a binary lens according to the wavelength to form a plurality of optical ring bands with different wavelengths, aberration and axial dispersion of the light beam are corrected through an optimally designed polarization folded lens group, and the optical ring bands with different wavelengths are obtained. Light of a certain wavelength is focused on the surface of an object to be measured, the light of the wavelength is reflected along an original light path through the object to be measured, a spectrograph is used for capturing a light signal of the wavelength, the displacement is determined through a wavelength-displacement measurement curve, and application of high-speed measurement is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-precision linear displacement measurement, and in particular relates to a color confocal linear displacement sensor based on annular structured light and a distance measurement method. Background Art

[0002] The color confocal line displacement sensor can achieve single-point measurement with high accuracy. Its working principle is: after the polychromatic light emitted by the broadband light source is diffused axially by the dispersive objective lens, a series of convergent focuses will be formed along the optical axis, and each focus corresponds to a unique wavelength. Therefore, the wavelength and the on-axis position form a set of definite linear correspondences. By extracting the peak wavelength of the reflected light beam on the sample surface and substituting the wavelength data into the corresponding wavelength displacement curve, the on-axis position of the object to be measured can be obtained. Since there is no need to use auxiliary equipment for deep scanning, compared with confocal microscopes and white light interferometers, color confocal line displacement sensors have become widely used measurement equipment in semiconductor manufacturing, precision testing, materials science and other fields. With the development of industrial manufacturing technology, higher requirements for high precision, miniaturization and high speed measurement are also put forward for color confocal line displacement sensors.

[0003] The existing color confocal line displacement sensor measurement solutions can be divided into traditional solutions and solutions: The traditional structure uses a complex dispersion objective lens for axial dispersion. Although it has high accuracy, it is bulky and cannot be used in places with limited space, such as film thickness detection, micro-nano manufacturing and other fields.

[0004] The color confocal line displacement sensor based on can effectively achieve miniaturization, but the axial dispersion is nonlinear and needs to be accurately calibrated before use, which will introduce measurement errors. At the same time, it takes longer to obtain displacement data from the nonlinear displacement-wavelength fitting curve, so it is not suitable for high-speed measurement scenarios. Summary of the invention

[0005] In view of this, the present invention aims to provide a color confocal line displacement sensor and ranging method based on annular structured light. By combining binary optical technology and polarization optical technology, the light beam propagation path is designed as a spatial staggered layout by utilizing the hollow characteristics of the annular structured light, which greatly improves the light energy utilization rate of the polarization folding system, improves the displacement measurement accuracy, and reduces the volume of the system, and can be applied to high-speed measurement scenarios.

[0006] To achieve the above object, the technical solution created by the present invention is implemented as follows: The present invention provides a color confocal line displacement sensor based on annular structured light, comprising a light source and a spectrometer, and the following components arranged in sequence along the outgoing light path: An axicon lens group, which is used to shape the light beam provided by the light source into a ring-shaped structured light; A diffraction element, which is used to diffract and split the annular structured light according to wavelength; A polarization folding lens group, which is used to correct aberrations and axial dispersion; After light of different wavelengths passes through the polarization folding lens group, the focal points of light of different wavelengths are linearly distributed on the optical axis. The object to be measured is located at the focal position of light of any wavelength on the optical axis, and the light of this wavelength is reflected along the outgoing optical path, and is incident on the spectrometer after passing through the polarization folding lens group, the diffraction element and the axicon lens group in sequence.

[0007] Preferably, it also includes an achromatic collimating lens disposed on the optical path between the light source and the axicon lens group, and the achromatic collimating lens is used to collimate the light beam provided by the light source into parallel light.

[0008] Preferably, the light beam provided by the light source is polarized light with a wavelength ranging from 400nm to 1000nm.

[0009] Preferably, the axicon lens group includes: a first axicon lens and a second axicon lens, the adjacent surfaces of the first axicon lens and the second axicon lens are matched conical surfaces, and the axicon lens group processes the parallel light emitted by the achromatic collimating lens into a ring-shaped structured light with no light in the center.

[0010] Preferably, the diffractive element is a binary lens, a grating or a Fresnel zone plate.

[0011] Preferably, the diffraction element is a binary lens, and the transmittance function of the binary lens is for: ; in, r represents the annular zone radius of the binary lens, represents the phase function of the binary lens, represents the intensity of the m-order diffracted light, represents the order of diffracted light, represents the initial phase of the ring structured light, i Represents an imaginary unit.

[0012] Preferably, the binary lens is made of PMMA.

[0013] Preferably, the polarization folding lens group includes a first polarization folding lens and a second polarization folding lens, wherein a reflective film is provided in the central area of ​​the rear surface of the first polarization folding lens; a quarter wave plate is provided on the front surface of the second polarization folding lens, and a polarization reflective film is coated on the rear surface of the second polarization folding lens.

[0014] Preferably, the diameter of the central area is less than or equal to the inner diameter of the central lightless area when the annular structured light is emitted from the rear surface of the first polarization folding lens.

[0015] Another aspect of the invention provides a distance measurement method, which uses a color confocal line displacement sensor based on annular structured light for distance measurement, determines the wavelength of the light beam focused on the surface of the object to be measured according to the single-peak signal detected by the spectrometer, and then determines the displacement through the wavelength-displacement measurement curve.

[0016] Compared with the prior art, the invention can achieve the following beneficial effects: The present invention combines binary optical technology with polarization optical technology, giving full play to the excellent dispersion performance of the diffraction element in a wide spectral range, while avoiding the problem of nonlinear axial dispersion of a single diffraction element; a polarization folding lens group is used to compensate for the nonlinear part of the axial dispersion of the binary lens, and the residual aberration and axial dispersion are corrected, so that a completely linearly distributed wavelength-displacement curve can be obtained, thereby omitting the traditional linear correction step, and can effectively improve the timeliness of the measurement, making it suitable for high-speed measurement scene application requirements; in addition, the design of the polarization folding lens group does not need to rely on a large number of optical lenses to build a linear dispersion system, which greatly reduces the size of the system. While reducing the system cost, it also makes it suitable for space-constrained application scenarios, making the sensor easy to integrate into various precision measurement equipment.

[0017] The present invention shapes the light beam into an annular structured light through an axicon lens group, and designs the light beam propagation path into a spatial dislocation layout by utilizing the hollow characteristics of the annular structured light, thereby optimizing the coating area and avoiding the problems that the traditional whole-mirror coating causes part of the light to be affected by the reflective film, thereby reducing the energy utilization rate. By coating the reflective film only on the central area of ​​the rear surface of the first polarization folding lens, the annular structured light is completely incident on the polarization folding lens group from the non-coated area, thereby avoiding the inhibitory effect of the reflective film on energy transfer. The design of the annular structured light increases the light energy utilization rate of the polarization folding system from 6.25% to 100%, thereby increasing the total light energy utilization rate of the measurement system by 16 times. In addition, the present invention can work with a light energy efficiency higher than 45% in a wide spectrum of 400nm~1000nm, which can effectively increase the measurement range, improve the flexibility and applicability of the measurement, and enable it to adapt to different application requirements, including semiconductor manufacturing, precision detection, and materials science. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings: Figure 1 is an optical structure diagram of a color confocal line displacement sensor based on annular structured light provided according to an embodiment of the present invention; Figure 2This is a diagram of the working principle of the traditional polarization folding system; Figure 3 is a working principle diagram of a polarization folding lens assembly provided according to an embodiment of the present invention; Figure 4 This is a ZEMAX software simulation optical path diagram of a color confocal line displacement sensor based on annular structured light provided in accordance with an embodiment of the present invention; Figure 5 is a wavelength shift curve provided according to an embodiment of the present invention; Figure 6 is a vertical axis aberration curve provided according to an embodiment of the present invention.

[0019] Reference numerals include: Light source 1, spectrometer 2, achromatic collimating lens 3, first axicon lens 4, second axicon lens 5, binary lens 6, first polarization folding lens 7, second polarization folding lens 8, object to be measured 9, optical fiber 10, reflective film 71, quarter wave plate 81, polarization reflective film 82. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical scheme and advantages of the invention clearer, the invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the invention and do not constitute a limitation to the invention. Similar components in different embodiments use associated similar component numbers. In the following embodiments, many detailed descriptions are to enable the invention to be better understood. However, those skilled in the art can easily recognize that some of the features can be omitted in different situations, or can be replaced by other components, materials, and methods. In some cases, some operations related to the invention are not shown or described in the specification, in order to avoid the core part of the invention being overwhelmed by too much description, and for those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations according to the description in the specification and the general technical knowledge in the art.

[0021] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other to form various implementation methods. At the same time, the steps or actions in the method description can also be interchanged or adjusted in a manner that is obvious to those skilled in the art. Therefore, the various sequences in the specification and the drawings are only for the purpose of clearly describing a certain embodiment and are not meant to be a necessary sequence, unless otherwise specified that a certain sequence must be followed.

[0022] In the description of the invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the invention, unless otherwise specified, the meaning of "multiple" is two or more.

[0023] In the description of the invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0024] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0025] See also Figure 1 In one embodiment of the present invention, a color confocal line displacement sensor based on annular structured light is provided, comprising: a light source 1, an achromatic collimating lens 3, an axicon lens group, a diffraction element, a polarization folding lens group, and a spectrometer 2 arranged on the echo light path reflected by the object to be measured 9 for detecting the wavelength of the echo signal.

[0026] The light source 1 is used to provide a ranging beam, and by emitting a beam in a specific wavelength range, the position of the object to be measured 9 is measured. Specifically, in the embodiment of the present invention, the wavelength range of the beam emitted by the light source 1 is 400nm~1000nm, which covers the visible light and part of the near-infrared region, providing the sensor with a wide spectrum measurement capability.

[0027] The light source 1 is connected to the spectrometer 2 through a T-shaped optical fiber 10. The spectrometer 2 is used to receive the echo signal reflected by the object to be measured 9, and the light beam emitted by the light source 1 is emitted from the output port of the optical fiber 10, and the emitted light beam is left-handed circularly polarized light. After being transmitted through the optical fiber 10, the light beam is emitted to the achromatic collimating lens 3 in a divergent state. The achromatic collimating lens 3 is used to reduce or eliminate the chromatic aberration problem caused by the dispersion of the material when the light beam passes through the lens. To solve this problem, in general, the achromatic collimating lens 3 can use the different refractive indices and dispersion characteristics of different materials to design a special lens structure to achieve collimation and imaging of light of different wavelengths. A more common design is a cemented lens, which offsets the dispersion effect of each other by gluing lenses of different materials, thereby reducing chromatic aberration. In an embodiment of the present invention, the achromatic collimating lens 3 collimates the divergent light beam emitted by the light source 1 into parallel light while eliminating chromatic aberration, so that subsequent optical elements can more effectively process and control the light beam.

[0028] The collimated parallel light continues to be directed to the axicon lens group, which includes a first axicon lens 4 and a second axicon lens 5 arranged in sequence along the outgoing light path. The first axicon lens 4 and the second axicon lens 5 work together to shape the parallel light into an annular structured light. The energy of the annular structured light is all distributed in the edge annular zone area, and there is no energy in the center. Specifically, the first axicon lens 4 shapes the incident parallel light into an annular beam distribution. A key feature of the lens is that it has a conical surface. In an embodiment of the present invention, the rear surface of the first axicon lens 4 is a conical surface, so that the parallel light is dispersed into a circular ring. Then, the second axicon lens 5 with a conical surface on the front surface is coordinated to shape the parallel light into an annular structured light through a group of adjacent conical surfaces. The outer diameter and inner diameter of the annular structured light can be changed by adjusting the first axicon lens 4 and the second axicon lens 5, that is, the annular zone area with beam distribution and the central area without energy.

[0029] After the annular structured light is emitted from the rear surface of the second axicon lens 5, it is directed toward the diffraction element. The diffraction element can be selected to adopt a binary lens, a grating or a Fresnel zone plate. In the embodiment of the present invention, a binary lens 6 is specifically used, and the binary lens 6 diffracts and splits the light of different wavelengths in the incident annular structured light. Since the diffraction efficiency of the binary lens 6 for light beams of different wavelengths in a wide band is inconsistent, it is necessary to select a suitable working wavelength to design the binary lens 6 so that the diffraction efficiency of each wavelength reaches a good level, and different annular lights are formed according to the wavelength. The hollow characteristics of the annular structured light are used to design the light beam propagation path to be spatially staggered according to different wavelengths. The design principle of the binary lens 6 is as follows: The diffraction surface transmittance function of the binary lens 6 can be expressed as: ; in, The diffraction surface transmittance function of the binary lens 6 is shown. It represents the working wavelength for which the binary lens 6 is designed, that is, the specific wavelength for which the binary lens 6 is designed. It indicates the focal length of the corresponding band of light at the designed working wavelength. represents the annular zone radius of the binary lens 6, Represents the initial phase of the annular structured light, which is derived from the diffraction surface transmittance function.

[0030] The phase function of the binary lens 6 can be expressed as: ; in, It represents the phase function of the binary lens 6, and is used to describe the phase change of the light wave on the binary lens 6. represents the actual working wavelength of the binary lens 6, It means that the binary lens 6 has a wavelength of The refractive index when It means that the binary lens 6 has a wavelength of The refractive index when It indicates the number of annular zones after the splitting of the binary lens 6, represents the radius of the inner circle of the Nth annulus, represents the radius of the inner circle of the Nth annulus, Indicates the Nth annular zone.

[0031] And assign values, namely: .

[0032] Then, the transmittance function of the binary lens 6 is: ; in, represents the transmittance function of the binary lens 6, r represents the annular zone radius of the binary lens 6, represents the order of diffracted light, i is an imaginary unit, represents the intensity of the m-order diffracted light, It can be expressed as: ; According to the intensity of the m-order diffracted light, the diffraction efficiency of the binary lens 6 can be further calculated: for: ; in, for The complex conjugate of .

[0033] The diffraction efficiency of the binary lens 6 is related to the preparation material, the designed working wavelength, and the diffraction order of the binary lens 6. In the embodiment of the present invention, according to the application requirements, the diffraction order of the binary lens 6 is set to +1, the preparation material is PMMA, and the working wavelength is designed to be 550nm. When the working wavelength is 550nm, the diffraction efficiency of the binary lens 6 for the entire spectrum of 400nm-1000nm is higher than 45%.

[0034] The binary lens 6 diffracts and splits the light with a wavelength of 400nm-1000nm, and the split light is incident on the polarization folding lens group, which corrects the aberration and axial dispersion and compensates for the nonlinear part of the axial dispersion. However, the existing polarization folding system design has high structural complexity, and the polarization folding system is bulky and cannot be used in places with limited space. In addition, the existing polarization folding system is based on the light beam folding propagation. In order to reduce the structural complexity of the polarization folding system, the lens can usually be made to pass light multiple times, thereby improving the utilization rate of optical focal length. By folding and propagating, the number of lenses is reduced in the process of aberration compensation, so as to greatly reduce the size of the system. For specific designs, please refer to Figure 2 , the existing polarization folding system usually needs to attach a semi-reflective and semi-transparent film to the surface of the first lens to ensure that the light beam can partially transmit into the space between the first lens and the second lens, and also needs to ensure that part of the light can be repeatedly reflected between the first lens and the second lens. The front and back surfaces of the second lens are attached with a quarter-wave plate and a polarization reflective film to ensure that the light beam can be emitted from the back surface of the second lens after polarization folding. Although the existing polarization folding system can reduce the complexity of the structure, the existing polarization folding system has very serious light energy loss. The light beam needs to pass through the semi-reflective and semi-transparent membrane twice during the propagation process. Each time it passes through the semi-reflective and semi-transparent membrane, the light energy will be seriously lost, which greatly reduces the light energy utilization rate, and will seriously affect the quality of the optical signal in the process of high-precision linear displacement measurement, and reduce the displacement measurement accuracy. After the light beam passes through the semi-reflective and semi-transparent membrane twice, the light energy reaching the object to be measured 9 is only 25% of the original light beam energy.

[0035] According to the principle of reversible optical path, the light incident on the surface of the object to be measured 9 will be reflected, and the reflected light beam will return along the original path along the outgoing optical path, so the light energy that finally reaches the spectrometer 2 for: ; in, represents the light intensity received by spectrometer 2, It represents the diffraction efficiency of the binary lens 6, that is, the diffraction efficiency of the binary lens 6 in the design process , It represents the light intensity of the light beam emitted by the light source 1. Therefore, the light energy utilization rate of the existing polarization folding system is only 6.25%, and the light energy loss is serious.

[0036] In order to solve this problem, the embodiment of the present invention uses the first axicon lens 4 and the second axicon lens 5 to shape the light beam provided by the light source 1 into an annular structured light, and then uses the hollow characteristics of the annular structured light to design the light beam propagation path into a spatial dislocation layout, and then optimizes the design of the polarization folding lens group to increase the light energy utilization rate from 6.25% to 100%. For details, please refer to Figure 3The polarization folding lens group includes a first polarization folding lens 7 and a second polarization folding lens 8, wherein a reflective film 71 is provided in the central area of ​​the rear surface of the first polarization folding lens 7; the central area corresponds to the inner diameter area of ​​the ring structure light without energy, and the diameter of the central area is designed to be less than or equal to the inner diameter of the central lightless area when the ring structure light is emitted from the rear surface of the first polarization folding lens, so as to ensure that when the ring structure light is emitted from the binary lens 6 into the first polarization folding lens 7, all light rays 100% pass through the first polarization folding lens 7 from the area not covered by the reflective film 71, thus solving the problem of excessive energy loss caused by the traditional arrangement of a semi-reflective and semi-transparent film on the surface of the first polarization folding lens 7, which causes part of the light rays to be reflected. Accordingly, a quarter wave plate 81 is provided on the front surface of the second polarization folding lens 8, and a polarization reflective film 82 is plated on the rear surface of the second polarization folding lens 8. After the annular structured light is transmitted through the area not covered by the reflective film 71 and passes through the first polarization folding lens 7, it continues to transmit for the first time and passes through the quarter wave plate 81 on the front surface of the second polarization folding lens 8. After being processed by the quarter wave plate 81, the light beam becomes S polarized light. Since the polarization reflective film 82 on the rear surface of the second polarization folding lens 8 has a total reflection effect on the S polarized light, the S polarized light is reflected by the polarization reflective film 82 on the rear surface of the second polarization folding lens 8 and propagates in the opposite direction and is emitted to the first polarization folding lens 7 again. In this process, the S polarized light will pass through the quarter wave plate 81 for the second time. After being processed by the quarter wave plate 81 for the second time, the S polarized light will become right-handed circularly polarized light. Under the focusing action of the first polarization folding lens 7 and the second polarization folding lens 8, the right-handed circularly polarized light will be incident on the central area of ​​the reflective film 71 attached to the rear surface of the first polarization folding lens 7, and the right-handed circularly polarized light will be 100% reflected by the reflective film 71 to the second polarization folding lens 8, and pass through the quarter wave plate 81 on the front surface of the second polarization folding lens 8 for the third time. At this time, the light beam becomes P polarized light, and the P polarized light can be completely transmitted through the polarization reflective film 82 on the rear surface of the second polarization folding lens 8 and focused on the optical axis, and 400nm~1 The focal points of light of different wavelengths within the range of 000nm are linearly distributed on the optical axis. The object to be measured 9 is located at the focal position of light of any wavelength on the optical axis. At its position, only the light beam of a single wavelength is in the best focus state, and the light beams of other wavelengths are in a defocused state. The light beam in the best focus state will return along the original path of the outgoing light path after being reflected by the object to be measured 9, and will pass through the second polarization folding lens 8, the first polarization folding lens 7, the binary lens 6, the second axicon lens 5, the first axicon lens 4, the achromatic collimating lens 3 in sequence, and will finally return through the optical fiber 10 to be received by the spectrometer 2.

[0037] According to the above-mentioned color confocal line displacement sensor based on annular structured light, an embodiment of the present invention further provides a distance measurement method using the same, wherein the color confocal line displacement sensor based on annular structured light is used to measure the distance of the object to be measured 9, and the wavelength of the light beam focused on the surface of the object to be measured 9 is determined according to the single-peak signal detected by the spectrometer 2. The spectrometer 2 detects a sharp single-peak signal, that is, an echo signal of the wavelength of the light beam focused on the object to be measured 9. Therefore, the wavelength of the light beam focused on the object to be measured 9 can be first determined by the spectrometer 2, and then the position information such as the displacement amount of the object to be measured 9 can be determined by the wavelength-displacement measurement curve.

[0038] The color confocal line displacement sensor based on annular structured light proposed in the embodiment of the present invention has been verified to be effective through simulation. For the simulation light path in ZEMAX software, please refer to Figure 4 . And obtained such Figure 5 The wavelength-displacement curves shown and Figure 6 It has been verified that the sensor of the embodiment of the present invention has the advantages of high light energy utilization, small size, high ranging accuracy, and fast ranging speed, and can be applied to scenes with limited space and high speed requirements, such as film thickness detection, micro-nano manufacturing and other fields.

[0039] In short, the above description is only a preferred embodiment of this specification and is not intended to limit the protection scope of this specification. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this specification shall be included in the protection scope of this specification.

[0040] The systems, devices, modules or units described in one or more of the above embodiments may be implemented by a computer chip or entity, or by a product having a certain function. A typical implementation device is a computer. Specifically, the computer may be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.

[0041] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0042] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0043] The above is a description of a specific embodiment of the specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in an order different from that in the embodiments and still achieve the desired results. In addition, the processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

Claims

1. A color confocal line displacement sensor based on annular structured light, comprising a light source and a spectrometer, characterized in that: It also includes the following components arranged in sequence along the outgoing light path: an axicon lens group, which is used to shape the light beam provided by the light source into an annular structured light; A diffraction element, used for diffracting and splitting the annular structured light according to wavelength; A polarization folding lens group, which is used to correct aberrations and axial dispersion; After light of different wavelengths passes through the polarization folding lens group, the focal points of light of different wavelengths are linearly distributed on the optical axis. The object to be measured is located at the focal position of light of any wavelength on the optical axis, and the light of this wavelength is reflected along the outgoing light path, and is incident on the spectrometer after passing through the polarization folding lens group, the diffraction element and the axicon lens group in sequence.

2. The color confocal line displacement sensor based on annular structured light according to claim 1, characterized in that: It also includes an achromatic collimating lens arranged on the optical path between the light source and the axicon lens group, and the achromatic collimating lens is used to collimate the light beam provided by the light source into parallel light.

3. The color confocal line displacement sensor based on annular structured light according to claim 1, characterized in that: The light beam provided by the light source is polarized light with a wavelength ranging from 400nm to 1000nm.

4. The color confocal line displacement sensor based on annular structured light according to claim 2, characterized in that: The axicon lens group includes: a first axicon lens and a second axicon lens, the adjacent surfaces of the first axicon lens and the second axicon lens are matched conical surfaces, and the axicon lens group processes the parallel light emitted by the achromatic collimating lens into an annular structured light with no light in the center.

5. The color confocal line displacement sensor based on annular structured light according to claim 1, characterized in that: The diffraction element is a binary lens, a grating or a Fresnel zone plate.

6. The color confocal line displacement sensor based on annular structured light according to claim 5, characterized in that: The diffraction element is a binary lens, and the transmittance function of the binary lens is for: ； in, r represents the annular zone radius of the binary lens, represents the phase function of the binary lens, represents the intensity of the m-order diffracted light, represents the order of diffracted light, represents the initial phase of the ring structured light, i Is an imaginary unit.

7. The color confocal line displacement sensor based on annular structured light according to claim 6, characterized in that: The binary lens is made of PMMA.

8. The color confocal line displacement sensor based on annular structured light according to claim 1, characterized in that: The polarization folding lens group includes a first polarization folding lens and a second polarization folding lens, wherein a reflective film is provided in the central area of ​​the rear surface of the first polarization folding lens; a quarter wave plate is provided on the front surface of the second polarization folding lens, and a polarization reflective film is coated on the rear surface of the second polarization folding lens.

9. The color confocal line displacement sensor based on annular structured light according to claim 8, characterized in that: The diameter of the central area is less than or equal to the inner diameter of the central lightless area when the annular structured light is emitted from the rear surface of the first polarization folding lens.

10. A distance measurement method, characterized in that: The color confocal line displacement sensor based on annular structured light as described in any one of claims 1 to 9 is used for distance measurement, the wavelength of the light beam focused on the surface of the object to be measured is determined according to the single-peak signal detected by the spectrometer, and the displacement is then determined by the wavelength-displacement measurement curve.

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