Spectral confocal lens and spectral confocal displacement sensor

Abstract

The invention provides a spectral confocal lens and a spectral confocal displacement sensor, and the spectral confocal lens sequentially comprises a dispersion lens group and a non-dispersion lens group from an image space to an object space. The dispersion lens group comprises a plurality of single lenses, and is used for generating axial dispersion. The non-dispersive lens group comprises at least one achromatic lens and is used for converging light and correcting aberration generated by the dispersive lens group; wherein the optical parameters of the non-dispersive lens group are configured to be separated from the dispersive lens group and are independently optimized, so that the dynamic balance between the imaging quality of the lens and the dispersion range is realized. According to the embodiment of the invention, the dispersion lens group and the non-dispersion lens group are respectively debugged and optimized, so that the dispersion range of the dispersion objective lens can be expanded, the aberration can be compensated, the imaging quality is remarkably improved, and the dynamic balance of high resolution and wide measurement range is realized.

Description

Technical Field

[0001] This application relates to the technical field of displacement measurement, specifically to a spectral confocal lens and a spectral confocal displacement sensor. Background Technology

[0002] Displacement sensors mainly include contact sensors and non-contact sensors. Contact displacement sensors, due to the contact force applied during measurement, may damage the surface of the object being measured, making them unsuitable for measuring objects with delicate surfaces. Non-contact displacement sensors do not require contact with the object, avoiding damage and are particularly suitable for fragile, soft, or easily damaged materials. Currently, electromagnetic and photoelectric types are the two most widely used types of high-precision, non-contact displacement sensors. Electromagnetic displacement sensors have requirements regarding the material properties of the object being measured. Eddy current displacement sensors, on the other hand, require the object to be metallic. Furthermore, interference from the external environment on the electromagnetic signal can also affect its measurement accuracy. Photoelectric displacement sensors include laser triangulation sensors and spectral confocal sensors. The accuracy of laser triangulation is affected not only by internal factors such as the size and shape of the light spot and stray light, but also by external factors such as the tilt, gloss, and roughness of the measured surface. In addition, because the light may be blocked, this technology is unsuitable for measuring objects with complex shapes such as small holes and grooves. The spectral confocal displacement sensor is a novel non-contact photoelectric displacement sensor renowned for its ultra-high precision and stability. Utilizing spectral confocal technology, it offers higher resolution and is insensitive to factors such as the texture and tilt of the measured object's surface, as well as stray light from the surrounding environment. Furthermore, because spectral confocal technology employs a single optical path for both emission and reception, it avoids the problems of light path obstruction or the inability to receive reflected light from overly smooth target surfaces, as seen in laser triangulation methods. Therefore, it exhibits strong adaptability to different target objects.

[0003] Dispersion lenses play a crucial role in spectral confocal displacement sensors. They are the core component of the sensor, responsible for generating axial dispersion, meaning that light of different wavelengths will have different focal points when passing through the objective lens. The linearity between this axial dispersion and wavelength directly affects the system's measurement accuracy. Furthermore, dispersion lenses help improve the system's resolution, enabling the detector to resolve finer spectral differences, which is essential for accurately measuring the displacement and geometric parameters of objects.

[0004] Existing dispersive lenses mainly fall into several categories. A single non-achromatic lens group can serve as a dispersive lens; however, the parameters of a non-achromatic lens group are fixed and lack chromatic aberration correction, resulting in inconsistent spot sizes at different wavelengths. This fails to meet the needs of diverse applications. Secondly, achromatic lens groups can also be used as dispersive lenses, achieving different dispersive lens parameters. However, this method involves complex optical design and requires more optical components. Adjusting and optimizing wave phase aberration is difficult. Furthermore, non-achromatic lens groups typically have a limited adjustable dispersive range, hindering high-resolution spectral analysis. Summary of the Invention

[0005] The purpose of this application is to provide a spectral confocal lens and a spectral confocal displacement sensor. By separately adjusting and optimizing the dispersive lens group and the non-dispersive lens group, the dispersive range of the dispersive objective lens can be expanded, and aberrations can be compensated, thereby significantly improving the imaging quality and achieving a dynamic balance between high resolution and wide measurement range.

[0006] To address the aforementioned technical problems, this application provides a spectral confocal lens, comprising a dispersive lens group and a non-dispersive lens group sequentially from the image side to the object side: the dispersive lens group includes multiple single lenses for generating axial dispersion; the non-dispersive lens group includes at least one achromatic lens for converging light rays and correcting aberrations generated by the dispersive lens group; wherein the optical parameters of the non-dispersive lens group are configured to be separate from and independently optimized from the optical parameters of the dispersive lens group to achieve a dynamic balance between the lens's imaging quality and dispersive range.

[0007] Optionally, the dispersive lens group includes at least: a positive meniscus lens, a biconcave lens, a biconvex lens, and a plano-convex lens.

[0008] Optionally, the dispersive lens group includes five single lenses, which are, from image side to object side, a positive meniscus lens, a biconcave lens, a first biconvex lens, a second biconvex lens, and a plano-convex lens.

[0009] Optionally, the non-dispersive lens group is a replaceable modular component; by replacing the non-dispersive lens group with different optical parameters, the working distance, numerical aperture, or measurement range of the entire lens can be changed.

[0010] Optionally, the working wavelength of the spectral confocal lens is 400nm-700nm.

[0011] Optionally, the axial dispersion range is 0-0.96mm, 0-1.18mm, or 0-1.45mm.

[0012] Optionally, both the dispersive lens group and the non-dispersive lens group lenses are fixed by retaining rings.

[0013] Optionally, the lens size of both the dispersive lens group and the non-dispersive lens group is 1 inch.

[0014] Another embodiment of this application provides a spectral confocal displacement sensor, including: a light source, an optical fiber coupler, a spectrometer, a signal processing unit, and the aforementioned spectral confocal lens.

[0015] Compared to existing technologies, the embodiments of this application, due to the separate and independently optimized dispersive and non-dispersive lens groups, allow for the adjustment and optimization of their optical parameters to achieve different dispersion ranges, thus realizing a dynamic balance between high resolution and a wide measurement range. On one hand, cascading multiple non-dispersive lens groups expands the dispersion range of the dispersive objective, thereby increasing the measurement range of the spectral confocal sensor and effectively improving the flexibility and controllability of the axial dispersion range. On the other hand, by focusing on improving the numerical aperture of the dispersive objective through the non-dispersive lens group, measurement accuracy and resolution are enhanced, wave phase aberration is reduced, and spot size is optimized, achieving both high resolution and a wide measurement range, effectively improving image quality and spot consistency. Furthermore, separating the dispersive and focusing functions allows for the independent design of both dispersive and non-dispersive lens groups, reducing design complexity and improving design efficiency; it also reduces the RMS error of different spot sizes, improving image quality. Attached Figure Description

[0016] One or more embodiments are illustrated by way of example with reference numerals in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0017] Figure 1a This is a schematic diagram of the structure of a spectral confocal lens according to an embodiment of this application;

[0018] Figure 1b This is a schematic diagram of the structure of a spectral confocal lens according to another embodiment of this application;

[0019] Figure 1c This is a schematic diagram of the structure of a spectral confocal lens according to yet another embodiment of this application;

[0020] Figure 2a It is a focal point distribution diagram based on a certain set of dispersive lens parameters when the dispersive range is 0-0.96mm;

[0021] Figure 2b It is a focal point distribution diagram based on a certain set of dispersive lens parameters when the dispersive range is 0-1.18mm;

[0022] Figure 2cIt is a focal point distribution diagram based on a certain set of dispersive lens parameters when the dispersive range is 0-1.45mm;

[0023] Figure 3a This is an aberration map with wavelengths of 400nm-700nm according to one embodiment of this application;

[0024] Figure 3b This is an aberration map with wavelengths of 400nm-700nm according to one embodiment of this application;

[0025] Figure 3c This is an aberration map with wavelengths of 400nm-700nm according to one embodiment of this application;

[0026] Figure 4 This is a schematic diagram of the structure of a spectral confocal displacement sensor according to an embodiment of this application. Detailed Implementation

[0027] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] It should be noted that the following description covers various aspects of embodiments within the scope of the appended claims. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this application, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number and aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0029] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this application. The drawings only show the components related to this application and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0030] Additionally, specific details are provided in the following description to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that practice can be carried out without these specific details.

[0031] Existing chromatic lenses primarily consist of either a single non-achromatic lens group or a single achromatic lens group. A single non-achromatic lens group has fixed parameters, lacks aberration correction capabilities, and cannot effectively correct chromatic aberration, resulting in inconsistent spot sizes at different wavelengths and failing to meet the needs of various applications. A single achromatic lens group, on the other hand, is typically composed of two or more lenses made of different materials bonded together, leading to a complex design. Achieving both large, controllable chromatic aberration and excellent aberration correction simultaneously requires a highly complex optical structure (more lenses), resulting in significant design challenges, high manufacturing costs, and long development cycles. The inventors of this application have discovered that by employing "functional separation" and "modular dynamic optimization," these contradictions can be resolved, allowing each component to be specifically optimized, thereby achieving high overall performance.

[0032] Based on this, this application provides a spectral confocal lens 10, as shown in Figure 1. The spectral confocal lens 10 includes two main functional modules, from the image side to the object side: a dispersive lens group 20 and a non-dispersive lens group 30. The dispersive lens group 20 includes multiple single lenses (e.g., 3 to 7 lenses) used to generate axial dispersion. Its main function is to use the principle of optical dispersion to separate incident composite white light (such as an LED light source) into light of different wavelengths along the optical axis, forming continuous axial dispersion, that is, light of different wavelengths is focused at different positions on the optical axis. The non-dispersive lens group 30 is positioned after the dispersive lens group 20, close to the object being measured. The non-dispersive lens group 30 includes at least one achromatic lens used to converge light rays and correct aberrations generated by the dispersive lens group 20. That is, the non-dispersive lens group 30 has two main functions: first, to finally converge the light rays dispersed by the dispersive lens group 20 onto the surface of the object being measured to form a measurement spot; and second, to correct various aberrations (such as spherical aberration, coma, etc.) generated by the dispersive lens group 20 in front. In this embodiment, the optical parameters of the non-dispersion lens group 30 are configured to be separated from and independently optimized from the optical parameters of the dispersion lens group 20 to achieve a dynamic balance between the lens's imaging quality and chromatic aberration range. During the optical design phase, the optical parameters of the dispersion lens group 20 and the non-dispersion lens group 30 are separated and independently optimized. Specifically, the curvature radius and spacing parameters of the dispersion lens group 20 can be optimized first to achieve the target chromatic aberration range and linearity. Subsequently, based on fixed parameters of the dispersion lens group 20, the parameters of the non-dispersion lens group 30 are independently optimized, specifically for reducing wave phase aberration, shrinking the spot size, and improving imaging quality. This step-by-step optimization and dynamic balancing strategy breaks through the bottleneck of mutual constraint between chromatic aberration and aberration correction in traditional single-lens group designs. Through functional separation and independent optimization, the optimal dynamic balance between imaging quality and chromatic aberration performance is achieved, enabling the lens to maintain excellent performance across a wide spectral range. The parameters of the lens groups in this embodiment are shown in Table 1.

[0033] Table 1 Lens group parameters

[0034]

[0035]

[0036] Optionally, the dispersive lens group 20 includes at least: a positive meniscus lens, a biconcave lens, a biconvex lens, and a plano-convex lens. This combination fully utilizes the dispersive characteristics of different lens types; for example, the biconcave lens provides strong negative dispersion, the biconvex lens and plano-convex lens provide positive optical power and participate in dispersion, and the positive meniscus lens helps balance aberrations. This lens combination is simple and effective, maintaining optical path stability while ensuring sufficient dispersion, thus laying a good foundation for subsequent aberration correction.

[0037] Preferably, the dispersive lens group 20 may include five single lenses, arranged from image to object side as follows: a positive meniscus lens 1, a biconcave lens 2, a first biconvex lens 3, a second biconvex lens 4, and a plano-convex lens 5. The non-dispersive lens group 30 includes at least one achromatic lens 6. This specific arrangement is the optimal solution obtained after extensive optical optimization, capable of producing axial dispersion with good linearity and a suitable range. The achromatic lens 6 is typically cemented from a crown glass and a flint glass, and is specifically designed to compensate for residual aberrations in the preceding dispersive lens group 20 based on its function of effectively correcting chromatic aberration, thereby significantly improving image quality. It can correct chromatic aberration and other monochromatic aberrations extremely efficiently, bringing the final focused spot close to the diffraction limit, and greatly improving measurement resolution and accuracy.

[0038] Preferably, the non-dispersive lens group 30 in this embodiment is a replaceable modular component; by replacing the non-dispersive lens group 30 with one having different optical parameters, the working distance, numerical aperture, or measurement range of the entire lens can be changed. The following explanation uses an achromatic lens 6 as an example to illustrate the non-dispersive lens group 30. Figure 1a , Figure 1b and Figure 1c As shown, Figure 1a The achromatic lens 6 shown is composed of three cemented parts. Figure 1b , Figure 1c The achromatic lens 6 shown is composed of two different cemented doublets. The achromatic lens 6 can be designed as an independent module that is easy to disassemble and install. Users or manufacturers can replace the achromatic lens 6 with different optical parameters (such as focal length and numerical aperture) according to different measurement needs. For example, when high resolution and a small measurement range are required, a short focal length, high numerical aperture achromatic lens 6 can be used. When a large measurement range and appropriate resolution are required, a long focal length, low numerical aperture achromatic lens 6 can be used. This achieves "one lens, multiple uses," greatly enhancing the product's flexibility and adaptability, and reducing the user's purchase and operating costs. There is no need to customize the entire lens; simply replacing a standardized module can meet diverse measurement needs. In other embodiments, the non-dispersive lens group 30 may also include multiple achromatic lenses 6.

[0039] In an optional embodiment, the spectral confocal lens 10 operates at a wavelength of 400nm-700nm, with a preferred axial dispersion range of 0-0.96mm, 0-1.18mm, or 0-1.45mm. The image-side numerical aperture can be 0.035, and the object-side numerical aperture can be 0.03. The operating wavelength and dispersion range in this embodiment enable it to handle most industrial inspection scenarios. This helps ensure that light from the object to the imaging plane is effectively collected and transmitted, thereby improving image quality. It simplifies optical path design, eliminates the need for additional optical components to adjust the focusing or divergence of light, reduces aberrations in the optical system, and more effectively utilizes the energy of the light source. Figure 2a , Figure 2b and Figure 2c The figure shows the distribution of the focal point of the spectral confocal lens 10 along the optical axis at different wavelengths, where the vertical axis represents the wavelength and the horizontal axis represents the offset of the focal point relative to the reference position. Figure 2a This indicates that the dispersion range under a certain set of dispersive lens parameters is 0-0.96mm. Figure 2b This indicates that the dispersion range of the other set of dispersive lenses, after parameter adjustment, is 0-1.18mm. Figure 2c With the third set of parameters configured, the dispersion range is 0-1.45mm, indicating that different dispersion ranges (such as 0-0.96mm, 0-1.18mm, or 0-1.45mm) can be achieved by adjusting the parameters of the dispersive lens group 20 in this embodiment of the application.

[0040] Optionally, the lenses of the dispersive lens group 20 and the non-dispersive lens group 30 are both fixed and secured by retaining rings. The retaining ring structure is simple, provides accurate positioning, facilitates assembly and adjustment, and ensures strict alignment of the optical central axes of each lens. The retaining rings improve the precision and efficiency of lens assembly, guarantee the stability of the optical system, and are particularly suitable for mass production.

[0041] The lenses of the dispersive lens group 20 and the non-dispersive lens group 30 are both 1 inch in size. The total length of the spectral confocal lens 10 is 84 mm, the maximum aperture is 25.4 mm, and the working distance is 20 mm. This structure is simple to assemble, flexible and variable, and can dynamically adjust the measurement range, effectively reducing the influence of mechanical mounting parts.

[0042] Compared to existing technologies, this embodiment of the application achieves a dynamic balance between high resolution and a wide measurement range by separating and independently optimizing the dispersive lens group 20 and the non-dispersive lens group 30 through separate debugging and optimization. On one hand, cascading multiple non-dispersive lens groups 30 expands the dispersive range of the dispersive objective, thereby increasing the measurement range of the spectral confocal sensor and effectively improving the flexibility and controllability of the axial dispersive range. On the other hand, by focusing on improving the numerical aperture of the dispersive objective through the non-dispersive lens group, measurement accuracy and resolution are improved, wave phase aberration is reduced, and spot size is optimized, achieving both high resolution and a wide measurement range, effectively improving imaging quality and spot consistency. Furthermore, separating the dispersive and focusing functions allows for independent design of the dispersive and non-dispersive lens groups, reducing design difficulty and improving design efficiency; it also reduces the RMS error of different spots and improves imaging quality. Figures 3a-3c Aberration diagrams are shown for wavelengths from 400nm to 700nm. The PV value represents the peak-to-trough value of the wavefront, indicating the maximum deviation; a lower PV value is better. The RMS value is the root mean square value of the wavefront, representing the average level of the overall deviation; a lower RMS value is better. It is generally considered that when the RMS value is less than λ / 14 (approximately 0.071λ), the imaging quality of the optical system reaches the "diffraction limit," which is the theoretically highest level. (Appendix) Figure 3a The peak-to-trough value in 3b is 3.546λ, and the RMS value is 1.018λ; the peak-to-trough value in 3b is 0.021λ, and the RMS value is 0.006λ; the peak-to-trough value in 3c is 0.563λ, and the RMS value is 0.161λ. It can be seen that the RMS values ​​shown in the desired state (0.006λ, 0.161λ, etc.) are far superior to this standard, which strongly proves the significant effect of the non-dispersive lens group 30 of the present application embodiment in improving imaging quality and reducing wave phase aberration.

[0043] This application also provides a spectral confocal displacement sensor, such as... Figure 4As shown, the system includes a light source 11, an optical fiber coupler 12, a spectrometer 13, a signal processing unit 14, and the aforementioned confocal spectral lens 10. Specifically, the point light source 11 (e.g., emitted by a white light source) passes through the optical fiber coupler 12 and the confocal spectral lens 10. Due to the wavelength-dependent optical characteristics of the confocal spectral lens 10, a series of continuously distributed focused light spots of different wavelengths are formed on the optical axis, which is the so-called color coding. When the sample 15 is placed within this color-coded segment, the sample 15 contains all the spectral information. Since the surface of the sample 15 scatters the incident light beam, the scattered light passes through the confocal spectral lens 10 and the optical fiber coupler 12 again in the opposite direction, reaching the spectrometer 13. Finally, the signal processing unit 14 analyzes and processes the obtained signal. The optical fiber coupler 12 plays a crucial role in preventing the entry of all light beams except those whose focal plane is located on the sample surface 15, especially light spots above or below the convergence plane on the optical axis. Due to the point detector focusing imaging principle, the spectral confocal displacement sensor has excellent spatial resolution and is insensitive to ambient stray light. When the sample 15 is moved up and down within the focused spot range of different wavelengths, a confocal system of different wavelengths is formed at each position. In addition, the use of fiber optic couplers instead of traditional pinholes enables system miniaturization, allowing larger light sources, spectrometers, and other equipment to be placed away from the probe, thereby effectively reducing the probe size.

[0044] This embodiment applies the spectral confocal lens of this application to the sensor system, enabling the entire system to possess high precision, high stability, strong anti-interference capability, and adaptability to measurement of complex surfaces and structures, resulting in superior overall performance.

[0045] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0046] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

[0047] Those skilled in the art will understand that the above embodiments are specific embodiments for implementing the present invention, and in practical applications, various changes in form and detail may be made without departing from the spirit and scope of the present invention.

Claims

1. A spectral confocal lens, characterized in that, From the image side to the object side, the lenses consist of dispersive and non-dispersive lens groups: The dispersive lens group includes multiple single lenses for generating axial dispersion; The non-dispersive lens group includes at least one achromatic lens for converging light rays and correcting aberrations generated by the dispersive lens group; The optical parameters of the non-dispersive lens group are configured to be separated from and independently optimized from the optical parameters of the dispersive lens group in order to achieve a dynamic balance between the lens imaging quality and the dispersive range.

2. The spectral confocal lens according to claim 1, characterized in that, The dispersive lens group includes at least: a positive meniscus lens, a biconcave lens, a biconvex lens, and a plano-convex lens.

3. The spectral confocal lens according to claim 2, characterized in that, The dispersive lens group comprises five single lenses, which, from the image side to the object side, are a positive meniscus lens, a biconcave lens, a first biconvex lens, a second biconvex lens, and a plano-convex lens.

4. The spectral confocal lens according to claim 1, characterized in that, The non-dispersive lens group is a replaceable modular component; by replacing the non-dispersive lens group with different optical parameters, the working distance, numerical aperture, or measurement range of the entire lens can be changed.

5. The spectral confocal lens according to claim 1, characterized in that, The working wavelength of the spectral confocal lens is 400nm-700nm.

6. The spectral confocal lens according to claim 5, characterized in that, The axial dispersion range is 0-0.96mm, 0-1.18mm, or 0-1.45mm.

7. The spectral confocal lens according to any one of claims 1-6, characterized in that, Both the dispersive lens group and the non-dispersive lens group lenses are fixed in place by retaining rings.

8. The spectral confocal lens according to any one of claims 1-6, characterized in that, The lens size of both the dispersive and non-dispersive lens groups is 1 inch.

9. A spectral confocal displacement sensor, characterized in that, It includes a light source, an optical fiber coupler, a spectrometer, a signal processing unit, and a spectral confocal lens as described in any one of claims 1-8.

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