A snapshot spectral confocal sensor and its measurement method

Abstract

The invention discloses a snapshot type spectral confocal sensor and a measuring method thereof, which relates to the technical field of sensors and comprises a collimating lens group, a beam splitter, a correction plate, a microlens array, a focusing mirror, a volume grating and a planar array detector. The collimating lens group is arranged horizontally, the beam splitter is located directly below the collimating lens group, and the beam splitter is arranged at an angle of 45 degrees, the correction plate is arranged horizontally and is located directly below the beam splitter, the focusing mirror is arranged vertically and is located in the plane where the beam splitter is located, and the focusing mirror is arranged on one side of the beam splitter, the focusing mirror is mirror-symmetrical with the correction plate, and the microlens array is arranged horizontally and is located directly below the correction plate. The invention adopts a planar array dispersion array and a system-integrated nonlinear dispersion compensation method to realize snapshot type acquisition of morphological information of a surface area, and has a height or displacement resolution of micrometers or even tens of nanometers.

Description

Technical Field

[0001] The invention belongs to the technical field of sensors, and in particular relates to a snapshot type spectral confocal sensor and a measurement method thereof. Background Art

[0002] Spectral confocal measurement sensors can be used for non-contact, fast displacement and distance measurement. The basic principle of the point-type spectral confocal displacement sensor currently used in the market is that the wide-band light beam emitted by the point light source enters the dispersive objective lens through the optical fiber. Under the axial dispersion of the objective lens, light of different wavelengths converges at different positions along the axial direction. When the focused light spot is reflected or scattered by the measured surface, it is re-converged on the end face of the optical fiber through the dispersive objective lens. The core diameter of the end face of the optical fiber can be used as a small hole in confocal imaging to reduce the interference of other wavelengths. When the re-converged light is received by the spectrometer after being transmitted through the optical fiber and forms a Gaussian-shaped spectrum line, the peak position of the spectrum should be the reflection signal of the best focus of a certain wavelength of light. Due to the different focal positions of different wavelengths, the wavelength forms a corresponding relationship with the height or distance of the measured surface. The size of the axial dispersion of the dispersive objective lens in the sensor determines the size of the depth of the measurement range. The core diameter of the optical fiber, the numerical aperture and dispersion distance of the objective lens, the wavelength range, the resolution of the spectrometer, etc. determine the resolution of the axial position of the sensor. The point spectral confocal displacement sensor can only measure one point on the measured surface. If you want to measure the morphology of a certain area, you need to use a mobile platform to drive the object to be measured or the measuring sensor to perform a two-dimensional scan. The imaging time required will be very long, and the system will become large and complex. Factors such as jitter during the scanning process will affect the measurement accuracy. Summary of the invention

[0003] The invention provides a snapshot type spectral confocal sensor and a measurement method thereof, which solves the existing technical problems.

[0004] In order to solve the above technical problems, the present invention provides a snapshot spectral confocal sensor, comprising a collimating lens group, a beam splitter, a correction plate, a microlens array, a focusing mirror, a volume grating and a planar array detector, wherein the collimating lens group is horizontally arranged, the beam splitter is directly below the collimating lens group, and the beam splitter is arranged at a 45° inclination, the correction plate is horizontally arranged and directly below the beam splitter, the focusing mirror is vertically arranged and located in the plane where the beam splitter is located, and the focusing mirror is arranged on one side of the beam splitter, the focusing mirror is mirror-symmetrical with the correction plate, the microlens array is horizontally arranged and located directly below the correction plate, a vertically arranged collimating mirror is arranged on the side of the focusing mirror away from the beam splitter, a vertically arranged pinhole panel is arranged in the middle position between the collimating mirror and the focusing mirror, and a pinhole panel is arranged on the side of the collimating mirror away from the pinhole panel. A vertically arranged volume grating is provided, a vertically arranged area array detector is provided on the side of the volume grating away from the collimator mirror 1, a vertically arranged focusing mirror 2 is provided in the middle position between the area array detector and the volume grating, and also includes a correction plate correction light path, the correction plate correction light path is composed of a wide-band point light source, a collimator mirror 2, a beam splitter 2, a narrow-band filter 1, a reflector, a narrow-band filter 2 and a focusing mirror 3, the focusing mirror 3 is horizontally arranged and is directly below the microlens array, the narrow-band filter 2 is horizontally arranged and is directly below the focusing mirror 3, the reflector is inclined and is directly below the narrow-band filter 2, the collimator mirror 2 is arranged on the upper part of one side of the reflector, the beam splitter 2 is on the upper side of the collimator mirror 2, the narrow-band filter 1 is on the upper side of the beam splitter 2, and the collimator mirror 2, the beam splitter 2 and the narrow-band filter 1 are on the same straight line.

[0005] Preferably, a plurality of microlens sub-units with radially gradient refractive index are arranged at equal intervals on the microlens array.

[0006] Preferably, a plurality of small through holes are provided on the pinhole panel, and positions of the small through holes correspond one-to-one to centers of the microlens subunits on the microlens array.

[0007] Preferably, the irradiated surface of the correction plate is coated with a holographic recording medium.

[0008] Preferably, the light beam emitted by the wide-band point light source is collimated by the collimator lens 2, and then directly irradiates the correction plate as a reference beam through the beam splitter 2 and the narrow-band filter 1. The light separated from the beam splitter 2 passes through the turning reflector and the narrow-band filter 2, and then converges into a point light spot through the focusing lens 3. The position of the point light spot is exactly at the focusing spot of the corresponding wavelength when the microlens subunit works normally. In this way, the light emitted from the microlens subunit is a parallel light beam. Since the narrow-band filter 1 and the narrow-band filter 2 have the same passing wavelength, wavefront interference fringes of the corresponding wavelength are formed on the correction plate. After a period of exposure, the passing wavelength of the narrow-band filter 1 and the narrow-band filter 2 are replaced, and the focusing lens 3 is moved to the focusing spots of other corresponding wavelengths when the microlens subunit works normally. In this way, the wavefront of the corresponding wavelength and the reference light form another set of interference fringes. Multiple sets of interference fringes can be formed after repeated multiple times. Therefore, when the correction plate is used, the spherical aberration of different wavelengths of the microlens unit can be corrected.

[0009] Preferably, the volume grating adopts a gradient refractive index period.

[0010] Preferably, the volume grating with a gradient refractive index period complements the dispersion characteristics of the microlens subunit, so that the focusing positions of different wavelengths of the microlens array form a linear correspondence with the wavelength positions of the dispersion strips on detection.

[0011] A measurement method for a snapshot spectral confocal sensor is disclosed. A wide-band light beam passes through a collimating lens group with chromatic aberration correction capability to form a wide-band parallel light beam, which then passes through a beam splitter to irradiate a correction plate. The light beam processed by the correction plate enters a microlens array, which performs beam splitting to obtain a surface array dispersion band for measurement. When the surface of a target to be measured is within the measurement range of the dispersion light spot of a microlens subunit, the light beam is reflected or scattered and then reenters the microlens array. The microlens array collects the reflected or scattered light, which enters a focusing lens after passing through a correction plate and a beam splitter, thereby forming a focused light spot array. A pinhole panel processes the light spot array to remove light beams of non-confocal wavelengths. The light beam passes through a small through hole and continues to be transmitted and becomes parallel light after passing through a collimator lens, which then forms multiple groups of dispersion light beams after being dispersed by a volume grating, which then forms a two-dimensional array of dispersion strips on a surface array detector after being collected by a focusing lens.

[0012] Compared with the prior art, the present invention has the following advantages:

[0013] The present invention adopts radially gradient refractive index microlens sub-units to form a microlens array to realize a detection array with a large dispersion distance; adopts a correction plate to correct the spherical aberration of the microlens array and eliminate the influence of the spherical aberration on the axial chromatic aberration; adopts a volume grating with a gradient refractive index period to complement the dispersion objective lens to realize that the dispersion distance of different wavelengths is in a linear relationship with the wavelength interval, and a simple one-to-one correspondence between distance or position and dispersion can be realized without complex nonlinear correction.

[0014] The present invention forms wavefront interference fringes of corresponding wavelengths on the correction plate, and after a period of exposure, the transmission wavelengths of narrowband filter 1 and narrowband filter 2 are changed, and focusing lens 3 is moved to the focusing light spots of other corresponding wavelengths when the microlens subunit works normally, so that the wavefront of the corresponding wavelength and the reference light form another set of interference fringes, and multiple sets of interference fringes can be formed by repeating this process for multiple times, so that when the correction plate is used, the spherical aberration of different wavelengths of the microlens unit can be corrected. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the main part of the snapshot type spectral confocal sensor of the present invention;

[0016] Figure 2 A schematic diagram of the correction light path of the correction plate of the present invention;

[0017] Figure 3 is a schematic diagram of the array distribution of microlens sub-units on the microlens array of the present invention;

[0018] Figure 4 A schematic diagram of the array distribution of small holes on the small hole panel of the present invention;

[0019] Figure 5 is a schematic diagram of a volume grating of the present invention;

[0020] Figure 6 It is a schematic diagram of compensation of dispersion of microlens subunit and volume grating diffraction dispersion of the present invention.

[0021] Numbers in the figure: 101, point light source; 102, collimating lens group; 103, spectroscope one; 104, correction plate; 105, microlens array; 106, focusing mirror one; 107, pinhole panel; 108, collimating mirror one; 109, volume grating; 110, focusing mirror two 110; 111, area array detector; 201, wide-band point light source; 202, collimating mirror two; 203, spectroscope two; 204, narrow-band filter one; 205, reflecting mirror; 206, narrow-band filter two; 207, focusing mirror three. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] See also Figure 1-6The present invention provides a technical solution: a snapshot spectral confocal sensor, comprising a collimating lens group 102, a beam splitter 103, a correction plate 104, a microlens array 105, a focusing mirror 106, a volume grating 109 and a planar array detector 111, wherein the collimating lens group 102 is horizontally arranged, the beam splitter 103 is located directly below the collimating lens group 102, and the beam splitter 103 is inclined at 45°, the correction plate 104 is horizontally arranged and located directly below the beam splitter 103, and the focusing mirror 106 is vertically arranged and located at The beam splitter 103 is in a plane, and the focusing mirror 106 is arranged on one side of the beam splitter 103. The focusing mirror 106 and the correction plate 104 are mirror-symmetrical. The microlens array 105 is arranged horizontally and is directly below the correction plate 104. A collimator 108 is arranged vertically on the side of the focusing mirror 106 away from the beam splitter 103. A pinhole panel 107 is arranged vertically in the middle position between the collimator 108 and the focusing mirror 106. A vertically arranged volume grating 109 is provided on one side of the volume grating 109 away from the collimating lens 108, and a vertically arranged area array detector 111 is provided at the middle position between the area array detector 111 and the volume grating 109. The volume grating 109 also includes a correction plate correction light path, which is composed of a wide-band point light source 201, a collimating lens 202, a beam splitter 203, a narrow-band filter 1 204, a reflector 205, a narrow-band filter 206 and a focusing lens 3 207. The focusing lens 3 207 is It is horizontally arranged and located directly below the microlens array 105, the narrowband filter 206 is horizontally arranged and located directly below the focusing mirror 3 207, the reflector 205 is inclined and located directly below the narrowband filter 206, the collimator 202 is arranged on the upper part of one side of the reflector 205, the beam splitter 203 is located on the upper side of the collimator 202, the narrowband filter 1 204 is located on the upper side of the beam splitter 203, and the collimator 202, the beam splitter 203 and the narrowband filter 1 204 are on the same straight line.

[0024] Further, preferably, a plurality of microlens sub-units with radially gradient refractive index are arranged at equal intervals on the microlens array 105, for example Figure 3 As shown, the microlens subunit has k rows and u columns, the lateral spacing and longitudinal spacing are a and b, and the diameter of the microlens subunit is c. These parameters can be set as needed. For example, if 1000 rows and 1000 columns are used, the lateral spacing, longitudinal spacing, and subunit diameter are all 30um, then the three-dimensional morphology of a 30mm×30mm area can be measured at one time.

[0025] Further, preferably, a plurality of small through holes are provided on the pinhole panel 107, and the positions of the small through holes correspond one-to-one to the centers of the microlens subunits on the microlens array 105, such as Figure 4 As shown, there are k rows and u columns of small through holes, with lateral and longitudinal spacings of a and b, and the diameter of the small through holes is generally several microns.

[0026] Further, preferably, the irradiated surface of the correction plate 104 is coated with a holographic recording medium.

[0027] Further, preferably, the volume grating 109 adopts a gradient refractive index period, which complements the dispersion characteristics of the microlens subunit, so that the focusing positions of different wavelengths of the microlens array 105 form a linear correspondence with the wavelength positions of the dispersion bands on detection.

[0028] Working principle: The wide-band light beam generated by the point light source 101 passes through the collimating lens group 102 with chromatic aberration correction capability to form a wide-band parallel light, and then passes through the beam splitter 103 to irradiate the correction plate 104. The correction plate 104 can perform wavefront modulation of the complex light to eliminate the influence of spherical aberration on axial chromatic aberration. The light beam processed by the correction plate 104 enters the microlens array 105, and the microlens array 105 performs beam splitting to obtain a planar array dispersion band for measurement. Each dispersion band is a continuous dispersion spot distributed along the axial direction of the microlens subunit, so that each microlens subunit constitutes a dispersion module of a point spectral confocal measurement sensor. When the surface of the target to be measured is within the measurement range of the dispersion spot of the microlens subunit, the light is reflected or scattered and then re-enters the microlens array 105. The microlens array 105 collects the reflected or scattered light. After passing through the correction plate 104 and the beam splitter 103, it enters the focusing lens 106, thereby forming a focused light spot array. The pinhole panel 107 processes the light spot array to remove the light beams of non-confocal wavelengths, thereby improving the system resolution. The light beams after passing through the small through hole continue to be transmitted and become parallel light after passing through the collimator lens 108, and then dispersed by the volume grating 109 to form multiple groups of nonlinear dispersion light beams, and then collected by the focusing lens 2 110 to form a two-dimensional array of dispersion strips on the surface array detector 111. Each dispersion strip corresponds to a group of spectral data, and the wavelength information corresponds to the position information of the measured point on the surface of the measured target. The volume grating 109 here adopts a gradient refractive index period, which complements the dispersion characteristics of the microlens subunit, so that the focusing positions of different wavelengths of the microlens array 105 form a linear correspondence with the wavelength positions of the dispersion strips on the detection.

[0029] When the correction plate is in operation, the light beam emitted by the wide-band point light source 201 is collimated by the collimator 202, and then directly illuminates the correction plate 104 as a reference beam through the beam splitter 203 and the narrow-band filter 1 204. The light separated from the beam splitter 203 passes through the turning reflector 205 and the narrow-band filter 206, and then converges into a point light spot through the focusing mirror 3 207. The position of the point light spot is exactly at the focusing spot of the corresponding wavelength when the microlens subunit is working normally. In this way, the light emitted from the microlens subunit is a parallel light beam. Due to the narrow-band filter The wavelengths transmitted by the narrow-band filter 1 204 and the narrow-band filter 2 206 are consistent, and wavefront interference fringes of corresponding wavelengths are formed on the correction plate 104. After a period of exposure, the transmission wavelengths of the narrow-band filter 1 204 and the narrow-band filter 2 206 are changed, and the focusing lens 3 207 is moved to the focusing spot of other corresponding wavelengths when the microlens subunit is working normally, so that the wavefront of the corresponding wavelength and the reference light form another set of interference fringes, and multiple sets of interference fringes can be formed by repeating this process for multiple times. Therefore, when the correction plate 104 is used, the spherical aberration of different wavelengths of the microlens unit can be corrected;

[0030] The dispersion characteristics are determined by the glass material. Generally, the dispersion rate decreases at long waves, as shown in pattern 301, where the dispersion rate gradually decreases from short wave s to long wave l. The volume grating 109 forms a large dispersion rate at the long wave end through nonlinear adjustment of the refractive index, as shown in pattern 302. In this way, the entire measurement sensor forms a linear dispersion measurement relationship, as shown in pattern 303.

[0031] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article 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, article or device. In the absence of further restrictions. The sentence "includes an element defined by ... does not exclude the existence of other identical elements in the process, method, article or device including the element".

[0032] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A snapshot spectral confocal sensor, characterized in that: The invention comprises a collimating lens group (102), a beam splitter (103), a correction plate (104), a microlens array (105), a focusing mirror (106), a volume grating (109) and a planar array detector (111), wherein the collimating lens group (102) is arranged horizontally, the beam splitter (103) is located directly below the collimating lens group (102), and the beam splitter (103) is arranged at a 45° inclination, the correction plate (104) is arranged horizontally and is located directly below the beam splitter (103), the focusing mirror (106) is arranged vertically and is located in the plane where the beam splitter (103) is located, and the focusing mirror (106) is arranged vertically and is located in the plane where the beam splitter (103) is located, and the focusing mirror (109) is arranged at a 45° inclination. 6) is arranged on one side of the beam splitter (103), the focusing mirror (106) is symmetrical with the correction plate (104), the microlens array (105) is arranged horizontally and is located directly below the correction plate (104), a collimating mirror (108) is arranged vertically on the side of the focusing mirror (106) away from the beam splitter (103), a pinhole panel (107) is arranged vertically in the middle between the collimating mirror (108) and the focusing mirror (106), and a volume grating (109) is arranged vertically on the side of the collimating mirror (108) away from the pinhole panel (107). ), a vertically arranged surface array detector (111) is arranged on one side of the volume grating (109) away from the collimating mirror (108), a vertically arranged focusing mirror (110) is arranged in the middle position between the surface array detector (111) and the volume grating (109), and also includes a correction plate correction light path, the correction plate correction light path is composed of a wide-band point light source (201), a collimating mirror (202), a beam splitter (203), a narrow-band filter (204), a reflector (205), a narrow-band filter (206) and a focusing mirror (207), the focusing mirror (207) being arranged horizontally and in a micro- Directly below the lens array (105), the narrowband filter 2 (206) is horizontally arranged and is directly below the focusing mirror 3 (207), the reflector (205) is tilted and is directly below the narrowband filter 2 (206), the collimator 2 (202) is arranged on the upper part of one side of the reflector (205), the beam splitter 2 (203) is located on the upper side of the collimator 2 (202), the narrowband filter 1 (204) is located on the upper side of the beam splitter 2 (203), and the collimator 2 (202), the beam splitter 2 (203) and the narrowband filter 1 (204) are on the same straight line.

2. The snapshot spectral confocal sensor according to claim 1, characterized in that: A plurality of microlens sub-units with radially gradient refractive indices are arranged at equal intervals on the microlens array (105).

3. The snapshot spectral confocal sensor according to claim 2, characterized in that: The pinhole panel (107) is provided with a plurality of small through holes, and the positions of the small through holes correspond one-to-one to the centers of the microlens subunits on the microlens array (105).

4. The snapshot spectral confocal sensor according to claim 1, characterized in that: The irradiated surface of the correction plate (104) is coated with a holographic recording medium.

5. The snapshot spectral confocal sensor according to claim 1, characterized in that: The light beam emitted by the wide-band point light source (201) is collimated by the second collimator (202) and then directly illuminates the correction plate (104) as a reference beam through the second beam splitter (203) and the first narrow-band filter (204). The light separated from the second beam splitter (203) is converged into a point light spot through the turning reflector (205) and the second narrow-band filter (206) and then through the third focusing mirror (207). The position of the point light spot is exactly at the focusing spot of the corresponding wavelength when the microlens subunit is working normally. In this way, the light emitted from the microlens subunit is a parallel light beam. The wavelengths transmitted by the narrow-band filter 1 (204) and the narrow-band filter 2 (206) are consistent, and wavefront interference fringes of corresponding wavelengths are formed on the correction plate (104). After a period of exposure, the transmission wavelengths of the narrow-band filter 1 (204) and the narrow-band filter 2 (206) are changed, and the focusing lens 3 (207) is moved to the focusing spot of other corresponding wavelengths when the microlens subunit is working normally. In this way, the wavefront of the corresponding wavelength and the reference light form another set of interference fringes. After repeated multiple times, multiple sets of interference fringes can be formed. Therefore, when the correction plate (104) is used, the spherical aberration of different wavelengths of the microlens unit can be corrected.

6. The snapshot spectral confocal sensor according to claim 1, characterized in that: The volume grating (109) adopts a gradient refractive index period.

7. The snapshot spectral confocal sensor according to claim 6, characterized in that: The volume grating (109) with a gradient refractive index period complements the dispersion characteristics of the microlens subunit, so that the focusing positions of different wavelengths of the microlens array (105) form a linear correspondence with the wavelength position of the dispersion strip on detection.

8. A method for measuring a snapshot spectral confocal sensor according to any one of claims 1 to 7, characterized in that: After the wide-band light beam passes through a collimating lens group (102) with chromatic aberration correction capability, it forms wide-band parallel light, and then passes through a beam splitter (103) and irradiates a correction plate (104). The light beam processed by the correction plate (104) enters a microlens array (105), and the microlens array (105) performs light beam splitting to obtain a planar array dispersion band for measurement. When the surface of the target to be measured is within the measurement range of the dispersion light spot of the microlens subunit, the light is reflected or scattered and then re-enters the microlens array (105). The microlens array (105) 5) Collect the reflected or scattered light, and enter the focusing mirror 1 (106) after passing through the correction plate (104) and the beam splitter 1 (103), thereby forming a focused light spot array. The pinhole panel (107) processes the light spot array to remove the light beams of non-confocal wavelengths. The light beams after passing through the small through hole continue to be transmitted and become parallel light after passing through the collimating mirror 1 (108), and then dispersed by the volume grating (109) to form multiple groups of dispersed light beams, and then collected by the focusing mirror 2 (110) to form a two-dimensional array of dispersion strips on the array detector (111).

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