A filter wheel confocal measurement system based on lateral encoding and its measurement method

Abstract

The present invention provides a filter wheel confocal measurement system based on lateral coding and a measurement method thereof, belonging to the field of optical detection technology. The measurement system realizes lateral coding of the spectrum by adding a spectroscopic dispersion component to the existing confocal measurement system. The measurement method solves the problem that the existing confocal measurement technology can only adopt a point-by-point scanning measurement method by combining the geometric optics of lateral coding with a mathematical algorithm. By means of lateral coding, the measurement dimension in one direction is reduced, and the confocal measurement technology is converted from a point measurement mode to a line scanning measurement mode. The measurement accuracy of the existing confocal measurement system is improved and the measurement time is shortened. The measurement system and method provided by the present invention not only measure the comprehensive three-dimensional information of the object to be measured, but also measure the tilt angle of the object to be measured in real time, thereby effectively overcoming the limitation that the prior art cannot simultaneously measure the three-dimensional spatial information and the angle tilt information of the object to be measured.

Description

Technical Field

[0001] The invention belongs to the technical field of optical detection, and in particular relates to a filter wheel confocal measurement system based on transverse coding and a measurement method thereof. Background Art

[0002] Confocal microscopy is an optical measurement technology that excels in three-dimensional surface topography measurement. The introduction of dispersive confocal microscopy further expands the capabilities of confocal microscopy. By adding dispersive elements, dispersive confocal microscopy can focus light of different wavelengths on different depth planes on the sample surface, thereby acquiring information at multiple depth levels in a single scan. This technology significantly improves the longitudinal resolution and measurement efficiency while maintaining the lateral resolution, making it very suitable for precise measurement and detection of complex surface structures.

[0003] However, the existing dispersive confocal microscopy technology faces some challenges in practical applications. The point-by-point scanning measurement method is easily affected by the long measurement time. When the measurement surface has an inclination angle, the measurement accuracy of the system tends to drop significantly. In addition, the long measurement time also increases the interference of environmental factors on the measurement results, further affecting the stability and reliability of the measurement.

[0004] In the field of tilt angle measurement, researchers have made a number of improvements to confocal microscopy technology. For example, a tilt angle measurement system based on dual-beam interference calculates the tilt angle of the sample surface through interference images at different angles. This method combines precise optical path design and advanced signal processing technology to achieve high-precision tilt angle measurement and is widely used in the detection of micromechanical systems and micro-optical devices. In addition, another related technology is multi-focal plane imaging tilt angle measurement equipment, which adjusts the focal position of the light beam to obtain imaging data of the sample at different depths, and determines the tilt angle of the surface through algorithm analysis.

[0005] The Chinese patent application "Linear differential confocal displacement sensor system based on lateral encoding" (patent application number CN202411349752.9) discloses a linear differential confocal displacement sensor system based on lateral encoding. While ensuring the measurement accuracy of the differential confocal microscope, it converts it from point measurement to line scanning mode measurement, and uses a blazed grating to achieve spectral lateral encoding, so that light of different wavelengths can be decomposed, and the measured components are measured through an achromatic lens in the desired order. By analyzing the light intensity signals of different wavelengths, all information on the lateral height of the sample can be obtained at the same time. Although this method solves the problem of long measurement time using point-by-point scanning measurement method. However, while measuring height information, it is still impossible to simultaneously measure the tilt angle. Summary of the invention

[0006] The present invention overcomes the deficiencies of the prior art and provides a filter wheel confocal measurement system based on transverse encoding and a measurement method thereof.

[0007] A filter wheel confocal measurement system based on lateral encoding includes a first measurement unit and a second measurement unit; wherein:

[0008] The first measuring unit includes a light source component arranged along the optical path, a first beam splitter, a second beam splitter, a first achromatic focusing lens, an object moving component for moving the object to be measured, and a first signal receiving component;

[0009] The second measuring unit includes a spectroscopic dispersion component and a second signal receiving component;

[0010] The light source component emits a continuous white light beam which is split by the first beam splitter. The transmitted light beam after the splitting is sequentially reflected by the light splitting and dispersion component, transmitted by the second beam splitter, and transmitted by the first achromatic focusing lens to the surface of the object to be measured. After being reflected by the surface of the object to be measured, the light beam forms a light beam carrying information of the object to be measured with a transverse coding. After being transmitted by the first achromatic focusing lens, the light beam carrying information of the object to be measured is split by the second beam splitter.

[0011] The transmitted light beam split by the second beam splitter is reflected by the light splitting and dispersion component and the first beam splitter in sequence, and is incident on the first signal receiving component, and the height analysis of the object to be measured is performed according to the signal received by the first signal receiving component;

[0012] The reflected light beam split by the second beam splitter is transmitted through the light splitting and dispersion component and incident on the second signal receiving component, and the tilt angle analysis of the object to be measured is performed according to the signal received by the second signal receiving component.

[0013] Furthermore, the light-splitting and dispersing component includes a blazed grating arranged along the optical path, a telecentric aperture, and a rotatable filter wheel provided with a plurality of filters for filtering different wavelength bands;

[0014] The blazed grating is used to disperse and separate light beams of different wavelengths, so that the light beams can be transversely encoded;

[0015] The telecentric aperture is used to eliminate the magnification change of the light beam and make the light beam parallel to the optical axis of the measurement system;

[0016] The filter wheel is used to select light beams of different wavelengths by rotating the filter.

[0017] Furthermore, the number of filters on the filter wheel is ≥N, matching the number of points to be tested of the object to be tested, wherein N is an integer ≥10.

[0018] Furthermore, the rotation frequency of the filter wheel, the data acquisition frequency of the second signal receiving component and the transverse axial scanning frequency of the test point of the object to be tested meet the following conditions:

[0019]

[0020] in, represents the rotation frequency of the filter wheel; Indicates the transverse-axial scanning frequency of the test point of the object to be tested; Represents the data acquisition frequency of the second signal receiving component; M is an integer ≥8.

[0021] Further, the first signal receiving component includes: a focusing lens, a pinhole and an imaging spectrometer;

[0022] The focusing lens is used to focus the parallel light beam;

[0023] The pinhole is used to suppress the defocused light beam and reduce the interference of the scattered light beam;

[0024] The imaging spectrometer is used to receive light beam signals of different wavelengths for imaging.

[0025] Further, the second signal receiving component includes a second achromatic focusing lens and an area array CCD camera;

[0026] The second achromatic focusing lens is used to focus light beams of different wavelengths and eliminate chromatic aberration;

[0027] The area array CCD camera is used to receive a light beam carrying information of the object to be measured for imaging.

[0028] The measurement method of the filter wheel confocal measurement system based on lateral encoding includes the following steps:

[0029] S1, placing a plane reflector with a zero tilt angle on the object moving assembly, starting the confocal measurement system, obtaining the center position of the light spot of the reflected light beam imaged on the area array CCD camera after the light beams of different wavelengths emitted by the light source assembly are respectively reflected by different positions of the plane reflector, and taking the center position of the light spot as the first position information;

[0030] S2, placing the object to be measured on the object moving assembly, the light beam emitted by the light source assembly is sequentially transmitted through the first beam splitter, reflected by the blazed grating, and passed through the telecentric aperture, and then transmitted through the second beam splitter and the first achromatic focusing lens to the surface of the object to be measured, the light beam reflected by the surface of the object to be measured forms a light beam with transverse coding and carrying information of the object to be measured, the light beam is optically split by the system, and the split light beams respectively form a light beam with transversely coded tilt angle information and a light beam with transversely coded height information, the light beam with tilt angle information is transmitted through the filter wheel and the second achromatic focusing lens, and is received by the area array CCD camera; the light beam with height information propagates along the system optical path and is received by the imaging spectrometer;

[0031] S3,

[0032] The method for measuring the tilt angle of the object to be measured is:

[0033] The filter wheel is rotated to synchronously control the area array CCD camera to complete the acquisition of imaging information under all filters, and light beams of different wavelengths are respectively reflected from different positions of the object to be measured and incident on the area array CCD camera, and the central position information of the light spot on the area array CCD camera is analyzed to obtain the corresponding lateral tilt angle information of the surface of the object to be measured, thereby completing the tilt angle measurement of the object to be measured;

[0034] The height measurement method of the object to be measured is:

[0035] By analyzing the spectrum information of the light beam received by the imaging spectrometer, the light intensity information of light beams of different wavelengths reflected at different positions of the object to be measured is obtained, and then the corresponding height information of the surface of the object to be measured in the horizontal direction is obtained to complete the height measurement of the object to be measured;

[0036] S4, controlling the object moving assembly to move the object to be measured, and repeating steps S2 and S3 until the measurement of the object to be measured is completed.

[0037] Furthermore, the method for measuring the tilt angle of the object to be measured in step S3 is specifically as follows:

[0038] Setting the rotation frequency of the filter wheel, the data acquisition frequency of the area array CCD camera and the transverse and axial scanning frequency of the test point of the object to be tested;

[0039] Rotate the filter wheel to synchronously control the area array CCD camera to complete a transverse and axial scanning of all sampling points under all filters to collect the center position information of the light spots, and obtain the second position information of light beams of different wavelengths that are imaged on the area array CCD camera after being reflected by different positions of the object to be measured;

[0040] Obtaining a light beam with the same wavelength at the first position information and the second position information, respectively, and calculating the measured displacements of the two position information;

[0041] Obtaining theoretical displacements of two pieces of position information corresponding to light beams of the same wavelength in the first position information and the second position information;

[0042] By calculating the measured displacement and the theoretical displacement, the tilt angle information of the measuring point of the object to be measured under the light beams of different wavelengths is obtained, and the tilt angle measurement of the object to be measured is completed.

[0043] Furthermore, the calculation formula of the measured displacement is as follows:

[0044]

[0045] Wherein, S represents the measured displacement of light beams of different wavelengths; S0 represents the size of the target pixel of the area array CCD camera; , respectively represent the position of the abscissa and ordinate of the area array CCD camera in the first position information; , respectively represent the position of the abscissa and ordinate of the area array CCD camera in the second position information; Indicates wavelength.

[0046] Furthermore, the calculation formula of the theoretical displacement is as follows:

[0047]

[0048] in, represents the theoretical displacement of light beams of different wavelengths; d represents the grating spacing of the blazed grating; represents the angle of the central axis of the incident light beam relative to the normal of the blazed grating; m represents the diffraction order of the blazed grating; Indicates the inclination angle of the surface of the object to be measured relative to the optical axis; represents the focal length of the first achromatic focusing lens and the second achromatic focusing lens.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] The present invention provides a filter wheel confocal measurement system based on transverse encoding and a measurement method thereof, which realizes transverse encoding of the spectrum by adding optical components for dispersion and filtering to the existing confocal optical measurement system. The existing confocal optical measurement system can only adopt a point-by-point scanning measurement method. Through the transverse encoding method, the measurement dimension in one direction is reduced, and the confocal optical measurement system is converted from a point measurement mode to a line scanning mode measurement mode. While improving the measurement accuracy of the existing confocal optical measurement system, the measurement time is shortened.

[0051] The present invention collects optical information in the measurement system. Through an analysis method combining optics and algorithms, it can not only measure the comprehensive three-dimensional information of the object to be measured and obtain the spatial imaging information of the object to be measured, but also can perform real-time measurement of the inclination angle of the measuring point on the surface of the object to be measured, thereby effectively overcoming the limitation of the prior art that it cannot simultaneously measure the three-dimensional spatial information and the angle inclination information of the object to be measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 is a schematic structural diagram of a filter wheel confocal measurement system based on transverse encoding in an embodiment of the present invention;

[0053] Figure 2 is a schematic flow chart of a confocal measurement method based on lateral encoding in an embodiment of the present invention;

[0054] Figure 3 It is a schematic diagram of the spectral information offset of a point to be measured with an inclined angle on the area array CCD camera in an embodiment of the present invention.

[0055] The reference numerals are as follows:

[0056] 1-light source, 2-collimating lens, 3-first beam splitter, 4-blazed grating, 5-telecentric aperture, 6-filter wheel, 7-second achromatic focusing lens, 8-array CCD camera, 9-second beam splitter, 10-first achromatic focusing lens, 11-object to be measured, 12-object moving assembly, 13-focusing lens, 14-pinhole, 15-imaging spectrometer. DETAILED DESCRIPTION

[0057] The following is a further detailed description of the embodiments of the present invention in conjunction with the accompanying drawings and embodiments. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict. 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.

[0058] Embodiment 1

[0059] The invention provides a filter wheel confocal measurement system based on transverse encoding.

[0060] Figure 1 A schematic structural diagram of a filter wheel confocal measurement system based on transverse encoding according to an embodiment of the present invention is shown.

[0061] like Figure 1 As shown, an embodiment of the present invention provides a filter wheel confocal measurement system based on transverse encoding, including a first measurement unit and a second measurement unit. The first measurement unit includes a light source assembly arranged along the optical path, a first beam splitter 3, a second beam splitter 9, a first achromatic focusing lens 10, a load moving assembly 12 for moving the object to be measured, and a first signal receiving assembly. The second measurement unit includes a spectroscopic dispersion assembly and a second signal receiving assembly. In the embodiment of the present invention, the light source assembly includes a wide-band white light source 1 and a collimating lens 2 for collimating the light source into a parallel light beam. The first signal receiving assembly includes: a focusing lens 13, a pinhole 14 and an imaging spectrometer 15. The focusing lens 13 is used to focus the parallel light beam; the pinhole 14 is used to suppress the defocused light beam and reduce the interference of the scattered light beam; the imaging spectrometer 15 is used to receive light beam signals of different wavelengths for imaging. The second signal receiving assembly includes a second achromatic focusing lens 7 and a planar array CCD camera 8. The second achromatic focusing lens 7 is used to focus the light beams of different wavelengths and eliminate chromatic aberration. The planar array CCD camera 8 is used to receive the light beam carrying the information of the object to be measured 11 for imaging. In the embodiment of the present invention, the object moving component 12 for moving the object to be tested adopts a piezoelectric ceramic driver in the prior art to move the object to be tested 11 .

[0062] In the embodiment of the present invention, the spectroscopic dispersion component includes a blazed grating 4, a telecentric aperture 5, and a rotating filter wheel 6 provided with multiple filters for filtering different wavelengths along the optical path. The blazed grating 4 is used to disperse and separate light beams of different wavelengths so that the light beams can be transversely encoded; the telecentric aperture 5 is used to eliminate the magnification change of the light beam so that the light beam is parallel to the optical axis of the measurement system; the filter wheel 6 is used to select light beams of different wavelengths by rotating. By rotating the wheel, the filters in the optical path can be quickly switched to select different wavelengths, thereby performing specific imaging or spectral analysis.

[0063] The technical solution provided in the embodiment of the present invention uses the area array CCD camera 8 as the receiving end for analyzing the tilt angle. The area array CCD camera 8 generates a gray value image, so it cannot distinguish the light spots of multiple wavelengths. Therefore, a filter wheel 6 is used, and the filter wheel 6 is driven by a motor to rotate, and the filter on the filter wheel 6 is switched so that the area array camera can only receive the light spot of one wavelength beam at a time, and the tilt angle of the test point of the test object 11 is analyzed based on the light spot offset of this wavelength.

[0064] The present invention also provides a preferred embodiment, in which the number of filters on the filter wheel 6 is ≥N, which matches the number of test points of the object to be tested 11, wherein N is an integer ≥10. The selection of different wavelengths is achieved through filters, and the more filters there are, the more wavelengths are split. For each wavelength that measures the angle of a test point, there should be a corresponding filter. That is, the number of filters is the same as the number of test points of the object to be tested 11. In practical applications, when measuring each test point, the inclination angle of the test point is measured by identifying the wavelength focused on the test point to obtain the information of the inclination angle. If the number of filters is small, the inclination angle of some test points may not be measured. That is, if the number of test points is small, the measurement efficiency is high, but the measurement accuracy will be reduced accordingly. If you want to improve the accuracy of the angle measurement, you need to increase the number of filters so that the number of filters matches the test points. In the embodiment of the present invention, considering the balance between measurement efficiency and measurement accuracy, the filter wheel 6 is equipped with 10 filters, each filter allows light of a specific wavelength to pass through, which is equivalent to the measurement beam within the measurement wavelength range provided by the light source 1 being divided into 10 parts. The number of transverse scanning points of the transverse encoding of the technical solution provided by the implementation of the present invention is consistent with the number of filters. The embodiment of the present invention is described by taking 10 filters as an example. The present invention does not limit the number of filters, and the number of filters can be selected according to the measurement accuracy required for the actual application.

[0065] The present invention further provides a preferred embodiment in which the rotation frequency of the filter wheel 6, the data acquisition frequency of the second signal receiving component and the frequency of the object carrier controlling the transverse and axial movement of the object to be tested 11 meet the following conditions:

[0066]

[0067] in, represents the rotation frequency of the filter wheel 6; Indicates the horizontal and axial scanning frequency of the test point of the object to be tested 11; Represents the data acquisition frequency of the area array CCD camera 8; M is an integer ≥ 8. It is necessary to ensure that the tilt angle measurement of the test point of all wavelengths is achieved during a horizontal scan. Therefore, during a horizontal axial scanning measurement, the filter wheel 6 must be able to rotate at least 8 circles to ensure that all wavelength tilt angle measurement information of a certain circle of the filter wheel 6 can be located at the focal position of the horizontal axial scanning to achieve accurate tilt angle measurement of the test point. The frame rate of the area array CCD camera 8 as the receiving end needs to rotate the filter wheel 6 once to achieve the acquisition of all wavelengths. In the embodiment of the present invention, the filter wheel 6 has 10 filters, so the frame rate of the area array CCD camera 8, that is, the data acquisition frequency of the area array CCD camera 8, needs to be at least 10 times the frequency of the filter wheel 6.

[0068] The light source 1 emits a continuous white measuring light beam which is collimated into a parallel light beam by the collimating lens 2. The parallel light beam is split by the first beam splitter 3. The transmitted light beam after the splitting is diffracted by the blazed grating 4 and dispersed and decomposed into light beams of different wavelengths, that is, the light beams of different wavelengths can be transversely encoded. The light beams of different wavelengths are incident to the second beam splitter 9 through the telecentric aperture 5 for splitting. The transmitted light beam after the splitting is incident to the surface of the object to be measured 11 through the first achromatic focusing lens 10 to scan the surface of the object to be measured 11. The scanned light beam forms a light beam with transverse coding and carries the information of the object to be measured 11. After being transmitted through the first achromatic focusing lens 10, it is split again by the second beam splitter 9.

[0069] The transmitted light beam split by the second beam splitter 9 passes through the telecentric aperture 5, is reflected by the blazed grating 4 and the first beam splitter 3, is incident on the focusing lens 13 for focusing, passes through the pinhole 14, and is received by the imaging spectrometer 15. The height analysis of the object to be measured 11 is performed based on the signal received by the imaging spectrometer 15.

[0070] The reflected light beam split by the second beam splitter 9 is transmitted through the filter on the filter wheel 6 and the second achromatic focusing lens 7, and is received by the area array CCD camera 8. The tilt angle of the object to be measured 11 is analyzed based on the signal received by the area array CCD camera 8.

[0071] The telecentric aperture 5 can eliminate the magnification change of the light beam, make the light beam parallel to the optical axis of the measurement system, and improve the overall measurement accuracy of the measurement system. The blazed grating 4 can disperse and separate the measurement light beams of different wavelengths, so that the measurement light beam can be transversely encoded. The pinhole 14 can suppress the defocused light of the measurement light beam, reduce the interference of the scattered light beam, and improve the measurement accuracy of the measurement system. Each filter of the filter wheel 6 allows a light beam of a specific wavelength to pass. By rotating the filter wheel 6, the filters in the optical path can be quickly switched to achieve the selection of light beams of different wavelengths, thereby achieving specific imaging or spectral analysis.

[0072] The filter wheel confocal measurement system based on transverse coding provided in an embodiment of the present invention uses a filter wheel 6 to switch the wavelength of the measuring light beam. The measuring light beam diffracted by the blazed grating 4 and the telecentric aperture 5 performs measurement scanning on the object to be measured 11. This not only eliminates the magnification change introduced by the transversely coded measuring light beam, but also uses transverse axial linear scanning. The measuring wavelength can be distinguished by the filter wheel 6 and the ordinary area array CCD camera 8, thereby realizing the inclination angle measurement of the point to be measured.

[0073] The system provided by the embodiment of the present invention can realize the scanning of a transverse axial plane through one measurement. After completing the scanning of a transverse axial plane, the object to be measured 11 can be moved in the longitudinal axial direction through the piezoelectric ceramic driver for scanning. Compared with the prior art, the confocal microscope technology needs to scan in three dimensions to obtain all the information of the object to be measured 11 in order to perform three-dimensional reconstruction. The measurement system provided by the embodiment of the present invention only needs to scan two dimensions through lateral encoding, which greatly improves the efficiency and workload of measurement while ensuring the measurement accuracy. By changing the wavelength of the measurement beam switched by the filter wheel 6, the grating pitch of the blazing grating 4, and the blazing angle, the emission angle of the light beam of a specific wavelength can be controlled, so that the light beam of a specific wavelength passes through the focal plane of the first achromatic focusing lens 10 in the expected order or arrangement, that is, the measurement beam is stably arranged at the designed or calibrated expected value to achieve transverse linear encoding. The measurement system provided by the embodiment of the present invention adds tilt angle measurement to the optical system only through common optical devices. It can not only scan the three-dimensional information of the object to be measured 11, but also realize the real-time measurement of the tilt angle of the measuring point of the object to be measured 11, so that the application range of the confocal system based on lateral encoding is wide and has better application prospects.

[0074] Embodiment 2

[0075] The invention provides a measurement method of a filter wheel confocal measurement system based on transverse coding.

[0076] Figure 2 A schematic flow chart of a measurement method of a filter wheel confocal measurement system based on lateral encoding according to an embodiment of the present invention is shown.

[0077] like Figure 2 As shown, the embodiment of the present invention provides a measurement method of a filter wheel confocal measurement system based on lateral encoding, comprising the following steps

[0078] S1. Place a plane reflector with a zero tilt angle on the piezoelectric ceramic driver and start the measurement system. The continuous white light beam emitted by the light source 1 propagates in the measurement system, and becomes measurement beams of different wavelengths after being dispersed and transversely encoded by the blazed grating 4. The measurement beams of different wavelengths are respectively reflected at different positions of the plane reflector and imaged on the area array CCD camera 8. The center position of the light spot of the reflected light beams of different wavelengths imaged on the area array CCD camera 8 is obtained, and the coordinates of the above center position are recorded { , }, the coordinate set of these center positions is called the first position information. , Respectively represent the horizontal coordinate and vertical coordinate in the first position information.

[0079] The measurement method step S1 provided in the embodiment of the present invention is a data collection work in a calibration step. The calibration is to reduce the error of the measurement system and the measurement method in practical applications and improve the measurement accuracy. In practical applications, other methods in the prior art can also be used for calibration, which is not limited in the embodiment of the present invention.

[0080] S2. Remove the plane reflector and place the object to be measured 11 on the piezoelectric ceramic driver. The continuous white light beam emitted by the light source 1 is transmitted through the first beam splitter 3, reflected by the blazed grating 4, passes through the telecentric aperture 5, is transmitted through the second beam splitter 9, and is transmitted through the first achromatic focusing lens 10 to the surface of the object to be measured 11. After being reflected by the surface of the object to be measured 11, a light beam with transverse coding and carrying information of the object to be measured 11 is formed. The light beam is optically split by the measurement system. The split light beams respectively form a light beam with transversely coded inclination angle information and a light beam with transversely coded height information. The light beam with inclination angle information is transmitted through the filter wheel 6 and the second achromatic focusing lens 7, and is received by the area array CCD camera 8; the light beam with height information propagates along the optical path of the measurement system and is received by the imaging spectrometer 15.

[0081] The measurement method provided in the embodiment of the present invention collects optical information of the area array CCD camera 8 and the imaging spectrometer 15 in the measurement system. Through the analysis method combining optics and algorithms, it can not only measure the comprehensive three-dimensional information of the object to be measured 11 and obtain the spatial imaging information of the object to be measured 11, but also can perform real-time measurement of the tilt angle of the measured point of the object to be measured 11, thereby effectively overcoming the limitation of the existing confocal display measurement technology that cannot simultaneously measure the spatial and angular tilt.

[0082] S3,

[0083] The specific method for measuring the tilt angle of the object to be measured 11 in the embodiment of the present invention is:

[0084] The filter wheel 6 is rotated to synchronously control the area array CCD camera 8 to complete the acquisition of imaging information under all filters, and light beams of different wavelengths are respectively reflected by different positions of the object to be measured 11 and then incident on the area array CCD camera 8, so as to obtain the center position information of the light spot on the area array CCD camera 8, and then obtain the corresponding lateral inclination angle information of the surface of the object to be measured 11, and complete the inclination angle measurement of the object to be measured 11.

[0085] Since the area array CCD camera 8 serves as the receiving end for analyzing the tilt angle, the area array CCD camera 8 generates a grayscale image and is therefore unable to distinguish light spots of different wavelengths. Therefore, a filter wheel 6 is used, and the filter wheel 6 is rotated by a motor to switch the filter so that the area array CCD camera 8 can only receive a light spot of one wavelength at a time. Based on the offset of the center position of the light spot of this wavelength, the tilt angle of the test point of the object to be tested 11 is analyzed.

[0086] Set the rotation frequency of filter wheel 6 , data acquisition frequency of area array CCD camera 8 The horizontal and axial scanning frequency is performed at the test point of the object 11 to be tested. . It is necessary to ensure that the tilt angle measurement of all wavelengths of the points to be measured is achieved during a transverse axial scanning process. Therefore, in the process of obtaining sampling points by a transverse axial scanning measurement, it is necessary to ensure that the number of sampling points is at least 8 to ensure the accuracy of positioning the focal position. Therefore, the filter wheel 6 must be able to rotate at least 10 circles to ensure that all wavelength tilt angle measurement information of a certain circle of the filter wheel 6 can be positioned at the focal position of the transverse axial scanning to achieve accurate tilt angle measurement of the points to be measured. The frame rate of the area array CCD camera 8 as the receiving end needs to rotate the filter wheel 6 once to achieve the acquisition of all wavelengths. That is, the image acquisition of the area array CCD camera 8 and the filter switching of the filter wheel 6 are synchronized in time sequence. One filter on the filter wheel 6 corresponds to one image acquisition and also corresponds to a measurement point of one wavelength. In a transverse axial scanning measurement, the number of filters on the filter wheel 6 corresponds to the number of photos collected by the area array CCD camera 8, and points of all wavelengths are acquired through a set of pictures. In the actual measurement process, if the measurement accuracy is taken into consideration, multiple wavelength acquisitions can be performed when measuring one measurement point, that is, the filter wheel 6 rotates multiple times. In the embodiment of the present invention, the filter wheel 6 has 10 filters, so the frame rate of the area array CCD camera 8, that is, the data acquisition frequency of the area array CCD camera 8, needs to be at least 10 times the frequency of the filter wheel 6.

[0087] The filter wheel 6 is rotated to synchronously control the area array CCD camera 8 to complete a transverse and axial scanning to collect the center position information of the light spots of all sampling points under all filters, and obtain the second position information of light beams of different wavelengths reflected by different positions of the object to be measured 11 and imaged on the area array CCD camera 8.

[0088] The embodiment of the present invention is illustrated by taking a single-wavelength light beam as an example, and the same is true for light beams with different wavelengths. Figure 3 FIG. 8 is a schematic diagram showing the spectrum information of a point to be measured with an inclined angle on the area array CCD camera 8. Figure 3 As shown, for ease of understanding, the area array CCD camera 8 is arranged along the x-axis and y-axis directions. is the center position of the spot of a single wavelength beam on the area array CCD camera 8 in the first position information when there is no tilt angle. A is the center position of the spot of a single wavelength beam on the area array CCD camera 8 in the second position information when there is a tilt angle. The distance between the two points is the amount of offset caused by the tilt angle of the point to be measured.

[0089] The positions where the light beams of different wavelengths are imaged on the area array CCD camera 8 after being reflected at different positions of the object to be measured 11, and the coordinates of the above positions are recorded { , }, the coordinate set of these positions is called the second position information. , Respectively represent the horizontal coordinate and vertical coordinate in the second position information.

[0090] Get the same wavelength beam, at the first position information and the second position information A, and calculate the measured displacement of the two position information.

[0091] The calculation formula (1) for the measured displacement is:

[0092] (1)

[0093] Where S represents the measured displacement of light beams of different wavelengths; S0 represents the size of the 8-target pixel of the area array CCD camera; , Respectively represent the horizontal coordinate and the vertical coordinate of the first position information in the area array CCD camera 8; , Respectively represent the horizontal coordinate and the vertical coordinate of the second position information in the area array CCD camera 8; Indicates wavelength.

[0094] Obtain the theoretical displacement of the two position information corresponding to the light beam of the same wavelength in the first position information and the second position information. That is, when the wavelength selected in the first position information is the same as the wavelength selected in the second position information, the calculation formula (2) for calculating the theoretical displacement of the same wavelength is:

[0095] (2)

[0096] in, represents the theoretical displacement of light beams of different wavelengths; d represents the grating spacing of the blazed grating 4; represents the angle of the central axis of the incident light beam relative to the normal of the blazed grating 4; m represents the diffraction order of the blazed grating 4; Indicates the tilt angle of the surface of the object to be measured 11 relative to the optical axis; denoted by the focal lengths of the first achromatic focusing lens 10 and the second achromatic focusing lens 7.

[0097] The specific value of the measured displacement can be calculated by formula (1). If the value of the measured displacement is equal to the value of the theoretical displacement, the inclination angle information of the measuring point of the object to be measured 11 under light beams of different wavelengths can be calculated by formula (2), and the measurement of the inclination angle of the object to be measured 11 can be completed, that is, measurement.

[0098] The measurement method provided in an embodiment of the present invention can control the emission angle of a light beam of a specific wavelength by changing the grating pitch and blaze angle of the blazed grating 4, so that the light beam of a specific wavelength passes through the focal plane of the first achromatic focusing lens 10 in an expected order or arrangement, and even the measuring light beam is stably arranged at the designed or calibrated expected value to achieve transverse linear encoding.

[0099] The following is a derivation of the formula for the theoretical displacement of light beams of different wavelengths in the tilt angle measurement method. In the measurement method provided by the embodiment of the present invention, the measuring light beam is reflected by the surface of the object to be measured 11 to form a light beam with a transverse coding and carrying information of the object to be measured 11, that is, in the transverse coding x-axis direction, if the point to be measured encounters a tilt angle relative to the optical axis The free-form surface, the inclination angle of the reflected beam relative to the optical axis will be Since the measuring light beam passes through the focus of the first achromatic focusing lens 10, the first achromatic focusing lens 10 converts the tilt angle into a displacement distance of the reflected light beam, that is, the tilt angle is converted into the displacement distance.

[0100] When the continuous white measuring beam emitted by the light source 1 passes through the blazed grating 4, it is separated into a single-wavelength diffracted beam, which satisfies the following relationship:

[0101] (3)

[0102] in, represents the angle between the mth order diffracted beam and the normal of the blazed grating 4; represents the angle between the incident light beam and the normal of the blazed grating 4.

[0103] According to the optical principle, Each wavelength of the light beam will be separated according to the following formula (4), and the diffraction angle of each wavelength of the light beam incident on the first achromatic focusing lens 10 is for:

[0104] (4)

[0105] The position where each wavelength beam is incident on the first achromatic focusing lens 10 is:

[0106] (5)

[0107] represents the position of the light beam with the center of the first achromatic focusing lens 10 as the origin on the first achromatic focusing lens 10; L represents the distance from the center of the blazed grating 4 to the first achromatic focusing lens 10.

[0108] Measuring the beam at an angle of inclination After incident on the first achromatic focusing lens 10, a focus will be formed on the focal plane. The position of the focus is related to the incident angle and the incident position When encoding horizontally, the horizontal coordinates of different wavelengths are It can be calculated by geometric relationship:

[0109] (6)

[0110] When the test point of the test object 11 has an inclination angle relative to the optical axis When, after reflection, we can obtain: the tilt displacement point of the reflected light beam after it exits the first achromatic focusing lens 10 for:

[0111] (7)

[0112] in, It represents the deviation caused by the tilt of the test point of the object 11 to be tested.

[0113] The tilt angle of the reflected light beam exiting the first achromatic focusing lens 10 is The parameters of the first achromatic focusing lens 10 and the second achromatic focusing lens 7 are the same. After being reflected by the first achromatic focusing lens 10 and the second beam splitter 9, the incident point and incident angle of the light beam entering the second achromatic focusing lens 7 are the same as the exit point and exit angle of the second achromatic focusing lens 7. After focusing, the light beam is focused and imaged on the area array CCD camera 8. The lateral coordinate of the wavelength is Calculated by optical geometric relationship:

[0114] (8)

[0115] make , we can get the single wavelength lateral coordinate when there is no tilt angle :

[0116] (9)

[0117] Finally, the theoretical displacement of beams of different wavelengths at tilt angles can be obtained. :

[0118] (10)

[0119] The height measurement method of the object to be measured 11 in the embodiment of the present invention is to measure the height of the object to be measured 11 by analyzing the spectral information received by the imaging spectrometer 15 in the existing confocal measurement technology, specifically:

[0120] When the light source 1 emits a continuous white measuring light beam and passes through the blazed grating 4, it is separated into a single-wavelength diffraction light beam. By analyzing the spectral information of the specific wavelength light beam received by the imaging spectrometer 15, the light intensity information reflected by light beams of different wavelengths at different positions of the object to be measured 11 is obtained. By analyzing the light intensity signals of different wavelengths, all the lateral information of the height of the object to be measured 11 can be obtained, thereby completing the height measurement of the object to be measured 11.

[0121] The measurement method provided by the embodiment of the present invention can simultaneously measure the inclination angles of the free-form surfaces of all the test points of the object to be tested 11 in the transverse axis during a transverse axial scanning process, and then control the piezoelectric ceramic driver to move the object to be tested 11 in the longitudinal axis to perform the next transverse scanning and deep scanning, thereby ensuring both the measurement accuracy and the measurement speed.

[0122] S4, moving and controlling the piezoelectric ceramic driver to control the longitudinal axial movement of the object to be tested 11, repeating steps S2 and S3 until the measurement of the object to be tested 11 is completed. The method provided by the present invention uses a transverse axial linear scan, and a plane scan can be achieved in one measurement. After the scan of a plane is completed, the object to be tested 11 is moved longitudinally by the piezoelectric ceramic driver for scanning until the measurement of the entire object to be tested 11 is completed.

[0123] The present invention verifies the effectiveness of the measurement method of the technical solution of the present invention through experiments. The parameters of the filter wheel confocal measurement system based on transverse encoding are as follows: the beam width of the light source 1 is 4.2 mm, the focal lengths of the first achromatic focusing lens 10 and the second achromatic focusing lens 7 are both 3.3 mm, and the pinhole size is 15 μm. A standard plane mirror is used as the object to be measured in the verification experiment, and the surface accuracy standard PV value is 3.74 μm and the RMS value is 0.95 μm.

[0124] Through experimental comparison, the measurement method provided by the embodiment of the present invention is compared with the traditional measurement method. The comparison results are as follows:

[0125] Comparison Table

[0126] name PV (μm) RMS (μm) Standard flat mirror type 3.74 0.95 Traditional method measurement 3.90 1.13 The present invention measures 3.88 1.11

[0127] By comparison, the measurement accuracy of the technical solution of the present invention and the traditional method is improved by 12%. It can be seen that the measurement method provided by the present invention can measure the tilt angle while measuring the height of the object to be measured, and effectively eliminate the error caused by the inclined surface while measuring the tilt angle, thereby significantly improving the measurement accuracy.

[0128] The measurement method provided by the embodiment of the present invention has a significant improvement in measurement time. The spectrometer takes about 1-30 seconds to measure once. The specific time depends on the required measurement accuracy. The higher the accuracy, the longer the measurement time. In contrast, the time for the area array CCD camera 8 to collect images each time in the technical solution of the embodiment of the present invention is in the millisecond level, usually between 5 milliseconds and 100 milliseconds. Even if the area array CCD camera 8 needs to take multiple images during one measurement, the time required for the overall measurement is still significantly shortened.

[0129] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0130] Although the embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and cannot be understood as limiting the present invention. Those skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

[0131] The above specific implementations of the present invention do not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A filter wheel confocal measurement system based on lateral encoding, characterized in that: It includes a first measuring unit and a second measuring unit; wherein, The first measuring unit comprises a light source component arranged along the optical path, a first beam splitter (3), a second beam splitter (9), a first achromatic focusing lens (10), an object moving component (12) for moving the object to be measured (11), and a first signal receiving component; The second measuring unit includes a spectroscopic dispersion component and a second signal receiving component; The light source component emits a continuous white light beam which is split by the first beam splitter (3); the transmitted light beam after the splitting is sequentially reflected by the light splitting and dispersion component, transmitted by the second beam splitter (9), and transmitted by the first achromatic focusing lens (10) to the surface of the object to be tested (11); after being reflected by the surface of the object to be tested (11), the light beam forms a light beam with transverse coding and carrying information of the object to be tested (11); after being transmitted by the first achromatic focusing lens (10), the light beam carrying information of the object to be tested (11) is split by the second beam splitter (9); The transmitted light beam split by the second beam splitter (9) is reflected by the light splitting and dispersion component and the first beam splitter (3) in sequence, and is incident on the first signal receiving component, and a height analysis of the object to be measured (11) is performed based on the signal received by the first signal receiving component; The reflected light beam split by the second beam splitter (9) is transmitted through the light splitting and dispersion component and incident on the second signal receiving component, and the tilt angle of the object to be measured (11) is analyzed according to the signal received by the second signal receiving component; The light-splitting and dispersion component comprises a blazed grating (4) arranged along the light path, a telecentric aperture (5), and a rotatable filter wheel (6) provided with a plurality of filters for filtering different wavelength bands; The blazed grating (4) is used to disperse and separate light beams of different wavelengths, so that the light beams can be transversely encoded; The telecentric aperture (5) is used to eliminate the magnification change of the light beam, so that the light beam is parallel to the optical axis of the measurement system; The filter wheel (6) is used to select light beams of different wavelengths by rotating the filter; The number of filters on the filter wheel (6) is ≥ N, matching the number of test points of the object to be tested (11), wherein N is an integer ≥ 10; The rotation frequency of the filter wheel (6), the data acquisition frequency of the second signal receiving component and the transverse-axial scanning frequency of the test point of the object to be tested (11) meet the following conditions: in, Indicates the rotation frequency of the filter wheel (6); Indicates the transverse-axial scanning frequency of the test point of the object to be tested (11); Represents the data acquisition frequency of the second signal receiving component; M is an integer ≥8.

2. The filter wheel confocal measurement system based on lateral encoding according to claim 1, characterized in that: The first signal receiving component comprises: a focusing lens (13), a pinhole (14) and an imaging spectrometer (15); The focusing lens (13) is used to focus the parallel light beam; The pinhole (14) is used to suppress the defocused light beam and reduce the interference of the scattered light beam; The imaging spectrometer (15) is used to receive light beam signals of different wavelengths for imaging.

3. The filter wheel confocal measurement system based on lateral encoding according to claim 2, characterized in that: The second signal receiving component comprises a second achromatic focusing lens (7) and an area array CCD camera (8); The second achromatic focusing lens (7) is used to focus light beams of different wavelengths and eliminate chromatic aberration; The area array CCD camera (8) is used to receive a light beam carrying information of the object to be measured (11) for imaging.

4. A measurement method using the filter wheel confocal measurement system based on lateral encoding according to any one of claims 1 to 3, characterized in that: The steps include: S1, placing a plane reflector with a zero tilt angle on the object moving component (12), starting the measurement system, obtaining the center position of the light spot of the reflected light beam imaged on the area array CCD camera (8) after the light beams of different wavelengths emitted by the light source component are respectively reflected by different positions of the plane reflector, and using the center position of the light spot as the first position information; S2, placing the object to be measured (11) on the object moving assembly (12), the light beam emitted by the light source assembly is sequentially transmitted through the first beam splitter (3), reflected by the blazed grating (4), passes through the telecentric aperture (5), is transmitted through the second beam splitter (9), is transmitted through the first achromatic focusing lens (10) to the surface of the object to be measured (11), and is reflected by the surface of the object to be measured (11) to form a light beam with transverse coding and carrying information of the object to be measured (11). The light beam carrying information of the object to be measured (11) is optically split by the measurement system, and the split light beams are respectively formed into a light beam with transverse coding tilt angle information and a light beam with transverse coding height information. The light beam with the tilt angle information is transmitted through the filter wheel (6) and the second achromatic focusing lens (7), and is received by the area array CCD camera (8); the light beam with the height information propagates along the optical path of the measurement system and is received by the imaging spectrometer (15); S3、 The method for measuring the tilt angle of the object to be measured (11) is: The filter wheel (6) is rotated to synchronously control the area array CCD camera (8) to complete the acquisition of imaging information under all filters, and light beams of different wavelengths are respectively reflected by different positions of the object to be measured (11) and incident on the area array CCD camera (8). By analyzing the central position information of the light spot on the area array CCD camera (8), the corresponding inclination angle information of the transverse axis of the surface of the object to be measured (11) is obtained, and the inclination angle measurement of the object to be measured (11) is completed; The height measurement method of the object to be measured (11) is: By analyzing the spectral information of the light beam received by the imaging spectrometer (15), light intensity information of light beams of different wavelengths reflected at different positions of the object to be measured (11) is obtained, thereby obtaining the corresponding height information of the surface of the object to be measured (11) in the transverse axis direction, thereby completing the height measurement of the object to be measured (11); S4, controlling the object moving assembly (12) to move the object to be measured (11), and repeating steps S2 and S3 until the measurement of the object to be measured (11) is completed.

5. The measurement method of the filter wheel confocal measurement system based on lateral encoding according to claim 4, characterized in that: The method for measuring the tilt angle of the object to be measured (11) in step S3 is specifically as follows: Setting the rotation frequency of the filter wheel (6), the data acquisition frequency of the area array CCD camera (8), and the transverse and axial scanning frequency of the test point of the test object (11); Rotate the filter wheel (6) to synchronously control the area array CCD camera (8) to complete a transverse-axial scanning of all sampling points to collect information on the center position of the light spot under all filters, and obtain second position information of light beams of different wavelengths that are imaged on the area array CCD camera (8) after being reflected by different positions of the object to be measured (11); Obtaining a light beam with the same wavelength at the first position information and the second position information, respectively, and calculating the measured displacements of the two position information; Obtaining theoretical displacements of two pieces of position information corresponding to light beams of the same wavelength in the first position information and the second position information; By calculating the measured displacement and the theoretical displacement, the tilt angle information of the measuring point of the object to be measured (11) under the light beams of different wavelengths is obtained, and the tilt angle measurement of the object to be measured (11) is completed.

6. The measurement method of the filter wheel confocal measurement system based on lateral encoding according to claim 5, characterized in that: The calculation formula of the measured displacement is: Wherein, S represents the measured displacement of light beams of different wavelengths; S0 represents the size of the target surface pixel of the area array CCD camera (8); Respectively represent the position of the abscissa and ordinate of the area array CCD camera (8) in the first position information; respectively represent the position of the abscissa and ordinate of the area array CCD camera (8) in the second position information; Indicates wavelength.

7. The measurement method of the filter wheel confocal measurement system based on lateral encoding according to claim 6, characterized in that: The calculation formula of the theoretical displacement is: in, represents the theoretical displacement of light beams of different wavelengths; d represents the grating spacing of the blazed grating (4); represents the angle of the central axis of the incident light beam relative to the normal of the blazed grating (4); m represents the diffraction order of the blazed grating (4); represents the inclination angle of the surface of the object to be measured (11) relative to the optical axis; Indicates the focal lengths of the first achromatic focusing lens (10) and the second achromatic focusing lens (7).

Images