A measurement method based on zero-crossing monitoring of differential confocal characteristic curve

Abstract

This invention provides a measurement method based on zero-crossing monitoring of differential confocal characteristic curves. Building upon a differential confocal measurement system, a sliding window algorithm is used to monitor the zero-crossing points of the differential confocal characteristic curves. This not only monitors the zero-crossing situation but also accurately predicts the arrival time of the zero-crossing point, thereby controlling the differential confocal system for sampling and measurement. It can simultaneously measure the tilt angle at the measured point in real time while measuring position information. During each scan measurement process, only one image of the area array detector's spot data is acquired, meeting high-speed acquisition requirements while ensuring measurement accuracy, reducing setup and adjustment requirements, and making it more suitable for practical applications. This method not only ensures measurement accuracy but also improves dynamic response speed.

Description

Technical Field

[0001] The invention relates to the technical field of optical detection, and in particular to a measurement method based on zero-crossing monitoring of a differential confocal characteristic curve. Background Art

[0002] In recent years, with the deepening of research on nano-scale technologies such as ultra-precision machining and their wider application, ultra-precision detection, as a key link, is of great importance. Traditional contact measurement technology is easy to damage the measuring components and has poor real-time performance, so it is no longer used in the field of ultra-precision detection. Sub-micron or even nano-level measurement accuracy has brought new challenges to the research of non-contact measurement methods.

[0003] Among the ultra-precision non-contact measurement methods in the current optical field, Laser Scanning Confocal Microscope (LSCM) is a modern optical microscopy technology with high resolution, which is widely used in biomedicine and optical precision measurement. The research direction of laser differential confocal microscopy is mainly divided into two parts, namely detector data acquisition and data processing to obtain distance information. In the first part, it is necessary to drive the detector objective lens to move axially, so that the surface of the object to be measured moves from the front of the detector objective lens to the back of the focus, and at the same time collect the light intensity signals of the two detection light paths. In the second part, it is necessary to analyze the collected objective lens position and the light intensity data of the detection light path, determine the zero-crossing position through the differential confocal characteristic curve, and extract the distance information of the position to be measured.

[0004] However, the method in the prior art is to complete differential data acquisition, and then use linear fitting to obtain the zero-crossing point after obtaining the complete curve. For example, the Chinese invention patent "Differential Confocal Measurement Method" (patent number: 202211088958.1) has very strict requirements on the installation accuracy, especially the placement of the linear array detector. Whether it is radial or axial tilt, it will cause large errors in the measurement, which cannot be met. Data is recorded at each sampling position, and it takes a long time to complete data acquisition. In ordinary applications, it is difficult to achieve and does not have the significance of wide application. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and propose a measurement method based on zero-crossing monitoring of a differential confocal characteristic curve.

[0006] To achieve the above object, the present invention adopts the following specific technical solutions:

[0007] A measurement method based on zero-crossing monitoring of a differential confocal characteristic curve is provided, and the zero-crossing monitoring of the differential confocal characteristic curve is realized based on a differential confocal measurement system.

[0008] The differential confocal measurement system includes a host computer, a laser light source, a first beam splitter, a focusing lens, an aperture, a second beam splitter, a planar array detector, and a differential confocal component arranged in sequence along the optical path;

[0009] The differential confocal assembly includes an interferometer, a transmission assembly, a third beam splitter, a pre-focus focusing lens, a pre-focus pinhole, a pre-focus photoelectric detector, a post-focus focusing lens, a post-focus pinhole, and a post-focus photoelectric detector; wherein,

[0010] The host computer is used to send control signals, collect data and calculate data, control the movement of the transmission component, and control the data collection of the area array detector, the pre-focus photoelectric detector, and the post-focus photoelectric detector;

[0011] The transmission assembly is fixedly connected to the focusing lens, and the transmission assembly drives the focusing lens to move back and forth along the direction of the laser beam to control the imaging position of the surface to be measured, and the interferometer is used to measure the displacement value of the focusing lens; the object plane of the pre-focus focusing lens is located before the focus, and the pre-focus photoelectric detector is arranged on its image plane; the object plane of the post-focus focusing lens is located after the focus, and the post-focus photoelectric detector is arranged on its image plane;

[0012] The light beam emitted by the laser light source is transmitted to the focusing lens and the aperture through the first beam splitter, and is incident on the surface of the object to be measured. After being reflected by the surface of the object to be measured, it returns along the original optical path, and is reflected by the first beam splitter to the second beam splitter for splitting. The reflected light beam is incident on the planar array detector as an angle measurement beam, and the transmitted light beam is incident on the third beam splitter for splitting as a position measurement beam. The reflected light beam is used as a pre-focus measurement beam, and the pre-focus measurement beam passes through the pre-focus focusing lens and the pre-focus pinhole in sequence and then is incident on the pre-focus photoelectric detector; the transmitted light beam is used as a post-focus measurement beam, and the post-focus measurement beam passes through the post-focus focusing lens and the post-focus pinhole in sequence and then is incident on the post-focus photoelectric detector;

[0013] The measuring method comprises the following steps:

[0014] S1, constructing the differential confocal measurement system, turning on the laser light source, sending a control signal to the transmission component, and the transmission component drives the focusing lens to move at a uniform speed along the direction of the laser beam to control the imaging position of the surface to be measured, so that the imaging position moves from the front focus position of the focusing lens to the back focus position;

[0015] S2, collecting light intensity data of the pre-focus photodetector and the post-focus photodetector, subtracting the light intensity data of the pre-focus photodetector from the light intensity data of the post-focus photodetector to obtain a differential confocal characteristic curve, and acquiring differential signal data of the differential confocal characteristic curve;

[0016] S3, using a sliding window algorithm to perform linear fitting on the differential signal data, obtain a linear relationship between time and the differential signal, and monitor the zero-crossing point of the differential confocal characteristic curve according to the linear relationship;

[0017] S4, according to the monitoring data of the zero-crossing point, measuring the displacement value of the focusing lens corresponding to the zero-crossing point position by the interferometer, and obtaining the position information of the to-be-measured point on the surface of the to-be-measured object;

[0018] At the same time, according to the monitoring data of the zero-crossing point, a control signal is sent to the area array detector to collect the spot image, and the corresponding relationship between the inclination angle and the peak position is obtained through the peak position of the spot image, thereby completing the inclination angle measurement of the test point on the surface of the object to be tested.

[0019] Furthermore, the sampling time in step S2 satisfies: T2≤T1 / 2; wherein T1 represents the exposure time of the area array detector for collecting images; and T2 represents the sampling interval time.

[0020] Furthermore, the step S3 is specifically as follows:

[0021] S301, obtain t n The nth group of differential signal data D at time n ;

[0022] S302, set the sliding window algorithm: the sliding window step size is T2, the end of the sliding window position is at t n The sliding window contains N+1 sets of differential signals at all times, where N is the preset number of data points in the linear interval of the differential confocal curve.

[0023] S303, Extract D n and t n The first N groups of differential signals at the time are used as data in the sliding window to monitor the zero-crossing point of the differential confocal characteristic curve;

[0024] S304, the data in the sliding window are linearly fitted according to the time sequence and the preset weights, so as to obtain the linear relationship between time and the differential signal; wherein the linear relationship is expressed as formula group (1):

[0025] D=k×t+b

[0026]

[0027] Where t represents time, D represents the differential signal, k and b represent the parameters of linear fitting, and i represents the n At time t, the i-th group of data in the sliding window, D iThe i-th group of differential signals represents t i Indicates the time of the i-th group of data;

[0028] S305, when D=0, t0=-b / k, which is the zero-crossing moment, thereby realizing the monitoring of the zero-crossing point of the differential confocal characteristic curve; wherein t0 represents the zero-crossing moment.

[0029] Furthermore, the preset weight in step S304 satisfies formula (2):

[0030]

[0031] Among them, w(i) represents the weight value of the i-th group of data in the sliding window.

[0032] Furthermore, the fitting goal in step S304 is to make the value of formula (3) approach the minimum value.

[0033]

[0034] Furthermore, the tilt angle measurement in step S4 is specifically as follows:

[0035] According to the monitoring data of the zero-crossing point, a control signal is sent to control the area array detector to start spot image acquisition at time t0-T1 / 2, and the area array detector ends spot image acquisition at time t0+T1 / 2. The position of the peak value of the test point on the surface of the object to be measured is obtained through the collected spot image, and the corresponding relationship between the inclination angle and the peak position is constructed through polynomial fitting, thereby completing the inclination angle measurement of the test point on the surface of the object to be measured.

[0036] The present invention proposes a measurement method based on zero-crossing monitoring of a differential confocal characteristic curve. In the zero-crossing monitoring based on the differential confocal characteristic curve, in the way of combining the differential confocal system with the algorithm, it is not only possible to monitor the zero-crossing situation, but also to accurately predict the arrival of the zero-crossing moment, so as to control the differential confocal system to perform sampling and measurement, and to measure the inclination angle at the measured point in real time while measuring the position information. It is not only possible to ensure the accuracy of the measurement, but also to improve the dynamic response speed. In each scanning measurement process, the spot image data of the array detector is only collected once, so as to meet the high-speed acquisition requirements while ensuring the measurement accuracy, reducing the adjustment requirements, and being more suitable for practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a schematic diagram of a differential confocal measurement system according to an embodiment of the present invention;

[0038] Figure 2 is a flow chart of a measurement method based on zero-crossing point monitoring of a differential confocal characteristic curve according to an embodiment of the present invention;

[0039] Figure 3 is a schematic diagram of the principle of a differential confocal curve according to an embodiment of the present invention;

[0040] Figure 4 is a schematic diagram of the principle of a sliding window according to an embodiment of the present invention;

[0041] Figure 5 is a schematic diagram of the exposure time of the area array detector of the differential confocal measurement system according to an embodiment of the present invention;

[0042] Figure 6 is a flow chart of zero-crossing point prediction of a differential confocal characteristic curve according to an embodiment of the present invention;

[0043] Figure 7 4 is a schematic diagram of the principle of tilt angle measurement according to an embodiment of the present invention.

[0044] Reference numerals include:

[0045] 1 laser light source, 2 first beam splitter, 3 focusing lens, 4 aperture, 5 object to be measured, 6 second beam splitter, 7 third beam splitter, 8 focusing lens before focus, 9 pinhole before focus, 10 photoelectric detector before focus, 11 focusing lens after focus, 12 pinhole after focus, 13 photoelectric detector after focus, 14 array detector, 15 host computer. DETAILED DESCRIPTION

[0046] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same modules are represented by the same reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, the detailed description thereof will not be repeated.

[0047] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0048] The specific working mode of the present invention is described in detail below with reference to the accompanying drawings:

[0049] The present invention provides a measurement method based on zero-crossing monitoring of a differential confocal characteristic curve, and implements zero-crossing monitoring of a differential confocal characteristic curve based on a differential confocal measurement system. Figure 1As shown, the differential confocal measurement system includes a host computer 15, a laser light source 1, a first beam splitter 2, a focusing lens 3, an aperture 4, a second beam splitter 6, an array detector 14, and a differential confocal component arranged in sequence along the optical path; the differential confocal component includes an interferometer, a transmission component, a third beam splitter 7, a pre-focus focusing lens 8, a pre-focus pinhole 9, a pre-focus photoelectric detector 10, a post-focus focusing lens 13, a post-focus pinhole 12, and a post-focus photoelectric detector 13.

[0050] In the embodiment of the present invention, the laser light source 1 can emit a Gaussian collimated beam with a wavelength of 642nm and a radius of 3.2mm. The focusing lens 3 uses a microscope with a focal length of 9mm. The pre-focus focusing lens 8 and the post-focus focusing lens 13 both use plano-concave lenses with a focal length of 10mm. The pre-focus pinhole 9 and the post-focus pinhole 12 use pinholes with an offset of 650μm and a size of 20μm. The transmission component uses a piezoelectric objective lens positioner with an axial moving speed of 1mm / s and a single axial scanning stroke of 50μm. In the embodiment of the present invention, the host computer 15 is used to send control signals, data acquisition and data calculation, control the movement of the transmission component, and control the data acquisition of the array detector 14, the pre-focus photodetector 10 and the post-focus photodetector 13. In the embodiment of the present invention, an aperture 4 with an aperture size slightly smaller than that of the focusing lens 3 is placed on the focusing side of the focusing lens 3. The aperture 4 can reduce the influence of ambient stray light and the side wall of the focusing lens 3. The transmission assembly is fixedly connected to the focusing lens 3, and the transmission assembly controls the focusing lens 3 to move back and forth at a uniform speed along the direction of the laser beam to control the imaging position of the surface to be measured, and the interferometer is used to measure the displacement value of the focusing lens 3. The interferometer used in the embodiment of the present invention should be able to perform precise measurement at the nanometer level. The object plane of the pre-focus focusing lens 8 is located before the focus, and a pre-focus photodetector 10 is set on its image plane; the object plane of the post-focus focusing lens 13 is located after the focus, and a post-focus photodetector 13 is set on its image plane.

[0051] In the embodiment of the present invention, the laser light source 1 emits a collimated laser light beam with Gaussian distribution. The light beam emitted by the laser light source 1 is transmitted to the focusing lens 3 and the aperture 4 through the first beam splitter 2, and is incident on the surface of the object to be measured 5. After being reflected by the surface of the object to be measured 5, it returns along the original optical path, and is reflected by the first beam splitter 2 to the second beam splitter 6 for splitting. The reflected light beam is incident on the area array detector 14 as an angle measurement beam, and the transmitted light beam is incident on the third beam splitter 7 as a position measurement beam for splitting. The reflected light beam is used as a pre-focus measurement beam, and the pre-focus measurement beam passes through the pre-focus focusing lens 8 and the pre-focus pinhole 9 in sequence and then is incident on the pre-focus photoelectric detector 10; the transmitted light beam is used as a post-focus measurement beam, and the post-focus measurement beam passes through the post-focus focusing lens 13 and the post-focus pinhole 12 in sequence and then is incident on the post-focus photoelectric detector 13.

[0052] The measurement method based on zero-crossing monitoring of the differential confocal characteristic curve provided in the embodiment of the present invention is used in conjunction with the differential confocal measurement system in the embodiment of the present invention to measure the position of the object 5 and the tilt angle of the object 5 at the same time.

[0053] The measurement method provided by the embodiment of the present invention is as follows: Figure 2 As shown, the following steps are included:

[0054] S1. Build a differential confocal measurement system, turn on the laser light source 1, send a control signal to the transmission component, and the transmission component drives the focusing lens 3 to move at a uniform speed along the direction of the laser beam to control the imaging position of the surface to be measured, so that the imaging position moves from the front focus position of the focusing lens 3 to the back focus position.

[0055] S2, collect the light intensity data of the pre-focus photoelectric detector 10 and the post-focus photoelectric detector 13, respectively recorded as I(u, -u m ) and I(u, +u m The light intensity data of the pre-focus photodetector 10 is subtracted from the light intensity data of the post-focus photodetector 13 to obtain the differential confocal characteristic curve FES = I (u, -u m )-I(u,+u m ), the principle diagram of the differential confocal characteristic curve, such as Figure 3 As shown, differential signal data of the differential confocal characteristic curve is obtained; FES represents the differential confocal characteristic curve.

[0056] The present invention provides a preferred embodiment, the sampling time in step S2 satisfies: T2≤T1 / 2; wherein T1 represents the exposure time of the area array detector 14 for collecting images; and T2 represents the sampling interval time. In the embodiment of the present invention, the exposure time T1 of the area array detector 14 is 5μs, and the sampling interval time T2 in the embodiment of the present invention is 1μs. That is, in the embodiment of the present invention, the focusing lens 3 moves at a uniform speed along the direction of the laser beam for scanning, and the host computer 15 collects a set of light intensity data of the pre-focus photodetector 10 and the post-focus photodetector 13 at intervals of 1μs, and obtains a set of differential signal data.

[0057] S3. Use a sliding window algorithm to perform linear fitting on the differential signal data to obtain a linear relationship between time and the differential signal, and monitor the zero-crossing point of the differential confocal characteristic curve based on the linear relationship.

[0058] S301, obtain t n The nth group of differential signal data D at time n .

[0059] Get in t n At the time, the light intensity data of the nth group of pre-focus photodetectors 10 and post-focus photodetectors 13 are subtracted to obtain the differential signal data Dn .

[0060] S302, set the sliding window algorithm: the sliding window step size is T2, the end of the sliding window position is at t n The sliding window contains N+1 sets of differential signals at all times, wherein N is the preset number of data points in the linear interval of the differential confocal curve.

[0061] In the embodiment of the present invention, the step length of the sliding window is 1 μs, and the end of the sliding window position is t n The time is aligned, and the sliding window contains 100+1 groups of differential signals. In the embodiment of the present invention, N is 1 / 5 of the number of data points in the linear interval of the differential confocal curve, and the value is 100. The value range of N can be any number of data points in the linear interval of the differential confocal characteristic curve. The larger the value of N, the more corresponding data points, the more accurate the calculation, but the amount of calculation is large. The smaller the value of N, the fewer corresponding data points, the faster the calculation speed, but the accuracy is not high. Therefore, the value of N can be selected according to the specific application environment, and the present invention is not limited to this.

[0062] S303, Extract D n and t n The first N groups of differential signals at the time are used as the data in the sliding window to monitor the zero-crossing point t0 of the differential confocal characteristic curve, where t0 represents the zero-crossing time. The schematic diagram of the sliding window principle is shown in Figure 4 shown.

[0063] S304, the data in the sliding window are linearly fitted according to the time sequence and the preset weights, so as to obtain the linear relationship between time and the differential signal; wherein the linear relationship is expressed as formula (1):

[0064] D=k×t+b(1)

[0065] Where t represents time, D represents the differential signal, k and b represent the parameters of linear fitting, and i represents the n At time t, the i-th group of data in the sliding window, D i The i-th group of differential signals represents t i Indicates the time of the i-th group of data.

[0066] The present invention provides a preferred solution, wherein the preset weight satisfies formula (2):

[0067]

[0068] Among them, w(i) represents the weight value of the i-th group of data in the sliding window.

[0069] The present invention provides a preferred solution, the fitting target is to make the value of formula (3) approach the minimum value,

[0070]

[0071] The fitting process is as follows:

[0072] Let the partial derivatives of the linear fitting parameters k and b be 0, and establish the equation group (4). The equation group (4) is as follows:

[0073]

[0074] Solving the equation group (4), we can obtain the linear fitting parameters k and b, as shown in the following formula (5).

[0075]

[0076] The embodiment of the present invention can realize tracking prediction or real-time tracking prediction of the zero-crossing moment of the dynamic differential confocal characteristic curve through a sliding window algorithm, thereby realizing real-time tracking and real-time monitoring of the zero-crossing point of the differential confocal characteristic curve.

[0077] S305, when D=0, t0=-b / k, which is the zero-crossing moment, thereby realizing the monitoring of the zero-crossing point of the differential confocal characteristic curve; wherein t0 represents the zero-crossing moment.

[0078] S4, according to the monitoring data of the zero-crossing point, that is, when t0 = -b / k, the pre-focus measuring beam passes through the pre-focus focusing lens 8 and is incident on fu m A pre-focus pinhole 9 is placed at the position of the pre-focus pinhole 9, and a pre-focus photodetector 10 is placed behind the pre-focus pinhole 9. Wherein, f is the focal length of the pre-focus focusing lens 8, u m is the defocus amount. After the post-focus measuring beam passes through the post-focus focusing lens 13, it is incident on the f+u m A post-focus pinhole 12 is placed at the position of the post-focus pinhole 12, and a post-focus photodetector 13 is placed behind the post-focus pinhole 12. Wherein, f is the focal length of the post-focus focusing lens 13, u m The focusing lens 3 moves under the drive of the transmission assembly. When the position measurement beam is just focused on the point to be measured on the surface of the object 5, the light intensity at the pre-focus pinhole 9 and the post-focus pinhole 12 is exactly equal. At this time, the light intensity signals received by the pre-focus photodetector 10 and the post-focus photodetector 13 are also equal, that is, I(u, -u m )=I(u,+u m ). The position of the focusing lens 3 is recorded as u by the interferometer, that is, the displacement value of the focusing lens 3 corresponding to the zero-crossing position measured by the interferometer is u, and the position information of the measured point on the surface of the object 5 to be measured is obtained.

[0079] According to the monitoring data of the zero-crossing point, a control signal is sent to control the array detector 14 to start spot image acquisition at time t0-T1 / 2, and the array detector 14 ends spot image acquisition at time t0+T1 / 2. The measurement method in the embodiment of the present invention is as follows: Figure 5 and Figure 6 As shown, the zero-crossing point t0 can be predicted, the arrival of the moment t0 can be monitored at least T1 / 2 in advance, and the exposure of the area array detector 14 is turned on at the moment t0-T1 / 2, and the spot image acquisition is turned on. In the embodiment of the invention, if the current time t is greater than or equal to t0-T1 / 2, and k<0, it is considered that after another T1 / 2, the transmission component drives the focusing lens 3 to move at a uniform speed along the direction of the laser beam to control the imaging position of the surface to be measured. When it just reaches the focal position of the focusing lens 3, the area array detector 14 is immediately turned on for exposure, and waits until the moment t0+T1 / 2 to complete the acquisition of a single frame of the spot image.

[0080] The peak position of the test point on the surface of the object 5 is obtained through the collected spot image, and the corresponding relationship between the tilt angle and the peak position is constructed through polynomial fitting, thereby completing the tilt angle measurement of the test point on the surface of the object 5.

[0081] In the embodiment of the present invention, the specific tilt angle measurement method is as follows: a plane reflector is placed at the position of the object to be measured 5, a laser light source 1 is turned on, the tilt angle of the plane reflector is changed, and the spot images on the array detector 14 corresponding to N groups of different tilt angles are collected. The tilt angle of each group of samples is recorded as The peak position is recorded as (x i ,y i ). The peak position in the embodiment of the present invention can be obtained by using the centroid method in the prior art, and the present invention is not limited to this. The function model of the peak position and the tilt angle in two directions is constructed by polynomial fitting. The method for constructing the function model is as follows: a total of N groups of samples are collected, and the tilt angles in two directions of each group of samples are recorded as The peak position is recorded as (x i ,y i ), the relationship functions f and g between the tilt angle and the peak position are fitted using the least squares fitting method of binary quadratic polynomials, expressed as formula (6):

[0082]

[0083] Among them, a0, a1, a2, a3, a4, a5, b0, b1, b2, b3, b4, b5 are constants to be determined;

[0084] The purpose of fitting is to find constants a0, a1, a2, a3, a4, a5 so that Minimum, find constants b0,b1,b2,b3,b4,b5 such that Minimum;

[0085] To minimize E1, Where j = 0, 1, ..., 5, we can get formula (7):

[0086]

[0087] Solving this system of equations gives a0, a1, a2, a3, a4, a5;

[0088] To minimize E2, Where j = 0, 1, ..., 5, we can get formula (8):

[0089]

[0090] Solving this system of equations gives b0, b1, b2, b3, b4, b5;

[0091] Substitute the above solution into formula (6) to obtain the function model of the peak position and the tilt angle.

[0092] Replace the plane reflector with the object to be tested 5, turn on the laser light source 1, drive the focusing lens 3 to move through the transmission component, send a control signal to control the area array detector 14 to start spot image acquisition at t0-T1 / 2 according to the monitoring data of the zero crossing point, and end the spot image acquisition at t0+T1 / 2, and collect the spot image on the area array detector 14 corresponding to the focusing. The peak position of the surface of the object to be tested 5 is obtained through the collected spot image, such as Figure 7 As shown, the peak position of the measured point on the surface of the object 5 to be measured is calculated and obtained. and will Substitute the relationship function formula (6) between the tilt angle and the peak position, and obtain the tilt angle of the surface of the object 5 to be tested according to the function model, thereby completing the tilt angle measurement of the surface of the object 5 to be tested.

[0093] The technical solution of the embodiment of the present invention combines angle measurement and position measurement to simultaneously obtain the position information and surface inclination information of the object to be measured, that is, it simultaneously measures the object to be measured once and obtains the distance measurement position information and inclination angle information.

[0094] The present invention verifies the effectiveness of the measurement method of the technical solution of the present invention through experiments. The selected systems have the same parameters as those in the present invention, as follows: the laser light source 1 has a wavelength of 642nm and a Gaussian collimated beam with a radius of 3.2mm, the focusing lens 3 uses a microscope with a focal length of 9mm, the pre-focus photodetector 10 and the post-focus photodetector 13 use a plano-concave lens with a focal length of 10mm, the pre-focus pinhole 9 and the post-focus pinhole 12 have an offset of 650μm, and the pinhole size is 20μm. The exposure time of the array detector 14 is set to T1=5μs, the differential signal sampling interval is T2=1μs, the sliding window size is N=100, the axial moving speed of the transmission device of the focusing lens 3 is 1mm / s, and the single axial scanning stroke is 50μm.

[0095] Through experimental comparison, let the measured surface be tilted at an angle θ∈[0°,8°], A total of 9720 sets of measurement experiments were conducted. The comparison of measurement accuracy and measurement time between this method and the traditional method of using linear fitting to determine the zero-crossing point position after a single scan and then moving to the zero-crossing point position for spot image acquisition is as follows.

[0096] Comparison table of accuracy and measurement time between this solution and traditional methods

[0097]

[0098] By comparison, the measurement accuracy of the technical solution of the present invention and the traditional method is basically the same, and the measurement time efficiency is improved by 59%.

[0099] The beneficial effects of the measurement method based on the zero-crossing monitoring of the differential confocal characteristic curve of the present invention are as follows: the present invention can monitor the zero-crossing situation based on the zero-crossing monitoring of the differential confocal characteristic curve, and accurately predict the arrival of the zero-crossing moment in the differential confocal system and the algorithm, so as to control the differential confocal system to perform sampling and measurement, and can measure the inclination angle at the measured point in real time while measuring the position information. It can not only ensure the accuracy of the measurement, but also improve the dynamic response speed. In each scanning measurement process, the spot image data of the array detector is collected only once, which is used to meet the high-speed acquisition requirements while ensuring the measurement accuracy and reducing the adjustment requirements, which is more suitable for practical applications.

[0100] 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.

[0101] 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.

[0102] 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 measurement method based on zero-crossing monitoring of a differential confocal characteristic curve, characterized in that: Based on the differential confocal measurement system, the zero-crossing point of the differential confocal characteristic curve is monitored. The differential confocal measurement system includes a host computer, a laser light source, a first beam splitter, a focusing lens, an aperture, a second beam splitter, a planar array detector, and a differential confocal component arranged in sequence along the optical path; The differential confocal assembly includes an interferometer, a transmission assembly, a third beam splitter, a pre-focus focusing lens, a pre-focus pinhole, a pre-focus photoelectric detector, a post-focus focusing lens, a post-focus pinhole, and a post-focus photoelectric detector; wherein, The host computer is used to send control signals, collect data and calculate data, control the movement of the transmission component, and control the data collection of the area array detector, the pre-focus photoelectric detector, and the post-focus photoelectric detector; The transmission assembly is fixedly connected to the focusing lens, and the transmission assembly drives the focusing lens to move back and forth along the direction of the laser beam to control the imaging position of the surface of the object to be measured, and the interferometer is used to measure the displacement value of the focusing lens; the object plane of the pre-focus focusing lens is located before the focus, and the pre-focus photoelectric detector is arranged on its image plane; the object plane of the post-focus focusing lens is located after the focus, and the post-focus photoelectric detector is arranged on its image plane; The light beam emitted by the laser light source is transmitted to the focusing lens and the aperture through the first beam splitter, and is incident on the surface of the object to be measured. After being reflected by the surface of the object to be measured, it returns along the original optical path, and is reflected by the first beam splitter to the second beam splitter for splitting. The reflected light beam is incident on the planar array detector as an angle measurement beam, and the transmitted light beam is incident on the third beam splitter for splitting as a position measurement beam. The reflected light beam is used as a pre-focus measurement beam, and the pre-focus measurement beam passes through the pre-focus focusing lens and the pre-focus pinhole in sequence and then is incident on the pre-focus photoelectric detector; the transmitted light beam is used as a post-focus measurement beam, and the post-focus measurement beam passes through the post-focus focusing lens and the post-focus pinhole in sequence and then is incident on the post-focus photoelectric detector; The measuring method comprises the following steps: S1, constructing the differential confocal measurement system, turning on the laser light source, sending a control signal to the transmission component, and the transmission component drives the focusing lens to move at a uniform speed along the direction of the laser beam to control the imaging position of the surface of the object to be measured, so that the imaging position moves from the front focus position of the focusing lens to the back focus position; S2, collecting light intensity data of the pre-focus photodetector and the post-focus photodetector, subtracting the light intensity data of the pre-focus photodetector from the light intensity data of the post-focus photodetector to obtain a differential confocal characteristic curve, and acquiring differential signal data of the differential confocal characteristic curve; S3, using a sliding window algorithm to perform linear fitting on the differential signal data, obtain a linear relationship between time and the differential signal, and monitor the zero-crossing point of the differential confocal characteristic curve according to the linear relationship; S4, according to the monitoring data of the zero-crossing point, measuring the displacement value of the focusing lens corresponding to the zero-crossing point position by the interferometer, and obtaining the position information of the to-be-measured point on the surface of the to-be-measured object; At the same time, according to the monitoring data of the zero-crossing point, a control signal is sent to the area array detector to collect the spot image, and the corresponding relationship between the inclination angle and the peak position is obtained through the peak position of the spot image, thereby completing the inclination angle measurement of the test point on the surface of the object to be tested.

2. The measuring method according to claim 1, characterized in that: The sampling time in step S2 satisfies: T2≤T1 / 2; wherein T1 represents the exposure time of the area array detector for collecting images; and T2 represents the sampling interval time.

3. The measuring method according to claim 2, characterized in that: The step S3 is specifically as follows: S301, obtain t n The nth group of differential signal data D at time n ; S302, set the sliding window algorithm: the sliding window step size is T2, the end of the sliding window position is at t n The sliding window contains N+1 sets of differential signals at all times, where N is the preset number of data points in the linear interval of the differential confocal curve. S303, Extract D n and t n The first N groups of differential signals at the time are used as data in the sliding window to monitor the zero-crossing point of the differential confocal characteristic curve; S304, the data in the sliding window are linearly fitted according to the time sequence and the preset weights, so as to obtain the linear relationship between time and the differential signal; wherein the linear relationship is expressed as formula group (1): D=k×t+b Where t represents time, D represents the differential signal, k and b represent the parameters of linear fitting, and i represents the n At time , the i-th group of data in the sliding window, D i The i-th group of differential signals represents t i Indicates the time of the i-th group of data; S305, when D=0, t0=-b / k, which is the zero-crossing moment, thereby realizing the monitoring of the zero-crossing point of the differential confocal characteristic curve; wherein t0 represents the zero-crossing moment.

4. The measuring method according to claim 3, characterized in that: The preset weight in step S304 satisfies formula (2): Among them, w(i) represents the weight value of the i-th group of data in the sliding window.

5. The measuring method according to claim 4, characterized in that: The fitting goal in step S304 is to make the value of formula (3) approach the minimum value.

6. The measuring method according to claim 5, characterized in that: The tilt angle measurement in step S4 is specifically as follows: According to the monitoring data of the zero-crossing point, a control signal is sent to control the area array detector to start spot image acquisition at time t0-T1 / 2, and the area array detector ends spot image acquisition at time t0+T1 / 2. The position of the peak value of the test point on the surface of the object to be measured is obtained through the collected spot image, and the corresponding relationship between the inclination angle and the peak position is constructed through polynomial fitting, thereby completing the inclination angle measurement of the test point on the surface of the object to be measured.

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