Differential Confocal Measurement Method

Abstract

The present invention provides a differential confocal measurement method, which extracts the peak position accurately and quickly, and constructs a function model of the peak position and the tilt angle in combination with the extracted peak position. The peak extraction accuracy can be improved, and even if the collected spot image is not an approximate Gaussian distribution, the peak position can still be accurately obtained, and the high-precision and accurate measurement of the tilt angle of the measurement position can be achieved. The differential confocal measurement method provided by the present invention realizes the distance measurement of the test point of the object to be measured by the cooperation of the differential confocal component, and can accurately obtain the distance information, and further improves the positioning sensitivity and anti-interference ability through the distance measurement of the differential confocal component, and realizes the acquisition of the tilt angle information of the object to be measured while differential confocal distance measurement, which is more accurate in optical morphology measurement, especially in the recognition of tiny surface defects.

Description

Technical Field

[0001] The invention belongs to the technical field of optical detection, and in particular relates to a differential confocal measurement method. Background Art

[0002] With the development of my country's advanced manufacturing industry, optical free-form surface devices are increasingly used in high-end optical systems. There are many different methods for manufacturing free-form surfaces. However, there is currently no universal and fast measurement method for measuring single-piece optical free-form surface optical components. How to measure the surface profile of optical components with high precision has become an urgent issue to be solved.

[0003] At present, commonly used measurement methods include contact measurement method and non-contact measurement method. The contact measurement method directly contacts the object to be measured through the probe to obtain the position information of the measured point. Non-contact measurement methods usually use optical means for measurement, including spectral confocal detection method, confocal microscopy measurement method, and differential confocal measurement method. Among them, the spectral confocal detection method uses the different focusing positions of different wavelengths of light when white light passes through a condenser to measure the distance. The confocal microscopy measurement method focuses a single wavelength light beam onto the surface of the object to be measured for distance measurement. The differential confocal measurement method derived from confocal microscopy measurement locates the focus position by placing two photoelectric sensors before and after the image focus. It is widely used due to its simple structure, high precision, and fast positioning speed.

[0004] Aperture-coded confocal profilometry, published in Optics Letters, proposes an aperture-coded confocal microscope. By tilting the surface to be measured, the light beam reflected from the sample surface will be partially blocked by the designed aperture. Therefore, by analyzing the intensity of the reflected light beam, the surface height and tilt angle can be measured simultaneously. However, this method is limited to measuring the tilt angle along one direction, and the tilt angle of the measurement point is often two-dimensional. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and propose a differential confocal measurement method.

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

[0007] A differential confocal measurement method is provided, which realizes measurement based on a differential confocal measurement system.

[0008] The differential confocal measurement system comprises 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 assembly which are sequentially arranged 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 transmission assembly is fixedly connected to the focusing lens, and the transmission assembly controls 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;

[0011] 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. A part of the light beam is reflected as an angle measurement beam and is incident on the area array detector, and another part is transmitted as a position measurement beam and is incident on the third beam splitter for splitting. A part of the light beam is reflected 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 is incident on the pre-focus photoelectric detector; another part of the light beam is transmitted 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 is incident on the post-focus photoelectric detector;

[0012] The differential confocal measurement method comprises the following steps:

[0013] S1, placing a plane reflector at the position of the object to be measured, turning on the laser light source, changing the tilt angle of the plane reflector, and collecting the light spot images on the area array detector corresponding to different tilt angles;

[0014] S2, integrating the light intensity in the horizontal and vertical directions of each collected light spot image respectively to obtain a corresponding one-dimensional sequence;

[0015] S3, acquiring the positions of the peaks in the corresponding one-dimensional single-peak signal sequences in the horizontal and vertical directions according to the corresponding one-dimensional sequence;

[0016] S4, constructing a function model of the peak position and tilt angle in two directions by polynomial fitting;

[0017] S5, replacing the plane reflector with the object to be measured, turning on the laser light source, driving the focusing lens to move through the transmission assembly, focusing the laser beam on the point to be measured on the surface of the object to be measured, and collecting the spot image on the area array detector corresponding to the focusing, the light signal intensity signals of the pre-focus photoelectric detector and the post-focus photoelectric detector respectively;

[0018] S6, using the collected spot image, repeating steps S2 and S3 to obtain the peak position of the point to be measured on the surface of the object to be measured, and obtaining the inclination angle of the point to be measured on the surface of the object to be measured according to the function model;

[0019] The differential confocal signal curve is obtained by using the collected light signal intensity signals of the pre-focus photodetector and the post-focus photodetector, and the focusing lens displacement value corresponding to the zero-crossing point position of the differential confocal signal curve is measured by the interferometer to obtain the position information of the test point on the surface of the object to be measured.

[0020] Furthermore, the calculation method of the peak positions in the one-dimensional single-peak signal sequences in two directions in step S3 is the same, and the specific calculation method is as follows:

[0021] The peak position is calculated according to formula (1):

[0022]

[0023] Among them, P n is the position of the peak in the one-dimensional single-peak signal sequence, n is the number of times the spot image is collected, and h is half of the half-peak width in the one-dimensional single-peak signal sequence.

[0024] Furthermore, P is calculated by formula (1) n and P n-1 When |P n -P n-1 |≤0.1, the currently obtained P n The value is the location of the peak.

[0025] Furthermore, in step S4, the specific method is as follows:

[0026] A total of N groups of samples were collected, and the inclination angles of each group of samples in two directions were 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, which is expressed as formula (2):

[0027]

[0028] Among them, a0, a1, a2, a3, a4, a5, b0, b1, b2, b3, b4, b5 are constants to be determined;

[0029] 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;

[0030] To minimize E1, Where j = 0, 1, ..., 5, we can get formula (3):

[0031]

[0032] Solving this system of equations gives a0, a1, a2, a3, a4, a5;

[0033] To minimize E2, Where j = 0, 1, ..., 5, we can get formula (4):

[0034]

[0035] Solving this system of equations gives b0, b1, b2, b3, b4, b5;

[0036] Substitute the above solution into formula (2) to obtain the function model of the peak position and the tilt angle.

[0037] The present invention can achieve the following technical effects:

[0038] 1. The differential confocal measurement method provided by the present invention can simultaneously obtain the surface shape information and surface inclination information of the object to be measured;

[0039] 2. The differential confocal measurement method provided by the present invention is used to calculate |P n -P n-1 The difference between | can be corrected while extracting the peak value, thus improving the peak extraction accuracy;

[0040] 3. The differential confocal measurement method provided by the present invention can achieve measurement in a large angle range;

[0041] 4. The differential confocal measurement method provided by the present invention is simple and easy to implement, easy to operate, and takes into account both accuracy and speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a schematic structural diagram of a differential confocal measurement system according to an embodiment of the present invention;

[0043] Figure 2is a flow chart of a differential confocal measurement method according to an embodiment of the present invention;

[0044] Figure 3 is a schematic diagram of the principle of two-dimensional tilt angle measurement in a differential confocal measurement method according to an embodiment of the present invention;

[0045] Figure 4 is a schematic diagram of light spot images collected by array detectors at different tilt directions in a differential confocal measurement method according to an embodiment of the present invention;

[0046] Figure 5 Schematic diagram of a differential confocal curve in a differential confocal measurement method according to an embodiment of the present invention.

[0047] Reference numerals include:

[0048] 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. DETAILED DESCRIPTION

[0049] 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.

[0050] 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.

[0051] Combine the following Figure 1 The specific working mode of the confocal measurement system of the embodiment of the present invention is described in detail:

[0052] Figure 1 A schematic structural diagram of a differential confocal measurement system according to an embodiment of the present invention is shown.

[0053] Figure 2 A flow chart of a differential confocal measurement method according to an embodiment of the present invention is shown.

[0054] Figure 3 The schematic diagram shows the principle of two-dimensional tilt angle measurement in the differential confocal measurement method according to an embodiment of the present invention.

[0055] Figure 4A schematic diagram showing spot images collected by array detectors at different tilt directions in a differential confocal measurement method according to an embodiment of the present invention is shown.

[0056] Figure 5 A schematic diagram of a differential confocal curve in a differential confocal measurement method according to an embodiment of the present invention is shown.

[0057] The embodiment of the present invention provides a differential confocal measurement method, which implements measurement based on a differential confocal measurement system, such as Figure 1 As shown, the differential confocal measurement system includes a laser light source 1, a first beam splitter 2, a focusing lens 3, an aperture 4, a second beam splitter 6, a planar array detector 14, and a differential confocal assembly arranged in sequence along the optical path; the differential confocal assembly includes an interferometer, a transmission assembly, a third beam splitter 7, a pre-focus focusing lens 8, a pre-focus pinhole 9, a pre-focus photodetector 10, a post-focus focusing lens 11, a post-focus pinhole 12, and a post-focus photodetector 13. In the embodiment of the present invention, 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 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 nanometer-level precise measurement. The object plane of the pre-focus focusing lens 8 is located before the focus, and the pre-focus photodetector 10 is arranged on its image plane; the object plane of the post-focus focusing lens 11 is located after the focus, and the post-focus photodetector 13 is arranged on its image plane.

[0058] In the embodiment of the present invention, the laser light source 1 emits a collimated laser beam with Gaussian distribution. -2 The radius is r (the intensity is the maximum intensity at the center e -2 times, the corresponding radius), and the wavelength is λ. The light beam emitted by the laser light source 1 is transmitted through the first beam splitter 2 to the focusing lens 3 and the aperture 4, 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. A part of the light beam is reflected as an angle measurement beam and is incident on the area array detector 14, and the other part is transmitted as a position measurement beam and is incident on the third beam splitter 7 for splitting. A part of the light beam is reflected 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 is incident on the pre-focus photoelectric detector 10; another part of the light beam is transmitted as a post-focus measurement beam, and the post-focus measurement beam passes through the post-focus focusing lens 11 and the post-focus pinhole 12 in sequence and is incident on the post-focus photoelectric detector 13.

[0059] The differential confocal measurement method 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 distance to the object 5 to be measured and the tilt angle of the object 5 to be measured at the same time.

[0060] Differential confocal measurement methods, such as Figure 2 As shown, the following steps are included:

[0061] When the surface of the object to be tested 5 is tilted, such as Figure 3 As shown, point O is the surface point to be measured of the object 5, and the direction of the surface normal at this point is Establish the I-XYZ coordinate system with point O as the origin. for Projection on the XOY plane. θ is and The angle of for and Angle. Figure 4 As shown, using To indicate the tilt direction of the position to be measured, when the tilt direction of the position to be measured is different, the area array detector 14 will collect different spot images. By using the different peak positions of the spot images under different tilt directions, the tilt direction of the position to be measured is measured.

[0062] S1, place the plane reflector at the position of the object to be measured 5, turn on the laser light source 1, change the tilt angle of the plane reflector, collect N groups of spot images on the area array detector 14 corresponding to different tilt angles, and record the tilt angle of each group of samples as The peak position is recorded as (x i ,y i ).

[0063] S2. Integrate the light intensity in the horizontal and vertical directions of each collected light spot image to obtain the corresponding one-dimensional sequence. The vertical integration obtains the one-dimensional sequence: Integrating horizontally yields a one-dimensional sequence:

[0064] S3. Obtain the positions of the peaks in the corresponding one-dimensional single-peak signal sequences in the horizontal and vertical directions according to the corresponding one-dimensional sequence.

[0065] The calculation method of the peak position in the one-dimensional single-peak signal sequence in both the horizontal and vertical directions is the same, and the specific calculation method is as follows:

[0066] According to formula (1), we can calculate The peak position and Peak position:

[0067]

[0068] Among them, P nis the position of the peak value in the one-dimensional single-peak signal sequence, that is, the position of the maximum value in the one-dimensional sequence in the vertical and horizontal directions; n is the number of times the spot image is collected, and h is half of the half-peak width in the one-dimensional single-peak signal sequence.

[0069] The embodiment of the present invention also provides a preferred method, which calculates P by formula (1): n and P n-1 When |P n -P n-1 |≤0.1, then the currently obtained P n The value is the location of the peak. |P n -P n-1 |The value will affect the accuracy of peak extraction. If the value is set too large, the accuracy will be reduced; if it is set too small, the algorithm will take longer to run. Considering the accuracy and program running time, 0.1 is selected. You can reduce |P according to the actual accuracy required. n -P n-1 The present invention does not limit the value of |. In the embodiment of the present invention, 0.1 corresponds to the length of 140.1 pixels of the array detector. The technical solution of the embodiment of the present invention can quickly extract the peak value by analyzing the peak point position of the light spot of the return beam on the inclined surface of the object to be tested 5 based on the differential confocal optical path and using the cooperation of the array camera and the algorithm, and calculate |P n -P n-1 The difference between | can be corrected while extracting the peak value, thus achieving high-precision and accurate measurement of the tilt angle of the measurement position.

[0070] S4. Construct a functional model of the peak position and tilt angle in two directions through polynomial fitting.

[0071] A total of N groups of samples were collected, and the inclination angles of each group of samples in two directions were 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 (2):

[0072]

[0073] Among them, a0, a1, a2, a3, a4, a5, b0, b1, b2, b3, b4, b5 are constants to be determined;

[0074] 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;

[0075] To minimize E1, Where j = 0, 1, ..., 5, we can get formula (3):

[0076]

[0077] Solving this system of equations gives a0, a1, a2, a3, a4, a5;

[0078] To minimize E2, Where j = 0, 1, ..., 5, we can get formula (4):

[0079]

[0080] Solving this system of equations gives b0, b1, b2, b3, b4, b5;

[0081] Substitute the above solution into formula (2) to obtain the function model of the peak position and the tilt angle.

[0082] In the embodiment of the present invention, a binary quadratic polynomial least squares fitting method is used to construct a function model of the peak position and the tilt angle. A binary cubic polynomial least squares fitting method can also be used to construct a function model of the peak position and the tilt angle. The higher the degree of the fitting function, the higher the accuracy. The selection can be made based on actual conditions, and the embodiment of the present invention is not limited to this.

[0083] S5. Replace the plane reflector with the object to be measured 5, turn on the laser light source 1, drive the focusing lens 3 to move through the transmission component, so that the laser beam is focused on the point to be measured on the surface of the object to be measured 5, and collect the light spot image on the area array detector 14 corresponding to the focusing, the light signal intensity signals of the pre-focus photoelectric detector 10 and the post-focus photoelectric detector 13 respectively.

[0084] S6, using the collected spot image, repeat steps S2 and S3. That is, the surface of the object 5 to be tested is calculated by formula (1) to obtain the The peak position and Peak position and will The relationship function formula (2) between the tilt angle and the peak position in step S4 is brought into play, and the tilt angle of the point to be measured on the surface of the object to be measured 5 is obtained according to the function model.

[0085] The differential confocal signal curve is obtained by using the collected light signal intensity signals of the pre-focus photodetector 10 and the post-focus photodetector 13, and the displacement value of the focusing lens 3 corresponding to the zero-crossing point position of the differential confocal signal curve is measured by an interferometer to obtain the position information of the surface of the object 5 to be measured.

[0086] The focusing lens 3 is driven to move by the transmission assembly to collect the light signal intensities of the pre-focus photoelectric detector 10 and the post-focus photoelectric detector 13 respectively.

[0087] like Figure 1 As shown, the pre-focus measuring beam passes through the pre-focus focusing lens 8 and is incident on f f -u m A pre-focus pinhole 9 with a diameter of D 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. f is the focal length of the focusing lens 8 before focusing, u m is the defocus amount. After the post-focus measuring beam passes through the post-focus focusing lens 11, it is incident on the b +u m A post-focus pinhole 12 with a diameter of D 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. b is the focal length of the post-focusing lens 11, u m The focusing lens 3 moves under the drive of the transmission assembly, and the position of the focusing lens 3 is recorded as u by the interferometer, so that the measurement position on the object to be measured 5 moves from the front focus position of the focusing lens 3 to the back focus position, and the front focus photoelectric detector 10 and the back focus photoelectric detector 13 record the light intensity change, which are recorded as I(u, -u m ) and I(u, +u m ).

[0088] 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 ). Will I(u,-u m ) and I(u, +u m ) minus, such as Figure 5 As shown, the differential confocal signal curve FES is obtained, FES = I (u, -u m )-I(u,+u m ).

[0089] The displacement value of the focusing lens 3 corresponding to the zero-crossing position of the differential confocal signal curve is measured by an interferometer, thereby obtaining the position information of the point to be measured on the surface of the object to be measured 5.

[0090] By using the principle that the absolute zero point of the axial light intensity response of the differential confocal signal curve accurately corresponds to the focus of the test point, the zero point of the FES curve corresponds to the displacement reading of the focusing lens 3 measured by the interferometer, thereby obtaining the distance information of the test point on the surface of the object 5 to be tested.

[0091] The technical solution of the embodiment of the present invention combines angle measurement and position measurement to simultaneously obtain the surface information and surface inclination information of the object 5 to be measured, that is, it simultaneously measures the object 5 to be measured once and obtains the distance measurement position information and inclination angle information.

[0092] The differential confocal measurement method provided in the embodiment of the present invention extracts the peak position accurately and quickly, and constructs a function model of the peak position and the tilt angle in combination with the extracted peak position. n -P n-1 | can be corrected while extracting the peak value, thereby improving the peak extraction accuracy. Even if the collected spot image is not an approximate Gaussian distribution, the peak position can still be accurately obtained, thereby achieving high-precision and accurate measurement of the tilt angle of the measurement position. The differential confocal measurement method provided in the embodiment of the present invention realizes the distance measurement of the test point of the object 5 to be tested by the cooperation of the differential confocal component. The linearity and sensitivity near the zero crossing point are the best, so the distance information can be accurately obtained, and the distance measurement of the differential confocal component further improves the sensitivity and anti-interference ability of the positioning, thereby achieving the acquisition of the tilt angle information of the object 5 to be tested while performing differential confocal distance measurement, and achieving higher accuracy in optical morphology measurement, especially in the identification of tiny surface defects.

[0093] 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.

[0094] 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.

[0095] 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 differential confocal measurement method, characterized in that: The measurement is realized based on the differential confocal measurement system. The differential confocal measurement system comprises 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 which are sequentially arranged 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 transmission assembly is fixedly connected to the focusing lens, and the transmission assembly controls 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. A part of the light beam is reflected as an angle measurement beam and is incident on the area array detector, and another part is transmitted as a position measurement beam and is incident on the third beam splitter for splitting. A part of the light beam is reflected 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 is incident on the pre-focus photoelectric detector; another part of the light beam is transmitted 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 is incident on the post-focus photoelectric detector; The differential confocal measurement method comprises the following steps: S1, placing a plane reflector at the position of the object to be measured, turning on the laser light source, changing the tilt angle of the plane reflector, and collecting the light spot images on the area array detector corresponding to different tilt angles; S2, integrating the light intensity in the horizontal and vertical directions of each collected light spot image respectively to obtain a corresponding one-dimensional sequence; S3, acquiring the positions of the peaks in the corresponding one-dimensional single-peak signal sequences in the horizontal and vertical directions according to the corresponding one-dimensional sequence; S4, constructing a function model of the peak position and tilt angle in two directions by polynomial fitting; S5, replacing the plane reflector with the object to be measured, turning on the laser light source, driving the focusing lens to move through the transmission assembly, focusing the laser beam on the point to be measured on the surface of the object to be measured, and collecting the spot image on the area array detector corresponding to the focusing, the light signal intensity signals of the pre-focus photoelectric detector and the post-focus photoelectric detector respectively; S6, using the collected spot image, repeating steps S2 and S3 to obtain the peak position of the point to be measured on the surface of the object to be measured, and obtaining the inclination angle of the point to be measured on the surface of the object to be measured according to the function model; The differential confocal signal curve is obtained by using the collected light signal intensity signals of the pre-focus photodetector and the post-focus photodetector, and the focusing lens displacement value corresponding to the zero-crossing point position of the differential confocal signal curve is measured by the interferometer to obtain the position information of the test point on the surface of the object to be measured.

2. The differential confocal measurement method according to claim 1, characterized in that: The calculation method of the peak positions in the one-dimensional single-peak signal sequences in two directions in step S3 is the same, and the specific calculation method is as follows: The peak position is calculated according to formula (1): Among them, P n is the position of the peak in the one-dimensional single-peak signal sequence, n is the number of times the spot image is collected, and h is half of the half-peak width in the one-dimensional single-peak signal sequence.

3. The differential confocal measurement method according to claim 2, characterized in that: Calculate P using formula (1) n and P n-1 When |P n -P n-1 |≤0.1, the currently obtained P n The value is the location of the peak.

4. The differential confocal measurement method according to claim 1, characterized in that: In step S4, the specific method is as follows: A total of N groups of samples were collected, and the inclination angles in two directions of each group of samples were 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, which is expressed as formula (2): Among them, a0, a1, a2, a3, a4, a5, b0, b1, b2, b3, b4, b5 are constants to be determined; 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; To minimize E1, Where j = 0, 1, ..., 5, we can get formula (3): Solving this system of equations gives a0, a1, a2, a3, a4, a5; To minimize E2, Where j = 0, 1, ..., 5, we can get formula (4): Solving this system of equations gives b0, b1, b2, b3, b4, b5; Substitute the above solution into formula (2) to obtain the function model of the peak position and the tilt angle.

Images