A differential confocal measurement method based on differential compensation

Abstract

The present invention provides a differential confocal measurement method based on differential compensation, which belongs to the field of optical detection technology. The differential confocal measurement method based on differential compensation constructs a function model between the voltage difference and the tilt angle of a first four-quadrant detector and a second four-quadrant detector, uses two four-quadrant detectors and a differential calculation method to obtain the tilt angle information of the measurement point of the object being measured. The error compensation capability of the existing differential confocal microscope is improved, the deviation in the optical system is eliminated, and the high precision and stability of the angle measurement results of the object being measured are ensured. The use of optical elements and detectors is reduced, the complexity of the measurement method is reduced, the error sources are reduced, and the stability and precision of the measurement method are improved.

Description

Technical Field

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

[0002] Differential confocal microscopy, a technique that utilizes the principles of confocal microscopy, can improve image contrast and resolution, particularly when imaging complex three-dimensional structures. Combining the advantages of traditional confocal microscopy and differential imaging, it can simultaneously acquire both height information and surface topography of the object being measured, thereby improving measurement accuracy and spatial resolution. Differential confocal microscopy utilizes a unique optical system consisting of two or more detection channels that measure different signals from the same object. By comparing the differences in signals from different focal points, differential confocal microscopy can eliminate background noise from surface scattering, improving image quality. A key advantage is its ability to simultaneously acquire optical information at different depths, reducing the effects of focal blur or surface scattering common in traditional confocal microscopy. Therefore, differential confocal microscopy holds broad application prospects for the precise measurement or observation of tiny structures.

[0003] The method of measuring distance and angle simultaneously with differential confocal microscopy in the prior art is to add a beam splitter and a two-dimensional lateral position detector to the parallel optical path before the return light beam reaches the focusing lens to measure the lateral movement of the parallel light beam. Therefore, the existing differential confocal microscopy technology has some shortcomings when measuring angles, including the inability to effectively compensate for errors in the optical system, such as differential pinhole offset and optical path asymmetry, resulting in a decrease in measurement accuracy. In particular, in small angle changes or dynamic scenes, the error will significantly affect the angle measurement results. In addition, the measurement accuracy of the prior art is limited, and it can usually only provide relatively rough angle measurements, which is difficult to meet high-precision requirements, especially for the measurement of asymmetric surfaces or small objects. The prior art also requires the introduction of multiple optical elements and detectors, which not only increases the complexity of the system, but also introduces other error sources, affecting the stability and accuracy of the measurement system. At the same time, the dynamic response of the measurement system of the prior art is slow, and it cannot effectively cope with rapidly changing measurement requirements, limiting its application in dynamic scenes. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects of the prior art and propose a differential confocal measurement method based on differential compensation.

[0005] To achieve the above objectives, the present invention adopts the following specific technical solutions:

[0006] The present invention provides a differential confocal measurement method based on differential compensation, which performs measurement based on a four-quadrant detector. The differential confocal measurement method comprises the following steps:

[0007] S1. Place a standard component in a differential confocal measurement system, rotate the standard component according to a preset tilt amount, and collect voltage values ​​of each quadrant of the first four-quadrant detector and the second four-quadrant detector at different tilt angles;

[0008] S2. constructing a function model according to the voltage values ​​and different tilt angles of each quadrant;

[0009] S3. Calculate the differential compensation coefficient and the differential pinhole error term in the function model;

[0010] S4. Placing the object under test in a differential confocal measurement system, collecting voltage values ​​of the measuring point of the object under test in each quadrant of the first four-quadrant detector and the second four-quadrant detector, and obtaining tilt angle information of the measuring point of the object under test according to the function model.

[0011] Furthermore, step S2 is specifically as follows:

[0012] S201, respectively obtaining voltage differences of the first four-quadrant detector and the second four-quadrant detector in the X-axis direction and the Y-axis direction;

[0013] S202 : Construct a function model between the voltage difference in the X-axis direction and the Y-axis direction and different tilt angles.

[0014] Furthermore, the method for calculating and obtaining the differential compensation coefficient and the differential pinhole error term in step S3 is specifically: least square method.

[0015] Furthermore, the calculation formula for obtaining the tilt angle information of the measuring point in step S4 is:

[0016] ;

[0017] ;

[0018] in, represent the differential compensation coefficients respectively; Respectively represent the tilt angles of the measuring point of the object under test in the X-axis direction and the Y-axis direction; Respectively represent the voltage differences in the X-axis direction and the Y-axis direction of the measuring point of the object under test on the first four-quadrant detector; They respectively represent the voltage differences of the measuring point of the object under test in the X-axis direction and the Y-axis direction on the second four-quadrant detector.

[0019] The present invention can achieve the following technical effects:

[0020] 1. The differential confocal measurement method based on differential compensation provided by the present invention improves the error compensation capability of the differential confocal microscope by using two four-quadrant detectors and a differential calculation method, thereby eliminating the deviation in the optical system and ensuring high precision and stability of the angle measurement results of the object being measured.

[0021] 2. The differential confocal measurement method based on differential compensation provided by the present invention can provide higher measurement accuracy, especially in the measurement of small angle changes and asymmetric surfaces, with higher resolution.

[0022] 3. The differential confocal measurement method based on differential compensation provided by the present invention can simplify the structure of the measurement system, reduce the use of optical elements and detectors, reduce the complexity of the measurement system, reduce error sources, and improve the stability and accuracy of the measurement system.

[0023] 4. The differential confocal measurement method based on differential compensation provided by the present invention can improve the dynamic response capability of the measurement system, quickly respond to changes in the spot position, adapt to the needs of real-time monitoring and high-speed measurement, and enhance the application capability of the measurement system in dynamic environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 2 is a schematic structural diagram of a differential confocal measurement system according to a differential confocal measurement method based on differential compensation according to an embodiment of the present invention;

[0025] Figure 2 is a schematic flow chart of a differential confocal measurement method based on differential compensation according to an embodiment of the present invention;

[0026] Figure 3 3 is a schematic diagram showing a variation trend of the tilt angle error of the object under test as a function of the actual angle in a differential confocal measurement method based on differential compensation according to an embodiment of the present invention.

[0027] Reference numerals include:

[0028] 1-laser light source, 2-collimating mirror, 3-first beam splitter, 4-objective lens, 5-measured object, 6-second beam splitter, 7-first imaging lens, 8-first differential pinhole, 9-first four-quadrant detector, 10-second imaging lens, 11-second differential pinhole, 12-second four-quadrant detector. DETAILED DESCRIPTION

[0029] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, identical modules are denoted by identical reference numerals. In the case of identical reference numerals, their names and functions are also identical. Therefore, their detailed description will not be repeated.

[0030] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be 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.

[0031] The following combination Figure 1 、 Figure 2 and Figure 3 The specific working mode of the differential confocal measurement method based on differential compensation according to an embodiment of the present invention is described in detail.

[0032] The embodiment of the present invention provides a differential confocal measurement method based on differential compensation, which performs measurement based on two four-quadrant detectors. To clearly and unambiguously describe the technical solution provided by the embodiment of the present invention, the solution of the present invention is now described in conjunction with an existing differential confocal measurement system. The differential confocal measurement method based on differential compensation provided by the embodiment of the present invention can be applied to different differential confocal measurement systems in the prior art. Therefore, the differential confocal measurement system can have other variations. The differential confocal measurement system in the embodiment of the present invention is only used for explanation and does not constitute a limitation of the technical solution of the present invention. Any differential confocal measurement system in the prior art can be used and can be selected according to actual conditions.

[0033] like Figure 1As shown, the differential confocal measurement system in the embodiment of the present invention includes a laser light source 1 capable of emitting a monochromatic image with a good Gaussian distribution, a collimator 2, a first beam splitter 3, an objective lens 4, a driver for the objective lens 4, a second beam splitter 6, a first imaging lens 7, a first differential pinhole 8, a first four-quadrant detector 9, a second imaging lens 10, a second differential pinhole 11, and a second four-quadrant detector 12, which are arranged in sequence along the optical path. The measuring beam emitted by the laser light source 1 is collimated into a parallel measuring beam by the collimator 2. The parallel measuring beam is transmitted through the first beam splitter 3 and the objective lens 4 to the object under test 5. The objective lens driver drives the objective lens 4 to move axially perpendicular to the object under test 5 along the optical axis to perform scanning measurement. The beam reflected by the object under test 5 is incident on the first beam splitter 3, and the beam reflected by the first beam splitter 3 is incident on the second beam splitter 6. The reflected light beam split by the second beam splitter 6 is a pre-focus light path, which is transmitted through the first imaging lens 7 and the first differential pinhole 8 in sequence to the first four-quadrant detector 9; the transmitted light beam split by the second beam splitter 6 is a post-focus light path, which is transmitted through the second imaging lens 10 and the second differential pinhole 11 in sequence to the second four-quadrant detector 12. In an embodiment of the present invention, the parameters of the first imaging lens 7 and the second imaging lens 10 are the same. Among them, the first imaging lens 7, the first differential pinhole 8, and the first four-quadrant detector 9 are a pre-focus light path, the first differential pinhole 8 is placed at a fixed distance before the focus of the first imaging lens 7, and the first four-quadrant detector 9 is closely arranged behind the first differential pinhole 8. The second imaging lens 10, the second differential pinhole 11, and the second four-quadrant detector 12 are a post-focus light path, the second differential pinhole 11 is placed at a fixed distance after the focus of the second imaging lens 10, and the second four-quadrant detector 12 is closely arranged behind the second differential pinhole 11. An embodiment of the present invention Figure 1 In the figure, the objective lens driver is not shown, and any objective lens driver in the prior art can be used, which is not limited in the embodiment of the present invention.

[0034] In an embodiment of the present invention, the first four-quadrant detector 9 and the second four-quadrant detector 12 in the differential confocal measurement system can provide two types of output information: the first is the position offset. The four-quadrant detector can accurately measure the lateral offset of the light spot of the light beam, that is, the offset of the light beam in the X-axis direction and the Y-axis direction. The second is the light intensity distribution. The four-quadrant detector can also provide light intensity distribution information. According to the intensity change of the light spot of the measurement beam, combined with the position offset information, the tilt angle of the object under test 5 can be accurately calculated. Two four-quadrant detectors are used to replace the photodiodes in the differential confocal measurement system of the prior art. While retaining the same energy transmission rate, it can also output the two-dimensional position information of the light spot of the measurement beam. The differential confocal measurement method based on differential compensation provided in the embodiment of the present invention can improve the dynamic response capability of the differential confocal measurement system, quickly respond to changes in the light spot position, adapt to the needs of real-time monitoring and high-speed measurement, and enhance the application capability of the differential confocal measurement system in dynamic environments.

[0035] In the embodiment of the present invention, Figure 2 As shown, the differential confocal measurement method based on differential compensation includes the following steps:

[0036] S1. Place a plane mirror in a differential confocal measurement system, rotate the plane mirror according to a preset tilt amount, and collect voltage values ​​of each quadrant of the first four-quadrant detector 9 and the second four-quadrant detector 12 at different tilt angles.

[0037] In the embodiment of the present invention, a plane mirror is used as a standard part, the plane mirror is placed at the position of the object to be measured 5, the tilt angle of the plane mirror is changed according to the preset tilt amount, and the voltage values ​​of each quadrant of the first four-quadrant detector 9 and the second four-quadrant detector 12 corresponding to the measuring point of the plane mirror at different tilt angles are collected. The smaller the preset tilt amount, that is, the more voltage values ​​corresponding to the tilt angles are collected as much as possible, the more accurate the function model constructed subsequently, that is, the higher the resolution of the measured tilt angle. However, the amount of calculation will also increase, so the value of the tilt amount can be set according to the actual situation to balance the relationship between the resolution and the measurement rate, which is not limited by the present invention. In the embodiment of the present invention, a precise rotary displacement stage is used to drive the plane mirror to achieve precise tilting at different angles and adjust the tilt angle of the plane mirror. , And record the output voltage of the first four-quadrant detector 9 and the second four-quadrant detector 12 under each set of tilt angles , , , and , , , .in, 、 They represent the tilt angle of the plane reflector in the X-axis direction and the tilt angle of the Y-axis direction at any tilt angle respectively; i represents any tilt angle; 、 Respectively represent the output voltage values ​​of the first quadrant, the second quadrant, the third quadrant and the fourth quadrant of the first four-quadrant detector 9; 、 They respectively represent the output voltage values ​​of the first quadrant, the second quadrant, the third quadrant and the fourth quadrant of the second four-quadrant detector 12.

[0038] S2. Based on the collected voltage values ​​of each quadrant, a function model of the output voltage value of each quadrant and different tilt angles is constructed.

[0039] S201 , respectively obtaining voltage differences between the first four-quadrant detector 9 and the second four-quadrant detector 12 in the X-axis direction and the Y-axis direction.

[0040] - ;

[0041] - ;

[0042] - ;

[0043] - ;

[0044] in, Respectively represent the voltage difference of the first four-quadrant detector 9 in the X-axis direction and the Y-axis direction; They respectively represent the voltage differences of the second four-quadrant detector 12 in the X-axis direction and the Y-axis direction.

[0045] S202 : Construct a function model between the voltage difference in the X-axis direction and the Y-axis direction and different tilt angles.

[0046] In the embodiment of the present invention, the output voltage values ​​of the first four-quadrant detector 9 and the second four-quadrant detector 12 depend on the tilt angle of the plane reflector and the offset of the first differential pinhole 8 and the second differential pinhole 11. By fitting the known tilt angle 、 The relationship between the output voltage of the four-quadrant detector and the tilt angle of the plane reflector in each set of experimental data can be established as follows:

[0047] ;

[0048] ;

[0049] ;

[0050] ;

[0051] in, They represent the differential compensation coefficients respectively; They respectively represent the error term of the first differential pinhole 8 in the X-axis direction, the error term of the first differential pinhole 8 in the Y-axis direction, the error term of the second differential pinhole 11 in the X-axis direction, and the error term of the second differential pinhole 11 in the Y-axis direction; represent the tilt angles of the plane mirror in the X-axis and Y-axis directions respectively.

[0052] In the differential confocal measurement system of the prior art, the offset of the differential pinhole, that is, the first differential pinhole 8 and the second differential pinhole 11 in the embodiment of the present invention, will have lateral and axial offsets, which will affect the results of the differential confocal measurement system. In particular, when measuring angles, the two-dimensional lateral offset of the differential pinhole has a greater impact on the accuracy of the angle measurement. The two-dimensional lateral offset of the differential pinhole causes the change in the light spot received by the detector to not completely correspond to the actual tilt angle of the object 5 to be measured. The compensation strategy of the technical solution of the present invention obtains the differential compensation coefficient by differentially calculating the output signals of the two four-quadrant detectors, which can effectively eliminate the error caused by the differential pinhole offset, improve the error compensation capability of the differential confocal microscope, thereby eliminating the deviation in the optical system and ensuring the high precision and stability of the angle measurement results of the object 5 to be measured. In particular, it has higher resolution in the measurement of small angle changes and asymmetric surfaces. In addition, the differential confocal measurement system used in the differential confocal measurement method based on differential compensation provided by the embodiment of the present invention has a simplified system structure, reduces the use of optical elements and detectors, reduces the complexity of the measurement system, reduces the error source, and improves the stability and accuracy of the measurement system.

[0053] S3. In the calculation function model: differential compensation coefficient and differential pinhole error term.

[0054] In the embodiment of the present invention, the tilt angle in the function model 、 Since the voltage differences are known, the differential compensation coefficient can be solved by the least squares method. and the differential pinhole error term .

[0055] S4. Place the object 5 under test in the differential confocal measurement system, collect the voltage values ​​of the measurement point of the object 5 in each quadrant of the first four-quadrant detector 9 and the second four-quadrant detector 12, and obtain the tilt angle information of the measurement point of the object 5 according to the function model. After obtaining the differential compensation coefficient and the differential pinhole error term, the voltage difference in the X-axis direction and the Y-axis direction can be calculated based on the collected voltage values ​​of the first four-quadrant detector 9 and the second four-quadrant detector 12, and then the actual tilt angle of the measurement point of the object 5 can be calculated. The calculation formula for obtaining the tilt angle information of the measurement point in step S4 is:

[0056] ;

[0057] ;

[0058] in, Respectively represent the tilt angles of the measuring point of the object 5 in the X-axis and Y-axis directions; respectively represent the voltage differences of the first four-quadrant detector 9 in the X-axis and Y-axis directions at the measuring points of the measured object 5; Respectively represent the voltage differences of the second four-quadrant detector 12 in the X-axis direction and the Y-axis direction at the measurement point of the object under test 5.

[0059] An embodiment of the present invention provides a differential confocal measurement method based on differential compensation. This method utilizes the voltage output values ​​of two four-quadrant detectors at different known tilt angles using a standard component, combined with a differential calculation method, to reversely derive differential compensation coefficients to eliminate optical system errors and improve the accuracy of tilt angle measurement. This technical solution eliminates the need for complex optical structures, reduces the complexity and environmental sensitivity of the measurement system, and eliminates inconsistencies in the outputs of the two detectors caused by pinhole offset in the differential confocal measurement system. By obtaining differential compensation coefficients, it compensates for errors caused by two-dimensional lateral offset of the pinhole, resulting in a more accurate calculated tilt angle.

[0060] The embodiment of the present invention verifies the effectiveness of the technical solution of the present invention through measurement experiments on standard parts. In simulating the actual differential confocal measurement system, due to the detection error caused by the pinhole installation error, a typical error scenario was constructed by placing pinholes with different lateral offsets in front of the two four-quadrant detectors. By setting a set of known two-dimensional tilt angles: from -5° to 5° in the X-axis direction and from -3° to 3° in the Y-axis direction, the change in the true posture of the object 5 under ideal conditions is simulated. In the embodiment of the present invention, a plane mirror is placed in the differential confocal measurement system and the least squares method is used to calculate the error term of the first differential pinhole 8 in the X-axis direction, the error term of the first differential pinhole 8 in the Y-axis direction, the error term of the second differential pinhole 11 in the X-axis direction, and the error term of the second differential pinhole 11 in the Y-axis direction. Differential pinhole error term is 0.10, is 0.05, is 0.15, 0.07. Differential compensation coefficient is 1.1, is 1.05, is 1.2, The value is 1.15. Object 5 was placed in a differential confocal measurement system, and the tilt angles of object 5 along the X and Y axes were calculated. The deviations between the measured results and the true values ​​were calculated to obtain the measurement error. This indicates that the error between the measured values ​​and the true values ​​obtained using the differential confocal measurement method based on differential compensation provided by the present invention is very small, ensuring high-precision angle measurement results for object 5. See Table 1 for specific values.

[0061] Table 1 Experimental data

[0062]

[0063] In the embodiment of the present invention, the trend of the tilt angle error changing with the actual angle is as follows: Figure 3 As shown. It can be seen from this that the differential confocal measurement method based on differential compensation provided by the embodiment of the present invention can ensure high precision of the angle measurement result of the object under test 5. The differential confocal measurement method based on differential compensation provided by the embodiment of the present invention calculates the tilt angle of the object under test 5 by the difference between the voltage signals output by the first four-quadrant detector 9 and the second four-quadrant detector 12, avoids the situation in which the detector output in the prior art is inconsistent due to the offset of the pinhole position, compensates and eliminates the influence of the lateral offset of the pinhole position on the angle measurement of the object under test 5, and ensures the accuracy of the tilt angle measurement of the object under test 5.

[0064] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean 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 can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0065] Although the embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art may make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

[0066] The above specific embodiments of the present invention do not constitute a limitation on the scope of protection 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 scope of protection of the claims of the present invention.

Claims

1. A differential confocal measurement method based on differential compensation, characterized in that: The differential confocal measurement method is based on a four-quadrant detector and includes the following steps: S1. Place a standard component in a differential confocal measurement system, rotate the standard component according to a preset tilt amount, and collect voltage values ​​of each quadrant of the first four-quadrant detector and the second four-quadrant detector at different tilt angles; The first four-quadrant detector is arranged in the pre-focus optical path, and the second four-quadrant detector is arranged in the post-focus optical path; S2. constructing a function model according to the voltage values ​​and different tilt angles of each quadrant; S3. Calculate the differential compensation coefficient and the differential pinhole error term in the function model; S4, placing the object under test in a differential confocal measurement system, collecting voltage values ​​of the measuring point of the object under test in each quadrant of the first four-quadrant detector and the second four-quadrant detector, and obtaining tilt angle information of the measuring point of the object under test according to the function model; The calculation formula for obtaining the tilt angle information of the measuring point in step S4 is: Wherein, k1, k2, k3, k4 represent the differential compensation coefficients respectively; θ x ,θ y Respectively represent the tilt angles of the measuring point of the object under test in the X-axis direction and the Y-axis direction; Respectively represent the voltage differences in the X-axis direction and the Y-axis direction of the measuring point of the object under test on the first four-quadrant detector; They respectively represent the voltage differences of the measuring point of the object under test in the X-axis direction and the Y-axis direction on the second four-quadrant detector.

2. The differential confocal measurement method based on differential compensation according to claim 1, characterized in that: Step S2 is specifically as follows: S201, respectively obtaining voltage differences of the first four-quadrant detector and the second four-quadrant detector in the X-axis direction and the Y-axis direction; S202 : Construct a function model between the voltage difference in the X-axis direction and the Y-axis direction and different tilt angles.

3. The differential confocal measurement method based on differential compensation according to claim 2, characterized in that: The method for calculating and obtaining the differential compensation coefficient and the differential pinhole error term in step S3 is specifically: least square method.

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