Differential confocal measurement method based on differential compensation

Abstract

The invention provides a differential confocal measurement method based on differential compensation, and belongs to the technical field of optical detection. According to the differential confocal measurement method based on differential compensation, a function model between a voltage difference value and an inclination angle of the first four-quadrant detector and the second four-quadrant detector is constructed, and the inclination angle information of a measurement point of a measured object is obtained by using the two four-quadrant detectors and a differential calculation method. The error compensation capability of the existing differential confocal microscope is improved, the deviation in an optical system is eliminated, and the high precision and stability of the angle measurement result of the measured object are ensured. The use of optical elements and detectors is reduced, the complexity of the measurement method is reduced, 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 particularly relates to a differential confocal measurement method based on differential compensation. Background Art

[0002] Differential confocal microscopy technology is a technology that utilizes the principle of confocal microscopy, which can improve the contrast and resolution of images, especially for imaging in complex three-dimensional structures. It combines the advantages of traditional confocal microscopy and differential imaging, and can simultaneously obtain the height information and surface topography of the object to be measured, thereby improving the measurement accuracy and spatial resolution ability. Differential confocal microscopy uses a unique optical system, which includes two or more detection channels that measure different signals of the same object to be measured. By comparing the signal differences from different focal points, differential confocal microscopy can eliminate the background noise scattered from the surface of the object to be measured and improve the image quality. Its important advantage is that it can simultaneously obtain optical information at different depths, reducing the influence of focus blur or surface scattering commonly found in traditional confocal microscopy. Therefore, differential confocal microscopy has broad application prospects in the precise measurement or observation of microstructures.

[0003] In the prior art, the method of measuring the angle while measuring the distance in a differential confocal microscope is to add a beam splitter and a two-dimensional lateral position detector on the parallel optical path before the return beam reaches the focusing lens to measure the lateral movement of the parallel beam. Therefore, there are some drawbacks in the existing differential confocal microscopy technology when measuring the angle, including the inability to effectively compensate for errors in optical system errors, such as differential pinhole offset and optical path asymmetry, resulting in a decrease in measurement accuracy. Especially in the case of small angle changes or dynamic scenes, the error will significantly affect the angle measurement results. In addition, the measurement accuracy of the existing technology is limited, usually only providing relatively rough angle measurements, which are difficult to meet high-precision requirements, especially for the measurement of asymmetric surfaces or small objects. The existing technology also needs to introduce 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 measurement system of the existing technology has a slow dynamic response and cannot effectively respond to 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 purpose, the present invention adopts the following specific technical solutions:

[0006] The present invention provides a differential confocal measurement method based on differential compensation, which is measured based on a quadrant detector. The differential confocal measurement method includes the following steps:

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

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

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

[0010] S4. Place the object to be measured in the differential confocal measurement system, collect the voltage values of each quadrant of the measurement point of the object to be measured on the first quadrant detector and the second quadrant detector, and obtain the inclination angle information of the measurement point of the object to be measured according to the function model.

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

[0012] S201. Respectively obtain the voltage differences of the first quadrant detector and the second quadrant detector in the X-axis direction and the Y-axis direction;

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

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

[0015] Further, the calculation formula for obtaining the inclination angle information of the measurement point in step S4 is:

[0016] ;

[0017] ;

[0018] Among them, respectively represent the differential compensation coefficient; respectively represent the inclination angles of the measurement point of the object to be measured in the X-axis direction and the Y-axis direction; respectively represent the voltage differences of the measurement point of the object to be measured on the first quadrant detector in the X-axis direction and the Y-axis direction; respectively represent the voltage differences of the measurement point of the object to be measured on the second quadrant detector in the X-axis direction and the Y-axis direction.

[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 uses two quadrant detectors and a differential calculation method to enhance the error compensation ability of the differential confocal microscope, thereby eliminating the deviation in the optical system and ensuring the high precision and stability of the measurement results of the angle of the object to be measured.

[0021] 2. The differential confocal measurement method based on differential compensation provided by the present invention can provide higher measurement precision, 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 the error sources, and improve the stability and precision of the measurement system.

[0023] 4. The differential confocal measurement method based on differential compensation provided by the present invention can enhance the dynamic response ability of the measurement system, quickly respond to the change of the spot position, meet the needs of real-time monitoring and high-speed measurement, and enhance the application ability of the measurement system in a dynamic environment. Description of the Drawings

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

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

[0026] Figure 3 is a schematic diagram of the change trend of the tilt angle error of the object to be measured with respect to the true angle of the differential confocal measurement method based on differential compensation according to an embodiment of the present invention.

[0027] The reference numerals therein include:

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

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

[0030] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to 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 to the present invention.

[0031] The following will Figure 1 , Figure 2 and Figure 3 be used to describe in detail the specific working mode of the differential confocal measurement method based on differential compensation in the embodiments of the present invention.

[0032] The embodiments of the present invention provide a differential confocal measurement method based on differential compensation, which is measured based on two quadrant detectors. To clearly and explicitly describe the technical solutions provided by the embodiments of the present invention, the present invention will be described with reference to the existing differential confocal measurement system. The differential confocal measurement method based on differential compensation provided by the embodiments of the present invention can be applied to different differential confocal measurement systems in the prior art. Therefore, there may be other forms of changes in the differential confocal measurement system. The differential confocal measurement system in the embodiments of the present invention is only for explanation and does not constitute a limitation to the technical solutions of the present invention. Any differential confocal measurement system in the prior art can be selected according to the actual situation.

[0033] As Figure 1As shown in the figure, the differential confocal measurement system in the embodiment of the present invention includes a monochromatic laser light source 1 that can emit a good Gaussian distribution, a collimating mirror 2, a first beam splitter 3, an objective lens 4, an objective lens 4 driver, a second beam splitter 6, a first imaging lens 7, a first differential pinhole 8, a first quadrant detector 9, a second imaging lens 10, a second differential pinhole 11, and a second quadrant detector 12, which are arranged in sequence along the optical path. The measurement beam emitted by the laser light source 1 is collimated into a parallel measurement beam by the collimating mirror 2, and the parallel measurement beam is transmitted through the first beam splitter 3 and the objective lens 4 to the measured object 5. The objective lens driver drives the objective lens 4 to move perpendicular to the axis of the measured object 5 along the optical axis for scanning measurement. The beam reflected by the measured object 5 is incident on the first beam splitter 3, and the reflected beam by the first beam splitter 3 is incident on the second beam splitter 6. The reflected beam split by the second beam splitter 6 is the pre-focus optical path, which is transmitted through the first imaging lens 7 and the first differential pinhole 8 to the first quadrant detector 9 in sequence; the transmitted beam split by the second beam splitter 6 is the post-focus optical path, which is transmitted through the second imaging lens 10 and the second differential pinhole 11 to the second quadrant detector 12 in sequence. In the 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 quadrant detector 9 are the pre-focus optical path. The first differential pinhole 8 is placed at a fixed distance in front of the focus of the first imaging lens 7, and the first 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 quadrant detector 12 are the post-focus optical path. The second differential pinhole 11 is placed at a fixed distance behind the focus of the second imaging lens 10, and the second quadrant detector 12 is closely arranged behind the second differential pinhole 11. In the embodiment of the present invention Figure 1 the objective lens driver is not shown, and any objective lens driver in the prior art can be used. The embodiment of the present invention does not limit this.

[0034] In the embodiment of the present invention, the first quadrant detector 9 and the second quadrant detector 12 in the differential confocal measurement system can provide two kinds of output information: The first is the position offset. The quadrant detector can accurately measure the lateral offset of the light spot of the beam, that is, the offset of the measurement beam in the X-axis direction and the Y-axis direction. The second is the light intensity distribution. The quadrant detector can also provide the light intensity distribution information. According to the intensity change of the light spot of the measurement beam and combined with the position offset information, the tilt angle of the measured object 5 can be accurately calculated. Using two quadrant detectors replaces the photodiode in the differential confocal measurement system of the prior art. While retaining the same transmission energy 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 by the embodiment of the present invention can improve the dynamic response ability of the differential confocal measurement system, quickly respond to the change of the light spot position, meet the requirements of real-time monitoring and high-speed measurement, and enhance the application ability of the differential confocal measurement system in a dynamic environment.

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

[0036] S1. Place a plane mirror in the differential confocal measurement system, rotate the plane mirror according to a preset inclination amount, and collect the voltage values of each quadrant of the first quadrant detector 9 and the second quadrant detector 12 at different inclination 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, and the inclination angle of the plane mirror is changed according to a preset inclination amount. The voltage values of each quadrant of the first quadrant detector 9 and the second quadrant detector 12 corresponding to the measurement points of the plane mirror at different inclination angles are collected. The smaller the preset inclination amount, that is, the more voltage values corresponding to different inclination angles are collected as much as possible, the more accurate the function model constructed subsequently, that is, the higher the resolution of the measured inclination angle. However, the calculation amount will also increase. Therefore, the value of the inclination amount can be set according to the actual situation to balance the relationship between the resolution and the measurement rate. The present invention does not limit this. In the embodiment of the present invention, a precise rotary displacement stage is used to drive and control the plane mirror to achieve precise inclination at different angles, and the inclination angle of the plane mirror is adjusted , and record the output voltages of the first quadrant detector 9 and the second quadrant detector 12 at each group of inclination angles , , , and , , , . Among them, 、 respectively represent the inclination angle of the plane mirror in the X-axis direction and the inclination angle in the Y-axis direction at any inclination angle; i represents any inclination angle; 、 respectively represent the output voltage values of the first quadrant, the second quadrant, the third quadrant and the fourth quadrant of the first quadrant detector 9; 、 respectively represent the output voltage values of the first quadrant, the second quadrant, the third quadrant and the fourth quadrant of the second quadrant detector 12.

[0038] S2. According to the voltage values of each collected quadrant, construct a function model of the output voltage value of each quadrant and different inclination angles.

[0039] S201. Obtain the voltage differences of the first quadrant detector 9 and the second quadrant detector 12 in the X-axis direction and the Y-axis direction respectively.

[0040] - ;

[0041] - ;

[0042] - ;

[0043] - ;

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

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

[0046] In the embodiments of the present invention, the output voltage values of the first quadrant detector 9 and the second quadrant detector 12 depend on the tilt angle of the plane mirror and the offsets of the first differential pinhole 8 and the second differential pinhole 11. By fitting the relationship between the known tilt angles , and the voltage differences, the differential compensation coefficients and the differential pinhole error terms are calculated. Specifically, for each set of experimental data, a linear function model can be established between the output voltage of the quadrant detector and the tilt angle of the plane mirror as follows:

[0047] ;

[0048] ;

[0049] ;

[0050] ;

[0051] Among them, respectively represent the differential compensation coefficients; 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; respectively represent the tilt angles of the plane mirror in the X-axis direction and the Y-axis direction.

[0052] In the differential confocal measurement system in the prior art, the offsets of the differential pinholes, namely the first differential pinhole 8 and the second differential pinhole 11 in the embodiments of the present invention, will have lateral and axial offsets, and these offsets will affect the results of the differential confocal measurement system. Especially during angle measurement, the two-dimensional lateral offset of the differential pinhole has a greater impact on the accuracy of angle measurement. The two-dimensional lateral offset of the differential pinhole causes the change of the light spot received by the detector not to exactly correspond to the tilt angle of the actual object to be measured 5. The compensation strategy of the technical solution of the present invention obtains the differential compensation coefficient through the differential calculation of the output signals of the two quadrant detectors, which can effectively eliminate the error caused by the offset of the differential pinhole, improve the error compensation ability of the differential confocal microscope, thereby eliminating the deviation in the optical system, and ensuring the high precision and stability of the angle measurement result of the object to be measured 5. Especially in the measurement of small angle changes and asymmetric surfaces, it has higher resolution. And the differential confocal measurement method based on differential compensation provided by the embodiments of the present invention uses a differential confocal measurement system with a simplified system structure, reduces the use of optical elements and detectors, reduces the complexity of the measurement system, reduces the error sources, and improves the stability and precision of the measurement system.

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

[0054] In the embodiments of the present invention, the tilt angle , and each voltage difference are known, and the differential compensation coefficient and the differential pinhole error term can be solved by the least squares method.

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

[0056] ;

[0057] ;

[0058] Wherein, respectively represent the tilt angles of the measurement points of the object to be measured 5 in the X-axis and Y-axis directions; respectively represent the voltage differences in the X-axis and Y-axis directions of the first quadrant detector 9 at the measurement points of the object 5 to be measured; respectively represent the voltage differences in the X-axis direction and Y-axis direction of the second quadrant detector 12 at the measurement points of the object 5 to be measured.

[0059] A differential confocal measurement method based on differential compensation provided by an embodiment of the present invention uses the output values of the voltages of two quadrant detectors of a standard part at known different tilt angles, and combines a differential calculation method to inversely deduce a differential compensation coefficient to eliminate optical system errors and improve the accuracy of tilt angle measurement. The technical solution of the present invention does not require a complex optical structure, reduces the complexity of the measurement system and environmental sensitivity, eliminates the inconsistency of the outputs of two detectors caused by pinhole offset in the differential confocal measurement system, compensates for the errors caused by two-dimensional lateral offset of the pinhole by obtaining the differential compensation coefficient, and makes the finally calculated tilt angle more accurate.

[0060] An embodiment of the present invention verifies the effectiveness of the technical solution of the present invention through a measurement experiment on a standard part. In a simulated actual differential confocal measurement system, due to the detection error caused by the pinhole installation error, a typical error scenario is constructed by respectively pre-setting pinholes with different lateral offsets for two quadrant detectors. By setting a group 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 of the true posture of the object 5 to be measured under ideal conditions is simulated. In an embodiment of the present invention, a plane mirror is placed in the differential confocal measurement system and calculated by the least square method, 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, is 0.07. Differential compensation coefficient is 1.1, is 1.05, is 1.2, is 1.15. The object 5 to be measured is placed in the differential confocal measurement system, the tilt angles of the object 5 in the X-axis and Y-axis directions are calculated, and the deviation between the respective measurement results and the true values is calculated to obtain the numerical value of the measurement error. It can be seen that the error between the measurement value obtained by the differential confocal measurement method based on differential compensation provided by the present invention and the true value is very small, ensuring the high precision of the angle measurement result of the object 5 to be measured. Specific numerical values are shown in Table 1.

[0061] Table 1 Experimental data

[0062]

[0063] In the embodiments of the present invention, the trend of the tilt angle error varying with the true angle is as Figure 3 shown. It can be seen from this that a differential compensation-based differential confocal measurement method provided by an embodiment of the present invention can ensure high-precision measurement results of the angle of the object to be measured 5. The differential compensation-based differential confocal measurement method provided by the embodiment of the present invention calculates the tilt angle of the object to be measured 5 through the difference between the voltage signals output by the first quadrant detector 9 and the second quadrant detector 12, avoiding the inconsistent output of the detector in the prior art caused by the offset of the pinhole position, compensating and eliminating the influence of the lateral offset of the pinhole position on the angle measurement of the object to be measured 5, and ensuring the accuracy of the tilt angle measurement of the object to be measured 5.

[0064] In the description of this specification, the descriptions referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection 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 a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

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

[0066] The above specific implementation manners of the present invention do not constitute a limitation to the protection scope of the present invention. Any other corresponding changes and deformations made according to 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 based on differential compensation, characterized in that Measurement is performed based on a quadrant detector. The differential confocal measurement method includes the following steps: S1. Place a standard part in the differential confocal measurement system, rotate the standard part according to a preset inclination amount, and collect the voltage values of each quadrant of the first quadrant detector and the second quadrant detector at different inclination angles respectively; S2. Construct a function model according to the voltage values of each quadrant at different inclination angles; S3. Calculate the differential compensation coefficient and the differential pinhole error term in the function model; S4. Place the measured object in the differential confocal measurement system, collect the voltage values of each quadrant of the measurement point of the measured object on the first quadrant detector and the second quadrant detector, and obtain the inclination angle information of the measurement point of the measured object according to the function model.

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

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

4. The differential confocal measurement method based on differential compensation according to claim 3, wherein The calculation formula for obtaining the inclination angle information of the measurement point in step S4 is: ； ； Among them, respectively represent the differential compensation coefficients; respectively represent the tilt angles of the measurement points 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 measurement points of the object under test on the first quadrant detector; respectively represent the voltage differences in the X-axis direction and the Y-axis direction of the measurement points of the object under test on the second quadrant detector.

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