Differential confocal measurement system based on space offset pinhole and measurement method thereof

Abstract

The invention provides a differential confocal measurement system and method based on a spatial offset pinhole, and the system comprises an illumination unit and a confocal measurement unit which are disposed along a light path, and also comprises a differential measurement unit which is disposed in the emergent direction of a measurement light beam of the illumination unit. And the differential measurement unit is used for receiving the pre-focus photoelectric intensity signal and the post-focus photoelectric intensity signal of the reflected light beam of the measured object and acquiring the position information of the measured object, and the differential measurement unit comprises two paths of pre-focus differential assemblies and two paths of post-focus differential assemblies. According to the invention, an existing differential measurement system is improved into two paths of pre-focus differential assemblies and two paths of post-focus differential assemblies, and two paths of differential signals in the prior art are expanded into four paths of differential signals, so that the range of a linear interval is obviously expanded on the basis of keeping high-precision measurement of the original differential signals; and the measurement range is greatly expanded on the basis of keeping the measurement precision.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical detection, and particularly relates to a differential confocal measurement system based on a spatially offset pinhole and a measurement method thereof. Background Art

[0002] A confocal microscope is a microscopic technique capable of achieving high resolution and optical sectioning. Its basic principle is to use a pinhole to exclude light from planes out of focus, thereby improving the clarity and contrast of the image. The main feature of a confocal microscope is its ability to scan in three-dimensional space, having a higher axial resolution compared to traditional microscopes. In a confocal system, the measurement is mainly through the intensity change of the axial response curve. Due to the optical structure and imaging mode of the system, the position information of the measurement object is obtained by scanning its axial response curve. The confocal axial response curve usually reaches a peak near the focus and then rapidly decays away from the focus. Therefore, a confocal microscope can usually only obtain signals near the focus, that is, near the endpoints of the axial response curve within the measurement range.

[0003] A differential confocal microscope is an improvement based on a confocal microscope. Its core idea is to introduce differential measurement on the basis of the confocal signal to improve the measurement accuracy of the system and expand its linear response range. A differential confocal microscope captures the light intensity signals of the front focus and the rear focus simultaneously and then calculates the difference between the two. This method not only improves the sensitivity of the signal but also expands the linear range of the confocal system. The signal of a traditional confocal microscope has a non-linear response near the focus, and the measurement range is limited to near the focus.

[0004] Therefore, in the prior art, although a confocal microscope has high precision in measuring surface topography, its measurement range is limited, mainly concentrated near the extreme points of the response curve. Although a differential confocal microscope can maintain a linear response within a certain range and is not limited to the extreme points near the focus, it is difficult to meet the accuracy requirements for some surfaces that require a larger measurement range. Summary of the Invention

[0005] The present invention overcomes the deficiencies of the prior art and provides a differential confocal measurement system based on a spatially offset pinhole and a measurement method thereof.

[0006] The present invention provides a differential confocal measurement system based on a spatially offset pinhole, including an illumination unit, a confocal measurement unit arranged along the optical path, and a differential measurement unit; wherein,

[0007] The illumination unit is used to provide a measurement beam with a polarization state for measuring the object to be measured;

[0008] The confocal measurement unit is arranged in the outgoing direction of the measurement beam of the illumination unit and is used to receive the optoelectronic intensity signal formed by the reflected beam of the object to be measured;

[0009] The differential measurement unit is arranged in the outgoing direction of the measurement beam of the illumination unit and is used to receive the pre-focus optoelectronic intensity signal and the post-focus optoelectronic intensity signal of the reflected beam of the object to be measured, and obtain the position information of the object to be measured;

[0010] The differential measurement unit includes two pre-focus differential components and two post-focus differential components.

[0011] Further, the two pre-focus differential components include: a front pre-focus differential component and a rear pre-focus differential component; the two post-focus differential components include a front post-focus differential component and a rear post-focus differential component; wherein,

[0012] The front pre-focus differential component includes a first beam splitter, a second beam splitter, a front pre-focus focusing lens, a front pre-focus pinhole, and a front pre-focus photodetector arranged along the optical path;

[0013] The rear pre-focus differential component includes a rear pre-focus focusing lens, a rear pre-focus pinhole, and a rear pre-focus photodetector arranged along the optical path;

[0014] The front post-focus differential component includes a third beam splitter, a front post-focus focusing lens, a front post-focus pinhole, and a front post-focus photodetector arranged along the optical path;

[0015] The rear post-focus differential component includes a rear post-focus focusing lens, a rear post-focus pinhole, and a rear post-focus photodetector arranged along the optical path;

[0016] The first beam splitter, the second beam splitter, and the third beam splitter are respectively used to split the measurement beam carrying the information of the object to be measured;

[0017] The front pre-focus focusing lens, the rear pre-focus focusing lens, the front post-focus focusing lens, and the rear post-focus focusing lens are respectively used to focus the measurement beam carrying the information of the object to be measured;

[0018] The front pre-focus pinhole, the rear pre-focus pinhole, the front post-focus pinhole, and the rear post-focus pinhole are respectively used for spatial filtering to block the defocused beam;

[0019] The front pre-focus photodetector, the rear pre-focus photodetector, the front post-focus photodetector, and the rear post-focus photodetector are respectively used to receive the pre-focus front defocus optoelectronic intensity signal, the pre-focus rear defocus optoelectronic intensity signal, the post-focus front defocus optoelectronic intensity signal, and the post-focus rear defocus optoelectronic intensity signal carrying the information of the object to be measured.

[0020] Further, the lighting unit includes a laser light source, a beam expander, a polarization beam splitter, and a quarter-wave plate arranged in sequence along the optical path; wherein,

[0021] The laser light source is used to emit a measurement beam;

[0022] The beam expander is used to expand the measurement beam into a parallel beam;

[0023] The polarization beam splitter is used to change the polarization direction of the parallel beam into a linearly polarized beam;

[0024] The quarter-wave plate is used to change the polarization direction of the linearly polarized beam into a circularly polarized beam.

[0025] Further, the confocal measurement unit includes an objective lens, an objective lens driver, a fourth beam splitter, a focusing lens, a pinhole, and a confocal photodetector; wherein,

[0026] The objective lens is used to focus the measurement beam on the surface of the object to be measured;

[0027] The objective lens driver is used to control the movement of the objective lens, and thus control the imaging position of the objective lens on the surface of the object to be measured;

[0028] The fourth beam splitter is used to split the measurement beam carrying the information of the object to be measured;

[0029] The focusing lens is used to focus the measurement beam carrying the information of the object to be measured;

[0030] The pinhole is arranged at the conjugate position of the focus of the object to be measured and is used for spatial filtering to block defocused light beams;

[0031] The confocal photodetector is used to receive the photoelectric intensity signal carrying the information of the object to be measured.

[0032] The present invention also provides a measurement method for a differential confocal measurement system based on a spatially offset pinhole, including the following steps:

[0033] S1. Adjust the position of the pinhole of the confocal measurement unit and the axial defocus amount and position of each pinhole in the differential measurement unit in sequence;

[0034] S2. Collect the photoelectric intensity signal of the differential measurement unit and obtain the differential confocal signal curve of the differential measurement unit;

[0035] S3. Fit the differential confocal signal curve, and divide the differential confocal signal curve into M linear intervals according to the fitting result; wherein, M≥1;

[0036] S4. Adjust the pinhole of the confocal measurement unit, collect the optoelectronic intensity signal of the confocal measurement unit, and obtain the confocal axial response curve of the confocal measurement unit;

[0037] S5. Obtain the voltage value corresponding to the measurement point of the measured object on the differential confocal signal curve, and obtain the position information of the measurement point of the measured object according to the voltage value, the linear interval, the confocal axial response curve, and the fitting result.

[0038] Further, step S1 is specifically:

[0039] S101. Set the pinhole of the confocal measurement unit at the conjugate of the focus of the measured object;

[0040] S102. Adjust the axial defocus amount of each pinhole in the two pre-focus differential components and the two post-focus differential components until a lateral shift appears in the optoelectronic intensity signals received by the pre-pre-focus photodetector, the pre-post-focus photodetector, the post-pre-focus photodetector, and the post-post-focus photodetector;

[0041] S103. Adjust the lateral shift amount of each pinhole in the two pre-focus differential components and the two post-focus differential components until the pre-pre-focus photodetector, the pre-post-focus photodetector, the post-pre-focus photodetector, and the post-post-focus photodetector receive a double-peak optoelectronic intensity signal.

[0042] Further, step S2 is specifically:

[0043] S201. Collect the optoelectronic intensity signals of the confocal photodetector, the pre-pre-focus photodetector, the pre-post-focus photodetector, the post-pre-focus photodetector, and the post-post-focus photodetector respectively;

[0044] S202. Subtract the optoelectronic intensity signal of the pre-pre-focus photodetector from the optoelectronic intensity signal of the pre-post-focus photodetector to obtain the first differential confocal signal curve; subtract the optoelectronic intensity signal of the post-pre-focus photodetector from the optoelectronic intensity signal of the post-post-focus photodetector to obtain the second differential confocal signal curve; process the optoelectronic intensity signal of the confocal photodetector to obtain the confocal axial response curve.

[0045] Further, step S3 is specifically:

[0046] S301. Use the sliding window algorithm to perform the first linear fitting on the data of the first differential confocal signal curve and the second differential confocal signal curve;

[0047] S302. Obtain a first linear interval according to the first linear fitting result and the change in the fitting slope, perform a second linear fitting on the first linear interval, and obtain a corresponding second linear interval between the position information and the optoelectronic intensity signal;

[0048] S303. Obtain the projection of the second linear interval on the X axis, process the straight line overlapping area of the projection, obtain M third linear intervals, and further obtain an extended linear interval; where M≥1.

[0049] Further, in step S303, when processing the straight line overlapping area of the projection to obtain the coordinates of the third linear interval, specifically:

[0050]

[0051] where, x start represents the starting abscissa; x end represents the ending abscissa; a represents the slope of the second linear interval; b represents the intercept of the second linear interval; a j-FES1 represents the slope of the third linear interval of the first differential confocal signal curve; b j-FES1 represents the intercept of the third linear interval of the first differential confocal signal curve; a j-FES2 represents the slope of the third linear interval of the second differential confocal signal curve; b j-FES2 represents the intercept of the third linear interval of the second differential confocal signal curve; x2k represents the abscissa of an even point; x 2k+1 represents the abscissa of an odd point.

[0052] Further, step S5 is specifically:

[0053] S501. Obtain a first voltage value corresponding to the measurement point of the measured object on the first differential confocal signal curve or the second differential confocal signal curve. If the first voltage value is positive, the measurement point is in front of the focal position; if the first voltage value is negative, the measurement point is behind the focal position;

[0054] S502. Obtain a second voltage value corresponding to the measurement point of the measured object on the confocal axial response curve, and the position information corresponding to the second voltage value is the rough measurement position information;

[0055] S503. Obtain the interval position of the rough measurement position information in the second linear interval;

[0056] S504. Substitute the first voltage value into the formula of the corresponding second linear interval to obtain the accurate position information of the measurement point of the measured object.

[0057] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0058] The differential confocal measurement system and its measurement method based on a spatially offset pinhole of the present invention combine an existing confocal measurement system and a differential measurement system, and improve the differential measurement system into two pre-focus differential components and two post-focus differential components, expanding the two differential signals in the prior art into four differential signals. On the basis of maintaining the high-precision measurement of the original differential signals, the linear range is significantly expanded, and the measurement range is greatly expanded while maintaining the measurement accuracy. The differential confocal measurement system and its measurement method based on a spatially offset pinhole of the present invention introduce a cooperative working mechanism of confocal signals and four differential signals, improving the measurement range of the linear interval of the differential confocal microscope technology while ensuring the axial resolution of the differential confocal microscope. Therefore, the technical solution provided by the present invention enhances the measurement ability for complex surfaces and increases the measurement range without sacrificing resolution. Description of the Drawings

[0059] Figure 1 is a schematic structural diagram of the differential confocal measurement system based on a spatially offset pinhole in an embodiment of the present invention;

[0060] Figure 2 is a schematic flow diagram of the measurement method of the differential confocal measurement system based on a spatially offset pinhole in an embodiment of the present invention;

[0061] Figure 3 is a schematic diagram of the relationship between the lateral offset of the pinhole and the photoelectric intensity signals of the double peaks in the differential measurement unit in an embodiment of the present invention;

[0062] Figure 4 is a schematic diagram of the relationship between the lateral offsets of the pre-focus pinhole, the pre-post-focus pinhole, the post-pre-focus pinhole, and the post-post-focus pinhole and the photoelectric intensity signals of the double peaks in an embodiment of the present invention;

[0063] Figure 5 is a schematic diagram of the first differential confocal signal curve and the second differential confocal signal curve in an embodiment of the present invention;

[0064] Figure 6 is a schematic diagram of the linear interval of the fitting of the first differential confocal signal curve and the second differential confocal signal curve in an embodiment of the present invention;

[0065] Figure 7 is a schematic diagram of the third linear interval of the fitting of the first differential confocal signal curve and the second differential confocal signal curve in an embodiment of the present invention;

[0066] Figure 8 is a schematic diagram of the fitting of the first differential confocal signal curve, the second differential confocal signal curve, and the confocal axial response curve in an embodiment of the present invention;

[0067] Figure 9 It is a flowchart of a method for obtaining accurate position information of measurement points of a measured object in an embodiment of the present invention.

[0068] The reference signs therein are as follows:

[0069] 1 - Laser light source, 2 - Polarizing beam splitter, 3 - Quarter-wave plate, 4.1 - Objective lens, 4.2 - Objective lens driver, 5 - Measured object, 6 - Test bench, 7 - Fourth beam splitter, 8 - First beam splitter, 9 - Third beam splitter, 10 - Second beam splitter, 11.1 - Focusing lens, 11.2 - Pinhole, 11.3 - Confocal photodetector, 12.1 - Front focal front focusing lens, 12.2 - Front focal front pinhole, 12.3 - Front focal front photodetector, 13.1 - Rear focal front focusing lens, 13.2 - Rear focal front pinhole, 13.3 - Rear focal front photodetector, 14.1 - Front focal rear focusing lens, 14.2 - Front focal rear pinhole, 14.3 - Front focal rear photodetector, 15.1 - Rear focal rear focusing lens, 15.2 - Rear focal rear pinhole, 15.3 - Rear focal rear photodetector. Specific embodiments

[0070] The following further describes in detail the embodiments of the present invention in conjunction with the accompanying drawings and embodiments. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0071] Embodiment 1:

[0072] The present invention provides a differential confocal measurement system based on a spatially offset pinhole.

[0073] Figure 1 Shows a schematic structural diagram of a differential confocal measurement system based on a spatially offset pinhole according to an embodiment of the present invention.

[0074] As Figure 1 shown, a differential confocal measurement system based on a spatially offset pinhole 11.2 includes an illumination unit and a confocal measurement unit arranged along the optical path, and further includes a differential measurement unit; wherein, the illumination unit is used to provide a measurement beam with a polarization state to measure the measured object 5; the confocal measurement unit is arranged in the outgoing direction of the measurement beam of the illumination unit and is used to receive the photoelectric intensity signal formed by the reflected beam of the measured object 5; the differential measurement unit is arranged in the outgoing direction of the measurement beam of the illumination unit and is used to receive the pre-focal photoelectric intensity signal and the post-focal photoelectric intensity signal of the reflected beam of the measured object 5 to obtain the position information of the measured object 5.

[0075] In the embodiment of the present invention, the lighting unit includes a laser light source 1, a beam expander, a polarization beam splitter 2, and a quarter-wave plate 3 arranged in sequence along the optical path. The confocal measurement unit includes an objective lens 4.1, an objective lens driver 4.2, a fourth beam splitter 7, a focusing lens 11.1, a pinhole 11.2, and a confocal photodetector 11.3. The differential measurement unit includes two pre-focus differential components and two post-focus differential components. The two pre-focus differential components include a pre-pre-focus differential component and a post-pre-focus differential component. The two post-focus differential components include a pre-post-focus differential component and a post-post-focus differential component. The pre-pre-focus differential component includes a first beam splitter 8, a second beam splitter 10, a pre-pre-focus focusing lens 12.1, a pre-pre-focus pinhole 12.1, and a pre-pre-focus photodetector 12.3 arranged along the optical path. The post-pre-focus differential component includes a post-pre-focus focusing lens 13.1, a post-pre-focus pinhole 13.2, and a post-pre-focus photodetector 13.3 arranged along the optical path. The pre-post-focus differential component includes a third beam splitter 9, a pre-post-focus focusing lens 14.1, a pre-post-focus pinhole 14.2, and a pre-post-focus photodetector 14.3 arranged along the optical path. The post-post-focus differential component includes a post-post-focus focusing lens 14.3, a post-post-focus pinhole 15.2, and a post-post-focus photodetector 15.3 arranged along the optical path. In the embodiment of the present invention, the object to be measured 5 is placed on the test bench 6 to ensure the stability of the measurement.

[0076] In the embodiment of the present invention, the laser light source 1 is used to emit a measurement beam; the beam expander is used to expand the measurement beam into a parallel beam; the polarization beam splitter 2 is used to change the polarization direction of the parallel beam into a linearly polarized beam; the quarter-wave plate 3 is used to change the polarization direction of the linearly polarized beam into a circularly polarized beam. The objective lens 4.1 is used to focus the measurement beam on the surface of the object to be measured 5; the objective lens driver 4.2 is used to control the movement of the objective lens 4.1, and further control the imaging position of the objective lens 4.1 on the surface of the object to be measured 5; the fourth beam splitter 7 is used to split the measurement beam carrying the information of the object to be measured 5; the focusing lens 11.1 is used to focus the measurement beam carrying the information of the object to be measured 5; the pinhole 11.2 is arranged at the conjugate position of the focus of the object to be measured 5 for spatial filtering to block the defocused beam; the confocal photodetector 11.3 is used to receive the photoelectric intensity signal carrying the information of the object to be measured 5. The first beam splitter 8, the second beam splitter 10 and the third beam splitter 9 are respectively used to split the measurement beam carrying the information of the object to be measured 5; the front-focus front focusing lens 12.1, the front-focus rear focusing lens 13.1, the rear-focus front focusing lens 14.1 and the rear-focus rear focusing lens 14.3 are respectively used to focus the measurement beam carrying the information of the object to be measured 5; the front-focus front pinhole 12.1, the front-focus rear pinhole 13.2, the rear-focus front pinhole 14.2 and the rear-focus rear pinhole 15.2 are respectively used for spatial filtering to block the defocused beam; the front-focus front photodetector 12.3, the front-focus rear photodetector 13.3, the rear-focus front photodetector 14.3 and the rear-focus rear photodetector 15.3 are respectively used to receive the front defocused photoelectric intensity signal in front of the focus, the rear defocused photoelectric intensity signal in front of the focus, the front defocused photoelectric intensity signal behind the focus and the rear defocused photoelectric intensity signal behind the focus carrying the information of the object to be measured 5.

[0077] In an embodiment of the present invention, a measurement beam with a wavelength of 633 nm is emitted by a laser light source 1. After the measurement beam is expanded into a stable parallel beam by a beam expander, it is incident on a polarization beam splitter 2. The linearly polarized beam transmitted by the polarization beam splitter 2 is incident on a quarter-wave plate 3 and becomes a circularly polarized beam. The circularly polarized beam is focused on the surface of a measured object 5 by an objective lens 4.1. An objective lens driver 4.2 is used to control the movement of the objective lens 4.1, and thus control the imaging position on the surface of the measured object 5. The beam reflected from the surface of the measured object 5 carries information of the measured object 5. The reflected beam carrying the information of the measured object 5 returns along the optical path and is incident on a fourth beam splitter 7. The beam reflected by the fourth beam splitter 7 is successively transmitted through a focusing lens 11.1 and a pinhole 11.2, and is received by a confocal photodetector 11.3. The beam transmitted by the fourth beam splitter 7 is incident on a first beam splitter 8. The beam reflected by the first beam splitter 8 is incident on a second beam splitter 10. The beam transmitted by the second beam splitter 10 is successively transmitted through a front focal focusing lens 12.1 and a front focal pinhole 12.1, and is received by a front focal front photodetector 12.3. The beam reflected by the second beam splitter 10 is successively transmitted through a rear focal front focusing lens 13.1 and a rear focal front pinhole 13.2, and is received by a rear focal front photodetector 13.3. The beam transmitted by the first beam splitter 8 is incident on a third beam splitter 9. The beam transmitted by the third beam splitter 9 is successively transmitted through a front focal rear focusing lens 14.1 and a front focal rear pinhole 14.2, and is received by a front focal rear photodetector 14.3. The beam reflected by the third beam splitter 9 is successively transmitted through a rear focal rear focusing lens 14.3 and a rear focal rear pinhole 15.2, and is received by a rear focal rear photodetector 15.3.

[0078] In an embodiment of the present invention, a measurement beam in a polarization state is used to measure the measured object 5. Using a measurement beam in a polarization state can reduce optical interference caused by surface scattering or reflection, thereby improving the accuracy and repeatability of the measurement. In actual use, an ordinary laser beam can be used for measurement. At this time, the polarization beam splitter 2 can be replaced with an ordinary beam splitter. The present invention does not limit this and can be selected according to actual situations. In an embodiment of the present invention, on the basis of the pre-focus differential component in the prior art, two measurement components are separated, namely a front focal front differential component and a rear focal front differential component; similarly, on the basis of the post-focus differential component, two measurement components are separated, namely a front focal rear differential component and a rear focal rear differential component. The added measurement components expand the linear range of the differential component while maintaining the accuracy of the original differential component. By analyzing the photoelectric intensity signals of the confocal photodetector 11.3 of the measured object 5 collected, and the photoelectric intensity signals on the front focal front photodetector 12.3, the rear focal front photodetector 13.3, the front focal rear photodetector 14.3, and the rear focal rear photodetector 15.3 in the two pre-focus differential components and the two post-focus differential components, the accurate position information, that is, the height information, of the measurement point of the measured object 5 can be obtained.

[0079] The differential confocal measurement system based on the spatial offset pinhole 11.2 provided by the embodiment of the present invention combines the existing confocal measurement system and the differential measurement system, improves the differential measurement system into two pre-focus differential components and two post-focus differential components, expands the two differential signals in the prior art into four differential signals, and significantly expands the range of the linear interval while maintaining the high-precision measurement of the original differential signals, and greatly expands the measurement range while maintaining the measurement accuracy. The differential confocal measurement system based on the spatial offset pinhole 11.2 of the present invention improves the measurement range of the linear interval of the differential confocal microscope technology while ensuring the axial resolution of the differential confocal microscope by introducing a cooperative working mechanism of the confocal signal and the four differential signals.

[0080] Embodiment 2:

[0081] Figure 2 Fig. shows a schematic flowchart of the measurement method of the differential confocal measurement system based on the spatial offset pinhole according to the embodiment of the present invention.

[0082] Figure 3 Fig. shows a schematic diagram of the relationship between the lateral offset of the pinhole and the photoelectric intensity signal of the double peak in the differential measurement unit according to the embodiment of the present invention.

[0083] Figure 4 Fig. shows a schematic diagram of the relationship between the lateral offset of the pre-focus pinhole, the pre-post-focus pinhole, the post-pre-focus pinhole, and the post-post-focus pinhole and the photoelectric intensity signal of the double peak according to the embodiment of the present invention.

[0084] Figure 5 Fig. shows a schematic diagram of the first differential confocal signal curve and the second differential confocal signal curve according to the embodiment of the present invention.

[0085] Figure 6 Fig. shows a schematic diagram of the fitted linear interval of the first differential confocal signal curve and the second differential confocal signal curve according to the embodiment of the present invention.

[0086] Figure 7 Fig. shows a schematic diagram of the fitted third linear interval of the first differential confocal signal curve and the second differential confocal signal curve according to the embodiment of the present invention.

[0087] Figure 8 Fig. shows a schematic diagram of the fitting of the first differential confocal signal curve, the second differential confocal signal curve, and the confocal axial response curve according to the embodiment of the present invention.

[0088] Figure 9 Fig. shows a flowchart of the method for obtaining the accurate position information of the measurement point of the object to be measured according to the embodiment of the present invention.

[0089] As Figure 2As shown, a measurement method for a differential confocal measurement system based on a spatially offset pinhole includes the following steps:

[0090] S1. Adjust the position of the pinhole 11.2 of the confocal measurement unit, the axial defocus amount and position of each pinhole 11.2 in the differential measurement unit in sequence.

[0091] S101. Set the pinhole 11.2 of the confocal measurement unit at the conjugate of the focus of the object to be measured 5, ensure that the measurement beam is incident on the confocal measurement unit, two pre-focal differential components and two post-focal differential components, so that all five photodetectors can receive photoelectric signals.

[0092] S102. Adjust the axial defocus amount of the pre-focal front pinhole 12.1, the post-focal front pinhole 13.2, the pre-focal rear pinhole 14.2 and the post-focal rear pinhole 15.2 in the two pre-focal differential components and the two post-focal differential components until the photoelectric intensity signals received by the pre-focal front photodetector 12.3, the post-focal front photodetector 13.3, the pre-focal rear photodetector 14.3 and the post-focal rear photodetector 15.3 show a lateral offset, that is, single-peak photoelectric intensity signals similar to the differential confocal signal curve appear on the pre-focal front photodetector 12.3, the post-focal front photodetector 13.3, the pre-focal rear photodetector 14.3 and the post-focal rear photodetector 15.3.

[0093] S103. Adjust the lateral offset amount of the pre-focal front pinhole 12.1, the post-focal front pinhole 13.2, the pre-focal rear pinhole 14.2 and the post-focal rear pinhole 15.2 in the two pre-focal differential components and the two post-focal differential components until the pre-focal front photodetector 12.3, the post-focal front photodetector 13.3, the pre-focal rear photodetector 14.3 and the post-focal rear photodetector 15.3 receive double-peak photoelectric intensity signals. First, adjust any one of the pre-focal front pinhole 12.1, the post-focal front pinhole 13.2, the pre-focal rear pinhole 14.2 and the post-focal rear pinhole 15.2, and then adjust the other three pinholes 11.2 in the differential measurement unit to the same lateral offset amount. The lateral offset amount of one pinhole 11.2 in the differential measurement unit and the double-peak photoelectric intensity signal are as Figure 3 shown. As the lateral offset amount v p of the pinhole 11.2 increases, it will cause the single-peak photoelectric intensity signal to gradually become wider until double peaks appear. The technical solution of the present invention is to expand the linear interval based on the double-peak photoelectric intensity signal. Adjust the pre-focal pinhole 11.2, the post-focal front pinhole 13.2, the pre-focal rear pinhole 14.2 and the post-focal rear pinhole 15.2 to the same lateral offset amount v p , then the photoelectric intensity signal curve in the differential measurement unit is as Figure 4 shown.

[0094] S2. Collect the optoelectronic intensity signals of the differential measurement unit to obtain the differential confocal signal curve of the differential measurement unit.

[0095] S201. Collect the optoelectronic intensity signals of the confocal photodetector 11.3, the front focal plane front photodetector 12.3, the rear focal plane front photodetector 13.3, the front focal plane rear photodetector 14.3, and the rear focal plane rear photodetector 15.3 respectively.

[0096] In the embodiment of the present invention, the defocus amount of the front focal plane differential component is -M, and the defocus amounts of the front focal plane front differential component and the rear focal plane front differential component separated from the front focal plane differential component are M1. The defocus amount of the rear focal plane differential component is M; the defocus amounts of the two measurement components, the front focal plane rear differential component and the rear focal plane rear differential component, separated from the rear focal plane differential component are M1. The defocus amount of the front focal plane front differential component is -M - M1, and the optical intensity signal is defined as I A , the defocus amount of the rear focal plane front differential component is -M + M1, and the optical intensity signal is defined as I B , the defocus amount of the front focal plane rear differential component is M - M1, and the optical intensity signal is defined as I C , the defocus amount of the rear focal plane rear differential component is M + M1, and the optical intensity signal is defined as I D , the radius of the pinhole 11.2 is defined as d. The pinhole 11.2 of the confocal measurement unit has no defocus amount, and the selected size of the pinhole 11.2 is larger than the diameters of the front focal plane front pinhole 12.1, the rear focal plane front pinhole 13.2, the front focal plane rear pinhole 14.2, and the rear focal plane rear pinhole 15.2. The radius of the pinhole 11.2 is defined as d0, and the optical intensity signal is defined as I E . Through the Huygens - Fresnel diffraction integral formula and coordinate normalization, the above five optical intensity distribution signals are obtained, which can be specifically expressed as:

[0097]

[0098] Among them, i represents the imaginary unit; v represents the radial normalized coordinate, u represents the axial normalized coordinate; ρ represents the pupil normalized radius; J 0 represents the Bessel function of the 0th order; v d0 represents the normalized coordinate of the radius of the pinhole 11.2 of the confocal measurement unit; v d represents the normalized coordinates of the radii of the front focal plane front pinhole 12.1, the rear focal plane front pinhole 13.2, the front focal plane rear pinhole 14.2, and the rear focal plane rear pinhole 15.2; u M represents the normalized coordinate of the axial defocus amount; u M1 represents the normalized coordinate of the deviation amount.

[0099] S202. Subtract the optoelectronic intensity signal of the front focal front optoelectronic detector 12.3 from the optoelectronic intensity signal of the front focal rear optoelectronic detector 14.3 to obtain the first differential confocal signal curve; subtract the optoelectronic intensity signal of the rear focal front optoelectronic detector 13.3 from the optoelectronic intensity signal of the rear focal rear optoelectronic detector 15.3 to obtain the second differential confocal signal curve; process the optoelectronic intensity signal of the confocal optoelectronic detector 11.3 to obtain the confocal axial response curve.

[0100] In the embodiment of the present invention, when v = 0, then I is obtained A (u, -u M -u M1 ), I B (u, -u M +u M1 ), I C (u, u M -u M1 ), I D (u, u M +u M1 ), and I E (u). The first differential confocal signal curve Fes1(u, u M , u M1 ) = I A (u, -u M -u M1 ) - I C (u, u M -u M1 ); the second differential confocal signal curve Fes2(u, u M , u M1 ) = I B (u, u M -u M1 ) - I D (u, u M +u M1 ); the confocal axial response curve: I E (u). The first differential confocal signal curve Fes1 and the second differential confocal signal curve Fes2 are as Figure 5 shown.

[0101] S3. Fit the differential confocal signal curve and divide the differential confocal signal curve into M linear intervals according to the fitting result; where M≥1. In the embodiment of the present invention, M is 10, that is, it is divided into 10 linear intervals. The value of M needs to ensure that the straight line segment of the differential curve used covers the bent part of another differential curve. The larger the value of M, the more corresponding extended linear intervals, and the more accurate the calculation, but the calculation amount is large. The smaller the value of M, the fewer corresponding extended linear intervals, the faster the calculation speed, but the accuracy is not high. Therefore, the value of M can be selected according to the specific application environment, and the present invention does not limit this.

[0102] In the embodiment of the present invention, the linear fitting methods for the data of the first differential confocal signal curve and the second differential confocal signal curve are the same, so a unified interpretation is given.

[0103] S301. Use the sliding window algorithm to perform the first linear fitting on the data of the first differential confocal signal curve and the second differential confocal signal curve.

[0104] In the embodiment of the present invention, the sliding window algorithm is set, and the size of the sliding window is N, that is, N consecutive data points are selected from the first differential confocal signal curve and the second differential confocal signal curve. The value range of N can be any number of data points in the linear interval of the differential confocal characteristic curve. The larger the value of N, the more corresponding data points, and the more accurate the calculation, but the calculation amount is large. The smaller the value of N, the fewer corresponding data points, the faster the calculation speed, but the accuracy is not high. Therefore, the value of N can be selected according to the specific application environment, and the present invention does not limit this. For the data points of the t-th sliding window: x t =[x t ,x t+1 ,…,x t+N-1 , y t =[y t ,y t+1 ,…,y t+N-1 . Among them, x t and y t represent the independent variable and the dependent variable in the t-th sliding window.

[0105] Perform the first linear fitting on the data points (x t , y t ) within the sliding window. The result of the first linear fitting is expressed as:

[0106] yt = atxt + bt;

[0107] Among them, the calculation formulas for the slope a t and the intercept b t are:

[0108]

[0109] Among them, represents the sum of the x coordinates within the window; represents the sum of the y coordinates within the window; represents the sum of the products of each x t and y t within the window; represents the sum of the squares of each y t within the window.

[0110] S302. According to the first linear fitting result and the change of the fitting slope, obtain the first linear interval, perform a second linear fitting on the first linear interval, and obtain the corresponding second linear interval between the position information and the optoelectronic intensity signal.

[0111] In the embodiment of the present invention, it is judged whether the current window belongs to the linear interval by comparing the slope changes of adjacent windows. Given a threshold ∈, if the slope change amount of adjacent windows satisfies: then it is considered that the current window and the previous window can be regarded as the same linear interval.

[0112] When a continuous linear interval is found, perform a second linear fitting on the x and y data of the entire interval to determine the straight line formula of this interval. Suppose the found linear interval is from the K 1 th to the K 2 th window. Re-fit all the data in this interval to obtain the linear equation of the second linear fitting: f L (x) = a L x + b L .

[0113] f L (x) represents the Lth fitting straight line equation; a L represents the slope of the Lth fitting straight line equation; b L represents the intercept of the Lth fitting straight line equation; the fitted linear interval is the corresponding second linear interval between the obtained position information and the optoelectronic intensity signal. As Figure 6 shown, where blue represents Fes1 and red represents Fes2.

[0114] S303. Obtain the projection of the second linear interval on the X axis. After processing the overlapping area of the projected straight lines, obtain 10 third linear intervals, that is, 10 straight line segments and 11 abscissas, so as to cover 11 points. In the embodiment of the present invention, M is 10.

[0115] In the embodiment of the present invention, after obtaining the second linear interval, it is necessary to perform a partitioning operation on it and re-divide the linear interval so that each X corresponds to only one Y value at the same time, which is convenient for subsequent solving of the position information. After obtaining the projection of the second linear interval on the X axis and processing the overlapping region of the fitted lines of Fes1 and Fes2 of the projection, the coordinates of the 10 processed third linear intervals are as follows:

[0116]

[0117] Among them, x start represents the starting abscissa; x end represents the ending abscissa; a represents the slope of the second linear interval; b represents the intercept of the second linear interval; a j-FES1 represents the slope of the third linear interval of the first differential confocal signal curve; b j-FES1 represents the intercept of the third linear interval of the first differential confocal signal curve; a j-FES2 represents the slope of the third linear interval of the second differential confocal signal curve; b j-FES2 represents the intercept of the third linear interval of the second differential confocal signal curve; x2k represents the abscissa of an even point; x 2k+1 represents the abscissa of an odd point.

[0118] In the embodiment of the present invention, there are a total of 10 third linear intervals and 11 abscissas. The starting point of the first linear interval is (x1, x2), the second third linear interval is (x2, x3), and so on. A total of 11 points x1, x2, x3... x11 can finally obtain an extended linear interval, as follows Figure 7 , and the third linear interval is composed of ten partitions.

[0119] S4. Adjust the pinhole 11.2 of the confocal measurement unit, collect the photoelectric intensity signal of the confocal measurement unit, and obtain the confocal axial response curve Fes3 of the confocal measurement unit.

[0120] In the embodiment of the present invention, the radius of the adjusted pinhole 11.2 of the confocal measurement unit is larger than the radius of each pinhole 11.2 in the differential measurement unit. By adjusting the size of the pinhole 11.2 and normalizing the confocal axial response curve, the first differential confocal signal curve, and the second differential confocal signal curve, observe the confocal axial response curve, the first differential confocal signal curve, and the second differential confocal signal curve. As Figure 8 shown, the confocal axial response curve can wrap the first differential confocal signal curve and the second differential confocal signal curve. Among them, the blue dotted line represents Fes1; the red dotted line represents Fes2; the blue solid line represents Fes3.

[0121] S5. Obtain the voltage value corresponding to the measurement point of the object 5 on the differential confocal signal curve, and obtain the position information of the measurement point of the object 5 according to the voltage value, the linear interval, the confocal axial response curve, and the fitting result.

[0122] S501. Obtain the first voltage value corresponding to the measurement point of the object 5 on the first differential confocal signal curve or the second differential confocal signal curve. If the first voltage value is positive, the measurement point is in front of the focus; if the first voltage value is negative, the measurement point is behind the focus.

[0123] In the embodiment of the present invention, the pre-focus front photodetector 12.3, the pre-focus rear photodetector 13.3, the post-focus front photodetector 14.3, and the post-focus rear photodetector 15.3 are all photodiodes. The collected optical signal is converted into an electrical signal through the photodiode. Therefore, the position information of different measurement points is different, corresponding to different optical signal intensities, that is, different voltage values. Therefore, collect the optical signal of the measurement point on the photodetector and convert it into a voltage value representing the electrical signal. Obtain the first voltage value U1 corresponding to the measurement point of the object 5 on Fes1, or the first voltage value U2 corresponding to the measurement point of the object 5 on Fes2. The voltage value on Fes1 or Fes2 has no effect on the result. If the first voltage value is positive, the measurement point is in front of the focus; if the first voltage value is negative, the measurement point is behind the focus. The specific steps are as Figure 9 shown.

[0124] S502. Obtain the second voltage value corresponding to the measurement point of the object 5 on the confocal axial response curve, that is, collect the corresponding signal intensity. The position information corresponding to the second voltage value is the rough measurement position information. The second voltage value U3 corresponding to the measurement point on Fes3, as Figure 8 shown. The second voltage value, that is, the signal intensity, is the ordinate in the figure. Determine the corresponding abscissa, that is, the position information. The position information corresponding to U3 is the rough measurement position information of the measurement point.

[0125] S503. Determine the interval position of the rough measurement position information X in the third linear interval.

[0126] S504. After determining the specific partition, if it is located in the linear partition of Fes1, that is, solve the high-precision position information through the U1 voltage in this partition; if it is located in the linear partition of Fes2, that is, solve the high-precision position information through the U2 voltage in this partition; if it is located near the boundary line of the partition, then it is necessary to judge the slopes of the left and right linear partitions and use the linear interval with a higher slope to solve the position information.

[0127] The extended linear range, i.e., the third linear range, obtained by the measurement method of the differential confocal measurement system based on the spatially offset pinhole 11.2 enables a voltage value to correspond to a displacement value, that is, one Y value has a corresponding X value. For example, if the first voltage value obtained is 0.5V, which is a positive value, the measurement point is in front of the focal position. Obtain the second voltage value U3 corresponding to the measurement point on Fes3, and determine the corresponding abscissa, i.e., the position information. The position information corresponding to U3 is the rough measurement position information X of the measurement point. Use the rough measurement position information X to find the corresponding Y value in the fitted third linear range. At this time, according to the Y value, after determining the specific partition, if it is located in the linear partition of Fes1, the high-precision position information is solved through the U1 voltage in this partition; if it is located in the linear partition of Fes2, the high-precision position information is solved through the U2 voltage in this partition.

[0128] In the embodiment of the present invention, experiments are carried out to verify the effectiveness of the measurement method of the technical solution of the present invention. The parameters of the differential confocal measurement system in the prior art are selected as follows: the focal length of the objective lens 4.1 is 3.3mm, the focal length of the focusing lens 11.1 is 50mm, the wavelength of the laser light source 1 is 633nm, the beam diameter is 2.24mm, the radius of the pinhole 11.2 is selected as 15um, and the defocus amount is 0.55mm. The obtained linear range is 2.1μm. The parameters of the differential confocal measurement system based on the spatially offset pinhole 11.2 are the same as those of the differential confocal measurement system in the prior art, and the lateral offset amount v of the pinhole 11.2 is set p to be 11.2μm. When the defocus amounts of the four-way defocus front-differential component, rear-focus front-differential component, front-focus rear-differential component, and rear-focus rear-differential component are ±0.15mm and ±0.5mm respectively, the linear range is extended to 4.9μm. It can be known from the experimental data that the measurement method of the differential confocal measurement system based on the spatially offset pinhole provided by the embodiment of the present invention can greatly expand the measurement range of the linear range.

[0129] The measurement method of the differential confocal measurement system based on a spatially offset pinhole according to the present invention combines an existing confocal measurement system and a differential measurement system, and improves the differential measurement system into two pre-focus differential components and two post-focus differential components, expanding the two differential signals in the prior art into four differential signals. On the basis of maintaining the high-precision measurement of the original differential signals, the linear range is significantly expanded, and the measurement range is greatly expanded while maintaining the measurement accuracy. The differential confocal measurement system based on a spatially offset pinhole according to the present invention and its measurement method introduce a cooperative working mechanism of confocal signals and four differential signals, improving the measurement range of the linear interval of the differential confocal microscope technology while ensuring the axial resolution of the differential confocal microscope. Therefore, the technical solution provided by the present invention enhances the measurement ability for complex surfaces and increases the measurement range without sacrificing the resolution.

[0130] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means 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 are not necessarily directed 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, 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.

[0131] 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.

[0132] The above specific embodiments 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 system based on a spatially offset pinhole, comprising an illumination unit and a confocal measurement unit arranged along an optical path, characterized in that: Also included is a differential measurement unit; wherein, The lighting unit is used to provide a polarized measurement light beam to measure the object to be measured; The confocal measurement unit is arranged in the emission direction of the measurement light beam of the illumination unit, and is used to receive the photoelectric intensity signal formed by the light beam reflected by the object to be measured; The differential measurement unit is arranged in the emission direction of the measurement light beam of the lighting unit, and is used to receive the pre-focus photoelectric intensity signal and the post-focus photoelectric intensity signal of the light beam reflected by the object to be measured, and obtain the position information of the object to be measured; The differential measurement unit includes two pre-focus differential components and two post-focus differential components.

2. The differential confocal measurement system based on spatially offset pinhole according to claim 1, characterized in that: The two-way front focus differential assembly includes: a front focus front differential assembly and a rear focus front differential assembly; the two-way rear focus differential assembly includes a front focus rear differential assembly and a rear focus rear differential assembly; wherein, The front-focus front differential assembly includes a first beam splitter, a second beam splitter, a front-focus front focusing lens, a front-focus front pinhole, and a front-focus front photoelectric detector arranged along the optical path; The back-focus front differential assembly includes a back-focus front focusing lens, a back-focus front pinhole, and a back-focus front photoelectric detector arranged along the optical path; The front-focus and rear-differential assembly comprises a third beam splitter, a front-focus and rear-focusing lens, a front-focus and rear-pinhole, and a front-focus and rear-photoelectric detector arranged along the optical path; The back-focus rear differential assembly includes a back-focus rear focusing lens, a back-focus rear pinhole, and a back-focus rear photoelectric detector arranged along the optical path; The first beam splitter, the second beam splitter and the third beam splitter are respectively used to split the measuring light beam carrying the information of the object to be measured; The front-focus front focusing lens, the rear-focus front focusing lens, the front-focus rear focusing lens and the rear-focus rear focusing lens are respectively used to focus the measuring light beam carrying the information of the measured object; The front pinhole of the front focus, the front pinhole of the back focus, the rear pinhole of the front focus and the rear pinhole of the back focus are respectively used for spatial filtering to block the defocused light beam; The front-focus photodetector, the front-focus photodetector, the rear-focus photodetector and the rear-focus photodetector are respectively used to receive the front defocus photoelectric intensity signal before focus, the rear defocus photoelectric intensity signal before focus, the front defocus photoelectric intensity signal after focus and the rear defocus photoelectric intensity signal after focus carrying the information of the object to be measured.

3. The differential confocal measurement system based on spatially offset pinhole according to claim 2, characterized in that: The lighting unit includes a laser light source, a beam expander, a polarization beam splitter, and a quarter wave plate arranged in sequence along the optical path; wherein, The laser light source is used to emit a measuring light beam; The beam expander is used to expand the measuring beam into a parallel beam; The polarization beam splitter is used to change the polarization direction of the parallel light beam into a linearly polarized light beam; The quarter wave plate is used to change the polarization direction of the linearly polarized light beam into a circularly polarized light beam.

4. The differential confocal measurement system based on spatially offset pinhole according to claim 3, characterized in that: The confocal measurement unit includes an objective lens, an objective lens driver, a fourth beam splitter, a focusing lens, a pinhole, and a confocal photodetector; wherein, The objective lens is used to focus the measuring light beam on the surface of the object to be measured; The objective lens driver is used to control the movement of the objective lens, and further control the imaging position of the objective lens on the surface of the object to be measured; The fourth beam splitter is used to split the measuring light beam carrying the information of the object to be measured; The focusing lens is used to focus the measuring light beam carrying the information of the measured object; The pinhole is arranged at a conjugate position of the focus of the object to be measured, and is used for spatial filtering to block the defocused light beam; The confocal photoelectric detector is used to receive a photoelectric intensity signal carrying information of the object to be measured.

5. A method for differential confocal measurement based on spatial offset pinholes, which is implemented by using the differential confocal measurement system based on spatial offset pinholes as claimed in claim 1, characterized in that: The steps include: S1, sequentially adjusting the pinhole position of the confocal measurement unit and the axial defocus amount and position of each pinhole in the differential measurement unit; S2, collecting the photoelectric intensity signal of the differential measurement unit to obtain the differential confocal signal curve of the differential measurement unit; S3, fitting the differential confocal signal curve, and dividing the differential confocal signal curve into M linear intervals according to the fitting result; wherein M≥1; S4, adjusting the pinhole of the confocal measurement unit, collecting the photoelectric intensity signal of the confocal measurement unit, and obtaining the confocal axial response curve of the confocal measurement unit; S5. Obtain a voltage value corresponding to a measurement point of the object under test on the differential confocal signal curve, and obtain position information of the measurement point of the object under test according to the voltage value, the linear interval, the confocal axial response curve and the fitting result.

6. The differential confocal measurement method based on spatially offset pinhole according to claim 5, characterized in that: Step S1 is specifically as follows: S101, setting the pinhole of the confocal measurement unit at a conjugate position of the focus of the object to be measured; S102, adjusting the axial defocus amount of each pinhole in the two-way front-focus differential assembly and the two-way rear-focus differential assembly until the photoelectric intensity signals received by the front-focus photodetector, the rear-focus photodetector, the front-focus rear-photodetector and the rear-focus rear-photodetector are laterally offset; S103, adjusting the lateral offset of each pinhole in the two-way front-focus differential assembly and the two-way rear-focus differential assembly until the front-focus photodetector, the rear-focus front photodetector, the front-focus rear photodetector and the rear-focus rear photodetector receive double-peak photoelectric intensity signals.

7. The differential confocal measurement method based on spatially offset pinhole according to claim 6, characterized in that: Step S2 is specifically as follows: S201, respectively collecting photoelectric intensity signals of the confocal photodetector, the front-focus photodetector, the back-focus photodetector, the front-focus photodetector, and the back-focus photodetector; S202, subtracting the collected photoelectric intensity signal of the front-focus photodetector from the photoelectric intensity signal of the rear-focus photodetector to obtain a first differential confocal signal curve; subtracting the collected photoelectric intensity signal of the front-focus photodetector from the photoelectric intensity signal of the rear-focus photodetector to obtain a second differential confocal signal curve; processing the photoelectric intensity signal of the confocal photodetector to obtain a confocal axial response curve.

8. The differential confocal measurement method based on spatially offset pinhole according to claim 7, characterized in that: Step S3 is specifically as follows: S301, performing a first linear fitting on data of the first differential confocal signal curve and the second differential confocal signal curve using a sliding window algorithm; S302, obtaining a first linear interval according to the first linear fitting result and the fitting slope change, performing a second linear fitting on the first linear interval, and obtaining a second linear interval corresponding to the position information and the photoelectric intensity signal; S303, obtaining the projection of the second linear interval on the X-axis direction, and after processing the straight line overlapping area of ​​the projection, obtaining M third linear intervals, and then obtaining an extended linear interval; wherein M≥1.

9. The differential confocal measurement method based on spatially offset pinhole according to claim 8, characterized in that: In step S303, the overlapping area of ​​the projected straight lines is processed, and the coordinates of the third linear interval obtained are specifically: Among them, x start Indicates the starting horizontal coordinate; x end represents the abscissa of the end point; a represents the slope of the second linear interval; b represents the intercept of the second linear interval; a j-FES1 represents the slope of the third linear interval of the first differential confocal signal curve; b j-FES1 represents the intercept of the third linear interval of the first differential confocal signal curve; a j-FES2 represents the slope of the third linear interval of the second differential confocal signal curve; b j-FES2 represents the intercept of the third linear interval of the second differential confocal signal curve; x2k represents the abscissa of the even-numbered points; x 2k+1 Indicates the horizontal coordinate of an odd point.

10. The differential confocal measurement method based on spatially offset pinhole according to claim 9, characterized in that: Step S5 is specifically as follows: S501, obtaining a first voltage value corresponding to a measuring point of the object under test on the first differential confocal signal curve or the second differential confocal signal curve, if the first voltage value is positive, the measuring point is at a pre-focus position, and if the first voltage value is negative, the measuring point is at a post-focus position; S502, obtaining a second voltage value corresponding to a measurement point of the object under test on the confocal axial response curve, wherein position information corresponding to the second voltage value is coarse measurement position information; S503, obtaining the interval position of the rough measured position information in the second linear interval; S504: Substitute the first voltage value into the corresponding formula of the second linear interval to obtain accurate position information of the measuring point of the object under test.

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