Measurement method and device based on differential confocal system

Abstract

The present invention provides a measurement method and a measurement device based on a differential confocal system. The measurement method drives an objective lens positioner to move along the optical axis direction to move the objective lens, and samples the displacement data of the objective lens positioner, the light intensity data of the pre-focus photodetector and the post-focus photodetector, analyzes the data, and obtains the position information of the object to be measured. When the method provided by the present invention measures the distance through a focusing error signal, the objective lens only needs to be driven once for the measurement of a point to be measured, and the displacement data of the objective lens, the light intensity data of the pre-focus photodetector and the post-focus photodetector are collected at the same time. Then, the collected data can be differentially processed, and the linear region of the differential signal is linearly fitted using the least squares method, and the zero-crossing position corresponding to the objective lens positioner position is extracted as the distance measurement information, thereby avoiding the error in the prior art in obtaining the zero-crossing point of the differential confocal response curve, which will affect the distance measurement result.

Description

Technical Field

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

[0002] Laser Scanning Confocal Microscope (LSCM) is a modern optical microscopy technology with high resolution, which is widely used in biomedicine and optical precision measurement. LSCM uses two symmetrically placed defocused pinhole detection light paths. When scanning the surface of the test piece longitudinally, it collects the light intensity signals of the two detection light paths, performs differential processing to obtain the axial light intensity response curve, and obtains the height information of the scanning position of the test piece after processing. Laser differential confocal microscopy detection technology has the characteristics of fast measurement speed and high measurement accuracy.

[0003] The research direction of laser differential confocal microscopy is mainly divided into two parts, namely detector data acquisition and data processing to obtain distance information. In the first part, it is necessary to drive the detector objective lens to move axially, so that the surface of the object to be tested moves from the front of the detector objective lens to the back of the focus, and at the same time collect the light intensity signals of the two detection light paths. In the second part, it is necessary to analyze the collected objective lens position and the light intensity data of the detection light path to extract the distance information of the position to be tested.

[0004] The current existing technology usually uses a data acquisition board to connect to a computer, and the computer controls and processes the data acquisition, which has a low degree of integration. A large amount of collected data needs to be sent to the computer for processing through an external data transmission line, which has high latency and low communication efficiency. In addition, when the method in the prior art measures the distance through the focusing error signal, it is necessary to determine whether the light intensity signals of the pre-focus detector and the post-focus detector are equal. The method is complicated and if the collected light intensity signals of the pre-focus detector and the post-focus detector are inaccurate, it will affect the distance measurement result. Summary of the invention

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

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

[0007] The present invention provides a measurement method based on a differential confocal system, comprising the following steps:

[0008] S1, driving the objective lens positioner to move along the optical axis direction to drive the objective lens to move, and sampling the displacement data of the objective lens positioner, the light intensity data of the pre-focus photodetector and the post-focus photodetector; wherein the displacement data is represented by d: {d1, d2, ..., d q}; the light intensity data of the pre-focus photodetector is represented by a: {a1, a2...a q}; The post-focus photodetector light intensity data is represented by b: {b1, b2...b q};

[0009] S2. Analyze the displacement data, the light intensity data of the pre-focus photodetector and the post-focus photodetector to obtain position information of the object to be measured.

[0010] Furthermore, the sampling period of data acquisition is set as follows: the sampling start time is the time when the objective lens positioner starts to move, and the sampling end time is the time when the objective lens positioner stops moving; wherein,

[0011] If the moment of starting displacement is the point where the travel range of the objective lens positioner is the smallest, then the moment of stopping displacement is the point where the travel range of the objective lens positioner is the largest;

[0012] If the moment of starting displacement is the point where the travel range of the objective lens positioner is the largest, then the moment of stopping displacement is the point where the travel range of the objective lens positioner is the smallest.

[0013] Furthermore, the step S2 is specifically as follows:

[0014] S201, subtract the light intensity data of the pre-focus photodetector from the light intensity data of the post-focus photodetector to obtain a focus error signal f: {f1, f2...f q}; where q is the number of sampling times;

[0015] S202, obtaining the mth data and the nth data in the focus error signal; wherein the mth data is the maximum value f m , the nth data is the minimum value f n ;

[0016] S203, obtaining the m+(nm) / 4th to n-(nm) / 4th groups of data in the focus error signal, the two groups of data are respectively expressed as: d: {d m+(n-m) / 4 ,...,d n-(n-m) / 4} and f: {f m+(n-m) / 4 ,...,f n-(n-m) / 4};

[0017] S204, fitting is performed by the two sets of data to obtain a fitting function f=c1×d+c2, and coefficients c1 and c2 of the fitting function are obtained respectively; wherein the coefficient formula of the fitting function is expressed as formula (1):

[0018]

[0019] Where i represents the i-th sampling point; c1 represents the slope of the fitting function; c2 represents the intercept of the fitting function;

[0020] S205. Obtain the position information of the object to be measured according to the obtained coefficient; wherein the position information is expressed as formula (2):

[0021] l=-c2 / c1 (2)

[0022] Among them, l represents the location information.

[0023] The present invention also provides a measurement device based on a differential confocal system, comprising a processing module, a programming logic module, a DA conversion module, at least one AD sampling module and a storage module; wherein:

[0024] The processing module is used to receive and transmit work instructions, and obtain distance information of the object to be measured after analyzing the collected data;

[0025] The programming logic module is used to drive the objective lens positioner to move and sample data; the data includes: displacement data of the objective lens positioner, light intensity data of the pre-focus photoelectric detector and the post-focus photoelectric detector;

[0026] The AD sampling module is used to convert the analog signals of the displacement data and the light intensity data collected within a sampling period into digital signals;

[0027] The DA conversion module is used to convert the digital signal into an analog signal;

[0028] The storage module is used to store the displacement data and the light intensity data.

[0029] Furthermore, the programming logic module includes a main control unit, a drive unit and a data acquisition unit; wherein,

[0030] The main control unit is used to receive the working instructions of the processing module and control the driving unit and the data acquisition unit to work;

[0031] The driving unit is used to drive the objective lens positioner to move axially along the optical axis and send a driving signal to the data acquisition unit to perform data acquisition;

[0032] The data acquisition unit is used to sample the displacement data of the objective lens positioner and the light intensity data of the pre-focus photodetector and the post-focus photodetector.

[0033] Furthermore, the processing module and programming logic module are ZYNQ chips.

[0034] Furthermore, the storage module includes a FIFO cache unit and a DDR memory unit.

[0035] Furthermore, there are three AD sampling modules, which are respectively used to convert the analog signals of the displacement data of the objective lens positioner, the light intensity data of the pre-focus photodetector and the post-focus photodetector into digital signals.

[0036] The present invention can achieve the following technical effects:

[0037] The present invention is based on a measurement method and a measurement device of a differential confocal system, and uses a ZYNQ system to solve the problem that the objective lens drive, light intensity collection, and data analysis cannot be performed on the same device. It also solves the problem that the prior art uses a data acquisition board to connect a computer, and the computer performs data acquisition control and data processing, and the integration is not high. A large amount of collected data needs to be sent to a computer for processing through an external data transmission line, which has high delay and low communication efficiency. When the method provided by the present invention measures the distance through a focusing error signal, for the measurement of a point to be measured, it only needs to drive the objective lens once, and at the same time collect the objective lens displacement data, the light intensity data of the pre-focus photodetector and the post-focus photodetector, and then the collected data can be differentially processed, and the linear region of the differential signal can be linearly fitted using the least squares method, and the zero-crossing position corresponding to the objective lens locator position is extracted as the distance measurement information, thereby avoiding the error in the prior art in obtaining the zero-crossing point of the differential confocal response curve, which will affect the distance measurement result. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a schematic structural diagram of a differential confocal system according to an embodiment of the present invention;

[0039] Figure 2 is a flow chart of a measurement method based on a differential confocal system according to an embodiment of the present invention;

[0040] Figure 3 is a schematic diagram of the principle of a focus error signal of a measurement method based on a differential confocal system according to an embodiment of the present invention;

[0041] Figure 4 is a schematic diagram of the principle of a measuring device based on a differential confocal system according to an embodiment of the present invention;

[0042] Figure 5(a) and (b) are schematic diagrams of the output voltage of the DA conversion module and the displacement of the objective lens positioner of the measurement device based on the differential confocal system according to an embodiment of the present invention.

[0043] Reference numerals include:

[0044] Laser light source 1, collimating lens 2, first beam splitter 3, objective lens 4, objective lens positioner 5, object to be measured 6, second beam splitter focusing lens 7, pre-focus focusing lens 8, pre-focus pinhole 9, pre-focus photoelectric detector 10, post-focus focusing lens 11, post-focus pinhole 12, post-focus photoelectric detector 13, processing module 14, programmable logic module 15, main control unit 15-1, drive unit 15-2, data acquisition unit 15-3, DA conversion module 16, first AD sampling module 17-1, second AD sampling module 17-2, third AD sampling module 17-3, FIFO cache unit 18-1, DDR memory unit 18-2, ZYNQ chip 19, host computer 20, AXI high-speed bus 21. DETAILED DESCRIPTION

[0045] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same modules are represented by the same reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, the detailed description thereof will not be repeated.

[0046] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0047] Figure 1 A schematic structural diagram of a differential confocal system according to an embodiment of the present invention is shown. Figure 2 A flow chart of a measurement method based on a differential confocal system according to an embodiment of the present invention is shown. Figure 3 A schematic diagram showing the principle of a focus error signal of a measurement method based on a differential confocal system according to an embodiment of the present invention is shown. Figure 4 The schematic diagram shows the principle of a measuring device based on a differential confocal system according to an embodiment of the present invention. Figure 5 (a) and (b) are schematic diagrams showing the principle of the output voltage of the DA conversion module and the displacement of the objective lens positioner in the measurement device based on the differential confocal system according to an embodiment of the present invention.

[0048] Combine the following Figure 1 The specific working mode of the measurement method based on the differential confocal system in the embodiment of the present invention is described in detail:

[0049] The technical solution provided by the embodiment of the present invention can be applied to a differential confocal system of any structure. The solution of the embodiment of the present invention is described in detail below in conjunction with a differential confocal microscope system in the prior art. Figure 1 As shown, the differential confocal system is only for illustration and the specific implementation is not limited thereto.

[0050] The light beam emitted by the laser light source 1 becomes a collimated light beam after passing through the collimating lens 2. After passing through the first beam splitter 3, the light beam enters the objective lens 4 carrying the objective lens positioner 5. Driven by the objective lens positioner 5, the objective lens 4 can move forward and backward along the direction of the incident light beam to adjust the light beam to accurately focus on the surface of the object to be measured 6. The reflected light of the object to be measured 6, after passing through the objective lens 4, is reflected by the first beam splitter 3 and enters the second beam splitter 7, and is divided into a pre-focus measurement beam and a post-focus measurement beam. After passing through the pre-focus focusing lens 8, the pre-focus measurement beam is irradiated on a surface at a distance of fu. m The position is placed on the front focus pinhole 9, where f is the focal length of the front focus lens 8, u m is a constant offset, and the energy of the beam passing through the pre-focus pinhole 9 is collected by the pre-focus photodetector 10. The post-focus measurement beam passes through the post-focus focusing lens 11 and irradiates the m The post-focus pinhole 12 is placed at the position, where f is the focal length of the focusing lens 11, and u m is a constant offset, and the energy of the light beam passing through the post-focus pinhole 12 is collected by the post-focus photodetector 13. In the prior art, the objective lens positioner 5 is required to drive the objective lens 4 to move. When the light intensity signals collected by the pre-focus photodetector 10 and the post-focus photodetector 13 are equal, the surface of the object to be measured 6 is located at the focal position of the objective lens 4. At this time, the displacement of the objective lens positioner 5 is recorded as the position of the object to be measured.

[0051] The measurement method based on the differential confocal system provided in the embodiment of the present invention is as follows: Figure 2 As shown, the following steps are included:

[0052] S1, drive the objective lens positioner 5 to move along the optical axis direction to move the objective lens forward or backward along the incident light beam direction, and sample the displacement data of the objective lens positioner 5, the light intensity data of the pre-focus photodetector 10 and the post-focus photodetector 13; wherein the displacement data is represented by d: {d1, d2, ..., d 10000}; The light intensity data of the pre-focus photodetector 10 is expressed as a: {a1, a2...a 10000}; The light intensity data of the post-focus photodetector 13 is expressed as b: {b1, b2...b 10000}.

[0053] The sampling start time in the embodiment of the present invention is the moment when the objective lens positioner 5 starts to move, and the sampling end time is when the objective lens positioner 5 moves to the maximum position of the travel range. The displacement travel range of the objective lens positioner 5 used in the embodiment of the present invention is 0-100μm, so the sampling start time is when the objective lens positioner 5 starts to move from the minimum position of the travel range 0, and the sampling ends when the objective lens positioner 5 moves the objective lens to the maximum position of the travel range of 100μm; similarly, the sampling start time can also be when the objective lens positioner 5 starts to move from 100μm, and the sampling ends when the objective lens positioner 5 moves the objective lens 4 to 0, that is, the objective lens can move forward or backward, which has no effect on the method provided in the embodiment of the present invention, and the direction of the objective lens movement can be selected according to the existing situation, and the embodiment of the present invention does not limit this. The time period of the sampling start time and end time in the embodiment of the present invention collects displacement data and light intensity data of two photoelectric detectors, including the light intensity data of the incident light beam at the pre-focus moment, post-focus moment and focusing moment of the object to be measured 6 and the displacement data of the objective lens. In the embodiment of the present invention, 10,000 sets of displacement data, light intensity data of the pre-focus photodetector 10 and the post-focus photodetector 13 are collected in one sampling cycle.

[0054] S2. The embodiment of the present invention analyzes the displacement data and the light intensity data of the pre-focus photodetector 10 and the post-focus photodetector 13 to obtain the position information of the object to be measured 6.

[0055] S201, in the embodiment of the present invention, the light intensity data of the pre-focus photodetector 10 is subtracted from the light intensity data of the post-focus photodetector 13 to obtain a focus error signal f: {f1, f2...f 10000}; wherein, in the embodiment of the present invention, q is 10000. The focus error signal obtained is as follows Figure 3 shown.

[0056] S202, the embodiment of the present invention obtains the mth data and the nth data in the focus error signal; wherein the mth data is the maximum value f m , the nth data is the minimum value f n .

[0057] S203, the embodiment of the present invention obtains the m+(nm) / 4th to n-(nm) / 4th groups of data in the focus error signal, and the two groups of data are respectively expressed as: d: {d m+(n-m) / 4 ,...,d n-(n-m) / 4} and f: {f m+(n-m) / 4 ,...,f n-(n-m) / 4 The data selected in the embodiment of the present invention is part of the data that is closer to linearity among all the data, which can provide more preferred and accurate data for subsequent fitting, improve the accuracy of linear fitting, and further improve the accuracy of the position information of the object to be measured 6.

[0058] S204. In the embodiment of the present invention, the two sets of data are linearly fitted by the least square method to obtain the fitted straight line function f=c1×d+c2, and the coefficients c1 and c2 of the fitted function are obtained respectively; wherein the coefficient formula of the fitted function is expressed as formula (1):

[0059]

[0060] Where i represents the i-th sampling point; c1 represents the slope of the fitting function; and c2 represents the intercept of the fitting function.

[0061] In the embodiment of the present invention, the least square method is selected to extract and fit the zero-crossing point of the focus error signal, which has a small amount of calculation. Combined with the closer linear data in step S203, the accuracy of the position information of the object to be measured 6 is guaranteed on the basis of a small amount of calculation.

[0062] S205. In the embodiment of the present invention, the position information of the object to be measured 6 is obtained according to the obtained coefficients; wherein the position information is expressed as formula (2):

[0063] l=-c2 / c1 (2)

[0064] Among them, l represents the location information.

[0065] The embodiment of the present invention moves the objective lens 4, sets the sampling start time, end time and sampling amount, collects displacement data and light intensity data of two photodetectors, so that the collected data includes all light intensity data of the incident light beam at the pre-focus moment, post-focus moment and focus moment of the object to be measured 6 and all displacement data of the objective lens, and linearly screens the collected data and extracts the zero-crossing point of the focusing error signal through an algorithm, thereby avoiding the method in the prior art that the distance measurement of the position of the object to be measured 6 depends on accurately determining that the light intensity signals of the pre-focus photodetector 10 and the post-focus photodetector 13 are equal to obtain the zero-crossing point of the differential confocal response curve. The method provided by the embodiment of the present invention improves the measurement accuracy of the differential confocal system by accurately positioning the zero-crossing point, and has fast processing speed and high sensitivity. The measurement of a point to be measured provided by the embodiment of the present invention only requires driving the objective lens once, and at the same time collecting the objective lens displacement data, the light intensity data of the pre-focus photodetector and the post-focus photodetector. By performing differential processing on the collected data, the linear region of the differential signal is linearly fitted using the least squares method, and then the position of the objective lens locator corresponding to the zero-crossing position is extracted as the ranging information.

[0066] The present invention also provides a measurement device based on a differential confocal system, such as Figure 4As shown, it includes a processing module 14, a programmable logic module 15, an extraction module, a DA conversion module 16, a first AD sampling module 17-1, a second AD sampling module 17-2, a third AD sampling module 17-3 and a storage module. In the embodiment of the present invention, the processing module 14 is responsible for receiving the start work instruction issued by the user host computer 20, analyzing the collected data, calculating the measured distance information, and returning the distance measurement information to the user. In the embodiment of the present invention, the programmable logic module 15 is used to drive the objective lens positioner 5 to move, and to collect the displacement data of the objective lens positioner 5, the light intensity data of the pre-focus photodetector 10 and the post-focus photodetector 13. In the embodiment of the present invention, the user host computer 20 is communicated with through the serial port protocol, and the user host computer 20 uses the serial port protocol to issue a start work instruction to the processing module 14. The transmission of the instruction can use other methods in the prior art, which is not limited by the present invention and can be selected according to actual conditions. The AD sampling module is used to convert the analog signals of the displacement data and light intensity data collected during the sampling period into digital signals; the DA conversion module 16 is used to convert the digital signals into analog signals; and the storage module is used to store the displacement data and light intensity data.

[0067] The present invention also provides a preferred storage module including a FIFO cache unit 18 - 1 and a DDR memory unit 18 - 2 .

[0068] The programmable logic module 15 includes a main control unit 15-1, a drive unit 15-2 and a data acquisition unit 15-3. The processing module 14 sends a working instruction to the main control unit 15-1, and the main control unit 15-1 sends a control signal to the drive unit 15-2 and the data acquisition unit 15-3 at the same time. After receiving the control signal, the drive unit 15-2 sends a single-cycle sawtooth wave signal to the DA conversion module 16, such as Figure 5 As shown in (a), T0=0ms is the start time of signal output, T1=50ms is the peak time of signal output, and T2=60ms is the end time of signal output. The DA conversion module 16 outputs a 0-10V voltage, which is amplified to 0-150V by the piezoelectric driver and input to the objective lens positioner 5 to control its axial movement. The displacement of the objective lens positioner 5 is shown in FIG. Figure 5 (b) In the embodiment of the present invention, T0 and T1 are respectively the start time and the end time of sampling, and the collected data is in the cache FIFO. At T1-T2, the objective lens positioner 5 is returned to the position to collect data of the next point to be measured of the object to be measured 6, and the processing module 14 analyzes and processes the collected data.

[0069] In the embodiment of the present invention, the data acquisition unit 15-3 simultaneously acquires three data channels, which are displacement data, light intensity data of the pre-focus photodetector 10 and the post-focus photodetector 13, and each channel of data acquires 10,000 sets of signals. In the embodiment of the present invention, the position signal fed back by the objective lens positioner 5 has a voltage range of 0-10V, corresponding to a displacement of 0-100μm, and is converted into a digital signal by a 16-bit AD sampling module. The pre-focus photodetector 10 signal has a voltage range of 0-3.3V, which is converted into a digital signal by a 16-bit AD sampling module. The post-focus photodetector 13 signal has a voltage range of 0-3.3V, which is converted into a digital signal by a 16-bit AD sampling module. The sampling frequency is 200kHz, and sampling is performed between T0=0ms and T1=50ms. A total of 10,000 sets of data are collected in one sampling cycle. After each sampling, the displacement data of the objective lens positioner 5, the signal data of the pre-focus photodetector 10, and the signal data of the post-focus photodetector 13, a total of 48 bits of data, are stored in the FIFO cache. The FIFO cache input bit width is 48 bits, the depth is 1024 bits, and the output bit width is 16 bits. The FIFO cache then stores the collected data in the DDR memory through the AXI high-speed bus 21. At T2=50ms, the programmable logic module 15 completes data acquisition and sends a measurement end signal to the processing module 14 through the AXI high-speed bus 21. The processing module 14 starts to read the sampled signal from the DDR memory and then processes it. The processing process in the embodiment of the present invention is described in detail in the measurement method, so it will not be described in detail. After the processing module 14 uses the measurement method for processing, it obtains the position information of the object to be measured 6 and transmits the position information to the user host computer 20 through the serial port.

[0070] The processing module 14 and the programmable logic module 15 in the embodiment of the present invention are ZYNQ chips 19, and the XC7Z020CLG400-2 chip of the ZYNQ series can be used. The DA conversion module 16 uses the DAC8563 chip, the drive unit 15-2 uses the CORE MORROW E53.D1S piezoelectric drive controller, and the objective lens positioner 5 uses the CORE MORROW P72.Z100S piezoelectric objective lens driver. The first AD conversion module used to convert the analog signal of the objective lens positioner 5 into a digital signal uses the AD7606 chip. The second and third AD conversion modules used to convert the analog signals of the pre-focus photodetector 10 and the post-focus photodetector 13 into digital signals both use the MAX11166 chip. The pre-focus photodetector 10 and the post-focus photodetector 13 both use the SM05PD2A large-area silicon photodiode. The DDR memory uses NT5CB256M16EP-DI with a capacity of 4Gbit.

[0071] In summary, the embodiment of the present invention utilizes the characteristics of parallel operation of the programmable logic module 15 to achieve the synchronous acquisition of the photoelectric detector light intensity data and the objective lens driver 5 position data within a time less than one clock cycle, ensuring the real-time correspondence between the photoelectric detector light intensity data and the objective lens driver position 5. The ZYNQ chip model used in the embodiment of the present invention is XC7Z020CLG400-2. The chip data sampling rate is as high as 200kHz. The data acquisition, storage and processing are completed in the same chip, and the delay of the data during transmission is lower. The zero point of the focusing error signal is extracted by the least squares method for the zero point of the differential signal, and the processing speed is faster. The technical solution of the embodiment of the present invention integrates the objective lens control, data acquisition, and data analysis and processing into one device, which reduces the development cost and reduces the size of the equipment.

[0072] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0073] Although the embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and cannot be understood as limiting the present invention. Those skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

[0074] The above specific implementations of the present invention do not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A measurement method based on a differential confocal system, characterized in that: The following steps are involved: S1, driving the objective lens positioner to move along the optical axis direction to drive the objective lens to move, and sampling the displacement data of the objective lens positioner, the light intensity data of the pre-focus photodetector and the post-focus photodetector; wherein the displacement data is represented by d: {d1, d2, ..., d q }; the light intensity data of the pre-focus photodetector is represented by a: {a1, a2...a q }; the post-focus photodetector light intensity data is represented by b{b1, b2...b q }; S2, analyzing the displacement data, the light intensity data of the pre-focus photodetector and the post-focus photodetector to obtain the position information of the object to be measured; S201, subtract the light intensity data of the pre-focus photodetector from the light intensity data of the post-focus photodetector to obtain a focus error signal f: {f1, f2...f q }; where q is the number of sampling times; S202, obtaining the mth data and the nth data in the focus error signal; wherein the mth data is the maximum value f m , the nth data is the minimum value f n ; S203, obtaining the m+(nm) / 4th to n-(nm) / 4th groups of data in the focus error signal, the two groups of data are respectively expressed as: d: {d m+(n -m) / 4,...,d n-(n-m) / 4 } and f: {f m+(n-m) / 4 ,...,f n-(n-m) / 4 }; S204, fitting is performed by the two sets of data to obtain a fitting function f=c1×d+c2, and coefficients c1 and c2 of the fitting function are obtained respectively; wherein the coefficient formula of the fitting function is expressed as formula (1): Where i represents the i-th sampling point; c1 represents the slope of the fitting function; c2 represents the intercept of the fitting function; S205. Obtain the position information of the object to be measured according to the obtained coefficient; wherein the position information is expressed as formula (2): l=-c2 / c1(2) Among them, l represents the location information.

2. The measuring method according to claim 1, characterized in that: The sampling period of data acquisition is set as follows: the sampling start time is the time when the objective lens positioner starts to move, and the sampling end time is the time when the objective lens positioner stops moving; wherein, If the moment of starting displacement is the point where the travel range of the objective lens positioner is the smallest, then the moment of stopping displacement is the point where the travel range of the objective lens positioner is the largest; If the moment of starting displacement is the point where the travel range of the objective lens positioner is the largest, then the moment of stopping displacement is the point where the travel range of the objective lens positioner is the smallest.

3. A measuring device based on the measuring method of the differential confocal system according to claim 1, characterized in that: It includes a processing module, a programming logic module, a DA conversion module, at least one AD sampling module and a storage module; wherein, The processing module is used to receive and transmit work instructions, and obtain distance information of the object to be measured after analyzing the collected data; The programming logic module is used to drive the objective lens positioner to move and sample data; the data includes: displacement data of the objective lens positioner, light intensity data of the pre-focus photoelectric detector and the post-focus photoelectric detector; The AD sampling module is used to convert the analog signals of the displacement data and the light intensity data collected within a sampling period into digital signals; The DA conversion module is used to convert the digital signal into an analog signal; The storage module is used to store the displacement data and the light intensity data.

4. The measuring device according to claim 3, characterized in that The programming logic module includes a main control unit, a drive unit and a data acquisition unit; wherein, The main control unit is used to receive the working instructions of the processing module and control the driving unit and the data acquisition unit to work; The driving unit is used to drive the objective lens positioner to move axially along the optical axis and send a driving signal to the data acquisition unit to collect data; The data acquisition unit is used to sample the displacement data of the objective lens positioner and the light intensity data of the pre-focus photodetector and the post-focus photodetector.

5. The measuring device according to claim 3 or 4, characterized in that The processing module and programming logic module are ZYNQ chips.

6. The measuring device according to claim 3, characterized in that The storage module includes a FIFO buffer unit and a DDR memory unit.

7. The measuring device according to claim 3, characterized in that The number of the AD sampling modules is three, which are respectively used to convert the analog signals of the displacement data of the objective lens positioner, the light intensity data of the pre-focus photodetector and the post-focus photodetector into digital signals.

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