CN115993695B - In-situ automatic focusing device and method based on spectral confocal - Google Patents

Abstract

The invention discloses an in-situ automatic focusing device and method based on spectral confocal. The measurement of the absolute defocus displacement is realized by adopting the mode of coaxially mounting the spectral confocal sensor, so that the closed-loop control response of the automatic focusing system is improved; the spectral interference of the focusing system on the existing optical path system can be avoided by matching the displacement signal of the moving table grating ruler with the triggering working time of the spectral confocal probe for measuring the defocus amount and the signal conversion module of the existing optical path system; by setting the defocusing measuring point to form a certain advanced offset relative to the imaging or processing position, the automatic focusing device can always realize dynamic focusing on the current working position, and the generation of lag of the focusing position is avoided.

Description

An in-situ autofocus device and method based on spectral confocal

technical field

The invention belongs to the technical field of automatic optical detection, and in particular relates to an in-situ automatic focusing device and method based on spectral confocal.

Background technique

As an important link in the field of precision engineering, optical detection and optical processing technology has become an indispensable part of human life and production. From the high-end chip lithography process, to the common industrial workpiece visual inspection, to the laser processing fields including laser cutting, laser cladding printing, laser micro-nano processing, laser annealing, laser welding and other laser processing fields, human beings are using various characteristics of optics to achieve more precise and complex inspection and processing requirements. As the main component of optical parameter manipulation, the larger the numerical aperture of the optical system, the smaller the critical dimension that the overall equipment can detect or process, and then the depth of field of the optical system becomes smaller, so that the quality of detection or processing is very sensitive to the defocus of the optical system relative to the workpiece. Therefore, sophisticated optical detection and optical processing technology will inevitably put forward higher requirements for the focus control of the optical system.

The autofocus device can usually be considered as an independent closed-loop control system, which consists of three parts: defocus detector, focus actuator and controller. The defocus detector can obtain the defocus signal on the surface of the workpiece through the striped structured light, and can also measure the defocus between the optical system and the workpiece surface through a high-precision displacement sensor. The focus actuator is mainly used for the defocus control of the optical system. It can move the overall optical system through a linear displacement platform, or control the position of a specific lens in the zoom optical system through a voice coil motor or piezoelectric ceramics. After the controller obtains the defocus data from the defocus amount detector, it drives and controls the focusing actuator, so as to realize the function of automatically focusing on the surface of the workpiece.

In the current prior art, the main forms of autofocus devices can be divided into three types: coaxial, off-axis and triangular reflection. In the coaxial autofocus device, the optical path of the autofocus system and the existing optical system for detection or processing are partly coaxial through a spectroscopic device, such as the AF series products of Japan Chuo Seiki Co., Ltd., and the ATF series products of Canada WDI Company. Astigmatism is characterized by the degree of astigmatism, which can only realize the characterization of defocus and defocus direction, but cannot quantitatively calculate the specific defocus displacement. Therefore, multiple closed-loop control cycles are often required to achieve single autofocus, resulting in the final closed-loop control bandwidth is not high, and high-response autofocus cannot be realized. However, if the spectral confocal-based autofocus device mentioned in the patent CN114047203A is used, the spectral confocal based on the principle of spectral dispersion needs to occupy a spectral bandwidth of hundreds of nanometers, which is often limited to spectrally insensitive applications, such as AOI detection equipment. In the off-axis autofocus device, the optical path of the autofocus system is independent of the existing optical system, so there is no need to consider the coupling and isolation of the spectral bands between the two. However, the measurement point of the off-axis autofocus device deviates greatly from the center of the field of view of the existing optical system. Therefore, it is often necessary to perform height position mapping. After detecting the defocus amount of a certain area of the workpiece, it enters the field of view of the existing optical system for detection or processing. The height data driven by the position mapping controls the focusing actuator to perform zooming actions. The control strategy is more complicated, such as patent CN11390 0219A. The optical system of the triangular reflective autofocus device is also independent of the existing optical system, and its measurement point can be moved to a position that coincides with the center of the field of view of the existing optical system by adjusting the angle of the triangular reflection. However, in order to match the large-aperture high-resolution characteristics of the existing optical system, the angle of the triangular reflection needs to be increased, which directly increases the complexity and cost of the structure, such as patent CN104749901A.

Therefore, it is a technical problem to be solved urgently by those skilled in the art to provide a high-response auto-focusing device and focusing method that does not affect the spectral characteristics of the existing optical system, can be measured in situ in real time, and has a simple structure.

Contents of the invention

In order to solve the problems in the background technology, the present invention proposes an in-situ autofocus device and method based on spectral confocal.

The technical scheme that the present invention adopts is as follows:

1. An in-situ autofocus device based on spectral confocal

Including focusing system, existing optical path system, existing optical path system signal conversion module, coaxial beam splitting module, workpiece, moving stage, grating scale, optical system mounting base and moving stage controller, focusing system includes spectral confocal probe, spectral confocal controller, autofocus controller, and optical system focusing actuator.

The existing optical path system, spectral confocal probe, coaxial spectroscopic module, and optical system focusing actuator are installed on the optical system installation base; the workpiece is placed on the moving table connected to the moving table controller, and a grating scale is installed on the moving table. The moving table controller is connected to the spectral confocal controller and the existing optical system signal conversion module through cables; The confocal probe achieves coaxial coupling with the existing optical path system through the coaxial spectroscopic module, and finally hits the spot on the surface of the workpiece.

The motion table controller reads the signal of the grating scale on the motion table, and generates two trigger signals, which are used to trigger the spectral confocal controller and the existing optical path system signal conversion module to work respectively; the autofocus controller reads the defocus data calculated by the spectral confocal controller, and drives and controls the focusing actuator of the optical system to adjust the focus.

The existing optical path system is an optical path system for optical detection or optical processing, and the signal conversion module of the existing optical path system is an imaging camera for optical detection or a laser light source for optical processing.

The time interval between two adjacent imaging trigger signals of the camera or two adjacent trigger signals of the laser light source is longer than the single measurement time of the spectral confocal probe.

The moving direction of the moving stage is parallel to the plane formed by the spectral confocal probe and the optical axis of the existing optical path system.

2. An in-situ autofocus method based on spectral confocal

Include the following steps:

Step 1) The motion table drives the workpiece to move two-dimensionally on the horizontal plane through the motion table controller, and the motion table controller continuously obtains the current position of the motion table by reading the grating scale data in real time;

Step 2) The moving table reaches the position where the workpiece is to be imaged or processed, and the spectral confocal controller calculates the defocus of the existing optical system and the surface of the workpiece;

Step 3) The autofocus controller reads the defocus data calculated by the spectral confocal controller, drives and controls the focusing actuator of the optical system to perform focusing operations until the existing optical path system reaches the focus height position;

Step 4) The motion table controller sends a trigger signal to the signal conversion module of the existing optical path system, and the signal conversion module of the existing optical path system starts to work after receiving the trigger signal to realize the work of optical detection imaging or optical processing.

Step 5) The motion table continues to scan, repeating step 2), step 3), and step 4) until the motion scan is completed.

The spectral confocal controller and the signal conversion module of the existing optical path system are configured as an external trigger mode.

In the step 1), according to the grating ruler signal and the distance between the moving stages corresponding to the interval working time of the existing optical path system during the movement of the workpiece, respectively set the frequency division numbers of the trigger signal of the signal conversion module of the existing optical path system and the trigger signal of the spectral confocal controller, and then set the phase and duty ratio parameters of the two trigger signals so that the trigger working time of the spectral confocal controller falls within the interval corresponding to two adjacent working points of the existing optical path system.

The step 2) specifically, when the moving table reaches the position where the workpiece is to be imaged or processed, the moving table controller sends a trigger signal to the spectral confocal controller. After receiving the trigger signal, the spectral confocal controller turns on the light source and transmits it to the spectral confocal probe through an optical fiber. Spectral analysis is carried out, and the defocus amount of the existing optical system and the workpiece surface is obtained through the mapping relationship between the axial dispersion spectrum and the spatial displacement in the spectral confocal probe (the mapping relationship between the spectrum and the spatial displacement is related to the design parameters of the spectral confocal probe 111 axial dispersion); after the trigger signal ends, the spectral confocal controller turns off the light source and stops the exposure calculation.

In the step 2), adjust the relative position of the spectral confocal probe and the coaxial spectroscopic module, so that the defocus measurement point forms a leading or lagging offset S on the scanning path relative to the imaging or processing position, S>(t+T)*V;

Among them, t is the single measurement time of the spectral confocal probe; T is the maximum setting time of the focusing actuator of the optical system, and the maximum setting time is the longest time required for the focusing actuator of the optical system to perform step motion according to the peak-to-peak value of the height change of the workpiece surface; V is the moving speed of the moving table.

The absolute height of the existing optical system relative to the workpiece surface can usually be obtained within a time t of less than 100us by using a spectral confocal probe, so that the defocus amount of the optical system can be calculated according to the focal length of the existing optical system.

In step 5), in order to ensure that the real-time focusing effect can always be achieved during the continuous scanning of the moving platform, the advance offset S of the defocus measurement point is smaller than the position distance between two adjacent working points of the existing optical path system.

Beneficial effects of the present invention:

The in-situ autofocus device and method based on spectral confocal of the present invention realizes the measurement of absolute defocus displacement by adopting the form of coaxial installation of spectral confocal sensor, and improves the closed-loop control response of the autofocus system; the grating ruler displacement signal of the moving table matches the trigger working time of the spectral confocal probe for defocus measurement and the trigger working time of the existing optical path system signal conversion module, which can avoid the spectral interference of the focus measurement system on the existing optical path system; by setting the defocus measurement point to form a certain advanced offset relative to the imaging or processing position, it can ensure that the autofocus device is always on the current The working position realizes dynamic focus, avoiding the lag of focus position.

Description of drawings

Figure 1 is a block diagram of autofocus control based on the relative defocus amount characterization and the absolute defocus amount measurement respectively;

Figure 2 is the working band of common optical processing and detection systems;

Fig. 3 is a schematic diagram of spectral confocal measurement; in the figure: spectrometer 201, light source 202, spectral confocal probe 203, object surface 204;

Fig. 4 is the spectral confocal working band distribution figure;

5 is a schematic structural view of an embodiment of the present invention; in the figure: a spectral confocal controller 101, an existing optical path system signal conversion module 102, an existing optical path system 103, an optical system mounting base 104, an optical system focusing actuator 105, a coaxial light splitting module 106, a workpiece 107, a moving stage 108, a grating ruler 109, and a moving stage controller 110. The focusing measurement system includes a spectral confocal probe 111 and an autofocus controller 112;

Fig. 6 is a schematic diagram of level signals for time-sharing triggering of the existing optical path system and focusing system according to the embodiment of the present invention;

7 is a schematic diagram of time-sharing triggering the work of the existing optical path system and triggering the focus of the focusing system in an embodiment of the present invention;

Fig. 8 is a structural schematic diagram of the coincidence of the measuring point of the focusing system with the center of the field of view of the optical system;

Fig. 9 is a structural schematic diagram of the measurement point of the focusing system deviating from the center of the field of view of the optical system to the left;

Fig. 10 is a structural schematic diagram of the measurement point of the focusing system deviating from the center of the field of view of the optical system to the right;

FIG. 11 is a flow chart of performing autofocus according to an embodiment of the present invention;

Figure 12 is a typical step motion response curve diagram of a linear motor;

Fig. 13 is the linear motor step motion settling time graph obtained by setting different step distances;

14 is a schematic flow chart of real-time auto-focusing during the scanning movement of the embodiment of the present invention; wherein, S is the leading offset of the defocus measurement point on the scanning path relative to the imaging or processing position, t is the single measurement time of the spectral confocal probe, T is the maximum setting time of the focusing actuator of the optical system, V is the moving speed of the moving table (the arrow indicates the scanning direction), P1 indicates the focusing position, and P2 indicates the imaging or processing position.

Detailed ways

The present invention will be described in more detail below with reference to the accompanying drawings, which show preferred embodiments of the present invention, and it should be understood that those skilled in the art can modify the present invention described herein and still achieve the advantageous effects of the present invention. Therefore, the following description should be understood as the broad knowledge of those skilled in the art, but not as a limitation of the present invention.

For clarity, in the following description, well-known functions and constructions are not described in detail since they would obscure the invention with unnecessary detail. In order to make the purpose and features of the present invention more comprehensible, the specific implementation manners of the present invention will be further described below in conjunction with the accompanying drawings. It should be noted that the drawings are all in a very simplified form and use imprecise ratios, which are only used to facilitate and clearly assist the purpose of illustrating the embodiments of the present invention.

In the current prior art, the main forms of autofocus devices can be divided into three types: coaxial, off-axis and triangular reflection. In the coaxial autofocus device, the optical path of the autofocus system and the existing optical system for detection or processing are partly coaxial through a spectroscopic device. In order to avoid the impact of the focusing system on the imaging of the existing optical system, it is generally necessary to spectrally isolate the two systems through an optical filter, thus resulting in the loss of information in a specific spectral segment of the existing optical system. At the same time, the current coaxial autofocus device is often characterized by analyzing the spot shape signal or spot signal intensity or the degree of imaging astigmatism, such as Japan Chuo Seiki Co., Ltd. AF series products, Canada WDI The company's ATF series products can only realize the characterization of defocus and defocus direction, but cannot quantitatively calculate the specific defocus displacement. Therefore, multiple closed-loop control cycles are often required to achieve single autofocus, resulting in the final closed-loop control bandwidth is not high, and high-response autofocus cannot be realized. The present invention improves on this, specifically as shown in Figure 1, if the absolute defocus displacement can be measured once, then only need to drive and control the focusing actuator to move a certain distance to realize focusing, thereby improving the overall control bandwidth.

In the off-axis autofocus device, the optical path of the autofocus system is independent of the existing optical system, so that there is no need to consider the coupling and isolation of the spectral bands between the two. However, the measurement point of the off-axis autofocus device deviates greatly from the center of the field of view of the existing optical system, so it is often necessary to perform height position mapping. After detecting the defocus amount of a certain area of the workpiece, it enters the field of view of the existing optical system for detection or processing. The height data driven by the position mapping controls the zooming action of the focusing actuator, and the control strategy is more complicated.

The optical system of the triangular reflection autofocus device is also independent of the existing optical system. The measurement point can be moved to a position that coincides with the center of the field of view of the existing optical system by adjusting the angle of the triangular reflection. However, in order to match the large aperture and high resolution characteristics of the existing optical system, the angle of the triangular reflection needs to be increased, which directly increases the complexity and cost of the structure.

Figure 2 shows the working bands of common optical processing and inspection systems. Chip lithography uses ultraviolet to extreme ultraviolet bands. Industrial visual inspection often uses visible light bands instead of naked eye evaluations. In the field of laser processing, infrared bands are widely used. The autofocus device can also be considered as an optical detection system. How to avoid mutual interference between the two optical systems, especially the coupling of spectral information, is an urgent problem in the industry. Therefore, it is of great significance to propose an autofocus device suitable for imaging detection and processing applications in various spectral segments, which is of great significance to promote the development of precision optical detection and processing.

Fig. 3 shows the principle diagram of spectral confocal measurement. After the wide-spectrum optical signal emitted by the light source 202 enters the spectral confocal probe 203 through the optical fiber, a high degree of axial dispersion is generated. The returned light from the object surface 204 is coaxially received by the spectral confocal probe 203 and forms a spectral peak in the spectrometer 201 through the optical fiber. Extract the peak position of the spectral peak through the CMOS image sensor, calculate the actual spatial distance, and realize high-speed non-destructive distance detection. With the development of 3C electronics, semiconductor, and new energy industries, the demand for high-precision processing and measurement of precision structural parts has been driven. Sensor products based on the principle of spectral confocal measurement have gained more application recognition and market development in recent years due to their high adaptability to various materials, high precision, and non-contact high-speed sampling capabilities. Therefore, from the application of a type of focus sensor, on the one hand, it can meet the scenes of different workpiece surface materials in different focusing scenes, and on the other hand, its measurement results correspond to absolute defocus displacement data, which helps to improve the closed-loop control bandwidth of the autofocus system.

Figure 4 shows the working band of the spectral confocal light source LED, which generally works in the visible light band range of 400-700nm. One way to avoid spectral interference between the focusing system and the existing optical path system is to use a time division method. However, if the focusing system requires a long time for defocus measurement or a large number of defocus measurement times during a single focusing process, the coaxial autofocus device can only be used to characterize defocus and defocus direction, and in the entire closed-loop cycle, it needs to measure the defocus displacement multiple times. A single focusing action often takes several seconds of working time, and the time-division method is bound to seriously reduce the bandwidth capability of the entire system. At present, the spectral confocal sensor can measure the absolute defocus displacement at a speed of up to 10kHz. It only needs less than 100us of light source lighting and exposure time to realize the defocus measurement, and the relative displacement feedback is controlled to the focusing actuator.

Fig. 5 is a schematic diagram provided by an embodiment of the present invention. It consists of an existing optical path system 103, an existing optical path system signal conversion module 102, a spectral confocal probe 111, a spectral confocal controller 101, a coaxial spectroscopic module 106, an optical system mounting base 104, an optical system focusing actuator 105, an autofocus controller 112, a workpiece 107, a moving table 108, a grating ruler 109, and a moving table controller 110. The existing optical path system 103, the existing optical path system signal conversion module 102, the spectral confocal probe 111, the spectral confocal controller 101, and the coaxial spectroscopic module 106 are installed on the optical system mounting base 104, the optical system focusing actuator 105 is rigidly connected to the optical system mounting base 104, and the spectral confocal probe 111 is coaxially coupled with the existing optical path system 103 through the coaxial spectroscopic module 106. In order to avoid mutual interference between the two sets of optical systems, the high sampling rate characteristics of the spectral confocal probe 111 can be fully utilized. The single defocus measurement time of the spectral confocal probe 111 only requires light source lighting and exposure time less than 100us. Therefore, as long as the time interval between two adjacent imaging trigger signals of the camera is greater than 100us, the requirements can be met, and most of the focus measurement scenarios can be met.

The workpiece 107 is placed on the moving table 108, and a grating scale 109 is installed on the moving table 108. The moving table controller 110 can control the moving table 108 to drive the workpiece 107 to move. The moving table controller 110 can calculate the current position of the moving table 108 by reading the data of the grating ruler 109.

Spectral co -focus probes 111 and spectral co -focus controller 101 connect through optical fiber, existing optical road system 103 and existing light road system signal conversion module 102, sports table controller 110 through cable and spectrum co -focus controller 101, existing light road system signal conversion module 102, and signal of the light grid 109 of the sports table 108, and the signal of the two -road trigger. Work on triggering spectral co -focus controller 101 and the existing optical path system signal conversion module 102. The auto-focus controller 112 can read the defocus data calculated and obtained by the spectral confocal control 101 , and drive and control the optical system focus actuator 105 to perform focus adjustment.

The existing optical system 103 may be an optical system for optical detection or optical processing, and the existing optical system signal conversion module 102 may be an imaging camera for optical detection or a laser light source for optical processing.

As shown in Figure 8, by adjusting the relative position of the spectral confocal probe 111 and the coaxial spectroscopic module 106, the offset of the defocus measurement point of the spectral confocal probe 111 relative to the center of the field of view of the existing optical system 103 can be changed. If the spectral confocal probe 111 is relatively moved upward, the defocus measurement point will fall on the left of the center of the field of view of the existing optical system 103, as shown in Figure 9; To the right of the center of the field of view, as shown in Figure 10. Therefore, by setting the scanning direction of the moving stage parallel to the plane formed by the spectral confocal probe 111 and the optical axis of the existing optical path system 103, the lead and lag of the out-of-focus measurement point relative to the imaging or processing position can be realized.

As shown in Figure 11, the autofocus method of the in-situ autofocus device based on spectral confocal in the present invention includes the following steps:

Step 1) The motion table starts motion scanning, and the motion table controller continuously obtains the position signal of the motion table by reading the signal of the grating ruler of the motion table.

Step 2) When the moving table reaches the position where the workpiece is to be imaged or processed, the moving table controller 110 sends a trigger signal to the spectral confocal controller 101. The spectral confocal controller 101 is configured as an external trigger mode. After receiving the trigger signal, the light source is turned on and transmitted to the spectral confocal probe 111 through an optical fiber. After the optical signal coaxially returns through the spectral confocal probe and optical fiber, spectral analysis is performed in the spectral confocal controller 101, and the defocus amount of the existing optical system 103 and the workpiece surface is finally obtained through the mapping relationship between the axial dispersion spectrum in the spectral confocal probe 111 and the spatial displacement of the axial dispersion. After the trigger signal ends, the spectral confocal controller turns off the light source and stops the exposure calculation.

Step 3) The autofocus controller 112 reads the defocus amount data calculated by the spectral confocal controller, and drives and controls the focusing actuator to perform focusing operations until reaching the focus height position.

Step 4) The motion table controller 110 sends a trigger signal to the existing optical system signal conversion module 102. The existing optical system signal conversion module is configured as an external trigger mode, and starts to work after receiving the trigger signal to realize optical detection imaging or optical processing.

Step 5) The motion table continues to scan, repeating step 2), step 3), and step 4) until the motion scan is completed.

In step 1), when the moving platform is moving at a constant speed at a speed V, the grating scale generates high and low level digital signals corresponding to the movement displacement, and the moving platform controller can obtain the current real-time position of the moving platform by calculating the number of high and low level pulses. According to the frequency division, phase and duty cycle setting of the grating ruler signal, a custom high and low level signal can be obtained, which are respectively used to trigger the spectral confocal controller to measure the defocus amount and the existing optical system signal conversion module to work. By configuring two trigger signals, the spectral confocal controller and the existing optical system signal conversion module can work alternately.

As shown in FIG. 7 , according to the grating signal of the moving table and the distance between the moving platforms corresponding to the working interval of the existing optical system 103 during the motion scanning process, the frequency division numbers of the trigger signal of the existing optical system signal conversion module and the trigger signal of the focusing system are respectively set, and then by setting the phase and duty ratio parameters of the two trigger signals, the triggering working time of the focusing system falls within the non-working interval of two adjacent working points of the existing optical system signal conversion module.

As shown in Figure 6, the rising edge of the square wave corresponds to the trigger action of the signal conversion module of the existing optical system and the focusing system, and the high-level time of the square wave corresponds to the exposure time of the signal conversion module of the existing optical system and the focusing system.

In the step 2), by adjusting the relative positions of the spectral confocal probe 111 and the coaxial spectroscopic module 106 , the defocus measurement point forms a certain lead or lag offset S on the scanning path relative to the imaging or processing position. The absolute height of the existing optical system 103 relative to the workpiece surface can usually be obtained within a time t of less than 100 us by using the spectral confocal probe, so that the defocus displacement of the optical system can be calculated according to the focal length of the existing optical system.

In the step 3), the time required for the focus actuator to move and stabilize to the focus height position is called the settling time. The operation of focusing to the focus position after calculating the defocus amount data each time can be considered as sending a step motion command to the focus actuator. The settling time of the step motion response is related to the maximum working power of the focus actuator, the inertial load of the mechanism, and the relative displacement of the step motion. Therefore, the maximum defocus amount of the workpiece surface is estimated in advance, which can be used to estimate the maximum settling time T required by the focus actuator during a single focusing process (the maximum settling time T is the longest time required for the focus actuator to perform step motion according to the maximum defocus amount of the workpiece surface), and usually a settling time of less than 100ms can be achieved under a 100um step motion command. Figure 12 is a typical step motion response curve of a linear motor, and Figure 13 is a graph of the settling time of a linear motor step motion obtained by setting different step distances. By taking the step motion setting time _T1 corresponding to the movement distance _D1 exceeding the maximum defocus amount of the workpiece surface as the maximum setting time required by the focusing actuator in a single focusing process.

In step 4), in order to ensure that the autofocus device has completed the focusing work of the optical system relative to the current workpiece position when the moving table reaches the designated working position, the condition S>(t+T)*V needs to be satisfied. As shown in Figure 14.

The step 5), as shown in Figure 14, in order to ensure that the real-time focusing effect can always be achieved during the continuous scanning of the moving stage, the advance offset S of the defocus measurement point needs to be smaller than the distance between two adjacent imaging or processing positions. In order to avoid the next "focus-imaging or processing" process from interfering with the previous "focus-imaging or processing" process.

Claims (8)

1. An in-situ autofocus device based on spectral confocal, characterized in that it includes a focusing system, an existing optical path system (103), an existing optical path system signal conversion module (102), a coaxial spectroscopic module (106), a workpiece (107), a moving stage (108), a grating ruler (109), an optical system mounting base (104) and a moving stage controller (110), and the focusing measurement system includes a spectral confocal probe (111), a spectral confocal controller (101 ), an autofocus controller (112), an optical system focusing actuator (105); The existing optical path system (103), spectral confocal probe (111), coaxial spectroscopic module (106), and optical system focusing actuator (105) are installed on the optical system installation base (104); the workpiece (107) is placed on the moving table (108) connected to the moving table controller (110), and a grating scale (109) is installed on the moving table (108). 1) Connect with the signal conversion module (102) of the existing optical path system; the spectral confocal controller (101) is connected with the autofocus controller (112) through a cable, and connected with the spectral confocal probe (111) through an optical fiber; the signal conversion module (102) of the existing optical path system is connected with the existing optical path system (103), the autofocus controller (112) is connected with the focusing actuator (105) of the optical system, and the spectral confocal probe (111) is connected with the existing optical path through a coaxial spectroscopic module (106) The system (103) realizes coaxial coupling, and finally hits the spot on the surface of the workpiece (107); The motion table controller (110) reads the signal of the grating ruler (109) on the motion table (108), and generates two trigger signals, which are respectively used to trigger the spectral confocal controller (101) and the existing optical path system signal conversion module (102) to work; The autofocus controller (112) reads the defocus data calculated by the spectral confocal controller (101), and drives and controls the optical system focus actuator (105) to perform focus adjustment. 2. A kind of in-situ autofocus device based on spectral confocal according to claim 1, characterized in that, The existing optical path system (103) is an optical path system for optical detection or optical processing, and the existing optical path system signal conversion module (102) is an imaging camera for optical detection or a laser light source for optical processing. 3. An in-situ autofocus device based on spectral confocal according to claim 2, wherein the time interval between two adjacent imaging trigger signals of the camera or two adjacent trigger signals of the laser light source is greater than the single measurement time of the spectral confocal probe. 4. The in-situ autofocus device based on spectral confocal according to claim 1, characterized in that the movement direction of the moving table (108) is parallel to the plane formed by the optical axis of the spectral confocal probe (111) and the existing optical path system (103). 5. An in-situ auto-focusing method of the device according to any one of claims 1-4, characterized in that, comprising the following steps: Step 1) The motion table (108) drives the workpiece to perform two-dimensional motion through the motion table controller (110), and the motion table controller (110) continuously obtains the current position of the motion table (108) by reading the data of the grating ruler (109) in real time; Step 2) The moving table reaches the position where the workpiece is to be imaged or processed, and the spectral confocal controller (101) calculates the defocus amount between the existing optical system (103) and the surface of the workpiece; Step 3) The autofocus controller (112) reads the defocus data calculated by the spectral confocal controller (101), drives and controls the optical system focusing actuator (105) to perform focusing operations until the existing optical system (103) reaches the focus height position; Step 4) The motion table controller (110) sends a trigger signal to the existing optical path system signal conversion module (102), and the existing optical path system signal conversion module (102) starts working after receiving the trigger signal to realize optical detection imaging or optical processing; Step 5) The motion table continues to scan, repeat step 2), step 3), and step 4) until the motion scan is completed; In the step 1), according to the grating ruler signal and the distance between the moving stages corresponding to the interval working time of the existing optical path system (103) during the movement of the workpiece, respectively set the frequency division numbers of the trigger signal of the existing optical path system signal conversion module (102) and the trigger signal of the spectral confocal controller (101), and then set the phase and duty ratio parameters of the two trigger signals so that the trigger working time of the spectral confocal controller (101) falls within the interval corresponding to two adjacent working points of the existing optical path system (103). 6. The in-situ auto-focusing method according to claim 5, wherein the step 2) is specifically as follows: when the moving table reaches the position where the workpiece is to be imaged or processed, the moving table controller (110) sends a trigger signal to the spectral confocal controller (101), and the spectral confocal controller (101) turns on the light source after receiving the trigger signal, and transmits it to the spectral confocal probe (111) through an optical fiber. ) hit the light spot on the surface of the workpiece, after the optical signal of the focused spectral segment on the workpiece surface is returned coaxially to the spectral confocal probe (111), the spectral analysis is performed in the spectral confocal controller (101), and the defocus amount of the existing optical system (103) and the workpiece surface is obtained through the mapping relationship between the axial dispersion spectrum and the spatial displacement in the spectral confocal probe (111); after the trigger signal ends, the spectral confocal controller (101) turns off the light source and stops the exposure calculation. 7. The in-situ autofocus method according to claim 6, characterized in that, in the step 2), the relative position of the spectral confocal probe (111) and the coaxial spectroscopic module (106) is adjusted so that the defocus measurement point forms a leading or lagging offset S on the scanning path relative to the imaging or processing position, S>(t+T)*V; Among them, t is the single measurement time of the spectral confocal probe (111); T is the maximum setting time of the focusing actuator (105) of the optical system, and the maximum setting time is the longest time required for the focusing actuator (105) of the optical system to perform step motion according to the peak-to-peak value of the height change of the workpiece surface as the moving distance; V is the moving speed of the moving table (108). 8. The in-situ auto-focus method according to claim 5, characterized in that, in step 5), the advance offset S of the defocus measurement point is smaller than the positional distance between two adjacent working points of the existing optical path system (103).