CN115993695A - In-situ automatic focusing device and method based on spectral confocal - Google Patents
In-situ automatic focusing device and method based on spectral confocal Download PDFInfo
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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
Technical Field
The invention belongs to the technical field of automatic optical detection, and particularly relates to an in-situ automatic focusing device and method based on spectral confocal.
Background
Optical detection and optical processing technology are important links in the field of precision engineering, and are now an indispensable part in human life production. From high-end chip photoetching technology, to industry common workpiece visual detection links, to laser processing fields including laser cutting, laser cladding printing, laser micro-nano processing, laser annealing, laser welding and the like, human beings are utilizing various optical characteristics to realize more precise and complex detection and processing requirements. As a main component of optical parameter manipulation, the larger the numerical aperture of the optical system, the smaller the critical dimension that the whole device can detect or process, and the smaller the depth of field of the optical system, so that the quality of detection or processing is very sensitive to the defocus amount of the optical system relative to the workpiece. Therefore, precise optical inspection and optical processing techniques are subject to higher demands on focus control of the optical system.
The automatic focusing device can be generally regarded as an independent closed-loop control system and consists of a defocus amount detector, a focusing actuator and a controller. The defocusing amount detector can acquire defocusing signals of the surface of the workpiece through stripe structure light, can also measure defocusing amount between the optical system and the surface of the workpiece through a high-precision displacement sensor, is mainly used for defocusing amount control of the optical system, can move through a whole optical system carried on a linear displacement platform, and can also control the position of a specific lens in a zooming optical system through a voice coil motor or piezoelectric ceramics. The controller obtains defocusing data of the defocusing amount detector and then drives and controls the focusing actuating mechanism, so that the function of automatically focusing the surface of the workpiece is realized.
In the current prior art, the main forms of autofocus devices can be divided into three types, coaxial, off-axis, and triangular reflective. In the coaxial type automatic focusing device, the optical path of the automatic focusing system and the existing optical system for detection or processing realize the coaxiality of partial optical paths through a light splitting device, such as an AF series product of Japanese Central precision machining Co, an ATF series product of Canada WDI company, in order to avoid the influence of the focusing system on the imaging of the existing optical system, the two systems are generally required to be subjected to spectral isolation through a light filter, so that the loss of information of a specific spectral section of the existing optical system is caused, meanwhile, the existing coaxial type automatic focusing device is often characterized by analyzing the appearance signal of a light spot or the strength of the signal of the light spot or the imaging astigmatism degree, only can realize the characterization of whether defocusing and the defocusing direction, but cannot quantitatively calculate the specific defocusing displacement, so that a plurality of closed-loop control periods are often required to realize single automatic focusing, the final closed-loop control bandwidth is not high, and the high-response automatic focusing function cannot be realized. However, if the auto-focusing device based on spectral confocal mentioned in the patent CN114047203a is adopted, the principle of spectral confocal based on spectral dispersion needs to occupy a spectral bandwidth of hundreds of nanometers, and thus the auto-focusing device is often limited to applications that are not spectrally sensitive, such as AOI detection devices. In the off-axis type automatic focusing device, the optical path of the automatic focusing system is independent of the existing optical system, so that the coupling and isolation of spectrum wave bands between the two are not needed to be considered, but the measuring point of the off-axis type automatic focusing device is greatly deviated from the center of a visual field of the existing optical system, so that high position mapping is often needed, a certain area of a workpiece is detected in an off-focus mode and then enters the visual field of the existing optical system for detection or processing, a focusing actuating mechanism is driven and controlled by the high data of the position mapping to perform zooming action, and a control strategy is complex, such as patent CN113900219A. The optical system of the triangle reflection type automatic focusing device is also independent of the existing optical system, and the measuring point of the optical system can be moved to a position coincident with the center of the field of view of the existing optical system by adjusting the angle of the triangle reflection, but in order to match with the large caliber high resolution characteristic of the existing optical system, the angle of the triangle reflection needs to be increased, and the complexity and cost of the structure are further directly improved, for example, patent CN104749901a.
Therefore, providing a high-response automatic focusing device and a focusing method which do not affect the spectral characteristics of the existing optical system, can perform in-situ real-time measurement, and have a simple structure is a technical problem to be solved by those skilled in the art.
Disclosure of Invention
In order to solve the problems in the background technology, the invention provides an in-situ automatic focusing device and method based on spectral confocal.
The technical scheme adopted by the invention is as follows:
1. in-situ automatic focusing device based on spectrum confocal
The device comprises a focusing system, an existing light path system signal conversion module, a coaxial beam splitting module, a workpiece, a motion platform, a grating ruler, an optical system mounting base and a motion platform controller, wherein the focusing system comprises a spectral confocal probe, a spectral confocal controller, an automatic focusing controller and an optical system focusing actuating mechanism.
The existing optical path system, the spectrum confocal probe, the coaxial light splitting module and the optical system focusing actuating mechanism are arranged on the optical system mounting base; the workpiece is placed on a moving table connected with a moving table controller, a grating ruler is arranged on the moving table, and the moving table controller is respectively connected with a spectrum confocal controller and an existing optical path system signal conversion module through cables; the spectral confocal controller is connected with the automatic focusing controller through a cable and is connected with the spectral confocal probe through an optical fiber; the signal conversion module of the existing optical path system is connected with the existing optical path system, the automatic focusing controller is connected with the focusing actuating mechanism of the optical system, the spectral confocal probe is coaxially coupled with the existing optical path system through the coaxial light splitting module, and finally light spots are beaten on the surface of a workpiece.
The motion platform controller reads the signals of the grating ruler on the motion platform and generates two paths of trigger signals which are respectively used for triggering the spectral confocal controller and the signal conversion module of the existing optical path system to work; and the automatic focusing controller reads the defocus amount data calculated by the spectral confocal controller and drives and controls the focusing actuating mechanism of the optical system to focus.
The existing optical path system is an optical path system for optical detection or optical processing, and the existing optical path system signal conversion module 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 spectrum confocal probe.
The motion direction of the motion stage is parallel to a plane formed by the optical axes of the spectral confocal probe and the existing optical path system.
2. In-situ automatic focusing method based on spectral confocal
The method comprises the following steps:
step 1), a moving table drives a workpiece to perform two-dimensional movement on a horizontal plane through a moving table controller, and the moving table controller continuously obtains the current position of the moving table through reading grating ruler data in real time;
step 2), the motion table reaches the position of a workpiece to be imaged or processed, and a spectral confocal controller calculates the defocus amount of the existing optical system and the surface of the workpiece;
step 3), the automatic focusing controller reads the defocus amount data calculated by the spectral confocal controller, and drives and controls the focusing actuating mechanism of the optical system to perform focusing operation until the existing optical path system reaches the focusing height position;
and 4) the motion platform controller sends a trigger signal to the existing optical path system signal conversion module, and the existing optical path system signal conversion module starts working after receiving the trigger signal, so that the optical detection imaging or optical processing work is realized.
Step 5) continuously moving the moving table for scanning, and repeating the steps 2), 3) and 4) until the moving scanning is completed.
The spectral confocal controller and the existing optical path system signal conversion module are configured in an external trigger mode.
In the step 1), according to the grating ruler signal and the distance between the motion stages corresponding to the interval working time of the existing optical path system in the workpiece motion process, the frequency division numbers of the trigger signal of the existing optical path system signal conversion module and the trigger signal of the spectrum confocal controller are respectively set, and then the trigger working time of the spectrum confocal controller falls in the interval time corresponding to the adjacent two working points of the existing optical path system by setting the phase and duty ratio parameters of the two trigger signals.
The step 2) is that the motion stage reaches the position of a workpiece to be imaged or processed, the motion stage controller sends a trigger signal to the spectral confocal controller, the spectral confocal controller starts a light source after receiving the trigger signal and transmits the trigger signal to the spectral confocal probe through an optical fiber, the spectral confocal probe carries out axial dispersion treatment on an input broad spectrum light source, a light spot is beaten to the surface of the workpiece through a coaxial light-splitting module, the surface of the workpiece generates screening action on the broad spectrum signal after focusing, after the light signal of a specific light spectrum section focused on the surface of the workpiece coaxially returns to the spectral confocal probe, spectral analysis is carried out in the spectral confocal controller, and the defocus amount (the mapping relation between the spectrum of axial dispersion and the space displacement amount is related to the design parameter of axial dispersion of the spectral confocal probe 111) of the existing optical system and the surface of the workpiece is obtained through the mapping relation between the spectrum of the axial dispersion and the space displacement amount of the spectral confocal probe; after the trigger signal is over, the spectral confocal controller turns off the light source and stops the exposure calculation.
In the step 2), the relative positions of the spectral confocal probe and the coaxial light splitting module are adjusted, so that the defocused measuring point forms an advance or retard offset S, S > (t+T) V on a scanning path relative to an imaging or processing position;
wherein t is the single measurement time of the spectral confocal probe; t is the maximum setting time of the optical system focusing actuating mechanism, and the maximum setting time is the maximum time required by the optical system focusing actuating mechanism to perform step motion according to the peak value of the height change of the surface of the workpiece as the motion distance; v is the movement speed of the movement table.
The absolute height of the existing optical system relative to the surface of the workpiece can be obtained in time t smaller than 100us by using the spectral confocal probe, so that the defocusing 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 be always realized in the continuous scanning process of the moving table, the advanced offset S of the defocusing measuring point is smaller than the position distance between two adjacent working points of the existing optical path system.
The invention has the beneficial effects that:
according to the in-situ automatic focusing device and method based on the spectral confocal, the measurement of the absolute defocus displacement is realized by adopting the mode of coaxially mounting the spectral confocal sensor, and the closed-loop control response of an automatic focusing system is improved; the spectral interference of the focusing measurement 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.
Drawings
FIG. 1 is a block diagram of an autofocus control based on a relative defocus characterization and an absolute defocus measurement, respectively;
FIG. 2 is a diagram of the operating bands of a conventional optical processing and inspection system;
FIG. 3 is a schematic diagram of spectral confocal measurement; in the figure: a spectrometer 201, a light source 202, a spectral confocal probe 203, an object surface 204;
FIG. 4 is a spectral confocal operating band distribution diagram;
FIG. 5 is a schematic diagram of an embodiment of the present invention; in the figure: the system comprises a spectrum 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 actuating mechanism 105, a coaxial beam splitting module 106, a workpiece 107, a motion table 108, a grating ruler 109 and a motion table controller 110, wherein a focusing measurement system comprises a spectrum confocal probe 111 and an automatic focusing controller 112;
FIG. 6 is a schematic diagram of a level signal of a time-sharing trigger of an existing optical path system and a focusing system according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of time-sharing triggering of an existing optical path system to operate and triggering of a focusing system to focus in an embodiment of the present invention;
FIG. 8 is a schematic view of a focusing system with a measurement point coincident with the center of the optical system field of view;
FIG. 9 is a schematic diagram of a focusing system with a measurement point offset to the left from the center of the field of view of the optical system;
FIG. 10 is a schematic view of the focusing system with the measurement point shifted to the right from the center of the optical system field of view;
FIG. 11 is a flow chart of auto-focusing according to an embodiment of the present invention;
FIG. 12 is a graph of a typical step motion response of a linear motor;
FIG. 13 is a graph of linear motor step motion set time obtained by setting different step distances;
FIG. 14 is a flow chart of real-time auto-focusing during a scanning motion according to an embodiment of the present invention; wherein S is the advance offset of the defocused measuring point relative to the imaging or processing position on the scanning path, T is the single measuring time of the spectral confocal probe, T is the maximum setting time of the focusing actuating mechanism 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 Description
The present invention will be described in more detail below with reference to the drawings, in which preferred embodiments of the invention are shown, it being understood that one skilled in the art can modify the invention described herein while still achieving the advantageous effects of the invention. Accordingly, the following description is to be construed as broadly known to those skilled in the art and not as limiting the invention.
In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. In order to make the objects and features of the present invention more comprehensible, embodiments accompanied with figures are described in detail below. It is noted that the drawings are in a very simplified form and utilize non-precise ratios, and are intended to facilitate a convenient, clear, description of the embodiments of the invention.
In the current prior art, the main forms of autofocus devices can be divided into three types, coaxial, off-axis, and triangular reflective. In the coaxial type automatic focusing device, the optical path of the automatic focusing system and the existing optical system for detection or processing realize the coaxiality of partial optical paths through the light splitting device, in order to avoid the influence of the focusing system on the imaging of the existing optical system, the two systems are generally required to be subjected to spectral isolation through the optical filter, so that the loss of specific spectral information of the existing optical system is caused, meanwhile, the existing coaxial type automatic focusing device is often characterized by analyzing the appearance signal of a light spot or the strength of the signal of the light spot or the imaging astigmatism degree, such as an AF series product of Japanese Central precision, an ATF series product of Canada WDI company, and only can realize the characterization of whether defocusing and the defocusing direction, but cannot quantitatively calculate the specific defocusing displacement, so that a plurality of closed-loop control periods are often required to realize single automatic focusing, the final closed-loop control bandwidth is not high, and the high-response automatic focusing function cannot be realized. The invention improves the above, particularly as shown in figure 1, if the absolute defocus displacement can be measured once, focusing can be realized only by driving and controlling the focusing actuating mechanism to move for a certain distance, thereby improving the whole control bandwidth.
In the off-axis type automatic focusing device, the optical path of the automatic focusing system is independent of the existing optical system, so that the coupling and isolation of spectrum wave bands between the two are not needed to be considered, but the measuring point of the off-axis type automatic focusing device is greatly deviated from the center of a visual field of the existing optical system, so that high position mapping is often needed, a certain area of a workpiece is detected in an off-focus mode and then enters the visual field of the existing optical system for detection or processing, a focusing actuating mechanism is driven and controlled through the high data of the position mapping to perform zooming action, and a control strategy is complex.
The optical system of the triangular reflection type automatic focusing device is also independent of the existing optical system, and the measuring point can be moved to a position coincident with the center of the field of view of the existing optical system by adjusting the angle of the triangular reflection, but in order to match with the large-caliber high-resolution characteristic of the existing optical system, the angle of the triangular reflection needs to be increased, so that the complexity and the cost of the structure are directly improved.
Fig. 2 shows the working band of a common optical processing and detecting system, the chip lithography adopts the ultraviolet to extreme ultraviolet band, the industrial vision detection often adopts the visible light band to replace the naked eye evaluation, and the laser processing field widely uses the infrared band. The auto-focusing device can also be regarded as an optical detection system, how to avoid mutual interference between two optical systems, especially the coupling of spectrum information is a problem to be solved in the industry, so the auto-focusing device suitable for imaging detection and processing application in various spectrum segments is provided, and has important significance in promoting the development of the precision optical detection and processing field.
Fig. 3 shows a schematic diagram of spectral confocal measurement, in which a broad spectrum optical signal emitted by a light source 202 enters a spectral confocal probe 203 through an optical fiber to generate high axial dispersion, and return light of an object surface 204 is coaxially received by the spectral confocal probe 203 and forms a spectral peak in a spectrometer 201 through the optical fiber. And extracting the peak value position of the spectrum peak through the CMOS image sensor, and solving the actual space distance to realize high-speed nondestructive distance detection. Along with the development of industries such as 3C electronics, semiconductors, new energy and the like, the high-precision processing and measurement requirements on precise structural members are driven, and the sensor product based on the spectral confocal measurement has been widely applied and developed in the market in recent years due to the excellent characteristics of high adaptability, high precision, non-contact high-speed sampling capability and the like of various materials. Therefore, for the application of the focusing sensor, on one hand, the focusing sensor can meet the requirements of scenes of different workpiece surface materials under different focusing scenes, and on the other hand, the measurement result corresponds to absolute defocus displacement data, so that the closed-loop control bandwidth of an automatic focusing system is improved.
Fig. 4 shows the operating band of a spectral confocal light source LED, which typically operates in the visible band range of 400-700 nm. 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 needs a longer defocus measurement time or more defocus measurement times in the single focusing process, the coaxial automatic focusing device can only be used for defocus and defocus direction characterization, and in the whole closed loop period, the defocus displacement needs to be measured for many times, the single focusing action often needs a working time of several seconds, and the bandwidth capacity of the whole system working is seriously reduced by adopting a time division method. The current spectral confocal sensor can measure the absolute defocus displacement at a speed of more than 10kHz, can measure the defocus quantity only by lighting a light source with the light source less than 100us and the exposure time, and can feedback control the relative defocus displacement to a focusing actuator.
Fig. 5 is a schematic diagram provided in an embodiment of the present invention. The device comprises 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 light splitting module 106, an optical system mounting base 104, an optical system focusing actuating mechanism 105, an automatic focusing controller 112, a workpiece 107, a motion table 108, a grating scale 109 and a motion table controller 110. The optical system focusing actuator 105 is rigidly connected with the optical system mounting base 104, and the spectral confocal probe 111 is coaxially coupled with the existing optical system 103 through the coaxial beam splitting module 106. In order to avoid mutual interference between the two sets of optical systems, the high sampling rate characteristic of the spectral confocal probe 111 can be fully utilized, and the single defocus measurement time of the spectral confocal probe 111 only needs to be less than 100us of light source lighting and exposure time, so that the requirement can be met as long as the time interval between two adjacent imaging trigger signals of the camera is greater than 100us, and most focusing measurement scenes can be met.
The workpiece 107 is placed on the moving table 108, the 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, and the moving table controller 110 can calculate the current position of the moving table 108 by reading the data of the grating scale 109.
The spectral confocal probe 111 is connected with the spectral confocal controller 101 through an optical fiber, the existing optical path system 103 is connected with the existing optical path system signal conversion module 102, the motion platform controller 110 is connected with the spectral confocal controller 101 and the existing optical path system signal conversion module 102 through cables, and the motion platform controller 110 reads signals of the grating scale 109 on the motion platform 108 and generates two paths of trigger signals which are respectively used for triggering the spectral confocal controller 101 and the existing optical path system signal conversion module 102 to work. The auto-focus controller 112 can read defocus amount data calculated by the spectral confocal control 101 and drive and control the optical system focusing actuator 105 to focus.
The existing optical path system 103 may be an optical path system for optical inspection or optical processing, and the existing optical path system signal conversion module 102 may be an imaging camera for optical inspection or a laser light source for optical processing.
As shown in fig. 8, by adjusting the relative positions of the spectral confocal probe 111 and the coaxial beam-splitting module 106, the offset of the defocus amount measurement point of the spectral confocal probe 111 with respect to the center of the field of view of the existing optical path system 103 can be changed, and if the spectral confocal probe 111 is moved upward, the defocus amount measurement point falls to the left of the center of the field of view of the existing optical path system 103, as shown in fig. 9; if the spectral confocal probe 111 is moved relatively downward, the defocus measurement point falls to the right of the center of the field of view of the existing optical path system 103, as shown in FIG. 10. Thus, by setting the stage scanning direction parallel to the plane made up of the optical axes of the spectral confocal probe 111 and the existing optical path system 103, both lead and lag of the defocus measurement point relative to the imaging or processing position can be achieved.
As shown in fig. 11, the auto-focusing method of the in-situ auto-focusing device based on spectral confocal of the present invention comprises the following steps:
step 1) starting motion scanning by the motion platform, and continuously obtaining a position signal of the motion platform by the motion platform controller through reading the grating ruler signal of the motion platform.
Step 2) the motion stage reaches the position of a workpiece to be imaged or processed, the motion stage controller 110 sends a trigger signal to the spectral confocal controller 101, the spectral confocal controller 101 is configured into an external trigger mode, a light source is started after the trigger signal is received and is transmitted to the spectral confocal probe 111 through an optical fiber, the spectral confocal probe carries out axial dispersion treatment on an input broad spectrum light source, a light spot is beaten to the surface of the workpiece through the coaxial light splitting module 106, a screening effect is generated on the broad spectrum signal after the surface of the workpiece is focused, after the optical signal of a specific spectrum section focused on the surface of the workpiece coaxially returns to the spectral confocal probe and the optical fiber, spectral analysis is carried out in the spectral confocal controller 101, and finally the defocusing amount of the existing optical system 103 and the surface of the workpiece is obtained through the mapping relation between the spectrum of the axial dispersion and the axial dispersion spatial displacement amount of the spectral confocal probe 111. After the trigger signal is over, the spectral confocal controller turns off the light source and stops the exposure calculation.
Step 3), the auto-focusing controller 112 reads the defocus amount data calculated by the spectral confocal controller, and drives and controls the focusing actuating mechanism to perform focusing operation until reaching the focusing height position.
Step 4), the motion stage 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 is configured into an external trigger mode, and starts working after receiving the trigger signal, so as to realize the working of optical detection imaging or optical processing.
Step 5) continuously moving the moving table for scanning, and repeating the steps 2), 3) and 4) until the moving scanning is completed.
In the step 1), in the process that the motion platform moves at a constant speed V, the grating ruler generates high-low level digital signals corresponding to the motion displacement, and the motion platform controller can obtain the real-time position of the current motion platform through calculating the high-low level pulse number. The frequency division, the phase and the duty ratio setting are carried out according to the grating ruler signal, the self-defined high-low level signal can be obtained and is respectively used for triggering the spectral confocal controller to carry out defocusing measurement and the existing optical path system signal conversion module to work, the spectral confocal controller and the existing optical path system signal conversion module can alternately work through configuration of two paths of trigger signals, the external trigger frequency of the spectral confocal controller can reach more than 10kHz at most, and the high-flux detection and processing work of the existing optical path system signal conversion module can be met.
As shown in fig. 7, according to the motion stage grating ruler signal and the motion stage distance corresponding to the working time interval of the existing optical path system 103 in the motion scanning process, the frequency division numbers of the trigger signal of the existing optical path system signal conversion module and the trigger signal of the focusing system are respectively set, and then the triggering working time of the focusing system falls in the non-working interval time of two adjacent working points of the signal conversion module of the existing optical path system by setting the phase and duty ratio parameters of the two trigger signals.
As shown in fig. 6, the rising edge of the square wave corresponds to the triggering actions of the signal conversion module of the existing optical path 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 path system and the focusing system, and the high level time of the configured focusing system is located in the low level time of the triggering signal of the signal conversion module of the existing optical path system, so that the triggering actions of the two sets of optical path systems at different times can be realized.
Step 2) is performed by adjusting the relative positions of the spectral confocal probe 111 and the coaxial spectroscopic module 106 so that the defocus measurement point forms a certain lead or lag offset S in the scan path relative to the imaging or processing position. The absolute height of the existing optical system 103 relative to the workpiece surface can be obtained in a time t of less than 100us by using a spectral confocal probe, so that the out-of-focus displacement of the optical system can be calculated according to the focal length of the existing optical system.
Step 3), the time required for the focusing actuating mechanism to move and stabilize to the focusing height position is called setting time (setting time), and the operation of focusing to the focusing position after calculating defocus amount data each time can be regarded as a step motion instruction sent to the focusing actuating mechanism, wherein the setting time of step motion response is related to the maximum working power of the focusing actuating mechanism, the inertial load of the mechanism and the relative displacement amount of step motion. Therefore, the maximum defocus amount of the workpiece surface is estimated in advance, so that the maximum setting time T required by the focusing actuating mechanism in the single focusing process (the maximum setting time T is the maximum time required by the focusing actuating mechanism to perform step movement according to the maximum defocus amount of the workpiece surface)) A settling time of less than 100ms is typically achieved with a step motion command of 100 um. Fig. 12 is a typical step motion response curve of a linear motor, and fig. 13 is a step motion setting time curve of a linear motor obtained by setting different step distances. By taking a distance D of movement exceeding the maximum defocus of the surface of the workpiece 1 Corresponding step motion setting time T 1 As the maximum setting time required by the focusing actuator during a single focus.
In step 4), in order to ensure that the automatic focusing device has completed the focusing operation of the optical system with respect to the current workpiece position when the motion stage reaches the specified working position, the condition S > (t+t) x V needs to be satisfied. As shown in fig. 14.
Step 5), as shown in fig. 14, in order to ensure that the real-time focusing effect can be always achieved during the continuous scanning process of the moving table, the advance offset S of the defocus measurement point needs to be smaller than the distance between two adjacent imaging or processing positions. So as to avoid the interference of the next focusing-imaging or processing flow to the last focusing-imaging or processing flow.
Claims (10)
1. The in-situ automatic focusing device based on the spectral confocal is characterized by comprising a focusing system, an existing optical path system (103), an existing optical path system signal conversion module (102), a coaxial beam splitting module (106), a workpiece (107), a moving table (108), a grating ruler (109), an optical system mounting base (104) and a moving table controller (110), wherein the focusing measurement system comprises a spectral confocal probe (111), a spectral confocal controller (101), an automatic focusing controller (112) and an optical system focusing executing mechanism (105);
the existing optical path system (103), the spectrum confocal probe (111), the coaxial light splitting module (106) and the optical system focusing actuating mechanism (105) are arranged on the optical system mounting base (104); the workpiece (107) is placed on a motion platform (108) connected with a motion platform controller (110), a grating ruler (109) is arranged on the motion platform (108), and the motion platform controller (110) is respectively connected with a spectrum confocal controller (101) and an existing optical path system signal conversion module (102) through cables; the spectral confocal controller (101) is connected with the automatic focusing controller (112) through a cable and is connected with the spectral confocal probe (111) through an optical fiber; the existing optical path system signal conversion module (102) is connected with the existing optical path system (103), the automatic focusing controller (112) is connected with the optical system focusing actuating mechanism (105), the spectral confocal probe (111) is coaxially coupled with the existing optical path system (103) through the coaxial light splitting module (106), and finally light spots are beaten on the surface of a workpiece (107).
2. An in-situ autofocus device based on spectral confocal according to claim 1, wherein,
the motion platform controller (110) reads signals of the grating ruler (109) on the motion platform (108) and generates two paths of trigger signals which are respectively used for triggering the spectral confocal controller (101) and the existing optical path system signal conversion module (102) to work;
the automatic focusing controller (112) reads out defocus amount data calculated by the spectral confocal controller (101) and drives and controls the optical system focusing actuating mechanism (105) to focus.
3. An in-situ autofocus device based on spectral confocal according to claim 1, wherein,
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.
4. An in-situ autofocus device based on spectral confocal according to claim 3 wherein the time interval between two adjacent imaging trigger signals of the camera or two adjacent trigger signals of the laser source is greater than the single measurement time of the spectral confocal probe.
5. An in-situ autofocus device based on spectral confocal according to claim 1, characterized in that the motion direction of the motion stage (108) is parallel to the plane formed by the optical axis of the spectral confocal probe (111) and the existing optical path system (103).
6. An in-situ autofocus method of the device of any of claims 1-5, comprising the steps of:
step 1), a motion table (108) drives a workpiece to perform two-dimensional motion through a motion table controller (110), and the motion table controller (110) continuously obtains the current position of the motion table (108) by reading data of a grating ruler (109) in real time;
step 2), the motion table reaches the position of a workpiece to be imaged or processed, and a spectral confocal controller (101) calculates the defocus amount of the existing optical system (103) and the surface of the workpiece;
step 3), the automatic focusing controller (112) reads defocus data obtained by calculation of the spectral confocal controller (101), and drives and controls the optical system focusing actuating mechanism (105) to perform focusing operation until the existing optical path system (103) reaches a focusing height position;
step 4), the motion platform 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, so as to realize the working of optical detection imaging or optical processing;
step 5) continuously moving the moving table for scanning, and repeating the steps 2), 3) and 4) until the moving scanning is completed.
7. The in-situ automatic focusing method according to claim 6, wherein in the step 1), according to the grating ruler signal and the distance between the motion stages corresponding to the working time interval of the existing optical path system (103) in the workpiece motion process, 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) are respectively set, and then the trigger working time of the spectral confocal controller (101) is within the interval time corresponding to the two adjacent working points of the existing optical path system (103) by setting the phase and duty ratio parameters of the two trigger signals.
8. The in-situ automatic focusing method according to claim 6, wherein the step 2) is specifically that the motion stage reaches a position where a workpiece is to be imaged or processed, the motion stage controller (110) sends a trigger signal to the spectral confocal controller (101), the spectral confocal controller (101) starts a light source after receiving the trigger signal and transmits the trigger signal to the spectral confocal probe (111) through an optical fiber, the spectral confocal probe (111) performs axial dispersion treatment on an input broad-spectrum light source, then a light spot is beaten to the surface of the workpiece through the coaxial light splitting module (106), after an optical signal of a focused spectrum section on the surface of the workpiece coaxially returns to the spectral confocal probe (111), spectral analysis is performed in the spectral confocal controller (101), and the defocus amount of the existing optical system (103) and the surface of the workpiece is obtained through the mapping relation between the spectrum of the axial dispersion of the spectral confocal probe (111) and the spatial displacement amount; after the trigger signal is over, the spectral confocal controller (101) turns off the light source and stops the exposure calculation.
9. The in-situ autofocus method of claim 8, wherein in step 2), the relative positions of the spectral confocal probe (111) and the coaxial spectroscopic module (106) are adjusted such that the defocus measurement point forms a lead or lag offset S, S > (t+t) V in the scan path relative to the imaging or processing position;
wherein t is the single measurement time of the spectral confocal probe (111); t is the maximum setting time of the optical system focusing actuating mechanism (105), and the maximum setting time is the maximum time required by the optical system focusing actuating mechanism (105) to perform step motion according to the peak value of the height change of the surface of the workpiece as the motion distance; v is the movement speed of the movement table (108).
10. The in-situ autofocus method of claim 6, wherein in step 5), the advanced offset S of the defocus measurement point is smaller than the position spacing between two adjacent working points of the existing optical path system (103).
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