Study On Fast Autofocus Method Of Microscope Based On Photodetector

In the field of microscopic optical imaging,autofocus technology is becoming more and more popular as a key technology.In recent years,for microsection scanning,researchers have mainly adopted the offline focusing method.This method can not obtain the axial defocusing amount in real time when moving horizontally.It is necessary to perform the fitting of the focal plane of the entire sample before scanning.This leads to low scanning efficiency.Some on-line focusing methods can acquire the defocus amount at any transverse position and avoid the focal plane modeling time.Some achievements have been made in the research,but there are still some problems such as delay,high cost and complex structure and so on.In order to solve these problems,a new differential focusing method based on photoelectric detector is proposed to obtain the axial defocus amount quickly.Two photoelectric diodes are used to detect differentially before and after the focal plane of the image plane,and the mapping relationship between the defocus amount and the differential voltage is obtained through signal processing,and the axial defocus amount is quickly acquired to complete focusing.In this paper,the principle of the dual-photodetector differential focusing,the modular design of the focusing platform and the realization of the focus platform are studied deeply.The performance of each circuit modules is tested,and the performance of the focusing platform is analyzed.The main research contents are as follows:(1)This paper analyzes and summarizes the work and achievements researched by the predecessors,describes the research trends of autofocus technology at home and abroad and the basic methods of autofocus.Then,according to the principle of optical imaging of ordinary microscope,the principle of dual photodetectors differential microfocusing method is introduced.In this paper,the process of photoelectric signal transduction from optical signal is analyzed in detail,and the theoretical relationship of rapidity is obtained.The three key technologies for achieving the differential focusing method are analyzed: The offset of ?M and ?R of the two photodetectors in the image square are selected,the positional relationship between the two photodetectors and the mapping relationship between the differential electrical signals and defocusing amount.The influence factors of the realization process of the differential focusing method are analyzed.(2)The fixed structure of photodetectors is designed.The types of photodetectors are compared and selected and the S2386-18 L photodiode is selected as the photoelectric conversion device.The signal conditioning circuit module includes signal amplifier circuit,low pass filter circuit,subtraction circuit and motion control module are designed.The motor control module realizes the movement control of the objective table.(3)The position of the two photodetectors is calibrated,and the conversion of optical signal into voltage signal is realized.The feasibility and correctness of the experimental platform are verified by experimental calibration of the relationship curve between the difference electrical signal and the decoy value.The relationship between the differential electrical signal and the defocus amount is calibrated through experiments,and the calibration curve of the mapping relationship is determined;The imaging camera is installed correctly and placed based on the imaging optical path design to realize computer-aided camera imaging,which facilitates the experimental testing and provides good sample images for processing in the later stage.By designing and installing imaging camera for imaging optical path,computer aided camera imaging is realized,which is convenient for experimental debugging.(4)The performance test and analysis of the built-focusing experimental platform is carried out.By doing experiment,the result indicated that the designed signal conditioning circuit has good performance and can realize the system function.In terms of focusing efficiency,the speed of 0.907 s is realized and the microsection scanning efficiency is improved.In terms of sensitivity,the measured sensitivity reaches 2mv/?m,which satisfies the system requirements.Under the 40 X objective,the measured working range is 80?m.The method of this paper is able to quickly obtain the direction and magnitude of the axial defocus,which is helpful for the rapid scanning of large target tissue samples.