Design And Implementation Of Automatic Focusing System Based On ZYNQ

Laser-Induced Breakdown Spectroscopy（LIBS）plays an important role in various fields because of its advantages of long-distance and rapid analysis.Focusing technology can make the detection results of LIBS detector more accurate and repeatable,which is an important part of LIBS detection.Based on the zynq platform,the subject uses the method of automatic focusing to focus the laser accurately to the desired position,so as to improve the stability of the spectral signal emitted by the laser-induced plasma.In this paper,the image sharpness evaluation function,the focus position search algorithm and the stepping motor control are deeply studied.The main work is as follows:1.The advantages and disadvantages of various auto focusing methods are analyzed.Finally,the auto focusing method combining focusing depth method and ranging method is determined,and the overall scheme block diagram,detailed focusing steps and Strategies of the auto focusing method are given.The image acquisition circuit of area array CCD is designed and manufactured,the relevant program is written to complete the simulation verification,and the image acquisition and display are realized through the test.According to the disadvantage that the traditional image sharpness evaluation function is easily affected by the background pixels,an image sharpness evaluation algorithm for local framing of the collected images is adopted.The experimental results show that the local framing evaluation algorithm not only reduces the calculation amount by about 50% compared with the improved algorithm,but also calculates the images with the resolution of the naked eye.The sharpness evaluation curve of the algorithm is basically consistent with the resolution of the naked eye,The reliability of the algorithm is proved.The evaluation function curve in the whole focusing area is also closer to the ideal evaluation function curve.2.Aiming at the motor drive which is essential in the focusing process,the design of its driving circuit and driver program is completed.The trapezoidal acceleration and deceleration algorithm is added to solve the problem of too small torque caused by too fast speed of the stepping motor when starting.The simulation and experimental results show that the control accuracy is higher under the trapezoidal acceleration and deceleration algorithm,and the relative error is 0.022% after adding feedback.3.The advantages and disadvantages of many traditional focus position search algorithms are compared.Aiming at the problem that the traditional search algorithm is easy to fall into the local extreme value of the image definition evaluation function curve,a mountain climbing search method based on look-up table method is adopted.The algorithm can quickly and effectively skip the local extremum to the focus position,and quickly complete the focusing near the maximum value through a small step size of times the accuracy requirements.The final step size of the method is the same as the required accuracy,which can fully ensure that the focusing accuracy is within the requirements.