The Auto-focus Reserach Of Digital Microscopic System

Digital microscopic system is indispensable and greatly needed in the fields of clinical medicine, medical research, systems biology and environics. Its application range is determined by its focus velocity and resolution. And the focus velocity is based on two aspects: the principle of focus and movement mechanism. In this paper, an active autofocus method and motion control based on piezoceramics are proposed for this two aspects. First, optical structure about the active autofocus method is designed by Zemax, then relative mathematical calculation has been done to prove it. And the device of active autofocus is designed and structure based on the simulation and calculation. Second, a semicircle spot image which is gained by the device has been processed and analyzed, in order to get the characters of spot’s radius and barycenter location. Then the relation between the characters and defocusing amount has been researched. Third, the piezoceramics is used for movement mechanism by using BP neural network and PID control. Both simulation and experiments have been done, and results both meet expectations that they can reduce the errors of piezoceramics and improve its velocity.Finally, the whole digital microscopic system has been fabricated by combining software and hardware and it can realize the auto-focus at last. A series of experiments have been done and the results indicate that the active autofocus method and piezoceramics movement mechanism can greatly increase focus velocity and maintain stability comparing with the conventional system.