Design And Implementation Of An Autofocus System For Optical Microscope

Optical microscope is a precision instrument. It is playing an important role in biology, medicine and chemistry for its advantage of high precision, strong ability of anti-interference and stability. In biomedical application, factitious error is easy to be brought in when observing the specimen by manual focusing, and the automation level is low-grade. So, if applying autofocus control to optical microscope, the speed of experiment and analysis will be increased and the quality of microscope imaging would be improved.In this paper, a microscope autofocus system is designed. The autofocus system is based on MCU control and digital image process. The system capture biology specimen image through CCD camera and image grab card, then judge the definition of image through image evaluation arithmetic and communicate with MCU under the control of auto-search arithmetic. Objective's movement is then driven by stepper motor through mechanical gear.In autofocus system, by directly matching flexible shaft coupling and focusing axis of microscope, integrating micro-step driver, the mechanical tolerance of gear was diminished while the accuracy of focus was improved effectively. Then, it is proved that the auto-correlation operator is one effective approach to evaluate low-contrast image specially based on the performance comparison of some image analysis operators. Biology experiments have shown that the proposed scheme meets the requirement of autofocus both on accuracy and speed.