Study On The Microscope Auto-focs System Based On The Spectrum Analysis Method

The development of Auto-focus technology, comprising Optical machinery and electronics, is driven by the trend of Intelligent and Automation, which are also the direction of modern instruments development. This technology is widely used in military, scientific research, industrial production, the daily application, etc., and has become the indispensable part of modern photoelectric system. Recently, the Auto-focus based on digital image processing has been widely studied because of their high accuracy and of requirement of digitization. However, this technology is high demands on the processor hardware, which makes it difficult to promote on the small costs low-end devices.In this paper, an auto-focus system applying to microscope is introduced. The defocus information comes from the processing of analog video signal, which is generated from CCD(Charge Coupled Device), through analog circuits. Subsequently the chip computes the information to get the driving signal of stepper motor.This paper focuses on the research of the spectrum analysis method. We studied how the spectrum of video signal changes during defocusing to find out the proper frequency range for the system, and designed corresponding experiments to verify it. To make full use of the spectrum, we use two different frequency ranges to realize coarse and fine adjustment of the autofocus process. We altered the software to make it meet the requirement of the design. The final design has a wider focusing range while remaining high accuracy. For instance, under the40x objective, the effective autofocus range of the microscope can reaches±300μm while the other system based on the same method only has about±100μm.The first two chapters introduce the background and development of auto-focus methods, compare the differences between these methods and why we chose the spectrum analysis method for our system. The third and fourth chapters introduce the hardware and software design, analyze the influence of defocusing to the video signal spectrum, find out the theory basis of the design. The fifth chapter analyzes the experimental data, verify the effectiveness and stability. The last chapter summary and outlook the system, point out the defection and possible research directions of the current system. The conclusion we get is not restricted in the microscope Auto-Focus system, other Auto-Focus systems based on the analysis of video signal can also benefit from it.