Design And Experiment Of Auto-focus System

In the focus variation instrument,the imaging device needs to track the initial focus position of the tested surface automatically and rapidly.So auto-focusing methods which can be used in the focus variation 3-D measurement system are designed in this paper,and they can also be used in other systems as well.What's more,the focusing motion control module is constructed,to drive the objective lens move up and down during automatic focusing.In the astigmatic auto-focusing experiment testing system based on refitted commercial DVD pick-up head,the voice coil motor and lens are removed,and the spectroscopes and objective lens are added,with the related signal processing circuit,the focusing error signal FES is output,which has one-to-one relationship with the defocus value.Then,the focusing characteristics of FES are evaluated,and the auto-focusing method using laser is put forward and constructed.By detecting the shapes of laser spots,the auto-focusing method using laser can determine defocus value of the measured surface,the building process of the system includes LD drive control,collimation and correction of laser,design of light path adjustment mechanism,image processing of laser spots and the conversion of defocus value,etc.Furthermore,motion control program with screw,stepper motor and motion control card is constructed,to realize positon adjustment of image acquisition module.In this paper,the construction of two kinds of auto-focusing method and motion control are introduced in detail,and the two groups of auto-focusing method are tested.According to the experimental results,in the astigmatic auto-focusing method based on refitted DVD pickup head,the dynamic range of FES is about 200?m,its average sensitivity is 34.98 m V/?m,the linear range is about 60?m,and its average sensitivity in linear range is 60.56 m V/?m.In the auto-focusing system using laser,there is a linear relationship between the radius of the spot and the defocus value,the maximum sensitivity of the linear range is 2.5729 pixel /?m,and 0.39?m resolution is achieved.