Fast Scanning System And Method Research Of White Light Vertical Scanning Interferometry

Comparing with traditional nondestructive testing methods, vertical scanning white light interferometry has the characteristics of non-contact, high precision and short measurement time which is widely used in ultra-precision non-destructive testing field. At present, most commercial white light interferometer needs to presetting before carrying out the scan work. The operation is time-consuming and the process is complex. In this regard, this dissertation developed a vertical scanning white light interferometer's image acquisition system then designed a vertical scanning white light interferometer's control software. On these bases, this dissertation presented a fast scan method for the vertical scanning white light interferometer. The mainly achievements involved are listed as follows:1. The hardware image acquisition system of white light interferometry based on FPGA. This system takes the CMOS photosensitive element as the front end, combining with optical micro interference system to obtain the white light interference images. The USB 2.0 chip is used as the back end of the image acquisition system, which transfers the image data to the PC side in real-time.2. Lower computer program design of the image acquisition system. Including CMOS sensor's configuration timing and pixel driving timing based on Verilog HDL; C-based USB firmware programming. Aiming at the drop-frame problem of USB module's Slave FIFO frame transmission mode, this dissertation puts forward a frame synchronous design of image data.3. Design of the vertical scanning white light interferometer's PC program. Includes a piezoelectric ceramic phase shifter's software design which achieves the movement control within the range; Stepping motor motion platform's control software which realizes the pulse number moving, jogging, mechanical origin setting; Image acquisition system's software which achieves the receiving, displaying and frame saving of white light interference image. And finally integrated the various modules to achieve the scanning control function of the vertical scanning white light interferometry.4. A fast scanning method of vertical scanning white light interferometer based on fringe identification and fringe extraction was presented. Applied the focus evaluation function to identify the white interference fringe in the specified area. Then using the exhaustive search method improved the identification speed of white interference fringe. Adopted the ViBe foreground extraction algorithm in motion detection area to exact the fringes from the image and thus determined the scanning range of the vertical scanning white light interferometer.