Study Of CCD Photoelectric Thickness Measurement Instrument And System

CCD(Charge Coupled Devices) is a semiconductor photoelectric device with particular performance, which is applied widely in some fields such as camera and industry measurement and so on recently. The measurement system with CCD has an advantage on the geometrical measure such as thickness for achieving high accuracy, on-line dynamic detection, non-contact measurement, and especially adapts to measure the little thickness alternation. Firstly, optical trigonometry measurement principle and wok principle of linear CCD are introduced, which are based on to design optical focusing and imagery system with He-Ne laser instrument as illuminant. Secondly, peripheral circuit of linear CCD is designed in theory and experiment. Finally non-contact thickness measurement instrument is constructed, using CCD as photoelectric transformation element and microprocessor as the controller. The principle of measurement system is inclined trigonometry measurement principle and CCD is photoelectric transformation element. The time order driving circuit of CCD is designed and debugged with CPLD (Complicated Programmable Logic Device), which make the whole driving circuit's volume smaller, shorten design period, modify design at any time, and enhance reliability and agility of circuit. The CPLD designing under MAX+PLUS II can complete all work, which makes hardware design convenient as software design. The video signal processing circuit realizes the primary catching, filtering and signal amplifying. Variable threshold binarization processing circuit and two-channel counter are designed to sample to count the output pulse signal, which is processed, deposited and displayed in microprocessor. The communication interface circuit with the computer is also designed. The experiment of CCD driving and signal processing circuit shows that the drivers can assort with CCD well, take advantage of the characteristic of CCD photoelectric transition and output steady and reliable electric signal. Video processing circuit can obviously restrain the main noise, enhance SNR and obtain high quality video signal for further signal processing. Hardware design and software program of the microprocessor are completed, and system erroris analyzed. Principle analysis and experiment result indicate that the non-contact thickness measurement method using CCD as photoelectric transformation element is feasible.