Design And Realization Of Film Thickness Measurement System Based On Astigmatism Method

Film thickness is main metric of film quality.At present,film products are developing in the direction of high-precision with increasing types.The existing methods for measurement of film thickness is difficult to realize the measurement for large thickness film and has a high cost in measurement.Aiming at this problem,this paper develops a system of film thickness measurement based on astigmatic method by using the DVD pickup head.The experimental results show that the range of measurement of the system is from 100?m to 800?m,the precision of repeated measurement is 8?m,the film size of measurement is 140mm×50mm.The main contents of the thesis are as follows:(1)The development of astigmatic displacement sensor.As for weak voltage signal of photodetector in optical system,a signal magnify circuit and a system of focus error signal acquisition and processing based on K60 microprocessor is designed,which realizes the conversion of the output signal in the astigmatic system to the focus error signal.The influence of astigmatic optical system parameters on the precision and range of measurement of the astigmatic displacement sensor is obtained by simulation analysis.The astigmatic displacement sensor with adjustable precision and range of measurement is designed and implemented.(2)Real-time correction about scanning jitter error.Scanning measurement system usually contains a linear motion platform,however,the linear motion platform generally exists random jitter error of more than 10?m,which will cause the system to increase the measurement error.Aiming at the random jitter error of linear motion platform,this paper proposes a scheme of double astigmatic displacement sensor to correct scanning jitter error in real time.The experimental results show that the random jitter error of the linear motion platform is reduced from 12?m to 2?m after the real-time error correction.(3)Design and implementation of film thickness measurement system.The advantages and disadvantages of scanning and array film thickness measurement scheme are analyzed and compared in detail.And considering the real-time correction of random jitter error of linear motion platform,a dual-sensor scanning film thickness measurement system based on astigmatism princ iple is designed and implemented in this paper.The experimental results show that the range of thickness measurement of this system is from 100?m to 800?m,the precision of repeated measurement is 8?m,the film size of measurement is 140mm×50mm.