High Precision Displacement Feedback Control on DVD Optical Probe System

• Main Authors: Kuang-I Chang, 張匡儀
• Other Authors: 范光照
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/86906869453416267133

碩士 === 國立臺灣大學 === 機械工程學研究所 === 92 === A novel DVD-pickup-head-measurement system is presented. In order to avoid any kind of error caused by hysteresis in the voice coil motor ( VCM ) located at DVD-pickup head, we develop an advanced system with an additional VCM observed by a Michelson inferometer. And the secondary VCM will be parallel with traditional VCM on DVD pickup head. According to Ohm’s law, these two VCMs are driven with equivalent current. As a result, both VCMs move in accord. The displacement of the secondary VCM can be obtained by counting the fringes. In addition, this system takes into account the auto-focusing control principle; therefore, when the distance between objective lens and workpiece is not exactly at focal distance, the focus error signal ( FES ) detected by the photodetector will actuate both the voice coil motor located on DVD pickup head and also the secondary VCM to keep the focal distance. Thus, by means of feedback signal of the FES, the auto-focus control can be completed. Furthermore, we are able to obtain surface profile of the workpiece and achieve a higher resolution.