| As the high definition video becomes the main stream of the digital players, the need of high-capacity disc is constantly growing. Developing the second generation products, that is NVD called in China, is put on the agenda. Compared with the first generation disc, the second generation disc will have much higher storage density and the narrower track pitch, which requires the tracking error to be decreased. In addition, servo system of optical discs must keep the robust in order to ensure compatibility with various products.The history of the research on servo control is relatively short in our country, so track-following servo system is accomplished by using PID control. At low frequency domain, the tracking error meets the requirements of disc. With the development of high definition discs, the higher rotation speed, the narrower track pitch, the shorter channel length, all kinds of disturbances and the parameter variation, it is difficult for PID control algorithm to reduce the tracking error. So it is quite necessary to find a new way to meet the development needs of high definition discs for tracking servo.Fuzzy control provides rule base depended on expert knowledge, reducing the influence caused by plant uncertainty. However, due to the subjectivity of expert knowledge and incomplete rule base, tracking error of the fuzzy control is not always met target tolerance. Hence, in term of the good performance of system identification and self-learning ability of neural network, an improved fuzzy control is proposed. Dynamically adjusting parameters of fuzzy rules, it makes the system meet the following requirements: good robustness of the parameter variation, higher accuracy at low-medium frequency and reaching the specifications at high frequency.To verify the performance of the proposed controller, a PID controller and a traditional fuzzy controller are designed additionally. A math model about actuator of some NVD is simply built. Some plant parameters are adjusted. The values of the three typical low-medium-high frequency signal and high-frequency noise signal are set up. The simulation is based on the MATLAB. The experimental results show that the proposed scheme provides better accuracy and robustness, and theoretically ensures the following test in the practical environment. |
