Abstract
This paper discusses the design and experimental verification of a new digital control method for suppressing disturbances in the positioning control system of a CD-ROM drive. The positioning control has generally been carried out by applying a conventional compensator, e.g. a phase lag-lead compensator, and implemented as digital control using the digital signal processor(DSP). We apply a disturbance observer to obtain satisfactory disturbance suppression as the disc rotation speed becomes higher. However, extra processing for calculating the disturbance observer is required. Therefore, we propose a multirate sampling scheme to decrease the realtime computation burden on DSP. The disturbance observer is computed with a lower sampling rate than the conventional compensator. The experimental results show that the positioning control system using the proposed multirate sampling scheme can reduce the positioning error caused by disturbances like disc vibration.
