Servo-error control to compensate the eccentricity of spindle motor and disk

To achieve higher and higher data storage density of optical discs and reading rate of the DVD drives need to improve the accuracy of servo control system and to raise rational speed of spindle motor. The spindle motor easily causes severe vibration in high speed especially while there are eccentricities of spindle motor and disk. The built-in automatic ball balancer, rubber damper and lead-lag control in the optical discs can reduce focusing and tracking error arisen from vibrations. The automatic ball balancer is capable of eliminating radial vibrations under the conditions that spindle eccentricity, damping and friction are not present. The rubber damper can only suppress vibration at a specific frequency but not overcome the focusing and tracking error for the harmonic vibration. The servo control of the optical disc drives makes a voice coil motor move the optical pickup head to data track accurately. The severe vibration causes focusing and tracking error over the allowed range and leads the spindle motor to decrease rotating speed for data pickup. In this study, the sensorless adaptive feedforward servo control ("AFSC" for short) is designed to promote the reading performance of optical drives. The AFSC is designed based on filtered-x-least-mean-square (FXLMS) with robust variable step size (RVSS) algorithm. The experimental results demonstrate that the sensorless AFSC can successfully eliminate focusing and tracking error arisen from the eccentricities of the spindle and the disks.