Interactions between servo loops of an optical disk drive

In optical disk drives, interactions between the electromechanical actuators and the servo error generation systems can cause instabilities in the operation of individual servo loops. We examine the effects of these interactions on the servo loops of an optical disk drive in which a galvano fine-tracking actuator, a push-pull tracking error detection scheme, and an astigmatic focus error detection method are used. Also, we describe a digital servo controller that effectively cancels the effects of the deleterious interactions, resulting in stable operation.