A hard disk drive seek error recovery using variable structure control

Modern hard disk drives require fast and reliable seeks from one data track to the other. Under certain circumstances, a malfunctioned seek can cause the actuator to be out of control, and subsequently crash read/write heads and damage the disk surfaces. To prevent such catastrophic damage, a robust controller is needed to recover the system from the seek failure. To reduce the seek time and improve the performance, it is desirable that the same controller will drive the actuator to the target track while recovering without issuing another seek. A variable structure controller has been designed and tested to accomplish such seek error recovery. This controller deals with high initial velocity. In order to obtain zero steady state error and zero overshoot, the integral augmented reaching mode law was developed. The controller was tested on a high end removable hard disk drive. This article describes the integral augmented reaching mode law, its application to the seek error recovery control, and the experimental results.