Autotuning of a servowriter head positioning system with minimum positioning error

This paper proposes a servopositioning system of a servowriter with autotuning capability. The position feedback is obtained through an interferometry-based laser positioning system. The retroreflector is mounted directly on the disk drive arm for hard coupling. The dynamics of the actuator are now included in the servopositioning loop. Since drive dynamics vary from drive to drive, a fixed controller may not provide optimal settling performance for a series of drives. In the proposed control method, the actuator dynamics are identified by injecting a pseudorandom binary sequence into a coarsely tuned feedback servoloop. The resulting frequency domain identification results are used to fine tune the compensator to enable faster settling and better following. Using this information in the servodesign, settling times of 9 ms and a following accuracy of 1 mu in. seem achievable using existing hardware. (C) 1996 American Institute of Physics.