Digital Servo Control of a Novel Disk Actuator

A novel disk actuator transported on parallel flexures is considered for digital servo control. A steady state Kalman filter-like full state estimator and a state variable controller are designed and implemented on a high speed digital signal processor. A pole-placement technique is employed in choosing the gain constants. The control scheme derives the state estimates from a position error signal which resembles a sawtooth wave form (high-resolution/short-range, but repetitive). The estimator is based on a second order actuator model with two augmented states for both track-following and track-access modes. The structure of the track-following controller is of a proportional-integral-derivative type. The time optimal track-access mode is based on a velocity servo with reference velocities stored as a profile, and incorporates a proportional-integral velocity error controller. The estimator's residue time history shows that the algorithms are sufficiently robust to accommodate the model uncertainty, measurement noise, and force disturbance that are associated with a disk drive mechanism. The performance characteristics of the actuator are presented in terms of transfer functions, a step input response, a track misregistration probability distribution function, and a 1/3 stroke seek dynamics. © 1991 IEEE