Output feedback control for disk drive commutational ramp loading

An output feedback controller for a commutational ramp load disk drive actuator is investigated. The controller eliminates the necessity of increased material requirements common in ramp load disk drives. Therefore, disk drives with lower cost, higher performance actuators can realize the linear shock protection benefits of ramp loading. While on the ramp, there exists a set in the state space where the actuator dynamics are uncontrollable. An input commutation is required within the uncontrollable region to sustain the direction of actuator motion. Additionally, the motor torque factor, magnetic restoration bias, and friction torque are nonlinear and can be represented by functions that are Lipschitz within the actuator ramp angle. Position and velocity information are not available while the actuator maneuvers along the ramp. An exponentially stable controller, using only current feedback, is designed to track a predetermined reference trajectory and move the actuator through the uncontrollable set for a successful load onto the disk at the desired load velocity. Experiments are performed to verify the efficacy of the output feedback control law