Using a Friction Observer to Compensate Friction Force at Head Actuator Bearings of Magnetic Disk Drives

Abstract

Under micro-displacement, pre-rolling friction at the head actuator bearings of magnetic disk drives has spring and damper characteristics. To compensate this friction, a force observer designed on the basis of a friction model of spring and damper characteristics has been developed. This observer enables precise estimation of the friction force at head actuator bearings and eliminates the influence of pre-rolling friction. Hence the dynamic property of the head actuator recovers its pure inertia property, which is represented by 1/s² in the frequency region below 100Hz. To compensate the friction force and recover its pure inertia property is important to apply a feed-forward control because it is designed on the basis of the model of the head actuator. By simulation and experiment, it is confirmed that this control method enables the head actuator to recover the inertia property in the low-frequency region.