The Optimal Design of a Rotary Type Actuator for Magnetic Disk Drives

One of the most important assemblies in any computer disk drive is the actuator which positions the read/write coil over the disk. Historically, actuators have been of the linear type, but in recent years the rotary actuator has become more popular because of its lower inertia and higher reliability. In this paper we describe the optimization of the rotary actuator geometry to achieve a minimum seek time. An objective function which approximates seek-time is derived based on the polar moment of inertia and the sweep of the actuator. A set of constraints is also developed which control mechanical resonances, skew angles, and physical position of the actuator. An optimal solution is presented as well as a sensitivity study of the final design. It is shown that the final design is relatively insensitive to changes in the problem parameters. Additionally, the sensitivity analysis reveals that a static balance constraint which is originally ignored, is not necessary.