Disk file access-time constraints imposed by magnetic air-bearing compliance

Use is commonly made of coil voltages which produce maximum acceleration and deceleration to wrest the fastest access performance from the actuator of a disk file. Alternatively, equivalent performance is easily obtained with less control optimality by simply increasing the coil voltage. A limit to greater coil voltage, however, arises from the need to avoid harmful effects when the servo loses control of the actuator, the actuator slams into its crash stop, and the crash force stresses the magnetic head air bearing. Magnetic head air-bearing compliance, therefore, is one of three fundamental constraints that limit the access-time performance of an actuator. To obtain improved access-time performance from a disk file, the following should be optimized: the air-bearing slider, the actuator crash stop, and the actuator mechanical time constant. This paper presents relevant design considerations.