Apparatus and method for reducing spindle power and acoustic noise in a

Abstract

An apparatus and method for reducing spindle power and acoustic noise in a self-commutating brushless d.c. motor for a disk drive adjusts the commutation angle of the motor until a point of optimum power consumption is reached. In a preferred approach implemented during disk drive operation, a direction in which to change the commutation angle is determined such that spindle power consumption is decreased. The commutation angle is the changed in the determined direction until a point of minimum spindle power consumption is identified. In order to determine the correct direction of commutation angle change, the commutation angle is varied in a first direction for so long as the spindle power consumption is decreasing. If varying the commutation angle of the motor in the first direction results in an increase in spindle power consumption, the commutation angle of the motor is varied in a second direction. During drive operation, the commutation angle may be varied back and forth in order to maintain the point of minimum spindle power consumption. The apparatus and method also minimizes torque ripple by determining a drive torque profile and storing that profile in memory as a table of torque constant values indexed to the rotational position of the disk. As the disk spins, its rotational position is sensed and the drive current is adjusted using a corresponding torque constant value. In this way, the drive current is varied inversely to the torque profile so as to produce a substantially uniform torque output, or a torque output that additionally compensates for structural resonance or other drive properties. Still further, a current offset value may be applied that is proportional to the difference between the torque profile and the average torque.