Mitigating rotational disturbances on a disk drive with mismatched linear accelerometers

Hard disk drives still form the backbone of the data storage business. While hard disks have been phased out of portable applications by solid state drives (SSDs), rotating media hard disks are still heavily used in data server farms. These disks, being tightly packed together are affected by external vibrations from their neighboring drives. These vibrations induce increased Position Error Signal (PES). As described in [1], [2], the samples on hard disks are limited, limiting the disturbance cancellation using just the main tracking loop. In [1] an adaptive feedforward method was used to significantly reduce the effects of rotational disturbances using an auxiliary signal from a rotary accelerometer. However, the push for lower costs has meant that rather than a perfectly calibrated rotary accelerometer, server drives typically difference the signals from two linear accelerometers which are often slightly mismatched. The mismatch limits the utility of the rotary feedforward signal. This paper describes an algorithm which solves the problem by calibrating not only the needed accelerometer feedforward gain, but the mismatch between the two linear accelerometers [3].