Novel hard disk drive actuator control method to solve micro jog problem

This paper demonstrates a complete solution to “micro jog” problem in hard disk drive (HDD) actuator control which appears as decline of the open loop gain at low frequency by non-linear friction of the actuator pivot bearing called Dahl friction and by non-linear flex cable tension. In many cases of HDD commercial products, the open loop gain at the lower frequency than 100Hz does not exceed 40dB at small actuator swing. It has been longstanding for more than 20 years and considered one of the biggest issues in nano-meter scale positioning. This method named Disturbance Jammer provides a voltage source for Voice Coil Motor (VCM) driver and a simple current local feedback then naturally compensates the nonlinear torque disturbance. It has been implemented in the HDD head/media evaluation system called “reference drive RD-2” by IMES Co. Ltd, and proved the accuracy which achieved pico-meter scale exceeding nano in practical head positioning on the spinning disk tracks, even under disturbances such as disk windage and flutter. The demonstration strongly supports the possibility of HDD track density to be improved to 1Mega Track Per Inch (TPI) in the near future.