Hard Disk Drive Servo System Based on Field-Programmable Gate Arrays

Servo systems are essential components of current magnetic storage hard disk drives (HDDs). In this paper, we demonstrate a novel servo scheme using a field-programmable gate array (FPGA). Adjacent magnetic tracks with two different frequencies are recorded on the magnetic disk and are used as servo tracks to encode the position information. A discrete Fourier transform is employed to decode the magnetic head position and to obtain the position error signal (PES). The PES is defined in terms of the difference of the magnitudes of the two frequencies. The relationship between the displacement and the PES is obtained by offline calibration. A real-time signal acquisition and processing system using a commercial FPGA, analog-to-digital converter chips, and digital-to-analog converter chips is built to do the high-speed spectrum analysis and generate the PES. The PES is transmitted to a laboratory virtual instrument engineering workbench (LabVIEW) real-time control target to implement the control algorithm. The computed control output from the real-time control target is amplified to drive a piezoelectric stage, which moves the magnetic head along the radial direction to compensate for the position error. A simple repetitive and proportional-integral-derivative control algorithm is implemented for head positioning and to verify this new servo scheme in this paper. With the controller, most of the major disturbances, such as the harmonics of the spindle runout, have been effectively attenuated compared with an open-loop control scheme.