PC-based position error signal generation and servo system for a spinstand

We describe a high-performance servo control system for enhancement of spinstand servo performance. This PC-based system uses a multifunction I/O card for controller output and a high-speed digitizer card capable of sampling the frequency-encoded servo pattern at 500 MS/s. The PC, running under the Linux operating system, uses the Goertzel algorithm decoding scheme to calculate the position error signal (PES) at a 15-kHz update rate for feedback control. The control signal drives a custom-made lead zirconate titanate (PZT) actuator, which moves the suspension and thus the read/write head. A proportional and integral (PI) type servo controller supports a 1.1-kHz servo bandwidth, producing a 21.9% improvement of the positioning accuracy of the spinstand.