Agilent PC-Based Hard Disk Storage Testing Platform for Position Error Signal Generation and Servo Control on Spinstand

The hard disk drive storage industry is driven to increase data storage density, with increasing tracks per inch (TPI) and bits per inch (BPI) on the recording media. In the development of higher density recording, high-speed testing of magnetic heads and media in engineering and manufacturing environments has traditionally focused on spinstands and disk head testers. This paper describes a high-performance Servo control system for enhancement of spin stand Servo performance. This PC-based system uses a multifunction I/O card for controller output and an Agilent Acqiris 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 feed-back 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[1]. Figure 1. Agilent Acqiris U1068A PCI digitizer card