Development of a Servowriter for Magnetic Disk Storage Applications

The design, development, and application of a research servowriter, which is necessary to record magnetic position encoding schemes, are presented. The servowriter is designed to evaluate emerging disk drive technologies. Submicron positioning accuracy of the disk actuator is achieved by integrating the state-of-the-art electronic, optic, electromechanical, and digital signal processing hardware. The servowriter also provides flexible and sophisticated signal encoding schemes through a programmable “pattern generator” and has several modules of customized electronic hardware, each controlled by a supervisory computer. The position of the R/W (read/write) head and actuator assembly is measured by a laser interferometric system. The measured position is used to estimate the velocity of the R/W head, which is then used to implement a state-variable-based proportional-integral-derivative controller on the Intel (8086/8087) microprocessor chip set. Both systematic and random error sources associated with phase and amplitude encoding schemes are described. Environmental factors, such as seismic vibration and temperature change, which indirectly contribute to servowriting errors, are identified and steps to contain these error sources are described. © 1990 IEEE