Minimization of tape transient disturbances in track following tape drives with a disturbance observer

Abstract

The primary purpose of the head servo in the track following tape drives is to track follow as accurately as possible during read/write operations in spite of disturbances such as tape edge movements or tape transients, internal and external vibrations transmitted to the head actuator and signal noise and dropouts. The track following and fine positioning is done using a position error signal (PES). Feedback controller design using proportional-integral-derivative (PID), lead-lag or estimator/controller techniques are used for maintaining accurate track following. This paper assumes that in addition to the PES signal, a head position signal is available for long seek, short seek, and track identification tasks, etc. In this paper, the development of a disturbance observer that supplements the nominal head servo controller in minimizing the effects of the tape transients is presented. The PES and the head position error signals are blended to provide a measure of the tape transient disturbance. This paper presents the theory of the disturbance observer and analyses to show the range of frequencies over which the disturbance observer will be effective. Finally, simulation results are presented for tape transients of various frequencies.