Lateral Vibration and Read/Write Head Servo Dynamics in Magnetic Tape Transport

Abstract

Magnetic tape is a flexible mechanical structure having dimensions that are orders of magnitude different in its thickness, width, and length directions. In order to position the tape relative to the read/write head, guides constrain the tape’s lateral motion, but even the modest forces that develop during guiding can cause wear and damage to the tape’s edges. This paper presents a tensioned axially-moving viscoelastic Euler–Bernoulli beam model used to simulate the tape’s lateral dynamics, the guiding forces, and the position error between the data tracks and the read/write head. Lateral vibration can be excited by disturbances in the form of pack runout, flange impacts, precurvature of the tape in its natural unstressed state, and spiral stacking as tape winds onto the take-up pack. The guide model incorporates nonlinear characteristics including preload and deadbands in displacement and restoring force. A tracking servo model represents the ability of the read/write head’s actuator to track disturbances in the tape’s motion, and the actuator’s motion couples through friction with the tape’s vibration. Low frequency excitation arising from pack runout can excite high frequency position error because of the nonlinear characteristics of the guides and impacts against the pack’s flanges. The contact force developed between the tape and the packs’ flanges can be minimized without significantly increasing the position error by judicious selection of the flanges’ taper angle.