Robust servo design for tape transport

This paper concerns the robust servo design for a direct drive tape transport testbed. The goal of the control system is to use two independently driven reels of the transport to maintain accurate speed and tension of the tape over range of 0.5-20m/sec and 0.25-2N(1-8oz). This multi-input/multi-output (MIMO) system has dynamics that make achieving these specifications difficult. These dynamics include slowly time-varying dynamics due to changing tape pack radii, stiction causing stick-slip phenomenon during start-up, air entrainment dynamics that rapidly and nonlinearly change spring constants in the system, and the periodic disturbances with time varying frequencies. There are basically two approaches to cope with the nonlinear and time-varying dynamics: gain scheduling and robust control. This paper examines the robust control algorithms for the tape transport, including H^∞ mixed sensitivity approach to obtain robust stability and disturbance observer (DO) architecture for the robust performance. The experimental data are presented to show the effectiveness of the algorithms