Tutorial on control systems design in tape drives

Like disk drive capacities, tape capacities are growing at unprecedented rates in recent years. Along with tape capacities, tape performance needs to be increased as well lest the high capacity tapes become a data archive serving seldom if ever used shelf-class data. Both these requirements have led to the use of thinner media, very high read/write velocity, and track following servos to achieve high track densities and high throughputs. This paper presents a tutorial on control systems design for reel-to-reel and track following tape drives while addressing how such capacity and performance goals can be met. This paper is divided into three parts. Part one of the paper describes the basic control system design of the tape transport with and without tension transducers using decoupled transfer function and optimal control design techniques. Part two of the paper discusses the control system design techniques for track following tape drives where there are inherent measurement delays in the output signal. Part three of the paper covers advanced controls such as disturbance observer and robust control techniques to provide superior performance in the presence of disturbances and uncertainties in plant parameters in tape transports. The common thread, which connects all these techniques presented in this paper, is that these are industrially proven and yet mathematically rigorous and robust enough to be applicable to tape drives and related products without undue complications.