In order to achieve the positioning accuracy required for the aggressive scaling of track density in future tape drives, the track-follow servo controller must be optimized. Tape path and tape guide disturbances are the main contributors to positioning errors during track-follow and are therefore one of the factors that limit track density.
Figure 1 shows a schematic of the track-follow and tape transport servo systems. In order to minimize these effects we are developing track-follow servo architectures using state space and advanced prediction techniques, see Figure 2. These techniques facilitate improved cancellation of stationary and non-stationary periodic disturbances, as well as improved mitigation of disturbances arising from stack shifts, leading to improved track follow performance. They can also be used to improve track following accuracy at low tape velocities, which is required for speed matching to a wide variety of host systems.