ABSTRACT
Optimal controllers are usually designed for high-speed motion and/or high-precision positioning in Hard Disk Drives (HDD). Time-optimal control plays an important role in achieving fast point-topoint motion. There are many examples in various industries which utilize mode switching in motion control. This chapter presents the Two-Degree-of-Freedom (TDOF) and accesses servo control considering saturation techniques are presented to improve the track-seeking performance of HDDs. Various TDOF control structures have been proposed and detailed analyses including equivalent transformation have been studied. The basic idea of Mode Switching Control is to switch the control mode based on a pre-defined criterion using measured or estimated state variables. Even if the feedforward controller can achieve an ideal characteristic where both phase and gain error becomes zero, the tracking performance of the TDOF control system depends on the given reference trajectory.
