Multirate state-space digital controller for sector servo systems

The author describes the design, performance analysis, and test results of a type of a multirate digital controller for actuator and voice coil motor (VCM) control in disk drives using sector servo systems. The state estimator runs at an integer multiple of the sector servo sample rate, so that the state feedback control of the VCM current can be computed and updated more frequently. Analysis indicates that a better closed-loop control performance can be obtained, and test results confirm the theoretical prediction. A method is also discussed which modifies the controller implementation and reduces the real-time computational burden for the control processor