Track following control of large capacity flexible disk drive with disturbance observer using two position sensors

We propose a track following control for large capacity flexible disc drives (FDDs) with a disturbance observer using two position sensors: an optical tracking sensor for large capacity mode; and a magnetic scale for compatible mode. The disk drive requires high resistance against vibration and drive tilting. One of the effective solutions is a disturbance observer. However, as tracking sensor outputs only a tracking error signal, there exists a problem in that the information required to design a 2-DOF controller is lacking. As two position sensor systems are indispensable in building a backwards compatible large capacity FDD, a 2-DOF track following controller can easily be designed. We show that a disturbance observer based controller with single positioning sensor is nothing more than a 1-DOF high gain controller which can easily become unstable and our proposed controller improves disturbance reduction satisfactorily