Takeyori Hara

Novel reference signal generation for two-degree-of-freedom controllers for hard disk drives

This paper considers the determination of reference trajectories for use with a two-degree of-freedom (2-DOF) controller for the head positioning of hard disk drives (HDD). The reference trajectories are designed in two stages-off-line simulation and online reference generation. The HDD model used for the design includes the back electromotive force of the voice coil motor. In the second stage, the idea of structural vibration minimized acceleration trajectory is utilized to adjust the errors at the end of the trajectories. 2-DOF control with the proposed reference trajectory is compared to conventional mode-switching control, and its effectiveness is verified.

Multi-rate controller for hard disk drive with redesign of state estimator

This paper describes a new multi-rate controller for hard disk drives, which has a modified state estimator to correct estimated states not only at measurement instances of the position error signal but also at every control instance of updating the control input. This modification makes the control input smoother compared to the conventional multi-rate scheme. The effectiveness of the modified scheme is demonstrated by experiments.

Openloop Gain Criteria of Sampled-data Control Systems with Mechanical Resonant modes above the Nyquist Frequency

For some sampled-data systems such as hard disk drives, which have mechanical resonant modes above the Nyquist frequency, suppressing the gain of these modes is a trade-off issue in mechanical/control design. In this paper, we propose a new method to determine openloop gain criteria above the Nyquist frequency. It clarifies the upper limit of the gain so that helps to design less conservative controllers. The method is derived from a frequency response analysis of multi-rate sampled system using frequency response matrix. The validity of the method is demonstrated by numerical simulations

Effect of dual-stage actuator on positioning accuracy in 10 k rpm magnetic disk drives

We have developed a piezoelectric micro-actuator for dual-stage actuator systems in magnetic disk drives. This microactuator, which drives the head suspension assembly, is based on the shear deformation of piezoelectric elements. We installed the microactuator in one of Fujitsus 3.5-inch commercial drives for evaluation of the servo system of dual-stage actuator. This paper describes the effect of the dual-stage servo system on positioning accuracy compared with the single actuator.

Two degree-of-freedom controllers for hard disk drives with novel reference signal generation

Considers the determination of reference trajectories for use with a two-degree-of-freedom (2-DOF) controller for the head positioning of hard disk drives (HDDs). The reference trajectories are designed in two stages-off-line simulation and online reference generation. The HDD model used for the design includes the back e.m.f. of the voice coil motor. In the second stage, the idea of SMART (Structural vibration Minimized AcceleRation Trajectory) is utilized to adjust the errors at the end of the trajectories. 2-DOF control with the proposed reference trajectory is compared to conventional mode switching control, and its effectiveness is verified. To minimize performance degradation due to disturbances and uncertainties, the use of adaptive robust control (ARC) is suggested.

Openloop Gain Criteria above the Nyquist Frequency for HDD Head Positioning Control

Head positioning systems of hard disk drives (HDDs) often have mechanical resonant modes above the Nyquist frequency. Suppressing the openloop gain of these modes is a complicated trade-off issue in mechanical/control design. Criteria of the openloop gain above the Nyquist frequency is obtained based on frequency response analysis for multi-rate sampled system using frequency response matrix. Examples of designing controller for HDD simulation models show the method is helpful to deal with the trade-off issue.