Keitaro Ohno

Adaptive resonant mode compensation for hard disk drives

This paper is concerned with a mechanical resonant mode compensation problem for hard disk drives. Conventional notch filters must have deep and wide enough frequency characteristics in order to accommodate all possible resonant mode characteristics perturbation, which results in deterioration in positioning accuracy and residual vibration after seeking. In this paper, we propose an easy-to-implement adaptive notch filter of which the center frequency follows the resonant frequency change. The basic idea of this adaptive filter is to balance two kinds of frequency-weighted variances of the control input signal.

A variable structure multirate State estimator for seeking control of HDDs

This paper is concerned with a new multirate state estimator for the seeking control of hard disk drives (HDDs), which has a proportional, integral, and discontinuous error feedback structure to improve robustness. Conventional linear state estimators do not have sufficient accuracy under the existence of external disturbances and model uncertainty. With our proposed estimator, output-tracking performance can achieve improved robustness. Integral and discontinuous actions are introduced to alleviate the estimation error caused by disturbances and model uncertainty, while the multirate technique is used to obtain a smoother control input and higher bandwidth. Integral action and the multirate technique also alleviate the chattering caused by the discontinuous control action. Simulations and experiments have been carried out to validate our proposed multirate state estimator. Finally, an experimental implementation of proposed seeking control for single-stage and dual-stage actuated hard disk drives is demonstrated.

Nonuniform multi-rate sampled-data H/sub /spl infin// following control of HDDs

This paper is concerned with the use of the sampled-data H/sub /spl infin//servo controller with generalized hold for the track-following control of hard disk drives (HDDs). Conventional input multi-rate control normally utilizes a fast zero order hold that is uniformly time-divided piecewise constant function. However, there is no need to assume such an uniformity in hold duration. Elimination of this assumption increases the design degree-of-freedom. In this paper, we propose to invoke the sampled-data H/sub /spl infin// servo control theory to have an optimal piecewise continuous hold function. The derived function is used as a basis of our proposed nonuniformly time-divided piecewise constant function, which is introduced to implement it on standard systems with digital-to-analogue conversion devices. We conducted a set of simulations as well as experiments, and confirmed that the proposed method can improve the control performance.

A multi-rate nonlinear state estimation for hard disk drives

In this paper, we propose a new multi-rate state estimator for seeking control of hard disk drives, which has a proportional, integral, and discontinuous error feedback structure to improve robustness. Conventional state estimators do not have enough accuracy under the existence of external disturbances and model uncertainty. With the proposed estimator, the seeking control system of hard disk drives can have better robustness. Our main focus is on the discontinuous action, which alleviates the estimation error caused by, for example, actuator gain variations. Integral action is secondarily introduced not only to cancel out a quasi-constant disturbance and uncertainty, but also to reduce the chattering motion caused by the discontinuous feedback. Simulations and experiments have been carried out to validate our proposed multi-rate state estimator. Finally, an experimental example of seeking control for a single stage actuated hard disk drive is demonstrated.

An adaptive resonant mode compensation for hard disk drives

This paper is concerned with a mechanical resonant mode compensation problem for hard disk drives. Conventional notch filters must have deep and wide enough frequency characteristics in order to accommodate all possible resonant mode characteristic perturbations, which result in deterioration in positioning accuracy and residual vibration after seeking. This paper proposes an easy-to-implement adaptive notch filter of which the center frequency follows the resonant frequency change. The basic idea of this adaptive filter is to balance two kinds of frequency weighted variances of the control input signal.

A comparative study of the use of the generalized hold function for HDDs

This work is concerned with the application of H/sub /spl infin// control with the generalized hold function (GHF) to track-following control of hard disk drives (HDDs). In HDDs, the sampling frequency is limited primarily by the fact that a high sampling frequency tends to decrease the available data storage capacity of the devices, since the position error signal (PES) must be stored on the disk. Under such conditions, GHF provides a possible way to enhance servo performance without requiring more PES data. We investigate its possibility, comparing the results with other conventional H/sub /spl infin// control design results, including continuous/discrete-time and single/multirate control. Our results show that this controller has better performance due to the nature of the control input of the GHF.