Hiromu Hirai

Track-following control of a dual-stage hard disk drive using a neuro-control system

Abstract This paper describes the track-following control of a dual-stage hard disk drive system using neural-networks. A neural-network approach to on-line learning control, and a real-time implementation for a dual-stage hard disk drive, are presented. The use of the dual-stage actuator in hard disk drive systems has become a means of achieving increased servo actuator bandwidth. The dual-stage actuator presented here uses a voice-coil motor (VCM) as a coarse actuator, and a piezoelectric actuator (PZT) as a fine actuator. The control system consists of a series combination of both a plant with a feedback loop and a neural-network with a feedforward loop. The neural-network functions as the reference input filter, and it organizes a new reference signal to the closed-loop circuit. Numerical and experimental results for the track-following control system of the dual-stage hard disk drive show the validity of the proposed neuro-control system.

A mode-switching controller with initial value compensation for hard disk drive servo control

Abstract In various kinds of servo positioning systems, both fast movement and precise positioning are required. To meet these demands, a mode-switching control (MSC) method, which has several controllers for each requirement and switches from one to the other, has been proposed. The issue raised by the use of this technique is the transient response after switching. This paper proposes the use of the initial value compensation (IVC) method to handle this problem. Under the IVC, initial values are placed in the controller state variables, or an additional input is added at switching. From experiments using hard disk drives, it is proved that the IVC improves transient responses after switching.

Fast head positioning method of magnetic disk drives

To improve the data rate of embedded-servo disk drives, data head switching at a high rate is required. To meet this requirement, a two-degree-of-freedom control method that compensates for the computation time delay and phase lag of filters is developed. This method reduces the head switching time by 50%. >

Ultrasonic linear motor for a high precision X-Y stage

Experiments on a mechanical configuration and control system for an ultrasonic linear motor for a high precision X-Y stage were conducted, and a velocity up to 100 mm/s and a positioning resolution of 0.016 mu m were obtained. The motor consists of a piezoelectric drive element using multilayer piezoelectric ceramic actuators. To realize both long-distance drive and very precise positioning, the ultrasonic linear motor has a coarse mode and a fine mode. The coarse mode is a friction drive mechanism and the fine mode is a direct-drive mechanism. The control system selects each mode according to the difference between a present position and an objective position.<<ETX>>

Improvement of servo robustness for digital sector servo system (hard disk drives)

In order to improve the servo performance of the digital sector servo, the authors developed initial value compensation for the digital variable structure control system and applied it to a 3.5-in disk drive. This compensation method involves inputting initial values, calculated by minimizing a performance index, into settling servo compensators when the servo mode is switched from seeking to settling. Implementation is quite easy for digital systems. Experimental results show good robust performances for large velocity fluctuations at switching. >

Control of transient response on a servosystem using mode-switching control, and its application to magnetic disk drives

Abstract In many servosystems, fast movement and precise positioning are required. A mode-switching control (MSC) method, which has at least two controllers designed for fast or precise specifications, respectively, and switches from one controller to the other, has been proposed and widely used to meet these requirements. The issue raised by the use of this technique is the transient response after switching. This paper proposes a new control method to shape the transient response. This method gives an additional input to a controller just after mode switching. The additional input, which is an impulse response of the initial state variables of the plant at mode switching, is designed to change transfer functions from the initial variables to the controlled variables, such as position, into better ones with assigned poles. In experiments using hard disk drives, it is proved that this technique improves the transient responses after switching.

Design of Mode Switching Controller with Initial Value Compensation and Its Application to Disk Drive Servo Control

Abstract In various kinds of servo positioning systems, both fast movement and precise positioning are required. To meet these demands, a Mode Switching Control (MSC) method., which has several controllers for each requirement and switches from one to the other, has been proposed. The issue is a transient response after switching. This paper proposes the initial value compensation (IVC) method. Under the IVC, initial values are placed in the controller state variables or an additional input is added at switching. From experiment using hard disk drives, it is proved that the IVC improves transient responses after switching.