Hidehiko Numasato

A mode-switching control for motion control and its application to disk drives: design of optimal mode-switching conditions

The mode switching control (MSC) is a kind of variable-structure control system with switching in only one direction. When the mode is switched from the fast-movement servo mode to the precise-positioning servo mode, the switching time is the initial time when the precise-positioning mode begins. As a result, initial value compensation (IVC), a method that takes into account the initial state values, can be applied. We (1996) previously proposed the design of IVC and showed its effectiveness in disk drive servo controls. In this paper, a design method for determining the optimal combination of initial states for mode switching is proposed. Here, the H/sub 2/ norm of the transfer function between the initial values and the control input is defined as the performance index of the transient response after mode switching. By combining the IVC method with this method of determining the optimal switching conditions, the issues of mode switching are resolved. Several experimental results show the effectiveness of these methods.

Settling control and performance of a dual-actuator system for hard disk drives

This paper presents a settling control of a dual-actuator system for hard disk drives. The dual-actuator system consists of a voice coil motor (VCM) as a first stage actuator and a push-pull-type piezo-electric transducer (PZT) as a second-stage actuator. The settling controller is designed in three steps. In the first step, the VCM controller is designed so that the VCM feedback loop has basic performance and appropriate stability. In the second step, the PZT controller and a decoupling filter are designed in order to achieve superior performance of the dual-actuator system. The decoupling filter, which is placed between the PZT controller output and the VCM controller input, is a PZT output estimator so that the PZT actuator output is canceled at the VCM controller input. In the third step, the reference trajectory is designed for fast and smooth settling. In this study, the closed-loop sensitivity function is used as a performance index, and the gain and phase margins of the open-loop characteristic are used as stability measures. Experimental results show that the dual actuator system with the proposed settling controller achieves better performance than a single actuator system with the same VCM and a conventional settling controller.

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.

Settling control and performance of dual-actuator system for hard disk drives

Presents a settling control of a dual-actuator system for hard disk drives. The dual-actuator system consists of a voice coil motor (VCM) as a first stage actuator and a push-pull type piezo-electric transducer (PZT) as a second stage actuator. The settling controller is designed in three steps. In the first step, the VCM controller is designed so that the VCM feedback loop has basic performance and appropriate stability. In the second step, the PZT controller and a decoupling filter are designed in order to achieve superior performance of the dual-actuator system. The decoupling filter, which is placed between the PZT controller output and the VCM controller input, is a PZT output estimator so that the PZT actuator output is canceled at the VCM controller input. In the third step, the reference trajectory is designed for fast and smooth settling. In this study, the closed-loop sensitivity function is used as a performance index, and the gain and phase margins of the open-loop characteristic are used as stability measures. Experimental results show that the dual actuator system with the proposed settling controller achieves better performance than a single actuator system with the same VCM and a conventional settling controller.

Modeling and TMR (track misregistration) budget design for head-positioning of high track-density disk drives

A design tool for track misregistration (TMR) budget of disk drives have been developed. This tool includes R/W head, disk, channel and head-positioning model. An appropriate parameter set which satisfies a given soft error rate (SER) and off-track capability (OTC), is derived using this tool. It is shown that results of simulations using this tool match experimental ones. A TMR budget design for 10 Gbit/in/sup 2/ is calculated. In this design, positioning accuracy of NRRO and RRO should be 0.096 /spl mu/m (/spl plusmn/3/spl sigma/) and 0.084 pm (/spl plusmn/3/spl sigma/) respectively to achieve 31.4 ktpi.

An analysis method for determining the head positioning error of hard disk drives-settling response analysis

A settling response analysis method for hard disk drives has been developed. In this method, the settling response is decomposed into its contributing modes using the Prony method, which is one of the experimental modal analysis methods. These modes are divided into servo modes and mechanical vibration modes based on the damping ratio in order to recompose a servo response and a mechanical vibration response. The impact of mechanical vibrations on settling response is quantified by their 2-norm. Relating to the track misregistration (TMR) budget design, each mechanical vibration mode is evaluated according to its initial amplitude and its decay rate.

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.

Single/dual-rate digital controller design for dual stage track following in hard disk drives

This paper presents the design of single rate and dual rate digital controllers for dual stage servo systems. The dual stage actuator system consists of a coarse actuator (voice coil motor) and a fine actuator (piezoelectric transducer, PZT). The design is divided into two steps. In the first step, the stability of the coarse actuator loop is an important consideration. In the second step, the fine actuator loop is designed by loop shaping for superior performance of the overall system. An important consideration in the second stage is to ensure that the phase difference is away from /spl plusmn/180 degrees between the coarse and fine actuator paths when the magnitudes of the two are close to each other. By loop shaping of fine actuator loop, appropriate contribution of each actuator to the final output is adjusted differently in different frequency range. In the dual rate control, the coarse actuator works at slow sampling frequency and the fine actuator works at fast sampling frequency. Simulation and experimental results justify the proposed design.