When a hard disk drive (HDD) performs track-seeking operations, mechanical vibration modes are often excited and the performance of the HDD is degraded. Unlike disturbances coming from outside of the drive, self-induced vibrations are excited by seek motions of the HDD, but they are amplified by internal and/or external mechanical modes of the HDD. A soft mounting mechanism of a HDD in a laptop PC to protect from externally-generated shock can be excited by seek motions and sometimes contributes to seek-settling vibrations. A method to cancel self-induced vibrations of the HDD using an adaptive technique without modifying the sensitivity function is presented in this paper. The vibration effects are cancelled by adding a vibration model in the servo loop. Since the vibration gain and frequency vary due to the properties of the soft mounting mechanism, an adaptive technique is developed to adjust the model in real-time to ensure robustness. Experimental results of seek settling waveforms and seek time variations show reasonable convergence speed and good suppression of the vibration effects.

A method to estimate the maximum achievable bandwidth of HDD actuators without closing the servo loop is presented. The actuator dynamics are characterized by the time delay created by the unstable zeros of the actuator dynamics. The achievable bandwidth is a simple function of the time delay and the sampling frequency. The feedback controller, including a notch filter, can be designed simultaneously. Effects of dynamics variation of the actuator are also considered, and a method to identify the time delay caused by the variation is provided by using the recursive least square method. By applying this method to a single-stage and a dual-stage actuator system of HDDs, it is observed that the variations of the high frequency modes play an important role in the bandwidth improvement, especially of the dual-stage actuator.

As the track density of hard disk drives increases, the tracking accuracy is becoming more sensitive to vibrations in the users' environments. This is more crucial when the drives are used in disk array systems, because the drives are very frequently performing seek operations and this causes a lot of mechanical vibration. Disturbance observers were originally developed to suppress the effects of low frequency disturbances. In this paper the disturbances in the disk array system are analyzed and the disturbance observer is modified to be more suitable for the hard disk drives in disk array systems. A parallel configuration is proposed to relieve the restrictions of the disturbance observer such as the realizability of the inverse plant, the issue of the timedelay in discretetime systems, and the distortion of the transient response. The effectiveness has been verified by the positioning accuracy and the 1/0 throughput performance of a disk array system.

An optimal design technique of both the actuator dynamics and the servo controller is presented. The actuator dynamics are characterized by the time delay created by the unstables zeros of the actuator transfer function. The achievable bandwidth is a simple function of the time delay and the sampling frequency. The feedback controller, including the notch filter, is designed, simultaneously. The performance with dynamics variations can also be evaluated by the time delay. It is shown that the variations of the high-frequency modes play an important role in the bandwidth improvement of the dual-stage system.

In this paper, integrated servo/mechanical design of HDD actuators and estimation of the achievable bandwidth have been discussed.

A method of designing a multi-rate servo controller for a HDD that operates at a higher sampling frequency than that of the position error signal (PES) is proposed. Multi-rate sampling has an advantage for increasing the track density of a HDD without increasing the overhead of the servo information on the disk. A plant model for a design with a higher sampling rate is obtained by adding a zero-interpolator at the output of the position error signal. The controller is calculated by the H-infinity method to suppress the noise at the PES sampling frequency that is created by the use of multi-rate sampling. The servo bandwidth and margins of the method are studied for 2.5 " and 3.5 " HDD's, and for a HDD with a dual-stage actuator. The multi-rate sampling is especailly effective for the dual-stage actuator because the MEMS actuator's transfer function is very clean.

A non-traditional mechanical modification technique to take care of the major servo bandwidth limited resonance mode (butterfly mode) is developed, analyzed, and validated. With an additional sensor on the actuator and an external feedback loop, the butterfly mode can be damped and stiffened such that the gain of the head mechanical transfer function is close to 1/s/sup 2/. Servo improvement is also studied comparing to notch filter approach. It shows that the butterfly mode notch filter can be removed, and the phase margin can be improved by 7 degrees.

Introduction Dual-stage actuator and s m controller have been proposed for &wing high track density in HDDs, since resonant frequencies in current VCM put a severe limit on servo bandwidth. Having very high m n a n t frequency and extremely clean mechanical transfer function, MEMS (Micro Electro Mechanical System) microactuator has demonstarted its advantage in achieving bigher bandwidth 111. However, one of the concerns in general dual-stage systems is the complexiQ' of the servo controller due to its MIMO (Multi-InpueMulti-Output) configuration. In this paper, a simple and e5cient design method of a dual-stage servo wntroller is described and experimental results ofa d d s t a g e system using a conventional VCM and a MEMS microactuator are presented.

A flexure-based rotary electrostatic microactuator is described. This microactuator is for application in a high track-density hard disk drive (HDD). It is fabricated using a high aspect-ratio stencil electroplating process. This paper emphasizes the practical system-level issues that affect the device design. The micro-actuator is demonstrated in a 3.5" form-factor HDD. With a servo bandwidth of 5 kHz, a one-track seek can be completed in under 0.2 ms. This batch-fabricated electro-static microactuator provides a low-cost, high-performance solution for achieving very high track-densities.

This paper describes a micro-actuator for high-bandwidth tracking servo, where a micro-actuator is attached between slider and suspension, and moves the slider relative to the suspension. The micro-actuator frequency response measurement proved that this micro-actuator can be modeled as an ideal spring-mass-damper system up to 80 kHz, so that very high bandwidth servo system can be easily designed. The maximum servo bandwidth of 6.4 kHz was achieved in a drive level experiment, which is the highest bandwidth ever demonstrated as a drive level. A rapid step response time of 0.2 mS for 0.6 /spl mu/m step was also achieved. The experimental bandwidth was not limited by the micro-actuator's resonance mode, but the saturation of the micro-actuator driver.

A MEMS microactuator provides a low-cost and high-performance solution to realize high track densities of HDD, because of the batch fabrication process and its clean mechanical characteristics. However, the servo system to control such a dual-stage system tends to be more complicated than a conventional HDD system. In this paper, a simple and efficient design method of a dual-stage servo controller for HDD applications is described. The experimental results of the track following control with the dual-stage actuator using a conventional VCM and a MEMS microactuator showed that the fourth-order servo controller can achieve a high bandwidth of more than 2 kHz.