A Two-Degree-Of-Freedom Time-Optimal Solution for Hard Disk Drive Servo Problems

This paper deals with the hard disk drive (HDD) servo problems. A novel discrete time-optimal control solution is proposed in a two-degree-of-freedom (2DOF) structure, employing both the feedback and feedforward controllers. The time-optimal feedback controller, derived from a simple, double integral plant model, shows remarkable robustness and disturbance rejection in the presence of resonant modes, measurement noises and position and torque disturbances. It eliminates the needs for two separate controllers for track-seeking and track-following operations. The proposed feedforward controller in this 2DOF structure proves to be quite beneficial in reducing the seek time. It also allows the feedback controller to be tuned more aggressively, which helps to improve the quality of track following. The proposed control scheme offers a novel basic control structure for HDD servo, upon which numerous further improvements can be made. It is successfully tested in simulation on an industrial 13.0-kTPI HDD

A Two-Degree-Of-Freedom Time-Optimal Solution for Hard Disk Drive Servo Problems

This paper deals with the hard disk drive (HDD) servo problems. A novel discrete time-optimal control solution is proposed in a two-degree-of-freedom (2DOF) structure, employing both the feedback and feedforward controllers. The time-optimal feedback controller, derived from a simple, double integral plant model, shows remarkable robustness and disturbance rejection in the presence of resonant modes, measurement noises and position and torque disturbances. It eliminates the needs for two separate controllers for track-seeking and track-following operations. The proposed feedforward controller in this 2DOF structure proves to be quite beneficial in reducing the seek time. It also allows the feedback controller to be tuned more aggressively, which helps to improve the quality of track following. The proposed control scheme offers a novel basic control structure for HDD servo, upon which numerous further improvements can be made. It is successfully tested in simulation on an industrial 13.0-kTPI HDD

ADVANCED SENSOR FUSION AND VIBRATION CONTROL TECHNOLOGIES FOR ULTRA-HIGH DENSITY HARD DISK DRIVES

Ph.DDOCTOR OF PHILOSOPH

A NEW PIEZOELECTRIC MICROACTUATOR WITH TRANSVERSE AND LATERAL CONTROL OF HEAD POSITIONING SYSTEMS FOR HIGH DENSITY HARD DISK DRIVES

In high density magnetic hard disk drives, both fast track seeking and extremely accurate positioning of the read/write head are required. A new piezoelectric microactuator with transverse and lateral control of the head positioning system for high density hard disk drives is proposed. First, the structure of the new piezoelectric microactuator is illustrated. Design of the new microactuator is based on the axial deformation of piezoelectric elements for lateral motion and the bimorph actuation of piezoelectric elements for transverse motion. Next, a mathematical model of the microactuator system is defined. Static properties associated with the displacement of the system are evaluated and then dynamic system equations of the system are evaluated. Frequency response of the system is studied based on the dynamic system equations of the actuator system. Dynamic properties of the system with a variety of system parameters are evaluated. Finally, the controller design for the actuator is presented. Simulation results show that the new actuator achieves a maximum stroke of displacement of more than 0.2m with servo bandwidth of more than 5 kHz in the lateral direction and the flying height is decreased to less than 6 nm with resonance frequency of more than 100 kHz under the 0.5 % damping assumption. The new piezoelectric microactuator improves performance of high density hard disk drives by increasing servo bandwidth and decreasing flying height

Advance Servo Control for Hard Disk Drive in Mobile Application

Ph.DDOCTOR OF PHILOSOPH

THE DEVELOPMENT OF A NOVEL SUSPENSION ARM WITH 2-DIMENSIONAL ACTUATION, FOR USE IN ADVANCED HARD DISK DRIVES

As magnetic computer disks are developed to ever-greater data storage densities, the accuracy required for head positioning is moving beyond the accuracy provided by present technology using single-stage voice-coil motors in hard disk drives. This thesis details work to develop a novel active suspension arm with 2-dimensional actuation for use in advanced hard disk drives. The arm developed is capable of high-bandwidth data tracking as well as precision head flying height control motion. High-bandwidth data tracking is facilitated by the use of piezoelectric stack actuator, positioned closer to the head. The suspension arm is also capable of motion in the orthogonal axis. This motion represents active flying height control to maintain the correct altitude during drive operation. To characterise the suspension arm's structural dynamics, a high-resolution measurement system based on the optical beam deflection technique has been developed. This has enabled the accurate measurement of minute end-deflections of the suspension arm in 2-dimensions, to sub-nanometre resolution above noise. The design process of the suspension arm has led into the development of novel piezoelectric-actuated arms. In the work involving lead zirconate titanate (PZT) thick films as actuators, work in this thesis shows that reinforcing the films with fibre improves the overall actuation characteristics of the thick films. This discovery benefits applications such as structural health monitoring. The final suspension arm design has been adopted because it is simple in design, easier to integrate within current hard disk drive environment and easier to fabricate in mass. Closed-loop control algorithms based on proportional, integral and derivative (PID) controller techniques have been developed and implemented to demonstrate high bandwidths that have been achieved. The suspension arm developed presents an important solution in head-positioning technology in that it offers much higher bandwidths for data tracking and flying height control; both very essential in achieving even higher data storage densities on magnetic disks at much reduced head flying heights, compared to those in existing hard disk drives

Improved performance of hard disk drive servomechanism using digital multirate control

Ph.DDOCTOR OF PHILOSOPH

INVESTIGATION INTO SUBMICRON TRACK POSITIONING AND FOLLOWING TECHNOLOGY FOR COMPUTER MAGNETIC DISKS

In the recent past some magnetic heads with submicron trackwidth have been developed in order to increase track density of computer magnetic disks, however a servo control system for a submicron trackwidth head has not been investigated. The main objectives of this work are to investigate and develop a new servo pattern recording model, a new position sensor, actuator, servo controller used for submicron track positioning and following on a computer hard disk with ultrahigh track density, to increase its capacity. In this position sensor study, new modes of reading and writing servo information for longitudinal and perpendicular magnetic recording have been developed. The read/write processes in the model have been studied including the recording trackwidth, the bit length, the length and shape of the transition, the relationship between the length of the MR head and the recording wavelength, and the SIN of readout. lt has also been investigated that the servo patterns are magnetized along the radial direction by a transverse writing head that is aligned at right angles with the normal data head and the servo signals are reproduced by a transverse MR head with its stripe and pole gap tangential to the circumferential direction. lt has been studied how the servo signal amplitude and linearity are affected by the length of the MR sensor and the distance between the shields of the head. Such things as the spacing and length of the servo-pattern elements have been optimised so as to achieve minimum jitter and maximum utilisation of the surface of the disk. The factors (i.e. the skew angle of the head) affecting the SIN of the position sensor have been analysed and demonstrated. As a further development, a buried servo method has been studied which uses a servo layer underneath the data layer, so that a continuous servo signal is obtained. A new piezo-electric bimorph actuator has been demonstrated. This can be used as a fine actuator in hard disk recording. The linearity and delay of its response are improved by designing a circuit and selecting a dimension of the bimorph element. A dual-stage actuator has been developed. A novel integrated fine actuator using a piezo-electric bimorph has also been designed. A new type of construction for a magnetic head and actuator has been studied. A servo controller for a dual-stage actuator has been developed. The wholly digital controller for positioning and following has been designed and its performances have been simulated by the MAL TAB computer program. A submicron servo track writer and a laser system measuring dynamic micro-movement of a magnetic head have been specially developed for this project. Finally, track positioning and following on 0.7 µm tracks with a 7% trackwidth rms runout has been demonstrated using the new servo method when the disk-was rotating at low speed. This is one of the best results in this field in the world

The Palomar Testbed Interferometer

The Palomar Testbed Interferometer (PTI) is a long-baseline infrared interferometer located at Palomar Observatory, California. It was built as a testbed for interferometric techniques applicable to the Keck Interferometer. First fringes were obtained in July 1995. PTI implements a dual-star architecture, tracking two stars simultaneously for phase referencing and narrow-angle astrometry. The three fixed 40-cm apertures can be combined pair-wise to provide baselines to 110 m. The interferometer actively tracks the white-light fringe using an array detector at 2.2 um and active delay lines with a range of +/- 38 m. Laser metrology of the delay lines allows for servo control, and laser metrology of the complete optical path enables narrow-angle astrometric measurements. The instrument is highly automated, using a multiprocessing computer system for instrument control and sequencing.Comment: ApJ in Press (Jan 99) Fig 1 available from http://huey.jpl.nasa.gov/~bode/ptiPicture.html, revised duging copy edi

Modeling and control of hard disk drive in mobile applications

Master'sMASTER OF ENGINEERIN