Disturbance attenuation with multi-sensing servo systems for high density storage devices

Ph.DDOCTOR OF PHILOSOPH

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

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

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

Improved performance of hard disk drive servomechanism using digital multirate control

Ph.DDOCTOR OF PHILOSOPH

An investigation into the head-disk interface technology leading to extremely small mechanical head-disk spacing

Ph.DDOCTOR OF PHILOSOPH

Design and control of a 6-Degree-of-Freedom levitated positioner with high precision

This dissertation presents a high-precision positioner with a novel superimposed concentrated-field permanent-magnet matrix. This extended-range multi-axis positioner can generate all 6-DOF (degree-of-freedom) motions with only a single moving part. It is actuated by three planar levitation motors, which are attached on the bottom of the moving part. Three aerostatic bearings are used to provide the suspension force against the gravity for the system. The dynamic model of the system is developed and analyzed. And several control techniques including SISO (single input and single output) and MIMO (multi inputs and multi outputs) controls are discussed in the dissertation. The positioner demonstrates a position resolution of 20 nm and position noise of 10 nm rms in x and y and 15 nm rms in z. The angular resolution around the x-, y-, and z-axes is in sub-microradian order. The planar travel range is 160 mm ?? 160 mm, and the maximum velocity achieved is 0.5 m/s at a 5-m/s2 acceleration, which can enhance the throughput in precision manufacturing. Various experimental results are presented in this dissertation to demonstrate the positioner??s capability of accurately tracking any planar trajectories. Those experimental results verified the potential utility of this 6-DOF high-precision positioner in precision manufacturing and factory automation

Single-Chip Scanning Probe Microscopes

Scanning probe microscopes (SPMs) are the highest resolution imaging instruments available today and are among the most important tools in nanoscience. Conventional SPMs suffer from several drawbacks owing to their large and bulky construction and to the use of piezoelectric materials. Large scanners have low resonant frequencies that limit their achievable imaging bandwidth and render them susceptible to disturbance from ambient vibrations. Array approaches have been used to alleviate the bandwidth bottleneck; however as arrays are scaled upwards, the scanning speed must decline to accommodate larger payloads. In addition, the long mechanical path from the tip to the sample contributes thermal drift. Furthermore, intrinsic properties of piezoelectric materials result in creep and hysteresis, which contribute to image distortion. The tip-sample interaction signals are often measured with optical configurations that require large free-space paths, are cumbersome to align, and add to the high cost of state-of-the-art SPM systems. These shortcomings have stifled the widespread adoption of SPMs by the nanometrology community. Tiny, inexpensive, fast, stable and independent SPMs that do not incur bandwidth penalties upon array scaling would therefore be most welcome. The present research demonstrates, for the first time, that all of the mechanical and electrical components that are required for the SPM to capture an image can be scaled and integrated onto a single CMOS chip. Principles of microsystem design are applied to produce single-chip instruments that acquire images of underlying samples on their own, without the need for off-chip scanners or sensors. Furthermore, it is shown that the instruments enjoy a multitude of performance benefits that stem from CMOS-MEMS integration and volumetric scaling of scanners by a factor of 1 million. This dissertation details the design, fabrication and imaging results of the first single-chip contact-mode AFMs, with integrated piezoresistive strain sensing cantilevers and scanning in three degrees-of-freedom (DOFs). Static AFMs and quasi-static AFMs are both reported. This work also includes the development, fabrication and imaging results of the first single-chip dynamic AFMs, with integrated flexural resonant cantilevers and 3 DOF scanning. Single-chip Amplitude Modulation AFMs (AM-AFMs) and Frequency Modulation AFMs (FM-AFMs) are both shown to be capable of imaging samples without the need for any off-chip sensors or actuators. A method to increase the quality factor (Q-factor) of flexural resonators is introduced. The method relies on an internal energy pumping mechanism that is based on the interplay between electrical, mechanical, and thermal effects. To the best of the author’s knowledge, the devices that are designed to harness these effects possess the highest electromechanical Qs reported for flexural resonators operating in air; electrically measured Q is enhanced from ~50 to ~50,000 in one exemplary device. A physical explanation for the underlying mechanism is proposed. The design, fabrication, imaging, and tip-based lithographic patterning with the first single-chip Scanning Thermal Microscopes (SThMs) are also presented. In addition to 3 DOF scanning, these devices possess integrated, thermally isolated temperature sensors to detect heat transfer in the tip-sample region. Imaging is reported with thermocouple-based devices and patterning is reported with resistive heater/sensors. An “isothermal electrothermal scanner” is designed and fabricated, and a method to operate it is detailed. The mechanism, based on electrothermal actuation, maintains a constant temperature in a central location while positioning a payload over a range of >35μm, thereby suppressing the deleterious thermal crosstalk effects that have thus far plagued thermally actuated devices with integrated sensors. In the thesis, models are developed to guide the design of single-chip SPMs and to provide an interpretation of experimental results. The modelling efforts include lumped element model development for each component of single-chip SPMs in the electrical, thermal and mechanical domains. In addition, noise models are developed for various components of the instruments, including temperature-based position sensors, piezoresistive cantilevers, and digitally controlled positioning devices

Robot Manipulators

Robot manipulators are developing more in the direction of industrial robots than of human workers. Recently, the applications of robot manipulators are spreading their focus, for example Da Vinci as a medical robot, ASIMO as a humanoid robot and so on. There are many research topics within the field of robot manipulators, e.g. motion planning, cooperation with a human, and fusion with external sensors like vision, haptic and force, etc. Moreover, these include both technical problems in the industry and theoretical problems in the academic fields. This book is a collection of papers presenting the latest research issues from around the world

Control performance comparison of PZT microactuator driven by voltage and current amplifiers in HDD dual-stage systems

In this paper, we investigate the effect of voltage and current amplifiers for PZT microactuators on the control performance of dual-stage servo systems in hard disk drives (HDDs), where the PZT microactuator is used as a secondary actuator and works together with the primary actuator of voice coil motor (VCM). First, the PZT microactuator's behavior in terms of motion linearization and frequency responses is experimentally studied and compared when it is driven by a conventional voltage amplifier and a charge or current amplifier. It is found that the PZT microactuator with current amplifier has less hysteresis than with voltage amplifier and its first resonance is relatively smaller. Inspired by this difference, the control performance of the dual-stage servo systems in track-seeking and track-following is then compared between the two driving methods for the PZT microactuator