Improved performance of hard disk drive servomechanism using digital multirate control

Ph.DDOCTOR OF PHILOSOPH

CHALLENGES OF CONTROL DESIGN FOR PRECISION SERVO SYSTEM WITH APPLICATION ON HARD DISK DRIVE

Ph.DDOCTOR OF PHILOSOPH

Vibration analysis and control in hard-disk drive servo systems

Master'sMASTER OF ENGINEERIN

Optimal control issues related to the hard disk drive servo systems

Ph.DDOCTOR OF PHILOSOPH

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

Ph.DDOCTOR OF PHILOSOPH

REAL-TIME SIGNAL PROCESSING FOR FLYING HEIGHT MEASUREMENT AND CONTROL IN HARD DRIVES SUBJECT TO SHOCK AND VIBRATION

Merged with duplicate record 10026.1/829 on 10.04.2017 by CS (TIS)Three readback signal detection methods are investigated for real-time flying height or head disk spacing variation measurement under vibration conditions. This is carried out by theoretical analysis, numerical simulation, and experimental study. The first method (amplitude detection) provides a simple way to study the head disk spacing change. The second method ( PW50 parameter estimation) can be used effectively for real-time spacing variation measurement in normally operated hard disk drives, primarily in low frequency spacing variation conditions. The third method (thermal signal detection), on the other hand, is more effective and suitable for high frequency spacing variation measurement. By combining the PW50 estimation and thermal signal detection methods, a noval spacing variation detection method for the whole frequency range is constructed. This combined signal detection method not only has been used to study the head disk spacing variation itself, but also has the potential of being used for real time flying height control. Analytical models are developed for head disk assembly and head position servo control mechanisms to analyse the operation failure of hard disk drives under vibration conditions. Theoretical analysis and numerical simulation show their good agreement with experimental results. A novel active flying height control method is proposed to suppress the flying height or head-disk spacing variation in hard disk drives under vibration conditions. Simulation results show that this active flying height control can effectively suppress the head-disk spacing variation, therefore the performance and reliability of HDDs can be well improved when working in vibration conditions: The method has a good potential to be applied to future ruggedized hard disk drives

Active stabilization to prevent surge in centrifugal compression systems

This report documents an experimental and analytical study of the active stabilization of surge in a centrifugal engine. The aims of the research were to extend the operating range of a compressor as far as possible and to establish the theoretical framework for the active stabilization of surge from both an aerodynamic stability and a control theoretic perspective. In particular, much attention was paid to understanding the physical limitations of active stabilization and how they are influenced by control system design parameters. Previously developed linear models of actively stabilized compressors were extended to include such nonlinear phenomena as bounded actuation, bandwidth limits, and robustness criteria. This model was then used to systematically quantify the influence of sensor-actuator selection on system performance. Five different actuation schemes were considered along with four different sensors. Sensor-actuator choice was shown to have a profound effect on the performance of the stabilized compressor. The optimum choice was not unique, but rather shown to be a strong function of some of the non-dimensional parameters which characterize the compression system dynamics. Specifically, the utility of the concepts were shown to depend on the system compliance to inertia ratio ('B' parameter) and the local slope of the compressor speedline. In general, the most effective arrangements are ones in which the actuator is most closely coupled to the compressor, such as a close-coupled bleed valve inlet jet, rather than elsewhere in the flow train, such as a fuel flow modulator. The analytical model was used to explore the influence of control system bandwidth on control effectiveness. The relevant reference frequency was shown to be the compression system's Helmholtz frequency rather than the surge frequency. The analysis shows that control bandwidths of three to ten times the Helmholtz frequency are required for larger increases in the compressor flow range. This has important implications for implementation in gas turbine engines since the Helmholtz frequencies can be over 100 Hz, making actuator design extremely challenging

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

Description of the Spacecraft Control Laboratory Experiment (SCOLE) facility

A laboratory facility for the study of control laws for large flexible spacecraft is described. The facility fulfills the requirements of the Spacecraft Control Laboratory Experiment (SCOLE) design challenge for a laboratory experiment, which will allow slew maneuvers and pointing operations. The structural apparatus is described in detail sufficient for modelling purposes. The sensor and actuator types and characteristics are described so that identification and control algorithms may be designed. The control implementation computer and real-time subroutines are also described