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

Modification of the rotary machining process to improve surface form

Planing and moulding operations carried out within the woodworking industry make extensive use of rotary machining. Cutter-marks are produced on the timber surface which are generally accepted as unavoidable. More noticeable surface defects may be produced by such factors as cutter-head imbalance, and until recently most research has concentrated on removing these defects. When a high quality finish is required, a further machining operation, such as sanding, is often required to remove cutter-marks. What is required, is a modified machining process which combines a surface closer to the ideal fixed knife finish, whilst retaining the flexibility, practicality and cost effectiveness of rotary machining. [Continues.

A state-of-the-art assessment of active structures

A state-of-the-art assessment of active structures with emphasis towards the applications in aeronautics and space is presented. It is felt that since this technology area is growing at such a rapid pace in many different disciplines, it is not feasible to cover all of the current research but only the relevant work as relates to aeronautics and space. Research in smart actuation materials, smart sensors, and control of smart/intelligent structures is covered. In smart actuation materials, piezoelectric, magnetostrictive, shape memory, electrorheological, and electrostrictive materials are covered. For sensory materials, fiber optics, dielectric loss, and piezoelectric sensors are examined. Applications of embedded sensors and smart sensors are discussed

Digital flight control actuation system study

Flight control actuators and feedback sensors suitable for use in a redundant digital flight control system were examined. The most appropriate design approach for an advanced digital flight control actuation system for development and use in a fly-by-wire system was selected. The concept which was selected consisted of a PM torque motor direct drive. The selected system is compatible with concurrent and independent development efforts on the computer system and the control law mechanizations

High data rate optical transceiver terminal

The objectives of this study were: (1) to design a 400 Mbps optical transceiver terminal to operate from a high-altitude balloon-borne platform in order to permit the quantitative evaluation of a space-qualifiable optical communications system design, (2) to design an atmospheric propagation experiment to operate in conjunction with the terminal to measure the degrading effects of the atmosphere on the links, and (3) to design typical optical communications experiments for space-borne laboratories in the 1980-1990 time frame. As a result of the study, a transceiver package has been configured for demonstration flights during late 1974. The transceiver contains a 400 Mbps transmitter, a 400 Mbps receiver, and acquisition and tracking receivers. The transmitter is a Nd:YAG, 200 Mhz, mode-locked, CW, diode-pumped laser operating at 1.06 um requiring 50 mW for 6 db margin. It will be designed to implement Pulse Quaternary Modulation (PQM). The 400 Mbps receiver utilizes a Dynamic Crossed-Field Photomultiplier (DCFP) detector. The acquisition receiver is a Quadrant Photomultiplier Tube (QPMT) and receives a 400 Mbps signal chopped at 0.1 Mhz

Large space structures and systems in the space station era: A bibliography with indexes (supplement 03)

Bibliographies and abstracts are listed for 1221 reports, articles, and other documents introduced into the NASA scientific and technical information system between January 1, 1991 and June 30, 1991. Topics covered include large space structures and systems, space stations, extravehicular activity, thermal environments and control, tethering, spacecraft power supplies, structural concepts and control systems, electronics, advanced materials, propulsion, policies and international cooperation, vibration and dynamic controls, robotics and remote operations, data and communication systems, electric power generation, space commercialization, orbital transfer, and human factors engineering

Diseño de fases cristalinas tipo perovskita con potenciales aplicaciones fotovoltaicas

En este trabajo se prepararon óxidos mixtos con estructura perovskita de la familia de titanocirconatos de plomo y lantano (PLZT) en forma de polvo y película delgada por el método citrato amorfo. Se encontró que las condiciones de preparación de la disolución precursora juegan un papel fundamental en las características de las muestras obtenidas. Para los sólidos en polvo se evaluaron sus características estructurales, morfológicas y ópticas en función de la adición de dopantes donadores, 3,0 % mol de La3+ en el sistema PZT(52/48) y 0,2 a 1,0 % mol de Nb5+, Ta5+ o W6+ en el sistema PLZT(3/52/48). Todas las muestras en forma de polvo con estructura cristalina tetragonal y con un tamaño de cristalito de alrededor de 20 nm se obtuvieron a una temperatura y tiempo de calcinación de 600 ºC y 2h respectivamente. Se encontró un mínimo de Eg = 3,26 eV para el sólido en polvo PLZT(3/52/48) dopado con 0,6 % mol de Ta5+. Se obtuvieron películas delgadas de PLZT(3/52/48) sobre sustratos de vidrio, a partir de la misma disolución precursora de su análogo en forma de polvo sin la adición de plomo en exceso. Para estas muestras se evaluaron sus propiedades estructurales y morfológicas en función del número de capas adicionadas. Se obtuvieron películas delgadas homogéneas y libres de grietas, con tamaños de grano que oscilan entre 50 y 300 nm, con estructura cristalina tetragonal, bajo tratamiento térmico de 600 ºC durante 1h. También se obtuvieron películas delgadas de 5 capas a 500 ºC durante 4 h.Abstract. In this work, powder and thin films of mixed oxides with perovskite structure of the lead and lanthanum titanozirconates (PLZT) were prepared by the amorphous citrate method. It was found that the conditions of preparation of the precursor solution play a fundamental role in the characteristics of the samples obtained. For solids in powder form, their structural, morphological and optical characteristics were evaluated as a function of the addition of donor dopants, 3.0% mol La3+ in the PZT system (52/48) and 0.2 to 1.0 % mol of Nb5+, Ta5+ or W6+ in the PLZT (3/52/48) system. All samples in powder form with tetragonal crystalline structure and a crystallite size around 20 nm were obtained by calcination at temperature and time of 600 ° C and 2 h respectively. A minimum of Eg = 3.26 eV was found for the powdered solid PLZT (3/52/48) doped with 0.6% mol Ta5+. Thin films of PLZT (3/52/48) were obtained on glass substrates, using the same precursor solution for its analogue in powder form without the addition of lead excess. For these samples their structural and morphological properties were evaluated as a function of the number of layers added. Homogeneous and cracks free thin film, with grain sizes varying between 50 and 300 nm and with tetragonal crystalline structure were obtained with heat treatment at 600 ºC during 1 h. Thin films of 5 layer were also obtained at 500 ºC during 4 h.Doctorad