2,170 research outputs found
Design aspects of a solar array drive for spot, with a high platform stability objective
A solar array drive mechanism (MEGS) for the SPOT platform, which is a prototype of a multimission platform, is described. High-resolution cameras and other optical instruments are carried by the platform, requiring excellent platform stability in order to obtain high-quality pictures. Therefore, a severe requirement for the MEGS is the low level of disturbing torques it may generate considering the 0.6 times 10 to the minus 3 power deg/sec stability required. The mechanical design aspects aiming at reducing the mean friction torque, and therefore its fluctuations, are described as well as the method of compensation of the motor imperfections. It was concluded, however, that this is not sufficient to reach the stability requirement
A high temperature fatigue and structures testing facility
As man strives for higher levels of sophistication in air and space transportation, awareness of the need for accurate life and material behavior predictions for advanced propulsion system components is heightened. Such sophistication will require complex operating conditions and advanced materials to meet goals in performance, thrust-to-weight ratio, and fuel efficiency. To accomplish these goals will require that components be designed using a high percentage of the material's ultimate capabilities. This serves only to complicate matters dealing with life and material behavior predictions. An essential component of material behavior model development is the underlying experimentation which must occur to identify phenomena. To support experimentation, the NASA Lewis Research Center's High Temperature Fatigue and Structures Laboratory has been expanded significantly. Several new materials testing systems have been added, as well as an extensive computer system. The intent of this paper is to present an overview of the laboratory, and to discuss specific aspects of the test systems. A limited discussion of computer capabilities will also be presented
Look-ahead seek correction in high-performance CD-Rom drives
As the performance of CD-ROM drives continues to increase, special attention should be paid to any element in the system that disturbs the desired specifications. When very low access times are considered, it is mandatory to reach the target track within only one seek action, i.e. without any consequent retry or correction seek. Many CD-ROM drives count the tracks crossed during seeking and, by comparing this count with the pre-calculated seek length, the exact target location can be detected. This paper considers the error that affects the track-counting mechanism due to the rotating disc spiral. It is shown that, for a given seek length, the number of crossed tracks differs between outside- and inside-oriented seeks. The involved equations are derived and an algorithm proposed for determining the correct number of tracks to be crossed during a seek action. The proposed algorithm, which is optimized for microprocessor implementation, relies on two look-up tables and a learning scheme that allows look-ahead seek correction for both spiral rotation and system tolerance
Conceptual design study for an advanced cab and visual system, volume 2
The performance, design, construction and testing requirements are defined for developing an advanced cab and visual system. The rotorcraft system integration simulator is composed of the advanced cab and visual system and the rotorcraft system motion generator, and is part of an existing simulation facility. User's applications for the simulator include rotorcraft design development, product improvement, threat assessment, and accident investigation
Pneumatic motion control systems for modular robots
This thesis describes a research study in the design,
implementation, evaluation and commercialisation of
pneumatic motion control systems for modular robots. The
research programme was conducted as part of a collaborative
study, sponsored by the Science and Engineering Research
Council, between Loughborough University and Martonair (UK)
Limited.
Microprocessor based motion control strategies have been
used to produce low cost pneumatic servo-drives which can be
used for 'point-to-point' positioning of payloads. Software
based realtime control strategies have evolved which
accomplish servo-controlled positioning while compensating
for drive system non-linearities and time delays. The
application of novel compensation techniques has resulted in
a significant improvement in both the static and dynamic
performance of the drive.
A theoretical foundation is presented based on a
linearised model of a pneumatic actuator, servo-valve, and
load system. The thesis describes the design and evolution
of microprocessor based hardware and software for motion
control of pneumatic drives. A British Standards based
test-facility has allowed control strategies to be evaluated
with reference to standard performance criteria.
It is demonstrated in this research study that the dynamic
and static performance characteristics of a pneumatic motion
control system can be dramatically improved by applying
appropriate software based realtime control strategies. This
makes the application of computer controlled pneumatic
servos in manufacturing very attractive with cost
performance ratios which match or better alternative drive
technologies.
The research study has led to commercial products
(marketed by Martonair Ltd), in which realtime control
algorithms implementing these control strategy designs are
executed within a microprocessor based motion controller
Available Techniques for Magnetic Hard Disk Drive Read Channel Equalization
This paper presents an extensive, non-exhaustive, study of available hard disk drive read channel equalization techniques used in the storage and readback of magnetically stored information. The physical elements and basic principles of the storage processes are introduced together with the basic theoretical definitions and models. Both read and write processes in magnetic storage are explained along with the definition of simple key concepts such as user bit density, intersymbol interference, linear and areal density, read head pulse response models, and coding algorithm
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