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Modelling of an electro-hydraulic servo-system

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Caney, Keith,1940- (1977) Modelling of an electro-hydraulic servo-system. Research Master thesis, University of Tasmania.

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Abstract

Many theoretical models have been developed to simulate the
performance of hydraulic Control components and systems, but all are
limited by the assumptions involved and uncertain factors associated
with practical hydraulic systems.
Authors warn that seal compressibility, inertia of oil in
lines, mounting compliance, structural damping, friction and cavitation
may each be significant in appropriate circumstances,and even the
bulk modulus of hydraulic oil is difficult to predict for practical
systems. Manufacturers may reject theoretically predictable designs
because they are prone to wear or expensive to make. For instance
sharp edged orifices are replaced by the short tube type and oil
passages consist of drilled holes intersecting at angles with frequent
changes in section.
The prospect of obtaining a comprehensive mathematical model
applicable to manufactured components is therefore remote due to
the uncertainties and complexities involved but the designer will
require models and methods of solution sufficient for his purposes
which are to obtain a reasonable prediction of performance at the
design stage.
'Design' may mean the design of a hydraulic circuit component,
such a pump or relief valve, or may involve matching standard components
to form a system. Ideally the designer requires a model of each
system component which can be assembled with all other component
models to form a comprehensive system model which can be solved
mathematically. If linear models are possible an exact final solution
may be feasible but when non-linearities are present, a digital
simulation of the model giving a time response to defined inputs may
be the only practical method of solution and, inevitably, the designer
is involved with the problems of computation. Computers are now commonplace in design offices, Small computer
installations offer a hands ,-on facility which is flexible and versatile
whilst large installations offer enormous capacity and capability
but are often remotely located with inflexible management procedures
ill-suited to the trial and error design techniques often required
for component design optimisation. As such,a small computer may offer
the most efficient means of solving these design problems.
This thesis is concerned with methods of modelling hydraulic
components and systems with particular emphasis placed on the use
of a small computer installation for digital simulation of models,
and for other tasks related to laboratory testing of actual systems.
The basic aims are to obtain physical and mathematical models of
an existing electro-hydraulic two-stage servo-valve, to use a small
computer to predict open and closed-loop responses, to obtain actual
system responses for comparison with those predicted, and to examine
non-linearities encountered.
The thesis is set out in the order in which the work was done.
Initially similar work was studied and extended after which the
servo-valve was measured and tests were conducted to ascertain
physical constants required for the system equations. A linear model
was then simulated and actual system responses were obtained for
comparison with the first linear model. After this the linear model
was slightly modified and other more advanced non-linear models
developed.
NOTATION
Symbols are defined when they are introduced and a comprehensive
table of symbols appears in section A3.1 in Appendix 3. Commonly
used servo-valve variables are defined on figure (2-4) in chapter 2.

Item Type: Thesis (Research Master)
Keywords: Hydraulic servomechanisms
Copyright Holders: The Author
Copyright Information:

Copyright 1977 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (M.Eng.Sc.)--University of Tasmania, 1977

Date Deposited: 25 Nov 2014 00:39
Last Modified: 11 Mar 2016 05:56
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