PhD-Theses completed in 2007
Condition Monitoring and In-line Maintenance of Oil and
On-line Diagnostics of Components in
Fluid Power and Circulating Lubrication Systems
Institute of Hydraulics and Automation
Tampere University of Technology, Tampere, Finland
In this thesis, condition monitoring of oil was based mainly
on on-line particle counting in different cases and applications. The thesis presents the effects of water and air and
other important error sources on particle counting, compares the
results of on-line analysis
and bottle sampling, and reports laboratory results of several online
contaminant monitors. The main practical results of this work are guidelines of how to avoid errors with a
particle counter. Thus measurement should be run at least 15 minutes
for reliable results. The
water content of oil must be known, because a water content of over 200
ppm increases on-line particle counts by several ISO classes. With bottle sampling, oil
cleaner than ISO (13)/11/9 gives results of at least two ISO classes
higher than on-line counting,
and these errors multiply with cleaner oil.
To
improve in-line maintenance of oil, the function of the reservoir for
removing gaseous and liquid contaminants from the main flow of a circulating lubrication system was
examined with the aid of a CFD program. The calculations developed for
studying the effective
volume of the reservoir are presented. For effective contaminant
separation, a full-flow in-line vacuum dehydrator was developed. The thesis also presents and discusses
full-scale laboratory measurements and field tests made to verify the
function of the components
developed. The most important result was a novel design of a
cylindrical lubrication oil reservoir with a volume one third of the rectangular and an ability to
separate three times smaller water droplets and air bubbles than was
possible with the calculated
rectangular reservoir model. Experimental verification showed an
accuracy of 5.8% in the weighted average of oil circulation times between modelled circulation time and
on-line particle counting.
Studied
also was on-line diagnostics of servo valves and return line filters.
Suitable identification of failure symptoms was sought by examining the characteristics of new and used
servo valves in a laboratory, and many diagnostic signals were proposed
for on-line analysis during
and between the rolling of steel strips. Trend analysis of analyzed
signals of servo valves was used with symptom and alarm limits. On-line diagnosis was developed on
the return line filter to substitute difficult flow measurements for
downstream pressure
measurements. Trend analysis and curve fitting were used for time
prognosis of upcoming filter blockage. Two diagnostic programs for the servo valve and one for the
return line filter were tested in industry for some years, but their
use has now been discontinued.
Back
to top
Characteristics of Valve Controlled Hydraulic Power
Transmission in Teleoperated Skid Steered Mobile Machine
Institute of Hydraulics and Automation
Tampere University of Technology, Tampere, Finland
Hydraulic mobile machines have reached a
turning point in their development and are on their way to becoming
fully autonomous; that is,
control of the machine’s action by human operators will be
increasingly autonomous. One large mobile machine can be replaced with several cooperating small mobile
machines, capable of doing the work of the larger machine. Costs and
environmental concerns are
some of the factors propelling the development work of modular, small
machines.
The objective of this thesis was to study the
accuracy and extent of control attainable by teleoperation and autonomy
in a skid- steered mobile
machine using standard mobile hydraulic components. The thesis
introduces the machine’s architecture and discusses the background of the development work.
Simulations were run to find suitable design parameters for the
machine’s drive and power transmission
of skid steered mobile machine. Also advanced velocity control for the
machine was studied by simulations. Finally, the thesis provides a glimpse into the future of
autonomous hydraulic mobile machines and proffers some new hydraulic
solutions.
The main result of this thesis is that an
autonomous mobile machine using mobile hydraulic components can be
realized with today’s
technology, though the task is challenging. A second result is that the
drive and power transmission system works well with advanced velocity control. With regard to
autonomy, the machine’s controllability is greatly affected
by the characteristics of its control
valve.
Back
to top
Damping of Low Frequency Pressure Oscillation
Institute of Hydraulics and
Automation
Tampere University of Technology, Tampere, Finland
A hydraulic line between a hydraulic pump and an actuator
comes under much stress when a pulsatile actuator is used. It causes a huge pressure oscillation in the hydraulic system
and thus decreases reliability. For example in a rock drill
transferable hydraulic power
is tens of kilowatts, so efficiency is also significant. The operating
frequency of the rock drill is usually between 30 and 60 Hz. The frequency of the pressure oscillation is then
very low compared for example to pressure oscillation of a hydraulic
pump.
The aim of this thesis is study pressure
dampers when the damped frequency is low and when they work as a part
of a wider system. After
theoretical inspection, pressure dampers were simulated and then
different dampers were tested with a pure sine wave pressure oscillation and then with the real rock
drill. Different sizes of accumulators, a Helmholtz resonator, a T-pipe
and an inline suppressor
were used in tests.
Dimension theories of dampers
worked even though the operating frequency was low. The simulation
models used operated well enough
so that they can be utilized for a definition of the pressure
damper.
The accumulator damped pressure
oscillation of the rock drill well when it was installed near the
hydraulic main line but it didn't damp
pressure oscillation of the rock drill as expected when it was tuned by
the "natural frequency" method. The T-pipe was easy to tune and the damping capacity was promising even
with the rock drill. The Helmholtz-resonator damped well, but the size
of the damper was too big
for mobile hydraulic applications. The inline-suppressor
didn't damp pressure oscillation between 30 - 60 Hz much but it damped high pressure oscillation (1200
Hz) well.
Back
to top
IElectrorheological Valves as Active Elements for the Control
of Hydraulic Drives
Institute for Fluid Power Drives and Controls (IFAS)
Aachen University (RWTH), Aachen, Germany
Electrorheological Fluids (ERF) can be classified as controllable
fluids. Their flow behaviour can be changed rapidly by applying a strong electric field. Within milliseconds, the
flow resistance is increased by several orders of magnitude. Because of
the high dynamic performance
these fluids are qualified for fast control tasks and therefore the
control of highly dynamic cylinder drives is a possible application. In such systems
electrorheological valves can be used as control elements. Due to the
lack of information about the
physical and chemical mechanism regarding the electrorheological effect
the design of valves and drives is mostly empirical. Furthermore, there are no standards for
characterization of ERF available, which turns the evaluation of
different ERF into a challenge.
The objective of this thesis is to close this gap. After the
description of relevant fluid properties, advices for their measuring are given. The main focus of this work is the
description of the design process for cylinder drives. In the scope of
this design process the
simulation of valves, based on phenomenological models, is essential.
Two different phenomenological models, a static and a dynamic one, are described and implemented into a
standard simulation tool. The design process is verified by applying it
on a new cylinder drive.
Every step of this process is exemplarily conducted. Measurements of
the new drive in a closed-loop control are shown and compared to simulation results. Finally,
an adaption of the signal amplitude on the current electrical power
consumption is introduced.
Using this new approach within a closed-loop control, the high dynamic
behaviour of the new cylinder drive is improved.
Back
to top
Mechatronic Systems for the Damping of Pulsations of
Hydrostatic Displacement Units
Institute for Fluid Power Drives and Controls (IFAS)
Aachen University (RWTH), Aachen, Germany
The method of finite elements (FEM) is a suitable tool for the
numerical solution of Maxwell’s field equations to calculate
electromagnetic
fields. Solenoids as electromechaThe discontinuous conveyance of fluid
by hydrostatic displacement units often influences the quality of
hydraulic systems. This can
have an effect on the noise behaviour, the system characteristics up to
the durability of components or systems. In the fight against fluid borne noise inside of
hydraulic systems a goal conflict often shows himself between system
characteristics like the
system efficiency or the system dynamic on the one hand and the damping
in a wide working parameters range on the
other hand.
Adaptive and active pulsation damping
methods present themselves as means to gain a degree of freedom inside
these goal conflicts.
Nevertheless they often fail because of a complex structure or the need
of high power- and/or high dynamic-actors. This thesis displays an Adaptive Helmholtz
resonator that needs – due to its structure –
little constructed space and can be operated
by a low-cost actuator. Adding to this the thesis offers a construction
of a valve as well as a control-algorithm that allow the design and operation of several active pulsation
damping methods without using dynamic actors – the so called
“Rotopuls”.
The characteristics of these are analyzed and
verified by test bench examinations as well as system simulations in
DSHplus. In order to enable
the simulation of the underlying pump – a suction-throttled,
pressure-controlled radial piston pump, a new simulation model including the description of cavitation is
derived and used.
Back
to top
Hydraulic Power Steering System Design in Road Vehicle,
Analysis, Testing and Enhanced Functionality
Division of Fluid and Mechanical Engineering Systems
Department of Management and Engineering
Linkoeping University, Linkoeping, Sweden
Demands
for including more functions in power steering systems in road vehicles
has increased with requirements on new active safety and comfort functions. Active safety
functions, which have been proven to have a positive effect on overall
vehicle safety, refer to
functions that give the driver assistance in more and less critical
situations to avoid accidents. Active safety features are going to play an increasingly important role in future
safety strategies; therefore, it is essential that sub systems in road
vehicles, such as power
steering systems, are adjusted to meet new demands. The traditional
Hydraulic Power Assisted Steering, HPAS, system, cannot meet these new demands, due to the control
unit's pure hydro-mechanical solution. The Active Pinion concept
presented in this thesis is
a novel concept for controlling the steering wheel torque and angel in
future active safety and comfort applications. The concept, which can bee seen as a modular add-on
added to a traditional HPAS system, introduces an additional degree of
freedom to the control unit.
Different control modes used to meet the demands of new functionality
applications are presented and tested in a hardware-in-the-loop test rig. This thesis also
covers various aspects of hydraulic power assisted steering systems in
road vehicles. Power
steering is viewed as a dynamic system and is investigated with linear
and non-linear modeling techniques. The shaping of the valve is essential for the function of the HPAS
system; therefore, a method involving optimization has been developed
to determine the valve
characteristic. The method uses static measurements as a base for
calculation and optimization; the results are used in both linear and the non-linear models. With the help of
the linear model, relevant transfer functions and the underlying
control structure of the
power steering system have been derived and analyzed. The non-linear
model has been used in concept validation of the Active Pinion. Apart from concept validation and
controller design of the active pinion, the models have been proven
effective to explain dynamic
phenomena related to HPAS systems, such as shuttering and hydraulic
lag.
Back
to top
Automatic Parallel Parking – Park Assist Systems for
Passenger Vehicles
Division of Fluid and Mechanical Engineering Systems
Department of Management and Engineering
Linkoeping University, Linkoeping, Sweden
This thesis discusses how the problem of
parking a passenger car can be solved. There are numerous obstacles
when creating a fully or
semi automated system for ass isting the
parking maneuver. The obstacles range from unobtrusive Man Machine
Interface issues to robust
algorithms for finding features in sensor data.
Such a system will also have to cope
with ever changing environments, most of which will not be discovered
during the design phase.
Misuse will also be common, since the function is aimed at a mass
market - the car buyers. These interesting problem areas are also coupled with the customer value. A car buying
customer today aims at feature content and comfort. So for a parking
system to survive it needs to
be extremely intuitive; the customer value must be discovered during a
short test drive with the vehicle. A learning period before the user can operate the system is not
feasible. The work presented here proposes an interesting algorithm for
finding parking space
features in sensor data collected using ultra sonic. The algorithm,
which is based on the well known Hough transform have been proved to be robust in real world experiments.
Furthermore it is also investigated how critical the mounting of the
environment sensing subsystem
is. Where should the sensors be placed and where should they be facing
to maximize the performance. Emphasis has also been put on designing a functional architecture
that fits in the car development process of today. The implementation
of a system in a car must
fit in the platform and component reuse is critical to keep cost down.
To test theories developed during the work a prototype car has been used. The prototype is essential to analyze
the robustness of algorithms in different parking scenarios. It has
also been an invaluable tool
when conducting customer surveys to find where the customer value of
these kinds of systems is.
Back
to top
Integrated Control and Estimation Based on Sliding Mode
Control Applied to Electrohydraulic Actuator
Department of Mechanical Engineering
University of Saskatchewan, SK, Canada
Many problems in tracking control have
been identified over the years, such as the availability of systems
states, the presence of noise
and system uncertainties, and speed of response, just to name a few.
This thesis is concerned with developing novel integrated control and estimation algorithms to overcome some
of these problems in order to achieve an efficient tracking
performance. Since there are
some significant advantages associated with Sliding Mode Control (SMC)
or Variable Structure Control (VSC), (fast regulation rate and robustness to uncertainties), this
research reviews and extends new filtering concepts for state
estimation, referred to as
the Variable Structure Filter (VSF) and Smooth Variable Structure
Filter (SVSF). These are based on the philosophy of Sliding Mode Control.
The VSF filter is designed to estimate
some of the states of a plant when noise and uncertainties are
presented. This is accomplished
by refining an estimate of the states in an iterative fashion using two
filter gains, one based on a noiseless system with no uncertainties and the second gain which reflects
these uncertainties. The VSF is combined
“seamlessly” with the Sliding Mode Controller to produce an integrated controller called
a Sliding Mode Controller and Filter (SMCF). This new controller is
shown to be a robust and
effective integrated control strategy for linear systems. For nonlinear
systems, a novel integrated control strategy called the Smooth Sliding Mode Controller and Filter
(SSMCF), fuses the SMC and SVSF in a particular form to address
nonlinearities. The gain
term in the SVSF is redefined to form a new algorithm called the
“SVSF with revised gain” in order to obtain a
better estimation
performance. Its performance is compared to that of the Extended Kalman
Filter (EKF) when applied to a particular nonlinear plant.
The SMCF and SSMCF are applied to the
experimental prototype of a precision positioning hydraulic system
called an Electro-Hydraulic
Actuator (EHA) system. The EHA system is known to display nonlinear
characteristics but can approximate linear behavior under certain operating conditions, making it
ideal to test the robustness of the proposed controllers. The main conclusion drawn in this research was
that the SMCF and SSMCF as developed and implemented, do exhibit robust
and high performance state
estimation and trajectory tracking control given modeling uncertainties
and noise. The controllers were applied
to a prototype EHA which demonstrated the use of the controllers in a
“real world” application. It was also concluded
that the application of the
concepts of VSC for the controller can alleviate a challenging
mechanical problem caused by a slip-stick characteristic in friction. Another conclusion is that the
revised form of the SVSF could obtain robust and fast state estimation
for nonlinear systems.
The original contributions of the
research include: i) proposing the SMCF and SSMCF, ii) applying the
Sliding Mode Controller to
suppress cross-over oscillations caused by the slip-stick
characteristics in friction which often occur in mechanical systems,
iii) the first application
of the SVSF for state estimation and iv) a comparative study of the
SVSF and Extended Kalman Filter (EKF) to the EHA demonstrating the superiority of the SVSF for
state estimation performance under both steady-state and transient
conditions for the
application considered.
The dissertation is written in a paper
format unlike the traditional Ph.D thesis manuscript. The content of
the thesis discourse is based
on five manuscripts which are appended at the end of the thesis.
Fundamental principles and concepts associated with SMC, VSF, SVSF and the fused controllers are
introduced. For each paper, the objectives, approaches, typical
results, conclusions and major
contributions are presented. Major conclusions are summarized and
original contributions reiterated.
Back
to top
Research on Acceleration Harmonic Cancellation of
Electro-Hydraulic Servo Shaking Table
School of Mechanical and Electrical Engineering
Harbin Institute of Technology, Harbin, China
Shaking table system is a very important experimental
apparatus in engineering research. It is widely applied to many main industrial fields including aerospace, automobile,
architecture, etc.. While performing a vibration test, specimen is
mounted to the test table
and simulative load force is applied to the specimen. Researchers
analyze the influence on load brings, the reliability of the specimen, or the damping system’s
performance. With the reliability requirement of industrial products,
especially for aerospace vehicles,
becoming higher and higher, the simulative vibration test system, as
the vital apparatus of reliability test, is placed more emphases on its performance. For electro-hydraulic
simulative vibration test system, how to get over the uncertainty of
the system, meeting the
special requirement of the shaking test, becomes a main subject.
Three variables controller is developed for the
shaking table based on pole placement theory to improve system
stability and extend its
bandwidth. Due to the nonlinearity characteristics present in the
electro-hydraulic servo shaking table, phase delay, amplitude attenuation and spurious harmonics appear in the
system acceleration response when corresponding to a simple sinusoidal
signal, which causes
harmonic distortion of the acceleration signal. Experiment demonstrates
that the harmonics are always integer multiples of the fundamental frequency.
To eliminate the phase delay and
amplitude attenuation of acceleration response, amplitude-phase control
(APC) network is developed.
The task is accomplished by adjusting the weights using LMS algorithm
when there exits phase delay and amplitude attenuation between the input and its corresponding
acceleration response. The reference input is weighted in such a way
that it makes the system
output track the input efficiently. The weighted input signal is added
to the control system such that the output phase delay and amplitude attenuation are all cancelled.
The above concept is used as a basis for the development of APC
algorithm.
The method for harmonic cancellation
based on adaptive notch filter technology is developed. The task is
accomplished by generating
reference signals with frequency that should be eliminated from the
output. The reference inputs are weighted by the adaptive filter in such a way that it closely matches the
harmonic. The output of the adaptive filter is a harmonic replica and
is injected to the fundamental
signal such that the output harmonic is cancelled leaving the desired
acceleration signal alone, and the total harmonic distortion (THD) is greatly reduced. The weights
of filter are adjusted on-line by using LMS adaptive filtering
algorithm. The above course is used as a basis for the development of
adaptive harmonic cancellation (AHC) algorithm. AHC algorithms, both
based on traditional LMS
algorithm and based on normalized LMS algorithm, are all developed and
are compared with each other. From the comparison
results, it is seen clearly that the AHC algorithm, based on normalized
LMS algorithm, has better harmonic elimination efficiency and faster weight
convergence.
Both the APC and the AHC need not to
estimate the system model. The advantages of the proposed control
schemes are that it has
simple structure, low computation burden and high real-time
performance.
Back
to top
Haptic Control of Hydraulic Machinery using Proportional
Valves
George W. Woodruff School of Mechanical Engineering
Georgia Institute of Technology, Atlanta, Georgia USA
Supplying haptic or force feedback to
operators using hydraulic machinery such as excavators has the
potential to increase operator
capabilities. Haptic, robotic, human-machine interfaces
enable several enhancing features including: coordinated motion control
and programmable haptic
feedback. Coordinated or resolved motion control supplies a
more intuitive means of specifying the equipment's motion. Haptic feedback is used
to relay meaningful information back to the user in the form of force
signals. These haptic forces
can relay information about digging force acting on the bucket,
programmable virtual constraints and system limitations imposed by the mechanism, maximum pressure or
maximum flow. In order to make this technology economically
viable, the benefits must
offset the additional cost associated with implementation.
One way to minimize this cost is to not use high-end hydraulic components. For smaller backhoes and
mini-excavators this means that the hydraulic systems are comprised of
a constant displacement pump
and proportional direction control valves. Hydraulic and
haptic control techniques suitable for backhoes/excavators are developed and tested on a small backhoe
test-bed. A virtual backhoe simulator is created for
controller design and human evaluation. Not only is the virtual simulator modeled after the
test-bed, but the control algorithm used in the simulator is the same
as the actual backhoe
test-bed. Data from human subject tests are presented that
evaluate the control strategies on both the real and virtual
backhoe. The end
goal of this project is to incorporate coordinated haptic control
algorithms that work with low-cost systems and maximize the enhancement of operator capabilities.
Back
to top
Awards in 2007
New Construction of an Electro-Conjugate Fluid-Jet-Driven Micromotor with an Inner Diameter of 2mm
Awarded to
Dr. Shinichi Yokota (Precision and Intelligence Laboratory, Tokyo Institute of Technology)
Dr. Kazuya Edamura (New Technology Management Co., Ltd, Tokyo, Japan)
Proc. IMech.E, Part I: Journal of Systems and Control Engineering, Vol.220, No.4, pp.251/256, (2006)
Invention of the Self-Energizing Electro-Hydraulic Brake (SEHB)
Awarded to
Dr.-Ing. Christian Stammen (Institute for Fluid Power Drives and Controls at
RWTH Aachen University, Aachen, Germany)
Awarded by the NRW Science Center and the Industry Club Duesseldorf on May 7th 2007
Back to top
Books & Proceedings Published in 2007
Publisher: Springer
Chapter 1 deals with the general background of the subject
matter, illustrating the reason for condition monitoring and some
general principles that apply or can be applied. Hopefully this sets
out the need for the ensuing chapters which then discuss some of the
important details.
Chapter 2 considers modelling and
computer simulation with appropriate basic theory and its practical
application. This Chapter was particularly difficult to minimize to a
sensible length but most of what is included is supported by practical
results. The reader will note the absence of any detailed control
theory, beyond some fundamental ideas, since this is not really
necessary within the context of this book; also background theory in
general is not exhaustive in this area for the same reason. More
importantly, what has been included is material found to be useful for
real monitoring applications particularly from work with the fluid
power and manufacturing industries. The reader will note several
applications of artificial neural networks and related ideas such as
data based modelling.
Chapter 3 considers condition monitoring
methods where the theory of Chapter 2 is put into practice. In
addition, pragmatic concepts of signal monitoring and processing are
included to illustrate the practical reality of combining a sensible
amount of both theory and intuition, perhaps experience. Some new
algorithms developed at Cardiff are introduced here but an important
message is again the practical limitations of each method and the fact
that in reality several approaches should be tried to give confidence
in the emerging diagnostic. Some sensor information is covered although
this is not an attempt to overview the general field of condition
monitoring, only what has been found to be useful from the
author’s modest contribution to the subject. Perhaps the main
themes of this chapter are pressure and flow monitoring, dynamic data
analysis including vibration, and oil/wear debris analysis. This
chapter also considers expert systems and knowledge based reasoning.
This is a fascinating area, quite complex and useful for situations
such as multiple fault conditions, but is still only enjoying a modest
evolution. It is intended to show how rules may be developed from some
rather basic theoretical concepts which then actually gives a great
deal of information on the probable fault state of the hydraulic
circuit. Again many practical examples are used to illustrate the
concepts from simple drives and lifting systems to a 7 stand steel
strip finishing mill.
Chapter 4 gives many examples of component faults in
pumps and motors taken from industrial sources on the cause and
solutions for breakdowns that may occur in a hydraulic circuit. It
considers many components and typical failures that have been deduced
over many year of experience.
A comprehensive list of books,
papers and further reading is included together with a detailed Index.
The intention has been to include important references with the view
that other works tend, but not always, to be covered in the
publications quoted. The reader will note some early references since
formative work now tends to be ignored, or certainly not acknowledged,
in modern publications.
Back
to top
BACK
©2007 Fluid
Power Net All rights reserved. Disclaimer