In this study, the automation of the maintenance task
of electric power live lines by electro-hydraulic manipulators as one of
typical outdoor tasks has been investigated.
An electro-hydraulic manipulator using hydraulic actuators
is superior to electrically driven manipulators by power/mass density and
insulation. Meanwhile an electro-hydraulic manipulator has many nonlinear
elements, and the outdoor task has many uncertainties including obstacles
and noise so that most of the manipulator system up to now is based on
the manual operation by human or tele-operation. Recently there is a strong
demand to the automation and autonomy of these manipulator system because
of the decreasing number of skilled workers and so on.
However it is relatively difficult to realize not only stable contact work but also robust force control as basic controller for the autonomous assembly tasks using hydraulic manipulators. In this thesis, we proposed a compliance control, which is based on the position control by a disturbance observer for our manipulator system. And we also proposed a reference trajectory modification method in order to achieve robust force control even though the contact position and stiffness of environment is unknown. Experimental results show that stable contact work and robust force tracking by 6-link electro-hydraulic manipulators can be achieved under unknown environmental conditions. Finally we realized the automation of electro-hydraulic manipulator system with respect to 2 typical tasks ((1)Approaching and wrenching task of bolt with Nut, (2) Insertion task of flexible electric line to sleeve) among the maintenance task of electric power live lines using the proposed basic controller.
Energy and weight saving technologies for hydraulic drives are favourable in many industrial applications. A modern, energy saving hydraulic rotary drive is the variable displacement hydraulic motor (VDHM, also referred to as "secondary controlled" motor) that automatically adapts the hydraulic input power to the required mechanical output power. Moreover, it is able to deliver hydraulic power back to the supply system in case of "aiding" loads. Compared to the common, fixed displacement motor, the VDHM requires more sophisticated control laws to achieve a high level of static and dynamic performance. This contributes to the fact that VDHMs can hardly be found in any industrial application - despite their obvious advantages.
This work presents a novel approach to the position and speed control of VDHMs operated from a constant pressure net. To improve the state of the art in terms of static and dynamic performance, a robust high bandwidth control system with a new structure is developed. Although highly non-linear phenomena like saturation and static friction occur, linear frequency domain methods are used successfully in order to meet demanding specifications.
A control structure is proposed that allows to minimize static errors without causing limit cycles and windup effects - phenomena which occur if the controller contains an integrator. The robustness of the control system in the face of model uncertainties in conjunction with the use of only "harmless" non-linear elements allows a rapid implementation procedure.
The thesis details the development of a fault detection tool for the hydraulic control systems of the 7 stand Hot Steel Strip Rolling Mill at Corus plc (formerly British Steel ) Port Talbot UK.
The thesis begins with a laboratory study aimed at leakage and servovalve fault detection using a variety of methods, but in particular a signal processing technique based upon Time Encoded Signal Processing (TESP). Dynamic information, extracted from the pressure transient responses, is coded in a novel way that enables changes in performance to be determined. The resulting code (CARCODE) may be used for fault classification using either statistical methods, which is the preferred approach, or neural networks.
CARCODE is then applied to all 28 servovalve pressure control systems on the Hot Rolling Mill using operational data via an on-line data acquisition system developed by the Cardiff group. Performance is analysed on an hourly basis and a fault condition graph is presented allowing decisions to be taken regarding servovalve replacement.
With the complexity of today's industrial processes the Early Fault Identification and Diagnosis gains ever increasing importance. The danger of failure can be detected before their occurring and a punctual intervention is made possible, because Early Fault Identification and Diagnosis systems serve to avoid these failure. The goal of this work is to develop a new Early Fault Identification systems, for operation in oil-hydraulic plants, with a minimum expenditure on sensor. The Fault Identification systems can be implemented by model-based or by signal based methods. The main object of investigation is an electro-hydraulical linear drive system (proportional valve and hydro-cylinder) in an oil-hydraulic plant. After a detailed system analysis and a literature search for the state of the art and for current developments an overall concept for Early Fault Identification and Diagnosis focussing on model based fault identification systems was developed. Typical potential errors with linear drive systems are: increased friction, increased internal leakage, interturn fault, cavitation and stream erosion. Some of these errors, e.g. increased friction at the slidegate valve, can be artificially generated. In order to simulate the error impacts, complex construction work is necessary. Errors, which may result from erosion, can be reproduced artificially only by special manufacturing of the respective component. This is very cost-intensive. In order to realise a more economic investigation of the particular faults, it is reasonable to integrate real faulted components in the test bench. The further work concentrates on selected errors like internal leakage of the hydro-cylinder, change of frictional force and interturn fault of the proportional valve. These faults can be reproduced by external changes and thus universally valid implemented. Methods used for Fault Identification in the developed model are: a numerical improved realisation of discrete square root filter in the information form (DSFI), a non-linear optimum filter (continuously discrete, extended Karman filter) and a frequency response method. A direct determination of the reason for the fault is achieved by variation of the estimated physical parameters. Therefore the time-continuos physical process model of square control for valve and hydro cylinder has been developed. To demonstrate the Fault Identification system an artificially increased internal leakage of the hydro-cylinder was generated, simulating a defective piston ring. An increased value of the leakage oil coefficient KL was reliably detected. That proves that both Fault identification and Fault Diagnoses are guaranteed. For the simulation of the increased friction at the valve slide, several solution variants were worked out. The goal is to guarantee an error free operation after the constructional alteration of the valve. The results of measurement must be reproducible and additionally it is required that wear due to the alteration must not occur. The investigations show a very good agreement in operation of the modified valve and the original valve.
Servovalve-controlled hydraulic actuators are characterised by high power density and small time constants. Due to the weak self-damping, these advantages cannot be fully used in the position tracking problem under conventional output feedback control. The measurement or observation of additional quantities (velocity, force, pressure, acceleration) in conjunction with state feedback control increases both the static and the dynamic closed-loop control qualities. In the case of large motions at high velocities - i. e. in those situations that reach the power limits of the drive - the non-linearities of hydraulic drives, especially the non-linear pressure drop at orifices, become essential. Oscillation drives are likely to show this non-linear behaviour, since they are operated at relatively large amplitudes and frequencies. In order to achieve satisfactory results with conventional controllers, the drives are often oversized. This thesis deals with the behaviour of a servo-hydraulic drive for translatory motion in the tracking of harmonic reference inputs under linear state feedback. The system state can be split up in slow variables (the dynamics of the driven mechanical system) and fast variables (the internal state of the servo-valve and the dynamics of the chamber pressures in the hydraulic cylinder). The behaviour of the entire system is governed by a singularly perturbed system of differential equations. In the reduced system (neglecting the fluid compressibility), the pressure difference shows a discontinuous behaviour in the zero transitions of the valve opening during sine tracking regardless of the choice of parameters of the linear state feedback. This jump in the solutions of the reduced problems is bridged by boundary layers in the solutions of the perturbed equations. The feedback of load pressure or acceleration decreases the step height of the discontinuity. Still, the boundary layers are not removed but only transferred into the solutions of the reduced equations. The large pressure gradients occurring at the zero transition of the valve opening cannot be avoided by any linear state feedback. If dry frictions effects can be neglected, a control input resulting in exact harmonic motion of the drive can be found. In the presence of dry friction, an optimisation problem can be solved in order to find the optimal control input in terms of some suitable error index. Closed-loop control is achieved by a two time-scale approach. The slow system is exactly linearised by state feedback. The fast system is controlled by proportional pressure feedback based on a linearised model. The proposed control method shows a significant improvement of the experimental results compared to linear optimal control design. Due to the non-linear control design, the entire range of operation of the drive becomes available and Oversizing can be avoided.
In developing hydraulic components the target has been smaller size and higher power. With regard to gear pumps, this has led to higher rotational speeds. In some cases this has also led to cavitation problems.
This study presents data collected on a number of gear pumps. The measurements provide an opportunity to study the suction characteristics of a gear pump. A theory for suction occurence has been formulated for external gear pumps with two gears. The theory and the measured data were compared and some correction coefficients were calculated. The suction behavior was partially explained but there are still unknown details that need more investigation. Modelling of the effect of rotational speed and centrifugal force was carried out successfully. The biggest uncertainty factor is how to express mathematically the effect of the shape of the housing of the pump on the suction characteristics.
The study shows that ignoring fluid aeration in models of hydraulic drive and control systems may lead to large qualitative and quantitative errors. Thus, fluid aeration should be regarded as a significant non-linearity in models of hydraulic systems. The thesis contains a review of the literature dealing with the effects of aeration on the functionality of hydraulic drive systems. The mathematical model of a hydraulic line, with the degree of aeration being variable along its length, was subsequently investigated experimentally. The objective of experimental tests was to determine values of parameters, especially the value of bulk modulus, used in mathematical models. Subsequently simulation tests, using ACSL simulation language, were carried out to determine effects of aeration on dynamic behaviour (amplitudes and frequency of pressure waveforms) of a hydraulic line.
This PhD thesis deals with the flow conditions in design of hydraulic poppet valves. The focus was on development of fluid mechanical based design rules and methods for a single-stage and a two-stage pressure control valve. CFD simulation technique was used and experimental results for validation of the CFD model. A hydraulic test rig was developed in order to measure the steady state flow and flow forces for a wide range of seat valves with different shapes.
The thesis work considered two fundamental fluid mechanical principles to achieve flow force compensation. The first principle, P1, involves control of the fluid momentum at the valve orifice, and the second principle includes of balance of the axial fluid momentum. The design methods for P1 are based on variation in the flow angle, variation in the overall shape of the seat valve and variation in the direction of the flow through the valve orifice. The second design principle, P2 is based on design of a lip on the rear edge of the poppet on the low-pressure side of the valve orifice. A mathematical model was developed for both principles to study the correlation between the most important design parameters and the flow and flow force characteristics. Evaluation was based on two valve applications. Based on the results obtained with principle P1, a method was formulated to dimension a single-stage pressure control valve, given the performance specifications. The reference was to formulate the performance specifications as a function of the design parameters expressed by the spring constant for the valve.
The second application was based on analysis and optimisation of a two-stage pressure control valve. The originate of this analysis was an experimentally measured characteristic of an unstable valve. Using simulation, a modification of the valve design was implemented in order to stabilise the valve and maintain the desired performance specifications.
The thesis is concerned with the investigation of the dynamic behaviour of a mobile hydraulic crane. The methods used in vehicle vibration control were reviewed. For analysis of crane's natural vibration the crane was represented by a mixed discrete-and-continuous model. To investigate crane dynamics due to stochastic excitation a discrete model of the crane was used. Experimental studies were conducted to verify the models and assumptions.
The thesis deals with the continuous trajectory tracking control to electro-pneumatic-servo system. At first, the development of electro-pneumatic-servo control and its frontiers are summarized. Then, the proposal and research content of the thesis are introduced.
In chapter 2, the friction character of cylinder is advanced. The static friction and kinetic friction of cylinder are tested. The mathematical model of friction is presented. Then author proposes the mechanical method to improve the friction character of cylinder. Through the simulation and experiment to friction, it is obtained that the friction model reflects the actual friction well.
In chapter 3, the mathematical model of the electro-pneumatic-servo system is founded. An accurate formula of flow rate to pressure is presented by experiment. At last, the model deviation is reduced by system identification.
In chapter 4, the control strategy is studied. A friction observer to cylinder and its feedforward transfer function are designed. It is shown that the nonlinear mechanical friction causes a stick-slip response in system. Simulation analysis shows that the friction feedforward control is effective to increase the system performance.
In chapter 5, the experiments are made about the electro-pneumatic-servo system. Several phenomena in the experiments are analyzed. At last, the best control strategy is presented.
In chapter 6, a three-degree-of-freedom electro-pneumatic-servo robot is designed. The robot is able to track the trajectory of Chinese calligraphy. The experiment demonstrates that the electro-pneumatic-servo-system has excellent tracking characteristics and can rival the expensive electro-servo system in many area of industry.
This research aims to improve the characteristics and reliability of pneumatic cylinder systems in three aspects: influence of parameters on cylinder response, friction force at low speeds and air temperature change in the cylinder and pipes. Advantages of pneumatic cylinder systems: low cost/maintenance, high reliability, high power/weight ratio, safety operation, have overcome in the last decades their disadvantages: high compressibility, non-linearities, low stiffness, temperature change. The remarkable progress in pneumatic cylinders is reflected in their widespread applications in factory automation. Applications of electronics and control theory has opened new fields of application in robotics, automobiles and bioengineering. The design and analysis of pneumatic cylinder systems is still difficult, it is still carried out using a combination of trial-and-error techniques and intuition. Only two non-dimensional parameters are considered but friction force or air temperature change are not taken into account. The seal friction limits application of pneumatic cylinders in low speed systems and causes steady errors in position control. Air temperature changes may freeze valves and render them inoperable. Low damping and high compressibility of air lead to variation in load stiffness with position making difficult optimum gain tuning in control systems. The influence of parameters on cylinder response is clarified by introducing eight dimensionless parameters. Stick-slip occurrence condition was studied. A pipe model integrated with a cylinder model was used for the study of the influence of the pipes including the air temperature change. Through the mathematical models, simulation results and validation through experiments, dynamic characteristics of pneumatic cylinder systems were clarified. It is expected that more effective and reliable design of pneumatic systems can be achieved by considering the dynamic characteristics of pneumatic cylinders and by predicting diverse phenomena as stick-slip motion and air temperature change in the cylinder and pipes.
This dissertation investigates the fundamental techniques of a hydraulic catapult system in a microgravity drop tower. The microgravity research facility was developed to support microgravity research and development programs that investigate various physical science, materials, fluid physics, and combustion and processing systems. The drop tower plays a key role in the support of many research programs. In order to double the microgravity time, one of the basic performance data of a drop tower, a catapult system is planned for the base of the shaft. This dissertation examines a hydraulic type of catapult system.
In chapter 1, the microgravity drop tower and catapult
system are explained and hydraulic systems introduced. In chapter 2, after
examining several types of hydraulic systems design, the uplifting type
multi-stages synchro hydraulic cylinder scheme was selected. A horizontal
system was proposed which would emulate the vertical drop conditions. In
chapter 3, The design of a three stage synchronous high-speed hydraulic
cylinder is discussed including seal material and shape, processing technology,
and friction characteristics. One of the requirements of the high-speed
hydraulic cylinder is a transient high-speed fluid flow and high power
station. In chapter 4, after analyzing the system demands and modeling
the accumulators, the design of a high-speed flow control valve is examined.
In chapter 5, a design of a high-speed hydraulic shock absorber required
for the cylinder is proposed. In chapter 6, by dynamic modeling and digital
simulation, design parameters of the hydraulic catapult system are investigated.
In chapter 7, the performance of the sensors and the design of the data
acquisition system are presented. Experimental results are persented and
analyzed on the performance of the flow control valve, the high-speed hydraulic
cylinder and the high-speed hydraulic shock absorber. Finally, in chapter
8, the author gives the main summarization and conclusions of this dissertation,
and puts forward some recommendations for further research.
197 pages
Publisher: Cracow Technical University - Monografia 224 (Docent Thesis)
Language: Polish
First Published 1999
The thesis is concerned with theoretical and experimental
investigations of counterbalance valves used in control of inertial loads
in hydraulic systems. Both linear and non-linear mathematical models were
used in simulation of systems which contained counterbalance valves with
and without load compensation. Criteria for stable operation of such systems
were also investigated. The thesis also presented the concept and theoretical
analysis of a microprocessor controlled, pilot operated counterbalance
valve applied in a hydraulic crane luffing system.
Edited by: P. Beater
259 pages
Publisher: Springer Verlag
Language: German ISBN 3-540-65444-5
Price: 129,- DM
First Published: 1999
Hydrostatic drives have a number of advantages. They are not only found in aerospace or automotive applications but also in machines and manufacturing processes. On the other hand their nonlinear and only lightly damped behaviour can cause surprises, especially if it wasn't considered during the design phase. However, there are only few books that cover this topic.
This book looks at hydrostatic machines from the point of system design and control theory. The dynamic response of components and circuits is investigated not their mechanical design.
After a short introduction two chapters on modelling follow. One shows how the known physical laws can be used to describe the behaviour of hydraulic components, e. g. hydraulic fluid, orifices, valves. Using long lines as an example it is shown that there are many modelling approaches. In some cases a lumped volume is sufficient to describe the long line, in other cases a discretized model that consists of many differential equations is needed. For all models the system equations are given and when appropriate also a comparison of different approaches. The third chapter shows how measured input and output signals can be used to model a component or system, e. g. a pump or a cylinder.
The next chapter gives a summary of the basic methods of control system analysis. These methods are used later on to analyse hydraulic circuits. The material in this chapter is usually covered in a first control course, the only extension is an introduction to the describing function technique for analysis of nonlinear systems.
The following chapters give an introduction to digital
simulation and numerical solution of differential equations. They present
the necessary background for an engineer to use today's modern simulation
tools. The last chapter gives three examples: A detailed model of a relief
valve, a study of a closed and an open circuit drive. Here the presented
methods are used to demonstrate that a complete drive can be analysed and
optimised using a digital computer before actually building a prototype.
466 pages
Publisher: Fluid Power Net
Language: Polish
First Published 1999
The book, is the outcome of the First International Forum
on Developments in Fluid Power Control of Machinery and Manipulators. The
book deals with general issues of fluid power technology and its future
directions, new trends in fluid power technology including heavy duty manipulators,
and off road machinery. Other parts deal with modelling and simulation
of fluid power systems applications of fluid power technology in heavy
duty machinery and mechanical handling.
386 pages
Publisher: Fluid Power Net
ISBN 83-86219-71-8
First Published: February 2000
The book, the outcome of the First International Forum on Developments in Fluid Power Control of Machinery and Manipulators consists of four parts. The first part deals with general issues of fluid power technology and its future directions. The second part is concerned with new trends in fluid power technology including heavy duty manipulators, pump controls, water hydraulics. The third part deals with modelling and simulation of fluid power systems. Finally, the fourth part is concerned with new applications of fluid power technology in offshore, heavy duty machinery and mechanical handling.
224 pages
Publisher: Zaklad Narodowy
im. Ossolinskich
ISBN 83-04-04446-3
Language: Polish
First Published 1999
306 pages (A5 format)
Publisher: Tokyo Denki University Press
ISBN 4-501-41490-1
Language: Japanese
Price: 3800 yen + 5% tax in Japan
First published in 20 November 1999
This book attempts to describe hydraulic control systems
from basic to advanced for both mechanical engineering students and fluid
power engineers. Chapter 1 illustrates the outline of simple hydraulic
drives thorough aerospace applications. Chapter 2 covers the basic concept
of fluid dynamics and the flow in various hydraulic elements. Chapter 3
presents the mechanics as well as operating characteristics of hydraulic
components. In Chapter 4, after the control engineering is briefly introduced,
the design method of hydraulic servo systems is considered based on dynamic
characteristics.
280 pages
Publisher: Wydawnictwo Kumunikacji i Lacznosci
ISBN 83-206-1282-9
Language: Polish
First Published 1999
The book presents the theory of hydraulic systems and
controls, describes their design and design procedures. Various types of
hydraulic controls and control methods are discussed. The book contains
material on design and calculation of hydraulic systems including hydrostatic
transmissions, hydraulic servo systems, vehicles' steering and braking
systems and mechanical handling systems. Numerous examples of design and
calculations are provided.
232 pages
Publisher: WNT
ISBN 83-204-2450-X
Language: Polish
First Published 1999
This Book deals with dynamic modelling of hydrostatic transmission components and systems. The proposed methodology is applicable to research work on hydrostatic transmissions as well as to computer aided analysis during system design.
1272 pages
Publisher: Marcel Dekker, Inc.
ISBN 0-8247-6022-0
Price: 195 $
First published in October 1999
This authoritative reference facilitates a broader understanding
of the total hydraulic system, including hardware, fluid properties and
testing, and hydraulic lubricants in a single volume providing a comprehensive
and rigorous overview of hydraulic fluid technology. Organized to unite
concepts with descriptions of the components and workings of liquid system
operations, the Handbook of Hydraulic Fluid Technology discusses lubrication
of rolling element bearings, examines fluid filtration and particle contamination,
particle quantification and fluid filterability, covers viscosity and its
relation to temperature and pressure, explains the use of vibrational analysis
as a diagnostic technique and for troubleshooting, offers strategies for
determining why certain hydraulic systems fail, describes the chemistry
and properties of petroleum oil, clarifies fluid maintenance and change-out
procedures, documents aerospace applications of synthetics fluids, considers
vegetable oil as a viable alternative to mineral-oil-based fluids and more.
Detailing fluid chemistry and physical properties of specific liquids,
the Handbook of Hydraulic Fluid Technology is a valuable guide suited to
mechanical, aerospace, automotive, design, control, development, chemical,
plant, power, system, maintenance, manufacturing, and project engineers,
and upper-level undergraduate and graduate students in these disciplines.