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PhD-Theses completed in 2002

From Editor

Through the listing of PhD theses and habilitations world-wide completed, books published as well as prizes awarded, the International Journal of Fluid Power strives to keep its readers informed of new literature and scientific works. Names of authors, title, number of pages, publisher, ISBN, date, abstract and in case of PhD theses, name of university and institute are desired. The abstract should not exceed 200 words. The Journal solicits your help in keeping the listing current by asking you to transmit conference and meeting information formally or informally by post, fax or email to
Prof. Dr.-Ing. Monika Ivantysynova, Technical University of Hamburg-Harburg, Institute for Aircraft Systems Engineering, Nesspriel 5, 21129 Hamburg, Germany, Phone: +49 40 428788 - 203, Fax: +49 40 428788 - 270, Email: M.Ivantysynova@tu-harburg.de

Frank Bauer

Frank Bauer Maßnahmen und Methoden zur Flexibilisierung pneumatischer Greifsysteme
Institute for Fluid Power Drives and Controls (IFAS), University of Aachen (RWTH), Aachen, Germany
Shaker Verlag Aachen, Aachen; ISBN 3-8322-0539-x

The rising demands in the automation technology especially in the range of the assembly will require flexible gripper systems, allowing the handling of a wide product spectrum with high variant varieties and small lot size in the future. A further indispensable aspect is the simple and compact design of the gripper system, in order to guarantee the necessary robustness and reliability of the sensitive automation industry.
A central constructional step for making the systems flexible represents the mechanical decoupling of the gripper jaws. This ap-proach makes it possible to extend gripper concepts and gripper strategies of commercial gripper systems. The necessary gripper hardware can be deduced with help of the structural design methodology.
In this context reliable open and closed loop control concepts are necessary, that allow the precise compliance of the given jaw position and the resulting gripping forces. For the parameterisation and optimisation of the adaptive control structures a digital simu-lation tool, that allows the description of the strictly non linear pneumatic circuit is applied.
Finally a new control concept allowing a finer proportioning of the volume flow with switching valves driven in modulation techniques is applied in order to reduce the system costs. By the independent ventilation and exhausting possibilities of the cylinder chambers the possibilities for compressed air saving and for load rigidity become obvious.

Lynnane E. George

Active Vibration Control of a Flexible Base Manipulator
George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA

A rigid (micro) robot mounted serially to the tip of a long, flexible (macro) robot is often used to increase reach capability, but flexibility in the macromanipulator can make it susceptible to vibration. A rigid manipulator attached to a flexible but unactuated base was used to study a scheme to achieve micromanipulator positioning combined with vibration damping of the base. Inertial interaction forces and torques acting at the base of the rigid robot were studied to determine how to use them to damp the base vibration.
The ability of the rigid robot to create inertial interactions varies throughout the workspace. There are also "inertial singularity" configurations where the robot loses its ability to create interactions in one or more degrees of freedom. A performance index was developed to quantify this variation in performance and can be used to ensure the robot operates in joint space configurations favorable for inertial damping. When the performance index is used along with appropriate vibration control feedback gains, the inertia effects, or those directly due to accelerating the rigid robot links, have the greatest influence on the interactions. By commanding the link accelerations out of phase with the base vibration, energy will be removed from the system. This signal is then added to the rigid robot position control signal. Simulated and measured interaction forces and torques generated at the base of a rigid robot are compared to verify conclusions drawn about the controllable interactions. In addition, simulated and experimental results demonstrate the combined position control and vibration damping ability of the scheme.

Juha Inberg

On Eliminating Cutting Damage by Advanced Control of Timber Cutting Process
Institute of Hydraulics and Automation, Tampere University of Technology, Finland
Finnish Academy of Technology. Acta Polytechnica Scandinavica, Mechanical Engineering Series, No. 158, ISBN 951-666-598-5

In this thesis a new type of timber cutting system is presented. It is based on a novel control system which includes the control of the saw unit and the harvester boom. In cutting control, a control concept of the saw unit actuated by a hydraulic motor and a hydraulic cylinder is presented. A new control strategy is developed, implemented and experimentally investigated with the aim to maximise cutting speed with good system efficiency. The results obtained in the initial experiments reveal that with the new control method and improvements in the hydraulic system, a reduction in cutting time is anticipated, making possible an improvement in the quality of cutting as well as the increased productivity of the harvester machine. In the acceleration control of the harvester boom tip, harvester head and log are accelerated downwards during the final stage of the cut with the aim to counterbalance the gravitational force of the log. The trajectory of the boom tip motion along the g-vector is developed with one, two and three linear hydraulic actuators. Because the boom studied is redundant in vertical plane motions, different pseudoinverse-based redundancy resolutions proposed in this study are experimentally verified and compared.

Timo Koivula

Cavitation in Hydraulic Valves - Aspects on the Effect of Oil Type, Erosion, and Detection Methods
Institute of Hydraulics and Automation, Tampere University of Technology, Finland
TUT Publications 395. Tampere 2002. 128p. ISBN 952-15-0914-7

Cavitation is, in most cases, a harmful and undesired phenomenon in fluid power systems. Understanding the basics of the cavi-tation phenomenon is fundamental to preventing cavitation in fluid power systems. One of the most harmful effects of cavitation is the mechanical degradation of a solid material caused by cavitation, which is referred as cavitation erosion. When actions to prevent cavitation are considered, it is first essential to identify the existence of cavitation and location of the cavitation inception point.
In this thesis, cavitation occurrence in various kinds of restrictors is studied. The effects of geometrical parameters of conduits as well as the effects of oil properties on cavitation and flow properties are studied. The significance of flow path geometry is presented and critical operation points for cavitation occurrence are established. Variation in the flow coefficient with various oil types was found and the importance of temperature rise in fine annulus was acknowledged.
The effect of oil properties on cavitation erosion is studied by means of a cavitating-jet apparatus. In addition to various oil types, the effect of various contamination levels of oil is investigated. Substantial differences in cavitation erosion between the studied oil types were found. Mass losses of test samples due to cavitation erosion are presented. The effect of normally encountered contami-nation levels on jet-cavitation is studied.
Several cavitation detection schemes are examined. Both direct and indirect detection methods of cavitation are discussed. Return line of high-speed on-off valves was studied with special reference to dynamic pressure measurement. Conditions here are very demanding as rapidly fluctuating flow rate causes aeration and cavitation downstream from the valve. Various effects of transducer mounting scenarios on obtained pressure responses are presented.

Petteri Multanen

Hydraulic Filter Performance under Variable Flow Conditions
Institute of Hydraulics and Automation, Tampere University of Technology, Finland
Finnish Academy of Technology. Acta Polytechnica Scandinavica, Mechanical Engineering Series, No. 162, ISBN 951-666-611-6

In this thesis the performance of hydraulic filters is studied under variable flow conditions. Filter performance refers here to fil-tration efficiency, contaminant capacity, and differential pressure of filter. The aim of this thesis is to define the influence of variable flow on filter performance, to define a filter rating method and a test procedure for large-scale testing with variable flow, and finally to improve the filtration efficiency under variable flow conditions.
The efficiency of a filter is generally defined using the standardized multi-pass test. The problem in the adaptation of the test results to a real system is that the test conditions often do not match real operating conditions. During this study a variable flow multi-pass filter test unit was developed. In the test unit several series of filters were tested using both variable and constant flow. The results show the effect of three different flow amplitudes and cycle rates on filter performance. A mathematical model is developed for the definition of filter rating. Essential test parameters are defined and a test procedure is suggested for variable flow. With the model, the filter rating can be presented as a function of amplitude and cycle rate on the basis of one constant flow test and two variable flow tests.
The effect of hydraulic dampers on filter performance with variable flow is also tested in multi-pass tests. Limitations for protecting the filter in a real system using traditional gas accumulators are presented. A new type of hydraulic damper is developed to improve filtration efficiency with variable flow. The operation of this damper is presented and its performance is tested in a laboratory and in an industrial hydraulic system. The test results show that a damper can be used to improve the filtration efficiency under variable flow conditions.

Amit Shukla

Stability Analysis and Design of Servo-Hydraulic Systems - A Bifurcation Study
Department of Mechanical, Industrial and Nuclear Engineering, University of Cincinnati, Cincinnati, Ohio, USA

Design for robust stability is one of the most important issues in nonlinear systems theory. The validity of linear system design in a small neighbourhood is not a sufficient criterion for systems that undergo parametric variations and have strong nonlinear characteristics. With rapid growth in the systems theory, the design of nonlinear systems using bifurcation theory-based procedures has been one of the key developments. Servo-hydraulic systems are one of the most commonly used actuation and control devices, due to their force to weight ratio. They also are highly nonlinear in nature and hence provide considerable difficulty in the design and analysis of these systems and their control algorithms.
The goal of this dissertation is to tackle some of the issues of the nonlinear systems theory with applications to servo-hydraulic systems. The use of bifurcation theory for the design and analysis of a nonlinear system is illustrated, and a detailed investigation into the dynamics associated with the servo-hydraulic systems is done. Further, the model decomposition/reduction strategy for parametric study in the nonlinear system is suggested. The idea of control-induced bifurcation is introduced and explained in light of servo-hydraulic systems. The servo-hydraulic system nonlinearities are explained and their effects on the robust stability are highlighted. This numerical work is also complemented with the experimental results on the servo-hydraulic circuits. This general procedure for robust stability design and control design, under the influence of nonlinearities, presented in this work can be used for any nonlinear system. The limitations of bifurcation theory based tools are also highlighted.

Uwe Wieczorek

A simulation model to determine the gap flow in swash plate type axial piston pump
(Ein Simulationsmodell zur Beschreibung der Spaltströmung in Axialkolbenmaschinen der Schrägscheibenbauart)
Technical University of Hamburg-Harburg, Hamburg, Germany

The thesis deals with the simulations of the gap flow of swash plate axial piston machines to predict the machine characteristics. The losses in hydrostatic machines are mainly influenced by friction and the leakage flow in the gap. In order to reduce friction and abrasion in the gaps, it is desirable to maintain fluid lubrication condition. The gap geometry depends on the operating conditions due the mobility of the components. Thus to determined the gap geometry the balance of forces between all external forces exerted on the components and the load bearing capacity of the lubricating film is considered. Therefore the motion equation has been solved for all concerned moveable parts. The simulation model considers the non-isothermal flow, thus energy dissipation due to viscous friction in the gap is taken into account. The new simulation tool CASPAR (Calculation of swash plate type axial piston pump and motor) that has been developed, enables the calculation of the main losses due to friction and leakage flow. Additional the pressure in the displacement chamber is calculated. The verification of the simulation model is done by means of measurements of the instantaneous cylinder bore pressure and efficiency tests on a real unit.

Awards in 2002

Award for innovation from the Chamber of Commerce of the Catalan Government
for its innovative work with sugarcane loaders in Cuba
LABSON (Laboratory of Oil-hydraulic and Pneumatic Systems), Department of Fluid Mechanics, UPC, Terrassa, SPAIN

ASME Fellow Award
Dr. Nagi Naganathan
Interim Dean of the College of Engineering at the University of Toledo, USA

Books & Proceedings Published in 2002

Bath Workshop on Power Transmission and Motion Control PTMC'2002

Edited by C. R. Burrows and K. A. Edge

Publisher: Professional Engineering Publishing Limited
ISBN: 1-86058-379-2

Hydraulic Servo-Systems: Modelling, Identification and Control

by M. Jelali and A. Kroll

356 pages
Publisher: Springer-Verlag, London
ISBN: 1852336927

Hydraulic Servo-systems details the basic concepts of many recent developments of nonlinear identification and nonlinear control and their application to hydraulic servo-systems: developments such as feedback linearisation and fuzzy control. It also reviews the principles, benefits and limitations associated with standard control design approaches such as linear state feedback control, feed-forward control and compensation for static nonlinearities, because of their continued practical importance.
Featuring: theoretical (physically based) modelling of hydraulic servo-systems; experimental modelling (system identification); control strategies for hydraulic servo-systems; case studies and experimental results. Appendices outline the most important funda-mentals of (nonlinear) differential geometry and fuzzy control. The book is very application-oriented and provides the reader with detailed working procedures and hints for implementation routines and software tools. It will interest scientists and qualified engi-neers involved in the analysis and design of hydraulic control systems, especially in advanced hydraulic industries, the aeronautical and space and automotive industries.

The Fourth International Conference on Machine Automation ICMA’02, Human-Friendly Reliable Mechatronics

Edited by M. Kivikoski

Publisher: Tampere University of Technology
ISBN: 952-15-0861-2

Design and Steady-state Analysis of Hydraulic Control Systems

by J. S. Stecki and A. Garbacik

280 pages
Publisher: Fluid Power Net Pty Ltd
ISBN: 8386219947

Modern hydraulic power and control systems must meet increased user expectations of high quality system performance, reliability and long life. To meet these expectations engineers involved in design and manufacturing these components and systems, as well as users, should have a good knowledge and appreciation of hydraulic technology. This book fills the gap in fluid power literature by providing both theoretical and practical information on how to carry out steady-state analysis of hydraulic control and power systems. Although it is primarily aimed at final year students in mechanical engineering courses and postgraduate student working in the area of fluid power, it will also be useful to practising engineers as it contains over 70 solved examples of typical hydraulic systems used in industry.
The first chapter deals with the general topic of system design. Each of the following chapters provide a short introduction to steady-state characteristics of basic hydraulic components e.g. pumps/motors, valves, and then illustrate application of steady-state analysis to hydraulic systems which incorporate these components. The last chapter provides general guidance, again illustrated by examples, to selection of system components, calculation of pressure losses and thermal conditions in a system. The book consist of 280 pages and contains 152 illustrations.

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