Chattering is a limiting factor for both metal removal rate and productivity within the milling process. Active suspension can help
to overcome this problem while a stable milling process with increased cutting velocities also increases the overall productivity. This
report describes the design and the testing of such a system.
The system is designed as a 3-chamber actuator where the piston houses the spindle conventionally using roller bearings. Due to
extremely small capacities and large pressurized areas, the 3-chamber actuator is having a remarkably large Eigen frequency, far
higher than those of the operating servo valves. The valve dynamic therefore limits the overall actuator dynamic.
In order to prove the ability of this new design, the dynamic stiffness of the whole machine with and without the active device is
being investigated. During these tests, it can be seen that the active device is able to improve the dynamic stiffness of the machine
tool.
Because the valves limit the system dynamic as shown, a further part describes the design of high-speed servo valves as well as
the design of a newly conceived piezo-hybrid actuator.
Hydraulic swash plate type machines are used as pump and as motor. The combination of pump and motor leads to an infinite
variable hydrostatic transmission.
To optimize hydrostatic transmissions, one has to improve the starting and slow speed behaviour of the hydraulic motors under full
load. In case of using a motor of the swash plate type the main source of losses consists in friction on the side-loaded working piston.
Within this thesis, a tribometer for piston friction force measurement with stiff piezoceramic sensors is presented. The important
mechanisms of friction force appearances under high load and slow speed are investigated by measuring and simulation. Particularly
designed working pistons have been manufactured in order to transfer the findings to practical application.
This study enlarges the knowledge about the working behaviour of pumps and motors in extreme slow speed condition and
shows that the swash plate design suits well into this particular field of application.
Institute for Fluid Power Drives and Controls (IFAS)
Aachen University (RWTH), Aachen, Germany
In automation technology, especially in the field of assembling and handling, there will be a large demand for flexible gripping
systems in future. These grippers need to allow the handling of a broad product spectrum with high variant varieties and small lot
sizes. A servo pneumatic 2-jaw gripper with individually movable jaws in force or position control in closed loop is one solution for
these demands. The methodical concept of construction theory is a useful support to design such a gripper. Indispensable condition
for the operation of a servo pneumatic 2-jaw gripper are powerful and robust control concepts. It has to guarantee the reliable solution
of the complex control request. Particularly, the connection of the two individually moveable jaws by means of the control strategy
is a challenging task. Also the communication between the gripper with its extensive functionalities and a necessary superior
control unit poses a challenge. A possible solution is a connection via field bus. Therefore functions, parameter and error states of the
gripper must be defined and fixed. A second important future trend is an energy efficient way of production. In the field of servo
pneumatic gripper technology there are a variety of options to reduce the energy consumption both in construction and control. These
solutions can also be used in other pneumatic applications.
Sliding and sealing contacts have central functions in hydraulic machines and devices. Important properties like good controllability
and operational availability as well as aspects of environment protection interfere with tribological system characteristics. Demands
for environmentally friendly materials and coating technologies result from automotive and mobile hydraulic applications in
particular. In the beginning the state of the art in the fields of choice of tribological materials and contact surface design is presented.
An optimization strategy for tribological contact surfaces is concluded from it.
The first part of the thesis deals with the substitution of a galvanic hard chrome plated piston rod in an automotive strut. The tribological
systems of piston rod and seal as well as piston rod and slide bearing are investigated on test benches especially developed
for this application. Plasma nitrified and oxidized piston rods stand out against flame sprayed self fluxing coatings. They reach the
tribological properties of conventional chrome plated rods under consideration of the determined contact area optimization. The test
bench results are confirmed in prototype testing.
In the second part of the thesis the influence of micro texturing using laser technology is discussed. The studies start with sliding
rings of different metallic material combinations in an experimental model according to Siebel/ Kehl. The obtained results are applied
to the sealing and sliding contact of a piston rod, to the radial shaft bearing of an internal gear pump and to the piston/ bushing
contact of an axial piston motor. The test results prove that micro textures work as fluid reservoirs independently from the materials
used. An additional load carrying capacity can be built up on micro textures. They support the restriction of the area of mixed friction
and the separation of contact areas from each other. These results are useful, especially in combination with the results of the first
part of the thesis, to substitute bearing materials containing heavy metals in the future.
It was possible to show that a systematic choice and parameterization of manufacturing technologies produces an optimized surface
design. By that the tribological properties of alternative material combinations thus can be improved and adjusted to existing
requirements.
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 electromechanic converters are an important component in various industries. Their technical design
can be supported and accelerated by the early application of FEM in the design process. This thesis shows the consistent use of FEM
to determine the stationary and dynamic properties of electromagnetic linear actuators. All simulation examples are compared to the
measurements of samples. The modelling and simulation parameters thus can be optimized in order to achieve best accuracy with
acceptable effort. The application of FEM to on/off and proportional actuators is separately investigated. The different physical effects
to generate forces in the electromagnetic field are mentioned, the typical characteristics of various actuator concepts thereby
justified. Possible improvements of existing actuator layouts are demonstrated with FE calculation.
This thesis addresses the dilemma concerning instabilities between counter rotating cylindrical surfaces. Further, it contains description
of the physical experiment and the measurement methods as well as the methodology used for numerical experiment and a
procedure for investigation of the time series for the individual types of flow instabilities. In the first part one focuses on the practical
examination of the flow instabilities originating between two counter rotating cylinders by means of physical experiment. Subsequently,
the author discusses the measurements resulting from the experiment. This part also has become the corner stone for the
carrying out of the numerical experiment using software FLUENT 6. In the last part of the thesis one deals with the problematic of
time series interpretation using the methods of chaos dynamic.
The overall purpose of the present work has been to develop a mathematical model of the gas injection in the oxygen high temperature
reactors, based on fundamental transport equations. The model development was divided into two major steps, where the
first step involved application of numerical simulation in the flow of hydrocarbon fuels through the tuyere of the high temperature
reactors at high gas flow rates. The second modelling step consisted of the development of full two-phase or three-phase real converter
model.
The aim of the tuyere model was to investigate fluid phenomena and changes of physical properties with consideration of heat
transfer that occur in tuyere during injection of gas at high flow rates. Simultaneously the existing approach was extended with influence
dissociation of hydrocarbons in high temperature. The resolution flow of gases by tuyere of converter was optimization of incoming
fuel with consideration of pressure the molten iron. It was necessary to define inlet and outlet boundary conditions, which are
corresponded to working information (oxygen reactor Oxyvit in Vitkovice a.s.) and physical quantity of gases in dependence of temperature.
The full multiphase converter model is CFD model, based on fundamental transport equations and includes the solution of the
steel and the gas phases. Two models of converter were investigated. The first solution was two-phase model of converter with bottom
blowing of gaseous phase (argon) into the liquid phase (molten iron). The second model was three-phase model of tandem furnace
with blowing of stream oxygen on the surface of molten iron. The drag, lift, and gravity forces have considerable influence on
the bottom blowing. The parameters of real model converter (Třinecké železárny a.s.) were defined with including of boundary conditions
for blowing gas (mass flow rate on the inlet). In model with bottom blowing was observed mainly interaction steam of argon
with molten iron. The results of modelling offer image of momentum the liquid iron inside the converter.
The three-phase mathematical model of tandem furnace (Nová Huť – Ostrava, spol. s. r. o) is operating furnace where it was observed
particularly reaction the stream of oxygen on the momentum of liquid phase. The three-phase model (liquid iron, oxygen and
air) was defined. When the oxygen is blowing on the surface is important to occupy with interface, surface tension and gravity forces.
Three variants of configuration the supply pipe of oxygen were performed for observed of momentum the liquid phase. One solution
is currently operating configuration. Next variant introduced the additional burner. Intensive mixing and better homogenization is
followed from numerical solution.
Direct operated pressure relief valves are hydraulic components where the pressure input is almost independent of the flow. An
understanding of basic physical principles taking place during the valve function is extremely important for developing new valve
designs or improving contemporary designs. Mathematical models are built for that purpose. In this work a mathematical model,
based on flow equations and an equation of motion, is built and made more accurate by chosen input parameters. Experience in hydraulic
component modelling shows that the parameters with difficulties are the discharge coefficient involved in the volumetric flow
rate equation through an orifice and the flow force that is used to suppress the influence of spring characteristics. These parameters
are obtained via a modern modelling tool based on the latest knowledge of fluid dynamics – CFD modelling (Computational Fluid
Dynamics). The mathematical model and the CFD model of the fluid flow of the valve were verified by comparing simulated and
measured data. The results have shown very good accuracy of the models. Through the valve model parameters that influence static
and dynamic characteristics are studied.
In this thesis, an application of numerical simulation of the non-isothermal turbulent flow is reported as a tool to investigate the
Jet in Cross Flow (JICF). Modelling of this specific problem is closely connected with the modelling of turbulence. From this point
of view and also due to many engineering applications, this problem has been investigated physically and numerically for many
years. The flow of turbulent jets in cross flow can be encountered in variety of problems like combustion chamber design, film cooling
of turbine blades, vertical and short takeoff/landing (VSTOL) and also pollutant discharges from point sources and their further
dispersion. This work was carried out within the solution of the project COST OC715.60 „Numerical Modelling of the Small Scale
Urban Air Flow and Pollutant Dispersion under Various Meteorological Conditions“. Presented numerical study was based on the
physical experiment carried out at the wind tunnel of the Institute of Thermo mechanics, Academy of Science, CR, Prague. The main
objectives were to test the capability of the mathematical models to account for steady and unsteady vortex structures in the region of
interaction. The influence of the mesh, turbulence models, boundary conditions and solution parameters were tested. The results were
partly compared with the measured data provided by the authors of measurement. Obtained results and conclusions will be applied in
further investigation of the problem.
Designing a new technical product can be compared with treasure-hunting. A designer is like an explorer, who needs navigation
tools to plot the course of a journey and maintain control over the destination. Nowadays, computer aided conceptual design methods
are such important navigational tools. A proper conceptual design reduces the time to market and is the basis for a new successful
technical product. Normally, different concepts must be established and comparatively evaluated to end up with a promising solution.
Concepts are typically described by sketches, drawings, circuit diagrams and a set of calculations based on rather simple mathematical
models. These different documents often use a person specific syntax, are not linked together, and are difficult to understand by
other people. Today, there exists hardly any computer support for working out and documenting the conceptual design. This documenting
is like plotting the course of a journey, should include the designer's ideas and considerations and should link together the
various forms of documents, like sketches, circuit diagrams, and mathematical models.
In this dissertation contributions to computer aided, interactive, graphical conceptual design for oil hydraulic components are
presented. A new developed software tool for conceptual design helps the designer to declare his/her physical understanding and
generates automatically a mathematical description of the model by simple analytic equations. It links together the graphical domain
of sketches/drawings with the symbol domain for reflecting the physical effects and the domain of basic mathematical models for
their quantification. It also calculates the constraint matrix from the mathematical model, which maps the functional requirements
(FR) from the functional domain to the design parameters (DP) from the physical domain. Certain features of this map gives valuable
information on the complexity of a design. The constraint matrix can be transformed into a bipartite graph. A bipartite graph is the
companion to the constraint matrix and shows exactly the same information. These two models are basic concepts of constraint theory
of Friedmann which is a powerful tool for evaluating mathematical model consistency and computational allowability.
To demonstrate this approach, a specific switching valve, developed at Linz University, and a comparative evaluation of three
different principles of a 2/2-way seat valve are discussed. These principles are a 2/2-way cartridge valve, a 2/2-way check valve,
which are state of the art and a new leakage free ball valve with an integrated deformable disk.
Haptic control of hydraulic actuated devices has been shown to offer substantial advantages to operators in terms of accuracy of
motion and error-free performance. In some cases it would be desirable to connect the operator’s master to a distant slave device, for
example over the internet. In conventional bilateral or force feedback teleoperation, transmission delay over the internet can potentially
cause instability. The wave variable algorithm guarantees stability under varying transmission delay at the cost of poor transient
performance. Adding a predictor on the master side can reduce this undesirable side effect, but that requires a slave model. An inaccurate
slave model used in the predictor as well as variations in transmission delay, both of which are likely under realistic situations,
can result in steady state errors. A direct drift control algorithm is used in this work to drive this error to zero regardless of the source
of error. A semi-adaptive predictor that can distinguish between free space and rigid contact environment is used to provide more
accurate force feedback on the master side. A full adaptive predictor is also used that estimates the slave environment parameters
using recursive least squares with a forgetting factor.
The system is tested using real master and slave. The master used is a commercially available PHANTOM haptic device, and the
slave used is either the Hydraulically Actuated Lifter (HAL) or another PHANTOM. The PHANTOM can be seen as a revolute robot
with three degrees of freedom where the feedback force is provided by electrical motors. HAL is a custom made hydraulically actuated
prismatic robot with two degrees of freedom modelled after a forklift. A hydraulic rotary motor actuates the horizontal axis, and a hydraulic cylinder actuates the vertical axis. The wave variable algorithm generates significant drift because the method does not
preserve position data in a PHANTOM-HAL teleoperation with varying transmission delay of about 400 ms. The proposed algorithm
with predictor and drift control has been shown to be effective in minimizing the steady state error. The results are consistent with
those obtained from extensive human experiments documented in the thesis in a PHANTOM-PHANTOM teleoperation with about
200 ms variable delay one-way. Without any compensation, the system becomes unstable. In a maze navigation test, the navigation
time for the proposed wave based algorithm is about half as long as that of the wave variable only algorithm.