The theoretical equations for a transmission line were used to shape the ANN topology such that distributed friction effects were modelled using delayed, measured, dynamic input data. This was aided by a simple transformation for the load dynamics thus eliminating a flow measurement at the end of the line.
The transient response of a pressure control system with a transmission line was successfully mapped using an ANN representa-tion (3-4-1) for both the mathematical model and the real system. It was found that under leakage fault conditions the change in a single neuron bias was remarkably consistent and robust in indicating the fault using either the mathematical model or the actual data. The predicting capability was more striking as the load actuator volume was reduced to its minimum.
The focus of this PhD dissertation is on the design of knowledge systems based on fuzzy logic for the control of electro-hydraulic drives. An electro-hydraulic drive is herein referred to as a linear hydraulic cylinder the piston of which, i.e. the direction of its movement, is controlled by means of a servo-valve.
The introducing chapters briefly deal with the relevant problems in the field of electro-hydraulic drives, fuzzy logic and fuzzy control, and evolutionary algorithms.
The following chapters are devoted to concrete designs of knowledge systems for the control of electro-hydraulic drives. Three distinct applications of knowledge methods based on fuzzy logic are evaluated. The first application represents a fuzzy controller put directly into a control loop. A particular elementary algorithm for the design of a fuzzy controller as well as the relevant optimization task using special evolutionary algorithms is presented. The next two applications represent the indirect use of fuzzy knowledge systems in a control loop intended for the adjustment of state controllers. Both the case of one-shot controller adjustment during the device initiation for the first operation, and the controller adaptation according to parameter changes in the controlled plant during the control process are considered.
In this PhD dissertation, verified simulation results are included. All simulation models and computing functions were created using a special block library and a special toolbox.
In the field of flexible gripper systems, vivid national and international research activities can be observed. This is a clear sign of an increasing demand for highly flexible manipulation systems. Future applications for these systems include - besides the wide area of classical applications - the field of autonomous exploration- and telemanipulation systems as well as the field of service robotics. Mechanic imitations of the human hand promise to transfer the multiple manipulation skills of the human hand to technical systems. In the past, those mechanic hand imitations were almost solely operated with electric drives. However, due to the recent developments in servo-pneumatics, an integration of pneumatic drive units into mechanic hands appears to be possible.
The thesis describes the systematic development of a servo-pneumatically-operated mechanical hand with eleven degrees-of-freedom. Starting with a methodology for the classification of mechanic hand designs, it describes the development of the required, miniaturised servo-pneumatic components and the mechanical hand design. Additionally, important aspects of highly miniaturised pneumatic drive units, operated in closed-loop-control are discussed.
The dynamics of high performance hydraulic drives is often limited by the performance of available servovalves. High dynamics, large volume flow and robust design are the valve requirements, that are asked for.
Available servovalves nowadays are usually equipped with electromechanical transducers based on the principle of electromagnetism. Their dynamics are restricted due to physical boundary conditions. The piezo stack actuator is an alternative electromechanical transducer that provides large forces and high dynamics. Therefore it is predestined for further improvement of the dynamic characteristics of servohydraulic valves.
This thesis deals with the development of a hydraulic piezo drive servovalve for the use with an universal hydraulic component testing machine. After defining a detailed catalogue of requirements, the development of all valve components is described. It is emphasised that the components have to be understood as a system. Using the developed components a prototype valve is built up which is finally being tested in practical use. The tests show that the prototypes static performance data reach the current state of art, which is significantly exceeded by the dynamic performance data.
The thesis develops the simulation program KSHAG for the kinematic simulation of hydrostatic axial-piston gears. The results of this program are used as the initial conditions for the dynamic simulation.
The likewise developed simulation program DSHAG serves for the dynamic simulation of hydrostatic axial-piston gears. The corresponding three-dimensional dynamic model is based on a multibody system with spring, damper and clearance elements connecting the discrete solid bodies and frictional forces are taken into account. Pipe elements containing operating fluid simulate the hydrostatic circulation. Inhomogeneous, nonlinear, coupled differential equations describe the dynamic behaviour. Their numerical solutions yield the movements and the corresponding loads of the individual components. The results set the prerequisite conditions for an appropriated stress-strain design of the resonance locations.
The dissertation work focuses on the field of energy saving electrohydraulic systems, especially electrohydraulic load - sensing systems based on the controlling of a flow through a constant pump by speed control.
The start point of the work is a presentation of basic types of electrohydraulic systems and summarize of the energetical charac-teristics of these systems. Further are presented load - sensing systems, especially LS system with speed control of the constant pump. After presentation of the principle we can find separation of the system to basic parts and elements. The next part of the work consists of the non-linear and liner models of the elements of the LS system and design of the control loops, which electrohydraulic load - sensing system consists. It is the speed control of asynchronous motor, the control of the pressure source and the control of the consumer. The test of a dynamical behave of the designed LS system is made by a simulation and by a experimental way in next part of the work. For the experimental test is used a test rig. The final part of the work consists of experiences and perceptions received during work on the theme.
The contribution of the work lie in a development of a technology of the electrohydraulic load - sensing system based on controlling of a flow throw a constant pump by speed control.
It is common knowledge that the majority of malfunctions in hydraulic systems are caused by impurities in the pressure fluid. Operational disturbances lead to economic losses because of downtime and repair costs. Such disturbances may also give rise to hazardous situations. Wear of the system’s components is also strongly dependent on cleanness.
Cleanness is particularly crucial in mobile systems. A mobile machine often operates in extremely difficult conditions, dusty, muddy and wet environments, varying temperatures and under varying loads.
A number of simulation models of hydraulic systems have been published. They have the drawback that they resolve only indi-vidual particle sizes in simple systems. So far there has been no model that would consider aspects like introduction of one or more filters into the system, the role of particles of varying sizes in the system fluid in the initial state after manufacture, inputs of particles into the system for various reasons, wear of components as a function of cleanness level and load, and filter capacity. With some limitations, earlier models have enabled analysis of a system’s cleanness level, but not, for example, design of filtering systems.
This research was undertaken with the object of producing computer software to simulate the cleanness level of a hydraulic sys-tem throughout its operation. The model developed constantly calculates the number and mass of the variously-sized solid particles in the system. The model considers:
This research deals with ten particle sizes 2 µm...50 µm since most particle-related phenomena are definitely size-dependent. It was demonstrated that these ten sizes are well representative of all the innumerable particle sizes in the system when their volume and mass are calculated using the method presented. A simulation model for the entire system was composed of partial models of individual particle sizes 2...50 µm. Their masses trapped by the filters are combined.
An important area of application for simulation is design of filtering systems. It is easy to determine necessary beta values, volume flows and dirt-trapping capacities for filters when operating and environmental conditions are known.
The model is eminently suited to design of cleaning procedure for a new system. Simulation is a useful tool in evaluating component wear and durability.
Pneumatic actuators are relatively simple to operate, cheap, clean, lightweight, and easy assembling devices. They also present a force/weight ratio that makes them quite attractive for applications in robotics.
However, in precise position control systems applications, the nonlinearities of the pneumatic systems and the difficulties of obtaining precise pneumatic models have been hindering the practical use of these systems. It has been verified that the standard controllers deficiencies, when applied to a servopneumatic drive, consist of gains tuning difficulties, robustness lack under payload variations and great sensibility to the friction effects. The main objective of this thesis is to verify whether it is possible to overcome these difficulties through feedback control with the appropriate synthesis of nonlinear control algorithms. In order to accomplish this task, we initially developed a nonlinear accurate model of a pneumatic servo drive with friction. To deal with the nonlinear airflow relationship between the pneumatic valve's driving voltage and the upstream/downstream pressures, an empirical model based on the flow nozzle formula is developed. A suitable model structure for friction (the so called Lugre model) is used as basis for the friction forces identification. This friction model takes into account the major known macroscopic friction nonlinear behavior, and its structure is suitable to be used in model based robust online friction observation and compensation schemes.
Using the appropriate system model and the available knowledge on pneumatic servodrives control problems, we propose a cascade control strategy to overcome the several structural dynamics problems of the pneumatic system, including the friction effects. Other researchers have successfully used this cascade strategy, without friction compensation, in electrical robots and in hydraulic actuators control. Such strategy consists in dividing the whole model into two subsystems: a mechanical subsystem and a pneumatic one. We present the cascade control stability properties with friction compensation and its confirmation through simulation and experimental results.
A pump test rig has been built to imitate the operation of the pumping portion of a Free-Piston Engine-Pump (FPEP). This test rig consists of two connected hydraulic pistons. One piston simulates the engine piston to drive the pumping piston. Check valves control flow in and out of the pumping chamber. The action of the suction check valve has been studied in detail. The dominant influence affecting flow into the pump chamber was the inertia of the fluid.
A hydro-pneumatic rebound system was designed and built for a FPEP with opposed pistons forming a combustion chamber between the pistons. A hydraulic cylinder was connected to each engine piston. Appropriate plumbing connected the cylinders to a poppet valve, which controlled the flow of oil from an accumulator to the cylinders. The design of the plumbing and location of the poppet valve influenced the operation of the rebound system.
Edited by Fördervereinigung Fluidtechnik eV Aachen
500 pages
Publisher: Shaker Verlag
ISBN: 3-8265-9900-4
Edited by Fördervereinigung Fluidtechnik eV Aachen
610 pages
Publisher: Shaker Verlag
ISBN: 3-8265-9901-2
Edited by Mc Lain and the American Society of Mechanical Engineers Staff
Publisher: Amer Society of Mechanical Engineers
ISBN: 0791819213
Contains 18 research papers presented during four sessions as part of the November 2000 ASME conference. The subject areas are fluid power component and system design, dynamic modelling of fluid power systems, analysis of fluid power system dynamics, and advanced control of fluid power systems. Topics include feed forward plus feedback control of an indexing valve plate pump, fluid power in large downhole seismic sensor arrays, pneumatic pipe modelling, and design of a high performance hydrostatic actuation system.
by H. Murrenhoff
403 pages
Publisher: Shaker Verlag
ISBN: 3826598784
Language: German
Edited by S. Noack
Publisher: Bosch Rexroth AG didacti, OMEGON Fachliteratur Ditzingen
ISBN: 3-933698-16-2
Distribution: SAE Society of Automotive Engineers, Wavendale, USA
ISBN: 0-7680-0886-7
Edited by K. D. Schäfer
Publisher: verlag moderne industrie, Landsberg/Lech
ISBN: 3-478-93246-7
Language: German