Rudolf Scheidl

Is the future of fluid power digital

This article presents digital fluid power as a new branch of fluid power which offers high potential for innovative solutions. The variety of digital concepts is quite large and digital concepts have long been successfully applied in low-power applications. Research and development is now becoming more intensive, being undertaken by several research groups and also more and more in industry. First applications will be brought to industry soon. A successful application requires new components, a sound understanding of system and new control principles.

Modelling of a Switching Control Hydraulic System

Modelling of a hydraulic system featuring a specific type of switching control is presented. Despite conventional hydraulic drive technology where rather smooth changes of pressure and flow rate are intended and where oscillations constitute undesired phenomena, switching control provokes oscillations as an indispensable element to achieve high energetic efficiency with valve control. The system under study is one which comprises a novel switching valve, a long line with considerable wave propagation dynamics, a hydraulic cylinder, and the valves dynamics.

A Novel Piloted Fast Switching Multi Poppet Valve

Abstract Switching and digital hydraulics require adequate switching valves for their practical application. A major criterion is the switching time which should in most cases be less than 5 ms. The demands on valve nominal flow rate are rather wide and range from less than 1 l/min (@ 5 bar) up to hundreds of litres. In this paper a new seat valve concept is presented. It is a piloted valve and employs a multi poppet concept. Its nominal flow rate is about 100 l/min and its switching time is about 1 ms for a pressure drop of 5 bar. With this valve energy efficient switching drives can be realized, for instance in the 10 kW to 20 kW range. Its seat type design makes the main stage a non leaking valve. Piloting is realized by a fast 3/2 solenoid actuated spool type switching valve with a nominal flow rate of 10 l/min @ 5 bar and a total switching time of about 2 ms. The paper presents the design of the poppet valve, simulation studies and experimental results concerning its static and dynamic characteristics.

Energy Efficient Fluid Power in Autonomous Legged Robotics

This paper is concerned with the application of fluid power in autonomous robotics where high power density and energy efficiency are key requirements. A hydraulic drive for a bioinspired quadruped robot leg is studied. The performance of a classical valve-controlled (“resistive-type”) and of an energy saving (“switching-control mode”) hydraulic actuation system are compared. After describing the bio-inspired leg design and prototyping, models for both drives are developed and energy efficiency assessments are carried out. It is shown through simulation that the switching-control mode hydraulic actuation can meet the challenge of legged robotic locomotion in terms of energy efficiency with respect to improving robot power-autonomy. An energy saving of about 75% is achieved. Limitations of the current system are identified and suggestions for improvements are outlined.Copyright

Power hydraulics - switched mode control of hydraulic actuation

This paper is concerned with the application of switching technology to hydraulic actuation. Over the last 50 years with advances in power electronics, faster and faster static switches have been developed and applied to the control of motors. Hydraulic technology evolved in the opposite direction: switching control was not considered, and more and more accurate proportional flow/pressure control devices (servovalves etc) were developed. However despite the sophistication of such valves, from an energetic viewpoint proportional control is dissipative and inefficient. Indeed, by analogy it can be seen as the equivalent of resistive (rheostatic) motor control.

Tensor analysis based symbolic computation for mechatronic systems

This contribution presents methods for the mathematical modeling of mechatronic systems based on tensor analysis in combination with graph theory. Tensor analysis is an effective and universal tool for the common description of electrical and mechanical systems in a geometric way. Efficient algorithms for time-dependent Lagrangian systems with nonholonomic constraints are developed as well as an extension of the theorem of Brayton–Moser to general n-port networks. Therefore, the combination of electrical and mechanical systems is achieved in a straightforward way. The so obtained methods for setting up the mathematical models are optimized for treatment by computer algebra as well as for numerical simulation.

Basics for the Energy-Efficient Control of Hydraulic Drives by Switching Techniques

Hydraulic drives currently are under strong pressure by the upcoming electric servo-drives. A main reason for this is the poor energy efficiency of many hydraulic drive systems. Switching techniques which are state of the art for electric drives are now also considered for application in hydraulics. This paper reports about a new principle of switching control of hydrostatic drives which is based on periodic wave propagation in a so called resonator. The need for such a resonator is demonstrated by some simple mechanical arguments first. Then a mathematical model in form of a damped wave equation is used to assess its basic performance characteristics and to derive criteria for optimum design. This system turns out to be a pressure converter which controls the output pressure by the pulse-width of the periodic switching between high and low pressure line. Further features to improve the system are described and discussed.

Complexity Analysis of Systems from a Functional and Technical Viewpoint

Nowadays, complexity analysis of functional and technical mechatronic system becomes more and more important. This is because of complexity influences almost all phases of product design and system engineering. Therefore, there is the demand for a good assessment of complexity. For this purpose, several questions have to be discussed. → What is complexity and what are its characteristics? → What are the criteria for a good method to evaluate complexity? → How could complexity be evaluated and which method fits the requirements best?.

An Oil Stiction Model for Flat Armature Solenoid Switching Valves

Oil stiction forces significantly influence the performance of fast switching valves. These forces stem from the significant lowering of the pressures between two oil filled plates relative to the surrounding pressure when the plates are quickly separated. If the pressure in the gap stays above the vapor pressure the stiction force can be derived from a solution of the Reynolds equation.However, for very fast motions — as occur in fast switching valves with a flat armature solenoid — cavitation is most likely to occur. The cavitation zone starts in central parts of the gap and extends as long as the gap volume increase cannot be fully compensated by the flow in the gap. Cavitation reduces the stiction force significantly. In many valves this stiction force reduction is decisive for a proper functioning of the valve.An important measure for stiction force control are flushing channels, in particular flushing bores. In this paper analytical models and Finite Volume method models are used to study the stiction force problems with and without cavitation and design measures for their mastering.Copyright

Some aspects of SysML application in the reverse engineering of mechatronic systems

The focus of this paper is the applicability of SysML [2] for modelling certain aspects of both, mechatronic systems and the corresponding engineering processes. SysML is derived from UML, which was developed for software engineering, with the intention to support the engineering of technical systems in general. Although the usefulness of UML is widely confirmed in the software context, the use of SysML in the more hardware oriented engineering domains and in Mechatronics is still an open issue. Mechatronic relevant applications (like reported in [4]) have their focus on automation and software issues, mechanical and electrical hardware aspects, however, are rarely addressed. In an ongoing research project with industry the authors study the potentials of SysML to make the engineering of such systems more structured, better documented and, hence, more transparent. In [6] SysML is nearly exclusively studied for the development of new systems. Its application for product improvement or design modification because of changing customer requirements is scarcely reported. In the following sections the authors will focus on these topics, first on mechanical sub-systems since this is seen most critical, and in future on overall mechatronic systems.