Rudolf Scheidl

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Papers by Rudolf Scheidl

A Hydraulically Controlled Multiple Buck Converter System

The hydraulic buck converter with a pipe as inertance element is mostly considered with magnetica... more The hydraulic buck converter with a pipe as inertance element is mostly considered with magnetically actuated fast switching valves. These valves are hardly available on the market and are costly. A further burden of most buck converters are the high hydraulic capacitances added on load side to flatten pulsation. They lead to a softness which requires sophisticated control. A previous study on a phase shifted operation of several buck converters showed a low pulsation which may make an extra pulsation attenuation device obsolete. Another study suggested a hydraulic actuation of the switching valves. In this paper a combination of these concepts is analyzed. It realizes a constant switching frequency with a variable duty cycle and a phase shifted switching of the several converter units. The performance is compared to control by a single servo valve and a multiple converter system using electrically actuated valves.

Simulation Study of Permanent Magnetic Actuation for a Hydraulic Valve With Hysteresis Response Behavior

For the realization of compact and lightweight digital hydraulic cylinder drives for exoskeleton ... more For the realization of compact and lightweight digital hydraulic cylinder drives for exoskeleton actuation the hydraulic binary counter concept was proposed. This counter principle is based on hydraulically piloted switching valves which feature a hysteretic response with respect to the pilot pressure. In first prototypes of that counter bistable mechanical buckling beams realized the hysteretic response. Their performance suffered from high friction in the hinges and high local stresses. Furthermore, they require tight manufacturing tolerances not only of themselves but also of their bearing structure. In this paper, the usage of a permanent magnet concept to realize the hysteresis function in an alternative way is studied. The valve spool is made of a ferromagnetic material and is attracted or repelled by a permanent magnet made of a Neodymium-Iron-Bor. The expected benefits are lower friction, lower demands on manufacturing tolerances, and an easier assembly of the valve. To find an advantageous embodiment of this functioning principle ring or disc shaped magnets of different sizes are analyzed. The magnetic forces exhibited by these different magnetic circuit designs are simulated with the Magnetic Finite Element code ‘FEMM’. The quasi-static magnetic forces at different spool positions are computed. Magnetic saturation and remanence are considered in this analysis. The aim is to achieve the required force on the piston and, thus, ensure the valve’s functionality. At the same time, however, the valve should be designed as compact and light as possible. The Finite element simulations are compared with an analytical model which provides a compact understanding of the influence of the design parameters on the functional and non functional performance criteria.

A Computer Aided Conceptual Design Method for Mechatronic Systems in Process Oriented Heavy Machinery

Elsevier eBooks, 1998

Driving Behavior of a Tractor-Semitrailer Vehicle in Steady State Downhill Motion

Vehicle System Dynamics, Jun 1, 1985

A New Elastic Non Contacting Sealing Concept for Valves

International journal of fluid power, Sep 28, 2022

The hydraulic binary counter concept was proposed as a means to realize compact and lightweight d... more The hydraulic binary counter concept was proposed as a means to realize compact and lightweight digital hydraulic cylinder drives for exoskeleton actuation. This counter principle is based on hydraulically actuated switching valves which have a hysteretic response with respect to the pilot pressure. Manufacturing tolerances of the tiny components caused unexpected high leakage which, in turn, led to a malfunction of the system. In this paper a new sealing concept, is introduced to solve this problem. It is based on a non-contact seal (sealing gap), which exploits a self-regulating, elasto-hydrodynamic effect to reduce a rather large initial gap h0-to allow a rough tolerance-into a very small sealing gap h(x) to avoid dry friction of valve spool movement on the one hand but have very small leakage on the other hand. As sealing, an annular flexible ring made, e.g. of PTFE, is used which combines sufficient flexibility to allow this self adapting mechanism to a sufficient extent and to stay the high pressure loads. For the mathematical analysis of the concept, an approximate elastohydrodynamic analytical model is used. It sets the gap pressure, obtained

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Actuators and Sensors for Smart Systems

Smartness of technical systems relies also on appropriate actuators and sensors. Different to the... more Smartness of technical systems relies also on appropriate actuators and sensors. Different to the prevalent definition of smartness to be embedded machine intelligence, in this paper elegance and simplicity of solutions is postulated be a more uniform and useful characterization. This is discussed in view of the current trends towards cyber physical systems and the role of components and subsystems, as well as of models for their effective realization. Current research on actuators and sensing in the fluid power area has some emphasis on simplicity and elegance of solution concepts and sophisticated modeling. This is demonstrated by examples from sensorless positioning, valve actuation, and compact hydraulic power supply.

On the Buckling and Postbuckling of Spherical Shells

Springer eBooks, 1984

For the axisymmetric buckling problem of a complete spherical shell we are able to give a complet... more For the axisymmetric buckling problem of a complete spherical shell we are able to give a complete imperfection sensitivity analysis for the most complicated case to occur, namely that of a double eigenvalue, if we restrict our analysis to nonlinear terms of quadratic order, which is correct mathematically as the bifurcation system turns out to be two determinate. As we make a classical bifurcation analysis our results are strictly local and therefore are of restricted practical importance in two respects. Firstly we do not take care of the fact that we have closely spaced eigenvalues. We comment on this in chapter 7. Secondly we are not able to show that the experimentally observed single dimple solution (Fig. 8) is one of the stable solutions found from our bifurcation equations up to terms of third order.

A Mathematical Model for the Calculation of Cooling Criteria for Round Bloom

Springer eBooks, 1991

In the continuous casting machine the solidification of the liquid steel is controlled by extract... more In the continuous casting machine the solidification of the liquid steel is controlled by extracting the heat in a defined way. One of the most difficult problems in the continuous casting process is to find the proper cooling conditions. High complexity arises form the correlation of thermal effects on product quality.

Bifurcation Theory and Vehicle Dynamics - with Application to the Tractor - Semitrailer

For a tractor-semitrailer system with four degrees of freedom the influence of variations of para... more For a tractor-semitrailer system with four degrees of freedom the influence of variations of parameters on the driving behavior for steady state and braking motions is investigated. As parameters the driving speed (for steady state motion), the steering angle, nonsymmetric loading and the braking force distribution are considered. The goal of the paper is not only to give stability boundaries but also to obtain at least qualitative information about the behavior of the system after the transition from the stable to the unstable regime. To achieve this goal a nonlinear mechanical model must be used, the nonlinearity of which is mainly due to the relationship between the tire side force and the tire slip angle. Results obtained in bifurcation theory during the last decade are used to give a complete description and classification of the driving behavior if the parameter values pass through critical values. For the steady state motion for practically important cases divergence bifurcation occurred, which is extensively discussed for a symmetric and a nonsymmetric model. In the motion during braking besides divergence bifurcation also Hopf-bifurcation was found. This means that an oscillatory motion sets in after the parameter values pass through a critical value. Which type of bifurcation is found is heavily dependent on the braking force distribution to the different axles and also the arrangement of the loading on the trailer. For the covering abstract of the conference see TRIS 378303. (Author/TRRL)

Is the future of fluid power digital?

Proceedings Of The Institution Of Mechanical Engineers, Part I: Journal Of Systems And Control Engineering, Mar 8, 2012

This article presents digital fluid power as a new branch of fluid power which offers high potent... more 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.

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Cavitation Driven Impact in a Hydraulic Piston Pump: A Theoretical and Experimental Investigation

The occurrence of cavitation in a huge hydraulic supply system of a rolling mill which caused a s... more The occurrence of cavitation in a huge hydraulic supply system of a rolling mill which caused a severe defect in an axial piston pump is investigated by a mathematical model of the complex suction system. It comprises wave propagation in pipes and hoses, a detailed model of the pump including each of its nine cylinders, cavitation therein, the charge and discharge processes of these cylinders with the intake duct, and several accessories influencing the hydraulic processes. Results obtained by this model are compared with on-site experiments. Countermeasures which have been proposed are evaluated by our model and their practical examination is reported. Due to the strong nonlinearity of cavitation the dynamical system shows two attracting limit sets, one with and one without cavitation. The operating conditions of the original supply system cause startup conditions which do not lie in the basin of attraction of the non-cavitating attractor.

Switching Type Control of Hydraulic Drives - a Promising Perspective for Advanced Actuation in Agricultural Machinery

SAE technical paper series, Sep 11, 2000

The buckling beam as actuator element for on-off hydraulic micro valves

International journal of hydromechatronics, 2020

On Robust Modelling Of Heavy Articulated Trucks

International Journal of Modelling and Simulation, 1987

Abst r act ; Robust, i.e. structurally stable modelling of the motion of articulated vehicles is ... more Abst r act ; Robust, i.e. structurally stable modelling of the motion of articulated vehicles is important in order to get 11 qualitatively possible ways of behavior. For the example of a tractorsemitrailer vehicle it is shown, that in a two parameter family (driving speed V and the loading co nd ition expr essed by the location d of the masscenter of the trailer) only three classes of qualitatively differe nt ways of behavior are possible. These cases are analysed by perturbing them in the most general way possible by means of imperfection parameters, to obtain a robust model. The mathe matical methods are supplied by Bifurcation Theory.

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High Pressure Capabilities of Slender Squeeze Gaps of Magneto-Rheological Fluids

International journal of fluid power, 2010

In the last decade ample of academic and industrial research work in the area of magneto-rheologi... more In the last decade ample of academic and industrial research work in the area of magneto-rheological fluids (MRF's) has been done. Most of the concepts and products developed in this time period (e.g. MRF brakes and clutches) feature a shear mode operation. Hence a majority of the published work is addressing this mode. Nevertheless, the MRF squeeze mode becomes more and more attractive (for damping applications for instance) due to its higher reachable force densities compared to the other modes. In this paper attainable MRF squeeze mode pressures for very small squeeze gaps are experimentally investigated. For squeeze gaps down to few hundredth of a millimetre the mean squeeze pressure reaches nearly 100bar. On the other hand, especially in the squeeze mode, the problem of MRF segregation occurs. In this work three different methods to avoid or to reduce this phenomenon are experimentally tested and discussed. Finally, a simplified analytical relation for the MRF squeeze mode pressure characteristics is presented and compared to experiments. This comparison shows that the analytical model predicts the MRF squeeze pressures with a satisfactory accuracy such that it can be used for dimensioning purposes.

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Advancements in the Control Strategy for Digital Hydraulically Driven Knee Exoskeleton

Compared to electromechanical drives, hydraulic drives can be a good actuation alternative for ex... more Compared to electromechanical drives, hydraulic drives can be a good actuation alternative for exoskeleton devices due to their advantages in terms of high force density and capabilities of energy recuperation, motion damping and locking. However, to promote a wider adoption of hydraulically driven exoskeleton devices, key challenges related to the compact lightweight design and energy efficient operation and control are needed to be addressed. To tackle these challenges, the authors have recently developed a novel design of digital hydraulically driven knee exoskeleton. In this work, the authors address the control challenges during the operation of the knee exoskeleton over multiple gait cycles. Proper control methods for different phases of the gait cycle are adopted. Furthermore, these methods are augmented with strategies to accomplish knee motion repeatability across gait cycles. These strategies involve steps to ensure that at the beginning of every gait cycle: (a) the knee angle returns to the same position, and (b) the pressure in the hydraulic chambers return to the same levels. These control strategies are investigated via a numerical model of the knee exoskeleton. The simulation results indicate that the device is able to repetitively track the motion of the knee over multiple gait cycles while delivering the required torque.

Fluid Stiction With Mechanical Contact: A Theoretical Model

A comparison of the postbuckling behavior of plates and shells

Computers & Structures, 1987

There is a basic difference in the mathematical treatment of postbuckling of plates and shells. W... more There is a basic difference in the mathematical treatment of postbuckling of plates and shells. Whereas for plates the classical methods of bifurcation theory (Liapunov-Schmidt method, Singularity Theory) in general are applicable, these methods fail for the analysis of thin-walled shells. For shells in general solutions of the boundary layer type are found and hence the methods of singular perturbation theory are required for an appropriate analysis. Applications are given for the postbuckling of a rectangular plate and a spherical shell.

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Sensor Placement in a Hydraulic Drive System

BATH/ASME 2022 Symposium on Fluid Power and Motion Control

Hydraulic drive systems consist of hydraulic and mechanical components, whose dynamic behavior is... more Hydraulic drive systems consist of hydraulic and mechanical components, whose dynamic behavior is coupled by fluid-structure interaction. The validation of hydraulic drive models relies on an appropriate placement of pressure and vibration sensors. Based on a vibroacoustical approximation of the model, this question can be treated by potential and kinetic energy related modal assurance criteria (POTMAC and KINMAC). In this paper, the KINMAC criterion is applied for the sensor placement problem in a hydraulic drive system. The system consists of a valve block, a pipeline with fluid-structure interaction, a double-acting cylinder, and a mass attached to the piston. Modal analysis of a distributed parameter model is carried out for theoretical assessment of the sensor placement along the pipeline. The resulting mode shapes are used to calculate the auto-KINMAC matrix, which is expected to be diagonal. The same type of assessment is made with mode shapes from a modal test. Under the lim...