Modeling the kinematics and Dynamics of Compliant Contact

In this paper, we discuss the modeling of the kinematics and dynamics of compliant contact between bodies moving in Euclidean space. First, we derive the kinematic equations describing the motion of the contact point when two rigid bodies are rolling on each other. Secondly, we extend these results to describe the motion of the closest points between two rigid bodies moving freely in space. Then, we use these results to model compliant contact between bodies, using a spatial spring and a damper to model energy stored and dissipated during contact

Modeling Framework and Software Tools for Walking Robots

In research on passive dynamic walking, the aim is to study and design robots that walk naturally, i.e., with little or no control effort. McGeer [1] and others (e.g. [2, 3]) have shown that, indeed, robots can walk down a shallow slope with no actuation, only powered by gravity.\ud In this work, we derive mathematical models of walking ro- bots to better understand the dynamics that determine the walking behavior, and to design controllers that e.g. in- crease robustness against changing environments. We use the port-Hamiltonian framework, as it has the advantage of explicitly showing energy-flows inside and into the system. Thus, it allows a direct efficiency study as well as the possi- bility to connect external elements in a ‘physical’ way using ports, instead of using just torque/force signals

Passive compensation of nonlinear robot dynamics

In this paper, we derive a coordinate-free formulation of a passive controller that makes a mechanical system track reference curves in a potential field. Contrary to conventional reference tracking, we do not specify a single time-varying trajectory that the system has to track. Instead, we specify a whole curve that the system has to stay on at all times. Using tools from differential geometry, we first derive a controller that makes the system move along arbitrary (smooth enough) reference curves while keeping the kinetic energy constant. We then apply the results to the case of movement in an artificial potential field, in which case, the reference curves are completely determined by the potential field and cannot be chosen arbitrarily. Simulation then shows the performance of the controller on a benchmark robot with two degrees of freedom

Port based modeling of spatial visco-elastic contacts

In this paper, the geometrical description of viscoelastic contacts is described using physical modeling concepts based on energy conservation and network theory. The proposed model is on one side simple enough to be used in real time applications and on the other captures the geometrical features and coupling of a complete spatial geometric unisotropical contact

Das Wohlbefinden der Väter und die Wochenarbeitszeit der Mütter

'In diesem Artikel wird der Zusammenhang zwischen dem Wohlbefinden der Väter und der Wochenarbeitszeit ihrer berufstätigen Partnerinnen untersucht. Vertreter der folgenden zwei Vätergruppen nahmen an der Studie teil: der moderne Vater, der Haushalts- und Familienaufgaben übernimmt und der traditionellere Vater, der oft Vollzeit arbeitet. Es zeigt sich, dass für beide Gruppen Folgendes gilt: Es besteht ein Zusammenhang zwischen der (relativen) Wochenarbeitszeit der Mütter und dem körperlichen und psychischen Wohlbefinden der Väter. In der Studie werden folgende zwei Hypothesen miteinander verglichen: Es besteht ein negativer Zusammenhang zwischen der tatsächlichen Wochenarbeitszeit der Frau und dem Wohlbefinden ihres Partners. Oder als zweite Hypothese: Diese Auswirkungen hängen mehr mit 'symbolischen' Faktoren zusammen, gemessen durch den relativen Anteil der Frau am Familieneinkommen oder durch die relative Stundenzahl, die sie berufstätig ist (die Wochenarbeitszeit der Frau im Vergleich zu der des Mannes). Beide Hypothesen wurden in der Studie bestätigt, die Hypothese des 'Unfulfilled Husband' (ihre relative Wochenarbeitszeit) wurde jedoch am meisten unterstützt. Finanzielle Faktoren spielen dabei eine weniger wichtige Rolle. Erwähnenswert ist außerdem, dass ein positiver Zusammenhang besteht zwischen der Wochenarbeitszeit erwerbstätiger Männer und ihrem körperlichen und seelischen Befinden.' (Autorenreferat)'This investigation studies the relation between the well-being of fathers and the number of hours that their wives work outside the home. Two groups of fathers were involved in the investigation: the modern, caring fathers, and the more traditional fathers, who are often in full-time employment outside the home. It would appear to be true for both groups that the amount of hours their wives work, correlates negatively with the well-being of fathers both physically and mentally. Two hypotheses were compared: does the well-being of fathers correlate mainly with the actual absence of the wife, measured by the absolute number of hours that she works? Or does it correlate more with 'symbolic' factors, measured by her relative share in the family income or the relative number of hours that she works (her working hours compared with his). Confirmation was found for both hypotheses, but the unfulfilled husband hypothesis had the most support. Financial factors play a rather less important rote. Finally, it must be observed that the number of hours that men themselves work still has a positive correlation with their well-being.' (author's abstract)

Port-based modeling and control for efficient bipedal walking robots

This thesis aims to provide a framework for modeling, analysis, and efficient control of walking robots. The framework uses a port-Hamiltonian system description to express the dynamics of rigid mechanisms and their interaction with the ground. The structure of the resulting models forms the basis for the development of general analysis and control techniques

Energy-Based Model-Reduction of Nonholonomic Mechanical Systems

Abstract — Research on nonholonomic mechanical systems has focused mainly on describing geometric structure, controllability, and motion planning, yet little attention has been paid to several energy aspects of these systems. This paper describes a method to model nonholonomic mechanical systems as reduced-order Port-Controlled Hamiltonian Systems, in which the energy structure is shown explicitly. We show how very simple equations are obtained for the example of the snakeboard, and then discuss how these equations can be used to derive an energy-based controller in an intuitive way. I