Dynamics and iterative learning control of robots with parallel kinematical structures / Bodo Heimann and Houssem Abdellatif

The paper deals with model-based control of robots with parallel kinematical structure (PKM). At first, an approach for the identification of friction and rigid-body dynamics of complex parallel kinematical structures is presented. The approach is based on optimal excitation trajectories. The trajectories are bounded, such they are easy to befit into the small and hard constraint workspace of PKM. Secondly, some results are presented using feedforward control in order to compensate nonlinear dynamical influences. Thirdly, Iterative Learning Control (ILC) is proposed in this paper for tracking accuracy enhancement of a parallel direct driven manipulator. It is shown both by means of simulation study and experimental results that linear ILC is appropriate for application to the considered high nonlinear and coupled systems

Practical Model-based and Robust Control of Parallel Manipulators Using Passivity and Sliding Mode Theory

This chapter provides a practical strategy to realize accurate and robust control for 6 DOFs (degrees of freedom) parallel robots. The presented approach consists in two parts. The first basic part is based on the the compensation of the desired dynamics in combination with controller/observer for the single actuators. The passivity formalism offers an excellent framework to design and to tune the closed-loop dynamics, such that the desired behavior is obtained. The basic algorithm is proved to be locally robust towards uncertainties. The second part of the control strategy consists in a sliding mode controller. To keep the practical and computational efficient implementation, the proposed switching control considers explicitly only the friction model. Here we opt for the so called model-decomposition paradigm and we use additional integral action to improve robustness. The proposed approach is substantiated with experimental results demonstrating the effectiveness and success of the strategy that keeps control setup simple and intuitive. Keywords parallel manipulators, robust control, passivity formalism, sliding mode control, desired dynamics compensation, velocity observe

Eine neue Integrationsideologie: Zu den Thesen zur Strategie und Taktik des demokratischen Sozialismus des Peter von Oertzen

Für jede Analyse der gegenwärtigen Entwicklung und Rolle der SPD ist der offenkundige, auch von SPD-Führern kaum noch bestrittene Tatbestand grundlegend, daß die Reformversprechen der beiden ersten sozialliberalen Regierungen sichals illusionär erwiesen haben. Die 1969 und im Wahlkampf 1972 erweckten Erwartungen nach Erhöhung der Staatsausgaben zur Erfüllung gesellschaftlicher Bedürfnisse, nach „Humanisierung der Arbeitswelt", nach effektiver Konjunkturregulierung und nach Erweiterung der Mitbestimmung im Produktionsbereich wurden enttäuscht. Die Reallöhne stagnierten, die Sicherheit der Arbeitsplätze wurde immer mehr gefährdet, die Ausbildungssituation verschlechterte sich. Das Versprechen der besseren „Lebensqualität" blieb leer, weil die Bedürfnisse der Kapitalverwertung sich im direkten Konflikt mit gesellschaftlichen Interessen stets als vorrangig erwiesen (z.B. Industrieansiedelung, öffentlicher Nahverkehr, Stadtsanierung). Auch die Grenze des Steuervolumens beschränkte die vom Staat dafür bereitstellbaren Mittel. Die objektiven Gründe dieses Scheiterns der Politik der „Inneren Reformen" brauchen hier nicht im einzelnen dargestellt zu werden; sie sind in der Kritik der Sozialstaatsillusion sowie in der Diskussion über Staatsinterventionismus und staatliche „Infrastruktur"-Politik in dieser Zeitschrift ausführlich diskutiert worden, auch wenn nicht immer auf die Politik der sozialliberalen Regierung direkt Bezug genommen wurde (1)

A novel multiple-heuristic approach for singularity-free motion planning of spatial parallel manipulators

The issue of motion planning for closed-loop mechanisms, such as parallel manipulators or robots, is still an open question. This paper proposes a novel approach for motion planning of spatial parallel robots. The framework for the geometric modeling is based on the visibility graph methodology. It is opted for a multiple-heuristics approach, where different influences are integrated in a multiplicative way within the heuristic cost function. Since the issue of singularities is a fundamental one for parallel robots, it is emphasized on the avoidance of such configurations. To include singularity-free planning within the heuristic approach, two heuristic functions are proposed, the inverse local dexterity as well as a novel defined "next-singularity" function, in such a way, well conditioned motions can be provided by a single planning procedure. The success of the method is illustrated by some examples. © 2008 Cambridge University Press

Rotationally acquired four-dimensional optical coherence tomography of embryonic chick hearts using retrospective gating on the common central A-scan

We introduce a new method of rotational image acquisition for four-dimensional (4D) optical coherence tomography (OCT) of beating embryonic chick hearts. The rotational axis and the central A-scan of the OCT are identical. An out-of-phase image sequence covering multiple heartbeats is acquired at every angle of an incremental rotation of the deflection mirrors of the OCT system. Image acquisition is accomplished after a rotation of 180°. Comparison of a displayed live M-mode of the central A-scan with a reference M-mode allows instant detection of translational movements of the embryo. For calculation of 4D data sets, we apply an image-based retrospective gating algorithm using the phase information of the common central A-scan present in all acquired images. This leads to cylindrical three-dimensional data sets for every time step of the cardiac cycle that can be used for 4D visualization. We demonstrate this approach and provide a video of a beating Hamburger and Hamilton stage 16 embryonic chick heart generated from a 4D OCT data set using rotational image acquisition

Construction and establishment of a new environmental chamber to study real-time cardiac development

Heart development, especially the critical phase of cardiac looping, is a complex and intricate process that has not yet been visualized "live" over long periods of time. We have constructed and established a new environmental incubator chamber that provides stable conditions for embryonic development with regard to temperature, humidity, and oxygen levels. We have integrated a video microscope in the chamber to visualize the developing heart in real time and present the first "live" recordings of a chick embryo in shell-less culture acquired over a period of 2 days. The time-lapse images we show depict a significant time window that covers the most critical and typical morphogenetic events during normal cardiac looping. Our system is of interest to researchers in the field of embryogenesis, as it can be adapted to a variety of animal models for organogenesis studies including heart and limb development. © MICROSCOPY SOCIETY OF AMERICA 2007