Wissenschaftliche Veröffentlichungen ohne Studienabschlussarbeiten

The development of sensor systems with a complex adaptive regulation of the operating sensitivity and behaviour is an actual scientific and technical challenge. Smart materials like magneto-sensitive elastomers (MSE) are seen as one potential solution for this problem, since their mechanical properties may be controlled by external magnetic fields. The present paper deals with the investigation of elastic and damping properties of MSE containing magnetically soft particles under the influence of a uniform magnetic field. Based on the measurement of the first eigenfrequency of free bending vibrations of a fixed beam, the effective Young's modulus is evaluated theoretically and also numerically using Finite Element Method. It is shown that this parameter, as well as the first eigenfrequency of the beam, increases monotonically with the magnitude of the applied magnetic field. The results are aimed to develop an acceleration sensor with adaptive magnetically controllable sensitivity range for the detection of external mechanical stimuli of the environment.

Sensorisierung der technischen Systeme hat in vielen Forschungsbereichen der Robotik zunehmend an Bedeutung gewonnen. Insbesondere für Mensch-Maschine-Schnittstellen sind sensorisierte und nachgiebige Systeme von Interesse. Die Nachgiebigkeit eines Systems kann zum Beispiel durch die Materialeigenschaften sowie durch die geometrische Gestaltung gewährleistet werden. In der vorliegenden Arbeit wird eine Möglichkeit zur Sensorisierung nachgiebiger Systeme, die für den Bereich der Robotik von Interesse sind, beschrieben. Dafür wird ein elektrisch leitfähiger Silikonkautschuk eingesetzt. Der Vorteil der Anwendung des leitfähigen Silikonkautschuks ist, dass die Nachgiebigkeit solcher Systeme weiterhin erhalten bleibt bzw. sich verbessert. Unter Nutzung experimenteller Untersuchungen von den leitfähigen Silikonkautschuken ELASTOSIL R 570/50 MH C1 und POWERSIL® 466 A/B VP konnte das elektrische Verhalten dieser Materialien unter den mechanischen Beanspruchungen charakterisiert werden. Die Einsatzmöglichkeiten des leitfähigen Silikonkautschuks als Sensorelemente werden am Beispiel von drei nachgiebigen Systemen aufgezeigt. Die hier verwendeten Sensorelemente beruhen auf dem Prinzip der elektrischen Widerstandsänderung unter den mechanischen Beanspruchungen. Das erste System ist eine taktile Struktur und hat eine einfache Gestalt. Mit dem ersten System wird die Anwendbarkeit von dem Material ELASTOSIL R 570/50 MH C1 als Sensorelement aufgezeigt. Verschiedene Tests werden an der taktilen Struktur zur Ermittlung der Kontaktstellen durchgeführt. Die Messergebnisse werden dargestellt und diskutiert. Bei dem zweiten System handelt es sich um einen nachgiebigen Greifer. Der Greifer kann sich an verschiedene Objekte beim Greifvorgang anpassen. Des Weiteren können durch die inhärente nachgiebige Sensorik Informationen über das gegriffene Objekt beim Greifvorgang geliefert werden. Im letzten Teil der Arbeit wird das dritte System, eine nachgiebige Gelenkverbindung mit inhärenter Sensorik, diskutiert. Die Sensorelemente des Systems können dank der Materialeigenschaften des Silikonkautschuks zusätzlich die Funktionen einer Feder und eines Dämpfers übernehmen. Dies ermöglicht einen kompakten Aufbau des Systems mit einer Steuerungsmöglichkeit der Drehrichtung mithilfe der gelieferten Sensorsignale bei einem Kollisionsfall.

Notch flexure hinges are often used as revolute joints in high-precise compliant mechanisms, but their contour-dependent deformation and motion behaviour is currently difficult to predict. This paper presents general design equations for the calculation of the rotational stiffness, maximal angular elastic deflection and rotational precision of various notch flexure hinges in dependence of the geometric hinge parameters. The novel equations are obtained on the basis of a non-linear analytical model for a moment and a transverse force loaded beam with a variable contour height. Four flexure hinge contours are investigated, the semi-circular, the corner-filleted, the elliptical, and the recently introduced bi-quadratic polynomial contour. Depending on the contour, the error of the calculated results is in the range of less than 2 % to less than 16 % for the suggested parameter range compared with the analytical solution. Finite elements method (FEM) and experimental results correlate well with the predictions based on the comparatively simple and concise design equations.

In this paper the mechanics and control of the motion of a straight chain of three particles interconnected with kinematical constraints are investigated. The ground contact is described by dry (discontinuous) or viscous (continuous) friction. Here, we understand this model as a methodological basis for the design of worm-like locomotion systems, i.e., non-pedal mobile robots. This kind of robots will prove an efficient form of locomotion in application to inspection of pipes or for rescue missions. In this paper, a number of issues related to the dynamics and control of artificial limbless locomotion systems are discussed. Simplest models of a limbless locomotor are two-body or three-body systems that move along a horizontal straight line. In the first part of the paper, the controls are assumed in the form of periodic functions with zero average, shifted on a phase one concerning each other. Thus, there is a traveling wave along the chain of particles. In the second part, actuator models are discussed. It is supposed that there are unknown actuator data or the worm system parameter are not known or exactly as well. The focus is on adaptive control algorithms for the worm-like locomotion systems in order to track given reference trajectories, like kinematic gaits. Finally, a prototype together with its signal processing and control software is presented. Theoretically (analytically and numerically) calculated results of the dynamical behavior of the mobile system are compared to experimental data.

In this paper, the vibrational motion of an elastic beam under the parametric excitation is investigated theoretically and numerically. The problem is motivated by biological tactile sensors, called vibrissae or whiskers. Mammals use these thin long hairs for exploration of the surrounding area, object localization and texture discrimination. We propose a mechanical model of the vibrissa sweeping across a rough surface as a straight truncated beam stimulated by a periodic following force. The equation of transverse motion of the beam is studied using the Euler-Bernoulli beam theory and asymptotic methods of mechanics. The numerical analysis is performed by means of the finite element method. It is shown that the parametric resonance of the beam occurs at the specific ranges of the excitation frequency, which depend on the parameters of the beam and the amplitude of the applied force. For these frequency values, the vibrations of the beam are unstable with exponentially increasing amplitude. The comparison of the resonance ranges obtained theoretically and numerically is made. Thus, together with the realisation of the viscoelastic support of an artificial tactile sensor, the parametric resonance may be a potentially useful method for amplifying small signals arising from the contact with an object.

The analog motion control of a microrobot with feedback requires a more complicated structure due to the corresponding sensors, microprocessors and actuators. Application of the digital control system allows the use of a control algorithm, such as the autopilot, without feedback, which allows us to simplify the system. We consider the stabilization of the motion of the microrobot on a horizontal surface along the given motion trajectory. Minimization of the deviation angle of the robots axis from the tangent to the motion trajectory is a criterion for quality control and can be implemented by the digital device with a hysteresis characteristic.

The book in hand grew out of the authors' current research and their long-continued experience in teaching mathematics and mechanics. In a wide sense, it aims at mathematical modeling of mechanical objects and their exploitation. This is done in a bit unconventional way by concentrating on the special object class worm-like locomotion systems and in proceeding with no use of recent sophisticated mathematical tools which most likely cannot be handled by freshmen in engineering or mathematics. Nevertheless, this does not harm the stringent line the physical object to the analytical interpretation of the final mathematical model. The basic model spiked worm in a straight line enables the authors to come up with a fairly self-contained theory which then allows one to study effects of friction and control. The considered system class has its importance in practice (motion in narrow canals, e.g.), but this book is not with an orientation to design and application, the theory developed here should rather be seen as a contribution to bionics.