Publications

A compliant mechanism gains its mobility fully or partially from the compliance of its elastically deformable parts rather than from conventional joints. Due to many advantages, in particular the smooth and repeatable motion, monolithic mechanisms with notch flexure hinges are state of the art in numerous precision engineering applications with required positioning accuracies in the low micrometer range. However, the deformation and especially motion behavior are complex and depend on the notch geometry. This complicates both the accurate modeling and purposeful design. Therefore, the chapter provides a survey of different methods for the general and simplified modeling of the elasto-kinematic properties of flexure hinges and compliant mechanisms for four hinge contours. Based on non-linear analytical calculations and FEM simulations, several guidelines like design graphs, design equations, design tools or a geometric scaling approach are presented. The obtained results are analytically and simulatively verified and show a good correlation. Using the example of a path-generating mechanism, it will be demonstrated that the suggested angle-based method for synthesizing a compliant mechanism with individually shaped hinges can be used to design high-precise and large-stroke compliant mechanisms. The approaches can be used for the accelerated synthesis of planar and spatial flexure hinge-based compliant mechanisms.

A vibration-driven locomotor (capsubot) consisting of a rigid housing and an internal body connected to the housing by a spring is considered. The system is driven and controlled by an electromagnetic actuator that provides a force interaction between the housing and the internal body. The housing moves along a line on a horizontal plane with dry friction. The control voltage is applied to the robot in a periodic pulse-width mode, the voltage polarity remaining unchanged. Theoretical analysis predicts that the speed and direction of motion of the robot can be controlled by varying the period or/and the duty cycle of the control signal. An experimental prototype of the robot is built and the experiments are performed. The experiments confirm the theoretical prediction.

Festkörpergelenke werden seit langem in verschiedensten Bereichen der Feinwerktechnik eingesetzt, besonders dort, wo erhöhte Anforderungen an die Präzision bestehen. Beispiele dafür sind Präzisionswaagen und Massekomparatoren, die bereits eine beeindruckende Leistungsfähigkeit erreicht haben. Dies ist nicht zuletzt auf die genaue Kenntnis der mechanischen Eigenschaften und deren Modellierung zurückzuführen. Dennoch ergeben viele in der Literatur verfügbare analytische Modellgleichungen zur Berechnung der Drehsteifigkeit der hier typischen, besonders dünnen Festkörpergelenke eine Abweichung von rund 10 % gegenüber dem 3D-Modell basierend auf der Finiten-Elemente-Methode. Dies wird anhand der genauen Betrachtung des Spannungszustandes im belasteten Gelenk aufgezeigt und ist ein relevanter Aspekt für die Entwicklung von Geräten für Präzisionsanwendungen und deren Justierung. Der Beitrag beleuchtet dieses Phänomen im Detail, zeigt Grenzen verschiedener Modellansätze in Abhängigkeit der Geometrie auf und bietet dem Leser einen Vorschlag zur präzisen Modellierung in einem großen Parameterraum an, die ohne eine aufwändige Finite-Elemente-Analyse auskommt.

Established robots for locomotion into sandy soil are dominated by hammering systems. In this paper, we study an alternative design using a screw-driven mechanism. A testbed to find an efficient design is developed. Dependencies between velocity, drilling torque and depth are measured for different screw prototypes. The results show that the design of the screw is critical for the creation of fast and efficient mobile robots. Based on the experimental results, a prototype of an autonomous drilling robot is designed. With a torque of 0.66 Nm it is able to reach a depth of 20 cm within 2 min.

Bristle bots are vibration-driven robots actuated by the motion of an internal oscillating mass. Vibrations are translated into directed locomotion due to the alternating friction resistance between robots' bristles and the substrate during oscillations. Bristle bots are, in general, unidirectional locomotion systems. In this paper we demonstrate that motion direction of vertically vibrated bristle systems can be controlled by tuning the frequency of their oscillatory actuation. We report theoretical and experimental results obtained by studying an equivalent system, consisting of an inactive robot placed on a vertically vibrating substrate.

A passive vibrissa (whisker) is modeled as an elastic bending rod that interacts with a rigid obstacle in the plane. Aim is to determine the obstacle's profile by one quasi-static sweep along the obstacle. To this end, the non-linear differential equations emerging from Bernoulli's rod theory are solved analytically followed by numerical evaluation. This generates in a first step the support reactions, which represent the only observables an animal solely relies on. In a second step, these observables (possibly made noisy) are used for a reconstruction algorithm in solving initial-value problems which yield a series of contact points (discrete profile contour).