Martin Pfurner

Gudrun Szewieczek, Daniel Huczala, Martin Pfurner et al.

We study mechanical structures composed of spatial four-bar linkages that are bistable, that is, they allow for two distinct configurations. They have an interpretation as quad nets in the Study quadric which can be used to prove existence of arbitrarily large structures of this type. We propose a purely geometric construction of such examples, starting from infinitesimally flexible quad nets in Euclidean space and applying Whiteley de-averaging. This point of view situates the problem within the broader framework of discrete differential geometry and enables the construction of bistable structures from well-known classes of quad nets, such as discrete minimal surfaces. The proposed construction does not rely on numerical optimization and allows control over axis positions and snap angles.

Thomas Stigger, Johannes Siegele, Daniel F. Scharler et al.

The aim of this paper is to give a detailed examination of the input and output singularities of a 3-RUU parallel manipulator in the translational operation mode. This task is achieved by using algebraic constraint equations. For this type of manipulator a complete workspace representation in Study coordinates is presented after elimination of the input parameters. Both, input and output singularities are mapped into a Study subspace as well as into the joint space. Therewith a detailed singularity investigation of the translational operation mode of a 3-RUU parallel manipulator is provided. This paper is an extended version of a previous publication. The addendum comprises the discovery of a possible transition between two operation modes as well as a self motion and an examination of another component of the output singularity surface, most of them for arbitrary design parameters.