Stewart Gough platforms with linear singularity surface

In the general case the singularity loci of parallel manipulators of Stewart Gough type is a cubic surface in the space of translations. In [G. Nawratil, Stewart Gough platforms with non-cubic singularity surface, Technical Report No. 204, Geometry Preprint Series, Vienna University of Technology (2010)] all manipulators with a non-cubic singularity surface were characterized. Based on this result we determine the whole set of parallel manipulators of Stewart Gough type possessing a linear singularity surface. These manipulators have the advantage, that their singularity surface can easily be visualized because it is a plane for any orientation of the platform. We also give a geometric interpretation of these manipulators.