Self-Motions of 6-3 Stewart-Gough Type Parallel Manipulators

In the paper we show that every 6-3 Stewart-Gough (SG) platform has self-motions. This yields an example of self-motions for a class of SG platforms which are not architecturally singular. We present three types of self-motions, general self-motion if the platform is in some sense congruent to the base, a butterfly type self motion and a spherical four-bar mechanism self-motion. For the last two cases there is no restriction for the geometry of the platform. We believe that this yields all possible self motions of the 6-3 platform. but we are not able to give the proof, corresponding equations are too complex.