On the infinitesimal motion of a parallel manipulator in singular configurations

The author considers a specific parallel manipulator and determines the features of the infinitesimal motions associated with each of the singular configurations. It is shown that every singular configuration for a MSSM is obtained when the 6 lines associated with the links of the manipulator belong to a linear complex of lines. Consequently, it is known that the corresponding infinitesimal motion is a screw motion. If the complex is singular (as in Hunt´s configuration) the pitch of this motion is equal to zero and therefore the resulting motion is a pure rotation around the ISA (which is the line intersecting all 6 lines of the manipulator). If the complex is general, one has determined the ISA and the pitch of the screw motion when the base and mobile plates are parallel