Singularity analysis and reconfiguration mode of the 3-CRS parallel manipulator

The 3-CRS manipulator is an original parallel mechanism having 6 degrees of freedom (DOFs) with only 3 limbs. This mechanism uses a motorized cylindrical joint per limb. This new paradigm of actuation opens research fields on new families of robots that should particularly interest the parallel robotics community. According to its dimensional synthesis, this mechanism can have remarkable kinematic properties such as a large orientation workspace or reconfiguration capabilities. In this paper, we introduce this mechanism and we study its singularities by using a geometric approach. This approach simplifies considerably singularity analysis problem by considering the relative geometric configurations of three planes defined by the distal links of the limbs. Thanks to that, a reconfiguration mode of the 3-CRS, that doubles its reachable workspace, is highlighted. This property is illustrated on a physical prototype of the robot.