NAVARO II, a Novel Scissor-Based Planar Parallel Robot 1

Abstract: This article presents a new variable actuation mechanism based on the 3-RPR parallel robot. This mechanismis an evolution of the NaVARo robot, a 3-RRR parallel robot, for which the second revolute joint of the threelegs is replaced by a scissor to obtain a larger working space and avoid the use of parallelograms to operate thesecond revolute joint. To obtain better spatial rigidity, the leg mechanism is constructed by placing the scissorsin an orthogonal plane to the plane of the manipulator displacement (3-RRR or even the 3-RPR). This geometricproperty brings the significant consequence of allowing the scissors to directly substitute the prismatic chains in the3-RPR and enjoy the same kinematics advantages for the overall robots as only one solution to the inverse kinematicmodel. From the Jacobian expression, surfaces of singularity can be calculated and presented in a compact form.The singularity equations are presented for a robot with a similar base and mobile platform. The properties of thescissors are then determined to have a prescribed regular workspace.