Study of planar three-degree-of-freedom 2-RRR parallel manipulators

Planar parallel robots are good candidates for microminiaturization into a microdevice. Fully-parallel planar robots have three kinematic chains (legs) connecting the moving platform to the fixed base. Functional workspace of planar fully-parallel robots is often limited because of interference among their mechanical components. Planar parallel robots with two kinematic chains connecting the moving platform to the base can be designed to reduce interference while still maintaining three-degree-of-freedom. This paper presents kinematics and singularity study of planar three-degree-of-freedom 2-RRR parallel manipulators. Forward displacement analysis of this type of robots is governed by a quadratic equation. The inverse problem is decomposed to yield up to four solutions. Singularity analysis reveals up to four singular orientations at each operation point (x,y) of the workspace, in addition to boundary singularities.