Coupling of two 2-link robots with a passive joint for reconfigurable planar parallel robot

This paper proposes a reconfigurable planar parallel robot by coupling two 2R open kinematic chains (or 2-link robots), the first joints of which are passive. We show that they can reconfigure to a 5R closed kinematic chain which has the same number of actuators as its degrees of freedom. They can also reconfigure to a 4R closed kinematic chain plus one actuated link. The parallel robot has only two actuators but can have multiple functions by reconfigurations. Due to the passive joints, whether or not the 2R open kinematic chains can couple with each other is a non-trivial problem. We propose coupling sequences for forming the 4R and 5R closed kinematic chains and verify those experimentally.