Forbal: Force Balanced 2–5 Degree of Freedom Robot Manipulator Built from a Five-Bar Linkage

A force balanced manipulator design based on the closed-chain planar five-bar linkage is developed and experimentally validated. We present two variants as a modular design: Forbal-2, a planar 2-DOF manipulator, and its extension to 5-DOF spatial motion, called Forbal-5. We first discuss the design considerations in terms of geometric, kinematic, and dynamic design that fulfill the force balance conditions while maximizing workspace, after which the inverse kinematics of both variants are derived from geometric principles. We validate the improvements from force balancing of the manipulator through experiments comparing the counter-mass-balanced and unbalanced configurations. For Forbal-2, the results show that force balancing yields a reduction in the average reaction moments of up to 66%, a reduction of average joint torques of up to 79%, and a noticeable reduction in position error. For Forbal-5, which has a higher end-effector payload mass, the joint torques are reduced up to 84% for the balanced configuration. The balanced manipulator design is suitable for applications which require a reduction of joint torques, reaction forces/moments, and energy consumption along with improved precision.