Adaptive gravity compensation of decoupled parallel and serial manipulators using a passive hydraulic transmission

摘要

This article addresses the gravity compensation of decoupled or partially decoupled parallel and serial manipulators. The proposed technique applies to manipulators in which the vertical motion is decoupled from other Cartesian degrees of freedom (DOFs). In the latter situation, only one DOF needs to be gravity compensated in order to eliminate actuator torques due to the weight of the moving parts. First, a passive hydraulic transmission consisting of two cylinders connected by hoses is introduced in order to perform gravity compensation using a remote counterweight (CW) affecting only the inertia of the equilibrated DOF. A complete system is then shown using a set of CWs, cylinders, and valves allowing to adapt rapidly and effectively to a variety of payloads. Finally, two experimental implementations using, respectively, hydraulic and pneumatic cylinders filled with water are presented and the practical limitations of the approach are discussed.