Design of an Actuation Device With the Capability of Automatically Distributing External Load Based on Stability Theorems

Actuation redundancy is widely used to enhance load-carrying capability of robot manipulators; however, it also causes the problems of uneven load distribution and internal forces. This paper presents a redundant actuation device which can automatically distribute the external load to the actuators equally. A structure, which has two additional rotational degree-of-freedom (DOF), is introduced to coordinate the inconsistent forces and motions of the redundant actuators. By an appropriate design of the coordinating structure, the proposed redundant actuation device can work stably at its equilibrium position, even when the system is imperfectly actuated. The automatic distribution property of the proposed actuation device is theoretically proved based on two stability theorems in classical mechanics, namely, the Lagrange's and the Chetaev's. Then, numerical simulations are performed to validate the effectiveness of the design by means of the observation of the phase planes and the load distribution. This study provides an alternative way to design redundant actuation devices with the capability of automatically distributing the external loads, such that the stability characteristics can be guaranteed in a mechanical way, rather than control strategies.