Development of a Human Symbiotic Assist Arm “PAS-Arm” (Basic Concept and Mechanism)

Abstract

We describe a new robotic assist device: a passive assist arm (PAS-Arm). PAS-Arms are intended for direct physical interaction with a human operator, handling a shared payload. PAS-Arms are physically passive. Their purpose is not to enhance human strength, but to provide virtual guiding surfaces, which constrain and guide the motion of the payload within a shared workspace. PAS-Arms have three joints and a three dimensional workspace, but possesses only a two degrees of freedom, due to the reduction of degrees of freedom created by a combination of Continuously Variable Transmissions (CVTs) and differential gears. The combination of CVTs and differential gears places one mechanical constraint on three angular velocities of the joints. PAS-Arms have no joint actuators and no force sensors. Thus they are potentially well suited to safety and low cost. This paper proposes a basic concept of PAS-Arms and explains a principle and a construction of PAS-Arms. We discuss the relation of PAS-Arms to conventionally actuated robots and another type of assist arms. We also describe range of transmission ratio of CVTs. 1 1. This paper is the full translation from the transactions of JSME, Series C, Vol.73, No.730, 2007.