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.