Development of a human symbiotic assist arm PAS-Arm : Design of CVT

This paper presents the PAS-Arm (Passive ASsist Arm), a novel assist arm based on passive robotics. PAS-Arms are intended for direct physical interaction with a human operator. PAS-Arms are physically passive. Their purpose is not to enhance human strength but to produce specified but arbitrary two-dimensional guiding surfaces that constrain and guide the motion of the human operator. PAS-Arms have three joints and a three dimensional workspace but possess only two degrees of freedom due to the reduction of degrees of freedom created by a combination of continuously variable transmissions (CVTs) and differential gears. We have built a CVT test apparatus and developed a prototype of the PAS-Arm. We discuss the design of the CVT and the experimental results of the CVT test apparatus. The experimental results of the prototype are then presented.