Development of a Human Symbiotic Assist Arm “PAS-Arm” (Design of Mechanism · CVT and Experimental System)

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 possess 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. We have developed an experimental system of the PAS-Arm. In this paper, we describe kinematic specification of the experimental system. We discuss the differential relation of transmission ratios created by the CVTs. We conducted the relationship between transmission ratio resolutions of the CVTs and resolutions of normal vector of the virtual guiding surface, and the relationship between angular velocities of PAS-Arm’s joints and time derivative of the transmission ratios. Assuming that the Euclidean norm of the angular velocities is constant, maximum time derivative of transmission ratios is in proportion to link lengths of the PAS-Arm. We also describe the design of the CVT for use in the experimental system. 1 1. This paper is the full translation from the transactions of JSME, Series C, Vol.75, No.749, pp. 104-112, 2009.