Design of a spherical robot arm with the Spiral Zipper prismatic joint

Abstract

A novel prismatic joint called a Spiral Zipper is used to create a 3DOF robot arm in a spherical robot configuration. The Spiral Zipper can be very compact as it has a large extension to compression ratio. An initial prototype has shown a ratio of over 14:1. The Spiral Zipper is very strong in compression, but maybe loose under tension and moments. A tether based system ensures the prismatic joint is always in compression while enabling spherical coordinate positioning with a long reach, high force, low mass design. While having typically an order magnitude higher strength to weight ratio for a given reach compared to standard industrial robot arms, the arm is slower and was not designed for high precision. These characteristics may be applicable for mounting on mobile robots or flying vehicles. This paper introduces the design and testing of several prototypes.