Design of a compact gravity equilibrator with an unlimited range of motion

A gravity equilibrator is a statically balanced system which is designed to counterbalance a mass such that any preferred position is eliminated and thereby the required operating effort to move the mass is greatly reduced. Current spring-to-mass gravity equilibrators are limited in their range of motion as a result of design limitations. An increment of the range of motion is desired to expand the field of applications. The goal of this paper is to develop a compact one degree of freedom mechanical gravity equilibrator that can statically balance a rotating pendulum over an unlimited range of motion. Static balance over an unlimited range of motion is achieved by a coaxial gear train that uses non circular gears. These gears convert the continuous rotation of the pendulum into a reciprocating rotation of the torsion bars. The shape of these gears are specifically designed to balance a rotating pendulum. Our gear train design and the method to calculate the parameters and the shape of the non circular gears are presented. A prototype is designed and built to validate that the presented method can balance a pendulum over an unlimited range of motion. Experimental results show that a work reduction of 86.8 \% is achieved compared to an unbalanced pendulum and the hysteresis in the mechanism is 36.3 \%.BMDBioMechanical EngineeringMechanical, Maritime and Materials Engineerin