Energy-Free Adjustment of Gravity Equilibrators With Application in a Mobile Arm Support

Static balancing is a useful concept to reduce operating effort of mechanisms. Very often, spring mechanisms are used to achieve a constant total potential energy, thus eliminating any preferred position. The springs and the mechanism dimensions are designed to exactly or approximately balance other forces present in the mechanism, such as gravity. Quasistatically, the mechanism, once statically balanced, can be moved virtually without operating energy. In some cases it is desirable to adjust the balancer characteristic, for instance due to a change of payload in a gravity balanced mechanism. The adjustment of present static balancers requires significant operating energy. This paper will present a novel principle to adjust spring and linkage-based static balancers with no need for external energy. This principle will be explained and several variants will be shown. A mobile arm support for people with neuromuscular diseases is used as a design example. These people have very limited force and rely on their arm support to move their arms. When picking up objects their support mechanism should ideally be adjusted. Due to the limited available muscle force, this application greatly benefits from an energy-free adjustment.