Generally, adjustment of gravity equilibrators to a new payload requires energy, e.g., to increase the preload of the balancing spring. A novel way of energy-free adjustment of gravity equilibrators is possible by introducing the concept of a storage spring. The storage spring supplies or stores the energy necessary to adjust the balancer spring of the gravity equilibrator. In essence, the storage spring mechanism maintains a constant potential energy within the spring mechanism; energy is exchanged between the storage and the balancer spring when needed. Various conceptual designs using both zero-free-length springs and regular extension springs are proposed. Two models were manufactured demonstrating the practical embodiments and functionality.

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Static balancing is a useful concept to reduce the operating effort of mechanisms. Spring mechanisms are used to achieve a constant total potential energy, thus eliminating any preferred position. Quasi-statically, the mechanism, once statically balanced, can be moved virtually without the operating energy. In some cases, it is desirable to adjust the characteristic of the balancer, for instance, due to a change in the payload in a gravity balanced mechanism. The adjustment of current static balancers requires significant operating energy. This paper will present a novel variant to adjust the spring-and linkage-based static balancers without the need for external energy. The variant makes use of the possibility to adjust the spring stiffness in an energy-conserving way by adjusting the number of active coils. The conditions under which it functions properly will be given, and a proof of the concept model will be shown.

People with neuromuscular diseases have very limited muscle force. Many of them rely on mobile arm supports to move their arms. Most of these supports incorporate gravity balancers, i.e., spring-loaded mechanisms that achieve a constant total potential energy, thus eliminating any preferred position. The springs and the mechanism topology and dimensions are designed to exactly or approximately balance the weight of the user’s arm. Quasistatically, the mechanism, once statically balanced, can thus be moved virtually without operating energy. In case of change of effective arm weight, e.g., due to picking up an object or putting on a coat, the support mechanism should ideally be readjusted. In all available support mechanisms, this adjustment is associated with considerable mechanical effort, while clearly this application would benefit greatly from an energy-free adjustment. This paper will present an arm support that includes a novel design concept to adjust spring-based static balancers with no need for external energy. This concept will be explained, and several variants will be shown. Subsequently, the application of this concept in a mobile arm support will be described in detail, including preliminary clinical trial results.

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