This paper presents the static balancing design of a special reconfigurable linkage that can switch between two one-degree-of-freedom (DoF) working configurations. We will show that the studied dual-mode linkage only requires one mechanical spring or one counterweight for completely balancing its gravitational effect in theory at both modes. First, the theoretical models of the spring-based and the counterweight-based designs are derived. The proposed design concepts were then demonstrated by a numerical example and validated by software simulation. Experimental tests on both designs were also performed. The result of this study shows that a reconfigurable mechanism with N working configurations can be completely statically balanced by using less than N passive energy elements.

Reconfigurable mechanisms are a relatively recent contribution to the field of mechanism design and authors have only just been producing real-life applications of these mechanisms. This paper builds on the application of two categories of reconfigurable mechanisms by elaborating on a generalised static balancing theory suggested in a previous review paper [1]. These categories are single loop mechanisms with one degree of freedom per mode, and single loop mechanisms with multiple degrees of freedom per mode. In this paper it is shown that all configurations of the single DoF mechanisms can be balanced using a single spring. The multiple DoF mechanisms can be balanced by balancing each link with respect to the previous link. These balancing strategies are mathematically shown to be valid. The balancing strategy is then applied to a reconfigurable rehabilitation mechanism for patients with a lower limb paralysis by Tseng et al. [2] of which a simulation and a prototype is made to validate the theory. From the simulation and prototype follows that the single spring balancing of multiple configurations of a single DoF mechanism is possible.