Modeling and design of a reconfigurable novel constant-force mechanism for assistive exoskeletons

Constant-force mechanisms can be used for gravity counterbalance and force regulation. While many constant-force mechanisms have been designed, most of them have a limited range of force adjustment, which brings very limited capability to maintain an equilibrium state when load changes. In this paper, a novel design of reconfigurable constant-force mechanism is proposed. The new design is inspired by a variable stiffness mechanism, which can work in a similar way as the hinged lever, but take a compact space. Moreover, the design allows to adjust the configuration parameters achieving a large range of the equilibrium state adjustment. Mathematical models are developed to simulate the equilibrium performance changed with configuration parameters. A prototype is constructed and validates the working principle of the design. A design case is included to show the application of the mechanism in a passive assistive upper-body exoskeleton.