Design of MMSD Six-Bar Rehab Device Toward the Realization of Multiple Gait Trajectories With One Adjustable Parameter

Single degree-of-freedom (DOF) mechanisms have been widely used as motion executers for their compact structure and simple control. However, a single-DOF device can only lead through one specific motion trajectory. This article proposes an approach to design multimode single-DOF (MMSD) six-bar devices, which could realize multiple task trajectories using only one driving motor via an optimized structure with a selected adjustable parameter (A-Parameter). First, a source mechanism for multimode Watt-I six bar linkage is designed with nine candidate adjustable parameters, which enables the same mechanism to fit multiple different trajectories by selecting one specific parameter to be adjustable. Next, to determine the optimal A-Parameter, a multiobjective optimization algorithm nondominated sorting genetic algorithm II (NSGA-II)-adaptive rotation-based simulated binary crossover (ARSBX) is used to demonstrate and analyze the Pareto frontier optimization under different A-Parameters. Then, we take a family of gait trajectories from three different groups of volunteers as the task to illustrate the design of the MMSD six bar device. It shows that the optimal result appears when selecting
$l_{1}$
as the A-parameter with the optimization window width
$m=1$
. Finally, a prototype of the multimode source mechanism is built, and an application on the design of the MMSD gait rehabilitation device is configured and tested on the prototype, in which kinematic and dynamic analysis results both show a good realization of the tasks.