Improvement of Transmission Torque Characteristics of Strain Wave Gear with Magnets

Lower limb exoskeletons with actuators aids disabled individuals in walking. However, the exoskeleton weight is greater than that of conventional medical devices such as orthoses and walking frames. In this study, we propose a novel strain wave gear for light exoskeletons, which is lighter than conventional commercial strain wave gears. The proposed gear uses magnets, rather than a mechanical cam. The thin-walled elastic cylinder is deformed by the magnetic force in the gear, and the torque is transmitted by tooth engagements. In this paper, strain wave gears with 4 pole- and 16 pole- magnets are designed. Next, we constructed dynamic analysis method. In this analysis method, the magnetic force distribution on the elastic cylinder at each deformation and posture conditions is obtained through static magnetic analysis with finite element method, and dynamic behavior is calculated through multi flexible body dynamics with the finite element method, the direct solver, and the obtained magnetic force distribution database. From analyzed and measured results, we clarified that the gear with 16 pole-magnets can transmitted larger torque than that with 4 pole-magnets.