Elucidation on step-out phenomenon of magnetic strain wave gear by multi flexible body dynamics and displacement measurement

Abstract

Lower limb exoskeletons with actuators aid physically challenged individuals in walking. We had developed a novel, lighter than conventional, magnetic strain wave gear for exoskeletons. However, output shaft was not rotated when overloaded even through input shaft was rotated (step out phenomenon). Then, the transmission torque was limited by a step-out phenomenon. In the paper, we aimed to elucidate a step-out phenomenon for future design. We observed deformation shape of two types of magnetic strain wave gears, through multi flexible dynamics analysis with magnetic force database and measurement using displacement sensors. Basically, the deformation shape was ellipse. The phase difference between rotational angle of input shaft and tilt angle of ellipse deformation shape was enlarged when the load was increased. The phase different became excessive and the deformation shape was changed to true circle when overloaded showed. Compared a gear with small 4-pole magnets, a gear with large 16-pole magnets could keep deforming shape and it had higher limitation torque.