Energy Regeneration System for Quasi-Direct Drive Actuated Knee Exoskeleton

Exoskeletons are limited by the amount of electrical energy on board which limits operating duration. A possible solution to increase the operating duration of exoskeletons is energy regeneration through regenerative braking. Existing exoskeletons with regenerative braking are limited by high transmission ratios and low backdrivability. This paper presents a novel energy regeneration system to enable regenerative braking using quasi-direct drive actuators at low speeds during human locomotion through the use of a reconfigurable battery management system and boost conversion technique. This enables the design of a knee exoskeleton actuated using quasi-direct drive actuators which have increased torque capability, higher backdrivability, and higher control bandwidth in comparison to conventional actuators. The exoskeleton provides assistive torque during uphill walking and stair ascent while performing energy regeneration during downhill walking and stair descent, which is charged back to the portable battery to elongate the operating duration of the exoskeleton. Using this system, harvesting energy during regenerative braking at low rotational speeds into a single-cell battery while enabling full battery access during the active mode is successfully achieved.