This research presents a novel semi-passive knee exoskeleton designed to provide running assistance. The semi-passive exoskeleton incorporates an energy-efficient clutch mechanism activated using a mini servo motor to engage and disengage springs, which support the leg during running. As the subject is running, the exoskeleton extracts energy from deceleration’s negative power, stores it in the spring, and injects it into the positive phase.

The exoskeleton relies on a microcontroller and an inertial measurement unit (IMU) sensor to estimate the leg's position during locomotion to determine the engagement and disengagement stances. Following an elucidation of the principles of knee dynamics during running, the research presents a detailed design of the exoskeleton, and a control method focused on precise spring integration during locomotion.

Furthermore, the research reports on three distinct experiments, with two focusing on evaluating the exoskeleton's timing precision and one examining its impact on human subjects. The experiments demonstrate that the implementation of the exoskeleton yields a reduction in the angular velocity of the knee during the stance phase, which in turn leads to a decrease in the muscular energy expenditure around the knee joint. The semi passive exoskeleton is extremely effective as the ratio of the consumed servo energy consumption divided by the subject’s saved energy is 1:​160.