Design of a mechanism for converting the energy of knee motions by using electroactive polymers

Harvesting energy from human body motions has become a promising option to prolong battery life for powering medical devices for autonomy. Up to now, different generating principles including dielectric electroactive polymers (DEAPs) have been suggested for energy conversion. However, there is a lack of mechanisms that are specifically designed to convert energy with DEAPs. In a proof of concept study, a mechanical system was designed for stretching DEAPs in those phases of the gait cycle, in which the muscles mainly perform negative work. Rotational movements of the knee joint are transformed into linear movements by using a cable pull. The DEAP can be charged during the stretching phase and discharged during releasing and allows for the conversion of kinetic energy into electric energy. To evaluate the concept, tests were conducted. It was found that the developed body energy harvesting (BEH) system has a performance in the range of 24-40 μW at normal walking speed. The converted energy is sufficient for powering sensors in medical devices such as active orthoses or prostheses.