Energy harvester for safety shoes using parallel piezoelectric links

[Display omitted] •Energy harvester using parallel piezoelectric links fits in safety shoes.•Power is generated by forces and moments with six degrees of freedom.•Input force and output voltage of the harvester were modeled.•Average electrical output per step was 1.29 mW.•Safety shoes were equipped with 0.5-cd LED light. Energy-harvesting devices in shoes have attracted much attention from the fields of elderly support, sports science, and disaster mitigation. In this study, we developed an energy harvester with a parallel link structure and six multi-layered piezoelectric transducers. By using this structure, we realized an effective energy conversion compared with conventional energy harvesters in terms of maximum power, comfort, durability, and availability of inputs with six degrees of freedom. A prototype of the parallel-link piezoelectric energy harvester generated 1.29 mW with human body weight. As a trial use, this energy harvester was installed in safety shoes for powering LEDs in the shoes. The assembly produced a brightness of 0.5 cd on average over a duration of 0.5 s, which is enough to show the wearer his or her position in a dark place.