Hydraulic system based energy harvesting method from human walking induced backpack load motion

Considerable energy can be harvested from human motions, and energy generated by human walking induced backpack load motion is capable of powering mechatronic systems to reduce energy consumption effectively. This paper mainly deals with the design and performance analysis of the energy recovery system with backpack load based on fluid power transmission technique. The kinematics modeling of the displacement of the gravity center of human body during walking was conducted to describe the generation of mechanical energy within the human gait cycle. Combined with the experimental measurement of gait characteristics, the displacement of cyclical motion of the gravity center was obtained. The energy recovery mechanism was designed making use of the vibration excitation of the backpack load motion to directly convert the human walking induced mechanical energy into hydraulic energy and achieve energy storage with accumulator instantaneously. Through numerical simulation and experimental verification, the energy harvesting results under different walking speeds and backpack loads are analyzed. It is shown that the average output power of the recovery mechanism goes over 6 W at a walking speed of 1.53 m/s with a backpack load of 15 kg, and the captured energy can be increased with the higher speed and larger load. The characteristics of accumulator is critical to achieve continuous energy conversion with increase of walking time. The comparison indicated that the output power and power density of the system proposed in this paper is superior to those based on electric generation, which provided potential solution for energy saving of the hydraulic exoskeleton.