Mechanical design and analysis of light weight hip joint Parallel Elastic Actuator for industrial exoskeleton

Abstract

Industrial wearable exoskeletons can assist the workers during manual handling of loads at manufacturing facilities. Today, one of their design challenges is to reduce weight so the worker can wear them for an extended length of time, without compromising torque and power requirements. Actuators can largely contribute to the overall weight of such devices. An elastic element in parallel can reduce the technical specifications of the actuator. However, such elastic elements are heavy with a large footprint. We present an innovative Parallel Elastic Actuator (PEA) using an elastic cord made of natural rubber elastomer, which can store energy during lowering and release it while lifting. Trunk exoskeleton requirements are analysed based on human subject data for industrial lowering and lifting scenarios. The mechanical design concept of a PEA for the hip joint of an industrial exoskeleton is discussed in detail. We formulate the mathematical model of the human-exoskeleton motion in the sagittal plane. We perform the virtual testing on industrial lowering and lifting scenarios to verify the actuator performance. The results show the improvement in weight, peak torque and peak power by 20%, 50% and 40% respectively as compared with the current prototype. The new integrated actuator consists of the direct current (DC) motor, the harmonic drive (HD) and the parallel natural rubber elements which reduce size and complexity of the trunk exoskeleton.