No abstract

This paper describes the development of a wearable exoskeleton system for the lower extremities of infantry soldiers and proposes appropriate design criteria based on existing case studies. Because infantry soldiers carry a variety of equipment, the interference with existing equipment and additional burden of the exoskeleton support system should be minimized. Recent studies have shown that a user only needs to be supported in the gravitational direction when walking on flat terrain; however, active joints are necessary to support walking over rough and sloped terrain such as mountains. Thus, an underactuated exoskeleton system was considered: passive joints are applied to the hip and ankle joints, and active joints are applied to the knee joints to exploit the dynamic coupling effect of the link structure and muscular activation patterns when the user is going up and down stairs. A prototype of the exoskeleton system was developed and validated through a simple stair-climbing experiment.

When a linear actuator is used for rotation motion by a knee joint of an exoskeleton, the specifications of the joint range of motion (ROM) and joint torque change according to how the linear actuator are attached. Moreover, while the linear actuator generates a constant amount of force, the joint torque generated by the actuator changes according to the joint angle, which causes the torque contraction. This makes it difficult to meet the required torque and ROM for walk and stand-to-sit and sit-to-stand (STS) motions while carrying a load. To solve these problems we propose a novel knee joint for an exoskeleton with good energy efficiency during walk and STS motions while carrying a load. The mechanism is composed of a four-bar linkage and an elastic element. Based on an analysis of human motion, the design variables of the joint were optimized and the feasibility of the optimized variables was verified through the simulation. The findings from the simulation results suggest that combining a four-bar linkage with a linear actuator allows a large ROM and good torque performance of the knee joint for walk and STS motions. Moreover, the energy efficiency can be improved because the spring mounted parallel to the actuator can store the energy dissipated as negative work and recycle the energy as positive work.