Mechanical design of an exoskeleton for load-carrying augmentation

The present study proposes a knee joint based on a four-bar linkage in the exoskeleton, which operates when the user is walking and moving from sitting to standing in loaded conditions. When the linear actuator for the rotation motion is used, the specifications of the joint range of motion (ROM) and joint torque change according to the attached position of the linear actuator. An additional problem is that although the linear actuator generates a constant force, the generated joint torque changes according to the joint angle, which causes torque-contraction. In order to solve this problem, the present study proposes a joint based on a four-bar linkage in the exoskeleton robot. First, we analyzed human motion to define the ROM, velocity, torque, and power required at the knee joint. Based on this analysis, the geometric parameters of the knee joint were optimized. The genetic algorithm (GA) method was used for the optimization. The optimal variable allows the knee joint to meet the required ROM and attain good torque performance. A simulation was conducted to confirm the effect of the optimal variable. The results showed that the joint's ROM was 150°, and the actuator's torque met most torque requirements. In particular, the torque met all torque requirements during stances involving positive work, without mechanical interference. Therefore, based on a four-bar linkage, the knee joint showed good ROM, torque performance, and feasibility.