Kinetics Modeling of a Six-Powered-Joint Exoskeleton for Heavy Load Lifting

Exoskeletons have been developed to address two critical challenges in industrial and daily assistance: reducing the incidence of work-related musculoskeletal disorders, particularly lumbar muscle strain, and enhancing workers' physical capabilities. While current upper-limb exoskeletons for load lifting predominantly employ passive assistance mechanisms, their limited adaptability often proves inadequate for demanding tasks, even causing damage to the wearer. To overcome these limitations, we present a 6-degree-of-freedom (6-DOF) powered exoskeleton to provide torque at the shoulder, elbow, and waist joints during 50 kg load handling operations, preventing critical injury for upper limbs. The kinetic model of the exoskeleton was calculated and divided into two parts: one was the static torque produced by the static equilibrium of the load and the other one was dynamic moment of inertia. Using combined kinetic modeling and ADAMS simulation validated by experimental data, we quantitatively analyzed joint torques during load handling. The results showed that the hip joint torque was highest at the start of lifting and then decreased as the body straightened. The torque of shoulder and elbow increased continuously from the start to the end of lifting. The torque trends observed in the calculation and simulation were consistent, demonstrating the model's accuracy. This model can serve as a theoretical control framework for hip, shoulder, and elbow joint exoskeletons.