Simulation-Based Analysis and Design of Passive Back Exoskeleton for Squat Lifting

Back pain is the most common musculoskeletal disorder (MSD) that manual material handling laborers face as they lift heavy objects. To overcome the back pain problem, an assistive device (Exoskeleton) can be worn during lifting. Through musculoskeletal simulation, this work investigates how the passive back exoskeleton affects the spinal muscle forces and spinal joint reaction loads. Such simulation findings can provide insights to improve the back exoskeleton design further. For this purpose, the passive exoskeleton is modeled as a set of elastic elements (springs), and dynamic analysis for a lifting cycle is done during a squat lifting task. Musculoskeletal simulations were carried out in opensim software utilizing the open-source opensim lifting full-body (LFB) model. The model is modified by adding an external spring that provides assistive forces like a passive exoskeleton. During the whole lifting cycle, the erector spinae muscle is strained, so unloading the erector spinae muscle is the primary goal of most back support exoskeletons. This work aims to identify optimal spring configurations and design parameters for a passive back exoskeleton to aid in squat lifting by varying spring parameters and through a formulation of a multi-objective optimization problem. The optimized back exoskeleton is expected to reduce compressive, shear forces on the L5S1 joint and erector spinae muscle force during lifting.