Design of a Passive Exoskeleton Spine

In this thesis, a passive exoskeleton spine was designed and evaluated by a series of biomechanics simulations. The design objectives were to reduce the human operator’s back muscle efforts and the intervertebral reaction torques during a full range sagittal plane spine flexion/extension. The biomechanics simulations were performed using the OpenSim modeling environment. To manipulate the simulations, a full body musculoskeletal model was created based on the OpenSim gait2354 and “lumbar spine” models. To support flexion and extension of the torso a “push-pull” strategy was proposed by applying external pushing and pulling forces on different locations on the torso. The external forces were optimized via simulations and then a physical exoskeleton prototype was built to evaluate the “push-pull” strategy in vivo . The prototype was tested on three different subjects where the sEMG and inertial data were collected to estimate the muscle force reduction and intervertebral torque reduction. The prototype assisted the users in sagittal plane flexion/extension and reduced the average muscle force and intervertebral reaction torque by an average of 371 N and 29 Nm, respectively. Abstract – In this chapter, a series of biomechanics simulations were conducted to reconstruct a specific movement – spine flexion/extension in sagittal plane of a subject. The motion capture was used to collect the kinematics information of the subject. These motions were used to drive a customized musculoskeletal model in OpenSim. Additionally, the muscle actuation forces and joint reactions were computed via forward simulations. The forward simulation results were then evaluated by comparing with prior published literature and were used to assist the design of a passive exoskeleton as described in Chapters 5-7. Abstract – An OpenSim musculoskeletal model is developed using a simplified multi-link model with only sagittal plane movement. Using this model, a “push-pull” strategy was evaluated to provide external assistance in the sagittal plane for spine flexion/extension. The external assistance was provided by two elastic elements to apply pushing and pulling forces on the lumbar and thorax, respectively, of the human torso in order to decrease muscular effort and to decrease intervertebral reaction torques between the vertebrae in the lumbar region. Simulations results are presented for different spring combinations that individually increment the spring constants. Abstract – In this chapter, the spring constants for the “push-pull” assistive strategy are optimized to minimize muscular efforts and intervertebral torques and forces of the operator. Since it is a multiple objective optimization problem, a Monte Carlo approach is employed to search for the global optimal solution. To iteratively update the design parameters Matlab scripting is used to run the OpenSim simulations. The optimal result is presented and discussed. Abstract – Due to the inevitable differences between the simulation and the physical implementation, a physical prototype was designed and constructed to evaluate the “push-pull” assistive strategy and simulation. A passive spine exoskeleton was designed to satisfy the specific requirements of the “push-pull” strategy and the significant parameters were converted from the simulation to the implementation through the mechanical design. Abstract – The prototype was evaluated on human subjects. Three subjects were asked to complete both dynamic and static sagittal plane flexion/extension tasks with and without wearing the exoskeleton device. The sEMG and inertial data were collected in both conditions on the certain levels of the dorsal muscles for each subject. The experimental setup and the signal post-processing are presented in detail. The effects of the prototype are evaluated by comparing the patterns and magnitudes of the signals collected under both conditions.