A Cable-Driven Pelvic Robot

Walking is a state of continuous imbalance that requires a complex control strategy and cyclic activation of leg muscles to achieve successful inter‐limb coordination. Neuro‐musculoskeletal impairments, such as stroke, cerebral palsy, and spinal cord injury, affect one's ability to voluntarily contract muscles to normal amplitudes. This change in muscle activation pattern reduces the joint level torque generation and as a result impairs the ability to walk normally. Technological advances over the last two decades have resulted in the development of rigid link robotic exoskeletons that aim to improve gait deficits. These devices reduce repetitive and manual labor of therapists while providing objective measurement of the therapy during the gait rehabilitation. Despite the development of these robotic devices, no consensus has emerged about the superiority of robot-aided gait rehabilitation over the traditional methods. This may be because of the inherent complexity of the human musculoskeletal system and the constraints that rigid linked systems impose on the human movement. In this work, we present a cable-driven Active Tethered Pelvic Assist Device (A-TPAD) for gait rehabilitation that can apply a controlled external wrench to the human pelvis in any direction and at any point of the gait cycle for a specified duration. The A-TPAD does not add undesirable inertia on the user and does not constrain the user's motion during training. The A-TPAD provides a technological platform to scientifically study human adaptation in gait due to externally applied forces and moments on the pelvis. Human studies with the A-TPAD can motivate new gait rehabilitation paradigms which can potentially be used to correct gait deficits in human walking. The human nervous system is capable of modifying the motor commands in response to alterations in the movement conditions. Several studies have demonstrated the flexibility of human locomotion despite motor impairments and have shown the potential of using such paradigms for gait rehabilitation. In this work, we present a number of human experiments using the cable-driven A-TPAD to propose novel force interventions that induce adaptation in human gait kinematics and kinetics. In particular, stance phase gait interventions have been developed for gait rehabilitation of hemiparetic patients. In these interventions, the external force vector was applied to the pelvis to target weight bearing during walking and to promote longer stance durations. A single-session force training experiment with hemiparetic stroke patients was also conducted as a part of this work. It is shown that hemiparetic stroke patients improved the ground reaction force symmetry, forward propulsion effort, and stance phase symmetry during walking. In this work, the A-TPAD is also used to develop an intervention to apply external gait synchronized forces on the pelvis to reduce the user's effort during walking. The external forces were directed in the sagittal plane to assist the trailing leg during the forward propulsion and vertical deceleration of the pelvis during the gait cycle. A pilot experiment with five healthy subjects was conducted. This study provides a novel approach to study the role of external forces in altering the walking effort, such understanding is important while designing assistive devices for individuals who spend higher than normal effort during walking.