Active Tethered Pelvic Assist Device (A-TPAD) to study force adaptation in human walking

An active Tethered Pelvic Assist Device (A-TPAD) has been presented in this paper. TPAD is a cable robot for studying force adaptation in human walking by applying external forces and moments on the human pelvis. A two stage control strategy was implemented to apply the desired force-moment profile. The controller includes (i) a quadratic programming based optimization scheme, (ii) a real-time human motion monitoring system and (iii) a PID feedback loop to plan and implement the required cable tensions. The control strategy was validated first by testing it on a dummy pelvis setup. A pilot experiment was then conducted with a human walking on a treadmill with A-TPAD. The goal was to apply a vertical downward force vector equivalent to 10% of subject´s body weight (BW) at the pelvis. Results showed that the applied vertical force was acting downwards over the full gait cycle and was between 8-13% of the BW. Other force-moment components were maintained within a specified range during the experiment. Increased foot pressure was reported in the presence of vertical force. In summary, A-TPAD provides the capability of applying and controlling a desired force-moment profile on the human pelvis over a gait cycle.