Abstract: The pelvis plays a significant role in creating smooth and efficient motion during gait. In this study, an orthosis is designed to support pelvis motion of patients with the inability to walk. This assistive device is un-powered and consists of only passive elements. By focusing on the motion of the lower extremities during treadmill walking, a 3D dynamic model of the human body is simulated through a coupled optimization process. Based on two approaches of direct and inverse dynamics, the optimization problems are defined to derive optimum structural parameters of the pelvic orthosis. The optimization results of the direct dynamics problem indicate good matches between the optimized time plots of pelvis rotations with corresponding desired ones. Moreover, by solving the inverse dynamics problem, the minimum value of torque vector of the hip joint of the stance leg during a gait cycle is obtained. Furthermore, by utilizing a prototype of the orthosis, preliminary experiments are conducted on a normal user to validate the model and to investigate the feasibility of using the device for rehabilitation. For this purpose, the rotational movements of the pelvis and energy consumption of the subject in two cases with and without the device are compared during gait on a treadmill. Decreased energy consumption and the compliant motion of the pelvis while using the device verify simulation results and confirm the favorable performance of the assistive device for pelvic support during walking rehabilitation.

Key words: Pelvic support , · Passive orthosis , · Dynamic model , · Optimization , · Treadmill gait