Conceptual Design of Portable Lower Limb Orthosis for Persons with Motor System Impairments

Design of a portable lower limb orthosis for persons with impairments of motor system is presented. Based on the anatomical structure and kinesiology of human lower limbs, it is observed that, during a walking gait, the position of the hip joint significantly varies due to a complex rotation of pelvis with respect to the body trunk. Since the movement of the hip joint is not negligible on the sagittal plane, this design, unlike most exoskeleton type of lower limb orthosis, considers the hip joint as a plane pair and knee joint as a revolute joint. As a result, the kinematic interference between the orthosis and the human lower limb can be minimized and discomfort can be eliminated. Moreover, in order to assist the persons who wear the orthosis to have the normal walking gait, passive device that composes of springs is used to balance the gravitational effect of the lower limb during the swing phase of the gait cycle.
In this paper, topological synthesis of the orthosis according to the functional requirements of the kinematic behavior of the human lower limb is first accomplished. Then, a methodology for the gravity-balancing of the lower limb is presented, and the minimum number of springs and installation of springs are determined. Then, the design is selected in accordance with type of springs and number of springs for achieves gravity-balancing. Based on the anthropometric parameters obtained from NASA, dimensional synthesis of the orthosis is implemented. Design of the orthosis is finally justified by the motion simulation of the orthosis as well as the human lower limb executed on ADAMS. Finally, simulation is accomplished on ADAMS, and the method for errors estimation and reduction is presented.