Rehabilitation of people with lower or upper limb disorders using mechanical systesms has attracted considerable attention in recent years. These mechanical systems can be active or passive and be used to realize two overall goals: 1. Therapy, 2. Independent living for people with abnormalities. The aim of this research is to investigate the performance of a special kind of such systems, namely lower limb orthosis, which are used for standing and walking of the paraplegic, for both therapy purposes and as assistive device. In the first part, we investigated static and dynamics standing of a paraplegic individual with the new designed orthosis. To this aim a serial five link chain with two degress of freedom, representing the subject and orthosis as a whole, has been considered in sagittal plane. Equilibrium points of the system can be calculated using equations of motion and must satisfy two constraints to achieve stable standing: first, dynamic stability of the system which is checked by the eigenvalues of the linearized form of equations of motion aournd each obtained equilibrium point; second, static stability, by which we mean that the projected Center of Gravity of the whole system must lie within support polygon. The results of the proposed model firstly have been verified with comparison to previous research in literature. Then the model also has been verified by test results and used to find the bounds on joint angles which can realize stable standing with the orthosis for spinal cord injured subjects. This finding is one of the most important achievements of this thesis and can be useful in designing new generations of orthosis. After a complete investigation into the problem of static standing, we have investigated dynamic standing of a paraplegic subject, while undertaking a hand task, with the consideration of dynamic stability of hip joint and Zero Moment Point constraint, and again a general framework has been proposed to find the bounds on joint angles which can realize stable dynamic standing with the orthosis for spinal cord injured subjects. After scrutinizing the passive system in both static and dynamic standing, assuming the system is equipped with actuators mounted on hip joints of the orthosis, the problem of active control of the system has been solved while the constraint of Zero Moment Point has been also taken into account. In the last section of this research, we investigated path generation of a biped and proposed trunk and arm sterategies to make the gait of the robot stable. Keywords : Spinal Cord Injury, quiet standing, static standing, dynamic standing, orthosis, stability.
