The joint torques in hip, knee and ankle are computed using inverse dynamic model during standing up for a paraplegic patient. The joint torque comprises the dynamical torque due to the inertia forces, and a passive torque due to the muscles and gravitational torque. It has been observed that the contribution to the joint torques by the gravitational torque is dominant. On the basis of this result, a gravity balanced assistive device is proposed for the elderly and impaired people such as spinal cord injury and paraplegic patients. This passive device uses a hybrid method to identify the center of mass of the system using auxiliary parallelograms first. Next appropriate springs are connected to the device to vanish the total potential energy of the system due to the gravity during standing up. A prototype with the underlying principles is currently being fabricated at the University of Delaware.

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