Dynamic analysis of an artificial hybrid leg

Abstract

When a system is subjected to external loads like external forces or torques, systems behave dynamically. Besides external effects, three types of torques which arise from the motion of a robot manipulator also act on the system. These dynamic torques include inertial, centripetal and Coriolis effects and they must be revealed correctly, if model-based control of the system is to be performed. In this manuscript, dynamics of an artificial hybrid leg with a polycentric knee joint is going to be derived. Distinctive feature of the artificial leg having polycentric knee is that it is a serial manipulator, one of the joints (the knee joint) of which is designed as a close chain, a four bar mechanism. The model of artificial leg is considered as an artificial hybrid leg having two degrees of freedom; one at the ankle joint and one at the exciting joint of the four bar mechanism. For the knee joint, iterative kinematic analysis is done in order to derive the pose of all joints of polycentric mechanism for the given arbitrary trajectory of hip joint. The ankle joint and hip joint poses are computed by using inverse kinematic analysis techniques for the solution of standard serial manipulator poses. After kinematic analysis is made, dynamic torques can be calculated as the external torques are taken into consideration, since all angular velocities and accelerations of the links are known. By obtaining the system dynamics, torque demands for the motors which actuate the artificial hybrid leg system can be computed. Computation of these torques have a great importance for the system design, since control systems can only be constructed after system dynamics is fully obtained.