Analysis of the dynamics and nonlinear control of under-actuated brachiation robots

This paper analyzes the dynamics and control of underactuated nonlinear mechanical systems which are systems with fewer actuators than number of degrees-of-freedom. Two nonlinear control methods are proposed and compared for the control of underactuated systems and applied to the control of a three-link brachiation robot. Although controllers designed by both methods are able to drive the brachiation robot to the desired position, the motion characteristics and described trajectories are different for both controllers. One of the control methods based on a separation of the state variables in active and passive variables, presents better control performance and a trajectory more uniform and symmetric than the other control method based on standard nonlinear servo-control with constant desired position.