Dynamics and control of underactuated brachiation robots

Summary form only given. Underactuated mechanical systems are systems with fewer actuators than degrees-of-freedom and arise in several mechanical systems in several ways, from intentional design, or because of the mathematical model used for control design, or because of the flexibility of the system (noncollocation problem). Moreover, systems which represent moving objects unattached to the ground are usually underactuated since it is not always possible to fix a controlled actuator between the moving object and ground. This study analyzes the dynamics and control of brachiation robots which are underactuated nonlinear mechanical systems whose motion resembles that of a brachiation monkey. Two control methods are proposed to control a three-link brachiation robot. One of the control methods (I) considers only the nonlinear characteristics of the robot while the other control method (II) considers both the nonlinear and underactuated characteristics of the 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. Control method II which considers the underactuated characteristics of the system by separating the state variable in active and passive variables, presents better control performance and a trajectory more uniform and symmetric than control method I which does not take into account the underactuated characteristics of the system. The control methods presented in this study are applicable not only to brachiation robots but also to any other underactuated system.