Abstract
Control of the Acrobat type hopping robot is considered in this paper. The Acrobot consists of two links connected by an actuated revolute joint, and is a good example of many underactuated mechanical systems. This property makes it impossible to apply the control methodology used in Raibert's well-known hopper. During a hopping gate, the dynamics of the system is divided into three phases called stance, flight, and collision, respectively. We consider the forces acting to the foot from the ground, i.e. the constraint force in stance phase and constraint impulse in collision phase. This idea has its origin in the necessity to avoid slipping during a hopping gate. We formulate the control system by taking the direction of constraint force as the output, and demonstrate the possibility of hopping without slip by giving this system a proper reference input. Next, a soft landing problem at touchdown is presented based on the analysis on constraint impulse in collision phase.
