Trajectory planning of a rolling robot of closed five-bow-shaped-bar linkage

A morphological rolling robot of closed five-bow-shaped-bar linkage is presented in this paper. The exterior of each bow-shaped-bar represents a portion of a circle, and then the robot could be propelled forward by displacing the center of mass of the robot relative to the contact point between the rounded exterior of the link and the ground. Herein, we present the mechanical design, kinematics modeling and the analysis of dynamic rolling constraints including the mechanical configuration and motion continuity. And then four schemes of rolling laws limited by the constraints are used to plan the joint paths and analyze the stability with zero moment point (ZMP) criterion. As the results of the trajectory planning with the principle of minimal module between the joint position and the reference trajectory, the rolling laws without sharp transition, such as sinusoid and modified trapezoidal curve, are more appropriate for the dynamic rolling on the robot. Furthermore, dynamic rolling experiments on the prototype are used to verify the trajectory planning. The experimental results show that the rolling locomotion of this robot has favorable characteristics in speed, compliance and continuity.