Prismatic Joint Mechanism for Wheel-Legged Locomotion with Pushing Force Enhancement

This paper proposes a prismatic joint mechanism composed of timing belts and pulleys to enhance the wheel-legged locomotion of a mobile quad-arm robot proposed by the authors. The previous mobile quad-arm robot had four arms composed of revolute joints only, and the pushing force was insufficient to walk and lift the torso simultaneously. In this study, the third revolute joints of the two rear arms are replaced with the prismatic joints. The arm with the prismatic joint mechanism achieves a maximum force of 222 N independent of other joint angles. The maximum force is enough to lift the robot while the robot walks, in which the robot's weight is almost 18 kg. We validated the prismatic joint mechanism via a simulation and experiment and conducted four tasks: standing, lateral wheel-legged locomotion, forward wheel-legged locomotion, and object grasping with the mobile quad-arm robot.