A Mobile Quad-Arm Robot ARMS: Wheeled-Legged Tripedal Locomotion and Loco-Manipulation

This paper proposes a mobile quad-arm robot, ARMS, that unifies wheeled-legged tripedal locomotion, wheeled locomotion, and loco-manipulation. ARMS’s four arms have different mechanical configurations for hybrid locomotion and loco-manipulation and are partially designed to be general-purpose arms. The one three-degree-of-freedom (DOF) arm has an active wheel that is used for wheeled-legged tripedal walking and wheeled driving with passive wheels attached to the torso. The two three-DOF general-purpose arms are series elastic and are used for wheeled-legged tripedal walking, object grasping, and manipulation. The upper two-DOF arm is used for manipulation only, and its position and orientation are determined by coordinating all the arms. Each motor is controlled using an angle controller and trajectory modification with angle, angular velocity, angular acceleration, and torque constraints. The capabilities of ARMS were verified with seven experiments involving joint control, wheeled-legged locomotion, wheeled locomotion and grasping, slope locomotion, block terrain locomotion, carrying a bag, and outdoor locomotion.