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

Abstract: This article proposes a mobile quad-arm robot: ARMS, which unifies wheeled-legged tripedal locomotion, wheeled locomotion, and quad-arm loco-manipulation. ARMS's four arms have different mechanisms and are partially designed to be general-purpose arms for the hybrid locomotion and loco-manipulation. One three-degree-of-freedom (DOF) arm has an active wheel, which is used for wheeled-legged tripedal walking and wheeled driving with passive wheels attached to the torso. Two three-DOF general-purpose arms are series elastic and used for wheeled-legged tripedal walking, object grasping, and manipulation. The upper two-DOF arm is used for manipulation only; its position and orientation are determined by coordinating all arms. Each motor is controlled by an angle controller and trajectory modification with angle, angular velocity, angular acceleration, and torque constraints. ARMS was 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.