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

This article proposes a mobile quad-arm robot: ARMS that unifies wheel-legged tripedal locomotion, wheeled locomotion, and quad-arm manipulation. The four arms have different mechanics and are designed to be general-purpose arms to enable the hybrid wheel-legged locomotion and manipulation. The three-degree-of-freedom (DOF) front arm has an active wheel, which is used for wheel-legged tripedal walking and wheel driving with passive wheels attached to the torso. The three-DOF rear arms are series elastic arms, which are used for wheel-legged tripedal walking, object grasping, and manipulation. The two-DOF upper 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 experimentally validated on the basis of the following six tasks: joint control, wheel-legged walking, wheel driving, wheel driving with grasping, wheel-legged walking on an uneven terrain, and carrying a bag.