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

This letter proposes a mobile quad-arm robot: ARMS that unifies wheel-legged tripedal mobility, wheeled mobility, and quad-arm manipulation. The four arms have different mechanics and are designed to be general-purpose arms to enable the wheel-legged hybrid mobilities 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 four tasks: wheel-legged walking, wheel-driving, wheel-driving with grasping, and carrying a bag.