Whole-body cooperative force control for a two-armed and two-wheeled mobile robot using Generalized Inverse Dynamics and Idealized Joint Units

This paper proposes a control framework for a two-armed and two-wheeled mobile robot that can coordinate all the joint forces to achieve diverse motion objectives such as position, velocity, acceleration, force and impedance at any part of the body. The framework comprises two components: 1) Generalized Inverse Dynamics (GID) that determines joint forces satisfying multiple objectives considering task priorities and various constraints and 2) the Idealized Joint Unit (IJU) that generates accurate torque with assigned apparent inertia and viscosity. GID treats the robot as a single manipulator with multiple branches using a joint model with 2-DOF motion subspace equivalent to two opposing wheels. A 21-DOF mobile robot equipped with IJUs is set up and GID is applied to it. The result shows that GID works well in the examples of physical human-robot interaction and object manipulation where motion objectives are attained coordinating the whole body while keeping passivity due to the redundancy and the assigned impedance property.