A Unified Framework of Hybrid Vision-Force Control With Nullspace Compliance for Redundant Robots

The ability to handle contact makes robots qualified for many complicated tasks, such as welding, hammering, and wiping. Robot cameras facilitate position planning and control without the geometric knowledge of contact surfaces since they can project contact surfaces onto a 2-dimensional image plane. However, existing hybrid vision-force control (HVFC) methods still rely on this knowledge to project the force on the constraint subspace and do not adequately leverage the redundant degrees of freedom (DoFs) for redundant robots with contact tasks. This paper proposes an enhanced HVFC solution for redundant robots equipped with an eye-to-hand camera to unify HVFC in the Cartesian space and impedance control in the joint nullspace into one closed-loop dynamics with rigorous stability guarantees. Any geometric knowledge of contact surfaces is not required by projecting the force into the redundant space of the visual task rather than the surface’s normal space. Experiments on a seven- DoF collaborative robot have verified that the proposed method is qualified for simultaneous contact tasks in the Cartesian space and compliant interaction in the joint nullspace.