Decoupled Model Predictive Control for Path Following on Complex Surfaces

The present letter proposes a predictive path following control (PPFC) that controls 5 degrees of freedom (DoFs) of the end-effector while the remaining (decoupled) translational DoF should be controlled by an external controller. This PPFC is particularly useful for the path following on surfaces with geometric uncertainties such that the external controller can be independently designed to manage the interaction between the tool and the surface. Therefore, the proposed strategy turns out to be a versatile control scheme that can be integrated with external controllers designed for applications such as robotic surface finishing, welding and 3D printing on complex surfaces. The corresponding optimal control problem (OCP) considers mainly the positioning and orientation errors, tangential velocity and control input amplitudes. The proposed PPFC is validated experimentally in the context of robotic 3D bio-printing. A 7-DoF redundant manipulator equipped with a distance sensor is used to handle a print head through the desired print path. The distance measurements are used by an external controller to correct the printed layer height. The obtained accuracy is consistent with the repeatability of the used manipulator and computation time is compatible with high frequency controllers.