Contact force plan and control of robotic grinding towards ensuring contour accuracy of curved surfaces

Curved parts in the industry have characteristics of large curvature variance and small error allowance, which makes it difficult to control material removal accuracy during the compliant grinding process. Existing studies mainly focused on controlling material removal accuracy by using constant contact force or pressure strategies, while there is no force plan study that takes the material removal as a direct target in the compliant grinding process. In order to ensure contour accuracy of curved surfaces, this paper proposes a novel contact force plan and control method of robotic grinding by taking the accurate material removal at different position of the workpiece as a direct target. First, a material removal model which considers contact force, spindle speed, contact speed and workpiece curvature is proposed. Then the contact force is planned in order to guarantee material removal requirement at different point of the workpiece. Finally, in order to track the planned force with the two degrees of freedom (DOF) smart end-effector, a 2-DOF force-position hybrid control algorithm is proposed. The proposed force plan and control method are verified by simulation and grinding experiments. The results show that the proposed method has higher and uniformer contour accuracy compared with the traditional grinding method using constant force strategy.