Triangular force/position control with application to robotic deburring

The triangular force/position control scheme for robot manipulators is described in this paper, together with its application to a deburring task. The triangular control allows an easy design of a force control loop closed around the inner position loops. It is shown that, in case of stiff contact, no disturbance to the motion control system is generated by the force controller. However, no information on the dynamic model of the manipulator is required, while the prominent dynamic effect of the joint elasticity is accounted for through the knowledge of the joint stiffnesses. The performance of the triangular control is assessed in a particularly challenging application, i.e. the deburring of light alloy wheels. In the paper it is shown, through several experimental results, that the control system is able to succesfully follow the free formed 3D geometry of the contour, while approximately keeping a prescribed contact force, but also that the large force disturbance generated by hand grinders lead to severe loss of performance.