In this work, an innovative force control module is presented, which can be
employed in CNC end milling machines in order to maintain a constant cutting force in the
presence of parametric uncertainty for a time varying end milling process. The controller is a
non-time based one; in fact, the desired tool position reference is delayed according to the
integral of a proper function related to the on-line cutting force measurement. Such a
controller, which is referred to as delayed reference control (DRC), consists in a outer force
feedback loop around an inner position feedback loop. Two main advantages make this
controller suitable for a commercial diffusion: it avoids complicate and time consuming
algorithms for re-planning the path in response to cutting force and it does not require to
design a new position feedback loop. Good experimental results are obtained by
implementing the controller on a wood milling machine prototype. The system has shown a
remarkable robustness in terms of immunity to the mechanical and electrical noise, working
properly also with unfiltered control signals.
