In this paper, we will show that contouring performance can be viewed as a regulation problem in a moving task coordinate frame that is attached to the desired contour. By transforming the machine tool feed drive dynamics to this task coordinate frame, a control law is designed to assign different dynamics to the tangential and normal directions. The transformation also illustrated the effect of contour curvature and feed rate in the control action as well as the system dynamics in the task coordinate frame. The resulting control law consists of a linear time-varying proportional-plus-'derivative (PD) position error feedback control law and a linear time invariant trajectory feedforward control law. Experimental results of the proposed control law on the motion axes of a machining center, Matsuura MC51OV, showed significant improvement of the contouring accuracy compared to the existing servo controller as well as the successful decoupling between the tangential dynamics and the normal (contouring) dynamics for feedrate up to 6 m/min (4 in/s).
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