Disturbance Forces Compensation in Machine Tools using Robust Controller

Milling machine is one of the most vital machinery applied in manufacturing industries worldwide. However, the typical control system of the machines is no longer able to cope with different disturbance forces, especially the unavoidable cutting forces during the milling process. This paper proposes the super twisting sliding mode controller to counter the cutting forces and compares the control performances of the proposed controller against the existing controller. Three controllers, namely; proportional-integral-derivative controller, pseudo-sliding mode controller, and super twisting sliding mode controller were designed and simulated using a direct drive positioning system. Three types of cutting forces produced from end-milling process with different spindle speed ranged from 1000 rpm to 2000 rpm were applied as disturbances. Evaluation and comparison of the designed controllers were performed in terms of tracking error reduction, and cutting forces rejection via spectral analysis. The simulated results revealed that the proposed controller outperformed the traditional linear controller in tracking error reduction with an average improvement of 99.8%. It also performed three folds better than the pseudo-sliding mode controller in terms of cutting forces compensation. The pronounced robustness in the proposed controller compared to standard controller would promote its application in real-time direct drive system.