Cutting Force Compensation Using Robust Control Strategy for Machine Tool

Low, Siew Loon (2025) Cutting Force Compensation Using Robust Control Strategy for Machine Tool. Final Year Project (Bachelor), Tunku Abdul Rahman University of Management and Technology.

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Abstract

Milling machines are essential tools in modern manufacturing, valued for their flexibility in performing tasks like face milling, end milling, and slotting. As the demand for higher precision and product quality continues to grow, achieving accurate control of machine tool positioning has become increasingly important. A significant challenge in this area is the presence of nonlinear disturbances, particularly cutting forces, which can lead to tool deflection, unwanted vibrations, and surface quality issues during machining. Traditional control methods, such as the Proportional Integral Derivative (PID) controller, often struggle to effectively manage these complex and dynamic disturbances, especially under real-time operating conditions. To overcome these limitations, this project investigates the implementation of two robust control strategies: Sliding Mode Control (SMC) and Super-Twisting Sliding Mode Control (STSMC). These are benchmarked against the PID controller. The control system design is applied to a simulated direct-drive axis model, where cutting forces are introduced as external disturbances. Experimental cutting force data was collected using a manual turret milling machine under varying spindle speeds and depths of cut, and then transformed into the frequency domain using Fast Fourier Transform (FFT) to identify dominant components for disturbance injection. The performance of each controller was evaluated in terms of maximum tracking error improvement, tracking error reduction, disturbance rejection, and chattering suppression. Tracking error reduction was quantified using Root Mean Square Error (RMSE), while disturbance rejection was assessed through frequency domain analysis using Fast Fourier Transform (FFT). All simulations and analyses were conducted using MATLAB and Simulink. Among the three controllers, the ST-SMC demonstrated the most consistent and robust performance across all conditions, offering substantial improvements in disturbance handling and precision tracking, while also effectively eliminating chattering. The stability of the system was further verified through Bode plots, Nyquist diagrams, and Lyapunov theory. Overall, the ST-SMC controller provides a reliable and efficient solution for enhancing machining accuracy, marking a significant step forward in the application of robust control techniques for milling operations.