Numerical Validation of a Robust Positioning Controller in Machine Tools Application

Abstract

Cutting force and friction force are two disturbance forces that directly affect the servo drive system during the milling process, causing a negative effect that reduces the positioning table’s precision. To maintain the final product’s quality and geo metric precision, this influence must be countered. The main goal of this thesis is to reduce the disturbance by designing effective controllers to compensate for these injected disturbance forces at a spindle speed of 1500 rpm. This thesis proposes PID, Cascade P/PI and Sliding Mode Control (SMC), with its modified structures Sigmoid SMC and SuperTwisting SMC (ST-SMC). The PID and cascade was de signed using conventional loop shaping method, while SMC was design using its traditional formulation and heuristic tuning methods. The numerical analysis was performed using MATLAB/Simulink software and performance was tested using performance index; Maximum Tracking Error (MTE), Root Mean Square Error (RMSE) and Fast Fourier Transform (FFT). The results obtained showed that Sigmoid SMC controller produced superior performance over the others. With Maximum Tracking error showed that Sigmoid SMC produced the best tracking error with percentage reduction of 85 % on reference to Cascade P/PI with highest tracking error. In terms of RMSE, PID produced the most percentage variation error of 45.9 % while cascade had the lowest of 2.70 %. In regards to the FFT results, the Sigmoid SMC showed the most reduction of peak amplitude of 68.3 % and PID showed the lowest peak reduction of 19.4 %. The chattering phenomenon in SMC is addressed by modifying the classical SMC, and the numerical analysis displayed a robust SMC to compensate disturbance forces while reducing chatter ing effect.