Design of Robust Controller for Cutting Force Compensation in Milling Table

Lee, Yit Chang (2023) Design of Robust Controller for Cutting Force Compensation in Milling Table. Final Year Project (Bachelor), Tunku Abdul Rahman University of Management and Technology.

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Abstract

Milling machine is one of the most typical machinery applied in manufacturing and production industries worldwide. However, rather than the size and many features that the machine possess, it is the control system and logic algorithm behind the machine that determines its performance. This is especially important when there is presence of disturbance forces such as structural vibrations, friction, and cutting force that impact the accuracy and precision of the machining tool used. These will also affect the frequency response function (FRF) of the system. To counter this, robust controller is introduced providing a fixed gain regulator to deal with the varying system parameters, constraining them within a boundary. In this work, the aforementioned cutting force is collected using a dynamometer for a linear drive system, which is then converted using Fast Fourier Transform (FFT) method from time domain to frequency domain for spectral analysis to be done. With the system model identified by obtaining the milling machine’s transfer function, and motor’s constant obtained, the analyzed cutting force is then injected into the system in voltage signal form. These are then applied in different controllers, which are Sliding Mode Controller (SMC), Super Twisting SMC for comparison, and Proportional-Integral-Derivative (PID) controller as the datum. The overall performance of the controller in compensating the cutting force is then determined through their transient response characteristics in time domain, and frequency domain. These are investigated by comparison of maximum tracking error, improvement in tracking error reduction, and disturbance rejection efficiency. In this work, these are all done through MATLAB/Simulink software with simulation basis to design the most optimal robust controller. Lastly, before the actual implementation of the controllers into milling machine, techniques such as Bode Plot and Nyquist Plot are used to verify stability of PID controller, while Lyapunov stability criterion is used on SMC and ST-SMC controller.