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Abstract-Positioning systems in machine tools lately insists for high accuracy and self adjusting mechanism to be implemented into the system in order to sustain against various disturbance forces. The disturbance forces are in the form of both cutting forces and friction forces. The aim of this paper is to propose a controller namely Nonlinear Proportional Integral Derivative (NPID) to control the position of the system. The tracking error will be compensated by the NPID controller. The tracking performance of NPID controller is compared with conventional PID controller. The degree of robustness of both controllers is quantified based on reduction in the amplitudes of cutting force harmonics using Fast Fourier Transform. It is obvious that the average tracking performance result of NPID controller outweigh the PID controller about 8 % to 40 % better. The finalize design of NPID controller do provide brighter prospect for machining application such as milling process. The execution of NPID controller will offer flexibility since the controller are an adaptive type of controller in which it can automatically adjust for better value of gain based on the error generated from the system. Finally, it is recommended that in order to improvise further the NPID controller, control designer could embedded any type of add on features like dead zone compensator and tracking differentiator into the controller to improve the tracking performance.

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The high demand in tracking performance is crucial in machine tools application. Therefore, the purpose of this paper is to design a Nonlinear PID (NPID) controller for improvement of tracking performance via cutting force. The method was then compared with another method which was conventional PID controller. The configuration included different cutting force disturbances of 1500rpm, 2500rpm and 3500rpm. The parameters were set to 0.4Hz and 0.7Hz frequency for every 10mm and 20mm of amplitude, respectively. The investigation was centred on a comparative study of these two techniques which focused on x-axis of Googol Tech XY ball screw drive system. Results between the designed controllers were validated based on two types of errors; the maximum tracking error and root mean square error. Results showed that the NPID controller recorded better tracking performance compared to PID controller with an error reduction of about 33%. In addition, the results proved that NPID controller is highly practical and suitable to be used for ball screw drive. The controller can be further improved with the implementation of observer such as disturbance observer to compensate the cutting forces.

Abstract. At present, positioning plants in machine tools are looking for high degree of accuracy and robustness attributes for the purpose of compensating various disturbance forces. The objective of this paper is to assess the tracking performance of Cascade P/PI, Nonlinear PID (NPID) and Nonlinear cascade (N-Cascade) controller with the existence of disturbance forces in the form of cutting forces. Cutting force characteristics at different cutting parameters; such as spindle speed rotations is analysed using Fast Fourier Transform. The tracking performance of a Nonlinear cascade controller in presence of these cutting forces is compared with NPID controller and Cascade P/PI controller. Robustness of these controllers in compensating different cutting characteristics is compared based on reduction in the amplitudes of cutting force harmonics using Fast Fourier Transform. It is found that the Ncascade controller performs better than both NPID controller and Cascade P/PI controller. The average percentage error reduction between N-cascade controller and Cascade P/PI controller is about 65 % whereas the average percentage error reduction between cascade controller and NPID controller is about 82 % at spindle speed of 3000 rpm spindle speed rotation. The finalized design of N-cascade controller could be utilized further for machining application such as milling process. The implementation of N-cascade in machine tools applications will increase the quality of the end product and the productivity in industry by saving the machining time. It is suggested that the range of the spindle speed could be made wider to accommodate the needs for high speed machining. .