Lokman Abdullah

Extensive Tracking Performance Analysis of Classical Feedback Control for XY Stage Ballscrew Drive System

Performance analysis in term of identifying the systems transient response, stability and systems dynamical behavior in control system design is undeniably a must process. There are several ways in which a system can be analyzed. An example of well known techniques are using time domain and frequency domain approach. This paper is focused on the fundamental aspect of analysis of classical feedback controller in frequency domain of XY milling table ballscrew drive system. The controller used for the system is the basic PID controller using Matlab SISOTOOL graphical user interface. For this case, the frequency response function (FRF) of the system is used instead of using estimated model of transfer function to represent the real system. Result in simulation shows that after proper tuning of the controller, the system has been successfully being controlled accordingly. In addition, the result also fulfill the set requirement of frequency domain analysis in terms of the required gain and phase margin, the required maximum peak sensitivity and complimentary sensitivity function and the required stability.

Development of System Identification for Piezoelectric Patch Actuator

This paper presents the development of the system identification (SI) for the highly nonlinear piezoelectric patch actuator. The transfer function is determined by using the nonlinear least square (NLS) method after the direct measurements of input-output data are taken from the actuator that is installed on a well-equipped platform. The results were validated to ensure that the transfer function derived fits well with the experimental output.

Theoretical Analysis of Velocity and Position Loop Behaviour of Nonlinear Cascade Feedforward Controller for Positioning of XY Table Ballscrew Drive System

The trend in machine tools and positioning systems nowadays are demanding for accuracy, precision and robustness attributes. In addition to those characteristics, a low-cost and adaptive control systems towards various disturbance forces also add a significant advantage to control engineers who can fulfill those needs. The objective of this paper is to introduce a newly improved control strategy named as Nonlinear Cascade Feedforward. It is basically, a cascade control structure with the additional of two add on modules called Nonlinear function plus independent feedforward function. Secondly, the aim of this article is to focus on the fundamental aspect on how to analyze the open loop and closed loop behavior for both velocity and position loop in the control structure by extracting the mathematical formulation of the controller. The outcome from this paper which is in the form of mathematical formula is beneficial and exceptionally significant during the validation and verification stage. The theoretical analysis involved are analysis on gain and phase margin, bandwidth frequency, sensitivity function, position error and finally analysis on dynamic stiffness of the system which is in this case the XY Table Ballscrew drive system. The strength of this controller is the self-adjusting mechanism towards variable disturbance cutting forces. Based on mathematical formulation, it is observed that the designed nonlinear cascade feedforward offer more flexibility and robustness in terms of the ability to compensate the tracking errors at variable disturbances.

Design and Implementation of Cascade NP/PI Controller for Feed Table Ball Screw Driven Milling Machine

This paper presents improvements on conventional cascade P/PI position control structure with implementation of nonlinear function onto the existing control structure resulting in cascade NP/PI controller. The controller design process involved three main steps, namely; (i) design of PI controller for the speed loop, (ii) design of P controller for the position loop, and (iii) design of the nonlinear function. The speed and position controllers were designed based on gain margin and phase margin considerations. There were three main elements involved in the design of the nonlinear function, namely; rate of variation of nonlinear gain (KO), maximum value of error, (emax) and sampling frequency, (δ). Results obtained from implementation on the x-axis of a milling machine feed table shows that the proposed cascade NP/PI controller generated an improvement of 1.3% in tracking performance in term of RMS error values compared to the classical cascade P/PI controller.

An Enhancement in Control Laws of Super Twisting Sliding Mode Servo Drive Controller Using Hyperbolic Tangent Function and Arc Tangent Smoothing Function

Super Twisting Sliding Mode (ST-SMC) controller belongs to a class of controller known as Sliding Mode Control (SMC). SMC is widely known as a robust controller and has been shown in literature to be an effective medium for excellent control performance especially regarding disturbance force rejection. However, the control performance of SMC is often affected by chattering phenomenon thus reducing the applicability of SMC as position controller of choice in machine tools application where chattering induced vibration cannot be tolerated. ST-SMC is constituted as a higher order SMC. This paper explores control performances of ST-SMC in term of chattering reduction by introducing two types of switching functions in the control laws of the controller; namely, a hyperbolic tangent function (HST-SMC) and an arc tangent function (Arc-ST-SMC). The control performances are analysed based on reduction in magnitude of the tracking error (RMSE) and reduction in magnitude component of the chattering elements observed in frequency domain. The optimized ST-SMC produced the best tracking performance but chattering effect is still persistent. In comparison, HST-SMC produced a comparable tracking performance to ST-SMC with minimal difference of only 12.5% (RMSE). HST-SMC offers a fair trade-off between tracking accuracy and chattering attenuation. On the other hand, arc-ST-SMC produced the most reduction in chattering.

Design of super twisting sliding mode control for single axis direct drive motor

Chattering effect is often associated negatively with the application of the robust nonlinear sliding mode control. This paper compares the tracking responses of system controlled with different controllers and demonstrates the ability of super twisting sliding mode control in chattering suppression and enhancement of tracking performance against classical controller and traditional sliding mode control. The controller was numerically analyzed and experimentally validated on a direct drive single axis positioning system which is described as a second order single-input-single-output system. Three controllers, namely; PID, pseudo sliding mode control and super twisting sliding mode control were designed, analyzed and compared. A Kalman-Bucy filter was designed for velocity estimation to reduce noises from numerical differentiation of position measurement. Results showed the superiority of super twisting sliding mode controller in smoothing the control input and suppressing the chattering effect compared to pseudo sliding mode control. Additional investigation was performed by replacing the signum function using a hyperbolic tangent function. However, only slight improvement in tracking performance was recorded. The results displayed the novelty of super twisting algorithm in chattering suppression making it an attractive option for real-time application.

Investigation on performance of Model Reference Adaptive Control (MRAC) and PI controller for machine tool application

This paper presents the potential of the Model Reference Adaptive Control (MRAC) and Proportional-Integral (PI) controller in improving the tracking performance and transient response of XY Table Ball Screw Driven System. The technique used to design MRAC controller is based on Lyapunov approach that is taken to account the stability of the system. Simulation and experimental test are conducted with two different inputs namely step and sinusoidal to evaluate the performance of this technique. The tracking performance is evaluated based on maximum tracking error and root mean square error (RMSE). In addition, the transient response properties are also evaluated. The results of the comparison between these two techniques are compared and presented.

Design and Analysis of Disturbance Force Observer for Machine Tools Application

In milling process, the quality of tracking performance is influenced by the characteristics of the cutting forces generated during the material removal process. The undesired frequency harmonics of the cutting force contributes negatively to the positioning accuracy. An effective compensation of these harmonics is desired. This paper presents and discusses a disturbance force observer as an approach to estimate and compensate effect of external disturbance forces on system performance. Knowledge of the properties of the disturbance signal is essential for the design of an observer. A Fast Fourier Transform analysis of the disturbance force reveals the harmonics content of the signal. The frequency harmonics is a function of the spindle rotational speeds. The results show effective compensation of the cutting force with reduced amplitudes of the harmonics frequency content.

Assessment on tracking error performance of Cascade P/PI, NPID and N-Cascade controller for precise positioning of xy table ballscrew drive system

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 N-cascade 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.

Theoretical Analysis of Close Loop Behaviour of Ideal Cascade Controller Structure for Positioning of XY Table Ballscrew Drive System

The implementation of Classical Cascade Controller for the purpose of controlling various type of engineering appliances has been vastly utilized by control engineer community. Cascade controller provides a simple structure of controller but yet functional and have the ability to satisfy the control design requirement. In general, the controller consists of two loops, namely velocity loop and position loop. This paper is focused on the fundamental aspect on how to analyzed the close loop behaviour for both velocity and position loop and to extract the mathematical formulation of the controller. The outcome from this paper which is in the form of mathematical formula is useful and very significant in order to validate the theoretical result with the simulation result. To be more precise, the result from this research work are in the form of transfer function for both velocity and position loop of the position output, position error, dynamic stiffness of the controller and the damping ratio of the system which is in this case the XY Table Ballscrew drive system.