Tsung Heng Chiew

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.

Theoretical Analysis of Friction Compensation Using Sliding Mode Control

Friction is an undesired nonlinear phenomenon that reduces position and tracking accuracy in machine tools application. This paper focuses on development of control technique to compensate friction force at motion reversal of a drive system that generates quadrant glitch phenomenon thus improving tracking accuracy. Sliding Mode Control (SMC) is designed to compensate friction. The Generalized Maxwell-Slip (GMS) friction model is applied for numerical analysis. The performance of the controller is analysed based on the reduction in the quadrant glitches magnitude. The performance of the SMC controller is compared with the classical PID controller. Results show that SMC controller yields the smallest quadrant glitch magnitudes.

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.

Suppression on Effect of Cutting Forces Towards Tracking Performance in Milling Cutting Process Using State Observers

In milling cutting process, tracking performance of the CNC servo drive system is influenced by the characteristics of the cutting forces generated during the milling operation. The undesired frequency harmonics of the cutting force contributes negatively to the positioning accuracy; thus an effective compensation of these harmonics is desired. This paper presents results related to suppression of cutting forces in milling process for minimal impact on tracking performance using controller design approach. A cascade P/PI position controller was designed and numerically analysed in combination with an Inverse Model Based Disturbance Observer (IMBDO) plus Disturbance Force Observer (DFO). The effectiveness of this control approach was validated on the x-axis of the XY feed table of a ball-screw driven milling machine. Results showed that the combined approach of cascade P/PI controller with IMBDO plus DFO produced the best tracking control performance with reduction of 78.8% in magnitude component of the cutting forces using Fast Fourier Transform (FFT) analysis of the tracking errors; compared to individual dedicated approach using IMBDO (62.7%) and DFO (78.2%) respectively.

Parameter Properties of a Sliding Mode Controller Design in Friction Compensation

An optimized controller provides consistent performance with high accuracy and precision even in the presence of disturbance forces. Disturbance forces can be a cutting force or friction force or both. Tracking performance of a drive system is critically influenced by the mechanical structure, disturbance forces and work piece mass. Sliding mode controller is designed to compensate disturbance forces especially friction. This paper presents parameter tuning strategies in designing a sliding mode controller in compensating a nonlinear friction behaviour occurred in machine tools application. The main parameter properties of a sliding mode controller are identified and analyzed. The proposed methods are analytically designed and numerically validated by variability index performance. The result analysis is presented by comparison of tracking position errors of linear motion using proposed methods with lower variability index. The result shows that method a with approach b has lower tracking position error and lower variability index, hence a better chattering effect and tracking position error performance.

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.

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.

Spectral Analysis of Cutting Forces Data for XY Table Ballscrew Drive System

. The utilization of spectral analysis for the purpose of investigating machining parameters in frequency domain has been widely practiced by group of researchers in engineering field. In this case the machining parameters involved are the cutting force parameter. By adapting spectral analysis to the cutting forces data, the researcher will have the access to identify the specific cutting forces exerted to the surface of the workpiece at each particular frequency under a set of frequency content. This paper is paying attention on the essential aspect on how to analyze the cutting forces data appropriately. It is recommended that those data need to be transformed first from the original form of cutting force data in time domain into the form of cutting force data in frequency domain. The outcome from this paper is in the form of graphical representation of cutting force data in frequency domain. It is obtained by applying Fast Fourier Transform (FFT) technique. To be more clear-cut, the result from this research work shows that the cutting force is directly proportional to the depth of cut and inversely proportional to the spindle speed of the end mill machine. The cutting force data later on will be used as an input disturbance for XY table ball screw drive system during the simulation process in the Matlab simulink diagram.