Design And Analysis On The Robust Control Of A X-Y Ballscrew Mechanism

This thesis presents the design and analysis on the robust control of a X-Y ballscrew mechanism. In this research, a practical and robust controller for positioning control is discussed. The Continuous Motion Nominal Characteristic Trajectory Following (CM NCTF) controller is investigated in this research for tracking motion of an AC driven X-Y ballscrew mechanism. The CM NCTF controller has a simple control structure and straightforward design procedure that does not require an exact model parameter of a plant. In order to enhance the accuracy of the control system, a suitable input signal is designed to make sure the X-Y ballscrew mechanism attenuate smoothly in the deceleration motion. The CM NCTF controller consists of a Nominal Characteristic Trajectory (NCT) and a Proportional and Integral (PI) compensator. The NCT is constructed using the open-loop experimental responses while the PI compensator is designed based on a practical stability limit obtained experimentally. The CM NCTF controller has been evaluated in tracking motion performance. In order to examine the adaptability of the controller to the change of the input, experiments with various inputs is carried out. Besides that, the robustness of the controller is validated through the change of the load of the system. In order to examine the usefulness of the CM NCTF controller, a PI-D controller that has a similar control structure is designed and compared. The tracking performance of the CM NCTF controller is evaluated in maximum peak error Emax, percentage of error Epercent, and root mean square of error Erms. Emax is the difference between the output peak and the reference input, and Epercent is the percentage of the peak error with respect to the reference input. The experimental results proved that the CM NCTF controller has demonstrated better positioning response than the conventional NCTF controller and the PI-D controller by showing a two times smaller motion error. The robustness of the CM NCTF controller is clarified using X-axis, which has heavier load than the Y-axis. The experimental results have again proved that the CM NCTF controller demonstrates better tracking performance than the conventional NCTF controller and the PI-D controller in X-axis. As a conclusion, the CM NCTF controller has better positioning performance as compared to the conventional NCTF controller and PI-D controller. In future, the contour motion for X-axis and Y-axis will be done to evaluate accuracy of the controller. Besides that, the robustness performance in term of change of disturbance force will be considered

Positioning control of XY table using 2-DOF PID controller

A two-degree-of-freedom (2-DOF) PID controller is designed for an AC servo ball screw driven XY table. XY table is widely used in manufacturing industry especially in CNC machineries. The most commonly used controller in industries is conventional PID controller. This controller has satisfactory performance, simple structure, and is one-degree-of-freedom (1DOF). Nonetheless, PID controller can only achieve either good set-point response or good disturbance response. This leads to introduction of 2-DOF PID controller which can achieve both good set-point response and disturbance response. In this project, 2-DOF PID is used for accurate tracking purpose. 2-DOF PID controller is designed using two-steps-tuning-method. Disturbance response is optimized by tuning parameters of 〖 K〗_P,T_i,〖and T〗_D using Ziegler-Nichols 2nd method, followed by optimization of set-point response by tuning of 2-DOF parameters, α and β. Tracking performance of 2-DOF PID controller is compared with conventional PI and 1-DOF PID. Maximum absolute error, sum of absolute error, and mean square error are analyzed for all tracking performance of compensated system. Result shows that tracking error compensation (set-point response) of 1-DOF PID controller is better than 2-DOF PID controller. However, this is due to tuning of α and β parameters in simulation in this project. α and β values should be tuned experimentally. Disturbance response of 1-DOF PID and 2-DOF PID are almost similar due to same 〖 K〗_P,T_i,〖and T〗_D values are used in both controllers

Investigation of model parameter variation for tension control of a multi motor wire winding system

Tension is the force required to pull the wire against the accumulation of all resistance, forces and loads. Tension is one of the important controlled parameters in winding process in order to determine the quality of the product. Winding process in electric discharge machine (EDM) wire manufacturing is the last process before the product is packed and sent to customers. In EDM wire manufacturing process, incorrect tension will result in wire winding failure and wire straightness failure. Since it is the last process in EDM wire manufacturing, it is needed to ensure that there is no reject product contributed in this process. The increase of the pendulum dancer fluctuation and deviation angle when the winding diameter gets bigger especially when it is in high speed will course winding tension problem. This project mainly describes about the modelling of the system and the variation parameters that affects the system performance. The system performance is validated by changing the value of radius of winder

Positioning control of an X-Y table based on practical NCTF control

This paper describes a practical control method for high positioning performance of a XY table motion system. The controller with the characteristics of ease of design, adjustment and without plant identification are paramount important especially in industry, in order to achieve the end objectives of high positioning motion control. For this aim, a practical controller, namely nominal characteristic trajectory following (NCTF) controller has been studied to satisfy the desired performance. Two NCTF control systems have been designed and investigated to realize high performance and ease of application of point-to-point (PTP) positioning and tracking motions. The NCTF controller is comprehensive, comprising of nominal characteristic trajectory (NCT) and PI compensator, which is free from exact modeling and parameter identification. The NCT works as the reference motion of control system and is determined from experimental open-loop time responses of the mechanism. While, the PI compensator makes the motion of the controlled object to follow NCT and ends at origin. The controller parameters can be determined easily, without any given model parameters. In this paper, the experimental comparative performances of the conventional and Continuous Motion (CM) NCTF controllers have been proposed and validated for the XY table in positioning and tracking control performance. Only the result of the one-axis of the table is examined in this paper. Sufficient continuous motion control performances are presented with the CM NCTF controller as compared to the conventional one

Fast Positioning Performance In Ball Screw Mechanism With Disturbance Observer

Ball screw mechanisms are widely applied in different industries due to their capability in achieving precise positioning performance as well as its long travel range for positioning,travelling and contouring actions.However, this mechanism exhibits nonlinearities in micro movement. In this paper,a disturbance observer and PD controller (PDDO) is proposed in ball screw mechanism to achieve fast and precise positioning performance.A macrodynamic mathematical model of the mechanism is derived.PDDO controller is designed to achieve fast positioning in micro travel range.The robustness of the controller against mass is examined.The experimental results demonstrated that the PDDO controller achieves better performance in fast tracking (3 Hz) with working range at 100 μm,1 mm and 3 mm as compared to the PID controller.Besides that,the PDDO controller also demonstrated its robustness in the presence of mass changes

Global economic burden of unmet surgical need for appendicitis

Background There is a substantial gap in provision of adequate surgical care in many low- and middle-income countries. This study aimed to identify the economic burden of unmet surgical need for the common condition of appendicitis. Methods Data on the incidence of appendicitis from 170 countries and two different approaches were used to estimate numbers of patients who do not receive surgery: as a fixed proportion of the total unmet surgical need per country (approach 1); and based on country income status (approach 2). Indirect costs with current levels of access and local quality, and those if quality were at the standards of high-income countries, were estimated. A human capital approach was applied, focusing on the economic burden resulting from premature death and absenteeism. Results Excess mortality was 4185 per 100 000 cases of appendicitis using approach 1 and 3448 per 100 000 using approach 2. The economic burden of continuing current levels of access and local quality was US $92 492 million using approach 1 and$73 141 million using approach 2. The economic burden of not providing surgical care to the standards of high-income countries was $95 004 million using approach 1 and$75 666 million using approach 2. The largest share of these costs resulted from premature death (97.7 per cent) and lack of access (97.0 per cent) in contrast to lack of quality. Conclusion For a comparatively non-complex emergency condition such as appendicitis, increasing access to care should be prioritized. Although improving quality of care should not be neglected, increasing provision of care at current standards could reduce societal costs substantially