In this article, a second-order sliding mode control (2-SMC) is proposed for second-order uncertain plants using equivalent control approach to improve the performance of control systems. A Proportional + Integral + Derivative (PID) sliding surface is used for the sliding mode. The sliding mode control law is derived using direct Lyapunov stability approach and asymptotic stability is proved theoretically. The performance of the closed-loop system is analysed through an experimental application to an electromechanical plant to show the feasibility and effectiveness of the proposed second-order sliding mode control and factors involved in the design. The second-order plant parameters are experimentally determined using input-output measured data. The results of the experimental application are presented to make a quantitative comparison with the traditional (first-order) sliding mode control (SMC) and PID control. It is demonstrated that the proposed 2-SMC system improves the performance of the closed-loop system with better tracking specifications in the case of external disturbances, better behavior of the output and faster convergence of the sliding surface while maintaining the stability.

Second-order sliding mode control with experimental application.

Intelligent welding system technologies: State-of-the-art review and perspectives

Robotics for engineers , Robotics for engineers , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Robotics for engineers

In this paper we extend the work done by Chen et al. (IEEE Trans Ind Electron 47(4):932---938, 2000) which proposed a nonlinear disturbance observer for two-link robot manipulators to n-link robot manipulators. A general form of dynamic equations of serial n-link robot manipulator is considered, and the stability analysis of the proposed observer is performed by using Lyapunov's direct method. Although it seems that the formulation of disturbance observer is easy to derive, choosing the disturbance observer gain to guarantee stability is really hard. In this paper it is shown that the design parameter can be selected depends on the maximum velocity and physical parameters of robot manipulator to guarantee the global asymptotic stability of the disturbance observer. Using this nonlinear disturbance observer, no accurate dynamic model is required to achieve high precision motion control, because it makes the system robust against internal disturbances such as unmodeled dynamics and external disturbances such as friction in joints. The effectiveness of the proposed observer is investigated by numerical simulation for three-Dofs robot manipulator. In fact, controller with disturbance observer has more superior tracking performance, with a wide range of payloads and in the presence of friction in joints. It is also found that, although the proposed observer is designed for slow varying disturbances, it can estimate rapid time varying disturbances very well.

Lyapunov-Based Nonlinear Disturbance Observer for Serial n-Link Robot Manipulators

A review on model reference adaptive control of robotic manipulators

Conventionally, shield metal arc welding (SMAW) has been performed by manual operator, and hence it is not easy to apply in hazardous areas such as in nuclear power plants. An image-guided mobile robotic welding system is developed in this study for the automation of the SMAW process. The position of cracks can also be determined by this image-guided mobile robotic welding system. We installed two CCD cameras, a five-axis SCORBOT-ER VII robot and SMAW equipment on a mobile vehicle. The cameras are installed in parallel and can be used to detect the position of any cracks beforehand; the robot is then driven at a constant welding speed along the welding path. Based on the binocular images captured by the CCD cameras, an on-line algorithm is used to compare the disparities between the two images and to obtain the welding paths for the cracks. Since the electrode is consumed during the SMAW process, the robotic joint trajectories need to be modified to keep the end of the electrode on tracking on the desired welding path. The control system determines the feeding velocity of the electrode from the measured welding current and joint positions and modifies the joint trajectories correspondingly. The experimental results show that our system can effectively perform SMAW operations resulting in good quality welding. Also, the variation of the welding current in our system is much smaller than that operated by even senior technicians.

An image-guided mobile robotic welding system for SMAW repair processes

Identification of a non-linear electromagnetic system: An experimental study

In this article we are concerned with the implementation of a dither signal for a closed-loop DC motor system. Experimental studies show that the system contains two nonlinearities that are saturated with dead zone and backlash. Parameter estimation techniques are used to identify the unknown system parameters with special care due to the existence of system nonlinearities. An analytical method is then presented to deal with the closedloop DC motor system with two nonlinearities in the loop. Self-excited oscillations are found to exist in the system. A good correlation between the theoretical and experimental results indicates the success of the system identification and modelling process. Also the ability of dither to quench the limit cycle is demonstrated from these results.

Experimental And Analytical Studies Of The Sinusoidal Dither Signal In A DC Motor System

This paper describes the development of an automatic welding control system for alternating current shield metal arc welding. This method could replace manual operations which require a well-trained technician. We have derived a mathematical model of the welding control system and identified system parameters. An adaptive sliding mode controller, estimates the bound of uncertainties, and modulates the rate of the electrode feed mechanism that regulates the arc current. The electrode feed-rate mechanism with this controller is driven by an AC servomotor, which can compensate for both the molten part of the electrode and undesirable fluctuations in the arc length during the welding process. The method can be easily applied to any welding system in which the electrode is consumed during the welding process. By maintaining the magnitude of the arc current at the desired value and the stability of the arc length, excellent welding performance is obtained. The simulation and the experimental results both show that this automatic welding control system, based on the adaptive sliding mode controller, can perform effectively.

Pi Cheng Tung

Papers

An image-guided mobile robotic welding system for SMAW repair processes

Identification of a non-linear electromagnetic system: An experimental study

Experimental And Analytical Studies Of The Sinusoidal Dither Signal In A DC Motor System

Development of an automatic arc welding system using a sliding mode control

Experimental and analytical studies of the sinusoidal dither signal in a DC motor system