Robust control for a class of interval model : application to the force control o piezoelectric cantilevers.

International audienceA method to design robust performances controllers is proposed in this paper. The method is valuable for a class of uncertain parametric systems: systems with zero-order numerator. In this work, interval model that accounts parametric uncertainties is described using interval analysis. Robust controller is derived by combining the interval arithmetic with the classical direct synthesis. As the derived controller is also an interval, we prove using numerical analysis that the midpoint can be taken as the final controller to be implemented. The proposed design method is applied to the control of manipulation force in piezocantilevers where the compliance of the manipulated objects is uncertain. The experimental results show the efficiency of the proposed method

Interval Modeling and Robust Control of Piezoelectric Microactuators.

International audienceMicrosystems are very sensitive to environmental disturbances (thermal variation, surrounding vibration, microobjects in contact with them, etc.) and they are often subjected to small degradation or their behaviors are often affected during the functioning. As a result, their parameters often change during the micromanipulation, microassembly or measurement tasks and the accuracy or even the stability may be lost. For that, robust control laws should be introduced to control them and to ensure the performance. H1 and μ-synthesis approaches were the classical robust techniques used to control microsystems. They are undeniably efficient but they lead to high-order controllers that are sometimes inconvenient for real-time embedded systems. In this paper, by the means of interval numbers that are used to characterize the uncertain parameters, we propose a method to synthesize simple controllers ensuring robust performance for microsystems. The controller synthesis is formulated as a set-inclusion problem. The main advantages of the proposed method are the ease of modeling the uncertain parameters thanks to intervals and the simplicity and low-order of the derived controllers. The method is afterwards applied to model and control piezoelectric microactuators and the experimental results show its efficiency. Finally, using the H1 technique, we also demonstrate numerically the performance robustness of the closed-loop with the designed controller

An Overview of Arc Welding Control Systems

In this paper an overview of arc welding control systems is given. At first some basic physical background of the process is given. Then the two most important subtypes Gas tungsten arc welding (GTAW) and Gas metal arc welding (GMAW) are presented in some detail. In order to understand the logic of feedback control systems, the most essential control theory is outlined shortly. In the overview of control systems a feedback signal is used a means of division. The analysis of recent research papers in the area has shown that recently image processing based control systems seem to be the most popular ones

Double-Electrode Arc Welding Process: Principle, Variants, Control and Developments

Double-electrode gas metal arc welding (DE-GMAW) is a novel welding process in which a second electrode, non-consumable or consumable, is added to bypass part of the wire current. The bypass current reduces the heat input in non-consumable DE-GMAW or increases the deposition rate in consumable DE-GMAW. The fixed correlation of the heat input with the deposition in conventional GMAW and its variants is thus changed and becomes controllable. At the University of Kentucky, DE-GMAW has been tested/developed by adding a plasma arc welding torch, a GTAW (gas tungsten arc welding) torch, a pair of GTAW torches, and a GMAW torch. Steels and aluminum alloys are welded and the system is powered by one or multiple power supplies with appropriate control methods. The metal transfer has been studied at the University of Kentucky and Shandong University resulting in the desirable spray transfer be obtained with less than 100 A base current for 1.2 mm diameter steel wire. At Lanzhou University of Technology, pulsed DE-GMAW has been successfully developed to join aluminum/magnesium to steel. At the Adaptive Intelligent Systems LLC, DE-GMAW principle has been applied to the submerged arc welding (SAW) and the embedded control systems needed for industrial applications have been developed. The DE-SAW resulted in 1/3 reduction in heat input for a shipbuilding application and the weld penetration depth was successfully feedback controlled. In addition, the bypass concept is extended to the GTAW resulting in the arcing-wire GTAW which adds a second arc established between the tungsten and filler to the existing gas tungsten arc. The DE-GMAW is extended to double-electrode arc welding (DE-AW) where the main electrode may not necessarily to be consumable. Recently, the Beijing University of Technology systematically studied the metal transfer in the arcing-wire GTAW and found that the desired metal transfer modes may always be obtained from the given wire feed speed by adjusting the wire current and wire position/orientation appropriately. A variety of DE-AW processes are thus available to suit for different applications, using existing arc welding equipment

Automatic Control of the Weld Bead Geometry

Automatic control of the welding process is complex due to its nonlinear and stochastic behavior and the difficulty for measuring the principal magnitudes and closing the control loop. Fusion welds involve melting and subsequent solidification of one or more materials. The geometry of the weld bead is a good indicator of the melting and solidification process, so its control is essential to obtain quality junctions. Different sensing, modeling, estimation, and control techniques are used to overcome this challenge, but most of the studies are using static single-input/single-output models of the process and focusing on the flat welding position. However, theory and practice demonstrate that dynamic models are the best representation to obtain satisfactory control performance, and multivariable techniques reduce the effect of interactions between control loops in the process. Also, many industrial applications need to control orbital welding. In this chapter, the above topics are discussed

Arc stability analysis of twin-wire welding using wavelet energy entropy

The broader aspect of this work is to convey newer observations in twin-wire gas metal arc welding. In the prior works, it has been observed that the dissimilar currents in lead and trail lead to stabilize the arc. The present work suggests that dissimilar current density in the two electrodes can also help with arc stability, resulting into a considerable influence on HAZ Hardness and aspect ratio. If the difference of current density in the lead and trail is more, the arc attains maximum stability. With the help of dissimilar wire diameter electrodes we can achieve a higher current density difference in lead and trail

MODEL ANALYSIS AND PREDICTIVE CONTROL OF DOUBLE ELECTRODE SUBMERGED ARC WELDING PROCESS FOR FILLET JOINTS WITH ROOT OPENING

Submerged Arc Welding (SAW) for fillet joints is one of the major applications in the shipbuilding industry. Due to the requirement for the weld size, a sufficient amount of metal must be deposited. In conventional SAW process, the heat input is proportional to the amount of metal melted and is thus determined by the required weld size. To meet this requirement, an excessive amount of heat is applied causing large distortions on the welded structures whose follow-up straightening is highly costly. In order to reduce the needed heat input, Double-Electrode (DE) technology has been practiced creating the Double-Electrode SAW (DE-SAW) method for fillet joints. The reduction in the heat input, however, also reduces the penetration capability of the process, and the ability to produce required weld beads has to be compromised. To eliminate the unwanted side effect after using DE-SAW, a root opening between the panel and the tee has been proposed in this dissertation to form a modified fillet joint design. Experimental results verified that the use of root opening improves the ability of DE-SAW to produce the required weld beads at reduced heat input and penetration capability. Unfortunately, the use of root opening decreases the stability of the process significantly. To control the heat input at a minimally necessary level that guarantees the weld size and meanwhile the process stability, a feedback is needed to control the currents at their desired levels. To this end, the fillet DE-SAW process is modeled and a multivariable predictive control algorithm is developed based on the process model. Major parameters including the root opening size, travel speed and heat input level have been selected/optimized/minimized to produce required fillet weld beads with a minimized heat input based on qualitative and quantitative analyses. At the end of this dissertation, a series of experiments validated the feasibility and repeatability of the predictive control based DE-SAW process for fillet joints with root opening