Sadek Crisóstomo Absi Alfaro

Predictive sensor guided robotic manipulators in automated welding cells

Abstract This paper presents an on-line tracking optimization scheme for sensor guided robotic manipulators by associating sensor information, manipulator dynamics and a path generator model. Feedback linearization-decoupling permits the use of linear SISO prediction models for the dynamics of each robot joint. Scene interpretation of CCD-camera images generates spline fitted segments of future trajectory. In the sensor vision field the proposed optimization criteria minimizes the error between state variables of the prediction model and the state variables of the spline trajectory generator. These techniques, allied with separation of disturbance rejection and path-tracking performance by the proposed feed-forward following model predictive (FMP) servo-controller design, permits very high path tracking dynamics (and consequently small errors). Experimental results on implementation of a CCD-camera guided hydraulic robot and a welding robot demonstrates the practical relevance of the proposed approach.

A Non-Intrusive GMA Welding Process Quality Monitoring System Using Acoustic Sensing.

Most of the inspection methods used for detection and localization of welding disturbances are based on the evaluation of some direct measurements of welding parameters. This direct measurement requires an insertion of sensors during the welding process which could somehow alter the behavior of the metallic transference. An inspection method that evaluates the GMA welding process evolution using a non-intrusive process sensing would allow not only the identification of disturbances during welding runs and thus reduce inspection time, but would also reduce the interference on the process caused by the direct sensing. In this paper a nonintrusive method for weld disturbance detection and localization for weld quality evaluation is demonstrated. The system is based on the acoustic sensing of the welding electrical arc. During repetitive tests in welds without disturbances, the stability acoustic parameters were calculated and used as comparison references for the detection and location of disturbances during the weld runs.

A novel framework to link Prognostics and Health Management and Product-Service Systems using online simulation

Product-Service Systems (PSS) and Prognostics and Health Management (PHM) have so far been researched individually in different domains and as unrelated research theme. However, to guarantee the availability of the asset, which is a typical demand in some PSS contracts, it is fundamental for PSS providers to be able to properly manage the assets lifetime variability in order to avoid unscheduled downtimes and contract penalties. This paper describes part of a research project to investigate how PHM can support more effective fulfilment of some PSS contracts. In particular, this paper aims to present a novel framework to link PHM and PSS using online simulation. The paper also presents a prototype of the online simulation model and three experimental cases comparing the outcomes of the online simulation model against those obtained from the traditional simulation model.

A weld defects detection system based on a spectrometer

Improved product quality and production methods, and decreased production costs are important objectives of industries. Welding processes are part of this goal. There are many studies about monitoring and controlling welding process. This work presents a non-intrusive on-line monitoriment system and some algorithms capable of detecting GTAW weld defects. Some experiments were made to simulate weld defects by disturbing the electric arc. The data comes from a spectrometer which captures perturbations on the electric arc by the radiation emission of chosen lines. Algorithms based on change detection methods are used to indicate the presence and localization of those defects.

Intelligent Systems for Welding Process Automation

This paper presents and evaluates the concept and implementation of two distinct multi-sensor systems for the automated manufacturing based on parallel hardware. In the most sophisticated implementation, 12 processors had been integrated in a parallel multi-sensor system. Some specialized nodes implement an Artificial Neural Network, used to improve photogrammetry-based computer vision, and Fuzzy Logic supervision of the sensor fusion. Trough the implementation of distributed and intelligent processing units, it was shown that parallel architectures can provide significant advantages compared to conventional bus-based systems. The paper concludes with the comparison of the main aspects of the transputer and the DSP-based implementation of sensor guided robots.

Sensoring Fusion Data from the Optic and Acoustic Emissions of Electric Arcs in the GMAW-S Process for Welding Quality Assessment

The present study shows the relationship between welding quality and optical-acoustic emissions from electric arcs, during welding runs, in the GMAW-S process. Bead on plate welding tests was carried out with pre-set parameters chosen from manufacturing standards. During the welding runs interferences were induced on the welding path using paint, grease or gas faults. In each welding run arc voltage, welding current, infrared and acoustic emission values were acquired and parameters such as arc power, acoustic peaks rate and infrared radiation rate computed. Data fusion algorithms were developed by assessing known welding quality parameters from arc emissions. These algorithms have showed better responses when they are based on more than just one sensor. Finally, it was concluded that there is a close relation between arc emissions and quality in welding and it can be measured from arc emissions sensing and data fusion algorithms.

An adaptive scheme for chaotic synchronization in the presence of uncertain parameter and disturbances

Recently, several schemes have been proposed in the literature to synchronize chaotic systems. However, in most of these approaches, the presence of uncertain parameters and external disturbances were not considered. Motivated by the above consideration, this paper proposes an adaptive methodology to synchronize any chaotic system with unified chaotic systems, even if bounded disturbances are present. The proposed controller is composed of both variable proportional and adaptive control actions for guaranteeing the convergence of the residual synchronization error to zero in the presence of disturbances. Two possible modifications are considered: 1) only adaptive control action is implemented to overcome the well-known assumption of prior knowledge of upper bounds to compensate for the disturbances, and 2) the control gain of the proportional part is saturated, when the residual synchronization error has, practically, been removed. Lyapunov theory, in combination with Barbalats Lemma, is used to design the proposed controller. Experimental simulations are provided to show the effectiveness of the proposed controller and its advantages, when compared with a recent work in the literature.

Exploring Infrared Sensoring for Real Time Welding Defects Monitoring in GTAW

This paper presents an evaluation of an infrared sensor for monitoring the welding pool temperature in a Gas Tungsten Arc Welding (GTAW) process. The purpose of the study is to develop a real time system control. It is known that the arc welding pool temperature is related to the weld penetration depth; therefore, by monitoring the temperature, the arc pool temperature and penetration depth are also monitored. Various experiments were performed; in some of them the current was varied and the temperature changes were registered, in others, defects were induced throughout the path of the weld bead for a fixed current. These simulated defects resulted in abrupt changes in the average temperature values, thus providing an indication of the presence of a defect. The data has been registered with an acquisition card. To identify defects in the samples under infrared emissions, the timing series were analyzed through graphics and statistic methods. The selection of this technique demonstrates the potential for infrared emission as a welding monitoring parameter sensor.

Computer based data acquisition for welding research and production

Abstract In view of the needs of todays advances welding techniques it is necessary to have the disposal of an accurate, fast and reliable measuring and control system to understand what is going on during the welding process. Since PC data acquisition and control units have become more cost-attractive and programming has become much easier, this kind of system offers a serious possibility for achieving the required features. Arc welding in general is, form a physical point of view, a fairly complex process. The arc is not only defined by the physical properties as a function of the temperature of the elements involved in the arc plasma area but also by the electrical characteristics of the power source. In order to be able to investigate the backgrounds of these power source influences it is necessary to have a measuring and control system. The benefit of using such a system is that differences in the welding behaviour of more or less similar power sources can be studied closer and more consistently. Afterwards, it may even be possible to draw conclusions to explain the different behaviour of these power sources and eventually the power source might even be controlled by such a system. Computers are now used in many areas of welding related research and their application has allowed substantial progress to be made in the analysis of process behaviour, the optimisation of welding parameters and the prediction of reliable welding procedures. Recent developments include the availability of cost effective computer based hardware for data acquisition, and software specifically designed for welding process analysis. The techniques originally developed for research have also been adapted for quality assurance and adaptive control in production. This paper describes some of recent data acquisition developments and indicates the likely trends for future development in this area.

A prototype of a specialized robotic system for repairing hydraulic turbine blades

This article presents an ongoing R&D project aiming at designing and constructing a specialized welding robotic system for repairing hydraulic turbine blades eroded by cavitation pitting, reducing human risks and increasing the efficiency of the process. The robotic system has a spherical topology with 5 degrees of freedom, electric stepper motors and a 2.5m-diameter workspace. The system has an embedded measurement system with a vision sensor built to produce range images by scanning laser beams on the blade surface. The range images are used to construct 3-D models of the blade surface and locate the damaged spots to be recorded into the robot controller in 3-D coordinates, enabling the robot to repair the flaws automatically by welding in layers. The robot controller and measurement system are built in an FPGA based reconfigurable system. The welding process is the GMAW with a tubular metal cored electrode with a pulsed GMA welding machine.