Guilherme Caribé de Carvalho

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.

A specialized robotic system prototype for repairing surface profiles of hydraulic turbine blades

This article presents the steps of an ongoing R&D project aiming at designing and constructing a prototype of a specialized welding robotic system for repairing the surface of hydraulic turbine blades eroded by cavitation pitting and/or cracked by cyclic loading, reducing human risks and increasing the efficiency of the process. The robotic system has a spherical topology with 5 d.o.f., electric stepper and DC servo motors. The system has an embedded vision sensor built to produce range images by scanning laser beams on the blade surface and to construct 3-D models to 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 prototype is at final stages to be fully operational, with some remaining procedures such as computer systems integration and calibration for final tests and commissioning.

Telerobotics: methodology for the development of through-the-Internet robotic teleoperated system

This work presents a methodology for the development of Teleoperated Robotic System through Internet. Initially, it is presented a bibliographical review of the telerobotic systems that uses Internet as way of control. The methodology is implemented and tested through the development of two systems. The first is a manipulator with two degrees of freedom commanded remotely through Internet denominated RobWebCam. The second is a system which teleoperates an ABB (Asea Brown Boveri) Industrial Robot of six degrees of freedom denominated RobWebLink.

Telerobotics : Through-the-Internet teleoperation of the ABB IRB 2000 industrial robot

Robotic systems can be controlled remotely through the use of telerobotics. This work presents a through-the-internet teleoperation system for remotely operating the IRB2000 industrial robot. The IRB2000 controller allows external access through a RS232 serial communication link, which is based on a 42 function proprietary communication protocol. The proposed teleoperation system uses this communication capability by connecting it to a local area network based on TCP/IP (Transport Control Protocol/Internet Protocol). The system was implemented using a Client/Server architecture, having as server a UNIX (LINUX) platform.

Analysis of weld pool oscillation in GMAW-P by means of shadowgraphy image processing

This paper presents a methodology for studying weld pool oscillation by measuring its oscillation frequencies using both the welding voltage signal and analysis of weld pool profile images. The intense brightness from the arc is reduced using the technique of shadowgraphy, and the images are obtained at 1000 fps with a high-speed CMOS camera. The geometry of the pool is viewed in profile and frequency spectra are obtained by fast Fourier transform by processing the images in MATLAB. The methodology was applied to analyse the oscillatory behaviour of the weld pool resulting from a pulsed gas metal arc welding process. Two different types of welding current pulse were tested: (a) the conventional trapezoidal pulse (with only one level of peak current) and (b) the trapezoidal pulse with the ‘detaching current’ (the welding current has a modified trapezoidal shape in which, at the end of the peak current time, the welding current is reduced to an intermediary level where it is maintained some time, after which it is further reduced to the background current level). The results show that it is possible to measure oscillation of the weld pool using this methodology, and that its measurement by images is more reliable than analysis of the voltage signal.

Transferência de calor aplicada à prototipagem rápida por deposição de metal em camadas sucessivas utilizando soldagem 3D

This work presents a study on the heat transfer phenomena that occur during the process of Rapid Prototyping by layered arc welding metal deposition, also called, 3D Welding. The main goal is to understand the heat transfer process and its relations with the welding parameters, in order to enable a control of the thermal cycles that the deposited material shall be subjected to. A numerical model is developed using the finite difference method to analyze the heat transfer, in order to allow the simulation of certain situations. The numerical model was validated by means of simulating specific cases for which analytical solutions are available. From the theoretical model equations, some dimensionless numbers were defined, among which the so called π1 number, mainly related to the welding speed. Some numerical experiments were carried out in order to allow the observation of its influence on the average and peak temperatures and also on the amplitudes of the thermal cycles which the part is subject to.

Heat transfer applied to rapid prototyping by metal deposition in successive layers using 3D welding

This article presents a study on heat transfer phenomena in the process of rapid prototyping by metal deposition in successive layers using arc welding, also called 3D welding. The main goal is to develop a simplified model and understand the heat transfer process and its relations with the welding parameters, in order to enable a control of the thermal cycles that the deposited material will be subjected to. The numerical model was validated by means of simulating specific cases for which analytical solutions are available. From the equations of the model, dimensionless parameters were defined, among which the so-called π1 dimensionless group can be cited, mainly related to welding speed. Some numerical experiments were carried out to observe the influence of this group on the maximum and mean temperatures, and on the amplitudes of the thermal cycles to which the piece is subjected.