18-07-2012, 04:40 PM
SEAM TRACKING FOR AUTOMATED WELDING MACHINES
SEAM TRACKING FOR AUTOMATED WELDING MACHINES.pptx (Size: 847.42 KB / Downloads: 57)
INTRODUCTION
Since the early 1980s, laser welding has developed from a tool only used for exotic applications into a full-fledged part of the metalworking industry. Nowadays innumerable laser welds are produced for a variety of common products such as cigarette lighters, razor blades, pacemakers and car parts. A bundle of laser light is focused onto a weld joint, which makes the material heat up and melt locally, resulting in a weld. The well controllable heat input, the small heat affected zone and the high welding speeds result in a fast production of high quality welds, which is the main benefit of laser welding over conventional welding techniques.
The small heat affected zone and the high welding speeds however, also result in very tight tolerances on the accuracy of positioning the weld spot on the seam. Especially when a robot is needed to carry the welding optics along complex geometries, it becomes difficult to assure accurate positioning. Therefore it is important to have a system that detects the position of the seam with respect to the robot. Using the data provided by such a system the robot can be trained to track the seam accurately, before the actual welding starts.
NEED FOR LASER SEAM TRACKING
Automatic welding uses welding machines to make welds automatically, in most cases without direct operator control. Welding machines normally execute fairly simple 3D trajectories, often straight line or circular paths.
However, without sensing, these weld paths are relative to the machine itself. Ideally, the correct weld trajectory should be relative to the parts to be welded. This is where laser seam tracking comes in. By sensing the actual joint, the laser seam tracking system corrects the weld path to follow the true path of the joint rather than a nominal weld path.
SYSTEM DESCRIPTION
The overall seam tracking system is composed of a laser line generator, an industrial welding vehicle, an industrial control computer, an industrial digital CCD camera, an electric welding machine and some other welding related devices.
The digital CCD camera is mounted on a bracket where the torch is attached. And the optical axis of the camera is perpendicular to the planar surface of the work piece.
Before welding, the torch is set to the adequate position manually. The digital camera captures image of the welding seam and transfers it to the industrial control computer.
The reference feature point is determined at the beginning of the welding. To obtain a robust result, the first group of N captured images are employed to do this job.
After that, the welding vehicle moves along its orbit, and the captured image is processed in real-time.
The industrial computer sends out control signals to the stepper motor through parallel port to align the torch along the seam according to the output of the torch adjusting algorithm.
ADVANTAGES
Benefits from the ability to follow the true weld path rather than a nominal path include:
Better weld quality. Laser based seam tracking provides optimum welding penetration to ensure welding quality meets international requirements.
Reduced defect rate.
Reduced rework/scrap.
Improved weld cosmetic appearance.
Reduced cost of fixtures and fittings.
Reduced need to touch up robot paths.
Reduced manning power.
Reduced rate of weld defects.
Simplification of machine design and build.
Improved productivity.
User-friendly and safe.