Product category:
Seam-tracking, guidance systems
News Release from: Meta Vision Systems | Subject: Laser Pilot MTR
Edited by the Manufacturingtalk Editorial
Team on 05 July 2001
Adaptive control of welding at
Caterpillar
Caterpillar's factory at East Peoria, Illinois, has around 35 operational vision systems in robot welding applications, the majority equipped with Meta Vision Systems sensors
Off-highway vehicle specialist, Caterpillar Inc, has been one of the largest users of arc welding technology in the world for many years Over the last two decades there has been a progressive shift away from manual welding to automated welding using robots, many of which are equipped with automated seam tracking supplied by Meta Vision Systems
This article was originally published on Manufacturingtalk on 14 Jul 2000 at 8.00am (UK)
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The reasons for this include better weld quality, higher productivity, lower production costs, less environmental impact and the need to combat a shortage of skilled manual welders.
A major consideration throughout for Caterpillar has been the control of the welding process.
Although modern profile cutting techniques such as laser and high definition plasma allow flat plate sections to be cut to very good levels of accuracy, there is nearly always some minor variation which needs to be compensated for at the welding stage.
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In addition, there is a requirement to join plate to castings as part of the fabrication process using groove and fillet welds, and it is therefore necessary to compensate for the fit-up variation that inevitably results.
The requirement here is not simply to ensure that the welding torch tracks the joint, but also to ensure that the joint is properly filled using the required number of passes of the welding torch.
Especially on plates-to-casting welds, this is not easy to achieve as the nature of castings is such that no two will behave in a similar manner.
As well as basic dimensional variation, reaction due to thermal distortion induced by the welding process itself can change from part to part.
Since the 1980s, Caterpillar has addressed the problem through the use of increasingly sophisticated vision sensing systems with the aim of developing a fully adaptive welding process.
At first Caterpillar developed these in-house, but towards the end of the 1980s it began to buy commercially produced systems as part of integrated robot welding packages.
One of the main suppliers of these systems was UK-based Meta Vision Systems, which through its North American subsidiary, Meta Vision Systems Inc of Quebec, Canada, continues to support these original installations and others made subsequently, although Caterpillar also has in-house maintenance facilities.
Today, Caterpillar's factory at East Peoria, Illinois, has around 35 operational vision systems in robot welding applications.
A majority is equipped with Meta sensors, some of which are still operating successfully after 11 years of continuous use.
The latest generation of welding robots are equipped with camera-based seam tracking systems supplied by Meta.
They have superseded older robots equipped with through-arc joint tracking, an unsatisfactory open-loop means of control which uses arc current and weaving to locate the joint.
The most recent Meta Laser Pilot MTR uses diodes to project a laser stripe onto the weld joint.
A filter blocks out most of the light coming from the working area including the welding arc but excluding the reflected laser frequency, allowing the stripe to be scanned by a CCD camera.
Image processing software takes the information gathered by the camera and automatically adapts the welding torch position and welding parameters.
Moreover it can do this rapidly at welding speeds up to 4 metres/minute, while the field of view of the scanning system is up to 60 mm, allowing it to compensate for considerable seam path variations.
The benefit for Caterpillar is a much higher degree of adaptive control of the welding process, ensuring right-first-time welding in the majority of situations.
More recently, Meta has built on its success in Caterpilar with the installation two years ago of several robotic welding vision systems in Brazil.
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