Railway carriages welded faster and more accurately using robot vision systems

Citation

(2001), "Railway carriages welded faster and more accurately using robot vision systems", Industrial Robot, Vol. 28 No. 4. https://doi.org/10.1108/ir.2001.04928daf.007

Railway carriages welded faster and more accurately using robot vision systems

Railway carriages welded faster and more accurately using robot vision systems

Keywords: Robots, Welding, Machine vision

Laser-based robot guidance equipment from a British company, Meta Vision Systems, is helping China's largest railway carriage manufacturer, Changchun Car Company, to produce more consistent welds in shorter cycle times (see Plate 3). With more than 1,000 overground and metro carriages produced annually – accounting for over half the total national output – the scope for savings is considerable.

Plate 3 Automated robotic welding of a railway carriage roof in progress at Changchun Car Company, China. Meta laser vision systems position the robots, resulting in top quality welds

Specifically it is the welding of the carriage roof which has been automated. A Meta Laser Pilot seam finding and tracking system has been fitted to each of two Cloos six-axis robots, one acting as a master and the other as a slave. The robots are inverted on a gantry which itself can rotate by 180 degrees, providing a very flexible automated welding facility with two working stations.

Before each weld starts, the respective sensors search independently for the longitudinal seams either side of the roof. The weld start positions are located unerringly even if the seams are initially outside the sensor's field of view.

Once the MIG guns are locked on, the sheet steel is welded automatically by the two robots working synchronously along the 25-metre carriages. A total of 17 cross joints are subsequently welded individually. All are lap joints, welded at 60cm/min using a single wire. The Meta laser sensors keep the robot-mounted guns continuously on the seams, resulting in accurate, repeatable, high quality welds.

Benefits of automatic seam finding and tracking are many. Workpiece positioning is not a problem, despite the use of simple fixtures. The robots do not have to be reprogrammed for each new part. Additionally, the system can cope with relatively wide seam deviation, particularly across the carriage roof.

The Meta Laser Pilot is mounted on each robot arm ahead of the weld gun. As well as incorporating laser seam finding, the microprocessor-based system is capable of keeping weld bead deposition on track at speeds up to 4m/min, compensating for any deviation to the pre-programmed path by feeding back offsets directly to the robot controller. Easy to use with minimal training, the system has no moving parts and is said to be faster and more reliable than touch sensing. High-speed tracking at up to 25m/min is also available.

For further information, contact Dr Andrew Pryce, Sales and Marketing Director, Meta Vision Systems Ltd, Oakfield House, Oakfield Industrial Estate, Eynsham, Oxfordshire OX8 1TH, UK. Tel: +44 (0)1865 887900; Fax: +44 (0)1865 887901; E-mail: sales@meta-mvs.com