Setup time optimisation and quick maintenance following a crash

Automotive engineering Underbody protection

The calibration time and the setup times for multiple robot portals need to be reduced.

Setup time optimisation and quick maintenance following a crash

Cell description

The customer operates multiple XY portals with Motoman HP20 robots and NX100 controllers. These are used for welding the steel frames required to build scaffolding and employ a MIG/MAG welding procedure. The frames are clamped onto jigs and these are pinned onto a positioner in the robot cell.

Task definition

The original task was to develop a procedure so that the robot and the portal axes could be mastered quickly and automatically. The customer's robots crash relatively often, with the result that the mastering of the robot or the portal axes is no longer correct. The subsequent calibration with the electronic measuring sensor supplied by Motoman takes 1-2 hours. Our task was to reduce this time significantly.

The second task we were assigned was to reduce the setup times. The jigs measure 2.5 m x 1.5 m and are lifted into the positioner with a forklift. The pinning of the jigs is relatively imprecise, however, so when the jig was changed, the robot program always shifted and had to undergo re-teaching. The smaller the lot size of the manufactured parts, the more important it was to optimise the setup time.

Implementation

A base plate was attached to a pillar of the portal and the LaserLAB flange-mounted onto it. A measuring rod with measuring ball was screwed onto the welding torch instead of the contact tip. The measuring rod was configured so that the central point of the measuring ball corresponded to the working point of the welding wire (TCP). With the LaserLAB and the loop:in software, all the robot axes and the axes of the XY portal were now controlled automatically so that the measuring ball always remained in the centre of the LaserLAB. This provided about 30 measurements from which the optimal values for the robot mastering were obtained.

The second step was to put 4 mating bores in the jig to hold the measuring rods. The robots are fitted with a quick-change system. The welding torch can be removed quickly and a holder for the LaserLAB inserted in its place. Using a taught-in robot program, the 4 measuring rods are now measured with the robot and the LaserLAB. The measurement produces the "user coordinate system" which is transferred directly to the robot. The accuracy with which the new position of the jig was measured was to within a maximum of 0.4 mm.

Customer benefit

Following a crash or if the robot needs to be checked, the customer is now able to master all 6 axes of the robot and the two portal axes within only 20 minutes. A climbing aid to reach the portal axes is no longer required.

When a jig is changed, the new jig is measured quickly and accurately with the robot and the LaserLAB so that no re-teaching is necessary.

LaserLAB is so easy to operate that the customer is gradually able to carry out the measuring of his jigs himself.