Accuracy of synchronized track

Anders Gallon

Hello,

 

I'm having some problems with an IRB6400 (S4C) that sits on top of a T6002.

 

In short, the accuracy of robot + track is within 1mm if I approach the same world-point from any point on the track. But only if the track is stationary at the time.

 

If I do the opposite and move the track while holding the TCP stationary at a certain world-point, the TCP will move as far as 4mm out of it's correct position while the track moves, and then return to the right place once the track stops moving.

 

While the track accelerates, the TCP moves in the opposite direction of the track. Depending on the speed of the track, the error can get as high as 4mm.

 

Once the track is moving at a constant velocity, the TCP stays at the (wrong) position it reached during acceleration of the track.

 

When the track stops, the error of the TCP gets smaller and smaller until the track has completely stopped moving. Then the TCP is once again at the correct place.

 

What I have done so far is to change a few parameters in the lag control master for the track:

 

- I have set the feed forward control to velocity instead of position. Before that, the error was even higher.

 

- I have tried various values for KP, ranging between 10 and 18 (originally 14). The difference is that higher values yields a slightly better accuracy during movement, but instead seems to lead to slight jitters and overshoots when the track stops.

 

I realise that using torque for the feed forward control would perhaps be better, but I don't know how to tune all variables.

 

Do you know if the precision of a synchronized track motion with an IRB6400 and a T6002 should be better than what I'm seeing, and if so, could you please point me in the right direction to tune the track accordingly?

 

Unfortunately we don't have ethernet on the robot, so TuneMaster can't be used.

 

Thank's in advance!

 

Anders Gallon

Henrik Berlin

Moved to RobotWare forum