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You see, the problem comes at random time, but I am sure it always arrives. And it is not very easy to repeat it, as it only comes after more than 30+ cycles.

It is a simple Pick’n’Place operation, where product is picked form a conveyor (static), placed on a laser and later placed on another conveyor for further processing. Problem is that over some cycles, the robot deviates form the waypoint coordinates and eventually will not pick up product from the conveyor, and then problem escalates till it feeds up empty laser and later on second conveyor has an empty shuttle and finally AOI (automatic optical interface) fails to pass a step as the shuttle is empty (I know I know, there should be some detection upon picking up the product, but this is not the biggest problem now). What I have seen is that X an Y coordinates are the problem here, and usually after these events I have to readjust all the Waypints (total of 8). The same thing happens after emergency stop or force related stop, where robot remains in active mechanical brakes (this I could understand as these are emergency related actions, those should be stopped immediately no matter what, with this event the difference is even worse – bigger, could be up to 5mm). Still after resuming a movement is detected (as if it is looking for a home point).

I have tried to investigate this, what is odd to me:

  • I have written down the coordinates of waypoints – after these events when I want to go to these waypoints (Move to Waypint -> Auto), I can see, that the numbers are the same (or a bit different, but 3rd digit after comma is nothing), but in the real life it could be several mm, even up to 5mm. As I have Pnemuatic double acting gripper, it couses robot not to pick up product or piking it up with sideways-forced movement and eventually with an error because the sideways resisitive force is too high and it has reached robot safety force limit.

Question 1 – is it possible, that over time, physical points deviates form the software saved XYZ? Couse this is what is happening here.

Question 2 – how to avoid this as this way robot can not be used independantly.