An unexpected shift of a trajectory during 90 degrees angle

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Mateusz_ABB
Mateusz_ABB ✭
in Robot Controller
When trying to make a 90 degrees turn with IRB 6700 robot, it makes weird jumps as if it begun to take a different route. We tried tracking paths with a pen and a plasma cutter and during both test the trajectory looked wrong in a similar way - with the wrong turns happening on 2 opposite sides out of 4 in a square (see a photo below). When MoveL and WaitTime are used the issue is much smaller but still noticable.  The robot was serviced by ABB and the 5th axis was replaced, it helped with the smoothness of movement but it didn't fix the problem. Additionally the circles aren't perfect either with jerking along the way in some parts.

 What may be the issue and how to solve this problem? Thank you in advance.
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  • lemster68
    lemster68 ✭✭✭
    Answer ✓
    I thought that the entire wrist was supposed to be replaced as an assembly whenever there was an issue with those axes.  Anyway, if you can safely activate the brake releases for axes 5 and six, move them by pushing them through their range of motions.  What you will be looking for is any feeling of crunching, grinding or spots where it becomes more difficult to move the axes.
    Next, are these motions very slow?  It might be necessary to change the motion mode in the motion planner.
    By the way, there is no picture.
    Lee Justice

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  • Mateusz_ABB
    Mateusz_ABB ✭
    edited July 11

    EDIT: I've learn that during the replacement of the wrist this check was done and the ABB provided servise couldn't solve my problem that way. However, as I said, it helped with the smoothness (there wasn't any difference of resistance when moving it by pushing) but it didn't affect the bug which was similar before and after.

    Thank you I will check that as soon as I'll be able to but in time before it, I'd like to add that when auxiliary point are added before and after the corner the problem is basically resolved but it isn't the solution that would be suitable for a normal use. Does it change anything? 

    Additionaly, when moving on a z-axis down, stopping and then up, the robot also makes this shift on the way up (it's the most noticable) 

    And yes I meant that the entire wrist was replaced but I meant that it was because of 5th axis. 

    Sorry, here's the image:
    (the upper right corner is expected (the starting point) and the lower left corner is also quite pretty but the upper left and lower right are problematic)



    Post edited by Mateusz_ABB on
  • lemster68
    lemster68 ✭✭✭
    Again, what are the programmed speeds?
    Lee Justice
  • Mateusz_ABB
    Mateusz_ABB ✭
    edited July 11
    I've tried both v200 and v1000 and some inbetween with overall 25% speed.
  • lemster68
    lemster68 ✭✭✭
    Oh, I assumed it would be much slower since you mentioned the plasma cutter.  Probably what you are seeing is backlash in the gearbox.  Observe the joint rotation direction when it does these motions.  What I want you to look for is a joint (or joints) reversing direction.  I am going to guess that they do not in the good corners and do reverse where you are seeing the jump.
    Lee Justice

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