IRB 140 Axis 6 *Solved*

[King_Kingston]

I am having an issue on an IRB140 with axis 6.  When the robot sits for the weekend, and 3rd shift comes in on Sunday night to begin running, the first few cycles will error out.  The errors are 50055, joint load too high and 50204, motion supervision.  After running a few cycles, the errors go away.

More recently, the robot will throw errors when the line goes to their break, which is twenty minutes and ten minutes.  But again, after running a few cycles it takes off with no further issue.

The wrist was removed today from the robot and checked for binding, but it felt free.  The brake release was engaged as well and the motor turned freely.  

At this point we suspect the motor brake for axis 6 could be sticking initially, and after running a few cycles, the brake "releases."

We've hit a little bit of a wall.  An idea was thrown around to change out the motor for axis six or just change out the robot.  The latter I would rather not do.  Does this sound like a motor brake issue?  Any feedback or possible further course of action would be appreciated.  Thanks!  

[prnuk2003]

Could be worth looking at the brake release contactor K44 (should be on the side wall, check your cabinet drawings). Occasionally these get a high resistance across the contacts that sometimes will clear after a few on/off attempts.
The system applies the breaks after a period of inactivity (3 minutes for example) which could explane the problems after the robot is started again after the workers return from their break.
If you check for 24v at terminal 4 on the contactor when is brake relay is on the off a few times the fault may appear as a no voltage or a very low voltage intermittently.
Axis 6 normally sees it first as it has very little torque compared thus more sensitive compared to the others and also depending on what axis rotates when moving from the home pos.

[King_Kingston]

Thanks prunk.  We did get a reply from ABB and they asked us to up the motion supervision values on the flex pendant.  According to him, this is something that he would like us to try to help narrow down what may be causing the issue.  What he is trying to help us narrow down may be exactly what you have mentioned.  I'll give it a whirl.  Thanks again. 

[TygerDawg]

Has there been a crash?  Wrist joints are the weakest link, especially on small arms.  I had similar experience with another brand.  Crashed the wrist, and the internal gears got dinked.  It didn't take much to create a high-torque condition, which the controller sensed and shut down the arm.  The motor was OK, but the gear train wasn't happy.

[King_Kingston]

Here are some of the descriptions of events that have occurred the last few days.  I have been told a little more about the behavior of the robot, which is more than what I had been originally told.  There have been a few small collisions that I was not aware of. 

Note - The original wrist has been changed out, but the issue is still persisting.  Anyway....

Yesterday we changed the motion supervision value from 100 to 200 and had the same issue at start up this morning.  The issue is happening between 2 points (move L) that only change in the x and z direction.  When it collides with the fixture, it appears to be off path in the y direction.

The brake contactor (K44) was checked after the advice from prunk.  It made sense to check it, and I was hoping that was the cause.  But....

This morning I checked the voltage at the contactor while a tech held the deadman in and turned on the motors,  there was 25V on wires 490 and 447/448.  I then put the meter probe on the 447/448 while he started it in auto and had 25V again, but the robot still hit the pick up plate.

Again, this is only happening on "start up."  In other words, it's only after the line has either went to break and come back or if the line is down between 2nd and 1st shift.  After the first cycle has been completed, it does not happen again, until the next stoppage. 

I wanna smash my face.  Oh, here we go.... 

[prnuk2003]

Write a routine with 13 absj moves in it. First absj all  axis 1 to 6 are at 0 degrees. 2nd absj azis 1 only to +45 degrees. 3rd absj all at 0. 4th absj axis 2 to 30 degrees etc etc. Only one axis moves at any one tome. Finally put a wait time of 240 seconds (long enough for the brake relay to drop out).
Run the routing continuously in auto or in manual without releasing the DMH to see if the fault is the common brake feed or maybe a sticking brake on axis 6.
The degrees of movement for each axis you must decide as you can see the safe working range of your robot.
Hope that makes sense.

[King_Kingston]

Thanks again prunk.  The ABB tech suggested changing out the harness, and I would rather not do that at this time until a few more things are tried and the harness is the last option. 

I like where you are coming from with isolating each axis and holding it long enough for the brake relay to drop out.  It's as if you've done this kind of stuff before.  Haha!   

I'll update again when I get more info.  Thanks.

[King_Kingston]

After heeding prunk's most recent advice by writing a program with 13 absj moves in it, we have narrowed the fault down to axis 6.  I does seem to be something related to the brake for the axis six motor and not the entire brake release contactor as this is the only axis that will fault out when executing the 13 absj move program.

One thing of note however.  It does seem that when we decrease the speed of each move, specifically axis six, the error does not appear.  Could this be because the brake for the axis six motor is going bad, and we only see the joint load error when moving at a higher speed?  In other words, by moving slower, am I giving the brake more time to release as to not cause a joint load error?  I mean, it makes sense to me, but I'm still a bit of a rookie at this stuff.

[prnuk2003]

Do you have any other robot that you could compare against if you manually release the brake and move axis 6?
Could be that the breake is partially releasing or not at all (load error when partially releasing, motion supervision when not released at all)

[King_Kingston]

Well, the decision has been made, from the powers that are way above me, to change out the axis six motor.  Everything that we could exhaust has been exhausted.  I've been asked to come in tomorrow morning (I work second shift) and change out the motor in between third and first shift.  I've done motors before, but never axis six.  This will be educational to say the least.  I'll let you know what is found!  Thanks for the feedback on this one, especially prunk.  The 13absj move routine is solid.  We've used it on a few other robots to isolate issues.  Thank you sir. 

[King_Kingston]

The motor was changed out successfully and after sitting for about three hours after changing it, it was run again with no further issues.  Four months later.... ha! 

We "pre-leveled" the robot before changing the motor and then after changing the motor, we drove axis 5 and 6 back to the pre-leveled positions.  That was a huge time saver.  Thanks again for everybody's input.  I have a few more issues with robots currently, and I know I'll be using this forum again.