Motoman SSA2000 --defective encoder data "B" axis

[sheps0101]

Hello All!


I was wondering if anyone has experienced  a defective encoder data (the "B" axis) alarm with mototman ssa2000 robot (nx-100 controller)

I dont have the exact Alarm number handy but I will post it once I find it

I seem to experiance this problem frequently with these robots and am unsure of the root cause. I have tried replacing the "B" axis servo motor several times on different robots, the motor will work fine for several days/weeks and then the problem will re-occur.

Also the "B axis" and the "T axis" on these robots use the exact same servo motor, but I never have problems with the "T axis"!!??

As an interesting footnote when this alarm is present the encoder data is out by 4096 pulse counts (I think this might be one complete shaft revolution?) and if the absolute data for this axis is recalibrated (without replacing the motor) it will again work fine for several days/weeks without issues!!

any information on this subject would be much appreicated!! Thanks in advance!


This is my first post

[sheps0101]

Ooops! I almost forgot, we also use motoman EA1900 robots that use the same B and T axis servo motor as the SSA2000 and I have not yet had the defective encoder data alarm

[sheps0101]

Alarm number is #1326

[tony gast]

a long time ago in the early xrc days....I had a similar issue......

I had to put the arm (on a couple of robots) in some very contorted positions......

It actually caused some wire chafing to the internal wire harness  (to the encoded wiring, and caused intermittent shorts) at the area where the wire harness was entering the the rear of the r axis......
I added a tie strap and a piece of thin rubber around the harness and the problem was solved

[sheps0101]

Thanks tonygast for your prompt reply, I will try and examine some of these internal wiring harnesses the next time the line is down.  Originally I didn't believe it could be a wiring issue simply because it appeared on multiple robots and all the same axis, but these robots are taught to some pretty "contorted" positions and move at a very high rate of speed!

I will post any results found!

[Robo Guru]

4096 is 1 complete revolution for NX encoders

Noise can cause this problem... so can a bad encoder.

Are you installing a new motor from Motoman???

RoboGuru

[sheps0101]

RoboGuru:

I have already ordered a new motor from motoman and installed it. Problem is still present (intermittent but present)

These robots have a welding whip/power cable ontop of the arm which could cause noise, do you think that could be the issue?  These cables are basically integrated into the robot though from the factory so it would be unfortunate if that was the issue.

thanks for your reply!

[Robo Guru]

I highly doubt it.  There are thousands upon thousands of welding robots out their.... and the whip cable is very well insulated.

[jax.]

Try looking at the pins on the plugs/sockets of 1BC & 2BC connectors as I have had exactly the same fault but with XRC.

[Industrialrobotix]

We have seen a lot of communication issues w/ MRC and XRC robots we have gotten in...many times it is a harness problem - whether you have worn through or just connection issues....I am not a big fan of the internal connectors that the older Motoman robots have on their harnesses...seems that they worked loose or corroded and caused various tracking / communication errors....not sure about the NX robots - havent had one apart yet...but being it is an intermittent problem, it could be harness/connection related...