RX60B: *Duty-cycle exceeded* Mtr n (–1021)

[Davros]

Hi All
We are running a RX60B with CS7MB. We are starting to see this error more and more only at one particular position. In the docu, it says:

Explanation: The indicated motor has been driven fast for too long a period of time.
The servo system has disabled Arm Power to protect the robot hardware.

User action: Turn on Arm Power; reduce the speed and/or acceleration for the motion
that was in progress, or for motions that preceded that motion; and repeat
the motion that failed.

Has anyone seen this problem before and can give a hint as to where the issue is ? The robot program has been running OK for years.
Thanks !

[TygerDawg]

The robot program has been running OK for years.

They don't last forever.  The RX60 motors were always very weak, the wrist mechanics were delicate, and besides the CS7B is obsolete.  I'd guess the motor or gearing is getting sticky and requiring more current to drive at the programmed speed.  More current = more heat.  System is reading the thermistors/thermocouples and shutting down to protect itself from burnout.

I'd guess that the short term solution is to replace the motor or gearing and / or slow down the application.  Long term:  It's time to upgrade.

[Davros]

Thanks TygerDawg. I know they don't last forever, I just mentioned that the program had been running ok for years so people new that the software was stable. I took your advice as a short term solution and reduced the speed for that one move, seems to have helped. This robot must have taken a hit some time ago as there is alot of backlash in axis 4. Long term I'll replace the robot with our spare RX60B and get this one refurbished by Staubli. Thanks again.

[TygerDawg]

hmmm...I vaguely remember J4 was driven by a servo motor driving a timing belt that required a very tricky tensioning adjustment.  Maybe that arrangement is showing its age.

[Juggernaut]

That could be a friction/lubrication issue.  Envelope errors and stalls typically come from broken gearing, jams, etc.  Duty cycle errors describe more subtle problems with keeping.  The RX60 was the Swiss Watch, but it was also very delicate in the areas of joints 4, 5, and 6 said. 

With that said, it is probably repairable.  You might want to pull the belt cover off and feel the resistance of the gearing.  They should be easy to spin with your fingers or pulling on the belt. 

[Jim C]

There is a not to exceed peak, current limit on the motors and a lower current limit for extended operation. I think you are see the latter. It could be several things. I'd start by checking your incoming voltage. If it is low on any phase, that can cause all sorts of problems including current issues. If that is OK, it could be an amplifier. It could also be a motor or the joint itself.