Universal Robots Forum

Power Loss Safe Shutdown

We ran into in issue recently where our robot temporarily lost power while running a program. Upon coming back online the encoder on the elbow joint had lost its position and had to be re-zeroed before we could start production again. We are looking at adding some kind of safegaurd so that upon power loss the robot can initiate a safe stop and shutdown sequence. Has anyone here dealt with a similar issue and has anyone set up some kind of safe shutdown procedure before?


The encoder position should not have changed due to a power outage. CB3 and e-Series robots have true absolute encoders that do not depend on power to maintain positional information.

You should probably have your robot checked out by your distributor.


It could have been an issue with the way the robot was reading the encoder values as well. The positions on the elbow joint were shifted by 360 degrees so what had been 0 was being read as 360 making anything under 190 degrees inaccessible due to the joint trying to swing through the robot. After re-zeroing the joint we have yet to have any other issues.

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We had that exact same thing happen to a 10e in the field. Thankfully the 0/360 swap is easy to zero. Still no idea why it happened. Knew something was wrong when the elbow was trying to swing through the base joint.

Just had another one get unplugged accidentally in the field here. Everything was fine except for some reason the installation variables weren’t present any more.

We had an issue with a power outage/surge that fried one of the communication modules on our grippers. Since then we have added battery backup/surge protection to all our robots. The battery backup has a contact that we can monitor with the robot that triggers the robot to safely shutdown if we loose power and the backup drains to a set point. Additionally the battery backup lets the robot run for around 30 minutes unplugged and has an alarm when it looses line power. It’s saved us from more than one accidental unplugging.


Did you write a custom CAP to shutdown the robot or are you just tied in to a standard input?

Can also check digital input from the UPS and run this script command:

That’s fantastic. What UPS did you end up using? Our control boxes are inside another panel and space is a bit tight in there. Also most little industrial UPS’ seem to cap off around 600VA.

We are using CyberPower OL1000RTXL2U UPS. They are 1000 Va / 900W but they are not small (almost the same size as the controller just narrower).

I am monitoring the input and using the powerdown() script.at the end of the program so the robot finishes it cycle and shuts down in its safe Home position.

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That’s a great idea, I will use that idea myself.

Maybe add a short wait, in case it is just a brown out and power returns right away.