Sudden Machine Stop

Yep. Put an alarm on every device that could operate to trip the motors off. Then, when the device operates, determining which one will be as simple as falling off a log.

Will figure out which devices and how to put that alarm on. We already inspected all cables and shielding from loadcells (used to measure tension) but did not find anything yet. Thanks for the input!

I'm sure 85% of statistics are made up on the spot

Finding and fixing the problem requires a skill commonly known as troubleshooting. Frequently the "hung" state of the PLC can be observed to determine which feedback signal did not occur as expected. Many maintenance technicians are experienced troubleshooters.

Thanks for the suggestion to try to observe the feedback signals. We got excellent technicians in from PLC-manufacturer but they also could not identify root-cause yet.

Can you say STUXNET ?

STUXNET very unlikely as machine has been running without any problems for three years. A WINDOWS-based laptop was only connected to the PLC after the problem started. Thanks for the suggestion.

Can you provide more detailed information. For example are there any alarms or indications that may lead you possibilities of the problem area. Are you able to look at the PLC code? if so identify the components that would cause the machine to stop.

As a reference I always use latches in my shut down circuits. in other words, any component that is used to control the stop function has a latch programed to its input and a master reset. When the machine stops you will be able to go to the source problem quickly. I find this very helpful when trouble shooting.

(a couple of hints to problem solving) When troubleshooting I always look for the obvious first (alarms) . Identify the circuits of possible causes, identify the components involved. then look for missing signals.

lastly (probably most important) KNOW! the sequence of operation.

Good luck!

Are these motors moving on an axis? If so, observe the position when problem occurs.

Good control cables have a flex life of several million cycles. Could be broken wire(s) where it's flexed.

The motors are fixed, with encoder. Brushless DC-drives, controlled by TAE servodrive. The servodrive blinks 'current limit' when such sudden stops happen.

In total there are three motors, three servo-drives; and problem can happen with any on these three. Switching - or replacing - any of these did not solve the problem.

Cables have been inspected several times - not yet showing any deteroriation.

So we keep searching...:-)

Thanks!

RE: The servodrive blinks 'current limit' when such sudden stops happen.

That would lead me to suspect a mechanical problem. Have you considered that--maybe:

• lack of grease--some operator failing to grease something as required
• change in raw materials--size, density, machinability
• ambient temperature
• ???
  

Does the error happen during any specific part of the operation, or maybe only during certain 'recipes'?

Spook

No. It seems to happen 'randomly'. Electricity 'spikes' or 'noise' have been taught to be potential causes... but filters seem ok, and adding 'ground' also did not change anything...

Thanks for your question.

It all seems to happen at random, not during specific parts of operation or certain settings, 'recipes'....

Machine problems almost never happen randomly. Most often we just don't understand what really is going on. I agree that the over current light should not be flickering unless dynamic braking is being applied, then that would be normal if the servo settings were set at the max limit (which they normally are).

With that said.... you need to provide specific information if you wish to solve this problem. can you post a schematic of tell us where to download one.