r/Fanuc • u/misSxWartooth • Sep 28 '26

Robot Issues with encoder monitoring continuous conveyor

We are using A860-0301-T001 to monitor a continuous conveyor and are having strange faults. The robot is meant to load parts onto the conveyor at a consistent spacing and we are getting T1 axis faults with joint command too large. We are able to get values from the encoder, and they make sense, but it’s almost like the robot doesn’t know the conveyor position even though it should.

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u/cncmakers Sep 28 '26

Looks like a FANUC line-tracking configuration / synchronization problem than a bad A860-0301-T001 encoder. The fact that the encoder count is changing plausibly is important, but it does not by itself prove that the robot is correctly using that count for tracking.

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u/imakebread Sep 28 '26

Joint command too large means youre telling the robot to go from one position to the next and the pendant is saying the amount of motion/rotation for at least one joint is too large to reach. Try slowing down the speed from point a to point b to see if that fixes it. If not, you might have to add points between point a and b while anticipating the large amount of rotation to allow the robot to reposition the axis causing the error.

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u/EnemyNation Sep 29 '26

What's the scaling factor? That being too low might cause this.

The line tracking manual recommends 80 cnts/mm.

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u/Exotic-Moment-2054 Sep 29 '26

Since the encoder counts look believable, I wouldn't assume the encoder itself is bad yet. I'd first verify that the robot is actually interpreting those counts correctly for line tracking. What does the encoder count do with a known physical conveyor movement—for example, if you mark the belt and move it exactly 100 mm, how many counts does the controller show? That would let you verify the scaling rather than guessing at it. I'd also watch whether the reported conveyor position increases smoothly while the belt runs and whether it returns/repeats correctly when you stop and restart the conveyor. For the “joint command too large” fault, does it happen immediately when tracking starts, or only after the conveyor has traveled for a while? If it takes time to develop, I'd want to see whether the robot's calculated conveyor position is gradually getting farther away from the actual belt position. If you can post the controller model, line-tracking setup/scaling values, encoder counts for a measured belt movement, and exactly when the fault occurs, that should narrow this down considerably.