This is happening to a coworker of mine, but so far no luck diagnosing the issue.
We have a pair of M900s, fresh out of the crate, that are running mostly okay. But as we crank the speed up, both controller cabinets (not the motors) begin making "buzzing" noises, reminiscent of how a 3-phase motor sounds if it's lost a phase. As we increase the Override towards 100%, the sound gets louder. After a short period running at 100%, the controllers throw OVC errors for Joint 2. There are no other errors. At low speeds, we seem to be able to run indefinitely.
We've checked all the obvious things we can think of:
- Motor connections
- power connections
- payload settings
- The max payload (EOAT plus picked item) is only about 75% of the robot's rated load, and we're well within both the mass and CoG/Inertia limits of the robot.
- correct phasing on all 3 phases of the 480VAC mains
- (we have several other robots running on this same bus with no issues, so we're pretty confident that the mains are good)
- Floor vibration harmonics
- We placed the controllers on some pallets with rubber padding -- it had no effect on the noise.
It's hard to isolate, as the cells these robots are located in are pretty tight, but we're reasonably confident the issue is limited to Joint 2, possibly including Joint 3. The problem doesn't seem to be limited to specific motions, beyond that the OVC error tends to occur during moves that move J2 quickly. The moves are almost all simple Joint moves, but there are a number of short fast moves with steep accel/decel ramps.
At the moment, I'm leaning towards thinking it's a hardware issue in the controller cabinet, but it would be odd to have the same hardware issue in two brand-new cabinets at the same time.
We're probably going to get a Fanuc service call, but I thought I'd ping the Forum hive-mind: does this sound familiar to anyone?