Fanuc spindle alarm 92 means the actual motor speed exceeded the overspeed level corresponding to the velocity command — the motor ran meaningfully faster than it was told to. Fanuc's triage: at first start, causes (a)–(c) all apply; on a machine that has been operating normally, noise (c) is highly likely.
The three causes
- (a) Configuration parameters wrong — sensor teeth / motor phases: wrong geometry makes the drive misjudge speed entirely. Verify per B-65280EN (the 4011/4334/4368 family) — first-start suspect only.
- (b) BiS motors: AMR offset parameters — on synchronous spindles, a wrong 4084 (AMR offset) — machine-specific, re-adjusted after sensor replacement, shaft slippage, or when loaded from another machine — corrupts commutation and speed behaviour; 4085 must normally be 0. Full AMR treatment in our AL-90 guide.
- (c) Noise-induced count errors in the motor sensor — the running-machine cause: corrupted feedback counts read as overspeed. The standing discipline: shield continuity, frame-ground clamps, separation from power leads — method per AL-47.
Tip: A genuine mechanical overspeed on a working machine is rare — AL-92 out of nowhere is almost always the feedback lying (noise) rather than the motor running away. But treat the first occurrence seriously enough to check: an actual runaway on a BiS motor with bad pole data is violent. Veteran machine → shielding/routing first; after any restore or sensor work → 4084.
Related guides
- Fanuc spindle alarm 90 (AMR offset procedures)
- Fanuc spindle alarm 47 (noise methodology)
- Fanuc αi drive alarms index
AL-92 you can't explain? JJ Automation diagnoses feedback noise, performs AMR adjustment, and repairs spindle amplifiers at component level — on site in NCR. WhatsApp us or call +91 88022 12394.