Fanuc spindle alarm 37 means the spindle motor did not decelerate properly after an emergency stop signal — either the motor accelerated when it should have been braking, or it was still not fully stopped when the configured acceleration/deceleration time (initial setting: 10 seconds) expired after the E-stop input. In plain terms: the E-stop fired, the control started its stopwatch, and the spindle was still turning when time ran out. This is a safety-relevant supervision — the control wants proof the spindle actually stops — and Fanuc's two causes are both parameter-side, though the second one hides a real-world subtlety.
Cause 1 — Speed detector parameter setting incorrect
If the drive has wrong information about the speed sensor, its idea of ‘decelerating’ and ‘stopped’ is wrong — a spindle that is braking normally can be judged as still running (or worse, as accelerating). Check the speed detector / sensor parameters against Chapter 1 of the AC Spindle Motor αi Parameter Manual (B-65280EN). Prime suspect when AL-37 appeared after an amplifier swap, motor change or parameter restore — the same forensic logic as AL-34: an untouched machine does not change its own settings.
Cause 2 — Acceleration/deceleration time parameter too short
The supervision window lives in parameter 4082 (FS16i/FS0i-B/C and FS30i/FS0i-D; 3082 on FS15i) — the acceleration/deceleration time setting.
- Measure reality first: time how long the spindle actually takes to stop from top speed after an E-stop. A big spindle with heavy chucks or a large workpiece has real inertia — stopping simply takes time.
- Compare with the value in 4082. If the machine genuinely needs longer than the parameter allows, set the actual measured deceleration time plus some margin — Fanuc's own instruction.
- Set the value with PWE per our write-protection guide, then verify with a full-speed E-stop test.
What AL-37 is not
It is not a feedback-loss alarm (that's AL-73/AL-31 territory) and not an overload — it is specifically the E-stop deceleration supervision. If it appears together with feedback alarms, fix the feedback first: the drive cannot judge deceleration through a broken speed signal.
Diagnosis checklist (in order)
- When did AL-37 start — after parameter/hardware work, or out of nowhere on an unchanged machine?
- After work → verify speed-detector parameters (B-65280EN) and re-check the motor code.
- Measure the real E-stop stopping time from top speed; compare against 4082 (3082 on 15i).
- Machine genuinely needs longer → set measured time + margin; verify with a full-speed E-stop test.
- Stopping time has degraded on an unchanged machine → investigate the regen/braking path before touching the parameter.
Related guides
- Fanuc spindle alarm 34 (parameter out of range)
- Fanuc spindle alarm 36 (error counter overflow)
- Fanuc αi drive alarms — PSM, SVM & SPM codes explained