Fanuc alarm 91: Magnetic pole position count miss
αi SPM · Fanuc αi SPM
What it means
A large difference was detected between the magnetic pole position at the one-rotation signal and the AMR offset parameter (No. 4084) on αi drives with BiS synchronous spindle motors. Indicates the rotor reference shifted or feedback counts are corrupted.
Likely causes
- Sensor ring slippage changing pole-position relationship
- Parameter setting error (sensor teeth / motor phases)
- Noise-induced feedback pulse count errors
Need the part urgently?
Send us alarm 91 with your machine details — typical RFQ turnaround is 24–48h.