Fanuc alarm SP9090: UNEXPECTED ROTATION (MAGNETIC POLE DETECTION)
spindle alarm (serial spindle, alpha i) · Fanuc 0i-D
What it means
Abnormal rotation of a synchronous spindle motor was detected during initial magnetic-pole position detection. Before exciting a permanent-magnet motor normally, the drive probes rotor position with test pulses; movement outside the expected envelope means the pole model does not match reality.
Likely causes
- Rotor/sensor alignment incorrect after motor or sensor replacement
- Wrong motor model parameters for a synchronous spindle
- Load dragging or back-driving the spindle during pole detection
Triage note: Re-execute magnetic pole detection after verifying mechanics and motor data.
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