Mitsubishi MDS alarm 16 means an initial magnetic pole position detection error — on linear motors or IPM (permanent-magnet) spindle motors using absolute position encoders, the drive attempted servo-ON before the magnetic pole shift amount was correctly established (parameter SV028 for servo axes, SP118 for spindles), or the pole detection routine itself failed. Like a Fanuc BiS motor with bad pole data, an IPM motor whose drive doesn't know where the magnets sit cannot apply torque safely — so it refuses.
Mitsubishi's investigation sequence, in prose
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Check SV028 (servo) / SP118 (spindle):
- Parameter never set (fresh commissioning, replaced motor/encoder, or a parameter restore that missed it) → set the magnetic pole shift amount — run the magnetic pole estimation procedure and store its result.
- Parameter is set but the alarm occurs → the stored value is wrong for this motor — carry out the magnetic pole estimation again. Wrong values arrive via sister-machine restores or after any mechanical change to the motor/encoder relationship.
- Re-running the estimation produces the same value and the alarm persists → move to repeatability.
- Check repeatability: the alarm always repeats → the drive unit itself is faulty — its pole-detection circuitry; bench repair or exchange. Returns to normal but recurs occasionally → environmental — continue.
- Check the ambient environment: temperature, electrical noise, grounding — Mitsubishi's two named checks: machine grounding and shield connection of the encoder cable. Intermittent pole-detection failures on a healthy drive are nearly always noise corrupting the encoder data during the detection routine.
Tip: After ANY work on a linear motor or IPM spindle — motor, encoder, coupling — treat magnetic pole estimation as a mandatory commissioning step, not an optional one; the old SV028/SP118 value describes a relationship that may no longer exist. And record the established value in the machine file: it is machine-specific, exactly like Fanuc's AMR offset (see our AL-90 guide for the same concept on the Fanuc side).
Diagnosis checklist (in order)
- Fresh install / after motor-encoder work → run (or re-run) magnetic pole estimation; store SV028/SP118.
- Alarm persists identically → drive unit to the bench.
- Intermittent → grounding and encoder cable shielding.
Related guides
- Mitsubishi MDS alarm 32 (power module overcurrent)
- Mitsubishi M70/M80 alarm list
- Mitsubishi zero point initialization
Alarm 16 on a linear or IPM spindle axis? JJ Automation performs magnetic pole estimation, repairs MDS drive units at component level, and diagnoses grounding/noise problems on site in NCR. WhatsApp us or call +91 88022 12394.