Polarity sequence
Confirm the intended alternating or specified multi-pole pattern.
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Vincent@vanguard-tech.cn
Rotor Quality Engineering
A practical inspection route for pole sequence, spacing and magnetic consistency before the rotor enters final motor assembly.
Engineering Overview
A single surface-flux reading can miss a reversed magnet, uneven pole pitch or a weak region between sample points. In rotor field mapping, a controlled sensor traverses the circumference while angular position is recorded. The resulting trace helps compare the magnetic pattern of each pole under one defined fixture setup. It is an inspection tool, not a direct measurement of motor torque, back-EMF or efficiency.
Confirm the intended alternating or specified multi-pole pattern.
Compare magnetic transitions against the design's angular spacing.
Assess peak levels and integrated field consistently by pole.
Add axial scan positions where end effects or placement may vary.
Image Gallery
Measurement Setup
A repeatable scan needs a defined probe type and orientation, sensor-to-rotor gap, axial position, rotational direction, angular reference, sampling density and temperature. Runout or a changing probe gap can alter the measured amplitude even when the magnetization has not changed. Record the setup with the trace so later production lots can be compared meaningfully.
For a sleeved rotor, state whether the scan is made before or after sleeve installation. For an interior permanent magnet rotor, an external field scan may be less directly diagnostic of individual magnets; review the intended measurement path with the magnetic design.
Inspection Matrix
| Feature | How to Evaluate | Potential Concern | Follow-Up |
|---|---|---|---|
| Pole count and polarity | Count and identify signed field regions over one full rotation | Missing, reversed or incorrectly magnetized pole | Confirm assembly map and magnetization record |
| Pole pitch | Compare zero crossings or defined transition points | Placement or magnetization-fixture error | Check segment location and angular datum |
| Peak amplitude | Compare like-for-like peaks at a fixed probe gap | Local variation, gap change or runout | Repeat after checking concentricity and sensor clearance |
| Integrated field per pole | Integrate the measured trace over defined pole sectors | Unequal field distribution across poles | Review magnet batch, geometry and assembly placement |
| Axial variation | Repeat scans at agreed axial stations | End effects, skew, misplaced segments or uneven length | Inspect physical build and design intent |
| Harmonic content | Compare spectrum using the same analysis settings | Pattern deviation requiring further study | Correlate with back-EMF, vibration and electromagnetic model |
Production Route
Specify pole map, reference angle, scan path and project-based limits.
Locate the shaft and sensor to limit runout and gap variation.
Record signed field against angle at the specified axial station.
Check sequence, pitch, amplitude and defined pole integrals.
Separate measurement error from magnet, assembly or magnetization causes.
Link scan file, rotor serial number, fixture and disposition.
Troubleshooting
| Observed Pattern | Possible Causes | First Checks |
|---|---|---|
| One low peak | Magnet variation, local gap, placement or sensor position | Repeat scan and inspect the corresponding physical pole |
| All peaks lower | Probe gap, calibration, sleeve, temperature or magnetization shift | Compare fixture and reference sample |
| Uneven transition spacing | Angular location error or magnetization pattern shift | Check datum, encoder and mechanical segment pitch |
| Different traces by axial station | End effects, skew, magnet length or assembly offset | Compare with drawing and approved master rotor |
| Unexpected polarity | Reversed segment or incorrect magnetization program | Quarantine and verify against approved polarity map |
Design to Production
Pole balance limits should come from the application's electromagnetic and manufacturing requirements. The scan can screen incoming or assembled rotors, but the allowable variation must be validated against back-EMF, torque ripple, noise and thermal performance where relevant. A symmetric free-rotor trace does not guarantee a good motor if the stator, air gap, winding or inverter has a separate issue.
Ningbo Vanguard Technologies can support rotor magnets, laminations, sleeves, assembly development and inspection planning. For prototype builds, retain representative scan traces alongside dimensional and motor-test data so the acceptance window is based on evidence rather than an arbitrary gauss value.
FAQ
Inspection decisions for engineering and purchasing teams.
It may be useful for spot checks, but a point reading cannot show the full pole sequence, pitch or distribution. Use a repeatable angular scan when those characteristics matter.
No. Torque also depends on the stator, winding currents, air gap, control method and operating condition. Correlate rotor data with motor-level tests and analysis.
Choose the stage that matches the control objective and document it. A sleeve changes probe distance and may affect the measured trace, so results from the two stages should not be compared without validation.
Comparing peak values obtained at different probe gaps or axial positions. Fixture repeatability and a reference rotor are essential.
A signed circumferential trace can reveal an unexpected polarity sequence, provided the sensor orientation and angular reference are defined correctly.
Share your rotor drawing and pole map to discuss an inspection plan for prototype or production builds.
