Permanent Magnet Rotors

Both small electric rotors for e.g. servo steering and larger rotors for e.g. electric vehicle (EV) drives are measured with Magcam’s Rotor or Combi Scanner, providing high speed measurements of the radial, tangential and axial field distribution on the rotor mantle.

The above figure shows the magnetic field (south/north poles) of the rotor (top), the zero crossings and peaks (bottom left) at the cross-section (grey line in top figure) and the Fourier spectrum (bottom right)

This figure shows the surface plot of the magnetic field with north/south poles measured at distance Zo from the surface of the rotor.

Magnet quality issues include:

• Pole angle deviations
• Skewing angle deviations
• Cogging torque
• Pole peak inhomogeneity
• Noise problems (harmonics)
• Micro cracks

Analysis possibilities include:

• Radial/tangential/axial (3D) field distribution 
• Pole peak detection and analysis
• Zero crossing detection
• Pole angle measurement
• Pole skewing angle measurement
• Fourier harmonics analysis (for e.g. noise problems)
• Cogging torque analysis
• Crack detection

Cogging torque analysis

With the Magcam system, it is possible to predict cogging torque from a bare rotor measurement:

• Measure the high resolution PM rotor surface magnetic field distribution in air
• Input the stator geometry parameters
• Calculate the qualitative cogging torque curve
• Derive the quantitative harmonics ratios
• Predict the cogging torque quality
• Screen out rotors that don't meet your requirements

Bad PM rotors can be screened out before being assembled with the stator, saving valuable time and cost, and improving PM motor yield.

Measuring skewing angle

MagScope makes it easy to measure the skewing angle of PM rotors. 

The figure shows the continues skew on an SPM (surface permanent magnet) rotor. The top image is of the magnetic field showing the skew. The middle and bottom images show the line plot of the magnetic field with the zero crossings on the left and the quanititative numbers on the right.

It's easy to program a simple pass/fail script in Python to screen out rotors that don't meet your skewing requirements.

The figure above shows the step skew of an IPM (internal permanent magnet rotor). The same analysis has been done as is explained on the previous figure.

Contact Magcam to discuss your PM rotor measurement needs and requirements.