Abstract
In small dc motors equipped with permanent magnets providing the field excitation, the torque can be dependent on the revolution angle of the armature. This phenomenon called pole sensitivity should be avoided as it produces an irregular run of the motor and, therefore, unwanted noise. There are two kinds of pole sensitivity: permanent magnetic and electromagnetic pole sensitivity. It is shown that permanent magnetic pole sensitivity in dc motors equipped with hard magnetic ferrite segments can be avoided or reduced considerably by choosing certain segment angles. The electromagnetic pole sensitivity will then also be reduced. The theoretical results are in good accordance with practical measurements. The calculated value of the permanent magnetic pole sensitivity too is in accordance with the measurements if effects resulting from the edges of the segments are taken into consideration.
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