Universal motors are compact, lightweight and high-revolving, and are widely used for the cleaners, electric tools, etc. However, universal motors have some problems. They generate the commutation sparks which cause wear on the brush and noise impediments. Therefore, we attempted to use a high-speed camera to visually elucidate the commutation spark mechanism. We reported the large pulses of the armature terminal voltage leading to the generation of commutation sparks. This time we accelerated the photographing speed, and probed commutation sparks which occur when the large pulses begin to decrease at the peak.
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