Correlations between Unevenness of Commutator Surface and Brush Bounce

Bouncing of brushes mounted on a laboratory-made mimic commutator was quantitatively investigated by the so-called electric capacity method. In combination with the measurement of contact potential drop simultaneously examined, following conclusions have been obtained: (1) The brush bounce is affected rather severely by the unevenness of commutator surface than its off-centricity, which takes place further violently as the backward inclination of the surface is steepened, (2) In order to prevent such bouncing of brushes when motor is operated under ordinary conditions the unevenness of commutator surface should be less than 3 microns in depth, and the off-centricity should not exceed 15 microns, (3) It produces fairly good effect for diminishing the bounce to strengthen the brush pressure, if the unevenness is not too large. For the effective suppression, the working points of pressure are desirable to be as close as possible to the trailing side.(4) The critical height of brush bounce at which commutator sparks are transformed into arcs is estimated to be 5-6microns.