The effect of friction and wear behavior on the signal transmission of brush-ring system during electrical contact sliding

Copper-graphite brush and slip-ring systems are often used to transmit electrical energy and signal between moving and stationary parts. At present, the research on the brush-ring system mainly focuses on power transmission, while on signal transmission is relatively lesser. In this study, the effects of friction and wear behavior on signal waveform distortion were in-situ analyzed using a custom-designed tribotester, which can specially synchronize the slip-ring rotation period with the input signal waveform. Results were analyzed comprehensively from tribological and electrical aspects to find out the key factors, including friction coefficient, friction temperature, contact resistance, surface morphology, roughness, wear particles, and compositions. It was found that the distortion of signal waveform is mainly affected by the friction film. During the sliding electrical contact motion, the increase of friction film will increase the contact resistance, which in turn increases the signal waveform distortion. At the same time, under the normal load and shear force, the friction film moves along the sliding direction, hence causing the signal phase angle to shift. From a tribological point of view, the friction coefficient and temperature decrease with increasing the friction film. So, for the brush-ring system, the formation of friction film is good for the friction stability but bad for signal transmission.