07:58 Oct 18, 2011 

A 'brush' is a device used to transmit electricity between a fixed and a moving object — cf the carbon 'brushes' (balai) found in some electric motors. I do not know if 'brush' always translates as 'balai', regardless of the actual form it takes and the application.

I would understand these two parts as being used for two different functions: the 'power brush' is used to convey the electrical power supply to the moving element; the 'signal brush', on the other hand, is used to transmit electrical signals to/from the moving element. Obviously, these two channels need to be kept separate!

I'm quite surprised about the suggested 'système de balayage', which sounds much more general than the specific component name you have here; I'd suggest confirming that by further research...