A printing system is described, which comprises: a conveyor belt; a first substrate supply mechanism to supply a cleaning substrate to said conveyor belt; wherein said conveyor belt is to advance a supplied cleaning substrate, and said first substrate supply mechanism is controllable to adjust motion of said substrate relative to said conveyor belt such that when said conveyor belt is activated said supplied cleaning substrate slides relative to the conveyor belt; and said printing system further comprising a friction adjustment mechanism to adjust an amount of friction between said conveyor belt and said supplied substrate.