...processed signal to at least one driving means for moving said automatic device (2) in relation to a surface, 12 - said driving means being arranged on said automatic device (2), 13 - said first signal generator (3,7,8) transmitting a current through said first cable (1,4,5,6), 14 - said current, during a part of time, being in a state of rest where it is substantially constant, 15 - said state of...