the current source 10 the second electrode configuration 12 c is same with the first electrode configuration 12 a the above mentioned substrate passage is the position or the moving path of the substrate at the working state if there are no supporting rollers 19 the substrate passage is determined by the movement scope of the substrate due to the variation of the amount of the substrate in the roll and is illustrated in fig1 b and 7 however the substrate edges always move in a plane due to the parallel installation of the rotation shafts 15 therefore the conductive metal strips 2 are fixed perpendicular to the substrate passage to keep them closely contact to the substrate edges as an improvement showed in fig1 c two extra supporting rollers 19 are added to determine the only substrate passage which are the plane containing the top edges of the rollers 19 the first electrode configuration 12 a consists of current distributing circuit and at least two electrode units each of which includes two conductive metal strips settled along two sides of the substrate passage and the electrode unit connects electrically with each other by the current distributing circuit the second electrode configuration 12.