GB1349055A - Method for the control of charge on a moving web - Google Patents

Abstract

1349055 Control of electrostatic charge on a moving web AGFA-GEVAERT 19 April 1971 [4 May 1970] 21365/70 Heading G3R The electrostatic charge on a web 10 being wound on to a roll 12 is reduced to zero or to below a predetermined maximum value by a control arrangement comprising an electrode 15 which measures the electrostatic field at one side of the web, an electro-meter 16 which receives the signal from electrode 15 and supplies a signal to a controller 17, and a source 18 of D.C. voltage whose value is varied as a function of the signal from controller 17 and which supplies an electrode 19 insulated from ground and in contact with the web 10, the electrodes 15, 19 being closely spaced. Electrode 19 is located to ensure substantial angular contact with the web, whose path is controlled so that its spacing from the electrode 15 remains constant as the diameter of the roll 12 increases. The electrode 15 comprises an elongate conductor extending transversely of the web and forms with the electrometer 16 a field strength meter producing a D.C. output signal which is amplified by the controller 17. In a modification for unwinding a web, Fig. 2, (not shown), the member 17 is omitted and the electrode 15 takes the form of a roller in contact with the web, member 16 being a vacuum tube electrometer controlling a fixed polarity D.C. source. Other modifications envisage the measurement of the field at both sides of the web and its control by respective electrodes located at such opposite sides, the two measurements being at locations close to each other or spaced apart, for example one at a winding station and the other at an unwinding station.