Abstract: A medium to be charged is conveyed past a corona charging device, so that charge emitted by the corona charging device is deposited on the medium surface. A measuring wire disposed between the medium and the corona charging device, but positioned near the medium, collects a part of the emitted charge. A first measuring circuit is used to determine a measure i.sub.d of the charge current collected by the measuring wire. A second measuring circuit determines a measure i.sub.f of that part of the emitted charge current that flows to the medium. In accordance with a predetermined relation, a value E of the surface potential is derived from these measures i.sub.f and i.sub.d.

Abstract: In a contact fixing system in which a heat-softened toner image is fixed onto a sheet material by being pressed against the sheet material in a nip between the peripheral surfaces of two circulating fixing members, such as rollers pressing one against the other or a roller pressing against an image carrying belt, residues of the toner of an image and paper dust are removed from the surface of a fixing member in a cleaning zone beyond the fixing nip by moving in rolling contact with that surface a circulating cleaning surface, such as a roller surface, to which the toner adheres preferentially and which has a multiplicity of spaced-apart perforations formed therein and so disposed that with continued movements of the cleaning surface through the cleaning zone a toner layer formed on the cleaning surface is repeatedly pressed thin and excess toner present in it is displaced to the perforations for discharge through them into a cavity inside the cleaning member.

Abstract: A corona device comprising a multiplicity of electrode pins embedded in a body of insulating material has each pin projecting from two sides of the insulating body and has this body disposed between two conductive elements, or electrodes, which are connectable to the opposite poles of a voltage source. The ends of each pin are in the electric field between the electrodes at locations between which a high potential difference is present, so that a corona discharge may develop between each end of a pin and the related electrode. The corona device may also comprise provisions for inhibiting deterioration of the pin ends subject to positive corona discharge, and/or for counteracting the positive potential so that no positive corona discharge will occur.

Abstract: An improved process for transferring a magnetizable developing powder from an insulating substitute, such as an electrostatic duplication master or photoconductive element to a receiving material, such as paper, in electrostatic image development enables the transfer of powder having a specific resistance greater than 10.sup.13 Ohm.cm. without the need for specially treated paper. The powder is applied imagewise, corresponding to a charge image, on an insulating substrate, the substrate with the powder image brought in contact with the receiving material to which the powder is to be transferred, two separate charges are applied to the free side of the receiving material during the period of contact with the substrate, the first of such charges, a pre-transfer charge, having a polarity opposite to that of the charge image and the second of such charges, a transfer charge, being greater than the first and having the same polarity as that of the charge image, and the powder transferred.