Fixing unit for electrostatic copiers

Claim 1

In a copying machine having means for making powder images on copying sheets of different selectable formats, a device for fixing the powder to a copy sheet comprising: a first roller having its outer surface covered with a layer of material adapted to resist adhesion of the powder thereto; a second roller cooperative with said first roller to define with said first roller a nip through which the copy sheet is advanced by the rotation of said rollers with the sheet face bearing the powder in contact with said first roller; and at least one heating roller rotated in contact with said first roller for heating said layer to a temperature sufficient to cause fusing of the powder to the copy sheet, said heating roller comprising a tube of good thermal conductive material having a plurality of axially adjacent cylindrical portions, each portion contactable with a different part of the periphery of the first roller and each portion having therein a heating unit, each heating unit selectively activatable in accordance with the selected format of the copy sheet for heating the corresponding part of the peripheral surface of the first roller, whereby for a selected format of the copy sheet only a corresponding part of said layer is heated.