Removable process unit with charging device located relative to main assembly

A process unit which is removably mounted in the main assembly of a reproducing machine such as a xerographic copier, has a housing enclosing an imaging member and, optionally, other processing capability such as a development device, and a cleaner. The unit also has two charging devices, namely a charge scoroton and a transfer corotron which are mounted so as to have a limited degree of vertical movement relative to the unit housing. The charging devices are provided with spacers at their opposite ends which abut a support member in the main assembly when the process unit is inserted therein. In this way the charging devices are automatically accurately located relative to the imaging member when the process unit is inserted in its operative position in the main assembly. Preferably the charging devices are urged towards the support by springs which, in the case of the charge scorotron are included within the cassette housing and, in the case of the transfer corotron form part of the main assembly of the copier.