Abstract: A plurality of copying machines (12), (13), (14) are connected to a control unit (16) which may control the copying machines (12), (13), (14) to operate individually in a conventional manner. Alternatively, two or more copying machines (12), (13), (14) may reproduce an original document scanned by one of the copying machines (12), (13), (14). Also, one or more copying machines (12), (13), (14) may reproduce two or more original documents scanned by respective copying machines (12), (13), (14) in a superimposed manner. As yet another alternative two more copying machines (12), (13), (14) may each reproduce two or more original documents which are sequentially scanned by respective copying machines (12), (13), (14), thereby collating the copies.

Abstract: An ink-landing-position control electrode is provided in such a way that one end of the control electrode is positioned adjacent to the back of a recording medium in opposed relationship with a predetermined position on the recording medium at which a charged ink drop must be deposited. The control electrode is charged oppositely of the charge on an ink drop in such a way that the electric lines of force of the electric field established by the control electrode are concentrated at the landing position, whereby a charged ink drop is forced to land at the predetermined position even when it is influenced by aerodynamic and electrostatic disturbances while it is in flight. The control electrode can also be used to eliminate an inclination of a line of dots deposited by a stream of charged ink drops issued from one nozzle when a recording medium is transported in the direction perpendicular to the traveling path of an ink-jet print head.

Abstract: An ink ejection nozzle acts as one electrode and is arranged to eject ink against another electrode during an ink ejection test of the nozzle. The ink stream electrically connects the electrodes when the ink is being ejected normally, whereby the ink flow rate is analogous to the electrical impedance or capacitance between the electrodes. If the nozzle is clogged with an ink deposit so that the flow rate is insufficient, the system ejects a solvent through the nozzle to dissolve the deposit. The flow rate of the solvent is also sensed and the solvent ejection is terminated when the solvent flow rate is sufficient. Ink is then again ejected to purge the solvent from the nozzle.