In ink drop printers wherein a portion of the propelled ink from an orifice is returned for reuse and other ink selected from the issuing ink filament proceeds to an ink receiving surface, a cover is disclosed, which substantially prevents gas from leaving the selection region, unless the exiting gas or a substantially solvent saturated replacement gas is returned after ink is extracted for reuse. Thus, except for an ink extraction route, mist, satellite drops, exploded drops, evaporated solvent, and unused drops, whichever are present, are substantially prevented from leaving the cover; whereas, print droplets do leave the cover. Problems solved are ink solvent replacement, ink drying on printer surfaces such as orifices, dust entry to electrostatic areas, and external ink build up and messiness. Electrodes, or gas passing thereover, may be heated slightly to prevent solvent condensation. Features of a selection system having no electrodes, except those washed by ink droplets are disclosed. Application of electrical voltages changes the contact angle of selected droplets, thus pulling them closer to a surface. Other droplets with the same initial conditions but to which less voltage is applied travel other paths and leave the surface at other positions. Contact configurations and departure modes are disclosed. The third aspect of this invention deals with voltages and the formation of conducting areas covered with a dielectric and having an exposed surface upon which a selected ink, possibly metallic, will form a reasonably large contact angle. A hydrophobic layer may be added above a high voltage dielectric.

Two methods of producing a ribbon-shaped stream of ink and of producing an orifice for the narrow ribbon stream under 0.0005 inches thick are disclosed. Also a rotating drum-like configuration with electrostatic sites on its surface is disclosed. The drum, due to irregularities on its surface, breaks the ribbon into segments corresponding to the sites. If desired, the segments will upon release from the drum form side by side broad streams of directionally controlled droplets. The axial spacing between the apparent origins of the droplet streams can be made less than the minimum center to center spacing between control sites, because the sites can, but need not, be located along helical paths so that successive sites on a helical path would participate in originating different streams. Site and segment spacing may be only a few thousandths of an inch. Drum construction, parallel wiring for duplicate wedges around the drum, slit cleaning, and drum cleaning are also disclosed.

An ink jet printer comprising one or more nozzles which are connected, via a pressure chamber, to an ink supply duct. The pressure chamber comprises a wall which can be moved by means of an electromechanical converter in order to realize droplet-like ejection of ink from the nozzle. The converter continuously vibrates during operation. In front of each nozzle there is arranged a brake electrode which can be connected to a voltage as desired. When the voltage is switched off, the ejected ink droplet is incident on the record carrier, and when the voltage is switched on, the ink droplet is intercepted by the brake electrode and is withdrawn into the nozzle by the converter. Special interceptors for the ejected ink and deflection devices are no longer required.

A method of controlling the impact points of successive selected droplets in a particular ink stream operating on a drum type printer capable of controlling uncharged non-magnetic droplets, as described in U.S. Pat. No. 4,138,686 is disclosed. Further the grid formed by any single stream can be made rectangular with one axis parallel to the direction of motion of the output medium relative to the droplet selector, to facilitate the simultaneous formation of properly oriented print characters. Phase and speed of contacting droplets relative to sites uniformly spaced around a rotating drum are sensed and controlled in a new way. Also an impacting sequence to produce a line of upright characters with the sequence to be reversed if the line is traversed in the opposite direction is disclosed. A method for producing both the sequence and the reverse sequence using a single droplet stream whose origin moves parallel to the line of characters, and whose droplet velocities are controllably changed only in a single plane, which plane contains the velocity of each controlled droplet with respect to the droplet stream origin, the same plane being used for all impacting droplets whether in sequence or reverse sequence, is shown. In other words, neglecting gravity and aerodynamics all image droplet velocities are controllably rotated about a single vector in space. Also an impacting sequence to produce a rectangular array of impact points more closely spaced in both array directions than the actual simultaneous impact points, while all impact points relative to the droplet selector remain in a constant position, is disclosed, i.e. the droplet stream directions need not be controlled.

A spraying control system for an electrically conducting liquid (3) emitted in the form of a pressurized jet (4) through at least one nozzle (2). The system contains apparatus for separating the liquid into drops, apparatus for electrically charging the drops and apparatus for applying an electrical deflection field to the charged drops. The system includes a first (8) and a second (6) monolithic element each with a continuous surface, laid out such that the continuous surfaces are facing each other and define a space (5) between them in which the pressurized jet (4) is emitted through the nozzle (2). The elements (6,8) include apparatus for continuously setting up potentials on the continuous surfaces to obtain the electrical charge of the drops and the electrical deflection field. The system also includes electronic control (31 to 36) for the potentials and apparatus for checking the intensity of electrical currents that can circulate on the continuous surfaces.