Abstract: A method is provided for adjusting the operating amplitude of a modulation signal which influences the separation of drops from an ink jet of an ink jet printer. The method includes (1) determining the phase relationship between the modulation signal and the instants when successive drops separate from the ink jet for a plurality of amplitudes of said modulation signal (2) identifying the amplitude of the modulation signal at a predetermined characteristic point in the function of the phase relationship with the amplitude from the magnitude of the change of the phase relationship with the change of the amplitude; and (3) selecting the operating amplitude for the modulation signal in accordance with the amplitude identified in step (2).

Abstract: An ink jet printer automatically adjusts the amplitude of the modulation signal applied to a transducer (159) to break the ink jet into droplets. Correct modulation amplitude is determined from changes in jet break-up length, as determined by changes in jet break-up length, as determined by changes in jet break-up phase relative to the modulation signal.The printer has interchangeable print heads (3), which may have different nozzle sizes. A calibration code, specifying the particular values of ink pressure, jet velocity and charge correction required for optimum performance of a particular print head (3), may be entered into control logic (93), which operates the printer accordingly.Most print head components are mounted on a mounting subtract (111), with all connections being made to the underside of the mounting subtract (111) and sealed with a potting compound, to avoid damage.Ink viscosity is controlled in response to ink pressure, which is in turn controlled in response to ink jet velocity.

Abstract: To flush ink out of the ink gun 15 of an ink jet printer, it is connected to a suction source 23 (normally used for gutter suction) through a purge line 33, purge valve 35 and gutter valve 27, while the ink feed line 13 is connected to the solvent reservoir 17 through a feed valve 11 and a flush valve 37. This draws solvent from the solvent reservoir 29 into the feed line 13 and the ink gun 15. Then, the purge line 33 is isolated from the suction device 23, and the feed valve 11 connects the feed line 13 to a supply of ink pressurized by ink pump 5. The pressurized ink is driven into the feed line 13, driving some of the solvent already in the feed line and the ink gun 15 out through the nozzle of the ink gun 15. The ink flow is then stopped before fresh ink reaches the ink gun 15. This avoids ink drying in the ink gun 15, blocking the nozzle, while the jet is not running.

Abstract: A fluid including a liquid solvent or carrier medium is applied to a substrate using an ink jet printing device in which the fluid composition is ejected through a nozzle as a jet of fluid, the jet is broken up into substantially uniformly sized droplets by the application of vibration to the composition, the droplets are passed by an electrode by which they are given an electrical charge, the charged droplets are passed through an electric field whereby they are deflected to a desired extent so as selectively to fall upon a substrate to form a symbol thereon or into a catch from which the composition is recycled for re-use. The viscosity of the fluid composition is monitored, and solvent or carrier liquid is added to the fluid to return the liquid content of the fluid to a desired value.

Abstract: The invention provides charge electrode means for an ink jet printer, comprising a pair of members which are preferably planar members of electrically insulating material, mounted in spaced relation to one another so as to provide a gap between opposed surfaces thereof, opposed charge electrode layers of electrically conductive material on said opposed surfaces and means electrically connecting said opposed charge electrode layers.