| 摘要 |
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 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 substrate (111), with all connections being made to the underside of the mounting substrate (111) and sealed with a potting compound, to avoid damage. Ink viscosity is controlled in response to ink pressure, which is in term controlled in response to ink jet velocity. Thus all three parameters are maintained without the need for a viscosity meter. Ink jet velocity is sensed by means of signals induced by charged drops on spaced apart sensors (89, 91), the outputs from which are wired together and fed to a common comparator (105), which simplifies construction. Internal conditions of the printer are output in response to interrogation. This permits remote fault diagnosis, e.g. over the telephone. Ease of operation is improved because the printer automatically performs the tests and operations required when starting and stopping the jet, and it automatically performs a nozzle cleaning routine when sensor inputs indicate a nozzle blockage. The ink gun (75) has an ink cavity (145) which tapers away from a bimorph piezoelectric crystal (159) which is restrained from flexing at one radius only. The gun is highly efficient and versatile, may operate at a range of frequencies and a range of nozzle sizes, and is preferably operated off resonance. Dot patterns for printed characters are stored in a character store (175), and charging electrode levels are stored in a charge level store (177), with several alternative levels being stored for each dot position for use according to whether other nearby dots are being printed. This provides compensation for the electrostatic and aerodynamic effects of ink droplets on one another. Similar compensation for unprinted droplets is provided by a historic correction store (179). The provision of guard drops is controlled by a sequencer (185). The voltage applied to the charging electrode (127), is compensated for variations in charging circuit amplification and jet-to-electrode capacitive coupling. <IMAGE> |
