This invention relates to a drop-on-demand ink jet printing device commonly used for large character printing. In such devices, used for marking products, the on/off control of ink to a nozzle is accomplished by using a separate valve, remote from the orifice, which is connected thereto by a tubing assembly. A typical large character printhead will have a plurality of such valves and nozzles forming, for example, a seven by one printhead which can mark alphanumeric characters on products which pass the printhead.
The subsystem defined by the on/off valve, the nozzle and the tubing which interconnects the two has a natural frequency. In typical printheads of this type, the resonant frequency of the system is low. As the valve operating frequency approaches the resonant frequency of the ink delivery system, print quality deteriorates. Thus, even if the valves are capable of operating at higher frequencies, the resonant interference from the ink delivery subsystem reduces maximum printing frequency.
For example, current drop on demand printers of the type described operate at about 240 Hz. Currently available valve designs permit theoretical operation to at least 700 Hz. As print speed increases, however, interfering resonant frequencies cause severe print quality deterioration preventing operation at such higher frequencies.
It is accordingly an object of the present invention to provide an improved printhead having the capability of operating at higher frequencies than in the prior art.
It is a further object of the invention to provide a printhead in which the valve/output tube/nozzle has a natural frequency above and sufficiently removed from a desired operating frequency range that there is no resonant interference and consequent degradation in print quality.
A further object of the invention is to provide a method of optimizing the valve/output tube/nozzle for a printhead of the type described to maximize print quality by adjusting the fluid resonant frequency thereof.
These and other objects of the invention will be apparent from the remaining portion of the specification.