Independent power supplies for color inkjet printers

Details Independent power supplies for color inkjet printers Independent power supplies for color inkjet printers

1999-10-29

2002-05-14

Barlow, John (Department: 2853)

Incremental printing of symbolic information

Ink jet

Controller

C347S012000, C347S043000

Reexamination Certificate

active

06386674

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to thermal ink jet printers, and more particularly to the supplying of power signals to the ink ejection elements of thermal ink jet printers.
BACKGROUND OF THE INVENTION
Inkjet hardcopy devices, and thermal inkjet hardcopy devices such as printers, plotters, facsimile machines, copiers, and all-in-one devices which incorporate one or more of these functions in particular, have come into widespread use in businesses and homes because of their low cost, high print quality, and color printing capability. These hardcopy devices are described by W. J. Lloyd and H. T. Taub in “Ink Jet Devices”, Chapter 13 of
Output Hardcopy Devices
(Ed. R. C. Durbeck and S. Sherr, San Diego: Academic Press, 1988). The basics of this technology are further disclosed in various articles in several editions of the
Hewlett
-
Packard Journal
[Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No. 1 (February 1994)], incorporated herein by reference.
The operation of such printers is relatively straightforward. In this regard, drops of a colored ink are emitted from a printhead onto the print media such as paper or transparency film during a printing operation, in response to commands electronically transmitted to the printhead. These drops of ink combine on the print media to form the text and images perceived by the human eye. Color inkjet printers use a number of different ink colors in order to form a wide range of colors and intensities. The colors can be produced through the use of dye or pigments in the ink. Printheads for one or more color inks may be contained in a print cartridge. The ink supply for the printheads may be contained in the print cartridge housing the printhead, or ink may be continuously or intermittently supplied to the printhead from an ink supply located elsewhere. An inkjet printer frequently can accommodate two to four print cartridges, or more. The cartridges typically are mounted side-by-side in a carriage which scans the cartridges back and forth within the printer in a forward and a rearward direction above the media during printing such that the cartridges move sequentially over given locations, called pixels, arranged in a row and column format on the media which is to be printed. Each print cartridge typically has an arrangement of individually controllable printhead ink ejection elements for controllably ejecting the ink onto the print media, and thus a certain width of the media corresponding to the layout of the ink ejection elements on the print cartridge, can be printed during each scan, forming a printed swath. The printer also has a print medium advance mechanism which moves the media relative to the printheads in a direction generally perpendicular to the movement of the carriage so that, by combining scans of the print cartridges back and forth across the media with the advance of the media relative to the printheads, ink can be deposited on the entire printable area of the media.
Each ink ejection element, or firing unit, includes an ink chamber connected to an ink source, and to an ink outlet nozzle. A transducer within the chamber provides the impetus for expelling ink droplets through the nozzles. In thermal ink jet printers, the transducers are thin film firing resistors that generate sufficient heat during application of a brief voltage pulse to vaporize a quantity of ink sufficient to expel a liquid droplet.
A power source in the printer connects to the print cartridge to supply electrical power (a certain amount of current at a certain voltage) to the firing resistors in the ink ejection elements for a certain amount of time in order to provide the electrical energy required to eject ink drops from the elements. The energy applied to a firing resistor affects its performance, durability, and efficiency. It is well known that the firing energy must be above a certain threshold, known as the turn-on energy, to cause a vapor bubble large enough to expel a drop to nucleate. Above this threshold is a transitional range, in which increasing the energy increases the drop volume expelled. Above a higher threshold at the upper limit of the transitional range, drop volumes do not increase with increasing energy. It is in this upper range in which drop volumes are stable even with moderate energy variations that printing optimally takes place, because the variations in drop volume that cause disuniformities in printed output can be avoided when operating in the upper range. If the applied energy levels increase above this optimal zone, however, drop volume uniformity is not compromised, but rather energy is wasted resulting in excessive temperature rise, and the printer components are prematurely aged due to excessive heating and ink residue build up.
For achieving high print quality, it is frequently desirable to print using different drop volumes for different color inks, or for different shades of the same color ink. Therefore, the design of the printheads may differ from ink to ink in order to produce different stable drop volumes. Different stable drop volumes require different amounts of firing energy; the amount of firing energy required to produce stable drop volumes is generally proportional to the stable drop volume. For example, an ink ejection element designed to produce 30 picoliter drops requires approximately 1.5 times the firing energy required to produce 20 picoliter drops from a differently-designed ink ejection element.
Producing different firing energies for different printheads with different stable drop volumes can be problematic if the printer uses a power supply having only a single output voltage. If a firing pulse of the same voltage is applied to the ink ejection elements of all printheads, then the firing time (the amount of time that the voltage is applied to the ink ejection elements) must be varied in order to provide the proper optimal energy. While this solution is adequate if the required .amount of variation in firing times is not too great between different printheads, there are limitations as to how much the firing time can be varied to compensate for different printheads which, if they are designed to deliver different drop volumes, require different firing voltages. If the voltage applied to a particular printhead is too low for that printhead, requiring that the pulse be lengthened in order to provide the proper firing energy, the pulse may become so long as to undesireably reduce the frequency at which the ink ejection elements can be fired, slowing down printing from the printer. Conversely, if the applied voltage is too high for the printhead, requiring the pulse be shortened in order to provide the proper firing energy, the voltage may be so high and the pulse so short as to cause premature aging and possible failure of the printhead. Thus the voltage appropriate to the design of each particular print cartridge must be supplied in order to avoid these problems, resulting in a need for multiple power sources in printing systems which use printheads having different drop volumes.
The need for supplying different power supply voltages to different print cartridges can also arise even in printheads having the same stable drop volume and firing energy. Parasitic electrical resistances within each print cartridge have the effect of reducing the firing voltage applied to the ink ejection elements below the voltage which is supplied to the electrical interconnection pads of the print cartridge by the power supply in the printer. Manufacturing tolerances can result in the parasitic resistances varying from print cartridge to print cartridge. Since the power supply voltage can only be set to match the parasitic resistances of one of the print cartridges, other print cartridges having different parasitic resistances must operate with non-optimal voltages and thus can suffer from the slower printing or premature aging problems discussed above. To

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