Thermal ink jet printhead with constant operating temperature
AssigneeXerox Corporation
InventorsGary A. Kneezel, Thomas A. Tellier, Richard V. LaDonna
Life of this patent
Estimating the term…
Abstract
A thermal ink jet printer is disclosed which has a printhead that is maintained at a substantially constant operating temperature during printing. Printing on demand is accomplished by the ejection of ink droplets from the printhead nozzles in response to energy pulses selectively applied to heating elements located in ink channels upstream from the nozzles which pulses vaporize the ink to form temporary bubbles. To prevent printhead temperature fluctuations during printing, especially in translatable carriage printers, the heating elements not being used to eject droplets are selectively energized with energy pulses having insufficient magnitude to vaporize the ink.
Claims23
A method of maintaining the operating temperature of a thermal ink jet printhead substantially constant while it is in a printing mode and ejecting ink droplets from a plurality of nozzles therein, comprising the steps of:
- counting a number of ink droplet ejecting electrical pulses applied to heating elements within the printhead that effect the ejection of ink droplets form the printhead nozzles during predetermined time periods;
- comparing the counted number of said droplet ejecting pulses per predetermined time period with a minimum number required per predetermined time period to maintain the desired operating temperature constant and determining a number of droplet ejecting pulses which is less than said minimum number;
- and
- pulsing predetermined heating elements not being used to eject droplets with electrical pulses insufficient in magnitude to vaporize ink when the number of droplet ejecting pulses are less than said minimum number to provide supplemental heat to the printhead which is equivalent to heat that would have been added by said determined number of droplet ejecting pulses which are less than said minimum number, so that the printhead is maintained at a substantially constant operating temperature, while the printhead is in the printing mode, without the need of continually sensing the printhead temperature.
The method of claim 4, wherein the width of the electrical pulses insufficient in magnitude to vaporize ink is established so that the predetermined heating elements pulsed therewith are all heating elements not ejecting droplets.
An improved thermal ink jet printhead of the type having an ink supply manifold, a plurality of capillary-filled, parallel ink channels that communicate at one end with the manifold and terminate at the other end with a nozzle, and a linear array of heating elements, one located in each ink channel, the printhead ejecting ink droplets on demand by the selective energization of the heating elements with electrical energy pulses having sufficient magnitude to vaporize instantaneously the ink in contact with the energized heating element, so that temporary vapor bubbles are formed which eject said ink droplets, wherein the improvement comprises:
- means for counting a number of electrical energy pulses which ejected ink droplets during predetermined time periods;
- means for comparing the counted number of electrical energy pulses which ejected ink droplets during said predetermined time periods with a minimum number of such pulses that are required to maintain the printhead operating temperature substantially constant;
- and
- energization of predetermined heating elements with electrical energy pulses insufficient i magnitude to vaporize the ink at times when said predetermined heating elements are not being energized for the ejection of ink droplets but concurrently when other heating elements are ejecting ink droplets to provide supplemental heat to the printhead, whenever the minimum number of droplet ejecting pulses is not met, so that the printhead is maintained at a substantially constant operating temperature while the printhead is in a printing mode without the need for continually sensing the printhead temperature.
A thermal ink jet printhead for use in an ink jet printer and of the type having a plurality of fully functional printhead subunits mounted on a structural bar, each printhead subunit having a linear array of equally spaced nozzles and a heating element for each nozzle, the printhead subunits being equally spaced from a recording medium and adapted to eject ink droplets on demand from selected nozzles in response to electrical energy pulses representative of data to be printed, which are applied to the heating elements of each printhead subunit, comprising:
- means for counting a number of droplet ejecting electrical energy pulses applied to the heating elements of each respective subunit which ejects ink droplets from nozzles therein during predetermined time periods;
- means for comparing each of the counted number of electrical energy pulses which ejected ink droplets during said predetermined time periods with a minimum number of such pulses that are required to maintain each printhead subunit operating temperature substantially constant and determining a number of droplet ejecting electrical energy pulses which are less than said minimum number of such pulses;
- and
- energization of predetermined heating elements in each printhead subunit not being used to eject droplets with subthreshold energy pulses insufficient in magnitude to vaporize ink to provide supplemental heat to the printhead subunits which is equivalent to heat that would have been added by said determined number of droplet ejecting electrical energy pulses which are less than said minimum number, in order to maintain all of the printhead subunits within the desired operating temperature.
A method of maintaining a desired operating temperature of a printhead in a thermal ink jet printer substantially constant, the printhead having a plurality of nozzles and a heating element for each nozzle, and the printer having a controller for selectively applying either droplet ejecting or non-droplet ejecting electrical pulses to the printhead heating elements, so that, when the printhead is in a printing mode, the printhead is capable of ejecting ink droplets from the nozzles having satisfactory velocities in response to droplet ejecting electrical pulses applied to selected heating elements, comprising the steps of:
- (a) providing a heat sink for the printhead having a known rate of heat dissipation to remove heat continually from the printhead;
- (b) counting droplet ejecting electrical pulses applied to the printhead heating elements during a predetermined time period, each droplet ejecting electrical pulse adding a first known amount of heat energy to said printhead;
- (c) comparing the counted droplet ejecting electrical pulses with a minimum number thereof required to maintain the desired printhead operating temperature constant, while said heat sink is dissipating heat, and deriving a number of such pulses which are less than said required minimum number;
- (d) determining a number of non-droplet ejecting pulses required to maintain the desired operating temperature of the printhead, when the counted droplet ejecting pulses are less than the minimum number required, each non-droplet ejecting pulse adding a second known amount of heat energy to the printhead;
- and
- (e) applying said determined number of non-droplet ejecting pulses to the printhead heating elements in nozzles not being used to eject droplets, so that the printhead is maintained at a substantially constant operating temperature without the need of continually sensing the printhead temperature.
Dependencies are inferred from the claim text.