Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-02-19
2001-06-12
Le, N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06244683
ABSTRACT:
The present invention relates to an ink protection device for an inkjet printhead, and in particular to a protection device which protects the electrical interconnect of a printhead from ink.
The present invention relates to the art of inkjet printing mechanisms whether of the thermal or piezo variety which may be included in a variety of different products including copiers and facsimile machines in addition to standalone printers either desktop mounted, portable or freestanding. Herein a freestanding printer will be used to illustrate the present invention. Printers of this type have a printhead carriage which is mounted for reciprocal movement on the printer in a direction orthogonal to the direction of movement of the paper or other medium on which printing is to take place through the printer. The printer carriage of a color printer typically has two or more, usually four, thermal ink Jet printheads mounted thereon which may be removable. Each of the printheads contains or is attached to a remote supply of ink which is fed via ink channels within the printhead to an ink ejection mechanism generally in the lower part of the printhead and ejected as drops through a nozzle plate mounted on an ink ejection surface of the printhead. The nozzle plate having numerous small orifices or nozzles therethrough. For thermal (as opposed to piezo-electric) inkjet printheads ink channels or conduits lead to firing chambers each associated with heater elements, Such as resistors, which are energized to heat ink within the firing chambers. Upon heating, an ink drop is ejected from a nozzle associated with the energized resistor.
To service, that is clean, maintain, protect or recover the correct operation of the printhead, typically a “service station” mechanism is mounted within the printer so the printhead can be moved over to the station for servicing. For storage, or during non-printing periods, the service stations usually include a capping system which hermetically seals the printhead nozzles from contaminants and prevents drying. Some caps are also designed to facilitate priming, such as by being connected to a pumping unit or other mechanism that draws a vacuum on the printhead. During operation, clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a process known as “spitting,” with the waste ink being collected in a “spittoon” reservoir portion of the service station. After spitting, uncapping, priming or occasionally during printing, most service stations have an elastomeric wiper that wipes the ink ejection surface of the printhead to remove ink residue, as well as any paper dust or other debris that has collected on the face of the printhead.
During printing and spitting, some small ink droplets may become airborne within the printer, forming what is known as “ink aerosol”. Unfortunately, this ink aerosol often lands in undesirable locations on the inkjet printhead that are not normally cleaned by the printhead service station. For example, this ink aerosol may collect along a portion of the printhead exterior next to the electrical interconnect that sends the firing signals to the printhead. Moreover, the process of wiping the printhead often deposits ink on this portion of the printhead adjacent the electrical interconnect. Beyond leaving the printhead dirty with ink residue, unfortunately, many inkjet inks are also electrically conductive, so any ink smeared on the conductors of the electrical interconnect has the potential for causing a short circuit between the conductors. Ink residue deposited on the printhead next to the electrical interconnect may be smeared on the interconnect conductors when the printhead is removed, and then further smeared across the interconnect when a new printhead is installed increasing the chances for a short circuit to occur. Furthermore such ink may cause corrosion of the electrical contact pads of either the carriage or the printhead. A prior art solution to ink residue adjacent the electrical interconnect comprises the use of a so called “snout wiper” which is a wiper similar to those conventionally used to wipe the ink ejection surface of the printhead, to wipe an area of the vertical interconnect face of the printhead below the electrical interconnect pads. However. in addition to imposing further complication on the service station of the printer and its associated servicing routines it has been found that such snout wiping is insufficient to remove all such ink residue. Furthermore any ink residue that remains has been found to migrate upwards towards the electrical interconnect pads of the printhead through capillary forces.
A further problem due to ink residue (and which is not resolved by snout wiping) is that it has been found that ink aerosol can build up within the stalls of the printer carriage in which the printheads are located and can make its way between the datum surfaces on the printhead and the carriage which serve to accurately align the printhead within the carriage. This can lead to printing errors in images printed due to misplacement of ink droplets fired by the printhead on print media.
A further factor in the buildup of ink residue on inkjet printheads is that the lifetimes required of the printheads is increasing, particularly for printheads that are utilised in combination with large volume ink reservoirs which are remote from the printhead (so called “off-axis” systems) and which may be replaced without replacing the printhead. The ink residue problem is exacerbated in an off-axis system because the printheads are replaced less frequently during the useful life of the printer so this residue may build-up over a longer period in contrast to a replaceable printhead system, which requires replacement of the printhead when empty.
According to the present invention there is provided an ink protection device for an inkjet printhead mountable within a carriage of a printer the printhead having an ink ejection surface through which ink is ejected and a plurality of faces extending from the ink ejection surface, the device comprising a flap member associated with the printhead and extending generally parallel to the ink ejection surface so that when the printhead is mounted in the carriage the flap member extends between the carriage and a face of the printhead. It has been found by the present Applicants that a simple physical barrier to the passage of ink which acts on the printhead when it is mounted in the carriage is effective in greatly reducing the level of ink passing into the carriage past the printhead either in the form of aerosol or liquid in contact with a face of the printhead.
Although the flap member may be mounted on the printhead, preferably, the flap member is mounted on the carriage and contacts a face of the printhead.
Advantageously, the flap member is composed of a material which is both compliant and resilient so that it is able to repeatedly contact the printhead and form a substantially ink tight seal.
Preferably, the flap member is generally parallel to the ink ejection surface of the printhead prior to the insertion of the printhead into the carriage, more preferably the flap member extends at an angle of less than 30 degrees to the plane of the ejection surface of the printhead, most preferably at an angle of less than 15 degrees.
However, it is advantageous that the printhead deflects the flap member when it is installed so that the flap member curves downwardly, preferably at an angle of less than 45 degrees.
In a specific embodiment, the ink protection device comprises four flap members per printhead, one associated with each face of the printhead. This has been found to be very effective at impeding the entry of ink aerosol in the carriage and thus preventing ink residue on the datum surfaces of the printhead and carriage.
Conveniently, the device comprises a first substantially laminar component formed of a flexible material and a second substantially laminar component formed of stiffer material, the first component comprising
Alvarez Jose A.
Taylor Christopher
Hewlett--Packard Company
Hsieh Shih-Wen
Le N.
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