The present invention relates to printheads for ink jet printers and, more particularly to a protective capping apparatus for such printheads.
Ink jet printing technology is known. Ink jet printers are generally classified according to technology as being of the drop on demand or the continuous ink jet varieties. Drop on demand printheads have an array of nozzles with an actuator associated with each nozzle that is capable of ejecting a drop of ink or other liquid from the nozzle on demand for the placement of a drop on the print media. As the ink in the nozzles remains static in the nozzle between drop ejections, it is possible for solvent to begin to evaporate from the ink in a nozzle between drop ejections. As a result, the fluid properties (including viscosity) in the nozzle can begin to change. It is common, therefore, to use inks for such printheads that tend to be slow drying. When not printing, it is common to place a cap on the nozzle to inhibit the drying of the ink in the nozzles, as dried ink can readily clog the nozzles. It is also common to use a squeegee to rub across the nozzle plate to remove any ink or other debris from the nozzles that might adversely affect drop ejection.
Continuous ink jet printers employ fluid systems that supply ink or other liquid under pressure to the printhead. The pressurized liquid then flows from the nozzles in the form of continuous streams of liquid. As drops break off from the continuous stream, certain drops are selected as print drops while non-selected drops are non-print drops. A catcher is used to intercept the trajectory of non-print drops, while the print drops are allowed to proceed to the print media. As continuous ink jet printheads have a constant flow of ink through the nozzles during normal print operation, the inks used such printheads don't require as much humectant as drop on demand inks, leading to faster dry time and thus the ability to print at a higher speed.
The fluid systems for continuous ink jet systems have commonly employed extensive shutdown and startup sequences to ensure that nozzles don't get clogged when the printhead is not in use and that dried ink or other debris doesn't cause any of the streams of liquid to be misdirected as they flow from the nozzles. When carrying out such startup and shutdown sequences, it is common to employ a sealing member to seal against the bottom of the catcher to prevent ink from spraying or dripping form the printhead during the various sequence steps. In other systems, the printhead is located at a maintenance station during startup and shutdown sequences. Such maintenance stations include sealing members to seal against the catcher which contain ink that sprays or drips from the printhead during the various sequences steps.
While ink jet printers typically use fluids which easily re-dissolve, allowing dried ink residues on the nozzle plate to be removed during a start up procedure, ink that readily re-dissolves dried ink can come at the expense of permanence of printed documents. The use of the sealing members to seal against the lower part of the catcher, whether incorporated into the printhead or into a maintenance station, does not prevent ink from ink from drying in and around the nozzles. Additionally, typical shut down techniques leave pigment ink residue on the nozzle plate which cannot be removed with standard start up techniques.
Accordingly, there is a need for a more effective way of preventing ink from drying in and around the nozzles of a continuous ink jet printhead.
According to one aspect of the invention, a printhead includes a jetting module including an array of nozzles, the jetting module being operable to form liquid drops from liquid emitted through the nozzles of the nozzle array, a catcher for collecting some of the liquid drops, a drop deflection mechanism for deflecting the liquid drops such that some of the liquid drops contact the catcher while other liquid drops are allowed to contact a print media, and a capping mechanism for capping the nozzle array. The capping mechanism includes a capping member located between the nozzle array of the jetting module and the drop deflection mechanism, and the capping member has a first position covering the nozzle array and a second position removed from the nozzle array. Advantageously, the capping member is in contact with the surface of the nozzle array when it is in the first position and the second position, and maintains contact with the surface of the nozzle array as it moves between positions.
According to another aspect of the invention, a method of capping a printhead includes providing a jetting module including an array of nozzles, the jetting module being operable to form liquid drops from liquid emitted through the nozzles of the nozzle array, providing a catcher for collecting some of the liquid drops, providing a drop deflection mechanism for deflecting the liquid drops such that some of the liquid drops contact the catcher while other liquid drops are allowed to contact a print media, providing a capping mechanism for capping the nozzle array, the capping mechanism including a capping member located between the nozzle array of the jetting module and the drop deflection mechanism, and moving the capping member to a first position covering the nozzle array from a second position removed from the nozzle array.
In the detailed description of the example embodiments of the invention presented below, reference is made to the accompanying drawings, in which:
The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art.
Referring to
The jetting module 12 includes a body 24 to which a nozzle plate 26 is attached. The body 24 includes a fluid channel 28 through which the liquid flows under pressure to the nozzle array 14 that is formed in the nozzle plate 26. The liquid flows through the nozzles of the nozzle array 14 forming a stream of continuous liquid from each nozzle. A stimulation device 45, such as a heater, a piezoelectric actuator, or an electrohydrodynamic stimulator, is associated with each nozzle of the nozzle array 14, and is actuated to selectively create drops of different sizes (large drops and small drops) from the continuous stream. These drops follow an initial drop trajectory 30.
The drop deflection mechanism 18 deflects the liquid drops such that some of the liquid drops, for example, the small drops, contact the catcher 16 while other liquid drops, for example, the large drops, are allowed to contact the print media 20. Typically, drop deflection mechanism 18 is either an electrostatic drop deflection mechanisms or a gas flow drop deflection mechanism.
In the embodiment shown in
Gas flow source 34 of drop deflection mechanism 18 causes gas flow across the initial drop trajectories 30 and through the gas flow duct 32 which causes the large and small drops traveling along trajectory 30 to diverge or deflect from trajectory 30. Drop deflection mechanism 18 can also include a second gas flow duct 36 connected in fluid communication to a second gas flow source 38. Second gas flow source 38 provides a gas flow through the second gas flow duct 36 and across the drop trajectories 30 that causes the large and small drops traveling along trajectory 30 to diverge or deflect from trajectory 30.
In the embodiment shown in
Capping mechanism 22, which operates to cap nozzle array 14, includes a capping member 46 located between the nozzle array 14 of the jetting module 12 and the drop deflection mechanism 18. Capping member 46 is affixed to the moveable wall portion 44 of the gas flow duct 32 of drop deflection mechanism 18. The capping member 46 can be affixed to the moveable wall portion 44 by being molded directly to the wall portion, by means of adhesive materials such as pressure sensitive tape, or mechanical means such as screws or clips that clamp a portion of the capping member.
In other embodiments of the present invention, the entire wall 40 can be moveable. In embodiments where the catcher 16 does not form a wall 23 of the gas flow duct 32, the entire drop deflection mechanism 18 or the entire gas flow duct 32 can be moveable. Thus, the moveable portion of the gas flow duct 32 can range from a portion of a wall of the gas flow duct 32 to the entire drop deflection mechanism 18, depending on the specific application contemplated and the specific configuration of the printhead 10.
Capping member 46 is made of an elastomeric material, such as rubber, or a compound including at least some elastomeric material, such as ethylene-propylene-diene monomer (EPDM) 30-35 durometer shore A. Other materials can be used, provided they are compatible with the inks and other fluids used in the printhead 10 and provide sufficient compliance to allow the capping member 46 to seal effectively against the nozzle plate 26.
Referring to
Additionally, when in the second position, as shown in
As a gas leak between the moveable wall portion 44 and fixed wall portion 42 could adversely affect the flow of gas across the drop trajectories needed for drop deflection, an air duct seal 52 provides a seal between the moveable wall portion 44 and fixed wall portion 42 when the capping member 46 is in the second, retracted position. Air duct seal 52 positioned between moveable wall portion 44 and fixed wall portion 42 of the gas flow duct 32 helps to prevent the gas or air flow from experiencing disturbances. In a similar fashion, air duct seals can also be located between the moveable wall portion 44 and the side walls 41 to help prevent air from leaking out of or into the gas flow duct 32 at these locations.
Referring to
In other embodiments, moveable wall portion 44 of gas flow duct 32 can include one or more ribs 50 which are positioned along the width of the gas flow duct 32 to help support the capping member 46. Ribs 50 can extend to the opposite wall 23 of gas flow duct 32 (to the wall of catcher 16 as shown in
Referring to
As actuator 48 moves capping member 46 between the first and second positions along a path perpendicular to the initial drop trajectory 30, capping member 46 maintains contact with the surface of nozzle plate 26 and nozzle array 14. This enables capping member 46 to function as a squeegee to wipe ink and debris from the surface 27 of the nozzle array 14. Positioning coupling frame 49 between moveable wall portion 44 and actuator 48 allows actuator 48 to be somewhat removed from the area of the capping member 46 which helps keep actuator 48 clean and provides fewer space restrictions for the actuator 48. Guide rails 56 engageable with coupling frame 49 help to maintain a linear path of motion when capping mechanism 22 is moving between its first position and its second position.
Referring to
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention.