Patent Application
20050146561
This invention relates to depositing drops on a substrate.
Ink jet printers are one type of apparatus for depositing drops on a substrate. Ink jet printers typically include an ink path from an ink supply to a nozzle path. The nozzle path terminates in a nozzle opening from which ink drops are ejected. Ink drop ejection is typically controlled by pressurizing ink in the ink path with an actuator, which may be, for example, a piezoelectric deflector, a thermal bubble jet generator, or an electrostatically deflected element. A typical print assembly has an array of ink paths with corresponding nozzle openings and associated actuators. Drop ejection from each nozzle opening can be independently controlled. In a drop-on-demand print assembly, each actuator is fired to selectively eject a drop at a specific pixel location of an image as the print assembly and a printing substrate are moved relative to one another. In high performance print assemblies, the nozzle openings typically have a diameter of 50 microns or less, e.g. around 25 microns, are separated at a pitch of 100-300 nozzles/inch, have a resolution of 100 to 3000 dpi or more, and provide drops with a volume of about 1 to 120 picoliters (pl) or less. Drop ejection frequency is typically 10 kHz or more.
Hoisington et al. U.S. Pat. No. 5,265,315, describes a print assembly that has a semiconductor body and a piezoelectric actuator. The body is made of silicon, which is etched to define ink chambers. Nozzle openings are defined by a separate nozzle plate, which is attached to the silicon body. The piezoelectric actuator has a layer of piezoelectric material, which changes geometry, or bends, in response to an applied voltage. The bending of the piezoelectric layer pressurizes ink in a pumping chamber located along the ink path. Piezoelectric ink jet print assemblies are also described in Fishbeck et al. U.S. Pat. No. 4,825,227, Hine U.S. Pat. No. 4,937,598, Moynihan et al. U.S. Pat. No. 5,659,346 and Hoisington U.S. Pat. No. 5,757,391, the entire contents of which are hereby incorporated by reference.
In an aspect, the invention features a drop ejector that includes a flow path in which fluid is pressurized to eject drops from a nozzle opening. Adjacent the nozzle opening are a plurality of projections that extend transversely to the plane of the nozzle opening.
In another aspect, the invention features a drop ejector that includes a flow path in which fluid is pressurized for ejection through a nozzle opening. Proximate the nozzle opening, there are at least four posts extending transversely to the plane of the nozzle opening. The posts and the nozzle opening are defined in a common body.
In another aspect, the invention features fluid ejection by providing a printhead that includes a flow path in which fluid is pressurized for ejection through a nozzle opening. Proximate the nozzle opening is a plurality of projections that extend transversely to the plane of the nozzle opening. A fluid is provided that is wicked by capillary forces into the space defined by the projections.
In another aspect, the invention features a drop ejector that includes a flow path in which fluid is pressurized to eject drops from a nozzle opening. Adjacent the nozzle opening are a plurality of projections that extend transversely to the plane of the nozzle opening. The nozzle opening and projections are defined in a common body fabricated from a silicon material and the nozzle opening is disposed on a platform and the projections are disposed proximate the platform.
Other aspects or embodiments may include combinations of the features in the aspects above and/or one or more of the following. The nozzle opening is surrounded by projections. The projections are posts or they are wall-shaped. The projections are arranged in a pattern. The pattern defines an array of rows and columns or the pattern defines an arc. The pattern defines ink-collection spaces. The projections have a width that is about twice the nozzle opening width or less. The spacing between the projections and the perimeter of the nozzle opening is about 20% of the nozzle opening width or greater. The spacing between projections is about twice the nozzle width or less. The number of the projections is four or greater. The height of the projections is substantially equal to the plane of the nozzle opening or the height of the projections are below the plane of nozzle opening.
The nozzle opening and projections are defined defined in a common body and the body is a silicon material. The drop ejector includes a channel proximate the projections. The drop ejector includes a vacuum source or wicking material proximate the projections. The nozzle opening is be disposed in a well and the well includes projections. The nozzle opening is be disposed on a platform and the projections are disposed proximate the platform. The nozzle opening is 200 micron or less. The drop ejector includes a piezoelectric actuator.
Embodiments may include one or more of the following advantages. Printhead operation is robust and reliable since waste ink about the face of the nozzle plate is controlled to reduce interference with drop formation and ejection. Drop velocity and trajectory straightness is maintained in high performance printheads in which large arrays of small nozzles must accurately eject ink to precise locations on a substrate. The projections control waste ink and permit desirable jetting characteristics with a variety of jetting fluids, such as inks with varying viscosity or surface tension characteristics, and heads with varying pressure characteristics at the nozzle openings. The projections are robust, do not require moving components, and can be economically implemented by etching, e.g., in a semiconductor material such as a silicon material.
Still further aspects, features, and advantages follow. For example, particular aspects include projection dimensions, characteristics, and operating conditions described below.
Referring to
The inkjet apparatus also controls the operating pressure at the ink meniscus proximate the nozzle openings when the system is not ejecting drops. Variations in meniscus pressure can cause variation in drop volume or velocity which can lead to printing errors and weeping. In the embodiment illustrated, pressure control is provided by a vacuum source 30 such as a mechanical pump that applies a vacuum to the headspace 9 over the ink 12 in the reservoir 11. The vacuum is communicated through the ink to the nozzle opening 17 to prevent ink from weeping through the nozzle opening by force of gravity. A controller 32, e.g. a computer controller, monitors the vacuum over the ink in the reservoir 11 and adjusts the source 30 to maintain a desired vacuum in the reservoir. In other embodiments, a vacuum source is provided by arranging the ink reservoir below the nozzle openings to create a vacuum proximate the nozzle openings. An ink level monitor (not shown) detects the level of ink, which falls as ink is consumed during a printing operation and thus increases the vacuum at the nozzles. A controller monitors the ink level and refills the reservoir from a bulk container when ink falls below a desired level to maintain vacuum within a desired operation range. In other embodiments, in which the reservoir is located far enough below the nozzles that the vacuum of the meniscus overcomes the capillary force in the nozzle, the ink can be pressurized to maintain a meniscus proximate the nozzle openings. In embodiments, the operating vacuum is maintained at about 0.5 to about 10 inches of water.
Referring to
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The spacing, size, location, shape, number and pattern of the projections are selected to prevent excessive pooling of ink on the nozzle surface by increasing the surface area of the nozzle plate in the area about the nozzle opening. The size of the spaces G between the projections is such that the fluid will be drawn into the openings and retained by capillary forces. In embodiments, the spacing G is between about 20% of the nozzle opening width WN or more and about twice the nozzle opening width WN or less. In embodiments, the pattern of projections define a series of rows and columns. In embodiments, the pattern defines an arc. The pattern of projections can be arranged to direct waste ink in a desired direction on the nozzle plate.
The width of the projections WP is small enough to provide substantial increase in surface area, but large enough to be sufficiently robust. In addition, the width of the projections is not so large that excessive waste ink builds up on outer surfaces. In embodiments, the width of the projections is about twice the nozzle opening width or less. The height of the projections HP can be greater than, equal to, or less than the plane of the nozzle opening. Longer projections can retain a greater amount of waste ink because they present greater surface area. Projections that are recessed below the nozzle opening plane are less susceptible to damage. Projections that are in the plane of the nozzle opening can, in some cases, be easier to manufacture, e.g., by etching.
The projections are disposed in locations on the nozzle plate in which waste ink may collect. In embodiments, the projections substantially surround the nozzle opening. In embodiments, the projections are spaced from the nozzle opening to discourage the collection of waste ink too close to the nozzle opening, where it could affect drop ejection. In embodiments, the projections are no closer to the periphery of the nozzle opening than about 20% or 200% of the nozzle opening width WN.
In embodiments, the shape of the projections can be elongated posts. The posts can be, e.g., circular in cross-section or irregular in cross-section. The posts can be substantially perpendicular to the plane of the nozzle opening or at other transverse angles with respect to the plane of the nozzle opening. In other embodiments, the projections are wall structures. The wall structures can be attached to the nozzle plate over a substantial area and, thus, resist dislodgement should the nozzle plate come into contact with a foreign body, e.g., a substrate.
The number of posts is selected to control a desired jetting fluid volume or to create a desired pattern, as discussed above. In embodiments in which the projections surround the nozzle opening, there are four or more posts, e.g., six or more.
In particular embodiments, the height HP of the projections is, e.g., from about 5 microns to about 100 microns or more, for example, 200 microns. The spacing S from the closest post to the edge of platform is, e.g., from about 10 microns to about 20 microns, while the gap, G, between the projections is, e.g., about 5 microns to about 25 microns. The width of the projections WP is, e.g., from about 5 microns to about 20 microns. In embodiments, the nozzle width is about 200 microns or less, e.g., 10 to 50 microns, the nozzle pitch is about 25 nozzles/inch or more, e.g., about 100-300 nozzles/inch, the ink drop volume is about 1 to 70 pL and the fluid is pressurized by a piezoelectric actuator In embodiments, the jetting fluid has a viscosity of about 1 to 40 centipoise. In embodiments, the the fluid has a surface tension of about 20-50 dynes/cm. In embodiments, the jetting fluid is ink. In embodiments, the jetting fluid is a biological fluid.
Referring now to
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The projections and/or the nozzle opening in any of the above described embodiments can be formed by machining, electroforming, laser ablation, and chemical or plasma etching. The projections can also be formed by molding, e.g., injection molded plastic projections. The projections and nozzle opening can be formed in a common body or in separate bodies that are assembled. For example, the nozzle opening can be formed in a body that defines other components of an ink flow path and the well can be formed in a separate body which is assembled to the body defining the nozzle opening. In other embodiments, the projections, nozzle opening, and pressure chamber are formed in a common body. The body can be a metal, carbon or an etchable material such as silicon material, e.g., silicon or silicon dioxide. Forming printhead components using etching techniques is further described in U.S. Ser. No. 10/189,947, filed Jul. 3, 2002, and U.S. Ser. No. 60/510,459, filed Oct. 10, 2003, the entire contents of each is hereby incorporated by reference.
In embodiments, the drop ejection system can be utilized to eject fluids other than ink. The deposited droplets can be ink or other materials. For example, the deposited droplets may be a UV or other radiation curable material or other material, for example, biological fluids, capable of being delivered as droplets. For example, the apparatus described could be part of a precision dispensing system. The projections can be formed of a porous material, e.g., porous silicon or porous metal, to increase the surface area and, thus, the waste ink handling capacity of the projections. The projections can be formed of an absorbent material that can help to wick away the waste ink from the nozzle plate.
The projections can be used in combination with other waste fluid control features such as apertures described in U.S. Ser. No. ______, filed ______ [Attorney Docket No. 09991-148001], wells as described in U.S. Ser. No. ______, filed ______ [Attorney Docket No. 09991-147001] and/or channels as described in U.S. Ser. No. ______, filed ______ [Attorney Docket No. 09991-151001]. For example, a series of channels can be included on the nozzle face proximate the projections. The cleaning structures can be combined with a manual or automatic washing and wiping system in which a cleaning fluid is applied to the nozzle plate and wiped clean. The cleaning structures can collect cleaning fluid and debris rather than jetted waste ink.
Still other embodiments are within the scope of the following claims.
