Moving liquid curtain catcher

A printhead includes a jetting module that forms liquid drops travelling along a first path. A deflection mechanism causes selected liquid drops formed by the jetting module to deviate from the first path and begin travelling along a second path. A moving liquid curtain is positioned relative to the first path such that the liquid drops travelling along one of the first path and the second path contact the liquid curtain in a drop interception region of the liquid curtain. A liquid collection device is positioned to collect the liquid curtain downstream from the drop interception region.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly-assigned, U.S. patent application Ser. No. 12/843,904, entitled “PRINTING METHOD USING MOVING LIQUID CURTAIN CATCHER” filed concurrently herewith.

FIELD OF THE INVENTION

This invention relates generally to the field of digitally controlled printing systems, and in particular to continuous printing systems.

BACKGROUND OF THE INVENTION

Continuous inkjet printing uses a pressurized liquid source that produces a stream of drops some of which are selected to contact a print media (often referred to a “print drops”) while other drops are selected to be collected and either recycled or discarded (often referred to as “non-print drops”). For example, when no print is desired, the drops are deflected into a capturing mechanism (commonly referred to as a catcher, interceptor, or gutter) and either recycled or discarded. When printing is desired, the drops are not deflected and are allowed to strike a print media. Alternatively, deflected drops can be allowed to strike the print media, while non-deflected drops are collected in the capturing mechanism.

Drop placement accuracy of print drops is critical in order to maintain image quality. Liquid drop build up on the drop contact face of the catcher can adversely affect drop placement accuracy. For example, print drops can collide with liquid that accumulates on the drop contact face of the catcher. As such, there is an ongoing need to provide an improved catcher for these types of printing systems.

SUMMARY OF THE INVENTION

According to one aspect of the present in invention, a printhead includes a jetting module that forms liquid drops travelling along a first path. A deflection mechanism causes selected liquid drops formed by the jetting module to deviate from the first path and begin travelling along a second path. A moving liquid curtain is positioned relative to the first path such that the liquid drops travelling along one of the first path and the second path contact the liquid curtain in a drop interception region of the liquid curtain. A liquid collection device is positioned to collect the liquid curtain downstream from the drop interception region.

DETAILED DESCRIPTION OF THE INVENTION

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. In the following description and drawings, identical reference numerals have been used, where possible, to designate identical elements.

The example embodiments of the present invention are illustrated schematically and not to scale for the sake of clarity. One of the ordinary skills in the art will be able to readily determine the specific size and interconnections of the elements of the example embodiments of the present invention.

As described herein, the example embodiments of the present invention provide a printhead or printhead components typically used in inkjet printing systems. However, many other applications are emerging which use inkjet printheads to emit liquids (other than inks) that need to be finely metered and deposited with high spatial precision. As such, as described herein, the terms “liquid” and “ink” refer to any material that can be ejected by the printhead or printhead components described below.

Referring toFIGS. 1 through 3, example embodiments of a printing system and a continuous printhead are shown that include the present invention described below. It is contemplated that the present invention also finds application in other types of continuous printheads or jetting modules.

Referring toFIG. 1, a continuous printing system20includes an image source22such as a scanner or computer which provides raster image data, outline image data in the form of a page description language, or other forms of digital image data. This image data is converted to half-toned bitmap image data by an image processing unit24which also stores the image data in memory. A plurality of drop forming mechanism control circuits26read data from the image memory and apply time-varying electrical pulses to a drop forming mechanism(s)28that are associated with one or more nozzles of a printhead30. These pulses are applied at an appropriate time, and to the appropriate nozzle, so that drops formed from a continuous ink jet stream will form spots on a recording medium32in the appropriate position designated by the data in the image memory.

Recording medium32is moved relative to printhead30by a recording medium transfer system34, which is electronically controlled by a recording medium transfer control system36, and which in turn is controlled by a micro-controller38. The recording medium transfer system shown inFIG. 1is a schematic only, and many different mechanical configurations are possible. For example, a transfer roller could be used as recording medium transfer system34to facilitate transfer of the ink drops to recording medium32. Such transfer roller technology is well known in the art. In the case of page width printheads, it is most convenient to move recording medium32past a stationary printhead. However, in the case of scanning print systems, it is usually most convenient to move the printhead along one axis (the sub-scanning direction) and the recording medium along an orthogonal axis (the main scanning direction) in a relative raster motion.

Ink is contained in an ink reservoir40and is supplied under pressure to the manifold47of the printhead30to cause streams of ink to flow from the nozzles of the printhead. In the non-printing state, continuous inkjet drop streams are unable to reach recording medium32due to a catcher42that blocks the stream and which may allow a portion of the ink to be recycled by an ink recycling unit44. The ink recycling unit reconditions the ink and feeds it back to reservoir40. Such ink recycling units are well known in the art. The ink pressure suitable for optimal operation will depend on a number of factors, including geometry and thermal properties of the nozzles and thermal properties of the ink. A constant ink pressure can be achieved by applying pressure to ink reservoir40under the control of ink pressure regulator46. Alternatively, the ink reservoir can be left unpressurized, or even under a reduced pressure (vacuum), and a pump is employed to deliver ink from the ink reservoir under pressure to the printhead30. In such an embodiment, the ink pressure regulator46can include an ink pump control system.

The ink is distributed to printhead30through an ink manifold47which is sometimes referred to as a channel. The ink preferably flows through slots or holes etched through a silicon substrate of printhead30to its front surface, where a plurality of nozzles and drop forming mechanisms, for example, heaters, are situated. When printhead30is fabricated from silicon, drop forming mechanism control circuits26can be integrated with the printhead. Printhead30also includes a deflection mechanism which is described in more detail below with reference toFIGS. 2 and 3.

Referring toFIG. 2, a schematic view of continuous liquid printhead30is shown. A jetting module48of printhead30includes an array or a plurality of nozzles50formed in a nozzle plate49. InFIG. 2, nozzle plate49is affixed to jetting module48. However, as shown inFIG. 3, nozzle plate49can be an integral portion of the jetting module48.

Liquid, for example, ink, is emitted under pressure through each nozzle50of the array to form streams, commonly referred to as jets or filaments, of liquid52. InFIG. 2, the array or plurality of nozzles extends into and out of the figure. Typically, the orifice size of nozzle50is from about 5 μm to about 25 μm.

Jetting module48is operable to form liquid drops having a first size or volume and liquid drops having a second size or volume through each nozzle. To accomplish this, jetting module48includes a drop stimulation or drop forming device28, for example, a heater, a piezoelectric actuator, or an electrohydrodynamic stimulator that, when selectively activated, perturbs each jet of liquid52, for example, ink, to induce portions of each jet to break-off from the jet and coalesce to form drops54,56.

Typically, one drop forming device28is associated with each nozzle50of the nozzle array. However, a drop forming device28can be associated with groups of nozzles50or all of nozzles50of the nozzle array.

When printhead30is in operation, drops54,56are typically created in a plurality of sizes or volumes, for example, in the form of large drops56having a first size or volume, and small drops54having a second size or volume. The ratio of the mass of the large drops56to the mass of the small drops54is typically approximately an integer between 2 and 10. A drop stream58including drops54,56follows a drop path, commonly referred to as a trajectory,57. Typically, drop sizes are from about 1 pL to about 20 pL.

Printhead30also includes a gas flow deflection mechanism60that directs a flow of gas62, for example, air, past a portion of the drop trajectory57. This portion of the drop trajectory is called the deflection zone64. As the flow of gas62interacts with drops54,56in deflection zone64it alters the drop trajectories. As the drop trajectories pass out of the deflection zone64they are travelling at an angle, called a deflection angle, relative to the un-deflected drop trajectory57.

Small drops54are more affected by the flow of gas than are large drops56so that the small drop path, commonly referred to as a trajectory,66diverges from the large drop path or trajectory68. That is, the deflection angle for small drops54is larger than for large drops56. The flow of gas62provides sufficient drop deflection and therefore sufficient divergence of the small and large drop trajectories so that catcher42(shown inFIGS. 1 and 3) can be positioned to intercept one of the small drop trajectory66and the large drop trajectory68so that drops following the trajectory are collected by catcher42while drops following the other trajectory bypass the catcher and impinge a recording medium32(shown inFIGS. 1 and 3).

When catcher42is positioned to intercept large drop trajectory68, small drops54are deflected sufficiently to avoid contact with catcher42and strike recording medium32. As the small drops are printed, this is called small drop print mode. When catcher42is positioned to intercept small drop trajectory66, large drops56are the drops that print. This is referred to as large drop print mode.

Referring toFIG. 3, jetting module48includes an array or a plurality of nozzles50. Liquid, for example, ink, supplied through channel47(shown inFIG. 2), is emitted under pressure through each nozzle50of the array to form jets of liquid52. InFIG. 3, the array or plurality of nozzles50extends into and out of the figure.

Drop stimulation or drop forming device28(shown inFIGS. 1 and 2) associated with jetting module48is selectively actuated to perturb the jet of liquid52to induce portions of the jet to break off from the jet to form drops. In this way, drops are selectively created in the form of large drops and small drops that travel toward a recording medium32.

Positive pressure gas flow structure61of gas flow deflection mechanism60is located on a first side of drop trajectory57. Positive pressure gas flow structure61includes first gas flow duct72that includes a lower wall74and an upper wall76. Gas flow duct72directs gas flow62supplied from a positive pressure source92at downward angle θ of approximately 45° relative to the stream of liquid52toward drop deflection zone64(also shown inFIG. 2). Optional seal(s)84provides an air seal between jetting module48and upper wall76of gas flow duct72.

Upper wall76of gas flow duct72does not need to extend to drop deflection zone64(as shown inFIG. 2). InFIG. 3, upper wall76ends at a wall96of jetting module48. Wall96of jetting module48serves as a portion of upper wall76ending at drop deflection zone64.

Negative pressure gas flow structure63of gas flow deflection mechanism60is located on a second side of drop trajectory57. Negative pressure gas flow structure includes a second gas flow duct78located between catcher42and an upper wall82that exhausts gas flow from deflection zone64. Second duct78is connected to a negative pressure source94that is used to help remove gas flowing through second duct78. Optional seal(s)84provides an air seal between jetting module48and upper wall82.

As shown inFIG. 3, gas flow deflection mechanism60includes positive pressure source92and negative pressure source94. However, depending on the specific application contemplated, gas flow deflection mechanism60can include only one of positive pressure source92and negative pressure source94.

Gas supplied by first gas flow duct72is directed into the drop deflection zone64, where it causes large drops56to follow large drop trajectory68and small drops54to follow small drop trajectory66. As shown inFIG. 3, small drop trajectory66is intercepted by a front face90of catcher42. Small drops54contact face90and flow down face90and into a liquid return duct106located or formed between catcher42and a plate88. Collected liquid is either recycled and returned to ink reservoir40(shown inFIG. 1) for reuse or discarded. Large drops56bypass catcher42and travel on to recording medium32. Alternatively, catcher42can be positioned to intercept large drop trajectory68. Large drops56contact catcher42and flow into a liquid return duct located or formed in catcher42. Collected liquid is either recycled for reuse or discarded. Small drops54bypass catcher42and travel on to recording medium32.

Alternatively, deflection can be accomplished by applying heat asymmetrically to a jet of liquid52using an asymmetric heater51. When used in this capacity, asymmetric heater51typically operates as the drop forming mechanism in addition to the deflection mechanism. This type of drop formation and deflection is known having been described in, for example, U.S. Pat. No. 6,079,821, issued to Chwalek et al., on Jun. 27, 2000. Deflection can also be accomplished using an electrostatic deflection mechanism. Typically, the electrostatic deflection mechanism either incorporates drop charging and drop deflection in a single electrode, like the one described in U.S. Pat. No. 4,636,808, or includes separate drop charging and drop deflection electrodes.

Referring toFIGS. 4 through 9, example embodiments of the present invention are shown. Generally described, a printhead made in accordance with the present invention includes a jetting module that forms liquid drops travelling along a first path. A deflection mechanism causes selected liquid drops ejected by the jetting module to deviate from the first path and begin travelling along a second path. A moving liquid curtain is positioned relative to the first path such that the liquid drops travelling along one of the first path and the second path contact and coalesce into the liquid curtain in a drop interception region of the liquid curtain. A liquid collection device is positioned to collect the liquid curtain downstream from the drop interception region.

Referring toFIG. 4, a cross-sectional view of printhead30including an example embodiment of the present invention is shown in more detail. As described above, jetting module48forms drops54,56travelling along drop trajectory57(shown inFIGS. 2 and 3). Gas flow deflection mechanism60deflects drops54,56such that drops54begin travelling along small drop trajectory66and drops56begin travelling along large drop trajectory68(shown inFIGS. 2 and 3). Catcher42, positioned downstream from gas flow deflection mechanism60relative to trajectory57, includes a liquid manifold100, a moving liquid curtain102, a liquid deflector structure104, and a liquid return106. Liquid manifold100includes a liquid inlet108and a liquid outlet110. Liquid outlet110is formed by attaching a spacer116and a cover118to liquid manifold100. Cover118helps guide liquid toward liquid deflector structure104or liquid return106. Alternatively, liquid manifold100and cover118can be an integrally formed one piece structure. Liquid deflector structure104and liquid return106are included in the liquid collection device described above.

Liquid from a liquid source112is pressurized using a pump, for example, or another type of liquid pressurization device134and provided to liquid manifold100through liquid inlet108. The pressurized liquid flows toward liquid outlet110(indicated in each FIG. by arrow111). As the pressurized liquid exits liquid manifold100through liquid outlet110, a moving liquid curtain102is created. Moving liquid curtain102is positioned substantially parallel to trajectory (first path)57. Typically, the angle between liquid curtain102and trajectory57is within ±20° from parallel. Non-printing drops, drops54as shown inFIG. 4, contact liquid curtain102in a drop interception region of liquid curtain102. In this sense, liquid curtain102functions as the drop contact face90(shown inFIG. 3) of catcher42. Typically, non-printing drops contact liquid curtain102in a region of liquid curtain102that is upstream from liquid deflector structure104. However, the drop interception region of liquid curtain102can be any portion of liquid curtain102between liquid outlet110and liquid return106.

Moving liquid curtain102continues along its travel path until liquid curtain102contacts liquid deflector structure104. Liquid deflector structure104causes liquid curtain to change direction and move toward liquid return106. A vacuum source114applies a vacuum to liquid return106to assist with liquid removal in liquid return106and liquid removal away from liquid deflector structure104. Typically, the liquid of liquid curtain102is the same liquid as that of the liquid drops54,56. However, the liquid used for liquid curtain102can be different than that of liquid drops54,56.

Liquid outlet110includes a width132dimension that extends in a direction substantially perpendicular to trajectory or first path57. Outlet width132determines the thickness of liquid film102. Outlet width132can vary and depends on the width of spacer116. Typically, the thickness of moving (flowing) liquid curtain102is selected such that variations in the liquid thickness and flow rate resulting from the non-printing drops coalescing with liquid curtain102are only small perturbations to liquid curtain102that have a minimal effect on the overall characteristics of liquid curtain102.

Referring toFIG. 5, another example embodiment of catcher42is shown. In this embodiment, liquid outlet110is formed in a discrete component120that is attached to liquid manifold100. A portion of component120is curved so that liquid curtain102can be positioned substantially parallel to the first path or trajectory described above. As shown inFIG. 5, liquid manifold100includes a filter122that filters the liquid prior to it exiting liquid outlet110. Alternatively, component120can include filter122, or both component120and manifold100can include filters.

Referring toFIGS. 6 and 7, and back toFIGS. 4 and 5, liquid curtain102is travelling in a direction (indicated in each FIG. by arrow124). The liquid collection device of catcher42includes a structure positioned to contact liquid curtain102to change the direction of travel of liquid curtain102after liquid curtain102has collected the non-printing liquid drops (indicated in each FIG. by arrow136). As shown inFIGS. 4 through 7, that structure is liquid deflector structure104. Liquid deflector structure104includes a curved surface126around which liquid curtain102contacts to change direction. Curved surface126can be a stationary surface as shown inFIGS. 4 and 5or a moving surface as shown inFIG. 6. When curved surface126is moving, curved surface126typically moves in the same direction as liquid curtain102in order to minimize turbulent interaction between curved surface126and liquid curtain102. Curved surface can be driven using a motor. As shown inFIG. 6, curved surface126is circular and movement of curved surface126is a rotational movement. As shown inFIG. 7, liquid deflector structure104includes a porous face128that contacts liquid curtain102. Porous face128helps to minimize turbulent liquid curtain102curved surface126interaction by removing some of the liquid of liquid curtain as it contacts porous face128. Porous face128is in liquid communication with liquid removal channel106. For each of these embodiments, the curvature of the curved surface126of liquid deflector structure104is application dependent and is typically determined by one of more of several factors including, for example, the properties of the liquid, liquid curtain thickness, liquid curtain velocity, and the amount of liquid curtain-liquid deflector structure overlap.

As shown inFIGS. 4 through 7, the liquid collection device of catcher42also includes liquid return channel106that receives liquid curtain102after liquid curtain102changes direction. When the liquid of the liquid curtain is the same liquid as that of the liquid drops (printed or non-printed), liquid return channel106typically returns the liquid to recycling unit44so that the liquid can be used again. Alternatively, liquid return channel106can deliver the liquid to a storage container so that it can be discarded.

Liquid curtain102is not supported by structure on the side of liquid curtain102that is opposite the drop contact face90of liquid curtain102. As such, liquid curtain102does not flow over or down a structure on the side of liquid curtain102that is opposite the drop contact face90of liquid curtain102. However, in some example embodiments of the present invention, catcher42includes structure130positioned to maintain the width of liquid curtain102. Typically, liquid curtain102extends beyond both ends nozzle array50of jetting module48. Maintaining the width of liquid curtain102, using edge guides as shown inFIGS. 8 and 9, for example, helps to ensure that liquid curtain102has consistent liquid properties, such as thickness and velocity from one end of the liquid curtain to the other end of the liquid curtain across the width of the nozzle array so that non-printing drops encounter the same consistency of liquid regardless of where contact with liquid curtain102occurs.

Referring back toFIGS. 4 through 9, liquid curtain102travels from liquid outlet110to liquid return channel106at a velocity. The specific velocity typically depends on the application contemplated with several factors taken into consideration. These factors can include, for example, print speed, printed liquid, for example, ink characteristics, and desired image quality. Printhead30includes a mechanism that regulates the velocity of liquid curtain102. This mechanism can be the device, for example, the pump, that pressurizes the liquid that forms liquid curtain102. Regulation of the velocity of the liquid curtain can occur throughout the printing operation such that the velocity is changed more then once depending on printing conditions. Alternatively, regulation of the velocity can occur once, typically, at the beginning of a printing operation. Preferably, the velocity of the moving liquid curtain is within ±50% of the velocity of the collected drops and, more preferably, the velocity of the moving liquid curtain is substantially the same as the speed of the collected drops and, more preferably, the velocity of the flowing liquid curtain is the same as the component of the drop velocity in the direction of liquid curtain flow.

Referring back toFIGS. 1-9, a printing operation of the printing system20will be described. Liquid drops are provided, travelling along a first path, using a jetting module. Typically, this is accomplished using one of the techniques described above. A moving liquid curtain is provided using a liquid source. This is accomplished by pressurizing the liquid to create the liquid curtain. Selected liquid drops are caused to deviate from the first path and begin travelling along a second path using a deflection mechanism such that the liquid drops travelling along one of the first path and the second path contact the liquid curtain in a drop interception region of the liquid curtain. Deflection of the selected drops is typically accomplished using one of the techniques described above. The liquid curtain is collected downstream from the drop interception region using a liquid collection device.

Collecting the liquid curtain downstream from the drop interception region can include changing the direction of travel of the liquid curtain after the liquid curtain has collected the liquid drops. This can be accomplished by causing the liquid curtain to contact a portion of the liquid collection device. When this is done, the liquid curtain can be caused to contact a curved surface around which the liquid curtain changes direction. The curved surface can be caused to move in the same direction as the liquid curtain. This can include driving the curved surface. After the liquid curtain changes direction, the liquid curtain is caused to flow through a liquid return channel.

The velocity of the liquid curtain can be regulated using a regulating mechanism. This mechanism can be the device, for example, the pump, that pressurizes the liquid that forms liquid curtain. Regulation of the velocity of the liquid curtain can occur throughout the printing operation such that the velocity is changed more then once depending on printing conditions. Alternatively, regulation of the velocity can occur once, typically, at the beginning of a printing operation. Preferably, the velocity of the moving liquid curtain is within ±50% of the velocity of the collected drops and, more preferably, the velocity of the moving liquid curtain is substantially the same as the speed of the collected drops and, more preferably, the velocity of the flowing liquid curtain is the same as the component of the drop velocity in the direction of liquid curtain flow.

In some example embodiments, providing the moving liquid curtain includes positioning the moving liquid curtain substantially parallel relative to the first path. In the same or other example embodiments, the width of the liquid curtain is maintained using suitably designed structures or devices. Typically, it is preferable that the liquid of the liquid curtain is the same liquid as that of the liquid drops.

The moving liquid curtain catcher42of the present invention is also suitable for use when high viscosity liquids are being supplied to and ejected by printhead30. In applications where a high viscosity liquid is being used for the print and non-print liquid drops, the viscosity of liquid curtain102can be lower than the viscosity of the liquid drops. This is done to facilitate movement of the higher viscosity print and non-print liquid drops along the surface of liquid curtain102of catcher42. A heater can be incorporated into the liquid source112to heat the liquid supplied to the liquid manifold100and thereby lower the viscosity of the liquid curtain liquid. Alternatively, the catcher42or the liquid manifold100can include heaters to heat the liquid as it passes through the liquid manifold100. In another embodiment, the liquid supplied to the liquid manifold can be distinct from the liquid of the print and non-print drops with the liquid supplied to the liquid manifold having the lower viscosity. Catcher42of the present invention finds application, for example, when liquids such as hot melt liquids are used. Typically, these liquids have a rapid increase in viscosity when they contact a relatively cooler catcher face. When used with such liquids, the curtain liquid can be heated to keep the liquid above the gelling or solidifying temperature.

The example embodiments of catcher42can be made using conventional fabrication techniques. For example, porous surface104, spacer116, or cover118can be made of photo etched stainless steel, electroformed Ni, or laser abated metal, ceramics, or plastics. Alternatively, the components of catcher42can be made using conventional MEMS processing techniques in silicon or other suitable materials.

Parts List