# Patent

## Title
Liquid film moving over solid catcher surface

## Abstract

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 catcher includes a liquid outlet, a stationary surface, and a liquid source that causes a liquid film to exit the liquid outlet and flow over the stationary surface of the catcher. The catcher 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 film.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
Reference is made to commonly-assigned, U.S. Patent Applications Ser. No. 12/843,907, entitled “PRINTING USING LIQUID FILM POROUS CATCHER SURFACE”, Ser. No. 12/843,910, entitled “LIQUID FILM MOVING OVER POROUS CATCHER SURFACE”, Ser. No. 12/843,909, entitled “PRINTING USING LIQUID FILM SOLID CATCHER SURFACE”, all 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 drops that accumulate 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 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 catcher includes a liquid outlet, a stationary surface, and a liquid source that causes a liquid film to exit the liquid outlet and flow over the stationary surface of the catcher. The catcher 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 film.



BRIEF DESCRIPTION OF THE DRAWINGS
In the detailed description of the example embodiments of the invention presented below, reference is made to the accompanying drawings, in which:
FIG. 1 is a simplified schematic block diagram of an example embodiment of a printing system made in accordance with the present invention;
FIG. 2 is a schematic view of an example embodiment of a continuous printhead made in accordance with the present invention;
FIG. 3 is a schematic view of an example embodiment of a continuous printhead made in accordance with the present invention;
FIG. 4 is a schematic cross sectional view of a printhead including an example embodiment of the present invention;
FIG. 5 is a schematic cross sectional view of a printhead including another example embodiment of the present invention;
FIG. 6A is a schematic cross sectional view of a printhead including another example embodiment of the present invention;
FIG. 6B is a schematic front view of the catcher of the example embodiment shown in FIG. 6A.



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 to FIGS. 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 to FIG. 1, a continuous printing system 20 includes an image source 22 such 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 unit 24 which also stores the image data in memory. A plurality of drop forming mechanism control circuits 26 read data from the image memory and apply time-varying electrical pulses to a drop forming mechanism(s) 28 that are associated with one or more nozzles of a printhead 30. 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 medium 32 in the appropriate position designated by the data in the image memory.
Recording medium 32 is moved relative to printhead 30 by a recording medium transfer system 34, which is electronically controlled by a recording medium transfer control system 36, and which in turn is controlled by a micro-controller 38. The recording medium transfer system shown in FIG. 1 is a schematic only, and many different mechanical configurations are possible. For example, a transfer roller could be used as recording medium transfer system 34 to facilitate transfer of the ink drops to recording medium 32. Such transfer roller technology is well known in the art. In the case of page width printheads, it is most convenient to move recording medium 32 past 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 reservoir 40 and is supplied under sufficient pressure to the manifold 47 of the printhead 30 to cause streams of ink drops to flow from the nozzles of the printhead. In the non-printing state, continuous inkjet drop streams are unable to reach recording medium 32 due to a catcher 42 that blocks the stream and which may allow a portion of the ink to be recycled by an ink recycling unit 44. The ink recycling unit reconditions the ink and feeds it back to reservoir 40. 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 reservoir 40 under the control of ink pressure regulator 46. 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 printhead 30. In such an embodiment, the ink pressure regulator 46 can include an ink pump control system.
The ink is distributed to printhead 30 through an ink manifold 47 which is sometimes referred to as a channel. The ink preferably flows through slots or holes etched through a silicon substrate of printhead 30 to its front surface, where a plurality of nozzles and drop forming mechanisms, for example, heaters, are situated. When printhead 30 is fabricated from silicon, drop forming mechanism control circuits 26 can be integrated with the printhead. Printhead 30 also includes a deflection mechanism which is described in more detail below with reference to FIGS. 2 and 3.
Referring to FIG. 2, a schematic view of continuous liquid printhead 30 is shown. A jetting module 48 of printhead 30 includes an array or a plurality of nozzles 50 formed in a nozzle plate 49. In FIG. 2, nozzle plate 49 is affixed to jetting module 48. However, as shown in FIG. 3, nozzle plate 49 can be an integral portion of the jetting module 48.
Liquid, for example, ink, is emitted under pressure through each nozzle 50 of the array to form streams, commonly referred to as jets or filaments, of liquid 52. In FIG. 2, the array or plurality of nozzles extends into and out of the figure. Typically, the orifice size of nozzle 50 is from about 5 μm to about 25 μm.
Jetting module 48 is 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 module 48 includes a drop stimulation or drop forming device 28, for example, a heater, a piezoelectric actuator, or an electrohydrodynamic stimulator that, when selectively activated, perturbs each jet of liquid 52, for example, ink, to induce portions of each jet to break-off from the jet and coalesce to form drops 54, 56.
In FIG. 2, drop forming device 28 is a heater 51, for example, an asymmetric heater or a ring heater (either segmented or not segmented), located in a nozzle plate 49 on one or both sides of nozzle 50. This type of drop formation is known with certain aspects having been described in, for example, one or more of U.S. Pat. No. 6,457,807 B1, issued to Hawkins et al., on Oct. 1, 2002; U.S. Pat. No. 6,491,362 B1, issued to Jeanmaire, on Dec. 10, 2002; U.S. Pat. No. 6,505,921 B2, issued to Chwalek et al., on Jan. 14, 2003; U.S. Pat. No. 6,554,410 B2, issued to Jeanmaire et al., on Apr. 29, 2003; U.S. Pat. No. 6,575,566 B1, issued to Jeanmaire et al., on Jun. 10, 2003; U.S. Pat. No. 6,588,888 B2, issued to Jeanmaire et al., on Jul. 8, 2003; U.S. Pat. No. 6,793,328 B2, issued to Jeanmaire, on Sep. 21, 2004; U.S. Pat. No. 6,827,429 B2, issued to Jeanmaire et al., on Dec. 7, 2004; and U.S. Pat. No. 6,851,796 B2, issued to Jeanmaire et al., on Feb. 8, 2005.
Typically, one drop forming device 28 is associated with each nozzle 50 of the nozzle array. However, a drop forming device 28 can be associated with groups of nozzles 50 or all of nozzles 50 of the nozzle array.
When printhead 30 is in operation, drops 54, 56 are typically created in a plurality of sizes or volumes, for example, in the form of large drops 56 having a first size or volume, and small drops 54 having a second size or volume. The ratio of the mass of the large drops 56 to the mass of the small drops 54 is typically approximately an integer between 2 and 10. A drop stream 58 including drops 54, 56 follows a drop path or trajectory 57. Typically, drop sizes are from about 1 pL to about 20 pL.
Printhead 30 also includes a gas flow deflection mechanism 60 that directs a flow of gas 62, for example, air, past a portion of the drop trajectory 57. This portion of the drop trajectory is called the deflection zone 64. As the flow of gas 62 interacts with drops 54, 56 in deflection zone 64 it alters the drop trajectories. As the drop trajectories pass out of the deflection zone 64 they are traveling at an angle, called a deflection angle, relative to the un-deflected drop trajectory 57.
Small drops 54 are more affected by the flow of gas than are large drops 56 so that the small drop trajectory 66 diverges from the large drop trajectory 68. That is, the deflection angle for small drops 54 is larger than for large drops 56. The flow of gas 62 provides sufficient drop deflection and therefore sufficient divergence of the small and large drop trajectories so that catcher 42 (shown in FIGS. 1 and 3) can be positioned to intercept one of the small drop trajectory 66 and the large drop trajectory 68 so that drops following the trajectory are collected by catcher 42 while drops following the other trajectory bypass the catcher and impinge a recording medium 32 (shown in FIGS. 1 and 3).
When catcher 42 is positioned to intercept large drop trajectory 68, small drops 54 are deflected sufficiently to avoid contact with catcher 42 and strike recording medium 32. As the small drops are printed, this is called small drop print mode. When catcher 42 is positioned to intercept small drop trajectory 66, large drops 56 are the drops that print. This is referred to as large drop print mode.
Referring to FIG. 3, jetting module 48 includes an array or a plurality of nozzles 50. Liquid, for example, ink, supplied through channel 47 (shown in FIG. 2), is emitted under pressure through each nozzle 50 of the array to form jets of liquid 52. In FIG. 3, the array or plurality of nozzles 50 extends into and out of the figure.
Drop stimulation or drop forming device 28 (shown in FIGS. 1 and 2) associated with jetting module 48 is selectively actuated to perturb the jet of liquid 52 to 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 medium 32.
Positive pressure gas flow structure 61 of gas flow deflection mechanism 60 is located on a first side of drop trajectory 57. Positive pressure gas flow structure 61 includes first gas flow duct 72 that includes a lower wall 74 and an upper wall 76. Gas flow duct 72 directs gas flow 62 supplied from a positive pressure source 92 at downward angle θ of approximately 45° relative to the stream of liquid 52 toward drop deflection zone 64 (also shown in FIG. 2). Optional seal(s) 84 provides an air seal between jetting module 48 and upper wall 76 of gas flow duct 72.
Upper wall 76 of gas flow duct 72 does not need to extend to drop deflection zone 64 (as shown in FIG. 2). In FIG. 3, upper wall 76 ends at a wall 96 of jetting module 48. Wall 96 of jetting module 48 serves as a portion of upper wall 76 ending at drop deflection zone 64.
Negative pressure gas flow structure 63 of gas flow deflection mechanism 60 is located on a second side of drop trajectory 57. Negative pressure gas flow structure includes a second gas flow duct 78 located between catcher 42 and an upper wall 82 that exhausts gas flow from deflection zone 64. Second duct 78 is connected to a negative pressure source 94 that is used to help remove gas flowing through second duct 78. Optional seal(s) 84 provides an air seal between jetting module 48 and upper wall 82.
As shown in FIG. 3, gas flow deflection mechanism 60 includes positive pressure source 92 and negative pressure source 94. However, depending on the specific application contemplated, gas flow deflection mechanism 60 can include only one of positive pressure source 92 and negative pressure source 94.
Gas supplied by first gas flow duct 72 is directed into the drop deflection zone 64, where it causes large drops 56 to follow large drop trajectory 68 and small drops 54 to follow small drop trajectory 66. As shown in FIG. 3, small drop trajectory 66 is intercepted by a front face 90 of catcher 42. Small drops 54 contact face 90 and flow down face 90 and into a liquid return duct 106 located or formed between catcher 42 and a plate 88. Collected liquid is either recycled and returned to ink reservoir 40 (shown in FIG. 1) for reuse or discarded. Large drops 56 bypass catcher 42 and travel on to recording medium 32. Alternatively, catcher 42 can be positioned to intercept large drop trajectory 68. Large drops 56 contact catcher 42 and flow into a liquid return duct located or formed in catcher 42. Collected liquid is either recycled for reuse or discarded. Small drops 54 bypass catcher 42 and travel on to recording medium 32.
Alternatively, deflection can be accomplished by applying heat asymmetrically to a jet of liquid 52 using an asymmetric heater 51. When used in this capacity, asymmetric heater 51 typically 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 to FIGS. 4 and 5, 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 formed by the jetting module to deviate from the first path and begin travelling along a second path. A catcher includes a liquid outlet, a stationary surface, and a liquid source that provides a liquid film flows over the stationary surface of the catcher. The catcher 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 film.
Referring to FIG. 4, a cross-sectional view of printhead 30 including an example embodiment of the present invention is shown in more detail. As described above, jetting module 48 forms drops 54, 56 travelling along drop trajectory, first path 57 (shown in FIGS. 2 and 3). Gas flow deflection mechanism 60 deflects drops 54, 56 such that drops 54 begin travelling along small drop trajectory, second path 66 (shown in FIGS. 2 and 3) and drops 56 begin travelling along large drop trajectory 68 (either the first path or a third path that is slightly deflected relative to the first path as shown in FIGS. 2 and 3). Catcher 42, positioned downstream from gas flow deflection mechanism 60 relative to trajectory 57, includes a liquid manifold 100, a moving liquid film 102, and a stationary surface 104. Liquid manifold 100 includes a liquid inlet 108 and a liquid outlet 110. Liquid outlet 110 is formed by, for example, attaching a spacer 116 and a cover 118 to liquid manifold 100. Stationary surface 104 is a solid surface and, as shown in FIG. 4, is a flat surface. Cover 118 helps guide liquid toward stationary surface 104. Alternatively, liquid manifold 100 and cover 118 can be an integrally formed one piece structure. Catcher 42 also includes a liquid return 106.
Liquid from a liquid source 112 of catcher 42 is pressurized using a pump, for example, or another type of liquid positive pressurization device 134 and provided to liquid manifold 100 through liquid inlet 108. The pressurized liquid flows toward liquid outlet 110 (indicated in FIG. 4 by arrow 111). As the pressurized liquid exits liquid manifold 100 through liquid outlet 110, moving liquid film 102 is created. Moving liquid film 102 flows over and is in contact with solid stationary surface 104 of catcher 42 as liquid film 102 moves toward liquid return 106. This is indicated using arrow 124 in FIG. 4.
A vacuum source 114 applies an amount of vacuum to liquid return 106 to assist with liquid removal (indicated using arrow 136) from liquid return 106. Vacuum source 114 can include a pressure regulator 142 that controls the amount of vacuum provided to liquid return 106. As shown in FIG. 4, pressure regulator 142 controls the amount of vacuum provided to liquid return 106 so that liquid film 102 is drawn into liquid return 106 after liquid film 102 collects the liquid drops (drops 54 as shown in FIG. 4). When the liquid of the liquid film is the same liquid as that of the liquid drops (printed or non-printed), liquid return channel 106 typically returns the liquid to recycling unit 44 so that the liquid can be used again. Alternatively, liquid return channel 106 can deliver the liquid to a storage container so that it can be discarded.
Moving liquid film 102 is positioned substantially parallel to trajectory (first path) 57. Typically, the angle between liquid curtain 102 and trajectory 57 is within ±5° from parallel. As liquid film 102 is moving or flowing over stationary surface 104 of catcher 42 the degree of parallelism depends on the shape of surface 104. In FIG. 4, surface 104 is substantially parallel to trajectory (first path) 57. Typically, the angle between stationary surface 104 and trajectory 57 is within ±5° from parallel. Non-printing drops, drops 54 as shown in FIG. 4, contact liquid film 102 in a drop contact region of liquid film 102. In this sense, liquid film 102 functions as the drop contact face 90 (shown in FIG. 3) of catcher 42. The drop contact region of liquid film 102 can be any portion of liquid film 102 between liquid outlet 110 and liquid return 106.
Liquid outlet 110 includes a width 132 dimension that extends in a direction substantially perpendicular to trajectory or first path 57. Outlet width 132 determines the thickness of liquid film 102. Outlet width 132 can vary and depends on the width of spacer 116. Typically, the thickness of moving (flowing) liquid film 102 is selected such that variations in the liquid resulting from the non-printing drops impacting liquid film 102 are small perturbations to liquid film 102 that have a minimal effect on the overall characteristics of liquid film 102. Typically, the liquid of liquid film 102 is the same liquid as that of the liquid drops 54, 56. However, the liquid used for liquid film 102 can be different than that of liquid drops 54, 56.
Referring to FIG. 5, another example embodiment of catcher 42 is shown. As described above, jetting module 48 forms drops 54, 56 travelling along drop trajectory (first path) 57. Gas flow deflection mechanism 60 deflects drops 54, 56 such that drops 54 begin travelling along small drop trajectory (second path) 66 and drops 56 begin travelling along large drop trajectory (either the first path or a third path that is slightly deflected relative to the first path) 68. Catcher 42, positioned downstream from gas flow deflection mechanism 60 relative to trajectory 57, includes a liquid manifold 100, a moving liquid film 102, and a stationary surface 104. Liquid manifold 100 includes a liquid inlet 108 and a liquid outlet 110. Liquid outlet 110 is formed by attaching a spacer 116 and a cover 118 to liquid manifold 100. Stationary surface 104 is a solid surface and, as shown in FIG. 5, is a convex surface toward first path 57. Catcher 42 also includes a liquid return 106.
In FIG. 5, stationary surface 104 is convex toward trajectory (first path) 57 in contrast to the flat stationary surface 104 shown with reference to FIG. 4. Accordingly, a portion (either or both of 146 and 148) of stationary surface 104 of catcher 42 curves away from the first path 57. This helps to control the thickness of liquid film 102. The transition between the stationary surface 104 and the upper surface of the liquid return 106 can include a fillet (shown in FIG. 3) to help direct liquid from the stationary surface 104 into the liquid return utilizing the Coanda effect.
Liquid from a liquid source 112 of catcher 42 is pressurized using a pump, for example, or another type of liquid positive pressurization device 134 and provided to liquid manifold 100 through liquid inlet 108. The pressurized liquid flows toward liquid outlet 110 (indicated in FIG. 5 by arrow 111). As the pressurized liquid exits liquid manifold 100 through liquid outlet 110, moving liquid film 102 is created. Moving liquid film 102 flows over and is in contact with solid stationary surface 104 of catcher 42 as liquid film 102 moves toward liquid return 106. This is indicated using arrow 124 in FIG. 5.
A vacuum source 114 applies an amount of vacuum to liquid return 106 to assist with liquid removal (indicated using arrow 136) from liquid return 106. Vacuum source 114 can include a pressure regulator 142 that controls the amount of vacuum provided to liquid return 106. As shown in FIG. 5, pressure regulator 142 controls the amount of vacuum provided to liquid return 106 so that liquid film 102 is drawn into liquid return 106 after liquid film 102 collects the liquid drops (drops 54 as shown in FIG. 5). When the liquid of the liquid film is the same liquid as that of the liquid drops (printed or non-printed), liquid return channel 106 typically returns the liquid to recycling unit 44 so that the liquid can be used again. Alternatively, liquid return channel 106 can deliver the liquid to a storage container so that it can be discarded.
Moving liquid film 102 is positioned substantially parallel to trajectory (first path) 57. Typically, the angle between liquid curtain 102 and trajectory 57 is within ±5° from parallel. As liquid film 102 is moving or flowing over stationary surface 104 of catcher 42 the degree of parallelism depends on the shape of surface 104. In FIG. 5, convex stationary surface 104 is substantially parallel to trajectory (first path) 57. Typically, the angle between stationary surface 104 and trajectory 57 is within ±5° from parallel. Non-printing drops, drops 54 as shown in FIG. 5, contact liquid film 102 in a drop contact region of liquid film 102. In this sense, liquid film 102 functions as the drop contacting catcher face 90 (shown in FIG. 3) of catcher 42. The drop contact region of liquid film 102 can be any portion of liquid film 102 between liquid outlet 110 and liquid return 106.
Liquid outlet 110 includes a width 132 dimension that extends in a direction substantially perpendicular to trajectory or first path 57. Outlet width 132 determines the thickness of liquid film 102. Outlet width 132 can vary and depends on the width of spacer 116. Typically, the thickness of moving (flowing) liquid film 102 is selected such that variations in the liquid resulting from the non-printing drops impacting liquid film 102 are small perturbations to liquid film 102 that have a minimal effect on the overall characteristics of liquid film 102. Typically, the liquid of liquid film 102 is the same liquid as that of the liquid drops 54, 56. However, the liquid used for liquid film 102 can be different than that of liquid drops 54, 56.
Referring to FIGS. 6A and 6B, liquid film 102 includes a width dimension that typically extends beyond nozzle array 50. However, in some example embodiments of the present invention, catcher 42 includes structure 130 positioned to maintain the width of liquid film 102 as liquid film 102 flows over surface 104 of catcher 42. Typically, liquid film 102 extends beyond both ends nozzle array 50 of jetting module 48. Maintaining the width of liquid film 102, using edge guides as shown in FIGS. 6A and 6B, for example, helps to ensure that liquid film 102 has consistent liquid properties, in particular thickness and velocity, from one end of the liquid film to the other end of the liquid film so that non-printing drops encounter the same consistency of moving liquid film regardless of where contact with liquid film 102 occurs.
Referring back to FIGS. 4 through 6B, liquid film 102 exits liquid outlet 110 at 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. Printhead 30 includes a mechanism that regulates the velocity of liquid film 102. This mechanism can be the device, for example, the pump, that pressurizes the liquid that forms liquid film 102. Regulation of the velocity of the liquid film 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.
Regulation of the velocity of liquid film 102 can occur before liquid film flows over surface 104 of catcher 42. Preferably, the velocity of the moving liquid film is within ±50% of the velocity of the collected drops and, more preferably, the velocity of the moving liquid film is substantially the same as the speed of the collected drops and, more preferably, the velocity of the flowing liquid film is the same as the component of the drop velocity in the direction of liquid film flow. Preferably the liquid film 102 thickness above the drop contact zone is between 15 micron and 100 micron. More preferably the liquid film thickness above the drop contact zone is between 30 micron and 75 micron. If the liquid film thickness is too small, however, the liquid film can slow down excessively as it moves down the catcher face and can as a result begin to bulge out excessively toward the drop trajectories. Alternatively, if the liquid film thickness is too large, waves in the surface of the liquid film produced by drops impacting the liquid film can reduce the drop deflection operating latitude of the printhead.
The moving liquid film catcher of the present invention is also suitable for use when high viscosity liquids are being supplied to and ejected by printhead 30. In applications where a high viscosity liquid is being used for the print and non-print liquid drops, the viscosity of liquid film 102 can 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 104 of catcher 42. A heater can be incorporated into the liquid source 112 to heat the liquid supplied to the liquid manifold 100 and thereby lower the viscosity of the liquid film liquid. Alternatively, the catcher 42 or the liquid manifold 100 can include heaters to heat the liquid as it passes through the liquid manifold 100. 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.
Referring back to FIGS. 1-6B, a printing operation of the printing system 20 will be described. Liquid drops are provided travelling along a first path using a jetting module. A catcher including a liquid outlet, a stationary surface, and a liquid source is also provided. A liquid film provided by the liquid source is caused to exit the liquid outlet of the catcher and flow over the stationary surface of the catcher. 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 film.
The velocity of the liquid film can be regulated using a regulating mechanism. This mechanism can be the device, for example, the pump, that pressurizes the liquid that forms liquid film. Regulation of the velocity of the liquid film 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. Velocity regulation can occur before the liquid film flows over the porous surface of the catcher. Preferably, the velocity of the moving liquid film is within ±50% of the velocity of the collected drops and, more preferably, the velocity of the moving liquid film is substantially the same as the speed of the collected drops and, more preferably, the velocity of the flowing liquid film is the same as the component of the drop velocity in the direction of liquid film flow. In some applications, the viscosity of the liquid film is lower than the viscosity of the print non-print liquid drops.
In some example embodiments, providing the moving liquid film includes positioning the moving liquid film substantially parallel relative to the first path. In the same or other example embodiments, the width of the liquid film is maintained using suitably designed structures or devices. Stationary catcher surface is solid and can be either flat or convex toward the first path with a portion of the surface of the catcher curving away from the first path. Typically, it is preferable that the liquid of the liquid film is the same liquid as that of the liquid drops. Catcher face 90 can include features to reduce the drag of the liquid flowing down across the surface. Examples of drag reducing features are discussed in commonly assigned U.S. patent application Ser. No. 12/504,050, entitled “Catcher Including Drag Reducing Drop Contact Surface,” incorporated herein by reference.
The example embodiments of catcher 42 can be made using conventional fabrication techniques. For example, surface 104, spacer 116, or cover 118 can be made of photo etched stainless steel, electroformed Ni, or laser abated metal, ceramics, or plastics. Alternatively, the components of catcher 42 can be made using conventional MEMS processing techniques in silicon or other suitable materials.
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.
Parts List
20 continuous printing system
22 image source
24 image processing unit
26 mechanism control circuits
28 device
30 printhead
32 recording medium
34 recording medium transfer system
36 recording medium transfer control system
38 micro-controller
40 reservoir
42 catcher
44 recycling unit
46 pressure regulator
47 manifold
48 jetting module
49 nozzle plate
50 nozzle
51 heater
52 liquid
54 drops
56 drops
57 trajectory
58 drop stream
60 gas flow deflection mechanism
61 positive pressure gas flow structure
62 gas
63 negative pressure gas flow structure
64 deflection zone
66 small drop trajectory
68 large drop trajectory
72 first gas flow duct
74 lower wall
76 upper wall
78 second gas flow duct
82 upper wall
88 plate
90 catcher face
92 positive pressure source
94 negative pressure source
96 wall
100 liquid manifold
102 moving liquid film
104 stationary surface
106 liquid return
108 liquid inlet
110 liquid outlet
111 arrow
112 liquid source
114 vacuum source
116 spacer
118 cover
124 arrow
130 structure
132 outlet width
134 liquid pressurization device
136 arrow
142 pressure regulator
146 catcher portion
148 catcher portion

## Claims

1. A printhead comprising:
a jetting module operable to form liquid drops travelling along a first path;
a deflection mechanism operable to cause selected liquid drops formed by the jetting module to deviate from the first path and begin travelling along a second path;
a catcher including:
a liquid outlet;
a stationary surface; and
a liquid source that causes a liquid film to exit the liquid outlet and flow over the stationary surface of the catcher, the catcher being 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 film, the liquid film including a width dimension, wherein the catcher further comprises a structure positioned to maintain the width of the liquid film as the liquid film flows over the surface of the catcher.

2. The printhead of claim 1, wherein the liquid film of the catcher is positioned substantially parallel to the first path.

3. The printhead of claim 1, the liquid film travelling at a velocity, the printhead further comprising:
a mechanism that regulates the velocity of the liquid film before the liquid film flows over the surface of the catcher.

4. The printhead of claim 1, wherein a portion of the stationary surface of the catcher curves away from the first path.

5. The printhead of claim 1, wherein the liquid of the liquid film is the same liquid as that of the liquid drops.

6. The printhead of claim 1, wherein the velocity of the liquid film is substantially the same as the velocity of the collected drops.

7. The printhead of claim 1, wherein the velocity of the liquid film is within ±50% of the velocity of the collected drops.

8. The printhead of claim 1, wherein the viscosity of the liquid film is lower than the viscosity of the liquid drops.

9. The printhead of claim 1, wherein the velocity of the flowing liquid film is the same as a velocity component of the drops in the direction of liquid film flow.

10. The printhead of claim 1, wherein the liquid outlet includes a cover for guiding the liquid toward the stationary surface such that the liquid film exits the liquid outlet and flows over the stationary surface of the catcher.

11. The printhead of claim 1, the liquid film including a thickness, wherein the liquid outlet includes a width dimension that extends in a direction substantially perpendicular to the first path, the width of the liquid outlet determining the thickness of liquid film.