CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Reference is made to commonly-assigned, U.S. patent applications Ser. No. ______ (Docket 95415), entitled “DEVICE INCLUDING MOVABLE PORTION FOR CONTROLLING FLUID”, Ser. No. ______ (95584), entitled “DEVICE FOR CONTROLLING DIRECTION OF FLUID”, Ser. No. ______ (Docket 95585), entitled “INTERACTION OF DEVICE AND FLUID USING FORCE”, and Ser. No. ______ (Docket 95586), entitled “DEVICE FOR CONTROLLING FLUID VELOCITY”, all filed concurrently herewith. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates generally to formation and control of fluid drops, and in particular to control devices that either actively or passively control fluid drops via interaction of a fluid jet and a control device surface at or near the region of fluid jet breakoff. 
       BACKGROUND OF THE INVENTION 
       [0003]    The ability to reliably and accurately position drops ejected from fluid ejectors, for example, inkjet printheads, at predetermined locations is a critical systems requirement for the printing of high-quality pictorial images and text. Accurate positioning of drops on the receiver is difficult because ejected drops suffer from both stochastic (random) placement inaccuracies and repeating (semi-permanent) placement inaccuracies. Examples of a stochastic (random) placement inaccuracy includes drop-to-drop variations in the contact point of the drop tail as is leaves the ejector surface and fluctuations in the airflow around the printhead. Examples of repeating (semi-permanent) placement inaccuracies include permanently malformed ejectors and particulate debris contacting the ejector nozzle plate. 
         [0004]    In some situations, accurate positioning of drops may be achieved by locating the receiver in close proximity to the printhead, so that drops which are angularly misdirected do not have time to travel too far from their desired location on the receiver in the plane of the receiver. However, overly close spacing may cause mechanical contact between the printhead and the receiver possibly resulting in printhead damage. 
         [0005]    Other strategies to control drop locations include the use of airflow or electric fields oriented in the direction of the drop trajectories to guide drops to desired locations as well as the application of electric fields perpendicular to the direction of the drop trajectories to guide drops to desired locations. However, these strategies need to use very large airflows or very high electric fields to influence drop trajectories which possibly resulting in image artifacts and reduced system reliability. 
         [0006]    Accurate positioning of drops on the receiver is also limited by the formation of satellite drops during drop breakup or by drop recombination as drops travel along their trajectories. Drops of unusually small or large sizes are produced which reduce image quality or cause reliability problems due to fluid accumulation at unwanted regions. Although satellite formation can be controlled to some extent by ink formulation or printhead operation parameters, these solutions typically reduce image quality or printer performance, for example by requiring special ink formulations not optimized for image quality or by necessitation reduced printing speeds. 
         [0007]    The inverse relationship between frequency of operation and drop control also contributes to accurately positioning drops. In general, it is desirable to operate inkjet printers at the highest possible frequencies for reasons of productivity. However, drop placement typically suffers at high frequency operation while the propensity of satellite formation or drop recombination typically increases. 
       SUMMARY OF THE INVENTION 
       [0008]    According to one aspect of the present invention, the formation and control of a fluid drop(s) produced by fluid drop ejectors, for example, drop ejectors of the drop-on-demand type or continuous type, are managed either passively or actively. 
         [0009]    The control device of the present invention can be positioned remotely from the surface of the drop ejectors. For example, when the drop ejector is a continuous type ejector, the control device can be positioned at or near the location of drop break-off from the jetting fluid column so that the fluid leaving the control surface of the control device after interacting with the control surface of the control device can be in the form of a fluid jet or a fluid drop(s). Additionally, an array of control devices can be remotely positioned from the surface of a corresponding array of drop ejectors. 
         [0010]    The control device of the present invention either passively or actively modifies drop velocity, trajectory, or combinations thereof through interaction of a surface of a control device and the fluid jet or the fluid drop(s). For example, the control devices of the present invention can modify drop trajectories through contact of the surface of a control device and the drop(s) as the drop(s) travels across the surface of the control device or exits the surface of the control device. This can occur on a drop by drop basis. Additionally, when incoming fluid jets suffering from variations in directionality interact with the control surface of the control device of the present invention, the trajectory of the corresponding exiting drops can be at least partially corrected. 
         [0011]    The control device of the present invention also has the ability to selectively suppress satellite drops and to reduce inadvertent drop merger. For example, the control surface of the control device can be designed to passively or actively control (modulate) the trajectory and velocity of the exiting drops relative to the that of the incoming drops on a drop by drop basis so as to cause satellite drops to merge with other drops or prevent drops from inadvertently merging with each other. 
         [0012]    According to another aspect of the present invention, a method of controlling fluid flow includes providing a moving fluid including a fluid flow characteristic; providing a fluid control device including a fluid control surface, the fluid control surface including a pattern; causing the fluid to contact the fluid control surface of the fluid control device; and causing the fluid to interact with the fluid control surface of the fluid control device using the pattern of the fluid control surface that, when activated, causes adjacent fluid drops to merge or coalesce while the fluid is in contact with the pattern of the fluid control device such that the fluid flow characteristic of the fluid after interacting with the fluid control surface of the fluid control device is different from the fluid flow characteristic of the fluid before interaction with the fluid control surface of the fluid control device. 
         [0013]    According to another aspect of the present invention, a microfluidic device includes a fluid source and a fluid control device. The fluid source provide a moving fluid with the moving fluid including a fluid flow characteristic. The fluid control device includes a fluid control surface. The fluid control surface includes a pattern that, when activated, causes adjacent fluid drops to merge or coalesce when the fluid drop is in contact with the pattern such that the fluid flow characteristic of the moving fluid after interaction with the fluid control surface of the fluid control device is different from the fluid flow characteristic of the moving fluid before interaction with the fluid control surface of the fluid control device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    In the detailed description of the example embodiments of the invention presented below, reference is made to the accompanying drawings, in which: 
           [0015]      FIG. 1  is a schematic view of a prior art continuous inkjet printhead including an array of fluidic ejectors with nozzles located on a printhead surface  10 ; 
           [0016]      FIG. 2  is a schematic view of a continuous inkjet printhead incorporating an example embodiment of the present invention; 
           [0017]      FIGS. 3A through 3C  are schematic views of an example embodiment of a drop control surface of the present invention; 
           [0018]      FIG. 4A  is a schematic view of another example embodiment of a drop control surface of the present invention; 
           [0019]      FIG. 4B  is a schematic view of another example embodiment of a drop control surface of the present invention; 
           [0020]      FIG. 5A  is a schematic view of another example embodiment of a drop control surface of the present invention; 
           [0021]      FIG. 5B  is a schematic view of another example embodiment of a drop control surface of the present invention; 
           [0022]      FIGS. 6A and 6B  are schematic views of another example embodiment of the present invention; 
           [0023]      FIG. 7  is a schematic view of another example embodiment of the present invention; 
           [0024]      FIGS. 8A and 8B  are schematic views of another example embodiment of the present invention; 
           [0025]      FIGS. 8C and 8D  are schematic views of another example embodiment of the present invention; 
           [0026]      FIG. 9  is a schematic view of another example embodiment of a drop control surface of the present invention; 
           [0027]      FIGS. 10A and 10B  are schematic views of another example embodiment of a drop control surface of the present invention; 
           [0028]      FIG. 11  is a schematic view of another example embodiment of a drop control surface of the present invention; 
           [0029]      FIG. 12A  is a schematic view of another example embodiment of the present invention; 
           [0030]      FIG. 12B  is a schematic view of another example embodiment of the present invention; 
           [0031]      FIG. 13A  is a schematic view of another example embodiment of a drop control surface of the present invention; 
           [0032]      FIG. 13B  is a schematic view of a continuous inkjet printhead incorporating another example embodiment of the present invention; and 
           [0033]      FIGS. 14A and 14B  are schematic views of another example embodiment of a drop control surface of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    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. 
         [0035]    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. 
         [0036]    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. 
         [0037]    Generally described, the present invention describes a microfluidic device that manages the formation and control of a fluid drop(s) produced by fluid drop ejectors through interaction of a surface of a control device and a fluid jet that breaks up into the drop(s) or through interaction of a surface of a control device and the drop(s) themselves. For example, fluid drops or fluid jets can impact on at least one control device surface and subsequently exit the surface. While in contact with the surface, the surface acts on the drops or jets to provide alteration, correction, or modulation of the trajectories or other properties of the drops or jets after the drops or jets subsequently exit the surface. As used herein, a fluid jet includes a fluid column with sufficient momentum to self-eject from an aperture, for example, a nozzle of a continuous inkjet printhead. 
         [0038]    Advantageously, the present invention provides a way to deliberately control the trajectories of drop(s) moving through the air. For example, slight and precise corrections to drop trajectories can be made to drop(s) exiting the control device of the present invention. Additionally, the present invention is applicable to either drops or jets entering the control device and includes, for example, drops or jets obliquely impacting a surface of the device with drops exiting the surface of the device. 
         [0039]    The surface of the control device can include patterned features, either passive, active, or combinations thereof, for passively or actively controlling the exiting trajectories and other properties of the exiting drops or jets. Typically, the control surface acts on the impacting droplets to improve or even correct the properties of the impacting drops before the drops exit the control surface. This results in improved printing performance attributes such as reliability or image quality. For example, impacting jets that suffer from directional errors or exhibit a propensity to form satellite drops exit the control surface with at least partially corrected trajectories or with fewer satellite drops formed when compared to jets that do not impact the control surface of the control device. 
         [0040]    Example embodiments of the present invention are discussed below with reference to  FIGS. 1 through 14B . 
         [0041]      FIG. 1  is a schematic view of a prior art continuous inkjet printhead including an array of fluidic ejectors with nozzles located on a surface of printhead  1 O. A continuous liquid jet  11  is ejected from each nozzle. Each continuous liquid jet  11  breaks up into drops  12  of controlled volume when a conventional device applies a stimulation energy to the continuous liquid jet(s). Liquid jet  13  illustrates a misdirected jet from a defective nozzle that results in the direction of jet  13  being different from the direction of jets  11  produced by non-defective nozzles. 
         [0042]      FIG. 2  is a schematic view of an inkjet printhead incorporating an embodiment of the present invention. In  FIG. 2 , a drop control device  20  includes a plurality of drop control surfaces  21  in a one to one association with the array of nozzles and disposed such that each drop control surface is located remotely from its respective nozzle. A fluidic interaction, for example, a physical contact, is made between the jet from the nozzle and the associated drop control surface  21  at or near (less than or approximately  20  times the jet diameter) the point of break off of the jet. The fluid drops or jets are controlled by the drop control surfaces  21  while in physical contact with the control surfaces in a one to one association until the drops or jets exit the drop control surface. 
         [0043]    The drop control device  20  includes a pattern on each drop control surface  21  which passively act to guide the direction of drops exiting the drop control surface  21  toward a preferred direction regardless of the direction of travel of the jet from the associated nozzle. The drop control surfaces  21  have geometry and properties such that the fluid drops or jets have high affinity to the drop control surfaces. The drop control surfaces  21  are separated by gap regions  22  having geometry and properties such that they have low affinity to the fluid drops or jets. As shown In  FIG. 2 , the drop control surfaces  21  are hydrophilic surfaces and the gap regions  22  are hydrophobic surfaces. In another example embodiment, the drop control surfaces  21  can be capillary grooves and the gap regions  22  can be ridges between the capillary grooves  21 . In another example embodiment, the capillary grooves  21  can have hydrophilic surface property and the gap region ridges  22  can have hydrophobic surface property. 
         [0044]      FIGS. 3A through 3C  are schematic views of an example embodiment of a drop control surface  21  of control device  20 . The surface pattern of the drop control surface  21  includes one or more lines of hydrophilic surface properties  31  space apart by lines of hydrophobic surface properties  32 . In  FIG. 3A  and  FIG. 3B , liquid drops misdirected by different degrees that are in contact with the drop control surface  21  are guided toward a same preferred direction by the surface pattern of the drop control surface  21 . The drops shown in  FIG. 3A  are more misdirected than the drops shown in  FIG. 3B . In  FIG. 3C , liquid drops break off from the misdirected liquid jet that is in contact with the drop control surface  21  and are guided toward a preferred direction by the surface pattern of the drop control surface  21 . 
         [0045]    Alternatively in  FIGS. 3A through 3C , the surface pattern of the drop control surface  21  can include one or more narrow ridges or wires  31  which preferentially guide the direction of drops exiting the drop control surface toward a preferred direction regardless of the direction of travel of the jet from the associated nozzle. In another example embodiment, the surface patterns  31  of the drop control surface  21  can be activated by a control means to guide the direction of drops exiting the drop control surface toward a preferred direction regardless of the direction of travel of the jet from the associated nozzle. 
         [0046]      FIGS. 4A and 4B  are schematic views of other examples of the drop control surface  21 . The drop control surface  21  includes one (shown in  FIG. 4A ) or more (three are shown in  FIG. 4B  although more or less are permitted) thin wires  41  arranged in three dimensional space in the path of the liquid drops or jets to capture and guide liquid drops or jets toward a desired common trajectory of exit. Preferably, the surfaces of the wires  41  are hydrophilic so that the liquid drops or jets can be captured by the wires upon contact. 
         [0047]      FIG. 5A  is a schematic view of another example embodiment of a drop control surface of the present invention. Drop control surface  21  includes a pattern of electrodes  51 ,  52 ,  53  and  54  for active steering of drops  12  due to asymmetric application of wetting forces or to dielectric attraction. This example embodiment operates by the principle of dielectrophoresis (or DEP), which is a phenomenon in which a force is exerted on a dielectric drop or particle when it is subjected to a non-uniform electric field. 
         [0048]    Dielectrophoresis is the translational motion of neutral matter caused by polarization effects in a nonuniform electric field. The dielectrophoresis force can be seen only when drops or particles are in the non-uniform electric fields. Since the dielectrophoresis force does not depend on the polarity of the electric field, the phenomenon can be observed either with AC or DC excitation. Drops or particles are attracted to regions of stronger electric field when their permittivity exceeds that of the suspension medium. When permittivity of medium is greater than that of drops or particles, this results in motion of drops or particles to the lesser electric field. DEP is most readily observed for drops or particles with diameters ranging from approximately 1 to 1000 μm. Above 1000 μm gravity, and below 1 μm Brownian motion, overwhelm the DEP forces. The main advantages of the electrical systems include geometric simplicity, easy of fabrication, absence of moving parts and voltage-based control. 
         [0049]    The basic geometry of the embodiment, shown in  FIG. 5A , includes long electrodes  51 ,  52 ,  53  and  54 , patterned on an insulating substrate and then coated with a dielectric layer to insulate them electrically and to passivate them against electrolysis. Such a structure can be obtained using conventional photolithography (see, for example, Ahmed R. and Jones. T. B., Dispensing Picoliter Droplet on Substrates Using Dielectrophoresis, Journal of Eletrostatics, 2006, vol. 64, No. 7-9, pp. 543-549). 
         [0050]    In this embodiment, the force does not require drops  12  to be charged. All drops exhibit dielectrophoretic activity in the presence of electric fields. However, the strength of the force depends strongly on the medium and the electrical properties and size of the drops, as well as on the frequency of the electric field. Consequently, fields of a particular frequency can manipulate drops with great selectivity. 
         [0051]      FIG. 5B  is a schematic view of another example embodiment of a drop control surface of the present invention. A mechanically controlled steering device  58  guides drops  12  after breakoff. Drops  12  are confined and contact the steering device  58  in the form of a trough, capable of angular movement. There are many ways known to the art to control the mechanical motion of the steering device  58 . For example, a camshaft  59  is utilized with a spring  61  that is attached to a fixed location  62 , the steering device  58  will be in contact with the camshaft  59  as the camshaft  59  rotates on its shaft  60 . Generally, the motion of the steering device  58  is from the left to the right (as viewed from left side of  FIG. 5B  to the right side of  FIG. 5B ) and back again. However, as the camshaft  59  is not circular, its profile  63  can determine the motion of the steering device  58 . 
         [0052]      FIGS. 6A and 6B  are schematic views of another example embodiment of the present invention. A deflection device  65  controls the trajectory of drops  12 . Deflection device  65  can be referred to as an active cantilever. Typically, the deflection device  65  has two main positions, on and off, although more positions are permitted. When the deflection device  65  is on the on-position, shown on the left side of  FIG. 6A , the deflection device  65  bends to the left, causing the drops  12  to follow gutter  66 . When the deflection device  65  is on the off-position, shown on the right side of  FIG. 6A , the deflection device  65  remains straight, allowing the drops  12  to travel along a non-gutter path. 
         [0053]    The deflection device  65  can be made of two metal sheets bonded together. The two metals have different coefficients of thermal expansion. When an electric current is applied to the metals, they will expand different in length. The deflection device  65  will bend toward to the metal with lower coefficient of thermal expansion. This type of device is often referred to as a thermal bi-morph or a bimetallic actuator although thermal tri-morphs (three metal layers) can also be used. 
         [0054]    Another mean to deflect is to utilize piezo-electric material to make a cantilever. A piezoelectric actuator works on the principle of piezoelectricity. Piezoelectricity is the ability of crystals and certain ceramic materials to generate a voltage in response to applied mechanical stress. The piezoelectric effect is reversible in that piezoelectric crystals, when subjected to an externally applied voltage, can change shape by a small amount. (For instance, the deformation is about 0.1% of the original dimension in PZT.) The effect finds useful applications such as the production and detection of sound, generation of high voltages, electronic frequency generation, microbalance, and ultra fine focusing of optical assemblies. Barium titanate can be caused to have piezoelectric properties by exposing it to an electric field. 
         [0055]    Piezoelectric materials are used to convert electrical energy to mechanical energy and vice-versa. The precise motion that results when an electric potential is applied to a piezoelectric material is of primordial importance for nanopositioning. Actuators using the piezo effect have been commercially available for 35 years and in that time have transformed the world of precision positioning and motion control. Piezo actuators can perform sub-nanometer moves at high frequencies because they derive their motion from solid-state crystalline effects. They have no rotating or sliding parts to cause friction. Piezo actuators can move high loads, up to several tons. Piezo actuators present capacitive loads and dissipate virtually no power in static operation. Piezo actuators require no maintenance and are not subject to wear because they have no moving parts in the classical sense of the term. 
         [0056]    For deflection device  65  in the present invention using piezoelectric material, the poling axis of the material is directed from one electrode to the other. Such a configuration is a thickness mode actuator. When the voltage is applied between the electrodes, the thickness of the piezoelectric will change, resulting in a relative displacement of up to 0.2%. Displacement of the piezoelectric actuator is primarily a function of the applied electric field of strength and the length of the actuator, the forced applied to it and the property of the piezoelectric material used. With the reverse field, negative expansion (Contraction) occurs. If both the regular and reverse fields are used, a relative expansion (strain) up to 0.2% is achievable with piezo stack actuators. The piezo material  67  should be placed only on one side of the deflection device  65  (shown in  FIG. 6B ). The other side  68  can be other material such as metal that do not have piezoelectric function. When the piezo material extends and contracts according to the electric field and the material on the other side  68  remains its original length, the deflection device will bend. Cantilever tip can be a patterned two-dimensional surface or in the form of a wire. 
         [0057]      FIG. 7  is a schematic view of another example embodiment of the present invention. Drops  12  reflect elastically from a hydrophobic control surface  70  whose angular position with respect to the trajectory of the impinging drops is controlled by a micromechanical actuator  71  (shown on the right side of  FIG. 7 ) to enable directional control of the drops exiting the control surface. Typically, actuator  71  is a piezo actuator, a bimetal actuator or a trimetal actuator as described above. Actuator  71  moves control surface  70  between the positions designated  70 A and  70 B (shown on the left side of  FIG. 7 ). The reflected travel path of the drops  72 A and  72 B depends on the location of control surface  70  relative to the travel path  73  of the drops. In this manner, the angle of reflection of the drops and the reflected travel path of the drops can be controlled and adjusted by actuator  71 . 
         [0058]      FIGS. 8A and 8B  are schematic views of another example embodiment of the present invention. Decreasing the hydrophobicity of the control surface, for example, by application of a voltage, slows the jet velocity near the control surface in comparison to the velocity on the side of the jet opposite the control surface, thereby altering the jet trajectory. In  FIGS. 8A and 8B , surfaces  80  and  82  include electrodes. Surface  80  contains surface pattern  81  that changes the hydrophobicity of the surface. In  FIG. 8A , no electric field is applied between the electrodes on surfaces  80  and  82 . Jet  13  remains traveling in its original direction (along its original travel path). In  FIG. 8B , electric potential is applied between the electrodes on surfaces  80  and  82 . Therefore, by the principle of dielectrophoresis, jet  13  is pulled to contact surface  80  and its surface pattern  81  changing the direction (the travel path) of the fluid jet  11 . 
         [0059]      FIGS. 8C and 8D  are schematic views of another example embodiment of the present invention. Decreasing airflow to the control surface  85 , for example, by application of air pressure to the side of a porous control surface  85  opposite the jet  13 , slows the jet velocity near the control surface  85 , thereby altering the jet trajectory. The decreasing of airflow can be accomplished using airflow control mechanism  86 , for example, a controllable positive pressure source, a controllable negative pressure source, or a combination of both types. 
         [0060]      FIG. 9  is a schematic view of another example embodiment of a drop control surface of the present invention. A fluid jet  100 , drop control surface  110 , and drops  120  are shown. The drop control surface  110  is positioned to physically contact the drops  120  formed from the breakup of jet  100 . Jet  100  is created using conventional techniques, for example, using a pressurized liquid source. The breakup of jet  100  into drops  120  is also accomplished using conventional techniques, for example, a piezoelectric transducer or thermo-capillary stimulation of the jet. 
         [0061]    The drop control surface  110  is patterned with modified surface regions  130  that have properties different than those of the unmodified surface regions  140  of drop control surface  110 . The modified surface regions  130  are substantially hydrophilic, while the unmodified surface regions  140  are substantially hydrophobic. It can be appreciated that the properties of the modified surface regions  130  can be different in many ways from those of the unmodified surface regions  140  including differences in surface roughness, the presence of grooves, ridges, or combinations thereof. 
         [0062]    The drop control surface  110  is positioned to contact the drops  120  formed from the breakup of jet  100  in such a way that the drops  120  simultaneously contact the modified surface regions  130  and the unmodified surface regions  140 . Since the properties of the modified surface regions  130  and the unmodified surface regions  140  are different, the motion properties of the drops  120  are altered. As shown, the drops  120  acquire a rotational motion as indicated by arrow  150  due to their simultaneous asymmetric interaction with modified surface region  130  and the unmodified surface region  140  of drop control surface  110 . However, it is understood that various other changes in the motion properties of the drops  120  including a change in drop velocity or drop trajectory. 
         [0063]      FIGS. 10A and 10B  are schematic views of another example embodiment of a drop control surface of the present invention. A fluid jet  200 , drop control surface  210 , and drops  220  are shown. The drop control surface  210  is positioned to physically contact the drops  220  formed from the breakup of jet  200 . Jet  200  is created using conventional techniques, for example, using a pressurized liquid source. The breakup of jet  200  into drops  220  is also accomplished using conventional techniques, for example, a piezoelectric transducer or thermo-capillary stimulation of the jet. 
         [0064]    The drop control surface  210  is patterned with a plurality of modified surface regions  230  that have properties different than those of the unmodified surface regions  240  of drop control surface  210 . In the preferred embodiment the modified surface regions  230  are substantially hydrophilic, while the unmodified surface regions  240  are substantially hydrophobic. It is understood that the properties of the modified surface regions  230  can be different in many ways from those of the unmodified surface regions  240  including differences in surface roughness, the presence of grooves, ridges, or combinations thereof. 
         [0065]    The drop control surface  210  is positioned to contact the drops  220  formed from the breakup of jet  200  in such a way that the drops  220  contact at least one of the modified surface regions  230 . The modified surface regions  230  interact with the drops  220  during contact in such a way that the drops  220  substantially maintain contact with the modified surface regions  230  until they separate from control surface  210 , thereby altering the trajectory of the drops  220  as shown in  FIGS. 10A and 10B . The other motion properties of the drops  220  can be altered during contact with modified surface regions  230  of drop control surface  210  including changes in the velocity and rotational motion of the drops  220  etc. 
         [0066]      FIG. 11  is a schematic view of another example embodiment of a drop control surface of the present invention. A fluid jet  300 , drop control surface  310 , main drops  320 , and satellite drops  330  are shown. The drop control surface  310  is positioned to physically contact the main drops  320  and satellite drops  330  formed from the breakup of jet  300 . Jet  300  is created using conventional techniques, for example, using a pressurized liquid source. The breakup of jet  300  into drops  320  is also accomplished using conventional techniques, for example, a piezoelectric transducer or thermo-capillary stimulation of the jet. 
         [0067]    The drop control surface  310  is patterned with a plurality of modified surface regions  340  that have properties different than those of the unmodified surface regions  350  of drop control surface  310 . The modified surface regions  340  have properties that act to reduce the velocity of the main drops  320  and satellite drops  330  upon contact. As shown, the modified surface regions  340  are substantially hydrophilic. However, the desired action of the modified surface regions  340  to slow down the main drops  320  and satellite drops  330  upon contact can be accomplished using other techniques, for example, by altering the surface roughness, adding ridges, or grooves to the modified surface regions  340 . 
         [0068]    The satellite drops  330  that contact the drop control surface  310  experience more deceleration than the main drops  320  because of their lower inertia. This will result in the merging of satellite drops  330  into the trailing main drops  320  to form large drops  360  upon separation from the drop control surface  310 . The patterns on the modified surface regions  340  are chosen to guide the main drops  320  and satellite drops  330  upon contact thereby keeping them from undesired displacement left or right from their original trajectory. 
         [0069]      FIG. 12A  is a schematic view of another example embodiment of the present invention. A fluid jet  400 , drop control surface  410 , drops  420 , slowed drops  430  and receiver  440  are shown. The drop control surface  410  is positioned to physically contact the drops  420  which form from the breakup of jet  400 . Jet  400  is created using conventional techniques, for example, using a pressurized liquid source. The breakup of jet  400  into drops  420  is also accomplished using conventional techniques, for example, a piezoelectric transducer or thermo-capillary stimulation of the jet. 
         [0070]    The drop control surface  410  has properties that act to reduce the velocity of the drops  420  and upon contact thereby transforming the stream of drops  420  from the breakup of jet  400  into a stream of slowed drops  430 . As shown, the control surface  410  is substantially hydrophilic. However, the desired action of the drop control surface  410  to slow down of the drops  420  upon contact can be achieved using other properties of the drop control surface  410 , for example, by modifying the surface roughness of the drop control surface  410 . 
         [0071]    As the drops  420  slow down upon contact with drop control surface  410  their spacing uniformly decreases while their volumes are preserved. The effective λ/D limit of the printing system (not shown) is therefore significantly increased, and the printing speed is proportionally increased. In this case, the impacting jet velocity can be greater than the maximum velocity allowed for drops landing on the receiver  450  (usually determined by the drop velocity at which drop ‘splattering’ occurs). Thus, the maximum fluid flow rate is increased over what would otherwise be possible. 
         [0072]      FIG. 12B  is a schematic view of another example embodiment of the present invention. A fluid jet  500 , drop control surface  510 , and drops  520  are shown. The drop control surface  510  is positioned to physically contact the jet  500 . Jet  500  is created using conventional techniques, for example, using a pressurized liquid source. 
         [0073]    As shown, drop control surface  510  is in the form of a cylinder  505  that is patterned with a plurality of modified surface regions  530  that have properties different than those of the unmodified surface regions  540  of drop control surface  510 . The modified surface regions  530  have properties that act to perturb the jet  500  upon contact so as to cause the jet to break into drops  520 . Drop control surface  510  is rotating counterclockwise as indicated by rotation arrow  550 . The rotation of drop control surface  510  enables a plurality of modified surface regions  530  to contact the jet in a periodic fashion thereby stimulating jet breakup using a periodic perturbation which can be adjusted by varying the rotational speed of drop control surface  510 . 
         [0074]    The modified surface regions  530  are substantially hydrophilic and the unmodified surface regions  540  are hydrophobic. However, the modified surface regions  530  that cause the jet  500  to breakup into drops  520  upon contact can be achieved using other properties, for example, by modifying the surface roughness of the modified surface regions  530 . 
         [0075]      FIG. 13A  is a schematic view of another example embodiment of a drop control surface of the present invention. A fluid jet  600 , drop control surface  610 , and drops  630  are shown. The drop control surface  610  is positioned to physically contact jet  600 . Jet  600  is created using conventional techniques, for example, using a pressurized liquid source. Control surface  610  imparts energy to the jet at or near a jet stimulation wavelength so that the exiting jet rapidly begins breaking up into drops  630 . The breakup of jet  600  into drops  630  can also be assisted using conventional techniques, for example, a piezoelectric transducer or thermo-capillary stimulation of the jet. 
         [0076]    The drop control surface  610  is patterned with modified surface regions  620  that have properties different than those of the unmodified surface regions  640  of drop control surface  610 . As shown, the modified surface regions  620  are substantially hydrophilic, while the unmodified surface regions  640  are substantially hydrophobic. The modified surface regions  620  are patterned in a periodic array where the spacing between modified regions can be adjusted to actively stimulate breakup of the fluid jet  600 . It can be appreciated that other properties of modified surface regions  620  can be different from those of the unmodified surface regions  640  including differences in surface roughness, the presence of grooves, ridges, or combinations thereof. 
         [0077]      FIG. 13B  is a schematic view of a continuous inkjet printhead  750  incorporating another example embodiment of the present invention. A fluid jet  700 , drop control surface  710 , and drops  730  are shown. The drop control surface  710  is positioned to physically contact the jet  700 . Jet  700  is created using conventional techniques, for example, using a pressurized liquid source. Control surface  710  imparts energy to the jet at or near a jet stimulation wavelength so that the exiting jet rapidly begins breaking up into drops  730 . The breakup of jet  700  into drops  730  can be assisted with a secondary stimulation device that employs conventional techniques, for example, a piezoelectric transducer or thermo-capillary stimulation of the jet. In  FIG. 13B , the secondary stimulation is a heater  760  positioned around the nozzle that ejects liquid jet  700 . 
         [0078]    The drop control surface  710  is patterned with modified surface regions  720  that have properties different than those of the unmodified surface regions  740  of drop control surface  710 . As shown, the modified surface regions  720  are substantially hydrophilic, while the unmodified surface regions  740  are substantially hydrophobic. The modified surface regions  720  are patterned in a periodic array where the spacing between modified regions can be adjusted to actively simulate breakup of the fluid jet  700 . It can be appreciated that other properties of modified surface regions  720  can be different from those of the unmodified surface regions  740  including differences in surface roughness, the presence of grooves, ridges, or combinations thereof. 
         [0079]      FIGS. 14A and 14B  are schematic views of another example embodiment of a drop control surface of the present invention. Two fluid jets  800 , a drop control surface  810 , and drops  830  are shown. The drop control surface  810  is positioned to physically contact the drops  830  formed from the breakup of jet  800 . Jet  800  is created using conventional techniques, for example, using a pressurized liquid source. The breakup of jet  800  into drops  830  is also accomplished using conventional techniques, for example, a piezoelectric transducer or thermo-capillary stimulation of the jet. 
         [0080]    The drop control surface  810  is patterned with modified surface regions  820  that have properties different than those of the unmodified surface regions  840  of drop control surface  810 . As shown, the modified surface regions  820  are substantially hydrophilic, while the unmodified surface regions  840  are substantially hydrophobic. The modified surface regions  820  interact with the two fluid jets  800  upon contact such that adjacent jets or drops from adjacent jets are caused to merge to form a bigger drop  850  when compared to drops  830 . 
         [0081]    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  
       [0082]      10  printhead 
         [0083]      11  fluid jet 
         [0084]      12  drops 
         [0085]      13  fluid jet 
         [0086]      20  drop control device 
         [0087]      21  drop control surface 
         [0088]      22  gap regions 
         [0089]      31  hydrophilic surface properties 
         [0090]      32  hydrophobic surface properties 
         [0091]      41  thin wires 
         [0092]      51  electrode 
         [0093]      52  electrode 
         [0094]      53  electrode 
         [0095]      54  electrode 
         [0096]      58  mechanically controlled steering device 
         [0097]      59  camshaft 
         [0098]      60  shaft 
         [0099]      61  spring 
         [0100]      62  fixed location 
         [0101]      63  profile 
         [0102]      65  deflection device 
         [0103]      66  gutter 
         [0104]      67  piezo material 
         [0105]      68  side 
         [0106]      70  hydrophobic control surface 
         [0107]      71  micromechanical actuator 
         [0108]      80  surface 
         [0109]      81  surface pattern 
         [0110]      82  surface 
         [0111]      85  control surface 
         [0112]      86  airflow control mechanism 
         [0113]      100  fluid jet 
         [0114]      110  drop control surface 
         [0115]      120  drops 
         [0116]      130  modified surface regions 
         [0117]      140  unmodified surface regions 
         [0118]      150  arrow 
         [0119]      200  fluid jet 
         [0120]      210  drop control surface 
         [0121]      220  drops 
         [0122]      230  modified surface regions 
         [0123]      240  unmodified surface regions 
         [0124]      300  fluid jet 
         [0125]      310  drop control surface 
         [0126]      320  main drops 
         [0127]      330  satellite drops 
         [0128]      340  modified surface regions 
         [0129]      350  unmodified surface regions 
         [0130]      360  large drops 
         [0131]      400  fluid jet 
         [0132]      410  drop control surface 
         [0133]      420  drops 
         [0134]      430  slowed drops 
         [0135]      440  receiver 
         [0136]      450  receiver 
         [0137]      500  fluid jet 
         [0138]      510  drop control surface 
         [0139]      520  drops 
         [0140]      530  plurality of modified surface regions 
         [0141]      540  unmodified surface regions 
         [0142]      550  rotation arrow 
         [0143]      600  fluid jet 
         [0144]      610  drop control surface 
         [0145]      620  modified surface regions 
         [0146]      630  drops 
         [0147]      640  unmodified surface regions 
         [0148]      700  fluid jet 
         [0149]      710  drop control surface 
         [0150]      720  modified surface regions 
         [0151]      730  drops 
         [0152]      740  unmodified surface regions 
         [0153]      750  printhead 
         [0154]      800  fluid jets 
         [0155]      810  drop control surface 
         [0156]      820  modified surface regions 
         [0157]      830  drops 
         [0158]      840  unmodified surface regions 
         [0159]      850  drop
A device and method of controlling fluid flow are provided. The method includes providing a moving fluid including a fluid flow characteristic; providing a fluid control device including a fluid control surface, the fluid control surface including a pattern; causing the fluid to contact the fluid control surface of the fluid control device; and causing the fluid to interact with the fluid control surface of the fluid control device using the pattern of the fluid control surface that, when activated, causes adjacent fluid drops to merge or coalesce while the fluid is in contact with the pattern of the fluid control device such that the fluid flow characteristic of the fluid after interacting with the fluid control surface of the fluid control device is different from the fluid flow characteristic of the fluid before interaction with the fluid control surface of the fluid control device.