Abstract:
A continuous ink jet apparatus is provided. The printhead includes a nozzle array with portions of the nozzle array defining a length dimension. A drop forming mechanism is positioned relative to the nozzle array. The drop forming mechanism is operable in a first state to form ink drops having a first volume travelling along a path and in a second state to form ink drops having a second volume travelling along the path. A system applies force to the ink drops travelling along the path. The force is applied in a direction such that the ink drops having the first volume diverge from the path and at least one of the ink drops having the first volume and the ink drops having the second volume are displaced relative to the length dimension.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly assigned, co-pending U.S. Ser. No. 09/750,946, entitled Printhead Having Gas Flow Ink Droplet Separation And Method Of Diverging Ink Droplets, filed in the names of Jeanmaire and Chwalek on Dec. 28, 2000; co-pending U.S. Ser. No. 09/751,232, entitled A Continuous Ink-Jet Printing Method And Apparatus, filed in the names of Jeanmaire and Chwalek on Dec. 28, 2000; and U.S. Ser. No. 09/777,461, entitled A Continuous Ink Jet Print Head and Method of Rotating Ink Drops, filed in the names of Hawkins and Jeanmaire, concurrently herewith. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to the design and fabrication of inkjet printheads, and in particular to printheads configured to uniformly translate the position of printed ink drops on a receiver without altering the position of the printhead with respect to the receiver. 
     BACKGROUND OF THE INVENTION 
     Traditionally, digitally controlled inkjet printing capability is accomplished by one of two technologies. The first technology, commonly referred to as “drop-on-demand”, ejects ink drops from nozzles formed in a printhead only when an ink drop is desired to impinge on a receiver. The second technology, commonly referred to as “continuous”, ejects ink drops from nozzles formed in a printhead continuously with ink drops being captured by a gutter when ink drops are not desired to impinge on a receiver. 
     Referring to FIG. 1, a printhead  120  typically includes an approximately linear row of nozzles  122  which define printhead length  124  (measured in a direction along the nozzle row). Printhead  120  is scanned across a stationary receiver  126  in a fast scan direction  128 . After fast scan  128  is complete, receiver  126  is moved in a receiver motion direction  130  relative to printhead  120 . Typically, receiver motion  130  is orthogonal or substantially orthogonal to fast scan direction  128  and receiver  126  is moved in receiver motion  130  rather than displacing printhead  120  in a slow scan direction  132 . Printhead  120  is subsequently scanned again in fast scan direction  128  with nozzles  122  having been physically displaced with respect to receiver  126  by an incremental amount (shown schematically so as to be easily compared to printhead length  124 ). The overall result is displacement of printhead  120  is in slow scan direction  132 . Typically, displacement of printhead  120  with respect to receiver  126  in slow scan direction  132  is a fraction of nozzle to nozzle spacing  134 . Typically, slow scan direction  132  is also orthogonal or substantially orthogonal to fast scan direction  128 . Alternatively, printhead  120  can be physically stepped in slow scan direction  132  in order to physically displace printhead  120  with respect to receiver  126 . Receiver  126  can also be moved in slow scan direction  132  in order to accomplish displacement of printhead  120  with respect to receiver  126 . In either situation, either printhead  120  or receiver  126  is moved. Typically, the above-described motions are controlled by a controller  134 . Many commercially available desktop printers (drop-on-demand printers, etc.) operate in this manner. 
     In continuous inkjet printers, receiver  126  is typically moved in fast scan direction  128  rather than printhead  120  because of the size and complexity of printhead  120 . In many cases, printhead length  124  is pagewide and extends across the entire width of receiver  126  with fast scan direction  128  of receiver  126  being perpendicular to printhead length  124 . This type of printhead and/or printer is commonly referred to as a “pagewidth” printhead/printer. Alternatively, printhead  120  can be scanned in fast scan direction  128 , then stepped in slow scan direction  132  before printhead  120  scanned again in fast scan direction  128 . 
     In some continuous printing applications, it is desirable to move printhead  120  in slow scan direction  132  in order to translate the pattern of printed ink drops (with respect to receiver  126 ) produced by nozzles  122 . For example, in several conventional pagewidth printers, printhead  120  is translated or dithered a small distance from side to side in a direction parallel to its length (slow scan direction  132 ). This motion can be used to compensate for irregularities in nozzle to nozzle spacing  134  of printhead  120 . Typical nozzle to nozzle spacing  134  is a multiple of the desired distance between printed dots. As such, printhead  120  can be displaced slightly along its length and fast scan  128  is repeated one or more times in order to print all desired dots. Typically, translated printed drop patterns are created by translating printhead  120  in slow scan direction  132  with respect to receiver  126 . However, receiver  126  can be translated or displaced in slow scan direction  132  while printhead  120  remains stationary in slow scan direction  132 . 
     Translation of the printhead in the slow scan direction is very precise. As such, commercially available mechanical devices that perform this task increase overall printer costs, are complex, and are prone to failure. Additionally, commercially available printheads often perform poorly when translated or dithered rapidly due to fluid acceleration along the length of the printhead. This is particularly true for pagewidth printheads because pagewidth printheads have extremely long fluid channels, typically distributed over the entire length of the printhead. Rapidly displacing the printhead intensifies the adverse affects of the fluid acceleration. As such, there is a need for an improved printhead translatable along its length (typically, in the slow scan direction relative to the receiver). 
     Additionally, it is advantageous to adjust the location of ink drop patterns printed on a receiver in the slow-scan direction in order to improve image quality. In this regard, displacing, dithering, or translating the printhead by an integral spacing relative to nozzle to nozzle spacing (the distance between nozzles) allows selected nozzles to print different data, thereby reducing image artifacts. The printhead motion (translation) needs to occur quickly in order to accomplish this. Typically, this motion is completed in a time much shorter in duration than the time required to scan in the fast scan direction. Again, currently available mechanical devices that accomplish this motion increase system cost and complexity. As such, there is a need for an improved printhead capable of adjusting the location of ink drop pattern printed on a receiver. 
     It is also advantageous to adjust the location of ink drop patterns printed on a receiver so as to slightly change the angle of the printhead relative to the fast scan direction in order to suppress image artifacts. This situation typically arises, for example, when the angle of the receiver changes while passing under the printhead. In many of these situations, changing the angle of the printhead relative to the fast scan direction needs to occur rapidly in order to prevent printed ink drops from misregistering (being printed on the wrong location) on the receiver. Again, currently available mechanical devices for moving the printhead at an angle relative to the fast scan direction add expense and complexity. Additionally, these devices can interfere with printhead performance during printhead motion in the fast scan direction due to the additional weight of the devices. As such, there is a need for an improved printhead capable of changing the angle of drops printed from a row of nozzles. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an improved printhead translatable along its length. 
     Another object of the present invention is to provide an improved printhead rapidly translatable along its length that accurately and rapidly produces displaced printed drops in a direction parallel to the length of the printhead without interfering with the performance of the printhead. 
     Another object of the present invention is to provide an improved printhead capable of rapidly rotating the pattern of printed ink drops through an angle with respect to the receiver. 
     Yet another object of the present invention is to produce a displaced pattern of ink drops printed on a receiver without having to displace the receiver or the printhead. 
     Yet another object of the present invention is to provide an improved printhead having reduced cost and increased reliability. 
     According to a feature of the present invention, a continuous ink jet printing apparatus includes a nozzle array with portions of the nozzle array defining a length dimension. A drop forming mechanism is positioned relative to the nozzle array. The drop forming mechanism is operable in a first state to form ink drops having a first volume travelling along a path and in a second state to form ink drops having a second volume travelling along the path. A system applies force to the ink drops travelling along the path. The force is applied in a direction such that the ink drops having the first volume diverge from the path with the ink drops having the first volume being displaced relative to each other along the length dimension. 
     According to another feature of the present invention, a method of translating ink drops ejected from a continuous ink jet printhead includes forming a first ink drop having a first volume travelling along a path; forming a first ink drop having a second volume travelling along the path; causing the first ink drop having the first volume to diverge from the path; forming a second ink drop having the first volume travelling along the path; forming a second ink drop having the second volume travelling along the path; and causing the second ink drop having the first volume to diverge from the path displaced relative to the first ink drop having the first volume. 
     According to another feature of the present invention, a method of translating ink drops includes forming a first ink drop having a first volume travelling along a path; causing the first ink drop having the first volume to diverge from the path; forming a second ink drop having the first volume travelling along the path; and causing the second ink drop having the first volume to diverge from the path displaced relative to the first ink drop having the first volume. 
     According to another feature of the present invention, a continuous ink jet printing apparatus includes a nozzle array. A drop forming mechanism is positioned relative to the nozzle array with the drop forming mechanism being operable to form a first ink drop travelling along a path and a second ink drop travelling along the path. A system which applies force to the first and second ink drops travelling along the path, the force being applied in a direction such that the first and second ink drops diverge from the path, at least a portion of the system being moveable between a first position relative to the nozzle array and a second position relative to the nozzle array such that the second ink drop is displaced relative to the first ink drop as the second ink drop diverges from the path. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a prior art inkjet printhead being scanned over a receiver; 
     FIGS. 2 a-   2   c  show schematic cross-sectional views of an apparatus incorporating the present invention; 
     FIGS. 3 a-   3   c  show a schematic top view of a portion of the apparatus of FIG. 2 a  and resulting printed ink drop patterns; 
     FIGS. 4 a  and  4   b  show schematic top views of the portion of the apparatus of FIGS. 3 a-   3   c  made in accordance with the present invention and resulting printed ink drop patterns; 
     FIG. 4 c  shows a row of printed ink drops produced by the apparatus of FIGS. 4 a  and  4   b;    
     FIG. 4 d  shows a row of printed ink drops produced by the apparatus of FIGS. 4 a  and  4   b;    
     FIGS. 5 a  and  5   b  show schematic top views of alternative embodiments of the apparatus of FIGS. 4 a  and  4   b;    
     FIG. 6 a  shows a schematic top view of an alternative embodiment of the apparatus of FIGS. 4 a  and  4   b  translated between a first position and an offset second position; 
     FIG. 6 b  shows a time history of the pattern of ink drops printed on a receiver for the printhead of FIG. 6 a;    
     FIG. 7 a  shows a schematic top view and a cross-sectional view of an alternative embodiment of the apparatus of FIGS. 4 a  and  4   b  with the resulting pattern of printed ink drops; 
     FIG. 7 b  shows a schematic top view and a cross-sectional view of the embodiment of FIG. 7 a  with the resulting pattern of printed ink drops; 
     FIG. 7 c  shows a schematic top view and a cross-sectional view of an alternative embodiment of FIG. 7 c  with the resulting pattern of printed ink drops; 
     FIG. 7 d  shows a schematic top view and a cross-sectional view of an alternative deflector system of FIG. 7 a  with the resulting pattern of printed ink drops; 
     FIG. 7 e  shows a cross-sectional view of an alternative embodiment of FIG. 7 d;    
     FIG. 7 f  shows a schematic top view, a side view, and an end cross-sectional view of an alternative embodiment of FIG. 7 a  with the resulting pattern of printed ink drops; and 
     FIG. 7 g  shows a control surface for the embodiment shown in FIG. 7 f.   
    
    
     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. 
     Referring to FIGS. 2 a-   2   c , an apparatus  10  incorporating the present invention is schematically shown. Although apparatus  10  is illustrated schematically and not to scale for the sake of clarity, one of ordinary skill in the art will be able to readily determine the specific size and interconnections of the elements of the preferred embodiment. Pressurized ink  12  from an ink supply  14  is ejected through nozzles  16  of printhead  18  creating filaments of working fluid  20 . Typically, nozzles  16  are formed in a membrane of printhead  18  overlying an ink cavity formed in printhead  18 . Ink drop forming mechanism  22  (for example, a heater, piezoelectric actuator, etc.) is selectively activated at various frequencies causing filaments of working fluid  20  to break up into a stream of selected ink drops (one of  26  and  28 ) and non-selected ink drops (the other of  26  and  28 ) with each ink drop  26 ,  28  having a volume and a mass. The volume and mass of each ink drop  26 ,  28  depends on the frequency of activation of ink drop forming mechanism  22  by a controller  24 . 
     A force  30  from ink drop deflector system  32  interacts with ink drop stream  25  deflecting (through angle D) ink drops  26 ,  28  depending on each drops volume and mass. Accordingly, force  30  can be adjusted to permit selected ink drops  26  (large volume drops) to strike a receiver W while non-selected ink drops  28  (small volume drops) are deflected, shown generally by deflection angle D, into a gutter  34  and recycled for subsequent use. Alternatively, apparatus  10  can be configured to allow selected ink drops  28  (small volume drops) to strike receiver W while non-selected ink drops  26  (large volume drops) strike gutter  34 . System  32  can includes a positive pressure source or a negative pressure source. Force  30  is typically positioned at an angle relative to ink drop stream  25  and can be a positive or negative gas flow. The gas can be air, nitrogen, etc. 
     Referring to FIGS. 3 a-   3   c , a schematic top view of deflection system  32  and a resulting pattern  36  of printed ink drops  38  printed on a receiver is shown. Fiducial lines  40  represent displacement of printed drops in slow scan direction from reference points. In FIG. 3 a , the reference points are edges  42  of system  32  with at least a portion of system  32  being positioned substantially parallel to nozzle row and the direction of force  30  being perpendicular to ink drops ejected from nozzle  16 . Alternatively, force  30  can be altered in a first altered direction (as shown in FIG. 3 b ) such that printed drops are displaced with respect to fiducial lines  42  (downward in FIG. 3 b ). Force  30  can also be altered in a second altered direction (as shown in FIG. 3 c ) such that printed drops are displaced with respect to fiducial lines  42  (upward in FIG. 3 c ). 
     FIGS. 4 a  and  4   b  show a first embodiment implementing the present invention. A portion  48  of system  32  is configured with a plurality of control vanes  44  used to control the direction of force  30  in a first direction (aligned with edges  42  of system  32  as shown in FIG. 4 a ) and in a second direction (angled from edges  42  of system  32  as shown in FIG. 4 b ). Alignment of control vanes  44  in FIG. 4 a  is perpendicular to nozzle row  122  while alignment of control vanes  44  in FIG. 4 b  can vary but is generally not perpendicular. The resulting printed drops  38  in FIG. 4 b  are displaced along the direction of the nozzle row (in slow scan direction  132 ) due to alteration of the direction of force  30  caused by angling of control vanes  44 . Control vanes  44  can be fabricated using known MEMS technology and techniques. Additionally control vanes  44  can be made from various known materials. For example, control vanes  44  can be made from small metallic pieces which are rotated about a common support point  46  located at an end of each control vane. A known controller can be used to angle control vanes  44  at an appropriate time with an appropriate amount of angle. 
     By printing with subsequent scans of printhead  120  in fast scan direction  128 , with each scan having an altered direction of force  30 , resulting patterns  36  of printed ink drops  38  with displaced drops  43  and non-displaced drops  45 , as shown in FIGS. 4 c  and  4   d , can be accomplished without having to mechanically displace printhead or receiver. In FIG. 4 c , ink drops  38  are displaced from one scan to another by one half the distance between nozzles. In FIG. 4 d , ink drops  38  are displaced by a amount greater than one half the distance between nozzles. Typically, a useful displacement includes a multiple of a simple fraction of the distance between nozzles. For example, in FIG. 4 d , ink drop displacement is two thirds the distance between nozzles such that subsequently displaced scans can “fill in” the scan line with additional evenly spaced ink drops. Useful displacement can also include a multiple of a simple fraction greater than one (for example, {fraction (5/4)}, etc.) and/or a multiple of a simple fraction less than one half (for example, ⅙, etc.) depending on the criteria for a particular situation. In these examples, the number of scans required to fill in a line with drops of regular spacing would be 4 and 6, respectively, as can be appreciated by one skilled in the inkjet printing art. 
     An inexpensive manufacturing method for making vanes  44  is electroforming a metal such as nickel, nickel-iron alloy, or the alloy known as permalloy, etc. into vane-shaped openings defined by an xray patterning of a thick polymer film, a technique known in the art of microfabrication as LIGA. Vanes  44  may be attached together by an electroformed bridge  47 , sufficiently thin to flex so as to allow vanes  44  to be angled, at their top and bottom surfaces as shown at the top side of vanes  44  by dotted lines  47  in FIGS. 4 a  and  4   b , so that all vanes  44  move together. The vanes  44  are made from a magnetic material such as permalloy, vanes  44  can be angled by application of a magnetic field from a magnet with poles spaced the same as vanes  44  and positioned above system portion  48  or at the sides of system portion  48  or bridge  47  near the front of system portion  48 . Alternatively, vanes  44  can be contacted mechanically by an arm from a servo motor. The positions of the drops, either before or after printing, can be easily monitored with a CCD camera and vanes can be then adjusted by programming a controller in a feedback loop to alter the magnet field (or to actuate the servo motor) until the desired drop position is achieved. As can be appreciated by one skilled in mechanical design, many additional ways of fabricating vanes and actuating their motion are possible. For example, vanes  44  can be fabricated by injection molding vanes  44  from a conductive plastic material and controlling their position by electrostatic attraction to an additionally provided set of interleaved vanes in system portion  48 , or by fabricating vanes  44  from a piezo material and electrifying that material to angle vanes  44 . 
     FIGS. 5 a  and  5   b  show a second and a third embodiment of the present invention. Again, control vanes  44  redirect force  30  in order to alter the position of printed ink drops. In these embodiments, at least a portion  48  of system  32  is aligned during one scan and angled with respect to fast scan direction during a subsequent scan. In FIG. 5 a , portion  48  has a rectangular shape and is rotated (shown at  50 ) using any known devices and techniques relative to nozzle row  122 . As portion  48  is rotated, the distance from ends of portion  48  relative to nozzles gradually changes causing displacement of printed ink drops. In FIG. 5 b , portion  48  has a trapezoidal shape such that the distance from the ends of portion  48  to nozzle row remains constant along an end of portion  48 . In practice, it has been discovered that the amount of deflection of printed ink drops is not very sensitive to (or dependent on) the distance of the ink drops from portion  48 . For example, a change in the distance of ink drops from portion  48  of 1 mm results in a change in drop deflection of less than 20 microns after the drop has traversed interaction distance L of portion  48  (a vertical direction dimension of 1 mm in FIG. 2 a ). As such, trapezoidal shapes are required only when extremely accurate and very uniform ink drop translations are desired. 
     Portion  48  can be rotated by commercially available rotational servo motors based on signals provided from controller  134 . Controller  134  can use a look-up table to determine the signal required for a given desired displacement of the printed drops or the positions of the drops, either before or after printing. This can be easily monitored with a CCD camera and the degree of rotation can be then adjusted by programming controller  134  in a feedback loop to alter signal to a servo motor until the desired drop position is achieved. If, as in FIG. 5 b , system portion  48  is to be held parallel to nozzle row  122 , a servo motor can be used to rotate the system portion  48  by rotating sidewalls  49 ,  51  of system portion  48 , but side walls  49 ,  51  of system portion  48  should be free to slide mechanically on top and bottom surfaces of system portion  48 . In this example, right end (as shown in FIG. 5 b ) of side walls  49 ,  51  should be located in a fixed position, and the top and bottom surfaces should be made to extend beyond sidewalls  49 ,  51  so that when sidewalls  49 ,  51  are angled and slide along the top and bottom airtube surfaces, sidewalls  49 ,  51  do not pass over the edges of the top and bottom surfaces of system portion  48 . 
     Referring to FIG. 6 a , another embodiment of the present invention is shown. This embodiment is especially appropriate when rapid or periodic translation of printed drops in the slow scan direction is desired. In FIG. 6 a , system portion  48  having control vanes  44  is displaced in alternating first (aligned  35  relative to fiducial lines  42 ) and second (offset relative to fiducial lines  42 ) directions  52 ,  54  (in a slow scan direction, etc.). This creates flow patterns in force  30  that translate printed ink drops  38  in directions corresponding to first and second directions. FIG. 6 b  shows lines  56  of ink drops  38  printed on a receiver  58  moving in a receiver scan direction  60  with the ink drops being ejected simultaneously from nozzles  16  in nozzle row  122  (of FIG. 2 b ). The line of printed ink drops is displaced in proportion to the speed of displacement of system portion  48  in slow scan direction. Displacement distance of printed ink drop corresponds to translation distance of system portion  48 . However, translation of system portion  48  is such that system portion  48  does not overshoot nozzles  16  positioned at ends of nozzle row  62 . As such, force  30  of system portion  48  does not miss ink drops ejected from nozzles  16  positioned at ends of nozzle row  122 . 
     System portion  48  may be translated as shown in FIG. 6 b  by commercially available linear servo motors based on signals provided from controller  134 . Controller can use a look-up table to determine the signals required for a given desired displacement of the printed drops or the positions of the drops, either before or after printing. This can be easily monitored with a CCD camera and the degree of translation can be then adjusted by programming controller  134  in a feedback loop to alter signal to the servo motor until the desired drop position is achieved. 
     The embodiments described above disclose apparatus and methods for translating a pattern of ink drops ejected from a nozzle row in a direction parallel to nozzle row  120  without moving printhead  120 . It is also useful in inkjet printing to have precise control of ink drop line rotation of ink drops printed from a nozzle row with respect to an edge of a receiver. Controlling ink drop line rotation helps to correct for receiver alignment problems (relative to a printhead, etc.) and prevent image artifacts. Alignment problems include a receiver initially misaligned, becoming slightly misaligned during a fast scan or while being moved after a fast scan of a printhead, etc. Roll fed printers are particularly susceptible to slight angular misalignment of paper as it slides or moves over the printing region. Alignment problems are significant in the printing art, as the human eye is extremely sensitive to image artifacts arising from an angular rotation of rows of printed drops relative to an edge of a receiver. 
     Referring to FIG. 7 a , a schematic top-view of system portion  48  and a pattern  36  of ink drops  38  printed on a receiver is shown. Typically, pattern  36  results when nozzles  16  in nozzle row  122  simultaneously eject printed drops. Printed drop pattern  36  is typically aligned perpendicularly to receiver edge  136  (shown in FIG. 1 a ) during printing. Receiver edges  136  can become misaligned (not aligned perpendicularly, angled, etc.). This can happen, for example, when there is a slight error in the direction of receiver motion which can occur in printers that periodically move the receiver (a roll-fed printers in which the receiver is unwound from a roll during printing, etc.). 
     Referring also to FIG. 7 b , in order to compensate for the misalignment of a receiver edge, system portion  48  has been deformed mechanically from a rectangular cross-section  64  (FIG. 7 a ) to a trapezoidal cross-section  66 . Deformation can be accomplished by applying a mechanical force  67  to system portion  48  with an elastic side member(s)  68 . Deforming system portion  48  reduces flow of force  30  causing less deflection of ink drops. As shown in FIG. 7 b , left side of system portion  48  has been deformed. As such, printed drops  38  on left side are deflected to a lesser degree (shown generally at  70 ) as force  30  is also reduced. The ink drop deflection reduction gradually decreases for drops ejected from nozzles positioned toward a right side of nozzle row because force  30  remains substantially constant (shown generally at  70 ) on right side of system portion  48 . The resulting printed pattern  36  of ink drops is rotated through a slight angle. Alternatively, ink drop rotation can be from right to left. The exact amount and shape of deformation of system portion  48  can be selected such that the printed ink drops are precisely aligned to the misaligned or angled receiver. Typically, the exact deformation is calculated using computational modeling of force  30  as known to one of ordinary skill in the inkjet printing art. As such, rotational alignment of printed ink drops relative to a receiver edge is accomplished without rotating either the printhead or the receiver. 
     System portion  48  may be constructed of side members  69  which are shaped in the form of a bellows having corregations (shown in FIG. 7 a ) that is easily compressed when a downward force is applied. Such a force may be provided by planar magnetic coils  71  attached to the inside top of system portion  48  near the side to be compressed and positioned directly over a similar set of planar magnetic coils attached to the inside bottom of system portion  48 . A current may be passed through both sets of coils from controller  134  to pull down the top surface of the airtube magnetically. Controller  48  can use a look-up table to determine the current required for a given desired displacement of printed drops  38  or the positions of the drops, either before or after printing. This can be easily monitored with a CCD camera and the degree of translation can be then adjusted by programming controller  134  in a feedback loop to alter the current until the desired drop position is achieved. Alternatively, a second bellows sidewall  73  can be positioned very near the first (dotted line in FIG. 7 a ), the open end between sidewalls  69  and  73  being sealed to air using a flexible material like latex, and a vacuum applied to the space between bellows sidewall  69 ,  73  to collapse the bellows and compress system portion  48 . 
     FIG. 7 c  shows a second embodiment of the invention shown in FIGS. 7 a  and  7   b . In FIG. 7 c , force  30  is reduced on left side of system portion  48  by changing the angle  72  between members of pairs of control vanes  44  so as to increase resistance to flow of force  30 . Control vanes  44  can be constructed using known MEMS techniques from small metallic pieces which are rotated about a common support point  46 . As flow of force  30  is reduced on left side of system portion  48 , printed ink drops  38  corresponding to left side are deflected to a lesser degree than on right side. Alternatively, ink drop rotation can be from right to left. As such, the printed pattern  36  of drops is rotated through an angle without moving the printhead or the receiver. 
     Vanes  44  may be fabricated by injection molding each of vanes  44  from a conductive plastic material, the mold including a rod portion  45  running vertically through vane  44  and extending above the top and bottom of the vane, the location of the rod being shown at  45  in the top view of vanes  44  in FIG. 7 c . Rod  45  is located away from vane center so that electrostatic forces to be described cause selected rotation of the vanes. Rods  45  of each vane  44  are cemented into locating holes in the top and bottom of system portion  48  to that vane  44  rotates on the rod  45  by twisting it. Each vane  44  is contacted electrically at the locating holes by a thin film conductor patterned on the top or bottom system portion  48 . Controller  134  is programmed to apply a selectable control voltages to each vane  44  and to thereby control pairwise the angular positions of vanes  44  by electrostatic attraction. A typical control voltage pattern on the vanes  45  can be positive and negative voltages for vane positions shown in FIG. 7 c . As can be appreciated by one skilled in electrostatics, electrostatic attractive forces occur for oppositely charged vanes whereas no forces occur pairwise between similarly charged vanes. Controller  134  can use a look-up table to determine the voltages required for a given desired angulation of vanes  44 ; or the positions of the drops, either before or after printing. This can be monitored with a CCD camera and the degree of angulation can be then adjusted by programming controller  134  in a feedback loop to alter magnitude of the voltages applied to vanes  44 . 
     FIGS. 7 d  and  7   e  show additional embodiments of the invention shown in FIGS. 7 a  and  7   b . In FIGS. 7 d  and  7   e  force  30  is reduced by positioning a shaped restrictor  74  (rectangular in FIG. 7 d , trapezoidal in FIG. 7 e ). Restrictor  74  increases resistance force  30  in proportion to its degree of penetration into the flow of force  30  and to its length along the direction of flow. Restrictor  74  can be a mechanically moved block, nominally positioned relative to system portion  48  (in a recessed area of portion  48 , etc.) and moved down into the flow of force  30  when rotation of a printed drop pattern is desired. A top view of restrictor  74 , shown in FIG. 7 d , is preferably trapezoidal helping to further reduce flow of force  30 . Additionally, a top view of restrictor  74 , shown in FIG. 7 e , is preferably rectangular so as not to reduce flow of force  30  too much. As flow of force  30  is reduced on left side of system portion  48 , printed ink drops corresponding to left side are deflected to a lesser degree than on right side. Alternatively, rotation can be from right to left. As such, the printed pattern of drops is rotated through an angle without moving the printhead or the receiver. 
     Airflow restrictor  74  is conveniently made from an elastic membrane affixed at its edges to the top inner surface of system portion  48 . A membrane of restrictor  74  may be inflated pneumatically by connecting it pneumatically to a narrow tube running along the top inner surface of system portion  48  and exiting system portion  48  through its top surface at a location chosen to prevent mechanical interference with system portion  48  supports or with a receiver. The narrow tube is connected to a pneumatic source through valves which can be opened and closed by controller  134 . When inflated, the shape of restrictor  74  is determined by the air pressure and by the distance of the elastic membrane from any point on its surface that is affixed to the top inner surface of system portion  48 . A membrane which is rectangular in top view and which is affixed to the inner top surface of system portion  48  only around its perimeter will inflate as shown in FIG. 7 d . A restrictor  74  whose top view is trapezoidal will inflate as shown in FIG. 7 e . Controller  134  can use a look-up table to determine the valve openings required for a given desired displacement of the printed drops; or the positions of the drops, either before or after printing. The degree of translation can be then adjusted by programming controller  134  in a feedback loop. 
     FIGS. 7 f  and  7   g  show another embodiment of the invention shown in FIGS. 7 a  and  7   b . In FIG. 7 f , flow of force  30  is reduced by positioning a control mechanism  76  such that control mechanism  76  interacts with force  30 . Control mechanism  76  has at least one adjustable cantilever  78  (as shown in FIG. 7 g ). Each cantilever  78  can be individually extended (bent, pushed, etc.) into force  30  thereby restricting flow depending on the degree of penetration of each cantilever  78  and the length of control mechanism  76  along the direction of flow of force  30 . Control mechanism  76  can be constructed using MEMS techniques well known to those skilled in the art. For example, control mechanism  76  can incorporate an electrical conductor and each cantilever  78  can be aluminum thin films patterned photolithographically into long, thin plates that are electrostatically attracted by application of a voltage to cantilevers  78 . When no voltage is present, each cantilevers  78  can be designed to have internal stresses causing them to extend away from control mechanism  76 . Alternatively, each cantilever  78  can be bimetallic strips which curl up when heated by an electric current passed through the strip or along its length. This is also well known to one of ordinary skill in the art. Typically, control mechanism  76  shown in FIG. 7 d  is rectangular as viewed from a top view. However, control mechanism  76  is not required to be rectangular as long as cantilevers  78  are individually controlled. As flow of force  30  is reduced on left side of system portion  48 , printed ink drops corresponding to left side are deflected to a lesser degree than on right side. As such, the printed pattern of drops is rotated through an angle without moving the printhead or the receiver. 
     A voltage applied to a particular cantilever  78  will cause that cantilever  78  to move from a contracted to an extended state. To control airflow through system portion  48  in accordance with the present invention, the position of each cantilever  78  on control mechanism  76  is adjusted by applying a plurality of voltage signals from controller  134 . The voltages being conveyed to control mechanism  76  through a plurality of electrical leads which may be fabricated on the inner top surface of system portion  48  which extend along the inner top surface and exit system portion  48  in order to connect to controller  134  through the top surface at a location chosen to prevent mechanical interference of the leads with system portion  48  supports or the receiver. 
     Due to the small size of cantilevers  78 , there is a need to have very many of them to effectively control force  30 . As such, there is a need to provide many, for example a hundred or more, electrical leads. Control mechanism  76  can be attached to these electrical leads within system portion  48  by techniques such as bump bonding, known in the art of semiconductor package fabrication. Controller  134  can use a look-up table to determine the values of the voltages required to achieve force  30  control sufficient to provide a desired displacement of the printed drops. Alternatively, the positions of the drops, either before or after printing, can be easily monitored with a CCD camera and the degree of rotation can be then adjusted by programming controller  134  in a feedback loop to alter the voltages applied to the cantilevers and hence the positions of the cantilevers until the desired drop position is achieved. It is possible to control the flow of force  30  in system portion  48  to a very high degree of accuracy due to the large number of voltage output from controller  134 . 
     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 spirit and scope of the invention.