Precise jet alignment for ink jet printer
United States Patent 1 Loeiffler et al.  
 [ Apr. 8, 1975 PRECISE JET ALIGNMENT FOR INK JET PRINTER [75] Inventors: Karl Heinz Loeffler, San Jose; Heinz Hermann Weichardt, Pebble Beach, both of Calif.  
 [73] Assignee: International Business Machines Corporation, Armonk, NY.  
  221 Filed: July 2,1973  
  2! Appl. No.: 376,072  
 [52] US. Cl. 346/75 [5i] Int. Cl. G0ld 18/00 [58] Field of Search 346/75 [56] References Cited UNITED STATES PATENTS 2.600.129 6/l952 Richards 346/75 X 3,596,275 7/197] Sweet 346/75 X 3,689,936 9/!972 Dunlavey 346/75 X OTHER PUBLICATIONS Meier, .I. H.; Nozzle Adjustments in Multinozzle Ink Jet Printers; IBM Tech. Disc. Bulletin, Vol. 14, No. 10, March 1972, p. 3101. Meier, J. H.; Mechanical X-Y Aiming of Ink Jet Printer Nozzles, IBM Tech. Disc. Bulletin, Vol. I5, No. 5, Oct. 1972, p. 1683.  
 Primary E.raminer.loseph W. Hartary Attorney, Agent, or FirmJohn H. Holcombe [57] ABSTRACT An ink jet printing system in which vernier jet alignment is achieved by positioning an electrode within close proximity to the continuous stream of ink being emitted by the jet and applying a voltage to the electrode so as to create an asymmetrical force field which has a component perpendicular to the ink stream direction and which affects the trajectory of the ink stream. The vernier jet alignment technique reduces the high cost involved in obtaining similar tolerances mechanically and the complexity of electronic alignment after drop formation, and is suitable for either single or multiple jet printer configurations.  
 2 Claims, 2 Drawing Figures FIITENTED PR 81975 BIAS CONTROL EXITATION SOURCE FIG.  
 FIG.2  
 PRECISE JET ALIGNMENT FOR INK JET PRINTER FIELD OF THE INVENTION This invention relates to an ink jet printer system and more particularly to a system which has the capability of vernier jet alignment.  
 BACKGROUND OF THE INVENTION Various types of non-impact printing processes have been developed primarily because this approach offers such attractive features such as speed and versatility in printing techniques. One form of non-impact printing process is known as ink jet printing and involves the modulation of a stream of fluid ink drops which are then recorded on a record medium. Various types of ink jet systems presently exist. One such system employs a small nozzle to which conductive fluid ink is delivered under pressure. As the ink exits the nozzle. instabilities due to surface tension forces cause the system to break up into a series of drops. This break up is synchronized by vibrating thefluid. which results in uniform drop size and spacing. A charging means is synchronized with the rate of drop formation which induces an electrostatic charge upon each drop as it is formed with the size of the charge directly related to the input signal voltage. The ink drops with their respective charges then pass through a constant electric field created by a pair of deflection plates which are maintained at a relatively high potential difference. The high electric field causes the ink drops to deflect according to the charge which they carry. The ink drops then either impact a record medium which results in printing or enter an ink sump for return to the ink reservoir. 1  
  In the manufacture of an ink jet system, whether it be a single jet or a multiple jet system, the amount ofali&#39;gnment of the ink jet is a function of the expense of the precisionrequired to achieve precise alignment. Since precision mechanical parts becomes more expensive as the precision is increased. there is a trade-off point at which any further mechanical alignment becomes too expensive. Unfortunately. this trade-off point often falls short of the desired alignment tolerances. Further precision alignment has been attempted by the addition of circuitry in the charge electrode system which adds an additional factor of variance in the charging of the drop based on alignment considerations. The drawback of such a technique is that it results in a single plane correction capability. Similar techniques which at tempt compensation at points further along the trajectory after drop formation have been also been em ployed. However, since these compensation techniques .operate on the individual drops, they must be synchronized with the drops adding a further degree of complexity and expense to the alignment process.  
 OBJECTS OF THE INVENTION Therefore, it is an object of this invention to align the ink jet in an improved manner.  
  It is a further object of this invention to align the ink jet prior to drop formation so as to remove any requirementfor synchronization in the alignment.  
  It is still a further object of this invention to align. the ink jet electrically prior to drop formation.  
  It is still a further object of this invention to increase the alignment capabilities to more than one plane.  
 SUMMARY OF THE INVENTION The above objects are accomplished by positioning a control means such as an electrode within close proximity to the continuous stream of conductive fluid ink after the fluid is emitted from the ink jet nozzle but prior a unilateral or asymmetrical electric force field which can be adjusted so as to provide precise vernier alignment. The electrode may be placed perpendicularly to the continuous stream, resulting in an electric field which exerts a force only on the jet without affecting the charges of the drops breaking off further down the stream. The applied force results in a velocity component at right angles to the direction of the jet. The electrode is connected to a control source which may be used to vary the potential of the electrode so as to affect the alignment whenever desirable.  
  The use of the alignment electrode prior to drop formation results in a printing system alignment technique which may be used on either single or multiple jet systems, is inexpensive to incorporate into the system, can operate in more than one plane, and provides precise jet alignment.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a multiple ink jet printing system in which correction electrodes are employed.  
  FIG. 2 shows in schematic form that area of an ink jet system between the nozzle and the charge electrode where the correction electrode is positioned for precise alignment.  
 DETAILED DESCRIPTION FIG. 1 shows a multiple ink jet printing system in which correction electrodes are used to attain precise jet alignment. Conductive fluid is delivered under pressure to manifold 10 where it exits by orifices 12 in continuous streams 14. The ink is excited in manifold 10 by means of piezoelectric crystals 16 mounted on the wall of manifold 10 opposite orifices 12. Piezoelectric crystals 16 are connected to an excitation source 17 which provides a constant frequency voltage. The agitation ofthe ink in manifold 10 by piezoelectric crystals 16 causes the ink streams 14 to break-up into uniform drops 18 which are uniformly spaced. Charge electrodes 20 are positioned within close proximity to ink streams 14 at the point of break-up. Charge electrodes 20 are connected to a signal source (not shown) which provides a voltage proportional to an input signal. The voltage supplied to the charge electrodes 20 are induced upon drops 18 as they pass by charge electrodes 20. Drops 18 then pass through constant electric fields created by deflection plates 22 and continue towards record medium 24. Depending upon the deflection of the ink droplets 18 which in turn is determined by the amount of charge placed on&#39;them by charge electrodes 20, ink droplets 18 either impact record medium 24 or enter ink sump 26 for recirculation in the system.  
  The system as described to this point is considered to be within the prior art. It can be seen by referring to FIG. 1 that precise alignment of the orifices would be an expensive and difficult process. This is especially true in the multiple jet system where the expense and difficulty increases with the number ofjets being used. This invention achieves precise ink jet alignment by means of correction electrodes 28 placed in close proximity to continuous streams 14 prior to break-up into drops 18. As is shown in FIG. 1, correction electrodes 28 are connected to bias control 30 which simply supplies an adjustable potential to correction electrodes 28. When correction electrodes 28 are biased by bias control 30, an electric force field is created which acts upon conductive ink 14. The applied force results in a component at right angles to the direction of continuous stream 14. Thus, the electric field exerts a force only on the jet without affecting the charges of the drops 18 which are breaking off further down the streams. While HO. 1 shows correction electrodes 28 affecting continuous streams 14 in the vertical direction, correction electrodes 28 would have the capability of being positioned around continuous streams 14 such that the force could be applied in any desired direction. Thus, vernier adjustment is achieved by the use of a unilateral electric force field applied to the liquid jet prior to thejets breaking in the drops. Such an apparatus is inexpensive, easily implemented and may be applied in any plane. FIG. 2 depicts in schematic form the placement of correction electrode 28 relative to continuous stream 14. It should be noted that while correction electrode 28 is shown and described as being placed between nozzle plane 32 and charge electrode 20, it is only necessary that correction electrode 28 be placed within close proximity to continuous stream 14 prior to stream 14 breaking up into drops 18. lt is desirable that correction electrode 28 have a large diameter and be placed in close proximity to continuous stream 14. This allows a lower voltage to be placed on correction electrode 28. However, it will be recognized that if correction electrode 28 is placed too close to continuous stream 14, ink may strike correction electrode 28. Therefore. there exists a minimum practical distance between correction electrode 28 and continuous stream 14. Further, while a large diameter is desirable for correction electrode 28, the space usually available between nozzle plane 32 and charge electrode is limited and, therefore. limits the diameter size of correction electrode 28.  
  In operation, ink is delivered under pressure to manifold 16 and exits through orifices 12 in continuous streams 14. Continuous streams 14 pass correction electrodes 28 which are biased at positive potentials by bias control 30. Since the ink is conductive, a dipole effect occurs on continuous streams 14 in which the surfaces of conductive streams 14 closest to correction electrodes 28 become negative with respect to the surfaces further away from correction electrode 28. This creates an attractive force between correction electrodes 28 and continuous streams 14 causing continuous streams 14 to realign in the directions of correction electrodes 28. This results in continuous streams l4 continuing at an angle at as shown in FIG. 2 to its normal projected flight path 34. The size of a is dependent on the potential supply to correction electrodes 28 by bias control which is adjustable. Continuous streams 14 then reach charge electrodes 20 at which point continuous streams l4 breakup into drops 18 and receives charges from charge electrodes 20 and proceed to pass through the electric fields created by deflection plates 22. Drops 18 deflect in the fields created by deflection plates 22 proportional to their charge and pass on to either impact print medium 24 or to enter sump 26 for return to the ink system.  
  While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those of skill in the art that various changes in form and detail may be made without departing from the spirit and scope of the invention. For example, while charge electrode 28 has been shown as straight wire electrode perpendicular to continuous stream 14, it is understood that various shape and configurations of electrodes which will produce an electric field having a component at right angles to the direction of continuous stream 14 may be employed. Further, the correction technique disclosed may be employed with any fluid jet stream which employs a conductive fluid which is emitted in a continuous stream.  
  We claim: 1. An alignable recording system for precisely recording on a recording medium comprising:  
 a source of conductive fluid, a nozzle means for ejecting said conductive fluid in a continuous stream towards said recording medium; excitation means for agitating said conductive fluid prior to ejection from said nozzle means to cause said continuous stream to break up into uniform droplets at a point spaced from said nozzle means; a charging means positioned between said nozzle means and said recording medium and in close proximity to said continuous stream at said point where said continuous stream breaks up into droplets for selectively imparting charges to said droplets. deflection plates positioned between said charging means and said recording medium such that said droplets pass through the electrostatic fleld created by said deflection plates for deflecting said charged droplets along one dimension; and a bias control means positioned between said nozzle means and said charging means and in close proximity to said continuous stream prior to said point of breakup for creating a constant force field to transversely deflect said continuous stream along a second dimension approximately perpendicular to said one dimension for alignment of said stream. 2. In an ink jet printer having a pressurized ink manifold means, an ink jet nozzle means for directing conductive ink from said manifold means in a continuous ink jet stream, excitation means in said manifold for actuating said ink jet to cause said stream to break into uniformly spaced droplets at a predetermined point,  
 continuous stream at said predetermined point for selectively charging said droplets, deflection plates posi-&#39; tioned subsequent to charging means such that said droplets pass through the field created by said deflection plates for deflecting said charged droplets along a first dimension, and record media means for receiving drops of ink produced by said ink jet, in combination therewith,  
 correction biasing means positioned in close proximity to said ink jet and intermediate said nozzle means and said charging means where the ink jet is still in a continuous stream prior to said predetermined point, for creating a constant force field for deflecting said ink jet stream along a second dimension perpendicular to the direction of said ink and perpendicular to said one dimension for alignment of said ink jet stream.