Method for improving performance of an ink jet bar code printer
United States Patent [191 Apr. 1,1975  
 Stone [54] METHOD FOR IMPROVING 3,596,275 7/1971 Sweet 346/75 X PERFORMANCE OF AN INK JET BAR 3,596,276 7/l97l Lovelady et a1. 346/75 X CODE PRINTER [75] Inventor: Joseph J. Stone, Northbrook, 11]. Primary Examiner-Joseph W. Hartary i Attorney, Agent, or Firm-Freilich, Wasserman, Rosen [73] Assignee. A. B. Dick Company, Chicago, Ill. &amp; Fernandez Lindenberg [22] Filed: Jan. 14, 1974 [21] Appl. No.: 432,870  
 [57] ABSTRACT [52] US. Cl. 346/1, 346/75 This invention improves the priming f b codes by [51] Int. Cl. Gold 18/00 an ink drop primer, by providing a cure for h prob [58] Field of Search 346/75 lem created by the aerodynamic effects on ink drop lets as they are directed toward the print receiving sur- [56] References Cited f UNITED STATES PATENTS 3,562,757 2/1971 Bischoff 346/75 X 5 Claims, 4 Drawing Figures D /A CONVERTERS JO 5 itztsisevs DROP bYNG RATE GATE. DROP COUNTER 56 CLOCK CARCU IT $OUI?C.E PE ET CF- 5 2e POTENTIAL 05C 5 4o 1 52. r 22 i 24 2s 4 DATA WRiTE RE$ERVOiR TRANS&#34; MM SOURCE g QE DueER =9 30 T 7 DROP COLLECTOR PATENTEU AFR I I975 SHEET 1 0F 2 TO DUMP METHOD FOR IMPROVING PERFORMANCE OF AN INK JET BAR CODE PRINTER BACKGROUND OF THE INVENTION This invention relates to ink drop printers and more particularly to an improved method and means for printing bar codes.  
  One of the current applications for ink drop printers is directed to the printing of machine readable bar codes on packages, such as mail packages. These machine readable bar codes are thereafter read for the purpose of enabling the automatic sorting of these packages. To produce a vertical bar requires the use of eight to ten droplets of ink. In a preferred configuration, a stationary ink jet nozzle produces these droplets and propels them towards a moving package surface. Appropriate electrical charges are generated for each droplet so that they are deflected in an upward scanning direction in their flight towards the package surface.  
  It is important, in the production of straight bars, that the sequence of ink droplets reach the recording surface in such a manner that approximately uniform time intervals exist between adjacent droplets. A significant variation in the time interval of one drop, as compared to the intervals between others, permits and package surface to move horizontally by a significant amount before the ink drop impinges upon it. This produces horizontal displacements and unacceptable bar codes.  
 OFJECTS AND SUMMARY OF THIS INVENTION An object of this invention is the provision of a method and means for compensating for the error introduced by aerodynamic effects on an ink drop bar code printer.  
  Another object of this invention is the provision of a method and means for improving bar code printing by an ink drop printer.  
  Still another object of this invention is the provision ofa novel and improved method and means for operating an ink drop bar code printer.  
 The aerodynamic effect which causes unacceptable .bar code printing is that the first drop of a group of droplets needed for printing a bar code has to pass through undisturbed air, from the drop forming nozzle to the receiving substrate. The droplets which come behind it are effectively flying through air which has already been disturbed. The first drop is slowed to the greatest extent, the second drop is not slowed as much as the first drop and the third drop still less. As a result, the first drop of a stream falls behind the other drops so that the paper which is moving horizontally moves to such an extent that the drop does not fall in line to assist in forming a proper straight bar code. Alternatively, the first drop can fall behind to the extent where it will be caught up to by the second drop and they merge to form a single larger drop which produces an enlarged spot on the paper.  
  To eliminate this effect, second and third drops are dumped or deflected so that they will be returned to the inkreservoir and will not participate in the printing. The first drop will still fall back relative to the following drops because of the increased aerodynamic drag. It has been found that the amount that the first drop falls back, when the second and third drops are eliminated, is such that it falls back into line with the fourth drop of an ink drop stream whereby a perfectly acceptable bar code is achieved by printing with the first, fourth, fifth, sixth, etc. drops. Obviously, the number of drops generated for printing a particular bar is increased by two in order to provide the bar with the proper length and to make up for the elimination of the second and third drops.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are schematic illustrations of aerodynamic effects caused on a drop in flight.  
  FIG. 3 is a block schematic diagram of a circuit arrangement which may be used for carrying out this invention.  
 FIG. 4 is an illustrative waveform drawing.  
 DESCRIPTION OF THE EMBODIMENT OF THE INVENTION FIG. 1 is a schematic illustration of a typical flight error problem which is encountered with equipment of the type indicated. To produce a proper bar code, droplets 1 through 4 (along with the remaining droplets of the bar code, which are not shown here) should fall along the dashed straight line 10. The droplets are represented by the dotted circles and numbered 1 through 4. The first drop, however, since it is effectively the path breaker, passes through undisturbed air. The following droplets do not have as much aerodynamic drag because of the pre-passage of the first drop. As a result, the first drop slows down more rapidly than those that follow it. The result can cause timing errors in the flight time of the droplets to the paper surface and the bar code has a resultant horizontal curvilinear distortion. It is also possible, as represented by the circle with 1 and 2 therein, that the droplets combine to form a single large droplet, which produces an enlarged spot on the paper surface.  
  FIG. 2 illustrates the method and means whereby compensation is provided for the aerodynamic problem. As represented by FIG. 2, the stream of drops is generated as before. The first drop, as before, encounters an aerodynamic drag and falls behind its intended position. However, droplets 2 and 3 are directed to the dump or collector for unused ink drops, permitting droplets 4 and 5 to assume the spatial position previously intended for the second and third droplets. The other drops fall in line so that a straight vertical bar is printed on the surface of the paper. This method of operating the ink drop printer permits the slowing down to occur as previously indicated and regroups the first drop into a linear relationship with a following sequence of drops whereby the increased flight time of the first drop has been anticipated and compensated forQIn the illustration given, only two drops need to be dumped. In some cases, more or less than two may be dumped in order to achieve proper compensation.  
  FIG. 3 is a block schematic diagram of an arrangement for compensating for the aerodynamic flight problem encountered by the ink drops, as described above. Also schematically shown in FIG. 3 is an ink drop writing system of a well known type. This comprises an ink reservoir 20, which supplies ink under pressure to a nozzle 22. The nozzle is alternately constricted and permitted to expand by a transducer 24, at a frequency determined by an oscillator 26, whose output drives the transducer.  
  A stream of ink is emitted from the nozzle 22, and in response to the action by the transducer, breaks down into a stream of drops between two charging plates 28, 30, which are spaced on either side of the drop path.  
  A charge is induced on each of the drops passing between plates 28, 30, having an amplitude determined by the voltage applied to the plates at drop formation time. The stream of drops next passes between a pair of deflection plates 32, 34. These deflection plates have a fixed bias applied thereto from a source of potential 36. As a result, a drop passing therebetween receives a vertical deflection determined by the interaction of the electric field established between plates 32, 34, and the charge on the drop.  
  Drops not required for writing are intercepted by a drop catcher 38 after passing through the region between plates 32 and 34. The remaining drops clear the barrier established by the drop catcher and are deposited on the receiving surface 40, which is moving in the direction shown by the arrow. The location at which the drops are deposited is determined by the charges which were applied to the drops as well as the effects of aerodynamic drag, as described above.  
  In accordance with this invention, a drop rate clock circuit 42, which is a clock circuit whose clock pulse output is used to determine the desired drop rate, has its output applied to a sync gate circuit 44 as well as to the oscillator 26, which is synchronized thereby. The sync gate circuit 44 is enabled to pass clock pulses in the presence of a write command signal from a write command signal source 46, and when the output of an inverter 48, which is connected thereto is high. The inverter output is high only when a drop counter 50 does not provide an 11 count output. The 11 count output of the counter is connected to the inverter 48. By way of example, the counter is shown to have eleven counts, three more than the number of drops required to write a bar. This is to be considered as exemplary only.  
  The write command signal is provided by the output signal from a data source 52. The data source provides an output which determines the bar code to be written.  
  In the presence of a write command signal, the drop counter 50 is reset to its first count whereby the sync gate circuit is enabled and the drop counter can commence counting clock pulses. All of the count outputs of the drop counter except the second and third count outputs are connected to a digital to analog converter 53, the output of which is applied to a summing amplifier 54. The digital to analog converter and summing amplifier convert the counts into a stair-step waveform 56 of the type shown in FIG. 4. It will be noted that the second and third counts of the counter are not connected to the digital to analog converter. Thus, as shown by the waveform 56 in FIG. 4, there are no corresponding outputs for the second and third counts of the counter, but the output occurring in response to the fourth count output is twice as large as the output occurring in response to the first count output and the following outputs increase incrementally. A stair-step charging voltage waveform 58 illustrative of the prior art is also shown in FIG. 4 and may be compared with waveform 56.  
  The output of amplifier 54 is applied to the charging plates 28, 30, and each drop is thereby charged to an amplitude level determined by the count occurring at the time it is formed. When the counter 50 reaches its eleventh count, the inverter 48 output goes low, the sync gate 44 is closed. The eleventh count output of the counter is not connected to the amplifier 54 and therefore any drops occurring now will have no charge and be caught by the drop collector. Upon receipt of the next write command signal, the circuit described operates to write another bar.  
  As a result of no charge being applied to the second and third drops, they are dumped. That is, they receive no upward deflection when passing through the field established between electrodes 32 and 34 and therefore do not get past the barrier established by deflector of the drop collector 38. Therefore, as previously explained, due to the aerodynamic drag on the first drop, it slows down until it is in proper position relative to the fourth, fifth and other drops to form a perfect bar in the bar code.  
  While the foregoing description shows a withholding of the charge to the second and third drops, it is considered within the ability of those skilled in the art to dispose of the unwanted drops by applying a lower amplitude charge than is applied to the other drops, or a negative charge. Thus, this is to be considered as being within the scope of the present invention and the claims. Also, while the drop rate clock 42 is shown as synchronizing the oxcillator 26, if desired, the alternative, using the oscillator 26 to synchronize the drop rate clock, may be used.  
  There has accordingly been described and shown herein a novel and useful method and means for compensating for the adverse effects of aerodynamic drag on an ink drop stream.  
  The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:  
  1. In an ink drop printer of the type wherein a stream of drops is emitted for printing a bar in a bar code, and wherein the leading drops in the stream are retarded, due to aerodynamic effects to thereby adversely affect the printing, the method of compensating for the adverse aerodynamic effects comprising generating a plurality of ink drops to form a stream, projecting said stream of ink drops in a path toward a receiving substrate for printing a bar thereon,  
 removing from each stream of drops those drops immediately following the first of the drops in each stream which due to aerodynamic effects cannot align themselves with the remaining drops in said stream for printing a bar in a bar code, and  
 deflecting the remainder of the drops in said stream of drops to desired locations on said substrate. 2. A method as recited in claim 1 wherein said step of removing one or more of the drops following the first drop in said stream of drops, and deflecting the remaining drops in said stream to desired locations on said substrate comprises intercepting said one or more drops following said first drop prior to reaching said substrate,  
 applying charges to the remaining drops in said stream representative of the locations desired to be reached by said drops on said substrate, and  
 establishing an electric field in the path of said drops toward said substrate through which said drops must pass to reach desired locations on said substrate.  
  3. In an ink drop printing system of the type wherein each bar in a bar code is printed by projecting a stream of ink drops in a path through the air toward a receiving substrate, and the leading drops in said stream of ink drops, due to aerodynamic drag, are slowed in their flight, thereby causing defective printing, the improvement comprising means for projecting successive streams of drops toward said substrate for correctly printing bars in a bar code, including means for removing those drops from each stream of drops immediately following the first ink drop in a stream of ink drops which, due to aerodynamic effects will not properly align themselves with the remaining ink drops in said ink drop stream for printing a bar in a bar code to thereby eliminate the defective printing caused by aerodynamic drag. 4. In an ink drop printing system as recited in claim 3 wherein said means for removing those drops from each stream of said ink drops following said first ink drop in an ink drop stream includes means for applying a charge to each of said ink drops in an ink drop stream having an amplitude in accordance with the location it is desired for each drop to reach on the surface of the receiving substrate,  
 means for establishing an electric field between said means for charging said drops in a stream and said substrate, and  
 means within said means for applying a charge, for  
 withholding a charge from each of said predetermined number of drops, to insure that they are deflected out of the path which the remaining drops in said stream take when passing through said electric field.  
  5. in an ink drop printer of the type wherein a stream of drops is emitted for printing a bar in a bar code, and wherein one or more of the leading drops in the stream are retarded, due to aerodynamic effect thereby adversely affecting the printing, apparatus for compensating for the adverse aerodynamic effect comprising means for projecting a stream of drops in a path towards a receiving substrate to print a bar thereon,  
 means along said path for intercepting drops having a predetermined charge and preventing them from reaching said substrate,  
 means, along said path and upstream of said means for intercepting drops, for charging each drop with a charge for deflecting each drop to a desired location on said substrate and for charging with said predetermined charge successive drops following the first drop in a stream, which, due to aerodynamic effects will not align themselves with the remaining drops in said stream for printing a bar in a bar code, whereby said predetermined charged drops are intercepted by said means for intercepting, and  
 means for establishing an electric field along said path for deflecting each of said drops in accordance with the charge applied thereto, whereby said first drop aligns itself with the remaining drops reaching said substrate to thereby eliminate said adverse printing effect.