Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/07—Ink jet characterised by jet control
  • B41J2/075—Ink jet characterised by jet control for many-valued deflection

Definitions

• the present invention relates to continuous ink jet printing and, more particularly to such printing when applied to the printing of bar codes such as those used in retailing or by postal authorities.
• Continuous ink jet printers are widely used for industrial coding and marking applications.
• a jet of ink is broken into a regular stream of uniform ink droplets which is then passed through a transverse electric field provided across a pair of deflector plates.
• droplets are not charged and are caught in a gutter to be recycled. If a droplet is charged, it is deflected from the recycling path by the electric field and is printed. Since the field across the deflector plates is constant, the deflection is proportional to the magnitude of the charge.
• the object or substrate being printed is generally moved at right angles to the deflection direction and this, together with deflection of droplets by varying amounts, provides the means for placing droplets at the desired position in a two dimensional array.
• a common raster, or sequence of printable (but not necessarily printed) and non-printable (uncharged) droplets is used to print each stroke of a line of print, in order to provide an acceptable linear response.
• each stroke of print is produced by the same number and sequence of printable and non-printable droplets, but the actual printable droplets which are printed will vary from stroke to stroke.
• the linearity of the strokes is particularly important when bar codes are being printed.
• Various techniques are already known for optimising the placement of droplets by using carefully designed rasters in which a predefined sequence of charged and non-charged droplets is used for each stroke. See for example EP-A-0206614.
• table 1 shows an interleaved raster in which sequential droplets numbered 1 to 9 are printed in interleaved droplet positions as indicated.
• Drops 1 and 2 for instance are printed at positions 1 and 5 on the substrata so that their flight paths are widely separated and there is little or no interaction. At high speed, however, this tends to produce a ragged line as shown in figure 1 and this is unacceptable for barcoding.
• Different segments of a vertical stroke may be printed to form a character by using uncharged drops rather than charged drops at the appropriate point within the raster.
• Postal bar codes in particular, demand very high speed operation and a selection of bars and half bars in the case of USPS Postnet code (figure 5) or four different bars for the British Post Office BPO 4 State Code (figure 4).
• the speed constraints are such that with current machines, it is not possible to design a raster with few enough guard drops to attain the required performance.
• the first printhead drop is decelerated most and the second drop catches up with it, so that, without a guard drop, the first and second drop are likely to coalesce and form a single large drop at the beginning of the stroke as shown in figure 2. If this does not occur, the delay in the initial drop will manifest itself as a misalignment or hook at the begining of the stroke as shown in figure 3.
• the present invention is intended to provide a solution to this problem, by enabling high speed and uniform lines to be printed.
• a method of high speed printing of bar codes with a continuous ink jet printer in which bars of varying length or in varied positions are printed by using a different raster of drops for each bar or at least for different bars and by switching rasters in real time to print the appropriate bar.
• Figure 1 illustrates a conventionally printed line of droplets for a bar code
• Figure 2 illustrates another conventionally printed line of droplets for a bar code
• Figure 3 illustrates a further line of droplets for a bar code in accordance with a prior art technique
• Figures 4 & 5 illustrate BPO 4 state bar code strokes and USPO Postnet bar code strokes respectively produced by the technique of the present invention
• Tables 1 and 2 show conventional rasters for printing bar codes
• Tables 3 to 6 show rasters used in accordance with the present invention.
• the rasters of tables 4 and 5 provide excellent print quality, well within the specifications of both the postal bar codes mentioned above.
• the three dot bar shown in figure 4 may be printed using the same raster as that of table 5, without the final 5 drops (drop positions 9-13) being printed, ie drop numbers 8 onwards in the raster all being uncharged drops and thus not being deflected for printing.
• This raster provides the important guard drop between the first and second drops of the raster.
• Table 6 illustrates the rasters used for printing the section of bar code shown in figure 4, a different raster being used for each bar of print.
• a host computer can download bytes of data, relating to the bars to be printed, to an ink jet printer and a memory in the printer which contains a raster sequence of droplets can then be accessed according to the respective types of bar and in order to provide respective commands to the printhead for printing of the required drops.
• a high level byte of data can be downloaded to the printer and converted to two 7-bit bytes which are stored in a printer buffer.
• Bits 1 to 12 may provide a code for the various bars (of 12 dots) to be printed and bits 13 and 14 used to select the related raster.
• the buffer may be sequentially fed with data until full.
• bits stored in the buffer are read sequentially, bits 13 and 14 being used to select the respective raster and bits l to 12 read sequentially to enable charge voltages from a look-up table to be applied to the droplets in order to cause the drops to be deflected to the corrct position.

Landscapes

• Particle Formation And Scattering Control In Inkjet Printers (AREA)
• Ink Jet (AREA)
• Printers Characterized By Their Purpose (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

Family

ID=10705475

Family Applications (1)

Country Status (6)

Cited By (6)

Citations (4)

• 1991
  • 1991-11-29 GB GB919125466A patent/GB9125466D0/en active Pending
• 1992
  • 1992-11-25 EP EP92923915A patent/EP0614417B1/de not_active Expired - Lifetime
  • 1992-11-25 WO PCT/GB1992/002180 patent/WO1993010977A1/en active IP Right Grant
  • 1992-11-25 DE DE69208890T patent/DE69208890D1/de not_active Expired - Lifetime
  • 1992-11-25 JP JP5509933A patent/JPH07501281A/ja active Pending
  • 1992-11-25 CA CA002124328A patent/CA2124328A1/en not_active Abandoned

Patent Citations (4)

Non-Patent Citations (1)

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