Abstract:
A method of printing a pre-defined symbology character set as a series of bars separated by spaces in which the bars are formed of horizontal rows of close adjacent dots while preventing ambiguous decoding of similar character pairs in which one character employs wide bars and one character employs narrow bars. The method comprises the steps of, subtracting at least a portion of one dot or more per horizontal row from bars of similar characters employing narrow bars; and, adding at least a portion of one dot or more per horizontal row to bars of similar characters employing wide bars. It is particularly useful in printing U.P.C./EAN symbology with a low-cost demand printer employing thermal printing techniques.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 08/518,423, filed Aug. 23, 1995, now U.S. Pat. No. 5,681,120. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates to on-demand printers printing U.P.C./EAN bar-codes and, more particularly, to a method and associated apparatus for printing a pre-defined symbology character set as a series of bars separated by spaces in which the bars are formed of horizontal rows of close adjacent dots while preventing ambiguous decoding of similar character pairs in which one character employs wide bars and one character employs narrow bars in which the method comprises the steps of, subtracting at least a portion of one dot or more per horizontal row from bars of similar characters employing narrow bars; and, adding at least a portion of one dot or more per horizontal row to bars of similar characters employing wide bars. 
     2. Background Art 
     U.P.C./EAN symbology is employed in marking products found in supermarkets and the like which are scanned by an optical reader connected to a pricing and inventory computer system. While for the most part a fault-tolerant system in which it is virtually impossible for a label to be misread as a valid identification number for another product, there is one big problem with the U.P.C./EAN symbology--ambiguity with the decode of the 1 &amp; 7 and the 2 &amp; 8 symbol characters. The problem can be understood from the U.P.C./EAN symbology character set as depicted in FIG. 1 taken with FIG. 2, which depicts the 1 and 7 characters. Due to the manner in which the characters are decoded, unless there is a clear distinction as to the bar sizes and spacing, both characters can be decoded as a &#34;T=4,4&#34; character. To achieve a scanable distinction between the 1, 2, 7, and 8 characters, these characters typically have slightly different dimensions by about 8% from the other characters (i.e. 0, 3, 4, 5, 6, and 9). The original specification required that film master based symbols, capable of resolution in excess of 10,000 dots per inch (dpi), precisely add the printing compensation required. 
     Original tolerances precluded any matrix demand printing platform printing U.P.C./EAN symbology from performing the correction. Consequently, the print quality measurements for these symbols always lagged web symbols. The newly published specification (September 1994) allows for a new method of measurement which includes this correction; but, it has been assumed to be impossible to successfully implement it on demand platforms. It turns out that the new method, called &#34;decodability&#34;, does not penalize print quality measurements for slight over-compensation of the ambiguous correction. Therefore, high resolution printing platforms, such as thermal demand printers with resolution on the order of 300 dpi or more, are capable of printing higher quality symbols with the adjusted font than any printing platform currently on the market or described in the art. What is needed is a way to use the new specification to advantage without having to procure expensive media or print at slow speeds to insure a high enough print quality that still passes specification after the decodability penalty is assessed. 
     Solving this problem in demand printers is not new in and of itself. The first demand printers for U.P.C. symbology had 10,000 dpi resolution elements (the same as film master based symbols) and, therefore, were able to print on demand with the same quality and resolution. One such printer was the model 8312 manufactured by Interface Mechanisms, Inc. (now known as Intermec, Inc., the assignee of the present invention). No other demand printing process has ever been able to print in-specification U.P.C./EAN symbols and have resorted to printing higher than necessary quality symbols to compensate and, hence, carried a higher cost. 
     The principal disadvantages of prior art approaches to solving this problem in on-demand printers are the higher cost and slower speed. Most demand processes are extremely cost sensitive and frequently borderline symbols are produced which, consequently, pass all parameters except decodability. Retail systems for reading and processing U.P.C./EAN symbols often keep accurate records of how many symbols are misread and how many codes must be hand keyed in by employees as a result of a failure to successfully read the symbols. The data are associated with the vendors who supplied the products. And, vendors have been subject to fines of up to $5,000 per infraction for supplying products with U.P.C./EAN symbols which are not decodable. Thus, in many cases, vendors have been forced to resort to expensive pre-printing processes in order to avoid the lack of quality of demand printing platforms. 
     Wherefore, it is an object of the present invention to provide an on-demand printer in which U.P.C./EAN symbols can be printed the same way as any other bar code symbology font and achieve the same performance levels. 
     It is another object of the present invention to provide an on-demand printer in which U.P.C./EAN symbols can be printed with low-cost consumables, higher throughput, and a lower likelihood of penalty fines. 
     Other objects and benefits of this invention will become apparent from the description which follows hereinafter when read in conjunction with the drawing figures which accompany it. 
     SUMMARY 
     The foregoing objects have been achieved in a demand printer printing a pre-defined U.P.C./EAN symbology character set having &#34;left odd&#34;, &#34;left even&#34;, &#34;right even&#34;, and &#34;right odd&#34; versions as a series of bars separated by spaces in which the bars are formed of horizontal rows of close adjacent dots by logic designating dots to be printed in the horizontal rows of the bars of the characters, by the improvement to prevent ambiguous decoding of &#34;1&#34;, &#34;2&#34;, &#34;7&#34;, and &#34;8&#34; characters printed by the printer of the present invention comprising the logic including adjusting logic which adjusts the pre-defined U.P.C./EAN symbology character set for the &#34;1&#34;, &#34;2&#34;, &#34;7&#34;, and &#34;8&#34; characters by, subtracting at least a portion of one dot or more per horizontal row from bars of left odd and right odd &#34;1&#34; and &#34;2&#34; characters and of left even and right even &#34;7&#34; and &#34;8&#34; characters; and, adding at least a portion of one dot or more per horizontal row to bars of left even and right even &#34;1&#34; and &#34;2&#34; characters and to left odd and right odd &#34;7&#34; and &#34;8&#34; characters. 
     The pre-defined U.P.C./EAN symbology character set can also be pre-modified in the same manner prior to printing. 
     In its broadest approach, the present invention is a method of printing a pre-defined symbology character set as a series of bars separated by spaces in which the bars are formed of horizontal rows of close adjacent dots while preventing ambiguous decoding of similar character pairs in which one character employs wide bars and one character employs narrow bars by subtracting at least a portion of one dot or more per horizontal row from bars of similar characters employing narrow bars and adding at least a portion of one dot or more per horizontal row to bars of similar characters employing wide bars so that the distinction between the wide bars and the narrow bars is more discernible to the optical scanning apparatus and decoding logic employed. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a drawing showing the U.P.C./EAN symbology character set. 
     FIG. 2 depicts how the 1 and 7 characters can be misread. 
     FIG. 3 depicts how the 1 and 7 characters are adjusted according to the present invention. 
     FIG. 4 is a simplified drawing of a printer according to the present invention. 
     FIG. 5 is a simplified drawing of a label printer printing in a &#34;drag&#34; mode. 
     FIG. 6 is a simplified greatly enlarged drawing of a printhead printing a bar in the manner of FIG. 5 and depicting how the present invention is implemented in the drag mode. 
     FIG. 7 is a simplified drawing of a label printer printing in a &#34;picket fence&#34; mode. 
     FIG. 8 is a simplified greatly enlarged drawing of a printhead printing a bar in the manner of FIG. 7 and depicting one way in which the present invention can be implemented in the picket fence mode. 
     FIG. 9 is a simplified drawing of a mechanism used in a label printer to step the media between dot positions in the picket fence mode according to the present invention. 
     FIG. 10 is a simplified logic flow diagram for implementing the present invention in a second way in the picket fence mode employing the drive system of FIG. 9. 
     FIG. 11 is a greatly enlarged and simplified drawing of two adjacent dots depicting how there are at least two steps of the stepping motor employed to move the media between dot printing positions in the usual manner of printing in the picket fence mode. 
     FIG. 12 is a greatly enlarged and simplified drawing of two adjacent dots depicting the outside width thereof when they are printed normally in the picket fence mode. 
     FIG. 13 is a greatly enlarged and simplified drawing of two adjacent dots depicting the outside width thereof when they are shave printed in the picket fence mode according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The implementation of the correction factor in a standard on-demand printer according to the present invention is straight forward and can be done on any base font, such as that of FIG. 1, having the problem addressed with particularity herein. FIG. 1 is a complete diagram of the twenty (7,2) character set which makes up the U.P.C. Version A (left odd and right even) and Version E (left odd and left even) symbols as well as the EAN-13 (left odd, left even, and right even) and EAN-8 (left odd and right even) symbols. Additionally, the right odd characters are included since Version D requires all four character types. 
     Table A designates the correction to be applied when printing the characters of FIG. 1 in order to achieve the objectives of the present invention according to one possible implementation thereof. The adjustment of &#34;plus one dot or more&#34; (+) and &#34;minus one dot or more&#34; (-) applies to each bar with the corresponding space decreased or increased, respectively, by one dot or more for printing resolutions of approximately 200 dpi or more. 
     
                       TABLE A______________________________________                                  RIGHTCHARACTER LEFT ODD  LEFT EVEN RIGHT EVEN                                  ODD______________________________________0         0         0         0        01         -         +         +        -2         -         +         +        -3         0         0         0        04         0         0         0        05         0         0         0        06         0         0         0        07         +         -         -        +8         +         -         -        +9         0         0         0        0______________________________________ 
    
     The drawing of FIG. 3 shows how this is applied to the &#34;left odd&#34; 1 and 7 characters of FIG. 2. Assuming a typical situation of five horizontal dots in each dot row for each bar position, Table A designates that the bars of the &#34;1&#34; character are to lose one dot or more per bar and the bars of the &#34;7&#34; character are to gain one dot or more per bar. Note that the adjustment is &#34;per bar&#34; and not per bar position. It will be seen that the &#34;bars&#34; of the U.P.C./EAN symbology employ one, two, three, and four bar positions. In the example of FIG. 3, each bar position is made up of five dots. Thus, with respect to the &#34;1&#34; character on the left side of FIG. 3, the bar comprising one bar position goes from five dots to four dots and the bar comprising two bar positions goes from ten dots to nine dots. Similarly with respect to the &#34;7&#34; character on the right side of FIG. 3 the bar having two bar positions goes from ten dots to eleven dots while the bar having three bar positions goes from fifteen dots to sixteen dots. The spaces between bars have a corresponding reduction or increase in the number of dot positions. 
     One manner in which the present invention can be implemented is depicted in simplified form in FIG. 4. The printer 10 has a printhead 12 positioned above a moving media 14 having labels 16 thereon. The printhead 12 is driven by the driving logic 18. The driving logic 18 obtains the definition of the characters to print from the pre-defined character set symbology 20. In this embodiment of the present invention, the driving logic 18 includes adjusting logic 22 which dynamically adjusts the character set in the manner defined above. Thus, if a new character set were to be installed having similar problems, the adjusting logic 22 could compensate dynamically at print time. An alternate approach to the present invention would be to pre-adjust the pre-defined character set symbology 20 according to the techniques described in detail above. In that case, however, the pre-defined character set symbology 20 would have to be re-adjusted if a new character set were to be printed by the printer 10. 
     Having thus looked at one implementation of the present invention broadly, let us now look at alternative ways in which the present invention can be implemented through the use of specialized printing apparatus and driving logic. A barcode printer printing barcodes as a series of dots prints in one of two modes--drag mode or picket fence mode. In the drag mode depicted in FIGS. 5 and 6, the printhead 12 prints the bars 24 of a barcode 26 simultaneously by printing each row 28 of dots 30 for all the bars 24 at the same time. Thus, each dot position is &#34;dragged&#34; along the length of its associated bar 24. In the drag mode, the present invention can be implemented only by adding or subtracting at least one dot or more 24 from all rows 28 of a bar 24. Each barcode is pre-defined. Thus, for example, the pre-defined character set symbology 20 of FIG. 4 would pre-define the U.P.C./EAN symbology character set for the &#34;1&#34;, &#34;2&#34;, &#34;7&#34;, and &#34;8&#34; characters with the changes of the present invention pre-defined. 
     A more common printing approach is the &#34;picket fence&#34; printing technique of FIG. 7. Each vertical column of dots 24 for a vertical bar 24 is printed simultaneously. That is, one vertical column of dots 24 for all rows 28 in the bar 24 are printed simultaneously. Thus, the barcode 26 is printed from end to end rather than from top to bottom (or bottom to top) as was the case with the drag mode. The picket fence approach offers several ways of implementing the present invention which are not available in the drag mode. One could, of course, implement the present invention by adding or subtracting a whole column (or more) of dots 24 as depicted in FIG. 8. This could be done by pre-defining the U.P.C./EAN symbology character set with the &#34;1&#34;, &#34;2&#34;, &#34;7&#34;, and &#34;8&#34; characters having the changes of the present invention pre-defined in total. It could also be done by defining &#34;normal&#34; bars and &#34;special&#34; bars modified according to the present invention and then defining the U.P.C./EAN symbology character set according to the bars employed with the &#34;1&#34;, &#34;2&#34;, &#34;7&#34;, and &#34;8&#34; characters employing the special bars. 
     Where a drive system such as that depicted in FIG. 9 is employed in the label printer, other possible implementations of the present invention in the picket fence more are made possible. This is more fully described in a co-pending application by the inventor herein entitled DOT PRINTERS WITH WIDTH COMPRESSION CAPABILITIES filed on even date herewith as Ser. No. 08/518,226 filed Aug. 23, 1995 and assigned to the common assignee of this application, the teachings of which are incorporated herein by reference. The media 32 upon which the printing is to take place is moved in steps by a stepping motor 34 driving a drive roller 36, or the like, operably connected to move the media 32. The stepping motor 34 is driven by logic 38. Typically, there are two steps of the stepping motor 34 between print position of adjacent dots 24 as depicted in FIG. 11. If more steps are employed, the method to be described can be employed by simply modifying the number of steps in the manner taught hereinafter. By employing the logic 38&#39; of FIG. 10 in the logic 38 of FIG. 9, &#34;normal&#34; and &#34;shaved&#34; bars of different width as depicted in FIGS. 12 and 13 can be produced. To produce a &#34;normal&#34; bar. All the dots 24 in each row 28 are spaced by two steps of the stepping motor 34 as depicted in FIG. 12. To produce a &#34;shaved&#34; bar, on the other hand, at least the last row 28 is spaced by only one step of the stepping motor 34 as depicted in FIG. 13. Thus, as can be appreciated by comparing FIGS. 12 and 13, the overall width of a bar 24 can be reduced by a portion of a dot (rather than a full dot) by printing the last dot at one step distance instead of two. Similarly, the same comparison will show that the overall width of a bar 24 can be increased by a portion of a dot by printing an extra row of dots at one step distance instead of two. This technique of bar width modification could have particular applicability in lower resolution printers employing say 200 dpi where the removal or addition of a full dot from or to the width of barcode bars being printed could adversely affect the print decodeability quality while a partial dot modification would actually improve the decodeability quality. 
     In a co-pending application entitled BAR SHAVING OF THE RESIDENT FONTS IN A THERMAL-PRINTING ON-DEMAND BARCODE PRINTER, Ser. No. 08/513,503, filed Aug. 23, 1995 by the inventor herein and assigned to the common assignee of this invention, a method of &#34;shaving&#34; dots from the bars of barcodes printed by thermal printers to increase readability by optical scanning apparatus is disclosed and claimed. It should be noted with particularity that the techniques of that application are not applicable to solving the problem solved by this invention. Any generic bar shaving that is applied on a symbology-wide basis according to that invention would be in addition to the character font adjustments of the present invention. 
     It should also be noted that the adjustment of the present invention includes both dot removal and dot addition. In actual tests of the present invention it was found that contrary to the common belief that the addition of dots to the bars would cause problems with the adjacent spaces (which are correspondingly reduced in width thereby), there was actually a benefit and an increase in accuracy of optical scanability and decoding which has been included as part of the best mode contemplated for the present invention.