EP1829692A2 - Method for improving printing quality with a thermal transfer print head and assembly to carry out the method - Google Patents

Abstract

The method is for quality improvement of printing with a thermotransfer printing head, wherein in one improvement step (30) an energy value calculation is carried in a manner according to which data of the image from a microprocessor is processed in order to also control those heating elements which lie in at least one of the edge regions of the heating element row, but where no dots are to be printed during printing of a barcode. Those heating elements which do not lie in the two edge regions of the heating element row are controlled by a heating impulse for a limited period of time. An independent claim is included for an arrangement for carrying out the method, wherein a high-resolution thermotransfer printing head has a row of heating elements, and a microprocessor evaluates energy values before the printing process to control the heating elements.

Description

The invention relates to a method for improving the quality of printing with a thermal transfer print head according to the preamble of claim 1 and an arrangement for carrying out the method according to the preamble of claim 10. The invention is used in printing devices with relative movement between the thermal transfer print head and the print material, in particular Franking machines and similar printing accounting or mail processing equipment. The purpose of the invention is to increase the quality of printing of data matrix barcodes at a high throughput of mail pieces, so that their machine readability is improved.

In the US 4,746,234 For example, a postage meter with a thermal transfer printing device has been proposed which makes it easier to change the print image information. In this case, semipermanent and variable print image information are electronically stored as print data in a memory and read out into the thermal transfer printing apparatus for printing. The printed image (postage stamp image) is known to include a message and postal information including postage data for carrying the mail piece, for example, a postage stamp image, a postal stamp image with the post office delivery point and date, and an advertising stamp image.

The entire print image is microprocessor-controlled printed image column by column by a single thermal transfer print head. In this case, a printing of printing columns in an orthogonal arrangement to the transport direction takes place on a moving mailpiece. The machine can thereby achieve a maximum throughput of mail of 2200 letters / hour at a print resolution of 203 dpi.

The franking machine T1000 has only a microprocessor for controlling a thermal transfer print head with 240 heating elements for column-wise printing. All heating elements are in a row, which is 30 mm long and is arranged orthogonal to the transport direction. Thermal transfer printers use for printing at least the same width thermal transfer ribbon, which is arranged between a surface to be printed - for example, a mail piece - and the series of heating elements. The energy of an electrical pulse is converted at the resistance of the driven heating element into heat energy, which transfers to the thermal transfer ribbon. Printing requires melting of a colored layer piece from the thermal transfer ribbon and application of the colored layer piece to the print material surface. The printing takes place only when the impinged with the pulse heating element was brought to the pressure temperature, ie a higher than the preheating temperature. When moving the thermal transfer ribbon at the same time with the mail piece relative to the heating element and running heat energy supply a line is printed parallel to the movement or transport direction in a row. A bar is printed orthogonal to the direction of transport in a printing nip when electrical impulses are applied simultaneously to all heating elements in the row of heating elements for a predetermined limited period of time (pulse duration). The pulse duration is subdividable into phases. Within the predetermined limited time duration (pulse duration), there exists a final phase (printing phase) in which the dots of a printing nip are printed. The last phase is preceded by further phases of control of the heating elements in order to heat the latter to the pressure temperature. Due to the transport of the mailpiece these phases print image columns are assigned. A long Single pulse for driving a heating element can be divided into several pulses whose pulse duration is equal and correspond to a specific heating phase. Print image columns of the moving mailpiece are thus also associated with these heating phases, as are the print columns with the printing phases.

The binary pixel data for driving the heating elements of all printing columns are stored in a pixel memory volatile. At a low print resolution, the spacing of adjacent print columns is large and the binary pixel data of the print phase reflects the print image. Usually, multiple pulses are required to generate enough heat energy to melt down a layer of paint beneath the heating element which is printed on the surface of the mailpiece as a dot ( DE 38 33 746 A1 ).

In principle could be printed to achieve a high printing resolution in each phase, if only in good time in previous phases, the control of the heating elements to heat them up. It should also be noted that also the resistance of the adjacent heating element in the series, the energy of an electrical pulse is converted into heat energy (heat conduction problem). The heat energy is reduced by cooling when the pulse is eliminated. Due to the adjacent energy input, an increase in heat energy by heat conduction is possibly given so far that the control of certain heating elements can be exposed to their heating in one phase and yet sufficient heat energy is present, which causes melting of a paint layer piece under the heating element. Therefore, in addition to providing and outputting binary pixel data for generating or not generating an electrical pulse, a microprocessor is also concerned with controlling the power distribution depending on the pattern to be printed. The original reflection of the print image by binary pixel data is changed accordingly in the pixel memory, so that a clean print image is created. This requires either an extensive forecast, such as the EP 536 526 B1 (= DE 41 33 207 ) bearing the title: "Method of Controlling Feed In the aforementioned historical control, the supplied energy for preheating a respective heating element of the thermal transfer printhead is set depending on whether frequent or infrequent printing operations have been initiated in the near past, the heating element being for Print had to be controlled.

Also from the JP 61-239966 It is known to control the temperature of the individual heating elements separately by pulse width modulation as a function of adjacent data and to raise the temperature to the value necessary for printing in the short term. Nevertheless, the relevant heating element and thus the entire thermal print head defies the preheating relatively cool. This is desirable for the temperature curve to drop relatively steeply so that the time between successive raster points may be short. This makes it possible to shorten the time required for a recording of dots on a print substrate and thus to increase the printing speed.

To achieve a higher print resolution, a microprocessor with higher computing speed could be used. The output of binary pixel data to the thermal transfer printhead would then occur more often per unit of time, in which a mailpiece or similar printed matter a similar piece of the transport path is moved on. At the same time, however, the storage space requirement in the pixel memory increases due to the pixel data for each additionally inserted virtual column or heating phase. A virtual column is to be understood here as a possibility of a further column in the printed image, which, however, is not visible during printing, since no dot is printed in the heating phase.

Since the market introduction of the franking machine T1000 of the applicant Francotyp-Postalia AG & Co.KG in 1991, which in addition to the date and post fees now for the first time also allowed to change the aforementioned advertising stamp image electronically by pressing a button, the demands on their microprocessor control were constantly increasing. On the one hand, more data is processed, the more variable data is required in the print image. On the other hand, there are other printed images which differ significantly in structure and content from a franking stamp image, for example, to print business cards, fee and court cost stamp images. The print resolution requirements in dpi (dot's per inch) are constantly increasing. In this case occurs when printing a dot, the aforementioned heat conduction problem between the adjacent heating elements by the adjacent in the printed image to be printed pixel, the closer the pixels are adjacent. The aforementioned problem associated with the thermal transfer printing method increases with high printing resolution.

Modern franking machines should enable a so-called security impression, ie an impression of a special marking in addition to the aforementioned message. For example, a message authentication code or a signature is generated from the aforementioned message, and then a character string or a barcode is formed as a marker. If a security print is printed with such a mark, this allows a verification of the authenticity of the security print in, for example, the post office or the private carrier ( US 5,953,426 . US 6,041,704 ).

The development of the postal requirements for a security print in some countries results in a very high amount of variable print image data that has to be changed between two prints of different postage stamp images. For example, for Canada, a Datamatrix barcode of 48 x 48 pixels is to be generated and printed for each individual franking imprint.

In order to streamline postal distribution and increase counterfeit security, Deutsche Post AG introduced a new standard called FRANKIT in Germany in 2004. Even at low printing speed, the print quality of known postage meters with thermal transfer printing is not good enough for the machine readability of a 2-D barcode. In addition to the printing speed but now the print resolution had to be increased to 300 dpi for printing a two-dimensional barcode. However, a high throughput of mailpieces is associated with a lower quality of printing, in particular Datamatrix barcodes so that their machine readability is not always guaranteed. The microprocessor of a suitable franking machine has to process more data in a shorter time. The heating energy for printing the image elements of the postage meter machine is to be calculated by microprocessor, taking into account the two immediately preceding print columns printed in the past. Such a historical control is known for history compensation and would now need to be extended to accommodate much more information to improve the readability of Datamatrix barcodes.

The printed data matrix barcode contains a continuous line at the left and at the bottom, which is also called 100% line and at the right and at the top a broken line of barcode elements, which is also called 50% line, because every second barcode image element is missing. Instead of being a dot, the bar code image elements (modules) are usually printed in square form (FIG. 1). The high-resolution images printed with previous methods, in particular barcode images, are printed differently on the edges than in their middle and thus not always mechanically readable.

The object of the invention is to provide a method of improving the quality of printing with a thermal transfer printhead and associated assembly which provides improved machine readability of bar codes.

The object is achieved with the features of the method according to claim 1 and the arrangement according to claim 10.

When printing Datamatrix barcodes, the print head heats up considerably, so that the generated barcode image elements (modules) are printed significantly wider than at the beginning of the print, especially in the printing direction. The barcode elements of the 50% line at the top make a checkered pattern but are often too small or too close to the other barcode image elements weakly printed. Both edge effects in combination with further unavoidable printing defects lead to failure of the readability of these barcodes. The barcode image elements should assume the same size on the left and right, above and below. Therefore, the heating elements and thus also the surrounding heat capacities are preheated to compensate for the edge effects, which are effective in the non-printing area in front of the barcode image, the so-called. Quietzone. With moving printing material, the heating phases can each be assigned print image columns in the quiet zone. A certain number of heating phases are provided in order to heat the heating elements to a preheating temperature so that the thermal transfer process is not yet triggered. This leads to a desired more favorable temperature distribution in the print head and, as a result, to an equalization of the printing, in particular an enlargement of the barcode image elements at the start of printing of the barcode image. The size of the barcode image elements at the end of the barcode image is thereby only slightly larger compared to the beginning.

In a border area between the 50% line and the edge of the franking strip, a small number of heating elements are controlled in such a way that they become sufficiently warm and the edge effect is compensated, whereby, however, the thermal transfer process is not triggered yet. This heats up the environment of the 50% line so that barcode images are displayed as well on the edge as in the middle of the barcode.

The number of Vorheizspalten and the border lines and / or the respective heating energies are adapted to the temperature of the printhead.

Although the invention is illustrated by the example of a franking machine, it should not be limited to this alone.

Fig. 1,

Vereinfachte Darstellung eines Frankierstreifens mit Barcode,

Fig. 2,

Draufsicht auf einen vereinfachten Thermotransferdruckkopf,

Fig. 3,

Vereinfachter Flussplan der zum Drucken erforderlichen Verarbeitung von Bilddaten nach dem Stand der Technik,

Fig. 4,

Temperaturverlauf und Impuls/Zeit-Diagramm beim Drucken eines Dots,

Fig. 5,

Vereinfachte Darstellung der Barcodedaten,

Fig. 6,

Barcodebild mit Verdeutlichung der Barcodedatenaufbereitung durch eine vergangenheitsbezogene Steuerung,

Fig. 7,

Barcodebild mit externen Bereichen zur Verdeutlichung einer für diese Bereiche unterschiedlichen Datenaufbereitung zur Vorwärmung von Heizelementen (Variante 1),

Fig. 8,

Schnitt durch einen Thermotransferdruckkopf entlang einer Reihe von Widerstandsheizelementen,

Fig. 9,

Verbesserter Flussplan der zum Drucken erforderlichen Verarbeitung von Bilddaten,

Fig.10,

Blockschaltbild zum Steuern des Druckens einer Frankiermaschine mit einer Druckdatensteuerung für einen Thermotransferdruckkopf,

Fig. 11,

Perspektivische Darstellung einer Frankiermaschine vom Typ Optimail 30,

Fig. 12,

Frankierabdruck nach der DPAG-Anforderung FRANKIT,

Fig. 13,

Programmroutine mit Ermittlung der Energiewerte zur Vorheizung und Randheizung eines Thermotransferdruckkopfes,

Fig. 14a,

Barcodebild mit externen Bereichen zur Verdeutlichung einer für diese Bereichen unterschiedlichen Datenaufbereitung zur Vorwärmung von Heizelementen (Variante 2),

Fig. 14b,

Frankierabdruck nach den postalischen Anforderungen für das Land Australien,

Fig. 14c,

Programmroutine mit Ermittlung der Energiewerte nach einer weiteren Variante zur Vorheizung und Randheizung eines Thermotransferdruckkopfes (Varianten 2 und 3),

Fig. 15a,

Impuls-/Zeitdiagramm zur Ansteuerung eines im Vorbereich B angesteuerten Heizelementes des Thermotransferdruckkopfes,

Fig. 15b,

Impuls-/Zeitdiagramm zur Ansteuerung eines im Randbereich N1 gelegenen Heizelementes des Thermotransferdruckkopfes,

Fig. 16,

Subprogrammroutine mit Ermittlung der Energiewerte nach der dritten Variante zur Vorheizung eines Thermotransferdruckkopfes,

Fig. 17,

Subprogrammroutine mit Ermittlung der Energiewerte nach der zweiten bzw. dritten Variante zur Randheizung eines Thermotransferdruckkopfes und zur Pixelenergiewertberechnung,

Fig. 18,

Barcodebild mit externen Bereichen zur Verdeutlichung einer für diese Bereichen unterschiedlichen Datenaufbereitung zur Vorwärmung von Heizelementen (Variante 3),

Fig. 19 ,

Frankierabdruck gemäß der Post-Anforderung in Kanada.

Advantageous developments of the invention are characterized in the subclaims or are presented in more detail below together with the description of the preferred embodiment of the invention with reference to FIGS. Show it:

Fig. 1,

Simplified representation of a franking strip with barcode,

2,

Top view of a simplified thermal transfer print head,

3,

Simplified flow chart of the prior art processing of image data required for printing;

4,

Temperature curve and pulse / time diagram when printing a dot,

Fig. 5,

Simplified representation of the barcode data,

6,

Barcode image with clarification of the barcode data processing by a historical control,

Fig. 7,

Barcode image with external areas to illustrate a different data preparation for these areas for preheating heating elements (variant 1),

8,

Cutting through a thermal transfer printhead along a series of resistive heating elements,

Fig. 9,

Improved flowchart of image data processing required for printing

10 shows,

Block diagram for controlling the printing of a franking machine with a print data controller for a thermal transfer print head,

Fig. 11,

Perspective view of an Optimail 30 franking machine,

Fig. 12,

Franking imprint according to the DPAG requirement FRANKIT,

Fig. 13,

Program routine with determination of the energy values for preheating and edge heating of a thermal transfer print head,

Fig. 14a,

Barcode image with external areas to illustrate different data preparation for these areas for preheating heating elements (variant 2)

Fig. 14b,

Franking imprint according to the postal requirements for the country Australia,

Fig. 14c,

Program routine with determination of the energy values according to a further variant for preheating and edge heating of a thermal transfer print head (variants 2 and 3),

Fig. 15a,

Pulse / time diagram for controlling a heating element of the thermal transfer printing head controlled in the pre-region B,

Fig. 15b,

Pulse / time diagram for controlling a heating element of the thermal transfer printing head located in the edge region N1,

Fig. 16,

Subroutine routine with determination of the energy values according to the third variant for preheating a thermal transfer print head,

Fig. 17,

Subroutine routine with determination of the energy values according to the second or third variant for the edge heating of a thermal transfer print head and for the pixel energy value calculation,

Fig. 18,

Barcode image with external areas to illustrate different data preparation for these areas for preheating heating elements (variant 3),

Fig. 19,

Franking imprint according to the post request in Canada.

Fig. 1 shows a simplified illustration of a franking strip 14 with a bar code 15. The franking strip or a mail piece, for example an envelope, with an equal size field for printing a franking stamp image and other information on its surface, is printed at a constant speed during printing v moves in the transport direction (arrow) under a thermal transfer print head along. The field has, for example, a width of 30 mm and a length of 160 mm. The thermal transfer printhead and a thermal transfer ribbon disposed between the thermal transfer printhead and the surface of the field to be printed in known manner in a printing device have been omitted from the illustration for the sake of clarity. At the beginning of the printing, dots are optionally printed in a first printing column C1 on the surface of the franking strip or envelope at a first distance from the right edge thereof. For simplicity, the franking stamp image printed on the surface from C1 to the printing nip Cn-4 was not shown. If a first heating element of the thermal transfer printhead were permanently driven and subjected to a current pulse, then a number of printed dots would lie on a line L1. Further lines L2, L3, ... to Lx are parallel to the first line L1 and orthogonal to the pressure gaps. The lines are shown as a thin line and the printing columns as vertical dashed lines. From a second larger distance from the right edge of the franking strip or envelope oa printing material, the first dots of a first bar code are printed in a predetermined printing column Cn. The barcode image 15 with last dots printed in a print column Cq printed on the surface up to a third distance from the right edge of the franking strip has been simplified. These last dots of the barcode image are abutting one another in a row. Likewise, the dots of the barcode image lie on a line Lx-2 and form a baseline. On the lines L1 and L2 as well as Lx and Lx-1, however, no dots are printed in the printing gaps Cn to Cq. The franking strip or envelope may be from the print column Cq + 1 to Cz, ie be further printed near the left edge with an advertising cliché, a second barcode or a logo.

FIG. 2 schematically shows a plan view of the heating element side of a simplified thermal transfer printing head 1. Whose heating element H1 to Hx are in a row and are closely adjacent. Simplified, it is assumed that with appropriate activation, in each case a heating element H1... Hx can print on an associated line L1... Lx dots if the franking strip is moved under the heating element row at a constant speed v.

FIG. 3 shows a simplified flow chart of the processing of image data required for printing according to the prior art. In a first determination step 10 ', the image information required according to the postal requirements is stored as data in the main memory (RAM) of the franking machine. In a second control step 20 ', the data is processed by the microprocessor in order to control heating elements differently, depending on which history exists. In addition to such a history-based control, the current activation state of the immediately adjacent heating elements and their history is taken into account for controlling a heating element. In addition, the ambient temperature and a temperature measured in the print head as well as other machine parameters when controlling a heating element are taken into account. In a formatting step 40 ', the print data is brought by a controller known per se in a suitable format for the print head and output via a corresponding interface. In a last feed step 50 ', the print data is converted by an internal electronics of the thermal transfer print head into pressure pulses of a predetermined voltage level and with a duration which can be set separately for the heating elements.

Fig. 4 shows a temperature profile and pulse / time diagram when printing a dot. For example, a drive pulse for a heater starts at time t ₁ and ends at time t ₆ . A temperature curve according to the solid line results when a first temperature Tw _{1 is} measured in the immediate vicinity of the heating element and is lower than the temperature Tp required for printing. Then the printing starts at time t ₅ and ends at time t ₇ , ie when the temperature required for printing Tp is exceeded. The dot seems too weak for us. A temperature curve according to the dotted line is obtained when a second temperature Tw ₂ in the immediate vicinity of the heating element is higher than a first temperature Tw ₁ and lower than the temperature Tp required for printing. Then, the printing starts at time t ₃ and ends at time t ₉ . The dot appears to us as being too bold. This can be partly compensated starting from the second temperature Tw ₂ in the second step 20 ', in that a drive pulse for printing does not begin until time t ₂ and ends at time t ₆ . The dot appears to us as normal possibly a bit richer printed because the printing at time t ₄ , ie earlier begins and ends only at time t ₈ (temperature curve of the dash-dot line). The cooling process of the heating element begins after the end of the drive pulse, but runs less intense and slower. This temperature profile can not be compensated in the second step 20 'of the method according to the prior art.

Figure 5 shows a simplified representation of the bar code data by conversion to a desired bar code image 15. A row R and a baseline G are formed at the left and bottom edges of square pixels. For simplicity, it is assumed that a heater H3 on the line L3 prints into the print column Cn + 1 a dot D of an attractive size (0.6 × 0.6 mm) to produce a picture element (pixel). At very low printing resolution, the second step 20 even omitted, since with appropriate size of the heating elements and thus also the enlarged dimensions of the dots D do not interfere with the history and the aforementioned Depositionierungs effect. Then the barcode image reflects the stored barcode data. In practice, of course, a number of dots are required to produce a quadratic bar code image (module). For example, in Canada 6 x 6 dots or in Germany 7 x 7 dots per module are required. For example, a module for FRANKIT in Germany is 0.583 x 0.583 mm.

A bar code data processing by a simple historical control is illustrated by the simplified representation as a barcode image in FIG. 6. A heating element H3 (not shown) is energized in each case in a heat phase W which, when the franking strip is moved, can be assigned a pressure column Cn which is located immediately before the pressure column Cn + 1. The heating element H3 is heated to a preheating temperature. The printing of a dot D occurs only in the print column Cn + 1, i. only when the pressurized heating element is at pressure temperature, i. a higher than the preheat temperature was brought. At least one thermal phase W precedes the printing in the aforementioned printing gaps. During the heat phase but also dots can be printed in a different pressure column. If this is provided on the same line, then the heating can be reduced to a preheat temperature, as is visible in the printed dot 17.

FIG. 7 shows a barcode image with external regions for clarifying a data preparation that is different for these regions for preheating heating elements for a first variant. In a dotted area B, which is also known as a so-called Quietzone and is located right in front of the barcode, exist for the heating elements at most heat phases but no pressure phases, that is, no heating element enough energy is supplied for printing. In lateral side areas N of the barcode image 15 does not become a heating element Energy supplied. The barcode data processing therefore takes place mainly in the area of the barcode image 15. This leads to a typical heat distribution in the print head with cooler edge areas.

Referring now to Figure 8, which shows a section through a thermal transfer printhead along the row of resistive heating elements, the heat distribution and construction of the thermal transfer printhead 1 will now be explained. The thermal transfer printing head 1 consists of a 0.65 mm thick substrate S, preferably of an electrically insulating ceramic plate, which is glued to an approximately 5 mm thick metal plate. During operation, for example, a first temperature T ₁ of approximately 50 ° C. prevails at the boundary layer ceramic / metal. At a second boundary layer E within the ceramic body is then a second temperature T ₂ of about 70 ° C. reached. The temperature increases non-linearly within the area shown in the line and reaches a third boundary layer T ₃ of about 80 ° C at a third boundary layer. The temperature increases within a dashed area around the heating elements H1, H2, ..., H6, ... on until a fourth boundary layer with a fourth temperature T ₄ of about 100 ° C is reached. This fourth boundary layer extends to the surface of an approximately 0.2 mm plus 2 micron thick insulating layer I and comes into contact with a thermal transfer ribbon (not shown). From about 65 ° C the color layer melts on the thermal transfer ribbon. An even higher fifth temperature T ₅ > T _{4 is} achieved in the heating elements themselves. From a thermal transfer print head of the KSL360AAF-PS type from Kyocera, a power of 0.285 W or 0.354 W on a heating element with an electrical resistance of 2 KOhm or 1.6 KOhm is converted into heat during printing per dot. Each heating element has a size of 0.0683 x 0.110 mm and is adjacent to the nearest heating element so close that in a row 12 dot per mm can be printed. The metal plate M is preferably made of aluminum and is much thicker than the substrate S. It therefore already has a good thermal conductivity and serves as a heat sink. The thermal transfer print head 1 is by means of the metal plate M on the chassis (not shown) of the printing device or

Postage meter attached. The substrate temperature can be measured in a known manner by means of a - not shown - thermistor. The equipotential line A shows a temperature drop from the center to the edge of the thermal transfer printhead 1, which can not be detected by a thermistor, if the latter - in a manner not shown - only at the edge on the substrate S is glued. The insulating layer I preferably consists of 2 glass layers (not shown). The inner glass layer is intended to insulate the heating elements very well and protect them from oxygen. The outer glass layer has a thickness of 2 microns and should have a high abrasion resistance.

FIG. 9 shows an improved flow chart of the processing of image data required for printing. In the first determination step 10, the image information required according to the postal requirements is stored as data in a random access memory (RAM) of the franking machine. The data not only reflects every colored dot (dot) to be printed, but also the amount of energy needed. The latter is represented as a binary code, for example with 4-bits per pixel as a quadruple and controls the necessary pulse duration of driving a heating element for printing a dot. This process of energy value calculation according to a first type is time consuming and therefore can not be done during printing. A microprocessor is programmed by software for energy value calculation and encoding as well as providing pixel energy data. The results of the energy value calculation and coding are buffered in the random access memory (RAM) of the franking machine, which is referred to below as pixel energy storage. This makes it possible to assign different energy values to the dots for printing different image sections of the franking stamp image. A corresponding method for driving a thermal transfer print head is the non-prepublished German patent application of the file number 10 2004 063 756.3 removable.
The good readability of the prints produced can only be achieved if the amount of energy supplied to each heating element with others Parameters, in particular ribbon parameters, is tuned. Therefore, a print parameter set is read from a memory attached to the ink ribbon cassette to thereby calculate the energy values. A corresponding method for driving a thermal transfer print head is the non-prepublished German patent application of the file number 10 2004 060 156.9 removable.
In a second control step 20, the data is processed by the microprocessor in a manner known per se in order to control the heating elements differently, depending on which history exists and on the different local heating by adjacent heating elements. For this purpose, energy values of the second kind are set at least at that memory location in the pixel energy store which immediately precedes the position of a dot to be printed in the barcode image, although no dot is to be printed in this position after the barcode image. From these energy values second calculation then results in a heat pulse duration, which is smaller than the pressure pulse duration, which would lead to the printing of a dot. In the simplest case, the heating pulse duration can be set to a predetermined fixed value which has been determined empirically. Normally, however, the heating pulse duration is variably set to a value selectable from a set of predetermined fixed values calculated by the microprocessor. However, such a method does not affect heaters that should not print dots. The beginning of the bar code, as well as the right and left edges of the bar code seen in the printing direction, appear too weak in conventional methods. As a result, the area coverage is poor and the printgrowth is lower than for the image elements / pixels of the barcode, which are not at the edge or beginning of the barcode image, which is printed from right to left. The known algorithms are only insufficiently suitable for amplifying the outer edge or front image elements / pixels of the barcode. The main reason given was the thermal resistance in the printhead, which is distributed three-dimensionally. The substrate S of the thermal transfer printhead can not be heated accurately enough by a simple history control mechanism that evaluates only one pixel or printing pixel environment information to be printed.

As a result, the high-resolution barcode images printed with previous methods appear to be printed differently at the margins than in the interior and may therefore be difficult to machine-read.

Therefore, to improve machine readability in a third enhancement step 30, the data is processed by the microprocessor to also drive those heaters that are in the two edge regions of the heater row but are not to print dots there during bar code printing. In addition, those heating elements which do not lie in the two edge regions of the heating element row are also activated for a limited period of time, wherein the aforementioned period of time directly precedes the printing of the barcode image. Prior to printing the beginning of the barcode image, as well as adjacent the printing direction right and left edges of the barcode image during printing, a plurality of heating elements are heated in sufficient proximity to those heating elements that print a barcode image with energy by varying the heating pulse duration is dimensioned so that taking into account the heat capacities and -Leitfähigkeiten just just no pressure. The number of rows and columns is dimensioned so that at the chosen subliminal energy (or different subliminal energies) is a sufficiently uniform heating of the three-dimensionally distributed heat capacities occurs before and while the barcode image is printed. For this purpose, the data to be printed barcode image in the pixel energy storage is supplemented such that the pixel energy storage in said Vor- and environment of the barcode image to be printed now contains data for energy values that preheat the thermal transfer print head in the manner described above, but not for printing dots lead these positions.
If, for example, the maximum pressure pulse duration comprises 10 phases, then energy values which are achieved by 0 to 3 phases may suffice. Up to 3/10 of the maximum energy value E _max is then supplied to each heating element, which is effective in region B of the illustration according to FIG. 7. It can take up to 2/10 of the maximum energy value E _max be supplied to each heating element, which is effective in the region N in the illustration of FIG. 7.
As a result of introducing a predetermined energy value of the third type of calculation, each heating element is driven at predetermined regions of the heating element row, the energy value being predetermined only for preheating, but not for printing. These energy values of the third type of calculation then result in a heat pulse duration which is also shorter than the pressure pulse duration which would lead to the printing of a dot. In the specific case, the heating pulse duration can be set to a predetermined fixed value which has been determined empirically. When superimposing an energy value of the second type of calculation (hatched picture elements of area B in the barcode image according to FIG. 7) with an energy value of the third type of calculation (dotted area B in the barcode image according to FIG. 7) for driving one and the same heating element, the energy value of the second type of calculation is set if this exceeds the energy value of the third type of calculation. By such heating pulses of shorter length in the heat phases of the heating elements, the different temperature distribution in the thermal transfer print head is compensated only to the extent that the machine readability of the barcode is improved. A program routine will be explained in more detail below with reference to FIG.
In a fourth step 40, the data (quadruples) reflecting the respective pixel energy value are transferred by the microprocessor via a bus to a print data controller. The print data controller is supplied with a respective predetermined pixel energy value for each heating element, which is converted into a corresponding number of binary pixel data having the same binary value. The pixel data is transmitted serially to the thermal transfer print head.
In the fifth feed step 50, each binary pixel data value associated with a heating element is output in an associated phase of successive phases of a pressure pulse duration to the respective drive unit of the thermal transfer print head, which feeds the energy thus selected to the heating element.

A block diagram for controlling the printing of a postage meter with a print data controller for a thermal transfer print head will be explained with reference to FIG. The franking machine is a special thermal transfer printing device with a microprocessor-based control 6, 7, 8, 9 and a print data control 4 for a thermal transfer print head 1 with high print resolution, the print data control 4 with an encoder 3 and a bus 5 with at least one microprocessor 6 and memory modules , 8, 9 of the controller is connected in terms of address, data and control. The quadruples are stored column by column in the pixel energy store (RAM) 7. In this case, the quadruples belonging to adjacent pixels of a printing column are stored next to one another. For printing a column, a number of 90 x 16 bit data words are provided. At a print resolution of 12 dot per 1 mm (≈ 300 dpi), up to 175500 × 16 bit data words must be stored in the pixel energy store (RAM) 7 for up to 1950 columns.
On the bus 5, a postal security device (PSD) 18 and other - not shown - assemblies, such as keyboard, display, etc. are connected according to the postal requirements. With a direct memory access (DMA) on the input side, the print data controller 4 can accept and buffer 16 bits of data in parallel from the BUS 5 word by word. The print data controller 4 is connected to the thermal transfer print head 1 in control and works according to a not previously published German Patent Application No. 10 2005 007 220.8-27 entitled "Method and Apparatus for Controlling the Printing of a Thermal Transfer Printing Apparatus". Each binary pixel data supplied to a heating element of the thermal transfer printhead is output from the print data controller 4 in an associated phase of successive phases of a print pulse duration. The thermal transfer printhead 1 is high-resolution and has an internal drive electronics and a number of 360 heating elements, which are arranged in a row of about 30 mm in length. A first part of 180 heating elements is driven in parallel by a first shift register 11 via a first latch unit 12 and first driver unit 13. A second part of 180 heating elements is from a second shift register 21 via a second latch unit 22 and second drive unit 23 driven in parallel. At the edge of the heating element row of the thermal transfer printing head 1, there is at least one heating element, which is supplied with energy of up to two-tenths of the maximum energy value as a result of an energy value calculation empirically or computationally carried out by the microprocessor 8, and which is immediately adjacent to a heating element Printing a 50% line at the top of the barcode.
A sensor / motor controller 46, on the one hand, a start sensor S1, a scooter sensor S2, a flap sensor S3, an end sensor S4 and a thermistor 19 and on the other hand, a motor 2a for driving a roller, not shown for winding the consumed thermal transfer ribbon, a motor 2b for driving a counter-pressure roller for Druckgutbeförderung during printing and a motor 2c for actuating the pressure mechanism of the counter-pressure roller to press the latter by means of the printed matter to the thermal transfer printing head 1 connected. The franking machine achieves a transport speed of approx. 150 mm per second for franking strips or for mail pieces up to 6 mm thick. An interrupt controller 47 is connected directly to the microprocessor 6 via a control line 49 for an interrupt signal 1. The print data controller 4, the sensor / motor controller 46 and the interrupt controller 47 can be implemented within an application specific circuit (ASIC) or programmable logic, such as a Field Programmable Gate Array (FPGA).

11 shows a front and top right perspective view of a known Optimail30 type thermal transfer postage meter.
Further views of this franking machine can be found in the Community Design at the Office for Harmonization in the International Market under the number 000199468-0001. Other variants of the type Optimai130 franking machine are registered under the numbers 000199468-0002 and 000199468-0003.

The supply and removal of a mail piece takes place on the feed table at a contact edge on the front of the franking machine from left to right. The franking machine is equipped with a flap to the cassette compartment, which is arranged on the right side and on the upper part. Further details are the German utility model DE 20 2004 015 279 U1 removable, bearing the title: "cassette holder with status recognition for a printing mail processing device".
The Optimai130 thermal transfer postage meter has a start sensor and an end sensor underneath a cash drawer in the feed table - not visible - which allows the microprocessor to reliably detect the beginning and end of a mailpiece or franking strip. Further details are the German utility model DE 20 2004 015 279 U1 removable, bearing the title: "Arrangement of a printing mailing machine.

In FIG. 12, a franking after DPAG request FRANKIT ^® is shown, which was printed with a thermal transfer franking machine of the type Optimail30 on a label 14 from right to left while the tape sheet 14 is conveyed from left to right. A franking stamp image 16 on the right-hand side is therefore printed first in columns and subsequently a two-dimensional data matrix barcode 15 with 36 × 36 pixels. Subsequently, an advertising cliché and / or additional texts can be printed in columns. A column counter, which is realized by means of the microprocessor, begins to count at the count Z: = 0. A first limit value G1 is reached at counter reading Z: = G1 and triggers the printing of the franking stamp image 16. This takes place until the meter reading Z: = G2 reaches a second limit value G2 at which the printing of the franking stamp image is ended. The franking stamp 16 includes in its upper half, the German Logo Post Posthörnchen followed by the provided on the next line brand FRANKIT ^® and a charge amount in euros. The franking stamp image 16 contains in the lower half the franking date and the serial number as well as possibly two additional lines (not printed). At a distance of 3 mm, ie at counter reading Z: = G4, the printed image of the data matrix code follows. For example, this printed image has a size of 21.336 x 21.336 mm with an allowable tolerance of ± 1 mm according to the FRANKIT version 2.06 of 11.01.06. The printed image ends with a count Z: = G5. At intervals of 3.8 to 5 mm then follows a printed image of an advertising cliché at a count Z: = G6. The aforementioned print image has a size of 45 x 30 mm here. However, the aforementioned print image may have a maximum size of 56 x 30 mm and ends at a count Z: = G7. At a distance of 3 mm, an additional text in the size of up to 50 x 30 mm can be printed in a separate printing stamp image if a meter reading Z: = G8 is exceeded. Alternatively, a printed image for supplementary lettering services can also be printed at the location of the advertising cliché and additional text. The printed image ends with a counter reading Z: = G9.

FIG. 13 shows a program routine with determination of the energy values for preheating / edge heating of a thermal transfer print head, which contributes to quality improvement in the thermal transfer printing method and thus in particular for better machine readability of bar codes. After the start in step 100, the column counter of the microprocessor is set in step 101 to the counter Z: = 0. In addition, limit values of the number of pressure columns are defined which define the length of the printing stamp image to be printed. Then, a first interrogation step 102 is reached. At the same time, the further transport of the franking strip takes place. The heating elements of the thermal transfer printhead are each at the end of a preheat phase above the next virtual pressure column. If it is determined in the first interrogation step 102 that the strip has not yet been transported by one column, the system branches back to the first interrogation step 102 for further interrogation. Otherwise, if it is determined in the first interrogation step 102 that the strip has been transported further by one column, then the column counter is incremented by the value 'one' in step 103.

Subsequently, a second interrogation step 104 is reached, in which it is asked whether the count value is already greater than / equal to the first limit value G1 = C1, printing starts with the pressure column C1. If this is not the case, the system branches back to the first query step 102 via a step 105. The printing gaps C1 are thus preceded by further phases, which serve only to preheat the thermal transfer printing head and thus are not visible as printing gaps. The preceding columns are therefore called virtual print columns. In each of such virtual printing columns, the heating elements of the thermal transfer printing head are driven with a pulse whose pulse duration is not sufficient for printing. Thereafter, in step 103, the column counter is incremented by the value 'one'. This continues until the pressure column C1 is reached.
If, however, it is determined in the second interrogation step 104 that the count value is already greater than / equal to the first limit value Z ≥ G1, then a branch is made to a third interrogation step 106, in which it is determined whether the count value is already greater than the second limit value, ie Z> G2 is. Here, G2 = Cf, where Cf is the column with which the printing of the franking stamp image ends. If this is not the case, the system branches back to the first interrogation step 102 via a step 107. In step 107, the pixel energy value calculation is performed according to a first type, which is performed in dependence on predetermined parameters and has already been described above. In step 107, the pixel energy value calculation also takes place according to a second type known per se, corresponding to the history of the driving of the heating elements and their adjacent heating elements by the microprocessor. Each time step 103 passes, the column counter is incremented by the value 'one'. The query step 106 is run through, the answer being yes. The answer in the third interrogation step 109 is NO, but only until the end of the franking stamp image with the print column to which a limit value G2 can be assigned is reached.
However, if it is determined in the third interrogation step 106 that the count value is already greater than the second limit value, ie Z> G2, then a branch is made to a fourth interrogation step 108, in which it is ascertained that whether the count is already greater than / equal to the third limit, ie Z ≥ G3. If this is not the case, then the first query step 102 is branched back. Again, in step 103, the column counter is incremented by the value 'one' and the query steps 104 and 106 are run, the answer being yes. This continues until a pressure column Cn-4 is reached, to which the limit value G3 can be assigned.
If it is determined in the fourth interrogation step 108 that the count value is already greater than / equal to the third limit value, ie Z≥G3, then a branch is made to a fifth interrogation step 109, in which it is determined whether the count value is already greater than or equal to the fourth limit value, ie Z≥ G4, which is assignable to a first pressure column at the beginning of the barcode image. If this is not the case, then the system branches back to the first interrogation step 102 via a step 110.
In step 110, the pixel energy value calculation also takes place according to a second type known per se, corresponding to the history of the control of the heating elements and their adjacent heating elements by the microprocessor. Before printing a dot of the barcode image, a predetermined first energy value E _H can be supplied to the respective heating element which is used in region B. However, the energy value E _H does not yet lead to the printing, but only causes a predetermined preheating of the corresponding heating element in at least one of the preceding phases (History Control method).
In addition, the pixel energy value calculation of a third kind is performed for all pixels in front of the barcode image in region B. For example, in the first four printing columns, before printing the barcode image, a predetermined second energy value E _{V should} also be supplied to each heating element associated with region B, but previously not used, because immediately after no dot is to be printed. With each phase of the heating of a heating element, the existing basic energy or the previously supplied energy in the phases is increased by one energy level. The predetermined second energy value E _V is applied to each of the heating elements in the region (B) before the printing of the barcode image (15). which are not used in the region (B) for a predetermined preheating with the first energy value E _H.
The second energy value E _V is at least one energy level, preferably two energy levels, below that first energy value E _H , which is to be supplied to the heating in each case the heating elements to be used in the area B according to the History Control method. The heating elements which are subsequently not used during printing or are not used immediately thereafter are thus likewise heated in contrast to the history control method.
After the first interrogation step 102, step 103 is again run through and the column counter is increased by the value 'one'. The query steps 104, 106 and 108 are run through, the answer being YES. The answer in the fifth query step 109 is NO, but only until a fourth limit value G4 having the pressure column Cn at the beginning of the barcode image has not yet been reached. If this is reached, then a branch to a sixth query step 111. In the sixth query step 111, it is asked whether the count value is already greater than the fifth limit value, that is to say Z> G5, printing ending with the print column Cq. If this is not the case, the system branches back to the first query step 102 via a step 112. The microprocessor performs a pixel energy value calculation of the first and second type for all pixels of the barcode image and a third pixel pixel energy value calculation for pixels in the edge region N of the barcode image in step 112 starting with the pressure column Cn and ending with the pressure column Cq, ie beginning to end of the barcode image , An edge area exists when the length of the barcode image is smaller than the length of the row of heating elements (stripe width). The microprocessor calculates energy values for heating the heating elements at the edge of the heating element row which are assigned to the pixels in at least one of the two edge regions N externally of the barcode image, the energy values being calculated from such a height, as a result of the corresponding heating elements on the Edge of the heating element row just no dots to be printed. It is envisaged that calculating in an adding one before empirically determined energy value E _N ≤ 2/10 E _max . Alternatively, it is provided that the substrate temperature of the thermal transfer print head 1 is measured and a threshold value comparison is carried out, with a threshold value undershooting of the substrate temperature from the microprocessor selecting a higher energy value E _N by one level.

After the first interrogation step 102, step 103 is again run through and the column counter is increased by the value 'one'. The query steps 104, 106, 108 and 109 are run through, the answer being YES. The answer in the sixth query step 111 is NO, but only until a fifth limit value G5 with the pressure column Cq at the end of the barcode image has not yet been exceeded. If this is exceeded, then a branch to a seventh query step 113. This continues until a sixth limit value G6 with a pressure column Cq + 50 at the beginning of the barcode image has been reached. If this is not the case, then the first query step 102 is branched back. But if that is the case, then it branches to other query steps, which are not shown, to calculate energy values for the remaining pressure stamp images until a penultimate query step 119 is reached in which it is asked if the last pressure column reaches Cz at the end of a franking imprint is. If this is not the case, then the first query step 102 is branched back. But if that is the case then the routine is stopped in step 120.
The routine may be adapted to the postal regulations in force in other countries, modified accordingly for the required franking imprints, or used analogously for other printed images of similar printing accounting or mailing machines.

FIG. 14 a shows a barcode image with external regions for clarifying a different data preparation for these regions for preheating heating elements for a second variant. A mailpiece is used to print a two-dimensional barcode a stationary printhead is moved onto the surface of the mail piece from a feed position post upstream of a print location in a post-downstream direction. If the feed position is upstream of the print location to the left of the postage meter (Figure 11), there is an adjacent pre-area B to the right of the printed bar code which reaches the print location during delivery of the mail piece rather than the area used to print the two-dimensional bar code is provided. The adjacent pre-area B externally of the bar-code image is hatched from top left to bottom right and is hereinafter referred to more precisely as an unprintable area B for preheating heating elements before printing the bar code.
Thus, prior to the printing of the dots in a first printing column of the two-dimensional barcode impression, all the heating elements of a thermal transfer printing head lying in a row are preheated, which act on the surface of the mail piece and are arranged orthogonally to the printing direction. The aforementioned heating elements are so controlled with a preheat pulse, which reaches at most 20% of the maximum pulse length of a pressure pulse, that the heating elements, although warm, but just not print. This leads to a predetermined favorable temperature distribution in the print head and in the result to a uniform pressure.

The heating elements and surrounding heat capacities are also preheated in the non-printable area N1, which is located in the illustration above the 50% line of the upper part of the barcode image. This edge area N1 external to the barcode image is marked with a checker pattern and is hereinafter referred to more precisely as a non-printable area N1 for heating heating elements during printing of the barcode.
During printing of the bar code, a heating element of the adjacent line directly above the barcode image is driven with a pulse length of 0.2 = 20% of the maximum print pulse length for a predetermined number of print columns so that the heater will be warm but just can not print. Thereby For example, the environment of the heaters used to print the 50% line will be heated to be as well mapped as the bar code elements (modules) inside the bar code.
In FIG. 14a, the square modules without preheating inside the two-dimensional barcode are displayed in black. No energy values of the second kind are set at least at that memory location in the pixel energy store which immediately precedes the position of a dot to be printed in the bar code image if the pixel energy calculation of the first kind is sufficient for printing readable modules inside the two-dimensional bar code Readability) or if, for higher readability requirements of the modules, another suitable energy value calculation method is used which replaces the aforementioned pixel energy value calculation of the first and second type for the modules.
In the dotted area N2 under the barcode image, no preheating of heating elements is required if they are not assigned to a region to be printed.
In the case of barcode prints of a different kind, it may well be useful to distinguish that the heating elements to be heated are to be heated differently in position to the edge regions (top, right, bottom and left) of the barcode imprint. In contrast, need in the aforementioned second variant of the data preparation for preheating of heating elements of the Heizelementreihe, for example, are not heated, which are associated with the transport of the mail piece the left portion of the Barcodeabdruckes, as in the image columns immediately behind no dots are printed and the print head already reached its operating temperature. Those heating elements in the edge region of the heating element row that lie in the transport of the mail item relative to the lower portion of the Barcodeabdruckes must also not be heated if the printhead has already reached its operating temperature by printing a 100% line with the immediately adjacent heating elements.

In Fig. 14b a franking imprint according to the postal requirements for the country Australia is shown. Here, the barcode 15 'is located to the right of the value stamp 16' and, unlike the printing of the barcode 15, is therefore printed earlier than the value stamp 16 ', according to the program routine shown in FIG.

FIG. 14c shows a program routine with determination of the energy values according to a further variant for preheating and edge heating of a thermal transfer printing head. As compared with the process of steps 100 to 120 in the routine of Fig. 13, the value of the thresholds G1 to G9 for the column counter changes in step 101 ', which is equivalent to step 101, and the subroutine is changed in step 110', which is equivalent to step 110 '. In step 110 ', it is provided that a predetermined energy value E _{H is} supplied to all heating elements of a heating element row, which are used in the pre-area B before printing the barcode image 15, wherein a first energy value E _H corresponds to a heat pulse length, but not yet for printing but only causes a predetermined preheating of the corresponding heating element in at least one of the preceding phases, wherein all heating elements in the pre-B and at least one non-printing in the edge region N1 heating element at the edge of the Heizelementreihe the thermal transfer printhead 1, an energy of up to two-tenths of the maximum energy value is supplied. Thus, in step 110 ', the per se known pixel energy value calculation of the second type is omitted and for the pixel energy value calculation of the third type, a second variant is selected in steps 110' and 112 '. For the third variant, it is provided that in a time range before the printing of the barcode image 15, when an image column of the front area B at a distance from the edge of the barcode image 15 reaches the print location, then preheat each non-printing heating element by an energy of one tenth of the maximum energy value a heating pulse is supplied during a period of time which has the duration of one phase of a pressure pulse, wherein the phase alternates with another phase, in which is not supplied with energy to the non-printing heating element. It is further provided that the distance from the edge of the barcode image 15 is at least two image columns when the heating element is supplied with an energy of one-tenth of the maximum energy value for preheating by a heat pulse during a period of one-phase duration of a pressure pulse.
This will be explained in more detail below by means of pulse / time diagrams for a preheated heating element at which the areas B and N1 are moved past, when the mailpiece is transported further during printing.

FIG. 15 a shows a pulse / time diagram for controlling a heating element of the thermal transfer printing head which is controlled in the pre-region B according to the third variant. In a first line, the printing gaps Cn and image columns Cn-1 to Cn-26 are each shown at a distance such that in each case a distance corresponds to the duration of the printing pulse duration plus a pulse pause. In a second line a pulse / time diagram is shown. The print nip Cn is that in which at least one heating element of the thermal transfer print head imprints a dot for a pixel of the bar code on the mailpiece surface. It takes several, for example, 12 immediately successive printing columns Cn, Cn + 1, Cn + 2, ..., Cn + 11 and twelve adjacent heating elements in the Heizelementreihe the thermal transfer print head to print a module designated square pixel of the bar code of Figure 14a. These heating elements are preheated in advance, for example in the image column Cn-26, ie when the printing location is still 26 image columns, already with a first pulse of energy E = 1/10 Emax. This is achieved by heating pulses of duration 0.1 = 10% of the maximum pressure pulse length. If a pressure pulse in phases of the same duration (eg 0.1) is time-divisible, with each phase of heating a heating element, the existing basic energy can be increased by one level.
It then passes according to the example, a period of 26 clocks to print the dots. A cycle results from a pressure pulse duration plus an associated pulse break. When the image column Cn-25 reaches the print location, a heat pulse is skipped, but when the image column Cn-24 reaches the print location, a heat pulse of energy E = 1/10 Emax is given off again. The Heizimpulsabgabe alternates with the Nichtabgabe until, for example, the image column Cn-2 is reached, in which a heat pulse of energy E = 2/10 Emax is delivered to the heating elements, which should print the barcode. When the succeeding image column Cn-1 is reached, a heat pulse of energy E = 2/10 Emax is again emitted. Alternatively, a heat pulse of energy E = 3/10 Emax would be possible. This variable energy supply is made possible by an electronically controlled changing of the pulse duration. For this purpose, a subprogram routine is used, which will be explained with reference to FIG.
By omitting the pulses in the image columns Cn-3 to Cn-26 results in - not shown - representation of a pulse / time diagram for controlling a driven in the pre-B heating element for the second variant of the quality improvement.

FIG. 15b shows a pulse / time diagram for controlling a heating element of the thermal transfer printing head located in the edge region N1. In the immediately successive pressure gaps Cn, Cn + 1, Cn + 2,..., Cn + 11,..., The adjacent heating element in the heating element row of the thermal transfer printing head is energized with a heating pulse of energy E = 2/10 Emax. which is not enough to print a dot. For this purpose, a subprogram routine is used, which will be explained with reference to FIG. The illustrations according to FIGS. 15b and 17 apply equally to the second and third variants of the quality improvement.

FIG. 16 shows a subprogram routine 110 'with determination of the energy values according to the third variant for preheating a thermal transfer print head. In the first step 1101 ', the count Z of Queried on the column counter. If the count Z is smaller than the limit value Cn-k (this is the case in the beginning), then a branch is made to a third step 1103 'and the count Z of the column counter is evaluated to determine whether the value Z = Cn-k has a k value whose value is even or odd. With an even k value, the pulse energy is set to E = 1/10 Emax. Otherwise, with an odd k value, the pulse energy is set to E = 0 Emax. If the counter reading Z is not smaller than the limit value Cn-k, then a branch is made to a second step 1102 'and the pulse energy is set to E = 2/10 Emax. The illustration according to FIG. 16 only applies to the third variant of the quality improvement.
A representation of a subprogram routine (not shown) also results for the second variant of the quality improvement if steps 1103 'to 1105' are omitted.

FIG. 17 shows a subprogram routine with determination of the energy values according to the second or third variant for the edge heating of a thermal transfer printhead and for the pixel energy value calculation 1123 '. The latter takes place when heating elements other than those requested in step 1121 'are activated in the edge region N1. Otherwise, the pulse energy is set to E = 2/10 Emax in step 1122 '.

FIG. 18 shows a barcode image with external areas for clarifying a different data preparation for these areas for preheating heating elements according to the third variant, which was developed by Francotyp-Postalia GmbH, taking account of postal regulations for the country Canada. The data content of the barcode is not essential for understanding the preheating. For the sake of simplicity, the modules were drawn only at the edge of the barcode image and displayed as part of the 50% or 100% lines. The thermal transfer printhead drive method takes into account a different edge heating for Datamatrix Barcode. Leading for the data matrix printed by the thermal transfer printing method barcodes to increase the read rate. The detail view of the upper right bar code corner of the Datamatrix bar code shows a pre-heat near the 50% line at the top and right edge of the Datamatrix barcode with a heat pulse of 20% of the maximum print pulse duration and also a pre-printing total of the Datamatrix barcode Pre-heating with a heat pulse of 10% of the maximum pressure pulse duration. It is provided that the aforementioned distance from the edge of the barcode image is at least two image columns. Preferably, the following method is proposed:

The heating elements and surrounding heat capacities are preheated in the non-printing area B, which is located on the right side of the barcode. It can thus be defined in the impression invisible image columns Cn-y to Cn-1, which are time before the printing of the Datamatrix barcode under the Heizelementreihe the printhead along along, in the image column Cn-y, which in a position below the Heizelementreihe rather reaches, as a subsequent image column Cn- (y-1), all heating elements are driven with a heat pulse of the pulse length of 10% of the maximum pressure pulse length, while in the subsequent image column Cn- (y-1) none of the heating elements is heated with a heat pulse , This is followed, for example, 12 times in alternation by a column-by-column heating of the heating elements of the row of heating elements with a pulse length of 0.1 of the maximum pressure pulse length and a column-wise non-heating of the heating element row of the heating element row which can be assigned to the following adjacent image column. In a column Cn-4 shown in FIG. 1, all heating elements are thus heated with a heating pulse of the pulse length of 0.1 of the maximum pressure pulse length. In an adjacent column Cn-3 shown in Fig. 1, none of the heating elements is heated with a heating pulse. But in the adjacent column Cn-2 and Cn-1, all the heating elements are heated with a heat pulse of the pulse length of 0.2 of the maximum pressure pulse length.

Fig. 19 shows a franking imprint according to the post request in Canada. The barcode 15 * is arranged to the left of the value stamp 16 * and, in contrast to the barcode 15 shown in FIG. 12, is printed at a distance from the value stamp 16 *. Within the distance, a stamp image 17 * is printed with further data prescribed by the postal authority. Thus, there is another - not shown - compared to the program shown in Figure 13 program routine modified program routine for determining the energy values for printing the barcode image in better quality, starting from the same basic idea of the invention.

For the generation of an image according to FIG. 19 variant 2 or 3 or another variant-not described in more detail-can be used to improve the quality, the latter, however, being based essentially on the same idea of the invention.

If in the above example of mail pieces, letter envelopes or franking strips is spoken, then other forms of printed matter should not be excluded. Rather, all printed matter should be included, which can be printed by printing devices by the thermal transfer printing process.

To improve the quality further other embodiments of the invention can be developed or used, which are based on the same basic idea of the invention and are encompassed by the appended claims.

Claims (19)

A method for improving the quality of printing with a thermal transfer print head (1) for a printing device, the control of which is equipped with a microprocessor (8) and memories, for data processing prior to printing, and for triggering and controlling a printing process in which a first amount of energy in a first Determining step (10) before printing is calculated at least with the aid of machine parameters, wherein the amount of energy in a feeding step (50) is supplied to a first heating element of the thermal transfer print head (1) to transfer ink from a ribbon associated with the thermal transfer print head (1) to a first heating element To transfer print carrier surface, characterized in that in an improvement step (30) an energy value calculation is performed in a manner according to which data of the printed image from the microprocessor (6) are processed to also control those heating elements which in at least one of the edge regions Heizelemen tseries, but where there are also no heating elements which are not located in the two edge regions of the heating element row for a limited period of time with a heating pulse, wherein the aforementioned period of time corresponds to the printing of a barcode image ( 15) immediately precedes and that energy values for each of the heating elements of the thermal transfer print head (1) in the pixel energy storage (7) are non-volatile buffered. A method according to claim 1, characterized in that the microprocessor (6) for areas (N1), (N2) and (B) externally of the barcode image (15) a different data processing for determining the energy values is made. A method according to claims 1 and 2, characterized in that after the energy value calculation in steps (10), (20) and (30), the data reflecting a respective pixel energy value is converted into a fourth formatting step (40) via a bus There, in a fifth feeding step (50), each binary pixel data supplied to a heating element is transferred in an associated phase of successive phases a pressure pulse duration to the respective drive unit of the thermal transfer print head (1) is output to convert the print data by an internal electronics of the thermal transfer print head in pressure pulses of predetermined voltage level and with a separately adjustable for the heating elements duration. A method according to claims 1 to 3, characterized in that a voltage is applied as a pressure pulse to the heating elements, wherein the pressure pulse in phases of equal duration is temporally subdivided, that with each phase of the heating of a heating element, the existing basic energy or in the phases previously added energy is increased by one energy level, that also not subsequently or not immediately following during printing heating elements used to be heated. Method according to claims 1 to 4, characterized in that the energy values for the heating of the heating elements at the edge of the heating element row are calculated by the microprocessor (6), which are assigned to the pixels in at least one of the two edge regions N1 and N2 externally of the barcode image, wherein the energy values are calculated from such a height, so that as a result of the corresponding heating elements at the edge of the heating element row just no dots are printed out. Method according to claim 5, characterized in that an energy of up to two tenths of the maximum energy value is supplied to each heating element at the edge of the heating element row of the thermal transfer printing head (1) while the barcode image is being printed. A method according to claim 5, characterized in that the calculation consists in adding a previously empirically or computationally determined energy value E _N. A method according to claim 6, characterized in that the substrate temperature of the thermal transfer print head (1) is measured and a threshold comparison is performed, wherein at a threshold below the substrate temperature from the microprocessor (6) a higher energy value E _{N is} selected. Method according to Claim 8, characterized in that the microprocessor (6) selects an energy value E _{N which} is one step higher. Method according to claims 1 to 4, characterized in that a predetermined energy value E _{H is} supplied to a heating element which is used in the region (B) before the printing of the barcode image (15), a first energy value E _H not being yet but causes only a predetermined preheating of the corresponding heating element in at least one of the preceding phases, that a predetermined second energy value Ev is supplied to each of the heating elements in the region (B) before printing the barcode image (15), which in the region (B ) not for a predetermined preheating with the first energy value E _H to Use come, the second energy value E _{V is} at least one energy level below the first energy value E _H. Arrangement for carrying out the method according to claim 1, characterized in that a high-resolution thermal transfer print head (1) comprises a number of heating elements, wherein the length of the row of heating elements of the thermal transfer print head (1) the length of a row (R) of barcode image elements at that edge of the barcode image printed last that the thermal transfer print head (1) is arranged in a printing apparatus and connected to a controller equipped with a microprocessor (8) programmed to perform energy value calculation before printing in which the heating elements at the ends of the row of heating elements of the high-resolution thermal transfer print head (1) are activated in heat phases even if no dot is provided on the edges externally of the barcode image and then, if printing of a dot is provided, a calculation a thermal transfer print head (1) to carry out the energy value according to different species. Arrangement according to claim 11, characterized in that an energy value calculation is carried out in a first and second way by the microprocessor (8), wherein the amount of energy to be supplied to each heating element of a thermal transfer print head (1), including machine parameters and dependent on is calculated in the different image sections of the franking stamp image and wherein in a known manner history-related information and environment information on the control of each heating element of the thermal transfer print head (1) is evaluated to modify the calculated amount of energy or to generate an amount of energy for preheating a heating element, as well as the a respective energy values associated with each heating element of the thermal transfer printing head (1). Arrangement according to Claims 11 to 12, characterized in that a pixel energy store (7) which non-volatile stores the energy values is connected to the thermal transfer print head (1) in data and control fashion via a print data controller (4). Arrangement according to Claims 11 and 13, characterized in that the print data controller (4) is realized as a field-programmable component (FPGA). Arrangement according to claims 11 and 13, characterized in that the print data controller (4) is realized as a user-specific integrated circuit (ASIC). Arrangement according to claim 11, characterized in that at least one heating element at the edge of Heizelementreihe the thermal transfer printhead (1) exists, which as a result of an empirically or computationally carried out by the microprocessor (8) energy value calculation, according to a third type, an energy of up to two-tenths of the maximum energy value, and that is immediately adjacent to a heating element used to print a 50% line at the top of the bar code. Method according to claims 1 to 4, characterized in that a predetermined energy value E _{H is} supplied to all heating elements of a row of heating elements which are used in the pre-region (B) before the printing of the barcode image (15), wherein a first energy value E _{H of} a Heating pulse length corresponds, but not yet leads to printing, but only causes a predetermined preheating of the corresponding heating element in at least one of the preceding phases, all heating elements in the pre-B and at least one non-printing in the edge region N1 heating element at the edge of the Heizelementreihe the thermal transfer print head (1) an energy of up to two Tenth of the maximum energy value is supplied. A method according to claim 17, characterized in that in a time range prior to printing the barcode image (15), when an image column of the leading area (B) spaced from the edge of the barcode image (15) reaches the printing location, for preheating, each non-printing heating element Energy of one-tenth of the maximum energy value is supplied by a heating pulse during a period of time which has the duration of one phase of a pressure pulse, wherein the phase alternates with another phase in which no energy is supplied to the non-printing heating element. A method according to claim 18, characterized in that the distance from the edge of the barcode image (15) is at least two image columns when the heating element has an energy of one-tenth of the maximum energy value for preheating by a heat pulse during a period of time of one phase of a pressure pulse is supplied.

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