Plastic card printing system with temperature and pixel density compensation

Abstract

Thermal printing on plastic cards, wherein the energization of each individually energizable heating element of a thermal printhead is adjusted based on the temperature of the thermal printhead and the density of the pixel to be printed. For each pixel, the printhead temperature and the pixel density of the pixel to be printed are used to adjust the length of the gate pulse used to energize the heating element to print the pixel. By compensating for both the printhead temperature and the pixel density, tighter tolerances in the resulting print density are obtained.

Description

TECHNICAL FIELD

[0001] The present technology discloses thermal printing on plastic cards using a thermal printhead and compensating for printhead temperature and density of individual pixels being printed. BACKGROUND

[0002] Printing on plastic cards using a thermal printhead is known. A thermal printhead includes a plurality of individually energizable heating elements that are individually energized based on a determined strobe pulse length for each heating element. An example of driving a heating element in a thermal printhead based on a strobe pulse length is disclosed in U.S. Patent 5,087,923. SUMMARY

[0003] Thermal printing on plastic cards is described in which the energization of individual, individually energizable heating elements of a thermal printhead is adjusted based on the temperature of the thermal printhead and the density of a pixel to be printed. For each pixel, the printhead temperature and the pixel density of the pixel to be printed are used to adjust the strobe pulse length for energizing the heating element to print the pixel. By compensating for the printhead temperature and the pixel density, tighter tolerances in the resulting print density are achieved.

[0004] The thermal printing described herein can be applied to direct-to-card thermal printing in which the printing is performed directly on a plastic card and to retransfer in which the printing is initially performed on a transferable substrate that is then laminated to a plastic card with the printing thereon.

[0005] As used herein, a plastic card includes, but is not limited to, a financial (e.g., credit, debit, etc.) card, an access card, a driver's license, an identification card, a business identification card, a gift card, and other plastic cards. In some embodiments, the technology described herein can be used to print on one or more pages of a passport, such as the cover or back cover of a passport, or an inner page (e.g., a plastic page) of a passport.

[0006] The data processing for compensating for printhead temperature and pixel density preferably occurs in a printer controller that is in direct or indirect communication with the thermal printhead. The printer controller can also be referred to as being associated with the thermal printhead. In one embodiment, the printer controller is located in a plastic card printer that includes the thermal printhead. In another embodiment, the printer controller can be located at a location that is remote (i.e., physically separate) from the plastic card printer.

[0007] The printer controller includes one or more data processing devices having sufficient data processing speed to maintain a desired print speed of the thermal printhead. In one embodiment, the one or more data processing devices include at least one field programmable gate array (FPGA). However, the data processing devices can be single core or multi-core processors or other data processing devices. In one embodiment, the thermal printhead can have a print speed from about 0.38 inches per second to about 1.75 inches per second. In one embodiment, the print speed can be about 1.55 inches per second. However, different print speeds are possible while still compensating for both printhead temperature and pixel density, as described herein.

[0008] In one embodiment, a plastic card printing system can include a print ribbon supply and a print ribbon take-up; a multi-color print ribbon supplied from the print ribbon supply and taken up on the print ribbon take-up, wherein the multi-color print ribbon includes a plurality of dye panels; and a thermal printhead having a plurality of individually energizable heating elements. Further, the plastic card printing system includes a printer controller in communication with the thermal printhead and generating data to control energization of the individually energizable heating elements to print an image to be applied to a plastic card. The printer controller can be part of or separate from a plastic card printer that includes the thermal printhead. For each pixel to be printed, the printer controller generates data to control energization of the individually energizable heating elements based on a temperature of the thermal printhead and a density of the pixel.

[0009] In another embodiment, a plastic card printing system can include a print ribbon supply and a print ribbon take-up; a multi-color print ribbon supplied from the print ribbon supply and taken up on the print ribbon take-up, wherein the multi-color print ribbon includes a plurality of dye panels; and a thermal printhead having a plurality of individually energizable heating elements. Further, the plastic card printing system includes a printer controller in communication with the thermal printhead and generating data to control energization of the individually energizable heating elements to print an image to be applied to a plastic card. The printer controller includes at least one FPGA having a data processing speed of at least about 96 MHz. The printer controller can be part of or separate from a plastic card printer that includes the thermal printhead.

[0010] In another embodiment, a plastic card printing system that performs printing on a plastic card can include a print ribbon supply and a print ribbon take-up; a multi-color print ribbon supplied from the print ribbon supply and taken up on the print ribbon take-up, wherein the multi-color print ribbon includes a plurality of dye swatches; and a thermal printhead having a plurality of individually energizable heating elements. Further, a printer controller is in communication with the thermal printhead and generates data to control energization of the individually energizable heating elements to print an image to be applied to the plastic card. The printer controller implements a compensation scheme that generates an 8% or less pixel density error across all pixel densities. The printer controller can be part of or separate from a plastic card printer that includes the thermal printhead.

[0011] In yet another embodiment, a method of direct-to-card thermal printing on a plastic card in a plastic card printing system is described. The plastic card printing system includes a thermal printhead having a plurality of individually energizable heating elements and a multi-color print ribbon including a plurality of dye swatches. The method includes receiving a print request to print on a plastic card in the plastic card printing system using the thermal printhead and the multi-color print ribbon, wherein the print request includes print data. The print data is processed and strobe pulse length data is generated for each pixel to be printed, the strobe pulse length data used to energize the individually energizable heating elements, wherein the strobe pulse length data for each pixel accounts for a temperature of the thermal printhead and a density of the pixel. The generated strobe pulse length data for each pixel is then used to energize the individually energizable heating elements to transfer dye from the dye swatches and print on the plastic card. The processing of the data and the generation of the strobe pulse length data can occur in a printer controller that is included in or separate from a card printer that includes the thermal printhead, the printer controller in communication with the thermal printhead. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 An example of a plastic card printing system implementing the compensation described herein is shown.

[0013] Figure 2 Another example of a plastic card printing system implementing the compensation described herein is shown.

[0014] Figure 3 An example curve showing the energy applied to the heating elements of a thermal printhead compared to the printhead temperature for various pixel density levels is shown.

[0015] Figure 4 An example of the method of compensating for both printhead temperature and pixel density described herein is shown. DETAILED DESCRIPTION

[0016] With reference toFigure 1 An example of a plastic card printing system 10 is shown. In this example, the system 10 is configured to perform direct-to-card thermal printing on a plastic card 12. The system 10 includes a print ribbon supply 14, a print ribbon take-up 16, a multi-color print ribbon 18, a thermal print head 20, a platen 22 positioned opposite the print head 20, and a printer controller 24. The print ribbon supply 14, the print ribbon take-up 16, the multi-color print ribbon 18, the thermal print head 20, and the platen 22 can be considered to be part of a plastic card printer and are disposed within a housing 25 of the plastic card printer.

[0017] The print ribbon 18 can be any multi-color print ribbon known in the art of plastic card printing. The print ribbon 18 is supplied from the print ribbon supply 14 and is taken up on the print ribbon take-up 16 after use. The print ribbon 18 includes a plurality of color panels arranged in a repeating order. For example, the print ribbon 18 can be a YMCK ribbon having a plurality of sequences of yellow (Y), magenta (M), cyan (C), and black (K) color panels, as is well known in the art. The YMC color panels are typically dye materials, while the K color panels are pigment materials. In some embodiments, the print ribbon 18 can include one or more additional color panels associated with each sequence of color panels, including but not limited to color panels of a topcoat material (typically designated as a YMCKT ribbon) and / or an overcoat material (typically designated as a YMCKO ribbon).

[0018] The thermal print head 20 can be any thermal print head known in the art of plastic card printing. As understood by one of ordinary skill in the art, the thermal print head 20 includes a plurality of individually energizable heating elements (not shown), each of which can be selectively energized by an electronic gating pulse that heats the corresponding heating element to transfer color material from one of the color panels of the print ribbon 18 to the plastic card 12. As shown in FIG. 1, in one round of printing, the thermal print head 20 can be moved toward the platen 22 to position the print head 20 during printing, and moved away from the platen 22 when not printing to reposition the card 12 for the next round of printing. Figure 1

[0019] ​A mechanical card transport mechanism, such as one or more pairs of transport rollers 26, transports the card 12 in the printing system 10. The card transport mechanism is preferably reversible to allow forward and reverse transport of the card 12 to allow multiple pass printing past the print head 20 to be implemented. Mechanical card transport mechanisms for transporting plastic cards in a plastic card printing system are well known in the art. Other examples of card transport mechanisms that can be used are known in the art, including but not limited to a transport belt (with and / or without tabs), a vacuum transport mechanism, a transport carriage, and the like, and combinations thereof. Card transport mechanisms are well known in the art, including those disclosed in U.S. Patents 6,902,107, 5,837,991, 6,131,817, and 4,995,501, and U.S. Published Application No. 2007 / 0187870, which are hereby incorporated by reference in their entireties. One of ordinary skill in the art would readily understand the types of card transport mechanisms that can be used and the structure and operation of such card transport mechanisms.

[0020] The printer controller 24 is in direct or indirect communication with the thermal print head 20. The printer controller 24 can be part of the plastic card printer and located within the housing 25, as shown by the solid line in Figure 1 , or the printer controller 24 can be remote from (i.e., physically separate from) the plastic card printer and located outside of the housing 25, as shown by the dashed line in Figure 1 . The printer controller 24 processes print data and generates data in the form of gating pulses to control energization of the individually energizable heating elements of the thermal print head 20 to generate a print on the card 12. The printer controller 24 can also control the drive of the ribbon supply 14 and / or the print ribbon take-up 16 during printing, control the movement of the thermal print head 20 during printing, and / or control the operation of the transport rollers 26 during printing. Alternatively, the drive of the ribbon supply 14 and / or the print ribbon take-up 16, the movement of the thermal print head 20, and / or the operation of the transport rollers 26 can be controlled by separate control mechanisms within or remote from the plastic card printer of the printing system 10. For example, in some embodiments, when the printer controller is remote from the plastic card printer, only the portion of the printer controller for processing print data and generating gating pulses to control energization of the individually energizable heating elements of the thermal print head 20 can be remote from or outside of the plastic card printer. Other functions of the printer controller 24, such as control of the card transport mechanism, control of movement of the print ribbon 18 and the thermal print head 20, and the like, can be on the plastic card printer.

[0021] Figure 2Another example of a plastic card printing system 100 is shown. In this example, the system 100 is configured to perform retransfer printing on a plastic card 12. The overall structure of a retransfer card printer is well known in the art. In this example, the same reference numerals are used to represent elements that are the same or similar to elements in the system 10 in Figure 1 The system 100 includes a print ribbon supply 14, a print ribbon take-up 16, a multi-color print ribbon 18, a thermal print head 20, a platen roller 22, and a printer controller 24.

[0022] In the system 100, rather than printing directly on the plastic card 12, printing is initially performed on a transferable material of a retransfer ribbon 30. The retransfer ribbon 30 is supplied from a retransfer ribbon supply 32, and used retransfer ribbon is wound on a retransfer ribbon take-up 34. The retransfer ribbon 30 is advanced along a path past the print head 20, on which path printing is performed on the transferable material. The retransfer ribbon 30 with the printed content is then advanced to a transfer station 36, where using a heated transfer roller 38, the transferable material with the printed content is transferred from the retransfer ribbon 30 and laminated onto the card 12. After the transferable material with the printed content is transferred, the used retransfer ribbon 30 is wound onto the take-up 34.

[0023] The printer controller 24 processes print data and generates data in the form of gating pulses to control energization of individually energizable heating elements of the thermal print head 20 to produce the printed content on the retransfer ribbon 30. The printer controller 24 can also control other operations of the printing system 100, such as driving the ribbon supply 14 and / or the print ribbon take-up 16, movement of the thermal print head 20, operation of the transport rollers 26, operation of the supply 32 and take-up 34, transfer roller 38, etc. Alternatively, other operations of the printing system 100 can be controlled by a control mechanism separate from the printer controller 24.

[0024] In each printing system 10, 100, the printer controller 24 is programmed to process data to compensate for the print head temperature and the density of the pixel to be printed. The printer controller 24 adjusts the length of the strobe pulse used to energize the heating elements of the thermal print head for each shade of each pixel based on the print head temperature and the current shade value. The print head temperature is known from a temperature sensor that senses the temperature and provides temperature data to the printer controller 24. The pixel shade to be printed for each pixel is known from the print data provided to the printer controller 24. As the print head temperature increases, lower density pixel shades (e.g., 25% or less) require less energy to be applied to the heating elements of the print head to transfer the dye. As the print head temperature increases, higher density pixel shades (e.g., 75% or more) require less energy to be applied to the heating elements to transfer the dye, but at a different rate than lower density pixel shades.

[0025] By compensating for the print head temperature and the pixel density, tighter tolerances in the resulting printed pixel density are achieved. For example, in one embodiment, the compensation scheme described herein can result in a pixel density error (i.e., the deviation of the actual pixel density after printing from the target pixel density) of approximately ±8.0% across all pixel densities; a pixel density error of approximately ±4.0% or less at pixel densities of 40% or higher; or a pixel density error of approximately ±2.0% at pixel densities of 70% or higher. In this embodiment, the density measurements were obtained from 10 plastic cards printed in a plastic card printer having a thermal print head using the compensation scheme described herein at print head temperatures of approximately 17°C to approximately 70°C and were accurate to 0.01 density units as measured using an XRite i1 Pro Spectrophotemeter available from X-Rite Inc. of Grand Rapids, Michigan. The plastic card printer used to print the 10 plastic cards was a Sigma DS3 desktop card printer from Entrust Corporation of Shakopee, Minnesota. In contrast, in a plastic card printing system without the compensation scheme, density errors of up to 40% are often encountered at lower pixel densities and density errors of 20% or more are encountered at higher pixel densities.

[0026] The compensation scheme described requires a significant amount of data processing. Conventional printing systems employing conventional data processing mechanisms will slow down due to the data processing requirements, thereby significantly reducing the card printing rate and overall card throughput of the card printing system.

[0027] Accordingly, the printer controller 24 is equipped with one or more data processing devices that can handle the increased data processing requirements. Preferably, to maintain a print speed of from about 0.38 inches per second to about 1.75 inches per second, or a print speed of about 1.55 inches per second, the printer controller 24 is preferably provided with one or more data processing devices having a data processing speed of at least about 96 MHz or greater. The one or more data processing devices can be any type of device suitable for achieving at least that data processing speed. For example, in one embodiment, the one or more data processing devices can comprise an FPGA. However, the data processing devices can be single core or multi-core processors or other data processing devices. However, if lower print speeds are acceptable, data processing devices having lower data processing speeds can be used while still compensating for printhead temperature and pixel density.

[0028] The compensation scheme used can vary based on a number of variables including printhead temperature. For example, in one embodiment, if the temperature of the printhead is below a minimum operating temperature of 15 °C, the following compensation equation can be used:

[0029]

[0030] TComp = change in energy applied to the printhead / change in printhead temperature.

[0031] CAL = worst case strobe length in clock frequency (e.g., clock frequency is about 96 MHz, resolution of CAL is about 10.4 nanoseconds).

[0032] Clock Frequency = clock frequency of the data processing device (e.g., FPGA).

[0033] Strobe Length = energy applied to the printhead in seconds.

[0034] In another embodiment, if the temperature of the printhead is above a minimum operating temperature of 15 °C, and the equation (2*TComp - DComp*(ShadeIndex - ShadeIndexZero) > 0) is true, the following compensation equation can be used:

[0035]

[0036] TPHTemp = measured value of the current printhead temperature.

[0037] TCompTempZero = minimum operating temperature of the printer.

[0038] ShadeIndex = current color of the pixel being printed.

[0039] ShadeIndexZero = minimum color at which to start increasing the density compensation.

[0040] TComp = change in energy applied to the print head / change in print head temperature.

[0041] DComp = change in energy / change in target print density.

[0042] CAL = worst case strobe length in clock ticks (e.g., clock frequency is approximately 96 MHz, resolution of CAL is approximately 10.4 nanoseconds).

[0043] Clock Frequency = clock frequency of the data processing device (e.g., FPGA).

[0044] Strobe Length = energy applied to the print head in seconds.

[0045] Conversely, if the temperature of the print head is above the minimum operating temperature of 15 °C and the equation (2*TComp - DComp*(ShadeIndex - ShadeIndexZero) > 0) is false, then the following compensation equation can be used:

[0046]

[0047] CAL = worst case strobe length in clock ticks (e.g., clock frequency is approximately 96 MHz, resolution of CAL is approximately 10.4 nanoseconds).

[0048] Clock Frequency = clock frequency of the data processing device (e.g., FPGA).

[0049] Strobe Length = energy applied to the print head in seconds.

[0050] Referring to Figure 3 , an example of compensating for print head temperature and pixel density when energizing each heating element with an adjusted strobe is shown. Figure 3 A plot of the energy (i.e., strobe) applied to the heating elements of a thermal print head versus the print head temperature is depicted for various pixel density levels. As shown, the plots are generally parallel to one another. In a conventional plot without the compensation scheme described herein, the plots tend to converge with one another and eventually merge as the print head temperature increases.

[0051] Figure 4A method 50 using the compensation schemes described herein is shown. In the method 50, a print request is received 52 by a printer controller. In one embodiment, the print request 52 can include print data for a print to be performed by the printing system 10, 100. In another embodiment, the print request 52 can cause the printer controller to retrieve print data from a data storage location. At step 54, the print data is then processed using the compensation schemes described herein, and for each pixel to be printed, a strobe pulse length is determined that is adjusted for the current print head temperature and the density of the pixel to be printed. At step 56, the strobe pulse is used to drive the heating elements of the thermal print head to perform the print. In one embodiment, for each print job, the data can be processed concurrently with driving the thermal print head (i.e., a set of computed strobe pulse lengths for a portion of the print job can be used to drive the thermal print head while new strobe pulse length data is determined for another portion of the print job). In another embodiment, all of the strobe pulse length data for an entire print job can be determined first, and then the determined strobe pulse length data is used to drive the thermal print head to perform the print job.

[0052] The printing systems 10, 100 described herein can be used in small volume desktop card processing systems or large volume batch production card processing systems (or central issuance processing systems). Desktop card processing systems are typically designed for relatively small scale, individual card personalization in relatively small volumes, for example, measured in tens or hundreds per hour. In these installations, individual plastic cards to be personalized are input to the card processing system, which typically includes one or two processing capabilities, such as printing and lamination. These processing machines are often referred to as desktop machines because they have a relatively small footprint to allow the processing machine to reside on a desktop. Many examples of desktop processing machines are known, such as the SD or CD series desktop card printers available from Entrust Corporation of Shakopee, Minnesota. Other examples of desktop processing machines are disclosed in U.S. Patents 7,434,728 and 7,398,972, the entire contents of each patent are incorporated herein by reference.

[0053] For high volume batch processing of personalized plastic cards (e.g., on the order of hundreds or thousands per hour), institutions typically utilize card processing systems that employ multiple processing stations or modules to simultaneously process multiple cards in order to reduce the overall processing time for each card. Examples of such machines include the MX and MPR series of central issuance processors available from Entrust Corporation of Shakopee, Minnesota. Other examples of central issuance processors are disclosed in U.S. Patents 4,825,054, 5,266,781, 6,783,067, and 6,902,107, all of which are incorporated herein by reference in their entirety.

[0054] The embodiments disclosed in this application are to be considered in all respects as illustrative and not restrictive. The scope of the application is indicated by the appended claims, rather than by the foregoing description; and all changes that come within the meaning and range of equivalency of the claims are embraced therein.

Claims

1. A plastic card printing system that prints on plastic cards, the plastic card printing system comprising: a print ribbon supply and a print ribbon crimping device; a multi-color print ribbon supplied from the print ribbon supply and crimped on the print ribbon crimping device, the multi-color print ribbon comprising a plurality of dye panels; a thermal printhead having a plurality of individually energizable heating elements; a printer controller in communication with the thermal printhead and generating data to control energization of the individually energizable heating elements to print an image to be applied to the plastic card; for each pixel to be printed, the printer controller generates data to control energization of the individually energizable heating elements based on a temperature of the thermal printhead and a density of the pixel.

2. The plastic card printing system of claim 1, wherein, the dye panels comprise a cyan panel, a magenta panel, and a yellow panel.

3. The plastic card printing system of claim 1, wherein, the multi-color print ribbon comprises a plurality of black pigment panels and a plurality of topcoat panels.

4. The plastic card printing system of claim 1, wherein, the printer controller comprises a field programmable gate array.

5. The plastic card printing system of claim 1, wherein, the thermal printhead is part of a plastic card printer and the printer controller is part of the plastic card printer.

6. The plastic card printing system of claim 1, wherein, the thermal printhead is part of a plastic card printer and the printer controller is remote from the plastic card printer.

7. The plastic card printing system of claim 1, wherein, the plastic card printing system has a pixel density error of 8% or less across all pixel densities.

8. The plastic card printing system of claim 1, wherein, the printer controller comprises at least one field programmable gate array having a data processing speed of at least about 96 MHz.

9. A method of direct-to-card thermal printing on a plastic card in a plastic card printing system having a thermal printhead provided with a plurality of individually energizable heating elements and a multi-color print ribbon comprising a plurality of dye panels, the method comprising: receiving a print request to print on the plastic card in the plastic card printing system using the thermal printhead and the multi-color print ribbon, the print request comprising print data; processing the print data to generate gating pulse length data for energizing the individually energizable heating elements for each pixel to be printed, wherein the gating pulse length data for each pixel takes into account a temperature of the thermal printhead and a density of the pixel; and energizing the individually energizable heating elements using the gating pulse length data generated for each pixel to transfer dye from the dye panels and print on the plastic card.

10. The method of claim 9, wherein, the dye panels comprise a cyan panel, a magenta panel, and a yellow panel.

11. The method of claim 9, wherein, the multi-color print ribbon comprises a plurality of black pigment panels and a plurality of topcoat panels, and the method comprises energizing the individually energizable heating elements using some of the generated gating pulse length data to transfer black pigment from one of the black pigment panels to the plastic card and / or to transfer topcoat material from one of the topcoat panels to the plastic card.

12. The method of claim 9, comprising processing the print data using a field programmable gate array.

13. The method of claim 9, wherein, The plastic card printing system has a pixel density error of 8% or less across all pixel densities.

14. The method of claim 9, wherein, The thermal print head is part of a plastic card printer, and wherein the processing of the data occurs on the plastic card printer.

15. The method of claim 9, wherein, The thermal print head is part of a plastic card printer, and wherein the processing of the data occurs remotely from the plastic card printer.

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