WO1997001444A1

WO1997001444A1 - Thermal ink transfer printer using a multistandard ribbon

Info

Publication number: WO1997001444A1
Application number: PCT/FR1996/000999
Authority: WO
Inventors: Paul Morgavi
Original assignee: Datacard Corporation
Priority date: 1995-06-27
Filing date: 1996-06-27
Publication date: 1997-01-16
Also published as: EP0835183A1; JPH11508497A

Abstract

A thermal ink transfer printer (1, 40, 41, 80) including a thermal print head (6), an ink ribbon (8) with a plurality of colour sequences (J, M, C, T, N), and means for converting the Red, Green, Blue coding of an image to be printed into a Yellow, Magenta, Cyan coding specific for the ink transfer. Said converting means include means (20, 25) for sensing the hues (FJ, FM, FC) of the colours (J, M, C) of the ribbon (8), and means (130, 133, TCJi, TCMi, TCCi) for converting the image coding depending on the sensed hues (FJ, FM, FC).

Description

DYE THERMAL TRANSFER PRINTER, TAPE

MULTISTANDARD

The present invention relates to a thermal transfer printer for dyes, which can be used in particular for personalizing plastic cards such as smart cards, magnetic cards, badges, etc. FIG. 1 schematically represents a printer 1 of the conventional type. The printer 1 comprises two pairs 2, 3 of secondary conveyor rollers for a plastic card 4 to be printed, a thermal print head 6 and a main conveyor roller 5 arranged below the print head 6. During printing, the print head 6 occupies a low position and the card 4 is sandwiched between the head 6 and the roller 5, with the interposition of an ink ribbon 8, consisting of a support film of a transparent material on which a layer of coloring material is deposited. The card 4 moves step by step in a conveying direction S identified in FIG. 1. Each movement of one step of the card 4 corresponds to an equivalent movement of the ribbon 8 and the printing of a line, by transfer of the coloring matter on the card 4. The scrolling of the ribbon 8 is ensured by a motorized winding system 9, and the advancement of the card 4 by a stepping motor 10 driving the rollers 2, 3, and 5 by l belt 11-1, 11-2, 11-3. The print head 6, the winding system 9 and the motor 10 are controlled by a central unit 13 with a microprocessor, which has in its memories a coding of the image to be printed.

The ribbon 8 is for example an indexed ribbon repetitively presenting three sequences of primary colors Yellow (J), Magenta (M) and Cyan (C) and a sequence of transparent varnish (T), separated by dark indexing bars. Thus, the printing of a pattern on the card 4 takes place in three steps, each step corresponding to the printing line by line of a primary color until the entire length of the card 4 is covered. At the end of each step, card 4 returns to the initial position for printing a new color sequence, etc. We thus obtain by combination of the three primary colors a whole palette of colors. A fourth and final optional printing step allows a protective varnish to be deposited on card 4.

The control of the running of the ribbon and the control of its position are ensured by means of an optical detector 14 comprising a light source 14-1 oriented towards one face of the ribbon and, on the other side of the ribbon, an optoelectronic cell 14-2 the electrical output of which is monitored by the central unit 13. When a ribbon indexing bar passes in front of the source 14-1, it prevents the light emitted from passing through the ribbon 8 and the output of the cell 14-2 passes at 0.

FIG. 2 schematically represents the electrical structure of the printer 1 of FIG. 1. There there are electrically connected to the central unit 13 and represented in the form of blocks the means 9 for moving the ink ribbon, the motor 10 of conveying, and the optical detector 14.

The central unit 13 comprises a microprocessor 130 associated with memories 131, 132, 133. The memory 131 is a program memory of the ROM type in which the operating program of the printer is stored. The memory 132 is a RAM type memory in which an image to be printed is stored in coded form. Finally, the memory 133 is an EEPROM type memory whose role will be explained below. According to one usual operating configuration illustrated in FIG. 2, the coded image stored in memory 133 is sent to the microprocessor 130 by a microcomputer 41. The microcomputer 41 itself receives the image of a peripheral element 42, for example a video camera, a computer diskette, etc.

The print head 6 is represented in its electrical form and comprises n resistive heating points Pi, referenced P _{1 #} P ₂ , ... P _{n (} i being an index ranging from 1 to n, each resistive point Pi being assigned to the printing of an elementary image point The print head 6 is controlled by a power circuit 30 controlled by the microprocessor 130. The circuit 30 is supplied by a voltage V and comprises a shift register 31 comprising n memory points Mi referenced M _{1 (} M ₂ , ... M _n , a buffer memory 32, a plurality of n switches, here bipolar transistors Ti referenced T _x to T _n , and a plurality of n logic gates Ei of type ET, referenced E _x to E _n . Each resistive point Pi of the print head 6 is linked to the supply voltage V via a transistor Ti, and each transistor Ti is controlled by a logic gate Ei. Each gate Ei receives on a first input a STR signal for controlling the duration of an electrical pulse, common to all the other gates Ei, and on its other input the output of a memory point Mi of the shift register 31, by means of the buffer memory 32 controlled by a validation signal LT. A phase of printing a line, for a primary color, comprises a predetermined number N of cycles of activation of the resistive points Pi, in general 255 cycles. At each cycle, the microprocessor 130 loads the shift register 31 according to a particular configuration, valid at the output of the buffer memory 32 the binary values contained in the memory points Mi of the register 31 by activating the signal LT, then sends the signal STR for shaping an electric pulse on all the doors Ei. Thus, when a memory point Mi is set to 1, the corresponding resistive point Pi is supplied by the voltage V for the duration of the signal STR and receives a voltage pulse V. The final temperature to which the resistive point Pi is brought depends on the number of electrical pulses received during the 255 cycles of a line printing phase, which makes it possible to control the intensity of the color deposit for each image point. After three printing cycles of the three primary colors, a whole palette of colors is obtained. The whole of this process is automatically controlled by microprocessor speech 130 which has in coding 132 a coding of the image to be printed, and generates from this coding an appropriate configuration of the shift register 31 at each of the 255 cycles that has a line printing phase. The coding of the image is conventionally a pixel by pixel coding, an elementary image point being made up of three pixels, a Yellow, a Magenta and a Cyan, each pixel being coded on a byte. Given that a coding byte can take 256 values ranging from 0 to 255, we understand that the decomposition into 255 cycles of a printing phase of a line makes it possible to send to each resistive point Pi of the head d printing 6 a number N of activation pulses ranging from 0 to 255 and equal to the value of the pixel coding byte that the resistive point Pi must print.

Such coding of the image is specific to dye transfer printers and does not correspond to the usual standards in the field of computer imaging, using the coding Red (R), Green (V), Blue (B). Thus, there is in the memory 133 of the central unit 13 digital data which allow the microprocessor 130, before starting to print an image, to convert the image code sent by the microcomputer 41 into a code allowing control of the power circuit 30. Such digital data is in the form of tables, in which there are: so-called correspondence tables, making it possible to transform codings of pixels B, V, R into codings of pixels J, M , VS,

- so-called shade tables, one for each primary color, making it possible to correct phenomena of non-linearity affecting the transfer of dyes, and - so-called regulation tables making it possible to take into account the temperature of the print head 6 at the time when printing must be performed.

These various tables being known to one skilled in the art, it will be considered for the sake of simplicity that the conversion of the image coding is ensured by three conversion tables TCJ, TCM, TCC, as shown in FIG. 2, the table TCJ comprising the all the tables necessary for Blue / Yellow transcoding, the TCM table all the Green / Magenta transcoding tables, and the TCC table all the Red / Cyan transcoding tables.

In such a printer, the tables TCJ, TCM, and TCC are developed for well-defined primary color shades. Such a printer therefore offers complete satisfaction in use insofar as the colors of the ribbon correspond well to those provided by construction. In practice, however, it can be seen that the commercially available ink ribbons exhibit a great disparity in color, since the manufacturers of ink ribbons do not use the same dyes or that some manufacturers do not comply with current standards. This represents a disadvantage for the user, who must take care to supply only ribbons compatible with his printer at the risk of obtaining images of poor quality. The user, and in particular the industrial user, is therefore forced to reduce his supply chains to this or that supplier of ribbons with the drawbacks that this represents. The present invention aims to overcome this drawback.

To this end, the present invention provides a thermal transfer printer for dyes using a thermal print head and an ink ribbon having several color sequences, comprising means for converting the coding of an image to be printed into a coding specific to the transfer of dyes, in which the conversion means comprise means for detecting the hues of the colors of the ribbon and means for converting the coding of the image according to the hues detected.

According to one embodiment, the conversion means comprise a plurality of conversion tables for coding the image to be printed, each conversion table corresponding to a range of hues of a color of the ribbon.

According to another embodiment, the conversion means comprise conversion algorithms taking into account the hue of the colors of the ribbon. According to one embodiment, the shade detection means comprise means for emitting on a first face of the ink ribbon a polychromatic incident light beam, an optoelectronic cell arranged opposite a second face of the ink ribbon, receiving a emerging light beam and delivering an alternating signal the frequency of which is representative of the wavelength of the color of the region of the ribbon traversed by the light beam, and means for measuring the frequency of the alternating signal. Advantageously, the shade detection means can also be used as means for recognizing the color sequences of the ribbon for controlling the position of the ribbon.

According to one embodiment, the printer is coupled to a microcomputer sending the image to be printed. In this case, the coding conversion of the image to be printed can be carried out by the microcomputer.

These characteristics and others of the present invention will be better understood on reading the following description of two embodiments of a printer, according to the present invention, in relation to the appended figures among which: FIG. 1 previously described schematically represents a dye thermal transfer printer,

FIG. 2 previously described is the electrical diagram of the printer of FIG. 1,

- Figure 3 shows means for detecting the wavelength of the colors of an ink ribbon, - Figure 4 represents a curve for recognizing the color sequences of an indexed ink ribbon, Figure 5 represents a curve recognition of the color sequences of an unindexed ink ribbon, FIG. 6 is the electrical diagram of a printer according to the present invention, in which the detection means of FIG. 3 are used as means of detecting the hues of the colors of the ribbon, - Figure 7 shows an element of the diagram of Figure 6, and Figure 8 shows an alternative embodiment of the printer of Figure 6. With reference to Figure 3, a dye thermal transfer printer according to the present invention comprises an optical detector 20 sensitive to the color wavelength. The detector 20 comprises a light source 21 sending on a face of an ink ribbon 8 a beam 22 of polychromatic light, for example white light. The beam 22 crosses the ribbon 8 and the emerging beam 23 is intercepted by an optoelectronic cell 24, for example the cell sold by the company Texas Instrument under the reference TSL 230 "light-frequency converter". The cell 24 is equipped with an integrated electronic circuit delivering an alternating signal of square shape whose frequency F is representative of the electromagnetic wavelength λ of the beam 23. The square signal delivered by the cell 24 is sent in a frequency meter 25 the output of which is read by the central unit 13 of the printer. By filtering phenomenon of the incident beam 22, the wavelength λ of the emerging beam 23 (or its electromagnetic frequency f) is representative of the color of the ribbon 8 in the zone crossed by the light beam 22. Thus, the frequency F delivered by the detector 20 is a function of the color of the ribbon 8.

According to a variant, the frequency meter 25 is integrated into the central unit of the printer, for example in the form of an impulse counter.

The detector 20 which has just been described is susceptible to several applications, which will now be described. First application: use of detector 20 to check the position of the ink ribbon.

Here, the idea of the present invention is to use the detector 20 as a means of recognizing the sequences of colors present on an ink ribbon. In this case, the detector 20 replaces purely and simply, in the conventional printer illustrated by FIGS. 1 and 2, the index detection system 14 described in the preamble. To use the detector 20 as a means of recognizing the sequences of colors, it is necessary to carry out beforehand calibration tests aimed at determining the relation existing between the colors and the frequency F delivered by the cell 24. Such tests have been produced by the applicant on a large number of ribbons of various origins by means of the aforementioned TSL 230 cell, and have confirmed the existence of a dispersion of shades for each of the primary colors according to the origin of the ribbons. Despite this dispersion, it has however been possible to define frequency bands which do not overlap and which make it possible to identify ambiguity of the various colors which an ink ribbon may contain, whatever its origin. This will be better understood by observing Table 1 below which summarizes the result of these tests, in which each frequency band is determined by a minimum frequency Fmin and a maximum frequency Fmax.

To take account of this dispersion, the central unit 13 is programmed so as to associate with each value of frequency F read at the output of the frequency counter

25 one of the frequency bands [Fmin, Fmax] of Table 1, according to the following criterion:

Fmin ≤ F ≤ Fmax

In other words, the frequency band chosen by the central unit 13 is that which includes the frequency F read at the output of the frequency meter 25. As each frequency band corresponds to a particular color, the operation amounts to identifying the color of the ribbon in the area crossed by the light ray. Thus, the central unit 13 is able to drive and control the movement and the position of any type of ribbon. The programming of the central unit, which is within the reach of those skilled in the art and will not be described here, can be carried out in various ways since any color or variation in color of the ribbon can be detected. For example, you can ignore the indexing bars if the ink ribbon has them, or on the contrary take them into account as additional information added to the detection of primary colors.

To fix the ideas, FIG. 4 represents a first curve as a function of the temperature of the frequency F delivered by the frequency meter 25 when an indexed ribbon is scrolled past the detector 20. FIG. 5 represents a second curve as a function of the temperature of the frequency F when a non-indexed ribbon is scrolled past the detector 20. On the curve of FIG. 5, we see that there are three levels J, M, C of decreasing frequencies corresponding to the primary colors Yellow, Magenta and Cyan, followed by a level T of higher frequency corresponding to transparent varnish (when the ribbon has a sequence of varnishes). In Figure 4, we see between each level J, M, C, T a level N low frequency corresponding to the color of the indexation bar separating each color sequence.

It goes without saying that the present invention is applicable to any type of printer and to the control of any type of ink ribbon. In addition, the color recognition frequency bands which appear in Table 1 are only given by way of example and depend on the optoelectronic cell used. These frequency bands can also be chosen narrower if one does not wish the printer to operate with ribbons of questionable quality having primary colors too far from the usual references. Finally, if you plan to always use the same type of ribbon, for example a ribbon from the same manufacturer and produced according to very strict manufacturing criteria, you can program the printer to recognize only the specific frequencies corresponding to the colors of this ribbon.

A second application of the detector 20 will now be described, which can be combined with the application which has just been described.

Second application: the detector 20 is used to optimize the operations for converting the coding of the image to be printed.

Here, the idea of the present invention is to use the detector 20 as a means of detecting the colors of an ink ribbon in order to intervene in the process of coding an image to be printed in order to optimize the quality of printing.

FIG. 6 represents the electrical diagram of a printer 40 according to the present invention, controlled here by the microcomputer 41 already mentioned. Most of the elements of the printer in FIG. 2 are found in the printer 40, the references of which are kept (the printing head 6 and the control circuit 30 being represented in an simplified manner in the form of blocks). The conventional optical detector 14 is replaced by the detector 20 and the frequency meter 25 already described. Furthermore, as shown in FIG. 7, the content of the conversion memory 133 is modified and includes a plurality of Blue / Yellow conversion tables TCJi, Green / Magenta conversion TCMi, and Red / Cyan conversion TCCi, here 30 TCJi tables referenced TCJ _{1 #} TCJ ₂ , ... TCJ ₃₀ , 30 TCMi tables referenced TCM _1; TCM ₂ , ... TCM ₃₀ and 30 TCCi tables referenced TCC _{1 (} TCC ₂ , ... TCC ₃₀ • To develop these various conversion tables TCJi, TCMi, TCCi, ^{we have} repr_, ε Table 1 below, each frequency band resulting from the dispersion of the hues of a primary color has been divided into a plurality of frequency sub-bands between a minimum frequency fmin and a maximum frequency fmax, here 30 sub-bands, each corresponding sub-band to a particular shade of a primary color. Then, according to the ordinary rules of the trade, a conversion table TCJi, TCMi, ^or TCCi was produced for each sub-band, giving the best print quality. equating each εouε-strip to a particular shade of a primary color results of course from an approximation (a sub-strip corresponding in reality to a range of shades) because it is not possible with the present embodiment of the invention to proceed a cutting strips of Table 1 in an infinite number of sub-bands, and to provide an infinite number of converεion tables TCJi, TCMi, TCCI.

To fix the idea, Table 2 below shows the division into εouε-bands made for the color Yellow and the TCJi conversion tables attached to each of the sub-bands.

We see that the band of dispersion of the hues for the Yellow, going from 1450 to 1750 Hz, was cut out proportionally in sub-band fmin-fmax with a width ΔF constant of 10 Hz, each sub-band corresponding to a range of shades. The division can however be carried out differently, for example according to constant logarithmic deεegments (log (ΔF) = summer).

The advantage of the invention is that, whatever the ink ribbon used, it is possible to find among the plurality of conversion tables TCJi, TCMi, TCCi available, three particular tables TCJ _X , TCM _y , TCC ₂ giving a good quality picture.

Thus, according to the present invention, when the microprocessor 130 has to convert the coding of a received image, the microprocessor first of all scrolls the ink ribbon by activating the scrolling means 9, and reads at the output of the frequency counter 25 the frequencies Fj, F _: M "of each of the primary colors J, M, C, these frequencies being representative of the hues of the three primary colors. Then the microprocessor 130 rewinds the ribbon at the start of printing position, performs test loops to identify the fmin-fmax sub-bands in which the frequencies Fj, F _M , F _{c are located} , and chooses three optimal tables TCJ _X , TCM _y , TCC _Z among the 90 conversion tables TCJi, TCMi, TCCi available.

The choice by the microprocessor 130 of the optimal tables TCJ _X , TCM _y , TCC _Z can be obtained by various programming methods within the reach of those skilled in the art. In particular, it is possible to load into a memory of the central unit 13, for example the ROM memory 131, the content of three tables of the type of table 2, the first table allowing the selection of the table TCJ _X , (table 2) , the second the selection of the table TCM _y , and the last the selection of the table TCC _Z. Once the tables TCJ _X , TCM _y , TCC _{Z have been} selected, the microprocessor 130 converts the image coding in a conventional manner and the printing process can begin. Ultimately, the printer 40 according to the present invention automatically adapts to the ink ribbon used, and delivers images of a quality equal to that obtained in the prior art by means of an ink ribbon recommended by the constructor. Of course, the two applications of the detector 20 which have just been described are not necessarily combined within the same device. For example, in the embodiment of FIG. 6, the conventional optical detector 14 of FIGS. 1 and 2 (or any other conventional detector) could control the ink ribbon and the detector 20 could only be used for detection colors and the selection of conversion tables.

Furthermore, it will be clear to a person skilled in the art that the present invention is capable of many variants and improvements. In particular, an alternative embodiment consists in storing the conversion table TCJi, TCMi, TCCi in the microcomputer 41. In this case, the microprocessor 130 sends to the microcomputer 41 the frequencies Fj, F _M , F _c read at the output of the frequency meter 25, the microcomputer 41 selects itself the three adequate conversion tables and sends them to the microprocessor 130. Also, the conversion of the image can be done by the microcomputer 41 itself, at the instead of being carried out by the central unit 13. Of course, such a microcomputer is not essential to the realization of the invention, the image to be printed can be sent to the printer by any known means. Finally, yet another alternative embodiment of the present invention consists in replacing the various conversion tables TCJi, TCMi, TCCi by conversion algorithms ensuring the transformation of the image code byte by byte. Studies carried out by the applicant have indeed shown that ^' we can develop, by synthesizing a large number of conversion tables of the classic type and in a way that is within the reach of man and following the know-how of each printer manufacturer, the following algorithms: an ACJ conversion algorithm making it possible to transform blue coding bytes into yellow coding bytes, an ACM conversion algorithm making it possible to transform coding bytes Green to bytes of Magenta coding, an ACC conversion algorithm used to transform Red coding bytes into Cyan coding bytes. Such algorithms ACJ, ACM, ACC are functions with several input parameters which take into account, with a view to obtaining the best image quality, the following input parameters: - the frequencies Fj, F _M , or F _c , of the primary colors of the ink ribbon as they are read by the detector 20, all the other known parameters necessary for the conversion of the image code and used to develop conversion tables, namely parameters of correction of the non-linearities in the transfer of the coloring matter, of the regulation parameters to take account of the temperature of the printing head, etc. FIG. 8 represents a variant embodiment 80 of the printer 40 of FIG. 6 using such algorithms ACJ, ACM, ACC. The conversion memory 133 is no longer of any use and is deleted. The image memory 132 is replaced by a dual-port RAM memory 134 comprising a first port A for communication with the microprocessor 130 and a second port B for communication with a processor 135 of the DSP (Digital Signal Processor) type with rapid operation of "pipe line" type. When the image code is received from the outside, it is first of all stored by the microprocessor 130 in the dual port memory 134 and then, at the request of the microprocessor 130, transformed by the processor 135 by means of the algorithms for conversion into a appropriate image code stored in place of the initial image code. Printing of the image is then carried out conventionally by the microprocessor 130. The communication of information and instructions between the microprocessor 130 and the processor 135, and in particular the communication by the microprocessor 130 of the frequencies Fj, F _M , F _C of the primary colors of the ribbon, is ensured via the dual port memory 134, an area of which is reserved for the communication protocol.

Claims

1. Printer (1, 40, 41, 80) for thermal transfer of dyes using a thermal print head (6) and an ink ribbon (8) having several color sequences (J, M, C, T, N) , comprising means for converting the coding of an image to be printed into a coding specific for the transfer of dyes, characterized in that the conversion means comprise means (20, 25) for detecting the hues (Fj, F _M , F _C ) colors (J, M, C) of the ribbon (8) and means (130, 135, TCJi, TCMi, TCCi, ACJ, ACM, ACC) to convert the coding of the image as a function of tones (Fj , F _M , F _C ) detected.

2. Printer according to claim 1, characterized in that the conversion means comprise a plurality of tables (TCJi, TCMi, TCCi) for converting the coding of the image to be printed, each conversion table corresponding to a range of shades ( fmin- fmax) of a ribbon color.

3. Printer according to claim 1, characterized in that the converεion means comprise deε algorithmeε de converεion (ACJ, ACM, ACC) taking into account the hue (Fj, F _M , F _c ) deε couleurε (J, M, C ) of the ribbon (8).

4. Printer according to one of claims 1 to 3, characterized in that the means for detecting colors include:

- Means (21) for emitting a polychromatic incident light beam (22) on a first face of the ink ribbon (8), - an optoelectronic cell (24) available opposite a second face of the ink ribbon (8 ), receiving an emerging light beam (23) and delivering an alternating signal whose frequency (F) is representative of the wavelength (λ) of the color (J, M, C, T, N) of the zone of the ribbon (8) traversed by the light beam (22, 23), and

- Deε means (25) for measuring the frequency (F) of said alternating signal.

5. Printer according to one of claims 1 to 4, characterized in that the hue detection means (20, 25) are also used as means for recognizing color sequences (J, M, C, T, N) tape (8) for checking the position of the tape (8).

6. Printer according to one of the preceding claims, characterized in that it is coupled to a microcomputer (41) sending the image to be printed.

7. Printer according to claim 6, characterized in that the conversion of the coding of the image to be printed is carried out by the microcomputer.