FR2508258A1 - Thermal printer for use with coloured ribbon - has electromagnet applying releasable pressure to platen behind paper for printing for stepwise movement of ink ribbon - Google Patents

Abstract

The unit includes a thermal head which comprises a line of point heating elements which are selectively excitable. A sheet of paper for printing passes at right angles to the head between two rollers under the control of a stepping motor. A ribbon carrying one or more printing colours passes between the thermal printing head and the paper. A roller behind the paper maintains the required pressure between the paper, ribbon and the thermal head. The ribbon extends along the thermal head and is driven by a stepping motor. It may be slightly inclined to the heating elements of the head. An electromagnet is linked to the roller to apply or release the pressure which is required between the head and the paper.

Description

 The invention relates to thermal transfer printing of a colored material, or ink, from a support to a sheet to be printed, which can be made of plain paper.

 In known devices of this kind, it is necessary to make a choice of compromise between several qualities, including the resolution of the printing, and its speed, in particular. This applies when printing in black and white. When printing in color (two or more inks), the compromise is of course more delicate, since the overall resolution and speed result from the resolution and the speed of printing on each color, multiplied by the number of colors .

This complication already occurs if the colors are printed adjacent (without overlapping). It is much larger if the colors have to be mixed by layering.

 The present invention provides a new arrangement which significantly improves the situation.

 The device proposed for thermal transfer printing comprises - a thermal head which defines a line of substantially punctual, selectively excitable heating elements - a sheet to be printed which extends transversely to the thermal head, - a ribbon carrying at least minus a printing pigment, placed between the thermal head and the sheet to be printed, the pigment being capable of passing over the sheet during the excitation of one or more of the heating elements, in locations corresponding to those of the one or more selectively excited heating elements, and - an opposing pressing member capable of maintaining a selected pressure between the paper, the ribbon and the head.

 According to an important characteristic of the invention, the ribbon runs longitudinally relative to the thermal head, according to a drive. Goes step by step, and there is provision for a relaxation of the pressure exerted by the opposing pressing member during the ribbon drive. This achieves a good resolution-speed compromise.

 According to a variant of the invention, the strip has a slight axis inclined on the line of swelling elements of the thermal head.

 Very advantageously, the device comprises means suitable for moving the strip over a plurality of different transverse positions relative to the thermal head.

 As a rule, the ribbon has several areas carrying pigments of different colors, although black and white printing may also be provided.

 This arrangement allows a large number of different colors, which can be deposited in any desired location on the document to be printed. It also makes it possible to obtain secondary colors, by mixing primary colors.

 Preferably, the zones of different colors are parallel colored bands aligned along the longitudinal axis of the ribbon.

 As will be seen below, the invention also offers the possibility of printing colors with different brightness.

 Other characteristics and advantages of the invention will appear on reading the detailed description which follows, given with reference to the appended drawings, given to illustrate without limitation a preferred embodiment of the present invention, and in which - Figure 1 is a schematic perspective view in principle of the mechanical part of a printing device according to the invention; - Figure 2 very schematically illustrates a ribbon for the implementation of the present invention - Figure 3 schematically illustrates a print head usable for the implementation of the present invention - Figure 4 illustrates a sorting printing mode -chrome using the ribbon of FIG. 2 - FIG. 5 illustrates the printing which results on paper from the configurations illustrated in FIG. 4; and - Figure 6 illustrates the block diagram of the electrical circuit associated with the mechanics of the printing device.

 In FIG. 1, we recognize at 10 a thermal head, which defines a line of substantially punctual heating elements, selectively excitable. The thermal head is here schematized in the form of a thin strip, in order to reveal the other parts of the drawing, and its attachment to the frame is also schematic. In practice, this is a slightly larger device.

 We also distinguish in FIG. 1 a sheet to be printed, denoted 20, which extends transversely to the thermal head 10, to pass from a supply roll 20 to a take-up roll 23, or else to a device for cutting paper ( not shown). Stepper motors 20, respectively denoted 22 and 21, are associated with debtor roller 20 and with receiver roller 23 respectively. In the case of a cutting device, the stepper motor 21 will be replaced by an electromagnet or a similar organ.

 A ribbon 30 carrying at least one printing pigment is placed between the thermal sheet 10 and the sheet to be printed 20. The pigment is capable of passing over the sheet, during the excitation of one or more of the elements heating elements, in locations corresponding to those of the heating element or elements which are selectively excited. Again, the ribbon starts from a supply roller 32, to go to a take-up roller 31, which produces the displacement of the ribbon under the effect of a stepping motor 34. Of course, more sophisticated drive may be necessary in certain cases. The ribbon is held between the thermal head and the sheet to be printed by a guide device 35, which is integral with a support device 38, the position of which is vertically adjustable under the effect of a step motor. step 36. The vertical adjustment can, for example, take the form of a toothed wheel 37 controlled by the stepping motor 36 and actuating a rack 38 which lifts the mobile equipment 35. Furthermore, provision is advantageously made for a sensor for longitudinal displacement of the ribbon, not shown, and capable of indicating the longitudinal displacement of this ribbon.

 The assembly is completed by an opposing pressing member, here consisting of a roller 40, capable of maintaining a selected pressure between the paper 20, the tape 30, and the thermal pad 10. This pressing member is advantageously actuated in rotation by a stepper motor 41 which makes it possible to precisely define the movement of the paper from one line to another. Finally, an electromagnet 45 makes it possible to achieve pressure by the roller 40 on the paper-tape-head assembly, or on the contrary to release this pressure.

 According to an important aspect of the present invention, the strip 30 runs longitudinally relative to the thermal head, with a stepping drive, defined here by the motor 34, or by a drive with a roller and capstan which would then be interposed directly on the ribbon 30 in the linear part of its path. And there is provision for a relaxation of the pressure exerted by the opposing presser member 40, here in the form of a de-excitation of the electromagnet 45, when the ribbon is woven.

 According to a variant of the invention, which is illustrated in FIG. 4, the ribbon has a longitudinal axis slightly inclined on the line of heating elements of the thermal head 10. This allows very good use of the different strips of pigment of the ribbon, with an overlap, as shown in Figure 4.

 Although the proposed device can also be used for black and white printing, as a rule, the ribbon has several areas of pigment of different colors. Thus, as shown in FIG. 2, the ribbon 30 comprises a yellow band 30J, a blue band 303, and a red band 30R. A large number of different printing colors can thus be obtained, which can be deposited side by side, or else superimposed, which allows mixing, as will be seen below.

 FIG. 3 illustrates a particular embodiment of the print head 10. In this embodiment, we see a strip of heating elements such as 101 to 124. The heating elements are rectangular with a large side twice as large. than the little one. They are distributed here in groups of eight elements, the first group being 101 to 108, the second 109 to 116, and the third 117 to 124. This arrangement allows a multiplexed control of the head, which will be described about of the first group, the connections of the other groups not being all represented.

 The heating zones 101 to 108 of the first group are connected by one of their end bands to the collector 150 of a transistor from which the emitter receives for example a negative power supply voltage.

the collector of the transistor will therefore constitute one of the multiplexed operation control terminals, acting for the entire group 101 to 108. On the other side, the electrode 101 is connected by a diode 131 to a connection 130, which receives also by a diode 132 the other terminal of the first electrode 10 9 of the second group, as well as by a diode 13 the other terminal of the first electrode 117 of the third group, and so on. Terminal 130, on the other side, therefore constitutes the other control terminal for each first electrode of each group. The second electrode 102 is likewise interconnected through a diode 141 to another control line 140, which receives by diodes 142 and 143 the other terminals of the other electrodes 110 and 118, and so on. Those skilled in the art immediately see that by controlling on the one hand the base electrode of the transistor 150 which takes the place of group control, then on the other hand each of the eight lines such as 130 and 140 which will control individually the different other terminals of the electrodes of each group, it is possible to control each desired writing element individually. Consequently, such a command makes it possible to carry out the printing group by group, therefore to spread over time the energy necessary for the printing.

 In practice, one can have thermal strips of this kind which include 1728 or 2048 points on a line making 200 to 210 mm.

 It can be seen that the above device makes it possible to apply the negative voltage present at the emitter of transistor 50 selectively to one or more of the electrodes placed in each group. According to another aspect of the invention, by varying the value of the positive voltage, the heating of each of the thermal elements 101 to 124 is modified, and by the same amount the amount of pigment transferred, therefore the brightness of the printing. in color, or in black and white.

 Although the thermal head includes a large number of printing elements, it will be assumed below that it comprises three groups of eight printing elements, to simplify the drawings. FIG. 4 illustrates such printing on three groups, the printing dots here being marked on the printing ribbon, while FIG. 5 illustrates the result obtained in the form of printing on the paper strip 20.

 On the part 30J of the ribbon 30 (FIG. 4), it is assumed that each of the printing elements of the three groups was excited when it was in front of the part 30J of the ribbon, which corresponds to yellow. After that, the ribbon is raised by the device 36, 37, 38, by a distance corresponding to the width of the strip of yellow, which now brings the strip of blue 30B opposite the print head. As shown in Figure 4, only one of the three thermal elements is excited in this situation, starting with the second element of the first group. Again, the ribbon 30 is made to rise with a colored bandwidth, and it is now the zone 30R pigmented in red which will be located opposite the print head. In this situation, a cell is excited thermal element on three, but starting with the third of the first group, so that each time we will excite the thermal element adjacent to the right of what has been done for the color blue. The result, illustrated in FIG. 5, consists of a yellow point, followed by a green point, then an orange point, and again a yellow point followed by a green point then by a orange dot, and so on, this pattern repeating over the entire length of the line.

 We can immediately see that the device according to the invention is capable of printing a line of dots selectively on each color, with the possibility of overprinting, and of modulating the brightness of each color (subject to individual control of the heating elements) . Of course, to print characters, these characters will be suitably defined by a series of dots in the horizontal direction, the dots then being printed simultaneously, then in the vertical direction, the dots being printed successively, after moving the paper.

 Reference will now be made to FIG. 6, which illustrates the block diagram of the electrical part of the device according to the invention.

The input of this electrical device is constituted by the input interface 60, which receives on the one hand data on the different colors print R, for red,
J, for yellow and B, for blue. It also includes clock signals for the intercommunication of this interface with the device located upstream; PE information which indicates that the upstream device is ready to send the RJB data, a PtR line, which indicates that the input interface 60 is ready to receive this data, as well as a last line marked "terminal ready," which indicates that the entire printing device is in a condition to perform printing. The inputs can be in the form of a scart socket, accompanied by an appropriate adaptation module.

 The device also comprises a memory capable of recording a line on each of the three basic colors red, yellow and blue, memory which will be filled from the data arriving at the input interface 60, under the control of a time base 62, as well as a processing and decision device 63, advantageously articulated around a microprocessor. For this purpose, communication buses connect the device 63 to the input interface, and to the time base 62, the latter being in turn connected by a line of the same kind to the memory 61. and decision 63 is also read back to a motor and sensor interface 65, as well as to a signaling device 66. 7) On its side, the memory 61 is connected to the print head 10, which also receives print control information emanating from the time base 62, directly, as well as via a print control circuit 64, which takes account of the multiplexed print structure already described with reference to the figure 3.

 Finally, there is provided a device 67 capable of supplying the assembly from the sector.

Inside the printing device are provided various sensors, one indicating that the cover of the apparatus is closed, another indicating that the paper is present, and in the printing position, another indicating as well as the ribbon is ready to print; finally, one or more sensors indicate that the pressures of the various devices in contact are at correct values, in particular the pressure of the roller 40 on the device constituted by the paper, the printing ribbon and the strip of thermal elements. These sensors are not shown in Figure 1 to simplify the drawing.

The information emanating from these various sensors arrives at the interface 65, and is suitably used by the circuit 63 2 in particular for preparing the PàR signals as well as "terminal ready", as well as for the control under good conditions of the impression itself.

 The interface 65 also controls various devices, including the actuation of the pressure roller 40 by means of its electromagnet 45, the step-up and / or step-down of the ribbon under the effect of the motor 36, the advance of the paper under the effect of the motor 41 which collects the pressure roller 40, and possibly of the motors 21 and 22. The interface 65 also controls the advance of the ribbon under the effect of the motor 34, or else of the capstan already mentioned.

 Finally, there is preferably provided an electromagnet capable of ensuring the cutting of the paper when the printing of a sheet is finished, and that it is desired that the sheets are delivered individually.

 Returning to FIG. 4, it can be seen that, with an inclined arrangement of the ribbon, it is possible to make a staggered selection of the printing areas on the ribbon, so as to avoid having to unroll each time times a length of ribbon equal to the length of the print line. Of course, the staggered printing of FIG. 4 is doubled by the use of the ribbon twice in each position, so as to make the most of the entire available width of the ribbon. In the case where the ribbon is straight, the ribbon will be used several times in the same position, until the height of the pigments available on each printing strip has been completely used, such as 30J, 30B or 30R.

 The device which has just been described can operate with plain paper. The printing ribbon advantageously consists of a sheet of mylar on which are deposited three, or possibly four, color bands (black being added).

 As previously indicated, we obtain not only the possibility of having several printing colors to choose from, but even of superimposing these, with excellent definition, since only the ribbon will move vertically, and this with excellent mechanical precision. Furthermore, as we saw above, by modulating the power applied to each of the thermal elements of the print head, it is possible to vary the elementary dimension of the transferred spot, and thus to obtain a variation of brightness for each of the different colors.

 The device described makes it possible not only to produce a very efficient multi-color printing with a mixture of colors, but also to produce a very fast black and white printing.

 Of course, the present invention is not limited to the embodiment described and extends to all variants in accordance with its spirit.

Claims (5)

 1. A thermal transfer printing device of the type comprising - a thermal head (10) which defines a line of elements  heaters noticeably punctual, excitable selective  ment, - a printing sheet (20) which extends transversely  at the thermal head, a ribbon (30) carrying at least one printing pigment,  placed between the thermal head and the sheet to be printed,  the pigment being capable of passing over the sheet  when one or more of the elements are excited  heated, in locations corresponding to those of  or selectively excited heating elements, and - an opposing pressing member (40) capable of being held  hold a selected pressure between paper, ribbon and  the head, characterized in that the strip (30) runs longitudinally relative to the thermal head (10), according to a step-by-step drive, and that there is provided a relaxation (45) of the pressure exerted by the Antagonistic pressing member during the ribbon drive.  2. Device according to claim 1, characterized in that the strip (30) is of axis slightly inclined on the line of heating elements of the thermal head.  3. Device according to one of claims I and 2, characterized in that it comprises means (35 to 38) of moving the ribbon on a plurality of different transverse positions relative to the thermal head.  4. Device according to one of claims I to 3, characterized in that the ribbon (30) comprises several areas carrying pigments of different colors.  5. Device according to claim 4, characterized in that the zones of different colors (30J, 30B, 30R) are parallel bands of color aligned along the longitudinal axis of the ribbon.