Two-sided thermal printing

ES 2 396 443 T3

DESCRIPTION

Two-sided thermal printing

Cross reference to related request

Priority benefit is claimed based on US Provisional Application No. 60 / 644,772 in the name of John L. Janning, filed on January 15, 2005.

Background

Direct thermal printing is a recognized means of printing silently without toner and ink. It is a relatively mature technology that has been available for more than forty years. Use by retailers for printing cash register receipts, postage labels, etc. it is widespread today.

An example of early single-sided direct thermal printing is thermal half-select printing as taught in US Patent Nos.^you 3,466,423 and 3,518,406 to John L. Janning. Such thermal half-selection printing was achieved by driving electrically resistive thermal printing elements on both sides of the thermal printing paper at the same time. Double-sided coincident electric current driving energy is additive to produce single-sided printing. The energy levels applied were such that, if applied only on one side, they were not sufficient to give rise to the impression. By applying sufficient heat to both sides of the media simultaneously, the applied energies would add up and one-sided printing could take place.

Duplex or double-sided direct thermal printing of receipts or transaction documents is described in US Patent Nos.^you 6,784,906 and 6,759,366. The printers were configured to allow printing on both sides of a thermal media moving along a feed path through the printer. In such printers, a direct thermal print head was arranged on each side of the media feed path. A print head was facing an opposing roller through the feed path from the print head.

In direct thermal printing, a print head selectively applies heat to a paper or other sheet support comprising a substrate with a thermally sensitive coating. The coating changes color when heat is applied, whereby the "print" is provided on the coated substrate. For duplex direct thermal printing, the sheet support substrate can be coated on both sides.

Duplex or double-sided direct thermal printing has been described to provide variable information on both sides of a paper receipt, for example, to save materials and provide flexibility in providing information to customers. The printing could be actuated electronically or by computer using a computer application program that directs double-sided printing.

Duplex or double-sided direct thermal printing as described in US Patent Nos.^you6,784,906 and 6,759,366 involve direct thermal print heads offset from each other while disposed on opposite sides of the media feed path for single-pass two-sided printing. Unless there is a print head offset, uneven print density can potentially occur. This is because thermal energy can be additive if it is applied simultaneously to both sides of the thermal printing paper when the print heads are directly opposite each other. EP-A-1321296 shows the preamble according to claim 1.

Summary

Two-sided direct thermal printing of a thermal imaging element having thermally sensitive coatings on opposite faces of a substrate is described, wherein the thermal imaging element is provided along a path of feed from a thermal printer having directly opposite print heads that are disposed on opposite faces of the feed path. Printing on both sides of the thermal imaging element is accomplished by applying variable energy thermal pulses from opposing print heads. Different levels of thermal pulse energy are applied to opposite faces of the thermal imaging element.

Brief description of the drawings

ES 2 396 443 T3

Figure 1a schematically shows opposing print heads for double-sided direct thermal printing in accordance with an exemplary variation of the invention.

Figure 1b shows a schematic detail of the print heads shown in Figure 1a.

Figure 2 shows exemplary energy level timing diagrams for thermal pulses applied to the front and back faces of a thermal imaging element for two-sided "half selection" printing. .

Figure 3 shows exemplary energy level timing diagrams for thermal pulses that are applied to the front face and back face of a thermal imaging element for a "partial selection" ("partial selection") print. -select ”) duplex.

Description

By way of example, various embodiments of the invention are described in the material that follows with reference to the accompanying drawings. Variations can be adopted.

Figure 1a of the drawings shows two thermal print heads 101a and 101b facing towards each other, separated by the thermal imaging element 104, for example, recording paper, which is provided along a path. feed 105. Figure 1b is a partial exploded view of Figure 1a. Resistive printing elements 103 are connected with electrical conductors 102. Print energies of variable energy thermal pulses that are supplied by the thermal print heads 101 a and 101 b can be added together to implement direct thermal printing on one or both sides of the thermal imaging element 104 in a printer.

Two-sided direct thermal printing of the front and back sides of the thermal imaging element 104 is achieved by the simultaneous use of the two adjacent print heads 101a and 101 b that are disposed on the opposite sides of the feed path. 105, for example, using thermal half-selection printing as taught in US Patent Nos.^you 3,466,423 and 3,518,406. The thermal print heads 101a and 101b are driven to provide two available energy levels of the thermal pulses, and printing of one side of the thermal imaging element 104 is achieved by using the thermal pulses of energy level. from one of the print heads 101a and 101b. Printing on both sides of thermal imaging element 104 is accomplished by the coincident use of lower energy additive thermal pulses from opposing print heads 101a and 101b.

The diagrams in Figure 2 show two-level energies that are used for direct thermal printing from the print heads 101 a and 101 b on both sides of the thermal recording paper 104. The level "half select" energies bottom are used for “at the same time - both sides” printing. The print energy of the thermal pulses from each of the print heads 101 a and 101 b is reduced to "half selection" levels when printing is to take place on both sides of the paper 104 at the same time. Otherwise, print density could lead to optical distraction in the print area if higher energy levels were used for simultaneous printing on both sides of, for example, paper 104. The higher thermal pulse energy levels shown in Figure 2 are used for printing on only one side of the paper 104.

In the print sequence - from print number 1 to print number 18 shown in figure 2, three prints (1-3) are made on the back side; followed by a single print (4) on the front face; followed by a print (5) on both sides; followed by no printing (6) on either side; followed by a print (7) on the back side; followed by a print (8) on both sides; followed by a print (9) on the front face; followed by two prints (10-11) on the back side; followed by two prints (12-13) on the front face; followed by a print (14) on both sides; followed by no printing on either side for two time periods (15-16); followed by a print (17) on the back side; and then followed by printing (18) on both sides of the double-sided thermal imaging element, eg, paper, 104.

Thermal partial selection printing is accomplished in a similar manner, except for the case where printing is to take place only on one side of the thermal recording paper 104 which has a thermal coating on both sides. In the present case, coincident energies are applied by the print heads 101 a and 101 b at uneven or uneven energy levels with most of the print energy being supplied to the print head on the desired print side of the paper 104 while a smaller amount of energy is supplied by the element on the opposite side of paper 104. The two energies add up and

ES 2 396 443 T3 printing takes place on the side of the paper 104 with the highest applied energy level. Figure 3 shows exemplary thermal pulse energies for partial select thermal printing.

In the embodiment shown in FIG. 3, three levels of thermal pulse energy are supplied from both the front and rear side print heads 101a and 101b. Printing cannot take place on either side of the paper 104 without the aid of both print heads 101a and 101b simultaneously, based on the selected energy levels chosen. For printing to take place only on the front face of the thermal imaging element 104, a "partial" thermal pulse of small energy level is generated by the rear face print head element at the same time as a thermal pulse Large energy level "partial" is generated by the front side print head element. For printing to take place on the back side only, a small energy level "partial" thermal pulse is generated by the front side print head at the same time as a large energy level "partial" thermal pulse is generated. by the back side print head. For printing on both the front side and the back side of the thermal recording paper 104, a "partial" thermal pulse of moderate energy level is generated by both the front and rear side print heads 101 a and 101 b.

During operation, the thermal pulses are generated by both the front and rear side print heads 101a and 101b. However, in the embodiment of Figure 3, none of the thermal pulses generated by the print heads 101 a and 101 b on the front face or the back face of the thermal paper 104 is chosen to be adequate enough to print a mark on one of the sides of the paper by itself.

In the print sequence - from print number 1 to print number 18 in FIG. 3, three prints (1-3) are made on the back face of thermal imaging element 104; followed by a single print (4) on the front face; followed by a print (5) on both sides; followed by no printing (6) on either side; followed by a print (7) on the back side; followed by a print (8) on both sides; followed by a print on the front face (9); followed by two prints (10-11) on the back side; followed by two prints (12-13) on the front face; followed by a print (14) on both sides; followed by no printing on either side for two time periods (15-16); followed by a print (17) on the back side; and then followed by printing (18) on both sides of the thermal imaging element 104.

Thermal imaging element 104 can be constructed in a variety of ways, in a known manner, generally including thermally sensitive coatings on opposite faces of a substrate. Thermal imaging element 104 is provided along a feed path 105 of a thermal printer having print heads 101 a and 101 b that are disposed on opposite faces of feed path 105. Printing on both sides of the thermal imaging element 104 is accomplished by applying thermal pulses of varying energy from each of the print heads 101 a and 101b. The energy level of a thermal pulse from one of the recording heads 101a and 101b can be made to vary by varying the magnitude of a voltage that produces the thermal pulse from the recording head. Both sides of the thermal imaging element 104 are printed by the coincident application of additive thermal pulses from each of the print heads 101 a and 101 b as shown in Figures 2 and 3. The printing on the Opposing faces of thermal imaging element 104 are controlled by the energy level of the thermal pulses.

The thermal pulses from each of the print heads 101 a and 101b may have at least two energy levels available where printing on one side of the thermal imaging element 104 is achieved through the use of pulses. higher energy level thermals from one of the print heads. Printing on both sides of the thermal imaging element 104 is achieved by the coincident use of lower energy level additive thermal pulses from the opposing print heads 101 a and 101b.

When the thermal pulses from each of the print heads 101a and 101b have at least three energy levels available, printing one side of the thermal imaging element can be achieved using the higher energy level thermal pulses. high from one of the print heads and the matching use of the lowest energy level thermal pulses from an opposite print head. Printing on only one side of the thermal imaging element 104 can be achieved by the coincident use of intermediate energy level thermal pulses from the opposing print heads 101a and 101b. Preferably, none of the three available energy levels would be selected to be suitable by itself for printing a mark on either side of the imaging element 104. The direct thermal printing on the opposite faces of the thermal imaging element 104 is controlled by the timing of the thermal pulses from the print heads 101a and 101b in the present example of double-sided direct thermal printing.

ES 2 396 443 T3

As taught in US Patent Nos.^you 3,466,423 and 3,518,406 in the name of John L. Janning, a printhead 101a or 101b may comprise a first group of parallel resistive heating elements that are disposed on one face of the feed path 105 and an opposite printhead 101a or 101b may comprise a second group of heating elements. parallel resistive heating that are arranged on the opposite face of the feed path 105, wherein the heating elements of the first group of heating elements are arranged perpendicular to the heating elements of the second group of heating elements. Therefore, a double-sided direct thermal printer is constructed in which each of the opposing print heads 101a and 101b comprises electrically resistive thermal printing elements in the form of orthogonal row and column conductors which are arranged on the opposing faces of feed path 105. In such a duplex direct thermal printer, printing takes place where the coincidentally excited orthogonal row and column conductors overlap. Alternative two-sided direct thermal printer constructions may be used, for example, as illustrated in Figures 1a and 1b, in which discrete electrically resistive print elements 103 on print heads 101 a and 101b may be adjacent to each other. to another and be arranged on the opposite faces of the feed path 105. Double-sided direct thermal printing on opposite faces of imaging element 104 is accomplished by driving coincident current from electrically resistive printing elements 103.

The preceding description above presents a number of specific embodiments or examples of a broader invention. The invention is also carried out in a wide variety of other alternative ways that have not been described here. Many other embodiments or variations of the invention can also be carried out within the scope of the following claims.