The present invention relates to a thermal marking printer and, more particularly, to an improved method for replenishing marking material on a donor ribbon utilized in such a printer.
Thermal printers have found increasing use in a variety of printing applications such as facsimile, printer-plotters and computer output printers. As office automation increases, low cost thermal printers appear as prime candidates for communicating terminals to provide office-quality, hard-copy outputs. The main advantages of such printers are reliability, quietness, clean operation, compactness, speed and low cost.
Thermal printers fall into two broad functional categories: direct and transfer. In the direct system, a paper having a thermally sensitive coating (either wax or an organic metal compound) is selectively heated causing color changes in the coating. This type of system has not found wide acceptance due to the cost of the coating and the unpleasant feel and appearance of the coating materials.
In the transfer type of printer a donor ribbon loaded with a marking material, typically a heat-sensitive ink, is transported intermediate a thermal print head and a plain paper recording sheet. The print head is electrically activated to selectively apply heat to the donor sheet causing melting and transfer of portions of the marking material onto the paper in an image configuration. This system does not have the disadvantages associated with the direct transfer papers but does have additional problems which have hitherto not been completely resolved. One problem has been the replenishment of the marking material on the donor ribbon in an efficient manner.
One prior art technique is disclosed in U.S. Pat. No. 3,719,261. As shown in FIG. 5, an endless tape 20 coated with a conductive ink, passes between a printing head 40 and a recording paper 51. Printing head 40 is energized and produces electrical currents within the ink layer on tape 20 causing localized heating and transfer of the ink to the paper. The ink is continually replenished on tape 20 by passing the tape through an ink reservoir 30 continually kept in a molten state by heating resistors 32. A similar reinking method is disclosed in U.S. Pat. No. 4,268,368. The main disadvantage to this type of marking renewal is the requirement to continually maintain the ink in heated form. The energy requirements add considerably to the cost of such a system.
A variation of this type of system which is subject to the same disadvantages is disclosed in Japanese Publication 49-26245. In this system, as shown in FIG. 2, an endless ink ribbon 1 passes between heat hammer 3 and recording paper 10. The heat hammers are energized to selectively heat the back of ribbon 1 causing localized melting and transfer of the ink layers onto paper 10. Following the print operation, the ink film passes through a reinking station comprising melting roller 4 and ink reservoir 6. Roller 4 applies heat through film 1 to reservoir 6 causing a portion of the ink wick to melt onto the surface of the ink film thereby replenishing the previously depleted portion. Roller 7 adjusts the thickness of the newly applied ink coating. This system is also energy inefficient in that it requires heating roller 4 to be constantly energized. In addition, the print operation is conducted in an intermittent fashion resulting in uneven distribution of the ink at the re-inking station.
The present invention is therefore directed to a more efficient donor replenishing system which does not require a continuously energized recoating station. More particularly, the invention relates to an apparatus for applying an ink coating to depleted areas of a ribbon used in a thermal transfer operation, the apparatus comprising:
an ink transfer ribbon connected between two feed rollers, PA1 means for advancing, during a print cycle, the ink-coated ribbon through a thermal printing station in a first direction, said ribbon being wound around a first feed roller acting as a take-up roller, PA1 an ink applicator positioned adjacent the ribbon path, said applicator out of contact with said ribbon during said print cycle, PA1 means for periodically reversing the direction of said ribbon during a non-print cycle so that the ribbon is rewound on said second roller, means for causing said ink applicator to come into contact with the ink-depleted ribbon surface during a time coincident with said reversed ribbon travel, whereby a uniform ink coating is applied to said surface, and PA1 means for reactuating said ribbon advancing means coincident with initiation of the next print cycle.