Incremental printing of symbolic information – Thermal marking apparatus or processes – Specific resistance recording element type
Patent
1997-07-22
1999-09-28
Tran, Huan
Incremental printing of symbolic information
Thermal marking apparatus or processes
Specific resistance recording element type
B41J 2335
Patent
active
059596511
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a thermal printhead to print on printing paper by thermal recording or by thermal transfer recording, and to a method of adjusting a characteristic of the printhead.
BACKGROUND ART
The arrangement of a typical prior art thermal printhead 10 is shown in FIGS. 8-11. Reference numeral 11 indicates a head substrate. The substrate, which is made of an insulating material such as alumina-ceramic, has an upper surface provided with a heating element 12 and a plurality of drive ICs 13 for driving the heating element 12. When the thermal printhead is a thick film-type, the heating element 12 is made by a thick film printing method and configured into a narrow strip extending along a side edge of the substrate. FIG. 11 shows a common electrode 14 having comb-like teeth 14a extending under the heating element 12 and individual electrodes 15 arranged like comb-like teeth. Each individual electrode 15 extends toward the other side edge of the head substrate to be wire-bonded to an output pad of a drive IC 13. Each drive IC 13 includes power pads and signal pads which are wire-bonded to a predetermined wiring pattern formed on the substrate.
When a selected individual electrode 15 is turned on by a corresponding drive IC 13, an electric current is passed across a portion (shaded in FIG. 11) defined by a pair of comb-like teeth 14a of the common electrode 14 which sandwich the selected individual electrode therebetween, and heat is generated at the portion. In this way, the respective portions defined between the comb-like teeth 14a of the common electrode 14 function as heating dots 17. Each of the comb-like teeth 14a of the common electrode 14 is rendered to have a very small width. The teeth are spaced from each other by 125 .mu.m when a desired printing density is 200 dpi for example. This also applies to the individual electrodes 15. The minute wiring patterns including the common electrode and individual electrodes are formed by etching a conductive layer made of e.g. gold applied over the substrate.
To produce a thermal printhead having the above-mentioned printing density of 200 dpi and capable of printing on A4-size printing paper, 1728 heating dots 17 are arranged in line on the head substrate. When the drive IC 13 has 64-bit output pads, 27 drive ICs are mounted on the head substrate. The head substrate 11 is also provided with a thermistor 18 as a temperature sensor for monitoring the temperature of the heating element 12. Generally, the thermistor 18 is disposed at a longitudinally central portion of the head substrate 11 and between two adjacent drive ICs 13 for convenience of arrangement of the wiring pattern. The drive ICs and wire-bonded portions are enclosed by a protective coating 19 made of an epoxy resin for example.
A heat sink 20 is made of a material providing good heat dissipation such as aluminum. The head substrate 11 is attached to the heat sink 20 via an acrylic resin adhesive 21 for example.
The head substrate 11 is made of a fragile insulating plate. However, the strength of the thermal printhead as a whole is properly maintained by mounting the head substrate 11 on the heat sink 20 which has great mechanical strength. Further, such an arrangement improves the printing quality, since heat generated at the heating element 12 during operation of the printhead is conducted to the heat sink.
The printing operation by the above thermal printhead is performed for each line. For this, output pads corresponding to selected bits are turned on for a predetermined time, based on the 1728-bit printing data serially input in shift registers of the drive ICs 13.
For high-speed printing, a printing period (the interval between the starting point of a printing operation and the starting point of the next printing operation) should be shortened. Also, it is necessary to control driving power supplied to the heating element 13 by monitoring the temperature of the heating element, so that so-called trailing phenomenon and fainting phenomenon are avoided. Sp
REFERENCES:
patent: 5335002 (1994-08-01), Nagahata et al.
Nagahata Takaya
Nishi Koji
Rohm & Co., Ltd.
Tran Huan
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