Incremental printing of symbolic information – Thermal marking apparatus or processes – Specific resistance recording element type
Patent
1995-12-07
1998-03-17
Hecker, Stuart N.
Incremental printing of symbolic information
Thermal marking apparatus or processes
Specific resistance recording element type
347182, 347209, B41J 234
Patent
active
057292752
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a thermal printhead and a drive IC therefor. The present invention also relates to a method for controlling the thermal printhead.
BACKGROUND ART
A thermal printhead used for a thermosensitive printing unit of a facsimile machine for example is designed such that a plurality of heating dots arranged in a line on an insulating head substrate are actuated for heating by drive IC arranged in an array. In the case of a so-called thick film thermal printhead, a linear heating resistor is formed on a head substrate by printing for example, whereas a common electrode having comb-like teeth is formed in parallel to the linear heating resistor with the comb-like teeth of the common electrode extending under the heating resistor. Heating dots are divisionally provided by portions of the heating resistor which are located between the comb-like teeth of the common electrode. Each heating dot is electrically connected to an end of an individual electrode. The other end of the individual electrode is electrically connected to a corresponding output pad of a relevant drive IC by wire bonding. The drive IC causes its output pads to be selectively turned on according to printing data. An electric current flows between the individual electrode corresponding to the turned-on output pad and the common electrode, thereby driving a desired heating dot for heating.
When printing on A4-size paper at a printing density of 200 dpi (8 dots in 1 mm) for example, 1728 heating dots are to be formed. At present, it is difficult to drive all of the heating dots by a single IC chip because of limitations in manufacturing semiconductors for example. Therefore, a plurality of IC chips are mounted on the head substrate, and each of the drive ICs is assigned to a predetermined number of heating dots for driving thereof. The respective drive ICs incorporate a shift register having a predetermined number of bits which corresponds to the number of output pads. The data-out pad of each drive IC and the data-in pad of another are connected in cascade, so that all shift registers are in substantial succession. When performing an A4-size printing, printing data comprise 1728 bits for one line. The printing data corresponding to the one line are serially fed to the data-in pad of a drive IC, which is located at an end. According to the 1728-bits printing data thus stored in the shift registers, the respective output pads are turned on or off in response to strobe signals fed to the respective drive ICs.
Basically, the number of output bits of a drive IC for a thermal printhead of this type is preferably a multiple of 8 bits for purpose of convenience in transmitting data between the drive ICs for example. In practice, the number of bits for a prior art drive IC is, for example, 32, 64, 96, or 128 bits which is simply a multiple of 32 bits. The number of bits for one chip has gradually increased due to the ability for high integration of ICs.
Usually, the 1728 bits are driven for printing according to the printing data for one line by time division but not simultaneously. This is because the amount of current passing through the common electrode becomes large if all of the 1728 dots are heated, so that the voltage drop along the common electrode circuit becomes remarkable to cause disadvantages, such as printing irregularities while requiring the use of a large capacity power source, which may increase the cost.
Therefore, after input of the 1728-bits printing data, strobe signals for controlling printing timings are fed, for example, with time difference respectively to those drive ICs assigned to the left half heating dots and to those drive ICs assigned to the right half heating dots.
For instance, twenty-seven 64-bits drive ICs are used to make an A4-wide 1728-dots thermal printhead. In this case, when printing is performed by 2-divisional control, the drive ICs must be divided, for example, into a left-side group having 13 drive ICs and a right-side group having 14 drive ICs, thereby providing
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patent: 5241326 (1993-08-01), Tagashira
patent: 5412405 (1995-05-01), Nureki et al.
patent: 5532723 (1996-07-01), Nagahata et al.
patent: 5543828 (1996-08-01), Minowa
Bednarek Michael D.
Hecker Stuart N.
Rohm & Co., Ltd.
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