Thermal printing head

Details Thermal printing head Thermal printing head

1999-09-22

2001-04-24

Tran, Huan (Department: 2861)

Incremental printing of symbolic information

Thermal marking apparatus or processes

Specific resistance recording element type

Reexamination Certificate

active

06222574

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a thermal printhead for forming images on thermosensitive paper or on recording paper via a thermal-transfer ink ribbon.
BACKGROUND ART
As is well known, thermal printheads are used for forming intended images by selectively providing thermal energy to thermosensitive paper or a thermal-transfer ink ribbon. Generally, thermal printheads are divided mainly into thin film-type thermal printheads and thick film-type thermal printheads depending on methods of forming their heating resistors. As an example, a typical thick film-type thermal printhead will be described below.
FIG. 1
shows a conventionally used thick film-type thermal printhead
1
. As will be described later, a thermal printhead according to the present invention has a structure similar to that shown in
FIG. 1
except for its characteristic portions.
The thermal printhead
1
shown in
FIG. 1
includes a head substrate
11
formed of alumina ceramic and an additional substrate
20
formed of glass-fiber-reinforced epoxy resin. The head substrate
11
is provided with a linear heating resistor
12
, a plurality of drive ICs
13
, a common electrode
14
and a plurality of individual electrodes
15
. The heating resistor
12
extends longitudinally of the head substrate. The drive ICs
13
are arranged in a row extending in the longitudinal direction of the head substrate.
The common electrode
14
is integrally formed with a plurality of comb-teeth like projections
16
extending parallel to each other. Each projection
16
has a free end electrically connected to the heating resistor
12
. Each individual electrode
15
is linear and has two free ends. As shown in
FIG. 1
, the individual electrodes
15
and the plurality of projections
16
are alternately disposed. One free end of each individual electrode
15
is positioned between two adjacent projections
16
of the common electrode
14
to be electrically connected to the heating resistor
12
, whereas the other free end is connected, via a conductive wire
19
, to an output pad (not shown) of a relevant drive IC
13
. With such an arrangement, the heating resistor
12
includes a plurality of regions
18
each defined between two adjacent projections
16
. These regions function as heating dots under the control of the drive ICs
13
. Specifically, a current is supplied to the region
18
selected by the drive ICs
13
via the adjacent projection
16
and the individual electrode
15
. As a result, the selected region is heated up to function as a heating dot.
The additional substrate
20
is formed with a wiring pattern (partially shown) which is connected to input pads (not shown) of the drive ICs
13
via a plurality of conductive wires
19
a
. The additional substrate
20
is further provided with a connector
17
connected to the wiring pattern. The connector
17
is also connected to a cable (not shown) for transmitting signals supplied from outside. With the above arrangement, the external signals are transmitted via the wiring pattern to the drive ICs
13
. The drive ICs
13
will operate based on the thus transmitted signals.
Each of the drive ICs
13
incorporates a shift register which has a predetermined number of bits corresponding to the number of the output pads of the drive IC
13
. The drive ICs
13
have their data-out terminals connected in cascade to their data-interminals, so that the shift registers in the respective drive ICs
13
are connected to each other.
The thermal printhead having the above structure operates as follows. In order to perform printing for one line, printing data for the line need be input to the drive ICs
13
in advance. To this end, the printing data for the line are serially fed to the leftmost drive IC
13
shown in
FIG. 1
via the data-in terminal. Then, the printing data are successively fed to the shift registers of the respective drive ICs
13
connected in cascade to each other, and retained in them. In accordance with the retained printing data, the output pads of the drive ICs
13
are selectively actuated in synchronism with a strobe signal fed to each drive IC
13
. As a result, the heating dots
18
are selectively heated up for performing a predetermined printing operation.
Unfavorably, the thermal printhead
1
having the above arrangement has the following problems. Since the printing data for one line are serially fed to the drive ICs
13
, the printing operation for the line cannot be started until the input of the serial data is completed. This means that, in the above thermal printhead, it is impossible to improve the printing speed beyond a certain limit due to the serial data input. Further, when all the heating dots
18
are actuated simultaneously, an increased amount of current will pass through the common electrode
14
. Consequently, the voltage drop along the common electrode
14
is intensified, which leads to uneven printing results.
To deal with the above problems, the following measures have conventionally been taken. To begin with, printing data for one line are divided into a predetermined number of pieces, while the drive ICs
13
are also divided into the same number of groups. Then, each piece of the divided printing data is simultaneously fed to a corresponding one of the groups of the drive ICs
13
. Compared with the serial input described above, this method is advantageous in that the printing data can be fed to the drive ICs
13
more quickly, so that the printing speed is improved. In addition, by staggering the timing of driving the respective groups of drive ICs
13
, the current flowing through the common electrode
14
will be decreased, thereby reducing the voltage drop along the common electrode
14
.
However, the above method suffers the following problem. To feed the divided data to the respective groups of drive ICs
13
, a special wiring pattern designed for that particular purpose is needed. Therefore, it is necessary to prepare different kinds of wiring patterns, such as a wiring pattern suitable for the use of two-grouped printing data or a wiring pattern suitable for the use of three-grouped printing data, depending on the characteristics of a device in which the thermal printhead
1
is incorporated or on the need of a user. To individually manufacture such thermal printheads having different kinds of wiring patterns requires additional time and trouble, thereby leading to an increase in cost. Further, in order to actuate the drive ICs
13
group by group with time difference, a wiring pattern for supplying strobe signals needs to be additionally designed in accordance with the particular divisional manner.
Moreover, the design of the various wiring patterns mentioned above may need to be altered after they are produced. For instance, a user may wish to use a wiring pattern designed for three-grouped printing data in place of the originally used wiring pattern designed for two-grouped printing data. Conventionally, in such a situation, a thermal printhead incorporating a wiring pattern designed for three-grouped printing data may need to be purchased additionally, which is very inconvenient.
DISCLOSURE OF THE INVENTION
Therefore, it is an object of the present invention to provide a thermal printhead which is capable of solving the above problems.
In accordance with the present invention, there is provided a thermal printhead comprising:
drive ICs divided into a plurality of groups;
a plurality of main conductor wirings for transmitting signals to the respective groups of the drive ICs; and
a plurality of auxiliary conductor wirings arranged to accompany the main conductor wirings, respectively, for connecting the drive ICs in adjacent groups;
wherein each main conductor wiring and each auxiliary conductor wiring include a severable site for severing electrical conduction of said each main conductor wiring and said each auxiliary conductor wiring.
In the thermal printhead having the above arrangement, a selected one of the severable site of said each main conductor wiring and the severable site of the aux

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