Incremental printing of symbolic information – Thermal marking apparatus or processes – Having driving circuitry for recording means
Reexamination Certificate
1999-09-23
2002-02-12
Le, N. (Department: 2861)
Incremental printing of symbolic information
Thermal marking apparatus or processes
Having driving circuitry for recording means
Reexamination Certificate
active
06346960
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a thermal head driving integrated circuit (IC). More specifically, the present invention is directed to a thermal head driving circuit capable of performing a multi-color printing operation by setting plural sets of energizing time with respect to respective heating resistive elements.
2. Description of the Related Art
While various sorts of office automation (OA) appliances such as personal computers (PCs) and word processors have been popularized, printers using thermal heads are widely utilized as printers for printing out documents and images formed by these OA appliances.
When a thermal head is employed so as to print, for example, on an A4-sized paper in a line sequential manner, the thermal head is provided with 1,728 heating resistive elements arranged along one column. Then, while the entire heating resistive elements are subdivided into plural element blocks for every 64 heating resistive elements, the heating resistive elements belonging to each of these sub-divided blocks are controlled by an ON/OFF control mode (namely energizing/energizing-stop control mode) by employing thermal head driving integrated circuits for every block.
FIG. 5
is a circuit diagram for indicating a drive unit which may control the ON/OFF state of one heating resistive element in such a thermal head driving integrated circuit.
As indicated in this drawing, a drive unit of a heating resistive element
100
is provided with a drive transistor
200
and a 2-input AND gate circuit
300
. The output terminal of this AND gate circuit
300
is connected to the gate of the drive transistor
200
, the driver output terminal DO
1
of the AND gate circuit
300
is connected to the drain of this drive transistor
200
, and also, all of the source terminals are connected to the ground potential. One terminal of this heating resistive element
100
for printing one dot is connected to the driver output terminal DO
1
.
To one input terminal of the AND gate circuit
300
, a data signal DAT is supplied via a shift register (not shown) and a latch circuit (not shown either) with respect to each of the data bits, whereas a strobe signal STB commonly applied to the other AND gate circuits is supplied to the other input terminal of this AND gate circuit
300
.
In accordance with such a drive unit, when either data DAT “1” (H level) or data DAT “0” (L level) produced based upon print data is supplied from the latch circuit to the AND gate circuit
300
, the strobe signal STB is supplied at predetermined timing, so that the level of the signal becomes an H level. As a result, the level of the output signal from the AND gate circuit
300
to which the data DAT “1” has been supplied is brought into an H level, so that the drive transistor
200
is turned ON. While the strobe signal STB is supplied to this AND gate circuit
300
, the heating resistive element
100
is energized to perform a printing operation.
On the other hand, in the case that the AND gate circuit
300
is turned ON/OFF in the drive unit shown in
FIG. 5
, if a voltage signal having a sharp rising edge, or a voltage signal having a sharp falling edge is applied to the gate of the drive transistor
200
, then an overshoot, or an undershoot phenomenon appears in the drain voltage of this drive transistor
200
. As a result, the drive transistor
200
must have such a maximum rating voltage capable of withstanding this overshoot of the drain voltage. Similarly, such an overshoot or an undershoot phenomenon appears even in a bipolar IC, or a single channel MOS. After all, in any cases, the drive transistor
200
must have a maximum rating voltage capable of withstanding the overshoot voltage.
Under such a circumstance, in the conventional AND gate circuit
300
, the internal circuit thereof is constructed in such a manner that a channel length, also referred to as an L-length, of a circuit side to which the ON/OFF-controlling strobe signal STB is supplied is made long. Thus, since the rising operation of this AND gate circuit
300
is delayed, the overshoot voltage is suppressed.
On the other hand, another case may be conceived. That is, a printing operation of plural gradation levels may be carried out, or a printing operation of plural colors may be performed by employing a single heating resistive element
100
for printing out 1 dot. In other words, by employing an integer “n” different the energizing times for one heating resistive element
100
so that n different colors or gradations may be produced, color development density may be varied. Otherwise, when recording paper is used which may develop different colors in response to heating thermal energy amounts defined by energizing time, the multi-color printing operation is carried out.
FIG. 6
represents both a drive unit and the heating resistive element
100
, in which such a 2-color printing thermal head driving IC is realized by using the conventional 1-color printing thermal head driving IC.
FIG.
6
(
a
) shows a circuit in which two sets of AND gate circuits
300
r
and
300
b
are connected to the gate of the drive transistor
200
connected to a single heating resistive element
100
. Similar to the AND gate circuit
300
indicated in
FIG. 5
, both the AND gate circuits
300
r
and
300
b
are arranged as follows: to suppress an overshoot phenomenon, L-lengths of sides to which strobe signals STBr and STBb are supplied are made long.
As explained above, although the output signals of both the AND gate circuits
300
r
and
300
b
are directly supplied to the gate of the drive transistor
200
, since the rising edges of the strobe signals STBr and STBb are suppressed, the overshoot phenomenon can be suppressed.
FIG.
6
(
b
) shows another circuit in which a 2-input OR gate circuit is connected to the gate of the drive transistor
200
, and AND gate circuits
301
r
and
301
b
are connected to the respective input terminals of this 2-input OR gate circuit. In this case, L-lengths of the AND gate circuits
301
r
and
301
b
on both input sides are not made long, but normal AND gate circuits are used.
On the other hand, the OR gate circuit
310
connected to the gate of the drive transistor
200
is so arranged that L-lengths of both input sides thereof are made long. As a result, although both the signals outputted from the AND gate circuits
301
r
and
301
b
have sharp rising edges, the sharp rising edges are delayed by this OR gate circuit
310
in which the L-lengths of the input sides are made long. As a result, the transistor
200
is driven under such a condition that the overshoot phenomenon is suppressed.
In the drive unit having such a circuit arrangement, since the output time of the strobe signal STBr and the output time of the strobe signal STBb are separately set, the pulse width of the pulse signal applied to the gate of the drive transistor
200
may be adjusted. As a result, the time when the drive transistor
200
is turned ON, and also the heating time defined by the heating resistive element
100
is changed, so that the printing operations of the plural gradation and also the multi-color printing may be carried out.
For instance, when such a recording paper is used where a red color is developed by energizing the heating resistive element
100
for a short time period and also a black color is developed by energizing the heating resistive element
100
for a long time period, while the print data DATr for developing the red color is supplied, such a strobe signal STBr having a short pulse width is supplied. As a result, a red color contained in one line is printed out. On the other hand, while the print data DATb for developing the black color is supplied, such a strobe signal STBb having a long pulse width is supplied. As a consequence, a black color contained in the same one line is printed out.
On the other hand, when either an AND gate circuit or an OR gate circuit is provided, if this gate circuit is arranged in such a manner that an L-length is made long, then
Goto Sumitaka
Ishii Kazutoshi
Kanakubo Yoshihide
Kitta Tatsuya
Moya Yasuhiro
Adams & Wilks
Feggins K.
Le N.
Seiko Instruments Inc.
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