JP3180290B2 - Thermal head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head used in a printer or a facsimile machine.

[0002]

2. Description of the Related Art A thermal head of this type is configured to generate heat by controlling a plurality of dots of a heating resistor provided on an insulating substrate by a driving IC.
For example, in the case of a thick-film thermal head, a heating resistor is formed linearly on a glaze layer formed on an insulating substrate by a printing technique or the like. The dot division is performed by making the common electrode sneak into the heating resistor in a comb shape.

[0003] The heating resistor in which the dot division is made,
One end of the individual electrode is connected, and the other end of the individual electrode is connected to a bonding pad of the driving IC by wire bonding. As will be described later, the drive IC is turned on / off to energize each dot of the heating resistor to generate heat, thereby printing on thermal paper.

For example, A4 size and resolution of 203 dp
In the case of the thermal head i, a heating resistor divided into a total of 1728 dots is formed. In this thermal head, a plurality of drive ICs, for example, in the case of a 64-bit drive IC, 27 drive ICs are arranged in parallel with the heating resistor.

FIG. 1 shows an example of an internal circuit (hereinafter referred to as a drive circuit) in which the 27 drive ICs are integrated.
FIG. 1 is incorporated into the description of the present invention together with the conventional example. As shown in FIG. 1, the serial data SI is data of one line, and in the case of the A4 size, data of 1728 dots is transferred to the shift register 15 as a time-division signal in synchronization with a clock signal, and then latched by a latch signal. The signal is converted into a parallel signal and temporarily stored in the latch circuit 16.

The output side of the latch circuit 16 is connected to all the dots of the heating resistor via the gate circuit 17, respectively. The parallel signal temporarily stored in the latch circuit 16 opens and closes each gate circuit 17 depending on the presence or absence of a strobe signal input to each gate circuit, and energizes predetermined dots of the heating resistor. Perform printing. The strobe signal is input in units of drive ICs, and sets the number of time-division driving of the heating resistor dots for one line in units of drive ICs.

[0007]

The printing of 1728 dots per line is generally not performed simultaneously but in a time-division manner as described above. This is 1
When 728 dots are simultaneously heated, a large current flows through the common electrode wiring and the ground electrode wiring, so that the voltage drop of the common electrode and the ground electrode cannot be ignored, which causes printing unevenness and attaches a thermal head. This leads to an increase in power supply size and cost in the set.

In order to drive 1728 dots of data using, for example, a 64-bit drive IC, the drive IC
Is generally divided into 6 to 7 blocks, and a strobe signal corresponding to each block is divided and controlled in time series.

Hereinafter, the above problem will be described in detail with reference to the thermal head shown in FIG. As shown in FIG. 2, on a glaze layer (not shown) provided on a rectangular insulating substrate 1, a heating resistor 6 is provided on the first long side 2 side thereof in parallel with the first long side 2. A common electrode 7 is formed between the heating resistor 6 and the first long side 2 in parallel with the heating resistor 6. One end of the common electrode 7 is connected to the first long side 2
At the end of the heating resistor 6 along the first short side 4
An extension 7a extends in a direction perpendicular to the direction. Also shown
One end of the common electrode 7 and the ground electrode 11
Side is connected to the external connection terminal 10 and the other end side
Are electrically open, the common electrode 7 and the
The resistance of the ground electrode 11 should be kept away from the external connection terminal 10.
It becomes larger as

A driving IC 9 for driving each dot of the heating resistor 6 is mounted at an end of each individual electrode 8 extending from each dot of the heating resistor 6 to the second long side 3 side. Each of the individual electrodes 8 is connected. A signal wiring (not shown) is provided near the lower part of the driving IC 9, and the signal wiring extends in the same direction as the long side of the insulating substrate 1, and is externally connected to the first short side 4. It becomes the connection terminal 10. The ground electrode 11 commonly connected to each drive IC 9 is arranged in the same direction as the heating resistor 6 between the row of mounting the driving IC 9 and the heating resistor 6. A connection electrode 13 extends from the ground electrode 11 toward the second long side 3. Another ground electrode (not shown) to which the ground terminal of the drive IC is connected is connected to the connection electrode 13. Further, the mounting portion of the driving IC 9
The thermal head substrate 14 is sealed by the sealing resin 12.

In the thermal head, the line resistance of the common electrode 7 and the ground electrode 11 formed along the first long side 2 of the insulating substrate 1 is determined by the common electrode terminal of the external connection terminal 10. The value near the second short side 5 side is larger than the value near the first short side 4 side with respect to the ground electrode terminal.

In this case, even if the time division control is performed by the strobe signal, the voltage drop of the common electrode 7 and the ground electrode 11 decreases as the distance from the common electrode terminal of the external connection terminal 10 and the ground electrode terminal increases. It cannot be neglected, and this variation in voltage drop causes printing unevenness. In addition, if the size of each block divided in time series is reduced and the number of divisions of the strobe signal is increased, the printing unevenness is reduced, but the printing speed is reduced because the strobe signal is controlled in time series. Occurs.

The present invention has been made in view of the problems caused by the voltage drop of the thermal head, and proposes a thermal head which does not degrade print quality while maintaining a conventional print speed.

[0014]

According to the present invention, there is provided a thermal head including an insulating substrate, a heating resistor formed on the insulating substrate, and an external connection terminal. The number of dots in each divided block when the dot is divided into a predetermined number and the time division driving is performed is set to be smaller than the number of dots in the divided block closer to the external connection terminal than in the divided block closer to the external connection terminal. Further, the resistance value of each of the plurality of dots constituting the heating resistor is reduced continuously or discontinuously for each divided block as the distance from the external connection terminal along the heating resistor increases.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the thermal head shown in FIG. 2 and the internal circuit diagram shown in FIG. When the thermal head shown in FIG. 1 has, for example, an A4 size and a resolution of 203 dpi, a heating resistor 6 of 1,728 dots in total is formed, and 27 64-bit driving ICs are formed.
C is arranged in parallel with the heating resistor 6.

The 1728 serial data is converted into parallel data as described above, and then the strobe signal is controlled in time series for each divided block, so that the corresponding driving ICs are driven in a time-division manner. And printing is performed by causing each dot of a predetermined heating resistor array to generate heat.

As an example, the table shown in FIG.
When the heating resistor of 8 dots is divided into four blocks, the number of drive ICs in the block corresponding to each strobe signal and the number of dots of the heating resistor in the divided block are shown. This point is also shown in FIG. 1 as a division example of the present invention. Here, the strobe 1 controls the eight drive ICs of the divided block of the heating resistor 6 on the first short side 4 side, that is, the external connection terminal 10 side, to control the dot 1 to the dot 512.
Is supplied for 512 dots. The strobe 2 controls the eight drive ICs of the divided block to
To 1024 dots 1024.

The strobe 3 is composed of the divided blocks 6
The drive ICs are controlled so that the dots 1025 to 14
08 of 384 dots is energized. The strobe 4 controls the five driving ICs of the divided block on the side of the second short side 5 farthest from the external connection terminal 10 to control the dot 140
A current of 320 dots from 9 to 1728 is energized. Here, in order to minimize the increase in supply power required on the set side, the size of the block on the strobe 1 side is set to 8
The number of driving ICs was set.

As described above, if the number of dots of the heating resistor remote from the external connection terminal 10, that is, the number of drive ICs that perform simultaneous driving by the strobe signal is reduced, the line resistance of the common electrode 7 and the ground electrode 11 of the divided block becomes smaller. The variation in the voltage drop can be eliminated by reducing the number of drive ICs.

Here, the block division method of the present invention and the conventional block division method shown in the table of FIG. 5 will be compared with reference to FIG. As shown in FIGS. 1 and 5
The strobe 1 controls seven drive ICs of the divided block of the heating resistor 6 on the first short side 4 side, that is, on the side of the external connection terminal 10, to supply 448 dots from the dot 1 to the dot 448. . The strobe 2 controls the seven drive ICs of the divided block to supply electricity for 448 dots from the dots 449 to 896.

The strobe 3 is a divided block 6
By controlling the number of driving ICs from dot 897 to dot 128
0 is supplied for 384 dots. The strobe 4 controls five drive ICs of the divided block on the second short side 5 farthest from the external connection terminal 10 to supply 448 dots from dots 1281 to 1728. As described above, in the related art, since the dot is divided into blocks so that the same number of dots is supplied to both the side having a large voltage drop and the side having a small voltage drop, it is apparent that unevenness in the voltage drop causes printing unevenness.

FIG. 6 shows an example of the average line resistance per dot of the common electrode 7 and the ground electrode 11 as an average value for each strobe signal. Here, the assignment of each strobe signal is set in the same manner as the numbers shown in the tables of FIGS. 4 and 5, and the average line resistance value is common to the values shown in the tables of FIGS.

In the table of FIG. 7, the average line resistance values shown in the table of FIG. 6 are used, and each block for each strobe signal of the conventional dot division method for the strobe signal and the dot division method of the present invention is used. Shows the sum of the average line resistance values. Each average line resistance was calculated using the following equation. Average line resistance value (Ω) = (Rcom + Rgnd) × N, where Rcom: Average line resistance value of common electrode 7 in an arbitrary divided block (Ω) Rgnd: Average line resistance of ground electrode 11 in an arbitrary divided block Value (Ω) N: Total number of dots in an arbitrary divided block

As is apparent from the average line resistance values shown in the table of FIG. 7, the difference between the average line resistance values of the respective blocks is 268.8 Ω at the maximum in the prior art, whereas the difference in the present invention is 158.8 Ω.
It becomes 3.6Ω, which can be reduced by about 43%.

As described above, as the distance from the external connection terminal 10 increases, the division number of the heating resistor dot corresponding to the strobe signal is reduced, so that the line resistance of the common electrode wiring and the ground electrode wiring can be suppressed. , Voltage drop and power loss can be minimized.

In the above-described embodiment, the number of divisions of the heating resistor dots in the divided block is reduced for each strobe as the distance from the connection terminal increases, but another embodiment will be described below. In this other embodiment, the resistance values of the plurality of heating resistor dots forming the heating layer are continuously changed as the resistance value of the heating layer is further away from the external connection terminal, or discontinuously for each of the plurality of dots. To lower.

FIG. 3 shows, as an example of reducing the resistance value, a change of each resistance value of the heating resistor of a total of 1728 dots for each dot in comparison with the conventional example. Here, the first dot is on the first short side 4 side, that is, the external connection terminal 1
0 side heating resistor, 1728th dot is external connection terminal 1
It corresponds to the heating resistor on the second short side 5 side furthest from the 0 side.

In the table of FIG. 8, the resistance value of each dot of the heating resistor is shown as an average resistance value for each strobe signal unit, and the supply power of each dot of the heating resistor is calculated based on the following equation. The results are shown. Supply power (W) = R × I ² = R × V ² set / ｛N × (Rco
m + Rgnd) + R + Ric｝ ²

Here, R: average resistance value of each dot of the heating resistor row in an arbitrary divided block Vset: voltage applied to the heating resistor row, 24V N: total number of dots in each divided block Rcom: each Average line resistance value of common electrode in divided block Rgnd: Average line resistance value of ground electrode in each divided block Ric: Sum of ON resistance of drive IC and lead resistance of drive IC, 44Ω

As shown in FIG. 3, by trimming the heating resistor farther from the external connection terminal 10 so that the resistance value becomes lower, a voltage drop due to an increase in the line resistance of the common electrode 7 and the ground electrode 11 results. , Predetermined power is supplied to each divided block of each heating resistor 6.

In each of the above embodiments, the external connection terminal 10
Is described at one end of the insulating substrate, but the external connection terminals may be provided at any location including the center of the insulating substrate. Further, the bit configuration of the driving IC to be used, the number of divided blocks, and the number of dots in the divided blocks are also within the scope of the present invention and can be arbitrarily changed.

[0032]

According to the present invention, it is possible to minimize the influence of a voltage drop due to an increase in the line resistance of the common electrode and the ground electrode corresponding to the divided block remote from the external connection terminal, and to achieve a predetermined printing speed. And a thermal head capable of obtaining good print quality while maintaining the above-mentioned conditions.

[Brief description of the drawings]

FIG. 1 is an example of an internal circuit diagram of a driving IC used in the present invention.

FIG. 2 is a plan view of a main part of a thermal head used in the present invention.

FIG. 3 is a diagram showing a change in trimming of a dot resistance value of a heating resistor.

FIG. 4 is a diagram showing an example of division of the number of heating resistor dots in the present invention.

FIG. 5 is a diagram showing a conventional example of dividing the number of heating resistor dots.

FIG. 6 is a diagram showing average line resistance values per dot of a common electrode and a ground electrode.

FIG. 7 is a diagram showing an average line resistance per strobe signal of a common electrode and a ground electrode.

FIG. 8 is a diagram showing power supply per dot of a heating resistor for each divided block.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating substrate 6 Heating resistor 7 Common electrode 9 Drive IC 11 Ground electrode

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Norio Yamachi 1 at 455 Kosai Minami-cho, Takamatsu City, Kagawa Prefecture Inside Aoi Electronics Co., Ltd. (56) References JP-A-3-292160 (JP, A) JP-A-6 -71923 (JP, A) JP-A-6-47943 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41J 2/355 B41J 2/345

Claims (3)

(57) [Claims] An insulating substrate, a heating resistor formed on the insulating substrate, and an external connection disposed at an end of the insulating substrate.
Connection terminal , one end is connected to the external connection terminal, and the other end is electrically open.
In the thermal head having a common electrode and the ground electrode is released, the number of dots each divided block when the heating time by dividing a plurality of dots in a predetermined number constituting the resistance division driving,
A thermal head, wherein the number of dots in a divided block far from the external connection terminal is smaller than the number of dots in a divided block near the external connection terminal. 2. An insulating substrate, a heating resistor formed on the insulating substrate, and an external connection disposed at an end of the insulating substrate.
Connection terminal , one end is connected to the external connection terminal, and the other end is electrically open.
In a thermal head including a released common electrode and a ground electrode, a plurality of dots constituting the heating resistor are divided into a predetermined number.
A thermal head characterized in that the resistance value of each dot during time-division driving is continuously reduced as the distance from the external connection terminal increases. 3. An insulating substrate, a heating resistor formed on the insulating substrate, and an external connection disposed at an end of the insulating substrate.
Connection terminal , one end is connected to the external connection terminal, and the other end is electrically open.
In a thermal head including a released common electrode and a ground electrode, a plurality of dots constituting the heating resistor are divided into a predetermined number.
A thermal head characterized in that the resistance value of each dot at the time of time-division driving is discontinuously reduced for each of a plurality of dots as the distance from the external connection terminal increases.