JPH0647943A - Thermal print head - Google Patents

Abstract

PURPOSE:To prevent density irregularity in heat-sensitive recorded result, by a method wherein a conductive path joining between heating elements each and individual electrode is controlled and formed so that an electrical loss between the individual electrode and, a common electrode becomes identical with each other extending over the whole heating bodies. CONSTITUTION:A common electrode 12 running along one side of a longitudinal direction of a ceramic electrical insulating base and common electrode lines 13, 14 extending vertically in the longitudinal direction from both ends of the common electrode are formed. One side ends of heating elements 16a, b are joined to a common electrode 12 and the when ends are joined to a plurality of driving ICs 18a, b through individual electrode lines 17a, b. The individual electrode lines 17a, b are formed so that the outside individual electrode line 17a close to the common electrode line 13 becomes longer than the individual electrode line 17b which is near the center. Electrical losses of heating bodies each of a series circuit to be formed along with the individual electrode lines 17a, b including the common electrode line 13 and common electrode 12 are made identical with each other by compensating that in electric resistance of the common electrode 12, the same of the inside individual electrode line 17b becomes higher than the same of the outside individual electrode line 17a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a recording device such as a facsimile machine and a printing device such as a printer.
Regarding a thermal print head.

[0002]

2. Description of the Related Art Conventionally, a facsimile apparatus has been shown in FIG.
The illustrated thermal print head 1 is used for thermal recording. The thermal print head 1 is formed on an electrically insulating substrate having heat resistance such as ceramics. On the surface of this substrate, the common electrode 2 is formed along one side parallel to the main scanning line direction. Common electrode lines 3 and 4 extending in a direction perpendicular to the longitudinal direction of the common electrode are connected to both ends of the common electrode 2, respectively. A plurality of heating elements 6a and 6b are formed on the heater line 5, which is an imaginary line parallel to the longitudinal direction of the common electrode 2. Each heating element 6a, 6b
Has one end commonly connected to the common electrode 2 and the other end connected to the plurality of individual electrode lines 7a and 7b, respectively. The plurality of individual electrode lines 7a, 7b include a plurality of driving ICs 8a,
8b is connected. Each driving IC 8a, 8b includes a driving circuit for driving each heating element 6a, 6b. When the drive circuit is activated, the individual electrode lines 7a and 7b are driven so that current flows from the power source to the heating elements 6a and 6b through the common electrode lines 3 and 4. The driven heating elements 6a and 6b generate heat due to Joule heat, and perform thermal recording using thermal recording paper or thermal transfer ribbon.

[0003]

In the conventional thermal print head 1 as shown in FIG. 8, the individual electrode lines 7a and 7b are formed to have substantially the same length, width and thickness, and have an electric resistance value. Are designed to be approximately equal. Also, the width and thickness of the common electrode 2 are constant,
The resistance value of each heating element 6a, 6b is also designed to be constant. Therefore, due to the voltage drop in the common electrode 2,
A constant power is not supplied from end to end, but the power supplied to the heating element 6b near the center is reduced. In particular, in a printer or the like, unlike a facsimile machine or the like, the printing rate is high, and all the heat generating elements 6a and 6b are often in a state close to heat generation.
Then, the heat generation amount unevenness of the heat generating element 6b on the inner side tends to be conspicuous as the density unevenness of the recording result.

In order to solve such a problem, the following measures have been considered. The width of the common electrode 2 is increased to reduce the electric resistance and reduce the influence of the voltage drop. Not all the heating elements 6a and 6b are driven at the same time, but the driving current is reduced by the division driving. It is also used in combination with split drive to adjust the printing energy according to the position. The measures as described above cause the following problems and cannot be effective measures. That is, regarding the measures of
The widening of the width of the common electrode 2 causes the thermal print head 1 to be upsized, and the manufacturing cost of the thermal print head 1 is increased. In the divided printing, the time required to print one line becomes long, and the thermal recording cannot be speeded up.
The adjustment of the printing energy increases the cost of the control drive IC and the like, and increases the manufacturing cost of the thermal print head.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal print head which prevents an increase in manufacturing cost and a decrease in recording speed and which does not cause uneven density in recording results.

[0006]

According to the present invention, a plurality of heating elements are formed, one end of each heating element is connected to a common electrode, and the other end of each heating element is an individual electrode provided for each heating element. In the thermal print heads that are connected to each other, the conductive path that connects each heating element and the individual electrode has an electrical resistance value so that the power loss between the individual electrode and the common electrode is the same for all heating elements. Is adjusted and formed.

Further, according to the present invention, power is supplied from at least one end of the common electrode, and the electric resistance of the conductive path is formed so as to be a quadratic function along the arrangement direction of the heating elements. To do.

[0008]

According to the present invention, the thermal print head is provided with a plurality of heating elements. One end of each heating element is commonly connected to a common electrode. The other end of each heating element is connected to each of the plurality of individual electrodes. The conductive path connecting between each heating element and the individual electrode is such that the power loss between the individual electrode and the common electrode is equal for all heating elements.
The electric resistance value is adjusted and formed. Since the power loss between the individual electrode and the common electrode is equal, when each heating element is driven, an equal drive current flows between the individual electrode and the common electrode. Since the electric resistance values of the heating elements are formed to be substantially equal to each other, the difference in the amount of heat generated between the heating elements is small, and uneven density does not occur in the result of thermal recording. Since it is possible to prevent the occurrence of density unevenness only by adjusting the electric resistance of the conductive path connecting the heating element and the individual electrode, it is possible to prevent a decrease in recording speed and an increase in manufacturing cost.

Further, according to the present invention, the conductive path connecting the individual electrodes and the heating elements is formed so that the electric resistance value becomes a quadratic function along the arrangement direction of the heating elements. As a result, when the cross-sectional area of the common electrode is constant, the electric resistance value per unit length is constant, and the electric resistance value of the heating element is also constant, the heating elements arranged at regular intervals are driven equally. An electric current can be supplied.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an electrode arrangement of a thermal print head 11 according to an embodiment of the present invention. The common electrode 12 is formed along one side in the longitudinal direction of an electrically insulating substrate having heat resistance such as ceramics. From both ends of the common electrode, the common electrode lines 13 and 1 are extended so as to extend in the vertical direction.
4 are formed respectively. A plurality of heating elements 1 are provided on the heater line 15 represented by a virtual line parallel to the common electrode 12.
6a and 16b are formed. Each heating element 16a, 16b
Is formed by adhering a heat generation resistance layer such as tantalum nitride Ta ₃ N ₄ on a heat storage layer formed of band-shaped glaze glass or the like. Such heating elements 16a, 16b
Is, for example, 21 in a facsimile machine for A4 paper.
The width of cm is formed so that it can be decomposed into 1728 dots.
One end of each of the heating elements 16a and 16b formed with a high density of about 8 pieces per 1 mm is commonly connected to the common electrode 12. The other end of each heating element 16a, 16b has a plurality of driving ICs 18 via individual electrode lines 17a, 17b.
a, 18b. Individual electrode lines 17a, 17
b is formed such that the outer individual electrode line 17a close to the common electrode line 13 is longer than the central individual electrode line 17b. Each individual electrode line 17a, 1
If the material, width and thickness of 7b are the same, the electric resistance value of the outer individual electrode line 17a becomes larger than the electric resistance value of the inner individual electrode line 17b. The electric resistance value of the outer individual electrode line 17a is made larger than the electric resistance value of the inner individual electrode line 17b because the electric resistance of the common electrode 12 is larger than that of the outer individual electrode line 17a. This is to compensate for the larger size. In this way, the common electrode line 13
And the individual electrode lines 17a including the common electrode 12,
The power loss of the series circuit formed together with 17b can be equalized.

FIG. 2 shows the outer shape of the thermal print head 11 shown in FIG. The thermal print head 11 is
It is composed of a head substrate portion 20 on which the heater line 15 is formed and a printed substrate portion 21 for electrical connection to the recording apparatus. The printed circuit board portion 21 is also provided with a screw hole 22 for mounting.

FIGS. 4 and 5 show changes in characteristic values in the longitudinal direction of the thermal print head 11 of the embodiment shown in FIG. FIG. 3 shows changes in voltage drop in the common electrode 12 of the head substrate, and FIG. 4 shows individual electrode lines 17a,
17b shows the change in the resistance value, and FIG. 5 shows the change in the total wiring resistance. In FIG. 3, when electric power is supplied from the common electrode lines 13 and 14 on both sides of FIG. 1, the voltage drop due to the common electrode 12 has a parabolic shape in which the voltage drop in the central portion becomes maximum. When the electric resistances of the individual electrode lines 17a and 17b are changed according to a parabola as shown in FIG. 4 which is symmetrical to the curve shown in FIG. 3, the common electrode 12 and each individual electrode line 17a, 1
The power loss including 7b has a constant value as shown in FIG.

FIG. 6 shows a process in which the voltage drop of the common electrode 12 is compensated by the resistance of the individual electrode lines 17a and 17b. As shown in FIG. 6, the heater line 15 has a length L, is line-symmetric with respect to the center line passing through the center point A, and the current I is supplied from the common electrode lines 13 and 14 on both sides. Suppose. That is, the current I supplied from the point B is subjected to a voltage drop due to the resistance value R0 in the common electrode lines 13 and 14 and reaches the points C and C at both ends of the heater line 15. The electric resistance value of the common electrode 12 between the points C is formed to have a constant width and thickness so as to be r (Ω / mm) per unit length. Moreover, since it is line-symmetric with respect to the point A, only the left side portion of the length L / 2 shown in FIG. 6 need be considered. The electric resistance value of the common electrode 12 at a position separated from the left side point C by x is represented by the following equation (1).

[0014]

[Equation 1]

Here, R0 is the common electrode lines 13 and 14
Is the electrical resistance value of. Per unit length, heating element 16a,
If the current flowing through 16b has a constant value i, the value of the current I (x) flowing through the common electrode 12 at the position of x is given by the following equation (2).

[0016]

[Equation 2]

Since I (x) becomes 0 at the point A in the central portion, I (x) is expressed by the following equation 3 under such a boundary condition.

[0018]

[Equation 3]

Since the common electrode 12 has a resistance value of r per unit length, its voltage drop E (x) is expressed by the following equation (4).

[0020]

[Equation 4]

In order to pass a current of i per unit length from the common electrode 12 whose voltage changes as shown in the equation 4,
The equivalent resistance W (x) of the heating element and the individual electrode needs to be expressed by the following equation (5).

[0022]

[Equation 5]

Here, a and b represent constants. Equivalent resistance W
If (x) changes as a quadratic function as shown in FIG. 5, the current i per unit length becomes constant. In order to make the amount of heat generated by Joule heat constant with this constant current i, the electric resistance value of the heating element must also be constant. Therefore, W
The change in the electric resistance value required as (x) must be achieved by adjusting the electric resistance value of the individual electrode lines 17a and 17b.

FIG. 7 shows the shape of individual electrode lines 27a and 27b according to another embodiment of the present invention. It should be noted that
The outer individual electrode line 27a is thin, and the central individual electrode line 27b is thick. The electric resistance value can be adjusted by changing the widths of the individual electrode lines 27a and 27b in this manner. Of course, the thickness may be changed or the conductivity of the material forming the electrodes may be changed.

Further, although the common electrode lines 13 and 14 are provided on both ends of the common electrode 12 in the above embodiments, it goes without saying that the common electrode lines may be provided on only one side. Further, even when the positions where the common electrode lines 13 and 14 are connected are not both ends of the common electrode 12, the electric resistance value of the individual electrode lines may be adjusted according to the distance from each connection point. Of course.

[0026]

As described above, according to the present invention, the electric resistance value of the conductive path connecting the heating element and the individual electrode is changed,
By adjusting the power loss between the common electrode and the individual electrode to be equal, it is possible to drive a plurality of heating elements from the same power source with the same current and prevent uneven density in the thermal recording result. . Even if a plurality of heating elements are driven at the same time, density unevenness does not occur, so there is no need for divided driving, and heat-sensitive recording can be performed quickly. The configuration of the drive circuit and the like may be simple, and it is not necessary to make the electric resistance value of the common electrode particularly small. This can prevent an increase in the manufacturing cost of the thermal print head.

Further, according to the present invention, the electric resistance value of the conductive path connecting the heating element and the individual electrode becomes a quadratic function along the arrangement direction of the heating element, so that between the common electrode and the individual electrode. It is possible to equalize the electric power loss of the above, and it is possible to prevent the occurrence of density unevenness in the thermal recording.

[Brief description of drawings]

FIG. 1 is a plan view showing a schematic electrode arrangement according to an embodiment of the present invention.

FIG. 2 is a schematic plan view of a thermal print head 11 according to the embodiment shown in FIG.

FIG. 3 is a graph showing changes in voltage drop in the common electrode 12 of the embodiment shown in FIG.

FIG. 4 shows individual electrode lines 17a, 1 of the embodiment shown in FIG.
It is a graph which shows the change of the electrical resistance of 7b.

5 is a graph showing changes in power loss due to the common electrode 12 and individual electrode lines 17a and 17b of the embodiment shown in FIG.

6 is a diagram showing an equivalent resistance for calculating a voltage drop across the common electrode 12 of the embodiment shown in FIG.

FIG. 7 is a plan view showing a schematic electrode arrangement according to another embodiment of the present invention.

FIG. 8 is a plan view showing a schematic electrode arrangement of a conventional thermal printhead.

[Explanation of symbols]

 11 Thermal Print Head 12 Common Electrodes 13 and 14 Common Electrode Lines 15 Heater Lines 16a and 16b Heating Elements 17a, 17b, 27a, and 27b Individual Electrode Lines 18a and 18b Driving IC 20 Head Board Section 21 Printed Circuit Board Section

Claims (2)

[Claims] 1. A thermal print head in which a plurality of heating elements are formed, one end of each heating element is connected to a common electrode, and the other end of each heating element is connected to an individual electrode provided for each heating element. , The conductive path connecting each heating element and the individual electrode shall be formed with the electric resistance adjusted so that the power loss between the individual electrode and the common electrode is equal for all the heating elements. A thermal print head featuring. 2. The electric power is supplied from at least one end of the common electrode, and the electric resistance of the conductive path is formed so as to have a quadratic function along the arrangement direction of the heating elements. 1. The thermal print head according to 1.