JPH05293994A - Method for correction of recording density of thermal head - Google Patents

Abstract

PURPOSE:To execute correction of recording density of a thermal head very easily at a low cost by a method wherein recording quality is significantly raised by decreasing irregularity in density in a line direction. CONSTITUTION:A group 3 of recording elements in a line type thermal head 2 is divided into a plurality of blocks 3a, 3b, 3c, 3d in a line direction. A magnitude of supply electric power to the recording element for each block 3a..., for example, time for a current made to flow to the recording element is corrected so that variation of recording density among respective blocks 3a... is minimized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head recording density correction method suitable for use in facsimiles, printers and the like.

[0002]

2. Description of the Related Art A conventional line type thermal head is shown in FIG. The thermal head 20 shown in the figure includes a recording element group 21 in which a large number of recording elements are arranged in the line direction, and a negative wiring 22 is arranged along one side of the recording element group 21 along the recording element group 21. Together with recording element group 2
The wiring 23 on the positive side along the recording element group 21 on the other side of
To arrange. Both ends of each of the wirings 22 and 23 are connected to a recording power source 26 via connectors 24 and 25 provided on both ends of the thermal head 20. Therefore, printing is performed based on the amount of heat generation corresponding to the power supplied to each printing element.

[0003]

In the thermal head 20, the wiring resistance r due to the wirings 22 and 23 becomes a problem depending on the position of the recording element. That is, as shown in FIG.
When the paths indicated by arrows H1 and H2 are compared as the current flow path, the wiring resistance r is larger in H1 than in H2, and the change characteristic of the wiring resistance r seen from each recording element is as shown by Pr in the figure. Change. The heat generation amount of each recording element is 0.24 (V / (R + r)) ² · R · T [cal] (where V is the voltage of the recording power supply, R is the resistance of the recording element, r is the wiring resistance seen from the connector, Since T is obtained by the heat generation time), the heat generation amount of each recording element is as shown by Pj in FIG. 4, and as a result, the recording density in the line direction is thin in the center and dark near the connectors 24 and 25. There is a problem that unevenness occurs and the recording quality is greatly deteriorated.

The present invention solves the problems existing in the prior art as described above. The density unevenness in the line direction can be reduced and the recording quality can be remarkably improved, and at the same time, it is extremely easy and low cost. An object of the present invention is to provide a recording density correction method for a thermal head that can be implemented.

[0005]

According to a recording density correction method for a thermal head according to the present invention, a recording element group 3 in a line type thermal head 2 is divided into a plurality of blocks 3a, 3b, 3c and 3d in a line direction. , Each block 3a
It is characterized in that the magnitude of the electric power supplied to the recording element, that is, the time of the current flowing through the recording element is corrected for each block 3a so that the deviation of the recording density between the recording elements is minimized. ..

In this case, the time of the current flowing through the recording element is
It is desirable to perform correction in accordance with at least the number of heat-generating pixels in the recording signal so that the recording density is constant at each recording time. In this case, the heat generating pixel means a pixel for which a current flowing through the recording element is equal to or longer than a certain time. Further, the time of the current flowing through the recording element can be calculated by dividing or integrating variable coefficient values and variable values corresponding to the number of heat-generating pixels.

[0007]

According to the recording density correction method of the thermal head according to the present invention, first, the recording element group 3 of the thermal head 2 is
Is a plurality of blocks 3a, 3b, 3c, 3 in the line direction.
It is divided into d. Then, the time (power) of the current passed through the recording element is corrected for each block 3a ..., By this, the deviation of the recording density between each block 3a ... Is minimized. That is, since density unevenness is generated in the line direction of the thermal head 2 due to the difference in the wiring resistance r, the recording element group 3 of the thermal head 2 is divided into a plurality of blocks 3a ... And the current time in a predetermined block 3a. By making them different, the recording density is offset in the direction in which the density unevenness is reduced.

Further, if the time of the current flowing through the recording element is corrected in accordance with at least the number of heat-generating pixels in the recording signal, the decrease in the recording density due to the decrease in the current generated when the number of heat-generating pixels increases. This can be prevented, and the recording density becomes constant at each recording. At this time, if the current time is calculated by dividing or integrating the variable value corresponding to the changeable coefficient value and the number of heat-generating pixels, it can be corrected by a simplified circuit.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments according to the present invention will be described in detail with reference to the drawings.

First, the constructions of a thermal head and a correction system capable of implementing the recording density correction method according to the present invention will be described with reference to FIGS.

FIG. 1 shows a line type thermal head 2
Indicates. The thermal head 2 includes a recording element group 3, and the recording element group 3 is configured by arranging a large number of recording elements in the line direction. As shown in FIGS. 1 and 2, the recording element group 3 has a plurality of blocks 3, that is, four blocks 3 in the line direction.
a, 3b, 3c, 3d. The wiring 4 on the negative side is arranged along the recording element group 3 on one side of the recording element group 3, and on the other side of the recording element group 3 is formed on the positive side along the recording element group 3. Wiring 5 is arranged. Both ends of each wiring 4 and 5 are connectors 6 and 7 provided on both ends of the thermal head 2.
To the recording power source 8 which is a stabilized DC power source.

On the other hand, as shown in FIG. 2, the correction system includes four correction circuits 10a, 10b corresponding to each block 3a.
10c and 10d are provided, and each correction circuit 10a ... Is connected to each block 3a. One correction circuit 10a (10b, 10c, 10d is the same) is configured as shown in FIG.
2, coefficient circuit 13, frequency dividing circuit 14, heat generation signal generation circuit 1
5 is provided. Each correction circuit 10a is provided with a recording signal (gradation data) Sp, a high frequency clock signal Sc of several hundreds KHz to several hundreds MHz, and a changeable coefficient value Sk for setting the time of the current flowing through the recording element. It A recording signal Sp is applied to the thermal head 2.

Next, a method of correcting the recording density of the thermal head according to the present invention will be described with reference to FIGS.

First, at the time of recording, a recording signal S for one line
p is transferred to the thermal head 2. At this time, the recording signal Sp is also given to each of the correction circuits 10a at the same time, and the number of heat-generating pixels is counted by the counter circuit 11 in the correction circuit 10a (the same applies to 10b, 10c, and 10d). In this case, the heat generating pixel means a pixel in which the current passed through the recording element is a certain time or more. Therefore, the threshold value for the gradation data is preset in the counter circuit 11, and the gradation data exceeding the threshold value is counted as one heat generation pixel.

Further, the counter value Na obtained from the counter circuit 11 is given to the conversion circuit 12, converted into the corresponding conversion value Nb by the conversion table, and the conversion value N is obtained.
b is given to the coefficient circuit 13. In the coefficient circuit 13, a correction coefficient for minimizing the deviation of the recording density between the blocks 3a, that is, a correction coefficient K for correcting the time of the current flowing through the recording element is set for each block 3a. There is. Therefore, the coefficient circuit 13 outputs a correction value Nc = K · Nb which is a product of the conversion value Nb and the correction coefficient K, and the correction value Nc is given to the frequency dividing circuit 14. In the frequency dividing circuit 14, the high frequency clock signal Sc is frequency-divided by the correction value Nc, and the correction signal Ss (variable value) obtained from this is given to the heat generation signal generation circuit 15. The heat generation signal generation circuit 15 generates a heat generation signal So by dividing the correction signal Ss (variable value) by the coefficient value Sk, and the heat generation signal So is given to the block 3a.

As a result, the period of the heat generation signal So is set according to the number of heat generation pixels. For example, when the number is large, the period becomes long, and when the number is small, the period becomes short, and the period is corrected according to the correction coefficient K. It

That is, the recording density based on the wiring resistance r of the four blocks 3a, 3b, 3c and 3d in the thermal head 2 is Pj shown by a virtual line in FIG. 1 when not corrected.
Block 3a in which the connectors 6 and 7 are located
And the recording density of 3d becomes higher than the recording density of 3b and 3c. Therefore, the correction coefficient K in the coefficient circuit 13 is set for each block 3a ... As shown in FIG.
Particularly, the correction coefficient K in the blocks 3a and 3d is selected so that the period of the heat generation signal So becomes short, and each block 3
The deviation of the recording density between a ... is minimized. As a result, the densities of the blocks 3a and 3d are offset in the direction in which they become thinner overall. In the case of the embodiment, block 3
The correction coefficient K of b and 3c becomes "1". Further, the magnitude of the correction coefficient K is set for each block 3a ... However, for example, it may be fixedly set at the time of product shipment, or the value of the correction coefficient K can be reset at the time of maintenance. 13 may be configured to be changeable.

As a result, the recording density becomes Pc in the line direction of the thermal head 2 in FIG. 1, and the deviation before correction of the recording density between the blocks 3a to 3d is H.
a, where the corrected deviation is Hb, Ha> Hb, and the corrected deviation is significantly reduced, so that the density unevenness is significantly improved.

During recording, a current flows through each recording element in the thermal head 2 only during a period when the heat generation signal So is effective, heat is generated, and recording is performed on the recording paper at a density corresponding to the amount of electric power supplied. Be seen.

In such a recording density correction method, since the correction signal Ss (variable value) is divided by the changeable coefficient value Sk to generate the heat generation signal So, the capacity and configuration of the conversion table in the conversion circuit 12 are greatly increased. The density unevenness in the line direction is reduced by the simplified circuit configuration of the coefficient circuit 13 for each block, which is particularly suitable for application to a multi-tone printer or the like.

Although the embodiments have been described in detail above, the present invention is not limited to such embodiments. For example, the blocks of the recording element group can be divided into blocks of an arbitrary number other than four. In addition, the detailed configuration, method, and the like can be arbitrarily changed without departing from the scope of the present invention.

[0022]

As described above, according to the recording density correction method for the thermal head of the present invention, the recording element group in the line type thermal head is divided into a plurality of blocks in the line direction, and the deviation of the recording density between the blocks. Since the magnitude of the power supplied to the printing element is corrected for each block so as to minimize, the density unevenness in the line direction can be reduced and the printing quality can be dramatically improved, It has a remarkable effect that it can be implemented at low cost.

[Brief description of drawings]

FIG. 1 is an operation explanatory view of a recording density correction method according to the present invention,

FIG. 2 is a block circuit diagram of a correction system capable of implementing the same recording density correction method;

FIG. 3 is a block circuit diagram of a correction circuit in the correction system,

FIG. 4 is an operation explanatory view of a recording density correction method according to a conventional technique,

[Explanation of symbols]

 2 thermal head 3 recording element group 3a block 3b block 3c block 3d block

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mamoru Mizunokura 1463 Tsuruga Nishi Tsuruga-cho, Nagano City, Nagano Prefecture Nagano Japan Radio Co., Ltd.

Claims (5)

[Claims] 1. A printing element group in a line-type thermal head is divided into a plurality of blocks in the line direction, and power is supplied to the printing elements for each block so that a deviation of printing density between the blocks is minimized. A recording density correction method for a thermal head, which is characterized by correcting the size of 2. The recording density correction method for a thermal head according to claim 1, wherein the time of the current passed through the recording element is corrected. 3. The time for applying a current to the recording element is corrected according to at least the number of heat generating pixels in the recording signal so that the recording density is constant at each recording time. Recording density correction method for thermal heads. 4. The recording density correction method for a thermal head according to claim 3, wherein the heat generating pixel is a pixel for which a current passed through the recording element is a predetermined time or more. 5. The recording of the thermal head according to claim 3, wherein the time of the current flowing through the recording element is calculated by dividing or integrating a variable coefficient value and a variable value corresponding to the number of heat-generating pixels. Density correction method.