JPH06143650A - Gray scale control type thermal printer - Google Patents

Abstract

PURPOSE:To obtain a high print quality recording image having no fluctuation in gray scale by providing means for correcting energy to be applied to each heating element for thermal effect of excess heat from an immediately preceding print line on a plurality of print lines onto a currently recording print line based on a conduction history. CONSTITUTION:A conduction history operating circuit 45 operates energy to be applied to each heating element R1-R512 in a currently recording print line based on a conduction timing data fed from a conduction timing buffer 20 and a conduction enable time fed from a strobe signal generating circuit 34 and then determines the extent of influence of excess heat onto each heating element R1-R512 at the time of recording next line based on the energy to be applied to each heating element R1-R512 in the currently recording print line. Gray scale data for each pixel stored in a line buffer 22 is then corrected for the influence of excess heat in preceding line and converted into a conduction timing data for each heating element R1-R512.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal printer capable of obtaining a desired density gradation by controlling the energy applied to a heating resistance element.

[0002]

2. Description of the Related Art In a thermal printer, the energy applied to each heating resistance element is an important parameter that determines the amount of heat generated by each heating resistance element, and thus determines the density of a recording pixel.

Therefore, conventionally, the applied energy during the unit energization time is controlled in accordance with the density gradation of the input to control the temperature of the heat generating resistance element.
The density gradation was controlled.

FIG. 6 shows a main structure of a conventional density gradation control type thermal printer.

The thermal head 110 includes a heating resistor 112 having heating resistors arranged in a line, and a shift register 11 having the same number of bit capacities as the heating resistors.
4 and a latch circuit 116 are provided.

In the line buffer 122, the density gradation data of each pixel of one printing line is input from the data input Din and stored. The density gradation data of each pixel of the line buffer 122 is the density-energization timing conversion circuit 136.
Thus, it is converted into energization timing data and stored in the energization timing buffer 120.

The energization timing buffer 120 continuously shifts the serial energization timing data corresponding to the heating resistance element a plurality of times in a constant cycle during the printing time of each printing line according to the count value of the energization number counter 138. Give to.

The gray scale data for each time is synchronized with the clock signal CK from the clock circuit 130, and the shift register 114
Then, it is sent to the heating resistor 112 via the latch circuit 116 at the timing of the latch signal LA from the latch signal generating circuit 132. This heating resistor 11
A power supply device 150 supplies a recording power supply voltage VR to the heating resistor element 2. Then,
These heating resistance elements selectively output the unit energization cycle ΔT according to the information content of the corresponding gradation bit.
Generates heat by energizing inside.

The unit energization cycle ΔT is defined by the latch signal LA. The strobe signal ST from the strobe signal generating circuit 134 in the unit energization cycle ΔT controls the energization enable time during which the current actually flows through the heating resistance element. The energization enable time can have different values for each unit energization cycle. The energization enable time of each unit energization cycle is the highest level of density for each pixel on one printing line, because energization is instructed in all unit energization cycles during the energization time of one printing line. It is set so as to rise to the temperature of the heating resistor element to which gradation is applied.

With the above structure, according to the density gradation data of each pixel on one printing line, the current is converted into the energization timing data which becomes the temperature of the heating resistor element for obtaining the target density gradation, and the current is energized to record. Done.

[0011]

However, in the density gradation control type thermal printer which controls the temperature of the heat generating resistance element in accordance with the density gradation of the input as described above, in each heat generating resistance element, the image currently being printed is printed. The energy applied by the energization of the immediately preceding printing line or a plurality of printing lines before the line is not completely cooled and is accumulated as residual heat.

As a result, in controlling the temperature of the heating resistor element in the printing line during recording, the temperature of the heating resistor element is adjusted to the target temperature of the heating resistor element in accordance with the input density gradation, depending on the amount of residual heat. There is a problem that variations occur, and desired density gradation cannot be accurately reproduced on the recording paper.

As a first measure against the above problem, there is a method of lengthening the recording time of one printing line and sufficiently cooling the heating resistance element for each printing line, but the recording time is very long and not practical. .

As a second measure against the above problems,
A thermal head temperature detection thermistor is attached to a thermal head on which a heating resistance element row (heating resistance element) in which multiple heating resistance elements are arranged is formed, and the amount of heat stored in the thermal head can be calculated from the thermal head temperature detected by the thermistor. There is a method of obtaining and correcting it, but only by detecting the heat storage amount of the entire thermal head, it is not possible to detect the difference in the amount of residual heat of each heating resistor element, and the distance between the heating resistor and the thermistor is large. Since the thermal head temperature detection accuracy is low due to the influence of the temperature gradient and heat transfer time, accurate correction could not be performed.

The present invention has been made in view of the above problems, and in each heating resistance element, the density level due to the effect of residual heat due to energization of the immediately preceding printing line or a plurality of printing lines before the currently printing printing line. An object of the present invention is to provide a density gradation control type thermal printer capable of obtaining a printed image with high print quality without variations in tonality.

[0016]

In order to achieve the above-mentioned object, the first density gradation control type thermal printer of the present invention comprises:
The energization history of the immediately preceding printing line or a plurality of printing lines is stored, and each heating resistance element is provided against the thermal influence of residual heat from the immediately preceding printing line or a plurality of printing lines from the energization history on the currently printing printing line. It is configured to include means for correcting the energy applied to the.

In the second density gradation control type thermal printer of the present invention, the current recording of the heating resistance element is caused by the thermal influence of the residual heat of the immediately preceding printing line or a plurality of printing lines before the currently printing printing line. A configuration is provided in which a means for correcting the variation in the temperature of the heating resistance element in the middle printing line to a target temperature of the heating resistance element is provided.

The third density gradation control type thermal printer of the present invention is the current recording of the heating resistance element due to the thermal influence of the residual heat of the immediately preceding printing line or a plurality of printing lines before the currently printing printing line. In order to obtain a desired density gradation with respect to the density gradation variation due to the temperature variation of the heating resistance element in the middle printing line, a means for correcting the energization time for applying energy to the heating resistance element is provided. .

In the fourth density gradation control type thermal printer of the present invention, as a means for calculating the energization history, application of each heating resistance element to each printing line in a plurality of printing lines before the currently printing printing line. The energy is multiplied by a coefficient that indicates the magnitude of the thermal effect of the applied energy on each printing line on the printing line currently being recorded, and the residual heat effect level of each printing line is calculated. A configuration is provided that includes means for adding up a plurality of printing lines and calculating the effect of residual heat on the plurality of printing lines.

[0020]

According to the first density gradation control type thermal printer of the present invention, in each heating resistance element, the influence of residual heat from the energization history on the immediately preceding printing line or a plurality of printing lines before the currently printing printing line. Is calculated, and the error of the applied energy in the printing line currently being recorded due to the influence of the residual heat is corrected.

In the second density gradation control type thermal printer of the present invention, in each heating resistance element, the influence of residual heat from the energization history of the immediately preceding printing line or a plurality of printing lines before the currently printing printing line. Is calculated, and the error of the heating resistor element temperature in the printing line currently being recorded due to the effect of residual heat with respect to the target heating element temperature is corrected.

In the third density gradation control type thermal printer of the present invention, due to the error of the heating resistance element temperature in the printing line currently being recorded due to the effect of residual heat, with respect to the target heating element temperature, on the recording paper for the target density gradation. Regarding the error of the density gradation of the pixel printed in, the effect of residual heat is calculated from the energization history of the immediately preceding printing line or a plurality of printing lines before the currently printing printing line in each heating resistor element. The error of the heating resistor element temperature with respect to the target heating element temperature is obtained, and the energization time is corrected so that the target density gradation can be obtained with the heating resistor element temperature including the error.

In the fourth density gradation control type thermal printer of the present invention, as a means for calculating the energization history, application of each heating resistance element to each printing line in a plurality of printing lines before the currently printing printing line. The energy is multiplied by a coefficient that indicates the magnitude of the thermal effect of the applied energy on each printing line on the printing line currently being recorded, and the residual heat effect level of each printing line is calculated. A means for calculating the influence of the residual heat of the plurality of printing lines by adding the plurality of printing lines is added, and the first to third density gradation control of the present invention is performed based on the influence of the residual heat of the plurality of printing lines. Type thermal printer correction.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the main structure of a density gradation control type thermal printer according to an embodiment of the present invention.

The thermal head 10 includes, for example, a heating resistor 12 formed by arranging 512 heating resistor elements R1 to R512 in a line, a shift register 14 having the same number (512) of bit capacities as those heating resistor elements, and And a latch circuit 16.

The energization timing buffer 20 has 512 heating resistance elements R1 to R51 during the printing time of each printing line.
The 512-bit serial energization timing data [CK P1j to CK P512j] corresponding to 2 is set to the count value (K) of the energization number counter 38 continuously for a plurality of times, for example, 256 times (K = 1 to 256). Therefore, it is given to the shift register 14.

Here, the nth bit CK Pnj has information as to whether or not the nth heating resistance element Rn should be energized during the unit energization cycle ΔT. That is, if "1", the energization is instructed, and if "0", the non-energization is instructed.

At the same time, the energization timing data [CK P1j to CK P512j] is transferred to the energization history calculation circuit 45.

When the gradation data of each time is loaded into the shift register 14 in synchronization with the clock signal CK from the clock circuit 30, each gradation bit CK P1j is next at the timing of the latch signal LA from the latch signal generating circuit 32. ~ CK
P512j is sent to the heating resistor 12 as an electric pulse via the latch circuit 16. A recording power supply voltage VR to be applied to the heating resistance elements R1 to R512 is applied to the heating resistor 12 from the power supply device 50. Then, these heating resistance elements R1 to R512 selectively generate electricity during the unit energization cycle ΔT in accordance with the information contents of the corresponding gradation bits CK P1j to CK P512j to generate heat.

The unit energization cycle ΔT is defined by the latch signal LA. Unit energization cycle ΔT
As shown in FIG. 2, the strobe signal ST from the strobe signal generating circuit 34 is composed of an energization enable time tE and a time tC during which the current actually flows through the heating resistance element. The energization enable time tE can have different values for each unit energization cycle. The energization enable time tE of each unit energization cycle is, for example, 64 steps (e.g., 64 steps) for each pixel on one printing line when energization is instructed in all the unit energization cycles during the energization time of one printing line. As shown in FIG. 4, up to the heating resistor element temperature (T = 63) that gives the highest level (G = 63) as shown in FIG. In addition, the heating resistor element temperature is set to rise.

The strobe signal ST is the thermal head 10
And the energization history calculation circuit 45. The energization history calculation circuit 45 stores the energization enable time tE.

The energization history calculation circuit 45 supplies the energization timing data [C
K P1j to CK P512j] and strobe signal generating circuit 34
The energy applied to each heating resistance element in the printing line currently being recorded is calculated from the energization enable time tE input from the above, and the energy applied to each heating resistance element in the printing line currently being recorded is used to record the next line. The degree of influence of residual heat on each heating element (EN (1, j) to EN (512, j)) is calculated.

Here, the degree of influence of residual heat (EN (1, j) to EN
The calculation of (512, j)) is performed, for example, by multiplying the energy applied to each heating resistance element in the printing line currently being recorded by a coefficient indicating the rate of remaining heat in the next printing line.

As a method of calculating the coefficient, the coefficient is experimentally obtained and one coefficient is prepared in advance on one screen. Further, it may be prepared for each printing line or each heating resistance element. Effect of residual heat (EN (1, j) ~ EN
(512, j)) is input to the concentration-energization timing conversion circuit 36.

In the line buffer 22, density gradation data (a1j to a512j) of each pixel of one printing line is input from the data input Din and stored. Line buffer 22
The density gradation data (a1j to a512j) of each pixel of
In the energization timing conversion circuit 36, the degree of influence of the residual heat of the previous line (EN (1, j-1) to EN (512, j-1)) is added and converted into energization timing data [CK P1j to CK P512j]. To be done.

Energization timing data [CK P1j to CK P
512j] is the density gradation data (a1j ~
a512j) to provide a density gradation (G = 0 to 63) that matches FIG.
In order to achieve the heating resistance element temperature (T = 0 to 63) shown in Fig. 5, energization ("
1 ") or non-conduction (" 0 ").
The energization timing data [CK P1j to CK P512j] is stored in the energization timing buffer 20.

As described above, the density gradation data (a1j to a1
512j) is converted into energization timing data [CK P1j to CK P512j] by correcting the effect of residual heat of the previous line, and each heating resistor element (R1 to R512) is converted to energization timing data [CK P1j to CK P512j]. Energize. This allows
Each heating resistor element (R1 to R512) has a density gradation (G = G = G) that matches the density gradation data (a1j to a512j) during the energization time.
0 to 63) is obtained to obtain the temperature of the heating resistor element (T = 0 to 63), and recording is performed on the recording paper with a desired density gradation.

[0038]

The present invention has the following effects by having the above-mentioned structure.

According to the thermal printer of the first aspect, the effect of residual heat is calculated from the energization history of the immediately preceding printing line or a plurality of printing lines before the currently printing printing line in each heating resistance element, and the residual heat is calculated. By correcting the error of the applied energy in the printing line currently being printed due to the influence of the effect, there is no variation in density gradation due to the effect of residual heat, and it is possible to reproduce the desired density gradation on the recording paper with high accuracy. Therefore, a recorded image with high print quality can be obtained.

According to the thermal printer of the second aspect, the effect of residual heat is calculated from the energization history of the immediately preceding printing line or a plurality of printing lines before the currently printing printing line in each heating resistance element, and the residual heat is calculated. By correcting the error of the heating resistance element temperature in the printing line currently being printed due to the effect of the target heating element temperature, there is no variation in density gradation due to the effect of residual heat, and the desired density gradation can be recorded with high accuracy. It is possible to reproduce on paper, and a recorded image of high print quality can be obtained.

According to the thermal printer of claim 3, the influence of the residual heat is calculated from the energization history of the immediately preceding printing line or a plurality of printing lines before the currently printing printing line in each heating resistance element, and Error of the heating resistance element temperature of the target heating element temperature is calculated, and the energization time is corrected so that the target density gradation can be obtained with the heating resistance element temperature including the error. It is possible to reproduce a desired density gradation on recording paper with high accuracy without variations in the image quality, and a recorded image of high print quality can be obtained.

According to the thermal printer of claim 4, the applied energy in each printing line is different from the applied energy in each printing line in the plurality of printing lines before the currently printing printing line of each heating resistance element. Multiply the coefficient indicating the magnitude of the thermal effect on the print line currently being recorded to obtain the residual heat effect level of each print line, and then add this residual heat effect level for multiple print lines to create multiple print lines. By calculating the effect of the residual heat of No. 1 and performing the correction by the thermal printer according to claim 1 based on the effect of the residual heat of the plurality of printing lines, there is no variation in the density gradation due to the effect of the residual heat. A desired density gradation can be reproduced on the recording paper with high accuracy, and a recorded image with high image quality can be obtained. .

[Brief description of drawings]

FIG. 1 is a block diagram showing a main circuit configuration of a density gradation control type thermal printer according to an embodiment of the present invention.

FIG. 2 is a diagram showing a timing of a unit energization cycle according to an embodiment.

FIG. 3 is a diagram showing a heating resistance element temperature-recording density characteristic by density gradation control.

FIG. 4 is a diagram showing a change in temperature of a heating resistance element during recording of one printing line.

FIG. 5 is a diagram showing the contents of an energization timing buffer according to the embodiment.

FIG. 6 is a block diagram showing a main circuit configuration of a density gradation control type thermal printer according to a conventional example.

[Explanation of symbols]

 10 Thermal Head 12 Heating Resistor 20 Energization Timing Buffer 36 Density-Energization Timing Conversion Circuit 38 Energization Counter 40 CPU

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location B41J 3/20 115 A 115 D

Claims (4)

[Claims] 1. A density gradation control type thermal printer for controlling the temperature of a heating resistance element of a recording head in accordance with a density gradation of an input image, immediately before a printing line of each heating resistance element currently being printed. Of the printing line or a plurality of printing lines is stored, and the heating resistance is set against the thermal influence of the residual heat from the immediately preceding printing line or the plurality of printing lines on the printing line currently being recorded from the energization history. A density gradation control type thermal printer comprising means for correcting the energy applied to the element. 2. A means for compensating for a target heating resistance element temperature with respect to variations in heating resistance element temperature in a printing line of the heating resistance element which is currently being recorded due to the thermal effect of the residual heat. The density gradation control type thermal printer according to claim 1. 3. A desired density gradation is obtained with respect to a density gradation variation caused by a temperature variation of the heating resistor element in a printing line of the heating resistor element which is currently being recorded due to a thermal effect of the residual heat. 2. The density gradation control type thermal printer according to claim 1, further comprising means for correcting an energization time for applying energy to the heating resistance element. 4. The energization history calculating means, with respect to the applied energy in each printing line in a plurality of printing lines before the currently printing printing line of each heating resistance element,
The residual heat influence of each printing line is obtained by multiplying the residual heat influence of each printing line by multiplying the coefficient indicating the magnitude of the thermal influence of the applied energy in each printing line on the printing line currently being recorded. 2. The density gradation control type thermal printer according to claim 1, further comprising means for adding and calculating the influence of the residual heat of the plurality of printing lines.