JPH04189552A - Thermal head driving device - Google Patents

Abstract

PURPOSE:To improve quality of image to be outputted, by calculating a determined result of heat accumulation quantity of a thermal head and a correction factor and controlling power quantity for the thermal head. CONSTITUTION:A correction factor ROM 7 outputs correction factors corresponding to each dot in accordance with a correction data outputted from a correction line ROM 6. That is, when the number of printing line and the correction factor of each dot are obtained, a heat accumulation correction ROM 3 outputs power quantity corresponding to each printing line in accordance with gradation data of each dot and a reference temperature table. When the power quantity and heat accumulation correction factor of each dot at every line are outputted, a calculation of the power quantity and the correction factor of each dot is performed by a multiplier 9. Dependent on a correction power quantity to be outputted by the multiplier 9, energizing time is controlled an power supply to a thermal head 11 is controlled by a thermal head driving circuit 10.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a color printer that is capable of reproducing color images with gradation, and particularly relates to a color printer that is capable of reproducing color images with gradation. The present invention relates to a color printer based on a sublimation recording method (hereinafter referred to as a sublimation printer) that reproduces a color image with gradation by heating and sublimating a sublimable dye by applying electricity.

[Conventional example]

Conventionally, such dye-sublimation printers use i! ! Since the gradation reproducibility of the output image is controlled by controlling the amount of heat generated by the head, the quality of the reproduced image fluctuates under the influence of the surrounding thermal environment. One change state of the thermal head (hereinafter referred to as head temperature) has a large effect on the quality of the reproduced image, as shown in Figure 11 (print density characteristics when head temperature is used as a parameter). At the same time, the thermal energy generated by energization is transferred to the hennode body and accumulated, causing the head temperature to rise during printing (this is called heat storage in the head), and as the print density changes as the heat builds up in the head, printing A problem arises in that there is a difference in print density between the start and end of the process.

To address the above problem, in the conventional thermal head drive device shown in FIG. 8, when image data 1 of an arbitrary image is sent, it is stored in the line memory 4 by the history correction ROMI 2. The printing gradation is converted according to the thermal history of each dot (image data of the previous line), and heat storage correction R
The OM 13 controls the amount of current to be applied to the thermal by selecting the amount of current to be applied to the thermal according to the head temperature data detected from the thermistor 8 buried in the inside.

Here, the history correction ROM 12 has a table of input gradation and output gradation corresponding to the printing gradation of the previous line as shown in FIG. The gradation according to the head temperature and i! I have a table of electric pulse widths.

[Problem that the invention is trying to solve]

However, in the heat control of the conventional thermal head drive device, 1. The heat storage correction table in the heat storage correction ROM is switched in response to density changes due to heat storage in the head during printing, so that the table changes as shown in FIG. A density difference occurs at the switching portion, and this density difference deteriorates the quality of the output image.

2. Since the heat storage in the head changes depending on the print gradation or temperature, the number of times the heat storage correction table is switched within one screen changes and becomes inconsistent depending on the print output conditions, and when multicolor printing is performed. Since the number of times the table is switched is different for each color, mixing the colors increases the density difference due to the table switching in the output image.
Furthermore, image quality is degraded.

3. In the initial printing line immediately after printing starts, due to the thermal time constant inherent to the heating element of the thermal head, sufficient heat generation cannot be obtained, and the head heat generation temperature does not reach the temperature required to obtain the target density value. The target density is not reached instantaneously and rises with a gentle curve, so the target density cannot be obtained until several tens of lines after the start of printing.

4. Since the history correction table can only correct one line before each dot, it cannot correct the influence of the history one or more lines before.

This caused such problems and significantly degraded the quality of the output image.

[Means to solve the problem]

In order to solve the above-mentioned problem, in the present invention, the amount of sublimation of the sublimable dye is changed by controlling the amount of electricity applied to the thermal head formed by disposing heating resistors in a line shape, thereby producing an image with gradation. In a dye-sublimation printer that reproduces image data, a temperature detection means for detecting the temperature of the head is provided in the thermal head, a means for counting the number of printed lines from the start of printing, and two or more for holding image data for one line. a line memory, a means for generating correction data according to the image data and data held in the line memory, and a correction coefficient for generating a correction coefficient according to the correction data of the correction data generation means. The line memory includes at least two of the line memories, one for holding the image data of the previous line and the other for holding the correction data of the previous line. , is counted by the counting means of the previous printing line. A means is provided to determine the amount of heat stored in the thermal head according to the number of printed lines, and the amount of current applied to the first thermal head is calculated by calculating the judgment result of the first judgment means and the correction coefficient obtained by the first correction coefficient generating means. and a means for controlling.

[Effect]

According to the present invention, whereas in the past, changes in printing density due to the temperature state of the head or heat accumulation in the head were corrected by converting a table according to the head temperature using a heat accumulation correction ROM, In addition, the reference temperature table is switched with reference to the dot temperature, and the amount of electricity applied during printing is controlled by referring to the amount of heat stored in each dot and the number of printing lines.

In addition, control is performed by referring to the correction data of one line before and the print gradation of one line before.

[Example] Next, an example of the thermal head driving device of the present invention will be described based on the drawings.

FIG. 1 is a block diagram showing an embodiment of the thermal control circuit of the thermal head driving device of the present invention, and is a block diagram showing an embodiment of the thermal control circuit of the thermal head driving device of the present invention.
When a is sent, first, before printing, the head temperature is detected by the thermistor 8 embedded in the thermal head 11, and the head temperature data detected here is sent to the heat storage correction ROM 3. The temperature table is i! !
translated.

When the reference temperature table is selected as above, Y, M
, C, or Y, M, C, Bk color numbers are processed line by line.

At this time, the number of lines of the image data 1 that is sent is counted by the line counter 2, and the image data of the current line of interest is stored in the correction rank ROM.
Transferred to 6. Here, the correction rank ROM 6 stores the image data of the current line and the line memory A designated by reference numeral 4 in the figure.
The correction data of the current line is output for each dot according to the image data of the previous line stored in the image data of the previous line and the correction data of the previous line stored in the line memory of intermediate code 5, and transferred to the correction coefficient ROM 7. do. Here, correction coefficient ROM7
outputs a correction coefficient corresponding to each dot in accordance with the correction data output from the correction rank ROM 6.

When the number of print lines and the correction coefficient for each dot are determined as described above, the heat storage correction ROM 3 outputs the amount of current applied to each print line according to the gradation data of each dot and the reference temperature table.

As described above, when the energization amount and heat storage correction coefficient of each dot are output for each line, the multiplier 9 calculates the energization amount of each dot and the correction coefficient, and the multiplier 9 outputs the corrected energization amount. The energization time is controlled according to the amount, and the thermal head drive circuit 10 controls the energization of the thermal head 11.

Here, the base II temperature table has a print line correction table corresponding to each head temperature, as shown in No. 21E (a), and the correction range of the head temperature and the temperature at which the table is switched are determined from experimental values.

Here, the 31st is when the head temperature is varied,
It shows the heat storage characteristics at a given amount of current applied to each print line, and as shown by Ho, the heat storage characteristics of the thermal head change depending on the state of the inlet temperature Th of the printing start character.

The fourth part showed the heat storage characteristics at an arbitrary line a at this time.If the concentration change with respect to the temperature change ΔT at an arbitrary point in the main depression is ΔD, ΔD is calculated from the reference temperature table mentioned above. By defining the correction accuracy based on the preliminary reference temperature table, the temperature range △T for switching the reference temperature table is determined,
The number of reference temperature tables is necessarily determined, but normally there are 10 tables for every 4°C in the correction range of the henode temperature of 20 to 60°C.

The reference temperature table also has a print line correction table that controls the amount of current applied to each print gradation for each print line, as shown in Figure 2(b), and the print on each print screen is based on the main print line. The amount of energization is selected according to the correction table and printing control for the thermal head is performed, and
The number of lines for which the print line correction table is switched and the amount of current applied to each print line for each print gradation are determined from experimental values.

Here, Figure 5 shows the heat storage characteristics during printing on the IWJ surface when the printing current amount is used as a parameter at an arbitrary printing start temperature. The heat storage characteristics of the head vary depending on the amount of current applied during printing and the number of printing lines.

The 6th article showed the heat storage characteristics at an arbitrary pulse width This is the correction accuracy of the correction table, and by predetermining the correction accuracy by the print line correction table, the print line radius ΔL for switching the reference temperature table is determined, which naturally determines the number of reference temperature tables. Normally, a print line correction table is provided for each print line in the initial print line of the 20th to 40th line of printing start characters, and for lines after this line, the table is converted every 200 lines.

In addition, as shown in FIG. 7(a), the burial history correction rank ROM
The history correction correction table stored in 6 has a table for each gradation data of the previous line, and as shown in FIG. The correction coefficient ROM 7 has a table of correction ranks for gradations, and the correction coefficient ROM 7 has a table that outputs correction coefficients corresponding to the correction ranks output from the history correction rank ROM 6. The correction ranks and correction coefficients are the same as those for heat storage correction. is obtained from experimental values.

〔Effect of the invention〕

According to the present invention, since it is possible to perform correction for each print line using the print line correction table or the print line correction coefficient, the lack of density in the initial print line can be completely eliminated, and the For changes in density due to heat accumulation in the head during printing, it is possible to set the width of the print line that changes the table according to the increase in density, making it possible to make highly accurate corrections and to set the standard for changing the table. By setting the density to 0.01 (optical density), which exceeds the human visual recognition limit, it becomes possible to eliminate the difference in density at the table switching portion.

Furthermore, since the temperature reference table that serves as a reference is switched by referring to the head temperature at the start of printing, it is also possible to correct changes in heat storage characteristics due to changes in the inlet temperature at the start of printing.

Furthermore, since changes in the printing rate of image data are also corrected, it is possible to correct any heat accumulation during printing.

Further, by referring to the correction ranks stored in the line memory B and selecting a history correction coefficient, it is possible to correct the influence of thermal history of one or more lines before.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the thermal head driving device of the present invention, and FIG. FIG. 3 is an explanatory diagram showing heat storage characteristics during printing. FIG. 4 is an explanatory diagram showing changes in heat storage characteristics with respect to head temperature. FIG. 5 is an explanatory diagram showing heat storage characteristics during printing with respect to printing pulse width. An explanatory diagram showing the characteristics,
FIG. 6 is an explanatory diagram of the setting method of the print line table, the seventh indentation (al, (bl) is the history correction rank RO, respectively.
A history correction table for each gradation data and each correction rank of the previous line stored in M is shown, FIG. 8 shows a block diagram showing the configuration of a conventional printer, and FIG. FIG. 1O, an explanatory diagram showing a correction table, is 1! of a conventional thermal head drive device. FIG. 11 is an explanatory diagram showing the i-history correction table, FIG. 11 is an explanatory diagram showing changes in printing characteristics due to changes in head temperature, and FIG. 12 is an explanatory diagram showing problems with conventional heat storage correction. 1991 Image Data 299. Line counter 310. Heat storage correction ROM 401. Line memory A 300. Line memory B 9111 multiplier 11, thermal head and above Applicant Seiko Electronic Industries Co., Ltd. Agent Patent attorney Takayuki Hayashi Section 1 Figure 3 Figure 4 Figure 5 Figure 6 Figure 8 Figure 9 Figure 10 figure

Claims (1)

[Claims] In a sublimation printer that reproduces an image with gradation by changing the amount of sublimation of a sublimable dye by controlling the amount of current applied to a thermal head formed by disposing heating resistors in a line, A temperature detection means for detecting the temperature of the head is provided, a means for counting the number of printed lines from the start of printing, and two or more line memories for holding image data for one line, the image data and means for generating correction data in accordance with the data held in the line memory; and correction coefficient generation means for generating a correction coefficient in accordance with the correction data of the correction data generation means; , one that holds the image data of the previous line and one that holds the correction data of the previous line, and the head temperature detected by the temperature detection means and the print counted by the printing line counting means. A means is provided to determine the amount of heat stored in the thermal head based on the number of lines.
A thermal head driving device comprising: means for controlling the amount of current applied to the thermal head by calculating the determination result of the determination means and the correction coefficient obtained by the correction coefficient generation means.