JPH0493266A - Thermal head driver - Google Patents

Abstract

PURPOSE:To prevent the deterioration of an image quality by a method wherein a temperature detection means for detecting a head temperature is provided in a thermal head, and an electric conduction amount to the thermal head is controlled in accordance with an input signal from the temperature detection means and the number of lines of printing dots from the start of printing. CONSTITUTION:The number of ON dots in one line is counted by a printing ratio counter 4, and the printing line number and a printing ratio are found. In accordance with gradation data of dots and a reference temperature table selected at the start of printing, a heat accumulation correction ROM 3 outputs a conduction amount for every printing line. A printing ratio correction ROM 5 outputs a printing ratio correction factor in accordance with a printing ratio per printing line. With the output of the conduction amount per dot and the printing ratio correction factor, a multiplier 7 operates the conduction amount per dot and the printing ratio correction factor. In accordance with a correction conduction amount outputted from the multiplier 7, a conduction time is set by a timer 8. In accordance with image data transmitted to a thermal head drive circuit 9, an electric conduction to a thermal head 10 is controlled.

Description

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 in particular, it relates to a color printer that is capable of reproducing color images with gradation. The present invention relates to a thermal head drive device in a color printer based on a sublimation recording method that reproduces a color image with gradation by sublimation.

[Prior Art] Conventionally, such a thermal head driving device controls the gradation reproducibility of an output image by controlling the amount of current applied to the thermal head, that is, the amount of heat generated by the head. The quality fluctuates depending on the surrounding environment, especially the temperature of the thermal head (hereinafter referred to as
The head temperature (referred to as head temperature) has a large effect on the quality of the reproduced image, as shown in Figure 10 (Printing 4 degree characteristic when temperature is used as a parameter). Due to the thermal energy generated, the head temperature during printing rises due to heat being transferred to the gutter body and accumulated, which increases the head's HP and tp), and the print density changes as the heat accumulates in the head, causing the start of printing. A problem arises in that there is a difference in print density between the time and the end.

To solve the above problem, in the conventional thermal head driving device shown in FIG. 8, when image data 1 of an arbitrary image is sent, the head temperature is detected by the thermistor 6 embedded in the thermal head. The temperature data of the helenoid 1' detected here is stored in the heat storage correction ROM 13 which has a table (heat storage correction table) of the amount of energization corresponding to each print gradation in an arbitrary head temperature range, as shown in FIG. The thermal correction table is switched according to the detected head temperature, and the amount of energization is selected according to the print gradation of the sent image data, thereby reducing the thermal output. The amount was poorly controlled.

[Problems to be Solved by the Invention] However, in the thermal 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 a change in density due to heat storage in the head during printing; 11th [! As shown in FIG. 1, a one-degree difference occurs at the table switching portion, and this one-degree difference deteriorates the quality of the output image.

(2) The number of times the heat accumulation correction table is switched within one screen varies depending on the print output conditions, as it changes depending on the heat accumulation, print gradation, or head temperature condition, and when multicolor printing is performed. In addition, the variation in table switching further causes image deterioration.

(3) In the first printing line immediately after printing starts, due to the retention constant of the color forming body of the thermal head, sufficient heat generation cannot be obtained, and the target value of 1 degree cannot be reached. stand up.

These problems caused a significant deterioration in the quality of the output images.

[Means for Solving the Problems] To solve the problems described above, the present invention provides a temperature detection means for detecting the temperature of the inside of the thermal head, and an input signal from the temperature detection means; The configuration is such that the amount of current applied to the thermal head is controlled in accordance with the number of lines of dots to be printed from the start of printing.

According to the present invention, the temperature state of the head or
The 74 degree print change due to heat storage in the head was corrected by converting the heat storage correction temperature stored in the heat storage correction ROM according to the head temperature. At the same time, the amount of current applied during printing is controlled by referring to the printing line.

〔Example〕

Next, an embodiment 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 head drive device of the present invention. When arbitrary image data is sent to the thermal head drive device of the present invention, Prior to printing, the head temperature is detected by a thermistor 6 embedded in the thermal head, and the head temperature data detected here is sent to the heat storage correction ROM 3 and a reference temperature table is selected.

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, in the sent image data, the number of lines from the start of printing is counted by the line counter 2, and the printing rate of the line, that is, the number of ON dots in one line is counted by the printing rate counter 4. .

When the number of printing lines and printing rate are determined as above, H
The thermal correction ROM 3 outputs the amount of current for each printing line according to the gradation data of each dot and the reference temperature selected at the start of printing, and also outputs the amount of current for each printing line.
M5 outputs a printing rate correction coefficient according to the printing rate of each printing line.

When the energization amount and printing rate correction coefficient of each dot are outputted for each line as described above, the multiplier 7 calculates the energization amount of each dot and the correction coefficient, and the multiplier 7 outputs the correction coefficient. The timer 8 sets the energization time according to the amount of energization, and the energization of the thermal head 10 is controlled in accordance with the image data sent to the thermal head drive device 9.

Here, the reference temperature table has a print line correction table according to each temperature as shown in FIG. 2 (al) for each head temperature, and a print line correction table according to each temperature, The range and temperature at which the table is switched are determined from experimental values.

Here, Fig. 3 shows the heat storage characteristics at arbitrary iJ1'gLI for each printing line when the head temperature is used as a parameter.As shown in this book, the track storage characteristics of the thermal head are Changes occur depending on the temperature Th over time.

FIG. 4 shows 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 this figure is ΔD, the said ΔD is the correction accuracy of the reference temperature table. By prescribing the correction accuracy based on the reference temperature table, the temperature width ΔT for switching the reference temperature table is determined, and the number of reference temperature tables is inevitably determined, but usually it is 20 to 60. It has 10 tables every 4 degrees Celsius in the head temperature correction range of degrees Celsius.

Also the group mentioned above! II! The temperature table has a print line correction table that controls the amount of energization for each print gradation for each print line as shown in Figure 2 (b), and printing within each print screen is performed according to the main print line correction table. The amount of energization is selected and printing control for the thermal head is performed, and the number of lines for switching the print line correction table and the amount of energization for each printing gradation for each print line are determined from experimental values.

Figure 5 shows the heat storage characteristics during printing of one screen when the amount of electricity per printing is used as a parameter at an arbitrary printing start temperature.As shown in this figure, The heat storage characteristics of the thermal head vary depending on the amount of current applied during printing and the number of printing lines.

Any iJ at this time! FIG. 6 shows the heat storage characteristics at the i-pulse width X. In this figure, ΔD is the density change with respect to the difference ΔL between the print lines at any point, and ΔD is the correction accuracy of the print line correction table. Then, by prescribing the correction accuracy according to the print line correction table, base 11! The width ΔL of the printing line for switching the temperature table is determined, and the number of the reference temperature tables is also determined, but normally, for the initial printing line of 20 to 40 lines at the start of printing, the width ΔL of the printing line is determined for each printing line. It has a print line correction table, and converts the table every 200 lines, for example, for lines after this line.

Next, other embodiments of the present invention will be described. 7th
FIG. 1 is a block diagram showing another embodiment of the thermal head driving device of the present invention, in which the correction for heat accumulation in the head, which was performed by the heat accumulation correction ROM explained in the embodiment of FIG. This is done using table ROM II and print line correction ROM 12.

When image data l of an arbitrary image is sent to the thermal head driving device of this embodiment, first, before printing, the head temperature is detected by the thermistor 6 embedded in the thermal head. The detected head temperature table is sent to head temperature table ROMII, and a reference temperature table is selected.

Here, the image data is sent line by line on each screen, the amount of energization is output from the reference temperature table according to the gradation data of each dot, and the number of lines of data is counted by the line counter 2. The print line correction ROM 12 outputs a print line correction coefficient according to the number of print lines, the print rate of one line is counted by the print counter 4, and the print rate correction ROM 5 outputs the print line correction coefficient.

As described above, when a printing line correction coefficient corresponding to the energization amount of each dot, the number of printing lines, and a printing rate correction coefficient according to the printing rate of each printing line is output, the multiplier 7 outputs the ij1 voltage of each dot. A calculation is performed between the print line correction coefficient and the correction coefficient for each line, and the energization time is set by the timer 8 according to the corrected energization amount output by the multiplier 7, which is sent to the thermal head drive circuit 9. Power supply control to the thermal head 10 is performed in accordance with image data.

Here, the reference temperature table and the print line correction coefficient are both set based on experimental values as in the above embodiment.

〔Effect of the invention〕

According to the present invention, it is possible to perform correction for each print line using the print line correction table or the print line correction coefficient, so that 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 helix during printing, it is possible to set the width of the printing line that changes the table according to the increase in density, making it possible to make highly accurate corrections and to make it easier to change the table. By setting the reference 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 possible to correct changes in heat storage characteristics due to changes in the head temperature at the start of printing.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the thermal head driving device of the present invention, FIG. 2 is an explanatory diagram showing a table stored in a heat storage correction ROM, and FIG. 3 is an explanatory diagram showing heat storage characteristics during printing. , Fig. 4 is an explanatory diagram showing changes in heat storage characteristics depending on throat temperature, Fig. 5 is an explanatory diagram showing encapsulant characteristics during printing with respect to printing pulse width, and Fig. 6 is an explanatory diagram showing the setting of the printing line table. Fig. 7 is a block diagram showing another embodiment of the thermal head driving device of the present invention, Fig. 8 is a block diagram showing the structure of conventional thermal head driving values, and Fig. 9 is an explanatory diagram of the method. An explanatory diagram showing a heat storage correction table of a conventional thermal head drive device, FIG. 10 is an explanatory diagram showing changes in printing characteristics due to changes in head temperature, and FIG. 11 is an explanatory diagram showing a change in heat storage correction table in a conventional thermal head drive device. FIG. 2 is an explanatory diagram showing a change in concentration difference.・Image data ・Line counter ・Heat storage correction ROM Multiplier ・Thermal transfer Figure 1

Claims (3)

[Claims] (1) In a thermal head driving device 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, Temperature detection means for detecting the temperature of the thermal head is provided in the thermal head, and the amount of current applied to the thermal head is controlled according to an input signal from the temperature detection means and the number of lines of dots to be printed from the start of printing. A thermal head drive device characterized by: (2) In a thermal head driving device 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, Temperature detection means for detecting head temperature is provided in the thermal head, means for storing a reference energization table corresponding to each head temperature detected by the temperature detection means, and head temperature detected by the temperature detection means. means for converting an energization table for the thermal head according to the number of lines to be printed from the start of printing; A thermal head driving device characterized in that the amount of current applied to the thermal head is controlled by means for converting a table of the amount of current applied to the thermal head. (3) In a thermal head driving device 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, Temperature detection means for detecting the temperature of the head is provided in the thermal head, means for storing an energization table according to the head temperature detected by the temperature detection means, and means according to the head temperature detected by the temperature detection means. means for converting an energization table for the thermal head; means for storing a correction coefficient according to the number of print lines from the start of printing; means for calculating energized printing data;
A thermal head driving device, characterized in that the amount of current applied to the thermal head is controlled for each dot according to the calculation result of the calculation means.