JPH03288673A - Sublimation type printer - Google Patents

Abstract

PURPOSE:To reproduce a stable image of high quality by providing a means controlling the preheating means of a thermal head, a means controlling a cooling means and a means controlling the supply quantity of a current. CONSTITUTION:The heat applied to a thermal head 1 is controlled corresponding to the temp. of the head detected by a temp. detection means 7. For example, when the temp. of the head is 20 deg.C or lower, a preheating means 8 is operated by a heat control circuit 13 to heat the thermal head 1 to 20 deg.C or higher. Printing becomes possible only when the temp. of the head is 20-60 deg.C and, by supplying a current to the thermal head 1 by selecting a proper current supply pulse from an LUT 11 corresponding to the temp. of the head, the sublimable dye on an ink sheet A is heated and sublimed to reproduce an image on image receiving paper B. Herein, a cooling means 9 is driven at the time of the supply of a current to cool the head. When the temp. of the thermal head 1 reaches 60 deg.C or higher, the heat control circuit 13 stops the printing due to the thermal head 1 and the forcible cooling of the head is carried out by a cooling means 9.

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. The present invention relates to a color printer (hereinafter referred to as a sublimation printer) based on a sublimation recording method that reproduces a color image with gradation by sublimation.

(Conventional example) Dye-sublimation printers are attracting wide attention as a technology that is small and simple in structure and yet can reproduce high-quality color images.However, the amount of current applied to the thermal head,
In other words, images with gradation are reproduced by controlling the amount of heat generated by the head, so the quality of the reproduced image varies depending on the surrounding thermal environment. The temperature state (hereinafter referred to as head temperature) has a large influence on the quality of reproduced images, as shown in FIG. 11 (print density characteristics with respect to changes in head temperature).

In addition, the head temperature rises because the thermal energy generated when electricity is applied is transferred to the head body and accumulated (this is called heat accumulation in the head), and the print density increases as the heat accumulates in the head, so the head temperature during printing increases. Not only does this cause a difference in the density reproduced by the printing method, but also a difference occurs in the print density at the start and end of printing even on the same screen.

Therefore, in order to obtain stable image quality in a dye-sublimation printer, thermal control of the thermal head is an indispensable and important issue, and to date, many specific thermal control methods and thermal control circuits have been proposed. The structure of thermal control in a conventional dye-sublimation printer will be described below.

FIG. 8 is a schematic diagram showing the basic configuration of a conventional dye-sublimation printer, in which a thermal head 1 consisting of a line-shaped heating resistor and a platen roller 2 are provided with a Ink sheet A coated with a sublimable dye coloring material
is stretched between a sheet supply roll 3 and a sheet take-up roll 4, and is coated with an image receptor that fixes sublimable dye and reproduces an image.
After passing between the thermal head 1 and the platen roller 2, the paper is discharged from the sublimation printer by the paper discharge roller 6.

Further, a thermistor 7 is embedded in the thermal head 1 to detect the head temperature, and the detected signal is transmitted to the A/
It passes through the D conversion circuit 10 and is sent to the thermal control circuit 13 as a temperature signal.
The thermal control circuit 13 switches the table of the LUT (look-up table) 14 according to the head temperature, and sends print data to the thermal head drive circuit 12 to energize the thermal head. , L.U.
In T14, a gradation-current pulse width table (hereinafter referred to as γ table) as shown in Fig. 2 is recorded for every 2°C of head temperature. This is done by switching the table of this LUT 14 accordingly.

Here, when the dye-sublimation printer receives image data, first, prior to printing, the ink sheet A and the image receiving paper B are cued and positioned, and the thermal head 1 is pressed against the platen roller 2. Ink sheet A
At the same time, the thermal head L is energized according to the received image data, and an appropriate energizing pulse is applied to the thermal head L according to the head temperature.
By selecting one of UT14 and energizing it, it becomes possible to heat the sublimable dye coated on the ink sheet A to cause a sublimation reaction, thereby reproducing an image on the image receiving paper B according to the image data. .

[Problem to be Solved by the Invention 1] As described above, according to the configuration of the conventional dye-sublimation printer, even if the temperature of the head changes due to heat accumulation in the head or the temperature of the outside air, the printer always responds to the head temperature. Since the optimum energization is performed, it is possible to always reproduce stable images without being affected by the surrounding thermal environment.

However, conventional head thermal control is limited to head temperature,
In other words, the temperature on the aluminum base side of the thermal head is used as the standard, and no consideration is given to the temperature state of the heating resistor of the head, which is the heat source. It is unavoidable that concentration errors occur due to factors such as the time it takes to reach the temperature (temperature rise characteristics of the heating resistor) and the time lag until heat is transferred from the heating resistor to the aluminum base side of the head. In particular, the temperature rise characteristics of the heating resistor of the head, as shown in Figure 12 (rise characteristics of print density), affect tens of lines from the print start line, resulting in insufficient density, and as a result, the reproduced image This has caused a problem in which the quality is greatly reduced.

In addition, in the thermal control of conventional dye-sublimation printers, Fig. 13 (
In response to an increase in density due to heat accumulation in the head that occurs during printing, as shown in γ of the LUT 14, the optimum amount of current is determined according to the head temperature.
By switching the head temperature every 2°C from the table,
During printing, even within the range of each γ table for every 2°C of head temperature, there is always an increase in density due to heat accumulation in the head. A sudden difference in density occurs due to the switching, and this difference in density is sufficiently recognized by human vision and gives a subjectively unpleasant impression.

In addition, as shown in Figure 14 (Temperature rise characteristics in one screen), the temperature rise in one screen due to heat accumulation in the head temperature varies depending on the print gradation for the thermal head, and therefore, the above-mentioned effect of heat accumulation in one screen Y because the table switching circuit for each differs depending on the printing gradation of the image data to be printed.

Differences also occurred between the M and C colors, and when the colors were mixed, large density unevenness occurred, giving an unpleasant impression, and significantly deteriorating the quality of the reproduced image.

As described above, in the configuration of a conventional dye-sublimation printer, there is a rise in density at the start of printing, a sudden difference in density when switching the γ table during one screen, and an increase in density within the range of the γ table that is switched depending on the head temperature. , and these also change depending on the image data to be printed. Therefore,
Image quality is greatly affected by the image data to be printed or the heat storage state of the head, making it difficult to obtain stable image quality.In order to achieve more stable and high quality image reproduction, the above Solving the problems was an important issue.

[Means for Solving the Problems] In order to achieve the above-mentioned problems, in the present invention, the amount of sublimation of the sublimation dye is controlled by controlling the amount of current applied to the thermal head formed by disposing heating resistors in a line shape. In a dye-sublimation printer that reproduces an image with gradation by changing the gradation, a preheating means for heating a thermal head;
A cooling means for cooling a thermal head is provided, a temperature detection means is provided in the thermal head, a means for inputting a signal from the temperature detection means, a means for controlling the preheating means, and a means for controlling the cooling means. , is constructed by means for controlling the amount of current applied to the thermal head.

[Function] According to the above configuration, by inputting the signal from the temperature detection means and controlling the amount of current applied to the thermal head, it is possible to prevent a large difference between the reproduced densities at the start and end sides of printing. At the start of printing for each color, the thermal head is heated by the preheating means. It is now possible to obtain more stable high-quality image reproduction without deterioration, and even if the density increases due to heat accumulation in the head within the range of the γ table that changes depending on the head temperature, the cooling Since the thermal head is cooled by the means, the temperature rise of the head is suppressed, and 1
Even if the printing gradation for the thermal head differs by the number of times the γ table is switched on the screen, the quality of the reproduced image can always be stabilized.

[Example] Next, an example of the dye-sublimation printer of the present invention will be described based on the drawings.

FIG. 1 is a schematic diagram showing an embodiment of a dye-sublimation printer of the present invention, and first, the configuration of the main body of the dye-sublimation printer of the present invention will be explained.

In this figure, reference numeral 1 denotes a thermal head consisting of a line-shaped heat generating resistor arranged on an aluminum base, and the reference numeral A in the figure is arranged opposite to the platen roller 2.
is an ink sheet, on the surface of which there are three colorants of Y (yellow), M (magenta), and C (cyan) made of sublimable dyes, or four colorants with Bk (black) added. Reference numeral B in the figure, which is sequentially coated on the surface and stretched by a sheet supply roll 3 and a sheet take-up roll 4, is an image receiving paper on which a sublimable dye is fixed to reproduce an image. The paper is coated with an image-receiving agent, is transported by a transport roller 5, passes between the thermal head 1 and the platen roller 2, and is then discharged to the outside of the dye-sublimation printer by a paper discharge roller 6. Reference numeral 7 denotes a temperature detection means such as a thermistor, which is embedded in the aluminum base of the thermal head and detects the head temperature.
The reference numeral 8 in the figure is a preheating means such as a ceramic heater or a nichrome heater, and the thermal head l
It is attached to the top surface or embedded in the aluminum base of the thermal head to heat the thermal head, and reference numeral 9 in the figure is a cooling means such as an axial fan that blows or exhausts air. The cooling device is arranged above and facing the head, and is configured to cool the head.

Next, the configuration of a thermal control device for a sublimation printer according to the present invention will be explained.

Reference numeral 10 in the figure is an A/D conversion circuit, which converts the terminal voltage of the temperature detecting means 7 into a temperature signal. Reference numeral 13 in the figure is a thermal control circuit, which is used in the dye-sublimation printer of the present invention. Reference numeral 14 in the figure is an LUT that controls the thermal control device.
A table (hereinafter referred to as γ table) of printing gradation and energization pulse width as shown in FIG. 2 is recorded for every 2°C of head temperature, and the energization to the thermal head 1 is , the energization time for the thermal head is determined by switching the table of the LUT (G) 11 according to the head temperature detected by the temperature detection means, and the reference numeral 15 in the figure is a thermal head drive circuit, Reference numeral 11 in the figure is a preheating control circuit that sets a timer according to the energization time of the table selected in the LUT (G) and energizes the thermal head. The reference numeral 12 in the figure, which controls the drive of the means 8, is a control circuit for the cooling means, and the reference numeral 15 in the figure, which performs the cooling means control circuit, is a line buffer, which is used in the dye-sublimation printer of the present invention. It serves as a buffer for the image data to be sent.

Next, the operation of the dye-sublimation printer of the present invention will be explained.

Here, in the sublimation printer of the present invention, thermal control for the thermal head is performed in the following three stages depending on the head temperature detected by the temperature detection means.

1 2 1) When the head temperature is 20°C When the head temperature is at the above temperature, the preheating control circuit 13 activates the preheating means 8 to heat the thermal head until the head temperature is 20°C or higher. (Considering the thermal characteristics of the head, especially the heat dissipation characteristics, the preheating range is desirably about 20° C. + 2 to 4° C.).

Here, if the head temperature is below 20°C, the head will not be energized, and if no image data is received, the temperature will rise to 20°C.
Preheating is repeated in the range from 20°C to 20°C to 2°C to 4°C.

2] 20° C. Head temperature < 60° C. It is possible to print the received image data only when the head temperature is within the above range.

Here, when the sublimation printer of the present invention receives image data, first, prior to printing, the ink sheet A and the image receiving paper B are cued and positioned, and the thermal head 1 is pressed against the platen roller 2. By doing this, the ink sheet A and the image receiving paper B are brought into close contact with each other, and while the above-mentioned cueing and positioning of the ink sheet A and the image receiving paper B are being performed, the preheating control circuit 13 controls the preheating. The means 8 is activated to heat the thermal head for a certain period of time.

As described above, when the cueing and positioning and preheating of the head are completed, the ink sheet A and image receiving paper B are conveyed in close contact with each other, and the thermal head 1 is moved according to the received image data and the head temperature. The sublimable dye coated on the ink sheet A is heated to cause a sublimation reaction, and an image according to the image data is formed on the receiver paper B by selecting an appropriate energization pulse from LUT II and energizing it. to recreate.

Here, when the head is energized, the cooling means 9 is driven by the cooling means control circuit 12 to cool the head.

3) Head temperature > 60° C. When the above temperature is reached, the thermal control circuit stops printing by the thermal head, and the cooling means forcibly cools the head.

As described above, in the sublimation printer of the present invention, three stages of control are performed.

Here, the set temperatures in each of the above steps 1) to 3) vary depending on the characteristics of the sublimable dye or the thermal response characteristics of the thermal head, so the set temperatures other than those shown in this example will be used. Even if the value is , the effect obtained will not change.

Further, FIG. 3 is a schematic diagram showing another embodiment of the dye-sublimation printer of the present invention, in which the LTJT
(b) shows the influence of the temperature rise characteristics of the heat generating resistor of the head shown in Fig. 7 by using a table of preheating time according to the head temperature shown in Fig. 4 for every 2°C. Preheating at the start of printing is performed by selecting an appropriate heating time using the LUT (b) according to the head temperature at the start of printing.

Further, FIG. 5 is a schematic diagram showing another embodiment of the dye-sublimation printer of the present invention, in which the LUT is not indicated by the reference numeral 18 in the figure.
(c) has a table of driving voltages for the cooling means according to the head temperature shown in FIG. The cooling of the head is controlled by changing the

Furthermore, FIG. 7 is a combination of the embodiments shown in FIGS. 3 and 5 above.

(Effects) According to the present invention, by inputting a signal from the temperature detection means and controlling the amount of current applied to the thermal head,
There is no large difference in the reproduced density between the start and end sides of printing, and as shown in the characteristic of (a) in Figure 9, the temperature rise characteristic of the heating resistor of the head varies from the printing start line to several tens of meters away from the printing start line. Even if the line is affected, the thermal head is heated by the preheating means at the start of each color printing, so the target can be quickly achieved without reducing the density as shown in (b) in the figure. It becomes possible to reproduce the density, and since the thermal head is heated by the above-mentioned preheating means, it becomes possible to print quickly even if the head temperature is low. Moreover, since the preheating described above is not performed by energizing the thermal head but by a dedicated preheating means, the life of the head is not deteriorated in the slightest.

Furthermore, due to the influence of heat accumulation in the head during printing,
As shown in the characteristic (a), even if a sudden rise in head temperature occurs, cooling is performed by the cooling means described above, so the temperature rise due to printing is gradual, and the γ table switching during one screen is The number of times is always the same even if the printing gradation for the thermal head is different, and the quality of the reproduced image can always be stably reproduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the dye-sublimation printer of the present invention, FIG. 2 is an explanatory diagram showing a γ table stored in LUT, and FIG. 3 is a diagram showing other embodiments of the dye-sublimation printer of the present invention. FIG. 4 is an explanatory diagram showing a heating time table stored in LUTb. FIG. 5 is a schematic diagram showing another embodiment of the dye-sublimation printer of the present invention. 7 is a schematic diagram showing another embodiment of the sublimation printer of the present invention. FIG. 8 is a schematic diagram showing the configuration of a conventional printer. , FIG. 9 is a characteristic diagram showing an example of the effects of the present invention, FIG. 10 is a characteristic diagram showing an example of the effects of the present invention, and FIG. 11 is a characteristic diagram showing changes in printing characteristics due to changes in head temperature. FIG. 12 is a characteristic diagram of the rise in print density with respect to head temperature; FIG. 13 is a characteristic diagram of increase in head temperature with respect to print gradation; FIG. 14 is a characteristic diagram of temperature increase in one screen with respect to print gradation. 1 ・ 2 ・ A ・ B ・ 7 ・ 8 ・ 9 ・ l 1 ・ 12 ・ 13 ・・Thermal head, platen roller, ink sheet, image receiving sheet, thermistor, preheating means, cooling means, preheating drive circuit, cooling means Drive circuit/thermal control circuit

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, and a cooling means for cooling the thermal head, the thermal head is provided with a temperature detection means, and a signal from the temperature detection means is input to control the preheating means. A dye-sublimation printer comprising: means for controlling the cooling means; and means for controlling the amount of current applied to the thermal head.