JPH0550639A - Thermal head driving method in thermal transfer recording device - Google Patents

Abstract

PURPOSE:To obtain excellent gradation expression and shorten printing cycle by avoiding overlap of heating periods of heating elements adjacent to each other when heating period, temperature holding period, and cooling period are supplied to applying pulse of a thermal head so as to drive a number of heating elements by dividing them. CONSTITUTION:In a thermal transfer recording device, an ink sheet and an image receiving paper are pressed to a platen by using a thermal head having fine heating elements in the shape of a line. By energizing the heating elements, dye of the ink sheet is transferred on the image receiving paper so as to form an image. In this case, pulse to be applied to the thermal head is made to have a heating period, a temperature holding period, and a cooling period. When a number of heating elements are divided for driving, the driving is controlled such that the heating periods of the heating elements adjacent to each other do not overlap. For example, the whole heating element 11 of the thermal head 10 is divided into 4 blocks, and pulse is applied to each block at a timing as shown by a graph drawn in the right side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal transfer recording apparatus for forming an image using a thermal head, an ink sheet, an image receiving paper, and a platen, and more specifically, it determines thermal pulses by applying a pulse to the thermal head. The present invention relates to a thermal head driving method for a thermal transfer recording apparatus.

[0002]

2. Description of the Related Art A conventional thermal transfer recording apparatus is shown in FIG.
As shown in FIG. 9, the thermal head 10 presses the ink sheet and the image-receiving paper against the platen roller to energize each heating element of the thermal head to generate heat, and the dyeing layer of the ink sheet adhered by the glaze layer. By raising the temperature of the image receiving layer of the image receiving paper, the dye in the dyeing layer is transferred to the image receiving layer to form an image. By the way, as a method for energizing the heating element of the thermal head 10 in this way, a pulse train as shown in FIG. 20 has been conventionally used. Since this pulse train is generated by pulse-converting print data consisting of 8 bits,
It is variable between 0 and 255. Further, when printing an image, it is necessary to process and correct the image data according to the characteristics of the thermal head. This correction is resistance value correction that corrects density unevenness that occurs in the main scanning direction due to variations in the resistance value of the heating element of the thermal head, and printing of the target dot due to heat generated by the dots that are printed simultaneously in the main scanning direction. Adjacent correction that corrects the change in density, history correction that corrects the change in the print density of the target dot due to heat generated by the dots that are sequentially printed in the sub-scanning direction, glaze in which the heating element is formed This is a medium-speed heat storage correction that corrects for changes in the temperature of layers and ceramic substrates due to printing. Such correction is generated from image data 25
This is done by changing the number of pulses of 5. Here, the temperature change of the heating element when the pulse train as shown in FIG. 20 is applied to the thermal head is as shown in FIG. That is, from the initial temperature of the heating element, which is determined by the environmental temperature of the thermal head, the medium-speed heat accumulation, and the heat generation history, the temperature rises for the duration of the applied pulse, and the temperature drops for the duration of the absence of the applied pulse. The temperature rises while being continuously applied, and the temperature monotonously drops after the pulse train ends. Such a temperature change of the heating element causes the heating period until the temperature of the heating element reaches the printable temperature at which the dye can be transferred, the printing period for determining the printing density, and the temperature monotonously decreases. It is divided into cooling periods.

[0003]

However, the method of applying the pulse train to the heating element of the thermal head to drive the heating element has the following drawbacks. (1) Since the pulse is continuously applied, the peak temperature of the heating element is increased and the glossiness of the printed image is lowered. (2) Since all the corrections are made only by increasing or decreasing the number of pulses generated from the 8-bit printing data, the number of pulses used for gradation expression is reduced, and the gradation is deteriorated. (3) Since the pulse train is applied in the same manner as the heating period and the printing period, the heating period becomes long and the printing time becomes long. (4) Since all corrections are performed simultaneously, they adversely affect each other. The present invention has been made in order to solve the above-mentioned conventional problems, and the glossiness does not decrease even when printing with high optical density, the gradation expression is high, and the printing cycle is short. It is an object of the present invention to provide a method of driving a thermal head of a thermal transfer recording apparatus that can perform correct correction.

[0004]

In order to achieve the above object, in the invention according to claim 1, the thermal head having a line-shaped minute heating element is used to press the ink sheet and the image receiving paper against the platen to generate the heat. When a dye is transferred from the ink sheet to the image receiving paper by energizing the body to form an image, the thermal head is driven by applying a pulse having a heating period, a temperature holding period and a cooling period to the thermal head. In addition, when a large number of heating elements are divided and driven in order to reduce the current supplied to the thermal head, the heating periods of adjacent heating elements do not overlap. The invention according to claim 2 is characterized in that, when the pulse applied to the thermal head has a heating period, a temperature holding period and a cooling period, the end of the heating period is the same for all the heating elements. Further, in the invention according to claim 3, when the pulse applied to the thermal head has a heating period, a temperature holding period and a cooling period, the number of the heating elements to be driven at the same time is different, so that the common electrode resistance exists. The number of elements is corrected by changing the pulse width during the temperature holding period to correct the difference in print density due to the difference in the current supplied to the heating element. It is characterized in that it is composed of pulses and is performed by changing the width of each pulse.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The inventions described in claims 1, 2 and 3 will be described below in detail with reference to the drawings. First, in order to solve the above-mentioned conventional problems, the invention according to claim 1 does not apply a pulse continuously as in the prior art, but as shown in FIG. 1, a heating period, a temperature holding period, and a cooling period. When a number of heating elements are divided and driven in an application pulse having a period, the heating periods of the adjacent heating elements are prevented from overlapping each other, so that the current supplied to the thermal head is reduced. Here, the heating period is a period in which the temperature of the heating element is raised from the initial temperature of the heating element, which is determined by the environmental temperature, the medium-speed heat storage, and the thermal history, to the printable temperature, and the temperature holding period is the temperature of the heating element. The temperature is kept constant and the dye is transferred to the image receiving paper to determine the printing density. The cooling period is a period in which the heating element is de-energized and the temperature of the heating element is lowered.
As a method of performing divided driving with applied pulses as shown in FIG. 1, as shown in FIG. 2, all the heating elements 11 of the thermal head 10 are divided into a plurality of blocks ,. By applying the pulse at such timing, the heating period does not occur at the same time in each block, and in order to prevent the temperature holding pulse from being applied simultaneously in each block even during the temperature holding period, all heat generation is performed. It requires half the supply current compared to driving the body at the same time.

However, in the driving for each block as described above, since the heating periods of the heating elements are the same in the block, the thermal effects of the adjacent heating elements are the same, but the heating elements in the vicinity of the boundaries of the blocks are Since thermal influences from adjacent blocks are different, density unevenness occurs at the boundaries of the blocks during printing. Further, in the driving for each block, the timing at which the printing start temperature is reached differs for each block, so that the printing dots deviate for each block. Such a shift between blocks significantly deteriorates the image quality. Therefore, in the present invention, as shown in FIG.
Pulses with different timings are applied so that the heating periods do not overlap. In this way, when the pulses whose timings are shifted so that the heating periods do not overlap with the adjacent heating elements are applied, each heating element is equally affected by the thermal effects of the adjacent heating elements. There is no uneven density at the boundary, which would be a problem when dividing each block. Further, although the dot position is displaced due to the difference in the timing at which the printing start temperature of each heating element is reached, it cannot be visually confirmed because the displacement is in dot units, and the image quality is not deteriorated.

A concrete embodiment of the invention described in claim 1 will now be described. First, the number of heating elements is 2560, 3
The A4 size thermal head of 00 dpi is divided into 4 blocks for each 640 elements.
When ,,, were applied to each block, it was confirmed that density unevenness occurred at the boundary of each block and the image was misaligned. On the other hand, when the pulses as shown in FIG. 5 were applied to the heating elements adjacent to the thermal head, the density unevenness as described above did not occur, and no image shift was observed. As described above, according to the thermal head driving method of claim 1, when the plurality of heating elements are divided and driven, the heating periods of the adjacent heating elements do not overlap with each other. The glossiness does not decrease with respect to copying, the gradation expression becomes high, the printing cycle can be shortened, and correct correction can be performed.

Next, in order to solve the above-mentioned conventional problems, the invention according to claim 2 does not apply pulses continuously as in the prior art, but as shown in FIG. When applying a pulse having a holding period and a cooling period,
The end of the heating period is the same for all heating elements. Here, the heating period is a period in which the temperature of the heating element is raised from the initial temperature of the heating element, which is determined by the environmental temperature, the medium-speed heat storage, and the thermal history, to the printable temperature, and the temperature holding period is the temperature of the heating element. The temperature is kept constant and the dye is transferred to the image receiving paper to determine the printing density. The cooling period is a period in which the heating element is de-energized and the temperature of the heating element is lowered.

When such a pulse is applied, if the start of each applied pulse is made the same in each heating element as shown in FIG. 7, the temperature rise curves of each heating element become different as shown in FIG. The peak temperatures also differ because the degrees of thermal influence exerted on each other vary. If the peak temperatures are different, the print densities are different even if they have the same temperature holding period. For example, the temperature rise of the heating element when a pulse such as in FIG.
Originally, the peak temperature should be the same, but the peak temperature of the heating element to which the pulse having the longest heating period is applied becomes the highest. For this reason, since it takes the longest time to cross the printable temperature in the cooling period after the pulse application is completed, the print density is the highest.
Therefore, in the present invention, as shown in FIG. 9, the start time of the applied pulse is different, but the end time of the heating period is the same. By controlling the applied pulse in this manner, the temperature of the heating element is on the same curve as shown in FIG. 10 and the peak temperature is also the same, so that the same printing is performed when the same temperature holding period is provided. It becomes a concentration.

A concrete embodiment of the invention described in claim 2 will now be described. When printing three dots continuously as shown in FIG. 11, paying attention to the dot in the middle, applying a pulse having a random heating period to the dots at both ends,
A pulse was applied to the target dot so as to obtain a constant print density. In the pulse application method according to the present invention in which the heating period ends at the same time, the density variation of the target dot was ± 2%, but in the pulse application method in which the heating period ends varied, the density variation was ± 20%. As described above, in the thermal head driving method according to the second aspect of the invention, since the end of the pulse applied to the thermal head is the same for all the heating elements, it is possible to suppress the variation in the density and yet to obtain a high optical density. The glossiness does not decrease even for the printing of, the gradation expression is improved, the printing cycle can be shortened, and correct correction can be performed.

Next, in order to solve the above-mentioned conventional problems, the invention according to claim 3 does not apply pulses continuously as in the prior art, but as shown in FIG.
In the applied pulse having a temperature holding period and a cooling period,
The heating pulse is composed of a plurality of pulses as shown in FIG. 13, and the number of elements is corrected by changing the width of each divided pulse. As described above, the heating period includes the environmental temperature, medium-speed heat storage, thermal history,
The period of time for raising the temperature of the heating element from the initial temperature of the heating element to the printable temperature, and the temperature holding period is the period for keeping the temperature of the heating element constant and transferring the dye to the image receiving paper to determine the printing density. The cooling period is a period in which the power supply to the heating element is stopped and the temperature of the heating element is lowered.

In the case of applying such a pulse to a large number of heating elements arranged in a line to conduct electricity, typically, the common electrode resistance R is obtained by connecting the resistance values r of the heating elements in parallel.
Are connected in series, and the applied voltage V _H is applied to their ends. Here, N is the number of heating elements that are simultaneously driven. At this time, the voltage V applied to both ends of the heating element
_r becomes V _r = [(r / N) / ((r / N) + R)] V _H , and the energization current I _r of each heating element becomes I _r = V _H / (r + NR), and they are driven simultaneously. The energizing current varies depending on the number N of heat generating elements. Therefore, the printing density differs depending on the number of driven heating elements. In order to solve this problem, the pulse width may be changed according to the number of heating elements that are driven. However, in the applied pulse as shown in FIG. 12, the width of the heating pulse varies depending on the ambient temperature, medium-speed heat storage, and thermal history. It cannot be changed because it is decided by.
Therefore, in the present invention, the heating pulse is composed of a plurality of pulses as shown in FIG. 13, and the width of each pulse is changed according to the number of drive elements. By controlling in this way, the electric power applied to each heating element can be made constant.

A concrete embodiment of the invention described in claim 3 will now be described. Now, when a pulse as shown in FIG. 14 is applied to the heating element and the number of driving elements is changed and the printing density is measured, it becomes as shown in FIG. Then, according to the present invention, the heating pulse is divided in a configuration as shown in FIG.
When the pulse widths x and y of the heating division pulse and the temperature holding pulse were changed as shown in FIGS. 17 (a) and 17 (b), respectively, the print density became constant regardless of the number of drive elements as shown in FIG. .. As described above, in the thermal head driving method according to the third aspect, the heating pulse is composed of a plurality of pulses, and the width of each pulse is changed according to the number of driving elements, whereby the electric power applied to each heating element is changed. The print density can be made constant, and the print density can be made constant regardless of the number of drive elements. Therefore, the glossiness does not decrease even for printing with high optical density, gradation expression is improved, the printing cycle can be shortened, and correct correction can be performed.

[0014]

As described above, in the thermal head driving method of the thermal transfer recording apparatus according to the first aspect, the pulse applied to the thermal head has a heating period, a temperature holding period and a cooling period, and a large number of heat generations. When driving by dividing the body, the heating periods of adjacent heating elements do not overlap, so the glossiness does not decrease even for printing with high optical density, and gradation expression becomes high, In addition, the printing cycle can be shortened and correct correction can be performed. In addition, claim 2
In the thermal head driving method of the thermal transfer recording apparatus described above, since the pulse applied to the thermal head has a heating period, a temperature holding period and a cooling period, and the end of the heating period is the same for all heating elements. , Even when printing with high optical density, the glossiness does not decrease, the gradation expression becomes high,
In addition, the printing cycle can be shortened and correct correction can be performed. Further, in the thermal head driving method of the thermal transfer recording apparatus according to claim 3, the pulse applied to the thermal head has a heating period, a temperature holding period and a cooling period,
Moreover, since the heating pulse is composed of multiple pulses and the number of elements is corrected by changing the width of each pulse according to the number of driving elements, the glossiness is high even for printing with high optical density. The gradation expression does not decrease, the gradation expression becomes high, the printing cycle can be shortened, and correct correction can be performed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of the invention according to claim 1, and is a pulse current waveform diagram showing an example of a pulse applied to a thermal head.

FIG. 2 is an explanatory diagram of a divisional driving method of a thermal head.

FIG. 3 is an explanatory diagram of the invention according to claim 1, and is a pulse current waveform diagram in the case where pulse currents are applied at different timings so that the heating periods of adjacent heating elements do not overlap.

FIG. 4 is an explanatory diagram of the invention according to claim 1, and is an explanatory diagram of a method of applying a pulse to the linear heating elements of the thermal head.

FIG. 5 is a diagram showing an embodiment of the invention described in claim 1, and is a pulse current waveform diagram in the case where pulse currents are applied with staggered timings so that the heating periods of adjacent heating elements do not overlap.

FIG. 6 is an explanatory diagram of the invention according to claim 2, and is a pulse current waveform diagram showing an example of a pulse applied to the thermal head.

FIG. 7 is a pulse current waveform diagram showing an example of applied pulses having different heating periods.

8 is a graph showing a temperature change of a heating element when each pulse current shown in FIG. 7 is applied.

FIG. 9 is an explanatory diagram of the invention according to claim 2, and is a pulse current waveform diagram showing an example of an applied pulse in which the end of the heating period is set to be the same.

10 is a graph showing a temperature change of a heating element when each pulse current shown in FIG. 9 is applied.

FIG. 11 is an explanatory diagram of an embodiment of the invention described in claim 2;

FIG. 12 is an explanatory diagram of the invention according to claim 3, and is a pulse current waveform diagram showing an example of a pulse applied to the thermal head.

FIG. 13 is an explanatory diagram of the invention according to claim 3, and is a pulse current waveform diagram showing an example of an applied pulse when the heating period is configured by a plurality of pulses.

FIG. 14 is an explanatory diagram of the invention according to claim 3, and is a pulse current waveform diagram showing a specific example of a pulse applied to the thermal head when the heating period is configured by a single pulse.

15 is a graph showing the relationship between the number of drive elements and the print density when the pulse current shown in FIG. 14 is applied.

FIG. 16 is a diagram showing an embodiment of the invention described in claim 3, and is a pulse current waveform diagram showing a specific example of a pulse applied to the thermal head when the heating period is constituted by a plurality of pulses.

FIG. 17 is a diagram showing the relationship between the pulse width x of the heating division pulse and the pulse width y of the temperature holding pulse with respect to the number of drive elements of the applied pulse having the waveform shown in FIG. 16.

FIG. 18 is a graph showing the relationship between the number of drive elements and the print density when the pulse current shown in FIG. 14 is applied.

FIG. 19 is a schematic configuration diagram at the time of printing around the thermal head of the thermal transfer recording apparatus.

FIG. 20 is a pulse current waveform diagram showing an example of a pulse applied to a conventional thermal head.

21 is a graph showing a temperature change of a heating element when a pulse current having the waveform shown in FIG. 20 is applied.

[Explanation of symbols]

 10 Thermal Head 11 Heating Element 12 Platen Roller 13 Ink Sheet 14 Image Receiving Paper

Claims (3)

[Claims] 1. A thermal head having a line-shaped minute heating element is used to press an ink sheet and an image receiving sheet against a platen, and the heating element is energized to transfer the dye of the ink sheet onto the image receiving sheet, thereby forming an image. In a thermal transfer recording apparatus for forming a plurality of heating elements, a plurality of heating elements are divided in order to reduce the current supplied to the thermal head when the thermal head is driven by applying a pulse having a heating period, a temperature holding period and a cooling period. A thermal head driving method for a thermal transfer recording apparatus, characterized in that the heating periods of adjacent heating elements do not overlap each other when driven. 2. A thermal head having a line-shaped minute heating element is used to press the ink sheet and the image receiving sheet against a platen, and the heating element is energized to transfer the dye of the ink sheet onto the image receiving sheet to form an image. In the thermal transfer recording apparatus for forming a heat transfer recording apparatus, when the application pulse to the thermal head has a heating period, a temperature holding period and a cooling period, the end of the heating period is the same for all the heating elements. Thermal head driving method. 3. A thermal heater having a line-shaped minute heating element.
Press the ink sheet and image receiving paper against the platen using the pad
The ink sheet by energizing the heating element.
Thermal transfer recording that transfers images of dyes onto image receiving paper to form images
In the device, the pulse applied to the thermal head is applied.
When having a heat period, a temperature holding period and a cooling period,
Common because the number of heating elements that are driven simultaneously is different
Due to the presence of electrode resistance, the current flowing to the heating element is different.
The number of elements that compensates for differences in print density
Positive, the pulse width may be changed during the temperature holding period.
Multiple heating pulses during the heating period.
Composed of individual pulses and varying the width of each pulse
Of the thermal transfer recording apparatus characterized by
Round head driving method.