JPH04250075A - Density correction device in thermal transfer printer - Google Patents

Abstract

PURPOSE:To correct the deterioration of a density gradation caused by a change in thermal head temperature with high accuracy. CONSTITUTION:Strobe data in accordance with the temperature of a thermal head 3 is stored in a look-up table 21. The temperature of the thermal head 3 is detected, and strobe data based on this temperature is transmitted from the look-up table 21 to a strobe controller 2. Based on the strobe data, the strobe controller 22 sets a strobe time. Namely, with a high thermal head temperature, a short strobe time is set, and a low thermal head temperature, a long strobe time is set. In this manner, independently of the temperature of the thermal head, a good gradation can be expressed. Furthermore, by storing line preheat data in the look-up table 21, the thermal head is preheated at the start of printing to ensure a gradation expression from the first line.

Description

Description: [Object of the Invention] [Field of Industrial Application] The present invention relates to a density correction device for a sublimation type thermal transfer printer. 2. Description of the Related Art Conventionally, images from personal computers, camera-integrated video tape recorders, electronic still cameras, and the like have been soft-copied using display devices capable of high-resolution display. In recent years, thermal transfer printers that can display high-definition images in full color have been developed as devices for hard copying images from these information sources. In addition to high resolution and good color reproducibility, this thermal transfer printer is also required to have good density and gradation expression. FIG. 8 is an explanatory diagram showing a sublimation type thermal transfer printer. During recording, the recording paper 1 is moved by the platen roller 2.
and the thermal head 3 together with the ink sheet 4. The ink sheet 4 is a base film 5 coated with a heat sublimable dye (shaded area) 6, and is arranged so that the heat sublimable dye 6 is pressed against the recording paper 1. A heating resistor 7 is provided on one surface of the thermal head 3. By energizing the thermal head 3, these heating resistors 7 generate heat appropriately according to the print data, and thermal sublimation occurs via the base film 5. Heat the sex dye 6. As a result, the heat sublimable dye 6 is sublimed and transferred and recorded onto the recording paper 1. [0005] In a color printer, an ink sheet is used in which, for example, yellow, cyan, and magenta inks are applied cyclically in a predetermined order. In this case, when recording of the first color (for example, cyan) is completed, the recording paper is conveyed to the same position as the recording start position of the first color, and the ink sheet is moved to print the second color (for example, yellow). Perform transcription recording. Similarly, transfer recording of the third color (magenta) is also performed. By the way, the print density on the recording paper 1 is determined by the temperature of the heating resistor 7. Therefore, by changing the amount of current flowing through the heating resistor 7 of the thermal head 3, the print density can be easily changed. As a method for changing the amount of current flowing through the heat generating resistor 7, a method is adopted in which the time period during which the current flows through the heat generating resistor 7 (hereinafter referred to as strobe time) is changed. FIG. 9 is an explanatory diagram for explaining the strobe time, and FIG. 9(a) shows print data, and FIG.
b) shows a strobe signal. The strobe time is indicated by the low level (hereinafter referred to as "L") of the strobe signal, and energization is performed based on print data during the "L" period of the strobe signal. That is, the strobe signal is composed of strobe units corresponding to each print data, and when printing one line, the number of strobe units corresponding to each print data is applied to the thermal head 3. A current flows through the heating resistor 7 of the thermal head 3 for a time corresponding to the strobe unit length, and heating is performed. By setting a long strobe time, it is possible to make the print high density, and conversely, by setting the strobe time short, the print can be made low density. In this way, the dye-sublimation thermal transfer method can easily express density gradations with good reproducibility. However, since the heating resistor 7 exhibits a heat accumulation phenomenon, the print density may fluctuate regardless of print data. For example, even when printing in a single gradation with a constant strobe time, if the temperature of the thermal head 3 is high, the print density will be dark, and if the temperature is low, the print will be thin. Therefore, if the thermal head 3 is at a low temperature, colors may not appear in low gradation areas, and if the thermal head 3 is hot, colors may be saturated in high gradation areas. The image may become distorted or the portion with a density of 0% (0 gradation) may be colored. Furthermore, in color printing, the three colors of ink, yellow, magenta, and cyan, are printed three times, one color at a time, so the temperature of the thermal head 3 during each printing differs due to heat accumulation in the thermal head 3. The print density of each color changes, resulting in a change in color tone. [0010] Furthermore, when printing a plurality of sheets in succession, there is a drawback that the image quality changes significantly between the first sheet and the last sheet due to heat accumulation in the thermal head 3. Conventionally, therefore, the print density is corrected by correcting the temperature of the heating resistor 7. FIG. 10 is a block diagram showing such a conventional density correction device for a thermal transfer printer. The thermal head 3 is supplied with a power supply voltage from a head power supply circuit 11, and generates heat at a temperature based on the power supply voltage. A thermistor (not shown) is attached to the thermal head 3, and the thermistor outputs a temperature output according to the temperature of the thermal head 3. Temperature output from thermistor is buffer 1
2 to the A/D converter 13, where it is converted into 8-bit parallel temperature data. Temperature data from the A/D converter 13 is given as an address to a look-up table (hereinafter referred to as LUT) 14. Control data is stored in each address of the LUT 14, and the LUT 14 outputs control data for causing the head power supply circuit 11 to generate a power supply voltage to be set in accordance with the temperature of the thermal head 3. That is, the LUT 14 generates control data for decreasing the power supply voltage when the temperature of the thermal head 3 rises, and for increasing the power supply voltage when the temperature of the thermal head 3 falls. The head power supply circuit 11 changes the power supply voltage applied to the thermal head 3 according to control data. In this way, regardless of the heat accumulation phenomenon of the thermal head 3, it is possible to print at a density based on the print data. However, since the load fluctuation and power consumption of the thermal head are relatively large, it is difficult to control the power supply voltage with high precision, and there is a problem that sufficient density correction is not performed. [0014] As described above, in the conventional density correction device for a thermal transfer printer described above, it is difficult to perform high-precision correction because the load fluctuation and power consumption of the thermal head are extremely large. There was a problem that. The present invention has been made in view of such problems, and provides a density correction device for a thermal transfer printer that can obtain density gradations with good reproducibility regardless of temperature fluctuations in the thermal head. The purpose is to [Structure of the Invention] [Means for Solving the Problems] A density correction device for a thermal transfer printer according to claim 1 of the present invention prints at a predetermined density by energizing for a time based on a strobe signal. A thermal head to be used, strobe data for generating the strobe signal corresponding to the temperature of the thermal head, and preheat data for preheating the thermal head are stored, and temperature data detected from the thermal head is stored. a lookup table for outputting stored strobe data and preheat data; and a strobe signal based on the preheat data and strobe data to be applied to the thermal head to preheat the thermal head and to adjust the temperature of the thermal head to correspond to the temperature of the thermal head. The density correction device for a thermal transfer printer according to claim 2 of the present invention is equipped with a strobe controller that energizes for only a certain amount of time, and the thermal head prints at a predetermined density by energizing for only a certain amount of time based on a strobe signal. a look-up table that stores strobe data for generating the strobe signal corresponding to the temperature of the thermal head and outputs the stored strobe data given the temperature data detected from the thermal head; a strobe controller that applies a strobe signal based on data to the thermal head to energize it for a time corresponding to the temperature of the thermal head; and a head power supply voltage switch that switches the power supply voltage supplied to the thermal head according to the temperature of the thermal head. It is equipped with means. According to the first aspect of the present invention, strobe data and preheat data based on the temperature of the thermal head are output from the look-up table. The strobe controller preheats the thermal head for a predetermined period of time based on the preheat data, and determines the energization time according to the temperature of the thermal head based on the strobe data. That is, when the temperature of the thermal head is high, a short energization time is set, and when the temperature of the thermal head is low, a long energization time is set. As a result, good gradation expression can be obtained regardless of the temperature of the thermal head. In claim 2 of the present invention, the strobe time is controlled according to the temperature of the thermal head, and
The head power supply voltage switching means controls the power supply voltage supplied to the thermal head according to the temperature of the thermal head. Therefore, even when the temperature of the thermal head is low, the strobe time can be shortened by increasing the power supply voltage. [Embodiments] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a density correction device for a thermal transfer printer according to the present invention. The thermal head 3 is provided with a heating resistor (not shown). The heating resistor is connected to the strobe signal.
It turns on when "L" and generates heat based on the print data. A temperature sensor (not shown) is attached to the thermal head 3, and the temperature sensor outputs a temperature output according to the temperature of the thermal head 3. This temperature output is It is applied to the A/D converter 13 via the buffer 12. The A/D converter 13 converts the temperature output into 8-bit parallel temperature data and outputs it to the LUT 21 as an address output. In this embodiment, the LUT 21 stores strobe data and line preheat data corresponding to the temperature of the thermal head 3. The strobe data is data for setting the strobe time according to the temperature of the thermal head 3. Line preheat data is generated when the temperature of the thermal head 3 is relatively low, for example, when the temperature at the start of printing is detected.
This data is used to generate a strobe signal for preheating and setting the temperature to a predetermined temperature. L.U.
T21 outputs strobe data and line preheat data based on the temperature data to the strobe controller 22. The strobe controller 22 provides the thermal head 3 with strobe data of the strobe time based on the line preheat data, and the thermal head 3
At the same time, a strobe signal corresponding to the gradation indicated by the print data is adjusted based on the strobe data and is applied to the thermal head 3. Next, the operation of the density correction device for the thermal transfer printer configured as described above will be explained with reference to the waveform diagram of FIG. 2 and the flowchart of FIG. 3. Figure 2 (a
) and (b) respectively show the print data and strobe signal at the start of printing, and FIGS. 2(c) and (d) respectively show the print data and strobe signal when the temperature of the thermal head 3 is relatively high. . When printing starts, step S1 in FIG.
At this point, the temperature of the thermal head 3 is detected. The temperature sensor measures the temperature of the thermal head 3 and outputs a temperature output. This temperature output is converted into 8-bit temperature data by the A/D converter 13 and output as an address of the LUT 21. In step S2, strobe data and line preheat data are read from the LUT 21. At this point, the temperature of the thermal head 3 is relatively low;
The LUT 21 outputs line preheat data based on the temperature output to the strobe controller 22. When the line preheat data is input, the strobe controller 22 generates a strobe signal having a pulse width based on this data and supplies it to the thermal head 3 . This results in
The heating resistor of the thermal head 3 is preheated, and the temperature of the thermal head 3 rises to a predetermined temperature. Next, in the next step S3, the strobe controller 22 generates a strobe signal having a strobe unit length based on the strobe data read from the LUT 21, and outputs it to the thermal head 3 in correspondence with the print data. The heating resistor of the thermal head 3 is energized according to print data for a time based on the strobe unit length. Since the thermal head 3 is preheated to a predetermined temperature by preheating, the gradation expression in the low density portion is good even in the first line. That is, coloring is not performed on the 0th gradation part, and reliable coloring is performed starting from the 1st gradation part. [0027] Also, the strobe unit length is LUT21.
When the temperature of the thermal head 3 is low, the strobe unit length is set to be long, and when the temperature of the thermal head 3 is high, the strobe unit length is set to be short. Therefore, thermal head 3
Regardless of the temperature, parts of the same gradation can be printed with the same density. Furthermore, color collapse does not occur in high gradation areas. When printing of one line is completed, it is determined in the next step S4 whether or not printing of all lines has been completed. If all lines have not been printed, the process returns to step S3 and the next line is printed. When printing of all lines is completed, in the next step S5, it is determined whether printing of all colors has been completed. At this point, only the printing of the first color has been completed, and the process moves to step S6 to prepare the printing of the next color. That is, the recording paper (not shown) is returned to the printing start position, and the ink sheet (not shown) is moved to the position where the heat sublimable dye of the second color is applied. Next, in step S1, the temperature of the thermal head 3 is detected again. After that, step S1
Repeat steps S6 to S6 to print in all colors. When all colors have been printed, the recording paper is ejected. In this way, in this embodiment, the temperature of the thermal head 3 is detected and the strobe data and line preheat data are generated, thereby setting the preheat time and strobe time according to the temperature of the thermal head 3. As a result, reliable coloring is possible from the first gradation, and color collapse does not occur in high gradation areas, and good gradation can be achieved from the first line regardless of the temperature of the thermal head 3. It is possible to express the tone. Moreover, even if continuous printing is performed, continuous printing is possible with stable image quality without being affected by the temperature rise of the thermal head 3. Furthermore, this embodiment may adopt the operation flow shown in FIG. 4. The operational flow in FIG. 4 differs from the operational flow in FIG. 3 in that step S7 is adopted instead of step S4. In step S7, it is determined whether printing of all lines has been completed, and if not, the process returns to step S1 and the temperature of the thermal head 3 is detected again. That is, strobe data and line preheat data based on the temperature of the thermal head 3 are generated every time one line is printed. Therefore, the print density is corrected for the temperature change of the thermal head 3 for each line, and there is an advantage that even finer density control is possible. FIG. 5 is a block diagram showing a density correction device for a thermal transfer printer according to another embodiment of the present invention. In FIG. 5, the same parts as those in FIG. 1 are given the same reference numerals, and the description thereof will be omitted. The temperature output of the thermal head 3 is given to a microcomputer (hereinafter referred to as microcomputer) 31. The microcomputer 31 converts the temperature output into 8-bit parallel temperature data and provides it to the LUT 32, and when the temperature output indicates that the thermal head temperature is, for example, 25 to 40 degrees Celsius, the microcomputer 31 outputs a low level (hereinafter referred to as , “L.
”) voltage switching signal to the head power supply circuit 34 and L
It is designed to be given to UT32. Also, microcontroller 3
1, the thermal head temperature changes to 4, for example, depending on the temperature output.
When it is shown that the temperature is between 0 and 55 degrees Celsius, a voltage switching signal of "H" is applied to the head power supply circuit 34 and LUT 32. FIG. 6 is an explanatory diagram showing the structure of the LUT 32. As shown in FIG. 6, the LUT 32 includes tables 35 and 35 corresponding to "L" and "H" of the voltage switching signal, respectively.
36, and each table stores strobe data corresponding to the temperature of the thermal head 3. L
The UT 32 is provided with temperature data and a voltage switching signal, and outputs strobe data corresponding to the temperature of the thermal head 3 to the strobe controller 33. The strobe controller 33 generates a strobe signal having a strobe unit length based on the strobe data and applies it to the thermal head 3. In this embodiment, the head power supply circuit 34
changes the power supply voltage based on the voltage switching signal to the thermal head 3.
is giving to That is, the head power supply circuit 34 is "L".
When a voltage switching signal of "H" is input, a high voltage power supply voltage is supplied to the thermal head 3, and when a voltage switching signal of "H" is input, a low voltage power supply voltage is supplied to the thermal head 3. There is. Next, the operation of the embodiment configured as described above will be explained with reference to the flowchart shown in FIG. In step S11 of FIG. 7, the temperature of the thermal head 3 is detected. Temperature output is microcontroller 31
is converted into 8-bit temperature data and sent to LUT.
Given to 32. Further, in the next step S12, the microcomputer 31 controls the thermal head 3 based on the temperature output.
It is determined whether the temperature is higher than 40°C. Now, assuming that the temperature of the thermal head 3 is higher than 40° C., the microcomputer 31 gives an "H" voltage switching signal to the head power supply circuit 34 and LUT 32. Then, the head power supply circuit 34 performs the next step S1.
6 generates a low power supply voltage and applies it to the thermal head 3. Further, the LUT 32 outputs strobe data corresponding to the temperature of the thermal head 3 from the table 36 in the next step S17. The strobe controller 33 outputs a strobe signal having a strobe unit length to the thermal head 3 based on this strobe data. As a result, the thermal head 3 performs the next step S1.
In Step 5, printing is performed by energizing the heating resistor for the strobe time based on the printing data. On the other hand, when the temperature of the thermal head 3 is lower than 40° C., the microcomputer 31 provides an "L" voltage switching signal to the head power supply circuit 34 and LUT 32. Then, the head power supply circuit 34 applies a high power supply voltage to the thermal head 3 in step S13, and the LUT3
2 outputs strobe data corresponding to the thermal head temperature from the table 35 in step S14. The strobe controller 33 generates a strobe signal having a strobe unit length based on this strobe data and supplies it to the thermal head 3. In step S15, the thermal head 3 energizes the heating resistor according to the print data for a time based on the strobe signal. It is clear that the same effects as in the embodiment shown in FIG. 1 can be obtained in this embodiment as well. Furthermore, this embodiment has the advantage that the correction time can be significantly shortened compared to the embodiment of FIG. That is, in the embodiment shown in FIG. 1, the print density is corrected only by changing the strobe unit length. When the temperature of the thermal head 3 is relatively low, the strobe unit length becomes long and the printing speed becomes slow. In contrast, in this embodiment, control of the strobe time and switching of the power supply voltage are used together, and when the temperature of the thermal head 3 is low, the power supply voltage supplied to the thermal head 3 is set to a high voltage. . Therefore, the strobe unit length can be made relatively short, and the correction time can be shortened. In this embodiment as well, highly accurate density correction is possible by controlling the strobe time. As explained above, according to the present invention, it is possible to obtain density gradations with good reproducibility regardless of temperature fluctuations of the thermal head.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a density correction device for a thermal transfer printer according to the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the embodiment.

FIG. 3 is a flowchart for explaining the operation of the embodiment.

FIG. 4 is a flowchart for explaining the operation of the embodiment.

FIG. 5 is a block diagram showing a density correction device for a thermal transfer printer according to another embodiment of the present invention.

FIG. 6 is an explanatory diagram showing the configuration of the LUT in FIG. 5;

FIG. 7 is a flowchart for explaining the operation of the embodiment of FIG. 5;

FIG. 8 is an explanatory diagram showing a thermal transfer printer.

FIG. 9 is an explanatory diagram for explaining strobe time.

FIG. 10 is a block diagram showing a density correction device for a conventional thermal transfer printer.

[Explanation of symbols]

3...Thermal head 21...LUT 22...Strobe controller

Claims (2)

[Claims] 1. A thermal head that prints at a predetermined density by being energized for a time based on a strobe signal; and a thermal head that stores strobe data for generating the strobe signal corresponding to the temperature of the thermal head; A look-up table that stores preheat data for preheating the head and outputs stored strobe data and preheat data given the temperature data detected from the thermal head, and a strobe signal based on the preheat data and strobe data. A density correction device for a thermal transfer printer, comprising: a strobe controller that applies electricity to the thermal head to preheat the thermal head and energizes the thermal head for a time corresponding to the temperature of the thermal head. 2. A thermal head that prints at a predetermined density by energizing for a time based on a strobe signal, and a thermal head that stores strobe data for generating the strobe signal corresponding to the temperature of the thermal head. a look-up table that outputs stored strobe data in response to temperature data detected by the thermal head; and a strobe controller that supplies a strobe signal based on the strobe data to the thermal head and energizes the thermal head for a time corresponding to the temperature of the thermal head. and head power supply voltage switching means for switching the power supply voltage supplied to the thermal head in accordance with the temperature of the thermal head.