JP3133469B2 - Thermal recording device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal recording apparatus for recording on a recording medium while energizing and heating a heating element and moving the heating element and a recording medium relative to each other. The present invention relates to a thermal recording device such as a thermal printer capable of expressing density gradation.

[0002]

2. Description of the Related Art Conventionally, there are a pulse width modulation method and a pulse number modulation method as this kind of density gradation control method. FIG. 6 is a timing chart of energizing pulses to the thermal head at high density and low density according to these methods. As shown in the figure, in the case of the pulse width modulation method, the energization rate to the heating resistor is increased for high density printing, and the energization rate is decreased for low density printing to reduce the density. Controlling. In the case of the pulse number control method, an energizing pulse composed of a plurality of unit pulses is applied to printing of one pixel. For high density printing, the number of unit pulses is increased, and for low density printing, the number of unit pulses is reduced to control density.

In such a thermal recording apparatus, since the print density changes due to heat storage in the thermal head, the temperature of the heating resistor at the time of printing of each pixel and the print pattern history are corrected to correct this. , The energizing pulse correction is performed.

[0004]

However, in the above-described conventional recording apparatus, the energizing energy applied to each pixel differs depending on the density, and therefore, the temperature of the heating resistor at the start of printing greatly varies. The circuit becomes complicated and the size of the device is increased.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has been made in view of the above circumstances. To provide.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a thermal recording apparatus for recording on a recording medium while energizing and heating a heating resistor and moving the heating resistor and a recording medium relative to each other. The duty ratio and the pulse width of the energizing pulse in the energizing pattern for printing a pixel are both variably controlled, and the sum of the pulse widths of a plurality of energizing pulses for printing one line is controlled to be constant. is there.

[0007]

[0008]

According to the present invention, the energizing energy to the heating resistor for each pixel can be made constant irrespective of the gradation data.

[0009]

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing embodiments thereof.

First, the density gradation by the frequency modulation of the energizing pulse will be described with reference to FIGS.

FIG. 1 shows a temperature change diagram of the heating resistor when three types of repetitive pulses having different frequencies are applied to the heating resistor. The duty ratio for each pixel is 5
0%. Here, the energization rate refers to the ratio of the pulse width of the energization pulse to the energization pattern composed of the pulse width of the energization pulse and the pause time.

The heating resistor temperature at the start of application of the repetitive pulse is equal to the ambient temperature, and during the first energizing time, the heating resistor temperature rises exponentially.
During each pause, the heating resistor temperature drops exponentially. However, normally, the cooling is not sufficiently performed during the pause time until the application of the second pulse, and the second pulse is applied at a temperature slightly higher than the ambient temperature. Such a heat cycle is repeated, and the temperature of the heating resistor gradually increases. This temperature rise stops when the amount of heat generated by the heat generating resistor and the amount of heat radiated from the thermal head become equal, and the temperature reaches an equilibrium state. in this way,
When a repetition pulse is given as the energization command, the heat cycle in the heating resistor becomes a steady state after the application of the N-line energization pulse. In this steady state, the temperature at the start of printing of each line of the heating resistor and the maximum temperature when a pulse of pattern 1 having a low frequency is applied are T _1B and T _1T, and the applied pulse frequency of pattern 1 is 2 When the doubled pulse of pattern 2 was applied, the temperature at the start of printing of each line of the heating resistor and the maximum temperature were T _2B and T _2T , and a very high frequency pulse of pattern 3 was applied. Assuming that the printing start temperature and the maximum temperature of each line of the heating resistor in the case are T _3B and T _3T , the following relational expressions are established.

[0014]

(Equation 1)

In the case of pattern 3, since a high-frequency pulse is applied, T _3B and T _3T are substantially equal in a steady state.

FIG. 2 shows a case where the threshold temperature T _{TH at} which the sublimation dye starts diffusion transfer onto the recording paper and T _1T , T _2T , and T _3T in the above patterns 1 to 3 have a relationship represented by the following equation. 3 shows a heating resistor temperature change diagram in FIG. FIG. 2 shows a diagram in the steady state.

[0017]

(Equation 2)

As shown in FIG. 2, when performing high-density printing, a low-frequency pulse as in pattern 1 is applied. Accordingly, the maximum temperature of the heating resistor is sufficiently higher than _{TTH, and the} temperature of the heating resistor is maintained at _TTH or higher for a long time, and many sublimation dyes are diffused and transferred onto the recording paper. When printing is not performed, a pulse having a very high frequency such as pattern 3 is applied. Therefore, since the maximum temperature of the heating resistor is always lower than _TTH , the sublimation dye is not transferred onto the recording paper by diffusion. When printing medium density,
A pulse having an intermediate frequency between the pattern 1 and the pattern 3 as shown in a pattern 2 is applied. Therefore, the amount of energizing energy at which the temperature of the heating resistor exceeds T _TH depends on the pattern 1
Therefore, the amount of the sublimation dye to be diffuse-transferred onto the recording paper is smaller than that of the pattern 1.

As described above, the density can be controlled by modulating the energizing pulse frequency applied to each pixel.

Next, a control circuit of a sublimation type thermal printer to which the present invention is applied will be described with reference to a schematic block diagram of FIG.

In FIG. 3, gradation data of an input image is temporarily stored in an image memory 1. Next, one line of the gradation data stored in the image memory 1 under the control of the CPU (microcomputer) 2 is input to the line memory 3 and supplied to the energizing pulse frequency modulation circuit 4 described later. .

The printing of one line is composed of a plurality of steps (0 to 255 steps in this embodiment), and the step counter 5 counts the number of steps. 6 is for each step of the step counter 5,
This is a ROM in which energization pulse data for gradation data is written in advance. Table 1 shows the contents of the energizing pulse data for the gradation data stored in the ROM 6.

[0023]

[Table 1]

As shown in Table 1, in the present embodiment, the energizing pulse data of 256, 128, 64, 32, 16, 8, 8, 4, 2, and 1 periods is used as energizing pulse data of 256 steps to energize one pixel. 50%, 8 gradation data is stored in the ROM 6.

The energizing pulse frequency modulating circuit 4 reads the gradation data of the line memory in response to the input of the step value from the step counter 5, and stores the gradation data for one line into the ROM 6 according to the step value and the gradation data. It is converted into stored energization pulse data. Therefore, first, the gradation data for one line in the 0 step is converted into the energizing pulse data, and the step counter 5 counts up.
A head driver control circuit 7 for controlling operation timings of the line memory 3, the energizing pulse frequency modulation circuit 4, the step counter 5, the thermal head 8, and the like.
In accordance with the input of the count-up signal of the step counter 5, a drive signal corresponding to the energizing pulse data for one line in the zero step converted by the energizing pulse frequency modulation circuit 4 is supplied to the thermal head 8, The head 8 is driven to generate heat.

Next, in the energizing pulse frequency modulation circuit 4, the gradation data for one line in one step is converted into energizing pulse data, and the thermal head 8 is driven to generate heat in the same manner as in the zero step. Then, similarly, the gradation data for one line is converted into the energized pulse data up to 255 steps, and the thermal head 8 is driven to generate heat, thereby completing the printing for one line. As a result, an energizing pulse having a maximum of 128 cycles and a minimum of one cycle can be supplied to the thermal head 8 for one pixel.

When printing of one line is completed, the CPU 2
, A count clear signal is input to the step counter 5, and printing is performed in the same manner for the next line and thereafter.

Next, the configuration of the driver IC of the thermal head 8 will be described with reference to FIG. First, the energizing pulse data 21 for one line in the step value of the step counter 5 is input and held in the shift register 23 serially in synchronization with the clock signal 22. When the input is completed, the contents of the shift register 23 are latched by the latch circuit 25 by the latch signal 24, and then the strobe signal 26 is input to drive the heating resistor 27. This operation is
By repeating 256 times up to 255 steps, 1
The printing for the line ends.

Further, in addition to the above embodiment, the energization rate to the heating resistor 27 for one pixel is fixed irrespective of the gradation data, and the energizing pulse frequency for energizing the heating resistor 27 according to the gradation data. In addition to variably controlling the energization ratio and / or the energization pulse width for one cycle of the energization pattern in accordance with the gradation data, finer gradation control can be performed.

In another embodiment, the duty ratio for one pixel is set to 50%, and density gradation control is performed between printing with two cycles of energizing pulse data and printing with four cycles of energizing pulse data. The case will be described as an example with reference to the timing chart of the energizing pulse in FIG. As shown in FIG. 5, one pixel is printed by energizing pulse data in two cycles (hereinafter, abbreviated as two-division printing), and is printed by four energizing pulse data (hereinafter, four-division printing). (Abbreviated), the energizing pulse frequency for one pixel is the same as that for four-division printing, and the energizing rate and / or energizing pulse width for one energizing pulse cycle are variable. Control.

More specifically, when the density gradation is performed by variably controlling only the energization rate (pattern A), the energization pulse 1
The energizing pulse width with respect to the cycle is t, which is the same as that at the time of four-division printing, the first and third energizing pauses during one pixel printing are r, and the second and fourth energizing pauses are 2t-r. By controlling r variably from 0 to t in accordance with the gradation data, a printing density between two-part printing and four-part printing can be obtained. In this case, as r is set to be large, low density printing is performed.

Next, in the case of performing the density gradation by variably controlling only the energizing pulse width (pattern B), the energizing rate in one cycle of the energizing pattern is set to 50% which is the same as that at the time of four-division printing, and one pixel printing is performed. The pulse width of the first and third energizing pulses during shooting is t + d, the pulse width of the second and fourth energizing pulses is t−d, and d is changed from 0 to t according to the gradation data.
The printing density between the two-part printing and the four-part printing can be obtained by variably controlling the printing density. In this case, the lower the value of d, the lower the density of printing.

When the density gradation is performed by variably controlling the duty ratio and the duty pulse width (pattern C), the pulse widths of the first and third duty pulses during one pixel printing, and The second and fourth energization pause times are t + d, the pulse widths of the second and fourth energization pulses, and the first and third energization pause times are t−d. Is variably controlled between 0 and t to obtain a printing density between two-part printing and four-part printing. In this case, the lower the value of d, the lower the density of printing.

As described above, the energizing pulse frequency for one pixel is the same as that for four-division printing, and the energizing rate and / or energizing pulse width for one energizing pulse cycle are variably controlled, so that two-division printing is performed. And the print density between 4 and 4 division printing are obtained, and fine density gradation control becomes possible. Also,
Similarly, it is possible to perform gradation control of the print density when the energizing pulse frequency for one pixel is the same.

Although the above embodiment has been described with reference to the case where the duty ratio is 50%, the present invention may be any other value as long as the energizing energy to the heating resistor is constant.

Although the present invention has been described as applied to a sublimation type thermal printer, the present invention can also be applied to a thermal recording apparatus such as a fusion type thermal printer for expressing density gradation and a sublimation type video printer.

[0037]

As described above, according to the present invention, since the sum of the pulse widths of the energizing pulses for printing one line is controlled to be constant, one line is printed regardless of the gradation data. The energy applied to the heating resistor during imaging can be made constant, thereby reducing the variation in the temperature of the heating resistor at the start of printing of each line and eliminating the need for a complicated history control circuit. .

Further, the gradation of the printing density is controlled by variably controlling not only the pulse width of the energizing pulse for printing one pixel but also the energizing rate in the energizing pattern for printing one pixel. Therefore, finer density gradation control can be performed for each pixel, and the printing quality can be improved.

[0039]

[Brief description of the drawings]

FIG. 1 is a diagram showing a temperature change of a heating resistor for explaining density gradation by energization pulse frequency modulation in the present invention.

FIG. 2 is a temperature change diagram of a heating resistor for explaining a density gradation by energization pulse frequency modulation in the present invention.

FIG. 3 is a schematic block diagram of a sublimation type thermal printer showing one embodiment of the present invention.

FIG. 4 is a thermal head driver I in the embodiment of FIG. 3;
It is a circuit diagram of C.

FIG. 5 is a timing chart of an energizing pulse for explaining the operation of another embodiment of the present invention.

FIG. 6 is a timing chart of an energizing pulse in a conventional density gradation control method.

[Explanation of symbols]

 Reference Signs List 1 image memory 2 CPU 3 line memory 4 energizing pulse frequency modulation circuit 5 step counter 6 ROM 7 head driver control circuit 21 energizing pulse data 22 clock signal 23 shift register 24 latch signal 25 latch circuit 26 strobe signal 27 heating resistor 28 driver array

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-265761 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B41J 2/36

Claims (1)

(57) [Claims] 1. An energizing pattern for printing one pixel in a thermal recording apparatus for recording on a recording medium while energizing and generating heat of a heating element and relatively moving the heating element and a recording medium. Wherein the duty ratio and the pulse width of the energizing pulse are both variably controlled, and the sum of the pulse widths of a plurality of energizing pulses for printing one line is controlled to be constant.