JP2962896B2 - 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. 7 shows 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]

Therefore, in the above-mentioned conventional recording apparatus, in order to eliminate the printing density unevenness, the above-described history control correction circuit is required, which complicates the configuration and increases the size of the apparatus. Was calling.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a thermal recording apparatus which eliminates variations in the temperature of a heating resistor at the start of printing in each pixel and does not cause uneven printing density. It is.

[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. A preheating means for preheating the heating resistor to a predetermined temperature before the operation is started; and an energization control for variably controlling an energization pulse frequency and an energization rate to the heating resistor for each pixel according to gradation data. Means, wherein the temperature at the start of energization of the heating resistor for each pixel is the predetermined temperature irrespective of the gradation data.

[0007]

According to the present invention, the temperature of the heating resistor at the start of energization in each pixel becomes constant regardless of the gradation data.

[0008]

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 modulation of the energizing pulse frequency in a sublimation type thermal printer to which the present invention is applied will be described with reference to FIGS.

FIG. 1 shows a temperature change diagram of the heating resistor when three kinds of repetitive pulses having different frequencies are applied to the heating resistor as energizing pulses. The duty ratio for each pixel is 50%.

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 becomes 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.

[0012]

(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 the steady state in the case where the energizing pulses of the patterns 1 and 2 and the energizing pulse of the pattern 2 ′ having the same frequency as the energizing pulse of the pattern 2 and having a reduced energization rate are applied. 3 shows a heating resistor temperature change diagram.

As shown in FIG. 2, since the duty ratio of the heating resistor for one pixel is the same in pattern 1 and pattern 2, the temperature at the start of printing of pattern 2 having a high energization pulse frequency is as described above. In comparison with pattern 1. On the other hand, in the case of the pattern 2 ′, since the duty ratio of the heating resistor for one pixel is smaller than that of the pattern 2, the printing start temperature in the steady state is lower than that of the pattern 2. Accordingly, by setting the duty ratio for the pattern 2 ′ so that the printing start temperature becomes T _1B , even if the energization pulse frequency is varied according to the gradation data, the heating resistor is not affected by the gradation data. The printing start temperature in the steady state can be set to a predetermined value.

FIG. 3 shows a threshold temperature T _{TH at} which the sublimation dye starts diffusion transfer onto the recording paper and a pattern 3 ′ in which the duty ratio of the pattern 3 is changed in the same manner as the patterns 1, 2 ′ and 2 ′. FIG. 4 is a diagram showing a temperature change diagram of the heating resistor in the steady state when the maximum temperature T _1T , T _2T ′, and T _3T ′ of the heating resistor in the steady state are in a relationship represented by the following equation.

[0017]

(Equation 2)

As shown in FIG. 3, when performing high-density printing, a low-frequency pulse such as 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 with 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 excitation energy that the temperature of the heating resistor exceeds T _TH, since less than that of the pattern 1, the amount of sublimation dye is diffused transferred onto the recording becomes smaller than the pattern 1.

In the patterns 1, 2 'and 3', in the steady state, the temperature of the heating resistor at the start of energization to each pixel is _T1B , and there is no variation in the temperature of the heating resistor.

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. 4, the gradation data of the input image is temporarily stored in the 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). 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. The ROM 6 stores, as energization pulse data of 256 steps for energizing one pixel, an energization rate gradually reduced as the energization pulse frequency increases, one cycle, 50% to 64 cycles, and 25% energization rate. 7 is stored.

The energizing pulse frequency modulating circuit 4 reads the gradation data of the line memory in response to the step value input from the step counter 5, and stores the gradation data for one line in the ROM 6 based on 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. The head driver control circuit 7 is controlled by the CPU 2.

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.

Next, the basic operation of image recording in the above embodiment will be described with reference to the flowchart of FIG.

First, prior to the start of printing, energizing pulse data corresponding to 0-level data, which is low-density gray scale data, is read from the ROM 6 (S1), and the heating resistor 27 is driven to generate heat in accordance with the read energizing pulse data. (S2).
Note that the 0 gradation data is gradation data at the time of non-printing. Then, in the next step, it is determined whether or not the heating drive for 50 lines has been performed (S3). This step S
If it is not determined in step 3 that the heating drive has been performed for 50 lines, the process returns to step S2. If it is determined that the drive for heating has been performed for 50 lines, the process proceeds to the next step S4. The heating drive for 50 lines in step S3 is performed by the heating resistor 27.
Is set in consideration of the energizing time required to bring the above into a steady state.

In the next step S4, energizing pulse data corresponding to the gradation data of the line memory 3 is read from the ROM 6, and the heating resistor 27 is driven to generate heat in accordance with the read energizing pulse data, and sublimates on the conveyed recording paper. The dye is diffusion-transferred (S5). Then, according to the gradation data of the input image stored in the image memory 1,
It is determined whether or not all the printing has been completed (S6). If the printing is being performed, the process returns to step S4, and the image recording ends with the printing of all the lines completed.

In the above embodiment, the case where the present invention is applied to a sublimation type thermal printer has been described.
The present invention is also applicable to a thermal recording device such as a fusion type thermal printer that performs density gradation expression and a sublimation type video printer.

[0032]

As described above, according to the present invention, the preheating means for preheating the heating resistor to a predetermined temperature before the start of the recording operation, and the heating resistor for each pixel in accordance with the gradation data. Power supply control means for variably controlling the power supply pulse frequency and the power supply rate, so that the temperature at the start of power supply of the heating resistor to each pixel is set to the predetermined temperature regardless of the gradation data. Can be.

Accordingly, there is no variation in the temperature of the heating resistor at the start of printing, and the history control circuit becomes unnecessary.

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

FIG. 4 is a schematic block diagram of a sublimation type thermal printer showing one embodiment of the present invention.

FIG. 5 shows a thermal head driver I in the embodiment of FIG.
It is a circuit diagram of C.

FIG. 6 is a flowchart for explaining a basic operation of image recording in the embodiment in FIG. 4;

FIG. 7 is a timing chart of an energizing pulse in a conventional density gradation control method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 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-2-248263 (JP, A) JP-A-63-264375 (JP, A) JP-A-61-197257 (JP, A) JP-A-2- 265761 (JP, A) JP-A-61-149370 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B41J 2/36 B41J 2/38

Claims (3)

(57) [Claims] 1. A thermal recording apparatus for recording on a recording medium while energizing and generating heat from a heating resistor and moving the heating resistor and a recording medium relative to each other. A preheating means for preheating the heating element to a predetermined temperature; and an energization control means for variably controlling an energization pulse frequency and an energization rate to the heating resistor for each pixel according to the gradation data, wherein the gradation data Irrespective of the temperature, the temperature at the start of energization of the heating resistor for each pixel is the predetermined temperature. 2. A thermal recording apparatus according to claim 1, wherein said preheating means drives said heating resistor to generate heat at an energizing pulse frequency in non-print gradation data by said energizing control means. 3. The energization control means increases the energization pulse frequency to the heating resistor for each pixel and decreases the energization rate gradually from high density gradation data to low density gradation data. 2. The method according to claim 1, wherein
Or the thermal recording device according to 2.