JPH05201057A - Thermal printer - Google Patents

Abstract

PURPOSE:To eliminate the variation of a density gradation due to a thermal influence from a recording in the past by providing a correcting means which corrects an applying energy to thermal elements under recording, according to a calculated thermal influence quantity. CONSTITUTION:The density improvement data (a1j-a512j) for respective picture elements of 1 image printing line is input an stored in a line buffer 22 from a data input Dim. The density gradation data for respective picture elements in the line buffer 22 is transferred to a density-power on timing converting circuit 36, and is converted to power on timing data there. The power on timing data gives a density gradation which is suitable for the density gradation data to each thermal resistor, when each thermal resistor is individually heated. The power on timing data is transferred to a thermal influence degree operation circuit 45, and the thermal influence degree operation circuit 45 obtains a thermal influence quantity to each thermal resistor in the image printing line under recording, from the previous line power connection timing data from a previous line power connection timing buffer 46 and a thermal influence degree coefficient from a correction coefficient ROM 47.

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 characters or images on a recording paper by using a thermal head having a plurality of heating resistance elements arranged in the main scanning direction.

[0002]

2. Description of the Related Art In a thermal recording apparatus, the energy applied to each heating resistance element is an important parameter that determines the amount of heat generated by each heating resistance element and determines the density of a recording pixel.

Therefore, conventionally, the applied energy during the unit energization time is controlled in accordance with the density gradation of the input, and the temperature of the heating resistor element is controlled.
The density gradation was controlled.

FIG. 6 shows the main structure of a conventional density gradation control type thermal printer.

The thermal head 110 has a heating resistor 112 in which heating resistors are arranged in a line, and a shift register 11 having the same number of bit capacities as the heating resistors.
4 and a latch circuit 116 are provided.

In the line buffer 122, the density gradation data of each pixel of one printing line is input from the data input Din and stored. The density gradation data of each pixel of the line buffer 122 is the density-energization timing conversion circuit 136.
Thus, it is converted into energization timing data and stored in the energization timing buffer 120.

The energization timing buffer 120 sequentially shifts the serial energization timing data corresponding to the heating resistance element a plurality of times in a constant cycle during the printing time of each printing line according to the count value of the energization number counter 138. Give to.

The gradation data of each time is synchronized with the clock signal CK from the clock circuit 130, and the shift register 114
Then, it is sent to the heating resistor 112 via the latch circuit 116 at the timing of the latch signal LA from the latch signal generation circuit 132. This heating resistor 11
A power source device 150 supplies a recording power source voltage VR to the heating resistor element 2. Then,
These heating resistance elements selectively output the unit energization cycle ΔT according to the information content of the corresponding gradation bit.
Generates heat by energizing inside.

The unit energization cycle ΔT is defined by the latch signal LA. The strobe signal ST from the strobe signal generating circuit 134 in the unit energization cycle ΔT controls the energization enable time during which the current actually flows through the heating resistance element. The energization enable time can have different values for each unit energization cycle. The energization enable time of each unit energization cycle is the highest level of density for each pixel on one printing line, since energization is instructed in all unit energization cycles during the energization time of one printing line. It is set so as to rise to the temperature of the heating resistor element to which gradation is applied.

With the above structure, according to the density gradation data of each pixel on one printing line, the current is converted into the energization timing data which becomes the temperature of the heating resistor element for obtaining the target density gradation, and the current is energized to record. Done.

[0011]

However, in the thermal recording apparatus which applies energy to the heating resistance element of the thermal head to generate heat as described above, when continuously driven,
As shown in FIG. 7, the temperature of the heat generating resistance element of the thermal head becomes higher than the target temperature due to the influence of the residual heat generated in the past recording.

[0012] In other words, the same energy E and the applied energy at an applied energy is time t ₀₂ time at the point of time t _{01 01}
Although, the heat producing temperature T of the heating resistor element is a temperature T ₀₁ at the time of time t _01, a temperature higher than the temperature T ₀₁ by residual heat generation temperature at the time of the previous time t ₀₁ in a subsequent time t ₀₂ time The temperature will be T ₀₂ .

Therefore, even if the heating resistance element temperature of each heating resistance element is controlled according to the density gradation of the input, the heating resistance element temperature fluctuates due to the thermal influence from the past recording, and the desired density is obtained. There is a problem that the gradation cannot be accurately reproduced on the recording paper.

Therefore, there is a configuration in which the temperature rise due to heat generation in the previous line is corrected for each latch by using the configuration shown in FIG. 8 and the target temperature is controlled as shown in FIG.

A signal indicating the energization time from the concentration-energization time timing conversion circuit 36 is corrected by the thermal influence degree calculation circuit 45 for each latch. At this time, in the heat influence degree calculation circuit 45, the electricity supply timing data from the electricity supply timing buffer 20 is stored in the previous line electricity supply timing buffer 46, and a signal indicating the electricity supply timing is output to the heat influence degree calculation circuit 45 for each latch. To be done. The heat influence degree calculation circuit 45 calculates the heat influence degree from the previous line for each latch and corrects the energization timing. However, this circuit configuration causes another problem that the scale of the circuit of the arithmetic circuit 45 becomes large and the time for performing the correction calculation becomes long.

The present invention has been made in view of such a problem. The energization time of one line is divided, and a correction coefficient for correcting the energy of the thermal influence amount is predetermined in each divided time. By calculating the correction energy using the correction coefficient to generate heat, there is no change in the density gradation due to the thermal effect from the past printing, a printed image of high print quality can be obtained, and the correction calculation circuit scale It is an object of the present invention to provide a density gradation control type thermal printer in which the above-mentioned reduction and the calculation time are shortened.

[0017]

In order to solve the above-mentioned problems, one line recording is performed in a thermal printer for recording characters or images on recording paper using a thermal head in which a plurality of heating resistance elements are arranged in the main scanning direction. A predetermined amount of energy is arbitrarily applied to a heating resistance element therein for a predetermined energization time, and in each divided time obtained by dividing the energization time of one line, the heat generation resistance during the recording from the residual heat of the past recording. There is provided a thermal printer characterized in that a thermal influence amount on an element is calculated, and the applied energy to the heating resistance element during recording is corrected in accordance with the thermal influence amount.

[0018]

The thermal printer of the present invention divides the energization time of the printing line during recording into a plurality of times, and in each of these divisions, recording is performed in accordance with the thermal influence from the past recording on the heating resistance element during recording. The energy applied to the heating resistor element during recording is corrected so that the pixel recorded by the heating resistor element therein has a desired density gradation, and the correction calculation circuit scale and the calculation time are shortened. Are doing

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the main structure of a density gradation control type thermal printer according to an embodiment of the present invention.

The thermal head 10 includes, for example, a heating resistor 12 in which 512 heating resistor elements R1 to R512 are arranged in a line, a shift register 14 having the same number (512) of bit capacities as those heating resistor elements, and And a latch circuit 16.

The energization timing buffer 20 has 512 heating resistance elements R1 to R51 during the printing time of each printing line.
The 512-bit serial correction energization timing data [C'K P1j to C'K P512j] corresponding to 2 are counted by the energization number counter 38 continuously for a plurality of times, for example, 256 times (K = 1 to 256). It is given to the shift register 14 according to the value (K).

Here, the nth bit CK Pnj has information as to whether or not the nth heating resistor element Rn should be energized during the unit energization cycle ΔT. That is, if "1", the energization is instructed, and if "0", the non-energization is instructed.

When the gradation data of each time is loaded into the shift register 14 in synchronization with the clock signal CK from the clock circuit 30, each gradation bit C ′ is next at the timing of the latch signal LA from the latch signal generating circuit 32. K P1j ~
C'K P512j is sent to the heating resistor 12 as an electric pulse via the latch circuit 16. A recording power supply voltage VR to be applied to the heating resistance elements R1 to R512 is applied to the heating resistor 12 from the power supply device 50. Then, the heating resistor elements R1 to R512 selectively generate electricity during the unit energization cycle ΔT according to the information content of the corresponding grayscale bits C′K P1j to C′K P512j to generate heat.

The unit energization cycle ΔT is defined by the latch signal LA. Strobe signal S from strobe signal generating circuit 34 in unit energization cycle ΔT
As shown in FIG. 3, T is composed of an energization enable time tE in which a current actually flows in the heating resistor element and a time tC in which no current flows. The energization enable time tE can be set to a different value for each unit energization cycle Δ. The energization enable time tE of each unit energization cycle is, for example, 64 levels for each pixel on one printing line by instructing energization in all the unit energization cycles during the energization time of one printing line ( G = 0 to 63) Among the evenly-spaced density gradations, as shown in Fig. 4, the heating resistance element temperature is up to the heating resistance element temperature (T = 63) at which the highest level (G = 63) is given. It is set to rise. Strobe signal S
T is input to the thermal head 10.

In the line buffer 22, density gradation data (a1j to a512j) of each pixel of one printing line is input from the data input Din and stored. Line buffer 22
The density gradation data (a1j to a512j) of each pixel of
It is transferred to the energization timing conversion circuit 36, and is converted into energization timing data [CK P1j to CK P512j] in the density-energization timing conversion circuit 36.

Energization timing data [CK P1j to CK P
512j] is the temperature of the heating resistor element, which gives a density gradation (G = 0 to 63) that matches the density gradation data (a1j to a512j) to each heating resistor element when it independently generates heat. (T
= 0 to 63), as shown in FIG.
Energized ("1") or de-energized ("0") in electric cycle
It is what decides. Energization timing data [CK
P1j to CK P512j] are transferred to the heat influence degree calculation circuit 45.

The heat influence degree calculation circuit 45 receives the preceding line energization timing data [C'K P1j-1 to C'K P512j-1] input from the preceding line energization timing buffer 46 and the correction coefficient ROM 47. From the thermal influence coefficient [α _i ] according to the above, the amount of thermal influence exerted on each heating resistance element in the printing line during recording is obtained.

Here, the calculation of the degree of thermal influence of the past recording on each heating element has, as shown in FIG. 2, for example, a quadratic time function that approximates the cooling of the residual heat of the past recording as a multiplier. The heat influence coefficient [α _i ] obtained by integrating and averaging the exponential function is multiplied by the recording temperature [T] in the previous line recording to integrate the residual heat temperature at a certain division time (t _{i to} t _i-1 ). The average value [T _i '] can be calculated.

[0029]

[Correction formula 1]

In the above correction formula, the multiplier part of the exponential function is
In the graph showing the time-heating resistance element temperature shown in FIG. 2, the temperature residual of the front line shown by the broken line is shown as a function of time t. Actually, this curve was drawn by an experiment, and then this curve was drawn. Find the time function that represents the curve. By this, the constants a, b, and c are obtained. In addition to the quadratic time function, it is also possible to approximate the cooling state of residual heat in the past record by using a time constant, a first-order time function, or a higher-order time function. It is also possible to perform approximation with a higher-order function.

Next, the energization timing data [CK P1j to CK P51 of each heating resistance element is used to correct the energy applied to each heating resistance element from the thermal influence of past recording.
2j] is corrected and corrected energization timing data [C'K P1j
.About.C'K P512j].

[0032] Here, the calculation of the correction energization timing data of each heating resistor element [C'K P1j~C'K P512j] is divided time remaining heat temperature integral average value in (t _i ~t _{i over 1)} [T _i '] is multiplied by a correction coefficient [β] to convert it to correction energy [ΔE _i ] and subtracted from the applied energy [E] of the heating resistance element to be corrected to obtain the required applied energy [E _i '], and energization Corrected energization timing data [C'K P1j to C'K P that gives the applied energy during the time
512j].

[0033]

[Equation 2] Correction equation E _i ′ = E−ΔE _i ΔE _i = β × T _i ′ (i = 1, ..., n) Corrected energization timing data [C′K P1j to C′K P512
j] is stored in the energization timing buffer 20.

As described above, the density gradation data (a1j to a1
512j) is converted to corrected energization timing data [C'K P1j to C'K P512j] by compensating for thermal influences from past recordings, and corrected energization timing data [C'K P1j to C'K.
P512j], each heating resistor element (R1 to R512) is energized. As a result, each heating resistance element (R1 to R512)
Is the density gradation data (a1j to a512) during the energization time.
The heating resistance element temperature (T = 0 to 63) is obtained to obtain the density gradation (G = 0 to 63) suitable for j), and the desired density gradation is recorded on the recording paper.

[0035]

The present invention has the following effects by having the above-mentioned structure.

The energization time of the printing line during recording is divided into a plurality of times, and the heating resistance elements during recording in each of these divisions are recorded in accordance with the thermal influence from the past recording to the heating resistance elements during recording. By correcting the energy applied to the heating resistance element during recording so that the pixels with the desired density gradation can be obtained, there is no fluctuation in the density gradation due to thermal effects from past recording, and the desired density It is possible to reproduce the tones on the recording paper with high accuracy, and a recorded image of high print quality can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main circuit configuration of a density gradation control type thermal printer according to an embodiment of the present invention.

FIG. 2 is a diagram showing a thermal head drive waveform and a temperature waveform of a heating resistance element according to an embodiment.

FIG. 3 is a diagram showing a timing of a unit energization cycle according to an embodiment.

FIG. 4 is a diagram showing a heating resistance element temperature-recording density characteristic by density gradation control.

FIG. 5 is a diagram showing the contents of an energization timing buffer according to the embodiment.

FIG. 6 is a block diagram showing the main circuit configuration of a density gradation control type thermal printer according to a conventional example.

FIG. 7 is a diagram showing a thermal head drive waveform and a temperature waveform of a heating resistance element according to a conventional example.

FIG. 8 is a block diagram showing the main circuit configuration of a density gradation control type thermal printer according to a conventional example.

FIG. 9 is a diagram showing a thermal head drive waveform and a temperature waveform of a heating resistance element according to a conventional example.

[Explanation of Codes] 10 Thermal Head 12 Heating Resistor 20 Energization Timing Buffer 36 Density-Energization Timing Conversion Circuit 38 Energization Counter 40 CPU 45 Heat Influence Calculation Circuit 46 Previous Line Energization Timing Buffer 47 Heat Influence Coefficient ROM

Claims (1)

[Claims] 1. A thermal printer for recording characters or images on a recording sheet using a thermal head having a plurality of heating resistance elements arranged in the main scanning direction, wherein a predetermined amount of energy is given to the heating resistance elements during one line recording. It is applied arbitrarily during the energization time, and in each divided time obtained by dividing the energization time of one line, the amount of thermal influence on the heating resistance element during the recording is calculated from the residual heat of the past recording, A thermal printer comprising a correction means for correcting the energy applied to the heating resistance element during recording in accordance with the amount of thermal influence.