JPH05201058A - Thermal printer - Google Patents

Abstract

PURPOSE:To eliminate the variation of a density gradation due to thermal influence by a method wherein a remaining heat quantity of thermal resistors for one line before from a line under recording at the present time if calculated, and a means, which corrects a feeding energy based on the calculated quantity, is provided. CONSTITUTION:The density gradation data for respective picture elements in a line buffer 22, which is input from a data input Din and stored, is transferred to a density-power on timing converting circuit 36. The power on timing data which has been converted by the converting circuit 36 determines the thermal resistor temperature to give a density gradation which is suitable for the density gradation data, to respective thermal resistors. The power on timing data is transferred to a thermal influence degree operation circuit 45. The thermal influence degree operation circuit 45 obtains a thermal influence quantity which is applied to respective thermal resistors in the image printing line under recording, from the previous line power on timing data which is input from a previous line power on timing buffer 46.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal printer for recording characters or images on recording paper by using a thermal head in which a plurality of heating resistance elements are arranged in the main scanning direction.

[0002]

2. Description of the Related Art In a thermal printer, the energy applied to each heating resistor element is an important parameter that determines the amount of heat generated by each heating resistor 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 which shows the relationship between the applied energy and the temperature of the heat generating resistance element and the time, the temperature of the heat generating resistance element of the thermal head is smaller than the target temperature by Δ due to the influence of the residual heat of the past recording heat generation.
H becomes higher.

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.

The present invention has been made in view of the above problems, and in each heating resistance element, there is no variation in density gradation due to thermal influence from past recording, and a density level in which a recorded image of high print quality can be obtained. An object of the present invention is to provide a thermal control type thermal printer.

[0014]

In order to solve the above problems, in the present application, a thermal head having a plurality of heating resistance elements arranged in the main scanning direction, and a heating resistance element of the thermal head is selectively selected according to an input image. And an energy supply means for supplying energy to the heating element, the energy supply means calculates the amount of residual heat of the heating resistance element one line before the line currently being recorded, and calculates the amount of supply energy based on the calculation result. Provided is a thermal printer, which is provided with a calculation correction means for correction.

[0015]

In the thermal printer of the present invention, the thermal effect on the heating resistance element during recording is calculated from the past recording of the heating resistance element during recording on the printing line during recording, and recording is performed in accordance with this. The energy applied to the heating resistance element during recording is corrected so that the pixel recorded by the heating resistance element therein has a desired density gradation.

[0016]

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 grayscale data of each time is loaded into the shift register 14 in synchronization with the clock signal CK from the clock circuit 30, each grayscale bit C'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.

This 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 have different values for each unit energization cycle. The energization enable time tE of each unit energization cycle is such that the energization is instructed in all the unit energization cycles during the energization time of one printing line, so that
For example, among 64 gradations (G = 0 to 63) of uniform density gradation,
As shown in FIG. 4, the heating resistance element temperature is set to rise up to the heating resistance element temperature (T = 63) at which the highest level (G = 63) is given. The strobe signal ST 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] gives a density gradation (G = 0 to 63) suitable for density gradation data (a1j to a512j) to each heating resistance element when each heating resistance element generates heat independently, as shown in FIG. As shown in FIG. 5, energization (“1”) or de-energization (“0”) is determined in each unit energization cycle so that the heating resistance element temperature (T = 0 to 63) is reached. The energization timing data [CK P1j to CK P512j] is transferred to the heat influence degree calculation circuit 45.

The heat influence degree calculation circuit 45 uses the preceding line energization timing data [C'K P1j-1 to C'K P512j-1] input from the preceding line energization timing buffer 46 to determine each print line in the printing line. Calculate the amount of thermal influence on the heating resistance element.

Here, the degree of thermal influence of the past recording on each heating element is calculated by, for example, as shown in FIG. 2, an index having a quadratic time function as a multiplier to the recording temperature T in the preceding line recording. By multiplying the function, the residual heat temperature T ′ at a certain time t, that is, the time including the residual heat time can be calculated.

Correction Formula T '= T × EXP ^ (a × t2 + b × t + c) In the above correction formula, the multiplier part of the exponential function is a time constant, a first-order time function or a higher-order time function other than the quadratic time function. It is possible to approximate the cooling state of the residual heat of the past record by using, and it is also possible to approximate the exponential function itself by a constant, a linear function or a higher-order function.

The applied energy E'corrected from this residual heat temperature T'is obtained.

The concrete method is to convert the residual heat temperature T'at a certain time t into a correction energy .DELTA.E by multiplying it by a correction coefficient .alpha. Ask for.

Correction formula E '= E-ΔE ΔE = α × T' Next, in order to correct the energy applied to each heating resistance element from this applied energy E ', energization timing data [for each heating resistance element] CK P1j to CK P512j],
Corrected energization timing data [C'K P1j to C'K P512
j].

Corrected energization timing data [C'K P1j ~
C′K P512j] is stored in the energization timing buffer 20.

As described above, the density gradation data (a1j to a1)
512j) to correct the thermal effect from the heat generating resistance elements near each heat generating resistance element and to correct the energization timing data [C'K
P1j to C'K P512j], and each heating resistor element (R1 to R512) is energized according to the corrected energization timing data [C'K P1j to C'K P512j]. As a result, each of the heating resistance elements (R1 to R512) has a density gradation (G = 0 to 6) that matches the density gradation data (a1j to a512j) during the energization time.
3) The heating resistance element temperature (T = 0 to 63) is obtained, and recording is performed on the recording paper with desired density gradation.

[0032]

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

With respect to the heating resistance element during recording in the printing line during recording, the thermal effect from the past recording to the heating resistance element during recording is calculated, and in accordance with this, the pixel to be recorded has a desired density level. By correcting the applied energy to the heating resistance element during recording, the density gradation does not change due to thermal effects from past recording, and the desired density gradation can be printed on the recording paper with high accuracy. Can be reproduced, and a recorded image of high print quality can be obtained. In addition, since the calculation is performed each time, the correction can be performed more accurately than that using a ROM or the like.

[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 resistor 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 resistor element according to a conventional example.

[Explanation of symbols]

10 Thermal Heads R1 to R512 Heat Generation Resistor Element 20 Energy Supply Means (Energization Timing Buffer) 36 Energy Supply Means (Concentration-Energization Timing Conversion Circuit 45) Calculation Correction Means (Thermal Influence Calculation Circuit) 46 Calculation Correction Means (Previous Line Power Supply Timing Buffer) )

Claims (1)

[Claims] 1. A thermal head having a plurality of heating resistance elements arranged in the main scanning direction, and an energy supply means for selectively supplying energy to the heating resistance elements of the thermal head according to an input image. The supply means includes a calculation correction means for calculating the amount of residual heat of the heating resistance element one line before from the line currently being recorded and correcting the amount of supplied energy based on the calculation result. Printer.