JPH0679902A - Density gradation control type thermal printer - Google Patents

Abstract

PURPOSE:To obtain a thermal printer in which a pixel size is constant even when density gradation varies and whose image printing quality is high by making a power supply time for the whole heating resistance elements constant and controlling temperatures of the heating resistance elements in accordance with density gradation inputted. CONSTITUTION:A thermal head 10 is provided with a heating resistor 12 consisting of, for example, 512 pieces of heating resistance elements R1 to R512 arranged in a row, a shift register 14 having the same number of bit capacities, and a latch circuit 16. During a period of image printing time for each image printing line, a power supply timing buffer 20 gives serial power supply timing data CKP 1j to CKP 512j on 512 bits with respect to 512 pieces of the heating resistance elements R1 to R512, respectively, to the shift register 14 in a predetermined period and in the number of plural times, for example, 256 times in succession, according to a value K counted by a counter 38 for the number of times of power supply.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal printer capable of obtaining a desired density gradation by controlling the energy applied to a heating resistance element.

[0002]

2. Description of the Related Art In a thermal printer, 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 thus determines the density of a recording pixel.

Therefore, conventionally, by controlling the energization time for supplying a current to each heating resistance element according to the density gradation of the input, the heat generation of each heating resistance element forms on the recording paper. The density gradation of the pixel was controlled.

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

The density gradation data of each pixel of one printing line stored in the line buffer 122 is the energization time data representing the time during which the density-energization time conversion circuit 136 applies the current to the heating resistance element corresponding to each pixel. Is converted to.
The energization time data is stored in the energization time buffer 120.

When energization is started, the value of the energization counter 138, which indicates the time from the start of energization, is compared with the energization time data for each heating resistance element, and the energization time for each heating resistance element is controlled. The energy applied to each heating resistance element is controlled so that a desired density gradation can be obtained in each pixel.

That is, for a low-density pixel, the applied energy is reduced and the amount of heat generation is reduced by shortening the energization time to the corresponding heating resistance element. Further, for a high-concentration pixel, the applied energy is increased and the amount of heat generated is increased by prolonging the energization time to the corresponding heating resistance element.

[0008]

However, as described above, in the gradation control method of controlling the density gradation by controlling the energization time, when the recording paper is continuously conveyed in the direction of the next printing line. Since the energization timing changes for each density gradation with respect to the recording paper conveyance time of one printing line, recording cannot be performed with a fixed pixel size, and the recorded image has a grainy feeling due to variations in the recording pixel size. Therefore, there is a problem that the print quality is deteriorated.

As a measure against the above problems, there is a method of intermittently conveying the recording paper for each printing line, but it is difficult to optimize the timing of the energization time and the recording paper conveyance time, and the recording paper is at the current position. Since the time of the transitional state during the time from moving from one to the position of the next printing line occupies a large proportion of the recording time of one printing line, the recording paper cannot be conveyed intermittently enough in practice, so that the uniform pixel It is not possible to record by size.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a density gradation control type thermal printer which has a constant pixel size even if the density gradation changes and has a high printing quality.

[0011]

In order to achieve the above-mentioned object, the density gradation control type thermal printer of the present invention has a constant energization time regardless of the density gradation of the input, and a heat generation resistance during the energization time. It is configured to have a means for changing the element temperature according to the input density gradation.

[0012]

When the recording paper is continuously conveyed by making the entire energization time constant regardless of the input density gradation and controlling the temperature of the heating resistor element according to the density gradation to perform the density gradation control. However, or even when the recording paper is conveyed intermittently for each printing line, within the recording time of one printing line,
By making the relationship between the recording paper conveyance timing and the energization timing and the ratio of the energization time to the recording time constant,
All density gradations are recorded with a uniform pixel size.

[0013]

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 formed by arranging 512 heating resistor elements R1 to R512 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 resistor elements R1 to R51 during the printing time of each printing line.
The 512-bit serial energization timing data [CK P1j to CK P512j] corresponding to 2 is set to the count value (K) of the energization number counter 38 continuously for a plurality of times, for example, 256 times (K = 1 to 256). The shift register 14 is supplied accordingly. Here, the nth bit CK Pnj
Holds information as to whether or not the nth heating resistance 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 CK P1j is next at the timing of the latch signal LA from the latch signal generating circuit 32. ~ CK
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, these heating resistance elements R1 to R512 selectively generate electricity during the unit energization cycle ΔT in accordance with the information contents of the corresponding gradation bits CK P1j to CK 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. 2, T is composed of an energization enable time tE in which a current actually flows in the heating resistance 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 set so that the energization is instructed in all the unit energization cycles during the energization time of one printing line, so that each pixel on one printing line is as shown in FIG. As shown in FIG. 4, the heating resistor element temperature is set to rise up to the heating resistor element temperature (T = 63) at which a high level (G = 63) is given.

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
The energization timing conversion circuit 36 converts the energization timing data [CK P1j to CK P512j]. The energization timing data [CK P1j to CK P512j] is the heating resistor element temperature (T = 0) that gives each heating resistor element a density gradation (G = 0 to 63) that matches the density gradation data (a1j to a512j). ~ 6
3), it is determined whether to energize (“1”) or de-energize (“0”) in each unit energization cycle as shown in FIG. The energization timing data [CKP1j to CKP521j] shown in FIG. 5 can be easily understood from the figure, and the density gradation data (a1
The energization number counter shows energization information (“1”) enough to set the element temperature (T = 0 to 63) such that the density gradation (G = 0 to 63) determined by j to a521j) can be obtained. Stored randomly during the maximum time. Therefore, the total energization time of each heating element is the maximum time indicated by the energization counter, that is, a fixed time. Energization timing data [CK P1j ~
CK P512j] is stored in the energization timing buffer 20.

As described above, the density gradation data (a1j to a1)
512j) is the energization timing data [CK P1j to CK P512
j], and energization timing data [CK P1j to CK]
P512j], each heating resistance element (R1 to R512) is energized. As a result, each heating resistance element (R1 to R512)
Is the density gradation data (a1j ~
a512j), a density gradation (G = 0 to 63) that matches the temperature of the heating resistor element (T = 0 to 63) is obtained, and the desired density gradation is uniformly printed on the recording paper. Record.

[0020]

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

Even when the recording paper is continuously conveyed by keeping the entire energizing time constant regardless of the input density gradation and controlling the temperature of the heating resistor element in accordance with the density gradation to control the density gradation. Alternatively, even when the recording paper is conveyed intermittently for each printing line, the relationship between the recording paper conveyance timing and the energization timing and the ratio of the energization time to the recording time are made constant in the recording time of one printing line. As a result, it is possible to perform recording with a uniform pixel size for each density gradation, so that it is possible to obtain a recorded image with high print quality that is free from the feeling of roughness due to variations in the recording pixel size.

[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 timing of a unit energization cycle according to an embodiment.

FIG. 3 is a diagram showing a heating resistance element temperature-recording density characteristic by density gradation control.

FIG. 4 is a diagram showing a change in temperature of a heating resistance element during recording of one printing line.

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

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

[Explanation of symbols]

 10 thermal head, 12 heating resistor, 20 energization timing buffer, 36 concentration-energization timing conversion circuit, 38 energization counter, 40 CPU,

Claims (1)

[Claims] 1. A thermal printer in which a color density of a thermal paper or a transfer density of ink from an ink sheet to a recording paper is controlled by controlling energy applied to a thermal resistance element formed on a thermal head. A density gradation control type thermal printer, characterized in that it is provided with means for controlling the temperature of the heating resistance element according to the density gradation of the input while keeping the entire energization time constant.