JPH02217266A - Density gradation-type thermal printer - Google Patents

Abstract

PURPOSE:To enable data of multidensity gradations to be printed at high speed by changing a voltage applied to a thermal head and thereby making an energization time which generates differences in a single density gradation uniform. CONSTITUTION:Density gradation data stored in a single line buffer 12 after being output from an interface 11 is sequentially read due to an address output from CPU 13. Then the data is compared with density gradation comparison data designated by a density gradation comparator 14 for each dot then is digitized. After the lapse of a time set by a timer 13a, CPU 13 outputs a latch signal and a strobe to a line thermal head 1. The counter 15 is incremented using this latch signal to enter the first density gradation data of a voltage table 16 to a variable voltage power supply 17 and apply a voltage corresponding to the data to the thermal head 1. Then each thermal element 2 prints the first density gradation data in its line. This process is repeated up to a final density gradation. Consequently, it is possible to increase a printing rate using a high voltage at the gradations of a low density area and a high density area and thereby ensure data transfer time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a density gradation type thermal printer that performs gradation recording by controlling the current supply time to a thermal head.

2. Description of the Related Art In recent years, graphic fix processing has become popular, and in order to obtain hard copies thereof, printing apparatuses have also begun to perform gradation recording that grades the shading of printing. As such a gradation recording device,
A thermal printer or the like is used.

There are two types of thermal printers: a thermal recording method that prints by placing a thermal head in direct contact with thermal recording paper that changes color due to heat, and a thermal transfer recording method that uses a thermal head to heat the ink, melt or sublimate it, and transfer it to the recording paper. be.

In either method, in order to record one gradation, the print density is controlled by the level of heat generation energy of the heat generating element of the thermal printer.

[Prior Art] Conventionally, this type of density gradation type thermal printer applies a constant voltage to a heating element of a thermal head, and performs gradation recording based on the difference in application time.

Specifically, print data is transferred line by line to the thermal head, and first, all 1,947 pieces of data are transferred to the thermal head, with dots lighter than the lightest density gradation set to "0" and the others set to "l". The data of dots that are lighter than that is set as "0" and the data of dots that are lighter than that is set as "0". All of the data for 1 is transferred again, and the heating elements corresponding to the dots "l" continue to generate heat, while the dots rQJ end their heat generation.

In this way, for each energization time that produces a density difference of one gradation, 1
947 minutes of print data is transferred to the thermal head, and gradation recording is performed by controlling the energization time for each heating element.

[Problems to be Solved by the Invention] However, in the conventional density gradation type thermal printer, the voltage applied to the heating element was a constant voltage, so for example, as shown in FIG. There was a large difference in the energization time depending on the gradation level. - Numerically, as shown in FIG. 6, the current application time t1 that produces a density difference of 1lIl tone in the medium density region is very short, and the density difference of 1 gradation in the high density region and the low density region is very short. The energization time t2. ta was getting longer.

However, even with the shortest energization time tI, it is necessary to be able to transfer all the data for one line during that time. This means that the energization time is much longer.

In particular, when the number of gradations is increased to, for example, several hundred gradations, in order to increase the print density resolution, the data transfer rate cannot keep up with t-, so the voltage applied to the heating element As a result, in conventional density gradation type thermal printers that apply a constant voltage, the energization time becomes longer in the low and high density areas, making it difficult to print. The speed had slowed down considerably. There was also an idea to increase the number of gradations by one in order to prevent the printing speed from decreasing, but this would reduce the density resolution and sacrifice the quality of the image.

SUMMARY OF THE INVENTION An object of the present invention is to provide a density gradation type thermal printer that can eliminate such conventional drawbacks and print data with a large number of gradations at high speed.

[Means for Solving the Problems] In order to achieve the above object, the density gradation type thermal printer of the present invention has a thermal head l in order to perform density gradation recording, as shown in FIG. An energization time control means 3 is provided to control the energization time to each arrayed heating element 2 according to the gradation level of print data, and the energization time control means 3 controls the energization time to the thermal head 1 for each energization time that causes a density difference of one gradation. In a density gradation type thermal printer that transfers print data, the voltage applied to the thermal head l is adjusted to equalize the energization time that causes a density difference of one gradation for each gradation. The present invention is characterized in that it is provided with an applied voltage control means 4 that controls the applied voltage for each energization time that causes a concentration difference.

[Function] The voltage applied to the thermal head l is finely controlled for each energization time that produces a density difference of one gradation, and the length of the energization time that produces a density difference of one gradation is made uniform for each gradation. During this time, print data is transferred to the thermal head 1.

[Example] Examples will be described with reference to the drawings.

In FIG. 4, l is a line thermal head, and one heating element l (heating resistor) is arranged as many as the number of dots in one line. Reference numeral 11 denotes an interface that receives gradation data from a host computer (not shown) or the like. 1
2 is a line buffer, which is a random access memory (
RAM), and stores one line of gradation data from the interface 11. 13 is a control unit (C
PU) controls reading/writing of the line buffer 12, outputs a latch signal and strobe to the line thermal head l, and outputs tone comparison data to the tone comparator 14.

The WjlW comparator 14 compares the print gradation data (a) from the line buffer 12 with the gradation comparison data (b) from the CPU 13, and outputs the rll signal when a≧b, and the rll signal when a<b. The rOJ signal is output to Todo 1 as serial data to the line thermal.

A counter 15 is incremented sequentially from 0 by a latch signal from the CPU 13, and the output signal from the counter 15 specifies which gradation level is to be specified as the head voltage signal to be output from the head applied voltage table 16. decide.

For example, as shown in FIG. 2, the head voltage table 16 is a ROM that stores the voltage to be applied to the heating element 2 (hereinafter referred to as "head applied voltage") at which gradation level. A certain 0 gradation is 0 to 0 in terms of hardware.
Although it is stored as 255, in FIG. 2 it is displayed as 1 to 256 to mean the oOth number.

As shown in the w4z diagram, in this example, the head voltage is set high for gradations in the low and high density areas, and low for gradations in the medium density area. The figure shows the characteristics using a line graph.

Returning to the diagram, reference numeral 17 is a variable voltage power supply, and according to the head applied voltage data outputted from the head applied voltage table 16, the voltage is applied to each heating element 2 of the line thermal head.

Note that the =r variable voltage power supply does not necessarily need to be one power supply, and may be configured by a plurality of power supplies with different voltages.

Next, the operation of the above embodiment will be explained.

lX) 1947 worth of gradation data input from the interface 11 is stored in the line buffer 12.

The gradation data stored in the small line buffer 12 is CP
They are read out sequentially by the address output from U13,
A gradation comparator 14 compares each dot with gradation comparison data specified by the CPU 13.

Here, print gradation data (a
) is sequentially compared with the gradation comparison data (b) (first gradation), and as mentioned above, if a≧b, the rlJ signal is output to the line thermal head l, and if a<b, the rlJ signal is output to the line thermal head l; A signal of "0" is output to the line thermal head l. (For example, in the print data of the 23rd gradation, since a≧b, the rll signal is output until the 23rd comparison, and after that, the “O” signal is output).

! When 311 lines worth of print gradation data is output to the line thermal head l, after a certain period of time has elapsed by the timer 13a, the CPU 13 outputs a latch signal and a strobe to the line thermal head l, and each heating element 2 Print the first gradation data of the line.

t4+ Meanwhile, the content of the counter 15 is incremented from 0 to 1 by the latch signal output from the CPU 13, and the applied voltage data for the first gradation (30V in this example) of the head voltage table 16 is changed to the variable voltage power supply 17. is input, and a voltage (30V) corresponding to the voltage is applied from the variable voltage power supply 17 to the line thermal head l. Therefore, when printing each dot of the first gradation in +3), the voltage (30V) is applied to each heating element 2' of the line thermal head l.

16) Continuing, the CPU 13 reads out the same contents of the line buffer 12 as in (2) again, compares it with the next second gradation comparison data using the gradation comparator 14, and, in the same way as in case (2), reads the second gradation comparison data. For dots with a smaller (that is, lighter) gradation than the gradation comparison data of
outputs a “0” signal to
Output.

At the same time, voltage data for the second gradation (29v in this example)
Therefore, for the dots to which the rlJ signal was output at the second gradation, the voltage of 30V was applied at the first gradation, and then the voltage of 2 was applied.
A voltage of 9V is applied. This is repeated until the final gradation (the 256th gradation in this example).

As a result, the line thermal head l has a head applied voltage table 16 for each energization time that causes a density difference of one gradation.
A voltage that changes according to the specification is applied, and the printing speed is increased by the high voltage for the gradations in the low and high density areas, and the printing speed is slowed by the low voltage for the gradations in the medium density area, and the line thermal head l The data transfer time can be secured.

When all printing operations for that line are completed, CPU1
3 releases the strobe and the counter 15 is reset and returns to 0. Then, the gradation data for one line of the next new line is stored in the line buffer 12, and the same printing operation is repeated.

FIG. 5 shows the relationship between the print density and the energization time to the heating element 2 of the line thermal head 1 in the above embodiment, and the print density is almost proportional to the energization time. As a result, the energization time for producing a density difference of one gradation is uniform, and print data can be transferred to the thermal head reliably and without waste during that time.

In addition, in the present invention, the current application time that causes a density difference of one gradation is
The present invention is not limited to the almost completely uniform one as in the above embodiment, but the current application time that produces a density difference of one gradation is made uniform by changing the voltage applied to the thermal head. Any of these seven types is included within the scope of the present invention.

[Effect of the invention 1] According to the density gradation type thermal printer of the present invention, by finely controlling the voltage applied to the thermal head,
Since the energizing time that causes density differences between gradations is equalized, for gradations where there was not enough time to transfer data to the thermal head, it is possible to lengthen the energizing time per gradation and reliably transfer the data. For gradations that require a longer energization time than the transfer time, one energization time can be shortened to increase the printing speed. Therefore, without increasing the speed of the data transfer circuit, printing with multiple gradations and high density resolution can be performed at a speed several to several tens of times faster than conventional printing.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of the present invention, FIG. 2 is a schematic diagram of the head applied voltage table of the embodiment; FIG. 3 is a head applied voltage characteristic curve diagram of the example. FIG. 4 is a configuration diagram of the embodiment, FIG. 5 is a characteristic diagram of the current application time and printing degree of the example, FIG. 6 is a characteristic diagram of conventional energization time and print density. In the figure, l...Thermal head de 2...Heating element 3...Electrification time control means 4...Applied voltage control means. OME Sand 1 lecture map Figure 4

Claims (1)

[Claims] In order to perform density gradation recording, energization time control controls the energization time to each heating element (2) arranged in a thermal head (1) according to the gradation level of print data. Means (3)
In a density gradation type thermal printer, in which print data is transferred to the thermal head (1) for each energization time that causes a density difference of one gradation, the energization time that causes a density difference of one gradation is set. The present invention is characterized in that an applied voltage control means (4) is provided for controlling the applied voltage to the thermal head (1) for each energization time that causes a density difference of one gradation so as to equalize the voltage for each gradation. Density gradation type thermal printer.