JPH0550907B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for driving a line thermal head used in a thermal printer that records information by heat sensitivity or thermal transfer.

<Summary of the Invention> The present invention is a method for driving a line thermal head used in a thermal printer that performs thermal recording, in which a plurality of heating elements that are not adjacent to each other among the heating elements on the line thermal head are combined into one block. Divide the entire heating element into multiple blocks as
By sequentially driving each block, it is possible to prevent unevenness in recording density.

<Prior Art> Generally, in a thermal printer using a line thermal head, recording is performed by applying electric power to each heating element on the line thermal head, but if you try to record one entire line at a time, for example, There are 512 heating elements on the line thermal head,
Assuming that the maximum power required for one heating element is 0.5W, if you want to record one entire line in black, you will need a power supply that can supply instantaneous power of 512 x 0.5 = 250W.
A problem has arisen in that the power supply device becomes larger and more expensive.

In order to solve this problem, conventionally, as shown in Figure 3, a fixed number of adjacent heating elements on a line thermal head are grouped together and divided into multiple blocks, and the power is sequentially applied to each block. A method is used in which instantaneous power is reduced by applying and recording. For example, if 512 heating elements are divided into 8 blocks of 64 each, and the maximum power required for one heating element is 0.5W, if one entire line is to be recorded in black, It can also be driven by a power supply that can supply instantaneous power of 512 x 0.5 ÷ 8 = 32W.

<Problems to be solved by the invention> However, in the conventional method described above, a heating element in which only one side of the adjacent heating element generates heat is better than a heating element in which adjacent heating elements on both sides generate heat. temperature becomes lower. (Figure 4 shows the temperature distribution when the line thermal head is driven. In this figure, the solid line is the temperature distribution of each block.
The dashed line is the temperature distribution across the line thermal head. ) For this reason, as shown in Figure 4, the temperature is high at the center of each block, and the temperature decreases toward both ends.When looking at the entire line thermal head, this occurs at the boundary between each block, as shown by the broken line. There will be areas where the temperature is low.

Therefore, when printing with such a line thermal head, there is a problem that density differences occur at the same position for each line, and many white lines appear in the vertical direction on the paper itself, which impairs the recording quality. was occurring.

<Means for Solving the Problems> In the present invention, a plurality of heating elements that are not adjacent to each other among the heating elements on the line thermal head are combined into one block, and all of the heating elements on the line thermal head are is divided into multiple blocks and each block is driven sequentially.

<Function> Therefore, it is possible to reduce the influence from adjacent heating elements and prevent unevenness in recording density.

<Examples> (a) First Example Table 1 shows the block division state of the heating element on the line thermal head driven by this driving method.

First, in this embodiment, recording is performed by dividing one line into four blocks. As shown in Table 1, every third heating element is selected from the 512 heating elements that make up the line thermal head, and each block is divided into 128 heating elements.

Next, a circuit for performing the above operation will be explained with reference to FIG.

First, the gradation data to be recorded for one line is
Sequentially by software according to the calculation time of CPU1
Input to RAM2 address bus.

RAM2 has color correction from 1 pixel gradation data,
Data calculated through processing such as gradation correction is written in advance from the CPU 1.

Therefore, correction data corresponding to the gradation data is converted and output from the RAM 2 in real time, and the data is written into the line memory (RAM 3). The output of the counter 6 and the output of the counter 7 are input to the RAM 3 via the multiplexer 9, and the output of the counter 6 is input to the address when writing, and the output of the counter 7 is input to the address when reading.

When one line of 512 bytes of data is written to RAM 3, RAM 3 enters the read mode, and the count 7 is sequentially incremented with a reference clock of 4 MHz, and the output is sent via multiplexer 9.
Input to RAM3 address.

On the other hand, 2 bits of preset data corresponding to the block number is input from the CPU 1 to the flip-flop 10 and latched therein. Every time the counter counts 512, the counter 8 is incremented by one count.

The output of the counter 8 and the data of the RAM 3 are converted through a comparator 4 into serial head data.

The head data is “1” when RAM3≧count 8 “0” when RAM3<count 8 Output.

XNOR11 is from CPU1 to flip-flop 1
Preset data (2 bits) output via 0 and RAM3 address output (lower 2 bits)
comparator 4 so that the conversion operation is executed when
controls the input signal to.

Recording time data for one gradation is input from the CPU 1 to the latch circuit 12, and its output and oscillator 13
The comparator 15 compares the outputs of the recording time counter 2 with (100 KHz) as the input clock, and if they match, a one shot signal is generated, which is used as the head latch signal. However, the first head latch signal of each block generates a one shot signal when the counter 7 counts 512.

Reference clock 4MHz as head clock signal
Enter.

When the counter 8 matches the number of gradations, the head strobe signal is turned off and one block recording is completed. Block termination is managed by CPU1.

In order to record the next block, preset data is input from the CPU 1 to the flip-flop 10, and the subsequent operations are similar to those described above, and one line recording is completed by repeating this four times.

(b) Second Embodiment FIG. 2 shows the voltage waveform applied to the heating element on the line thermal head by this driving method.

In this example, every seventh heating element was selected from a line thermal head with 512 heating elements.
It is divided into 8 blocks with 64 pieces each as one block. The order of voltage application is as follows:
First, one block is driven, and then voltage is sequentially applied to the blocks on the left, which are opened by two heating elements each. Therefore, the heating element that generates heat immediately before it always generates heat with an interval of at least two heating elements, so that it is not affected by the residual heat of other heating elements.

<Effects of the Invention> As described above, in this invention, the line thermal head is divided into eight blocks every seven dots, and
By sequentially driving blocks spaced two dots apart in one longitudinal direction of the line thermal head and completing this process eight times, printing for one line is completed, and the heat generated just before is removed. Since the heat is generated at a distance of at least two heating elements from each other, it is not affected by residual heat from other heating elements, and uneven shading in the recording can be reliably prevented, improving recording quality. Moreover, it is possible to perform multi-gradation printing in which density differences between dots are prevented.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a control circuit used in a first embodiment of the invention, FIG. 2 is a voltage waveform diagram applied to a heating element on a line thermal head according to a second embodiment of the invention, and FIG. The figure is a voltage waveform diagram applied to a heating element on a line thermal head according to the conventional method, and FIG. 4 is a temperature distribution diagram on the line thermal head driven according to the conventional method.

Claims (1)

[Claims] 1. In a thermal printer that performs thermal recording using a line thermal head in which at least 500 heating elements are connected in series, all dots in the line thermal head are divided into eight blocks every seven dots, and the line thermal head is A thermal head driving method in which blocks separated by two dots are sequentially driven in one longitudinal direction of the printer, and printing for one line is completed by repeating this process eight times.