JPS62218151A - Intermediate tone thermal printer - Google Patents

Abstract

PURPOSE:To enable a high quality intermediate tone recording with low cost by confining the fluctuation in the intermediate concentration due to the fluctuation in the resistance of a heating element in a thermal head within an allowable range. CONSTITUTION:A thermal head 26 comprises a heating element and a drive circuit, and main scanning pulse MSP is applied with a constant period at the starting time point of recording period of each line upon elapse of predetermined time after application of a line start signal LS. The line start signal LS is applied onto the thermal head 26 while lagging by a longer time than that required for completing input of all main scanning pulses MSP. The thermal head 26 is driven by the rising portion of the lagging line start signal LS. A thermal head direct drive circuit control the energy to be applied onto a the heating element of thermal head corresponding to a gradation level, thus performing a desired recording. Since intermediate concentration recording can be achieved with high accuracy irrespective of the electrical accuracy of thermal head, a high quality intermediate tone thermal printer can be formed with low cost and the running cost can be reduced.

Description

[Detailed Description of the Invention] [Summary] The present invention mainly uses a density modulation method when the fluctuation width of the intermediate density is small in order to suppress fluctuations in the intermediate density in the density gradation thermal imaging mode. The present invention relates to a thermal printer that is capable of recording halftone images with high precision by mainly using area gradation when the range of variation in halftone density is large.

The first aspect of the present invention is that in density gradation thermal pre/re:
In order to solve the problem that the accuracy of the recorded intermediate density fluctuates due to variations in the resistance value of the heating element of the thermal head, the density gradation method and the area gradation method are used together. During adjustment.

During periodic maintenance, thermal head replacement, etc., when the fluctuation range of intermediate density is small, the density modulation method is mainly used, and when the fluctuation range of intermediate density is large, the area gradation method is mainly used. This makes it possible to record halftone images with high precision over a wide range of areas.

The second aspect of the present invention is a density gradation thermal printer, which includes:
Due to the longitudinal distribution of mechanical strain in the thermal head and the circumferential and longitudinal distribution of variations in the platen diameter and degree, the pressure distribution between the thermal head and the platen is uneven, resulting in the recorded intermediate density. In order to solve the problem of fluctuations in accuracy, we use a combination of the density gradation method and the area gradation method, and use the density gradation method and area gradation method together to improve accuracy during initial adjustment after product assembly, periodic maintenance, thermal bed replacement, platen replacement, etc. When the fluctuation width of the intermediate density within the area is small, the density gradation method is used as the main method, and when the fluctuation range of the intermediate density is large, the area gradation method is used as the main method. This allows halftone images to be recorded at once.

The eighth aspect of the present invention is a density gradation thermal printer,
In order to solve the problem that the intermediate density accuracy decreases depending on the type of recording paper, the density gradation method and the area gradation method are used together, and for recording paper with high intermediate density accuracy, the density gradation method is used as the main method. In the case of recording paper with low intermediate density accuracy, the area gradation method is used as the main method, so that intermediate tones can be recorded with high precision regardless of the type of recording paper.

[Industrial application field]

The present invention relates to a halftone thermal head, and in particular, it is possible to suppress the influence of halftone density fluctuations due to variations in the resistance value of the heating element of the thermal head to a negligible level.
Furthermore, the influence of intermediate density fluctuations due to mechanical distortion of the thermal head or platen can be suppressed to a negligible level, and the influence of intermediate density fluctuations due to the type of recording paper can be suppressed to a negligible level. Regarding thermal printers that can be used.

[Conventional technology]

Thermal printers that use heat to record information such as characters include a thermal recording method and a thermal transfer recording method. The former method records by bringing the thermal head into direct contact with the recording paper, which changes color due to heat, and heats the heating element of the thermal head to change the color of the recording paper.The latter method heats the ink using the thermal head. In this method, the liquid is melted or sublimated, and then transferred to recording paper for recording. Furthermore, based on the heating element scanning method, there are two main types: line recording method and V-real recording method. A line recording method is used for high-speed recording, and a serial μ recording method is used for low-speed recording.

FIG. 6 shows an outline of a line recording type thermal transfer recording apparatus.

The thermal head 41 has an ink sheet 42 and recording paper 43
It faces the platen 44 via the t.

The ink sheet 42 is heat-meltable, and the thermal head 4
1, by heating this ink sheet 42,
The ink on the ink sheet 42 is melted and transferred to the recording paper 48 to perform recording. The thermal head 41 has heating elements for one line arranged along the direction perpendicular to the plane of the paper, and records for one line are performed almost simultaneously. When one line of recording is completed, the recording paper 4B and ink sheet 4
2 is simultaneously transported in the direction of the arrow.

When performing binary recording, sufficient energy is applied to the thermal head at the timing at which dots are to be recorded to cause the ink on the ink sheet to be melt-transferred or sublimated-transferred to the recording paper. Further, when halftone recording is performed, the energy applied to the thermal head is changed in accordance with the density of the dots to be recorded.

This energy value is determined by the characteristics of the ink sheet.

However, the resistance values of the heating elements of the thermal head are not all the same but vary, so even if an attempt is made to apply the same amount of energy, the actual energy applied will vary in inverse proportion to the resistance value. As a result, the intermediate concentration will fluctuate.

In conventional halftone thermal pre-printing/reflection, no 'JL pneumatic countermeasures against this intermediate density variation are used.
It was largely dependent on the electrical accuracy of the thermal head.

Therefore, processing costs are high and the rate of defective products is also high, which is a factor that increases the cost of the device. Furthermore, the thermal head is a consumable item and must be replaced after recording a certain number of sheets, which is a factor that increases the processing cost.

It is also known to measure the resistance value of each heating element, store the resistance value in the ROIA in advance, and then correct the driving conditions so that the desired applied energy is obtained. However, this has not been put to practical use because the circuit is expensive and adjustments such as when replacing the thermal head are complicated.

Further, the energy value to be applied is mainly determined by the characteristics of the ink/ink, but it also changes depending on the pressure between the thermal head and the defen. Therefore, if this pressure distribution becomes uneven, the intermediate density will fluctuate.

Conventional halftone thermal printers do not take any precautionary measures against this halftone density variation, and rely on the mechanical M degree of the thermal head and grating. Therefore, these require high precision, which increases processing costs and increases the rate of defective products, which is a factor that increases device costs. Furthermore, both the thermal head and the differential gear are consumable items and must be replaced after a certain number of records have been recorded, which is a factor that increases running costs.

The applied energy also changes depending on the type of recording paper.

Therefore, the intermediate density will vary depending on the type of recording paper. Conventional halftone thermal printers have adopted a method of varying the energy applied to the thermal head in response to variations in intermediate density depending on the type of recording paper.

However, although this method allows the average value of each intermediate density level to be constant regardless of the recording paper, the magnitude of the variation in intermediate density differs depending on the recording paper, so in the end, the average value of the intermediate density level varies depending on the recording paper. The image quality changed significantly.

Problems to be Solved by Invention C] In the conventional system, no measures were taken against fluctuations in the intermediate concentration due to variations in the resistance value of the heating element of the thermal head. However, this method has the drawback of increasing equipment cost and running cost.

Furthermore, with conventional systems, no countermeasures were taken against fluctuations in intermediate density due to fluctuations in the mechanical accuracy of the thermal head and grating, which required high precision for the thermal head and platen, resulting in increased equipment costs and running costs. It had the disadvantage of being bulky.

Further, the conventional method does not take into account the variation in the intermediate density variation between recording sheets, and therefore has the drawback that the image quality changes significantly when the recording paper is changed.

[Means for solving problems]

The present invention applies the technology of the "multi-level area gradation method" filed by the inventors as Japanese Patent Application No. 174224/1982 to keep intermediate density fluctuations within an allowable range due to fluctuations in the resistance value of the heating element of the thermal head. It is possible to achieve high-quality halftone recording at low cost.

[Function] During initial adjustment, periodic maintenance, and adjustment of the pond, the variation range of the resistance value of the heating element of the thermal head is inspected and adjusted, and if the intermediate density variation caused by this is small, the density gradation method is mainly used. Using an area gradation matrix with a small density difference between adjacent pixels such as , the area gradation matrix is switched according to the intermediate density variation width, and if the variation width is large, Ii! The density difference between the two adjacent elements is increased to make the area gradation method the main method. As a result, even in the case of a thermal head with large fluctuations in resistance value, there is no longer a noticeable increase in the roughness (graininess) of the image quality or fluctuations in intermediate density depending on the location within the recording area, as was the case with conventional methods. High-quality halftone images can be obtained regardless of width.

Furthermore, during initial adjustment, periodic maintenance, and other adjustments, we inspect and adjust the unevenness of the pressure distribution between the thermal head and the platen, and if the intermediate density fluctuation caused by this is small, we recommend using the density gradation method as the main method. An area gradation matrix with a small density difference between adjacent pixels is used, and the area gradation matrix is switched according to the intermediate density variation width, and when the variation width is large, the density difference between adjacent pixels is increased and the area gradation method is applied. Make it the main thing.

As a result, even in the case of a combination of a thermal head and a defensor with large fluctuations in the pressure distribution, the image quality becomes noticeably rougher (graininess) than before, and the intermediate degrees vary depending on the location within the recording area. A high-quality intermediate g4 image can be obtained regardless of the pressure distribution.

Note that when the area gradation method is used as the main method, the texture is more noticeable than when the density gradation method is used as the main method, but since the texture is canceled out when there is an intermediate density variation, By switching the area gradation matrix using
It is possible to bring the overall image quality to the best condition by taking into account the fluctuations in intermediate density and the texture.

In addition, in the case of recording paper with small intermediate density fluctuations, an area gradation matrix with a small density difference between adjacent pixels, such as a density gradation method, is used, and the area gradation matrix is switched according to the intermediate density fluctuation width. In the case of recording paper with large intermediate density fluctuations, the difference in density between adjacent pixels is increased to mainly use the area gradation method.

As a result, even on recording paper with large intermediate density fluctuations, unlike conventional methods, the image quality does not noticeably increase the roughness + a (graininess) or the intermediate density does not vary depending on the location within the recording area. High-quality halftone images can be obtained regardless of paper.

1 is a first configuration diagram of a thermal printer to which the present invention is applied), 11 is a thermal head, 12 is an ink sheet, 1B is a recording paper, and 14 is a platen.

15 is a heat radiator of the thermal head, -16 is a temperature sensor installed on the radiator 15, 17 is a generating means for an image gater to be recorded, 18 is a thermal head drive circuit, 18
1 is a density variation width output circuit that outputs the density variation width; 182
183 is an area gradation matrix output circuit, and 183 is a thermal head drive data generation circuit that generates thermal head drive data by referring to the image data from the S-elevation data generating means 17 and the area gradation matrix from 182.

The concentration fluctuation width output circuit 181 inputs a heating element resistance value fluctuation signal output from a resistance value fluctuation amount storage circuit (not shown),
A value proportional to the intermediate concentration variation width is output. Therefore,
The area gradation matrix outputted from the area gradation matrix output circuit 182 is the one with the optimum aIf level difference between adjacent pixels.

FIG. 2 shows a second configuration example to which the present invention is applied.

All reference numbers are the same as in FIG. 1, and refer to the same parts, but the concentration 'i1. Input No. 18 to the dynamic width output circuit tgt is a pressure variation signal output from a pressure variation storage circuit (not shown).

FIG. 8 shows an eighth configuration example to which the present invention is fully applied.

In this figure, the same parts as in FIG. 1 are given the same reference numbers. In the figure, 181-1 is a recording paper identification circuit 69,
It identifies the recording paper and outputs a value proportional to the intermediate density fluctuation range.

FIG. 4 is a block diagram of an embodiment of the present invention, 21-2
8 is a delay circuit, 24 is a latch circuit, 25 is a read oil memory (RoM), and 26 is a thermal head. Also L
S is the line start signal.

MSP is a main scanning path, Dn is a gradation gator, MSA is a main scanning direction address signal, and SSA is a sub-scanning direction address signal.

FIG. 5 is an explanatory diagram of the operation, where (■) is the line start signal LS, (6) is the main scanning bus MSP1 (c) is the delayed signal by the delay circuit 28, and (2) is an enlarged version of (b). The main scanning path μ MSP shown in FIG.
A% (1) is the latch output signal S of the latch circuit 24, (j
) indicates a read gate of the read only memory 25, and (6) indicates a delayed signal by the delay circuit 22.

The thermal head 26 is composed of a heating element and a drive circuit, and assuming that the recording paper is A4 size and the recording dot density is 8 dots/mm, the number of heating elements is 1728. Therefore, within the recording period of one line, 1728fi
It is necessary to receive the 114-minute gator, convert it into a recording dot pattern, and transfer it to the thermal head 26. If the recording cycle of 1747 minutes is 10 m5, the conversion time per heating element III is approximately 600 nS. becomes.

At the start of the recording cycle of each line, the line start signal LS shown in (9) of FIG. , 17211 are applied at regular intervals.The line start signal LS is applied to the delay circuit 28 for a time T2, which is longer than the time required to complete the input of the entire scanning pulse MSP, as shown in FIG. 5(G). The signal is delayed as shown in FIG.

Furthermore, by the time the line start signal LS delayed by the delay circuit 28 by the time T2 is output, the conversion process of the gradation gator Dn for all the heat generating elements has been completed; Fin start signal LS
The thermal head 26 is driven at startup.

Furthermore, in synchronization with the rising edge of the main scanning pulse MSP shown in (to) and (4) in FIG. 5, the gradation gator Dn and the main scanning direction address signal MSA shown in (f) and Ig) in FIG. is added. The main scanning pulse MSP is delayed by the delay circuit 21 for a time TO, which is longer than the time required for the gradation data Dn and the main scanning direction address signal MSA to become valid, and the fifth pulse MSP is delayed by the delay circuit 21.
The delayed signal shown in (@) in the figure is obtained. This delayed signal from the delay circuit 21 causes the latch circuit 24 to output the gradation gate Dn.
, a main scanning direction address signal MSA, and a sub-scanning direction address signal SSA are latched.

Further, the output signal of the latch circuit 24 shown in (i) of FIG. 5 is an address signal of the read-only memory 25, and the output signal of the latch circuit 24 shown in (i) of FIG.
A reading gator of the pattern is output.

Further, the delay signal shown in (6) in FIG. 5, which is delayed by the delay circuit 22 by the time T1, which is longer than the time when the read gate of the read-only memory 25 is valid, is applied to the thermal head 26, and the rising edge of this delay signal is applied to the thermal head 26. The read data from the read-only memory 7 is read into the thermal head 26 in synchronization with the recording paper, and a recording pulse corresponding to the successive gators is applied to the heating element from a drive circuit (not shown) to print the recording paper. Multi-value recording dots are recorded.

The density variation width data output from a density variation width output circuit (not shown) is input to the latch 24, latched at the rising edge of the output SO of the delay circuit 21, and inputted to the upper address of the ROM 25. By writing in each address of the ROM 25 an area gradation matrix corresponding to the density variation range of the output of the latch 24, a part of the latch 24 and R
A part of the OM 25 constitutes the area gradation matrix output circuit 182 in FIG.

The embodiment circuit shown in FIG. 4 outputs the gradation rep/L' value to be recorded. A thermal bed direct drive circuit (not shown) controls the energy μ applied to the thermal head heating element in accordance with this gradation level lv value, and performs desired recording. An outline of the operation of the direct drive circuit will be described in the case of driving a double-shaped thermal head at a constant voltage.

In the direct drive circuit, first, the drive energy μ corresponding to the gradation repetition μ value is calculated by referring to the temperature near the heating element, the temperature of the radiator, and in the case of a color printer, the color 9 of the ink sheet. Since it is a constant voltage drive, the energizing pulse width of the heating element is immediately calculated from the driving energy μ, and is transferred to the heating element drive IC mounted on the thermal head.

In the case of the configuration shown in FIG. 1 as a first configuration example of the present invention, the heating element resistance value fluctuation amount storage circuit and the density fluctuation width output circuit of the thermal head will be explained. Since the thermal head is normally replaced at least once every few months, the amount of variation in resistance value of the heating element can be set in the D/P switch and translated into the range of concentration variation in the ROM. Alternatively, the concentration fluctuation range may be set directly in the drilling P switch.

Furthermore, in the case of the second configuration example shown in FIG. 2, the press variation amount storage circuit and the density variation width output circuit will be explained. The thermal head and platen are usually replaced every few months by one concave diameter or less, so the amount of pressure fluctuation is
It is sufficient to set it in the switch and translate it into the concentration fluctuation width in the ROM.

Alternatively, the concentration fluctuation range may be set directly in the drilling P switch.

In addition, in the case of the configuration shown in FIG. 8 as an eighth configuration example of the present invention, the identification means and circuit for identifying the recording paper and outputting the density variation width table will be explained. When replacing the recording paper, it is done with a clear purpose, such as using inexpensive paper for gator checking, or using long-lasting recording paper for particularly important data.

Therefore, there is almost no need to take the trouble to provide a means for automatically identifying the type of recording paper at the same time as the recording paper is replaced. Normally, it would be sufficient to input the density variation range gator from the keyboard when replacing the recording paper. Of course, it is also easy to allocate a number to the recording paper in advance and enter the number from the keyboard so that it is translated into the density variation range gator in the ROM.

(Effects of the Invention) According to the present invention, intermediate densities can be recorded with high precision regardless of the t5Fc accuracy of the thermal head, so a high-quality half-tone thermal printer can be manufactured at low cost, and running costs can also be reduced. effective.

Furthermore, according to the present invention, it is possible to record intermediate densities with high precision regardless of the mechanical precision of the thermal head or platen, so a high-quality half-tone thermal printer can be manufactured at low cost, and it is also effective in reducing printing costs. There is.

Furthermore, according to the present invention, intermediate densities can be recorded with high precision regardless of the @ type of recording paper, so the range of use of high-quality halftone thermal printers can be expanded, and it is also effective in reducing printing costs. .

[Brief explanation of drawings]

1 to 8 are the first and second cases to which the present invention is applied, respectively.
The eighth configuration example, FIG. 4 is an embodiment of the present invention, FIG. 5 is an explanatory diagram of the operation of the embodiment of the present invention, and FIG. 6 is a diagram showing a conventional example. In the figure, 11 is a thermal head, 12 is a 4-ink sheet, 13 is a recording paper, 14 is a platen, 15 is a heat radiator of the thermal head, 16 is a temperature sensor installed in the heat radiator 1115, and 17 is the generation of image data to be recorded. 18 is a thermal head drive circuit, 181 is a density variation width output circuit, 181-1 is a recording paper identification circuit, 182 is an area gradation matrix output circuit, and 188 is a thermal head drive data generation circuit. Figure 2

Claims (3)

[Claims] (1) In a halftone thermal printer that uses a multi-level area gradation method in which pixels are configured with an m x n area gradation matrix (m and n are natural numbers) of recording dots having multiple density levels, the thermal head A half-tone thermal printer comprising means for storing the amount of variation in resistance value of a heating element, and means for changing the density level value arrangement in the area gradation matrix according to the output of the storage means. (2) In a halftone thermal printer that uses a multi-level area gradation method in which pixels are configured with an m x n area gradation matrix (m and n are natural numbers) of recording dots having multiple density levels, a thermal head and A halftone thermal printer comprising: means for storing the amount of variation in pressure between platens; and means for changing the arrangement of density level values in the area gradation matrix in accordance with the output of the storage means. (3) In a halftone thermal printer that uses a multi-value area gradation method in which pixels are configured with an m x n dot area gradation matrix (m and n are natural numbers) of recording dots having multiple density levels, A halftone thermal printer, comprising: means for detecting the type; and means for changing the density level value arrangement within the area gradation matrix in accordance with the output of the detecting means.