JP2994855B2 - Multi-tone thermal recording method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-gradation thermal recording method for performing recording with multiple gradations.

[0002]

2. Description of the Related Art Normally, in a thermal recording apparatus, as shown in FIG. 5, heating elements are independently arranged in a row (hereinafter referred to as main scanning direction) on a thermal head in an island shape. The recording paper and the ink sheet are interposed between the thermal head and the platen in a direction orthogonal to the main scanning direction (hereinafter referred to as a sub-scanning direction) while applying heat to the heating element by applying a printing pulse signal to the heating element. The recording is performed by transporting.

That is, by applying a printing pulse signal to the heating elements, the temperature of the heating elements becomes higher than the sublimation temperature of the ink sheet. As a result, the ink of the ink sheet in contact with the heating elements sublimates, Recording is performed by adhering in dot form on recording paper.

[0004] By increasing the time length of the printing pulse signal applied to the heating element during the recording,
The amount of ink sublimated from the ink sheet increases substantially in proportion to the time length. As a result, gradation recording with shading can be performed by changing the time length of the printing pulse signal.

For example, in a multi-gradation thermal recording apparatus capable of performing thermal recording with an accuracy of n (n is an integer of 2 or more) gradations, a k-th (k is an integer of 1 or more and n or less) gradation. To obtain a corresponding density, the heating element is set to k by applying a printing pulse signal corresponding to the density of the k-th gradation to the heating element.
The temperature is set to be equal to or higher than the sublimation temperature of the ink sheet necessary for obtaining the gradation density.

FIG. 6 shows that a printing pulse signal corresponding to the density of the k-th gradation is applied to one heating element continuously from the beginning of the printing section of one dot, thereby obtaining the k gradations. This shows the relationship between the printing pulse signal waveform for obtaining the eye density and the thermal head temperature at that time. At this time, the times T0 to T3 are the times required to print one dot, and even if a printing pulse signal is applied continuously from the beginning of the printing section of one dot, the heating element The temperature exceeds the sublimation temperature (hereinafter, referred to as target temperature) of the ink sheet of the k-th gradation only during the period from T1 to T2, and is lower than the target temperature except during this period. In printing, when observing a density change in the sub-scanning direction, the central portion of the dot becomes dark, and the portions before and after the dot become thin, resulting in uneven density.

[0007] This is because even if a printing pulse signal is applied to the heating element to cause the heating element to generate heat, the heat generated by the heating element moves to the side of the thermal head having a lower temperature in the early stage of printing. As a result, the temperature of the heating element does not reach the target temperature corresponding to the density of the k-th gradation, and since the printing pulse is not applied to the heating element at the end of printing, the thermal head radiates heat. Is believed to be.

Here, in order to solve the problem of density unevenness in the sub-scanning direction within the same dot, the temperature of the thermal head is set over substantially the entire printing section of one dot by the gradation at which printing is to be performed. A dispersion printing method in which a desired density is immediately obtained by applying a desired printing pulse signal while keeping the temperature at or below a target temperature corresponding to the target temperature has been considered.

According to this method, as shown in FIG. 7, the printing pulse signal corresponding to the density of the k-th gradation is substantially evenly distributed over the entire printing section of one dot. Can be obtained over the entire width of one dot.

[0010]

FIG. 8 shows the relationship between the printing pulse signal waveform and the thermal head temperature when the printing density shifts from low density to high density for each dot in accordance with this method. Show. Each density section in the figure is a time width required for printing one dot.

At this time, in the low-density section, the thermal head almost reaches the target temperature and the recording is performed at a low density. However, in the medium-density section, the temperature of the thermal head is reduced to the target temperature in the low-density section. Since the temperature must be higher, even if a printing pulse signal corresponding to the medium density is applied to the heating element in the medium density section, the heat generated by the heating element escapes to the lower temperature thermal head side. However, the thermal head does not immediately reach the target temperature, and there is a problem that the medium density recording is performed only at the center of one dot.

Further, in the subsequent high density section, the temperature of the thermal head must be further increased.
As with the medium density section, there is a problem that desired recording cannot be performed from the beginning of the printing section.

As described above, the present invention has been made in view of the above-mentioned problem, and when multi-tone printing is performed by a dispersion method, adjacent dots in the sub-scanning direction of dots to be printed are used.
By appropriately and sparsely dispersing the printing pulse signal within the printing section of one dot in accordance with the change in the gradation of the dot, the temperature of the thermal head is set in advance near the sublimation temperature of the ink sheet corresponding to the desired density. It is an object of the present invention to provide a multi-gradation thermal recording method capable of immediately performing recording at a desired density when a printing pulse signal necessary for obtaining a desired density is applied to a heating element. And

[0014]

According to the present invention, three adjacent dots D ₁ and D ₂ located in a direction orthogonal to the arrangement direction of the heating elements are provided.
And a data set mode determining device for comparing changes in the gradations S ₁ , S ₂ and S ₃ of the image data with gradations of D ₃ and D ₃ to determine a mode of increasing or decreasing the gradation. a pulse signal converter for generating a gradation signal consisting of binary gradation number based on the mode designation data sent from the determination unit, the gradation image data with the dot D ₂ fed from the line buffer gradation S comparing the binary gradation number of gradation signals sent from the ₂ and the pulse signal converter, the gradation S ₂ of the image data with the tone is marked not less than the binarization gradation number A comparator for sending, for each dot, binarized data for performing copying, and binarized data for not performing printing if smaller, and stores the binarized data based on the binarized data. The above thermal at the time of printing Characterized by comprising the binarized image storage memory in head delivering Shirushiutsushi pulse signal.

[0015]

The gradation change of the gradations S ₁ , S ₂ and S ₃ of the adjacent three dots D ₁ , D ₂ and D _{3 in} the direction orthogonal to the arrangement direction of the heating elements is compared, and the gradation is S ₁ < When S ₂ <S ₃ , the printing pulse signal is concentrated on the front part of the printing section of the dot D ₂ , and when the above-mentioned gradation is S ₁ > S ₂ > S ₃ , the dot D ₂ Is printed by dispersing the printing pulse signal in the front part of the printing section.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention is shown in FIGS. 1 to 4. Each section is the time required for printing one dot as in the prior art.

The features of the present invention are: 1) the previous dot D ₁ , the current dot D _2, and the next dot D _2
3 when the density is shifted to the high concentration of low density, when a transition to the current dot D ₂ marks shooting interval, the dot D ₂ a Shirushiutsushi pulse signal corresponding to the density of the current dot D ₂ rapidly by heating a heating element by concentrating the head start of the sign copy section, (see FIG. 2) that is raised to the vicinity of the following target temperature the temperature of the thermal head, 2) before the dot D _1, the current Dot D ₂ and the next dot D
If _{the third} density is shifted from a high concentration to a low concentration in the forward portion of the current dot D ₂ marks shooting interval, the current dot D ₂
Lowering the temperature of the thermal head by dispersing Shirushiutsushi pulse signal corresponding to the concentration of up to the vicinity of the target temperature below corresponding to the density of the dots D ₃ in the following (see FIG. 3), 3) mark copy dot is changed However, if the density difference is within a certain range, the printing pulse signal is to be substantially uniformly distributed within the printing section of the printing dot (see FIG. 4).

FIG. 1 is a block diagram showing a circuit configuration for implementing a multi-gradation thermal recording method according to the present invention.

In FIG. 1, reference numeral 1 denotes a line buffer having a capacity capable of storing image data of three adjacent lines parallel to the main scanning direction. That is, line buffer 1
Is a line buffer 1a for storing the image data of the line printed immediately before (the previous line), a line buffer 1b for storing the image data of the current line, and a line to be printed immediately after the current line ( The line buffer 1c stores the image data of the next line).

The line buffer 1 is supplied with a read address signal from the read address counter 10, and according to the read address signal, data of three adjacent lines,
That is, the gradations S ₁ , S ₂ and S ₃ of the gradation-added image data at the same address are read out from the line buffers 1 a, 1 b and 1 c and sent to the data set mode determination device 2.

The data set mode determination device 2 determines the gradations of the image data for three lines sent from the line buffer 1, more specifically, the gradations S _{1 of} the dots D ₁ , D ₂ and D ₃ ,
By comparing the gradation change in S ₂ and S _3, discussed above 1), 2) or 3) to select whether belonging to any of the modes. The result selected by the data set mode determination device 2 is sent to the pulse signal converter 4 as mode designation data.

The pulse signal converter 4 has a binarization gradation number corresponding to the binarization strobe number given from the binarization strobe counter 5 and a mode designation given from the data set mode determination device 2. According to the data, the gradation number for binarization is sent to the comparator 3. Specifically, in a thermal recording device capable of printing 256 gradations,
The gradation is sequentially incremented from 0 to 255, and this signal is sent from the pulse signal converter 4 to the comparator 3 as a binarization gradation number.

The comparator 3 binarizes the current dot gradation image data sent from the line buffer 1b according to the binarization gradation number sent from the pulse signal converter 4, and stores the binarized image data for storage. It is sent to the image storage memory 6. Specifically, the comparator 3 determines the gradation of the image data of the current dot sent from the line buffer 1b,
A comparison is made with the binarization gradation number sent from the pulse signal converter 4. If the gradation of the image data is not smaller than the binarization gradation number, a signal "1" for causing the heating element to generate heat.
Is a signal that does not cause the heating element to generate heat if it is small.
"0" is sent to the binarized image storage memory 6.

At this time, the binarized data sent from the comparator 3 to the binarized image storage memory 6 is stored at a position based on the binarization strobe number sent from the binarization strobe counter 5. With this, the binarization process ends.

More specifically, the strobe number for binarization in the case of the above 1) is such that if the current dot D ₂ is in the medium density section B, the printing pulse signal corresponding to the medium density is obtained. As shown in FIG. 2, the signal concentrates on the head start portion of the middle density section B.

As for the binarization strobe number in the case of the above 2), assuming that the current dot D ₂ is in the medium density section E, the printing pulse signal corresponding to the medium density is as shown in FIG. Is a signal to be dispersed in the front part of the middle density section E.

Further, assuming that the current dot D ₂ is in the low-density section H, the binarization strobe number in the case of the above 3) is such that the printing pulse signal corresponding to the low-density is as shown in FIG. Is a signal dispersed throughout the low-concentration section H.

The storage state of the binary data in the memory 6
Specifically, in the case of the above 1), the binarized image
The current dock is stored in the image storage memory 6 in chronological order from the front position.
D _TwoOf the gradation number of the image data of
Binary data "1" up to the fractional value if is a fraction)
Are stored continuously, and the data of “1” is
It is stored alternately with data of "0" in descending order.
You.

In the case of the above 2), in the binarized image storage memory 6, three binarized data with the binary data "1" being "0" are located at the front position in chronological order. The binary data "1" and "0" are stored alternately thereafter.

Further, in the case of 3), the binarized image storage memory 6 stores binary data of "1" and "0" alternately from the front position in time series.

Next, when performing the printing process, the control circuit 9
To dot counter 7 and printing strobe counter 8
In accordance with the control signal output to the dot counter 7, the dot number being printed from the dot counter 7 and the strobe counter 8
Are sent to the binarized image storage memory 6, the binarized image data is sequentially sent to the thermal head 11 as a printing pulse signal, and printing is performed.

Here, the features of the present invention of the above-described embodiment will be described.
At point 2), the previous dot D ₁, The current dot D_Two
And the next dot D_ThreeConcentration shifts from high to low
The current dot D_TwoThe front part of the printing section of
And the current dot D_TwoPulse signal corresponding to the density of
Are dispersed, but this is not a limitation. In addition,
And the current dot D_TwoEven in the rear part of the printing section of
Dot D_TwoOf the printing pulse signal corresponding to the density of
By setting the temperature of the thermal head to the next dot D
_ThreeDrops rapidly to below the target temperature corresponding to the concentration of
Can be done.

In the case of the above 1), the binarized data "1" is stored in the binarized image storage memory 6 in the time series from the front position to the gradation number 4 of the current dot image data. 1 /
(Rounded up when the value is a fraction), but is not limited thereto, and may be any other value as long as the effects of the present invention can be achieved.

In the case of the above 2), in the binarized image storage memory 6, three binarized data of which the binary data "1" is "0" are located at the forward position in time series. It is stored every four in between, but is not limited to this, as long as the effects of the present invention can be achieved as in 1) described above.
It goes without saying that other cases may be used.

[0035]

According to the present invention, in accordance with the gradation variation in gray S _1, S ₂ and S ₃ of the gradation image data with the sub-scanning direction of the continuous three dots D _1, D ₂ and D ₃ when the value of the large, near the beginning initiation temperature of the thermal head by heating the intensive heating elements, the following sublimation temperature of the ink sheet corresponding to the desired concentration of indicia shooting interval of the dot D ₂ Can be approached.

When the values of the gradations S ₁ , S ₂ and S ₃ become small, the temperature of the thermal head is reduced by causing the heating elements to dispersely generate heat in front of the printing section of the dot D _1. The ink density can be lowered to a temperature lower than the sublimation temperature of the ink sheet corresponding to the desired density.

As described above, by setting the temperature of the thermal head to a temperature lower than the sublimation temperature of the ink sheet corresponding to the gradation for which printing is to be performed, it is possible to cope with the density for which printing is to be performed. When the printing pulse signal is applied to the heating element, the density is immediately obtained, and there is almost no extreme density change in the sub-scanning direction within the same dot, and the printing quality is improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration for performing a multi-gradation thermal recording method according to the present invention.

FIG. 2 is a diagram showing a relationship between a printing pulse signal waveform and a thermal head temperature at the time of transition from low density to high density in the present invention.

FIG. 3 is a diagram illustrating a relationship between a printing pulse signal waveform and a thermal head temperature at the time of transition from high density to low density according to the present invention.

FIG. 4 is a diagram showing a relationship between a printing pulse signal waveform and a thermal head temperature at the time when a density change changes within a certain range.

FIG. 5 is a partially enlarged perspective view of a thermal head.

FIG. 6 is a relationship diagram between a printing pulse signal waveform and a thermal head temperature at the time when a printing pulse signal corresponding to the density of the k-th gradation in the related art is applied.

FIG. 7 shows a conventional printing pulse signal waveform when a printing pulse signal corresponding to the density of the k-th gradation is substantially uniformly distributed over a printing section of one dot, and the thermal head temperature and the temperature at that time. Relationship diagram

FIG. 8 is a diagram showing a relationship between a printing pulse signal waveform and a thermal head temperature at the time of performing printing with a change in density in the related art.

[Explanation of symbols]

 1a, 1b and 1c Line buffer 2 Data set mode determination device 3 Comparator 4 Pulse signal converter 5 Binarization strobe counter 6 Binary image storage memory 10 Read address counter 11 Thermal head

Claims (2)

(57) [Claims] 1. A thermal head having a plurality of heating elements arranged in at least one row, and gradation-added image data required for printing dots on three adjacent lines parallel to an arrangement direction of the heating elements. A line buffer and three adjacent dots D located in a direction orthogonal to the arrangement direction of the heating elements.
₁ , a data set mode determination device that compares changes in the gradations S ₁ , S ₂ and S ₃ of the gradation-added image data of D ₂ and D ₃ and determines a mode of increasing or decreasing the gradation. a pulse signal converter for generating a gradation signal consisting of binary gradation number based on the mode designation data sent from the data set mode determining apparatus, tone image with a dot D ₂ fed from the line buffer Data gradation S ₂
Binarization for comparing the gradation number, sign to be smaller than the gradation S ₂ of the image data with the tone gradation number for the binarization of the gray-scale signal sent from the pulse signal converter A comparator for sending, for each dot, binarized data for performing copying, and binarized data for not performing printing if smaller, and stores the binarized data based on the binarized data. A binary image storage memory for sending a printing pulse signal to the thermal head during printing, and comparing the gradations S ₁ , S ₂ and S ₃ of the dots D ₁ , D ₂ and D _3. When the gradation is S ₁ <S ₂ <S ₃ , the dot D ₂
, The above-mentioned printing pulse signal is concentrated in the front part in the time series of the printing section, and when the gradation is S ₁ > S ₂ > S ₃ , the printing pulse signal is concentrated in the time series of the printing section of the dot D _2. And performing printing by dispersing the printing pulse signal in the front part. 2. When the gradation is S ₁ > S ₂ > S ₃ ,
_2. The multi-gradation thermal recording method according to claim 1, wherein the printing is performed by dispersing the printing pulse signal in a time-series rear part of the printing section of the dot D2.