JP3329078B2 - Thermal transfer recording device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal transfer recording apparatus for printing image data using a thermal head in which a plurality of heating resistors are arranged in the main scanning direction, and more particularly to a width of the heating resistors in the sub-scanning direction. Is shorter than the width of one recording pixel, and a thermal transfer recording apparatus capable of recording image information such as a picture in halftone.

[0002]

2. Description of the Related Art Conventionally, as a color halftone recording method of a thermal transfer recording apparatus for printing image data using a thermal head, there are sublimation type thermal transfer recording and fusion type thermal transfer recording. The sublimation type thermal transfer recording has a problem that it requires a large amount of energy, takes a long time to print, and uses special paper to increase the cost. On the other hand, fusion type thermal transfer recording can be printed with small energy and the cost is low,
Since the ink donor film itself cannot obtain a gradation even when the applied energy is changed, it is difficult to perform multi-gradation recording. For this reason, in the fusion type thermal transfer recording, a matrix method such as a dither method, and a method in which gradation is obtained by reducing a heat generation region such as sub-scanning division and heat concentration are proposed.

For example, JP-A-60-248074 and JP-A-3-219969 use a heating element whose width in the sub-scanning direction is shorter than that in the main scanning direction.
A method for recording a halftone (hereinafter, referred to as a sub-scanning division method) is described. FIG. 8 is a plan view of a heat-generating portion of a thermal head used in the sub-scanning division system, and shows a common electrode 100 having a plurality of comb-like portions 101 and a comb-like selection member disposed between the respective comb-like portions 101. It has an alternate lead type electrode structure including an electrode 102 and a strip-shaped resistor 103 arranged in a row in the main scanning direction on the comb-shaped portion 101 and the selection electrode 102.

In the printing by the thermal head, by selecting and energizing the selection electrode 102, a resistor portion (the sub-scanning direction) sandwiched between the selected selection electrode 102 and the comb portions 101 of the common electrode 100 on both sides thereof is selected. The heating element having a short width is heated. That is, the thermal head is relatively continuously moved with respect to the recording paper placed on the thermal head, and the ink of the thermal transfer ink donor film provided on the thermal head side of the recording paper is heated by the heat of each heating element. This is to melt and transfer this to recording paper to record one recording pixel X corresponding to the image data. Therefore, while the thermal head moves a distance of one recording pixel (sub scanning direction) with respect to the recording paper, energy (driving time, applied voltage, etc.) given to each heating element according to the density of the pixel to be recorded. By controlling the
Halftone recording is possible.

[0005]

FIGS. 9 and 10 show examples of printing and recording when halftone recording is performed using the thermal head having the above structure. When the number of gradations is increased by increasing the energy given to the heating element, FIGS.
As shown in (1), the print area increases mainly in the sub-scanning direction, and halftone recording becomes possible. FIG. 9 shows a print dot 10 of one recording pixel when the energy given to the heating element is increased.
FIG. 10 shows a comparison of the print dots 105 of one recording pixel. As can be seen from each figure, the print area also increases in the main scanning direction due to the heat distribution due to diffusion with the increase in the number of gradations, so that the print dot shape becomes trapezoidal. If the print dot shape is trapezoidal, when printing an image composed of continuous rectangular dots such as characters and fine lines, the connection between adjacent dots is deteriorated, resulting in a problem that print quality is reduced.

In order to solve the above problem, a large dot is applied from the trapezoid to a rectangle by applying a large amount of energy to the heating element at the beginning of printing and thereafter reducing the energy. In this case, while the quality of characters and thin lines does not deteriorate, the dot size in the initial stage of printing increases, and the problem arises that the highlight characteristics when printing halftones deteriorate.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a thermal transfer recording apparatus capable of improving both halftone reproducibility in printing a picture and the like and reproducibility in printing a character and a thin line. It is also intended to provide.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a server in which a plurality of heating resistors whose width in the sub-scanning direction is shorter than the width of one recording pixel are arranged in the main scanning direction.
A thermal transfer recording apparatus that prints image data using a multi-bed has the following configuration. Picture / character determining means for determining whether the image data is a picture, a character, or a thin line is provided. A data conversion means for converting the image data into binary data for a thermal head composed of a plurality of pulses is provided. The pulse density of the binary data of the data conversion means is controlled based on a signal from the picture / character determination means.

[0009]

According to the present invention, there is provided a thermal head for image data comprising a plurality of pulses by a data conversion means.
The data is converted into value data, and printing is performed by causing the heating resistor to generate heat according to the binary data. At this time, the image / character determining means determines whether the image data is a picture, a character, or a thin line. If the image data is determined to be a picture, the heating resistor is heated by a plurality of pulse trains. To print. Since the heating resistor has a width in the sub-scanning direction shorter than the width of one recording pixel, the printing area within one recording pixel can be adjusted by changing the number of pulses, and halftone recording can be performed. it can.

When it is determined that the image data is a character or a thin line, by changing the pulse densities of a plurality of pulse trains, it becomes possible to print with rectangular dots that satisfy all of one print pixel. It is possible to eliminate a decrease in print quality in which connection with dots becomes a problem. In other words, when it is determined that the data is a character or a thin line, the density of a plurality of pulses in the initial stage of the binary data is increased and the pulse density is gradually reduced, so that one recording pixel printed by the heating resistor is formed. It can be a rectangular dot.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a thermal transfer recording apparatus according to the present invention will be described with reference to FIGS. FIG.
Is a block diagram of a thermal transfer recording apparatus according to the embodiment,
An image input unit 1 such as a scanner, an A / D converter 2 for converting data from the image input unit 1 into image data of a digital signal, an image data memory 3 for storing image data,
An image data processing circuit 4 having a determination circuit for determining whether image data is a picture, a character, or a thin line, and a gradation conversion circuit
And a binary conversion circuit 5 for converting image data into binary data
A buffer memory 6 for storing the binary data as print data for a thermal head, and a thermal memory in which a plurality of heating resistors whose width in the sub-scanning direction is shorter than the width of one recording pixel are arranged in the main scanning direction. A head 8, a driver 8 for outputting a drive signal (print pulse) for causing each heating resistor of the thermal head to generate heat, and a pulse generating circuit for outputting a strobe signal for controlling the driving of each heating resistor to the driver 8. 9 and a control circuit 10 connected to each circuit or memory and operating while synchronizing a series of processes.

The thermal head is of an alternating read type as shown in FIG. 8 and has a resolution of 300 DPI in the main scanning direction.
The width of the heating resistor in the sub-scanning direction is set to about 43 μm, and recording is performed on synthetic paper using a high-resolution ink donor film (PET substrate thickness: 4.5 μm, ink coating amount: 2.0 g / m ² ). Has become. The recording paper relatively moving on the thermal head is set to be fed at a constant speed, and the speed is set to a speed at which the printing period T = 25 ms and the width of one recording pixel X in the sub-scanning direction (170 μm). Is set. The size of one recording pixel recorded on recording paper by one heating resistor is as follows: the width in the sub-scanning direction is 170 μm (about four times the width of the heating resistor), and the width in the main scanning direction is 84.7 μm.
The width in the sub-scanning direction is twice as large as the width in the main scanning direction, and a printing method that easily obtains halftone printing is adopted, so that halftone printing of about 64 gradations can be obtained. That is, according to the thermal head of this embodiment, 1 is used in the sub-scanning direction.
It is configured to be capable of printing at a resolution of 50 DPI, and as described later, the printing density is set to 150 DPI or 300 DPI depending on the type of print image (whether it is a picture, a character, or a thin line).
Can be printed.

Next, with reference to FIGS. 2A and 2B, the principle of halftone expression by the thermal transfer recording apparatus of the above embodiment will be described. Each heating resistor constituting the thermal head is shown in FIG.
As shown in FIG. 3B, the print head is driven by a print pulse that periodically applies a pulse of the same width, and is driven by a maximum of 88 short pulses per print cycle T. The short pulse has a period of about 284 μsec as shown in FIG. 2 (b).
56W. FIG. 2A shows a print dot shape corresponding to the number of short pulses when the heating resistor is driven.
Printing is not performed with about 0 to 10 pulses, but printing is started from about 10 or more pulses, and 15 pulses are alternate lead electrodes (the comb-like portion 101 of the common electrode 100 is disposed on both sides of the selection electrode 102). Since one recording pixel in the main scanning direction is divided into two, printing in which the width of the heating resistor in the main scanning direction and the width of the printing dot in the main scanning direction are equal in the vicinity of 20 pulses is possible. Furthermore, when the number of short pulses of the printing pulse to be sequentially added is increased, the printing dots are enlarged in the sub-scanning direction, and halftone recording can be performed. Accordingly, the area gradation of the halftone expression is almost performed only in the sub-scanning direction, but actually, as shown in FIG. 9, the print dots are expanded in the main scanning direction due to thermal diffusion. However, such printing conditions can improve the halftone characteristics, particularly the highlight characteristics.

FIG. 3 shows the results of actual measurement of the relationship between the number of short pulses and the concentration. X-Rit
Using a densitometer (model number 938) manufactured by Company e, a 2 cm square halftone patch was measured. As can be seen from FIG. 3, according to the above printing conditions, a smooth halftone characteristic is obtained from the highlight, and the gradation expression can be 64 gradations or more.

Next, a case where characters and thin lines are recorded will be described. In order to record characters and fine lines satisfactorily, it is necessary to obtain a rectangular print dot that satisfies the entire recording pixel X by the heating resistor. Under the above-described halftone recording condition (pulses of the same width are applied periodically), the highlight characteristics are good, but conversely, the area sufficiency of the print dots in the main scanning direction of one recording pixel is poor at the beginning of printing. Therefore, in order to record rectangular print dots, a large amount of energy is applied to the heating resistor in the initial stage of printing, and thereafter, the energy is gradually added to the heating resistor so as to prevent unnecessary expansion of the printing dots due to diffusion of heat. Try to reduce energy. Such printing conditions can be realized by changing the applied voltage, pulse width, and pulse density.

Next, the image data processing circuit 4 shown in FIG.
And processing of image data in the binary conversion circuit 5 will be described. The image data is data having a resolution corresponding to a print density of 300 DPI in both the main scanning direction and the sub-scanning direction in order to express both pictures and characters. This image data is input to the image data processing circuit 4, and an internal determination circuit first determines whether the image is a character, a thin line, or a picture composed of a halftone image. This determination is made based on the number of gradations of the image data of the print pixel and the image data of the peripheral pixels. That is, for example, if the number of gradations of the image data of the print pixel is an intermediate value, it is determined that the image is halftone. If the same number of gradations continues for a plurality of pixels, it may be determined as a character or a thin line.

If the image data of the print pixel is determined to be halftone, the print density of the print image in the sub-scanning direction is set to 150.
Since printing is performed in DPI, the printing density in the sub-scanning direction of image data of 300 DPI is converted. That is, two pixels in the sub-scanning direction are averaged to obtain 150 DPI image data. In this example, the conversion of the printing density is 2 of image data.
Although the pixels are averaged, the pixels may be further averaged by adding neighboring pixels.
PI image data may be obtained.

Next, the averaged image data (1 to 256 tones) is subjected to γ correction by the gradation conversion circuit in the image processing circuit so as to conform to the gradation characteristics corresponding to the print density. Pulse data for halftone recording is obtained. The halftone recording pulse data is input to a binary conversion circuit, and is converted into halftone recording print data composed of a plurality of binary data suitable for printing by a thermal head.

If the image data of the print pixel is determined to be a character or a thin line, the image data is 30 pixels in both the main scanning direction and the sub-scanning direction.
Since recording is performed at a print density of 0 DPI,
This image data (pulse data for character and fine line recording)
Input to the value conversion circuit and print data for character and fine line recording (0
Pulse or multiple pulses). The printing density in the sub-scanning direction was set to 150 DPI in halftone printing, and the printing density was set to 300 DPI in character and fine line printing. This is because thin line reproducibility cannot be obtained.

The print data output from the binary conversion circuit is guided to the driver 8 via the buffer memory 6,
Further, a strobe signal from the pulse generation circuit 7 is guided to the driver 8. In a thermal head equipped with a commercially available general-purpose driver, a print pulse is generated by a logical product of a strobe signal and print data. Therefore, as shown in FIG. / 2, and by changing the ratio of “1” and “0” of the print data, the pulse density of the print pulse can be reduced to ２ ，, ４ ，, ８.
Can be changed. That is, by changing the print data using the same strobe signal, the print density is constant at a pulse density of 1/4 for halftone printing, and the pulse density at the beginning of printing for characters and fine lines. Is reduced to １ ／, and thereafter, printing pulses changed to ４ ， and ８ can be obtained. As a result, the highlight characteristics are good for halftone printing,
For printing characters and thin lines, the energy is controlled by the pulse density to increase the energy at the initial stage of printing, thereby simultaneously printing such that rectangular dots can be obtained.

FIG. 5 shows a print pulse for halftone recording and a print pulse for character and fine line recording obtained by the logical product of the strobe signal and the print data. In this embodiment, a halftone recording print pulse having a pulse density of 1/4 over the entire area (halftone recording print pulse in FIG. 5) was used. For the print pulse for recording characters and fine lines,
In a cycle of 12.5 ms (half cycle), at the same applied power as the print pulse for halftone recording, 20 pulses out of 44 print pulses for halftone recording have a pulse density of 1/2.
The pulse whose density is 1/4 is 14 pulses of the printing pulse for halftone recording, and the pulse whose density is 1/8 is 10 pulses of the printing pulse for halftone recording (printing pulse for character and thin line recording in FIG. 5). By using, rectangular dots suitable for character and fine line recording could be recorded.

The print data input to the driver 8 is such that the pulse density of the strobe signal is 1 /
2 (the strobe signal A in FIG. 5), the period 1
At 2.5 ms, "1" or "0" must be associated with each pulse (88 in total) of the strobe signal, so the number of print data is 88. In order to reduce this, the number of print data can be reduced by lowering the pulse density of a part of the strobe signal in the latter half of the cycle when a pulse having a half density is not necessary. That is, as shown in the strobe signal B in FIG.
Only in the initial stage, the print pulse for recording characters and fine lines is made the same (40 pulses at a density of 1/2), and the remaining portion is made up of 24 pulses at a pulse density of 1/4.
The print pulse for halftone recording and the print pulse for character and fine recording shown in FIG.

Next, the operation of the thermal transfer recording apparatus will be described with reference to FIG. That is, image data sent from a computer, a scanner, or the like is a digital signal having 256 gradations, and the resolution of the image data is 300 DPI in both the main scanning direction and the sub-scanning direction in order to express pictures and characters. (Step 60).

The image data is sent to the image data processing circuit 4, and it is determined whether the image data is a picture, a character, or a thin line based on the number of gradations of the print pixel and its surrounding pixels (step 61). When the image is determined to be a picture (halftone), since the resolution of the image data in the sub-scanning direction is 300 DPI and the actual printing is 150 DPI, the averaging process is performed on two pixels in the sub-scanning direction. The sub-scanning resolution of the image data is converted in the same manner (step 6).
2).

Next, the averaged image data (1 to 256 gradations) in the gradation conversion circuit in the image data processing circuit 4
Is corrected to γ so as to conform to the gradation characteristics of the present method, and
Pulse data for halftone recording consisting of pulse data is obtained (step 63). Subsequently, the halftone recording pulse data is converted into halftone recording print data which is binary data (step 64).

If the image data processing circuit determines that the image data is a character or a thin line, it is sufficient to record 300 DPI pixels in both the main scanning direction and the sub-scanning direction. Then, pulse data for recording characters and fine lines composed of 128 pulse data is generated (step 65). That is, pulse data of characters and thin lines
In order to match the pulse data for halftone recording, the data generator generates 150 DPI at a time, and creates 64 pulses × 2 dots, that is, 128 pulses. Thereafter, the pulse data for character and fine line recording is sent to the binary conversion circuit, and is converted into print data for character and fine line as binary data (step 6).
6).

The pulse data for halftone recording and the pulse data for character and fine line recording are collectively transferred to the thermal head 67, and the print data for halftone recording as described above is generated by the strobe signal generated by the pulse generating circuit. Data and characters,
Fine line recording print data is created, which enables simultaneous printing of pictures (halftones), characters, and fine lines. These series of processes are performed by a look-up table using a microprocessor for controlling the thermal head or a ROM.

Next, an example of printing using the thermal transfer recording apparatus of the above embodiment will be described with reference to FIG. The halftone print dot 105a shown in FIG. 7 is a print dot recorded by using a print pulse for halftone recording.
Reference numeral 05b denotes a print dot recorded using a print pulse for recording characters and fine lines. The halftone print dot 105a recorded by the halftone recording print pulse is one recording pixel X
(84.7 μm width in the main scanning direction, 170 μm width in the sub-scanning direction
m), the printing area increases mainly in the sub-scanning direction, and halftone recording is possible. Since the width in the sub-scanning direction is twice as large as the width in the main scanning direction, the area of the white portion when the pulse train of the print pulse is small can be increased, and the halftone can be easily obtained. In addition, the character print dot 105b recorded by the character and fine line print pulse has a rectangular dot shape and records almost one entire recording pixel with two dots, so that the connection with adjacent dots is good and the quality is high. Good characters and fine lines can be printed. Also,
In this case, since two rectangular dots having the same width in the main scanning direction and the width in the sub-scanning direction are printed in one recording pixel X, the printing quality can be maintained even when printing characters and fine lines. Therefore, in a recording in which a picture and a character are mixed, it is possible to realize good printing recording.

According to the thermal transfer recording apparatus of the above embodiment, the following effects can be obtained. The image / character determining means determines whether the image data is a picture, a character, or a thin line,
If the image data is determined to be a picture, the heating resistor is heated by a plurality of pulses of a fixed density to perform printing, and the width in the sub-scanning direction is recorded in one recording pixel longer than the width in the main scanning direction. As a result, the highlight characteristics can be improved during printing, and a halftone print record with excellent print quality can be obtained.

When it is determined that the image data is a character or a thin line, the energy can be increased by increasing the pulse density of a plurality of pulses at the beginning of printing.
It is possible to print with a rectangular dot that satisfies all of one recording pixel, and it is possible to improve the print quality by improving the connection with the adjacent dots. Further, in this case, since the width of the print pixel in the main scanning direction and the width in the sub-scanning direction are the same, it is possible to prevent a decrease in print quality.

The energy applied to the thermal head is controlled by changing the density of the print pulse by changing the print data, so that only one type of strobe signal is required and a special driver is mounted. Server
There is no need to be a round head. Therefore, halftone recording and character and fine line recording can be performed simultaneously with an inexpensive thermal head equipped with a commercially available general-purpose driver.

[0032]

According to the present invention, since the image data is determined by the picture / character determining means and print recording suitable for each is performed, when the image data is characters or fine lines, the dot shape is substantially rectangular and Since one pixel is printed and recorded, the connection with adjacent dots is good and the reproducibility of characters and fine lines is improved, so that the printing quality can be improved. Further, in the case of performing halftone recording, good halftone reproducibility can be obtained since the printing area can be modulated mainly in the sub-scanning direction to perform area gradation. These printings can be performed at the same time, and recording can be performed with good printing quality even when pictures and characters are mixed.

Although the present invention can be applied to any of the thermal recording systems, it can be applied to melt transfer recording, particularly color halftone recording, which cannot conventionally be expressed in multiple gradations, and can be applied to these recordings. Good quality print records can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of a thermal transfer recording apparatus according to one embodiment of the present invention.

FIGS. 2A and 2B are for explaining the principle of halftone recording, FIG. 2A shows print dots when a print pulse is changed, and FIG. 2B corresponds to FIG. The printing pulse to be performed is shown.

FIG. 3 is a graph showing halftone recording characteristics in an example.

FIG. 4 is a timing chart illustrating a method of creating a print pulse in the embodiment.

FIG. 5 is a timing chart illustrating a relationship between a print pulse for driving a thermal head and a strobe signal in the embodiment.

FIG. 6 is a flowchart for explaining the operation of the thermal transfer recording apparatus according to the embodiment.

FIG. 7 is an explanatory plan view showing a print record when printing is performed by the thermal transfer recording apparatus of the embodiment.

FIG. 8 is an explanatory plan view showing the structure of the thermal head.

FIG. 9 is a print record diagram showing a print example when the energy for driving the thermal head is changed.

FIG. 10 is an explanatory diagram of a print record in which the print dots of FIG. 9 are superimposed.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image input part, 2 ... A / D converter, 3 ... Image data memory, 4 ... Image data processing circuit, 5 ... Binary conversion circuit, 7 ... Thermal head, 8 ... Driver, 9
... pulse generator, 10 ... control circuit, 100 ... common electrode, 101 ... comb-shaped part, 102 ... comb-shaped selection electrode, 1
03: strip-shaped resistor, 105: print dot, 105a
... halftone print dots, 105b ... character print dots
X: One recording pixel

Continuation of front page (56) References JP-A-3-219969 (JP, A) JP-A-3-142257 (JP, A) JP-A-6-91915 (JP, A) JP-A-2-8064 (JP) JP-A-64-22554 (JP, A) JP-A-5-147251 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41J 2/36 B41J 2/355 H04N 1/19 H04N 1/40 H04N 1/405

Claims (1)

(57) [Claims] 1. A thermal transfer recording apparatus for printing image data using a thermal bed in which a plurality of heating resistors whose width in the sub-scanning direction is shorter than the width of one recording pixel is arranged in the main scanning direction. A picture / character judging unit for judging whether the image data is a picture, a character, or a thin line; and a data converting unit for converting the image data into binary data for a thermal head composed of a plurality of pulses. A thermal transfer recording apparatus, wherein the pulse density of binary data of the data conversion means is controlled based on a signal from the picture / character determination means.