JP2530170B2 - Thermal transfer gradation control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal transfer gradation control device, and more particularly to a device that reduces image quality deterioration due to heat accumulation in a line thermal head during printing.

2. Description of the Related Art Conventionally, a thermal transfer printing apparatus has been used as a still image hard copy apparatus for business use such as copying machines and facsimiles or for consumer use. This thermal transfer printing apparatus uses an ink film in which a heat-melting ink or a heat sublimation ink is applied to one surface of a polyester film having a thickness of 5 to 6 μm, and the front ink surface of the ink film is brought into contact with a recording paper. A line thermal head is applied to the back surface, and an electric current is passed through the line thermal head to generate heat, and the ink of the ink film at a position corresponding to the line thermal head is melted and transferred to a recording sheet. This line thermal head has a plurality of heating resistors arranged in a line, and a current is sequentially applied to each heating resistor.

The density that determines the gradation of printed characters, figures, pictures, etc. is determined according to the area and density of each dot on the recording paper onto which the molten ink has been transferred. The area and density of the molten ink dot are determined according to the current applied to each heating resistor. Generally, the longer the duration of the current flowing through the heating resistor, the larger the amount of heat generation, the larger the area and density of the molten ink dot, and the closer the gradation becomes to the saturation density.

In the printing apparatus using the line thermal head, in order to store heat due to the heat generated by the line thermal head,
It is known that the image quality deteriorates in the sub-scanning direction. For example, the fifth
When it is desired to print with a change in density as shown by the broken line in the figure, as shown by the solid line in FIG. 4, the input data rapidly changes from the low density level to the high density level at time 0, and then is input at time t ₁ . When the data suddenly changes from a high density level to a low density level, it takes 1 second or longer until the density reaches a predetermined value (1 line printing cycle is about 10ms, 100
Above the line) is required. In other words, when the density level suddenly changes from low density to high density, the density is printed lighter than the desired density near the time when the density changes, and near the time when the density changes rapidly from high density to low density. The density is printed darker than the desired density, and the image quality deteriorates.

In order to correct the deterioration of the image quality in the sub-scanning direction and obtain a high-quality output image, a device that stores the density data of the line thermal heads of a plurality of lines in the past and corrects the density data of the next line has been considered. . As such a device,
A device as disclosed in JP-A-60-65663 has been proposed. This device corrects the line to be recorded from the density data of the past plural lines (for example, 7 lines) corresponding to the gradation data grouped in consideration of the influence on the heating resistor. It was

Problems to be Solved by the Invention However, in order to obtain a high-quality output image,
It is necessary to store more than 100 lines of data, which is not practical. Further, the apparatus described in Japanese Patent Laid-Open No. 60-65663, which performs correction using data of several lines in the past, has drawbacks such as insufficient correction effect.

The present invention has been made in view of the above points, and an object of the present invention is to provide a thermal transfer gradation control device capable of simply and sufficiently correcting image quality deterioration due to heat storage in a line thermal head.

Means for Solving the Problems The present invention uses a first delay means for delaying the density data of a line to be recorded by one line, an output density data of the first delay means and a delayed correction data for correction. Computation means for producing data, second delay means for delaying the correction data produced by the computation means by one line and supplying it to the computation means as delayed correction data, and compensation means produced by the computation means And a correction means for subtracting the data and the density data of the line to be printed to correct and output the density data of the line to be printed.

According to the present invention, the first delay means delays the density data of the line to be recorded by one line, and the second delay means is the first delay means.
The correction data created by the calculation means is delayed by one line by the density data delayed by one line by the delay means of
Output to calculation means. Further, the calculation means creates correction data from the output density data of the first delay means and the output correction data of the second delay means and supplies it to the second delay means and the correction means. The correction unit corrects the density data of the line to be recorded by subtracting the output correction data of the calculation unit and the density data of the line to be recorded.

Embodiment FIG. 1 shows a circuit system diagram of an embodiment of a thermal transfer gradation control device according to the present invention. In the figure, the line thermal head 6 is composed of n heat generating resistors R _{1 to} R _n formed in a line on a ceramic substrate. The structure of this line thermal head 6 is the same as that of the conventional thermal transfer type printing apparatus.
As shown in the drawing, it extends in the width direction of the ink film 1. In the figure, an ink film 1 as a transfer paper has a polyester film on which a heat-melting (or heat subliming) ink 3 is applied in a predetermined thickness. The recording surface of the recording paper 4 is brought into contact with the surface of the ink 3 of the ink film 1, and the recording paper 4 is sent in the direction of arrow A together with the ink film 1 by the roller 5. A line thermal head 6 is provided facing the roller 5 and is in contact with the back surface of the ink film 1.

The ink 3 of the ink film 1 at a portion corresponding to the energized heat generating resistors of the heat generating resistors R _{1 to} R _n of the line thermal head 6 is melted (or sublimated) and transferred to the recording paper 4. Ink film 1 is line thermal head 6
After passing through, the roller 7 is guided by the roller 7 and separated from the recording paper 4, and is wound as a used ink film 1a on a winding spool (not shown). The transferred ink 3a remains on the printed recording paper 4a. For convenience of illustration, the transferred ink 3a is shown as having a large area, but actually it is composed of a collection of small dots.

One dot is formed by one heating resistor element, and the size of the one dot is determined by the current value or the energization time passed through the heating resistor element. Then, depending on the size of each dot, the shade or gradation of the printed figure or the like is determined.

The present invention is a gradation control device applicable to such a thermal transfer type printing device. Next, referring to FIG. 1, the analog video signal supplied from the image data generating device 8 is A / D converted. After being converted into a digital signal by the device 9,
The data is sent to and stored in the data storage device 10. On the other hand, the address counter 11 receives the reference clock signal from the terminal 12 and
The start address from 19 is supplied and the first address is sent to the data storage device 10. The data storage device 10 sends the density data (the first data of the density data from the A / D conversion device 9) corresponding to the first address to the density data correction circuit 13 which is the main part of this embodiment, The data correction circuit 13 sends the density data whose density has been corrected corresponding to the density data to the density data comparison circuit 14. At this time, the count of the data counter 15 is set to, for example, "1", and the reference density data which is sequentially increased according to the count number is supplied from the data counter 15 to the grayscale data comparison circuit 14. The density data comparison circuit 14 compares the density data with the reference density data "1" indicating the minimum color density, and if the density data is equal to or larger than the reference density data "1", the shift register 16 receives the control data "1". , And if it is smaller, control data “0” is sent to the shift register 16.

In this way, when the processing at the first address is completed, the address counter 11 sequentially sends the addresses of the 2, 3, ..., Nth times to the data storage device 10, and the data storage device 10 receives the second to nth addresses each time. The density data corresponding to each address is sequentially sent to the density data comparison circuit 14. Where 1 ~
The density data from the n-th address corresponds to the density data printed by the heating resistors R _{1 to} R _n of the line thermal head 6, respectively. The grayscale data comparison circuit 14 uses the above 2
The density data corresponding to the nth address and the reference density data "1" are compared, and the control data "0" or "1" is sent to the shift register 16 in the same manner as above. The n-stage shift register 16 sequentially fetches n-bit control data corresponding to the 1st to n-th addresses supplied from the grayscale data comparison circuit 14 and sends it to the latch circuit 17.

When the address counter 11 finishes counting the first to nth addresses, it sends a data transfer pulse to the data counter 15.
And to the latch circuit 17 and the correction circuit 18. At the same time as the data transfer pulse is sent to the data counter 15, the heating pulse is corrected by the correction circuit 18, the address counter 11 and the AND circuit 20.
The second data, which has been “1” until then, is increased from the smallest value to the value “2” indicating the second color density. On the other hand, a reference clock signal is supplied from one terminal 12 to one end of the AND circuit 20, and at the same time when the heating pulse comes in, a pulse is output to the shift register 16 and the address counter 11 receives the 1st to nth address. The n-bit control data corresponding to is transferred from the shift register 16 to the latch circuit 17
Transferred to When the data transfer pulse comes in, the latch circuit 17 latches the control data supplied from the shift register 16 and sends it to each one of the input terminals of the gate circuits G _{1 to} G _n .

Next, the address counter 11 is reset by the input of the heating pulse, and sequentially counts 1 to n addresses again, and the n density data is the second data of the above value "2", The grayscale data comparison circuit 14 sequentially compares the sizes. Even when the second data is "2", the data counter 15, the shift register 16, the latch circuit 17, the AND circuit 20 and the like perform the same operation as described above, and are latched by each of the gate circuits G _{1 to} G _n . Send control data. Gate circuit G ₁
Each other input terminal of ~G _n heating pulse through a terminal of the correction circuit 18 is applied, each output signal is applied to the base of the corresponding NPN transistor T ₁ through T _n, which is switching control. Among the transistors T _{1 to} T _n , current is flowed only through the heating resistor connected to the collector side of the turned-on transistor to generate heat.

Further, the correction circuit 18 corrects the density unevenness due to the voltage drop of the thermal head based on the voltage drop data of the thermal head from the voltage drop detection circuit 21.

Next, the operation of the density data correction circuit 13 which is the main part of this embodiment will be described.

FIG. 2 shows a block diagram of an embodiment of the present invention. 22 is an input terminal, 23 and 24 are delay means, 25, 26, 27 and 28 are coefficient multipliers, 29 is an adder, 30 is a subtractor, and 31 is an output terminal.

Digital data d _{i of} data to be recorded is input to the input terminal 22. Digital data input from input terminal 22
The d _i is supplied to the subtractor 30 and the delay means 23. Delay means 23
Is a delay means for delaying the density data for one line, and, for example, a random access memory (RAM) is used. The output density data d _i-1 of the delay means 23 is ₁ of the input density data d _i .
A line before the data is supplied to a coefficient multiplier 25 with a coefficient K _2, after the coefficient K ₂ is multiplied, is supplied to the adder 29.

The adder 29 multiplies the history data d _fi-1 two lines before the input density data d _i delayed by the delay means 24 by the coefficient K ₃ by the coefficient multiplier 27 having the coefficient K ₃ to obtain the data K ₃ × d _fi-1 and the output data K ₂ × d _{i-1 of the} coefficient multiplier 25 are added, and the data (K ₂ × d _i-1 + K ₃ × d _fi-1 ) is output. The output data of the adder is multiplied by a coefficient K ₄ by a coefficient multiplier having a coefficient K ₄ , and correction data d _fi = K ₄ × (K ₂ × d _i-1 + K ₃ × d _fi-1 ) is obtained.
This data is delayed by one line by delay means 24 as history data d _fi and used for correction of the next line.

Further, the output data d _fi of the coefficient multiplier 26 is supplied to the coefficient multiplier 28 having the coefficient K ₁ , the correction data dd _i = K ₁ × d _fi, and supplied to the subtractor 30. Subtractor 30 from the input data d _i, obtain the data d ₀ corrected by subtracting the correction data dd _i. The corrected data d ₀ is output from the output terminal 32 and used as density data.

When the above operation is expressed by an equation, Can be expressed as

The coefficient K ₁ is the input data after sufficient time has passed in Fig. 4.
It is a coefficient indicating the ratio of the difference between the input data D _i and the corrected data D ₀ with respect to D _i . The coefficients K ₂ , K ₃ and K ₄ are the coefficients that determine the time constant of the corrected data.If the coefficient K ₂ is decreased and K ₃ is increased, the time constant of the corrected data tends to increase. Change.

Figure 4 shows t ₁ = 1sec, K ₁ = 0.2, K ₂ = 0.02, K ₃ = 0.98, K ₄ =
In the example of data correction when it is set to 1, in the figure, the alternate long and short dash line is the data input D _i to be recorded, and the solid line is the corrected data D ₀ . By making such a correction, it is possible to perform recording as shown by the alternate long and short dash line in FIG.

Further, in this state, if the power or energization time for one-line printing is increased substantially uniformly, it is possible to obtain the density to be originally recorded as shown by the broken line in FIG.

Further, as shown in FIG. 3, by providing a coefficient multiplier 32 having a coefficient {1 / (1-K ₁ K ₄ )} in front of the output terminal 31 of the block diagram of FIG. Therefore, it is possible to obtain the density to be recorded shown by the broken line in FIG. 5 without changing the power per unit time or the energization time.

Although each block in FIGS. 2 and 3 can be configured by an individual element, blocks I, II, and III in the area surrounded by a broken line are read-only memories (ROMs), respectively. Can be configured. For example, if the input data is 6 bits, I has a capacity of 128 Kbits (d _i-1 : 6 bits, d _f , d _f-1 : 8 bits) and II has a capacity of 2 Kbits. is there.

EFFECTS OF THE INVENTION As described above, according to the present invention, since the correction data is sequentially created by the recording data of the previous line and the correction data of the previous line, the line thermal storage can be easily performed by the storage means for only two lines. It has features such as being able to sufficiently correct the deterioration of image quality due to heat accumulation in the head.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a block diagram of an embodiment of a density data correction circuit which is an essential part of the present invention, and FIG. 3 is another embodiment of the density data correction circuit. FIG. 4, FIG. 4 is a diagram showing density data after correction, FIG. 5 is a diagram showing density data before correction, and FIG. 6 is a main part of a thermal transfer printing device to which the device of the present invention can be applied. It is a schematic perspective view of an example. 6 ... Line thermal head, 13 ... Density data correction circuit, 22 ... Input terminal, 23, 24 ... Delay means, 25-28 ...
Coefficient multiplier, 29 ... Adder, 30 ... Subtractor, 31 ... Output terminal, 32 ... Coefficient multiplier.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Terumi Ohara Inventor Terumi Ohara 3-12 Moriya-cho, Kanagawa-ku, Kanagawa Prefecture Victor Company of Japan, Ltd. (72) Kenichi Miyazaki 3-12 Moriya-cho, Kanagawa-ku, Kanagawa Prefecture Within Victor Company of Japan (72) Hiroki Kitamura, 3-12 Moriya-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Inside Victor Company of Japan (72) In-house Tadao Shinya 3-12 Moriya-cho, Kanagawa-ku, Yokohama, Japan Victor Company of Japan Incorporated (72) Inventor Yutaka Mizoguchi, 3-12 Moriya-cho, Kanagawa-ku, Kanagawa, Japan Victor Company of Japan, Ltd. (72) Inventor Katsuhiko Terada, 3-12 Moriya-cho, Kanagawa-ku, Yokohama, Japan Victor Company of Japan, Ltd. (56) Reference JP-A-63-306058 (JP, A) JP-A-62-235 876 (JP, A) JP 58-120370 (JP, A) JP 62-138262 (JP, A) JP 61-270976 (JP, A)

Claims (1)

(57) [Claims] 1. A line thermal head comprising a plurality of heating resistors arranged in a row, wherein the time of each current individually passed is recorded according to density data indicating the density of the heating resistor. In the thermal transfer gradation control device for controlling, the first delaying the density data of the line to be recorded by one line
Delay means, an operation means for creating correction data from the output density data of the first delay means and the delayed correction data, and the correction data from the operation means is delayed by one line, The second delay means for supplying the delayed correction data to the computing means, the correction data created by the computing means and the density data of the line to be recorded are subtracted to obtain the line to be recorded. And a correcting unit for correcting and outputting the density data of 1.