JPH0630899B2 - 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 the size of a printed dot depending on the energization time of a constant current flowing through a plurality of heat generating resistors forming a line thermal head. The present invention relates to a thermal transfer gradation control device for controlling density and gradation.

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 the area of each dot on the recording paper on which the molten ink is transferred,
It depends on the concentration. And the area of the molten ink dot,
The concentration depends on 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. Therefore, in the conventional thermal transfer gradation control device, in order to suppress the gradation of printing, the energization time of the current flowing through each heating resistor is controlled.

Problems to be Solved by the Invention In the conventional thermal transfer gradation control device described above, a large current is supplied to the line thermal head during transfer, and a voltage drop occurs between the supply voltage of the power supply and the terminal voltage applied to the line thermal head. Will occur.

In this case, the value of the current supplied to the line thermal head at one time differs depending on the recording data, and therefore the amount of voltage drop also changes. As a result, the energizing current value of the heating resistor, which should be originally constant, changes, and an error occurs between the originally desired density and the actual recording density depending on the contents of the recording data. There is a problem in that density unevenness occurs in the scanning direction.

In order to solve the above problems, the present applicant has previously filed Japanese Patent Application No.
The above problem was solved by controlling the energization time of each heating resistor according to the voltage drop between the power source and the line thermal head by No. 2-78997 (the name of the invention "thermal transfer gradation control device"). A thermal transfer gradation control device was proposed.

However, the density unevenness in the sub-scanning direction is not limited to the density unevenness due to the voltage drop between the power supply and the line thermal head.
The density correction by the above-mentioned apparatus proposed by the present applicant is insufficient because there is unevenness in density due to uneven feeding (pitch deviation) due to insufficient mechanical precision of the platen drive system.

That is, for example, when a line thermal head having a density of 11.8 dots / mm is used, the pixels are formed into a substantially square shape, so the feed pitch in the sub-scanning direction is 11.8 dots / mm, and one pitch is 84.7 μm.
Becomes In order to obtain such a feed pitch, the platen roller is not directly driven by the motor, but is always driven through the speed reduction mechanism.

A spur gear, a worm and a worm wheel, a timing belt, etc. are used as this reduction mechanism, but all of them use gears and it is difficult to obtain a constant feed pitch due to insufficient manufacturing precision of the gears. Therefore, the printing result has a drawback that the density is high at a fine pitch and is low at a coarse pitch, resulting in density unevenness in the sub-scanning direction.

The present invention has been made in view of the above points, and corrects density unevenness due to voltage drop using a density unevenness correction circuit that corrects the energization time of each heating resistor by the voltage drop between the power supply and the line thermal head. Another object of the present invention is to provide a thermal transfer gradation control device that corrects density unevenness due to platen roller feed pitch unevenness.

MEANS FOR SOLVING PROBLEMS The thermal transfer gradation control device according to the present invention detects a power supply voltage drop for each gradation energization and generates and outputs voltage drop data, and print pitch unevenness depending on a transfer line. First correction data output means for outputting the first correction data in a preset pattern based on the above, switch means for selectively switching the voltage drop data and the first correction data at a preset ratio, and the voltage The second correction data in which the relationship between the recording density and the density data is set directly or in accordance with the drop data is set in advance, and the voltage correction data or the first correction data is stored by the switch means. Storage means for supplying second correction data when supplied with
And means for controlling the energization time of the heat generating resistor to be transferred based on the correction data.

Action According to the present invention, the voltage drop data corresponds to the voltage drop of the power supply voltage supplied to the line thermal head during transfer,
The first correction data corresponds to the correction density of each transfer line. Either the power supply drop data or the first correction data is selectively taken out by the switch means at a preset ratio, and the storage means stores the recording density and the density data based on the voltage drop data from the selected data. Is set to be a straight line or a predetermined curve, the stored second correction data is output, and the second correction data controls the energization time of the heating resistor to be transferred.

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 1
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 1 is the same as that of the conventional thermal transfer gradation control device, and extends in the width direction of the ink film 2 as shown in FIG. In the figure, the ink film 2 as the transfer paper is a polyester film coated with a heat-melting (or heat-subliming) ink in a predetermined thickness. The recording paper 3 is fixed to the platen roller 5 by the clamper 4 and wound around the platen roller 5, and the recording surface is brought into contact with the ink surface of the ink film 2, and the platen roller 5 causes the arrow A
Sent in the direction.

The platen roller 5 is driven by the power of the motor 6 being transmitted to the first wheel 8 via the first worm gear 7 and further transmitted to the second wheel 10 via the second worm gear 9. A slit plate 11 is provided on the shaft of the platen roller 5, and the slit detection sensor 1
The motor 6 is controlled so that the clamper 4 stops at a fixed position when the slit plate 2 detects the slit of the slit plate 11. Next, when the print switch is turned on, the clamper 4 opens and the recording paper 3 is fed. When it is detected that the recording paper 3 has been fed, the clamper 4 is closed, the motor 6 is rotated, and the platen roller 5 moves the recording paper. 3 is wound and rotated in the direction of arrow A. When the platen roller 5 rotates at a predetermined position, the line thermal head 1 holds the ink film 2 and the recording paper 3 and a start pulse is generated to start printing.

At this time, the ink film 2 is sent together with the recording paper 3 in the direction of arrow A '. The line thermal head 1 is provided so as to face the platen roller 5 and is held by the line thermal head holder 13, and is in contact with the back surface of the ink film 2.

Ink of the ink film 2 in a portion of the heating resistors R _{1 to} R _n of the line thermal head 1 corresponding to the energized heating resistor is melted (or sublimated) and transferred onto the recording paper 3.

One dot is formed by one heating resistor element, and the size of 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 printing device, and next, referring to FIG.
The analog video signal supplied from the image data generator 14 is converted into a digital signal by the A / D converter 15 and sent to the data storage device 16 for storage. Here, assuming that the maximum number of gradations is 64, for example, the A / D conversion device 15 and the data storage device 16 are each composed of 6 bits. On the other hand, the address counter 17 has a terminal 18
And the start pulse from the terminal 19 are supplied to send the first address to the data storage device 16. The data storage device 19 sends the image data (the first data of the image data from the A / D conversion device 15) corresponding to the first address to the grayscale data comparison circuit 20. At this time, the count of the data counter 21 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 21 to the grayscale data comparison circuit 20. The grayscale data comparison circuit 20 and the data counter 21 are each composed of 6 bits corresponding to the maximum gradation number 64. On the other hand, the grayscale data comparison circuit 20 compares the image data with the reference density data "1" indicating the minimum color density, and the control data is stored in the shift register 22 although the image data is equal to or larger than the reference density data "1". "1" is sent, and if smaller, control data "0" is sent to the shift register 22.

In this way, when the processing at the first address is completed, the address counter 11 sequentially sends the 2, 3, ..., Nth addresses to the data storage device 16, and the data storage device 16 outputs the 2nd to nth addresses each time. Image data corresponding to each address is sequentially sent to the grayscale data comparison circuit 20.
Here, the image data from the 1st to nth addresses correspond to the image data printed by the heating resistors R _{1 to} R _n of the line thermal head 1, respectively. The grayscale data comparison circuit 20 compares the image data corresponding to each of the 2nd to nth addresses with the reference density data "1" and outputs the control data "0" or "1" in the same manner as described above. Send to. The n-stage shift register 22 sequentially fetches n-bit control data corresponding to each of the 1st to nth addresses supplied from the grayscale data comparison circuit 20 in synchronization with the reference clock and sends it to the latch circuit 23.

When the address counter 17 finishes counting the 1st to nth addresses, it sends a data transfer pulse to the data counter 2.
Correction circuit 2 via 1 and latch circuit 23 and terminal 24
Send to 5. At the same time that this data transfer pulse is sent, the data counter 21 supplies the heating pulse to the correction circuit 25 via the terminal 26, and the reference density data, which has been "1" until then, is the second color density from the smallest. The value increases to "2". The latch circuit 23 latches the control data supplied from the shift register 22 at the time when the data transfer pulse comes in, and the gate circuits G ₁ to
It is sent to each one of the input terminals of G _n .

Next, the address counter 17 is reset when the data transfer pulse b is output, and sequentially counts 1 to n addresses again, and the n image data are the reference density data having the above value “2”, The grayscale data comparison circuit 20 sequentially compares the sizes. Even when the reference density data is "2", the data counter 21, the shift register 22, the latch circuit 23, etc. perform the same operation as described above, and the gate circuit G
_The latched control data is sent to each of _{1 to} G _n . A heating pulse is applied to the other input terminal of each of the gate circuits G _{1 to} G _n by a terminal of a correction circuit 25 described later,
Each of the output signals corresponds to the corresponding NPN type transistor T ₁ ...
It is applied to the base of T _n and controls switching of it. Current is applied only to the heat generating resistor which is connected to the collector of the turned-on transistors of the transistor T ₁ through T _n, generates heat.

Next, the voltage drop detection circuit 28 will be described. FIG. 3 shows a block system diagram of an embodiment of the voltage drop detection circuit 28. In the figure, the input terminal 50 is supplied with a reference voltage V _P having a constant voltage value obtained from a fixed voltage source (not shown) or by holding the line thermal head power supply voltage during non-printing. Supplied.

On the other hand, the head terminal voltage V _T of the line thermal head 1 is supplied to the input terminal 51. This head terminal voltage V
_As shown in FIG. 4, _T changes due to the energization of the line thermal head 1 as described above. Therefore, the difference between V _P and V _T shown by the shaded area in FIG. 4 occurs as a voltage drop. When the number of energized dots is large, the head terminal voltage becomes V _T ′, and the voltage drop between V _P and V _T ′ becomes even larger.

The differential amplifier 29 amplifies the difference voltage between the reference voltage V _P and the head terminal voltage V _T , as shown in FIG. 5 (A).
The voltage drop V _D corresponding to the voltage drop between the power supply voltage and the line thermal head 1 is output to the A / D converter 30 in the same waveform. The A / D converter 30 has an input terminal 31.
Based on such a clock shown in FIG. 5 (C) is more supplied, and outputs the converted to the voltage drop data voltage drop V _P incoming (FIG. 5 (D)). The timing of this data conversion is set near the end of the energization period.
Since the power supply fluctuation is stable near the end of the energization period, if data conversion is performed at this timing, the present applicant previously proposed a circuit that integrates the peak value of the voltage drop V _D and samples and holds it. Compared with the device described above, even if the integrating circuit and the sample-hold circuit are omitted, it is possible to obtain voltage drop data more practically and sufficiently stably.

Next, the pitch unevenness correction data generation circuit 32, which is a main part of the present invention,
Will be described. FIG. 2 is a block system diagram of an embodiment of the pitch unevenness correction data generation circuit and the correction data generation circuit. In the figure, the input terminal 33 receives a line pulse g (FIG. 8A) generated for each recording of one line, and the input terminal 19 receives a start pulse indicating the start of printing.

The line counter 34 receives a start pulse from the input terminal 19 and receives a line path g from the input terminal 33.
Counting is started, and a line address according to the count number is output. The read only memory (ROM) 35 outputs the pitch unevenness correction data corresponding to the print line in synchronization with the line address from the line counter 34 at the timing shown in FIG. The voltage drop data and the pitch unevenness correction data output from the pitch unevenness correction data circuit 32 are input terminal 3 of the correction data generation circuit 36.
7 and the input terminal 38, respectively.

The correction data generation circuit 36 includes a switch signal generation circuit 39 and a switch circuit 40. Switch signal generation circuit 3
Reference numeral 9 is an output of the address counter 17, and a data transfer pulse b as shown in FIGS. 8 (B) and 11 (B) is inputted from a terminal 52 and a counter or a shift register is used, for example, FIG. 11 (E). The switch signal shown in FIG. The switch circuit 40 is set, for example, to select pitch unevenness correction data in a high potential state of the switch signal and voltage drop data in a low potential state.
In the case of the switch signal shown in (1), the ratio between the pitch unevenness correction data and the voltage drop data is 1: 3.
A signal as shown in FIG. 1 (F) is generated. A in FIGS. 3C and 3F indicates pitch unevenness correction data.
The correction degree of the pitch unevenness correction data and the voltage drop data can be adjusted by changing the pulse ratio of the switch signal.

Next, the configuration of the correction circuit 25 in FIG. 1 will be described with reference to FIG. In FIG. 6, the correction circuit 25 is composed of a counter 41, a read only memory (ROM) 42, a comparator 43, an inverter 44 and an AND circuit 45. Here, the ROM 42 is supplied with the reference density data c (FIG. 7C) from the data counter 21 through the terminal 46, while the correction data generating circuit 36 receives the voltage drop data and the voltage drop data through the terminal 47. Pitch unevenness correction data is supplied.

Here, for example, when the maximum number of gradations according to the present embodiment is 64, for example, the relationship between the recording density and the input gradation becomes a straight line or a predetermined curve based on the 6-bit reference density data c. One type of correction data is created. on the other hand,
If the voltage drop data is 4 bits, the voltage drop will be detected in 16 stages. In this case, 16 kinds of correction data based on the reference density data c are created according to the 4-bit voltage drop data, and the ROM 42
Stored in. Pitch unevenness correction data is also created with 4 bits.

Therefore, in the ROM 42, one type of correction data is selected from the above 16 types of correction data in accordance with the incoming data, and further, this type of correction data is selected in accordance with the reference density data c.
Of the types of correction data, the data corresponding to each gradation level are sequentially read as indicated by f in FIG. 9 (A).

On the other hand, the counter 41 receives the data transfer pulse b (FIG. 7 (B), FIG. 5 (B)) from the terminal 24 and the clock signal a (FIG. 7 (AA)) from the address counter 17 via the terminal 48. Has been supplied and the data transfer pulse b
Each time a clock signal from the time when the pulse of
For example, comparison data d ((D) in the figure) that sequentially increases from “0” is generated, and the comparison data d is inverted (d ′) by the inverter 44 and then supplied to one end of the comparator 43. The comparison data d is reset at the time when the next pulse of the data transfer pulse b comes in, and returns to "0" again. The inverter 44 can be omitted by operating the counter 41 as a subtraction counter. On the other hand, the output correction data f (FIG. 9A) of the ROM 42 is supplied to the other end of the comparator 43 and is digitally compared with the inverted signal d'of the comparison data d.

The comparator 43 compares the value of the output correction data f of the ROM 42 with the value of the comparison data d ′ for each pulse section unit of the data transfer pulse b (FIG. 8 (B)), and the level of the output data of the ROM 42 is compared. When it is small, it becomes a low level, and when it becomes large, it becomes a high level.
The pulse e as shown in FIG. 9 (E) and FIG. 9 (B) is output. This pulse e is set so that its pulse width becomes small at an intermediate level in order to make the density change in each gradation substantially linear, for example, the rising edge of the pulse changes depending on the data, and the falling edge is at the end of one pulse section. It will always be constant.

On the other hand, at one end of the AND circuit 45 shown in FIG.
A heating pulse (strobe signal) that goes high when the transfer of the comparison result with the reference concentration data “1” is completed via 6 is supplied to the other end.
Is passed through the AND circuit 45 as it is and input to the terminal 49.

Therefore, the pulse e is applied to the gate circuit G via the terminal 49.
_The heating pulse is supplied to each of the other input terminals _{1 to} G _n . Each of the gate circuits G _{1 to} G _n gate-processes the pulse e and the control data supplied from the latch circuit 17 and outputs a gate signal obtained by the NPN-type transistor T.
Supply to each base of _{1 to} T _n . Transistor T ₁
˜T _n is turned on while the gate signal supplied to its base is at a high level, and the head terminal voltage V _T causes the collector current of the heating resistors R _{1 to} R _n to be turned on. It is made to flow only to the heating resistor connected to.

In this way, a heating current whose energization time changes according to the color density is applied to some of the heating resistors R _{1 to} R _n corresponding to the portion to be recorded. At this time, each time the data counter 21 finishes counting 1 to m times (m is the value of the maximum color density), one line is recorded on the recording paper 3, and after the recording of this one line, the timing is changed. The generation of the pulse g (FIG. 7 (A)) causes the data counter 21 to start counting 1 to m times again.

FIG. 10 shows an example of correcting the energization time based on the voltage drop data. Here, if the ratio of the number of energized heat generating resistors to the total number n of heat generating resistors is called the head energization rate, II in FIG. 10 (B) is the average head energization rate. In the case of (for example, 50%), I represents the corrected pulse width of the pulse e in the case of a low head energization rate (eg, 1%) and III in the case of a high head energization rate (eg, 100%).

As can be seen from FIG. 10, when the head energization rate is high and the voltage drop between the power source and the line thermal head 1 is large, the pulse width of the pulse e is corrected to be large, whereby each heating resistor is corrected. The energization time is controlled so that the desired recording density can be obtained regardless of the decrease in the temperature of the head terminal voltage V _T. On the other hand, when the head energization rate is low and the voltage drop is small, the pulse width of the pulse e is corrected to be small, whereby the temperature of each heating resistor does not rise excessively and the desired recording density is obtained. The energization time is controlled so that it can be obtained.

The configuration of the voltage drop detection circuit 28 is not limited to that shown in FIG. 3 and may be another configuration as long as it detects a voltage drop, and the configuration of the pitch unevenness correction data generation circuit is also possible. The configuration is not limited to that shown in FIG. 2, and other configurations may be used as long as they can output pitch unevenness correction data according to the transfer line. Further, the energization time of each heating resistor based on the correction data is not limited to the correction example shown in FIG. Further, it goes without saying that the analog video signal supplied from the image data generator 8 may be an information signal of an image such as another character or figure.

EFFECTS OF THE INVENTION As described above, according to the present invention, the energization time of each heating resistor is controlled according to the voltage drop between the power supply and the line thermal head. Therefore, the capacity of the power supply is increased in consideration of the voltage drop. Therefore, the power source can be downsized, and even if the power source is downsized, the energizing time of each heating resistor is automatically controlled so that a desired recording density can be obtained according to the voltage drop. Therefore, it is possible to prevent the occurrence of print density unevenness in the sub-scanning direction of the line thermal head due to the voltage drop, and it is not necessary to provide a large-capacity capacitor for absorbing the voltage drop (or smoothing the power supply voltage). Therefore, it is possible to reduce the size and cost of the entire thermal transfer printing apparatus, and further, to reduce the voltage drop of the power supply voltage supplied to the line thermal head, the timing near the end of one gradation energization period of each density data. Since the peak voltage of the drop voltage is detected, the peak voltage of the drop voltage is detected and integrated, and the drop voltage can be obtained more stably compared to the method of sampling and holding, and the integrating circuit and sample and hold circuit can be omitted. , The circuit can be configured easily, the practicality can be improved, and at the same time, the density in a preset pattern can be corrected according to the transfer line. Therefore, for example, the pitch deviation of a certain pattern of the gear used for driving the platen motor or the like can be corrected. It is possible to correct density unevenness in the sub-scanning direction due to the above.

[Brief description of drawings]

FIG. 1 is a circuit system diagram of an embodiment of a thermal transfer gradation control device according to the present invention, FIG. 2 is a block system diagram of an embodiment of a density correction circuit and a switch circuit, and FIG. 3 is a voltage drop detection circuit. 4 is a block system diagram of one embodiment, FIG. 4 is a diagram showing voltage drop, FIG. 5 is a signal waveform diagram for explaining operation of the block system diagram shown in FIG. 3, and FIG. 6 is a block system shown in FIG. FIG. 7 is a block system diagram showing an embodiment of a correction circuit in the figure.
FIG. 9 is a signal waveform diagram for explaining the operation of the correction circuit shown in FIG. 6, FIG. 10 is a diagram showing an example of correcting the energization time according to the present invention, and FIG. 11 is an operation explanation of the block system diagram of FIG. A signal waveform diagram, FIG. 12 is a schematic perspective view of an example of a main part of a thermal transfer printing apparatus to which the apparatus of the present invention can be applied. 1 ... Line thermal head, 16 ... Data storage device, 17 ... Address counter, 18 ... Reference clock signal input terminal, 19 ... Start pulse input terminal, 20
...... Gray data comparison circuit, 21 ... Data counter, 2
2 ... Shift register, 23 ... Latch circuit, 25 ...
Correction circuit, 28 ... Voltage drop detection circuit, 29 ... Differential amplifier, 30 ... A / D converter, 31 ... Clock input terminal, 32 ... Density correction data generation circuit, 34 ... Line counter, 35 ...... RO for storing pitch irregularity correction data
M, 36 ... Correction data generation circuit, 39 ... Switch signal generation circuit, 40 ... Switch circuit, 41 ... Counter, 42 ... Correction data storage ROM, 43 ... Comparator, 44 ... Inverter, 45 ...... AND circuit, G ₁ ~
G _n ...... gate _circuit, R 1 _{~R n} ...... heat generating resistor, T
₁ ~T _n ...... transistor.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Kenichi Miyazaki, 3-12 Moriya-cho, Kanagawa-ku, Yokohama, Kanagawa, Japan Victor Company of Japan, Ltd. (72) Toshinori Takahashi 3--12, Moriya-cho, Kanagawa-ku, Yokohama Address In Victor Company of Japan, Ltd. (72) Hiroki Kitamura 3-12 Moriya-cho, Kanagawa-ku, Yokohama City, Kanagawa Prefecture In Victor Company of Japan, Ltd. (72) Tadao Shinya 3-12 Moriya-cho, Kanagawa-ku, Kanagawa Prefecture Address In Japan Victor Co., Ltd. (72) Inventor Yutaka Mizoguchi 3-12 Moriya-cho, Kanagawa-ku, Yokohama-shi Kanagawa Prefecture In Japan Victor Co., Ltd. (72) Inventor Katsuhiko Terada 3--12 Moriya-cho, Kanagawa-ku, Yokohama Address inside Victor Company of Japan, Ltd.

Claims (1)

[Claims] 1. A line thermal head comprising a plurality of heating resistors arranged in a row, wherein the time of each current individually passed through the heating resistors is transferred individually according to concentration data indicating the concentration of the heating resistor to be transferred. In a thermal transfer gradation control device for controlling, a detection means for detecting a power supply voltage drop supplied to the line thermal head during transfer for each gradation energization of each density data and generating and outputting voltage drop data, and a transfer line The first correction data output means for outputting the first correction data in a preset pattern based on the print pitch unevenness, and the voltage drop data and the first correction data are selectively set at a preset ratio. And a second correction data set so that the relationship between the recording density and the density data becomes a straight line or a predetermined curve according to the voltage drop data. Storage means for supplying the voltage drop data selectively output from the switch means or the first correction data to output the second correction data, and transferring based on the second correction data. And a means for controlling the energization time of the heat generating resistor.