JPS63257660A - Thermal transfer type printer - Google Patents

Abstract

PURPOSE:To ensure uniform density of printed dots and attain higher printed image quality, by detecting insufficient cooling or overcooling of a head, and variably controlling an energizing pulse duty in an optimum manner based on the result of detection. CONSTITUTION:A counter 19 counts reference clock signals during a cooling period for a thermal head 1, and supplies a counted value to a correction table memory 21. An optimum energizing pulse duty to gradation characteristic in accordance with the variations in the cooling period for a recording paper 5, which is read according to the counted value outputted from the counter 19, is supplied to a pulse generator 27. An auxiliary heating preset value previously set by an auxiliary heating presetting source 18 is supplied to a control counter 17. Therefore, even when the cooling period is varied, the energizing pulse duty against gradation characteristic is corrected according to data values read from the correction table memory 21, and the energizing pulse duty is variably controlled in an optimum manner, so that a uniform printed density in printing is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a thermal transfer printing device, and more particularly, to a thermal transfer printing device that prevents unevenness in print density.

(Prior Art) As a terminal printing device (hard copy device), there are wire dot printing devices, inkjet printing devices, thermal transfer printing devices, and the like. A thermal transfer printing device uses, for example, an ink film (or ink ribbon) that is a polyester film (or ribbon) with a thickness of 5 to 6 μm, and heat sublimable ink is applied to the negative side of the film, and the ink side of the front side of the ink film is applied to a recording paper. A configuration in which a thermal head is placed on the back side of the recording paper, a current is passed through the thermal head to generate heat, and the ink on the ink film at the position corresponding to each part of the thermal head in the thermal head is sublimated and transferred to the recording paper. It is said that This thermal head has a plurality of heat-generating resistors arranged in a row, and a current is sequentially applied to each heat-generating resistor.

The density, which determines the gradation of printed characters, figures, pictures, etc., is determined according to the transfer density and area of each dot on the recording paper to which the sublimable ink has been transferred. The transfer density and area of the sublimation ink dots are determined by the duration of the current applied to each heating resistor and the applied energy depending on the level of the applied voltage.

However, the relationship between the print density and the time during which current is passed through the heating resistor (recording time) in the thermal transfer printing device is not linear, and there may be a density error between the original density and the density actually obtained. There was a drawback that this could occur.

Therefore, in Japanese Patent Application No. 5Q-49119, the present applicant proposed a thermal transfer gradation control device that corrects the relationship between density and recording time to be a straight line or a predetermined curve, and controls printing density. Proposed. Such a thermal transfer gradation control device is
For example, convert an analog video signal into a digital signal (image data), send this to a data storage 4R device such as a semiconductor memory, determine and store addresses for the required number of pixels, and then use the address sent from the address counter. The data is read out accordingly and output to the grayscale data comparison circuit. This gradation data comparison circuit sequentially compares - standard density data sent from the data counter (data initially indicating the minimum density) and image data of the same number as the number of heating resistors sequentially read out from the data storage device. If the value of this image data is equal to or larger than the value of the reference density data, a high level output signal is supplied to the gate circuit via the shift register circuit, and if it is smaller than the reference density data, a low level output signal is supplied. A signal is supplied to one input terminal of the gate circuit. The gradation data comparison circuit then compares the second standard density data from the one with the lowest density with the image data of the same number as the heating resistors sequentially read out from the data storage device in the same manner as above. , sends a high level or low level signal to one input terminal of the gate circuit in the same manner as above. Thereafter, the above operation is repeated in the same manner as above until the reference density data reaches the maximum density.

On the other hand, the correction circuit is supplied with the reference density data and corrects it using a correction table in which correction data is stored in advance so that there is a linear relationship between recording time and density. As a result, the correction circuit supplies to the other input terminal of the gate circuit a heating pulse whose pulse width changes for each unit of the reference concentration data based on the correction data.

Therefore, the heating pulse passes through only the gate circuit to which the high level signal is input to one input terminal.
Make the corresponding heating resistor generate heat. In this way,
A heating pulse is applied to the plurality of heating resistors for a time corresponding to the concentration, causing a pulsed current to flow, thereby controlling the gradation.

However, in the thermal transfer printing apparatus, the minimum density and the density level close to it are hereinafter referred to as "white level". ” and the density cannot be reproduced substantially linearly at the maximum density and a density level close to it (hereinafter referred to as the “black level”), resulting in the occurrence of overexposure and underexposure phenomena.

As a method of correcting the above-mentioned mill skipping, there is a method in which electricity is supplied in advance only to the heating resistor to be transferred to reheat it.

According to this method, it was possible to reproduce the density linearly from the white level to the halftone level, but due to heat accumulation in the heat generating resistor, the range from the halftone level to the black level was easily crushed by black, and the density could not be reproduced linearly. was not possible.

In addition, as a method for correcting the blackout, there is a method of controlling the amount of current applied to the heating resistor for each density, such as in the thermal transfer gradation control device proposed by the present applicant. According to this method, linear concentration reproduction was obtained for each concentration, but
There were problems such as the impossibility of linear density reproduction at the white level.

Therefore, in the previous Japanese Patent Application No. 60-117996, the present applicant reheated only the heating resistor to be transferred, and the printing density was reduced to 1.
We have proposed a thermal transfer gradation control system that solves the above problems by controlling the energization time of each heating resistor for each unit. Such a thermal transfer gradation control device includes a control counter that generates and outputs a signal corresponding to a preset reheating time, and a control counter that generates and outputs a signal corresponding to a preset reheating time. a means for generating reference concentration data that holds a value indicating the concentration) and changes sequentially from the minimum concentration to the value indicating the maximum concentration in a short time after the reheating time has elapsed, and the reference concentration data during the reheating time; means for comparing the reference density data obtained and the input data to be transferred, and generating control data indicating which heat generating resistor to conduct current among the plurality of heat generating resistors in a row for each unit of density; Correction data that is supplied with reference density data and outputs correction data that is set so that the relationship between the pre-stored recording density and the reference density data becomes a straight line or a predetermined curve according to the input reference density data. It is composed of a generating circuit, and a means for supplying correction data and control data, respectively, and for causing a current to flow through a heating resistor indicated by time control data corresponding to the value of the correction data.

The control counter maintains the reference concentration data at a value indicating the minimum concentration during the reheating time.

Therefore, the control data generating means causes current to flow only to the heat generating resistor to which input data having a value greater than the minimum density is to be transferred, thereby reheating the heat generating resistor. Further, since the reference concentration data changes sequentially from the minimum concentration to the value indicating the maximum concentration in a short time after the reheating time has elapsed, the mill data generation means generates a heating resistor to which the input data should be transferred for each unit of concentration. Electric current is passed through the body. This heating resistor has
Based on the correction data supplied from the correction data generation circuit, a current is applied to generate heat for a time set so that the relationship between one recording and the reference density data becomes a straight line or a predetermined curve.

This eliminates the need for the thermal transfer gradation control device described above.
Since only the heating resistor to be transferred is heated, optimal density characteristics can be obtained in the highlight area, and the period of data transfer pulses has been made considerably shorter than before, reducing recording time. Furthermore, since the energization time of each heat generating resistor was controlled for each density so that the recording time and density had a substantially linear relationship, the blackout described above would not occur even at high density levels. It has the advantage that it is possible to perform substantially linear density control from the highlight part to the maximum number of gradations without any problems, and it is possible to achieve high image quality in printing.

(Problem to be Solved by the Invention) The transport speed of the recording paper is not necessarily constant due to the state of transport by the recording paper transporting means, and there may be fluctuations in motor rotation, fluctuations in R mechanical power transmission characteristics, slippage of the recording paper, etc. Therefore, although it is controlled to be constant, it actually fluctuates. The pitch between lines printed on recording paper can be virtually controlled by controlling the timing of current application to the thermal head according to the output of an encoder that detects the recording paper transport speed (transfer opening) with high precision. It is possible to keep it constant. However, current technology cannot eliminate fluctuations in the transport speed of the recording paper.

Therefore, if the timing of current application to the thermal head is variably controlled in order to keep the pitch constant in accordance with fluctuations in the transport speed of the recording paper, the length of the cooling time between two consecutive current application periods will vary. FIG. 7(a') shows the energization control pulse that controls energization to the thermal head, and FIG.
') indicates the energization start pulse that instructs the start and end of energization to the thermal head;
Corresponding to b), the heat generation temperature vs. time characteristics of the thermal head are shown.

As is clear from FIG. 7(C), when the cooling time is shortened, the thermal head is not completely cooled down at the end of the cooling period, and therefore generates more heat than necessary during the next reheating period. Furthermore, if the cooling time becomes longer, the heat-sensitive head will be overcooled at the end of the cooling period, resulting in insufficient heat generation during the next reheating period.

Figure 8 (a) shows an example of printing where the pitch between lines is uniform, Figure 8 (b) shows an example of printing where the pitch between lines is uneven, and Figure 8 (C) shows an example of printing where the pitch between lines is equal. An example of printing is shown in which the density of each dot remains uneven. Figure 8 (a
') As is clearer, in the conventional thermal transfer printing device,
Even if the transport speed of the recording paper changes, the pitch between lines printed on the recording paper can be controlled to be constant;
As shown in (c), the length of the cooling period of the thermal head changes due to fluctuations in the transfer speed, and as shown in (c) of the same figure, insufficient cooling or overcooling of the thermal head causes the thermal head to fail during the next reheating period. There is a problem in that the head generates more heat than necessary (overheating) or not enough, resulting in uneven density of printed dots.

Therefore, the present invention detects insufficient cooling or overcooling of the thermal head by measuring the cooling period or one printing cycle period using a reference pulse, and optimally variably controls the energization pulse duty based on the detection result. The purpose is to provide a thermal transfer printing device that solves the problems.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention uses a thermal transfer printing device to apply an electric current to each of a plurality of heating resistors arranged in a line constituting a thermal head. In addition to individually controlling the application time of the current according to the print density, there is also a heating period in which current is applied to the corresponding heating resistor of the thermal head to reheat it, and A thermal transfer type printing device that prints each dot on recording paper during a printing period consisting of a thermal transfer period by energization and a cooling period in which the corresponding heat generating resistor is cooled, wherein an ink film is provided between the thermal head and the recording paper. a platen that clamps the recording paper and transports the recording paper at a predetermined speed; an encoder that detects the rotation of the platen and generates an energization start signal in accordance with the transport speed of the recording paper; and an incoming image. a data storage device in which image data corresponding to the signal is stored; and an address corresponding to the image data printed by the heating resistor in response to the energization start signal is output to the data storage device, and then a transfer signal is transmitted. an address counter for outputting, a reheating preset source in which a reheating preset value that determines the reheating period is stored, a control counter that is supplied with the energization start signal and the transfer signal and counts the reheating preset value; A data counter that stops counting during the counting period of the control counter and outputs a reference concentration signal and a heating signal, and a data counter that is reset by the inverted energization start signal and starts the next energization during the cooling period or from the energization start signal. A counter that counts the reference signal during one printing cycle immediately before the signal is supplied, and the output count value of this counter and the reference density signal are supplied, and the length of the cooling period is caused by fluctuations in the transport speed of the recording paper. a correction table storage memory that stores correction data values as a correction table in accordance with fluctuations in the printing cycle period from the energization start signal to just before the next energization start signal; When the image data>the reference density signal, first control data is sent; and when the image data is smaller than the reference density signal, second control data is sent. It has a predetermined pulse width for a predetermined period including the reheating period according to the correction data value supplied from the grayscale data comparison circuit that sends out data and the correction table storage memory, and the pulse width is varied after this period. a pulse generator that outputs a signal; a shift register that is supplied with the first and second control data from the gray data comparison circuit and that transfers control data corresponding to the address of the address counter; and a shift register that is synchronized with the transfer signal. a latch circuit that latches the control data of the shift register; an AND circuit that outputs the AND of the output from the pulse generator and the heating signal; A gate circuit that intermittents the output,
and an energizing means for energizing each of the heat generating resistors arranged in a row constituting the thermal head in accordance with the output from the gate circuit, and a time axis during one line printing on the platen. The system is configured to eliminate print density changes of each dot in one line due to fluctuations, and to obtain a predetermined 1!1llft characteristic for the input video signal.

(Example) The thermal transfer printing device according to the present invention has the following configuration.

That is, the application time of the current applied to each of the heat-generating resistors R1 to Rn arranged in a row constituting the thermal head 1 is individually controlled according to the print density, and the corresponding current of the thermal head 1 is controlled. Each printing period consists of a heat replenishment period in which heat is supplied to the heat generating resistor by energizing it, a thermal transfer period in which the corresponding heat generating resistor is energized, and a cooling period in which the corresponding heat generating resistor is cooled down. This is a thermal transfer printing device that prints dots on a recording paper 5, and includes a platen 6 that sandwiches the recording paper 5 with an ink film 4 between it and a thermal head 1 and transports the recording paper 5 at a predetermined speed; an encoder 8 that detects the rotation of the platen 6 and generates an energization start signal a corresponding to the transport speed of the recording paper 5; a data storage device 12 that stores image data corresponding to an incoming video signal; In response to the energization start signal a, the heating resistor R1~
An address counter 13 that outputs a transfer signal after outputting an address corresponding to the image data to be printed by Rn to the data storage device 12, and a reheating preset source 18 that stores a reheating preset value that determines a reheating period. and a control counter 17 which is supplied with the energization start signal a and the transfer signal I and counts the reheating preset value, and which stops counting during the counting period of this control counter 17 and also outputs the reference concentration signal d and the heating signal e. A data counter 16 and a counter 19 that is set by the inverted energization start signal a and counts the reference signal during the cooling period or during one printing cycle up to just before the energization start signal.
Then, the output count value of this counter 19 and the reference density signal d are supplied, and the change in the length of the cooling period due to the change in the transport speed of the recording paper 5 or the period from the energization start signal to just before the next energization start signal is detected. A correction table storage memory 21 that stores correction data values corresponding to variations in length during one printing cycle as a correction table, and this data storage device 12
The image data supplied from the reference density signal d is compared with the reference density signal d, and when the image data>reference density signal d, the first control data is sent out, and when the image data is the reference density signal d, the second control data is sent out.
It has a predetermined pulse width for a predetermined period including a reheating period according to the correction data value supplied from the gradation data comparison circuit 22 which sends control data of the correction table storage memory 21, and the pulse width is variable after this period. First and second control data are supplied from a pulse generator 27 that outputs a signal to output a signal, and a grayscale data comparison circuit 22, and the address counter '1.
A shift register 23 that transfers the control data corresponding to address 3, a latch circuit 24 that latches the control data of this shift register 23 in synchronization with the transfer signal, and an output from the pulse generator 27 and the heating signal e. an AND circuit 26 that outputs the logical product of 1, and energizing means for individually energizing a plurality of heating resistors R1 to Rn arranged in a row constituting one line. This thermal transfer printing apparatus is characterized in that it is configured to eliminate print density changes and obtain predetermined gradation w4 density characteristics for input video signals.

FIG. 1 shows a circuit diagram of an embodiment of a thermal transfer printing apparatus according to the present invention. In the figure, a thermal head 1 includes n heating resistors R1 to RO formed in a row on a ceramic substrate. The configuration of this thermal head 1 is the same as that of a conventional thermal transfer type device, and extends in the width direction of the ink film 2, as shown in FIG. 3, for example. In Figure 3,
An ink film 2 serving as a transfer paper has a heat sublimable ink 4 coated on the surface of a polyester film 3 to a predetermined thickness. The recording surface of the recording paper 5 is coated with the ink 4 of the ink film 2.
The ink film 2 is placed in contact with the surface of the ink film 2 by the platen 6.
It is also sent in the six directions of the arrow.

A thermal head 1 is provided opposite the platen 6,
It is in contact with the back surface of the ink film 2.

The ink 4 of the ink film 2 in the portion corresponding to the energized heat generating resistor among the heat generating resistors R1 to Rn of the thermal head 1 is sublimated and transferred onto the recording paper 5. After passing through the thermal head 1, the ink film 2 is guided by a roller 7 and separated from the recording paper 5, and is placed on a take-up spool (not shown).
It can be wound up as a used ink film 2a. The transferred ink 4a remains on the printed recording paper 5a. For convenience of illustration, the transferred ink 4a is shown as having a large area, but it actually consists of a collection of small dots.

Reference numeral 8 denotes a high-precision encoder, which detects the rotation of the platen 6 to obtain the transport speed (transfer amount) of the recording paper 5, and outputs an energization synchronization pulse.

Therefore, even if there is a fluctuation in the transport speed of the recording paper 5, a well-known circuit (not shown) generates an energization start pulse as shown in FIG. By controlling the energization period, it is possible to keep the pitch between lines printed on the recording paper 5 constant.

One dot is formed by a negative heating resistor, and the size of the negative dot is determined by the level of the voltage heard or applied when the heating resistor is energized. The shading, or gradation, of the printed figure is determined according to the size and density of each dot.

Returning to FIG. 1 again, the TV signal generator 10
An analog video signal supplied from the controller is converted into a digital signal by an analog/digital (A/D) converter 11, and sent to a data storage device 12 for storage. on the other hand,
The address counter 13 is supplied with a constant frequency reference OFF signal from a terminal 14 and an energization start pulse a as shown in FIG. 2 (A>) from a terminal 15. It is started by the energization start pulse a that comes in at time t1.The control counter 17 is loaded with a preset reheating preset value from the reheating preset source 18 in response to the energization start pulse a.

This reheating reset value is a value that determines the reheating period (time), which will be described later, and includes the period of pulse b shown in FIG. It is determined by the pressing force of the
” will be selected.

Further, the heating period is selected to be a time during which pixel data for one line is read out repeatedly an integer number of times.

Locally, the reference clock signal from terminal 14 is sent to counter 19.
is also supplied and counted. This counter 19 is reset by a pulse D obtained by inverting the energization start pulse a from the terminal 15 using an inverter 20. That is, the counter 19 counts the reference clock signal during the cooling period for the thermal head 1 in FIG. 7(b). counter 19
The output count value of is supplied to the correction table storage memory 21. The correction table storage memory 21 is shown in FIG. 7(C).
The optimum energization pulse duty corresponding to the variation in the length of the cooling period caused by the variation in the transport speed (transfer amount) of the recording paper 5 is stored in advance as a correction table based on the characteristics as shown in FIG. The energization pulse duty vs. gradation characteristic read from the output count value of the counter 19 is supplied to the pulse generator 27. The reheating preset source 18 supplies the reheating preset value set in advance to the control counter 17 as an initial value.

The control counter 17 is generated based on the standard O-check signal from the address counter 13 as shown in FIG. 2(B).
The pulse b shown in Fig. 2 (
As shown in C), a low level signal C is supplied to the data counter 16 to stop its counting operation. Therefore,
The value of the reference density data d shown in FIG. 2(D) supplied from the data counter 16 to the correction table storage memory 21 and the density data comparison circuit 22 is set to the reset value "0" during the above-mentioned time ΔT (heating period). , that is, it is held at the value "0" indicating the minimum density white. Note that the period of the pulse b is, for example, 1 compared to the period of the output pulse of a conventional address counter.
It has been selected as short as /10.

The address counter 13 sends the first address to the data storage device N12 upon reception of the energization start pulse a.

The data storage device @12 sends the first data (the first data of the image data from the A/D transformation @11) corresponding to this first address to the IT light data comparison circuit 22.

The density data comparison circuit 22 compares the first data with reference density data (hereinafter referred to as "second data") "O" indicating the minimum density from the data counter 16, and determines whether the first data is the second data or not. If the data is larger than the data rOJ, control data "1" is sent to the shift register 23, and if they are equal, the control data rOJ is sent to the shift register 23.

In this way, when the processing at the first address is completed, the address counter 13 is sequentially updated to 2°3, . . .
The n-th address is sent to the data storage device @12, and the data storage device 12 sequentially sends the first data windowed to the 2nd to n-th addresses to the grayscale data comparison circuit 22 each time. Here, the first data from the 1st to nth addresses correspond to image data printed by each of the heating resistors R1 to Rn of the thermal head 1, respectively. The gray data comparison circuit 22 compares the first data and second data "0" corresponding to the 2nd to nth addresses, respectively, and outputs the control data "0" or "1" as described above. shift register 2
Send to 3. The n-stage shift register 23 sequentially takes in n-bit control data corresponding to the 1st to nth addresses supplied from the grayscale data comparison circuit 22 and sends it to the latch circuit 24 .

When the address counter 13 finishes counting the 1st to nth addresses, the data counter 16 and the latch circuit 2 use the pulse b shown in FIG. 2(B) as a data transfer pulse.
4 and control counter 17'. At the same time as this data transfer pulse b is sent, the data counter 16 supplies a heating pulse e shown in FIG. 2(E) to the address counter 13 and one input terminal of the AND circuits 25 and 26.

On the other hand, a reference clock signal is supplied from the terminal 14 to one end of the AND circuit 25, and simultaneously with the input of the heating pulse e from the data counter 16, the pulse is output to the shift register 23, and the pulse is outputted to the shift register 23. 1~n
The n-bit control data corresponding to the second address is transferred from the shift register 23 to the latch circuit 24. When the data transfer pulse b is received, the latch circuit 24 latches the control data supplied from the shift register 23 and sends it to one input terminal of each of the gate circuits G1 to Gn.

The address counter 13 is reset by the arrival of the heating pulse e and sequentially counts addresses 1 to n again in response to the energization start pulse a, but during the reheating period Δ
During T, the address counter 13 controls the data storage device 12.
repeatedly reads n pieces of first data on the same line, and the second data is held at "0", so the n pieces of first data for the same line have the above value "o". ”
It is repeatedly compared in magnitude with the second data of , in the grayscale data comparison circuit 22 .

Therefore, during the reheating period ΔT, a heating current is applied by the power supply voltage VCC only to the heating resistor to be transferred when the first data is "1" or more, that is, the first data is reheated. Therefore, the first data of the white level is held as white and is not transferred, and the rise of the transfer density can be optimized for the density above the white level by the preset heating preset value.

Thereafter, when the pulse C1 becomes high level at time t2 when the control counter 17 has finished counting the pulses b for the reheating preset value, the data counter 16 starts counting operation and repeats the same operation as above for one line. Once for the first data of , the next incoming pulse b is counted at time t3, and the pulse b of FIG.
> is increased to the value "1" indicating the second smallest density.

From this, the gray data comparison circuit 22 sequentially compares the n pieces of first data for the same one line with the second data having the value "1". When the second data is NJ, the shift register 23, latch circuit 24, AND circuit 25, etc. perform the same operation as above, and send the latched control data to one input terminal of each of the gate circuits G1 to Qn. do.

On the other hand, the second data "0" shown in FIG. 2(D) is supplied to the correction table storage memory 21 which outputs a signal that takes into account the density correction and 8-character correction according to the output count value of the counter 19. The pulse generator 27 corrects this data using a correction table in which correction data is stored in advance so that there is a linear relationship between recording time and density.
Send to. The pulse generator 27 is at a high level during a predetermined period including the reheating period ΔO according to the incoming correction data;
After this period, the pulse width gradually decreases as shown in Figure 2 (F
) is generated and output to the other input terminal of the AND circuit 26. The AND circuit 26 generates a pulse Q shown in FIG. 2(G) using the incoming heating pulse e and pulse f, and sends it to the other input terminal of the gate circuits G1 to Gn.

As shown in FIG. 2(G), the pulse Q is applied for a predetermined period including the reheating period Δt after time t1 (i.e., the second data d
period from time 11 to time t3 when is "O") has a predetermined pulse width, and after this period, the pulse width gradually changes depending on the data content of the correction data read from the correction table storage memory 27. Decrease.

Each of the gate circuits G1 to Gn applies a gate signal obtained by gate processing the pulse q and n-bit control data supplied from the latch circuit 24 to the NPN transistor T1.
~Tn to the bases of each of them and performs switching control. Transistor T! ~Tn, a current is passed only through the heating resistor connected to the collector side of the turned-on transistor to generate heat.

Moreover, after time t2, the second data output from the data count 16 is synchronized with pulses b and e, and the second data is synchronized with rob, rI.
J, r2J, ..., rl (where m is a value indicating the maximum density), and the grayscale data comparison circuit 22 outputs control data "1" if the first data is larger than the second data. However, if it is equal to or smaller than the second data, control data "0" is output. Depending on the rOJ or "1" control data and the pulse width of the pulse generator, the energization time of the heating current flowing through the heating resistor changes, and gradation recording of data for one line is performed.

Thereafter, when the next start pulse a arrives, the address counter 13 and data counter 16 are each reset, and the data counter 16 again outputs the second data at time t! in FIG. 2(D)! The tone is changed sequentially as shown below, and the same operation as above is performed to record the gradation of the first data for the next one line.

FIGS. 4(a) to 4(C) are diagrams for explaining the 8-character correction.

In figure 8 correction, when gradations are recorded using a data signal with a constant duty ratio, the number of gradations versus density characteristic becomes non-linear, as shown in the figure <a), and this is changed to the same characteristic as shown in the figure (b). This is a correction to provide linearity.

Specifically, the duty ratio of the data signal of each output of the gate circuits 01 to Qn is determined by the duty ratio characteristic of the number of gradations versus the energization pulse as shown in FIG.
The number of gradations vs. density characteristic shown in FIG.

In addition, the present invention also attempts to correct density unevenness due to cooling time fluctuations, as shown in the nonlinear characteristic of cooling time fluctuations versus concentration fluctuations, as shown in FIG. 5(a). .

In other words, the density fluctuations caused by the cooling time fluctuations as shown in FIG.
As shown in FIG. 4(b), by taking into consideration the duty ratio variation width characteristic of the cooling time variation versus the energizing pulse, the duty ratio characteristic of the number of gradations versus the energizing pulse shown in FIG. By changing the dots, it is possible to maintain the linearity versus density characteristic of the number of gradations shown in FIG.

Therefore, according to this embodiment, the number of gradations is "0" to rfflJ
In other words, it is possible to perform approximately linear density control from the white level to the black level. In addition, the period of pulse b is 1/1/2 compared to the conventional one.
Since it is about 10, the recording time can be shortened. Furthermore,
Even if there is a variation in the cooling period, the energization pulse duty is optimally variably controlled by correcting the energization pulse duty vs. gradation characteristic using the data value in the correction table storage memory 21, so uneven printing density will not occur. do not have.

In this way, each time the data counter 16 finishes counting from 1 to I11 times, one line is recorded on the recording paper 5, and when the recording of this one line ends, the data counter 16 again counts from 1 to I11. Start counting.

Incidentally, the structure of the thermal head 1 may be as shown in FIG. 6. In the figure, the same parts as in Fig. 3 are given the same reference numerals.
The explanation will be omitted. The recording paper 5 is wound and fixed around the outer periphery of the platen 31 by a clamper 30. The encoder 8a detects the rotational speed (rotation angle) of the platen 31 via the belt 32, and generates the energization synchronization pulse.

In the example of FIG. 3, the recording paper 5 may be continuous paper, but the 6th
In the illustrated example, the recording paper 5 is fixed to the platen 31 one by one.

It goes without saying that the present invention can also be applied to color printers.

Note that the analog video signal supplied from the TV signal generator 10 may be an information signal of images such as other characters or two figures.

Furthermore, although the above embodiments have been described in the case where the relationship between the recording time and the density is a straight line, the relationship between the recording time and the density may be a predetermined curve.

Moreover, it is natural that the same effect can be obtained even if the variation in the energization cycle is measured in order to measure the variation in the cooling time.

(Effects of the Invention) As described above, according to the present invention, only the heating resistor to be transferred is heated, so it is possible to obtain the optimum density characteristic in the highlight part, and also to reduce the period of the data transfer pulse. Since it is much shorter than the conventional method, it is possible to shorten the recording time, and furthermore, the energization time of each heating resistor is controlled for each density so that there is a nearly linear relationship between the recording time and the density. Therefore, it is possible to perform almost linear density control from the highlight area to the maximum number of gradations without causing the aforementioned black-out even at high density levels, and it is possible to improve the image quality of printing. Insufficient cooling or overcooling of the thermal head is detected by measuring the length of the cooling period of the thermal head, and the duty of the energizing pulse is variably controlled based on the detection result, so the temperature is reduced due to fluctuations in the cooling period. It has features such as being able to effectively prevent uneven printing density caused by excessive heat generation or insufficient heat generation in the thermal head.

[Brief explanation of drawings]

FIG. 1 is a circuit system diagram showing an embodiment of the thermal transfer printing apparatus according to the present invention, FIG. 2 is a signal waveform diagram for explaining the operation of the circuit system shown in FIG. A schematic perspective view of an example of a main part of a wet thermal transfer printing VR device, FIG.
) to (C) are diagrams showing examples of the number of gradation levels vs. density characteristics and the number of gradation levels vs. duty ratio characteristics of energizing pulses;
b) is a diagram showing an example of the cooling time variation vs. density variation characteristic and the duty variation width characteristic of the energizing pulse, and FIG. 6 is a schematic perspective view of another example of the main part of a thermal transfer printing device to which the device of the present invention can be applied. , FIG. 7 is a diagram for explaining the dot printing period,
FIGS. 8(a) to 8(0) are diagrams for explaining the unevenness of printing density that occurs in the conventional apparatus. 1... Thermal head, 4... Ink film, 5...
・Recording paper, 6...platen, 8...encoder,
12...Data recording device, 13...Address counter, 14°15...Terminal, 16...Data counter, 17...Control counter, 18...Heating preset source, 19... Counter, 21... Correction table storage memory, 22... Grayscale data comparison circuit, 23
...Shift register, 24...Latch circuit, 26.
...AND circuit, 27...Pulse generator, a...Electrification start signal, b...Transfer signal, d...Reference concentration signal, e...Heating signal, 01-Gn...Gate circuit, R
1-Rn...Resistor for heat generation. Saitara tb)

Claims (1)

[Claims] The application time of a current applied to each of a plurality of heating resistors arranged in a line constituting a thermal head is individually controlled according to print density, and the corresponding heating of the thermal head is controlled individually. a reheating period in which the resistor is reheated by energizing it;
A thermal transfer printing device that prints each dot on recording paper during a printing period consisting of a thermal transfer period in which the corresponding heat generating resistor is energized and a cooling period in which the corresponding heat generating resistor is cooled. , a platen that sandwiches a recording paper with an ink film between it and the thermal head and transports the recording paper at a predetermined speed; and a platen that detects the rotation of the platen and generates an energization start signal in accordance with the transport speed of the recording paper. a data storage device that stores image data corresponding to the incoming video signal; and a data storage device that stores an address corresponding to the image data printed by the heating resistor in response to the energization start signal. After outputting to the device,
an address counter that outputs a transfer signal; a reheating preset source that stores a reheating preset value that determines the reheating period; and a control counter that is supplied with the energization start signal and the transfer signal and that counts the reheating preset value. and a data counter that stops counting during the counting period of this control counter and outputs a reference concentration signal and a heating signal, and a data counter that is reset by the inverted energization start signal and is reset during the cooling period or after the energization start signal. A counter for counting a reference signal, the output count value of this counter, and the reference density signal are supplied during one printing cycle immediately before the energization start signal, and the cooling period due to fluctuations in the transport speed of the recording paper is supplied. a correction table storage memory that stores, as a correction table, correction data values corresponding to variations in length or changes in length during one printing cycle from the energization start signal to just before the next energization start signal; and this data storage device. The image data supplied from the reference density signal is compared with the reference density signal, and when the image data>the reference density signal, first control data is sent, and when the image data=the reference density signal, the first control data is sent. 2
has a predetermined pulse width for a predetermined period including the reheating period in accordance with the correction data value supplied from the correction table storage memory, and the pulse width after this period. a pulse generator that outputs a variable signal; and a pulse generator that outputs a variable signal;
and a shift g register to which second control data is supplied and which transfers control data corresponding to the address of the address counter; a latch circuit which latches the control data of this shift register in synchronization with the transfer signal; an AND circuit that outputs the logical product of the output from the pulse generator and the heating signal; a gate circuit that intermittents the output from the latch circuit according to the output of the AND circuit; and energizing means for individually energizing a plurality of heat generating resistors arranged in a line constituting the thermal head, and each dot of one line is printed by a time axis variation during printing of one line of the platen. A thermal transfer printing device characterized in that it is configured to eliminate density changes and obtain predetermined gradation density characteristics for input video signals.