JPS6195960A - Thermal heat driving method and its apparatus - Google Patents

Abstract

PURPOSE:To obtain high-quality image drawing printing without uneven density using simple technique by generating a density correction signal after density correction processing referring to a weighted picture signal and controlling time for applying electric power to be applied to a heat-resistance element or a crest value of such electric power. CONSTITUTION:Assuming that adjacent dots each at right and left of a dot 'X' on the 'n' line is S, a dot in the same location of the 'n'-1 B and adjacent dots at right and left on the 'n'-1 line C, density variations to be caused to the dot 'X' by the densities of the dots S, B and C vary according to each dot. A weight for correction is given to the density of each dot S, B and C in accordance with a degree of influence and a picture signal is generated to the dot X on these weighted density correction information. The time for applying and the peak value of electric power to be applied to the heat- resistance element corresponding to the dot X are controlled by this corrected picture signal.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for driving a thermal head used in a thermal printer, etc., and an apparatus for implementing the same, and particularly relates to a technique for automatically adjusting the density of drawing print to an appropriate level. be.

In general, thermal printers are equipped with a thermal head with multiple heating resistive elements installed in the line.

The heating resistor elements are made to generate heat in a predetermined order according to commands from a control device, and images such as two characters are formed and recorded as dots through thermal paper or a thermal transfer member.

In thermosensitive or thermal transfer recording, a method is generally used in which color density is controlled by the application time T or peak value P of electric power applied to a heating resistor element. It is known that the color density in this heat-sensitive or thermal transfer recording is generally a monotonically increasing function having saturation characteristics with respect to the power application time T or peak value P of one heating resistor element, as shown in FIG. There is.

However, when drawing and printing are performed, the actual color density varies depending on the amount of heat stored in the heating resistor element. As an example, the printing density D n -r of the n-1th line and the m-th dot when the power application time to the n-1th line and the m-th dot is constant.

The relationship between the printing density Dn of the nth line and the mth dot is expressed as
As shown in the figure. As another example, if the power application time to be applied to all dots in one line is constant for each line, then
− The time from the start of printing of the first line to the start of printing of the nth line, that is.

Printing cycle T0 and printing density Dn of the nth line and mth dot
The relationship is shown in Figure 3.

As in the above example, in thermal recording, the color density varies depending on the amount of heat stored in the heat generating resistor when printing, resulting in uneven density. In particular, density unevenness often occurs in halftone expression.

As a solution to this problem, for example, a method of driving and controlling a heat generating resistor element array as described below has been proposed.

(1) In the drive control circuit for the heating resistor array for thermal printing, power is applied to each heating resistor element corresponding to each pixel of the nth line in response to a single image signal, and printing is performed in accordance with the image signal of the nth line. When obtaining, the nth line, n-1th line,...
- Means for storing the image signal of the n-Qth line, the time from the start of printing of the n-1st line to the start of printing of the n-th line, and the time from the start of printing of the n-2nd line to the n-1st line means for correcting the density of the image signal of the n-th line according to the time from the start of printing of the n-t-1 line to the start of printing of the n-t-th line; The density of the image signal is corrected by a means for controlling the application time or the peak value of the electric power applied to the heating resistor array for thermal printing, and the electric power applied to each pixel of the n-th line using this corrected image signal. A method of reducing density unevenness by correcting density by controlling the application time or peak value of .

(2) At a certain dot timing, the width of the drive pulse energized from the head drive circuit to each heat generating resistor element of the print head is changed to the width of the drive pulse energized from the head drive circuit to each heat generating resistor element of the print head to the heat generating resistor element energized at the two previous dot timings and the one before the dot timing.・As for the heating resistance element adjacent to the heating resistance element that is energized at the timing,
By making the driving pulse width narrower than the heating resistor element,
Method for making the applied density uniform for each dot (Japanese Patent Application Laid-Open No. 57-3
(See Publication No. 4986).

(3) In a thermal printer that has N heating resistance elements and prints by applying a drive pulse to each heating resistance element according to a predetermined order and causing one heating resistance element to generate heat, it generates heat for printing. The past of resistive elements,
Detecting current and future heat generation information and changing the number of drive pulses to be applied to the heat generating resistor element that is currently to generate heat so that the temperature of the board to which the heat generating resistor element is attached becomes equal to or higher than a predetermined temperature. 1 The heat generated by the heating resistor element that should generate heat is generated at a constant substrate temperature so that the heat generation does not add excess heat to other heat generating resistor elements via the board, and the temperature is sufficient for printing. Method of heating a resistive element to obtain uniform printing quality (Japanese Patent Application Laid-Open No. 57-1179
78).

However, in these conventional methods.

There are the following problems.

In method (1), the density of the image signal is corrected in accordance with the printing cycle time of the previous line, so the correction effect is small and is therefore insufficient for halftone printing.

In the method (2), density correction is performed by changing the pulse width of the electric power applied to each pixel according to the previous print information and the two previous print information.

With this much information, the correction effect is insufficient.

In method (3), the past of the heating resistor element for printing,
It detects current and future heat generation information, that is, information only on the heat generation resistor elements of the previous line, the current line to be printed, and the next line, and records these past lines.

Currently, future heat generation information is being collected as reference information for concentration correction with the same weight, and the temperature of the substrate is being controlled, but the power applied to the heat generation resistor element, ! Direct control 5 "C'Ne't" - I concentration correction information "Insufficient. Also, since meaningless future heat generation information is also referenced, the configuration of the control device becomes complicated. 1. An object of the invention is to provide a technique that enables high-quality drawing and printing without density unevenness using a simple method in a thermal head driving method and an apparatus for implementing the method.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

C. In order to achieve the above-mentioned object, the present invention provides a thermal head driving method and an apparatus for performing drawing printing by selectively generating heat from a heating resistance element provided in a thermal head, in which a heating resistance element that is currently to be subjected to drawing printing is provided. Detects the heat generation information of the heat generating resistor elements on both its left and right sides, as well as the heat generation information of the heat generating resistor element that is currently to be drawn and printed and the heat generation information of the heat generating resistor elements on its left and right sides, and adjusts these heat generation information according to the degree of influence. Perform weighting for density correction.

A density-corrected image signal is generated based on these density-corrected heat generation information, and this density-corrected image signal determines the application time or wave of power to be applied to the heating resistor element that is currently generating heat. By controlling the high value, it is possible to obtain high quality drawing prints with no density unevenness using a simple method.

Hereinafter, a detailed explanation will be given based on one embodiment of the present invention.

In addition, in all the episodes, parts having the same function are given the same reference numerals, and the explanation of the reversing of the edges will be omitted.

Example 1 is an application of the present invention to a thermal printer.

11th in thermal printers! As shown in l,
The line to which power is currently being applied is the nth line,
The line to which the previous power was applied is defined as the (n-1)th line, and for a certain dot 1
U, if the dots on both the left and right sides of the in are C, then each S, B
, the density change that the C dot density gives to the X dot is the second
It will be like U4. As shown in Figure 2, each S, B
.

The influence of the concentration of C dots on X dots differs depending on each dot. This is because the concentration of each dot is proportional to the amount of heat generated by the corresponding heating resistor element, and the influence on the X dots differs depending on its position.

In FIG. 2, the horizontal axis represents the energy (power) P applied to the heating resistor element, and the vertical axis represents the density (dot surface M) D of the drawn and printed image. In addition, in FIGS. 1 and 3, the direction of the arrow m is the main scanning direction, and the direction of the arrow n is the sub-scanning direction.
For example, as shown in FIG.
A weight of rlJ is applied to the dot, rlJ is applied to the B and C dots, and r4J is applied to the X dot to the density of each dot of S, B, and C, and the X dot is calculated based on these weighted density correction information. The corrected image signal is used to control the application time or peak value of the power to be applied to the heating resistor element corresponding to the X dot.

Embodiment 1 Thermagend driving method and the embodiment device thereof will be described below with reference to the drawings.

FIG. 4 is a block diagram showing a schematic configuration of an apparatus for implementing the thermal head driving method, FIG. 5 is a diagram showing the contents of the ROM, and FIG. 6 is a diagram showing the correspondence between dot area and binary code. , FIG. 7 is a diagram showing the correspondence between the binary code and the application time of electric power applied to the heating resistor element.

In FIG. 4, 1 is an image signal input terminal, 2A.

2B is a first shift register for storing 3 bits of a 4-gradation image signal represented by 2 bits. The first shift register 2A inputs the image signal M S B (
The first shift register 2B stores the LSB (least bit of the image signal) of the image signal.
gn1ficanj Bij: Stores the smallest bit in binary data. 3A, 3B
A second shift register is used to store image signals corresponding to one line of m dots sent from the first shift registers 2A and 2B, respectively. Second
The shift register 3A stores the MSB of the image signal, and the second shift register 3B stores the LSB of the image signal. 4 is a ROM for generating a density correction image signal (Re-ad ONLY
Memory) and the input address terminal A of this ROM4. -All includes the first shift register 2A,
2B and the outputs of the second shift registers 3A and 3B (No. 1 is input. That is, the output of the first shift register 2A,
The second bit is connected to terminal A4, and the second bit is connected to terminal A4.
1, the third bit is input to the terminal A5, and the first bit of the first shift register 2B is input to the terminal A5.
2, the second bit is terminal A. Then, the third bit is input to terminal A3.

Further, the first bit of the second shift register 3A is input to the terminal A9, the second bit is input to the terminal A7, and the third bit is input to the terminal All, and the first bit of the second shift register 3B is input to the terminal A9. The bit is connected to terminal A8, and the 3rd mth bit is connected to terminal A8.

The third bits are respectively input to terminals AIO.

D o -D 3 are density correction image signals, and R
This is the output image signal of OM4. The contents of this ROM 4 are such that when the input image signal is input to the input address terminal 80-All, density correction weights as shown in FIG. 3 are applied to the input image signal, and these weighted images are Predetermined density-corrected image signals Do to D3 of X dots corresponding to the heat-generating resistive elements that are currently to be heated, whose density has been corrected with reference to the signal.
It is a table to be converted to. This conversion table is created from preliminary measured values. An example of the conversion table is shown in FIG.

5 is a power application time control circuit and output data D of the ROM 4; -D3 is converted into a binary code representing the dot area size or density gradation level as shown in Figure 6, and based on this binary code, the application time is determined as shown in Figure 7. It outputs an application time signal with a corresponding pulse width. Reference numeral 6 denotes a heat generating resistor element array drive circuit for driving a heat generating resistor element array provided in the thermal head, and numeral 7 denotes a plurality of heat generating resistor element arrays provided in a line in the thermal head.

Next, the operation of the apparatus for implementing the thermal head driving method of the present embodiment (2) will be explained.

In Fig. 4, the image signal of the n-th line consisting of m° dots composed of 2 bits is now transmitted from input terminal 1 to 3.
The bits are sequentially input and stored in respective addresses of the first shift registers 2A and 2B. At this time, all m dots for the (n-1)th line are stored in the second shift registers 3A and 3B. When the image signal is shifted by two dots from this state, the input address terminal A1 of the ROM4 is shifted. The image signal stored at the second address (m) of the first shift registers 2A and 2B is input to Ao. At the same time, this address (m)
Both signals stored at the first address (+, . . . +1) and the third address (m-1) before and after are input to the input address terminals A2, A3 . Input to A4A3. At the same time, the image signals stored in the second address (m), first address (m+1), and third address (m-1) of the n-1th line are transferred to the ROM4.
Input address terminal As, A7-Aa-A@, Aro-
It is input to Al1. According to these input image signals (data), the ROM 4 generates an output density correction image signal as shown in FIG. -D3 is output and input to the power application time control circuit 5. This power application time control circuit 5 receives the density correction image signal from the ROM 4. -D3 is converted into a binary code representing the dot area size or density gradation level as shown in Figure 6, and based on this binary code, the application time is determined as shown in Figure 7. An application time signal with a corresponding pulse width is generated. This application time signal is input to the heating resistor element driving circuit 6, and at a predetermined timing, a predetermined amount of power is applied to each heating resistor element of the heating resistor element row 7 provided in the thermal head according to the application time signal. The voltage is applied for a certain amount of time to generate heat, and high-quality drawing printing with appropriate density is performed.Thereafter, the input image signal is sequentially shifted one dot at a time, and the same operation as described above is repeated.

At the same time that the 1 and 2 signals are input manually, the image signal of the X dot to be currently drawn and printed shown in FIG. To A5.

The image signal of the S dot is input to the input address terminals A s and A 7
Then, the image signal of C dot is sent to the input address terminal 〇～All
The image signal of the X dot is generated and the density is corrected by referring to the heat generation information of the surrounding S, B, and C dots, which are input with density correction weights according to the degree of influence of each. By controlling the power application time of the heating resistor element corresponding to the image signal of the X dot currently to be drawn and printed based on the image signal thus obtained, high quality drawing and printing without density unevenness can be obtained.

In the above embodiment I, the power application time to the heating resistor element was controlled based on the density-corrected image signal, but the peak value of the power applied to one heating resistor element may also be controlled.

Further, instead of the first and second shift registers, any type of shift register may be used as long as it has a storage function.

Figure 8 is a block diagram schematically showing the construction of an apparatus for implementing the thermal head driving method according to the ninth embodiment (2) of the present invention.

The apparatus for implementing the thermal head driving method of this embodiment (2) is m
The signal is composed of two gradations of one bit, and as shown in FIG. When the image signal of the S dot is input to the encoder 9 through the decoder 8, both signals of the X dot are input to the input address terminal of the ROM 4 at 〇''A.
The S dot and S dot image signals are sent directly to the encoder 9.
The S dot and S dot image signals and the S dot image signal from the decoder 8 are converted by the encoder 9 to the input address terminals A4 to A6 of the ROM 4.
.

By using the decoder 8 and the encoder 9 in this way, the number of input address terminals of the ROM 4 can be reduced, so the structure of the contents of the ROM 4 can be simplified.

As explained above, according to the present invention, the heat generation information of the heating resistor element to be currently drawn and printed and the heating resistor elements on both its left and right sides, as well as the heat generation information of the heating resistor element to be currently drawn and printed and its left and right neighbors Detects the heat generation information of the heating resistor element one line before, weights this heat generation information for density correction, and refers to these weighted image signals to correspond to the current density-corrected heat generating resistor element that should be heated. By photogenerating a density-corrected image signal and controlling the application time or peak value of the power to be applied to the heating resistor element that is currently to be fully ripened, the density can be adjusted to 1 by a simple method.
1. It is possible to obtain high-quality drawing prints.

The present invention has been specifically explained above using examples, but
It goes without saying that the present invention is not limited to the embodiments described above, and that the species can be changed without departing from the gist thereof.

[Brief explanation of the drawing]

1 to 3 are diagrams for explaining a thermal head driving method according to Embodiment 1 of the present invention, and FIG. 4 shows a schematic configuration of an implementation apparatus for the thermal head driving method according to Embodiment 1 of the present invention. Figure 5 is a diagram showing the contents of the ROM, Figure 6 is a diagram showing the correspondence between dot area and binary code, and Figure 7 is a diagram showing the relationship between the binary code and the heating resistor element. FIG. 8 is a block diagram showing a schematic configuration of an apparatus for implementing a thermal head driving method according to an embodiment of the present invention. FIGS. FIG. 3 is a diagram for explaining a thermal head driving method. In the figure, l...image signal input terminal, 2A, 2B...first shift register, 3Δ, 3B...second shift register,
4...R, OM for f degree correction image signal generation, 5...Power application time control circuit, 6...Generation! $, resistor string drive circuit. 7...5@thermal resistor array, 8...decoder, 9...
・It is an encoder.

Claims (2)

[Claims] (1) In a thermal head driving method in which drawing and printing is performed by selectively generating heat from a heat-generating resistor provided in a thermal head, heat generation information of the heat-generating resistor that is currently to be drawn and printed and the heat-generating resistors on both its left and right sides, as well as the current The heat generation information of the heat generation resistor element to be drawn and printed and the heat generation resistance elements on both its left and right sides is detected, and the density correction weighting is performed on these heat generation information according to the degree of influence. It is characterized by generating a density-corrected image signal based on the heat generation information, and controlling the application time or peak value of the power to be applied to the heating resistor element that is currently to generate heat using the density-corrected image signal. Thermal head driving method. (2) In a thermal head drive device that selectively generates heat from a heat-generating resistor provided in a thermal head for drawing and printing, an image signal corresponding to the heat-generating resistor that is currently to be drawn and printed and image signals on both its left and right sides are stored. When performing drawing and printing according to the image signals of this line by applying electric power to the first storage means and each heating resistor element corresponding to each image signal of the line of the current image signal to be drawn and printed, a second storage means for storing the image signal of the line drawn and printed one line before this line; heat generation information of the heat generating resistor element to be drawn and printed now, the heat generating resistor elements on both its left and right sides, and the line one line before. Detecting from the first and second storage means heat generation information of the heat generating resistor element to be currently drawn and printed on the line drawn and printed, and the heat generating resistor elements on both the left and right sides thereof, and adjusting these heat generation information according to the degree of influence. A means for weighting density correction and generating a density-corrected image signal based on the density-corrected heat generation information, and a heating resistor element that is currently to be heated by the density-corrected image signal. A thermal head driving device characterized by comprising means for controlling the application time or peak value of the power to be applied.