JPH01200974A - Heat correction device of thermal printer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a thermal correction device for a thermal printer.

(Prior art) Conventionally, one pixel is represented by multiple IWm by bringing a thermal print head in which heating elements are lined up into contact with a thermal recording medium, and adjusting the energization time or applied voltage to heat each heating element. A heat-sensitive so-called thermal printer is known.

This thermal printer is often used because it does not require any development processing, the paper is relatively inexpensive, and the printer head and paper feeding mechanism are simple.

By the way, in the above-mentioned conventional thermal printer, when the same element is continuously energized, the element gradually heats up, and when the energization is removed, the element gradually cools down, so that the printing density is not uniform. There is a problem in that it is necessary to incorporate data from thermal history to make the print density uniform. Japanese Patent Laid-Open Publication No. 146176/1984 is known as a thermal printer that corrects the thermal history, particularly taking into account the influence of heat accumulation. The thermal printer disclosed in this document corrects image signal data from past image signal data and progress data, but if it attempts to completely correct heat accumulation, the printing time will be extremely long and the circuit configuration will be required. On the other hand, there is the problem that when printing at high speed, the correction is not completed completely and high image quality cannot be maintained.

(Objective) An object of the present invention is to provide a thermal correction device for a thermal printer that can perfectly perform heat storage correction in a short period of time.

(Structure) In order to achieve the above object, the thermal correction device for a thermal printer of the present invention includes means for comparing gradation data of the next printing line with thermal history data of the printing line up to the present; If the thermal history data of the current printing line is larger than the gradation data of the next printing line, the printing timing of the next line will be changed depending on the cooling effect of the thermal history data of the current printing line. The present invention is characterized in that it includes a delay means for delaying the printing until the gradation data of the next printing line becomes lower than the gradation data of the next printing line.

Embodiments of the present invention will be described below with reference to the drawings. The figure is a block diagram of a color video printer to which a thermal printer thermal correction device according to an embodiment of the present invention is applied.

Code 1 is RGB decoder, 2, 8.17 is selector, 3
is an A/D converter, 4 is a line buffer, 5 is a comparator, 6, 7.10.11 is a multiplier, 9 is a history data buffer, 12 is an R-S flip-flop, 13.1
6 is an adder, 14 is a PWM converter, 15 is a thermal printer head, 18 is an NTSC signal signal preload terminal is 11
017 is a level data output terminal, 20 is a color selection signal output terminal, 21 is a reset signal output terminal, 22 is a history data designation signal output terminal, and 23 is a clear designation signal 8 output terminal.

First, when an NTSC signal, which is the standard method for color televisions used in Japan, the United States, etc., is output from the output terminal 18, the output signal is converted into luminance signals of three colors, relado, green, and blue, by the RGB decoder 1. separated. When an image is actually formed using a color video printer, three surfaces are sequentially transferred using a thermal sublimation transfer method, so the selector 2 sequentially selects the luminance signals based on the output signal from the color selection signal output terminal 20. Start. The selected signal is converted into a digital value by an analog-to-digital converter 3, and the digital signal is stored in a line buffer 4 for only one line to be transferred. This line buffer 4 is used to compensate for differences in data flow speed between components of a data processing system, and is well known.

The gradation data of the next printing line from the line buffer 4 is input to a comparator 5 serving as comparison means, a multiplier 6, and a multiplier 7, respectively. The printing gradation data is converted into a coefficient a1 by a multiplier 6 and a coefficient a by a multiplier 7.

are multiplied respectively.

On the other hand, in the line on the history data buffer 9 side, II Oj# level data is initially input to the selector 8 based on the output signal from the clear designation signal output terminal 23. This is because there is no need to consider the influence of thermal history at first. This value is stored in a history data buffer 9 that uses the value calculated by an adder 16 (to be described later) as the history data for the next line, and is outputted to the comparator 5, multiplier 10, and multiplier 11 at appropriate times. Ru. The thermal history data of the printing line up to the present is multiplied by a coefficient (-a,) by a multiplier 10 and by a coefficient a4 by a multiplier 11, respectively.

By the way, the signal input to the multiplier 6 has a coefficient a□ as described above, and the signal input to the multiplier 10 has a coefficient (-a,
) are respectively multiplied, and their output signals are both input to the adder 13 and added. Then, the actual print data of the next line outputted from the adder 13 is subjected to PWM conversion by the P8 converter 14, and transferred to the thermal head printer 15 for printing. In this embodiment, both coefficients a and a2 are set to "1".

Furthermore, the signal input to the multiplier 7 has a coefficient a as described above.
, the signals input to the multiplier 11 are each multiplied by a coefficient C4, and both output signals are input to the adder 16 and added. Then, the signal output from the adder 16 is input to the selector 17, and then the signal is input to the selector 8.
This transferred power value is rewritten in the history data buffer 9 as the history data of the next line. Here, in this example, the coefficient a is "1"
The coefficient a is based on the assumption that the degree of influence of heat accumulation will be reduced to 1/4 when the printing time for one line is delayed.
It is said to be 1/4".

On the other hand, the gradation data of the next printing line inputted to the comparator 5 mentioned above and the thermal history data of the printing lines up to now are sequentially compared, and even if there is even one piece of data in which the thermal history data is larger, In this case, R-S flip-flop 1
2 and issues a command to a so-called paper feed control unit such as a line feed motor control to temporarily stop paper feed. At the same time, a signal is sent from the history data designation signal 8 input terminal 22 to the selector 17, and the selector 17 ignores the output signal from the adder 16 and outputs the signal from the multiplier 1.
Only the output signal of 1 is sent to the selector 8.

Here, in the correction device of this embodiment, paper feeding and printing are stopped until the thermal history data of the printing line up to the present becomes equal to or less than the gradation data of the next printing line. There is. That is, the data in the history data buffer 9 is compared with the gradation data of the next printing line (output data of the line buffer 4), and if the data in the history data buffer 9 is large, the data in the history data buffer 9 is compared. The thermal history data is looped along the lines of the multiplier 11, selector 17, selector 8, and history data buffer 9 until the value becomes smaller, and the history data is rewritten each time. Here, the coefficient 84 is set so that each time the data in the history data buffer 9 is looped, it becomes smaller than the data in the previous history data buffer 9. The data rewritten each time in the buffer 9 is lower than the gradation data (output data of the line buffer 4) of the next printing line. If such a state occurs, paper feeding is started, and the finally rewritten history data is sent to the multiplier 1o, and the history data and the tone data of the next printing line (line buffer 4 Printing is resumed based on the output data (output data). Here, the addition of the multipliers 6 and 10 is performed only when the data rewritten each time in the history data buffer 9 is lower than the gradation data of the next printing line (output data of the line buffer 4). Therefore, even if the coefficients a1=1 and C2=1, the added value will not become negative, and the effect of heat storage will not be unable to be corrected. Here, when the history data Q is looped n times, the rewritten history data for the nth time becomes (aJB, and if the gradation data of the next printing line is P, then as described above, P≧(a Jx Q Paper feeding and printing are restarted only after this happens, and the time it takes until P≧(C4)SQ is reached is approximately equal to the time for the element to cool down. When feeding and printing are resumed, the R-S flip-flop 12 is reset by the output signal from the reset signal 8 input terminal 21. In this way, in this embodiment, the selectors 8 and 17, the history data buffer 9, Multiplier 11, R-
The S flip-flop 12 constitutes a delay means.

Next, this embodiment will be explained using specific numerical values.

For example, when the gradation is 64 (data is O to 63), the gradation data P8 of the next printing line of element No.
20″, the thermal history data of the printing line up to the present Q process is 1
110JP, the actual printing data C1 of the next printing line becomes C1="10" from Ci=:Pi-Qi (from coefficient a=1, at=1), and element No. The gradation data P2 of the next printing line after 2 is set to °'8.
”, the thermal history data Q2 of the printing line up to the present is “5’
Then, the actual printing data C2 of the next printing line is C
Since 1=Pi−Qi, C2=“3”.

Similarly, for element No. 3, if P3 is li 311 and thermal history data Q of the printing line up to the present is 11311, the actual printing data C1 of the next printing line is "0".
becomes. Here, 1, in the case of element No. 4,
P, is 2″, thermal history data of the printing line up to now Q,
When is set to ``4'', the actual printing data C4 of the next printing line becomes ``-2'', which is negative. Then, paper feeding and printing are stopped, and the thermal history data is transferred to the multiplier 11, selector 17, selector 8, and history data buffer 9 until the thermal history data Q4 becomes lower than the gradation data P4 of the next printing line. Loop along the line. That is,
As mentioned above, when the history data Q is looped once, the rewritten nth history data becomes (a JL, Q, so in the -th loop, the thermal history data Q4 becomes q4
It can be rewritten as 1/4×4=1. Here, number of times n=
1, coefficient a4 = 1/4° Therefore, the actual printing data C4 of the next printing line is C,
=2-1="1", and paper feeding and printing are stopped during this loop, that is, until the element cools down.
When the thermal history data that has been rewritten each time becomes less than the gradation data of the next printing line (in this embodiment, when it becomes '1'), paper feeding and printing are restarted.

Incidentally, i here represents a natural number.

Pi, Qi, Ci, q obtained in this way
If you organize i into a table, it will look like a numerical table.

In this way, according to this embodiment, the paper feed is continued until the thermal history data of the printing line up to the present becomes equal to or higher than the gradation data of the next printing line, that is, until the element cools down.
Since printing is stopped, heat accumulation correction can be performed perfectly in a short time.

It goes without saying that the present invention is not limited to the above-mentioned embodiment, and can be modified in various ways without departing from the gist thereof. For example, in the correction device of the above-mentioned embodiment, the coefficient a = 1 , a, = 1, but it is also possible to take other values to further increase the printing speed, and the coefficient a, = 1, a, -1/4. However, these values can also be changed by changing assumptions about the effects of heat storage and cooling.

(Effects) As described above, according to the present invention, a thermal correction device of a thermal printer is provided with a means for comparing gradation data of the next printing line with thermal history data of the printing line up to the present, and a thermal correction device of a thermal printer. If the thermal history data of the current printing line is larger than the gradation data of the current printing line, the printing timing of the next line will be determined based on the cooling effect of the thermal history data of the current printing line. Since the configuration includes a delay means for delaying until the gradation data of the next printing line becomes lower than the gradation data of the next printing line, it becomes possible to perform the heat accumulation correction perfectly in a short time.

[Brief explanation of the drawing]

The figure is a block diagram of a color video printer to which a thermal printer thermal correction device according to an embodiment of the present invention is applied. 4... Line buffer, 5... Comparison means, 8, 17
... Selector, 9... History data buffer, 11.
... Multiplier, 12 ... R-S flip-flop, 15
...Thermal print head.

Claims (1)

[Claims] A thermal printer that expresses one pixel in multiple gradations by bringing a thermal print head lined with heating elements into contact with a thermosensitive recording medium and adjusting the energization time or applied voltage to heat each heating element. means for comparing the gradation data of the printing line with the thermal history data of the printing line up to the present, and the thermal history data of the current printing line being larger than the gradation data of the next printing line; In this case, the printing timing of the next line is delayed until the thermal history data of the current printing line becomes equal to or less than the gradation data of the next printing line due to a cooling effect. Thermal printer heat correction device.