JPH0353887Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Industrial Application Field] The present invention relates to thermal head drive devices used in facsimile machines and printers that use thermal heads, for example, and is particularly concerned with the problem that "fainting" of print occurs even when printing is performed at high speed. This invention relates to a thermal head drive device that does not require ``Prior Art'' Facsimile devices and printers perform printing operations by receiving print data from the other party's facsimile device, host computer, etc., but the print data is not always supplied continuously. That is, for example, in a facsimile machine, the printing sequence is interrupted when it is in a state of waiting for reception. If the printing sequence is interrupted, the thermal dot will be left de-energized during this time.
Therefore, the heating element once warmed up cools down, and immediately after the printing operation starts, the printing energy becomes insufficient and the printed parts such as characters become "fainted".
Occasionally, this occurred. In Japanese Patent Laid-Open No. 58-131080, the heating element is electrically excited and preheated even at times other than the printing cycle, thereby preventing the temperature of the heating element from dropping excessively. With this invention, if the printing operation is relatively slow at 5 mS (milliseconds) per line or less, stable printing operation can be performed without blurring even if characters appear after consecutive white lines (non-printing lines). It can be carried out. This is because in such a low-speed printing state, the printing cycle is long, so the influence of heat accumulation in each heating element is weak, and control of the heating elements by preheating can be realized relatively easily. However, when such a device performs a relatively high-speed printing operation of 2 to 0.8 mS/line, the printing cycle becomes short and the influence of heat accumulation in the thermal dot becomes stronger. To avoid this effect,
It is necessary to reduce the time width of both the preheating pulse for preheating the heating element and the printing pulse for printing. When the time width of the printing pulse is made small, it becomes necessary to raise the temperature of the heating element in a short time. However, in reality, the temperature cannot rise so quickly due to heat diffusion to surrounding heating elements. In other words, if the technology described in the above-mentioned publication is applied as is to the area of high-speed printing, "fading" of characters cannot be avoided. Therefore, the inventors of the present invention previously proposed a thermal dot drive device capable of preventing "fading" of printed dots in Japanese Patent Application No. 81275/1983. This thermal dot drive device includes an image information input section that inputs at least image information of a future portion to be used for later recording, and a current image information that is based on the future image information input to this image information input section. a preheating determination unit that individually determines the necessity of preheating each unit heating element that is not printing; and a preheating means that preheats the unit heating element for which the necessity of preheating has been determined by the preheating determination unit. It is equipped with That is, in this apparatus, it is checked whether or not print data corresponding to so-called black print dots exists up to several lines before printing is performed. When such printing data exists several lines before the printing line, a preheating pulse is supplied if necessary until the corresponding heating element is energized several lines later and performs the printing operation. Controls the temperature of the heating element. For this purpose, information such as the heat storage state of the heating element and whether or not this heating element is excited in other lines before it is energized and controlled by the print data of the black printed dots mentioned above can be used as a reference. be done. "Problem to be Solved by the Invention" The invention related to this latter application uses a preheating pulse to shorten the time width of the printing pulse for the first printing line after the white line where no black printing dots are present. I can do it. However, this effect could not be achieved to the point where the printing pulses for all lines were shortened. Therefore, the purpose of this invention is to be able to raise the temperature of the heating element to the appropriate temperature for printing in a short time even during high-speed printing operations, to prevent "fading" from occurring, and to prevent excessive temperature rise. It is an object of the present invention to provide a thermal dot driving device that can prevent the image from rising and also prevent so-called "collapse" of the image. "Means for solving the problem" The present invention includes a pixel of interest as a specific pixel for which energization control is currently being performed, a heat storage data calculation means for calculating heat storage data representing the heat storage level for the pixel of interest, and a heat storage data calculation means for calculating the heat storage data representing the heat storage level for the pixel of interest, a thermal dot; It is provided in the drive device. Here, the preheating energy is composed of a first preheating energy calculated from heat storage data and temperature data, and a second preheating energy calculated from the heat storage data for a heating element that will be energized in the future. It's fine. The first preheating pulse is a pulse applied to a heating element with a low heat storage level in accordance with the ambient temperature during the thermal dot drive sequence. The second preheating pulse is determined by the heat storage level of a heating element that will be excited in the future when examining the future image signal several lines before the printing line, and is determined by the heat storage level of a heating element that will be excited in the future. This is a pulse that is applied until the Regarding the relationship between the first and second preheating energies, the second preheating energy is applied following the first preheating energy, and the second preheating energy is larger than the first preheating energy. is preferred. According to the present invention, since preheating control is performed using the first and second preheating energies, the temperature of the heating element can always be well controlled. "Example" The present invention will be described in detail with reference to Examples below. FIG. 1 shows the basic structure of a thermal dot driving device as an embodiment of the present invention. The thermal dot drive device includes a heat storage calculation unit 11 that calculates heat storage data, a print bit detection unit 12 that detects a print dot corresponding to a print dot in an image signal, and a peripheral unit that detects the temperature around the thermal dot. The temperature detection section 13 is also provided. The output data of each of these parts is supplied to the applied energy calculation part 14. The applied energy calculation section 14 includes an applied pulse width calculation circuit 15 and first and second preheating pulse width calculation circuits 16 and 17. Of these, the printing pulse width calculation circuit 15 outputs printing energy data E _i1 using the heat storage data 18 output from the heat storage calculation unit 11 and other data (temperature data of the thermal dot substrate in this embodiment). The preheating pulse width calculation circuit 16 of No. 1 generates heat storage data of the heat insulating layer based on temperature data 21 such as the substrate temperature of the thermal dot outputted from the ambient temperature detection unit 13 and heat storage data 18 (in this embodiment, based on this data). ) to calculate the first preheating pulse width, and
Outputs preheating energy data E _i2 . The second preheating pulse width calculation circuit 17 is connected to the print bit detection section 1.
A second preheating pulse width is calculated using the print bit detection data 24 outputted from 2, the heat storage data 18, etc., and second preheating energy data E _i3 is output. Three types of energy data E _i1 after these calculations,
E _i2 and E _i3 are supplied to an MPX (multiplex) 26, where they are selectively output according to predetermined conditions. The output of the MPX 26 is applied energy data E _i representing the energy of the print pulse as pulse width information. Therefore, in order to transfer this to the thermal dot shift register, it is necessary to convert it into a predetermined signal form. An example of a thermal dot transfer data conversion circuit as a conversion circuit for this purpose is described in, for example, Japanese Patent Application No. 59-088438. Note that in this thermal dot driving device, the total number of heating elements that are simultaneously energized in one line increases.
Therefore, depending on the printing form and the scale of the power supply, the voltage applied to the thermal dot may decrease, which may affect the printing density. Such a case can be solved by providing a circuit or the like that compensates for the voltage drop by expanding the pulse width, as described in the above-mentioned Japanese Patent Application No. 59-088438. Now, the heat storage calculation section 11 is a part that calculates the heat storage data 18 using the past printing history. FIG. 2 shows a pixel group on the recording surface which is the basis for performing such calculations. In this figure, the line currently being printed is defined as i-line. The pixel of interest is placed at the position marked with an x in the figure. The lines that go in the past direction one line at a time with respect to this i line are defined as i-1, i-2, . . . lines. Also, the lines heading towards the future one by one are i+1, i-
There will be 2 lines. The symbols ~ in the figure represent each pixel used when calculating the applied energy in the device of this embodiment. However, the heat storage calculation unit 11 calculates the heat storage data using the print data for 11 pixels from pixel to pixel. The pixels ~ on the i+1 and i+2 lines will be used when calculating second preheating energy, which will be explained later. FIG. 3 shows the weights of the 11 pixels used for the heat storage calculation as the heat storage contribution rate when these pixels are black printed dots. Generally, the closer a pixel is arranged to the pixel of interest, the greater the influence of heat storage on the pixel of interest, and the greater the heat storage contribution rate. The basic calculation of the heat storage data in the heat storage calculation section 11 is obtained by adding the weights of the pixels corresponding to the black printed dots. In the thermal dot driving device of this embodiment, after being calculated in this way, the final applied energy data E _i is calculated by adding other factors to the heat storage data X _i classified according to the addition. The other factors mentioned here are
There is data regarding heat storage in the heat insulation layer of thermal dots (insulation layer heat storage data B _i ). FIG. 4 shows a part of the apparatus for inputting the image signal 30 and determining the applied energy data E _i . Here, the peripheral pattern extraction circuit 31 is a circuit that extracts print data of pixels located around the pixel of interest, as shown in FIG. The print data regarding the 11 pixels ~ extracted by the peripheral pattern extraction circuit 31 is input to the X _i calculation section 32, where the heat storage data X _i is obtained. The heat storage data X _i is
This data is the sum of the weights of black printed dots for 11 pixels and up, classified into 11 levels from 0 to 10. FIG. 5 shows the relationship between the weight addition value and the heat storage data X _i . For example, the highest added value is 4
If it is 45, the heat storage data X _i is the highest level 10
Therefore, if it is the lowest value of 1, the heat storage data X _i becomes the lowest value of 0. Such heat storage data X _i is, for example,
X _i arithmetic unit 32 in ROM (read only memory)
Thermal storage data X _i written in advance using the output of the peripheral pattern extraction circuit 31 as address information
It can be easily obtained by reading .
The heat storage data X _i is supplied to the E _i calculator 33, and
It is supplied to the first ROM 34. The first ROM 34 is data obtained by converting the heat storage data X _i to a level contributing to the heat insulation layer heat storage data B _i . Here, in order to understand the heat storage in the heat insulating layer of the thermal dot, the structure of the thermal dot will be briefly explained. FIG. 6 shows the general structure of a thermal dot. Thermal dot heating resistor 3
5 is made of ruthenium (RuO ₂ ), etc.
It is formed by screen printing or the like on a heat insulating layer 37 with a thickness of about 45 μm that covers a ceramic substrate 36. The heating resistor 35 and the heat insulating layer 37 are covered with a wear-resistant layer 38 made of tantalum (Ta ₂ O ₅ ) or the like. The ceramic substrate 36 is an aluminum heat dissipation substrate 39.
The heat dissipation is promoted and the progress of local heat accumulation in the thermal dots is suppressed as much as possible. On the other hand, the insulation layer 3, which is also generally called a glaze layer,
7 uses a material with low thermal conductivity such as glaze, so that the thermal energy generated by each heating element constituting one heating resistor 35 can be effectively used for printing or displaying. There is. It goes without saying that the time constant of heat storage and heat radiation of the heat insulating layer 37 is sufficiently shorter than the thermal excitation cycle of repeated heating and heat radiation of the heat generating resistor 35, and this accelerates heat storage depending on the recording state, resulting in thermal This causes the temperature of the dot substrate to rise. The following Table 1 shows the contents of the first ROM 34 described above.

[Table] In this way, the first ROM34 stores heat storage data.
The heat storage contribution data X _i ′ is read using X _i as address information. The B _i calculator 41 calculates the heat storage layer heat storage data B _i using this heat storage contribution data X _i ′, the substrate temperature data K of the thermal dot, and the past heat storage layer data B _{i -1} for one line. . A RAM (random access memory) 42 is a random access memory for delaying the heat insulation layer heat storage data B _i output from the B _i calculator 41 by one line to create the heat insulation layer heat storage data B _i-1 . It is. In order to calculate the heat insulation layer heat storage data B _i , the B _i calculator 41 is equipped with a conversion table having the contents shown in Table 2 below.

【table】

【table】

[Table] The heat insulation layer heat storage data B _i calculated by the B _i calculation unit 41 is supplied to the second ROM 44 . The second ROM 44 is a conversion circuit for converting the heat insulation layer heat storage data B _i to be suitable for calculating the applied energy data E _i , and the heat insulation layer heat storage data B _i expressed as 10-bit data is as follows. It is converted into heat insulation layer heat storage data B _i ' expressed as 3-bit data as shown in Table 3.

【table】

[Table] The E _i calculator 33 calculates heat storage data X _i , substrate temperature data K, heat insulation layer heat storage data B _i ′, and print data D _i for the pixel of interest and pixels to be printed in the future.
is input, and energy data E _i applied to the heating element corresponding to the pixel of interest is calculated. Here, print data D _i for the pixel of interest and pixels to be printed in the future are extracted from the peripheral pattern extraction circuit 32. The applied energy data E _i is ()
Printing energy data E _i1 as energy during printing and () first preheating energy data E _i2
and () second preheating energy E _i3 , which are determined based on the balance of four types of data input to the E _i calculator 33. In the E _i calculator 33, these three energy data E _i1 , E _i2 ,
E Perform the calculation of _i3 . FIG. 7 shows the calculation contents of the print energy data E _i1 . In this embodiment, the printing energy data E _i1 is obtained by using the heat storage data X _i and the heat insulation layer heat storage data B _i ′ as address information in the E _i calculator 33.
The format is read from the ROM, and the printing energy data E _i1 is obtained experimentally from the relationship between the two. Of course, instead of using such an experimental method, it is also possible to use a computing device that solves the thermal diffusion equation. In this embodiment, the reference time at which the printing energy data E _i1 is obtained is when first preheating energy data E _i2 , which will be described next, is supplied to the heating element and the heating element reaches a thermal equilibrium state. Next, FIG. 8 shows the first preheating energy data E _i2
represents the content of the calculation. The first preheating energy data E _i2 is determined from the heat insulation layer heat storage data B _i ' and the substrate temperature data K. The calculated first preheating energy data E _i2 is
Applied energy data E _i selected by MPX26
The condition for outputting is when the heat storage level of the heating element is low, that is, the print data D _i for the pixel of interest and the pixel to be printed in the future do not both correspond to black print dots, and ( ) When the heat storage data X _i is 0 (zero). Finally, Figure 9 shows the second preheating energy data.
This shows the calculation contents of E _i3 . The second preheating energy data E _i3 is determined from the heat storage data X _i and the heat insulation layer heat storage data B _i ′. The calculated second preheating energy data E _i3 is
Applied energy data E _i selected by MPX26
The condition that is output as is when the heat storage level of the heating element is low and there is a heating element that will be excited in the future,
That is, () the pixel of interest is not a black print dot, and () there will be print data corresponding to a black print dot in the future. In this embodiment, the applied energy data E _i is expressed as pulse width information, and is output as the number of unit pulses of, for example, 0.03 mS. Printing energy data representing the number of unit pulses
E _i is supplied to a thermal head transfer data conversion circuit as described above. After the signal form is converted, it is supplied to a shift register of a thermal head (not shown), and a printing operation is performed by the thermal head. "Effects of the invention" As explained above, in this invention, two types of preheating energy are calculated under different conditions and preheating control of the heating element is performed. Temperature control is performed well, and the device can be manufactured at a lower cost and with higher reliability than when a larger amount of print data is subjected to calculations.

[Brief explanation of drawings]

The drawings are for explaining one embodiment of the present invention. Among them, Fig. 1 is a block diagram showing the main parts of the thermal head driving device, and Fig. 2 shows the arrangement of pixels referred to in this embodiment. An explanatory diagram, Fig. 3 is an explanatory diagram showing, as an example, the weight for _the pixel of interest when these pixels correspond to black printed dots, and Fig. 4 shows the main parts of the device. A block diagram specifically representing the 5th
The figure is an explanatory diagram showing the calculation contents of heat storage data X _i ,
Fig. 6 is a sectional view showing the structure of the thermal head, Fig. 7 is an explanatory drawing showing the calculation contents of the printing energy data E _i1 , and Fig. 8 shows the calculation contents of the first preheating energy data E _i2 . The explanatory diagram, FIG. 9, is an explanatory diagram showing the calculation contents of the second preheating energy data E _i3 . 11... Heat storage calculation section, 12... Print bit detection section, 13... Ambient temperature detection section, 15... Print pulse width calculation circuit, 16... First preheating pulse width calculation circuit, 17... Second Preheating pulse width calculation circuit, 3
1...X _i computing unit, 33...E _i computing unit, 41...B _i
Arithmetic unit, B _i ′...Insulating layer heat storage data, E _i1 ...Printing energy data, E _i2 ...First preheating energy data, E _i3 ...Second preheating energy data, K...
...Substrate temperature data, X _i ...Heat storage data.

Claims (1)

[Claims for Utility Model Registration] 1. Heating elements as the smallest unit of heat generation are arranged in a line, and the temperature of these heating elements is controlled by individually controlling the energization of these heating elements. In a recording device, there is provided a temperature data output means for measuring the temperature around the heating element and outputting temperature data representing the temperature, and a current temperature of the heating element corresponding to a pixel of interest as a specific pixel for which energization control is currently being performed. a heat storage data calculation means for calculating heat storage data representing a heat storage level of the heat storage data, a printing pulse width calculation means for calculating a printing pulse width necessary for printing a pixel of interest based on the heat storage data, and the heat storage data and the pixel of interest. a first preheating pulse width calculation means for calculating a first preheating pulse width necessary for preheating a heating element corresponding to a pixel of interest based on ambient temperature data; a second preheating pulse width calculating means for calculating a second preheating pulse width necessary for preheating the heating element using the image signal of the heating element; a printing pulse output means for outputting a pulse, and a pulse having the first preheating pulse width or a pulse having the second preheating pulse width when printing is not being performed, and selecting the pulse having the first preheating pulse width or the second preheating pulse width according to a future image signal to generate the corresponding heat generation. 1. A thermal head driving device comprising: preheating pulse output means for outputting a preheating pulse for preheating a body. 2. Utility model registration claim 1, characterized in that a second preheating pulse is output following the first preheating pulse, and the pulse width of the second preheating pulse is longer than that of the first preheating pulse. The thermal head drive device according to item 1.