JPH0339470B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for correcting heat accumulation in a thermal head in which a plurality of heat generating elements are arranged in a row, and particularly to a method for correcting heat accumulation in a thermal head in which each heat generating element is divided into at least two groups and driven separately. This relates to a correction method. [Prior Art] Thermal heads used for thermal recording usually have a plurality of heating elements (for example, record image information on recording paper No. 4 in column A of the Japanese Industrial Standards) to correspond to the number of pixels in the main scanning direction of the thermal recording medium. In this case, the number of heating elements required is 1728, and in the case of recording paper number 4 in row B,
By making only the required heating elements generate heat according to the image information, it colors the thermal recording medium such as thermal recording paper or ink donor sheet that slides into contact with the heating element. I'm letting you do it. By the way, when recording using such a thermal head, the recording period of one line should be set to 10
If you try to achieve high-speed driving at msec or less, for example, if the same heating element is made to generate heat continuously, the next row of data will be recorded before the heating element cools down due to the effect of heat storage. This resulted in variations in recording density and reduced image quality. Conventionally, therefore, each heating element is divided into at least two groups, _C1 group and _C2 group, as shown in FIG. 1A, and each group is time-divisionally driven as shown in FIG. 1B. This reduces the width of the drive pulse even with the same power supply capacity,
Cooling time for each heating element was ensured. Note that the period after pulse _C2 in FIG. 1B is a period for conveying the ink donor sheet and the like in the sub-scanning direction. Then, for each heating element, the recording pulse width (current application time), applied voltage, etc. for the heating element currently performing recording is variably controlled depending on whether or not the previous line, the previous line, and the line before the previous line have been recorded. For example, if there is data for the heating element in the previous line, the width of the recording pulse applied to the heating element is shortened when recording the current line. However, the conventional method described above is a heat storage correction method that focuses on each heating element individually, and does not take into account the effect of heat storage in heating elements adjacent to the heating element on the heating element. It cannot be said that a correction is being made. especially,
In transfer-type thermal recording using an ink donor sheet, the influence of heat accumulation in the adjacent heating elements is amplified by the spread of heat within the surface of the ink donor sheet, and it is difficult to obtain a sufficient effect of heat accumulation correction. I couldn't do it. [Object of the invention] The present invention has been made in view of the above circumstances, and
When dividing a plurality of heating elements into at least two or more groups and driving each group in a time division manner, only the recorded information of the current and past rows of each heating element and the heating elements adjacent to each heating element is used. In addition, by performing heat accumulation correction in consideration of the influence of heat accumulation caused by the difference in drive timing between the group to which each heating element belongs and the group to which the adjacent heating element belongs, It is an object of the present invention to provide a method for correcting heat accumulation in a thermal head, which can constantly variably control applied energy to an optimal value and obtain suitable recording quality without density variations. [Structure of the Invention] Therefore, in the present invention, in a heat storage correction method for a thermal head in which line-shaped heating elements are sequentially driven in each group in a time-division manner, each heating element and the heating element adjacent to each heating element are The heat storage state information is calculated based on the recorded information of the current and past rows, and the difference in drive timing between the group to which each heating element belongs and the group to which the adjacent heating element belongs. The energy applied to each heating element is independently and variably controlled based on heat storage state information and information indicating the recording pulse width in recording of the row immediately before each heating element. [Embodiments] Hereinafter, a method for correcting heat accumulation in a thermal head according to the present invention will be described in detail with reference to embodiments shown in the accompanying drawings. In this embodiment, the pulse width Ti to be applied to each heating element of the thermal head is determined based on the following equation. Ti=f(Xi, T _i-1 )...(1) That is, in the above equation (1), Xi is heat storage state information, and T _i-1 is information indicating the applied pulse width of the previous line for the heating element. The applied pulse width Ti in the current line of the heating element is determined as a function of these two pieces of information Xi and Ti _-1 . In addition,
When recording is not performed, the applied pulse width T _i-1 and Ti are not 0, and the applied voltage is set to 0. First, the heat storage state information Xi will be explained. FIG. 2 shows the arrangement of recording pixels, where each line represents a currently recorded scanning line, each line represents a previously recorded scanning line, and each line represents a previously recorded scanning line. In this embodiment, the heat storage state for the pixel D is determined based on whether or not the pixels D ₁ to D ₆ are recorded.
Moreover, weight values as shown in Table 1 are assigned to these pixels D ₁ to D ₆ depending on the degree of influence of heat accumulation on the pixel D, respectively.

【table】

[Table] Table 2 shows an example of the summation Yi of the above-mentioned weight values depending on whether or not the pixels D ₁ to D ₆ are recorded. In addition, in Table 2, the presence or absence of recording for each pixel is "1",
Each is indicated by "0", "1" is black, and "0" is white.

〔Effect of the invention〕

As explained above, according to the present invention, the electric energy applied to each heating element is variably controlled by taking into consideration the heat storage state of surrounding heating elements adjacent to each heating element, so high-speed driving and time-division driving are possible. Even if it is done, it is possible to always obtain good recording quality without density variations.

[Brief explanation of the drawing]

FIG. 1 is an arrangement diagram and a time chart showing an example of grouping of heating elements and their time-division driving;
Fig. 2 is a diagram showing the arrangement of recording pixels, Fig. 3 is a graph for calculating heat storage state information, and Fig. 4 is a graph of heat storage state information and correction pulse width using the recording pulse width of the immediately previous row as a parameter. Graph showing relationships, 5th
6 is a block diagram showing an embodiment of the present invention, FIG. 7 is a block diagram showing a specific example of a heat storage state calculator, and FIG. FIG. 2 is a block diagram of main parts showing another embodiment of the present invention. 10... Heat storage correction circuit, 20... Line buffer, 21... Register, 22... Correction circuit, 23
...Heat storage state calculator, 24...Pulse width calculator,
25...Memory, 26...Data buffer, 27
...Ratsuchi.

Claims (1)

[Claims] A heat storage correction method for a thermal head in which a plurality of heating elements arranged in a row are divided into a plurality of groups, and each of the plurality of groups is sequentially driven in a time-sharing manner. Current and past row record information of a heating element and a heating element adjacent to each heating element, and a drive timing difference between a group to which each heating element belongs and a group to which the adjacent heating element belongs. heat storage state information is calculated based on the heat storage state information, and the energy applied to each of the heat generating elements is independently and variably controlled based on the calculated heat storage state information and information indicating the recording pulse width in the recording of the row immediately before each of the heat generating elements. A method for correcting heat accumulation in a thermal head, characterized in that: