JPS6076362A - Compensating method of heat accumulation in thermal head - Google Patents

Abstract

PURPOSE:To enable the attainment of a uniform recording density, by controlling an electric energy variably and separately on the basis of a calculated heat-accumulation information, a temperature information on the base plate of a thermal head and a recording pulse width information on a line just before each heating element. CONSTITUTION:Line buffers 201-204 corresponding to the total number of picture elements of a head respectively store the video data on n+1-th, n-th, n-1-th and n-2- th lines respectively. The data thus stored are written selectively in a register 21 through a selector, weighted by a compensation circuit 22 respectively, and formed into the informations on the condition of heat accumulation by a heat-accumulation operator 23. Based on these informations and a recording pulse width information on a line just before read from a memory 25, the width of a recording pulse to be impressed on each heating element is calculated by an operator 24. The value of this width is sent to a data buffer 26, together with the video data for current recording sent through a latch 27, and these informations are outputted therefrom as a printing signal of the pulse width. Thus, a record having a uniform density and an excellent quality can be obtained constantly.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for correcting heat accumulation in a thermal head in which a plurality of heating elements are arranged in a row, and in particular, a method for correcting heat accumulation in a thermal head in which a plurality of heating elements are arranged in a row. The present invention relates to a heat storage correction method when driving each group separately.

[Prior art]

The thermal head used for thermosensitive recording has a plurality of heating elements corresponding to the number of pixels in the main scanning direction of the electrothermal recording medium. In this case, the number of heating elements required is 172.
(2048 pieces in the case of the recording paper No. 4 in row B)), and by making only the Pfr heating element generate heat in accordance with the image information, the heat-sensitive element that comes into sliding contact with the heating element It colors thermal recording media such as recording paper and ink donor sheets.

By the way, when recording using such a thermal head drive, especially if you try to achieve high-speed driving by setting the recording period of one line to 10 mθθC or less, for example, if the same heat generating element is made to generate heat continuously, heat storage Due to the influence of
This resulted in a decrease in image quality.

Conventionally, in order to ensure cooling time for the heating elements, each heating element was heated to at least 0.000000000000000000000000000000,000
, Group C, and Group C, and each group is configured to be time-divisionally driven as shown in FIG. The recording pulse width (energization time) or applied voltage for the heating element currently being recorded was variably controlled depending on whether or not a line was recorded.For example, if there was data for the heating element in the previous line. In this case, the width of the recording pulse applied to the heating element is made very short when recording the current line.

However, the conventional method described above is a learning correction method that focuses on each heating element individually, and does not take into account the effect of heat storage of heating elements adjacent to the heating element on the heating element. It cannot be said that correction has been made. In particular, 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, making it difficult to obtain a sufficient heat accumulation correction effect. could not.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and it divides a plurality of heating elements into at least two or more groups and provides a time division section for each group! &lI'1'', by performing heat storage correction while also taking into account the influence of heat storage in the same group of heating elements adjacent to each heating element, the energy applied to each heating element can always be varied to the optimum value. It is an object of the present invention to provide a method for correcting heat accumulation in a thermal head that can obtain suitable recording quality without density variation with control 1°.

[Structure of the invention]

Therefore, in the present invention, heat storage is calculated by assigning appropriate weight values to the recorded information of past rows of each heating element and the recorded information of current and past rows of heating elements of the same group adjacent to each heating element. Electrical energy applied to each heating element is individually controlled for each heating element based on status information, information indicating the substrate temperature of the thermal head, and information indicating the recording pulse width of the row immediately before each heating element. I try to do that.

〔Example〕

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for correcting heat accumulation in a thermal head according to the present invention will be described in detail below with reference to embodiments shown in the accompanying drawings.

In this embodiment, the pulse width Tii applied to each heating element of the thermal head is determined based on the following equation.

Ti=f(XiyTi-1) (1) That is, in the above equation (1), Xi is heat storage state information, Ti
-1 is information indicating the applied pulse width of the previous line for the heating element, and the applied pulse width T1 of the current line of the heating element is based on these two pieces of information Xi, Ti-4
determined as a function of Note that when recording is not performed, the applied pulse width Ti-r and T1 are not 0 (the applied voltage is 0).

First, the heat storage state information X1 will be explained.

The m2 diagram shows the arrangement of recording pixels, (6) Line summer shows the scanning line currently recorded, line ■ shows the scanning line recorded last time,
Line 4 indicates the scanning line recorded two times before.

In this embodiment, the heat storage state for each pixel is determined based on whether or not the pixels DI to D6 are recorded. Furthermore, weight values as shown in Table 1 are assigned to these pixels D6, depending on the degree of influence of heat accumulation on the pixels.

Tables 1 and 2 show an example of the total sum Y1 of the weight values according to whether or not the pixels D1 to D6 are recorded. The presence or absence of recording for the middle pixel in Table 2 is indicated by "1" and "0", respectively, with "1" being black and "0" being white.

Table 2 According to Table 2 above, for example, as shown in example (c), pixel D1. When recording is performed on D and D4, Yl is 187. Then, this Yl is converted into heat storage state information x1 in eight stages from "0" to "7" based on the relationship in the graph shown in FIG.

In FIG. 3, the horizontal axis is KYi, and the vertical axis is Xl. Examples of Xl are shown at the bottom of Table 2. For example,
In the case of C), Yl is 187 and Xl is 5.

This heat storage state information X1 and the applied pulse width Ti- of the previous line
1, if the applied pulse width T 1/ of the line to be printed this time of the heating element is set, the result will be as shown in FIG. The upper limit value of Ti' (msec) of 1.2 in Fig. 4 is the applied pulse width that allows suitable recording when there are continuous white pixels, and the lower limit value of 0.5 is the applied pulse width when there are continuous black pixels. This is the pulse width that allows suitable recording. For example, if the heat storage state information X1 is 3, T1-1
When is 9.5 m sec, the pressure is Ti' is 0.5 m5e
c, and xl is 4 and T1-1 is 1.0 m se
In the case of c, T i' becomes 0.8 m aeaK.

By the way, in the present invention, the heating element has at least two
1 group and 0. It is divided into groups and driven in a time division manner as shown in FIG. 1(A).

Therefore, as shown in FIGS. 5(A) and 5(B), when recording pixel D1, regardless of whether pixel D2 of the 01 group is recorded or not, the effect of heat accumulation on pixel D1 from its surroundings is the same. You can think that.

Therefore, in the present invention, the pixels of group C.

The heat storage state information X1 is calculated by setting the weight value to "0".

FIG. 6 is a block diagram showing an embodiment of a heat storage correction circuit 1o constructed based on the heat storage correction method as described above.

In the figure, the line buffer 20 to which video data is input is composed of line buffers for four lines, a first line buffer 201 to a fourth line buffer 204, each having a storage area corresponding to the total number of pixels of the thermal head. Each line buffer 201 to 204 has an n+
1. nth.

The video data of the (n-1)th and (n-2)th lines are stored line by line by a multiplexer or the like (not shown).

When the video data to be recorded next is stored in the first line buffer 201, the video data for X3 lines stored in the remaining second line buffer 202 to fourth line buffer 204, that is, the video data to be recorded this time is scanned. The video data of the line, the video data of the scanning line recorded last time, and the video data of the scanning line recorded the day before last are selectively written into the register 21 by a selector (not shown). Of the video data stored in the register 21, the weight value described above is set to "0" in the video data to be recorded this time.
, p is forcibly changed to white pixel data and input to the heat storage state calculator 23.

On the other hand, the video data in the previous scan line and the scan line before the previous scan are input to the heat storage state calculator 23 as they are. Further, the video data to be recorded this time is transferred to the data buffer 26 via the latch 27.

The heat storage calculator 23 uses the video data of the current recording line that has been changed in the first correction path 22 and the video data of the previous and two previous times in which no changes have been made, for example, to the learning state information X1 of each heating element of the line to be recorded this time. Based on the data, calculations are performed for each group sequentially, and the calculation results are sent to the pulse width calculator 24.
Output to j veterinarian.

As shown in FIG. 7, the heat storage state calculator 23 is composed of a weight value addition circuit 230 and a Yi/Xi conversion circuit 231, and the weight value addition circuit 230 inputs 6 bits for each dot of heating element. After adding the weight values shown in Table 1 to the image information to be displayed, these 6 bits v are added, and the sum Y1 is outputted to the Yi/Xi conversion circuit 231. The Y1/Xi variation circuit 231 sequentially inputs Y
For example, based on the relationship in the graph shown in Figure 3, l is ``o''.
Convert to 8 stages of heat storage status information X1 from to "7",
This '4g: Sequentially output to the pulse width calculator 24. The memory 25 stores information indicating the recording pulse width of each dot calculated by the pulse width calculator 24, and the stored contents of this memory 25 are updated every time the scanning line to be recorded advances. Therefore, T1-1 outputted from the memory 25 and fed back to the pulse width calculator 24 becomes information indicating the recording pulse width of the previous scanning line for the pulse width calculator 24.

The pulse width calculator 24 is composed of these two fi@Xi.

Recording pulse width T applied to each heating element based on T1-1
1 is calculated from the relationship shown in FIG. 4, for example, and input into the memory 25 and data buffer 26.

The data buffer 26 has a storage area for 8 lines corresponding to "m stages IR8" of the information Based on the information T1, the video data of each pixel is converted into a print signal having a pulse width specified by the recording pulse width information T1 and output. That is, if the pixel to be recorded is a black pixel and has the highest density, the longest print signal of 1.2 msec is output.

From this K, each heating element of the thermal head is driven with a print signal having an optimal pulse width depending on the surrounding heat storage state.

In the embodiment shown in FIG. 6, among the recorded information of pixels around the pixel Di to be recorded, the recorded information of pixels in other groups is forcibly changed to white pixel information by the correction circuit 22 to maintain the heat storage state. As shown in Fig. 8, heat storage state calculators 23-1 and 23-2 are provided for each group.
These are 0. group and 0. Switch alternately using switches 30A and 130B according to the group timing,
A similar effect can be obtained by calculating the heat storage state independently for each group.

Furthermore, the pixels referred to in order to determine the heat storage state information X1 are those shown in FIG. 2, and a sufficiently satisfactory result can be obtained, but the pixels are not limited to those shown in FIGS. Depending on conditions such as high speed and cost, the number of reference pixels may be slightly reduced, or if greater precision is desired, the number of reference pixels may be increased.

In addition, in the embodiment, the heat storage state information X1 is set from "0" to "7".
Although the number of divisions is of course arbitrary, it is possible to perform more precise heat storage correction by increasing the number of divisions to 16, 32, or 5, for example.

Although the pulse width of the applied pulse is increased or decreased, the selection of the threshold value for the above classification is of course arbitrary.
An appropriate one may be adopted depending on various conditions.

Incidentally, in this embodiment, the recording pulse width (current application time) of the pulse applied to each heating element of the thermal head is variably controlled to prevent density variations in recording pixels. A pulse may be applied and the duty of the high frequency pulse may be changed.

Further, the applied voltage may be variably controlled, as long as the electrical energy applied to each heating element is variably controlled as a result.

Furthermore, there is a method in which the heating element of a long thermal head is divided into a plurality of blocks in order to save power supply, and these are dividedly driven, and this method can be applied in exactly the same way.

〔Effect of the invention〕

As explained above, according to the present invention, the electrical energy applied to each heating element is variably controlled in consideration of the heat storage state of surrounding heating elements adjacent to each heating element.
Even when high-speed driving and time-division driving are performed, good recording quality without density variations can always be obtained.

[Brief explanation of drawings]

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 an arrangement of recording pixels, Fig. 3 is a graph for calculating heat storage state information, Figure 4 is a graph showing the relationship between heat storage state information and correction pulse width using the recording pulse width of the immediately preceding row as a parameter, Figure 5 is a diagram showing the arrangement of recording pixels in the case of time-division driving, and Figure 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,
FIG. 8 is a block diagram of main parts showing another embodiment of the present invention. 10... Heat storage correction circuit, 20... Line buffer,
21...Register note 22...Correction circuit, 23...
Heat storage state calculator, 24...Pulse width calculator, 25...
・Memory% 26...Data buffer, 27...Latch. − °−ψ Hε 目…− 目１−

Claims (1)

[Scope of Claims] (1) A thermal head drive circuit that arranges a plurality of heating elements in a row, divides each heating element into at least a first group and a second group, and drives each group in a time division manner, Heat storage state information calculated based on current and past record information of each of the heating elements and the heating elements of the same group that are in contact with the heating elements, including electric energy applied to the plurality of heating elements, and the row immediately before the heating element. A method for correcting heat accumulation in a thermal head, characterized in that the heat accumulation correction method for a thermal head is controlled individually based on information indicating the recording pulse width of the recording pulse width. (2) The method for correcting heat accumulation in a thermal head according to claim (1), wherein the electrical energy is variably controlled by increasing or decreasing the pulse width of a recording pulse applied to each heating element. (1) ReA1 (3) The heat storage state LAMI report is calculated by adding a predetermined weight value corresponding to the degree of influence of heat storage on the heat generating element to the σIJ diary information, respectively. A method for correcting heat accumulation in a thermal head according to claim M(1). (4) The calculation of the electric energy is performed for each group by a heat storage state calculator provided corresponding to the group of heating elements.
The heat accumulation correction method of the thermal head described in .