JPH0788097B2 - Thermal history correction method for thermal printer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention corrects energization signals to a plurality of heating elements of a thermal printer according to the thermal history of the heating elements to perform printing with uniform print density. The present invention relates to a thermal history correction method for a thermal printer.

[Conventional technology]

In general, a thermal printer is provided with a thermal head in which a plurality of heating elements are arranged in one row, and a thermal transfer medium such as an ink ribbon or a thermal recording paper and the thermal head are relatively moved in a direction perpendicular to the rows of the heating elements. In addition, printing is performed by energizing while controlling the energization time for each dot movement (1 cycle) of each heating element.

A thin film resistor that uses Joule heat to generate heat is often used for such a heating element. Conventionally, in order to prevent uneven printing density due to the influence of past heat generation of each heating resistor, OF does not energize the heating element in the cycle OF
After the F time is increased and each heating element is sufficiently cooled, the heating element is energized for a predetermined time to generate heat and print.

However, taking a large OFF time for each cycle is an obstacle to increasing the printing speed. Also, if the OFF time is shortened to increase the printing speed, each heating element has a longer heat radiation time than the heating time, so the thermal head gradually accumulates heat and the temperature rises, eventually The print density was uneven. In particular, when the dot density is increased by using a large number of heating elements and the printing speed is increased, print density unevenness occurs.

This is because the cycle of energizing pulses to each heating element becomes shorter than the heat radiation time constant of each heating element as the printing speed increases and the dot density of the thermal head increases.

Therefore, conventionally, the thermal history correction device grasps the current temperature state of the heating element from the past energization state of each heating element,
The length of the energization time in the case of energizing in the next cycle was adjusted so that the peak temperature of each heating element would be constant.

To further explain, conventionally, as shown in FIGS. 5 (a) to 5 (n), the energization patterns are formed into a matrix, and the past energization patterns of the heating elements to be energized are shown in FIG. 5 (a). It is determined which one of (n) is applicable, and the drive pulses P _a , P _b , P _c ... P _n having a pulse width corresponding to the energization pattern are energized. Each energization pattern of FIGS. 5 (a) to (n) determines whether the energization state of the heating element to be energized for the past 5 cycles and the energization state of both adjacent heating elements in the immediately preceding cycle. The white circles in the figure are OFF
State, black circle indicates ON state, × mark indicates either ON or OFF state.The black circle at the right end means that power is to be supplied, and each cycle is traced to the left from that and power is supplied. Is shown.

As described above, in the related art, when each heating element is energized, it is corrected according to the past energization state of the heating element and the past energization state of the heating element adjacent to the heating element. The correction of skew history was performed.

[Problems to be solved by the invention]

However, in the above-mentioned conventional example, as shown in each energization pattern of FIGS. 5A to 5N, the contents including both the history correction data and the skew history correction data for the heating element to be energized are handled. Therefore, both correction data cannot be distinguished. In other words, the pulse width of the drive pulse cannot be determined separately corresponding to each of the correction data, and the correction that appropriately corresponds to the thermal history of the heating element cannot be performed. In particular, when performing solid black printing, there is a problem in that proper thermal history correction cannot be performed and printing density unevenness remarkably occurs.

The present invention has been made in view of these points, and it is possible to independently obtain a plurality of correction elements related to thermal history correction, and to correct the energization time corresponding to each correction element. You can freely set the importance as element data, always apply proper thermal history correction,
An object of the present invention is to provide a thermal history correction method for a thermal printer that can perform printing with a uniform print density.

[Means for solving problems]

A thermal history correction method for a thermal printer according to the present invention is a thermal history correction method for a thermal printer, which corrects the energization time during each cycle to a plurality of heating elements provided in a thermal head according to the thermal history of the heating elements. In addition, the correction values of the plurality of correction elements relating to the thermal history correction are separately obtained, and the correction values for each heating element are obtained by adding these correction values, and based on this correction data It is characterized in that the energization time of is corrected.

[Action]

According to the present invention, a plurality of correction elements related to thermal history correction are individually obtained, and then these correction elements are added to obtain correction data, and each heat generation is performed based on the correction data thus calculated. The energization time to the element is corrected to an appropriate value, the peak temperature of each heating element is held constant, and printing with uniform print density is always performed.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a schematic view showing an example of an apparatus for carrying out the method of the present invention.

In this embodiment, as the correction elements related to the thermal history correction, three elements including area correction in addition to the prior history correction and the skew history correction similar to the conventional one are adopted. Here, the area correction is to correct according to the thermal history state of all the heating elements, and by energizing each heating element, heat is accumulated in the thermal head and the temperature of the entire thermal head rises. The correction for this heat storage is performed.

In the present embodiment, the correction values for the previous history correction, the skew history correction, and the area correction are separately obtained. Each correction value is obtained as a value of a part of the ON time or a part of the OFF time of the drive pulse in one cycle, corresponding to the thermal history state. In case of ON time, total ON time which added ON time by each correction value is set as pulse width of drive pulse. In case of OFF time, OFF time by each correction value from maximum pulse width of drive pulse in one cycle. The pulse width is the time obtained by subtracting the total OFF time obtained by adding.

To further explain, the correction value by the previous history correction is, for example, the second
As shown in Figures (a) to (c), the matrix is created in advance, and the OFF time depends on the energization status of the heating element (the rightmost white circle in the figure in the figure) that is about to energize in the past three cycles. _Find T _a1 , T _b1 , and T _c1 . Similarly, the correction value by the skew correction is also made into a matrix in advance as shown in FIGS. 3 (a) and 3 (b), and a heating element to be energized from now on (the rightmost white circle in the figure) The OFF times T _a2 and T _b2 are obtained according to the energization state of the heating element adjacent to the previous cycle. The correction value by the area correction is calculated by giving a predetermined OFF time to each heating element when the number of energized dots in the past predetermined cycle of all the heating elements exceeds the set value.

Next, the thermal history correction method according to this embodiment will be described.

First, as shown in FIG. 1, in the history correction calculator 1, the skew correction calculator 2, and the area correction calculator 3, the history correction value and the skew correction value are separately calculated from the energization state of each heating element in the past cycle. The history correction value and the area correction value are obtained and output to the adder 4. The minimum OFF time for turning off the power supply to each heating element at the beginning of each cycle is also input to the adder 4 at the same time. Then, when each value is input to the adder 4, the previous history correction value, the skew history correction value, the area correction value and the minimum OFF time, which respectively represent the OFF time, are added and output to the OFF time register 5 as correction data. To do. The correction data once held in the OFF time register 5 is output to the drive pulse shaper 6, and the value obtained by subtracting the total OFF time indicated by the correction data from the total time of one cycle in the drive pulse shaper 6 is set as the pulse width. A drive pulse is applied to each heating element.

FIG. 4A shows the case where each correction value is 0 and the pulse width of the drive pulse is maximum, and FIG. 4B shows the drive pulse when the thermal history correction is performed.

As described above, in the present embodiment, the history correction, the skew correction, and the area correction are separately performed, and the pulse width of the drive pulse is calculated corresponding to each correction value. It is possible to perform the correction appropriately corresponding to the state, and the weight of each correction element can be arbitrarily set according to the printing conditions and the like.

Although each correction value is obtained as the OFF time in the above embodiment, it may be obtained as the ON time. Further, the number of cycles going back to the past in consideration of the heat history may be determined according to the printing purpose, conditions, and the like.

Further, as the correction element related to the thermal history correction, in addition to the three elements of the above-described embodiment, two or four or more elements may be used depending on the printing conditions and the like.

Further, the present invention is not limited to the above-mentioned embodiments, but can be modified as necessary.

〔The invention's effect〕

As described above, the present invention is constructed and operates,
It is possible to independently obtain a plurality of correction factors related to thermal history correction, and to correct the energization time corresponding to each correction factor, so that the importance of each correction factor as data can be set freely. Therefore, it is possible to perform appropriate thermal history correction and perform printing with uniform print density.

[Brief description of drawings]

1 to 4 show an apparatus or the like for carrying out the thermal history correction method for a thermal printer of the present invention, FIG. 1 is a block diagram showing a correction calculation unit, and FIGS. 2 (a) to 2 (c) are respectively Explanatory diagram showing matrix contents of history correction, FIG. 3 (a)
And (b) are explanatory views showing the matrix contents of skew history correction, and FIGS. 4 (a) and 4 (b) are diagrams showing the states of drive pulses with and without thermal history correction, respectively. 5 (a) to 5 (n) are explanatory views showing the matrix contents of the conventional thermal history correction. DESCRIPTION OF SYMBOLS 1 ... Previous correction calculator, 2 ... skew correction calculator, 3 ... area correction calculator, 4 ... adder, 5 ... OFF time register, 6 ... drive pulse shaper.

Claims (2)

[Claims] 1. A thermal history correction method for a thermal printer, which corrects the energization time during each cycle to a plurality of heating elements provided in a thermal head according to the thermal history of the heating elements, wherein the thermal history correction is performed. The correction values of the plurality of correction elements are separately calculated, and the correction values for the heating elements are added by adding these correction values, and the energization time to each heating element is corrected based on the correction data. A thermal history correction method for a thermal printer, characterized by: 2. The correction element includes a history correction value according to a thermal history state of each heating element, an oblique history correction value according to a thermal history state of a heating element adjacent to each heating element, and all heating elements. The thermal history correction method for a thermal printer according to claim 1, characterized in that the area history correction value comprises an area correction value according to the thermal history state of.