JPH0825294B2 - Energization control method for thermal head - Google Patents

Description

The present invention relates to a method for controlling energization of a thermal head, and more particularly to a uniform printing density by correcting the energization time of a plurality of heating elements provided in the thermal head. The present invention relates to a method for controlling energization of a thermal head for performing various printing.

[Conventional technology]

Generally, in a thermal printer, a thermal head in which a plurality of heating elements are arranged in one row is provided, 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.

Then, conventionally, in order to prevent the occurrence of print density unevenness due to the influence of past heat generation of the heat generating element, after each heater element is sufficiently cooled by increasing the OFF time during which no power is supplied to the heat generating element in each cycle. Printing is performed by energizing each heating element for a predetermined time to generate heat.

However, taking a large OFF time for each cycle is an obstacle to speeding up the printing speed.If the OFF time is shortened to increase the printing speed, the thermal head gradually accumulates heat. There is a problem in that the temperature rises and the print density becomes uneven. This is particularly noticeable when a large number of heating elements are used to increase the dot density and the printing speed is increased.

Therefore, the present inventors grasp the current temperature state of the heating element from the past energization state of each heating element by the thermal history correction device, and adjust the length of the energization time when energizing in the next cycle. , A means for controlling so that the peak temperature of each heating element is constant is proposed.

FIG. 5 shows an outline of an apparatus for carrying out the above-mentioned control method.
Three elements, skew correction and area correction, are used. Here, the history correction is a correction performed according to the past energization state of the heating element, and the skew history correction is a correction performed according to the past energization state of the heating element adjacent to the heating element. Further, the area correction is a correction in accordance with the thermal history state of all the heating elements, that is, the heat storage of the entire thermal head.

Then, the correction values for the previous history correction, the skew history correction, and the area correction are separately obtained. Each correction value corresponds to the thermal history state,
Calculated as a value of either part of ON time or part of OFF time. 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 the case of the OFF time, the time obtained by subtracting the total OFF time obtained by adding the OFF times for each correction value from the maximum pulse width of the drive pulse in one cycle is the pulse width.

Further, the correction values by the history correction are made into a matrix in advance as shown in, for example, FIGS. 6A to 6C, and a heating element to be energized from now on (the rightmost white circle in FIG. 6). OFF times T _a1 , T _b1 , and T _c1 are obtained according to the energization state during the past three cycles of. In the figure, ○ indicates an OFF state, ● indicates an ON state, and × indicates an ON or OFF state. Further, similarly, the correction value by the skew history correction is also made into a matrix in advance as shown in FIGS. 7 (a) and 7 (b), and the heating element to be energized (the white circle on the rightmost side in FIG. 7). The OFF times T _a2 and T _b2 are obtained according to the energization state in the past cycle of the heat generating element adjacent to the (part). 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.

In the energization control method, as shown in FIG. 5, first, in the history correction calculator 1, the skew correction calculator 2, and the area correction calculator 3, from the energization state of each heating element in the past cycle, The previous history correction value, the skew history correction value, and the area correction value are separately obtained and output to the adder 4. The minimum OFF time for turning off the energization to each heating element at the beginning of each cycle is also input to the adder 4 at the same time.
Then, in the adder 4, when each value is input, 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 to the OFF time register 5 as correction data. Output. 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 defined as the pulse width. The generated driving pulse is applied to each heating element.

FIG. 8A shows the case where each correction value is 0 and the pulse width of the drive pulse is the maximum, and FIG. 8B shows the drive pulse when the thermal history correction is performed. ing.

As a result, it is possible to perform the correction appropriately corresponding to the thermal history state of each heating element based on the previous history correction value, the skew history correction value, and the area correction value.

[Problems to be Solved by the Invention]

However, in the conventional energization control method, each of the correction values is made into a matrix in advance and turned off according to the past energization state of the heating element to be energized from now on.
Since the time is obtained, it is necessary to store history data for multiple dots in the previous history direction of each heating element, and each correction value is matrixed according to head resolution, printing speed, etc. There is a problem that the control program becomes extremely complicated because it is necessary to change the amount of data to be processed. Further, since the history correction, the skew correction, and the area correction are separately performed, it is difficult to adjust each correction value.

The present invention has been made in view of these points, and without using correction values and the like that are matrixed in advance,
An object of the present invention is to provide a thermal head energization control method capable of easily and appropriately controlling the energization amount and capable of performing beautiful printing with uniform print density.

[Means for solving the problem]

In order to achieve the above object, a thermal head energization control method according to the present invention is a thermal head that controls energization energy during each cycle to a plurality of heating elements provided in the thermal head based on a thermal history of the heating elements. In the head energization control method, a plurality of elements corresponding to each heating element of the thermal head is set, the heat generation amount of each element is calculated based on the energization data to each heating element, and each calculated element is calculated. The temperature after energization of each element is calculated for each dot by calculating the amount of heat radiated to each element, the amount of heat diffusion such as the amount of heat exchange based on the amount of heat generated by Based on the above, the next energization energy for each heating element of the thermal head is controlled.

[Work]

According to the present invention, a plurality of elements corresponding to each heat generating element of the thermal head are set, the heat generation amount of each element is calculated based on the energization data to each heat generating element, and the heat generation of each calculated element is performed. The temperature after energization of each element is calculated for each dot by calculating the amount of heat radiation to each element, the amount of heat diffusion to each element based on the amount, and based on the calculated temperature of each element Since the next energizing energy for each heating element of the thermal head is controlled,
It is not necessary to matrix the correction values in advance,
Moreover, since it is not necessary to store history data for multiple dots in the previous direction of each heating element, and the same control is always performed even when the printing speed is changed, a simple control program Thus, it is possible to easily and properly control the energization.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

FIG. 1 shows an embodiment of a thermal head for carrying out the energization control method according to the present invention.
Forms a substrate 9 on the upper surface of the heat dissipation plate 8 and forms a lower glaze layer 10 on the substrate 9. An upper glaze layer 11 is formed on each of the lower glaze layers 10,
A heating element 12 is formed on each of the upper glaze layers 11. Further, a protective layer 13 is formed on the upper surface of the heating element 12. Then, when printing is performed using the ink ribbon 14, each heating element 12 is energized based on a desired printing signal.
The desired printing is performed by causing the paper to generate heat and press it against the paper via the ink ribbon 14 arranged on the protective layer 13.

Further, FIG. 2 shows a control block of the present embodiment, in which an MPU 15 for controlling is provided, and an element temperature storage section 16 to which initial values of temperatures of respective elements preset by the MPU 15 are sent is provided. ing. Further, each element is set so that one unit corresponds to one heating element 12 such as the heating element 12 or the upper glaze layer 11 on which each heating element 12 is mounted.

In addition, a heat generation amount addition unit that calculates the heat generation amount of each element based on the temperature of each element sent from the element temperature storage unit 16 and ON / OFF data for each heating element 12 of the thermal head 7 sent from the MPU 15. 17 is provided, and a heat diffusion amount calculation unit 18 that calculates a heat diffusion amount such as heat exchange and heat release to each element based on the heat generation amount of each element from the heat generation amount addition unit 17 is provided. Based on the thermal diffusion amount of the thermal diffusion amount calculation unit 18, an element temperature calculation unit 19 for calculating the temperature of each element after energization is provided, and each element temperature from the element temperature calculation unit 19 is stored in the element temperature storage. It is sent to the section 16 and stored.

Further, each element temperature calculated by the element temperature calculation section 19 is sent to the energization time calculation section 20, and an appropriate energization time is calculated based on each element temperature. At this time, each element temperature is sent from the element temperature calculation unit 19 to the energization time calculation unit 20, for example, when the energization time to one heating element 12 is set as a unit time, the element temperature calculation unit 19 It is sent to the energization time calculation unit 20 every time each element temperature is calculated. When the unit time is 1/2 of one dot energization time, the heat generation amount addition unit 17, the heat diffusion amount calculation Part 1
8. The element temperature calculation unit 19 and the element temperature storage unit 16 are adapted to send each element temperature only once every time the calculation loop is circulated twice. Instead of the energization time calculated by the energization time calculator 20, a value such as an energization pulse number or a driving voltage may be calculated.

Further, the MPU 15 sends the calorific value addition unit 17, the thermal diffusion amount calculation unit 18, and the energization time calculation unit 20 calculation coefficients and the like necessary for the calorific value calculation, the thermal diffusion amount calculation, and the energization time calculation, respectively. It is done like this.

Further, an energization control unit 21 is provided which inputs the energization time data calculated by the energization time calculation unit 20 and controls the energization time of the thermal head 7.

Next, the operation of this embodiment will be described with reference to FIGS. 3 and 4.

As shown in FIG. 3, first, in step ST ₁₁ ,
The initial value of each element temperature such as the environmental temperature or the heat sink temperature is set, and based on the initial value of this element temperature and the ON / OFF data of each heating element 12 of the thermal head 7 from the MPU 15, the calorific value adding unit 17 is used. The calorific value of each element is calculated. Next, in step ST ₁₂ , the heat diffusion amount calculation unit 18 calculates the change in the heat energy distribution due to heat exchange between the respective elements based on the heat generation amount of each element, and the element temperature calculation unit 19 calculates The current element temperatures are calculated based on the calculated heat distribution. Then, each element temperature is sent to the element temperature storage unit 16 and stored therein, and the energization time calculation unit
Sent to 20. Subsequently, in step ST _13, by the energization time calculation unit 20, on the basis of the respective elements temperature, set the proper energization time of the heating element 12 to ON next time, the energization control unit 21 based on the energization time Thus, proper energization control is performed.

Then, printing of one line in step ST ₁₄ it is determined whether or not it is completed, until one line printing is completed, but is intended to repeat the control described above, after the energization to the heating elements 12 , heat energy amount which is proportional to the energizing time of each element as shown in step ST _15, sequentially adds the element temperature, subsequently calculates a thermal diffusion amount and the like based on in step ST ₁₂ to the summed element temperature Is.

When the printing of one line is completed, the thermal head 7 is cooled by moving the carriage or the like, so that the initial values of the respective element temperatures are set again and the above-described arithmetic control is performed. In this case, if the actual temperature detected by a sensor such as a thermistor at the beginning of each row is used as an initial value, more appropriate control can be performed.

In addition, FIG. 4 shows, for example, that the above-mentioned element is formed in the upper glaze layer.
Shows a processing example of the heat distribution in the case of setting to 11, first, in step ST _21, the temperature of the n-th upper glaze layer 11 was set to ambient temperature, the initial temperature and
ON / OFF of each heating element 12 of thermal head 7 from MPU15
Based on the data, the calorific value addition unit 17 causes the upper glaze layer
Calculate the calorific value of 11. Next, in step ST ₂₂ ,
Based on this heat generation amount, the thermal diffusion amount calculation unit 18
The amount of heat exchanged with 13 is calculated, and subsequently, in step ST ₂₃ , the adjacent n−1th upper glaze layer 11 and n +
The amount of heat exchanged with the first upper glaze layer 11 is calculated. Furthermore, in step ST ₂₄ , the amount of heat exchanged with the substrate 9 via the lower glaze layer 10 is calculated, and in step ST ₂₅ , the element temperature calculator 19 calculates the amount of heat exchanged from each of the above values after the heat exchange. The temperature of the glaze layer 11 is calculated. Then, the temperature of the upper glaze layer 11 is sent to the energization time calculation unit 20, and in step ST ₂₆ , the energization time calculation unit 20 turns on the heating element next in proportion to the temperature of the upper glaze layer 11. Set by subtracting 12 appropriate energization times. Then, in step ST ₂₇ , it is judged whether or not the printing of one line is completed, and until the printing of one line is completed, in step ST ₂₈ , the heat energy proportional to the energization time is converted into the temperature of the upper glaze layer 11. Is sequentially added to.

Therefore, in this embodiment, the temperature of each element is set to 1
It is calculated for each dot energization, and the energization time for each heating element 12 of the thermal head 7 is controlled based on the calculated temperature of each element, so that it is not necessary to matrix the correction values in advance, Moreover, since it is not necessary to store history data for multiple dots in the previous direction of each heating element 12, and even when the printing speed or the like is changed, similar control is always performed, so simple control is possible. It is possible to easily and properly control energization by a program.

In the above embodiment, one heating element 12 and one heating element 1
Although each element is made to correspond to one element, if one heating element has a heating portion localized at a plurality of locations, if each element is set to a plurality corresponding to each heating portion. ,
Very good control can be performed.

Further, the present invention is not limited to the above-mentioned embodiment, and various modifications can be made as necessary.

〔The invention's effect〕

As described above, the energization control method for the thermal head according to the present invention calculates the temperature of each element for each dot energization, and based on the calculated temperature of each element, the energization time for each heating element of the thermal head. Since the control is performed, the energization control can be easily and properly performed by a simple control program, and beautiful printing can be performed with uniform print density.

[Brief description of drawings]

1 to 4 show an embodiment of the present invention.
FIG. 1 is an exploded perspective view of a thermal head, FIG. 2 is a block diagram of an energization control device, FIG. 3 is a flow chart when energization control is performed, and FIG. 4 is a calculation means when an element is an upper glaze layer. Flowchart shown, FIGS. 5 to 8
Each of the figures shows the conventional energization control means.
The figure is a block diagram of the energization control device, FIG. 6 (a),
(B) and (c) are explanatory diagrams showing the matrix contents of the history correction, respectively. FIGS. 7 (a) and (b) are explanatory diagrams showing the matrix contents of the skew correction, respectively, and FIGS. 8 (a) and (a). b)
FIG. 4 is a diagram showing the states of drive pulses with and without thermal history correction. 7 ... Thermal head, 8 ... Heat sink, 9 ... Substrate, 10 ... Lower glaze layer, 11 ... Upper glaze layer, 12 ... Heating element, 13 ... Protective layer, 15 ... MPU, 16 ... ... Element temperature storage unit, 17 ... Exothermic heat addition unit, 18 ... Heat diffusion amount calculation unit, 19 ... Element temperature calculation unit, 20 ... Energization time calculation unit, 21 ... Energization control unit.

Claims (1)

[Claims] 1. A thermal head energization control method for controlling energization energy of a plurality of heating elements provided in a thermal head during each cycle based on a thermal history of the heating elements. Set a plurality of elements corresponding to the element, calculate the heat generation amount of each element based on the energization data to each heating element, the heat radiation amount to each element based on the calculated heat generation amount of each element, By calculating the amount of heat diffusion such as the amount of heat exchange, the temperature of each element after energization is calculated for each dot, and the next temperature for each heating element of the thermal head is calculated based on the calculated temperature of each element. An energization control method for a thermal head, characterized in that energization energy is controlled.