JPH0467959A - Thermal head driving device - Google Patents

Abstract

PURPOSE:To control the density level so that a fixed printing characteristic property can be obtained by a method wherein the heat accumulated quantity of a thermal head heating element for a recording cycle is calculated based on the heat accumulated quantity and pulse width of a first memory means and maximum and minimum values for the pulse width of a second memory means. CONSTITUTION:In a first table 23 and a second table 24, tables to show the relationship between recording density and applied pulse width are stored. When a recording cycle is intermediate, the table is stored in the first table 23, a heat accumulated quantity operation circuit 22 selects a curve to correspond with a heat accumulated quantity at that point from the table and calculates the applied pulse width. Also, when the recording cycle becomes longer, the heat accumulated quantity decreases, however, when the recording cycle is at the minimum, the applied pulse is single, and when the recording cycle is at the maximum, it corresponds when the applied pulse is continuous. Therefore, curves only for all the recording cycles are made into a table previously, and it is stored in the second table 24 to calculate an approximate heat accumulated quantity Hi easily. When the recording cycle is shorter, the heat accumulated quantity increases, and the heat accumulated quantity is calculated using the heat accumulated quantity operation circuit 22, first and second tables 23, 24 and a heat accumulated quantity approximation circuit 25. As the result, the density level can be accurately controlled, and a fixed printing characteristic property can be obtained.

Description

[Detailed Description of the Invention] [Summary] A thermal head drive device used in a thermal printer is controlled so that constant printing characteristics can be obtained regardless of the printing pattern regardless of the past printing history. In a thermal printer that heats a heating element of a thermal head in response to a recording signal to record on paper, the present invention includes a heat storage amount calculation means for calculating the amount of heat stored in the thermal head heating element in a recording cycle, and a first storage means for storing a pulse width to be applied to the heating element according to the amount of heat storage, and storing a maximum value and a minimum value of the pulse width to be applied to the heating element in a recording period different from the recording period; inputting the amount of heat storage from the second storage means and the heat storage amount calculation means;
and a heat storage amount approximation means for calculating an approximate heat storage amount with reference to the second storage means, the maximum value of the heat storage amount and pulse width of the first storage means and the pulse width of the second storage means. Based on the minimum value, the amount of heat stored in the thermal head heating element in the recording cycle is calculated.

[Industrial application field]

The present invention relates to a thermal head drive device used in a thermal printer.

Thermal printers that use a heating element to record information such as characters include a thermal recording method and a thermal transfer recording method. The former is a recording method in which a thermal head is brought into direct contact with a recording paper that changes color due to heat, and a heating element is heated to change the color of the recording paper according to information. On the other hand, the latter method heats ink using a thermal head to melt or sublimate the ink, and then transfers the ink onto recording paper for recording.

Furthermore, heating element scanning methods are broadly classified into line recording methods and serial recording methods. The former line recording method is often used for high-speed recording, and the latter serial recording method is used for low-speed recording.

These thermal printers are greatly affected by ambient temperature because the heating element of the thermal head has a heat storage effect, and therefore, there is a need for a means for compensating for fluctuations in recording density caused by changes in ambient temperature.

[Conventional technology]

FIG. 7 is a block diagram of the main parts of a line recording type thermal transfer recording apparatus. The thermal head 71 faces a platen 74 with an ink sheet 72 and a recording paper 73 in between. The ink sheet 72 is heat-meltable, and when heated by the thermal head 71, the ink is melted and transferred onto the paper 73. The thermal head 71 has heating elements for one line arranged in a direction perpendicular to the plane of the paper, and records for one line are performed almost simultaneously.

When one line of recording is completed, the ink sheet 72 and paper 73 are simultaneously transported in the direction of the arrow.

FIG. 8 is a block diagram of the main parts of the thermal head.

The thermal head 71 has a multilayer structure as shown. That is, on the substrate 85, a glaze layer 84, a heating element 83,
An electrode 82 and a protective layer 81 are laminated. Note that 86 is a heat sink.

In the thermal head having such a configuration, a phenomenon occurs in which heat generated by the heating element as described below is accumulated in the body 5. That is, (1) a high-speed heat accumulation phenomenon on the order of "milliseconds" in the glaze layer 84; (2) a medium-speed heat accumulation phenomenon on the order of "seconds" in the glaze layer 84 and the substrate 85; (2)a rapid heat accumulation phenomenon on the order of "seconds" in the glaze layer 84, the substrate 85, and the heat sink 86. This is a slow heat accumulation phenomenon on the order of minutes in the entire thermal head including the thermal head.

Among these, the heat accumulation phenomenon (■) becomes a big problem when characters, etc. are recorded in binary format at high speed. This has a large effect because the line recording period is usually about 1 to 2 milliseconds, which is almost the same as the time constant of a high-speed heat accumulation phenomenon. In addition, binary recording requires only a fraction of the recording energy compared to multi-level recording;
The heat storage phenomenon can be ignored.

On the other hand, in multilevel recording, the line recording period is usually 30 milliseconds or more, and the fastest one is about 10 milliseconds, so the high-speed heat accumulation phenomenon in (■) can be ignored, but the effects of (2) and (3) are growing. In particular, when the line recording cycle is as fast as 10-odd milliseconds, the influence of the medium-speed heat accumulation phenomenon in (2) is extremely large, and it is important to compensate for the heat accumulation phenomenon in (2) in addition to the compensation for the heat accumulation phenomenon (2), which will be described later. .

Since this heat accumulation phenomenon is a phenomenon inside the thermal head substrate, it is difficult to detect it from the outside with a sensor or the like. Therefore, a method has already been proposed in which the amount of heat accumulation is compensated for from the history of recorded data by predictive calculation.

Regarding the low-speed heat accumulation phenomenon (2), since it is a heat accumulation phenomenon at a low speed on the order of minutes, it can be detected with high accuracy by the temperature detection element attached to the heat sink of the thermal head. 2
Compensation can be performed simultaneously by using the sum of the predicted results of ■ and ■ in value recording, and the sum of the predicted results of ■ and ■ in multi-value recording, as the total heat storage amount. Note that the influence of changes in the ambient temperature of the thermal head is also included in (2), and this can also be compensated for with high accuracy.

[Problem to be solved by the invention]

When the recording period is constant, all heat accumulation can be corrected with high accuracy as described above. Even when the recording cycle is variable, in principle all heat accumulation can be corrected with high accuracy if all parameters for heat accumulation calculation are considered as functions of the recording cycle.

However, when the recording cycle is variable, the heat storage prediction calculation is generally quite complex, and the circuit that provides all the parameters as a function of the recording cycle becomes extremely large.
There was a cost issue.

As described above, it is extremely difficult to perform heat storage prediction calculations for all recording cycles, so it is limited to the case where the recording cycle is constant, and as a result, when the ambient temperature of the printer is low, was forced to record at unnecessarily low speeds. Further, when the ambient temperature of the printer is high, the recording speed is too fast, so the temperature of the thermal head immediately exceeds the upper limit, and recording often has to be interrupted for cooling.

As a countermeasure against this problem, a method is generally known in which the applied pulse width is increased or decreased in accordance with the amount of heat storage, thereby maintaining the recording density constant.

Therefore, the purpose of the present invention is to focus on the applied pulse width, which is the final control value, perform heat storage calculation for a certain recording cycle, and convert this result into an approximate value for an arbitrary recording cycle. An object of the present invention is to provide a thermal head driving device that can be controlled so that constant printing characteristics are obtained without being influenced by past printing history even when printing a recording pattern.

[Means to solve the problem]

FIG. 1 is a diagram showing the basic configuration of the present invention.

The present invention provides a thermal printer that records on paper by heating a heating element of a thermal head in response to a recording signal DA, with a recording period T. a heat storage amount calculation means 11 for calculating the heat storage amount Ha of the thermal head heating element in the recording period T0;
The pulse width P to be applied to the heating element according to the heat storage amount Ha. and the recording period T. The second storage means 13 for storing the maximum value Pmax and minimum value Pm1n of the pulse width to be applied to the heating element in the recording period T1 different from and a heat storage amount approximation means 14 that calculates an approximate heat storage amount H1 with reference to the first and second storage means, the heat storage amount) 1a and the pulse width P of the first storage means.

and a maximum value Pmax and a minimum value Pm1n of the pulse width of the second storage means, the heat storage amount Hi of the thermal head heating element in the recording period T1 is calculated. The heat storage amount Hi of the thermal head heating element in Ti is the pulse width Pomax, l! at the maximum value of the heat storage amount Ha. : Calculated by linear approximation based on the difference between the minimum value of the heat storage amount Ha and the pulse width Pom1n, and the heat storage amount (Hi) is calculated using the following formula, fl=Pmax-(Pmax-Pmin)(Poma
x -Ha)/(Pomax-Pomin), and the second storage means 13 further includes a minimum recording density storage means for storing pulse widths Pmax' and pmin'' corresponding to the minimum recording density level, and Maximum recording density storage means that stores pulse widths Pmax" and Pm1n"' corresponding to recording density levels, and pulse widths Pmax and pmin corresponding to arbitrary recording density levels,
max', Pmin', Pmax'', P
m1n'', Pomax, and Pom+n.

[Effect]

Heat storage amount Ha and pulse width P of the first storage means. and the maximum value Pmax and minimum value Pm1n of the pulse width of the second storage means.
The oldest heat storage of the thermal head heating element in the recording period T1 is calculated by referring to The difference between the pulse width Pom1n at the minimum value of and the following formula, Hi=Pmax-(Pmax-Pmin)(Poma
Calculated by linear approximation using x - Ha)/(Pomax-Pomin).

〔Example〕

FIG. 2 is a block diagram of an embodiment of the present invention.

In FIG. 2, DA is data to be recorded, T is a recording period, and TH is a thermal head. Further, 21 is an applied pulse width calculation circuit, 22 is a heat storage amount calculation circuit, and 23 is a first table novel 24 which is a first storage means constituted by a ROM.
is a second storage means similarly constituted by ROM.
25 is a heat storage amount approximation circuit, and 26 is an application pulse generation circuit. The output order of the accumulation approximation circuit 25 is the amount of heat stored in the thermal head heating element in the recording period T1.

The applied pulse calculation circuit 21 is disclosed in Japanese Patent Application No. 62-12016.
As described in Publication No. 5, recording data OA is subdivided into recording cycles to be applied using a predetermined threshold value, and gradation data corresponding to a memory tone is uniquely divided into two within each minute recording cycle.
After converting into a value and comparing this threshold value with the gradation data, the recording pulse width is monotonically increased and the auxiliary pulse width is monotonically decreased for each gradation level.

Specifically, as shown in FIG. 6, the main part is an adder/subtracter.

As described in Japanese Patent Application No. 62-044657, the heat storage amount calculation circuit 22 generates a heating amount table associated with the number of gradations, recording period, and predicted temperature immediately before the start of the recording period, and this heating amount table. It consists of a constant table for scaling output values, a thermal time constant table associated with recording cycles, and a subtractor for obtaining the difference value between the predicted temperature and the ambient temperature.

The first table 23 and the second table 24 store tables showing the relationship between recording density and applied pulse width, as will be described later.

FIG. 3 shows a characteristic curve of the relationship between the applied pulse width P of the thermal head and the recording density. As shown, the applied pulse width P. , P+, and P2, if the applied pulse width is the same, the recording density will be the thermal head heat storage temperature t. +
It changes with l+t2. Conversely, the recording density is higher than the thermal head heat storage temperature t. ,tl,
Even if it changes from t2, it can be kept constant by changing the applied pulse width. That is, by changing the applied pulse width P in accordance with the heat storage temperature t, the recording density can be kept constant.

Figures 4 (a) to (C) show (a) when the recording cycle is intermediate.
This is a characteristic curve showing the relationship between the applied pulse width and the recording density for the long case (b) and the short case (C).

(In al, these curves a-b and c-d are the recording period.) This is the case between (C) and (C).
The applied pulse width-recording density curve for is stored in the table in FIG.
is stored in The heat storage amount calculation circuit 22 in FIG. 2 selects a curve corresponding to the heat storage amount at that time from the table and calculates the applied pulse width.

In this case, when the recording cycle becomes longer, the heat accumulation generally decreases as is clear from the narrow intervals between the curves a'-b' and c'J'.

At this time, the curve a' - b' and the curve c' - d'
are the cases where the heat storage amount is the minimum and maximum, respectively; the minimum case corresponds to a single applied pulse, and the maximum case corresponds to a case where the applied pulses are continuous (infinite number). Therefore, the curve a'-b' and the curve c for all recording cycles
'-d' is made into a table in advance, and the second table 2 is created.
4, for curve a'-b' and curve c'-d', curve a-b and curve c-d
, it is possible to easily calculate the approximate oldest heat storage that gives the same positional relationship as the heat storage amount Ha.

In (C), this case is a case where the recording cycle is short. As is clear from the relatively large spacing between the curves, the heat storage generally increases. In this case, as before,
Heat storage amount calculation circuit 22, first and second tables 23, 2
4. The heat storage amount can be calculated using the heat storage amount approximation circuit 25.

FIG. 5 is a detailed block diagram of the heat storage amount approximation circuit 25 of FIG. 2, and FIG. 6 is a diagram showing the main part configuration of the applied pulse width calculation circuit of FIG. 2. The point on the curve a-b corresponding to the recording density level L is Lab, and the point on the curve needle d is Lad.

The point on the curve a' - b' is la'b', and the point on the curve C
If the point on "-d" is Lc'd', the amount of heat storage is Ha, and the applied pulse width is Pw, then the approximated shortest heat storage and applied pulse width Pw are given by the following equation.

,', H+ = La'b' - (La'b' - Lc' d) (Lab - Ha
)/(Lab-Lcd)...(1)
Pw = La'b' -H+...(
2) As is clear, the circuits in Figures 5 and 6 are based on the above equation (
This is a configuration in which 1) and (2) are converted into a circuit.

In FIG. 5, 51, 52, 53, 56 are subtracters, 54 is a multiplier, and 55 is a divider. Further, 61 in FIG. 6 is an adder/subtractor. These subtracters, multipliers, and dividers allow the expression (
1) and (2) are calculated and the heat storage amount H1 is output.

As shown in the figure, the heat storage amount approximation circuit 25 of this embodiment has a simplified configuration and a high operating speed. However, there is a drawback that the number of circuit elements increases. Therefore, if the operating speed is to be sacrificed to some extent, the multiplier (arithmetic operation unit) (ALtl) 5
4 human output sequentially, Altl
A circuit can be constructed at low cost by using one, register, and multiplexer. Furthermore, although equation (1) uses linear approximation, the method of approximating the amount of heat storage according to the present invention is not limited to this.

In this example, the curve a'-b' and the curve c'-d
' as a storage method, the point Lab on the curve a-b and the point Lc on the curve c-d corresponding to all memory density levels L.
d to the first table (ROM), and point La' on the curve a'-b' corresponding to all memory density levels.
b' and point Lc'd' on curve c' - d'
are stored in a second table (ROM).

However, the second table is not limited to this, and can also be calculated from La'b' and Lc'd' for the minimum and maximum values of the density level L. In this case, although the circuit becomes a little more complicated, the number of La'b' and Lc'd' to be written into the memory is reduced by an order of magnitude, so that the time required for measurement can be significantly shortened.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to calculate the amount of heat stored in the thermal hemostatic pad with high accuracy for a wide range of recording cycles without complicating the heat storage calculation circuit, which is generally large in circuit scale. The recording density level can be accurately controlled. As a result, it is possible to increase the recording speed and save power consumption when the ambient temperature of the printer is low, and by reducing the recording speed when the ambient temperature of the printer is low, recording interruptions due to rise in temperature of the thermal head can be avoided. This can significantly improve the reliability of the printer.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the principle of the present invention, FIG. 2 is a block diagram of an embodiment of the thermal head driving device of the present invention, and FIG. 3 is a characteristic curve showing the relationship between the applied pulse width of the thermal head and the recording density. Figures 4 (a) to (C) are characteristic curves showing the relationship between the applied pulse width and recording density in each recording cycle, Figure 5 is a detailed block diagram of the heat storage amount approximation circuit in Figure 2, and Figure 6 is the FIG. 2 shows the main components of the applied pulse calculation circuit, FIG. 7 shows the main parts of the line recording type thermal transfer recording apparatus, and FIG. 8 shows the main parts of the thermal head. 84... Glaze layer, 85... Substrate, 86... Heat sink. (Explanation of symbols) 21... Applied pulse calculation circuit, 22... Heat storage amount calculation circuit, 23... First table, 24... Second table novel 25... Heat storage amount approximation circuit, 26 ...Applied pulse generation circuit, 51-53.56゜61... Adder/subtractor, 54... Multiplier, 55... Divider, 71... Thermal head, 72... Ink sheet, 73 ...Memory paper, 83...Heating element,

Claims (1)

[Claims] 1. In a thermal printer that records on paper by heating the heating element of the thermal head using a recording signal (DA), calculate the amount of heat storage (Ha) of the thermal head heating element in the recording cycle (T_0). and a first pulse width (P_0) that stores a pulse width (P_0) to be applied to the heating element according to the heat storage amount (Ha) in the recording period (T_0).
a storage means (12) of , and a maximum value (Pmax) of the pulse width to be applied to the heating element in a recording cycle (Ti) different from the recording cycle (T_0).
and a second storage means (1) for storing the minimum value (Pmin).
3) and the heat storage amount (Ha) from the heat storage amount calculation means, and calculate the approximate heat storage amount (Ha) with reference to the first and second storage means.
and a heat storage amount approximation means (14) for calculating the heat storage amount (Ha) and the pulse width (P_0) of the first storage means.
and the maximum value of the pulse width of the second storage means (Pmax)
and a minimum value (Pmin), the thermal head driving device calculates the amount of heat storage (Hi) of the thermal head heating element in the recording period (Ti). 2. The amount of heat storage (Hi) of the thermal head heating element in the recording period (Ti) is determined by the pulse width (Pomax) at the maximum value of the amount of heat storage (Ha) and the pulse width (Pomin) at the minimum value of the amount of heat storage (Ha). 2. The thermal head driving device according to claim 1, wherein the calculation is performed by linear approximation based on the difference between . 3. The heat storage amount (Hi) is calculated using the following formula, Hi=Pmax-(Pmax-Pmin)(Pomax
-Ha)/(Pomax-Pomin) The thermal head drive device according to claim 2, wherein the calculation is performed by: 4. The second storage means includes a minimum recording density storage means for storing pulse widths (Pmax') and (Pmin') corresponding to the minimum recording density level, and a pulse width (Pmax'' corresponding to the maximum recording density level). ) and (Pmin"), and pulse widths (Pmax) and (Pmin) corresponding to arbitrary recording density levels are stored as each pulse width (Pmax'), (Pmin'), (Pmax
”), (Pmin”), (Pomax), (Pomin
2. The thermal head driving device according to claim 1, further comprising calculation means for calculating based on ).