JPS63209956A - Heat accumulation predicting device for thermal head - Google Patents

Abstract

PURPOSE:To make a thermal recording stably, by developing the temperature immediately before current recording as shown by a specific formula with reference to the temperature predicted before start of previous recording thereby obtaining a predicted temperature having reduced accumulation error and controlling the application voltage of a thermal head based on the predicted temperature. CONSTITUTION:Prediction temperature is equal to an ambient temperature Ta at a time point when recording is started, and rises as the recording proceeds. In the formula, the temperature being achieved through cooling during previous recording interval is operated to be equal to the difference from the ambient temperature Ta, then it is added with the ambient temperature to provide a prediction temperature Tn. Consequently, addition of starting temperature Tn-l having accumulated operational error can be avoided, and highly accurate prediction can be made. A thermal head control section feeds temperature Tn predicted at a temperature predicting section 11, gradation number of recording pixel, recording speed, etc., to a pulse table 14 where the pulse width is determined. A thermal head drive section 13 controls power of a head 12 according to the pulse width.

Description

[Detailed Description of the Invention] [Table of Contents] Overview Industrial Application Fields Prior Art (Figures 5 to 9) Problems to be Solved by the Invention Means for Solving the Problems (Figure 1) Functional Examples (Figs. 2 to 4) Effects of the Invention [Summary] The present invention provides an apparatus for recording two images of characters equipped with a thermal recording means, in which the thermal energy for performing thermal recording is transferred to the inside of the thermal head. In order to solve the problem that the recording density on the recording paper changes even if the same applied power is applied due to heat storage in the A cooling amount output section that associates cooling elements with reference to , and a sum-of-products calculation section are provided.

By determining the total amount of heating and cooling for the ambient temperature, and adding the ambient temperature to this, a predicted temperature with a small cumulative error is obtained, and based on this predicted temperature, the power applied to the thermal head is controlled. The present invention relates to a heating recording device that performs stable heating recording regardless of the amount of heat storage, and is a heat storage prediction calculation device that predicts the amount of heat storage in a 411F thermal head. Regarding.

When recording on thermal paper using a thermal head, a current corresponding to output data is passed through the thermal head to generate heat. Since the thermal head itself is heated by this heat generation, when performing multilevel gradation recording, it is necessary to control the energization according to the amount of heat stored in the thermal head.

[Conventional technology]

Density control in thermal recording involves detecting the amount of heat stored in the thermal head, and controlling the power applied to the thermal head in accordance with the amount of heat stored. The applied power can be controlled by controlling the pressure or by changing the pulse width depending on the time during which the current is applied.

The thermal head's heat storage response phenomenon, which is a problem in thermal recording, is
It can be classified into three main levels depending on its physical structure. The second level is due to the heating resistor 41 shown in FIG. 5 which obtains the thermal energy necessary for thermal recording, and is related to its thermal time constant.

The second level involves a layer of relatively low thermal conductivity called the glaze layer 42. This glaze layer 42 prevents thermal energy that does not directly contribute to thermal recording from dissipating to the outside, and serves to save electrical energy to the thermal head by keeping the thermal recording surface warm. The third level relates to a heat sink 43 that releases excess thermal energy from the glaze layer 42 to the outside of the thermal head. The heat storage phenomenon at this level is characterized by the fact that it is in contact with the outside air and is strongly affected by temperature changes in the outside air. Glaze layer 42. The response becomes slower in the order of heat sink 43. In thermal recording, good recording is possible by fully understanding these heat accumulation phenomena0 These heat accumulation phenomena can be calculated by solving the heat conduction equation based on the recorded image and the physical constants of the thermal head. However, once the recorded image has been identified, analysis that includes the complex structure of the thermal head is impractical. Therefore, various inventions have been made in the past.

Figure 6 shows that a thermal constant that approximates the structure of the thermal head is determined, temperature simulation is performed using a time constant circuit consisting of a resistor R51 and a capacitor C52, and the pulse width is determined by gating the drive signal according to the temperature value. The thermal recording density is controlled by changing the density.

FIG. 7 is for controlling the thermal recording density between adjacent lines. When recording lines n and m continuously as shown in Figure 7, column 0, which records on line m without recording on line n, is compared to column a, which records on line n but records on line m. hand.

concentration becomes lower. To prevent this, after writing the n line,
An auxiliary line n' line as shown in (B) is provided. n
' line is the inversion of n line.

In FIG. 8, the density is controlled by calculating the temperature of the glaze layer of the thermal head from the recording pattern consisting of two values and the applied pulse power. Temperature memory 6
Based on the glaze layer temperature within the entire recording cycle of the previous recording stored in 1 and the binary recording data 67, the pulse width is determined by a pulse width determination calculation 63 so as to obtain a constant density, and the recording pulse width data 65 The thermal head 66 is driven accordingly. The pulse width records the glaze layer temperature change due to this drive.

The glaze layer temperature of the next line is predicted by temperature prediction calculation 64 from the glaze layer temperature at the time of previous recording, and the ninth line temperature data 62 is obtained.

In FIG. 9, a temperature detection element 72 is attached to the heat sink of a thermal head 71 to sense the surface temperature.

The pulse width is determined based on the pulse width table 73 based on the number of recording gradations, recording speed, etc., and the thermal recording density is controlled.

FIG. 6 shows two heating resistors, FIGS. 7 and 8 show a glaze layer, and FIG. 9 shows a heat sink mainly controlling the concentration of the amount of heat stored in the heat dissipation plate. Moreover, these things may be used alone or in combination.

In this type of technology, understanding the amount of heat storage that affects thermal recording is based on a rough calculation as shown in Figure 6.
Measures based on local conditions as shown in FIG. 7 and methods based on estimation from actual measurements as shown in FIG. 9 have been put into practical use. These methods can only roughly predict heat accumulation phenomena and cannot obtain highly accurate temperature values. On the other hand, the one shown in Figure 8 can achieve highly accurate predictions, but the recording pattern is limited to two values, and there is a problem that it cannot follow changes in the ambient temperature or recording cycle. Ta.

Therefore, the present inventor proposed a method for determining the heat accumulation phenomenon in the thermal head by predictive calculation by sequentially accumulating the temperature of the thermal head immediately before the start of the previous recording and the amount of heating and cooling within the previous recording period. These relationships are shown in equation (1). n-
The temperature change during recording 1 line and n line is (1)
As shown in the equation, the first term of the temperature rise ΔTn due to heat generation in the n line, and the second term that is cooled due to the difference between the actual temperature T, -1, and the ambient temperature T, in the previous n-1 line. is the sum of

%-Tfl-t=ΔTn-(Tk-t-Tm)(1
-exp(-t/r))--(1) In equation (1), t is the recording period between lines, and τ is a thermal time constant.

FIG. 1 shows this situation. In FIG. 1, the horizontal axis shows the time course of recording in units of one recording period, and the vertical axis shows temperature changes. 1 shows the temperature change in the heating resistor of the thermal head.

2 indicates the predicted temperature of the glaze layer; 0 indicates the predicted temperature.

At the 10 points where recording begins, the ambient temperature is equal to T.

The temperature increases as the record is recorded. i, my tfi...
During the period, the second term 'rn-1 of equation (1) becomes the ambient temperature T, so the second term is zero, and only the heating in the first term contributes to the temperature rise. tfi-1~t,
In the period t3, the temperature at t3 is determined by the amount of heating due to recording and the cooling in this section. What is the time constant for cooling?

The value including the glaze layer is 0. In this way, by calculating the predicted temperature, heating amount, and cooling amount in the previous recording period, the amount of heat storage can be predicted one by one.

The final heat storage prediction calculation formula immediately after the current recording is calculated using equation (2).

'l'fi-'l'? l=Δ'rfixx-(Ta-t
-Ta)x(i→field(-t/f))...(2)
When formula (1) is interpreted in this way, both the first term and the second term are in the form of a product, which results in the accumulation of product-sum operations. By converting it into a product-sum operation, a commercially available product-sum calculation unit (
This can be easily realized using a digital signal processor (digital signal processor).

The final actual predicted temperature is expressed by the first-order equation (3).

Tn""Tfi-s+ΔT, X 1- (Tn-x
-'r,) X (1-exp(-t/f)) ・(3
) [Problems to be Solved by the Invention] In the conventional technology, the predictive calculation of the amount of heat storage that affects thermal recording is sequentially calculated using equation (2) (that is, equation (3)). Focusing on this equation (2), the first term.

The value of 'rn-x predicted in the previous recording period is used in the second term. Normally, calculations are performed with a finite number of digits, so 'ra' contains errors and has the characteristic of accumulating as shown in equation (2).
The more -t there is in the arithmetic expression, the greater the error.

Expanding. If the error becomes large, it becomes impossible to select an appropriate pulse width, which adversely affects the recording quality.For this reason, it is necessary to increase the number of effective digits in the calculation to improve the calculation accuracy.

[Means for solving problems]

As is clear from the above equation (3), the temperature immediately before the current sickle is expressed as (4) based on the predicted temperature 'rn-t at the start of the brass.
It can be expressed by a formula.

% == 'r, -1 + Δ% - ('rl-s -
T, ) (1-exp (-Vv)) """ (4)
Here, ΔTn is the amount of heating within the previous recording cycle, T is the ambient temperature, t is the recording period, and τ is the thermal time constant.0 Expanding the third term of equation (4), equation (5) is obtained. becomes.

Tn=Ta+Δ%+(Tn-t-Ta)exp(-'/
τ) - - Curved Song - (5) Comparing equations (4) and (5), in the first term, equation (4) is the predicted temperature at the start of the previous recording.

Equation (5) is expressed in terms of ambient temperature. In the third term, only the multiplication coefficient is changed.

Next, using equations (4) and (5), the errors in the process of recursively calculating and predicting the temperature are evaluated. The number expressions have the same bit structure, and the calculation accuracy between the two terms is also the same. The quantization and operations in the second and third terms are the same, but
Tn-1 in the first term of equation (4) includes calculations and quantization errors in the previous recording cycle, whereas T in the first term of equation (5) is the measured value (64), which is simply a quantum of ambient temperature. There is only a conversion error.

That is, recursive calculation errors can be reduced and highly accurate calculations can be realized. The equation (5) is illustrated in FIG. 1, which is a diagram of the principle of the present invention.

In FIG. 1, the horizontal axis shows the time course of recording in units of one recording cycle, and the vertical axis shows temperature changes.

1 shows the temperature change in the heating resistor of the thermal head,
2 shows the predicted temperature change in the glaze layer.

The predicted temperature is equal to the ambient temperature T1 at the 10 points where recording starts, and the temperature increases as recording progresses. t0~tfi
During the period -□, the third term Tn-1 of equation (5) becomes the ambient temperature T8, so the third term becomes zero, and only the amount of heating in the second term contributes to the temperature rise. tn-,% During the tnO period, the heating amount ΔTn according to the record? 1n-
The predicted temperature at 1fi becomes the temperature cooled by 1fi, that is, the sum of the second and third terms in equation (5).

[For production]

The temperature reached by cooling during the previous recording period is calculated as the difference from the ambient temperature, and the predicted temperature is calculated by adding this to the ambient temperature, so calculation errors will accumulate at the start of the previous recording. Temperature addition can be avoided. As a result, highly accurate prediction calculations can be performed.

〔Example〕

An embodiment of the present invention will be explained with reference to FIGS. 2 to 4.

FIG. 2 is a block diagram showing one embodiment of the present invention;
The figure is a detailed diagram of the temperature prediction section in FIG. 2.

FIG. 4 is a time chart showing the operation of the temperature prediction section.

In FIG. 2, 11 is a temperature prediction section which is the main part of the present invention, 12 is a thermal head, 13 is a thermal head drive section that drives the thermal head, and 14 is a Luhalus width table that determines the applied power to the thermal head drive section 13. , 15 is a thermistor that detects the temperature of the thermal head 12, 16 is a temperature detection section that converts the temperature detected by the thermistor 15 into a digital signal, and 17 is a thermal head control section that controls the above blocks.

Thermal head control if [7c] Immediately before starting thermal recording by the thermal head 12, the thermistor 15. The temperature detection section 16 senses the temperature of the thermal head 12 and performs control for converting it into 74 digits. Next, data necessary for temperature prediction, such as sensed temperature data corresponding to the atmosphere data, the number of gradations of recording pixels, and recording speed, is transferred to the temperature prediction unit 11. The temperature prediction unit 11 sequentially predicts the temperature of the thermal head based on these data. The thermal head control unit 17 receives the temperature value predicted by the temperature prediction unit 11,
The number of gradations of recording pixels, recording speed, etc. are determined by the pulse width table 14.
send to The pulse width table 14 is as follows.

The pulse width is determined according to these data. Thermal spatula)" JEK moving part 13 C. Optimal thermal recording is performed by controlling the power of the thermal head 12 according to the output pulse width of the pulse width table 14. Below, the detailed operation of the temperature prediction part 12 is explained in the block diagram of FIG. 3. .

This will be explained using the time chart in Figure 4.

FIG. 3 is a block diagram showing details of the temperature prediction section of the present invention. In Figure 3, 34 and 35 are signals indicating the number of gradations and recording speed (recording cycle) for each pixel that determine the amount of heating, 36 is a signal for inputting the ambient temperature, and 28 is a temperature sensor at the start of recording. An atmosphere temperature line buffer 29 stores the actually measured atmospheric temperature values for one line for each pixel, and 29 stores the calculated predicted temperature values for each pixel by 1. 25 is a heating amount table that calculates the heating amount between recording lines; 23 is a subtracter that calculates the difference between the predicted temperature in the previous line and the ambient temperature; 27 is a constant that outputs a constant 1. 26 is a thermal time constant table including the glaze layer, 31, 32, and 33 are multiplexers, and 21 is a heating amount table 2 for determining the heating amount between recording lines.
5. A multiplier 22 multiplies the output of the constant table 27, the output of the subtracter 23 to obtain the cooling amount relative to the ambient temperature, and the output of the thermal time constant table 26. 22 is a multiplier for obtaining the total amount of heating and cooling relative to the ambient temperature. 24 is an adder that adds the ambient temperature to the temperature difference with respect to the ambient temperature that is the output of accumulator 22; 30 is a register that temporarily stores the output data of adder 24 for each pixel. , 37 is a signal indicating the predicted temperature which is the calculation output 0
Next, the operation shown in FIG. 3 will be described below using the time chart shown in FIG. This time chart.

It represents the first line at which the recording operation starts, and the second and subsequent lines, and relates to predictions for the first and second pixels at the head of the line. signal a
is a line signal indicating the period for performing predictive calculation for each line,
The IN signal is the first line signal indicating the first line to be predictively calculated, and the signal C is the gradation number signal 34 for each pixel in Fig. 3.
．． Recording speed signal 35. Indicates that the ambient temperature data signal 36 is input, and the pixel data input signal generated by the number of pixels in one line, signal d, is the ambient temperature line buffer 10.
Ambient temperature line buffer 1 data representing input/output data; signal e represents predicted temperature line buffer 1 data representing input/output data of the predicted temperature line buffer 128; signal f represents a pixel prediction calculation signal indicating a period for performing predictive calculation for one pixel. , signal g is a basic tally signal for predictive calculation, signal 1 is an accumulator reset signal that resets accumulator 22 prior to cumulative calculation, signal i is a multiplexer control signal for multiplexers 32 and 33, and signal j, has a multiplexer 32
．． 33, the signal l shows the output data of the accumulator 22, and the signal m shows the final predicted temperature data of the register 30.

In the first line starting the prediction calculation.

As the line signal a becomes "1", the first line signal becomes "1°".The 0 pixel data input signal C indicates that the data transfer is accompanied by the ambient temperature data, and the recording starts for each pixel. Ambient temperature data T1 is written to the ambient temperature line buffer 128. At the same time, the multiplexer 31 predicts the ambient temperature data using a control signal (not shown) obtained by ANDing the first line signal and the pixel data input signal C. Input to temperature line buffer 29.

As a result, the same ambient temperature data is stored in the memory address corresponding to the same pixel in the #ambient temperature line 67a 28 and the predicted temperature line buffer 129, and the predicted temperature line buffer 129 is initialized only at the start of page recording. In addition, since the 2-pixel data input signal C becomes °l", 9
A gradation number signal 34 and a recording speed signal 35 are input, and a heating amount table 25. The thermal constant table 26 is finalized, and predictive calculations can be made for the first pixel. When the prediction calculation preparation is completed, the one-pixel element measurement calculation signal f becomes 11'' in synchronization with the fall of the basic lock signal g.

When the pixel prediction calculation signal f reaches "1°," an accumulator reset signal and a multiplexer control signal i are generated.

The accumulator blade set signal resets the accumulator 22.

The multiplexer control signal i is the multiplexer 32
, 33, the heating amount from the heating amount table 25 necessary for calculating the heating amount at the first pixel of the first line and the output coefficient value=1 from the constant table 27 are input to the multiplier 21. The multiplier 21 takes in the multiplexer output data j, k, which is the output of the multiplexer 32 and 33, at the rising edge of the basic clock signal g.The multiplier 21 accumulates the multiplication result ΔTh1l in the accumulator 22, and outputs the basic clock signal. The next rising edge υ of g is set as accumulator output data l. Note that, prior to this rise, the multiplexer control signal i is set to "0".

The multiplexers 32 and 33 output the temperature difference and thermal time constant obtained by subtracting the predicted temperature line buffer 29 and the ambient temperature line buffer 28 necessary for calculating the amount of cooling at the first pixel of the first line by the subtractor 23. The output of table 26 is multiplier 2
Enter 1. That is, the output of the calculation result of the heating amount and the seven etchings of the data for calculating the cooling amount are performed at the same timing.

Subsequently, the 1 multiplier 21 calculates the cooling amount.

Since the difference between the predicted temperature line buffer 29 and the ambient temperature 2 in-buffer 128 is zero for all pixels in the first line of recording, the accumulated result in the accumulator 22 is ΔTA! 11 is
The calculation result of the heating amount is exactly ΔTh1l. The calculation result becomes accumulator output data l at the rising edge of the secondary basic clock signal g. The temperature value Tal of the first pixel immediately before the start of recording stored in the ambient temperature line buffer 129 is added to the heating and cooling amount ΔT111 calculated for the first pixel of the first line.
are added by the adder 24. The result of this addition becomes the predicted temperature after recording of the first pixel on the first line to be determined. The predicted temperature is temporarily stored in the register 30.

The predicted temperature line buffer 29 is input via the multiplexer 31 to 'l'al+ΔTA! Update to 11. continue.

By the pixel data input signal C becoming 1'', the second
Gradation number signal 34 regarding pixels. The recording speed signal 35 is input, and the heating amount table 25. The thermal time constant table 26 is determined, and predictive calculation for the second pixel becomes possible. Below, the 12th
These operations are repeated until the input is completed.

From the second line onwards, where prediction calculation starts,
Only line signal a becomes °1". Pixel data input signal C
becomes 111, resulting in a two-level numerical value 34. The recording speed signal 35 is input, the prediction temperature line buffer 29 has already been updated by the calculation in the previous line, the heating amount table 25° and the thermal constant table 26 are determined, and the prediction calculation for the first pixel is possible. becomes. When the prediction calculation preparation is completed, the one-pixel element measurement calculation signal f becomes "1" in synchronization with the fall of the basic clock signal g. Pixel prediction calculation signal f is “1”
, it generates an accumulator reset signal and a multiplexer control signal i. The accumulator reset signal resets accumulator 22.

The multiplexer control signal i is the multiplexer 32
．． The heating amount from the heating amount table 25 necessary for calculating the heating amount at the first pixel of the second line and the output coefficient value = 1 from the constant table 27 are input to the multiplier 21 as the output of 33. The multiplier 21 receives multiplexer output data j, which is the output of the multiplexers 32 and 33, at the rising edge of the basic clock signal g.

Take in k. The multiplication result ΔTh21 is accumulated in the accumulator 22, and is set as accumulator output data l at the next rising edge of the basic clock signal g. In addition, by setting the multiplexer control signal to 10" before this rising point is 91C, the multiplexers 32 and 33 set the predicted temperature line necessary for calculating the cooling amount at the first pixel of the second line. Buff 129
The temperature difference obtained by subtracting and the ambient temperature line buffer 28 by the subtracter 23 and the output of the thermal time constant table 26 are input to the multiplier 211C. That is, the output of the calculation result of the heating amount and the seven etchings of the data for calculating the cooling amount are performed at the same timing. Subsequently, the 9 multiplier 21 calculates the predicted side temperature immediately before recording the first pixel of the second line - Rinichi 14 bases ＾ I - Ura - 6a 4≦P1 A to A C21 The 0 predicted temperature Tp11 is: Heating and cooling amount Δ at the first pixel on the first line
The 0 calculation result obtained by adding the ambient temperature Tal of the same pixel to T111 is accumulated by the accumulator 22, and the total heating and cooling amount ΔTh21+ΔTC21 from the start of recording to immediately after recording of the 22nd in first pixel is calculated. At the next rising edge of the basic clock signal g, the accumulator output data becomes l. For the fourth factor, the total amount of heating and cooling for this ambient temperature is ΔT12
The adder 24 adds the temperature value Tal of the first pixel of the first line immediately before the start of recording stored in the ambient temperature line buffer 128 to the output data ΔT121 of the accumulator 22.
Add by. The 0 predicted temperature, which is the predicted temperature immediately after recording of the first pixel on the second line to be determined by this addition result, is 0 or less, which is temporarily stored in the register 30 and updated in the predicted temperature line buffer 29 via the multiplexer 31.

Repeat these operations until the prediction line ends.

0 to predict all lines and this predictive calculation value is the second
The pulse width is sent to the pulse width table 14 shown in the figure, and a pulse width corresponding to this is output to the thermal head drive unit 13.

Note that in this embodiment, predictive calculations are performed in units of two pixels, but it is also possible to perform calculations on a plurality of pixels at once. This grouping allows the ambient temperature line buffer 28. The capacity of the predicted temperature line buffer 129 can be reduced, the calculation speed of the square multiplier 21° accumulator 22 can be reduced, and the cost can be reduced. Furthermore, in the two embodiments, the amount of cooling is calculated following the amount of heating, but reverse layers are also possible.

〔Effect of the invention〕

According to the present invention, the cumulative components of calculation errors can be provided in a reduced form compared to the temperature prediction means.

It is possible to calculate highly accurate predicted temperatures and achieve higher quality thermal recording.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the principle of the present invention. FIG. 2 is a boot diagram of an embodiment of the present invention. FIG. 3 is a detailed configuration block diagram of the temperature prediction section in the present invention. FIG. 4 is a time chart showing details of the temperature prediction section in the present invention. FIG. 5 is an explanatory diagram of the structure of the thermal head. FIGS. 6 to 9 are diagrams showing conventional examples. 11...Temperature prediction section. 12...Thermal head. 13...Thermal head drive unit. 14...Pulse width table. 15...Thermistor. 16...Temperature detection section. 17...Thermal head control section.

Claims (1)

[Claims] A thermal recording device that is equipped with a thermal head heat storage detection mechanism for each pixel or multiple pixels, and that controls applied power based on the detected amount of heat storage. A heating amount table associated with the predicted temperature immediately before the start, a constant table for scaling the output value of this heating amount table, a thermal time constant table associated with the recording cycle, and the predicted temperature and atmosphere immediately before the start of the previous recording cycle. a subtracter to obtain the difference in temperature; a first multiplication between the output of the heating amount table and the output of the constant table to obtain the heating amount within the previous recording cycle; and the temperature at the start of the previous recording cycle is A multiplier that performs a second multiplication between the output of the thermal time constant table and the output of the subtractor to find the difference between the temperature reached by cooling and the ambient temperature, and the total amount of heating and cooling up to the previous recording cycle with respect to the ambient temperature. An accumulator that accumulates the first and second multiplication results by the multiplier, and an adder that adds the ambient temperature to the output of this accumulator are installed, and the predicted temperature immediately before the start of the current recording cycle is calculated for each recording cycle. A thermal head heat storage prediction calculation device characterized in that: