JPS60161163A - Thermal accumulation correction device for thermal head - Google Patents

Abstract

PURPOSE:To arrange so that a high image quality may be obtained at low cost by seeking an applied energy to be supplied to each heating element and further correcting applied energy data meant only for a heating element through consideration of an effect on ambient dots. CONSTITUTION:In order to obtain a recorded image of homogeneous concentration, an energy value which is expected to be taken by each heating element at the time of each recording after being stored in an energy status buffer 4 is substracted from each target energy value to be taken by each heating element stored in an energy constant buffer 2 by a subtractor 3. Thus an applied energy to be supplied to each heating element is sought. In addition, applied energy data meant for only a heating element is corrected by an applied energy arithmetic circuit 6 through consideration of an effect upon ambient dots from recorded data of an ambient pattern buffer 1. In this way, an applied energy to be actually applied to each heating element is calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal head used for heat-sensitive recording, and more particularly to an improvement of a heat accumulation correction device for completely improving recording characteristics.

[Prior art]

Thermal heads used for thermal recording usually have a plurality of heating elements corresponding to the number of pixels in the main scanning direction of the thermal recording medium (for example, when recording image information on Japanese Industrial Standards A column No. 4 recording paper, The number of heating elements is 1728, B row 4
(2,048 pieces in the case of No. 1 recording paper)K, and by generating heat only in the required heating element according to the image information, the heat-sensitive recording paper, ink donor sheet, etc. that comes into sliding contact with the heating element is The thermal recording medium is colored.

By the way, when recording using such a thermal head, the recording cycle of one line is particularly set to 10 msec.
If you try to achieve high-speed driving by doing the following, for example, if the same heating element is made to generate heat continuously, the next row of data will be recorded before the thermal energy applied to the heating element is sufficiently diffused and released. As a result,
/J luck occurred in the energy state of each heating element, degrading the image quality.

Recently, in order to solve this problem for ICs, a heat storage correction method has been developed which calculates the optimal energy to be applied to each heating element from the current and past printing history of each heating element and the heating elements adjacent to the heating element. is proposed. However, with this method, it is necessary to memorize the past printing M history of each heating element, and if you attempt to perform detailed and accurate correction, the amount of information that must be stored becomes enormous, and It had the disadvantage of requiring a large amount of memory.

Furthermore, the increase in the number of memory elements naturally affects the cost of the device, and it is inevitable that the device price will rise.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a heat storage correction device for a thermal head that realizes effective and accurate heat storage correction without using a large capacity memory.

[Structure of the invention]

The present invention includes a buffer memory for storing input recording data, and a predetermined target energy value that each heating element should take in order to obtain uniform density from recording by the plurality of heating elements. a first storage circuit that separately stores the energy values of the plurality of heat generating elements at each predetermined recording time point for each scanning line; Based on the output of the subtracting means and the recording data output from the buffer memory, the applied energy value actually supplied to each heating element at each predetermined recording time point of each heating element is determined by the heating element adjacent to each heating element. a first arithmetic circuit that calculates and outputs the energy value after one scanning line recording cycle has elapsed for each heating element stored in the second storage circuit; a second arithmetic circuit that sequentially performs predictive calculations for each scan line; and a second arithmetic circuit that sequentially adds the arithmetic output of the second arithmetic circuit and the output of the first arithmetic circuit, and adds the added output to each heating element during recording of the next scanning line. an adding means for inputting the energy value into the second storage circuit and sequentially updating the storage contents of the second storage circuit; The apparatus further includes a driver circuit that supplies power to a heat generating element that is a heat generating element among the plurality of heat generating elements. That is, in this invention, from the valley target energy value that each heating element should take in order to obtain a recorded image with uniform density,
By subtracting the energy value of each heating element that each heating element is predicted to burn at each recording time, the applied energy supplied to each heating element = (-taking into account the interaction with the surrounding dots) Furthermore, by correcting the applied energy data focused on only one heating element by taking into account the influence of surrounding dots, the applied energy actually supplied to each heating element of the scissor head is calculated. I try to do that.

〔Example〕

FIG. 1 shows an embodiment of the present invention.

In FIG. 1, recording data VD input from an external device, such as a facsimile original reading device or a host computer, is stored in line buffer L1 or line buffer L2vC for each predetermined scanning line. Line buffers L1 and L2 have a 2-line buffer configuration,
Recorded data V of the scanning line that becomes one line buffer
When D is manually input, the other line buffer is in a state where it is outputting the recorded data VD of the previous scan line that has already been stored. The recording data VD serially output from the line buffer Ll or L2 is input to the peripheral i9 turn buffer IVC. The peripheral pattern buffer 1 is a serial input/parallel output type shift register consisting of several bits of latches, and the number of bits is determined according to the number of peripheral dots whose interaction with the heat generating element is to be considered.

Next, to the energy constant buffer 2VcId thermal,
The target energy value Ei, which indicates how much energy each heating element of It is stored for each heating element. This target energy value Ei may be determined by measuring the resistance value of each heating element in advance, determining the optimum energy value based on the measured result, and fixedly storing this in a non-volatile ROM. Alternatively, it includes a measurement circuit that measures each resistance value of each heating element, and a conversion circuit that converts the measurement output of the measurement circuit into a target energy value according to the measurement output,
For example, it is possible to reset the target energy value Ei every time the device is powered on. No consideration is given to the interaction effect that the heat accumulation of a heating element close to the element (printed dot) has on the heating element. The stored output El of the constant energy buffer 2 is inputted to the subtracter 3 in sequence.

As will be explained in detail later, the energy state buffer 4vc is a value Ed that is a prediction of how much energy each heating element of the thermal head actually has at each recording time.
is stored for each heating element. The output Ed of the energy state buffer 4 is then input to the subtracter 3 1111 in synchronization with the energy constant buffer 2.

Subtraction is performed using the output of the 3-digit energy constant buffer 2, ie, the target energy value Ei, as the minuend, and the output of the energy state buffer 4, ie, the actual energy value at each time, as the predicted value Ed, as the subtractor. Therefore, the value Δp output from the subtracter 3 is determined by the value Δ for each heating element at each recording time point VC so that each heating element has the above-mentioned target energy value E at each recording time point VC and a recording dot of a constant size is obtained. This indicates the applied energy value that should actually be supplied. However, as described above, this subtraction result is a value focused on only one heating element, and the interaction with heating elements adjacent to the heating element is not yet taken into consideration. The output ΔE' of the subtracter 3 is sequentially input to the calculation buffer 5 in synchronization with the input of the recording data VD to the peripheral pattern buffer 1. Operation buffer 5
is the applied energy data ΔE′ output from the subtractor 3
It has a capacity that can store several dots of
Similar to the peripheral pattern buffer 1, this number of dots is determined according to the number L of dots whose interaction should be taken into account when simultaneously recorded. In this determination, the heat conduction characteristics between each heating element, the energy application time, the interval time indicating the time interval between recordings, etc. are taken into consideration. FIG. 2 shows the pixel arrangement, and in this embodiment, the heating element Do with cross hatching [applied energy value to be supplied is applied to the adjacent heating element DI h D2].
*Corrected according to the heat storage state of Ds and D4. This correction is performed by the applied energy calculation circuit 6.

By the way, in this case, the target energy value El of each heating element stored in the energy constant number buffer 2 is a value that takes into account the resistance value variation of each heating element. Furthermore, since the applied voltage applied to each heating element can be considered to be constant when a constant voltage circuit is used, the applied energy value corrected by the applied energy correction circuit 6 is based on the voltage applied to each heating element. It is only necessary to variably control the i4 pulse width, that is, the energization time. Therefore, the target energy value Ei stored in the constant energy buffer 2 and the energy data Ed stored in the energy pure buffer 4 are also correspondingly stored as time data.

FIG. 3 shows an example of the internal configuration of the applied energy calculation circuit 6. In FIG. 3, each bit of peripheral pattern buffer 1 1-I) 1 # 1-D2 1l-Do *'-D3s
1-D4 has the pixel DI shown in FIG.

Recorded data for D2 +Do sD3 +D4 ■
are stored respectively, and each storage area 5-DI+5-D2e5- of the calculation buffer 5
D @ e5”'D! + 5- D4 has the above pixel D
1*D2, 1D6, 1D3, and 1D4, applied energy data Ed that does not take into account the influence of surrounding dots is stored, and based on these data, the applied energy calculation circuit 6 calculates the value of the heating element concerned. The optimal applied energy value is sequentially calculated for the surrounding dots Dl*D2*I)a#D4 in consideration of heat storage. First, ROM table 6 A-DI + 6 A-02*
6A-DO+6A-Dsa 6A-D4 VC is each heating element D1.

D2 r (Do) + Ds w A weight value that takes into account the relative influence of D4 on the heating element D0 is stored, and the RO to which recorded data with storage is input is stored.
In the M table, a predetermined multiplier value (weight value) is applied to the multiplier 6B.
-Dt l 6 B-D2 g 6B-Do r 6B
-Ds + 6 Output to B-D4 respectively. squared p-
6B-DI +6B-Do 56B-Do +68-
D3+6 B - D4 each ROM table 6A-D
th 6A-D 2 #6 A-D @ , 6
A - D 3 z 6 Multiplication is performed in parallel using the multiplier value output from A - D 4 as a multiplier and the applied energy data output from the operation buffer 5 as a multiplicand, and the multiplication result is sent to the adder 6CK. input. Adder 6
At C, these five multiplication results are added, and the addition result is inputted to one input terminal of the AND circuit 7 as the optimum applied energy value ΔE considering the influence of peripheral dots on the heating element DoK.

The other input terminal of the AND circuit 7 is manually supplied with an enable signal en based on a scanning line synchronization signal for each scanning line and a line buffer ready signal indicating the presence of unprinted data in the line buffer L1 or L2. %, the applied energy value ΔE is keyed with the enable signal en, and after being synchronized with the dot-by-dot transport lock, it is applied to one input terminal of the adder 8 and to the final buffer 9. is input.

The final buffer 9 has a capacity capable of storing the applied energy value ΔE corresponding to the heating element for one scanning line, and the applied energy ΔE output from the final buffer 9
g) This is the applied energy value to be applied to each heating element of the thermal head, and this output ΔE is the voltage J? applied to each heating element of the thermal head. All signals are input to the driver circuit 13 which actually forms the signal. Driver circuit 1
In step 3, electric power corresponding to the applied energy ΔE is supplied to each of the plurality of heating elements that is to be heated, so that only the required heating element generates heat.

On the other hand, the applied energy value Δ output from the AND circuit 7
E is manually input to the energy state buffer 4 via the adder circuit 8, and is also used to update the storage contents of the energy state buffer 4.

As mentioned above, the energy state buffer 4 stores a predicted value of how much energy each heating element of the thermal head actually has at each recording time, for each heating element. . A configuration for updating the storage contents of the energy state buffer 4 will be explained.

The calculation buffer 10 has a capacity of 7 to store several dots of the energy data Ed output from the energy state buffer 4, and this number of dots is the same as that of the peripheral patterns and the calculation buffer 1. It is determined according to the number of adjacent heating elements whose thermal interaction should be considered.

In FIG. 4, each storage area of the calculation buffer 10 is IQ-D1+10-02 r 10-D o 110
- D3* 10-04 has the pixel Dl shown in FIG.
+ Dz lDo # Dl *Energy data corresponding to p4 are stored in memory.

Next, the thermal diffusion calculation circuit 12 is a circuit that preliminarily calculates the value of the energy Ed possessed by each heating element after one scanning line elapses due to thermal diffusion. An example of internal configuration is shown.

In FIG. 4, the thermistor 11 is provided at an appropriate location on the thermal head board once or in plural numbers, and the temperature information TH of the thermal head's substrate which has been sampled at a predetermined period is transferred manually to the ROM table 12Flc at a predetermined period. . The ROM table 12Fifc receives the substrate temperature information Tl input from the thermistor 11 (and the calculation buffer 1
Energy values corresponding to various types of energy Ed during current scanning line recording of the heat generating element No. 0 inputted from 0 are stored, and the stored energy values are calculated based on the relationship between the thermal head substrate and the heat generating element. This is a prediction of the energy value that the heating element can take after a predetermined period of time, taking into consideration the amount of energy radiated due to temperature differences and changes over time until the next scanning line is recorded. However, this value does not take into account the influence of thermal diffusion due to the temperature difference between the heat generating element and a neighboring heat generating element.

The output of the ROM table 12F is input to the adder 12EK.

Next, the subtractor 12 A-D 1 s 12 A-D
2.

12A-Dl and 12A-D4 represent the energy of the heating element DO and the surrounding heating elements Ds #Da *D
g # D Difference from each energy of 4 (can take positive or negative values)'t- respectively and ROM table 12B-
D 1 # 12 B-D 2 # 12 B-D s
e 12 B-D4 and multiplier 12C-Dt, 1
2C-D2112C-Dl*12 Output to C-D4 respectively. ROM table 12B-DI-12B
-Da -12B-Ds112B-D4 respectively store predetermined multiplier values x('0(x(1,)) for calculating the thermal energy state after one scanning line recording cycle, respectively. Subtractors 12A-D, 12A-D, 1
2A-Day Synchronizing with the arithmetic operation of 12A-D4, the stored multiplier values X are sent to the multiplier 12C-Dl.
.

12 CD 2 a 12 CD s * 12
Output to C-D a. Multiplier 12C-DI, 12C
-Dz -12C-D 3 -12 C-D In a,
Subtractor 12A-DI + 12A-Dz e 12A-
Dl # The heating element D output from 12A-D4
The energy of o and the surrounding heating element Dt *D2 *
The difference between each energy of D31D4 and ROM table 12B-DI # 12B-Dz t 12B-Dl
, 12B-04, and output the multiplication results to the adder circuit 12F. As is clear from the above configuration, the value output from the multipliers 12C-D, for example, is determined by the temperature difference between the heating element Do and the adjacent heating element D1 during one scanning line recording period. It shows the amount of thermal energy flowing into and out of the heating element. The same applies to the outputs of the multipliers 12C-D, 12C-Di #120-D4, - the heating element Dz+ during the scanning line recording period;
Each corresponds to the amount of thermal energy flowing in and out of the heating element D0 from DsDa. Addition circuit 12F
is the result of these four multiplications and the ROM table IZF
The addition result Et is input to one input terminal of the adder 8.

That is, from the output of the adder circuit 12E in the thermal diffusion calculation circuit 12, the energy Ed and thermal of the heating element Do at the time of recording the current scanning line are calculated, and the energy Ed and the thermal energy of the heating element Do, which is predicted from the substrate temperature distribution of the heating element Do, are calculated. The heating element DI*Dz*DBI that is close to the energy value during scanning line recording
D4 outputs a value Et which is the sum of the amount of thermal energy flowing in and out of the heating element Do.

The adder 8 receives the output F]t of the thermal diffusion calculation circuit 12 and the output Δ of the applied energy calculation circuit 6 via the AND circuit 7.
E, and the added output is sent to the energy state buffer 4.
output sequentially. The addition output is sequentially input to the energy state buffer 4 as the energy state signal Ed of each heat generating element used in recording the next scanning line, and the storage contents of the energy state buffer 4 are sequentially updated. That is, and times ll! When the supply energy value ΔE for the heating element consisting of 87 during current scanning line recording is output, the thermal diffusion calculation circuit 12 outputs the energy value ΔE for the heating element that is predicted to have during current scanning line recording. The value E obtained by subtracting the thermal diffusion energy during a fixed scanning line recording period
t is output, and the output obtained by adding these values by the adder 8 can be predicted to be the energy value that the heating element has when recording the next scanning line.

Note that the energy state buffer 4, after the thermal head is driven such as when the power is turned on, transfers data to the thermal
An appropriate energy value is initially set based on the output of a thermistor 11 that measures the substrate temperature distribution of the board.

The energy ΔE supplied to the thermal head is sequentially calculated by operating each component of the heat storage correction device having such a configuration in synchronization with the scanning line synchronization signal and the transport lock for each dot, and the driver circuit 13 calculates the energy ΔE supplied to the thermal head. By applying a voltage pulse signal corresponding to ΔE to each heating element of the thermal head, the required heating elements corresponding to the image information are selectively heated to perform suitable recording on the thermal recording medium.

Note that in the above embodiment, the applied energy to be supplied to the heating elements is determined by referring to the heat storage state of the heating elements of the two dots on the left and right sides, but depending on conditions such as high speed and cost, the reference pixel may be changed slightly. The number of reference pixels may be decreased, or if higher precision is required, the number of reference pixels may be increased.

In addition, in this embodiment, the energy constant value B and F2 are stored with values that take into account the resistance value variations of each heating element, and a constant voltage circuit is used to keep the voltage level applied to each heating element constant. The values and calculated values used in each arithmetic circuit 6.12 are also time data, and the application time of the voltage is controlled based on this data so that the amount of heat generated from each heating element is substantially equal. In addition, for example, the values and calculated values used in each arithmetic circuit 6.12 are used as level data, and the i4 pulse level of the pulse signal applied to each heating element is controlled so that the amount of heat generated from each heating element is substantially equal. You can do it like this.

In addition, the duty of high frequency and/or pulse may be changed.

〔Effect of the invention〕

According to the heat storage correction device for a thermal head according to the present invention, precise and accurate heat storage correction can be performed at low cost without using a large memo IJ2 for referring to recorded data, etc. It becomes possible to obtain recorded images with extremely high image quality.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the thermal head heat storage correction device according to the present invention, and FIG. 2 is a diagram showing the recording arrangement. FIG. 3 is the applied energy calculation circuit shown in FIG. FIG. 4 is a block diagram showing an example of the internal structure of the thermal diffusion calculation circuit shown in FIG. DESCRIPTION OF SYMBOLS 1... Peripheral turn buffer, 2... Energy constant number buffer, 3... Subtractor, 4... Energy state buffer, 5.10... Calculation buffer, 6...
Applied energy calculation circuit, 7 rivers and r-), 8...
Adder, 9... Final buffer, 11... Thermistor, 12... Thermal diffusion calculation circuit, 13... Driver circuit, Ll. L2...Line buffer. Figure 1 [1 Figure 2 Figure 3

Claims (3)

[Claims] (1) To thermal configured with multiple heating elements,
The heat storage correction device of the thermal head that corrects the applied energy applied to each heating element of the card according to the heat storage state of each heating element is equipped with a 14.7-fur memory that stores input record data, and a a first storage circuit that separately stores each predetermined target energy value for each heating element to be taken by each heating element in order to obtain uniform density from recording by the element;
a subtraction means for calculating the predicted energy value of the plurality of heat generating elements at each predetermined recording time point for each scanning line; and a subtraction means for performing a predictive calculation of the energy value of the plurality of heat generating elements for each heat generating element, and an output of the subtracting means and an output from the Nofa memory. A first step that calculates and outputs the applied energy value actually supplied to each heating element at each predetermined recording time point of each heating element based on the recorded data, including the thermal influence of the heating element adjacent to each heating element. a second calculation circuit that sequentially predicts and calculates the value of the energy value for each heating element stored in the second storage circuit after one rectangular line recording period has elapsed for each heating element; , sequentially adding the calculation output of the second calculation circuit and the output of the first calculation circuit, and storing the added output in the second storage circuit as the energy value of each heating element at the time of recording the next scanning line. an addition means for inputting and sequentially updating the stored contents of the second storage circuit; and an addition means for sequentially updating the stored contents of the second storage circuit; A thermal storage correction device that includes a driver circuit that supplies heat to the heating element. (2) The first storage circuit stores a target energy value corresponding to the resistance value 1c of each heating element separately for each heating element. correction device. (3) The second arithmetic circuit calculates the relative relationship between the energy state of the heat generating element and the temperature distribution state of the thermal head substrate, and the energy state of the heat generating element and the energy state of the heat generating element adjacent to the heat generating element. The thermal storage correction according to claim (1), characterized in that the energy value stored in the second storage circuit is a value after one scanning line recording cycle has elapsed based on the relative relationship with the energy value. Device.