JP3016110B2 - Control method of thermal head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal transfer recording apparatus, and more particularly to a method for controlling a thermal head.

[0002]

2. Description of the Related Art In general, thermal heads used for thermal transfer recording have variations in the resistance values of a plurality of heating resistors arranged in a line, and (1) average head resistance value and (2)
And the resistance value in the head.

[0003] The former head average resistance value indicates the average resistance value of all dots, and the variation thereof is, for example, 1%.
100Ω ± 15%, ± 15% of reference value (specification)
There is also variation. This value is directly used as a density difference between the thermal transfer recording apparatuses.

Therefore, in order to eliminate the density difference between the devices, conventionally, based on the average resistance value written on each head, the applied voltage is calculated from the thermal energy E = (V ² / R) · t. Or adjust the heat generation time to compensate for the difference in density (Japanese Patent Publication No. Sho 6
JP-A-3-4933, JP-A-60-54870). The same applies when a plurality of heads are used with one power supply.

On the other hand, the variation (dR / R) of the resistance value in the head is a variation in the resistance value of the heating resistor in the thermal head, and is ± 12% (−) with respect to the average resistance value. 12% ≦ dR / R ≦ + 12%). This causes density unevenness in the main scanning direction, and in particular, when gradation expression is performed, the image quality is significantly reduced. Specifically, as shown in FIG. 8B, it appears as a vertical streak.

Therefore, conventionally, the ratio of each dot is obtained from the average resistance value or the maximum resistance value of all the dots, and density unevenness is corrected by outputting data obtained by multiplying the output planned data by this value at the time of printing. .

[0007]

However, when all the dots of the heating element are not used in printing an image, a difference occurs between the average resistance value written on the thermal head and the average resistance value of the dots used. Density differences also occur depending on the density difference between the thermal transfer recording apparatuses and the dot range used. For example, as shown in FIG. 8A, a density difference occurs between images A and B having different use ranges.

In the case of density unevenness correction in the main scanning direction of the head, the 8-bit data has 255 gradations, but ± 12%
, The expression for ± 30 gradations cannot be performed. Then, the head of the curve A1 shown in FIG.
With the head No. 1, a density difference appears even if the average resistance value b0 is the same.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide a method of controlling a thermal head which performs more accurate correction than conventional correction when all the heating element dots are not used.

[0010]

In order to achieve the above object, a method for controlling a thermal head according to the present invention uses resistance data of a heating element of each dot of a thermal head stored in a memory in advance and uses the data for printing. From the range information of the heating element to be used, the maximum resistance value of the heating element in the usage range is searched, and the ratio of the resistance value of each heating element to this maximum resistance value is obtained and stored. And data obtained by multiplying the output scheduled data by the ratio value (claim 1).

Another aspect of the thermal head control method according to the present invention is a method of controlling the resistance value data of the heating element of each dot of the thermal head, the range information of the heating element used for printing, stored in a memory in advance. From this, the average resistance value of the heating elements in the range of use is determined, the ratio of the resistance value of each heating element to this average resistance value is determined and stored. And outputs the data (claim 2).

[0012] In any of the above embodiments, a one-gray-scale strobe width for a heating time when the applied voltage is constant is determined from the maximum resistance value or the average resistance value. It is possible to determine the applied voltage when it is constant (claim 4).

[0013]

According to the first aspect of the present invention, in FIG. 1A, the maximum resistance value b of the dot within the use range is obtained by obtaining the range information a of the dot used for the current printing. The ratio d (d = c / b) of each resistance value c within the use range a to the resistance value b is obtained and stored. Then, based on the heat energy E = (V ² / R) · t, at the time of printing, data (ed) obtained by multiplying the output scheduled data e by the ratio value d is output.

Conventionally, as shown in FIG. 1 (b), since the maximum resistance value b ₀ for all bits is obtained, the maximum correction amount y ₀ of the resistance value is relatively large, and the waste amount corresponding to the hatched portion f is wasted. Occurs.

On the other hand, in FIG. 1A, such waste does not occur. That is, when all the dots of the heating element are not used for printing an image, the use range a is specified and the maximum resistance value is searched. It can be eliminated, and it is not necessary to reduce the gradation data unnecessarily. Accordingly, a high quality print image with less density unevenness in the main scanning direction than in the related art can be obtained.

According to the second aspect of the present invention, in FIG. 2, by obtaining the range information a of the dot used in the current printing, the average resistance value g of the use range of the dot within the use range is obtained. The ratio h (h = c / g) of each resistance value c within the use range a to the value g is determined and stored. Then, based on the heat energy E = (V ² / R) · t, at the time of printing, data (e · h) obtained by multiplying the output scheduled data e by the ratio value h is output.

In the prior art, as shown in FIG. 2, since the average resistance value g ₀ for all bits is obtained, waste as shown by a hatched portion f occurs. In addition, when not using all the heating element dots for printing an image, there is a difference between the average resistance value written on the thermal head and the average resistance value of the dots to be used. Density differences also occur depending on the range, but these are accurately corrected.

According to a third aspect of the present invention, one gradation strobe width is determined from a maximum resistance value or an average resistance value in a use range, and in the fourth aspect, an applied voltage is changed. Even when a plurality of heads are used, the density at 100% is constant (E = V ²
/ R · t).

In the present specification, in the case of thermal transfer recording, thermal recording in which recording is performed by the chemical change of the recording paper itself due to heat generation, thermal recording using thermal fusion transfer paper, and sublimation transfer paper are used. Includes thermal sublimation type thermal recording, and all other types of recording by applying heat.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 3 shows a hardware configuration of a thermal transfer recording apparatus for printing a color image or the like on a card. In the figure, the CPU 10 and the DSP 13 share one memory 20, and can be read and written from both the CPU 10 and the DSP 13. This shared memory 2
0 is an address area for storing the dot number of the “start” of the used dot, an address area for storing the dot number of the “stop” of the used dot, and the average resistance value data or the resistance value of each dot with respect to the maximum resistance value. It has an address area for storing the ratio, that is, the “ratio”. CPU1
0 and the DSP 13 are connected by an I / O port line 18, so that a ready signal and a print start signal can be controlled.

The DSP 13 is a digital signal processor capable of processing at a higher speed than a normal CPU.
To communicate with the user to know the use range information and the print mode.

The image data is once stored in the frame memory 11, and at the start of printing, the data is transferred line by line to the first line memory 12 ("line memory 1").

The DSP 13 reads and calculates the data in the first line memory 12 at the start of printing, and writes the result in the second line memory 14 ("line memory 2"). The data written in the second line memory 14 is transferred to a P / S (parallel / serial) conversion circuit 16 by a timing generation circuit 15, and the data converted to serial data by the P / S conversion circuit is Input to the thermal head 17.

Reference numeral 21 denotes a resistance ROM in which resistance values of all dots of the heating element of the thermal head 17 are sequentially stored. Table 1 below exemplifies the stored contents of the resistance ROM 21.

[0026]

[Table 1]

(Embodiment 1) In this embodiment 1, the maximum resistance value of the use range is retrieved by obtaining the range information of the dots used in the current printing, and the 1-gradation strobe width is determined from this value. (The applied voltage may be changed).
The maximum resistance value is set to 100%, and the ratio to the other resistance values is calculated and stored. Energy = (V ² / R) · t
Thus, at the time of printing, data obtained by multiplying the output scheduled data by this ratio value is output.

A description will be given according to the control procedure shown in FIG. (1) First, the DSP 13 obtains use range information as follows (step (1)). The CPU 10 sets the flag of the use range information, and writes the start dot number and the stop dot number in a predetermined address area of the shared memory 20. The correspondence between the address of the shared memory 20 and the data content is known, and for example, address 0 is defined as the start of the used dot and address 1 is defined as the stop of the used dot. The DSP 13 reads the data of the addresses 0 and 1 to know the “use range” of the heating element.

(2) Find the maximum value of the resistance of the dots used.
That is, the DSP 13 utilizes the total dot resistance value stored in the resistance value ROM 21 in advance and the use range information,
The maximum value of the resistance of the dot in the use range is obtained (step (2)). The maximum value is obtained by reading and comparing the data from the resistance value ROM 21 for each dot from the above use range, and is written to a predetermined address of the shared memory 20.

The CPU 10 reads the content (the maximum value of the resistance in the use range) written in the shared memory 20 and determines the strobe width of one gradation based on the value.

That is, when E = (V ² / R) · t, V
Is a constant voltage (here, 10 V), and R is the maximum resistance value to find the value of t. This is nothing but determining the heat energy E of one gradation. The same is true even if V is varied while t is kept constant.

The heat energy E is determined according to the specifications of each head. In FIG.
Ω, 10 μS, the same heat energy E is 1
0V, 900Ω, 9μS, 10V, 1100Ω, 11
can be obtained in μS.

Therefore, if the thermal energy E of one gradation is determined by the strobe width in this manner, even if the printing is partially performed by the same head, the density difference can be eliminated.

(3) Next, the data is developed into "ratio" data and stored in the memory. That is, the ratio of each dot is obtained from the maximum value and stored in the shared memory 20 (step (3)).

The ratio is obtained by calculating the ratio of the resistance value of each dot to the maximum resistance value data, that is, (resistance value of each dot in the use range) / (maximum resistance value). For example,
When the maximum resistance value is 100Ω, the resistance value of the n-th dot is 90
For Ω, the ratio is 0.90. Similarly, the “ratio” is obtained as shown in Table 2.

[0036]

[Table 2]

This ratio is a correction factor for correcting output so as not to cause density unevenness in the main scanning direction, that is, for eliminating vertical streaks, due to variations in resistance values in the head (variations in resistance values of dots). Used as

(4) A preparation OK signal is output to the CPU (step (4)). (5) Wait for a print start signal and start printing (step (5)). (6) Data for each dot is obtained, calculated with ratio data corresponding to the dot, and output (step (6)).

The correction is performed by multiplying the output scheduled data by the above ratio, and the result is used as output data.
For example, if the data (gradation value) of the n-th dot is “100”, “90” data is output from 100 × 0.9. If the data of the (n + 1) th dot is “200”, “19”
Correction is performed by outputting data "0".

This is correction control for eliminating unevenness in density in the main scanning direction due to variation in resistance value in the head (variation in resistance value of each dot), that is, vertical streaking.

Specifically, the resistance value of each dot “110”
Assuming that the ratios “1.0”, “0.91”, “0.82”, “0.73”,... In “0”, “1000”, “900”, “800”,.
0 "" 91 "" 82 "" 73 "... The total output (W) of the thermal energy at this time becomes the same value for each dot, for example, 0.1 mW as shown in Table 3.

[0042]

[Table 3]

(7) It is checked whether one line has been completed, that is, whether the work for one line has been completed (step (7)). (8) Clear the dot pointer, that is, reset flags and the like for the next line (step (8)). (9) Check whether printing is completed (step (9)).

(10) When printing is completed, flags such as use range information are cleared, and the next printing is performed (step (1)
0)).

(Embodiment 2) In this embodiment, instead of obtaining the maximum resistance value in the above-mentioned use range, the average resistance value in the use range is obtained, and the one-gradation strobe width is determined from this value. Then, the average resistance value is set to 100%, and the ratio to the other resistance values is calculated and stored. Then, at the time of printing, data obtained by multiplying the output schedule data by this value is output.

A description will be given according to the control procedure of FIG.

(1) First, use range information is obtained from the CPU 10 as follows (step (1)).

In the shared memory 20, the start dot number and the stop dot number are written by the CPU 10 in the predetermined address area, and the DSP 13 knows the "use range" of the heating element by reading them.

(2) Find the average value. That is, the resistance value R
Based on the total dot resistance value stored in the OM 21 and the range information, an average value of the use range is obtained (step
(2)).

This average value is obtained by adding the resistance values within the range of use in the resistance ROM 21 and dividing by the number of dots. For example, if the contents of the resistance ROM 21 are as shown in Table 1 above, if the range using 2 to 4 dots is (110 + 120 + 130) / 3 = 12
Assuming 0, the average resistance value is determined to be 120Ω.

(3) The ratio data is developed and stored in the memory. That is, the ratio of each dot is obtained from the above value and stored in the memory (step (3)). The ratio is obtained as a ratio of the resistance value of each dot to the average resistance value data.

The DSP 13 performs the above calculation to obtain an average resistance. Then, the average value data is written to a predetermined address of the shared memory 20. This allows the CPU
10 reads the average value data. This value allows the CPU
10 determines the strobe width (or applied voltage).

Steps (4) to (10) are the same as those already described.

According to the first and second embodiments, the following effects can be obtained.

Since the gray scale strobe width is determined by the maximum resistance value and the average resistance value in the use range, the same thermal head can be used in any range or any thermal head. Even when a plurality of heads are used, the density at 100% is always constant from E = (V ² / R) · t.

By designating the range of use, it is possible to eliminate a useless correction area, and it is not necessary to reduce the gradation data unnecessarily, so that a high quality print image can be obtained.

In practice, there is no difference in density between the apparatuses, and the gradation expression power is enhanced by eliminating useless correction areas.

[0058]

In summary, according to the present invention, the following excellent effects can be obtained.

(1) According to the first or second aspect, when all dots of the heating element are not used for printing an image, the use range a is designated and the maximum resistance value or the average resistance value is searched or calculated. Therefore, the conventional useless correction area f can be eliminated, and the grayscale data does not needlessly be reduced. Therefore, it is possible to obtain a high-quality print image in which density unevenness in the main scanning direction is eliminated as compared with the related art.

(2) According to the second aspect, as shown in FIG. 6, for the resistance curves A1 and B1 having completely opposite slopes, two appropriate different average resistance values RA in the present use range a, respectively. , RB are obtained, so that an error in the case of processing with one common average resistance value B0 as in the case of the conventional FIG. 7 is eliminated.

(3) According to the third aspect, the strobe width of one gradation is determined from the maximum resistance value or the average resistance value in the use range. In the fourth aspect, since the applied voltage is changed, which range or which thermal head is used , Or using a plurality of heads, the concentration at 100% is constant.

[Brief description of the drawings]

FIG. 1 is a diagram provided for describing one control method of the present invention;
(A) is a diagram showing a method of the present invention, and (b) is a diagram showing a conventional method.

FIG. 2 is a diagram provided for describing another control method of the present invention.

FIG. 3 is a diagram showing a configuration of a thermal transfer recording apparatus embodying the control method of the present invention.

FIG. 4 is a flowchart showing a printing procedure of the apparatus of FIG. 3;

FIG. 5 is a diagram showing a relationship between time and a resistance value when a strobe width of one gradation is determined with a constant voltage.

FIG. 6 is a diagram showing how an average resistance value is obtained for each of two resistance value curves according to the present invention.

FIG. 7 is a diagram showing a state in which one average resistance value is obtained for two resistance value curves according to the related art.

FIG. 8 is a diagram illustrating a state in which a density difference occurs due to a variation in a resistance value of a head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 CPU 11 Frame memory 12 1st line memory 13 DSP 14 2nd line memory 15 Timing generation circuit 16 P / S conversion circuit 17 Thermal head 18 I / O port line 20 Shared memory 21 Resistance ROM

Claims (4)

(57) [Claims] 1. A maximum resistance value of a heating element in a use range is searched from resistance value data of a heating element of each dot of a thermal head stored in a memory in advance and range information of a heating element used for printing. The ratio of the resistance value of each heating element to the maximum resistance value is determined and stored, and at the time of printing, data obtained by multiplying the output scheduled data by this ratio value for each dot is output. Control method. 2. An average resistance value of a heating element in a use range is obtained from resistance value data of a heating element of each dot of a thermal head previously stored in a memory and range information of a heating element used for printing. Controlling the thermal head, wherein the ratio of the resistance value of each heating element to the average resistance value is obtained and stored, and at the time of printing, data obtained by multiplying the output scheduled data by this ratio value for each dot is output. Method. 3. A strobe width of one gradation for a heat generation time when an applied voltage is fixed is determined from the maximum resistance value or the average resistance value.
The control method of the thermal head described in the above. 4. The thermal head control method according to claim 1, wherein an applied voltage when the heating time is fixed is determined from the maximum resistance value or the average resistance value.