JPH1178094A - Driving method for thermal head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress density variation due to temperature fluctuation in the recording of one line. SOLUTION: Multiple heating elements are divided one-by-one into first and second groups alternately in a main scanning direction. A time period of one line recording for recording dots of one line is divided into equal two parts and the two parts of the recording time periods are designated as first and second sub-line recording time periods. A bias pulse is applied to the first group of heating elements during the first sub-line recording time period and a gradation pulse is applied thereto in the second sub-line recording time period. The bias pulse is applied thereto during the entire sub-line recording time period. As either the first or second groups of the heating elements is heated by the bias pulse, the heating elements are not simultaneously cooled so that the temperature fluctuation in the recording of one line can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a thermal head, and more particularly, to a method for driving each heating element of a thermal line printer.

[0002]

2. Description of the Related Art Thermal printers include a thermal transfer printer and a thermal printer. The former thermal transfer printer has
There are a fusion type and a sublimation type. In these, an ink film is superimposed on a recording material, and a thermal head is pressed from behind the ink film and heated to transfer the ink of the ink film to the recording material. In the latter thermal printer, the thermal recording material is heated by a thermal head, and the thermal recording material is colored to perform thermal recording. These thermal heads have a heating element array in which a large number of heating elements (resistance elements) are arranged linearly in the main scanning direction, and a driver for driving each heating element. Then, the recording material is fed in a sub-scanning direction orthogonal to the main scanning direction, and thermal recording is performed line by line.

When thermal recording is performed by a thermal printer using a thermal head in which a large number of heating elements are arranged in a line as described above, as shown in FIG. At the same timing, a bias pulse B and a grayscale pulse K are provided subsequently thereto. The bias pulse B is for applying heat energy to the thermosensitive coloring layer immediately before coloring, and the gradation pulse is for applying heat energy for gradation expression so as to have a gradation level corresponding to image data. . As the bias pulse B and the gradation pulse K, a single pulse (continuous energization) having a large pulse width is used, and a pulse train including a large number of pulses is used.

[0004]

In order to uniformly apply a bias pulse to all the heating elements as described above, FIG.
As shown in (B), the average temperature of the entire thermal head during one-line recording changes, and the change width also increases. Due to the temperature fluctuation during the thermal recording of this one line, (C)
As shown in (1), the coefficient of friction between the heating element and the recording material fluctuates, and the load of the recording material transport system fluctuates accordingly. For example, the higher the applied thermal energy, the higher the surface temperature of the heating element, and thus the lower the coefficient of friction. The coefficient of friction increases as the thermal energy decreases. This is due to the fact that the temperature of the surface coating layer of the recording material rises due to the pulse and the state of the surface changes.
Therefore, since the coefficient of friction between the thermal head and the recording material changes, the force applied to the recording material conveyance force transmission system, the head holding portion, and other structural systems fluctuates, and slight deformation of the mechanical portion occurs. The amount will vary depending on the image to be recorded. This change in the amount of deformation appears as a change in the feed amount of the recording material, and the feed speed changes as shown in FIG. Therefore, the applied amount of the heat energy per unit area changes depending on the unevenness of the feed speed, so that the unevenness of the density occurs.

For this reason, it has been studied to reduce the number of heating elements that generate heat at the same time and to disperse the heat. For example, Japanese Patent Application Laid-Open No. 63-275268 describes a thermal recording apparatus in which heating elements for one line are divided into a group in which the heating elements are thinned out at equal intervals and another group, and each group is heated in a different time zone. . In this thermal recording apparatus, the heating elements of each group are alternately arranged as compared with the conventional apparatus in which the heating elements for one line are simply divided into two right and left parts.
The temperature distribution of the thermal head in the main scanning direction becomes uniform, and it is possible to eliminate a difference in color density based on the temperature difference. However, since the uniformity of the temperature distribution in the sub-scanning direction is not sufficiently considered, there is a problem that the temperature fluctuation in the sub-scanning direction during one-line printing cannot be suppressed efficiently. In particular, when printing a low-density portion, a period occurs in which all the elements are cooled at the same time, and the temperature in the sub-scanning direction during one-line printing tends to fluctuate.

Further, Japanese Patent Application Laid-Open No. 6-270454 discloses a thermal intermediate recording method using an area gradation method. In this heat-sensitive intermediate recording method, the recording start position of a pixel is set to a fixed amount, for example, 1 /
It is shifted by eight so as to suppress the generation of lines (streak-like noise) in the main scanning direction caused by the connection with adjacent pixels. However, even in this thermal recording method, when printing a low density portion, a period occurs in which all the elements are simultaneously cooled, and the temperature in the sub-scanning direction during one-line recording tends to fluctuate.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and the temperature fluctuation in the sub-scanning direction during one-line printing is made gentle to change the friction coefficient between the recording material and the heating element based on the temperature fluctuation. It is an object of the present invention to provide a method of driving a thermal head, which suppresses the occurrence of density unevenness due to uneven feed speed caused by frictional fluctuation.

[0008]

To achieve the above object, a method of driving a thermal head according to claim 1 is provided.
Many heating elements are divided into N (N ≧ 2) groups,
These are referred to as first to N-th groups, one-line recording time for recording dots for one line is divided into N equal parts, and these recording times are referred to as first to N-th sub-line recording times.
A bias pulse and a gradation pulse following the bias pulse are applied to the heating elements of the first group from the start position of the recording time of the first sub-line, and the heating elements of the second group are given the second pulse.
A bias pulse and a gradation pulse are successively applied from the start position of the recording time of the sub-line, and the bias pulse is applied in the entire period of one sub-line recording time. It is preferable that the grouping is performed so that the number of the heating elements is substantially equal, and the heating elements of each group are alternately arranged in an appropriate number in the group order. In addition, it is preferable that the grouping be performed for each driver IC for driving a certain number of heating elements. Further, the heat-sensitive recording material includes first to third heat-sensitive coloring layers in order from at least the surface layer side.
It is preferable that the heat-sensitive coloring layer develops any one of yellow, magenta, and cyan, and that the heat-recording pattern determined by the group and the sub-line printing time is changed for each heat-sensitive coloring layer. Further, it is preferable that the number of divisions N be changed for each thermal recording of each thermosensitive coloring layer, and that the number of divisions be smaller as the thermosensitive coloring layer is deeper.

According to a sixth aspect of the present invention, there is provided a method for driving a thermal head, wherein a large number of heating elements are alternately divided by a fixed number in the main scanning direction into first and second groups to record dots for one line. The one-line recording time is divided into two equal parts, and these recording times are defined as first and second sub-line recording times. A bias pulse is applied to the heating elements of the first group during the first sub-line recording time. 2
A gradation pulse is applied to the sub-line recording time, and a gradation pulse is applied to the heating elements of the second group at the first sub-line recording time and a bias pulse is applied to the second sub-line recording time. This is provided for the entire recording time.

In the method of driving a thermal head according to the present invention, a number of heating elements are divided into four groups so as to be substantially equally divided, and these are divided into first to fourth groups. The elements are arranged so that an appropriate number of elements are arranged in the group order. The one-line recording time for recording one line of dots is divided into four equal parts, and these recording times are divided into first to fourth sub-line recording times. The gradation pulse is divided into first and second gradation pulses in units of one sub-line recording time, and in the first sub-line recording time,
Any one of the application of the bias pulse, the application of the first gradation pulse, the application of the second gradation pulse, and the cooling period is assigned to the heating elements of the first to fourth groups, and the second subline recording time and thereafter Then, the first gradation pulse is applied to the heating elements of the group to which the bias pulse is applied in the previous subline recording time, and the second gradation pulse is applied to the heating elements of the group to which the first gradation pulse is applied. , A cooling period for the heating elements of the group to which the second gradation pulse is applied,
A bias pulse is applied to the heating elements of the group that has been in the cooling period, and the bias pulse is applied during the entire period of one subline recording time.

According to a tenth aspect of the present invention, in the method of driving a thermal head, the number of divisions N is set at the time of thermal recording of each thermosensitive coloring layer.
In the first thermosensitive coloring layer on the surface side, P was set, in the second thermosensitive coloring layer, Q was set, and in the third thermosensitive coloring layer, R was set (provided that P>Q> R, P ≧ 5). It is preferable that the grouping of the large number of heating elements is performed for each driver IC for driving a fixed number of heating elements. Further, it is preferable to change the thermal recording pattern determined by the group and the sub-line recording time for each thermal recording of each thermosensitive coloring layer.

[0012]

When recording one line, for example, when the number of heating elements is two,
When divided into two groups, as shown in FIG. 2A, the recording time of one line is also divided into two equal parts, and these are defined as first and second sub-lines. Then, a bias pulse is applied to the heating elements of the first group (odd group) from the recording start position of the first sub-line, and subsequently, a gradation pulse is applied from the recording start position of the second sub-line. Further, to the heating elements of the second group (even group), a gradation pulse is applied from the recording start position of the first sub-line, and then a bias pulse is applied at the recording start position of the second sub-line. Moreover, the bias pulse is given during the entire recording time of the sub-line,
In addition, since the bias pulse is alternately applied to the first and second groups, any one of the heating elements is always bias-heated in the entire thermal head, so that all of the heating elements do not simultaneously enter the cooling period. . Therefore,
As shown in (B), the temperature fluctuation in the sub-scanning direction of the entire thermal head during one-line printing becomes gentle.
As a result, as shown in (C), the fluctuation of the coefficient of friction between the recording material and the heating element due to the temperature fluctuation can be made gentle. Therefore, as shown in (D), the occurrence of unevenness in the feeding speed of the recording material due to the change in the friction coefficient is eliminated, and the occurrence of unevenness in density due to the unevenness in the feeding speed is suppressed. Similarly, even when the heating elements are divided into three or more groups, any one of the heating elements is always bias-heated in the entire thermal head during one-line recording, so that all the heating elements simultaneously enter the cooling period. In the same manner, temperature fluctuation in the sub-scanning direction during one-line printing is suppressed, and the occurrence of density unevenness due to this is suppressed. Further, by dividing a large number of heating elements into groups of driver ICs for driving a fixed number of heating elements, control is further simplified.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 showing a color thermal printer, a color thermal recording material (hereinafter simply referred to as a recording material) 10 is fed by a feed roller pair 11 in a printing direction indicated by an arrow A1 and a pullback direction indicated by an arrow B1. Is reciprocated. The feed roller pair 11 is rotated by a pulse motor 12. The rotation of the pulse motor 12 is controlled by a system controller 13 via a motor driver 12a.

As shown in FIG. 3, a recording material 10 is provided on a support 5 by a cyan thermosensitive coloring layer 6, a magenta thermosensitive coloring layer 7 having a light fixing property by ultraviolet rays of approximately 365 nm, and a purple visible light beam of approximately 420 nm. A yellow thermosensitive coloring layer 8 having a light fixing property and a protective layer 9 are sequentially provided.
These thermosensitive coloring layers 6 to 8 are arranged in order from the surface layer in the order of thermal recording. In FIG. 3, each thermosensitive coloring layer 6
In order to make it easier to understand, the yellow thermosensitive coloring layer 8
, "M" for the magenta thermosensitive coloring layer 7, and "C" for the cyan thermosensitive coloring layer 6. Although not shown in FIG. 3, an intermediate layer for adjusting the thermal sensitivity of the magenta thermosensitive coloring layer 7 and the cyan thermosensitive coloring layer 6 is formed between the thermosensitive coloring layers 6 to 8. An opaque coated paper or a plastic film is used as the support 5, and a transparent plastic film is used when an OHP sheet is produced.

FIG. 4 shows the coloring characteristics of each thermosensitive coloring layer. In the recording material 10 of this embodiment, the coloring heat energy of the yellow thermosensitive coloring layer 6 is the lowest, and the coloring heat energy of the cyan thermosensitive coloring layer 8 is the highest. When the yellow (Y) pixel is thermally recorded, the color thermal recording material 10 is provided with coloring thermal energy obtained by adding gradation thermal energy GY _J to bias thermal energy BY. This bias heat energy B
Y is thermal energy immediately before the yellow thermosensitive coloring layer 6 develops a color, and is applied to the color thermosensitive recording material 10 during a bias heating period at the beginning of recording of one pixel. The gradation expression heat energy GY _J is determined according to the gradation level J corresponding to the color density of the pixel to be recorded, and is applied to the recording material 10 during the gradation expression heating period following the bias heating period. Can be Since the same applies to magenta M and cyan C, only symbols are given.

As shown in FIG. 1, the recording material 10 is reciprocated by the feed roller pair 11, and in the first feed in the printing direction A1, the recording material 10 is moved by the thermal head 14.
A yellow image is recorded on the image. A magenta image is sequentially recorded in the second transport, and a cyan image is sequentially recorded in the third transport. Thus, a full-color image is recorded by three-color surface sequential recording. The thermal head 14 has a heating element array 15 on the lower surface thereof, and a platen roller 16 is pressed to the heating element array 15 via the recording material 10.

The heating element array 15 is shown in FIG.
As shown in FIG.₁~ 15_nIs in the main scanning direction
They are arranged in a line. Each heating element 15₁~
Fifteen _nConsists of resistive elements, each of which generates heat.
Element 15₁~ 15_nIs the color developed when one pixel is thermally recorded.
Depending on the bias heat energy for heating up to just before and the color density
Is applied to the recording material 10.

As shown in FIG. 1, a yellow fixing lamp 17 and a magenta fixing lamp 18 are sequentially arranged downstream of the feed roller pair 11 in the feed direction. The yellow fixing lamp 17 has an emission peak of 420 n.
m magenta fixing lamp 1
8 emits ultraviolet light having an emission peak near 365 nm. For example, during yellow image recording, the yellow fixing lamp 17 is turned on, and the yellow thermosensitive coloring layer immediately after thermal recording is optically fixed. When recording a magenta image, the magenta fixing lamp 18 is turned on, and the magenta thermosensitive coloring layer immediately after the thermal recording is optically fixed.

As shown in FIG. 1, R (red), which constitutes color image data, is stored in a frame memory 20 from an external device such as a personal computer or a digital still camera (not shown).
G (green) and B (blue) signals are written in a state of being separated for each color. The memory controller 21 reads one line of image data from the frame memory 20 and sends it to the color conversion unit 22. The color conversion unit 22 converts the thermosensitive coloring layers into yellow, magenta, and cyan image data based on the image data from the frame memory 20 in order to develop each thermosensitive coloring layer into a density and a color corresponding to the color image data. For example, when printing a yellow image, the image data is converted into one line of yellow image data,
Send to

The color correction section 23 performs color correction by adding the color correction data input from the system controller 13 and, for example, yellow image data from the color conversion section 22, and converts the color corrected yellow gradation data. The data is written into the gradation line memory 24. The gradation data is variable data of “00 _H ” to “FF _H ” according to the image data.

The bias data for one line is written into the bias line memory 25 by the memory controller 21. This bias data is fixed data of “FF _H ”.

The first switching circuit 26 alternately reads data from the bias line memory 25 and the gradation line memory 24 for each pixel, and writes the data to the first and second sub-line line memories 27 and 28. Thus, as shown in FIG. 6 (A), the first subline line memory 27, B from the first heating element 15 ₁ in order, K
_{2J, B, K 4J, B} , K 6J, ··· B, K nJ is written. The numbers in the subscripts represent the numbers of the heating elements, and J represents the gradation level. Further, as shown in FIG. 6 (B), the second subline line memory 28, the first heating element 15 ₁ from the order _{K 1J, B, K 3J,} B, K 5J, B ··
・ K _{(n-1) J} and B are written. The second switching circuit 29 reads and switches the first and second line memories 27 and 28 every ラ イ ン line (one subline), and sends the read print data to the thermal head driver 30.

As shown in FIGS. 7 and 8, the thermal head driver 30 includes a shift register 31, a down counter 32, a latch array 33, an AND gate array 34,
And the transistor 35, and is incorporated in the substrate of the thermal head 14. Shift register 3
1 is 8 for one line from the first switching circuit 29
Bit printing data is shifted by a dot shift clock signal, and this is preset in a down counter 33 provided for each heating element. For printing data, for example, in the case of a bias pulse, “FF _H ” is set,
In the case of the gray scale pulse corresponding to the image data "00 _H" -
The variable data of “FF _H ” is set. Note that assigns remaining "80 _H" - "FF _H" in the cooling period as a variable data to be allocated to the tone pulses, for example, up to "00 _H" - "7F _H" in the case of providing a cooling period.

The down counter 32 is provided with a shift register 3
The count clock signal is counted down from the value preset by 1. This down count is started by a load signal from the system controller 13. Then, when the count value becomes “0”, a borrow signal is output to the reset terminal of the latch array 33. If the print data “FF _H ” for the bias pulse is preset in the down counter, the load signal is input before the count value becomes “0”.
The borrow signal is not output to the reset terminal of the latch array 33. In the case of print data for a gradation pulse, any one of “00 _H ” to “FF _H ” is preset, and when the count value reaches the preset value, a borrow signal is output from the latch array 33. Output to the reset terminal.

A set signal is input to the latch array 33 from the system controller 13. This set signal is input to the set terminal of the latch array 33 every time one line starts recording. The borrow signal is input to the reset terminal of the latch array 33. Therefore, the latch array 33 outputs the latch signal from the input of the set signal to the input of the AND gate array 34 until the input of the borrow signal.
Send to

The AND gate array 34 outputs an "H" signal when the latch signal is "H" during a period in which the enable signal from the system controller 13 is being input. A transistor 35 is connected to each output terminal of the AND gate array 34. These transistors 35 are turned on when the output of the AND gate array 34 is "H". The transistor 35 includes a heating element 15 ₁
To 15 _n are connected in series. The head power supply circuit 36 is connected to the heating elements 15 ₁ to 15 _n. Thus, the heating elements 15 ₁ to 15 _n are successively energized based on the data for printing, thereby the bias heat energy and the gradation thermal energy is applied to the heat-sensitive coloring layer, dots having a density corresponding to the image data recording material Recorded at 10. FIG. 8 shows this thermal head driver 30.
4 shows a timing chart of the above operation.

The first sub-line line memory 27 and the second
The printing data for one line written in the sub-line memory 28 is switched for each sub-line recording and sent to the thermal head driver 30, so that each heating element 15 ₁ as shown in FIG. A heat generation pattern of n15 _n is obtained. The heating elements of the even-numbered groups to which the gradation pulse K is assigned in the first sub-line in the printing of the first line do not develop color because they are not bias-heated immediately before. However, since only the first line is used, the image quality is deteriorated. There is no effect. If it is desired that the even-numbered heating elements also be colored from the first line, a dummy line may be provided before the first line, and bias thermal energy may be applied here.

The heat generation pattern is shown in FIG.
The pattern shown in FIG. The minimum unit of this heat generation pattern is indicated by a thick dotted line. In magenta printing, the pattern shown in (C) is selected, and in cyan printing, the pattern shown in (D) is selected. “B” is applied to the bias heating process, and “K” is applied to the gradation heating process.
Is filled in. During yellow recording, the odd-numbered heating elements are driven by a bias pulse B and a gradation pulse K as shown in FIGS. Further, the even-numbered heating elements are driven by pulses B and K as shown in FIGS. As a result, FIG.
As shown in (B), when recording the first sub-line,
Bias thermal energy is applied to the odd-numbered heating elements, and gradation thermal energy is applied to the even-numbered heating elements. When recording the second sub-line,
Gradation heat energy is applied to the odd-numbered heating elements, and bias heat energy is applied to the even-numbered groups.

Therefore, during the recording of one line, the heating elements of either group are bias-heated without fail, and as shown in FIG. As compared with the case where all the heating elements shown in (B) are driven simultaneously, the fluctuation is made gentle. As a result, as shown in FIG. 2C, a change in the coefficient of friction between the heating element and the recording material due to the temperature change can be suppressed. Accordingly, the variation in the transport load is suppressed, and as shown in FIG. 2 (D), the uneven feeding is reduced, so that the occurrence of density unevenness due to the uneven feeding can be effectively suppressed. Incidentally, in the case of cyan recording, the recording is performed at a higher temperature than in the recording of other colors, and since the yellow recording and the magenta recording have already been completed, the surface of the recording material is smoothed by these thermal recordings. The feed rate unevenness caused by temperature fluctuations does not occur much,
As in the conventional pattern, all the heating elements are bias-heated at the same time in the first sub-line, and then gradation heating is performed. Of course, the temperature fluctuation during one-line printing may be suppressed by using the first or second heat generation pattern.

Since the bias heating is performed during the entire sub-line recording time and the continuous energizing method is used, shading correction for bias heating and resistance value variation correction of the heating element can be performed by changing the energizing time. Heat history correction (heat storage correction) cannot be performed, but in this case, the applied heat energy can be changed by changing the drive voltage in the head power supply circuit 36 according to the correction value. When bias heating is performed by a pulse train composed of a large number of pulses, the amount of heat generated is controlled by changing each pulse width in addition to changing the thermal head drive voltage. Various corrections for the bias heating may be performed on the gradation heating side.

Next, an embodiment in which each heating element is divided into four groups will be described. In this case, the recording time of one line is divided into four equal parts, divided into four sub-line recording times, and bias heating, first gradation heating, second gradation heating, and cooling periods are assigned to each sub-line. . And
For the sub-line on which the bias heating is performed, fixed data of “FF _H ” is given during the entire period. Further, with respect to the sub-line to perform image heating, "000 _H" - "1FF _H"
The variable data is divided by "00 _H" - "FF _H" units,
The variable data of “000 _H ” to “0FF _H ” is given by the first gradation heating, and the remaining “100 _H ” to “1 F” by the second gradation heating.
F _H ”. Also, fixed data of “00 _H ” is given to the sub-line to be cooled.

FIGS. 9A and 9B illustrate a heat generation pattern when the heat generating element is divided into four parts. FIG. 9B shows a pattern for yellow recording, FIG. 9C shows a pattern for magenta recording, and FIG. 9D shows a pattern for cyan recording. . In the present embodiment, the heat generation pattern is changed for each recording of each color, thereby changing the arrangement of the bias heating portion. For example, as shown in (B), during the recording period of the first sub-line, each heating element of the first group is bias-heated, and a cooling period in which each heating element of the second group is not heated is set to a third period. Each of the heating elements in the group is heated in gradation by the second gradation data, and each of the heating elements in the fourth group is heated in gradation by the first gradation data. Note that “B” is used for the bias heating process, “K1” is used for the first gradation heating process, and “K2” is used for the second gradation heating process.
However, “R” is written in the cooling period.

During the recording of the second sub-line, the processing following the processing performed in the first sub-line is performed. That is, each heating element of the first group is heated by the first gradation, each heating element of the second group is bias-heated, each heating element of the third group is used as a cooling period, and each heating element of the fourth group is used as a heating element. Heat two gradations. Hereinafter, the processing following the processing performed on the previous sub-line is performed on the third and fourth sub-lines in the same manner as the processing during recording on the second sub-line. The assignment of each process to each group is not limited to the illustrated one, and the permutation may be changed. The minimum unit of the heat generation pattern is enclosed by a thick dotted line.

FIG. 10 is an electric circuit diagram for performing the above-mentioned heating pattern. The same components as those in the embodiment shown in FIG. 1 are denoted by the same reference numerals. In this embodiment, two sets of four line memories are provided to divide the line memories into four groups and four sub-lines, and these line memories 41 to 48 are selectively read by the switching circuits 49 and 50 and sent to the head driver 30. .

The image data of each color of yellow, magenta, and cyan is written into the frame memory 51 after being separated for each color. Then, one line of image data is sequentially read from the frame memory 51, and this is
Sent to 2. The adder 52 includes a correction data calculation unit 53
, The correction data is sent in synchronization with the one-line reading of the frame memory 51. The correction data is color correction data,
There are shading correction data, resistance value unevenness correction data of each heating element, and the like. The shading correction data is determined according to the number of recording lines. Further, the resistance value unevenness correction data of the heating element is obtained for each heating element. The image data and the correction data are 8 bits, which are added by an adder to carry to 9-bit data (“000 _H ” to “1FF _H ”), which are sent to the separation circuit 54.

The separation circuit 54 divides the 9-bit corrected image data into first and second gradation pulses K1 and K2 in units of one subline recording time. Specifically, for example, if the ninth bit is “1”, K1 is set to “FF”.
_H ”and K2 are the lower 8 digits of 8-bit data“ 00 _H ”to“ F
To separate the F _H ". If the ninth bit is “0”,
8 K1 of the under 8-digit bit data "00 _H" - "F
F _H ", to separate the K2 to" 00 _H ". Then, K1 is written into the first gradation data line memory 42 and K2 is written into the second gradation data line memory 43. Further, fixed data “FF _H ” is written in the bias data line memory 41. Fixed data of “00 _H ” is written in the line memory 44 for the cooling period. Note that, besides using these bias data and cooling period line memories 41 and 44, simply “FF _H ” and “00
_H "data generator may be used.

The first switching circuit 49 reads data from the first to fourth line memories 41 to 44 in order for each pixel, and writes the data to the first to fourth sub-line line memories 45 to 48. As a result, as shown in FIG. 11A, B, _K12J , _K23J , R, B, K16J _,.
K2 _7J , R,... K1 _{(n-2) J} , K2 _{(n-1) J} , R are written. Further, as shown in (B), the second subline line memory, in order from the first heating element K1 _{1 J,
K22J} , R, B, _K15J , _K26J , R, ... K2
_{(n-2) J} , R, B are written. Also, as shown in (C), the line memory for the third sub-line includes _K21J , R, B, _K14J , _K25J , R _,.
.. K2 _{(n-3 ) J} , R, B, K1 _nJ are written. Further, as shown in (D), R, B, _K13J , and K2 are sequentially stored in the line memory for the fourth sub-line from the first heating element.
_4J , R, ... K2 _{(n-3) J} , R, B, K1 _{(n-1) J} , K2
_nJ is written.

The second switching circuit 50 comprises a first to a fourth line memory 45 for each quarter line (one sub line).
The print data is sent to the thermal head driver 30. The thermal head driver 30 in the same manner as the embodiment described above, heating the heat-sensitive recording layer by driving the heating elements 15 ₁ to 15 _n based on the data for printing. Thus, heat energy corresponding to the image data is applied to the thermosensitive coloring layer, and one line of dots is recorded. FIG. 12 shows a timing chart of the thermal head driver 30 at this time.

FIG. 13 shows an embodiment in which the heat generation pattern and the size are changed for each color recording. As shown in FIG. 13A, when recording the uppermost yellow thermosensitive coloring layer, Each heating element is divided into five groups so as to be substantially equally divided, and these are referred to as first to fifth groups. Then, the heating elements of each of these groups are arranged so as to be arranged one by one in the group order.

A one-line recording time for recording dots for one line is divided into five equal parts, and these recording times are defined as first to fifth sub-line recording times. At the same time, the gradation pulse is separated into first, second, and third gradation pulses in units of one sub-line recording time. Then, during the first sub-line recording time, a bias pulse is applied to the heating elements of the first to fifth groups, a first gradation pulse is applied, a second gradation pulse is applied, and a third gradation pulse is applied. One of the application period and the cooling period is assigned, and after the second sub-line recording time, the first heating element is applied to the heating element of the group to which the bias pulse is applied in the previous sub-line recording time.
A gradation pulse is applied, a second gradation pulse is applied to the heating elements of the group to which the first gradation pulse is applied, and a third gradation pulse is applied to the heating elements of the group to which the second gradation pulse is applied. The cooling is performed on the heating elements in the group to which the third gradation pulse has been applied, and the bias pulse is applied to the heating elements in the cooling group.

At the time of thermal recording of the magenta thermosensitive coloring layer, as shown in FIG. 13B, each heating element is divided into four groups so as to be substantially equally divided, and these are divided into first to fourth groups. The heating elements of each group are arranged in the order of groups in units of an appropriate number. Also, one line recording time for recording one line of dots is divided into four equal parts, and these recording times are defined as first to fourth sub-line recording times.

In the thermal recording of the cyan thermosensitive coloring layer, FIG.
Like the heating pattern of FIG. 3C, each heating element is divided into three groups so as to be substantially equally divided, and these are divided into first groups.
To the third group, and the heating elements of each of these groups are arranged so as to be arranged one by one in the group order. Also,
One line recording time for recording one line of dots is divided into three equal parts, and these recording times are referred to as first to third sub-line recording times. In the first sub-line recording time, one of the application of the bias pulse, the application of the gradation pulse, and the cooling period is assigned to the heating elements of the first to third groups. Then, the processing next to the processing performed in the previous subline recording time is performed.

As described above, by making the size of the heat generation pattern smaller as the layer becomes deeper, the bias heating period during one-line recording can be made longer as the layer becomes deeper.
Optimal bias heating according to each thermosensitive recording layer can be easily performed without changing the voltage or the pulse width.

In the above embodiment, the bias heating and the gradation heating are performed by continuous energization. In addition, the bias heating and the gradation heating may be performed by a pulse train composed of a large number of pulses. . Again, in this case,
During the subline recording time for performing the bias heating, a bias pulse train is applied in all sections.

In the above-described embodiment, the thermal head driver 30 that performs gradation control using a down counter is used. However, the present invention is not limited to this. Any thermal head having a thermal head driver capable of gradation control can be used. Thus, the present invention can be implemented.

In the above embodiment, the linear heating elements 13 _{1 to} 13 _n are alternately arranged one by one in groups G 1 and G 1.
However, in addition to the above, the data may be allocated to the groups G1 and G2 in units of two or more. Also,
Although gradation heating is performed using a plurality of sub-lines, bias heating may be performed using a plurality of sub-lines.

In the above-described embodiment, the thermal color developing layer is preheated to the temperature immediately before the color development by the bias thermal energy, so that the color is developed when a slight amount of gradation heating is applied after the bias heating. However, in the present invention, in addition to the preheating to the temperature immediately before the color development in the strict sense as described above, the preheating including the temperature immediately before the color development in a range where the image quality does not deteriorate and the bias heating are also included.

In the above-described embodiment, the recording material is reciprocated using the feed roller pair 11 to sequentially record three colors with one thermal head. The present invention may be applied to a three-head one-pass type thermal printer in which three colors are sequentially recorded by one feed of a recording material by a head. In the above-described embodiment, the capstan drive type thermal printer is used. However, the present invention may be applied to a platen drum type thermal printer that sends a recording material using a platen drum. Further, the present invention is applied to a color thermal printer, but the present invention may be applied to a thermal melting type thermal printer. Further, the present invention may be applied to a serial printer other than the line printer.

In each of the above embodiments, the grouping of a large number of heating elements may be performed for each driver IC for driving a fixed number of heating elements. For example, as shown in FIG. 14, when one line is recorded by 512 pixels, eight driver ICs 70 each including 64 AND gate arrays 34 and transistors 35 (7
0 ₁ to 70 ₈ ) Used. The same components as those in the embodiment shown in FIG. 7 are denoted by the same reference numerals. Driver IC7
0 may include other elements in addition to the one including the AND gate array 34 and the transistor 35, or may include only the transistor 35. In short, what is necessary is just to drive each heating element in a group unit.

[0050] Figure 15 (A) are those showing the grouping of the heating elements of this time, the first 64 heating element 15 ₆₄ to the first group G1 from the first heating element 15 _1, 65
The heating element 15 ₆₅ to the 128 th heating element 15 _{128 form a} second group G2, and the 129 th heating element 15 ₁₂₉ to the 19 th heating element 15 ₁₂₈ .
The second heating element 15 ₁₉₂ is set in a third group G3,
The heating element 15 ₁₉₃ to the 256th heating element 15 ₂₅₆
Group G4.
The group is divided into a group G1 to a fourth group G4.

[0051] FIG. 15 (B), (C) , (D) is shows a heating pattern in the case of grouping in this way, the heating element groups each one unit of the driver IC 70 ₁ to 70 ₈ Since G1 to G4 are driven, control can be further simplified. Further, when recording each color, the heat generation pattern can be changed, so that the occurrence of moire can be eliminated. Note that the number of driver ICs divided into groups is not limited to “4”, and may be “2” or more.

FIG. 16 shows a driver IC according to the color to be recorded.
It is obtained by changing the number of groups of 70 _{1-70 8.} As shown in FIG. 3A, at the time of yellow recording, the driver I
C70 ₁ to 70 ₈ four groups G1, G2, G3,
Each heating element is driven by a heating pattern as shown in FIG. Further, when the magenta and cyan records, as shown in (C), the driver IC 70 ₁ to 70 ₈
Are divided into two groups G1 and G2, and each heating element is driven by a heating pattern as shown in FIG. In this case, during magenta and cyan printing, higher bias heat energy is required than during yellow printing, so bias heating is performed using two sub-lines obtained by dividing one line printing time into four equal parts.

[0053]

According to the present invention, a large number of heating elements are set to N
(N ≧ 2) groups and divide them into first to Nth groups.
, The one-line recording time for recording dots for one line is divided into N equal parts, and these recording times are set to the first.
To the Nth subline recording time, and a bias pulse and a gradation pulse are applied to the heating elements of each group from the start position of the recording time of the subline corresponding to each group. Since all the heating elements are always bias-heated in the entire thermal head during one-line printing, the heating elements are not subjected to the cooling period all at once because the heating is applied during the entire sub-line recording time. Temperature fluctuation in the sub-scanning direction during one-line printing is suppressed. Therefore, the fluctuation of the coefficient of friction between the heating element and the recording material due to the temperature fluctuation can be suppressed. As a result, fluctuations in the feeding amount of the recording material within one line recording cycle are suppressed, and the feeding speed is averaged, so that the occurrence of density unevenness can be suppressed.

Further, since the temperature of the entire thermal head does not excessively decrease every recording cycle of one line, the bias heating period for recording the next line can be shortened, and the printing efficiency can be improved. A power consumption type thermal printer can be provided. In addition, the peak current of the power supplied to the thermal head can be reduced, and the power can be reduced in size. Further, since the temperature fluctuation during one-line recording is suppressed, it is possible to eliminate the undulation of the recording material surface which occurs every one line cycle after the thermal recording.

The grouping is performed so that the number of the groups is substantially equal, and the heating elements of each group are alternately arranged in a proper number of units in the group order, so that the thermal balance of the thermal head in the main scanning direction is good. And efficient thermal recording becomes possible.

The thermosensitive recording material has at least a first to a third thermosensitive coloring layer in order from the surface layer side, and the first to the third thermosensitive coloring layers develop a color of any one of yellow, magenta and cyan. By changing the thermal recording pattern determined by the group and the subline recording time for each thermal recording of the thermosensitive coloring layer, the occurrence of color shift can be suppressed.

The number of divisions N is changed for each thermal recording of each thermosensitive coloring layer, and the number of divisions is set to be smaller as the thermosensitive coloring layer is deeper, so that the bias heating period is set longer according to the depth. And efficient thermal recording can be performed.

Since a large number of heating elements are grouped in units of driver ICs for driving a fixed number of heating elements, each heating element is driven in units of driver ICs, so that control is further simplified. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a main part of a thermal printer according to the present invention.

FIG. 2A shows an example of print data on a thermal head, FIG. 2B shows an average temperature variation of the entire thermal head,
(C) is an explanatory diagram showing a change in the friction coefficient between the recording material and the heating element, and (D) is an explanatory diagram showing a change in the feeding speed of the recording material.

FIG. 3 is a schematic view showing a layer structure of a color thermosensitive recording material used in the thermal printer.

FIG. 4 is a graph showing color development characteristics of the recording material.

5A is a plan view showing an enlarged heating element array, FIG. 5B is a heating pattern used in yellow printing, FIG. 5C is a heating pattern used in magenta printing,
FIG. 4D is an explanatory diagram showing a heat generation pattern used during cyan printing.

FIG. 6A shows a line memory for a first sub line,
FIG. 3B is an explanatory diagram showing an example of print data written in the second subline line memory.

FIG. 7 is an electric circuit diagram showing an example of a thermal head driver.

FIG. 8 is a timing chart in the thermal head driver.

9A is a plan view of a thermal head, FIG. 9B is an example of a heat generation pattern during yellow printing in another embodiment, FIG. 9C is an example of a heat generation pattern during magenta printing, and FIG. () Shows an example of a heat generation pattern during cyan recording.

FIG. 10 is an electric circuit diagram in the same embodiment.

FIG. 11 is an explanatory diagram showing an example of data recorded in each sub-line line memory in the embodiment.

FIG. 12 is a timing chart in the thermal head driver of the embodiment.

FIG. 13 is an explanatory diagram showing an example of a heat generation pattern on the heat generation element array in the embodiment in which the size of the heat generation pattern is changed according to the color to be recorded.

FIG. 14 is an electric circuit diagram showing an example of a thermal head driver using a driver IC that drives each heating element in a group unit.

15A is a plan view of a thermal head illustrating an embodiment using a driver IC, and FIG. 15A is a plan view of a thermal head showing a grouping of each heating element by a driver IC;
(B) shows an example of a heat generation pattern at the time of yellow printing, (C) shows an example of a heat generation pattern at the time of magenta printing, and (D) shows an example of a heat generation pattern at the time of cyan printing.

16A and 16B are diagrams for explaining another embodiment using a driver IC. FIG. 16A illustrates a driver I for yellow printing.
FIG. 3B is a plan view of a thermal head showing the grouping of each heating element in C units, FIG. 2B shows an example of a heating pattern in yellow printing, and FIG. 2C shows each heating element in driver IC units in magenta and cyan printing. FIG. 4D is a plan view of the thermal head showing grouping, and FIG. 4D shows an example of a heat generation pattern during magenta and cyan recording.

17A and 17B show a conventional thermal head driving method. FIG. 17A shows an example of print data on a thermal head.
(B) shows the variation of the average temperature of the entire thermal head,
(C) is an explanatory diagram showing a change in the friction coefficient between the recording material and the heating element, and (D) is an explanatory diagram showing a change in the feeding speed of the recording material.

[Explanation of symbols]

Reference Signs List 10 color thermal recording material 11 feed roller pair 13 system controller 14 thermal head 15 heating element array 15 ₁ to 15 _n heating element 20 frame memory 21 memory controller 22 color conversion unit 23 color correction unit 24 gradation line memory 25 bias line memory 26, 29, 49, 50 Switching circuit 27, 28, 45-48 Line memory for sub-line 30 Thermal head driver 41-44 Line memory

Claims (12)

[Claims] 1. A thermal head in which a number of heating elements are arranged in a line in a main scanning direction and a thermosensitive recording material having at least one thermosensitive coloring layer. The element is supplied with a bias pulse for applying bias thermal energy to the thermosensitive coloring layer immediately before the thermosensitive coloring layer develops a color and a gradation pulse for applying gradation thermal energy to the thermosensitive coloring layer in accordance with the color density. In the method of driving a thermal head for recording dots for one line, the large number of heating elements are divided into N (N ≧ 2) groups, and these groups are referred to as first to N-th groups. The one-line recording time for recording dots is divided into N equal parts, and these recording times are defined as first to N-th sub-line recording times. A bias pulse and a grayscale pulse are applied from the start position of the recording time, and the second group of heating elements are given a second pulse.
A method for driving a thermal head, characterized in that a bias pulse and a gradation pulse are successively applied from a start position of a recording time of a sub-line, and the bias pulse is applied in the entire period of one sub-line recording time. . 2. The thermal device according to claim 1, wherein the grouping is performed so that the number of the heating elements is substantially equal, and the heating elements of each group are arranged alternately in the order of the group in a suitable number. Head driving method. 3. The method according to claim 1, wherein the grouping is performed in units of driver ICs for driving a fixed number of heating elements. 4. The heat-sensitive recording material includes at least a first to a third heat-sensitive coloring layer in order from the surface layer side, and the first to third heat-sensitive coloring layers color one of yellow, magenta, and cyan. 4. The method of driving a thermal head according to claim 1, wherein a thermal recording pattern determined by the group and the sub-line recording time is changed for each thermal recording of each thermosensitive coloring layer. . 5. The division number N for each thermal recording of each thermosensitive coloring layer.
5. The method of driving a thermal head according to claim 4, wherein the number of divisions is made smaller as the heat-sensitive coloring layer is deeper. 6. A thermal head in which a number of heating elements are arranged in a line in the main scanning direction, and first to third heat-sensitive elements arranged in order from a surface layer which emits one of yellow, magenta, and cyan. A bias pulse for applying a bias heat energy to the heat-sensitive coloring layer immediately before the heat-sensitive coloring layer develops a color to each heating element while feeding the heat-sensitive recording material in the sub-scanning direction using a heat-sensitive recording material having a coloring layer; And a gradation pulse for applying gradation heat energy to the thermosensitive coloring layer according to the following formula, and printing one line of dots on the thermosensitive recording material. The first and second groups are divided alternately by a fixed number to divide the one-line recording time for recording the dots for one line into two equal parts, and divide these recording times into the first and second groups. A sub-line recording time, a bias pulse is applied to the first sub-line recording time to the heating element of the first group, a gradation pulse is applied to the second sub-line recording time, and a heating element of the second group is Driving a thermal head, wherein a gradation pulse is applied during a first sub-line recording time and a bias pulse is applied during a second sub-line recording time, and the bias pulse is applied during the entire period of one sub-line recording time. Method. 7. The thermal device according to claim 6, wherein the grouping of the plurality of heating elements into first and second groups is performed in units of driver ICs for driving a fixed number of heating elements. Head driving method. 8. A thermal head in which a large number of heating elements are arranged in a line in the main scanning direction, and first to third heat-sensitive elements arranged in order from the surface layer which develops any one of yellow, magenta and cyan. A bias pulse for applying a bias heat energy to the heat-sensitive coloring layer immediately before the heat-sensitive coloring layer develops a color to each heating element while feeding the heat-sensitive recording material in the sub-scanning direction using a heat-sensitive recording material having a coloring layer; And a gradation pulse for applying gradation heat energy according to the following formula to the thermosensitive coloring layer to record one line of dots on the thermosensitive recording material, wherein the plurality of heating elements are divided into four groups. These are divided so as to be substantially equally divided into the first to fourth groups, and the heating elements of each of these groups are arranged so as to be arranged in an appropriate number of units in the group order. The one-line recording time for recording the dots of the line is divided into four equal parts, and these recording times are defined as first to fourth sub-line recording times. During the first sub-line recording time, a bias pulse is applied to the heating elements of the first to fourth groups, a first gray-level pulse is applied, and a second gray-level pulse is generated. One of the application period and the cooling period is assigned, and after the second sub-line recording time, the first gradation pulse is applied to the heating elements of the group to which the bias pulse was applied in the previous sub-line recording time, and the first gradation is applied. A second gradation pulse is applied to the heating elements of the group to which the pulse has been applied, and a cooling period is set for the heating elements of the group to which the second gradation pulse has been applied. A method of driving a thermal head, wherein a bias pulse is applied, and the bias pulse is applied during the entire period of one subline recording time. 9. The grouping of the plurality of heating elements includes:
9. The method according to claim 8, wherein the driving is performed for each driver IC for driving a fixed number of heating elements. 10. A thermal head in which a number of heating elements are arranged in a line in the main scanning direction;
A heat-sensitive recording material having first to third heat-sensitive coloring layers arranged in order from the surface layer which develops any one of cyan, and heat-sensing is applied to each heating element while feeding the heat-sensitive recording material in the sub-scanning direction. One line is applied to the heat-sensitive recording material by applying a bias pulse for applying the bias heat energy immediately before the color-forming layer develops color to the heat-sensitive coloring layer and a gradation pulse for applying the gradation heat energy corresponding to the color density to the heat-sensitive coloring layer. In the method of driving a thermal head for recording minute dots, the thermal recording of the first thermosensitive coloring layer is such that the plurality of heating elements are substantially equally divided into P (where P ≧ 5) groups. Divided into the first to P-th groups,
The heating elements of each of these groups are arranged so as to be arranged in an appropriate number of units in the group order. The one-line recording time for recording the dots for one line is equally divided by P, and these recording times are defined as first to first. .., The P-th sub-line recording time, the gradation pulse is divided into first, second,..., P-2th gradation pulses in units of one sub-line recording time. Applying a bias pulse, applying a first gradation pulse, applying a second gradation pulse,..., Applying a P-2th gradation pulse, and cooling the heating elements of the first to Pth groups One of the periods is assigned, and after the second sub-line recording time, the first gradation pulse is applied to the heating elements of the group to which the bias pulse was applied in the previous sub-line recording time, and the first gradation pulse is applied. Group of heating elements To the heating element of the group to which the second gradation pulse is applied, the next gradation pulse to the heating element of the group to which the second gradation pulse is applied, and the heating element of the group to which the P-2 gradation pulse is applied. Cooling, applying a bias pulse to the heating element of the cooled group,
The bias pulse is applied for the entire period of one sub-line recording time, and when performing thermal recording of the second thermosensitive coloring layer, the large number of heating elements are substantially divided into Q (where Q <P) groups. Divide them so that they are equally divided into groups 1 to Q,
The heating elements of each group are arranged so as to be arranged in an appropriate number of units in the group order. The one-line recording time for recording the dots for one line is equally divided by Q, and these recording times are defined as first to first. .. Are divided into first, second,... Gradation pulses in units of one sub-line recording time. , And one of the cooling periods is assigned to the heating elements of the group No. 1 and the cooling period is assigned. Performing a process subsequent to the process performed in the previous sub-line recording time, and applying the bias pulse during the entire period of one sub-line recording time; and performing the thermal recording of the third thermosensitive coloring layer, Many fever The elements are divided into R (where R <Q) groups so as to be approximately equally divided, and these are referred to as first to R-th groups,
The heating elements of each of these groups are arranged so as to be arranged in an appropriate number in the group order. The one-line recording time for recording the dots for one line is equally divided into R, and these recording times are defined as first to first. The gradation pulse is divided into first,... Gradation pulses in units of one sub-line recording time, and the first sub-line recording time is defined by the first to R-th groups. Any one of the application of the bias pulse, the application of the first gradation pulse,..., The cooling period is assigned to the heating element, and after the second subline recording time, the processing performed in the previous subline recording time is performed. A method for driving a thermal head, characterized in that the following processing is performed, and the bias pulse is applied during the entire period of one subline recording time. 11. The method according to claim 11, wherein the grouping of the plurality of heating elements includes a driver IC for driving a fixed number of heating elements.
11. The method according to claim 10, wherein the driving is performed in units. 12. A thermal head according to claim 6, wherein a thermal recording pattern determined by said group and sub-line recording time is changed for each thermal recording of each thermosensitive coloring layer. Drive method.