JP2605934B2 - Thermal recording device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal recording apparatus capable of high-precision multi-tone recording.

2. Description of the Related Art In recent years, full-color and high-speed thermal recording apparatuses have been developed, and high-precision multi-tone recording has been required in order to obtain good halftone recorded images.

Generally, this type of thermal recording apparatus has a configuration as shown in FIG.

That is, reference numeral 1 denotes a thermal head in which the heating elements 1R are arranged in a line in a direction perpendicular to the plane of the drawing. 3
Is a thermal transfer ink sheet, on which a heat-meltable ink 3a is applied on a base film 3b. Reference numeral 4 denotes a recording paper, which includes the thermal transfer ink sheet 3 and the thermal head 1
And the platen 2. Platen 2
Is sufficiently pressed toward the thermal head 1 so that the recording paper 4 and the thermal transfer ink sheet 3 and the thermal transfer ink sheet 3 and the heating element are sufficiently adhered to each other.

Next, the heating element 1R of the thermal head 1 has a configuration as shown in FIG. 7 (a).

That is, 1e is a heating element, and a pair of electrodes 1f is connected to both ends thereof. The heating element 1e is formed such that the width is larger in the vicinity of the electrode 1f and narrower in the center between the electrodes 1f. Thereby, as shown in FIG. 7 (b), the resistance value of the heating element 1e decreases in the vicinity of the electrode 1f and increases in the center between the electrodes 1f. Therefore, when a constant voltage is applied to the heating element 1R for a fixed time, the heating value increases in the central portion of the heating element 1R because the heating value increases as the resistance value increases. By using this to change the voltage application time of the voltage applied to the heating element 1R, a heating value corresponding to the voltage application time is generated in the heating element 1R in a form concentrated in the center of the heating element 1R, The recording area per dot can be freely changed according to the heat generation amount. That is, multi-tone recording can be performed (Japanese Patent Application Laid-Open No. 60-58877).

The operation of the thus configured thermal recording apparatus will be described below.

FIG. 8 is a block diagram of a thermal recording apparatus using a conventional signal generating circuit, which is divided into a thermal head section 1A and a signal generating circuit section 5.

The thermal head section 1A is arranged in a row on an insulating substrate, and a plurality of heating elements electrically divided into N groups of M each due to a problem of securing heat dissipation time of the heating elements. An element 1R, N driver circuits 6 provided for each group of the heating elements 1R, N latch circuits 7 provided corresponding to each of the driver circuits 6, and each of the latch circuits 7 It is composed of N shift registers 8 provided correspondingly.

In the thermal head section 1A, one electrode of the heating element 1R is commonly connected and connected to a power supply for printing, and the other electrode is connected to an output terminal of the driver circuit 6. The input terminal of the driver circuit 6 is connected to the output terminal of the latch circuit 7, and the input terminal of the latch circuit 7 is connected to the output terminal of the shift register 8. further,
Each of the driver circuits 6 is configured such that enable signals for controlling the operation of the driver circuit 6 are applied independently and in parallel.

Next, in the signal generation circuit section 5, reference numeral 9 denotes a RAM (random access memory) in which image information (having gradations) composed of a plurality of bits is recorded for one line. Reference numeral 10 denotes a counter, which outputs, to the RAM 9, position information indicating the address of the RAM 9 in which image information is stored for each heating element, and outputs threshold information to be compared with the image information to the comparator 11. Reference numeral 11 denotes a comparator which compares the image information in the RAM 9 with the threshold information from the counter 10 and sequentially outputs to the shift register 8 whether the image information is larger or smaller as a print data signal.

As a result, the print data signals input to the respective shift registers 8 are sent to the corresponding latch circuits 7 as parallel signals, and the driver circuits 6 are driven by the print data signals sent from the latch circuits 7 to print. Heat is applied to the heating element 1R corresponding to the data signal, and thermal recording is performed.

The above operation will be further described with reference to FIG. In order to make the description easy to understand, the image information stored in the RAM 9 is 2 bits, and M = 256, N = 4, and each line is composed of 1024 heating elements 1R.
Four heating element groups each including 256 heating elements are denoted by 1a to 1d.

FIG. 9 (a) is a circuit diagram of a signal generation circuit section,
The image information corresponding to the 1024 heating elements of the line is stored in order from address 0, and 256 pieces of information from address 0 to 256 correspond to the heating element group 1a, and 256 pieces of information are sequentially stored. They correspond to the heating element groups 1b, 1c, 1d in order. The counter 10 has a 10-bit output, and outputs from the least significant bit to the 8th bit are sequentially output to the least significant bit to the 8th bit terminal of the address terminal of the RAM 9, and 256 of the heating element groups are output. Specify one of the heating elements. The output of the 9th and 10th bits from the lower of counter 10 is
It is output to the lower 9th and 10th bit terminals of the address of the RAM 9 and designates one of the four heating element groups. The image information is sequentially output from the RAM 9 to the comparator 11 one by one in series. The contents of each storage unit are shown in parentheses in the figure.
This is a number in decimal notation. In comparator 11, each of these elements
The image information corresponding to 1R is compared with the output of the seventh and eighth bits (threshold information) from the least significant bit of the counter 10, and the result is sequentially sent to the shift register 8.

For example, if the output (threshold information) of the counter 10 to the comparator 11 is 0, it is determined whether the gradation is 0 or more for each image information shown in FIG. For example, if "1" is less than 0, "0" is output. Each time 256 of these are completed, the counter 10
Output to the comparator 11 (threshold information) is 1
As the number increases from 0 to 2, the comparator 11
Outputs a signal as shown by C in FIG. 9 (b). Next, when a signal as shown at C in FIG. 9 (b) is input to the shift register 8, the signal is sent in parallel to the corresponding latch circuit 7, and further sent to the latch circuit 7. The driver circuit is driven by the signal, and the waveform output indicated by D in FIG.
Applied to 1R. Then, only an element of a desired heating element group (256) generates heat by an enable signal applied in parallel to each driver circuit 6 independently. At this time, a pulse is consequently generated in each element 1R as shown at D in FIG. 9 (b), and the recording area per dot is changed according to the width of the pulse as shown in FIG. 9 (b). ), The gradation is controlled in four steps and the gradation is controlled in four steps.

Then, the above-described series of operations is performed in the order of 1a → 1b → 1c → 1d for the four heating element groups 1a to 1d corresponding to the outputs of the ninth and tenth bits from the lower order of the counter 10, thereby completing the recording of one line. Further, by repeating the recording of one line while feeding the recording paper, an image composed of a plurality of lines is formed as shown in FIG.

However, the above-described configuration has an advantage that the heating elements of the thermal head are divided and driven in a plurality of groups, so that a sufficient time for cooling the heating elements after heat generation can be secured. However, among the heating elements at both ends of the heating element group that generates heat at the same time, there is only one side of the heat interference between the adjacent heating elements, that is, since the heat dissipation to the outside of the group is large, the recording area per dot is large. Is smaller than when the same gradation is recorded by the heating elements other than the end of the group, and a print gap (white stripe in the printing direction) as shown in FIG. Is observed, and the image quality is degraded.

Conventionally, as a technique used to prevent image quality deterioration due to printing gap, a method of driving only the elements at both ends again for a predetermined time immediately after driving the heating element group (Japanese Patent Laid-Open No.
61-224772) has been proposed, which is effective as a means for correcting the printing gap in two-recording.
In multi-tone printing, since the drive time varies from element to element depending on the recording gradation (low gradation: short high gradation: long), good correction without excess or deficiency in all gradation areas by re-driving for a certain period of time Was difficult. Also, a method of making the element shapes at both ends of a heating element group driven simultaneously in a thermal head different from other elements (Japanese Patent Application Laid-Open Nos. 61-144467 and 61-14367).
185462) has been proposed, but in this method, correction is performed so that the calorific value of the element at the end of the group is always at a constant ratio with respect to elements other than the end of the group regardless of the recording gradation. In order to determine the shape of the element at the end of the group, it is difficult to make good correction without excess or deficiency in the gradation range, and to eliminate print gaps in binary recording without excess or deficiency, several thermal head prototypes are required. Was needed.

The present invention has been made in view of the above problems, and provides a thermal recording apparatus for multi-tone recording that eliminates print gaps generated at boundaries between heating element groups.

Means for Solving the Problems In order to achieve this object, a thermal recording apparatus according to the present invention has a structure in which a large number of heating elements are arranged in a line, and the large number of heating elements are divided into groups in a continuous form. In a thermal head driven in units, the heating elements at both ends of the group or a plurality of heating elements from the both ends are made different in shape to eliminate printing gaps, and the heating elements having different shapes are used. A signal generating circuit for correcting gradation information is provided to correct the printing time longer than a heating element for which the shape is not changed, thereby further eliminating printing gap. Heat generated at the heating elements at both ends of the heating element group with respect to the point where the print gap occurred at the position of the recording surface corresponding to the boundary between the element groups In order to compensate for the amount of heat corresponding to the shortage, the gradation of the image information corresponding to the plurality of heating elements is increased in advance by a predetermined amount from both ends or both ends of the heating element group in accordance with the image information. Even at the end heating elements, a recording area per dot equivalent to that of the heating elements other than the end of the heating element group can be obtained in all gradation ranges, and multi-gradation recording that eliminates the printing gap can be performed. It is.

First Embodiment Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. The thermal head 1, the platen 2, the thermal transfer ink sheet 3, and the recording paper 4 are the same as those in the conventional example, and the description of the structure and characteristics thereof will be omitted.

FIG. 1 is a block diagram of a thermal recording apparatus according to the present invention, which is divided into a thermal head section 1A and a signal generating circuit section 12.
Among them, the thermal head 1A is shown in FIGS. 5 (a) and 5 (b).
And will be described later.

Next, in the signal generation circuit section 12, reference numeral 9 denotes a RAM which stores image information of a plurality of bits for one line. Reference numeral 10 denotes a counter which counts up by a clock signal and stores image information for each heating element.
The position information indicating the address of the RAM is output to the RAM 9, the same position information is output to the selector 13 at the same time, and the threshold information to be compared with the image information is output to the comparator 11. Reference numeral 13 denotes a selector, which outputs 1 of a ROM (read only memory) 14 only when the position information from the counter 10 is a value indicating the heating elements at both ends of the heating element group.

Reference numeral 14 denotes a ROM, and a RAM 9 according to an output from the selector 13.
The image information after the change when the image information output from is changed is stored. 11 is a comparator, RO
The image information of M14 is compared with the threshold information output from the counter 10, and whether it is larger or smaller is output to the shift register 8 as a print data signal.

The operation of the thermal recording apparatus configured as described above will be described with reference to FIG. As in the conventional example, to make the description easy to understand, the image information stored in the RAM 9 is 2 bits, M = 256, N = 4, and one line is 1 line.
Four heating element groups each including 024 heating elements 1R and each including 256 heating elements are denoted by 1a to 1d.

Image information corresponding to 1024 lines of heating elements is stored in the RAM 9 in the same configuration as the conventional example, and the address of the RAM 9 is designated by the position information output from the counter 10 in the same configuration as the conventional example, The output of RAM9 is the lower 2 of the address of ROM14.
Output to bits. The position information output from the counter 10 is also output to the selector 13. The selector 13 reads the ROM when the position information is a value (0 and 255) indicating the end of the heating element group.
1 is output to the third bit from the lower order of the address 14, and 0 is output in other cases. The ROM 14 is a change table of image information. The ROM 14 is an address based on image information (lower 2 bits) from the RAM 9 and information (hereinafter abbreviated as group end information) (third bit from the lower end) indicating the end of the heating element group from the selector 13. The same information as the lower 2 bits of the address is stored in the address where the third lower bit of the address is 0, and information different from the lower 2 bits of the address is stored in the address where the third bit of the address is 1 from the lower bit. It is remembered. This allows the selector
If the group end information from 13 is 0 indicating a heating element other than the group end, the same information as the image information output of the RAM 9
When the group end information is 1 indicating the heating element at the end of the group, which is output from the ROM 14 and is different from the image information output from the RAM 9, for example, information in which the number of tones is increased by one level is RO
Output from M14. Further, the output information of the ROM 14 is compared with the threshold information from the counter 10 by the comparator 11 in the same manner as in the conventional example as shown in FIG. 8 (b). The data is output to the shift register 8 of the head unit 1 and printing is performed.

As described above, according to the present embodiment, by increasing the gradation of the image information corresponding to the heating element at the end of the heating element group, the heat amount is insufficient due to the dissipation of heat to the outside of the heating element group. An extra amount of heat corresponding to the shortage can be supplied in advance to the heating element at the end of the heating element group where the recording area per dot to be recorded could not be recorded. The recording area having the same recording area as that of the heating element can be recorded, and the printing gap generated on the recording surface corresponding to the boundary between the heating element groups as shown in FIG. 3 is eliminated.

In FIG. 2, for the sake of simplicity, the image information is made up of 2 bits, and the ROM 14 is incremented by 1 only when the image information is "01" and "10" for the group end heating element. Although it is used, by increasing the number of bits of image information, it is possible to perform highly accurate correction that is more faithful to the phenomenon. When the number of bits of the image information is increased, the relationship between the image information before and after the change in the group end heating element is the most significant in the intermediate gradation because the printing gap is most remarkable in the intermediate gradation. It is preferable to make the relationship as shown in FIG.

In this embodiment, the gradation of the image information is changed only for the group end heating elements. However, the number of output bits of the selector 13 is increased, and the area used by the ROM 14 is increased to be the second third from the end of the group. The gradation may be changed independently for the third and the plurality of heating elements, and the correction may be made more accurately.

FIG. 5 shows a thermal head section of the present embodiment. In FIG. 5 (a), 1R denotes a plurality of heating elements 1a, 1b, 1c and 1d arranged in a line and 4 Heating element groups (each including m heating elements). Next, the heating element 1R of the thermal head
It has a configuration as shown in FIG.

That is, 1e is a heating element, and a pair of electrodes 1f is connected to both ends thereof. The heating element consisting of 4m pieces is divided into four groups 1a to 1d each of m pieces, and m pieces are simultaneously
It is driven in the order of 1a → 1b → 1c → 1d. The first and m-th heating elements of the group of m heating elements are configured such that the heat generating body length l is shorter than the second to m-1 heating elements.

In the thermal recording apparatus using the thermal head configured as described above, the length l of the first and mth heating elements is smaller than that of the second to m-1th heating elements. Since the resistance value of the heating element is generally proportional to (length / width), the resistance values of the first and mth heating elements are smaller than those of the other heating elements. The first and (m-1) th heating elements are larger than the other heating elements. When printing is performed by using such m heating elements, the amounts of heat generated by the first and mth heating elements, which have been insufficient due to the escape of heat to the outside of the heating element group in the past, are insufficient due to the above configuration. By generating a large amount of heat in advance, the amount of heat is approximated to the amount of heat generated by the second to (m−1) th heating elements, and the signal generation circuit unit 12 in FIG. By correcting the calorific value, the first and mth and the second to m
The difference between the calorific values of the first heating element is negligible.

Therefore, the printing gap between the heating element groups and the printing gap between the heating element groups, which has conventionally occurred, is eliminated by storing the printing dots of the same size from the first to the mth in the image receiving paper 4.

Therefore, the absolute value of the correction amount by the signal generation circuit unit 12 can be reduced by configuring the thermal head unit 1A as shown in FIG. 5, and correction with higher accuracy than when the same signal generation circuit is used is achieved. It becomes possible.

In this embodiment, the shape of the heating element and the gradation of image information are changed only for the heating element at the end of the group, but the shape of the heating element is independently set for the second and third heating elements from the end of the group. Alternatively, the gradation may be changed to perform more accurate correction.

Furthermore, in the present embodiment, the width of the heating element 1e of the thermal head 1 is wider in the vicinity of the electrode and narrower in the center, but the heating element may have any shape other than the above. .

Finally, in this embodiment, the thermal transfer ink sheet 3
And the recording paper 4 was used, but these may be a combination of a thermosublimable dye sheet and an image receiving paper or a thermal paper.

Effect of the Invention As described above, the present invention provides a thermal head that arranges a large number of heating elements in a line, divides the large number of heating elements into groups in a continuous form, and drives the groups in groups. It is configured to eliminate printing gaps by making the shape of the heating elements at both ends or the plurality of heating elements from both ends, and a signal generating circuit for correcting gradation information for the heating elements having the different shapes is provided. hand,
By correcting the printing gap by correcting the energization time longer than that of the heating element that does not change the shape, the printing gap generated at a position corresponding to the boundary between the heating element groups on the recording surface can be eliminated. Can,
It is possible to realize a thermal recording apparatus capable of performing multi-gradation recording with excellent image quality.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a thermal recording apparatus according to an embodiment of the present invention, FIG. 2 is a circuit diagram of a signal generating circuit unit in the embodiment, and FIG. FIG. 4 is a relationship diagram showing control contents relating to image information in the embodiment, and FIG.
7A and 7B are a perspective view of a thermal head unit and a configuration diagram of a heating element according to a second embodiment of the present invention, FIG. 6 is a configuration diagram of a conventional thermal transfer recording apparatus, and FIG. a), (b)
FIG. 8 is a block diagram and a characteristic diagram of the heating element of the conventional example, FIG. 8 is a block diagram of the conventional example, and FIGS. 9A and 9B are a circuit diagram and a principle explanatory diagram of a signal generating circuit unit of the conventional example; FIG. 10 is a diagram for explaining the operation of the conventional example. 1A: Thermal head, 1R: Heating element, 9: RA
M, 10: Counter, 11: Comparator, 12: Signal generation circuit unit, 13: Selector, 14: ROM.

Claims (1)

(57) [Claims] 1. A thermal head which arranges a large number of heating elements in a line, divides the plurality of heating elements into a group in a continuous form, and drives the heating elements on a group basis. In order to eliminate the printing gap by making the shape of a plurality of heating elements different from each other, a signal generating circuit for correcting gradation information is provided for the heating element having the different shape, and the shape is made different. A thermal recording apparatus in which printing gaps are further eliminated by correcting the energization time to a heating element that does not have a longer heating time.