JPH03132366A - Thermal head driver - Google Patents

Abstract

PURPOSE:To enable an image to be obtained to which a dividing line is not generated by a method wherein a difference in application start time of an application pulse between each heating element of a thermal head and an adjacent heating element is so controlled as not to exceed a maximum application pulse width. CONSTITUTION:A data conversion circuit 3 receives one line content data, which is converted to a specified data of each heating resistant element designated with an address counter 7 and is stored in a line memory 4. Successively, it is read a specified number of times conforming to print timing of each heating resistant element, and is transmitted to a middle tone control part 5. A printing start signal per each one line and at the same time, a storobe pulse number are set to a density counter 9 and are successively counted up. Since an extreme time difference of application pulse timing is not generated between adjacent pixels by controlling each heating resistant element, decrease of temperature at a specified part is not generated, and an image with no dividing line can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal head driving device for driving a thermal head in which a plurality of heating elements are arranged in a row.

[Prior Art] Generally, the printing characteristics of thermal printers tend to be affected by the heat generation temperature of the thermal head.

For this reason, conventionally, the thermal head is divided into a plurality of blocks and driven in segments to prevent a sudden temperature rise.

At the same time, this also aims at the effect that even when a large number of heating elements are used, by performing divided driving, it can be used with a small-capacity power supply.

[Problems to be Solved by the Invention] However, even when such conventional divisional driving is performed, there is a problem in that a portion of low print density called a so-called division line occurs at the boundary of each block. .

This is because the dividing boundary portion is always in contact with the end of the energized heat generating element, which causes a temperature drop due to heat radiation.

In order to prevent this dividing line, JP-A-60-132
As in No. 771, the density data at the end of the divided block is multiplied by a correction coefficient, or as in JP-A-61-29272, one element at the boundary of the divided block is used in common between both blocks. Methods are known.

However, even in these methods, the effects of differences in ambient temperature, differences in temperature rise and fall, differences in gradation levels, etc. cannot be avoided, and clear dividing lines still occur.

Examples of conventional thermal head heat generation control are shown in FIGS. 5 and 6.

FIG. 5 shows the application pulse timing for each heating element in conventional solid printing, where the horizontal axis shows the heating element position, and the vertical axis shows time and strobe pulse number.

Similarly, FIG. 6 shows the print pulse timing at each heating element when image data is input using the conventional driving method.

As is clear from the above, both in the case of solid printing and when image data is input, an extreme time difference in application pulse timing occurs at the divisional drive boundary. As a result, a temperature drop occurs at the division boundary due to heat radiation, and a division line appears that significantly degrades image quality.

[Means for Solving the Problems] The present invention aims to solve the above-mentioned problems, and solves the problems of the conventional drive device described above, eliminates the above-mentioned drawbacks, and produces high-quality images without dividing lines. An object of the present invention is to provide a thermal head driving device that can be obtained.

In order to achieve the above object, the following configuration is provided, for example.

That is, the time difference between the application start time of the application pulse to each heating element and the application start time of the application pulse to the adjacent heating element is
A control means is provided for controlling the pulse width to be applied to the heating element so as not to exceed a maximum pulse width.

[Function] In the above configuration, since there is no extreme time difference in the applied pulses between adjacent heating elements, the temperature does not decrease only at a specific position.

Therefore, C1, so-called dividing lines, do not occur, and a high-quality image can be obtained.

[Embodiment] An embodiment of the present invention will be described below with reference to the accompanying drawings 1j and 6.

1 and 2 are block diagrams of an embodiment according to this embodiment, FIG. 1 is a block diagram of a thermal printer according to this embodiment, and FIG. 2 is a halftone control section shown in FIG. 1. 5 is a block diagram showing a detailed configuration of a thermal head drive section 50 in FIG.

In the figure, ■ is an input terminal for RGB color image data connected to, for example, a host device that outputs image data, and 2 is a corresponding MMC (
3 is a data conversion circuit that converts data according to the position of the heating element; 4 is a line memory that records one line of data; 5 is a color image This is a halftone control circuit that controls the energy applied to the thermal head 10 to produce halftones, and includes a thermal head drive section 50. 6 is a control unit that controls the entire thermal printer, 7 is an address counter that counts the position of the heating element, and 8 is a unit that determines a predetermined gradation level corresponding to each color of the ink sheet and the temperature around the head. A temperature compensation ROM in which data is stored, 9 a concentration counter that counts the number of strobe signals, 10 a thermal head in which a plurality of heating resistive elements are arranged in a row, and 11 a temperature detection element for detecting head temperature. , 12 is an ink sheet, 13 is a receiving paper, 14 is a platen roller, 15 is a heating resistor element,
16 is a latch that latches parallel data from shift register 17; 17 is a shift register that converts serial print data into parallel data; 18 is a common electrode;
19 is an input terminal for a strobe signal that controls heat generation time; 2
0 is an input terminal for a serial data signal, and 50 is a thermal head drive section.

The operation of this embodiment having the above configuration will be described below.

From an image input terminal l, B, G, and R signals are sequentially inputted to a color image memory of a host computer (not shown) corresponding to Y, M, and C prints. This input B, G,
The R signal is converted into corresponding Y and M signals in the color conversion circuit 2.
, is converted into a C signal. Y converted by color conversion circuit 2,
The M and C signals are transferred to the data conversion circuit 3 for each printing line. The data conversion circuit 3 receives data for 1 line and 2, converts it into predetermined data for each heating resistor element specified by the address counter 7, and stores it in the line memory 4. Subsequently, the data for each heating resistor element stored in this manner is transferred from the line memory 4 a predetermined number of times (1 in this embodiment) in accordance with the print timing for each heating resistor element.
4 times) and transferred to the halftone control section 5. Simultaneously with the print start signal for each line, "1" is set in the density counter 9 as a strobe pulse number, and "14" is set every time the line memory 4 is read out.
It counts up sequentially until it reaches (.

On the other hand, the halftone control unit 5 compares the data for one line from the line memory 4 with the Rk data to be printed.
For the heating element at the position, energization is started when (k≦strobe pulse number), and energization is ended when (strobe pulse number + input data 10k) is reached.

The amount of energy that the thermal head drive unit 50 gives to the heat generating resistor element 15 of the thermal head is controlled according to the data in the temperature compensation ROM, and a strobe signal with a time width corresponding to this is sent from the halftone control unit 5 to the strobe of the head drive circuit 50. The signal is transferred to the signal input terminal 19. This strobe signal corresponds to the amount of heat generated by the heat generating resistor 15 at the same timing as the data transfer from the line memory 4.
This is a pulse with a predetermined time width.

According to the above-mentioned system, the data signal according to the density gradation from the halftone control section 15 inputted to the head drive circuit 50 is inputted to the shift register 17 and converted into parallel data.
It is latched by latch 16.

Simultaneously with the latch, the signal is output to the AND gate (A, to AI,), and is output to the gate of the heating resistor element corresponding to the density of one gradation portion of one line. Here, it is logically summed with the strobe signal, and a predetermined heating resistor element 15 that is to perform printing at this gradation density generates heat for the pulse time of the strobe signal.

In this embodiment, heat generation is repeated once for a density of 1 gradation and five times for a density of 5 gradations.

In this way, heating is repeated 14 times according to the printing density of each heating resistor element, thereby controlling printing for 5 gradations per line.

Corresponding to the amount of thermal energy of the heating resistive element 15, the sublimable ink or meltable ink applied to the ink sheets 1 to 12 sublimates or melts, and is transferred to the receiving paper 13 to form an image.

FIG. 3 shows the application pulse timing of each heating element 15 during solid printing using the thermal head driving method in this embodiment described above, where the horizontal axis shows the heating element position, and the vertical axis shows time and strobe pulse number. There is.

Figure 3 shows the case of solid printing at five gradations of density (maximum density), with a time difference of one strobe pulse for each adjacent heating element, and a maximum of 10 heating resistor elements of R1-RIO. This is an example in which heat generation driving is performed five times, which is the concentration.

Further, FIG. 4 is an example showing the timing of application pulses to each heating element when inputting general image data in the driving method of this embodiment.

The first pulses applied to each heating element all have a time difference of one strobe pulse for each heating element, and then a second pulse, a third pulse, and the number of pulses corresponding to the gradation are applied.

By controlling in this way, there is no extreme time difference in the applied pulse timing between adjacent pixels, whether in solid printing or when image data is manually generated, so there is no temperature drop in a specific part, and the division line It is possible to obtain high-quality images without any blemishes. Furthermore, since the number of elements that generate heat simultaneously is five or less, normal printing is possible with a small-capacity power supply.

[Effects of the Invention] As explained above, according to the present invention, the time difference between the start time of application of a printing pulse to each heat generating element of the thermal head and the start time of application of an application pulse to an adjacent heat generating element is Since the maximum pulse width applied to the element is not exceeded, high-quality images without dividing lines can be obtained with a small-capacity power supply.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a thermal transfer recording device according to an embodiment of the present invention, FIG. 2 is a block diagram showing a detailed configuration of the thermal head drive section shown in FIG. 1, and FIG. 3 is a solid printing in this embodiment. FIG. 4 is an application pulse timing chart for each heating element in the present embodiment when normal image data is input; FIG. 5 is a conventional application pulse timing chart for each heating element. FIG. 6 is an application pulse timing chart for each conventional heating element. In the figure, l...image data input terminal, 2...color conversion circuit, 3...data conversion circuit, 4...line memory, 5
...Intermediate tone i wholesale department, 7...Address counter, 8
...Temperature compensation ROM, 9...Concentration counter, lO・
...Thermal head, 12...Ink sheet, 13.
. . . receiving paper, 14 . . . platen roller, 15 . . . heating resistive element, 16 . . . latch, 17 . Figure R+ 2 33rd 4RsRiR F1 Mot91 Igo [t e 9 R+. Fig. 4 1 2 Rj R4Rs R6Ry 8 9 Rh.

Claims (2)

[Claims] (1) In a thermal head drive device that drives a thermal head in which a plurality of heating elements are arranged in a row, the difference between the application start time of an application pulse to a given heating element and the application start time of an application pulse to an adjacent heating element is determined. A thermal head driving device characterized by comprising a control means for controlling the time difference so that it does not exceed the maximum applied pulse width applied to the heating element. (2) The thermal head driving device according to claim 1, wherein the control means sets a time difference in the application start time of the application pulse at at least one location between adjacent heating elements.