JPS60151072A - Thermal recorder - Google Patents

Abstract

PURPOSE:To eliminate switching wires and enhance printing quality, by a method wherein only the dots at a boundary part between printing blocks are printed by repeating overlap printing two times, while using data which are less than the original printing data, in each overlap printing. CONSTITUTION:A partition printing circuit drives elements 0-256 of a thermal head SL in a phase phi1, and drives elements 255-511 in a phase phi2, thereby printing. To carry out the method of driving only the elements 255, 256 at the boundary part over the phases phi1 and phi2, a CPU stores actual printing pulse width data for the elements 0-256 and non-printing dummy data for the elements 257-511 into a line buffer 4 to conduct printing in the phase phi1, and stores non-printing dummy data for the elements 0-254 and actual printing data for the elements 255-511 into the line buffer 4 to conduct printing in the phase phi2.

Description

[Detailed Description of the Invention] 2. Field of Industrial Application The present invention relates to a thermal recording device capable of multi-gradation printing that can be applied as a hard copy device in the computer graphics field, video system field, and communication field such as facsimile. be.

Conventional configurations and their problems Recently, improvements in integrated head manufacturing technology have increased the areal density of head elements, making it possible to make high-resolution hard copies.However, on the other hand, the number of head elements has increased. Along with this, the current capacity and instantaneous power required for printing increased, and in order to meet the required power, a large-capacity power supply was required, which led to the miniaturization of equipment.

This was a major hindrance to weight reduction.

A split printing method is used as one method of reducing the power required for printing using a multi-element head. This method does not print on all elements of the head at the same time, but instead divides the head into n blocks and prints sequentially on each block, reducing the instantaneous power required for printing to 1/n. It can be suppressed.

However, when the above method is used, as shown in FIG.
4, linear noise (switching line) 15 occurs along lines 15 and 15 that are not printed sufficiently, resulting in a disadvantage that the image quality is greatly degraded.

The cause of the above switching line will be explained using FIG. 2. In FIG. 2, φ1. φ2 is a waveform indicating block sequential driving. SL is a line-shaped thermal head,
T1. T2 indicates the temperature distribution generated by the thermal head when uniform gradation data is printed, and DEN indicates the density distribution of dots printed by the head.

In the example in the figure, the left half of the head is ○~265, and the left half of the head is 256.
It is divided into the right half of ~511, and the left block is sequentially printed in phase φ1, and the right block is sequentially printed in phase φ2-.

Now, considering the case where uniform gradation data is printed, the density distribution DEN of printing is obtained according to the temperature distributions T1 and T2 generated by the head. It is assumed that TI and T2 also take into consideration the influence of heat diffusion to the peripheral parts of printing paper and the like that come into contact with the head. Here, as shown in TI and T2, the elements at both ends of each block are 0.256 and 256°61
1 has a temperature distribution different from that of other elements.

That is, in the elements 1 to 264 and 257 to 510, since the elements on both sides thereof generate heat at the same time, the gaps between the elements also reach a certain temperature due to mutual thermal diffusion l. Therefore, the gap between each dot of printing is also the same as D in Figure 2.
A certain concentration can be obtained as shown in EN. However, 0, 255, and 25 located at both ends of each block
In the element No. 6,511, only the element in one corner generates heat, and the heat is excessively diffused in the direction where it is not generating heat, resulting in T1. It exhibits a temperature distribution as shown at T2. As a result, the print density DEN around that element becomes closer than the gaps between other elements, as shown in FIG. In the case of elements O and 511, which are located at both ends of the entire head, there is no major deterioration in image quality because they are at the edges of the image, but the gap between elements 255 and 266 located at the joint between two blocks is The density becomes extremely low compared to the gaps between the two, and a white linear defect occurs in the center of the image, significantly degrading the image quality. If the heat diffusion to the periphery of the elements at the end of the block is even greater, not only the gaps between the elements but also the printed dots themselves of the corresponding elements may have a lower density than other elements. This causes even greater deterioration in image quality. When printing an image using the conventional divided printing method as described above, a switching line that causes noise is newly generated between the blocks of the head, resulting in a problem of deterioration of image quality.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned problems, and an object of the present invention is to provide a thermal recording device that takes measures to reduce the deterioration in image quality caused by switching lines that occur when using a divided printing method. Structure of the Invention The present invention has a line-shaped thermal head, divides one line of printing into a plurality of blocks, prints each block, and prints only one or more dots at the boundary between the blocks before and after printing. DESCRIPTION OF THE EMBODIMENTS Thermal recording device of the present invention is a thermal recording device characterized by printing in two times, each time printing with reduced data compared to the original print data, and performing two overlapping printings. An example of this is shown in FIG.

In Fig. 3, 1 is an image signal input unit, 2 is a CPU for data processing, 3 is a conversion table for converting image signals into pulse width data to be applied to the thermal head, and 4 is a pulse width for one line. line memory that stores data;
5 is a division printing circuit for performing division printing of one line; 6
is a line-shaped thermal head. In this embodiment, it is assumed that the print density is controlled by controlling the pulse width for driving the elements of the thermal head.

The image signal input section 1 converts the image signal into gradation data and outputs the CP
Input to U2. The CPU 2 refers to the conversion table 3 and converts the gradation data into pulse width data for driving the thermal head, and outputs the pulse width data to the line memory 4. At this time, since overlapping printing is performed for several dots at the printing boundary, the pulse width data is converted to lower pulse width data than that at the other than the printing boundary. The divided printing circuit 5 generates pulses for driving each element of the thermal head 6 according to the pulse width data of the line memory 4 to perform printing. The printing method at this time will be explained using FIG. 4. The abbreviations in FIG. 4 are the same as in FIG. 2. The divided printing circuit 5 prints the thermal head SL from 0 to 0 in the phase φ1.
256 elements are driven, and in phase φ2, elements 255 to 511 are driven to perform printing. As described above, the boundary portion 255.
Only the 266 elements have a phase of φ1. For example, the method of driving over φ2 is to use the CPU 2 to drive from 0 to 2 during phase φ1.
For 66, the actual printing pulse width data is 257~
For 511, dummy data without printing is stored in the line buffer 74 and printed, and at phase φ2, Q~264
This can be realized by storing non-printed dummy data for 256 to 511 and storing actual print data for 256 to 511.

When uniform gradation data is printed using this divided printing method, since the elements 255 and 256 are simultaneously driven over φ1° and φ2, the temperature distribution T1 in FIG. T2
As shown in the figure, no extreme temperature distribution valleys occur between the elements 256° and 266°. Therefore, as shown in the concentration distribution DEN, 25
No extreme drop in density occurs between the 5,256 and 1 to 1, and no switching line occurs at all as would occur with the conventional divided printing method. Unfortunately, in the end point element 256 of the drive block in phase φ1, as explained in the conventional example, heat diffusion to the periphery becomes large, and both the density and shape of the dot become small. However, in phase φ2, elements 255,2
Since elements 56 and 257 are driven at the same time, element 256
, 257 are not drive block end points, and printing is performed in a state with little heat diffusion. Therefore, the phase φ1. By overlapping the printing densities of φ2, the density distribution DE in Fig. 4 is obtained.
As shown in N, there is a slight decrease in density between 266.257 and yl-, so some switching lines may occur, but unlike the conventional split printing method, no noticeable switching lines will occur. The same goes for the dots 264 and 255, but the phase φ1. Since printing is performed twice for φ2, printing is performed with pulse width data that is smaller than that for other dots for each phase, and φ1. By superimposing φ2, φ1. It is necessary to obtain the same print density as when printing is performed only once in either of φ2. If the rate at which this pulse width data is reduced is incorrect, printing will be done with a relatively high or low density only at the print boundary, greatly reducing the image quality. The appropriate rate of reduction varies for each gradation depending on the characteristics of the thermal recording system. Therefore, as shown in FIG.
6, φ1. By providing a table 2 that is separate from the pulse width data conversion table 1 used when printing only once in either φ2, the pulse width data reduction rate can be changed for each gradation to change the dot density at the print boundary for each gradation. can be finely adjusted to prevent the image quality from deteriorating as described above.

Furthermore, regarding the drivers l-255 and 256 at the print boundary, the thermal histories of the elements are different in the phases φ1 and φ2. In other words, the printing sequence is 0 at φ1 as shown in Figure 4.
266 dots are printed, and 255 to 511 dots 1- are printed at φ2. Normally, after φ2, there is a printing pause period for paper feeding, etc., and then the next line printing sequence begins.

Therefore, the elements of dots 255 and 256 generate some heat at φ1 and are further driven at φ2. For this reason, it is better to have a slight difference between the pulse width data of phases φ1 and φ2, and to make the driving pulse width at φ1 slightly wider than that at φ2, so that printing with equal density can be performed every printing cycle.
Print image quality can be improved.

The above processing is performed as shown in Figure 6.
For 255 and 256, in phase φ1, gradation data is converted to pulse width data with reference to table 2 and printed, and in phase φ2, gradation data is converted to pulse width data with reference to another table 3 and printed. This can be achieved by doing. As described above, for the dots at the print boundary, the phase φ1. A separate table is prepared for φ2, fine concentration adjustments are made taking thermal history into account, and phase φ1. With φ2, printing can be performed with a balanced density, further reducing the influence of the switching line and improving image quality.

Effects of the Invention The thermal recording device of the present invention divides one line of printing into a plurality of blocks and prints the blocks sequentially, and 1'f! , by dividing only the plurality of dots into two times, one before and the other, and printing with data reduced from the original print data each time, and performing overlapping printing twice.
Eliminates switching lines caused by conventional split printing methods,
Print image quality can be improved. Also, as a result,
The divided printing of the present invention allows the use of a power supply with a small capacity, and can be expected to have many effects such as miniaturization, weight reduction, and cost reduction of the apparatus.

[Brief explanation of the drawing]

Figure 1 is a printing state diagram showing the state of switching lines that occur in images printed by the conventional division printing method, Figure 2 is a diagram showing the temperature distribution and print density around the head generated by head drive, and Figure 3 FIG. 4 is a block diagram showing the configuration of a thermal recording device according to an embodiment of the present invention, FIG.
FIG. 5 is a diagram showing the case where the printing pulse width data reduction rate of dots at the printing boundary area is changed depending on the gradation, and FIG. φ2
1. Image input section, 2. CP II, 3. Conversion f -7", 4. ...Line memory, 5...
...Divided printing section, 6...Thermal head.

Claims (3)

[Claims] (1) It has a line-shaped thermal head, divides one line of printing into multiple blocks, prints each block, and prints only one or more dots at the boundary of the printing block twice, before and after. A thermal recording device characterized in that printing is performed with data reduced from the original printing data each time, and overlapping printing is performed twice. (2) The thermal recording device according to claim 1, wherein the rate at which the print data is reduced is changed for each gradation in the door at the boundary of the print block. (3) The thermal recording device according to claim 2, wherein the rate at which the print data is reduced is changed for each printing cycle before and after the dots at the boundaries of the print blocks.