JPS61206366A - Thermosensitive printing system - Google Patents

Abstract

PURPOSE:To prevent generation of stripes in printing an intermediate tone picture by decreasing the pitch of width scanning more than the print width at main scanning to overlap ends of the printed part and decreasing the density of the overlapped part to make the density of the overlapped part nearly equal to the density of the part without overlapping. CONSTITUTION:The feeding pitch in the width scanning direction is not set to the arranging length (b) of heaters 12 but to a distance (d) shorter than the (b) by n-dot's share of the heater (n is a positive integer). Further, the temperature at heating at a position by n-dot's distance from both ends of the heater 12 is set lower than the temperature at heating of parts of m dots (m is a positive integer) of the remaining heater part. Since the width scanning pitch corresponds to (m+n)-dots content shorter by the n dots of the heater than the dot arrangement length (b), each n-dot length are printed duplicatedly twice at printing. Thus, even when the width scanning pitch is in variation or the relative position between the paper 6 and the thermal head 1 in the width scanning direction is changed due to vibration of a carriage 2 attended with the main scanning, the print is never missing between lines.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a serial type thermal printer, and more particularly to a thermal printing method suitable for printing images with extreme gradations.

[Background of the invention]

In recent years, thermal printers that print images including halftones have been announced. When printing a halftone image, uneven density or scanning lines significantly degrade the image quality. For example, even if main scanning is performed only electrically using a heat-sensitive line head, smudges due to thermal causes will occur at the boundaries of the main scanning, and vibration control as shown in Japanese Patent Application Laid-open No. 12677/1983 will occur. Is required.

On the other hand, if an attempt is made to print a thick image, it becomes uneconomical to use a line thermal head with a large number of heating elements covering the width of the screen, as shown in the above-mentioned publication. As disclosed in the publication, printing is performed by moving a small thermal head in the main scanning direction and the paper in the sub-scanning direction.A so-called serial type is preferable.

However, when halftone images are recorded using the serial method, due to variations in the sub-scanning distance and a decrease in the density of the end heating element, etc.
Stripes are formed at the sub-scanning distance pitch in the main scanning direction, which can seriously impair image quality.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a printing method that prevents the occurrence of stripes when printing halftone images in the above-mentioned serial printer.

[Summary of the invention]

In order to achieve this purpose, in the present invention, the pitch of the sub-scanning is made smaller than that of the printing part in the main scanning so that the edges of the printing part overlap, and the density of the overlapped part is reduced. The density of the overlapping part is
The density should be approximately the same as the non-overlapping area.

[Embodiments of the invention]

The present invention will be explained below using examples.

Figures 2 and 3 show a plan view and a side view, respectively, of a serial printer to which the present invention is applied. A thermal head 1 having a plurality of heating elements is mounted on a carriage 2, and the carriage 2 is connected to a feed belt 3. Pulley 4. and a motor (not shown) that rotates pulley 4
It moves in the direction of arrow A (hereinafter referred to as the main scanning direction) by a main scanning mechanism consisting of the following. Note that the carriage 2 is guided by a guide mechanism (not shown).

A platen 5 is in pressure contact with the thermal head 1 within the movement range of the thermal head 1 . After the paper 6 passes between the thermal head 1 and the platen 50, it passes through, for example, a friction roller 7, a pinch roller 8. The pinch roller 8 is moved in the direction of arrow B (hereinafter referred to as the sub-scanning direction) by a sub-scanning mechanism including a motor (not shown) that rotates the pinch roller 8.

If the paper 6 is thermosensitive coloring paper, the above configuration may be used, but if the paper 6 is plain paper or dye-receiving paper,
An ink ribbon 9 coated with heat-fusible or heat-sublimable ink is provided between the thermal head 1 and the paper 6.

Note that the ink ribbon 9 is wound between a supply shaft 10 provided on the carriage 2 and a take-up shaft 110.
A weak winding torque is appropriately applied to the winding shaft 11.

The printing operation based on the above-described configuration will be explained with reference to Figure 4. The thermal head 1 is provided with a plurality of heating elements 12 arranged side by side in the sub-scanning direction. In printing, the heating element 12 is energized to generate heat to a desired temperature to print, and then the length of each heating element 12 is C in the main scanning direction.
move by a length approximately equal to . When this operation is repeated to print one line, the paper 6 is fed in the sub-scanning direction and the next line is printed. Thereafter, the above operations are repeated to print one screen.

At this time, the feed pitch in the sub-scanning direction is set not to the length b of the heating elements 12, but to a distance d that is shorter than b by n tods of heating elements (n is a positive integer). Among them, the temperature at the time of heat generation of n dots from both ends is set lower than the temperature at the time of heat generation of the remaining heating elements (m dots) (m is a positive integer). Figure 1 shows an example of a printing result produced by the present invention. In Figure 1, the vertical axis represents the printing density of the printing result, and the horizontal axis represents the distance in the sub-scanning direction in terms of the pitch of the heating elements, which shows the density distribution of the printing result in the sub-scanning direction. In the case of , it shows the result of busy printing so that the density is uniform.

In the case of the present invention, the sub-scanning pitch is shorter than the dot arrangement length -gb of the heating element 12 by n dots of the heating element (m
+n) dots, so when printing, each n dot is printed twice. Therefore, even if the sub-scanning pitch varies or the relative position of the paper 6 and thermal head 1 in the sub-scanning direction changes due to the movement of the carriage 2 during main scanning, printing will not be missed between the lines. do not have.

In addition, as will be described later on in the area with a width of n dots, which is printed twice, the density of each print is low because the heat generation temperature is low, and even if it is printed twice, the density will not become extremely high. In particular, in the case of n5w1 dots, the density is 40 to 8
It is desirable to lower the temperature during heat generation so that the temperature becomes 01. In addition, in the case of n≧2 dots, among the n dot heating elements,
A more favorable result can be obtained than by setting the heat generating elements at the ends to a low temperature, and by setting the heat generating elements near the center to a high temperature.

Hereinafter, a means for setting the printing density by the heating element n dots at both ends to be lower than the printing density by the heating element m dots at the other end parts will be exemplified.

Figure 5 shows a method of reducing the temperature during heat generation by limiting the time when electricity is applied to the heating element 12, thereby lowering the print density. In FIG. 5(a), data of one gradation mark in a halftone print is stored from the terminal S1 to the buffer memory 21 having addresses equal to the number of heating elements. The print data is synchronized with the print signal input from terminal S.
n0m+n) is read out by the address generation circuit 22 that generates addresses for each pixel, and is stored in the gradation pulse memory 2.
5.24, the pulse train is output. On the other hand, the address signal is input to the address discrimination circuit 25, and the address discrimination circuit 25 discriminates whether it is the first n data, the middle m data, or the last n data. Switching circuit 26
switches and outputs the pulse train from the gradation pulse memory 23 or 24 to the output terminal S, based on the determination result. The output pulse train becomes an input pulse train to the thermal head 1. Here, the gradation pulse memo 1325 VC is for the middle m buttons as shown in Figure 6 (-), and the gradation pulse memory 24 is for the first and last n buttons as shown in Figure 6 (b). , output gradation pulse width for input gradation data, so-called gamma characteristics are stored.

Therefore, the width of the grayscale pulses output for the same grayscale data is shorter for the first and last n pieces,
Is the energization time in the heating element 12 short (therefore, the print density becomes low? In addition, in the case of n≧2, the difference in Figure 6 (C
), (d), etc., are added in parallel to the gradation pulse memories 2s and 24, and these outputs are switched in the same way.
You can also input it.

Figure 5(b) shows another means of limiting the energization time.

In this case, print data of a certain gradation from the buffer memory 21 is input to the gradation correction circuit 27. (ll correction circuit 27 uses the determination result of the address judgment circuit 250 to subtract a certain amount of gradation from the input gradation, or to add 1 The output is multiplied by the following values. Therefore, the output from the gradation pulse memory 24 has a shorter pulse width for the first and last n heating elements, and has the same effect as the above-mentioned embodiment. play.

Figure 7 shows a method of lowering the printing density by limiting the current applied to the heating element.

In Figure 7 (a), among the heating elements 12 arranged in a row, the heating elements 124° 12b at the ends have a greater resistance value than the heating element 12c at the center. For this purpose, the thickness of the heating elements 12α and 12b is reduced. Although there are methods such as narrowing the effective width or using a material with a high specific resistance, in this embodiment, the length is increased.

As a result, when the same voltage is applied between the terminals 4+a and 41h, the current flowing through the heating elements 12a and 12b is smaller than the current flowing through the heating element 12C, resulting in a lower temperature when generating heat and a lower printing density. Become. In particular, as in the illustrated example, by setting the resistance value of the heating element 12a at the extreme end to be larger than the resistance value of the next heating element 12b, the printing density characteristic shown in FIG. 4 can be obtained.

Figure 7(b) shows another embodiment. In this case, the heating elements 12d and 12e at the ends are the same in size and material as the heating element 12c at the center 6 in 4.
Resistors 426.e which are not involved in printing are connected in series with each other.
42b is connected.

Therefore, when the same voltage is applied between the terminals 414 and 42h, the current flowing in the heating elements 12c and 12d due to the voltage drop due to the resistors 42a and b is smaller, and the temperature reached during heating can be set lower, making it possible to Effects can be obtained. In this case as well, by setting the value of the resistor 42a connected to the heating element 12C at the end to be thicker than the value of the resistor 42b connected to the next heating element 12dK, it is possible to print as shown in Figure 1. Concentration characteristics can be obtained.

Figure 8 shows an embodiment of the present invention in which three-color printing is performed. In the thermal head 1, the heating element 1
2 is divided into three heating element groups 12f, 12g, and 12h, and each group prints three colors, for example, cyan, magenta, and yellow. The ink ribbon 9 is provided with a cyan ink portion 96, a magenta ink portion 9b, and a yellow ink portion 9C in the form of bands, each of which has a heating element group 12f.
, 12g, and 12h. Figure 9 shows print density when color printing is performed using the thermal head 1 and ink ribbon 9 shown in Figure 8. The vertical axis in the figure represents the distance in the sub-scanning direction in units of the number of dots on the heating element. For color printing, 3 groups of heating elements 12f, 12g
, 12 hours, the print density of the n dots at the end of each group is adjusted to the central part m by the means described above.
Lower the print density than the dot print density. In addition, in the case of this example, there is a distance of / dot between each heating element group.
A non-printing area is provided in consideration of the meandering of the ink ribbon 9, but it is also possible to provide a heating element in this area so that it is not energized during printing and effectively serves as three groups of heating elements. . When printing, the heating element groups 12f, 12g,
From 12hK, by printing cyan and azentau yellow print data by applying the above-described embodiments to each, the print density after printing one line decreases at the edge of each color. After printing one line, it is moved in the sub-scanning direction by a distance of (m+n) dots, and the next line is printed. By repeating this operation, a printing result is obtained in which the end portions of each row of each color overlap by a distance of n dots, and the three colors overlap.

At this time, if the length of the non-printing part t is set to a non-integer multiple of the pitch of the heating elements 12, for example, in the case of color, the remainder obtained by dividing 1 by the pitch of the heating elements 12 is set to 1/kK, then k colors are printed one on top of the other. When this is done, since each color is printed shifted by 17 dots on the print, the area where each color is subtractively mixed is reduced, and a good color mixture is obtained. Also, the feed pitch in the sub-scanning direction is (n
+ m ), so in Fang 9 diagram, (n+t)≦
By setting it to m, the overlapping parts of each color can be
Since the color can be shifted at the top and sudden changes in hue in the overlapping area can be avoided, better prints can be obtained.

〔Effect of the invention〕

As explained above in detail (according to the present invention, in a serial type thermal transfer method, it is possible to eliminate stripes due to density unevenness and hue unevenness at each sub-scanning pitch. without using a head,
There is an effect that halftone recording of good image quality can be obtained using a small and inexpensive thermal head.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the printing result according to an embodiment of the present invention, Fig. 2 and Fig. 3 are top and side views of the printer to which the present invention is applied, and Fig. 4 is an explanatory diagram showing the printing result according to an embodiment of the present invention. An explanatory diagram of the printing operation, Figure 5 is a block diagram of the embodiment of the first embodiment of the present invention, Figure 6 is a graph showing the contents of the gradation pulse memory in Figure 5, and the off diagram is the second embodiment of the present invention. FIG. 8 is an explanatory diagram showing the printing operation when color printing is performed according to the present invention; FIG. 9 is an explanatory diagram showing the density distribution in the sub-scanning direction of the printing result; It is. DESCRIPTION OF SYMBOLS 1...Thermal head, 6...Paper, 9...Ink ribbon, 12...Heating element. Figure 4 Figure 27 Figure 5 (b) Step 4 data Figure 7 O81!1 O9 Closed E91! lmiu,

Claims (1)

[Scope of Claims] 1) A thermal head having a heating element forming a plurality of dots (l dots) lined up in the sub-scanning direction, the head being orthogonal to the sub-scanning direction with respect to the recording medium. In a thermal printing method that performs thermal recording on a recording medium by moving the recording medium in the sub-scanning direction after scanning in the main-scanning direction, both ends of a plurality of bits in the sub-scanning direction of the thermal head A means is provided for setting the amount of heat generated per dot of each of the heating elements corresponding to n dots to be lower than the amount of heat generated per dot of the heating element corresponding to m dots in the central portion, and the feeding pitch of the recording medium in the sub-scanning direction is set. A thermal printing method characterized by a distance equivalent to (m+n) dots (where l, m, and n are integers, and l=m+2
n relationship). 2) In the thermal printing method as set forth in claim 1, the heat generation amount setting means sets the per-dot energization time for the heating elements corresponding to n dots at both ends to m at the center.
A heat-sensitive application method characterized by comprising means for limiting the heating element to a shorter length than that for a heating element corresponding to a dot. 3) In the thermal printing method as set forth in claim 1, the heat generation amount setting means sets the current per dot to the heating elements corresponding to n dots at both ends to m at the center.
A thermal printing method characterized by comprising means for setting a heating element smaller than that for a heating element corresponding to a dot.