JPS6067175A - Thermal printer - Google Patents

Abstract

PURPOSE:To maintain a uniform printed density without lowering printing speed, by a method wherein the number of printing elements operated to generate heat is counted by referring to a table based on a printing pattern, and the heating value of the printing elements is controlled. CONSTITUTION:In accordance with a printing command fed from a host computer 21, a CPU22 refers to a printing pattern stored in a RAM26 incorporated therein to count the number of the printing elements DT1, DT2, ... operated to generate heat. A driver 23 is controlled through the CPU22 in accordance with the result of counting, whereby the width of a driving pulse for each of the elements DT1, DT2, ... is set to be smaller as the number of the elements operated becomes smaller, thereby controlling the heating value of the elements. Accordingly, heat is prevented from being generated in an amount in excess of a required amount, without taking sufficient heat-releasing time, and printed density can be maintained to be uniform without lowering the printing speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to print density control for thermal printers, and in particular to the use of thermal [Prior Art] In general, the print density by the thermal dot method is mostly determined by the amount of heat generated by the dot heating element.

This heat generation utilizes Joule heat using a resistor material, and the resistance of the dot heating element is R [Ω], the voltage applied to the dot heating element is 1 V [V], and the heating time is t.
[If m81, the amount of heat generated per dot heating element W [
mJ) is given by the following equation.

W=Vt/R・・・・・・・・・・・・・・・・・・
(1) Figure 1 shows the heating time t when the resistance per dot heating element is 11 [Ω] and the calorific value per dot heating element is 2.1 (rnJ) in equation (1). [ms
] and the applied voltage V [V]. From FIG. 1, it is possible to know the relationship between the heating time and the applied voltage for a predetermined amount of heat generation, that is, a predetermined print density.

In a thermal printer, it is particularly important to keep the amount of heat generated constant in order to keep the print density constant. or,
Thin film resistors are generally used in thermal heads because of their good thermal response, high resolution, good adhesion to the base material, and excellent mechanical strength75).

FIG. 2 is a graph showing the relationship between the heating element surface temperature and heating time of this thin film type thermal head.

From Figure 2 2. OW power 1. It can be seen that if the injection is performed for a period of Oms, a heating element surface temperature S of 250 to 260° C. can be obtained. This heat is used to tactileize the solid coloring material on the thermal paper or thermal inkjet printer, and the color is developed on the thermal paper or dyed by transfer to plain paper.

P1 Non Tough with such a thermal head! It has been conventionally used as an output device for printing out text and graphic information in information equipment. However, conventional printers of this type have various problems in controlling print density. .

In FIG. 3(A), the horizontal axis represents the time t, and the vertical axis represents the printing timing V and the surface temperature T of the heating element.
The relationship between printing timing V and surface temperature T is shown when five dots of continuous print are printed in the scanning direction of the thermal head.

As shown in Fig. 3 (4), space cycles are provided before and after the 5-dot conduction/gutter, in which 1 cycle (3 mS) of force U heat is not applied, and cycles 1 to 5 are space cycles. When the dot iQ turn 75 is true, a heating time of 1 ms and a heat dissipation time of 2 mS are allocated to each of them. This cycle will hereinafter be referred to as a heat cycle.

Although the heat dissipation time is set considerably longer than the heating time of the dot heating element as described above, the surface temperature of the dot heating element is not completely initialized as shown in FIG. Cycle] ~ Toward cycle 5, the heating element surface temperature T gradually accumulates in the thermal head as shown in the figure, and therefore the print density also gradually becomes darker.

By the way, when printing characters, if measures are taken to prevent heat from accumulating too much in the printing area of one character, the difference in density can be reduced to an inconspicuous level.

Moreover, if the thermal head was sufficiently dissipated in the space cycle provided between the characters, it was possible to suppress the difference in density between the characters at the beginning and end of the - line to some extent. As an example of a device for this purpose, a control method as shown in FIG. 3(B) has been proposed.

In FIG. 3(B), if heating was performed in cycle 1 as shown in the diagram, in the next cycle 2, a determination is made as to whether or not heating was performed in the immediately preceding cycle (cycle 1). Heat radiation time f 0 set to standard value 2.0 ms
．． The heating time is increased by 3 ms to 2.3 ms, and in accordance with this, the heat generation time f 0.3 ms, which was previously set to the reference value 1.0 ms, is controlled to be decreased to 0.7 ms. . Since this control is common to all cycles in which the dot pattern is true, the printing timing V and dot surface temperature T as shown in FIG. The difference has improved considerably.

However, the functionality required of a thermal printer is also required to print out images and graphs displayed on a monitor screen.

Particularly in such applications, the dot heating elements arranged in a single vertical row are often used to continuously generate heat in the scanning direction, that is, to print a flat black image, so the method described in Fig. 3 (B) is often used. With the control method, it is not possible to suppress the temperature rise, and it becomes impossible to achieve sufficient concentration uniformity.

The state in which print density changes in the case of continuous peta black printing will be explained below with reference to FIG. 4 (4).
As shown in Fig. 4(B), when performing continuous flat black printing starting from heat cycle 1 and ending with heat cycle n, heat accumulates in each dot heating element, and the dot surface temperature rises as shown in Fig. 4(B). do.

In this case, unlike the case of character printing, the heat dissipation effect cannot be expected in the space cycle between characters, and the duty ratio of heating and heat dissipation is changed by monitoring whether or not there was heating in the previous cycle. Even with this control method, in the case of character printing, the driving is performed at the same duty ratio in the section up to tscyc/L'n, which exhibits any effect, and it is not possible to maintain a uniform print density.

Figure 3 (C) is a diagram explaining one method for solving density changes in the case of such flat black printing. In this method, the basic period of the cycle is lengthened to ensure sufficient heat dissipation time. By doing this, we tried to initialize the heating element surface temperature each time. However, such a method has a fatal drawback in that the printing speed is significantly reduced, and it is virtually impossible to apply it to an actual printer.

〔the purpose〕

The present invention has been made in view of the drawbacks of the prior art described above, and its main purpose is to make the print density uniform not only in character printing but also in peta black printing without reducing the printing speed. The purpose of the present invention is to provide a thermal printer that can maintain high performance.

A feature of the present invention is that all dots generated in one line are counted as a means for monitoring the heating state of the thermal head along the time series of continuous printing control, and when controlling a certain dot printing cycle, the number of dots generated in one line is counted. The objective is to achieve uniform printing density by providing an optimal heat pulse width to the thermal bed based on the number of counts.

[Explanation of Examples]

The present invention will be described in detail below with reference to FIGS. 5 to 8.

In FIG. 5, a block diagram showing a control unit of a thermal printer according to the present invention, a host computer 21 that controls the thermal printer as a peripheral device and a CPU 22 that performs main control of the printer are connected via a signal line 21. ing. The CPU 22 is provided with a ROM 27 containing a printer control program and a RAM 26 used by the CPU 22.

On the other hand, the CPU 22 controls the driver 23'i via signal lines 82 and 83. This driver 23 includes heating elements DTi to DT8 of the thermal head 2 (see FIG. 6).
is connected. Further, the driver 23 includes a nozzle motor 4 (for driving the thermal head 2 in the scanning direction).
(See Figure 6) excitation phases Sφ1 to Sφ4 and platen 1.
Excitation phases Fφ1 to Fφ of the pulse motor 5 (see FIG. 6) for rotating the motor 2 (see FIG. 6) and feeding the paper.
4 is connected. In this way, each heating element and each /
? By excitation of the phases of the pulse motor under the control of the CPU 22, predetermined printing is performed.

Reference numeral 28 in FIG. 5 is the power switch of the thermal printer, and turning on the power is necessary for the CPU 22,
Driver 23. Thermal head 2. Pulse motor 4, 5
etc. become operational.

In addition, the CPU 22 uses the RAM 26 when the power is turned on.
Reset the internal heat cycle counter.

Next, the schematic structure of the thermal printer will be explained with reference to FIGS. 6(A) and 6(B) 1r.

In FIGS. 6(4) and 6(B), the carriage 1 carrying the thermal head 2 moves along the guide shaft 6 which is disposed in parallel with and facing the platen 12 while moving the mark 'ji!' f
fh 4'E 6 g et al -2-θ) base-1k--'
This is carried out by driving the pulse motor 4 through the gears 7, 8, and Li.

During the printing operation, move carriage 1 to the printing start position (6th position).
Printing is performed by moving the PT force direction from the left side in the figure), and when the specified printing is completed, the carriage 1 is moved in the CR force direction to perform a return operation, and the carriage is returned to the printing start position to start the next line. An example of a state in which printing can be started is given below. The return of the carriage 1 to the return position is detected by the endless switch 3, and the return information i when the carriage returns is
The information is input to the CPU 22.

The platen 12, which is in pressure contact with the paper, is driven by the pulse motor 5 via the shifters 10, 11, 13, and the paper is advanced to carry out a feed change operation.

In this thermal printer, the thermal head 2 has eight printing elements (heating elements) D as shown in FIG.
TI to DT8 are arranged in a line in the vertical direction, and while the thermal head is moved in the scanning direction (horizontal direction), selected printing elements in the printing element row are heated to perform thermal transfer, and the dots at that time are Characters or figures can be printed using a combination of the following.

Therefore, in the thermal solinter, a table is provided for the number of dots to be printed for each printing pattern of the printing element array, and the number of printing elements that generate heat is counted based on this table for each printing/mother turn. The total number of dots can be detected at any time. Furthermore, when the count number increases and reaches a predetermined position, the heat generation amount is changed (reduced) by controlling the heat noyral width of each printing element, thereby preventing the dot surface temperature from rising and reducing the printing density. It is becoming more uniform.

FIG. 7 is a diagram illustrating the table showing the number of dots to be printed for each printing i+turn. Hereinafter, a method of counting the number of printing elements that generate heat will be explained with reference to FIG.

In Figure 7, the 4th turn of printing is 2 hexadecimal numbers.
The code is displayed by a combination of two digit numbers, and the eight printing elements D1 to D8 are divided into two groups, D1 to D4 and D5.
- D8, and print/lean is displayed in hexadecimal for each group.

In other words, the printing pattern depending on whether or not each printing element generates heat,
As shown in Fig. 7, if the elements that generate heat are marked with ○ and the elements that do not generate heat are marked with Since the number of dots that generate heat is uniquely determined for each of the print turns 01 to F'F, the number of dots that generate heat for each print/lean is registered for each print/gutter in this table. The number of heating dots for each print pattern can be immediately read by searching the address using the print number or turn code.

For example, if the printing pattern is only heating element D3 and all other heating elements do not generate heat, the number is 04 in hexadecimal, and the number of heating dots at this time is 1 from the table in Figure 7. This can be detected immediately and the location can be counted. Moreover, the heating elements DI, D2 and D4
In the case of printing i4 turn, which causes the other heating elements to generate heat, it is encoded with QB, and the table above reads that the total number of heating dots in this printing pattern is 3. can be counted immediately. Furthermore, heating elements DI, D2. D3. In the case of printing a4 turn in which D7 and D8 generate heat and the other heating elements do not generate heat, the corresponding 05, that is, the number of heating dots 5, is read by the address signal C7, and this can be counted immediately.

Similarly, for example, when the printing pattern is FB, the total number of heating dots is 7, and when the printing pattern is FF, the total number of heating dots is 8, that is, all the heating elements generate heat. The number of heating dots can be immediately read and counted.

As is clear from the above explanation, by using a table in which the number of heating elements for each printing pattern as shown in FIG. 7 is registered, the total number of heating elements can be counted for each printing turn. Ru.

Furthermore, if you use a table like the one shown in Figure 7, you can immediately read the state in which all heating elements do not generate heat, such as the spaces between characters, for each print/print turn, so the number of heating dots can be reduced. If the value of 0 continues for an appropriate number of times, it is also possible to control the temperature by a negative counting method, in which a predetermined number is subtracted from the total count that has been counted so far, taking into account the drop in the dot surface temperature.

The operation mode for fully controlling the lasing width applied to the thermal head according to the embodiment of the present invention described above with reference to FIGS. 5 to 7 will be described below with reference to FIG. 8.

In this case, the CPU 22 is the host computer 21
The print pattern stored in the RAM 26 is referred to according to the print command from the signal line S2. The optimum application and pulse width to be applied to the thermal head 2 via the driver 23 are determined.

In FIG. 8, the CPU 22 is in a state of waiting for data from the host computer 21 via the signal line S1, and in step 100 it judges whether or not data has been received, and when it has received it, it starts the next step. In step 101, it is determined whether the code is a control code or not.

If it is a control code, the CPU 22 performs control processing by switching modes such as LF or CR, but if not, it is determined in the next step 102 whether or not it is a print code. In the case of unspecified data, error processing is performed, but in the case of specified data, a printing operation is started based on the print code.

After starting the printing operation, the number of dots that have generated heat since the start of printing is referred to by the dot counter in the RAM 26, and in step 103, the number of dots counted by the dot counter, the current print heat generation, and the pulse width are determined.

Next, in step 104, the current printing pattern is set to signal S2. For example, if the current printing pattern is FF in FIG. 7, that is, flat black printing, that effect is set.

In this way, the heat generation/glue width determined in step 103 is applied, and printing is performed based on this.

In the next step 106, the table start address is added to the current printing pattern, that is, the start address is set to 000.
If it is set to 0, the current printing pattern FF is added to this, and 0O
The FF address is specified.

Next, in Stella f107, the contents of the address (for example, 0OFF address) determined in step 106 are referred to (the total number of heating dots of the current printing pattern) 'fr. That is, as shown in the table of FIG. 7, a table value of 08 (indicating that the number of heating dots is 8) is stored at address 0OFF, and this is referred to.

Then, in Stella 7'108, the table value is 0.
It is determined whether the number of heating elements is 0 or not, that is, whether there are no heating elements and the number thereof is O. If it is not 0, i.e. 8 like FF address
If so, in the next step 109, this table value (8) is added to the dot counter. On the other hand, if the table value is oo in the Stella f108, (
If no printing is performed, the number of times no printing is performed is added to the swish counter in step IIO.

If no printing continues n times during the printing operation, it is determined in step 111 whether the space counter has reached n times or not, and if it has reached n times, the next step is performed. In step 112, the count number of the dot counter is decremented by the value of XX.

In this way, using the table shown in Figure 7, the table value for each printing pattern, that is, the number of heating dots, is added up, and if the number of non-printing reaches a predetermined n times, the predetermined number is subtracted. The printing heating pulse width is controlled according to the total number of heating dots requested by adding the above operations, thereby controlling the dot surface temperature and achieving uniform printing density. Incidentally, after performing the negative count in the snap 112, step 113 is performed.
reset the system space counter.

〔effect〕

As is clear from the above explanation, the thermal printer of the present invention is configured to count the number of heat-generating printing elements for each printing pattern and control the amount of heat generated based on the counted number, so that the counting speed can be increased. It is possible to improve the width, and even when performing flat black printing such as image printing with a high-speed printer, the dot surface temperature can be appropriately controlled, and unevenness in print density can be effectively prevented.

[Brief explanation of drawings]

Figure 1 shows the heating time t [
ms] and applied voltage V; FIG. 2 is a graph illustrating the relationship between heating element surface temperature T and heating time t (ms) of a thin-film thermal head for each amount of heat generation; FIG. (A), CB), (c) are graphs illustrating the printing timing V and heating element surface temperature T with respect to the elapse of printing time t in various conventional printing density control methods; ) is a diagram illustrating the state of print density change and the state of increase in heating element surface temperature T when performing peta black printing, FIG. 5 is a block diagram illustrating the outline of the control unit of the thermal printer according to the present invention, and FIG. Diagram (A)
, (B) is a plan view and front view illustrating the overall structure of a thermal printer suitable for carrying out the present invention, and FIG. 7 shows the number of heating dots for each printing pattern used in the thermal printer according to the present invention. An explanatory diagram illustrating a table, and FIG. 8 is a flowchart illustrating an operating procedure of a thermal printer according to the present invention. 1... Carriage, 2... Thermal head, 4.5.
...Pulse motor, 12...Platen, 22...CPU that controls the main control of the printer, 23...Driver,
26...RAM with built-in heat cycle counter,
27...ROM containing a printer control program
, DTI to DT8... heating elements (printing elements). - 1 Figure 92 Figure 92) w43 Figure (A) Figure 3 (B) w43 Figure (C) in the dark → 1 to 6 Figure (A) Figure 6 (B) CRPT @ 7 Figure 03 X X XXXX0O02 04 XXXXX XO○××02 1 1 1 1 1 1 FD 0OOOOOX○ o7 FE 0000000× 07 FF ○00QOOo0 08

Claims (1)

[Claims] (1) A thermal printer that uses a thermal head with printing elements arranged in one or more rows and prints υ characters or figures by combining dots by generating heat in selected printing elements in the printing element row. With Niji, printing and printing of the printing element row
A table is provided for the number of dots to be printed for each turn of printing, and the number of printing elements that generate heat is counted based on the table every four turns of printing, and the amount of heat generated by the printing element is changed based on the counted number. A thermal printer that is characterized by its ability to uniformize printing density.