JP2003039721A - Thermal printer and method for controlling energization of thermal printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the printing quality from decreasing due to a voltage drop of a driving power source when a head is energized in a thermal printer. SOLUTION: A dummy load-generating means for falsely generating a state of impressing a voltage to the head is set to the thermal printer which prints through thermal coloring or thermal transfer by energizing a plurality of heating units arranged to the head. Based on a voltage drop amount of the driving power source obtained by comparing a first driving voltage in a state in which the head and the dummy load-generating means are not energized with a second driving voltage in a state in which the dummy load-generating means is energized, a maximum number of simultaneous excitation dots for printing by simultaneously energizing the heating units is set, and moreover, a width of pulses to be excited to the head is calculated by correcting a voltage impressed to the head.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique effective when applied to a thermal printer for printing with a thermal head, and more specifically to a method for controlling energization of the thermal head in a thermal printer using a battery as a driving power source.

[0002]

2. Description of the Related Art A thermal printer includes a thermal head in which a plurality of heating elements are arranged, and supplies an energizing pulse signal according to print data to the heating element to perform printing by thermal color development or thermal transfer. Is.

FIG. 2 is a block diagram showing a schematic structure of a thermal head. The thermal head 10 temporarily stores a plurality of (384 in FIG. 2) heating elements 11, 11, ..., An output driver 12 for driving the heating elements 11 with current, and print data. It is composed of a latch register 13 and a shift register 14.

The print data DAT serially input from the input terminal is taken into the shift register 14 in synchronization with the clock signal CLK and transferred to the latch register 13 by the latch signal LATCH at an appropriate timing.
When the head print energization instruction signals DST1 to 6 are input, the heating elements corresponding to the stored print data DAT are energized and printed.

In the thermal head shown in FIG. 2, 384 heating elements 11 are divided into six blocks each having 64 heating elements, and the heating elements of the corresponding blocks are controlled by the head print energization instruction signals DST1 to DST6. .

In recent years, thermal printers have been widely used in small electronic devices having a printing function, and in such small electronic devices, a battery is used as a driving power source so as not to impair portability and convenience. In many cases.
Therefore, like the thermal head shown in FIG. 2, one line is divided into a plurality of blocks, and printing of one line is sequentially energized in block units to reduce the maximum current. .

By the way, the energizing pulse width can generally be easily determined by using the following equation. From this equation, in order to obtain an appropriate energization pulse width t, the accurate energization voltage Vp
It can be seen that the head resistance value R is important.

[0008]

[Formula 1]

Here, t is the energizing pulse width (ms), E is the standard printing energy (mj), V is the energizing voltage (V), R is the head resistance value (Ω), and C is a correction coefficient according to the energizing pulse period. is there.

Further, when the energizing pulse width t is determined, in addition to the energizing voltage Vp to the head and the resistance value R of the head required by the above equation (1), the temperature of the head (heating element) and the like immediately before energizing. It is also possible to determine the energizing pulse width t by taking into consideration the influence of the resistance and the energizing voltage due to the head temperature and the like.

[0011]

However, when a battery is used as the driving power source, the current flowing through the head becomes large depending on the print data to be output, and the power supply voltage drops greatly due to the internal resistance of the battery. There is. In this case, since the actual energization voltage Vp becomes lower than the preset energization voltage Vp ′, the pulse width t ′ calculated in advance from the above formula becomes shorter than the actually required pulse width t, The print becomes faint. Further, if the amount of voltage drop is large, uneven printing is likely to occur, and there arises a problem that the printing quality cannot be ensured.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thermal printer and a method for controlling energization of a thermal printer, which can prevent the voltage of a driving power source from being lowered when the head is energized to deteriorate the printing quality.

[0013]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a plurality of heating elements, and the heating elements are energized in accordance with print data to generate printing paper by thermal coloring or thermal transfer. A line dot type head for printing on, and a voltage applying means for applying a predetermined voltage to the head,
Voltage measuring means for measuring the drive voltage of the voltage applying means, pseudo load generating means for pseudo generating a state in which a voltage is applied to the head, and the head and the pseudo load generating means in a non-energized state Based on a voltage drop amount of the voltage applying unit obtained by comparing a first drive voltage of the voltage applying unit with a second drive voltage of the voltage applying unit in a state where the pseudo load generating unit is energized. A maximum simultaneous energization dot number setting means for calculating the number of simultaneously energized dots for printing by energizing the heating elements at the same time and energizing the head by correcting the voltage applied to the head based on the voltage drop amount of the voltage applying means. The thermal printer is provided with at least an energization pulse width calculating means for calculating a pulse width.

According to this thermal printer, the drive voltage for actually energizing the head can be predicted to calculate the energizing pulse width, and the maximum number of simultaneously energized dots is limited so that the voltage drop of the voltage generating means does not become large. Therefore, it is possible to prevent the print quality from deteriorating due to a decrease in print density or occurrence of print unevenness.

Particularly, when a battery is used as the voltage applying means, the voltage drop of the drive voltage due to the internal resistance becomes large in relation to the amount of current flowing through the head. Therefore, the present invention can be applied to effectively suppress the voltage drop. Thus, the print quality can be secured.

Further, the pseudo load generating means is composed of a resistor having a resistance value corresponding to a total resistance of a predetermined number of the heating elements, and a switch means for enabling the pseudo load generating means. It should be set to. As a result, the pseudo load generating circuit can be enabled only when the second drive voltage is measured, so that it does not affect the actual printing and there is no fear of degrading the printing quality. Further, it is possible to easily correct the head applied voltage according to the number of heating elements that are actually energized, calculate the optimum pulse width for printing, and energize.

The maximum number of simultaneously energized dots can be easily set by using a preset table for the number of simultaneously energized dots which is preset in relation to the degree of the first drive voltage and the amount of voltage drop. can do. However, it is desirable to change this table according to the resistance of the pseudo load generating means.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the schematic arrangement of a thermal printer P according to this embodiment. The thermal printer P is a line dot type thermal head 10 that is driven by energizing pulses to print on a printing sheet, and a CPU (Central Processing Uni) that controls the entire printer.
t) 20, a ROM (Read Only Memory) 30 for storing programs executed by the CPU 20, parameters, etc.,
RAM (Random A) for temporarily storing print data, etc.
ccess Memory) 40, an input section 50 to which a key operation signal input by operating the operation panel and a print data signal from an external device are input, a motor drive circuit 60 that controls the operation of the motor 70, and a thermal A motor 70 for moving the head, feeding a printing paper, etc., a battery 80 as a driving power source for the thermal head 10, a voltage measuring circuit 90 for measuring a driving voltage of the thermal head 10, and a time when the thermal head 10 is energized. And a pseudo load generation circuit 100 that generates the above state in a pseudo manner. In addition,
The thermal head 10, the voltage measuring circuit 90, and the pseudo resistance generating circuit 100 are connected in parallel to the battery 80.

FIG. 2 is a block diagram showing a schematic structure of the thermal head 10.

The thermal head 10 of this embodiment includes a plurality of (384 in FIG. 2) heating elements 11, 11 ,.
An output driver 12 for driving the heating element 11,
Latch register 13 for temporarily storing print data
And a shift register 14. The print data DAT serially input from the input terminal is taken into the shift register 14 in synchronization with the clock signal CLK and transferred to the latch register 13 by the latch signal LATCH at an appropriate timing. When the head print energization instruction signals DST1 to 6 are input, the heating elements corresponding to the stored print data DAT are energized and printed.

In the thermal head shown in FIG. 2, 384 heating elements 11 are divided into 6 blocks each having 64 heating elements, and a strobe signal DST1 for instructing the head to be energized.
The heating elements of the corresponding blocks are controlled by ~ 6.

In this embodiment, one strobe signal D
In ST1 / DST2 / ..., the energization to 64 heating elements 11 corresponding to 64 dots is controlled, but the number of dots that can be energized simultaneously (hereinafter referred to as the maximum number of simultaneously energized dots) is 3
It is set to 2 dots.

Further, the thermal head 10 is provided with a thermistor so that the temperature of the head can be measured.

In FIG. 1, a battery 80 is a Ni-based battery capable of applying a voltage of 4.2 to 8.5 V to the thermal head 10.
It is a battery composed of Cd (nickel-cadmium) or the like. The battery 80 has internal resistance, and the thermal head 1
When a large load current flows to 0, 4.2 to 8.5V
The voltage drop due to the internal resistance may be 1 V or more with respect to the power supply voltage. At this time, it is necessary to perform printing if the thermal head 10 is energized with the energization pulse width calculated as the voltage applied to the thermal head when the battery voltage is not energized (hereinafter referred to as the no-load state). Energy cannot be obtained sufficiently and the print density becomes thin.

Therefore, in this embodiment, the voltage drop due to the internal resistance is measured by artificially generating a state in which the thermal head 10 is energized (hereinafter referred to as a load state) before the start of printing, and the voltage is measured. The voltage applied to the thermal head is corrected based on the voltage drop, and the maximum number of simultaneously energized dots is limited according to the degree of voltage drop. That is, the print density is secured by calculating the energization pulse width based on an appropriate applied voltage and limiting the maximum number of simultaneously energized dots that can be supplied by the set energization pulse width.

The voltage measuring circuit 90 is connected to the voltage supply path from the battery 80 to the thermal head 10, and the load state,
Measure the battery voltage with no load. In this embodiment,
Resistors R1 and R2 having the same resistance value and several tens of kΩ are connected in series, and the potential at the intermediate point A between the two resistors R1 and R2 is set to CPU2.
0 to the battery 80 by doubling this voltage
Drive voltage is calculated. In this embodiment, CP
Since the voltage value that can be taken in by U20 is about 5 V, the voltage measuring circuit has the structure shown in FIG.
If the voltage value that can be taken in at 0 is large, the voltage on the voltage supply path from the battery 80 to the thermal head 10 is directly CP.
You may make it take in in U20.

The pseudo load generating circuit 100 is connected to the voltage supply path from the battery 80 to the thermal head 10, and has a resistance R3 corresponding to the resistance of the heating element 11 when printing the maximum number of simultaneously energized dots (32 dots). The switching transistors T are connected in series. For example, when the resistance of one heating element is 180Ω, the resistance corresponding to 32 heating elements is 5.625Ω (= 180/32), so in this embodiment, a resistance of 6Ω which is slightly larger than that is connected. ing. As a result, when the switching transistor T is turned on, it is possible to create a state in which the maximum load that occurs when the thermal head 10 is energized is generated in a pseudo manner.

FIG. 3 is a flowchart relating to the printing process when printing is performed according to the print data DAT.

First, the voltage Vp1 of the battery 80 is measured by the voltage measuring circuit 90 shown in FIG. 1 while the thermal head 10 is not energized (step S1). Conventionally, the pulse width was calculated by using this voltage value Vp1 as the applied voltage Vp to the thermal head, but in the present embodiment, this voltage value Vp is calculated.
By correcting 1, the more optimum pulse width can be calculated.

Next, the switch of the switching transistor T is turned on so that the voltage is applied to the pseudo load generating circuit 100 (step S2). That is, a state is generated in which the load when the 32 heating elements (corresponding to the maximum number of simultaneously energized dots) of the thermal head 10 are energized is generated in a pseudo manner.

Next, the voltage Vp2 is measured with the voltage applied to the pseudo load generating circuit 100 (step S).
3). Thereby, the voltage dropped due to the internal resistance of the battery is measured.

Next, the switch of the switching transistor T is turned off to release the pseudo load state (step S4).

Then, the voltage difference between the voltage Vp1 in the unloaded state and the voltage Vp2 in the loaded state is calculated. If the voltage difference is 1 V or less, the influence of the voltage drop can be ignored, so the process proceeds to step S7. If the difference is 1 V or more, it is necessary to set the maximum number of simultaneously energized dots in consideration of the influence of the voltage drop, so the process proceeds to step S6 (step S6).
5).

When the voltage difference is 1 V or more in step S5, the maximum number of simultaneously energized dots is set according to Table 1 (step S6). The table for setting the maximum number of simultaneously energized dots shown in Table 1 is stored in the ROM 30 in advance.

[0036]

[Table 1]

For example, the unloaded voltage Vp1 is 4.2.
When the voltage drop (Vp1−Vp2) is 1.0V or less, the maximum number of simultaneously energized dots is set to 32 dots, and the voltage drop is within the range of 1.0 to 1.5V. For example, the maximum number of simultaneously energized dots is set to 24 dots,
If the voltage drop is within the range of 1.5 to 2.0 V, the maximum number of simultaneously energized dots is set to 16 dots, and the voltage drop is 2.
If it is 0 V or more, the maximum number of simultaneously energized dots is set to 8 dots.

Similarly, the voltage Vp1 in the no-load state is 5.0.
When the voltage drop (Vp1−Vp2) is 1.0 V or less, the maximum number of simultaneously energized dots is set to 32, and the voltage drop is 1.0 to 1.5 V. For example, the maximum number of simultaneously energized dots is set to 24 dots,
If the voltage drop is within the range of 1.5 to 2.0 V, the maximum number of simultaneously energized dots is set to 16 dots, and the voltage drop is 2.
If it is 0 V or more, the maximum number of simultaneously energized dots is set to 8 dots.

The voltage Vp1 in the no-load state is 6.0 to
In the case of 7.2V, if the voltage drop (Vp1-Vp2) is 1.5V or less, the maximum number of simultaneously energized dots is set to 32 dots, and if the voltage drop is 1.5V or more, the maximum number of simultaneously energized dots is It is set to 16 dots.

The voltage Vp1 in the unloaded state is 7.2 to
In the case of 8.5V, if the voltage drop (Vp1-Vp2) is 1.5V or less, the maximum number of simultaneously energized dots is set to 32 dots, and if the voltage drop is within the range of 1.5 to 2.0V. The maximum number of simultaneously energized dots is set to 24 dots,
If the voltage drop is 2.0 V or more, the maximum number of simultaneously energized dots is set to 16 dots.

As described above, by limiting the maximum number of simultaneously energized dots in accordance with the degree of voltage drop with respect to the voltage Vp1 in the no-load state, the voltage drop during energization can be suppressed to such an extent that print quality is not affected. it can.

Next, the head applied voltage Vp necessary for calculating the energizing pulse width is calculated based on the voltage Vp1 in the no-load state and the voltage Vp2 in the loaded state (step S7).
For example, in the present embodiment, the voltage drop value (Vp1-Vp2) when 32 heating elements are energized is known.
Based on this, the voltage drop value corresponding to the number of heating elements (the number of print dots obtained from the print data) actually energized is obtained, and the voltage applied to the head is corrected by correcting the voltage Vp1 in the no-load state with this voltage drop value. The voltage Vp may be calculated.

Next, the energizing pulse width to the head (see equation 1) is calculated based on the voltage Vp calculated in step S7,
Dots are printed by energizing the heating element corresponding to the print data with the calculated energizing pulse width (step S
8).

Next, it is judged whether or not the printing process is completed. If it is judged that the printing process is completed, a series of printing processes is completed. If it is judged that the printing process is not completed, step S1 is executed.
It shifts to 0 (step S9).

Further, in step S10, it is determined whether or not printing has been performed continuously for 50 lines. If it is determined that printing has been performed for 50 consecutive lines, the process proceeds to step S1 to check whether the maximum number of simultaneously energized dots is appropriate. A series of processes of steps S1 to S10 is repeated. On the other hand, if it is determined in step S10 that printing has not been performed on 50 consecutive lines, the process proceeds to step S7 to continue the printing process. That is, in consideration of battery consumption due to continuous printing, an appropriate maximum number of simultaneously energized dots is set for each predetermined printing process (50 lines printing in this embodiment).

In this embodiment, the voltage Vp applied to the thermal head 10 is changed according to (the number of print dots of) the print data to calculate the optimum energizing pulse width, and the maximum number of simultaneous energizing dots is limited. As a result, the current value is prevented from increasing and the voltage drop due to the internal resistance of the battery is prevented from increasing, so it is possible to prevent thin printing density and uneven printing, and realize high-quality printing. it can.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments. The table for setting the maximum number of simultaneously energized dots shown in Table 1 can be applied when the pseudo load generating circuit 100 of the present embodiment is used, and when the resistance R3 of the pseudo load generating circuit 100 is different. You should change the table accordingly. When the resistance value of the resistor R3 is larger than 6Ω of the present embodiment, the degree of the voltage drop is small, so the voltage drop amount (Vp1-
It is desirable to set the maximum number of simultaneously energized dots by reducing the range of Vp2).

It is also possible, for example, to provide a plurality of different types of resistors in the pseudo load generating circuit 100 and change the resistance value variously to measure the drive voltage at that time. It is desirable to prepare multiple tables according to the values.

[0049]

According to the present invention, the first drive voltage when the thermal head and the pseudo load generating means are not energized is compared with the second drive voltage when the pseudo load generating means is energized. Based on the obtained voltage drop of the driving power supply, set the maximum number of simultaneously energized dots that energize multiple heating elements arranged in the thermal head at the same time and correct the voltage applied to the thermal head. Since the pulse width for energizing the head is calculated, it is possible to prevent the print quality from being deteriorated due to the print density becoming thin or the print unevenness occurring.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a thermal printer P according to the present embodiment.

FIG. 2 is a block diagram showing a schematic configuration of a thermal head 10.

FIG. 3 is a flowchart regarding a printing process when printing is performed according to print data DAT.

[Explanation of symbols]

10 thermal head 20 CPU 30 ROM 40 RAM 50 Input section 60 motor drive circuit 70 motor 80 Drive power supply (battery) 90 Drive voltage measuring circuit 100 Pseudo load generation circuit P thermal printer

Claims (7)

[Claims] 1. A line dot type head having a plurality of heating elements, which prints on a printing paper by heat coloring or thermal transfer by energizing the heating elements according to print data, and applying a predetermined voltage to the head. For applying the voltage to the head, the voltage measuring means for measuring the drive voltage of the voltage applying means, the pseudo load generating means for artificially generating a state in which a voltage is applied to the head, the head and the pseudo load generating means A first drive voltage of the voltage applying means in a state where no current is applied to
Simultaneously energize and heat the heating element simultaneously based on the voltage drop amount of the voltage applying unit obtained by comparing with the second drive voltage of the voltage applying unit in the state where the pseudo load generating unit is energized. Maximum simultaneous energization dot number setting means for calculating the energization dot number, energization pulse width calculation means for correcting the voltage applied to the head based on the voltage drop amount of the voltage applying means, and calculating the pulse width for energizing the head A thermal printer characterized by comprising at least. 2. The thermal printer according to claim 1, wherein the voltage applying unit is a battery. 3. The pseudo load generating means comprises a resistor having a resistance value corresponding to the total resistance of a predetermined number of heating elements, and a switch means for enabling the pseudo load generating means. The thermal printer according to claim 1 or 2, which is characterized in that. 4. The maximum simultaneous energization dot number setting means,
The maximum number of simultaneously energized dots is set using a table for setting the maximum number of simultaneously energized dots set in relation to the degree of the first drive voltage and the amount of voltage drop. The thermal printer according to claim 3. 5. The thermal printer according to claim 4, wherein the table can be changed according to the resistance of the pseudo load generating means. 6. A method for controlling energization of a thermal printer, which uses a battery as a driving power source and prints on a sheet by a line dot type thermal head composed of a plurality of heating elements, the first method in a state in which no voltage is applied. A drive voltage is measured, a second drive voltage is measured in a state in which a voltage is applied to the thermal head in a pseudo state, and the second drive voltage is measured based on the first drive voltage and the second drive voltage. The amount of voltage drop is calculated, and the number of simultaneously energized dots that are energized to the heating element simultaneously to print is set based on the amount of voltage drop, and the pulse width to energize the head is calculated by correcting the voltage applied to the head. A method for controlling energization of a thermal printer, comprising: 7. The maximum number of simultaneously energized dots is set using a preset table for the number of simultaneously energized dots which is preset in relation to the degree of the first drive voltage and the amount of voltage drop. The energization control method for the thermal printer according to claim 6.