JP3094169B2 - Thermal printer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a thermal head.
The present invention relates to a thermal printer , and more particularly, to a method of driving a heat generating element group for forming print dots.

[0002]

2. Description of the Related Art In recent years, a thermal printer using a thermal head as a printing mechanism has been widely used as an output terminal of a measuring device, an information device or a medical device. The thermal head is generally constituted by a heating array in which a plurality of heating elements selectively driven in accordance with print data are linearly arranged. Each heating element receives a drive current and converts it into Joule heat to form print dots on thermal paper. When a drive current is supplied to all the heating elements simultaneously, a large amount of drive current is required when a printing rate per line is high, and a large-capacity power supply must be prepared. In order to avoid this, the heating array is divided into a plurality of physical blocks, and time-division driving is performed by applying a strobe signal to each physical block.

Conventionally, each heating element has a structure in which a driving current is supplied from a power supply via one common electrode. This common electrode is formed in parallel with the heating array and has a considerably long span. Therefore, a voltage drop occurs between a portion near and far from the power source due to the resistance, and the power supply amount of each heating element varies. As a result, the print dot density varies depending on the individual positions of the linearly arranged heating elements.

In order to improve this point, it has been proposed to divide the common electrode. That is, a structure has been proposed in which a plurality of stem electrodes are provided so as to form a power supply path for a drive current for each set of a predetermined number of physical blocks. Then, driving is performed for each of a predetermined number of physical blocks supplied with power via the same stem electrode. That is, time-division driving is performed in units of individual stem electrodes.

[0005]

A thermal printer using a thermal head has a relatively simple structure and is suitable for miniaturization. For this reason, thermal printers have been widely used as output terminals of various portable devices or desktop devices. In such a case, a battery is often used as a power source, and low voltage driving of the thermal head is required. Therefore, it is necessary to reduce the resistance value of each heating element, and a low-resistance heating element of several hundred Ω has been developed. When the resistance value of the heat generating element is reduced, the influence of the voltage drop due to the wiring resistance of the stem electrode forming the power supply path of the driving current relatively appears.

Considering the case where time-division driving is performed in units of stem electrodes as in the prior art, when a printing rate is close to 100%, a considerable amount of drive current flows. The density of the printed dots becomes low due to the heating element that receives power from the stem electrode. On the other hand, when the printing rate at the next time-division driving timing is low, the amount of power supplied to the next stem electrode is reduced, and the effect of the voltage drop does not appear, and the printing dot density becomes a normal level. As described above, when the resistance value of the heating element is low and time-division driving is performed in units of the stem electrode, uneven printing density occurs between physical blocks due to a local difference in printing rate, and printing is performed. There was a problem that the quality deteriorated.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to improve print quality by removing print dot density unevenness between physical blocks.

[0008]

SUMMARY OF THE INVENTION A thermal according to the present invention is provided.
Applying the printer as its basic configuration requirements, a heating array linearly arranged a plurality of heating elements are selectively driven in accordance with print data, the strobe signals for each physical block obtained by dividing a plurality of heating elements The control circuit has a control circuit for driving the heating array in a time-division manner, and a plurality of stem electrodes provided so as to form a power supply path for a drive current for each set of a predetermined number of physical blocks. As a characteristic component of the present invention, the control circuit controls the strobe signal so that the strobe signal is not applied at the same timing to all of a predetermined number of physical blocks supplied through the same stem electrode. A means for performing timing control is provided. For example, when a predetermined number of physical blocks are collectively driven at a certain time-division driving timing, control is performed so that a predetermined number is selected from physical blocks to which power is supplied from different stem electrodes. Therefore, a predetermined number of physical blocks fed from the same stem electrode are not driven simultaneously.

[0009]

According to the above-mentioned structure, the printing rate is assumed to be 100%.
Therefore, the number of heating elements that receive power from the same stem electrode in one time-division driving timing must be smaller than the total number of heating elements belonging to that stem electrode, and the amount of drive current must be reduced. Can be. As a result, even when the resistance value of each heating element is set low, it is possible to suppress the adverse effect of the voltage drop caused by the wiring resistance of the main electrode. That is, since the magnitude of the voltage drop is determined by the product of the resistance and the current, the voltage drop can be reduced by suppressing the current amount.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a thermal printer according to the present invention.
FIG. 3 is a circuit block diagram illustrating an electrical configuration of the data processor . As shown in the drawing, the thermal printer is provided with a heating array in which a plurality of heating elements 1 selectively driven according to print data are linearly arranged. The resistance value of each heating element 1 is set to several hundreds Ω, preferably 300 Ω or less to enable low-voltage driving, and a physical block obtained by dividing a plurality of heating elements 1 is provided. The heat generating element 1 to which it belongs is selectively driven by a corresponding driver IC.

For example, as shown, the first physical block is driven by the driver IC 21, the second physical block is driven by the driver IC 22, the third physical block is driven by the driver IC 23, and the fourth physical block is driven. Is driven by the driver IC 24, and the last m-th physical block is the driver IC
Driven by 2 m. That is, in this example, the driver IC and the physical block correspond to each other. However,
The number of physical blocks driven by one driver IC may be two or more.

The driver ICs 21, 22, 23, 24,
, 2m are connected to a control circuit, for example, CPU3.
The CPU 3 sends print data DATA to each driver IC, and applies a strobe signal to each driver IC, that is, to each physical block, and drives the heating array in a time-division manner. That is, the driver IC 21 outputs the strobe signal STB
1, the driver IC 22 is selected by the strobe signal STB2, and the driver IC 23 is selected by the strobe signal STB3.
4 is selected by the strobe signal STB4, and the driver IC 2m is selected by the strobe signal STBm.

A plurality of stem electrodes are provided so as to form a power supply path for the drive current for each set of a predetermined number of physical blocks (two in this example). This stem electrode is divided into a power stem electrode connected to the power source Vp side and a ground stem electrode connected to the ground GND side. Each stem electrode is formed close to the heating element 1 and has an extremely small wiring resistance of about 0.1Ω. The drive current supplied via the main electrodes is distributed to the individual heating elements 1 via the branch electrodes 4. The branch electrodes 4 are all patterned so as to have substantially the same wiring resistance.

Now, focusing on the ground side, the first and second physical blocks receive power supply via the ground stem electrode 51, and the third and fourth physical blocks receive the ground stem electrode 52.
And the m-th physical block is supplied with power by the ground stem electrode 5k. on the other hand,
Focusing on the power supply side, the first physical block is supplied with power by the power supply main electrode 61, the second and third physical blocks are supplied with power by the power supply main electrode 62, and the fourth physical block is supplied with the power supply main electrode 63. Receiving power, m
The physical block is powered by the power supply main electrode 6k.

As described above, in this embodiment, the set of physical blocks supplied from the grounding main electrode and the set of physical blocks supplied from the power supply main electrode are different, but this makes the layout of the main electrode compact. It is to do. Of course, the same set of physical blocks may be supplied with power by a pair of ground stem electrodes and power supply stem electrodes. Finally,
As a characteristic part of this embodiment, the CPU 3 controls the strobe signals STB1 and STB2 so that the strobe signals are not applied at the same timing to all of the predetermined number of physical blocks supplied through the same stem electrode. , ST
B3, STB4,..., STBm. For example, the first and second physical blocks supplied with power via the ground stem electrode 51 are not driven simultaneously. In other words, the strobe signal STB
1 and STB2 are not output simultaneously.

Next, the configuration of the driver IC 21 will be briefly described with reference to FIG. The other driver ICs have the same configuration. As shown, the driver IC 21 has n
It has a stage shift register 7 so that a total of n heating elements 1 can be driven. That is, the number of heating elements divided into one physical block is n. The print data DATA is sent from the CPU 3 to the n-stage shift register 7 bit by bit in synchronization with the clock signal CLK.
Each stage of the shift register 7 is also connected to a latch 8 composed of n stages.

The latch 8 similarly latches and holds the print data stored in the shift register 7 bit by bit in synchronization with the latch signal LTC sent from the CPU 3. One input terminal of a corresponding AND gate circuit 9 is individually connected to each stage of the latch 8. AND gate circuit 9
The strobe signal STB1 supplied from the CPU 3 is commonly applied to the other input terminal. The output terminal of each AND gate circuit 9 is connected to each heating element 1 via a corresponding output driver 10.

In such a configuration, the strobe signal ST
When B1 is applied, each AND gate circuit 9 is simultaneously opened, and the output driver 10 is excited according to the latched bit data to selectively drive the heating element 1. That is, when the bit data indicates dot printing, a driving current flows through the corresponding heating element 1 to actually perform dot printing. Next, the operation of the heat generating element group shown in FIGS. 1 and 2 will be described in detail with reference to the timing chart of FIG. This thermal
The printer performs a printing operation for each line. In synchronization with the high-speed clock signal CLK, the CPU 3 drives the driver ICs 21 and 2 connected in series with one line of print data DATA.
Transfer to 2, 23, 24, ..., 2m. When the transfer of the print data is completed, the latch signal LTC is output, and the print data DATA for one line is latched all at once.

Subsequently, the CPU 3 controls the application timing of the strobe signal to perform time-division driving of the heating array.
In this embodiment, the number m of the physical blocks shown in FIG. 1 is set to 6. Accordingly, there are six strobe signals STB1 to STB6. First, at the first time division drive timing, the strobe signal STB1 is applied to the driver IC 21 and the strobe signal STB4 is applied to the driver IC 24. Therefore, for example, focusing on the ground stem electrode 51, power is supplied only to the first physical block, and is not supplied to the second physical block. Therefore, even if the printing rate is 100%, the number of heating elements that are energized simultaneously at one time-division driving timing is only half of the total.

Next, a strobe signal STB2 is applied to the driver IC 22 at the second time-division driving timing,
The strobe signal STB5 is applied to the corresponding driver IC. Referring again to the ground stem electrode 51, power is supplied only to the second physical block and not to the first physical block. Finally, the strobe signal STB3 is supplied to the driver IC2 at the third time-division driving timing.
3 and the strobe signal STB6 is applied to the last corresponding driver IC. Similarly, the ground stem electrode 52
Focusing on, power is supplied only to the third physical block and power is not supplied to the fourth physical block. Thus, the printing operation for one line is completed by the three time-division driving. As described above, focusing on one ground stem electrode, only one physical block is supplied with power at one time-division driving timing, and the remaining physical blocks are not supplied with power. This relationship is the same even when focusing on the power supply main electrode.

Returning to FIG. 1, the description will be continued. Now, suppose that the number of heating elements 1 included in the first physical block is 100
And It is assumed that the second physical block also includes 100 heating elements 1 in the same manner. It is assumed that each heat generating element 1 has a specific resistance of, for example, 100Ω. In this case, the combined resistance of each physical block is 1Ω. On the other hand, the wiring resistance of the ground stem electrode 51 constituting the power supply path for the first and second physical blocks is about 0.1Ω.

In such a configuration, according to the driving method of the present invention, only one physical block is driven by one energizing timing. Therefore, even in the case of full dot printing, the voltage drop due to the wiring resistance of the ground stem electrode 51 is only about 10% of the power supply voltage. Such an energy loss does not adversely affect the actual dot print density. On the other hand, even when the same three-division driving is performed, when the first and second physical blocks that are energized through the grounding stem electrode 51 are simultaneously driven at one energization timing as in the related art, Under the condition of all dot printing, a driving current twice as large as that of the present invention flows, and the voltage drop is about 20% of the power supply voltage. When the energy loss reaches 20%, the actual print dot density is adversely affected and the print quality deteriorates.

[0023] The server according to the last in the present invention, with reference to FIG. 4
Another embodiment of the multi-printer will be described. In this example, a total of twelve physical blocks 121 to 132 are arranged in a line. Three ground stem electrodes 151, 152 and 153 are arranged on one side of this linear array, and three power supply stem electrodes 161 and 162 are also arranged on the other side.
And 163 are provided. In this example, a pair of grounding main electrodes and a power supply main electrode opposing each other make 4
A power supply path for the physical blocks is formed.

For example, the grounding main electrode 151 and the power supply main electrode 1
The physical blocks 121, 122, 123 and 124 are connected between the physical blocks 121 and 61. Similarly, a pair of stem electrodes 15
2 and 162, four physical blocks 125, 1
26, 127 and 128 are connected. Also, four physical blocks 129, 130, 131 and 132 are connected between the remaining pair of stem electrodes 153 and 163. The CPU 31 controls the timing of the strobe signals STB1 to STB12 applied to these twelve physical blocks to perform time division driving.

For example, in the case of performing two-division driving, odd-numbered strobe signals are simultaneously output at the first half of the drive timing, and the remaining even-numbered strobe signals are simultaneously output at the second half of the drive timing. In this way, even if the printing rate is 100%, the number of physical blocks to be supplied with power in one time-division driving timing is two for each stem electrode, and the voltage in the power supply path that adversely affects the printing quality is reduced. Descent can be suppressed.

[0026]

As described above, according to the present invention, the strobe signal is prevented from being applied at the same timing to all of the predetermined number of physical blocks supplied through the same stem electrode. Since the strobe signal timing is controlled, the amount of drive current flowing through each stem electrode at one drive timing can be suppressed as compared with the conventional case, so that the voltage drop or energy loss due to the wiring resistance of the stem electrode is reduced. This has the effect of preventing print density unevenness between physical blocks from occurring and improving print quality.

[Brief description of the drawings]

FIG. 1 is a schematic circuit block diagram showing an embodiment of a thermal printer according to the present invention.

FIG. 2 is a circuit block diagram illustrating a circuit configuration example of a driver IC that drives a physical block of a heat generating element group of the thermal printer .

FIG. 3 is a timing chart for explaining the operation of the thermal printer shown in FIG.

FIG. 4 is a schematic circuit block diagram showing another embodiment of the thermal printer according to the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (72) Katsuaki Saida, Inventor 6-31-1, Kameido, Koto-ku, Tokyo Inside Seiko Electronic Industries Co., Ltd. (72) Yoshinori Sato 6-31-1, Kameido, Koto-ku, Tokyo (56) References JP-A-48-64843 (JP, A) JP-A-62-13367 (JP, A) JP-A-63-74662 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) B41J 2/35-2/37

Claims (1)

(57) [Claims] 1. A heating array in which a plurality of heating elements selectively driven according to print data are arranged in a straight line, and a strobe signal is applied to each physical block obtained by dividing the plurality of heating elements, so that time division is performed. a control circuit for driving the heating array, and a plurality of stem electrodes provided so as to form a feed path for the driving current for each set that summarizes the physical blocks of the predetermined number, the control circuit identical Out of a predetermined number of physical blocks fed through the
Lock one or more physical blocks so that the strobe signal is not applied to the lock at the same timing.
A thermal printer comprising means for selectively applying a strobe signal and controlling timing of the strobe signal.