JPH0253232B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal printer that prints a dot pattern by driving a heating resistor element to color recording paper or by thermally transferring thermal carbon onto recording paper, and particularly relates to a thermal printer that prints a dot pattern by driving a heat-generating resistor element. This invention relates to a thermal printer that maintains a constant print density regardless of the situation.

In order to keep the print density of a thermal printer constant without being affected by changes in ambient temperature, it is necessary to apply driving energy to the heating resistive element in accordance with the ambient temperature. For this reason, various driving methods have been proposed in which the driving energy of the heating resistor element is changed in response to changes in ambient temperature.

One of these methods is the method disclosed in Japanese Unexamined Patent Publication No. 143839/1983, and an outline thereof will be explained below.

This method detects the temperature of a heat-sensitive recording head (thermal head) and calculates the number (N) of recording signals given to the heating resistor element within a unit recording time (T) allocated to print one dot. The driving energy of the heating resistor element is thereby changed in accordance with the temperature of the thermal head. Specifically, two methods have been considered for changing the number (N) of recording signals within this unit recording time (T).

One method is to include a circuit that gates a clock signal with a constant period, which is the basis of the recording signal, and to vary the gating time depending on the temperature of the thermal head.
This changes the number (N) of recording signals within a unit recording time (T). That is, when it is desired to increase the number of recording signals, the gating time (W) is lengthened, and conversely, when it is desired to decrease the number of recording signals, the gating time (W) is shortened.

Another method is to change the number (N) of recording signals within a unit recording time (T) by changing the cycle of recording signals. That is, when it is desired to increase the number of recording signals, the period of the recording signal is shortened, and conversely, when it is desired to decrease the number of recording signals, the period of the recording signal is lengthened.

However, the method cited in this reference controls the driving energy of the heating resistor element by changing the number (N) of recording signals within a unit recording time (T), and therefore the following problems still remain.

One is that when the number of recording signals (N) within a unit recording time (T) is changed using the former method, that is, when the gating time (W) is changed, the gating time ( Since no recording signals are given to the dots other than W), the gating time (W) becomes shorter and the number of recording signals (N) decreases, resulting in the width of the recorded (printed) dots becoming narrower. As a result, gaps are created between the dots, resulting in a decrease in print quality.

Furthermore, when the number (N) of recording signals within a unit recording time (T) is changed by the latter method, that is, when the period of the recording signals is changed, a simple control circuit can drive the heating resistor element. The problem is that it is not possible to precisely control energy. In other words, the control circuit becomes complicated in order to finely control the drive energy of the heating resistor element. As shown in the cited example, it is possible to reduce the number of recording signals (N) by half from 10 to 5 with a simple circuit, but in this case the driving energy of the heating resistor element is divided into two stages. I can only control it. In order to finely control the drive energy of the heating resistor element, a special control circuit is required that can freely change the period of the recording signal.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal printer that solves these problems and can obtain higher quality printing results with a simple configuration.

The present invention allocates a fixed drive time to print one dot, and uniformly chops the entire drive time using a chopping pulse of a fixed cycle, depending on the temperature of the thermal head. The pulse width of this chopping pulse is changed accordingly.

Since the present invention drives the heating resistor element throughout the driving time in this manner, the width of the printed dots does not become narrower and gaps are not formed between the dots as described above. Furthermore, since the width of the predetermined pulse is changed in accordance with the temperature of the thermal head, the drive energy of the heating resistor element can be precisely controlled by a simple control circuit.

The present invention will be explained below with reference to the drawings.

FIG. 1 shows a drive control circuit for explaining an embodiment of the present invention, and D ₁ to _{D o} are print data signals transferred from a print data source (not shown);
1 is a timing pulse generation circuit that generates a drive timing pulse TM, and 2 is the print data signal.
It is a NAND gate that receives D ₁ -D _o and drive timing pulse TM as input, and outputs drive pulses ₁ - _o for selecting and driving a desired one from heat generating resistive elements R ₁ -R _o . In the present invention, a fixed driving time (T) for printing one dot is allocated using these driving pulses ₁ to _o . For details, see Figure 3 (c). 3 is a thermal head having heating resistive elements R ₁ to _{R o} ; 4 is a head temperature detecting means for detecting the temperature of the thermal head 3; Reference numeral 5 represents a stepping control circuit that outputs a stepping pulse, and the details will be explained later. 6 is the chopping pulse
A NOR gate, TR _{1 ~} , which receives CHP and drive pulses ₁ ~ _o , which are the outputs of the NAND gate 2, as inputs.
TR _o is a drive transistor as a drive element that is turned on and off by the output signals S ₁ to _{S o} of the NOR gate 6 and causes a drive current to flow through the heating resistive elements R ₁ to _{R o} .

FIG. 2 shows an example of the above-mentioned chopping control circuit 5, where MS is a monostable multivibrator,
PG ₁ is a pulse generator that continuously generates a trigger pulse TP to trigger this monostable multivibrator MS at a constant cycle, and outputs this trigger pulse TP to the trigger input terminal of the monostable multivibrator MS, and 7 is the pulse generator mentioned above. monostable multivibrator
An inverter that inverts the output of the MS and sends out a negative stepping pulse, TH is a thermistor as the temperature detection means 4 mentioned above, and a resistor
It is connected in series with R _a and connected to the control terminal that controls the pulse width of the monostable multivibrator MS. The above-mentioned monostable multivibrator MS may be a general commercial product (for example, Texas Instruments SE555, NE555, etc.), and the time constant r is determined by the capacitor C, the resistor R _a , and the resistance value R _T of the thermistor TH. (R _a +R _T ) The width of the generated pulse changes depending on C. i.e. thermistor
Since the resistance value R _T of TH changes following the change in temperature of the thermal head 3, the pulse width changes following the change in temperature of the thermal head 3.

Therefore, as the temperature of the thermal head 3 increases and the resistance value R _T of the thermistor TH decreases, the pulse width generated by the monostable multivibrator MS becomes narrower.On the other hand, as the temperature of the thermal head 3 decreases, the resistance value R T decreases. As _T increases, this pulse width becomes wider.

Next, the operation and effect of the above structure will be explained with reference to FIG.

When the print data signals D ₁ to D _o are supplied as shown in FIG. 3A, the drive pulses ₁ to _o gated by the drive timing pulse TM shown in FIG. The output is as shown in c. On the other hand, in the chopping control circuit 5, the monostable multivibrator is activated by the trigger pulse TP of FIG. _3D generated from the pulse generator PG1.
The MS operates and a chopping pulse is output.

Two types of chopping pulses 1 and 2 are shown in FIG. 3. When the temperature of the thermal head 3 is low, the chopping pulse 1 shown in FIG. This shows a case where the temperature of the thermal head 3 is high.

In the NOR gate 6, the driving pulse ₁ in Figure 3 C is
Chopping pulses in Figure 3 E and F by DV _o
CHP1 and CHP2 are gated, and signals S ₁ to _{S o} of FIG. 3 are output. As shown in FIG. 3, this NOR gate 6 inverts the chopping pulses 1 _and 2 in _FIG .
It outputs the signals S ₁ to S _o of each.

Therefore, when the temperature of the thermal head 3 is low, the signals S ₁ to S _o in FIG. 3G are input, whereas when it is high, the signals S ₁ to _{S o} in _FIG . be done. The drive transistors TR ₁ -TR _o are turned on when the input signal is at a high level (H), thereby causing a drive current to flow through the heating resistive elements R ₁ -R _o .

Here, when the temperature of the thermal head 3 is low, as shown in FIG. 3, the high level (H) time of the signals S ₁ -S _o is long, so that the ON time of the drive transistors TR ₁ -TR _o becomes long. Therefore, the heating resistance elements R ₁ ~ _{R o}
The heat generation time becomes longer, and the driving energy of the heat generating resistive elements R ₁ to _{R o} becomes larger. On the other hand, if the temperature of the thermal head 3 is high, the signal as shown in Figure 3
Since the high level (H) time of S ₁ to S _o is short, the on time of the drive transistors TR ₁ to T R _o is shortened. Therefore, the heating time of the heating resistance elements R ₁ to R _o becomes shorter,
The driving energy of the heat generating resistive elements R ₁ to _{R o} becomes smaller.

As described above in detail, the thermal printer of the present invention includes a head temperature detection means for detecting the temperature of the thermal head, a pulse generator that continuously generates trigger pulses at a constant cycle, a trigger input terminal and a pulse generator. The pulse generator is connected to the trigger input terminal, and the head temperature detection means is connected to the control terminal, the period is the same as the trigger pulse, and the pulse width is the same as the head temperature detection means. A monostable multivibrator that outputs a chopping pulse that changes in accordance with changes in the means, a drive pulse to which a fixed driving time is allocated to print one dot, and the chopping pulse are input. , has a gate circuit that outputs the stepping pulse for this driving time, and a driving element that is turned on and off by the output signal of this gate circuit and flows a driving current to the heating resistor element of the thermal head. This method has the following effects that could not be obtained using the above method.

First, in the first conventional method, the gating time (W) of the recording signal is changed depending on the temperature of the thermal head, so no recording signal is given at all times other than the gating time, and the gating time (W) is short. Then, as mentioned above, gaps are created between the dots. In contrast, in the present invention, since the driving time of the driving pulse is constant regardless of the temperature of the thermal head, the chopping pulse, that is, the time for gating the recording signal is constant regardless of the temperature of the thermal head. Also,
The period of the stepping pulse is the same as the period of the trigger pulse, and this period is also constant regardless of the temperature of the thermal head. Therefore, regardless of the temperature of the thermal head, the heating resistor element is driven for a constant period of time and at a constant cycle. Therefore, the width of the printed dots is constant regardless of the temperature of the thermal head, and it is possible to obtain extremely high quality printing results with no variation in printing density.

Furthermore, since the second conventional method changes the period of the recording signal depending on the temperature of the thermal head, the drive energy of the heating resistor element cannot be precisely controlled with a simple control circuit as described above. In contrast, in the present invention, the head temperature detection means is connected to the control terminal for controlling the pulse width of the monostable multivibrator, and the pulse width of the chopping pulse is changed in accordance with the temperature of the thermal head.
The drive energy of the heating resistor element can be precisely controlled by a simple control circuit. As a result, extremely high quality printing results with no variation in print density can be obtained with a simple control circuit.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a diagram showing the configuration of a part of FIG. 1 in detail, and FIG.
The figure is an operational waveform diagram of an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Timing pulse generation circuit, 3... Thermal head, 4... Head temperature detection means, 5...
Chopping control circuit, PG ₁ ...Pulse generator,
MS...Monostable multivibrator, R ₁ ~ R _o ...
Heat generating resistor element.

Claims (1)

[Scope of Claims] 1. A thermal printer that includes a thermal head having a plurality of heat-generating resistive elements and prints a dot pattern on recording paper by passing a driving current through the heat-generating resistive elements, comprising: a head that detects the temperature of the thermal head; Temperature detection means, a pulse generator that continuously generates trigger pulses of a constant period, a trigger input terminal and a control terminal that controls the pulse width are provided, the pulse generator is connected to the trigger input terminal, and the pulse generator is connected to the control terminal. The head temperature detection means are connected to each other, and the period is the same as the trigger pulse,
A monostable multivibrator outputs a chopping pulse whose pulse width changes in accordance with a change in the temperature of the thermal head detected by the head temperature detection means, and a monostable multivibrator which outputs a chopping pulse whose pulse width is constant in order to print one dot. A NOR gate circuit inputs a driving pulse to which a driving time is assigned and the stepping pulse, and outputs the stepping pulse for this driving time; and a NOR gate circuit that is turned on and off by the output signal of this NOR gate circuit, and the heating resistor. 1. A thermal printer comprising: a drive element that causes a drive current to flow through the element.