JPH08318633A - Print head driving circuit - Google Patents

Abstract

PURPOSE: To stabilize the input energy to magnet coils without using a firmware. CONSTITUTION: A driving circuit of a print head for a dot printer has magnet coils corresponding to two or more print pins, and selectively applies power to the magnet coils based on specified driving pulses to drive the correspondent print pins, thus printing is carried out. A base pulse generating circuit 1 that generates base pulses having a fixed pulse width, a temperature detecting circuit 2 that produces temperature information near the magnet coils, a correction pulse-generating circuit 3 that generates correction pulses, whose width changes corresponding to the temperature information, in synchronization with the base pulses, and a driving pulse generating circuit 4 that synthesizes the base pulses and the correction pulses to produce driving pulses are provided for each of the print pins.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a print head driving circuit for a dot printer, and more particularly to a print head capable of stabilizing the energy applied to a magnet coil regardless of variations in temperature conditions of the print head. The present invention relates to a drive circuit.

In a dot printer, a print head having a large number of pins is provided, and by energizing a magnet coil provided corresponding to each pin, each pin is individually driven to perform printing. Is configured.

In such a print head drive circuit for a dot printer, in order to stabilize the print quality,
It is necessary to keep the input energy to the magnet coil constant, but at this time, it is required to reduce the capacity of the firmware required for control and to speed up the process.

[0004]

2. Description of the Related Art In a conventional print head drive circuit of a dot printer, a large number of tables are provided in firmware (F / W) in order to perform control by a CPU, and this table is referred to for each printing operation. By changing the drive pulse width of the magnet coil according to the operating conditions, the applied energy to the magnet coil is stabilized regardless of the change in the characteristics of the print head.

[0005]

However, in the prior art, if precise control is attempted, a large amount of tables are required in the firmware, and the capacity of the ROM constituting the storage unit increases. There was a problem.

This is for controlling all the combinations of temperature change data obtained by monitoring changes in the print head internal temperature and ambient temperature, and in all cases according to each print mode and each pin position. This is because it is necessary to store the data in the table.

Further, in the prior art, there is a problem that it may not be possible to prepare a table that determines the optimum input energy depending on the accuracy of the monitored temperature.

This is because when the temperature is monitored by using a CPU, the detected temperature data is converted into digital data by an A / D converter. Since the output data of the / D converter is a stepwise value at regular intervals, A
This is because when the accuracy of the / D converter is low, it may not be possible to set the optimum drive pulse width.

On the other hand, for example, Japanese Patent Laid-Open No. 3-2615
According to Japanese Patent Laid-Open No. 70-70, in a thermal printer, unevenness in print density can be prevented by controlling a control pulse width for controlling on / off of a current supplied to the thermal head according to temperature detection data of the thermal head. Has been described. However, since the thermal printer and the dot printer have different operating principles and configurations, it is difficult to apply such a technique to the dot printer.

Further, in Japanese Patent Application Laid-Open No. 1-1101164, in a dot printer, the pulse width of the energy control pulse is changed in accordance with the value of the head drive voltage, and the complete energization time is changed, whereby the magnet is changed. It is described that the energy supplied to the coil is controlled to obtain stable print quality against voltage fluctuations. However, such a technique cannot be applied when temperature fluctuation is a problem.

[0011]

SUMMARY OF THE INVENTION The present invention is intended to solve such problems of the prior art, and in a print head drive circuit of a dot printer, heat generation due to loss of a magnet coil itself and a change in ambient temperature are prevented. Regardless, it is an object of the present invention to provide a print head drive circuit that does not require processing by firmware and can speed up the processing when stabilizing the energy input to the magnet coil precisely. There is.

[0012]

In order to achieve the above object, the present invention is provided with the following means.

(1) Dots having magnet coils respectively corresponding to a plurality of print pins and selectively energizing each magnet coil based on a predetermined drive pulse to drive corresponding print pins to perform printing In a drive circuit of a printer print head, a basic pulse generation circuit 1 for generating a basic pulse having a fixed pulse width, a temperature detection circuit 2 for generating temperature information in the vicinity of a magnet coil, and a pulse width according to this temperature information. Each of the print pins includes a correction pulse generation circuit 3 that generates a correction pulse that changes with the basic pulse, and a drive pulse generation circuit 4 that combines the basic pulse and the correction pulse to generate a drive pulse. It was

(2) In the case of (1), the correction pulse generating circuit 2
A / D converter and multiplexer 11 which convert temperature information into digital values and generate outputs corresponding to a plurality of temperature ranges, and a correction having different pulse widths according to outputs for each temperature range It is composed of a plurality of temperature-based pulse generation circuits 12 _{1 to} 12 ₃ which generate pulses.

(3) In the case of (1), the correction pulse generation circuit has a function of setting the pulse width of the correction pulse to be long when the temperature according to the temperature information is equal to or higher than a certain temperature.

[0016]

FIG. 1 shows the basic configuration of the present invention. In the print head drive circuit of the present invention, the basic pulse generating circuit 1 generates a basic pulse having a fixed pulse width. On the other hand, the correction pulse generation circuit 3 generates a correction pulse whose pulse width changes according to the temperature information from the temperature detection circuit 4. The drive pulse generating circuit 4 combines the basic pulse having a fixed pulse width from the basic pulse generating circuit 1 with the correction pulse from the correction pulse generating circuit 2 to drive the magnet coil. Generate a pulse. Further, the print head drive circuit energizes the corresponding magnet coil according to the drive pulse.

Such control is performed for each set of each print pin and the magnet coil provided corresponding thereto.
Thus, in the print head drive circuit of the present invention,
In order to stabilize the energy input to the magnet coil, the processing is performed by hardware when controlling the drive pulse width according to the temperature detection data.
A large-capacity firmware table, which is required when performing CPU control as in the past, is no longer necessary.

Further, when the processing is performed by the firmware, the control for changing the driving pulse width of the magnet coil based on the temperature monitoring data is performed every time one dot is printed, so that complicated control is required. Although the capacity of the firmware and the processing speed of the CPU have been problems, the processing speed can be improved in the present invention because the processing by the firmware is unnecessary.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The print head driving device of the present invention will be described in detail below with reference to FIGS.

FIG. 2 shows an embodiment of the present invention in which the print head of a dot printer is controlled by a transistor on the sink side (ground side). The same applies to the case of controlling by the side transistor. In the figure, (a) shows a circuit configuration, and the same components as those in FIG. 1 are designated by the same numbers. (B) illustrates the magnet coil current.

In FIG. 2A, the gate array (G /
The basic pulse generation circuit 1 provided on the side A) generates a basic pulse having a fixed pulse width. The temperature detection circuit 2 provided on the sink side is composed of a resistor 21 and a thermistor 22 which are connected in series to a power supply (5V), and outputs a temperature detection voltage that changes according to an increase in ambient temperature and the temperature of the print head. , From the thermistor 22. The correction pulse generation circuit 3 generates a correction pulse whose pulse width changes according to the temperature detection voltage, and the drive pulse generation circuit 4 synthesizes the basic pulse and the correction pulse to generate a drive pulse. The temperature detecting element in the temperature detecting circuit 2 is not limited to the thermistor and may be another type of temperature detecting element.

The pin drive circuit 5 for driving each print pin in the print head is composed of a drive transistor 51 and a magnet coil 52 connected in series to a power source (V _DRV ). When the drive transistor 51 is turned on in response to the drive pulse, the magnet coil 52 is energized. As a result, a pin (not shown) is driven and a printing operation is performed.

Since the printing operation of the pins in the print head is determined by the applied energy to the magnet coil, it is necessary to keep the applied energy constant in order to keep the print quality constant.

On the other hand, in the print head, the resistance value of the magnet coil changes according to the temperature coefficient of the magnet coil due to the heat generation due to the loss of the print head itself and the temperature rise determined by the change of the ambient temperature. The current value of changes.

Therefore, in order to keep the input energy to the magnet coil constant, the resistance value is low and the current value is large at low temperature, so that the drive pulse width is shortened and the resistance value is high and the current value is high at high temperature. Since it becomes smaller, it is necessary to control the drive pulse width to be longer.

Correction pulse generation circuit 3 shown in FIG.
Generates a correction pulse whose pulse width changes according to the temperature information from the temperature detection circuit 2. Drive pulse generation circuit 4
Changes the pulse width of the drive pulse by synthesizing the correction pulse and the basic pulse having a fixed pulse width.

As a result, the current of the magnet coil becomes as shown in FIG. 2 (b). That is, the current value i is large at low temperatures, but the drive pulse width is the predetermined value t. On the other hand, the current value i becomes small at high temperature,
The drive pulse width is t + α, and the pulse width becomes longer than that at low temperature, so that the energy applied to the magnet coil can be kept constant.

FIG. 3 shows an example of the configuration of the correction pulse generating circuit. In the A / D converter and the multiplexer 11, the temperature information consisting of the analog signal from the temperature detection circuit is converted into a digital value, and the outputs classified according to the temperature range are generated. Then, any one of the temperature-specific pulse generation circuits 12 _{1 to} 12 ₃ generates a correction pulse having a different width depending on the temperature range.

In the above-mentioned embodiment, the case where the drive pulse width is controlled according to the temperature information has been described, but as another application example of the present invention, the voltage for driving the print head is only the rectifier diode from the commercial power source. In the case where the drive voltage changes according to the load change, as in the case where the drive voltage is directly supplied via the above, by inputting the voltage information instead of the temperature information, the input energy to the magnet coil is also kept constant. Control can be performed.

[0030]

As described above, according to the present invention, the drive current is controlled by hardware in the print head drive circuit of the dot printer.
As compared with the conventional CPU control method, the table used for generating the drive pulse for the magnet coil is unnecessary, and the capacity of the firmware ROM can be reduced.

In the conventional CPU control system, 1
Since the temperature monitoring and pulse width correction control by the firmware, which was performed for each dot impact, is no longer necessary, there is no processing delay based on the processing time of the CPU, etc.
It is possible to speed up the process of driving the print head.

As described above, according to the present invention, it is possible to provide a print head drive circuit having an excellent effect which cannot be realized by the conventional print head drive circuit.

[Brief description of drawings]

FIG. 1 is a diagram showing a principle configuration of the present invention.

2A and 2B are diagrams showing an embodiment of the present invention, in which FIG. 2A shows a circuit configuration and FIG. 2B illustrates an electric current of a magnet coil.

FIG. 3 is a diagram illustrating a configuration example of a correction pulse generation circuit.

[Explanation of symbols]

 1 Basic pulse generation circuit 2 Temperature detection circuit 3 Correction pulse generation circuit 4 Drive pulse generation circuit 1 1 A / D converter and multiplexer 1 2 Temperature-dependent pulse generation circuit

Claims (3)

[Claims] 1. A dot printer having a magnet coil corresponding to each of a plurality of print pins, selectively energizing each magnet coil based on a predetermined drive pulse to drive a corresponding print pin to perform printing. In the print head driving circuit, a basic pulse generation circuit that generates a basic pulse having a fixed pulse width, a temperature detection circuit that generates temperature information near the magnet coil, and a pulse width that changes according to the temperature information. A correction pulse generating circuit for generating a correction pulse for synchronizing with the basic pulse and a drive pulse generating circuit for generating a drive pulse by combining the basic pulse and the correction pulse are provided for each print pin. Characteristic print head drive circuit. 2. The A / D converter and the multiplexer, wherein the correction pulse generating circuit converts the temperature information into a digital value and generates outputs corresponding to a plurality of temperature ranges, and an output for each temperature range. 2. A plurality of temperature-specific pulse generation circuits for generating correction pulses each having a different pulse width in accordance with the above.
The print head drive circuit described. 3. The printing according to claim 1, wherein the correction pulse generation circuit has a function of setting a long pulse width of the correction pulse when the temperature according to the temperature information is equal to or higher than a certain temperature. Head drive circuit.