JPH0832464B2 - Thermal head drive system - Google Patents

Description

The present invention relates to a thermal head that has a plurality of heating resistors and enables printing by energizing the heating resistors.

(B) Conventional technology It is a well-known fact that the thermal density of the thermal head tends to fluctuate due to the temperature, the printing cycle, the thermal history of the heating resistor, and the like. A drive device that controls the current value for driving the resistor and the energization time has been considered.

FIG. 10 is a block diagram of a thermal head drive device in the conventional example. The thermal head 1 has a heating resistor 2, a driver IC 3 that drives the heating resistor 2, and a thermistor 13 that detects the temperature of the thermal head. The A / D converter 4 has an analog temperature from the thermistor 13. The data is converted into digital temperature data and input to the microcomputer 7. The microcomputer 7 stores the data in the ROM table 10 at the address of the ROM table 10 determined from the digital temperature data, the print cycle data, the heat history data, and the like. The data is accessed to obtain the drive pulse width data, and the drive pulse width data is input to the pulse width control circuit 5 to generate a drive pulse signal (▲ ▼ signal) having a controlled pulse width, and the thermal head 1 The print density is kept constant.

(C) Problems to be Solved by the Invention However, in such a conventional thermal head drive device, the memory capacity of the circuit for externally driving the thermal head and the amount of the control program of the microcomputer become large. Also, an expensive A / D converter is required due to the digital processing of the microcomputer. Further, if the thermal head is provided with a control system for the drive pulse for the heating resistor, there is a problem that the shape and size of the thermal head itself becomes very large.

The present invention has been made in consideration of such circumstances.
It is an object to provide a thermal head which can obtain a uniform print density at a low cost with a relatively simple circuit and control program and which is compact in shape.

(C) Means for Solving the Problems The present invention is designed to perform printing by applying a drive voltage corresponding to print data to each heating resistor of a thermal head in which a plurality of heating resistors corresponding to print dots are arranged. In the thermal head driving device configured as described above, temperature detecting means for detecting the temperature of the thermal head, voltage control means for controlling the drive pulse voltage applied to the heating resistor, and crest value or pulse width of the drive pulse are controlled. The thermal head driving system is characterized in that the voltage or pulse width of the driving pulse applied to the heating resistor is controlled by analog processing of the output of the temperature detecting means.

In the present invention, the crest value of the drive pulse may be controlled inside the thermal head according to the temperature of the thermal head, and at the same time the pulse width of the drive pulse may be controlled externally according to other factors. The pulse width may be controlled internally and at the same time the crest value of the drive pulse may be controlled externally.

The thermal head is usually formed by linearly arranging 500 to 5000 heating resistors on an insulating substrate such as ceramic having excellent heat resistance and flatness, and each of which is capable of outputting a pixel. Is preferred. The means for energizing the heating resistor includes a shift register for inputting serial print data in synchronization with a normal clock signal, and a latch circuit for latching the serial print data by a ▲ ▼ signal. Data and
A driver IC that outputs an energization pattern to the heating resistor according to the pulse waveform of the signal can be used. When detecting the temperature of the thermal head, for example, Fe ₃ O ₄ and MgCr ₂ O ₄ or MgAl are used as temperature detecting means.
A solid solution of ₂ O ₄ , a thermistor obtained by mixing and sintering NiO, Mn ₂ O ₃ , and CO ₂ O ₃ can be used. In that case, it is preferable that the temperature detecting means is disposed in the vicinity of the heating resistor and detects the temperature of the thermal head and converts it into a resistance value.

If a 4-terminal regulator (for example, PQ3ORV manufactured by Sharp Corporation) whose output voltage changes due to resistance change is used as the control means for controlling the peak value of the drive pulse, it is inexpensive and simple in circuit. When the drive pulse width control means is provided inside the thermal head, if a sawtooth-shaped integrated wave is converted into a rectangular wave by a voltage comparator whose reference voltage changes due to resistance change and pulse control is used, It is cheap and simple in circuit.

(E) Operation When the thermal head is provided with a temperature sensor, the print density of the thermal head can be easily made uniform by analog-controlling the crest value or pulse width of the drive pulse corresponding to the temperature.

(F) Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. The thermal head 101 detects a plurality of heating resistors 102, a plurality of driver ICs 103 for driving the heating resistors 102, and the temperature of the thermal head 1. Voltage control circuit 1 for controlling the voltage for driving the thermistor 105 and the heating resistor 102
Equipped with 04.

In the case of a facsimile or printer, the print data normally handled by the main CPU is parallel data (for example, 8-bit data), so the parallel print data sent from the main CPU is serialized by the parallel / serial converter 106. Converted to print data, thermal head 101
It is sent together with the driver control signal to the driver IC 103 provided in.

FIG. 2 is a basic circuit diagram of the driver IC 103. The driver IC 103 includes a driver (inverter) 201 composed of transistors, a gate circuit 202, and a latch circuit 203.
The signal input to the driver IC 103 is serial print data (input from the DATAIN terminal), driver control signal (BEO signal and ▲ ▼ signal and CLOCK signal) and ▲ ▼. Composed of signals.

As shown in FIG. 4, the voltage control circuit 104 of FIG.
A 4-terminal regulator IC for stabilizing a DC output voltage in which an arbitrary DC output voltage can be set by an external resistor is intended to convert a resistance change of the thermistor 105 into a voltage (pulse peak value) change.

Next, referring to the timing chart of FIG. 3 and the basic circuit diagram of the driver IC 103 of FIG. 2, the case of driving the thermal head in 1 line and 8 divisions will be described. First, DATAIN
The serial print data input from the terminal 209 is sent to the shift register 204 in synchronization with the CLOCK signal input from the CLOCK terminal 210. Next, ▲ ▼ Shift register with pulse signal input to terminal 208
The serial print data 204 is latched by the latch circuit 203. After that, the BEO terminal 206 is set to “High” by the BEO signal so that the driver 201 can be driven.
▼ The heating resistor 102 is driven by the ▲ ▼ signal of the drive pulse input via the terminal 207, and as shown in FIG.
Switch ▼. Finally, return BEO to "LOW" and set 1
Line printing is completed.

Next, how the drive voltage (the peak value of the drive pulse) is determined will be described with reference to FIGS.

FIG. 4 is a connection diagram of the voltage control 4-terminal regulator used in this embodiment.

This 4-terminal regulator (for example, Sharp Corporation)
Made PQ30RV) RG has a reference voltage and a comparator inside,
The output voltage is determined by the external resistors R1 and Rth. Fig. 5 shows output voltage V with respect to resistance Rth when resistance R ₁ = 390Ω
It is a graph showing the change of o. Figure 6 shows the thermistor 1
This is the temperature characteristic of 05 (Fig. 1), and the resistance value Rth of the thermistor 105 decreases as the temperature rises. Therefore, in the case of connection as shown in FIG. 4, when the temperature of the thermal head rises, the resistance of the thermistor drops and the output voltage of the four-terminal regulator also drops. Therefore, if this output voltage is used as the drive voltage of the heating resistor, The print density will be uniform.

The above is an example in which the voltage control circuit for controlling the drive voltage is provided in the thermal head, the drive voltage (peak value) is controlled with respect to the temperature, and the pulse width is controlled from the outside by another factor. Next, a pulse width control circuit is installed inside the thermal head to control the pulse width according to the temperature.
An example in which the drive voltage is controlled from the outside by another factor will be described with reference to FIGS. 7 to 9. FIG. 7 is a block diagram showing the pulse width control circuit 701 in this case.
Are provided in the thermal head, and the drive voltage is controlled by the voltage control circuit 702 from outside the thermal head.
The other structure is the same as that of the embodiment shown in FIG. As shown in FIG. 8, the pulse width control circuit 701 includes an integrating circuit 802 including a capacitor C, a resistor R and a diode D, a voltage comparing circuit 801 including a resistor R0, a thermistor 105 and a comparator CP, and the thermistor 105. Resistance value
The reference voltage Vth of the comparator changes due to the change of Rth,
The drive pulse width tp changes. FIG. 9 shows waveforms at points (A), (B) and (C) of the circuit shown in FIG. That is, when the temperature rises, the resistance value Rth of the thermistor 105 decreases and the reference voltage Vth of the voltage comparison circuit 801 decreases, so that the width tp of the output pulse increases and the print density is made uniform with respect to the temperature.

As described above, the drive voltage control or the drive pulse width control based on the temperature can be independently performed inside the thermal head with a relatively simple circuit. Furthermore, the energy applied to the heating resistor can be controlled by controlling the drive pulse width or the drive pulse voltage from the outside as needed.

Although the thermal head is divided into eight divisions in the above embodiment, the present invention is not limited to this. Further, in the above-mentioned embodiment, the voltage control means or the pulse width control means is disposed inside the thermal head, but either may be placed inside.
Both may be external.

(G) Effect of the Invention According to the present invention, since the print density with respect to the temperature change can be kept constant by a simple and inexpensive circuit provided uniquely to the thermal head, an inexpensive and compact thermal head drive device is provided. Can be provided.

Further, at the same time, the energy applied to the heating resistor can be controlled from the outside in response to the factor of the fluctuation of the print density, so that the predetermined print density can be obtained with high accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention,
2 is a basic circuit diagram of the driver IC, FIG. 3 is a timing chart for explaining the operation of the embodiment of the present invention, FIG. 4 is an electric circuit diagram of the voltage control circuit of the embodiment shown in FIG. 1, and FIG. 4 is a graph showing the output voltage characteristic of the voltage control circuit for thermistor resistance input of FIG. 4, FIG. 6 is a graph showing the temperature / resistance characteristic of the thermistor, and FIG. 7 is another embodiment of the present invention corresponding to FIG. Fig. 8 is a pulse width control circuit diagram of the embodiment shown in Fig. 7, Fig. 9 is a waveform diagram showing waveforms of respective parts of the electric circuit of Fig. 8, and Fig. 10 is a conventional example of Fig. 1. FIG. 101 ... Thermal head, 102 ... Heating resistor, 103 ...
Driver IC, 104 ... voltage control circuit, 105 ... thermistor, 106 ... parallel / serial converter, 107 ... pulse width control circuit, 108 ... microcomputer, 109 ... oscillation circuit, 110 ... ROM table, 111 ... Memory, 201 ...
… Driver, 202 …… Gate circuit, 203 …… Latch circuit, 204 …… Shift register, 205 …… Output protection circuit, 20
6 …… BEO terminal, 207 …… ▲ ▼ terminal, 208…
… ▲ ▼ terminal, 209 …… DATAIN terminal, 210 …… CL
OCK terminal.

Claims (1)

[Claims] 1. A thermal head drive system configured to apply a drive voltage corresponding to print data to each heating resistor of a thermal head in which a plurality of heating resistors corresponding to print dots are arranged for printing. A pulse output means for outputting a drive pulse for printing, a density control means for arbitrarily setting a print density by controlling one of a crest value and a pulse width of the drive pulse, and a temperature of a thermal head are detected. The temperature detecting means and the temperature compensating means for correcting the other of the crest value and the pulse width of the drive pulse corresponding to the output of the temperature detecting means to keep the print density constant, the temperature detecting means and the temperature The compensation means is provided inside the thermal head, and the pulse output means and the density control means are provided outside the thermal head. The thermal head drive system according to.