JPS641078Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a thermal printer, which is a non-impact printer that uses a thermal head and is used as an output device for microcomputers, etc., and is particularly concerned with printing errors caused by disturbances in the output of the main control unit (MPU), etc. The present invention also relates to a thermal printer equipped with a circuit for preventing overheating of a heating element.

FIG. 1 is a block diagram of a thermal printer that can print 40 digits, for example. 1 is the main control unit (MPU) which is TTLIC. Reference numeral 2 denotes C-2, in which 8-bit data input from a video copy section or an interface section (not shown) to the main control section 1 via a data bus selector is serially output in synchronization with a clock signal from an output port CLCK.
It is a MOSIC shift register. 3 is a thermal head unit having 20 heating elements which are resistors (92 to 135 Ω) printed on a substrate. Reference numeral 4 denotes a thermal head driver which turns on and off an internal Darlington-connected transistor circuit in response to the output of the shift register 2, thereby determining whether or not to energize each heating element. In this thermal printer, one heating element prints two-digit numbers or characters. A single digit number or character is composed of a 7 (horizontal) x 10 (vertical) dot matrix. The thermal head unit 3 moves horizontally by 14 dots, then feeds the paper by 1 dot, then moves horizontally by 14 dots in the opposite direction, and feeds the paper by 1 dot. Reference numerals 5 and 6 are a drive mechanism and a motor for moving the thermal head unit 3 and feeding paper, respectively. 7 is the output port HEAT of main control unit 1
The pulse width as shown in Figure 2 output from
This is the driver control section where the open emitter of the Darlington-connected transistor is grounded for 1.7ms and energized by the heat signal, which is a 1.7ms negative pulse. Reference numeral 8 denotes a timing pulse generation unit that follows the rotation of the motor 6 to generate print start pulses and heat timing pulses, which are timing pulses, and inputs these pulses to the main control unit 1 from input ports SLR and SPU, respectively. . The heat signal is output from the main control section 1 to the driver control section 7 in synchronization with these print start pulses and heat timing pulses. 9 is the output port of main control unit 1
This is a motor control unit that controls on/off of the motor 6 based on signals from the MTR. 10 is
This is a transformer that extracts AC voltages of E ₁ (V) and E ₂ (V) from an AC voltage of 100V. Reference numeral 11 denotes a power supply circuit that rectifies and smoothes the AC voltage of E ₁ (V) to obtain a DC voltage of +5 (V), which is the power supply voltage of a circuit that performs logical operations such as the main control section 1 . 12 rectifies and smoothes the AC voltage of E ₂ (V) and energizes the heating element +19.5
This is a power supply circuit that obtains a DC voltage of (V).

In this way, in a thermal printer, the power supply circuit for supplying the voltage to the heating element and the power supply circuit for supplying the voltage to the logic operation circuit such as the main control unit 1 are separate, and the power supply circuit for supplying the voltage to the circuit that performs logical operation such as the main control unit 1 is separate, and the power supply circuit is included in the former power supply circuit. The capacity of the smoothing capacitor is larger than the capacity of the smoothing capacitor included in the latter power supply circuit due to the maximum amount of current consumption. Therefore, when the power switch is turned off, the voltage of the main control section 1 drops faster than the voltage of the heating element, and if it drops below about 4 (V), the main control section 1 malfunctions and black dots are printed. Or the heating element may overheat. The power supply voltage of +5 (V) for the shift register 2 is also supplied from the power supply circuit of the main control unit 1, and similarly, data indicating whether or not to malfunction and heat the heating element is output and a black dot is printed. To prevent this, when the power supply to the printer head drive circuit starts up,
There is also one with controlled fall time (Japanese Patent Laid-Open No. 129185-1985). In this case, overheating of the printer head and erroneous printing when the power is turned on and off are prevented, but such malfunctions of the main control unit 1 and shift register 2 can be caused by abnormalities in the power supply, noise entering the power supply voltage, software This can also occur due to out of control wear.

The present invention was proposed in view of the above-mentioned problems, and it is an object of the present invention to provide a thermal printer equipped with a circuit that prevents printing errors and overheating of the heat generating elements of the thermal printer.

For this purpose, in the present invention, first the shift register 2
A DC voltage of +5 (V), which is the power supply voltage of the heating element, is obtained by regulating +19.5 (V), which is the power supply voltage of the heating element. Therefore, even when the power switch is turned off, the power supply voltage of the shift register 2 remains at +5 (V) for a long time, and there is no malfunction before the power supply voltage of the main control section 1 reaches 0 (V).
Next, when the power switch is turned off and the power supply voltage of the main control unit 1 drops below +4.5 (V), the main control unit 1
The heat signal output from the shift register 2 is prevented from being input to the enable terminal EN of the shift register 2. (The heat signal input circuit is different from that shown in Figure 1, and the thermal head driver 4 is always grounded.) Furthermore, the main controller 1 malfunctions and a series of heat signal pulses are output. In this case, a heat signal exceeding a predetermined pulse width is prevented from being input to the enable terminal EN of the shift register 2.

The present invention will be described below with reference to the drawings. FIG. 3 is a circuit diagram of a thermal printer according to an embodiment of the present invention. 1 to 12 are the same as in FIG. TR ₁ has power supply circuit 11 on the base side
The transistors are PNP transistors whose emitters are connected to the power input terminal V _DD of the shift register 2, and whose collectors are grounded. R ₁ is a protection resistor for the PNP transistor TR ₁ . _C1 is a capacitor for noise absorption. This PNP type transistor TR ₁ becomes conductive when the power supply voltage of the main control unit 1 supplied from the power supply circuit 11 becomes lower than the power supply voltage of the shift register 2 by 0.6 (V) or more. TR ₂ is
It is an NPN type transistor. R ₂ and R ₃ are transistors when PNP type transistor TR ₁ conducts.
This is a resistor for setting the base potential of TR ₂ to 0.6 (V) or higher. IN is an inverter circuit that inverts the heat signal from the main controller 1. D ₂ and
_R5 is a diode and a resistor, respectively, which convert the level of the heat signal inverted by the inverter circuit IN from TTL to C-MOS. R ₄ and C ₂ are a resistor and a capacitor, respectively, which constitute a time constant circuit, and at point P ₁ there is a capacitor C that increases gradually with the rise of the pulse of the heat signal inverted by the inverter circuit IN, and decreases sharply with the fall of the pulse. A charging voltage V is obtained. The ratio of the resistor R ₂ to the resistor R ₃ determines the value of the charging voltage V _SAT of the capacitor C when the pulses of the heat signal inverted by the inverter circuit IN continue, that is, when the capacitor C is saturated. When the inverted heat signal is a pulse signal with a duty cycle t, the charging voltage V follows the charging voltage curve where the charging voltage when the capacitor C is saturated is t×V _SAT , and the rising edge of the pulse signal, It gradually rises while repeating increases and decreases according to the falling voltage, and ultimately the voltage value t×V _SAT
Repeats increases and decreases between constant voltage values including. Note that the values of the resistors R ₃ and R ₄ and the capacitor C ₂ are such that, for example, around 6 (ms) from the rise of the inverted pulse of the heat signal, the charging voltage V of the capacitor C ₂ changes to the base level when the transistor TR ₂ is conductive. It is set to reach the emitter voltage of 0.6 (V). Therefore, when the heat signal of the pulse signal (duty cycle = 1.7/2.7≒0.63) as shown in Fig. 2 is output from the main control unit 1, charging when the capacitor _C2 is saturated The peak value of voltage is approximately 0.4 (V)
become. Here, D ₁ is a diode for preventing backflow. ZD is a constant voltage diode provided in the +19.5 (V) power supply line to supply the shift register 2 with a +5 (V) power supply voltage. _R6 is a current limiting resistor. C ₂ and C ₃ are noise absorbing capacitors.

Next, the operation of this circuit will be explained. First, we will discuss the operation when the power switch is turned off. The +19.5 (V) power supply voltage of the thermal head unit 3 maintains its value for a while even after the power switch is turned off, because the smoothing capacitor of the power supply circuit 12 has a large capacity as described above. And since the +5 (V) power supply voltage of shift register 2 is generated by regulating this +19.5 (V) voltage, the power supply voltage of shift register 2 also maintains +5 (V) for a while. . On the other hand, main control unit 1
The power supply voltage of +5 (V) decreases faster than the power supply voltage of +19.5 (V) because the capacity of the smoothing capacitor of the power supply circuit 11 is small. Therefore, the shift register 2 will not malfunction and data will not be output before the power supply voltage of the main control section 1 reaches 0 (V). Further, when the power supply voltage of the main control section 1 becomes lower than the power supply voltage of the shift register 2 by 0.6 (V) or more, the transistor _TR1 becomes conductive. As a result, a predetermined voltage of 0.6 (V) or higher is applied to the base of the transistor TR ₂ , and the transistor TR ₂ becomes conductive.
Therefore, the _P2 point is grounded, and no heat signal is input to the enable terminal EN of the shift register 2. In other words, +
Even if a power supply voltage of 19.5 (V) is applied, data on whether to heat each heating element is not output from the shift register 2 to the thermal head driver 4, so incorrect printing may occur when the power switch is turned off. It never happens. Note that after a certain amount of time passes, the power supply voltage of the thermal head unit 3 decreases, and the power supply voltage of the shift register 2 also decreases accordingly, but even if the shift register 2 malfunctions, the power supply voltage of the thermal head unit 3 is already low. Since the temperature is lowered, black dots will not be printed or the heating element will not overheat.

Next, it is assumed that the main control section 1 malfunctions due to the above-mentioned cause, and a heat signal with a pulse width of 10 (ms), for example, is output. In this case, the potential at point _P1 reaches the base voltage of 0.6 (V) when transistor TR ₂ is conductive in about 6 (ms) after the rise of the heat signal inverted by the inverter circuit IN, and then 2 to 3 seconds after that.
(ms), the transistor _TR2 is conductive and the point _P2 is grounded. In other words, a maximum of approximately 6 (ms) is applied to the enable terminal EN of shift register 2.
Input only a heat signal with a pulse width of . Therefore, the maximum continuous energization time for each heating element is approximately 6
(ms), and overheating of each heating element is prevented. Note that the maximum continuous energization time of this heating element can be set according to the actual situation by changing the conduction voltage of the transistor _TR2 .

As explained above, in the present invention, the power supply voltage of the shift register 2 is generated by regulating the power supply voltage of the thermal head unit 3, so even if the power is turned off, the power supply voltage of the shift register 2 remains at that voltage for a long time. , so the shift register 2 will not malfunction, and even if the power supply voltage of the shift register 2 drops over time, the power supply voltage of the thermal head unit 3 will have also dropped considerably at that time, so the shift register 2 will not malfunction. There is no problem even if the shift register 2 malfunctions, and erroneous printing when the power is turned off due to the shift register 2 is prevented. In addition, when the power supply voltage of the main control unit 1 drops below a predetermined voltage value, input of the heat signal to the shift register 2 is prohibited. This prevents incorrect printing. Furthermore, since a heat signal having a pulse width greater than a predetermined pulse width is not input to the shift register 2, even if the main controller 1 malfunctions and a series of heat signal pulses are output, the heating element will not overheat.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional 40-digit thermal printer, Figure 2 is a waveform diagram of a heat signal, and Figure 3 is a diagram of a heat signal waveform.
The figure is a circuit diagram of a thermal printer according to an embodiment of the present invention, which is equipped with a circuit for preventing erroneous printing and overheating of the heating element. 1... Main control unit, 2... Shift register, 3...
...Thermal head unit, 4... Thermal head driver, 5... Drive mechanism, 6... Motor, 1
DESCRIPTION OF SYMBOLS 1...First power supply circuit, 12...Second power supply circuit, ZD...Regulator circuit, _C1 , _R1 , _R2 ,
R ₃ , TR ₁ ... Power supply voltage monitoring circuit, C ₂ , R ₃ , R ₄ ...
...Charging circuit, TR ₂ ...Switching circuit, heat signal monitoring circuit.

Claims (1)

[Claims for Utility Model Registration] A heating element that generates dots on paper using the Joule heat generated when electricity is applied, and a dot that forms figures such as letters and numbers to be printed on the paper by aggregation of these dots. A thermal head unit having a plurality of matrices is inputted in parallel with data indicating whether to print each dot of the dot matrix, and then outputted in series in synchronization with a clock signal, and synchronized with the synchronization signal. a main control section that outputs a predetermined number of heat signals with a constant cycle and a paper feed command signal having a time difference from the heat signals; a shift register that inputs data in series, and inputs the data input into this shift register in parallel only during the period when a heat signal is given from the main controller, and controls the thermal head unit according to the input data. a thermal head driver that is energized; a drive mechanism that feeds the paper by a predetermined amount in response to command signals supplied at appropriate timings from the main controller; and a first power supply circuit that supplies power to the logic circuit; , a second power supply circuit whose supply voltage is set to a value higher than the power supply voltage of the first power supply circuit, and which supplies power to each heating element of the thermal head unit; A thermal printer comprising: a regulator circuit that regulates a power supply voltage to generate a power supply voltage for driving the shift register; a power supply voltage monitoring circuit that outputs a first control signal when the power supply voltage of the first power supply circuit drops below a predetermined level from the drive power supply voltage value; and a power supply voltage monitoring circuit that performs charging and discharging every cycle of the heat signal. a heat signal monitoring circuit that repeatedly outputs a second control signal when some of the predetermined number of heat signals disturb the period so that the charging voltage exceeds a predetermined level; 1. A thermal printer comprising: a switching circuit configured to cut off input of the heat signal to the shift register in response to the first control signal and the second control signal.