JPH03216374A - Thermal alarm detector of printing head - Google Patents

Abstract

PURPOSE:To obviate the use of two comparators and to reduce the cost by providing a thermistor for detecting the temperature of a printing head and a comparing means which comparing the voltage generated at both terminals of the thermistor with reference voltage. CONSTITUTION:The voltage VTH1 generated at both terminals of a thermistor 13 is inputted to the (-) terminal of a comparator 11 and the reference voltage VREF formed by resistors 14, 15 is inputted to the (+) terminal of the comparator 11. Not only the partial voltage of the power supply voltage Vcc obtained by the resistors 14, 15 is inputted to the (+) terminal of the comparator 11 but also a HEAD TMPCT signal is inputted thereto from the controller of a printer through a resistor 18 whose resistance value is R5. Therefore, the reference voltage VREF can be changed base on whether the HEAD TMPCT signal is set to an H-level or an L-level. Therefore, by setting only one reference voltage VREF and the disconnection of a thermal alarm and the thermistor can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a thermal alarm detection device for a print head in a printer.

(Prior Art) Conventionally, in an impact print head, when the print duty becomes high and the time during which wire dots are driven increases, the temperature of the print head increases accordingly.

Therefore, a temperature detector is disposed inside the print head, and when it detects that the temperature has increased, the print duty is reduced and an alarm is issued.

The operation of the conventional thermal alarm detection circuit is shown in Figure 5 below.
This will be explained using FIG.

FIG. 5 is a diagram of a conventional thermal alarm detection circuit, and FIG. 6 is a diagram showing the relationship between the voltage across the thermistor and the output voltage of the hend alarm signal in the conventional thermal alarm detection circuit.

In Figure 5, 1 is a temperature detection comparator that compares the voltage across the thermistor with a reference voltage to detect the temperature of the thermistor, and 2 compares the voltage across the thermistor with the reference voltage to determine if the thermistor is disconnected. This is a thermistor disconnection detection comparator for determining whether or not the thermistor is disconnected.

3 is a thermistor housed in the print head to detect the temperature of the print head; 4.5 is a resistor for dividing the power supply voltage VCC to create a reference voltage; the resistance values are R1 and R2, respectively. . 6 is the power supply voltage ■ between it and thermistor 3. , and has a resistance value of R3. Also, 7 is a pull-ahead resistor whose resistance value is R4. The voltage VTMI generated across the thermistor 3 is input to the (-) terminal of the comparator 1 and the (+) terminal of the comparator 2, and
The reference voltage v+ttr formed by comparator 1
The reference voltage +2.5■ is connected to the (+) terminal of comparator 2.
is input to the (1) terminal of.

In the thermal alarm detection circuit configured as described above, when the printing operation continues for a long time and the temperature of the print head increases, the resistance value of the thermistor 3 built into the print head decreases. Assuming that the above resistance value is RTIII (Ω), the voltage V TMI (V) across the thermistor 3 is expressed by the following equation.

? ■A■ is determined from the thermal alarm detection temperature? If the reference voltage V*tv (V) is lower than the reference voltage V
AD ALM (V) becomes H level. Note that the above ■■ is expressed by the following formula.

Rl +R2 Next, the thermistor disconnection detection operation will be explained.

The thermal alarm detection circuit generally also has a thermistor disconnection detection function. If the thermistor is disconnected due to a rise in the temperature of the print head, RTMI → ω, but from equation (1), R? MI, so at this time, as shown by the dashed line in Fig. 6, the converter 2 is ONL and the output voltage HEAD ALM (V).
becomes H level, and it is possible to know that the thermistor is disconnected by detecting a thermal alarm.

(RM to be Solved by the Invention) However, in the conventional print head thermal alarm detection device described above, a comparator is required for temperature detection and thermistor disconnection detection, which increases the cost.

The present invention solves the problems of the conventional print head thermal alarm detection device, and provides a print head thermal alarm that can detect a thermal alarm and a thermistor disconnection without using two comparators. The purpose is to provide a detection device. (Means for Solving the Problems) To this end, in the thermal alarm detection device for a print head of the present invention, a thermistor is provided to detect the temperature of the print head, and a voltage generated across the thermistor and a reference voltage are provided. Comparison means, for example a comparator, is provided for comparing the values.

The comparison means is provided with means for changing the reference voltage when detecting a thermistor disconnection and when detecting a thermal alarm, for example, so that it is high when a thermistor disconnection is detected and becomes low when a thermal alarm is detected. The reference voltage is then changed by a firmware algorithm.

(Operation) According to the present invention, a reference voltage is first set high, and the reference voltage is compared with the voltage generated across the thermistor to detect a disconnection alarm of the thermistor.

Subsequently, the reference voltage is reduced and the voltage developed across the thermistor is compared with the reference voltage to perform thermal alarm detection.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. Fig. 1 is a thermal alarm detection circuit diagram of the print head of the present invention, Fig. 2 is a relationship diagram of the voltage across the thermistor/output voltage of the head alarm signal of the thermal alarm detection circuit of the present invention, and Fig. 3 is a diagram of the print head of the present invention. The printer control circuit diagram with the thermal alarm detection circuit shown in Fig. 4 is the printing hand of the present invention? It is an operation flowchart of a thermal alarm detection device.

In Figure 1, 1l compares the voltage across the thermistor with the reference voltage to determine whether the detected temperature of the print head is in a thermal alarm state, and also to determine whether the thermistor is disconnected. It's a combo barre evening.

13 is a thermistor housed within the print head and for detecting the temperature of the print head; 14. 15 is the power supply voltage VC
These are resistors for dividing C to create a reference voltage VREF, and their resistance values are R1 and R2, respectively. 16 is a resistor for dividing the power supply voltage VCC between the thermistor 13 and creating a reference voltage, and 17 is a pull-up resistor, the resistance values of which are R3 and R4, respectively.

Then, the voltage VTκ1 generated across the thermistor 13
is input to the (-) terminal of the converter 11, and the resistor 14
．． 15 is input to the (+) terminal of the comparator 11. Further, a resistor 14. is connected to the (+) terminal of the comparator 11. In addition to inputting the partial voltages of the power supply voltages v and C obtained by 15, HE is input from the printer control device via a resistor with a resistance value of R5.
The AD TMPCT signal is input.

Therefore, it is possible to change the reference voltage VIIEF depending on whether the }IEAD TMPCT signal is set to H level or L level.

That is, by setting only one reference voltage v*tr as shown in FIG. 2, it is possible to detect a thermal alarm and a disconnection of the thermistor.

Next, a printer control circuit provided with the thermal alarm detection circuit having the above configuration will be described.

In FIG. 3, 21 is a central processing unit (CPU), which is connected to a higher-level device such as a personal computer via an interface control circuit 22, and based on print information sent from the higher-level device, the print head is Controls the feed mechanism, paper feed mechanism, platen drive mechanism, etc. 23 is a program memory in which various instructions are stored, and the CPU 21 takes out the instructions and sequentially executes them to control each element. Further, 24 is a buffer memory for temporarily storing print information etc. sent from the host device. The processing speed of a higher-level device, such as a personal computer, is extremely faster than the printing speed of a printing device, and if transmission is performed in accordance with the printing speed, the processing efficiency of the personal computer, etc. will decrease. The print information received from the host device is stored in the buffer memory 24 without being processed.

Reference numeral 25 denotes a font memory that stores fonts selected based on print information, that is, print data from the host device.

26 is the thermal alarm detection circuit described above. CP02
1 to the above HEAD TMPCT signal to the print head 2.
9 receives the signal of the voltage across the thermistor 13, and the CPU
The HEAD ALM signal is sent to 21.

Further, 27 is an input device, 28 is a head drive circuit that conducts printing by energizing the coil of the print head 29 based on print data, and 30 is a motor control circuit. Above C
The PU 21 operates the head drive circuit 28 using the dontomatolinks taken out from the font memory 25.

Next, the operation of the thermal alarm detection device will be explained.

Step■ Set the HEAD TMPCT signal input to oven (high impedance state) and set the reference voltage V IIE
Let F be H level.

Step■ At this time, if the thermistor 13 is disconnected, the input voltage VtH+ of the (=) terminal of the comparator l3
is the power supply voltage +V eC, while the reference voltage VII
Since EF is the partial pressure of +V cc and is R1+R2, V > VIIEF, and the converter 11 is in the ON state and HEAD
ALM output becomes L level. On the contrary, I{HAD AL
If the M output is at H level, the thermistor is not disconnected.

Step (2) If the HEAD ALM output is at H level and the thermistor 13 is not disconnected, the process moves to thermal alarm detection processing.

? Step■ Set the HEAD TMPCT input to L level.

Step ■■ If the value determined by the voltage division ratio of the thermistor 13 and resistor 16 is lower than the reference voltage V■y+[v] set from the thermal alarm detection temperature, the comparator 11 turns OF.
It enters the F state and the HEAD ALM output becomes H level.

As a result, a thermal alarm is detected.

Base 1 at this time! The voltage VIEFI (V) is expressed by the following formula.

R2/R5 On the other hand, the comparator 11 is expressed by the following formula.

(1) Human power voltage at the terminal? Therefore, if VtH+<V■■, a thermal alarm is detected.

Note that the present invention is not limited to the above embodiments,
Various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

(Effects of the Invention) As described above in detail, according to the present invention, the voltage generated across the thermistor is provided with a comparison means, such as a comparator, for comparing the voltage generated across the thermistor with the reference voltage. and change when thermal alarm is detected,
A single comparator can detect disconnection of the thermistor and detect a thermal alarm, reducing costs.

[Brief explanation of drawings]

Fig. 1 is a thermal alarm detection circuit diagram of the print head of the present invention, Fig. 2 is a relationship diagram of the voltage across the thermistor/output voltage of the head alarm signal of the thermal alarm detection circuit of the present invention, and Fig. 3 is a diagram of the print head of the present invention. FIG. 4 is an operation flowchart of the thermal alarm detection device for the print head of the present invention, FIG. 5 is a conventional thermal alarm detection circuit diagram, and FIG. 6 is a conventional thermal alarm detection circuit diagram. FIG. 3 is a diagram showing the relationship between the voltage across the thermistor and the output voltage of the head alarm signal in the thermal alarm detection circuit. 1, 2.11...Comparator, 3.13...Thermistor, 4-7, 14-18...Resistor, 21...C
PU, 26...Thermal alarm detection circuit.

Claims (1)

[Claims] (a) a thermistor for detecting the temperature of the print head; (b) a comparison means for comparing a voltage generated across the thermistor with a reference voltage; (c) the reference voltage. A thermal alarm detection device for a print head, characterized in that it has means for changing when a thermistor disconnection is detected and when a thermal alarm is detected.