Method for preventing overheating of thermal printer and control circuit thereof

Abstract

The invention provides a method for preventing overheating of a thermal printer and a control circuit thereof, and the method comprises the following steps: S1, setting a resistor R1 and a resistor R2 to be connected in series and respectively connected with + 3.3 V and grounding to form resistance voltage division, recording the voltage on the R2 as Vref, and enabling the voltage value of # imgabs0 # Vref to be equal to the voltage value of a thermistor R4 at 200 DEG C of a printing head as 1V; s2, a Vref voltage end generated after resistor voltage division is connected with a V-end of a voltage comparator, and a V + end of the voltage comparator is connected with a thermistor voltage output end of the printing head; and S3, VOUT of the voltage comparator is connected with a heating control pin of the printing head, the voltage of the thermistor of the printer is monitored by utilizing the characteristics of the voltage comparator, and when the voltage of the thermistor is monitored to be reduced to 200 DEG C of the printing head, the voltage comparator immediately sends out a low-level signal, a heating module of the printing head is turned off, and the printing head is prevented from being damaged due to too high temperature. According to the scheme, heating control over the printing head is achieved through hardware, and control is more timely.

Description

Technical Field

[0001] The invention belongs to the technical field of thermal printer processing, and in particular relates to a method for preventing a thermal printer from overheating and a control circuit thereof. Background Art

[0002] Thermal printers print out the required images and texts by heating the print head and contacting it with thermal printing paper. The temperature of the print head needs to be controlled between 180℃ and 200℃. When it exceeds 200℃, heating must be stopped to prevent overheating and burning the print head. The existing solution uses the characteristic that the resistance of the thermistor decreases as the temperature increases. So when the temperature changes, the voltage applied to the thermistor will change due to the change in the resistance of the thermistor. The ADC of the MCU reads the voltage value on the thermistor and converts it into the corresponding temperature. When it detects that the print head temperature exceeds 200℃, the MCU will issue a command to stop heating. When the ADC of the MCU detects that the print head is below 200℃, the MCU issues a command to start heating. Figure 1 As shown, the MCU includes at least 3 GPIOs and 1 ADC. The 3 GPIOs are respectively connected to the stepper motor, the heating control module, and the photoelectric sensor of the print head, and the ADC is connected to the thermistor circuit.

[0003] In the above solution, the MCU detects the print head temperature through the ADC and then determines whether the temperature exceeds 200°C. However, this solution requires the MCU to detect the print head temperature at regular intervals and then determine whether the temperature exceeds 200°C, which greatly affects the efficiency of the MCU. Moreover, if the temperature of the print head exceeds 200°C between two temperature detections, then stopping heating the print head may cause damage to the print head due to untimely issuance of the stop heating instruction.

[0004] In addition, commonly used technical terms include:

[0005] Thermal printer: The working principle of a thermal printer is that a semiconductor heating element is installed on the print head. After the print head is heated and contacts the thermal printing paper, the required pattern can be printed. The image is generated by heating and producing a chemical reaction in the film. This thermal printer chemical reaction is carried out at a certain temperature. High temperature will accelerate this chemical reaction. When the temperature is below 60℃, it takes a long time, even several years, for the paper to turn dark; when the temperature is 200℃, this reaction will be completed in a few microseconds.

[0006] Thermal printing paper: Thermal paper is a special coated paper, which looks similar to ordinary white paper. The surface of thermal paper is smooth. It is made of ordinary paper as the base paper, and coated with a thermal color-producing layer. The color-producing layer is coated on one side of the surface of ordinary paper. The color-producing layer is composed of adhesive, color developer, and colorless dye (or hidden dye). It is not separated by microcapsules, and the chemical reaction is in a "latent" state. When the thermal paper encounters a heated print head, the color developer and the colorless dye at the place where the print head prints will react chemically and change color to form pictures and texts.

[0007] NTC thermistor: NTC thermistor generally refers to negative temperature coefficient thermistor. Negative temperature coefficient thermistor, also known as NTC thermistor, is a type of sensor resistor whose resistance value decreases as the temperature increases. It is widely used in various electronic components, such as temperature sensors, resettable fuses and automatically adjustable heaters.

[0008] GPIO: General Purpose Input / Output pin, general purpose input and output pin of the chip. Summary of the invention

[0009] In order to solve the above problems, the purpose of this application is to detect the temperature of the print head in a hardware manner, and to quickly stop heating when the temperature reaches 200°C. The entire process does not require the participation of the MCU, saving MCU resource usage.

[0010] Specifically, the present invention provides a method for preventing a thermal printer from overheating, the method comprising the following steps:

[0011] S1, suppose resistors R1 and R2 are connected in series and connected to +3.3V and ground respectively to form a resistor voltage divider, where the voltage on R2 is recorded as Vref, and the calculation formula of Vref is: Here, the voltage value of Vref is equal to the voltage value on thermistor R4 when the print head is at 200°C, that is, the resistance value of R1 is 10K, and the resistance value of R2 is 4.4K. Substituting into the above formula, the Vref value is 1V.

[0012] S2, assuming that the Vref voltage generated by the resistor voltage division is connected to the V- terminal of a voltage comparator, and the V+ terminal of the voltage comparator is connected to the output terminal of the thermistor voltage of the print head;

[0013] S3, the VOUT of the voltage comparator is connected to the heating control pin of the print head, and the characteristics of the voltage comparator are used to monitor the voltage of the thermistor of the printer. The resistance of the thermistor in the print head changes with the temperature of the print head. The print head includes an NTC thermistor R4, which is a type of sensor resistor whose resistance decreases with increasing temperature. At room temperature of 25°C, the resistance of R4 is 30K. As the temperature increases, when the temperature of the print head is 200°C, its resistance decreases to 4.4K. The resistance of the thermistor can be found through the resistance-temperature table provided by the thermistor manufacturer; Figure 3 As shown, resistors R3 and R4 are connected in series and connected to +3.3V and ground respectively. The voltage on resistor R4 can be calculated by the following formula

[0014]

[0015] The resistance of thermistor R4 at room temperature is 30K, and the resistance of R3 is 10K. Substituting the resistance of R4 and R3 into the above formula, the voltage on thermistor R4 at room temperature is 2.475V. When the print head is 200℃, the resistance of thermistor R4 is 4.4K, and the resistance of R3 remains unchanged at 10K. Substituting the resistance of R4 and R3 into the above formula, the voltage on thermistor R4 is 1V when the print head is 200℃. The voltage comparator V+ is connected to the voltage output end of the thermistor R4 of the print head. As the temperature of the print head increases, the resistance of thermistor R4 decreases, and the voltage on R4 also decreases. When the temperature of the print head exceeds 200℃, the voltage on R4 is less than 1V, that is, V+<V-. The voltage comparator sends a low-level signal to shut down the heating module of the print head to prevent the print head from being damaged by excessive temperature.

[0016] The characteristics of the voltage comparator further include:

[0017] The voltage comparator compares the sizes of two voltages. When V+>V-, the voltage comparator output VOUT is VCC, a high level H. When V+<V-, the voltage comparator output VOUT is 0V, a low level L.

[0018] The step S3 further comprises:

[0019] When the print head temperature is lower than 200℃, the voltage on the thermistor is higher than the Vref voltage, that is, V+>V-, and the voltage comparator outputs VOUT of 3.3V, high level H, and the print head continues to heat; as the print head temperature rises, due to the characteristic of the thermistor that the resistance decreases with increasing temperature, the voltage on the thermistor also decreases, that is, the voltage of V+ decreases. When the print head temperature exceeds 200℃, the voltage of V+ is less than Vref, that is, V+<V-, the voltage comparator outputs VOUT of 0V, low level, and the print head heating module is turned off.

[0020] The present application also relates to a control circuit for preventing a thermal printer from overheating, the control circuit being applicable to any of the above methods, the control circuit comprising at least:

[0021] A resistor R1 and another resistor R2. Resistors R1 and R2 form a divided voltage and are connected to the V- terminal of a voltage comparator. The V+ terminal of the voltage comparator is connected to the voltage output terminal on the thermistor of the print head. The VOUT of the voltage comparator is connected to the heating control module of the print head for heating control.

[0022] Therefore, the advantage of the present application is that the technical solution of the present invention uses hardware to realize the heating control of the print head, which is more timely than the solution of using the ADC of the MCU to detect the temperature and then determine whether the temperature exceeds 200°C and then turn off the heating module. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings described herein are used to provide a further understanding of the present invention, constitute a part of this application, and do not constitute a limitation of the present invention.

[0024] Figure 1 It is a schematic diagram of MCU controlling the heating of the print head in the prior art.

[0025] Figure 2 is a schematic diagram of a voltage comparator in this method.

[0026] Figure 3 is a schematic diagram of the control circuit in this application.

[0027] Figure 4 It is a flow chart of the present application method. DETAILED DESCRIPTION

[0028] In order to more clearly understand the technical content and advantages of the present invention, the present invention is now further described in detail in conjunction with the accompanying drawings.

[0029] This application proposes a technical solution to prevent thermal printers from overheating, using a voltage comparator. The function of the voltage comparator is to compare the magnitude of two voltages. When V+>V-, the voltage comparator outputs VOUT as VCC, a high level H. When V+<V-, the voltage comparator outputs VOUT as 0V, a low level L. Figure 2 shown.

[0030] The specific technical solution of the present invention is as follows Figure 3As shown, a control circuit for preventing a thermal printer from overheating includes: a resistor R1 and another resistor R2. The resistors R1 and R2 form a divided voltage and are connected to the V- terminal of a voltage comparator. The V+ terminal of the voltage comparator is connected to the voltage output terminal of the thermistor on the print head. The VOUT of the voltage comparator is connected to the heating control module of the print head for heating control.

[0031] The technical solution of the present invention is to utilize the characteristics of a voltage comparator to monitor the voltage of a printer thermistor. When the thermistor voltage is detected to drop to the voltage of a print head at 200°C, the voltage comparator immediately sends a low-level signal to shut down the heating module of the print head to prevent the print head from being damaged by excessive temperature.

[0032] like Figure 4 As shown, a method for preventing a thermal printer from overheating comprises the following steps:

[0033] S1, suppose resistors R1 and R2 are connected in series and connected to +3.3V and ground respectively to form a resistor voltage divider, where the voltage on R2 is recorded as Vref, and the calculation formula of Vref is: Here, the voltage value of Vref is equal to the voltage value on thermistor R4 when the print head is at 200℃, that is, the resistance value of R1 is 10K, and the resistance value of R2 is 4.4K. Substituting into the above formula, the Vref value is 1V.

[0034] S2, assuming that the Vref voltage generated by the resistor voltage division is connected to the V- terminal of a voltage comparator, and the V+ terminal of the voltage comparator is connected to the output terminal of the thermistor voltage of the print head;

[0035] S3, the VOUT of the voltage comparator is connected to the heating control pin of the print head, and the characteristics of the voltage comparator are used to monitor the voltage of the thermistor of the printer. The resistance of the thermistor in the print head changes with the temperature of the print head. As shown in the figure, resistor R4 is an NTC thermistor, which is a type of sensor resistor whose resistance decreases with increasing temperature. At room temperature of 25°C, the resistance of R4 is 30K. As the temperature increases, when the temperature of the print head is 200°C, its resistance decreases to 4.4K (the resistance of the thermistor can be found through the resistance temperature table provided by the thermistor manufacturer). Figure 3 As shown in , resistors R3 and R4 are connected in series and connected to +3.3V and ground respectively. The voltage on resistor R4 can be calculated by the following formula

[0036]

[0037] The resistance of thermistor R4 at room temperature is 30K, and the resistance of R3 is 10K. Substituting the resistance of R4 and R3 into the above formula, the voltage on thermistor R4 at room temperature is 2.475V. When the print head is 200℃, the resistance of thermistor R4 is 4.4K, and the resistance of R3 remains unchanged at 10K. Substituting the resistance of R4 and R3 into the above formula, the voltage on thermistor R4 is 1V when the print head is 200℃. The voltage comparator V+ is connected to the voltage output end of the thermistor R4 of the print head. As the temperature of the print head increases, the resistance of thermistor R4 decreases, and the voltage on R4 also decreases. When the temperature of the print head exceeds 200℃, the voltage on R4 is less than 1V, that is, V+<V-. The voltage comparator sends a low-level signal to shut down the heating module of the print head to prevent the print head from being damaged by excessive temperature.

[0038] According to the comparator principle, when the print head temperature is lower than 200℃, the voltage on the thermistor is higher than the Vref voltage, that is, V+>V-, and the voltage comparator outputs VOUT of 3.3V, high level H, and the print head continues to heat. As the print head temperature rises, due to the characteristic of the thermistor that the resistance decreases with increasing temperature, the voltage on the thermistor also decreases, that is, the voltage of V+ decreases. When the print head temperature exceeds 200℃, the voltage of V+ is less than Vref, that is, V+<V-, the voltage comparator outputs VOUT of 0V, low level, and the print head heating module is turned off.

[0039] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the embodiments of the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preventing a thermal printer from overheating, characterized in that: The method comprises the following steps Steps: S1, suppose resistors R1 and R2 are connected in series and connected to +3.3V and ground respectively to form a resistor voltage divider, where the voltage on R2 is recorded as Vref, and the calculation formula of Vref is: Here, the voltage value of Vref should be equal to the voltage value on thermistor R4 when the print head is at 200℃, that is, the resistance value of R1 is 10K, and the resistance value of R2 is 4.4K. Substituting into the above formula, the Vref value is 1V; S2, assuming that the Vref voltage generated by the resistor voltage division is connected to the V- terminal of a voltage comparator, and the V+ terminal of the voltage comparator is connected to the output terminal of the thermistor voltage of the print head; S3, the VOUT of the voltage comparator is connected to the heating control pin of the print head, and the characteristics of the voltage comparator are used to monitor the voltage of the thermistor of the printer. The resistance of the thermistor in the print head changes with the temperature of the print head. The print head contains an NTC thermistor R4, which is a type of sensor resistor whose resistance decreases with increasing temperature. At room temperature 25°C, the resistance of R4 is 30K. As the temperature increases, when the temperature of the print head is 200°C, its resistance decreases to 4.4K. The resistance of the thermistor can be found through the resistance temperature table provided by the thermistor manufacturer. Resistors R3 and R4 are connected in series and connected to +3.3V and ground respectively. The voltage on resistor R4 can be calculated by the formula The resistance of thermistor R4 at room temperature is 30K, and the resistance of R3 is 10K. Substituting the resistance of R4 and R3 into the above formula, the voltage on thermistor R4 at room temperature is 2.475V. When the print head is 200℃, the resistance of thermistor R4 is 4.4K, and the resistance of R3 remains unchanged at 10K. Substituting the resistance of R4 and R3 into the above formula, the voltage on thermistor R4 is 1V when the print head is 200℃. The voltage comparator V+ is connected to the voltage output end of the thermistor R4 of the print head. As the temperature of the print head increases, the resistance of thermistor R4 decreases, and the voltage on R4 also decreases. When the temperature of the print head exceeds 200℃, the voltage on R4 is less than 1V, that is, V+<V-. The voltage comparator sends a low-level signal to shut down the heating module of the print head to prevent the print head from being damaged by excessive temperature.

2. A method for preventing a thermal printer from overheating according to claim 1, characterized in that: The characteristics of the voltage comparator further include: The voltage comparator compares the sizes of two voltages. When V+>V-, the voltage comparator output VOUT is VCC, a high level H. When V+<V-, the voltage comparator output VOUT is 0V, a low level L.

3. A method for preventing a thermal printer from overheating according to claim 2, characterized in that: The step S3 further comprises: When the print head temperature is lower than 200℃, the voltage on the thermistor is higher than the Vref voltage, that is, V+>V-, and the voltage comparator outputs VOUT of 3.3V, high level H, and the print head continues to heat; as the print head temperature rises, due to the characteristic of the thermistor that the resistance decreases with increasing temperature, the voltage on the thermistor also decreases, that is, the voltage of V+ decreases. When the print head temperature exceeds 200℃, the voltage of V+ is less than Vref, that is, V+<V-, the voltage comparator outputs VOUT of 0V, low level, and the print head heating module is turned off.

4. A control circuit for preventing a thermal printer from overheating, characterized in that: The control circuit is applicable to the method described in any one of claims 1 to 3 above, and the control circuit at least comprises: A resistor R1 and another resistor R2. Resistors R1 and R2 form a divided voltage and are connected to the V- terminal of a voltage comparator. The V+ terminal of the voltage comparator is connected to the voltage output terminal on the thermistor of the print head. The VOUT of the voltage comparator is connected to the heating control module of the print head for heating control.

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