A method for preventing a thermal printer from overheating and a control circuit thereof

Abstract

The application provides a method for preventing a thermal printer from overheating and a control circuit thereof, and comprises the following steps: S1, connecting a resistor R1 and a resistor R2 in series and connecting the resistor R1 to +3.3V and the resistor R2 to ground respectively to form a resistor voltage division, and the voltage on the resistor R2 is recorded as Vref, and the voltage value of Vref is equal to the voltage value on the thermal resistor R4 when the print head is at 200 DEG C and is 1V; S2, connecting the Vref voltage generated after the resistor voltage division to the V- end of a voltage comparator, and connecting the V+ end of the voltage comparator to the output end of the thermal resistor voltage of the print head; and S3, connecting the VOUT of the voltage comparator to the heating control pin of the print head, and monitoring the thermal resistor voltage of the printer by using the characteristics of the voltage comparator, and when the thermal resistor voltage is monitored to drop to the voltage when the print head is at 200 DEG C, the voltage comparator immediately sends a low-level signal to turn off the heating module of the print head to prevent the print head from being damaged due to high temperature. The print head heating control is realized by using hardware in the scheme, and the control is more timely.

Description

Technical Field

[0001] This invention belongs to the field of thermal printer processing technology, and specifically relates to a method and control circuit for preventing thermal printers from overheating. Background Technology

[0002] Thermal printers print text and images by heating the printhead, which then contacts the thermal paper. The printhead temperature needs to be controlled between 180℃ and 200℃. Heating must stop when it exceeds 200℃ to prevent overheating and burning out the printhead. Current solutions utilize the characteristic that the resistance of a thermistor decreases with temperature. When the temperature changes, the voltage across the thermistor changes accordingly. The MCU's ADC reads this voltage value and calculates the corresponding temperature. When the printhead temperature exceeds 200℃, the MCU sends a command to stop heating. When the MCU's ADC detects that the printhead temperature is below 200℃, the MCU sends a command to start heating again. Figure 1 As shown, the MCU includes at least 3 GPIOs and 1 ADC. The 3 GPIOs are connected to the stepper motor of the print head, the heating control module, and the photoelectric sensor, respectively, and the ADC is connected to the thermal circuit.

[0003] In the above solution, the MCU detects the printhead temperature through the ADC and then determines whether the temperature exceeds 200℃. However, this solution requires the MCU to detect the printhead temperature every once in a while and then determine whether the temperature exceeds 200℃. This greatly affects the efficiency of the MCU. Moreover, if the printhead temperature exceeds 200℃ between two temperature detections, stopping the heating of the printhead at this time may cause damage to the printhead due to the untimely issuance of the stop heating command.

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

[0005] Thermal printers: Thermal printers work by using a semiconductor heating element mounted on the print head. The print head heats up and comes into contact with the thermal paper, allowing the desired image to be printed. The image is generated through a chemical reaction within the film caused by heating. This chemical reaction occurs at a specific temperature. High temperatures accelerate this reaction. When the temperature is below 60°C, the paper takes a considerable amount of time, even several years, to darken; while at 200°C, the reaction is completed within microseconds.

[0006] Thermal printing paper: Thermal paper is a special type of coated paper that resembles ordinary white paper in appearance. It has a smooth surface and is made with ordinary paper as the base, coated with a thermal color-developing layer. This layer is applied to only one side of the paper and consists of adhesives, developers, and colorless dyes (or leuco dyes). These components are not separated by microcapsules, so the chemical reaction is in a "latent" state. When the thermal paper comes into contact with a heated printhead, the developer and colorless dyes at the printed area react chemically, changing color and forming the image.

[0007] NTC thermistors: NTC thermistors generally refer to negative temperature coefficient thermistors. Also known as NTC thermistors, they are a type of sensor resistor whose resistance decreases as temperature increases. They are widely used in various electronic components, such as temperature sensors, resettable fuses, and automatically adjustable heaters.

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

[0009] To address the aforementioned issues, the purpose of this application is to detect the printhead temperature using hardware and to quickly stop heating when the detected temperature reaches 200°C. The entire process does not require MCU involvement, thus saving MCU resource usage.

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

[0011] S1. Assume resistors R1 and R2 are connected in series and connected to +3.3V and ground respectively, forming a resistor voltage divider. The voltage across R2 is denoted as Vref. The formula for calculating Vref is: Here, the voltage value of Vref must be equal to the voltage value of the thermistor R4 when the printhead is 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.

[0012] S2, suppose the Vref voltage generated after the resistor voltage divider 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 printhead;

[0013] S3, the VOUT of the voltage comparator is connected to the heating control pin of the printhead. Utilizing the characteristics of the voltage comparator, the voltage of the printer's thermistor is monitored. The resistance of the thermistor in the printhead changes with the temperature of the printhead. The printhead contains an NTC thermistor R4. This thermistor is a type of sensor resistor whose resistance decreases as temperature increases. At room temperature (25℃), R4 has a resistance of 30K ohms. As the temperature increases, at a printhead temperature of 200℃, its resistance decreases to 4.4K ohms. The thermistor resistance value can be found in 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 across resistor R4 can be calculated using the following formula.

[0014]

[0015] The thermistor R4 has a resistance of 30KΩ at room temperature, and R3 has a resistance of 10KΩ. Substituting the resistances of R4 and R3 into the formula above, the voltage across the thermistor R4 at room temperature is calculated to be 2.475V. When the printhead is at 200℃, the resistance of thermistor R4 is 4.4KΩ, and the resistance of R3 remains unchanged at 10KΩ. Substituting the resistances of R4 and R3 into the formula above, the voltage across the thermistor R4 at 200℃ is calculated to be 1V. The voltage comparator V+ terminal is connected to the voltage output terminal of the thermistor R4 on the printhead. As the printhead temperature increases, the resistance of thermistor R4 decreases, and the voltage across R4 also decreases. When the printhead temperature exceeds 200℃, the voltage across R4 is less than 1V, i.e., V+ < V-. The voltage comparator sends a low-level signal to shut off the printhead heating module to prevent damage from overheating.

[0016] The voltage comparator further includes the following characteristics:

[0017] A voltage comparator compares the magnitudes of two voltages. When V+ > V-, the voltage comparator outputs VOUT, which is VCC (high level, H). When V+ < V-, the voltage comparator outputs VOUT, which is 0V (low level, L).

[0018] Step S3 further includes:

[0019] When the printhead temperature is below 200℃, the voltage across the thermistor is higher than the Vref voltage, i.e., V+ > V-, and the voltage comparator outputs VOUT as 3.3V, a high level (H), at which point the printhead continues to heat up. As the printhead temperature rises, the thermistor's resistance decreases with increasing temperature, and the voltage across it also decreases, i.e., the V+ voltage decreases. When the printhead temperature exceeds 200℃, the V+ voltage becomes less than Vref, i.e., V+ < V-, and the voltage comparator outputs VOUT as 0V, a low level (0), shutting down the printhead heating module.

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

[0021] A resistor R1 and another resistor R2 form a voltage divider, which is then 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 printhead. The VOUT of the voltage comparator is connected to the heating control module of the printhead for heating control.

[0022] Therefore, the advantage of this application is that the technical solution of this invention uses hardware to implement the printhead heating control, which is more timely than the solution of using the MCU's ADC to detect the temperature and then determine whether the temperature exceeds 200°C before turning off the heating module. Attached Figure Description

[0023] The accompanying drawings, which are provided to further illustrate the invention and form part of this application, are not intended to limit the scope of the invention.

[0024] Figure 1 This is a schematic diagram of MCU-controlled printhead heating in existing technology.

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

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

[0027] Figure 4 This is a flowchart illustrating the method described in this application. Detailed Implementation

[0028] To better understand the technical content and advantages of the present invention, the present invention will now be described in further detail with reference to the accompanying drawings.

[0029] This application proposes a technical solution to prevent thermal printer overheating, which uses a voltage comparator. The function of the voltage comparator is to compare the magnitudes of two voltages. When V+ > V-, the voltage comparator outputs VOUT as VCC (high level H); when V+ < V-, the voltage comparator outputs VOUT as 0V (low level L). Figure 2 As shown.

[0030] The specific technical solution of this invention is as follows: Figure 3As shown, a control circuit for preventing thermal printer overheating includes: a resistor R1 and another resistor R2. Resistors R1 and R2 form a voltage divider 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 printhead. The VOUT of the voltage comparator is connected to the heating control module of the printhead for heating control.

[0031] The technical solution of this invention utilizes the characteristics of a voltage comparator to monitor the voltage of the printer's thermistor. When the thermistor voltage is detected to drop to the voltage required for the printhead to reach 200°C, the voltage comparator immediately sends a low-level signal to shut off the printhead heating module, preventing the printhead from being damaged due to excessive temperature.

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

[0033] S1. Assume resistors R1 and R2 are connected in series and connected to +3.3V and ground respectively, forming a resistor voltage divider. The voltage across R2 is denoted as Vref. The formula for calculating Vref is: Here, the voltage value of Vref must be equal to the voltage value of the thermistor R4 when the printhead is 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 value of Vref is 1V.

[0034] S2, suppose the Vref voltage generated after the resistor voltage divider 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 printhead;

[0035] S3, the VOUT of the voltage comparator is connected to the printhead heating control pin. Utilizing the characteristics of the voltage comparator, the voltage of the printer's thermistor is monitored. The resistance of the thermistor in the printhead changes with the printhead temperature. As shown in the figure, resistor R4 is an NTC thermistor, a type of sensor resistor whose resistance decreases as temperature increases. At room temperature (25℃), R4 has a resistance of 30KΩ. As the temperature increases, when the printhead temperature reaches 200℃, its resistance decreases to 4.4KΩ (thermistor resistance values ​​can be found in 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 across resistor R4 can be calculated using the following formula.

[0036]

[0037] The thermistor R4 has a resistance of 30KΩ at room temperature, and R3 has a resistance of 10KΩ. Substituting the resistances of R4 and R3 into the formula above, the voltage across the thermistor R4 at room temperature is calculated to be 2.475V. At 200℃, the resistance of thermistor R4 is 4.4KΩ, and the resistance of R3 remains unchanged at 10KΩ. Substituting the resistances of R4 and R3 into the formula above, the voltage across the thermistor R4 at 200℃ is calculated to be 1V. The voltage comparator V+ terminal is connected to the voltage output terminal of the thermistor R4 on the printhead. As the printhead temperature increases, the resistance of thermistor R4 decreases, and the voltage across R4 also decreases. When the printhead temperature exceeds 200℃, the voltage across R4 is less than 1V, i.e., V+ < V-. The voltage comparator sends a low-level signal to shut down the printhead heating module to prevent damage from overheating.

[0038] According to the comparator principle, when the printhead temperature is below 200℃, the voltage across the thermistor is higher than Vref, i.e., V+ > V-, and the voltage comparator outputs VOUT as 3.3V, a high level (H), at which point the printhead continues to heat up. As the printhead temperature rises, because the thermistor's resistance decreases with increasing temperature, the voltage across the thermistor also decreases, i.e., the voltage V+ decreases. When the printhead temperature exceeds 200℃, the voltage V+ becomes less than Vref, i.e., V+ < V-, and the voltage comparator outputs VOUT as 0V, a low level (H), shutting down the printhead heating module.

[0039] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, various modifications and variations can be made to the embodiments of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preventing overheating of a thermal printer, characterized in that, The method includes the following steps Suddenly: S1. Assume resistors R1 and R2 are connected in series and connected to +3.3V and ground respectively, forming a resistor voltage divider. The voltage across R2 is denoted as Vref. The formula for calculating Vref is: Here, the voltage value of Vref must be equal to the voltage value of the thermistor R4 when the printhead is 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, suppose the Vref voltage generated after the resistor voltage divider 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 printhead; S3, the VOUT of the voltage comparator is connected to the heating control pin of the printhead. Utilizing the characteristics of the voltage comparator, the voltage of the printer's thermistor is monitored. The resistance of the thermistor in the printhead changes with the printhead temperature. The printhead includes an NTC thermistor R4. This thermistor is a type of sensor resistor whose resistance decreases with increasing temperature. At room temperature (25℃), R4 has a resistance of 30KΩ. As the temperature increases, at a printhead temperature of 200℃, its resistance decreases to 4.4KΩ. The thermistor resistance value can be found using a 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 across resistor R4 can be calculated using a formula. The thermistor R4 has a resistance of 30KΩ at room temperature, and R3 has a resistance of 10KΩ. Substituting the resistances of R4 and R3 into the formula above, the voltage across the thermistor R4 at room temperature is calculated to be 2.475V. When the printhead is at 200℃, the resistance of thermistor R4 is 4.4KΩ, and the resistance of R3 remains unchanged at 10KΩ. Substituting the resistances of R4 and R3 into the formula above, the voltage across the thermistor R4 at 200℃ is calculated to be 1V. The voltage comparator V+ terminal is connected to the voltage output terminal of the thermistor R4 on the printhead. As the printhead temperature increases, the resistance of thermistor R4 decreases, and the voltage across R4 also decreases. When the printhead temperature exceeds 200℃, the voltage across R4 is less than 1V, i.e., V+ < V-. The voltage comparator sends a low-level signal to shut off the printhead heating module to prevent damage from overheating.

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

3. The method for preventing overheating of a thermal printer according to claim 2, characterized in that, Step S3 further includes: When the printhead temperature is below 200℃, the voltage across the thermistor is higher than the Vref voltage, i.e., V+ > V-, and the voltage comparator outputs VOUT as 3.3V, a high level (H), at which point the printhead continues to heat up. As the printhead temperature rises, the thermistor's resistance decreases with increasing temperature, and the voltage across it also decreases, i.e., the V+ voltage decreases. When the printhead temperature exceeds 200℃, the V+ voltage becomes less than Vref, i.e., V+ < V-, and the voltage comparator outputs VOUT as 0V, a low level (0), shutting down the printhead heating module.

4. A control circuit for preventing overheating of a thermal printer, characterized in that, The control circuit is applicable to the method described in any one of claims 1-3, and the control circuit comprises at least: A resistor R1 and another resistor R2 form a voltage divider, which is then 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 printhead. The VOUT of the voltage comparator is connected to the heating control module of the printhead for heating control.

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