CN113815316B

CN113815316B - Thermal printing head heating control method and device based on differential constant-current heating

Info

Publication number: CN113815316B
Application number: CN202011351630.5A
Authority: CN
Inventors: 孙玉萌; 孙华刚; 周祥岗; 张东娜
Original assignee: Shandong Hualing Electronics Co Ltd
Current assignee: Shandong Hualing Electronics Co Ltd
Priority date: 2020-11-26
Filing date: 2020-11-26
Publication date: 2022-10-04
Anticipated expiration: 2040-11-26
Also published as: CN113815316A

Abstract

The invention relates to a thermal printing head heating control method and a thermal printing head heating control device based on differential constant-current heating, which are characterized in that differential constant-current heating control is carried out on more than two heating points in a thermal printing head heating body, so that the heating power of each heating point is consistent, wherein the following contents are executed on each heating point in the thermal printing head heating body: measuring voltage V1 at two ends of a heating point; the measured voltage value V1 is sent to a voltage comparator to be compared with a reference voltage Vc, if V1 is less than Vc, a heating circuit of the heating point is cut off, and the temperature begins to be reduced; judging whether the temperature of the heating point is reduced below a safe temperature, if so, starting a heating circuit of the heating point, and continuing to heat until the line of printing is finished, otherwise, continuing to reduce the temperature below the safe temperature; compared with the prior art, the invention can reduce the negative influence on the printing effect caused by temperature accumulation and can avoid the damage of the heating element of the printing head caused by overhigh temperature.

Description

Thermal printing head heating control method and device based on differential constant-current heating

The technical field is as follows:

the invention relates to the technical field of thermal printing head manufacturing, in particular to a thermal printing head heating control method and device based on differential constant-current heating, which can ensure that the heat transfer amount of printing media of heating points is the same, and further improve the printing density uniformity.

The background art comprises the following steps:

as is well known, a thermal print head is configured with a plurality of consecutive thermal heating units linearly configured according to a certain resolution, a printer drives a logic signal according to a print content to apply a voltage for a corresponding time to each heating unit through a control IC to cause the heating units to generate joule heat, heat energy generated by the heating units is applied to a thermal medium to cause the thermal medium to develop color to realize printing, the resistance values of heating points on the print head have a difference in a certain range, the phenomenon of uneven density is printed in a use scene such as engineering drawings, medical images, and color printing by using a common control method, and rough compensation can be generally performed only by controlling the heating time of individual points with large differences.

The relevant prior documents are as follows: CN 108569036A: the negative temperature coefficient resistor R is adhered to a thermal head radiating fin of the thermal printer, when the temperature of the thermal printer is low, the base voltage of the NPN type triode is high, the NPN type triode is conducted, the internal resistance between the collector and the emitter of the NPN type triode is small, current mainly flows through the NPN type triode, large working current is rapidly provided for the thermal printer, and normal large-data-volume printing is guaranteed; when the temperature of the thermal printing head is gradually increased, the internal resistance of the negative temperature coefficient resistor R is gradually reduced, the conduction degree of the NPN type triode Q1 is gradually weakened, the current supplied to the thermal printing head is weakened, the printing is slowed down, and the thermal printing head is protected.

CN110466260A: the heating control sequence is used for heating one dot row for multiple times by dividing the paper feeding time for printing one dot row into N heating time periods and setting N-1 rest time periods between two adjacent heating time periods, so that the problems that black lines are not full and rendering is not uniform when data is printed in a non-heating time period, and obvious thin white lines appear on the thermal paper, and the printing effect is improved are solved.

JP1993278251A: the influence on the control point when the dots around the print point to be controlled generate heat is quantified as the start point temperature and the peak temperature of the control point temperature curve and the temperature rise of the generated peripheral dots. The temperature profile of the control point is configured by summing the temperature rises, and the printing energy is controlled so that the peak temperature of the control point becomes a reference value by comparing the temperature profile with a reference profile.

CN1467090A: a print control apparatus and method utilizes a thermal head having a set of micro-heating elements that can be used as both heating elements and temperature detectors and a drive circuit that provides current to drive the heating elements; a control circuit for switching a current supplied to each heating element between a heating drive state and a temperature detection state, a circuit for converting a temperature value on each heating element to a voltage value, and 1 which can detect a voltage value using a current flowing in the temperature detection state; an analog/digital conversion circuit for converting the voltage to a digital value, an adder for cumulatively calculating the digital value obtained by the digital conversion from the start of heating, a comparator for comparing the cumulative value obtained by the adder with a preset target printing density value sent by a superordinate apparatus with respect to a given point to be printed to determine which is larger; circuitry for stopping the heating drive of the heating element when the comparator detects that the target print density value has been reached.

The methods mentioned in these prior documents either protect the print head by measuring the temperature control current on the heat sink through the ntc resistor, or by presetting a fixed multi-segment pulse print, or by obtaining the temperature of the thermistor and performing a rough temperature compensation operation using the temperature of the thermistor, or by switching the print circuit and the resistance measuring circuit at a high speed to realize the measurement of the temperature of the heat generator itself at the print gap and perform frequent temperature correction. The method for protecting the printing head by controlling the current magnitude through the temperature on the radiating fin can play a certain protection role, but the temperature measuring position is away from the heating body by a certain distance, the accuracy is low, the printing speed is reduced when the current becomes small, the fixed multi-stage printing method is preset, the printing quality can be effectively improved, but the temperature is difficult to control below the critical temperature, the temperature of the thermistor is used as a basic temperature control method, the temperature difference between the thermistor and the heating body is too large, the delay time of the thermistor and the temperature of the heating body is usually dozens to hundreds of us compared with the temperature of the heating body, the reaction is too slow, and the requirement cannot be met on the occasion requiring precise control; in the situation of iTPH control mentioned in CN1467090A, since the working circuit and the resistance measuring circuit need to be switched at high speed and frequently, the requirements on hardware circuits and software are too high, and a special driving IC, a peripheral control circuit and software are needed to perform correspondence, the technical difficulty and the cost are very high, and the wide application is difficult to obtain.

The invention content is as follows:

aiming at the defects and shortcomings in the prior art, the invention provides a thermal printing head heating control method and device based on differential constant-current heating, which can ensure that the heat transfer amount of printing media of heating points is the same, and further improve the printing density uniformity.

The invention is achieved by the following measures:

a thermal printing head heating control method based on differential constant-current heating is characterized in that differential constant-current heating control is carried out on more than two heating points in a thermal printing head heating body, so that the heating power of each heating point is consistent, wherein the following steps are carried out on each heating point in the thermal printing head heating body:

step 1: measuring voltage V1 at two ends of a heating point;

step 2: sending the measured voltage value V1 into a voltage comparator, comparing the voltage value with a reference voltage Vc, if V1 is less than Vc, cutting off a heating circuit of the heating point, and starting to cool;

and 3, step 3: and judging whether the temperature of the heating point is reduced to be below the safe temperature, if so, starting a heating circuit of the heating point, and continuing to heat until the line of printing is finished, otherwise, continuing to reduce the temperature to be below the safe temperature.

The invention also comprises initial heating, during the initial heating, more than two heating points of a heating body in the thermal printing head are heated by constant current, and heating pulses are output to the heating circuits of more than two heating points through a register, the heating current of each heating point is set according to the resistance value (known) of the heating point, so that the heating power of each heating point is consistent.

The heating adjustment of any heating point in the invention is specifically as follows: the register obtains data representing the current value of each heating point through a communication interface between the drive IC and the printer, the obtained data is converted into a voltage value for controlling the current of each heating point after being processed by the DA converter, the obtained voltage value is applied to the MOS tube, and the current value in the heating circuit is controlled by the MOS tube.

In the step 3, whether the temperature of the current heating point is reduced to below the safe temperature is judged through the cooling time t1, an estimated cooling value is obtained by combining the cooling time t1 and the cooling rate of the heating point material, and further, the cooling time t1 is between a few microseconds and dozens of microseconds, so that the temperature can be reduced to below the safe temperature.

The invention also provides a thermal printing head heating control device based on differential constant-current heating, which is characterized by comprising more than two paths of heating control mechanisms which correspond to more than two heating points in a heating body of the thermal printing head one by one, wherein the heating control mechanisms are provided with a heating adjusting circuit and a heating on-off control circuit.

The heating control mechanism can be realized by adopting the following structure: the heating circuit comprises a heating current adjusting circuit, a voltage comparator and a heating on-off control circuit, wherein a DA converter used for receiving a logic control signal output by a register is arranged in the heating circuit adjusting circuit, the output end of the DA converter is connected with the G pole of an MOS (metal oxide semiconductor) tube used for controlling the current, the S pole of the MOS tube used for controlling the current is connected with the VH end, and the D pole of the MOS tube is connected with the heating on-off control circuit; one input end of the voltage comparator receives a reference voltage value, the other input end of the voltage comparator receives voltage values at two ends of a current heating point, the output end of the voltage comparator is connected with one input end of the logical OR gate, the other input end of the logical OR gate is connected with the output end of the time delayer, the output end of the logical OR gate is connected with one input end of the logical AND gate, the other end of the logical AND gate is connected with an STB (set Top Box) signal (a heating time control signal of one line when a printing head works), the output end of the logical AND gate is connected with the input end of the time delayer through a logical NOT gate and is also connected with a heating on-off control circuit, an on-off control MOS (metal oxide semiconductor) tube is arranged in the heating on-off control circuit, the S pole of the on-off control MOS tube is connected with the D pole of an MOS tube for controlling the current, the D pole of the on-off control MOS tube is connected with the current heating point, and the G pole of the on-off control MOS tube is connected with the output end of the logical AND gate.

The invention also provides a thermal print head with the heating control device, wherein the thermal print head comprises a heating substrate, a control IC, a radiating substrate and a heating resistor body with a stable temperature resistance coefficient (TCR), wherein the control IC can selectively heat the heating body on the heating substrate according to an input control logic, the heating adopts a constant current mode for heating, the thermal control method comprises the steps of setting different current values according to the resistance value of the heating body at each point, enabling the power of all heating points to be consistent, calculating the resistance value of the heating body by measuring the voltage of the heating points and the set current value, obtaining the temperature of the heating body according to the TCR characteristic of the heating body, cutting off the power supply of the current heating point for a few mu s-dozens of mu s if the temperature of the heating body is judged to be close to the critical temperature, stopping heating the heating point, cooling and recovering to the safe temperature, and then recovering to the normal heating until the line heating is stopped, wherein the critical temperature is generally lower than the damage temperature of the heating body, and the safe temperature is lower than the critical temperature but higher than the color development temperature of a printing medium. The method can ensure the printing density among all the heating points to be uniform and can also avoid the damage of the heating element of the printing head due to overhigh temperature.

In the invention, the control IC can adopt an independently controllable constant current heating mode for each heating point, the current is set according to the resistance value of the heating point, so that the heating points with different resistance values can realize the same power heating, the setting of the current is realized through an IC internal register, the register obtains data representing the current of each point through a communication interface between the IC and a printer, the data is converted into a voltage value for controlling the current of each heating point through a DA, and the current is controlled to be small or large in a circuit through a mos tube. The method can ensure that the heating rates of all heating points are consistent and the printing density is uniform.

The individual electrode and the common electrode are arranged on two sides of the heating element, a voltage measuring point is arranged in the control IC on the side of the individual electrode, the other end of the voltage measuring point is connected with a voltage comparator, the voltage of the reference end of the voltage comparator is obtained by combining TCR of the heating element and constant current calculation of the heating element according to the critical temperature of the heating element, and when the voltage of the voltage measuring point is lower than the reference voltage of the voltage comparator, the comparator outputs a signal to cut off the heating circuit. After a period of time delay, when the voltage is higher than the reference voltage, the circuit is switched on to recover heating, and the pulse type heating mode is formed by repeatedly switching on and off, so that the method can reduce the negative influence on the printing effect caused by temperature accumulation and can avoid the damage of a heating body of the printing head due to overhigh temperature.

Description of the drawings:

FIG. 1 is a schematic diagram of a thermal print head according to the present invention.

FIG. 2 shows a connection mode of the common electrode and the individual electrode to the heating element in the present invention.

Fig. 3 is a schematic diagram of a structural principle of controlling connection of a part of points in an IC and a heating element in the invention, the magnitude of a single-point constant current is determined by a printer according to a resistance value of the point at normal temperature, and the current resistance value (voltage value) of the heating element in the printing process, a preset value of the printer, a result of a comparator and an STB signal jointly determine on-off of a heating circuit.

FIG. 4 is the lifting curve of the single-point continuous printing temperature under the control of STB signal and comparator on-off, the heating element begins to heat up when STB is turned on, the heating element stops heating and cooling when STB is turned off, when the temperature rises to the critical temperature, the comparator controls IC to cut off power supply when STB is in the on state, when the temperature drops to the safe temperature, IC resumes power supply, and so on, the heating element heats until STB signal is turned off.

Reference numerals: 1. the circuit board comprises a heating substrate, 2 a control IC,3 a radiating substrate, 4 a heating resistor body, 5 a socket, 6 packaging glue, 7 a PCB circuit board, 8 a common electrode and 9 individual electrodes.

Detailed Description

The invention is further described with reference to the following figures and examples:

example 1:

the thermal printing head comprises a heating substrate, a control IC, a heat dissipation substrate and a heating resistor body with a stable temperature resistance coefficient (TCR), wherein the IC can selectively heat the heating body on the heating substrate according to an input control logic, the heating adopts a constant current mode, the current of each point can be set according to different resistance values, the resistance value of each point is measured before the printing head is used, the printing equipment calculates and generates a current value corresponding to each point according to the resistance value data of the printing head and the same power of all points, a register obtains data representing the current of each point through a communication interface between the IC and a printer, the data is converted into a voltage value for controlling the current of each heating point through DA, and the detail figure 3 shows the current of all points in a control circuit through mos tubes, so that the temperature consistency of all points can be ensured during printing, and the printing concentration is uniform.

The heating method is characterized in that an individual electrode and a common electrode are arranged at two ends of a heating body to be detailed as shown in figure 2, a voltage measuring point is arranged in a control IC at the side of the individual electrode, the other end of the voltage measuring point is connected with a voltage comparator, the voltage of a reference end of the voltage comparator is obtained by combining TCR of the heating body and constant current calculation of the heating body, the voltage measuring point is provided with a voltage comparator to be detailed as shown in figure 3, the printing current is constant current for each point, the current temperature of the heating body can be obtained equivalently according to the TCR characteristic of the heating body by measuring the current voltage of the two ends of the heating point when a printing head works, when the voltage of the two ends of the heating point is lower than the reference voltage, the temperature exceeds the critical temperature, the comparator outputs a signal to cut off a heating circuit, the heating body starts to be cooled, the cooling speed is about 0.2 ℃/us, the cooling time can be set through a time delay device, generally a plurality of us to a plurality of us, when the temperature is reduced to a safe temperature, the switching on circuit recovers heating, and the heating is repeatedly switched on and the heating mode is formed until a gating signal is switched off to finish the printing, and a heating mode pulse type is formed as shown in figure 4. The destruction temperature of the heating body is generally 600 ℃ and above, different heating body materials are different, the temperature of a plurality of lines of initial printing generally does not trigger the IC to protect the heating body, when a plurality of lines are continuously printed, the temperature rise speed is far faster than the temperature drop speed, the temperature can rapidly rise along with the heat accumulation, in order to better protect the heating body, the critical temperature is generally set to be 250 ℃ -400 ℃, the temperature is determined according to the situation, the dynamic color development temperature higher than the printing medium is ensured to be lower than the destruction temperature of the heating body, and is slightly higher than or equal to the saturation temperature of the color development medium, so that the negative influence of heat accumulation on the printing effect can be effectively reduced, and the heating body can be effectively protected from being destroyed due to overhigh temperature.

Claims

1. A thermal print head heating control method based on differential constant current heating comprises a heating substrate, a control IC, a heat dissipation substrate, a heating resistor body with stable temperature resistance coefficient and a thermal print head heating control device based on differential constant current heating, wherein the thermal print head heating control device based on differential constant current heating is provided with a heating current adjusting circuit, a voltage comparator and a heating on-off control circuit; one input end of the voltage comparator receives a reference voltage value, the other input end of the voltage comparator receives voltage values at two ends of a current heating point, the output end of the voltage comparator is connected with one input of the logical OR gate, the other input of the logical OR gate is connected with the output of the time delayer, the output end of the logical OR gate is connected with one input of the logical AND gate, the other end of the logical AND gate is connected with an STB signal, the STB signal is a heating time control signal of one line when the printing head works, the output end of the logical AND gate is connected with the input of the time delayer through a logical NOT gate and is also connected with a heating on-off control circuit, an on-off control MOS tube is arranged in the heating on-off control circuit, the S pole of the on-off control MOS tube is connected with the D pole of the MOS tube for controlling the current, the D pole of the on-off control MOS tube is connected with the current heating point, and the G pole of the on-off control MOS tube is connected with the output end of the logical AND gate;

the heating control method is characterized by comprising the following steps:

the method comprises the following steps of carrying out initial heating, wherein during the initial heating, more than two heating points of a heating body in the thermal printing head are subjected to constant-current heating, heating pulses are output to heating circuits of the more than two heating points through a register, and the heating current of each heating point is set according to the resistance value of the heating point, so that the heating power of each heating point is consistent;

the differential constant-current heating control is carried out on more than two heating points in a heating body of the thermal printing head, so that the heating power of each heating point is consistent, and the heating adjustment of any heating point is as follows: the register obtains data representing the current value of each heating point through a communication interface between the drive IC and the printer, the obtained data is converted into a voltage value for controlling the current of each heating point after being processed by a DA converter, the obtained voltage value is applied to an MOS (metal oxide semiconductor) tube, and the current value in a heating circuit is controlled by the MOS tube, wherein the following steps are carried out on each heating point in a heating body of the thermal printing head:

step 1: measuring voltage V1 at two ends of a heating point;

and 3, step 3: judging whether the temperature of the heating point is reduced below a safe temperature, if so, starting a heating circuit of the heating point, continuing to heat until the line of printing is finished, otherwise, continuing to reduce the temperature below the safe temperature, judging whether the temperature of the current heating point is reduced below the safe temperature through the temperature reduction time t1 in the step 3, and obtaining an estimated temperature reduction value by combining the temperature reduction time t1 and the temperature reduction rate of the heating point material.