Non-destructive resistance repair method for thermal print head based on temperature control

Abstract

The present invention relates to the technical field of resistance correction of heating resistors in thermal print heads, and more specifically to a non-destructive resistance correction method for thermal print heads based on temperature control, comprising the following steps: obtaining a tolerance inflection point temperature T of the heating resistor material; i , refer to the inflection point temperature T i Set the detection temperature T s ; Test the resistance of all the heating points in the heating resistor, and obtain the repairable resistance rate of the heating resistor material accordingly: measure the resistance of all the heating resistor units, i.e. the heating points, in the heating resistor, and determine the target resistance R0 of each heating point with reference to the measured initial resistance. Specifically, a single pulse is applied to the heating point, and the printing pulse voltage is gradually increased in a step-like manner, while testing the resistance change rate △R before and after the pulse. Compared with the prior art, the present invention can effectively ensure that the printed pulse signal is a safe pulse signal, thereby ensuring that there is no thermal stress damage caused by overheating inside the heating resistor, and achieving damage-free high-quality resistance repair.

Description

Technical field:

[0001] The present invention relates to the technical field of resistance correction of heating resistors in thermal print heads, and in particular to a non-destructive resistance correction method for thermal print heads based on temperature control, which can prevent cracking or bubble defects caused by local fragmentation or secondary melting of the heating resistor. Background technology:

[0002] As we all know, the core component of a thermal print head is a heating resistor composed of multiple heating resistor units arranged in a certain order. When working, a voltage is applied to the heating resistor through a control switch such as an IC to generate Joule heat, thereby causing the thermal medium consumables in contact with the heating resistor to color and achieve printing. Generally speaking, it is a device that converts electrical energy into thermal energy; however, due to the differences in the uniformity of the distribution of components such as internal components and conductive substances in the material, as well as the deviation in the molding process of the heating resistor material, the resistance distribution of the existing heating resistor is relatively discrete; and the different resistance values ​​of the heating resistor units in the heating resistor will result in different applied energies under the same voltage when printing, which will cause the uniformity of its printing concentration to deteriorate.

[0003] In order to eliminate the concentration difference caused by the difference in resistance value of the heating resistor, the prior art adjusts the resistance value by applying an electric pulse to the heating resistor unit; as described in CN108016141B, the internal structure of the heating resistor is adjusted by applying a certain energy electric pulse, thereby achieving the purpose of adjusting the resistance value of the resistor. Figure 1 The temperature control resistance repair flow chart of a conventional thermal print head is shown, which mainly includes: step S1, testing the resistance of the heating element unit; step S2 setting a fixed resistance repair target resistance according to the measured resistance of the heating element unit; step S3, applying a pulse voltage to the heating element whose resistance is higher than the target resistance to correct the resistance; step S4, testing the resistance of the heating element after the heating element has cooled down, and judging whether the resistance of the heating element unit after the resistance repair is less than or equal to the target resistance; if not, returning to step S2; if yes, the resistance repair at this point is finished.

[0004] The existing standard for applying the repairing electric pulse only considers the change of resistance value, and cannot overcome the tiny defects caused by the internal micro cracks or secondary melting of the heating resistor unit due to the influence of the repairing electric pulse signal. The repaired product is also difficult to detect with the naked eye or metal microscope because the surface is covered with a protective layer. When the thermal print head is working later, due to repeated heating and cooling, the micro cracks will expand and grow again, eventually leading to a sudden change in the resistance value of the heating resistor, which will cause faults such as white lines in printing. Summary of the invention:

[0005] In view of the shortcomings and deficiencies in the prior art, the present invention proposes a non-destructive resistance repair method for a thermal print head based on temperature control, which can prevent cracking or bubble defects caused by local fragmentation or secondary melting of a resistance repair heating resistor.

[0006] The present invention is achieved by the following measures:

[0007] A non-destructive resistance repair method for a thermal print head based on temperature control, characterized in that it comprises the following steps:

[0008] Step 1: Obtain the tolerance inflection point temperature T of the heating resistor material i By testing the resistance change curve of the heating resistor material under different applied energies, the energy value corresponding to the inflection point of the resistance change is obtained. Under this energy value, the temperature of the heating resistor is the inflection point temperature T i , where the resistance change inflection point refers to the resistance point when △R is greater than 5%, △R = (resistance value after energy addition - initial resistance value) / initial resistance value * 100%;

[0009] Step 2: Refer to the inflection point temperature T i Set the detection temperature T s ;

[0010] Step 3: Test the resistance of all heating points in the heating resistor, and obtain the repairable resistance rate of the heating resistor material: Determine the resistance of all heating resistor units, i.e., heating points, in the heating resistor, and refer to the measured initial resistance to determine the target resistance R0 of each heating point. Specifically, a single pulse is applied to the heating point, and the printing pulse voltage is gradually increased in a step-by-step manner. At the same time, the resistance change rate △R before and after the pulse is tested. The change rate △R is equal to (R 后 -R 前 ) / R 前 *100%, and finally obtain the target resistance value R0≥R 初始 *(1-△R);

[0011] Step 4: Referring to the target resistance R0, apply electric pulses point by point to the heating resistor whose resistance is higher than the target resistance to adjust the resistance, and adjust the pulse signal in time to avoid the pulse signal from damaging the heating resistor unit, specifically:

[0012] Step 4-1: While applying an electric pulse to each heating point (i.e., each heating resistor unit), measure the current heating resistor body temperature T a And the current heating resistor resistance R a ;

[0013] Step 4-2: Determine the current resistance value of the heating resistor R a The size of the target resistance R0, when Ra≤R0, it is judged that the current heating point resistance repair is completed, otherwise, it is judged that the current heating resistor body temperature Ta and the detection temperature T s If the current heating resistor temperature T a ≤Detection temperature T s , then repeat step 4-1, otherwise, execute step 4-3;

[0014] Step 4-3: Turn off the pulse signal and adjust the width or peak voltage of the pulse signal to turn it off, according to the decrease proportional to △T, △T = T a / T s , after reducing the pulse width or peak voltage, repeat step 4-1 until the resistance value of the current heating resistor unit is less than or equal to the target resistance value;

[0015] Step 5: Determine whether the current point is the last heating resistor unit. At this time, for thermal print heads of different sizes and resolutions, the number of heating resistor units is different, and the number of points is different. When the product model is determined, the total number of heating resistor units is fixed, and the points that have been repaired are counted during the resistance repair process. For example, the total number of points of a certain product is 384 points. When the test count is less than 384, the resistance repair program is executed in a loop. When the count is equal to 384, it is determined to be the last point and the resistance repair is completed. If the current point is not the last point, repeat step 4 to repair the next point until the current point is the last point, and the resistance repair is completed.

[0016] In step 4-3 of the present invention, the pulse width is adjusted according to a decrease proportional to ΔT, specifically: the pulse width is adjusted to ΔT on =(1 / (1+x))*A(1), where x is the adjustment coefficient, the value range of x is preferably 1%-20%, and A is the resistance compensation coefficient, A=1-△R.

[0017] In step 4-3 of the present invention, the pulse peak voltage is adjusted according to a decrease proportional to ΔT, specifically: according to the energy formula E = (U 2 / R)*T on ,but

[0018] △E=(U 2 / R)*T on *(1 / △T b ), where T b is the temperature compensation coefficient, △T b =1+x, x is the adjustment coefficient, then the adjustment of the peak voltage of the pulse signal is realized as follows: U 后 2 =(A / △T b )*U 前 2 , where U 后 is the peak voltage of the pulse signal after adjustment, U 前is the peak voltage of the pulse signal before adjustment.

[0019] The temperature of the heating resistor of the present invention is measured by an infrared thermometer.

[0020] The present invention can effectively ensure that the pulse signal is a safe pulse signal, thereby ensuring that there is no thermal stress damage caused by overheating inside the heating resistor, thereby achieving damage-free and high-quality resistor repair. Description of the drawings:

[0021] Attached Figure 1 It is a schematic diagram of the resistance repair process of the prior art.

[0022] Attached Figure 2 It is a flow chart of the present invention.

[0023] Attached Figure 3 This is a resistance spectrum curve diagram for searching the tolerance inflection point energy in Example 1 of the present invention. Figure 4 Schematic diagram of temperature test distribution under Ei energy in Example 1 of the present invention.

[0024] Attached Figure 5 Schematic diagram for finding the maximum value of the resistance repair rate of the heating resistor in Example 1 of the present invention. Figure 6 Schematic diagram of the initial resistance of the heating resistor in Example 1 of the present invention.

[0025] Attached Figure 7 This is a schematic diagram of pulse type step compensation in Example 1 of the present invention. Specific implementation method:

[0026] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings.

[0027] Embodiment 1:

[0028] This example provides a non-destructive repair method for a thick-film thermal printhead heating resistor, wherein the thick-film heating resistor contains glass components with different softening points, as well as conductive fillers such as ruthenium oxide and zirconium oxide. During electric pulse repair, an electric pulse signal is applied to the heating resistor to achieve soft breakdown of its internal glass component, thereby changing its internal conductive network structure, increasing the number of conductive paths and causing the resistance of the heating resistor to decrease. Since the glass components contained in the heating resistor are different and the glass softening point temperatures are different, the resistance transition temperatures of heating resistor materials of different systems are often different and need to be measured separately.

[0029] As described in patent document CN1110825A, the resistor material composition contains lead oxide silicate glass with a softening point of 400-650° C. Different manufacturers have different internal glass components, which often contain one or more softening point glass components, which will not be described in detail.

[0030] This example uses ruthenium oxide thick film heating resistor material T01 to adjust the resistance. The target resistance is 700Ω with a resistance range of ±5%, that is, 665-735Ω. The specific steps include:

[0031] Step S101: testing the tolerance inflection point temperature Ti of the heating element material; applying the ruthenium oxide heating resistor paste to the heating resistor area by drawing or printing, and sintering at 800°C for 20 minutes;

[0032] A protective layer of glass is printed on the surface of the heating resistor and sintered at 750°C. The resistance value of the sintered heating substrate is tested under different printing energies, and the following is plotted: Figure 1 The curve shown in the figure shows that when the resistance value changes by 5%, the corresponding energy Ei = 0.23 mj. The temperature distribution of the heating resistor under this energy is measured using an infrared thermometer. Figure 2 As shown, the highest temperature Ti in the central area is read as 440°C; the resistance range of the heating resistor material is tested, that is, the resistance value reduction ratio under different pulse signals, and the plot is as follows Figure 5 curve;

[0033] Step S102: referring to the inflection point temperature Ti, the detection temperature is set to Ts at 440°C;

[0034] Step S103: testing the resistance of all heating points, the current resistance of the first point is 900Ω;

[0035] Step S104: Reference Figure 5 The resistance repair rate curve of the heating resistor shows that the maximum resistance repair rate △R of the T01 resistor paste is about 43%; the minimum repairable resistance at this point is 900*(1-0.43)=513Ω; therefore, the target resistance value R0=700Ω of the heating point is determined to be greater than 513Ω;

[0036] Step S105: the initial electric pulse signal is set to a peak voltage of 160V and a pulse width of 0.3μs; Step S106: referring to the resistance adjustment target value, applying electric pulses with a peak voltage of 160V and a pulse width of 0.3μs point by point to adjust the resistance value;

[0037] Step S107: Applying electrical pulses and measuring the temperature T of the heating resistor a , T a =380℃, and the current heating resistor resistance Ra, Ra=820Ω;

[0038] Step S108: Determine the current resistance of the heating resistor and the target resistance: in this example, Ra=820Ω is greater than the upper limit of R0, 735Ω;

[0039] Execute S109: Determine whether the current temperature is less than or equal to the set temperature: measure the current temperature Ta =380℃, less than the set temperature T s Then repeat S106, continue to apply voltage, and at the same time, measure the temperature T of the heating resistor when the second resistance is repaired. a =420℃, which is lower than the set temperature Ts=440℃. The resistance value of the heating resistor during the second repair is R a =720Ω, then R a Within the target resistance range (665-735Ω), the resistance adjustment at this point is completed and the next resistance adjustment is carried out;

[0040] After the next point of resistance repair begins, S106 is executed again and the temperature T is measured. a =450℃, pulse printing resistance R a =680Ω, since R a It is within the target resistance range, so the resistance adjustment of this point is completed and the test of the next point is continued;

[0041] Step S106 is executed again, the sampled resistance is R=1000Ω, a peak voltage of 160V and a pulse signal of 0.3μs are applied, and the resistance of the heating resistor R is measured. a =850Ω, determine whether the current resistance value is ≤ the target resistance value: the current resistance value 850Ω is greater than the target resistance value, and go to step S109;

[0042] Step S109: Determine whether the current temperature is less than or equal to the set temperature: In this example, the current temperature T a =480℃ greater than T s (440°C), then execute S105, turn off the original pulse signal, and adjust the pulse width to 63.6% of the original value, i.e. 0.19μs (reference Figure 7 Pulse model step compensation diagram), as described in the previous section of the manual, due to △T = T a / T s That is △

[0043] T = 480 / 440 = 109%, corresponding to Figure 7 Find the corresponding interval, and Ton is adjusted to 63.6% of the original value, that is, 0.3*0.636μs=0.19μs;

[0044] Inca 160V, 0.19μs electric pulse signal;

[0045] Step S107 is then executed to measure the temperature of the heating resistor T a =420℃, R a =770Ω; the cycle is repeated and no further description is given. The process proceeds to step S109 to determine whether the current heating point is the last point. If so, the resistance repair is completed; otherwise, the process returns to step S106.

[0046] In this example S109, it is measured that the thick film heating resistor material T01 has a resistance value reduction ratio △R of about 30% after the repair when the peak voltage is 160V and the pulse width Ton is 0.3μs; after the voltage pulse signal is applied, the heating resistance value is reduced to 70% of the original value. Based on E=(U 2 / R)*T on To ensure that the added energy is equal to the previous energy, the corresponding T on The value should be revised to 70% of the original value, that is, the resistance compensation coefficient is 70%;

[0047] This example Figure 7 As shown in the figure, the compensation temperature interval is divided into pulse adjustment steps according to the 5% change of △T. a Greater than or equal to T s When the heating resistor is applied, the resistance value has changed to 70% of the original value after the previous return pulse signal is applied; it needs to be multiplied by the resistance compensation coefficient, which is 70%; the pulse width is adjusted to △T on =(1 / (1+x))*A(1), where x is the pulse width adjustment coefficient, the value range of x is 5%, A=7%, and the pulse width adjustment is 1 / 1.05*0.7*100%=66.7% (1.05 is the upper limit of the interval 100%-105% of △T);

[0048] It can be seen that in this example, the pulse width is adjusted to 0.3*0.667, that is, 0.20 μs.

[0049] In this example, if the pulse signal is adjusted by adjusting the peak voltage of the pulse signal, the pulse peak voltage is adjusted according to a decrease proportional to △T, specifically: according to the energy formula E = (U 2 / R)*T on ,but

[0050] △E=(U 2 / R)*T on *(1 / △T b ), where T b is the temperature compensation coefficient, △T b =1+x, x is the adjustment coefficient, then the adjustment of the peak voltage of the pulse signal is realized as follows: U 后 2 =(A / △T b )*U 前 2 , where U 后 is the peak voltage of the pulse signal after adjustment, U 前 is the peak voltage of the pulse signal before adjustment.

[0051] The present invention can effectively ensure that the pulse signal is a safe pulse signal, thereby ensuring that there is no thermal stress damage caused by overheating inside the heating resistor, thereby achieving damage-free and high-quality resistor repair.

Claims

1. A non-destructive resistance repair method for a thermal print head based on temperature control, characterized in that: The following steps are involved: Step 1: Obtain the tolerance inflection point temperature T of the heating resistor material i By testing the resistance change curve of the heating resistor material under different applied energies, the energy value corresponding to the inflection point of the resistance change is obtained. Under this energy value, the temperature of the heating resistor is the inflection point temperature T i , where the resistance change inflection point refers to the resistance point when △R is greater than 5%, △R = (resistance value after adding energy - initial resistance value) / initial resistance value * 100%; Step 2: Refer to the inflection point temperature T i Set the detection temperature T s ; Step 3: Test the resistance of all heating points in the heating resistor, and obtain the repairable resistance rate of the heating resistor material: Determine the resistance of all heating resistor units, i.e., heating points, in the heating resistor, and refer to the measured initial resistance to determine the target resistance R0 of each heating point. Specifically, a single pulse is applied to the heating point, and the pulse voltage is gradually increased in a step-by-step manner. At the same time, the resistance change rate △R before and after the pulse is tested. The change rate △R is equal to (R 后 -R 前 ) / R 前 *100%, and finally obtain the target resistance R0≥R 初始 * (1-△R); Step 4: Referring to the target resistance R0, apply electric pulses point by point to the heating resistor whose resistance is higher than the target resistance to adjust the resistance, and adjust the pulse signal in time to avoid the pulse signal from damaging the heating resistor unit, specifically: Step 4-1: While applying an electric pulse to each heating point, i.e., each heating resistor unit, measure the current heating resistor body temperature T a And the current heating resistor resistance R a ; Step 4-2: Determine the current resistance value of the heating resistor R a The size of the target resistance R0, when Ra≤R0, it is judged that the current heating point resistance repair is completed, otherwise, it is judged that the current heating resistor body temperature T a and the detection temperature T s If the current heating resistor temperature T a ≤Detection temperature T s , then repeat step 4-1, otherwise, execute step 4-3; Step 4-3: Turn off the pulse signal and adjust the width or peak voltage of the pulse signal to turn it off, according to the decrease proportional to △T, △T=T a / T s , after reducing the pulse width or peak voltage, repeat step 4-1 until the resistance value of the current heating resistor unit is less than or equal to the target resistance value; Step 5: Determine whether the current point is the last heating resistor unit. At this time, for thermal print heads of different sizes and resolutions, the number of heating resistor units is different, and the number of points is different. When the product model is determined, the total number of heating resistor units is fixed, and the points that have been repaired are counted during the resistance repair process; the total number of points of a certain product is 384 points. When the test count is less than 384, the resistance repair program is executed in a loop. When the count is equal to 384, it is determined to be the last point and the resistance repair is completed. If the current point is not the last point, repeat step 4 to repair the next point until the current point is the last point, and the resistance repair is completed.

2. The non-destructive resistance repair method for a thermal print head based on temperature control according to claim 1, characterized in that: In step 4-3, the pulse width is adjusted according to the decrease proportional to △T, specifically: the pulse width is adjusted to T on =(1 / (1+x))*A (1), where x is the pulse width adjustment coefficient, the value range of x is 1%-20%, A is the resistance compensation coefficient, A=1-△R.

3. The non-destructive resistance repair method for a thermal print head based on temperature control according to claim 2, characterized in that: In step 4-3, the pulse peak voltage is adjusted according to the decrease proportional to △T, specifically: according to the energy formula E=(U 2 / R)*T on ,but △E=(U 2 / R)*T on *(1 / △T b ), where T b is the temperature compensation coefficient, △T b =1+x, x is the adjustment coefficient, then the adjustment of the peak voltage of the pulse signal is achieved as follows: U 后 2 =(A / △T b )*U 前 2 , where U 后 is the peak voltage of the pulse signal after adjustment, U 前 is the peak voltage of the pulse signal before adjustment.

4. The non-destructive resistance repair method for a thermal print head based on temperature control according to claim 1, characterized in that: The temperature of the heating resistor is measured by an infrared thermometer.

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