JPH068055B2 - Method of manufacturing thermal head - Google Patents

Description

The present invention relates to a method for manufacturing a thick film type thermal head, and more particularly to uniforming the resistance value of its heating resistor.

[Conventional technology]

The thick film type thermal head forms a heating resistor by printing a paste-like resistance material in a predetermined pattern by a screen printing method or the like and then firing it. Therefore, the thick-film type thermal head can be manufactured at a low cost by a relatively short manufacturing process, but has a drawback that the resistance value of the heating resistor varies greatly. Since the variation in the resistance value of the heating resistor directly affects the quality of printing or the like, it is an extremely important factor to make the resistance value of the heating resistor uniform in the manufacture of the thick film type thermal head. . To make the resistance values of the heating resistors uniform, there is a trimming process utilizing the phenomenon that the resistance value decreases when a relatively high voltage pulse is individually applied to each heating resistor after the heating resistors are formed. .

FIG. 4 is a flow chart showing a conventional method of manufacturing a thermal head disclosed in Japanese Patent Laid-Open No. 61-83053. In the figure, ST1 is an initial setting step,
ST2 is a step of prober and switching following the step ST1, ST3 is a step of applying a voltage pulse following the stap ST2, and ST4 is the step ST.
3 is a resistance value measuring step, ST5 is a step of comparing with previous data following step ST4, ST6 is a step of detecting a resistance value decreasing following step ST5,
ST7 is a step of detecting the end of all dots of trimming following step ST6, ST8 is a step of reprobing branched from step ST5, ST9 is a step of voltage adjustment of the voltage pulse branched from step ST6, and step ST7 Step ST from branch
The processing is returned to step 2, from step ST8 to step ST4, and from step ST9 to step ST3.

Next, the operation will be described. First, in step ST1, initial conditions such as an initial value of a voltage pulse applied to a heating resistor to be trimmed and a trimming target value are set. Next, in step ST2, the thermal head is probed, the dot to be trimmed is selected, and the heating resistor is connected to the voltage pulse generating means.
At T3, the voltage pulse having the initial value set in step 1 is applied. Next, in step ST4, the resistance value of the heating resistor is measured, and in step ST5, it is discriminated whether or not the resistance value has decreased. If not, it is considered that the probe has poor contact, and probing is repeated in step ST8. After returning to step ST4, the resistance value is measured again. If the resistance value has decreased, it is compared with the target value for trimming set in step ST1 in step ST6. If it is not smaller than the target value, the voltage value of the voltage pulse is increased by ΔV in step ST9. Step ST
Returning to step 3, the voltage pulse is reapplied. This process is repeated until the resistance value of the heating resistor becomes smaller than the target value, and when it becomes smaller than the target value, trimming of the heating resistor of the dot is completed and the process proceeds to step ST7. In step ST7, it is identified whether or not trimming of all dots has been completed. If trimming of all dots has not been completed, the process returns to step ST2. Step ST2
Then, a new dot is selected, the heating resistor is connected to the voltage pulse generating means, and the same processing is repeated until the trimming of all dots is completed.

FIG. 5 is a diagram showing a decrease in the resistance value of the heating resistor. The resistance value which was largely varied with R ₁ , R ₂ and R ₃ before trimming is slightly lower than the target value R ₀ , It is homogenized within a narrow range. In the figure, V _s is the initial value of the voltage pulse, and is set to, for example, 25 V because the boundary voltage at which the resistance value of the heating resistor begins to decrease due to the application of the voltage pulse is usually around 25 V. Also, ΔV is the step S
This is an increase in the voltage value of the voltage pulse due to T9, and is set to, for example, 2.5 V so that the resistance value of the heating resistor does not decrease too much, and the resistance value is gradually decreased.

[Problems to be solved by the invention]

Since the conventional method of manufacturing a thermal head is configured as described above, it takes two steps to trim a 1-dot heating resistor.
The voltage pulse must be applied 0 to 30 times and the resistance value must be measured, which requires a great deal of time to equalize the resistance value of the heating resistor.

The present invention has been made to solve the above problems, and an object thereof is to obtain a method of manufacturing a thermal head that does not require a great deal of time to equalize the resistance values of the heating resistors. To do.

[Means for solving problems]

The method of manufacturing a thermal head according to the present invention measures the average initial resistance value of the heating resistor of the thermal head and its standard deviation, and selects some samples from the dots and determines the number of different voltage values. These voltage pulses are applied in order from the lowest one, and the resistance change curve of each heating resistor is measured each time to approximate the resistance drop curve.When trimming each dot, first measure the resistance value of that heating resistor. Then, it discriminates whether or not it is within a predetermined range given by the average value and the standard deviation, and further, based on the resistance drop curve, the voltage pulse to be applied based on the resistance drop curve from the required resistance drop amount. It determines the voltage value.

[Action]

The method of manufacturing a thermal head according to the present invention approximates a resistance drop curve by measuring sample dots in the thermal head, and uses this resistance drop curve during trimming to measure the resistance value of the heating resistor of the dot. The voltage value of the voltage pulse to be applied is determined so that the resistance value of the heating resistor is close to the target value with one application of the voltage pulse, and the initial resistance value of the heating resistor is within the predetermined range. Whether the probe is in contact or not is determined by determining whether or not the probe is inside, and erroneous trimming due to probe contact error or the like is prevented.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. First
In the figure, ST11 is an initial setting step, ST12
Is an average value following step ST11, a standard deviation measurement step, ST13 is a sample resistance change measurement step following step ST12, ST14 is a resistance drop curve approximation step following step ST13, and ST
Reference numeral 15 is a step of measuring a resistance value following the step ST14, ST17 is a step of determining an applied voltage following the step ST16, ST18 is a step of applying a voltage pulse following the step ST17, and ST19 is a step of the step S.
The step of detecting the end of all dots of trimming following T18, ST20 is the step of the probe branched from step ST16, and the process is returned from step ST19 to step ST15 and from step ST20 to step ST15.

FIG. 2 is a block diagram showing an example of an apparatus for carrying out the method for manufacturing a thermal head according to the present invention.
Is a thermal head on which a trimming process is performed, 2 is a probing device for pressing a probe against the terminals of each heating resistor of the thermal head 1, and 3 is a probing device 2.
A relay network which is connected to and selects the heating resistor,
A switch 4 is connected to the relay network 3 to switch between application of a voltage pulse and measurement of a resistance value. Reference numeral 5 is a pulse generator connected to one of the switches 4 for sending a voltage pulse of a designated voltage value. An ohmmeter connected to the other side of the switch 4, an input / output unit 8, a central processing unit (hereinafter referred to as a CPU) 9, a memory 10, a keyboard 11 and the like are provided to control the above-mentioned devices and perform required arithmetic operations. A control calculation unit 12 for performing processing is a printer connected to the control calculation unit 7.

Next, the operation will be described. FIG. 3 is a diagram showing an example of the resistance drop curve, in which the solid line Y is the resistance drop curve, and the vertical axis shows the applied voltage value by the voltage pulse.
The vertical axis shows the resistance change rate of the heating resistor due to the voltage pulse application. As a result of the experiment, when the vertical axis of FIG. 5 is taken as the resistance change rate and the% drop from the initial resistance value is plotted, as shown by the broken line in FIG. 3, it is almost constant regardless of the initial resistance value. Follow the curve Y of
It was found that it can be approximated by Eq. (1).

In equation (1), R ₀ is the initial resistance value of the heating resistor, V ₀ is the boundary value of the applied voltage at which the resistance value begins to change, and ΔV
Is the step of changing the applied voltage, and α and β are constants determined by the thermal head structure, dot density, and the like.

In addition, as a result of another experiment, a voltage pulse of a predetermined voltage value is set to 1
It was also found that the resistance reduction rate when applied only once showed the same value as that of the same voltage value when the voltage pulse was applied many times while temporarily increasing the voltage value as shown in FIG. The present invention is based on the results of these experiments.

In this embodiment, first, in step 11, initialization is performed, and then in step 12, the average value and the standard deviation σ are measured. That is, the resistance meter 6 is connected to the relay network 3 by switching the switch 4, and the heating resistor of each dot of the thermal bed 1 is sequentially connected to the resistance meter 6 by the control of the relay network 3 and its initial resistance value is changed. It is measured, and the measured value is sent to the control arithmetic unit 7 and the memory 10
Stored in. The CPU 9 calculates the average value and the standard deviation σ of the measured values stored in the memory 10 according to the equations (2) and (3).

In the equations (2) and (3), Ri is the initial resistance value of the heating resistor of the dot number i, and n is the number of dots of the thermal head 1.

Subsequent to this, the resistance change measurement of the sample is performed in step ST13. That is, the relay network 3 is controlled to select the heating resistor of the dot designated as the sample of the thermal head 1, and this is selected via the switch 4 for the resistance meter 6
And the resistance value is measured, and the measured value is controlled by the calculation unit 7
Then, the CPU 9 of the control calculation unit 7 stores it in the memory 10. Next, switch the switch 4 to change the pulse generator 5
A voltage pulse having a predetermined voltage value is applied to the heating resistor. Here, this voltage pulse is, for example, a pulse train in which 15 pulses having a width of 2 μsec are continuous with a period of 50 μsec. Next, the switch 4 is switched again, the heating resistor to which the voltage pulse is applied is connected to the resistance meter 6, the resistance value is measured, and the measured value is sent to the control calculation unit 7. CPU of control calculation unit 7
9 stores it in the memory 10 together with the voltage value of the applied voltage pulse. Thereafter, similarly, these processes are repeated while appropriately increasing the voltage value of the voltage pulse. This process is repeated at least three times, switching the relay network 3 and executing for some samples.

Next, in step ST14, the approximation of the resistance drop curve based on the resistance change thus measured is performed. That is, the CPU 9 of the control calculation unit 7 obtains the resistance change rate ΔR = (RR ₀ / R ₀ at each applied voltage due to the voltage pulse from the resistance change stored in the memory 10, and this is expressed by the equation (1). This creates an equation with unknowns α, β, and V ₀ for each sample and solves it, where if there are four or more equations for three unknowns, The solution is statistically processed to obtain a solution. The obtained solution is further statistically processed between each sample, and the obtained constants α and β and the boundary voltage value V ₀ are substituted into the equation (1),
A resistance value drop curve showing the relationship between the resistance change rate ΔR and the applied voltage V is approximated.

This completes the preparatory stage and starts the trimming process from step ST15. First, in step ST15,
Select a dot to be trimmed with the relay network 3, connect it to the ohmmeter 6 with a switch, and set its resistance value R
To measure. Next, in step ST16, it is determined whether or not the resistance value R is within the range of ± 2σ of the average value, and the contact state of the probe by the probing device 2 is determined. That is, when the resistance value exceeds the upper limit value of R + 2σ, it is determined that the probe has a poor contact, and when it exceeds the lower limit value of −2σ, it is determined that the probe short-circuits the adjacent patterns. Probing is performed again in ST20, and the process returns to step ST15 to measure the resistance value R again. If the resistance value R is within the range of ± 2σ, the process proceeds to step ST17.

In step ST17, the resistance change rate ΔR when the resistance value R is lowered to the target value is calculated by the CPU 9, and the applied voltage Vn of the voltage pulse is determined using the resistance value decrease curve Y described above. The state is shown in FIG. 3, and specifically, the applied voltage Vn is calculated by substituting the ΔRn into the relational expression in which the α, β and V ₀ are substituted. The obtained applied voltage Vn is sent from the control calculation unit 7 to the pulse generator 5. When the switch 4 is switched in step ST18, a voltage pulse having a voltage of Vn is sent from the pulse generator 5 and applied to the heating resistors of the dots to be trimmed. As a result, the resistance value of the heating resistor drops to a value close to the target value. Thereafter, until step ST19 detects the end of trimming of all dots, step ST1
The processes after 5 are repeated.

In the above embodiment, the initial values of the resistances of the heating resistors of all the dots of the thermal head 1 are measured to obtain the average value R and the standard deviation σ. The average value and standard deviation σ may be obtained from the resistance value of, and the measurement for obtaining the average value and standard deviation σ may be performed simultaneously with the measurement when approximating the resistance drop curve. The measurement data for approximating the descent curve may be used as it is as the data for calculating the average value R and the standard deviation σ.

Further, in the above embodiment, the resistance drop curve is approximated to the case where the voltage pulse is applied three times or more to one sample, but the boundary value V ₀ of the applied voltage at which the resistance value starts to change is 25 V. If fixedly applied, the resistance drop curve can be approximated by applying the voltage pulse twice.

Further, in the above-mentioned embodiment, the pulse train in which the predetermined number is continuous is used for the voltage pulse, but a single pulse may be used, and the same effect as that in the above-mentioned embodiment is obtained.

〔The invention's effect〕

As described above, according to the present invention, the resistance change curve of a small number of samples is measured to approximate the resistance drop curve, and at the time of trimming, the resistance value of the heating resistor of the dot is measured to reduce the resistance drop. Since the voltage value of the voltage pulse is determined using a curve, trimming is completed by applying the voltage pulse once for each dot, so the time required to equalize the resistance value of the heating resistor is greatly increased. In addition, when trimming, the contact state of the probe is judged by identifying whether or not the initial resistance value of the heating resistor is within the predetermined range. When the measured initial resistance value is excessive, the trimmed resistance or the heating resistor is destroyed, and the measured pattern of the initial resistance causes the measured initial resistance value to be too small. Such an effect trimming insufficient when we, or non-crop can be prevented.

[Brief description of drawings]

FIG. 1 is a flow chart showing a method of manufacturing a thermal head according to an embodiment of the present invention, FIG. 2 is a block diagram showing an example of an apparatus for carrying out the method, and FIG. 3 is an example of a resistance drop curve. FIG. 4 is a flow chart showing a conventional method of manufacturing a thermal head, and FIG. 5 is a diagram showing decrease in resistance value of the heating resistor. 1 is a thermal head, 2 is a probing device, 3 is a relay network, 4 is a switch, 5 is a pulse generator, 6 is an ohmmeter,
7 is a control calculation unit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yu Ozaki 8-1-1 Tsukaguchi Honcho, Amagasaki City, Hyogo Prefecture Sanryo Electric Co., Ltd. Communication Machinery Works (72) Inventor Yahei Takase 8-chome, Tsukaguchi Honcho, Amagasaki City, Hyogo Prefecture No. 1-1 Sanryo Electric Co., Ltd. Communication Equipment Factory (56) Reference JP-A-61-131404 (JP, A)

Claims (1)

[Claims] 1. A thermal head for applying a voltage pulse to each of the dot heating resistors of a thermal head having a plurality of dot heating resistors to lower and equalize the resistance value of the dot heating resistors. In the manufacturing method of the head, while measuring the average value and the standard deviation of the initial resistance value of the heating resistor of the dot, select the sample dot from the heating resistor of the dot, the voltage pulse of different voltage values of low voltage Sequentially from the one applied to the heating resistor selected as the sample dot, the resistance value drop curve showing the relationship between the applied voltage and the resistance value is approximated, and the voltage pulse is applied to each of the heating resistors of the dot. When applying, it is identified that the initial resistance value of the heating resistor of the dot is within the predetermined range given by the average value and the standard deviation, and the probe contact is made. With determining condition, manufacturing method for a thermal head and determines a voltage value of the voltage pulse to the application than the resistance value drops curve based on the resistance value of the initial.