JPH0667635B2 - 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, a trimming process using the phenomenon that when the heating resistors are formed and a relatively high voltage pulse is individually applied to each heating resistor, the resistance value decreases is used. is there.

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 prober and switching step following step ST1, ST3 is a voltage pulse applying step following step 2, ST4 is a resistance value measuring step following step ST3, and ST5. Is a step of comparing with previous data following step ST4, ST6 is a step of detecting resistance value decrease following step ST5, ST7 is a step of detecting all dots of trimming following step ST6, and ST8 is from step ST5. Step of branching reprobing, ST9 is step S
This is the step of adjusting the voltage of the voltage pulse branched from T6, and the processing is returned from the branch of step ST7 to step ST2, 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, the heating resistor is connected to the voltage pulse generating means, and the voltage pulse of the initial value set in step 1 is applied in step ST3. To do. Next, measure the resistance value of the heating resistor in step ST4, identify whether or not the resistance value has decreased in step ST5, and if not, consider probe contact failure and redo probing in step ST8, Returning to step ST4, the resistance value is measured again. If the resistance value has decreased, it is compared with the trimming target value 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. Returning to step St3, the power 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. In step ST2, a new dot is selected, its 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, Vs is the initial value of the voltage pulse, and is set to, for example, 25V because the boundary voltage at which the resistance value of the heating resistor starts to decrease due to the application of the voltage pulse is usually around 25V.

Further, ΔV is an increase in the voltage value of the voltage pulse in step ST9, 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.

Since the above-mentioned conventional thermal head manufacturing method is configured as described above, it is necessary to apply a voltage pulse 20 to 30 times and measure the resistance value in order to trim a 1-dot heating resistor. There is a problem that it takes a lot of time to make the resistance value of the heating resistor uniform.

Therefore, the present applicant has previously proposed a method of manufacturing a thermal head that does not require a large amount of time to make the resistance values of the heating resistors uniform.

FIG. 6 is a flowchart showing the method of manufacturing the thermal head. In FIG. 6, ST11 is an initial setting step, ST12 is a step of measuring the resistance change of the sample following step ST11, ST13 is a step of calculating trimming constants α and β following step ST12, and ST14 is the step described above.
Step of detecting trimming constants α and β following ST13, ST
15 is the step of resistance drop curve approximation following step ST14, ST16 is the step of resistance measurement following step ST15, ST17 is the step of determining the applied voltage following step ST16, and ST18 is the voltage pulse following step ST17. Application step, ST19 is the step of detecting the end of all dots of trimming following step ST18, and ST20 is the step ST
It is a step of selecting another sample branched from 14, and from the branch of step ST19 to step ST16,
The process is returned from ST20 to step ST12.

FIG. 7 is a block diagram showing an example of an apparatus for carrying out this method of manufacturing a thermal head. In the figure, 1 is a thermal head on which trimming processing is performed, and 2 is a terminal of each heating resistor of the thermal head 1. A probing device for pressing a probe, 3 is a relay cord connected to the probing device 2 for selecting the heating resistor, and 4 is a switch connected to the relay cord 3 for switching application of a voltage pulse and measurement of a resistance value, 5 is a pulse generator that is connected to one of the switches 4 and sends out a voltage pulse of a specified voltage value; 6 is an ohmmeter connected to the other of the switches 4;
Is an input / output unit 8, a central processing unit (hereinafter referred to as a CPU) 9,
A control arithmetic unit including a memory 10, a keyboard 11, etc., for controlling the above-mentioned devices and for performing required arithmetic processing,
Reference numeral 12 is a printer connected to the control calculation unit 7.

Next, the operation will be described. FIG. 8 is a diagram showing an example of the resistance drop curve, and the solid line Y in the figure is the resistance drop curve, and the horizontal axis shows the applied voltage value V by the voltage pulse.
However, the vertical axis shows the resistance change rate ΔR 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. 8, it is almost constant regardless of the initial resistance value. It was difficult to trace the curve Y on the curve Y and to approximate the curve Y by the equation (1).

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

Further, the mutual relationship between the trimming constants α and β is as follows.
As shown in the figure, when plotting α on the horizontal axis and β on the vertical axis, it was found that the curve Z follows a substantially constant curve Z, and the curve Z is a hyperbola that can be approximated by the equation (2).

β = 1 / α ^- m (2) In the formula (2), l and m are constants that take constant values regardless of the dot density.

Further, as a result of another experiment, the resistance decrease rate when the voltage pulse having the predetermined voltage value is applied only once is as shown in FIG. 8 when the voltage pulse is applied many times if the voltage value is temporarily increased. It was also found to show a value equivalent to that of the same voltage value.

First, in step 11, initial setting is performed, and then in step 12, resistance change measurement of the sample is performed. That is, the relay network 3 is controlled to select the heating resistor of the designated dot as the sample of the thermal head 1, the switch 4 is switched to connect to the resistance meter 6, the resistance value is measured, and the measured value is controlled. The data is sent to the calculation unit 7, and the CPU 9 of the control calculation unit 7 stores it in the memory 10.

Next, the switch 4 is switched to apply a voltage pulse of a predetermined voltage value from the pulse generator 5 to the resistance heating element. Here, this voltage pulse is, for example, a pulse having a width of 2 μsec.
It is a pulse train that is continuous with an individual 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. The CPU 9 of the control calculation unit 7 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 ST13, the trimming constants α and β for approximation of the resistance drop curve are calculated based on the resistance change measured in this way. That is, the CPU 9 of the control calculation unit 7 uses the resistance change stored in the memory 10 to calculate the resistance change rate Δ at each applied voltage due to the voltage pulse.
R = (R−R ₀ ) / R ₀ is stopped and this is substituted into the equation (1). As a result, α, β, V ₀
Create an equation with unknown and solve it. here,
When there are four or more equations for three unknowns, this is statistically processed to obtain a solution. The obtained solution is further statistically processed between each sample to obtain the boundary value of the applied voltage.
The desired trimming constants α and β can be obtained together with V ₀ .

Deviations of the trimming constants α and β thus obtained from the relationship of the expression (2) are detected in step ST14. That is, as shown by point A in FIG. 9, if the deviation deviates from a certain range, for example, the ± 5% area hatched in FIG. Repeat the measurement. If so, step
The ST20 selects a dot for which no voltage pulse was previously applied as the new sample.

As shown by point B in FIG. 9, when the deviation is within a certain range, the trimming constants α and β are substituted into the equation (1) together with the boundary value V _{0 of the} applied voltage in step ST15, A resistance value drop curve showing the relationship between the resistance change rate ΔR and the applied voltage V is approximated.

This completes the preparation stage and the trimming process starts from step ST16. First, in step ST16, a dot to be trimmed is selected by the relay network 3, and this is connected to the resistance meter 6 by a switch to measure the resistance value.

Next, in step ST17, the CPU 9 calculates the resistance change rate ΔRn for lowering the obtained resistance value to the target value, and further determines the applied voltage Vn of the voltage pulse using the resistance value decrease curve Y described above. .

The situation is shown in FIG. 8, and specifically, the above α, β, V ₀
The applied voltage Vn is calculated by substituting the resistance change rate ΔRn into the relational expression in which is 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, the voltage pulse of the voltage Vn is sent from the pulse generator 5 and is applied to the heating resistor of the dot to be trimmed. As a result, the resistance value of the heating resistor drops to a value close to the target value. Thereafter, the processes from step ST16 are repeated until step ST19 detects the end of trimming of all dots.

[Problems to be solved by the invention]

Since the conventional thermal head manufacturing method is performed as described above, the resistance value that drops by the voltage pulse application of the voltage value determined by the equation (1) becomes the target value due to the physical difference of the resistors. There was a case of slippage.

Further, even in one thermal head, there may be a difference in the descending curve depending on the location of the resistor, and there is a problem in that the resistance value obtained depending on the location of one resistor deviates from the target.

The present invention has been made to solve the above problems, the resistance value of the heating resistor is trimmed to the target value at high speed and accurately, without being affected by the difference in the physical properties of the resistor. It is an object of the present invention to obtain a method of manufacturing a thermal head that is uniform.

[Means for solving problems]

The method of manufacturing a thermal head according to the present invention uses an approximate expression of a resistance drop curve obtained by measuring a resistance change of a sample, and actually applies a voltage pulse to an appropriate number of heating resistors, When the resistance drop of the heating resistor due to the application is out of the specified range, it is updated by correcting the approximate expression of the resistance drop curve by the dropped resistance value or by repeating the test with another sample. It was done like this.

[Action]

The method of manufacturing a thermal head according to the present invention is such that the approximate expression of the resistance drop curve obtained by measuring the resistance change of the sample is corrected and updated according to the actual trimming result in a timely manner so that the pulse is applied once every time. It is possible to accurately drop the resistance value of the dot near the target value.

Example of Invention

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1 in which the same parts as those in FIG.
ST21 is a step of resistance drop curve approximation following step ST12, ST22 is a step of applying a test pulse for actually performing test trimming of several dots using the approximation formula following step ST21, and ST23 is an approximation formula test following step ST22. Steps ST24 are steps of the approximate expression correction following step ST23, and the processing shifts from step ST24 to step ST16 and from step ST19 to step ST16.

The following operation will be described. First, initialization is performed in step ST11, and then resistance change measurement of the sample is performed in step ST12. As a result, the voltage is increased by an appropriate ΔV in order from the lowest voltage and applied.
At 21, the resistance drop curve as shown in FIG. 8 is obtained. And
Approximate expressions are obtained by calculating α and β in the expression (1). This is the curve indicated by Y in FIG.

Next, in step ST22, trimming is performed on a resistor having several dots in a test manner. That is, the initial resistance value of each dot is measured, the applied voltage value suitable for lowering the resistance value to the target value is calculated by using the approximate expression, and the pulse of the calculated voltage value is generated once. Then, the resistance value after the pulse is applied is measured.

Next, in step ST23, the approximation formula (1) is verified from the resistance value obtained in step ST22. As shown in FIG. 8, an appropriate allowable range is set for the approximate expression (determined from product specifications, etc., here ± 10%), and if it is within the area A, the approximate expression is appropriate. Judge, step ST16
Then, the transition is performed and all dots are trimmed as in the conventional example.

If the data obtained in step ST22 is not in the area A, it is determined that there is a difference between the approximate expression and the case where trimming is performed by one actual pulse application, and step ST24
Move to and correct the approximate expression.

An example of the correction will be described below. First, step ST22
Obtain the average of the resistance values after trimming obtained in (the number of dots for test trimming is determined so that the reliability of the average is obtained).

The fact that the approximate expression is not appropriate means that there is an error between the average resistance value and the target value R ₀ . That is,
Resistance after trimming of each dot is not it if only even lower (higher) ₀ min -R, which is equivalent to the target value by -R ₀ lower (higher).

That is, by considering R ₀ − (− R ₀ ) = 2R ₀ − as the target value, it is possible to correct the average of the actual resistance values to the vicinity of R ₀ .

Therefore, the approximate expression (1) can be corrected as follows.

After performing this correction, the process proceeds to step ST16 and thereafter, all dots are trimmed in the same manner as described above. Although this correction is an approximate correction, there is no practical problem due to variations in trimming of each dot, and the arithmetic processing is simple.

In the above embodiment, the correction of the approximate expression is shown before the actual trimming of all dots.
The drawing shows the second embodiment of the present invention in the case where this correction is performed as the best mode in a timely manner. For example, all dots of one thermal head are divided into an appropriate number of blocks, the average of resistance values is calculated at the end of each block in step ST25, and if there is a deviation from the initial resistance value R ₀ , the approximation is made in step ST26. The equation (1) is corrected to always correct the error from the target value.

FIG. 3 is a flow chart showing a third embodiment of the present invention. In this embodiment, the approximation formula is tested in step ST22, and if it is determined that the approximation formula is not appropriate, the correction is not made in step ST20. Another sample is selected, the process returns to step ST12 again, the operation from step ST12 is repeated, the resistance change of the sample is measured, and a new approximate expression is obtained. This process is repeated until an appropriate approximate expression comes.

〔The invention's effect〕

As described above, according to the present invention, since the approximate expression for determining the voltage to be applied in order to lower the resistance value of the heating resistor to the target value is tested and corrected by the trial trimming, the heat generation is reduced. The resistance value of the heating resistor can be trimmed to the target value at high speed and accurately without being affected by the physical properties of the resistor. Further, even if the characteristics of the heating resistor differ depending on the location in one unit, there is an effect that the resistance value of the heating resistor can be trimmed accurately and uniformly to the target value.

[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, and FIG.
FIG. 3 is a flowchart showing an embodiment (best mode) of FIG. 3, FIG. 3 is a flowchart showing a third embodiment of the present invention, and FIG.
FIG. 5 is a flow chart showing a conventional method for manufacturing a thermal head, FIG. 5 is an explanatory view showing a decrease in the resistance value of the heating resistor, and FIG. 6 is a method for manufacturing the thermal head previously proposed by the applicant. Flowchart, FIG. 7 is a block diagram showing an example of an apparatus for carrying out the manufacturing method, and FIG.
FIG. 9 is an explanatory diagram showing an example of the resistance drop curve, and FIG. 9 is an explanatory diagram showing the mutual relationship between the trimming constants α and β. 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. In the drawings, the same reference numerals indicate the same or corresponding parts.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location B41J 3/20 114 G 8906-2C 113 A

Claims (2)

[Claims] 1. A method for manufacturing a thermal head, wherein a voltage pulse is applied to each of the heating resistors of a thermal head having a plurality of heating resistors, and the resistance value thereof is lowered to make the resistance uniform. A sample is selected from the inside, voltage pulses with different voltage values are sequentially applied from the low voltage one to the heating resistor selected as the sample, and an approximate expression of the resistance drop curve showing the relationship between the applied voltage and the resistance change is calculated. Seeking,
The voltage value of the test pulse applied to each of the heating resistors is determined based on the initial resistance value of the heating resistor by this approximate expression, and the test pulse of the determined voltage value is applied to the heating resistor. , The resistance value of the heating resistor dropped by the application of this test pulse is used to test the quality of the approximation formula, and if this approximation formula is good, the voltage of the voltage pulse to be applied to the heating resistor by the approximation formula. A value is determined, and if the approximate expression is not correct, the approximate expression is corrected by the resistance value dropped by the application of the test pulse, or another sample is selected from the heating resistors and the test is repeated. A method of manufacturing a characteristic thermal head. 2. The heating head of the thermal head is divided into an appropriate number of blocks, and an approximate expression is corrected for each block.
Method of manufacturing thermal head