JPS6359551A - Manufacture of thermal head - Google Patents

Abstract

PURPOSE:To obtain a thermal head not requiring much time for uniformizing the resistances of heat generating resistors, by determining a voltage value of a voltage pulse to be applied based on a resistance fall curve. CONSTITUTION:Voltage pulses are applied to selected samples of dots in a thermal head, in the order of increasing voltages, and the changes in the resistances of heat generating resistors are measured on each application of the voltage pulse. Then, a resistance fall curve Y representing the relationship between resistance change rate DELTAR and applied voltage V is approximated. After selection of one of the dots for which trimming is to be carried out by a relay network 3, the resistance of the selected dot is measured by connecting the dot to a resistance meter 6. Then, the resistance change rate DELTARn for lowering the resistance to a target value is calculated by a CPU 9, and a voltage value Vn of a voltage pulse to be applied is determined by using the resistance fall curve Y, whereby the resistance of the relevant heat generating resistor is lowered to a value approximate to the target value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method of manufacturing a thick film thermal head, and particularly to making the resistance value of a heating resistor thereof uniform.

[Conventional technology]

In the thick film type thermal head, a heat generating resistor is formed by printing a paste-like resistive material into a predetermined pattern by screen printing or the like, and then firing it. Therefore, although the thick film type thermal head can be manufactured at low cost through a relatively short manufacturing process, it has the disadvantage that the resistance value of the heating resistor varies widely. Variations in the resistance value of the heating resistor directly affect the quality of printing, so uniformity of the resistance value of the heating resistor is an extremely important factor in the manufacture of thick-film thermal heads. . To make the resistance values of the heating resistors uniform, there is a trimming process that utilizes the phenomenon that after the heating resistors are formed, when a relatively high voltage pulse is applied to each heating resistor individually, the resistance value decreases. .

FIG. 4 is a flowchart showing a conventional thermal head manufacturing method disclosed in, for example, Japanese Unexamined Patent Publication No. 61-83053. In the figure, STI is the initial setting step,
Sr1 is a prober and switching step following step ST1, Sr1 is a voltage pulse application step following step ST2, and Sr1 is step ST
Sr5 is a step of comparing with the previous data following step ST4, Sr6 is a step of detecting a decrease in resistance value following step ST5,
Sr1 is a step for detecting the end of all trimming dots following step ST6, Sr1 is a step branching from step ST5 or a probe step, and Sr1 is a step for voltage adjustment of a voltage pulse branching from step ST6.

From the branch of step ST7, the process goes to step ST2, from step ST8 to step ST4, and from step ST9.
From there, the process returns to step ST3.

Next, the operation will be explained. First, in step STl, initial conditions such as the initial value of the voltage pulse applied to the heating resistor to be trimmed and the target value for trimming are set.Next, in step ST2, the thermal head is probed and a dot to be trimmed is selected. Then connect the heating resistor to voltage pulse generating means, and step ST
In step 3, a voltage pulse having the initial value set in step l is applied.Next, in step ST4, the resistance value of the heating resistor is measured, and in step ST5, it is determined whether the resistance value has decreased. If not, it is assumed that the contact of the probe is poor and the probing is repeated in step ST8.
Return to step ST4 and measure the resistance value again. If the resistance value has decreased, proceed to step ST6 and measure the resistance value again.
It is compared with the trimming target value set in step I, and if it is not smaller than the target value, the voltage value of the voltage pulse is increased by ΔV in step ST9, and the process returns to step ST.3 to reapply the voltage pulse. This process is repeated until the resistance value of the heating resistor becomes smaller than the target value, and when the resistance value of the heating resistor becomes smaller than the target value, the trimming of the heating resistor of the dot is completed and the process moves to step ST7. In step ST7, it is determined whether or not all dots have been trimmed. If all dots have not been trimmed, the process returns to step ST2. In step ST2, a new dot is selected and its heating resistor is is connected to the voltage pulse generating means, and the same process is repeated until all dots are trimmed.

Figure 5 is a diagram showing the decrease in the resistance value of this heating resistor. Before trimming, the resistance value varied widely as R1, R2, R, but fell within a narrow range slightly lower than the target value R0. In the 0 diagram, v5 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 heat generating resistor starts to decrease due to the application of the voltage pulse is usually around 25V. . Also, ΔV
is the increment 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.

[Problem that the invention seeks to solve]

Since the conventional thermal head manufacturing method is configured as described above, it takes two steps to trim one dot of the heating resistor.
There is a problem in that it is necessary to apply a voltage pulse 0 to 30 times and measure the resistance value, and it takes a lot of time to equalize the resistance value of the heating resistor.

This invention was made in order to solve the above-mentioned problems, and its purpose is to provide a method for manufacturing a thermal head that does not require a large amount of time to equalize the resistance value of the heating resistor. shall be.

[Means for solving problems]

The method for manufacturing a thermal head according to the present invention involves selecting several samples from among the dots of the thermal head, applying several voltage pulses with different voltage values to the samples in order from the lowest to the lowest, and each time increasing the resistance of the heating resistor. Measure the change and approximate the resistance drop curve. When trimming each dot, first measure the resistance of the heating resistor, and calculate the required resistance drop based on the resistance drop curve. This determines the voltage value of the voltage pulse to be applied.

[Effect]

The method of manufacturing a thermal head according to the present invention approximates a resistance drop curve by measuring a sample dot in the thermal head, and uses this resistance drop curve during trimming to determine the measured resistance of the heating resistor of the dot. The voltage value of the voltage pulse to be applied is determined, and the resistance value of the heating resistor is made close to the target value with one application of the voltage pulse.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, 5TII is the initial setting step, 5T12
5T13 is a step of approximating a resistance value drop curve following step 5T12, 5T14 is a step of measuring resistance value following step 5T13, and 5T15 is an application step following step 5T14. Voltage determination step, 5T
16 is a step of applying a voltage pulse following step 5T15, and 5T17 is a step of detecting completion of all trimming dots following step 5T16. From the branch of step 5T17, the process returns to step 5T14.

FIG. 2 is a block diagram showing an example of an apparatus for carrying out the method of manufacturing a thermal head of the present invention, and in the figure, 1
2 is a thermal head where trimming processing is performed; 2 is a blowing device that presses a probe against the terminal of each heating resistor of this thermal head 1; 3 is a blowing device 2
a relay network connected to select the heating resistor;
4 is a switch that is connected to the relay network 3 and switches between applying a voltage pulse and measuring a resistance value; 5 is a pulse generator that is connected to one side of the switch 4 and sends out a voltage pulse of a specified voltage value; and 6 is a A resistance meter 7 connected to the other side of the switch 4 is an input/output section 8. Central processing unit f! (Hereinafter, CPU
9. Equipped with memory 10, keyboard 11, etc.
A control/arithmetic unit 12 which controls the various devices and performs necessary arithmetic processing is a printer connected to this control/arithmetic unit 7.

Next, the operation will be explained. FIG. 3 is a diagram showing an example of the resistance value drop curve, and the solid line Y in the figure is the resistance value drop curve, and the horizontal axis shows the applied voltage value due to the voltage pulse.
On the vertical axis, the rate of change in resistance of the heating resistor due to voltage pulse application is scaled.

As a result of the experiment, when we plot the percentage drop from the initial resistance value with the vertical axis in Figure 5 as the resistance change rate, we find that it remains almost constant regardless of the initial resistance value, as shown by the broken line in Figure 3. It was found that the curve Y can be approximated by equation (1).

Ro ΔV In formula (1), Ro is the initial resistance value of the heating resistor,
vo is the boundary value of the applied voltage at which a change in resistance value begins to appear, ΔV is the change step of the applied voltage, and α and β are constants determined by the structure of the thermal head, dot density, etc.

In addition, as a result of another experiment, a voltage pulse of a predetermined voltage value was
It was also found that the resistance reduction rate when the voltage pulse is applied only once is equivalent to that when the voltage pulse is applied many times with the same voltage value while gradually increasing the voltage value as shown in FIG. This invention is based on these experimental results.

In this embodiment, first, initial settings are performed in step 11, and then, in step 12, resistance change measurement of the sample is performed. That is, the dot heating resistor specified as a sample of the thermal head 1 is selected by controlling the relay IIj3, and the resistance value is measured by switching the switch 4 and connecting it to the resistance meter 6.

The measured value is sent to the control calculation unit 7, and the CP of the control calculation unit 7 is
U9 stores this in the memory 10. The primary 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 includes, for example, 15 pulses each having a width of 2 μsec and a period of 50 μsec.
This is a pulse train that continues in seconds. Next, the switch 4 is switched again, the heating resistor to which this voltage pulse is applied is connected to the resistance meter 6, the resistance value is measured, and the control calculation unit 7
send to The CPU 9 of the control calculation section 7 stores it in the memory 10 together with the voltage value of the applied voltage pulse.

Thereafter, these processes are repeated in the same manner while appropriately increasing the voltage value of the voltage pulse. This process is repeated at least three times, and is executed for several samples by switching the relay network 3.

Next, in step 5T13, a resistance value drop curve is approximated based on the resistance change thus measured. That is, the CPU 9 of the control calculation unit 7 determines the resistance change rate ΔR= (R-RI,) /R, at each applied voltage due to the voltage pulse, from the resistance change stored in the memory 10.
is calculated and substituted into the above equation (1). By doing this, equations with α, β, and vl as unknowns are created and solved for each sample, and if there are four or more equations for three unknowns, this is done statistically. Process and get the solution. The obtained solution is further statistically processed between each sample, and the obtained constants α, β, boundary voltage value v
0 is substituted into equation (1), and 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 starts the re-trimming process at step 5T14. First, in step 5T14,
The relay network 3 selects the dot to be trimmed, and the switch connects it to the resistance meter 6 to measure its resistance value.Next, in step 5TI5, the CPU 9 lowers the obtained resistance value to the target value. The rate of change in resistance ΔRn for this purpose is calculated, and the applied voltage Vn of the voltage pulse is determined using the resistance value drop curve Y described above.

The situation is shown in FIG. 3, specifically the above-mentioned α.

β, ■. The applied voltage Vn is calculated by substituting ΔRn into the relational expression in which ΔRn is substituted. The obtained applied voltage Vn is sent from the control calculation section 7 to the pulse generator 5. Step 5T1
When the switch 4 is switched at step 6, a voltage pulse of voltage Vn is sent out from the pulse generator 5 and applied to the heating resistor of the dot to be trimmed. As a result, the resistance value of the heating resistor falls to a value close to the target value.

Thereafter, the processing from step 5T14 onward is repeated until step 5T17 detects that all dots have been trimmed.

In addition, in the above example, the voltage pulse is applied at least three times to one sample to approximate the resistance value drop curve, but the boundary value V of the applied voltage at which the resistance value starts to change is shown. . If it is fixedly given as 25V, it becomes possible to approximate the resistance value drop curve by applying voltage pulses twice.

Further, in the above embodiment, a predetermined number of continuous pulse trains are used as the voltage pulses, but a single pulse may be used.

The same effects as in the above embodiment are achieved.

〔Effect of the invention〕

As described above, according to the present invention, a resistance drop curve is approximated by measuring the resistance change of a small number of samples, and when trimming, the resistance value of the heating resistor of the dot is measured, and the resistance value drop is calculated by measuring the resistance value of the heating resistor of the dot. Since the configuration uses a curve to determine the voltage value of the voltage pulse, trimming is completed by applying one voltage pulse to each dot, significantly reducing the time required to equalize the resistance value of the heating resistor. It has the effect of reducing This effect is particularly noticeable when applied to a multi-dot thermal head, such as a facsimile thermal head, which has a heating resistor of 1000 dots or more.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing a method for 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 value drop curve. FIG. 4 is a flowchart showing a conventional method for manufacturing a thermal head, and FIG. 5 is a diagram showing a decrease in the resistance value of the heating resistor. 1 is a thermal head, 2 is a blobbing device. 3 is a relay network, 4 is a switch, 5 is a pulse generator, 6 is a resistance meter, and 7 is a control calculation unit. Patent applicant Mitsubishi Electric Corporation Figure 1 Figure 2 Figure 4

Claims (1)

[Claims] In a method for manufacturing a thermal head in which a voltage pulse is applied to each of the heating resistors of a thermal head equipped with a plurality of heating resistors to lower and equalize the resistance value, a sample is selected from among the heating resistors. , voltage pulses with different voltage values are sequentially applied to the heat generating resistor selected as the sample, starting from the lowest voltage pulse, and a resistance value drop curve showing the relationship between the applied voltage and resistance change is approximated, and each of the heat generating resistors is A method for manufacturing a thermal head, characterized in that the voltage value of the voltage pulse applied to the heating resistor is determined using the resistance value drop curve based on the initial resistance value of the heating resistor.