JP2563642B2 - Thermal head and its resistance trimming method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head used in a thermal recording apparatus such as a printer or a facsimile machine and a resistance value adjusting method thereof.

2. Description of the Related Art Thermal recording devices such as printers and facsimiles use a conventional thermal head to perform thermal recording on thermal paper or plain paper laminated with ink sheets. The recording density during thermal recording is determined by the amount of heat generated by the heating resistors of the thermal head per unit volume (self-generated Joule heat). As a result, uneven printing density is caused.

Conventionally, the dot resistance value of a thick film type thermal head using a sintered body of ruthenium oxide frit as a heating resistor is
Within the same head, there was variation of more than ten percent. As a resistance value trimming method for reducing the variation, a so-called energization overload trimming method that utilizes a resistance value change that occurs when a pulse voltage is supplied to a heating resistor is generally used. The cause is that the resistance value changes by several tens% with respect to the applied pulse voltage as shown in the figure.

This conventional energization overload trimming method statically presses a large number of probe (probe) electrodes (8 to 32) to an energization electrode group which is in electrical contact with a heating resistor. In this state, trimming is performed so that all probes can be accurately
It is difficult to make contact with the electrode group having a pitch of μm, and when the contact is insufficient, there is a drawback that it is necessary to shift the probe position again and press it, that is, re-probe operation takes too much time.

An object of the present invention is to provide a method for accurately trimming the resistance value of a resistor in a short time and a thermal head suitable for the method.

Means for Solving the Problems The present invention is characterized by applying a trimming pulse voltage to a resistor while scanning a trimming probe electrode on the electrode group. Further, the present invention is characterized by providing a thermal head suitable for the trimming.

Operation With the above configuration, the resistance value trimming of the resistor is quickly and accurately realized, and a low-cost and highly-accurate thermal head can be obtained.

Embodiment FIG. 1 is a block diagram of an embodiment of a system of a trimming device using a trimming method according to an embodiment of the present invention. FIG. 2 shows the probe electrode part of FIG.

DC power supply 2 is used for resistor 1 of the thermal head to be adjusted.
The voltage is applied by. Each resistor is connected to the drive circuit 3 via the probe device. The drive circuit receives the trimming pulse signal (a) from the pulse generation circuit 6 and
The trimming inhibition signal (b) sent from the control operation unit 7 through the interface 8 is ANDed by an AND circuit and added.

The resistance measuring circuit 10 is connected to the thermal head via the relay unit 9. The stage controller 11 enables relative scanning of the probe electrodes by moving the thermal head substrate with a pulse motor or the like. The control calculation unit 7 controls the entire trimming system, and includes a CPU 14 and a CRT.
It consists of 15, keyboard 16 and memory unit 17. A printer 18 outputs a trimming result. The control calculation unit 7 controls each circuit via the interface 8 to measure the resistance of each dot, control the movement of the stage, set the output voltage of the DC power supply 2, and output the trimming pulse signal and the control signal of the pulse generation circuit 6. ON / OFF, output of trimming prohibition signal to stop the application of trimming pulse, etc. Further, the data measured by the resistance measuring circuit 10 is input through the interface, the average resistance value is calculated, and the dot resistance value data is recorded in the memory.

Next, the procedure for adjusting the resistance value using this system will be described.

First, in order to measure the resistance value of each dot, the probe electrode 4 is pressed against the substrate 1 of the thermal head, and the stage 5 is moved at a constant speed to scan the individual electrode with the probe electrode. At this time, the relay unit 9
Is set on the resistance measuring circuit side, the resistance value of each dot is sequentially measured, and the control calculation unit 7 determines the resistor for which the average resistance value is calculated and the trimming is performed, and records it in the memory.

Next, trimming is executed, and the detailed procedure will be described below. First, the resistance measuring circuit side is set to OFF by the switch of the relay unit 9, the output voltage of the DC power supply 2 is set to a predetermined trimming voltage, and the cycle and duty of the trimming pulse signal (a) output from the pulse generating circuit 6 are set. Set the ratio to the desired value. Next, among the trimming prohibition signals (b), only those corresponding to the resistors to be trimmed are set to logic 1, and the others are set to logic 0. Then, while moving the stage 5 again, when the probe electrode 4 comes into contact with the individual electrode of the dot to be trimmed, by inputting the logic 1 of the trimming prohibition signal (b), only the resistor to be trimmed Apply trimming pulse to. That is, the position of the probe electrode can be controlled by the moving distance of the stage and the pitch between the individual electrodes, and the same clock signal can be used to control the stage controller.
By synchronizing 11 and the trimming prohibition signal (b), a trimming pulse can be applied to any dot.

The timing of this trimming will be described with reference to FIG. As shown in FIG. 2, when the dots that require trimming of the individual electrodes formed at the (L1 + L2) pitch are the individual electrodes 21 and 24, only T1 after the probe electrode 4 contacts the individual electrode 21. Delay for a few μs between T2
The following trimming pulse voltage is applied to the
Trim the heating resistor of the dot electrically connected to 21.

At this time, the relative scanning speed V of the probe electrode is V = (L1 + L2) / T, where T = (T1 + T2 + T3 + T4) and V * (T1 + T2) <L1.

Here, the trimming is completed by simply applying a few pulses of a constant voltage, and then the individual electrodes 24 that need to be trimmed are automatically scanned and delayed by T1 after the probe electrode 4 contacts the individual electrodes 24. Pulses are applied at the same timing. However, the voltage does not necessarily have to be the same as that of the individual electrode 21.

For example, in the case of an A4 size thermal head with an individual electrode pitch of 100 μm, T1 is preferably 2 to 4 ms and T2 is 1 to 3
ms is preferred. In addition, the number of trimmings is basically only one, and several is sufficient for surely trimming.
The total time required for trimming the thermal head is 30se
It was within c.

After the end of trimming, the probe may be scanned again to measure the resistance value, and a higher voltage than the first time may be applied to the dots that need to be retrimmed to perform the trimming again.

As described above, by applying the trimming pulse voltage while scanning the probe electrode, it was possible to trim the resistance value of the heating resistor 10 times faster than the conventional method.

Further, in order to increase the speed, a plurality of probe electrodes may be provided and trimmed by independent signal processing under simultaneous scanning.

In the above case, the resistance values of all dots were measured in advance, and then trimming was performed based on the data, but as another method different from that, a constant target resistance value is set in advance and shown in FIG. When scanning the probe electrode shown, it is natural to measure the dot resistance value within the time T1 and compare the resistance value with the target resistance value to perform trimming within the time T2 if necessary. While effective. T4
Is the time for scanning between the individual electrodes. FIG. 2 (a) is a side view of the thermal head placed on the stage driven by the pulse motor. FIG. 2 (b) is a diagram showing a contact position relationship between the probe electrode and the individual electrode, L1 indicates a contact region, and L2 indicates a non-contact region. FIG. 2C is a diagram showing the application timing of the trimming pulse.

Next, the scanning part of the probe electrode will be described in more detail with reference to FIGS. 3 and 4. As shown in FIG. 3, a heating resistor 32, a common electrode 33 for energizing the resistor, and an individual electrode group are provided on a substrate 31, and wear resistance is provided so as to cover the resistor and a part of the electrode group. In the thermal head in which the layer 35 is formed, a probe electrode contacting exposed portion 37 is provided in the middle of the individual electrode terminal 36 of the individual electrode and the heating resistor. Here, the pitch of the individual electrode terminals is
Designed narrowly for B implementation. As the scanning position of the probe electrode, two methods are effective as shown in the figure. One is a specially provided exposed portion 37 for contacting the probe electrode.
This is method A, which scans the top. According to this method, by providing the exposed portions for probe electrode contact at the widest and uniform pitch possible, it is possible to relax the probe scanning accuracy,
Enables more reliable trimming. For example, in the case of an A4 size 8 head / mm dot thermal head, the exposed portion pitch for probe electrode contact can be secured at 125 μm, and the electrode width L
Widely applicable with 1 <100 μm.

Another method is the B method of scanning over the individual electrode terminals. According to this method, it is possible to perform trimming in which the wiring resistance of the individual electrodes is accurately taken into consideration, and the resistance can be more accurately aligned, but scanning accuracy of the probe electrodes is required. For example, in the case of a thermal head of 8 A4 size / mm dots, the pitch of the electrode terminals is 50 to 100 μm pitch due to the IC mounting or the TAB mounting, which is different for each block of 64 dots or 128 dots.

Further, as shown in FIG. 4, when the individual electrode terminal group is formed in the direction perpendicular to the heating resistor, the probe electrode scanning for each block can be performed at high speed by scanning like C method or D method. . Here, C and D may be simultaneously scanned.

The scanning position of the probe electrode has been described above,
Next, the relative scanning method of the probe electrodes will be described in detail. As for the scanning of the probe electrode, the method of scanning at a constant speed while pressing the probe electrode enables the highest trimming, which is effective in the probe electrode scanning positions A and B. Further, in the C and D methods, it is necessary to raise and lower the probe electrode for each block. further,
The step method is effective as a scanning method. That is, scanning may be performed at high speed from the probe electrode contacting exposed portion that requires trimming to the next exposed portion that requires trimming, and the probe may be stationary on the individual electrode during trimming. This is a more effective method when the number of dots to be printed is small.

The specific numerical values such as the pulse conditions used for trimming the resistance value are not limited to the examples described above, and it goes without saying that various numerical values can be taken within the range in which the effect of the present invention is achieved.

One example of the trimming device according to the present invention is shown in FIG. 1, but the present invention is not limited to this, and any device or circuit capable of exhibiting the same function may be used.

EFFECTS OF THE INVENTION According to the present invention, the resistance value of the resistor can be accurately adjusted in a short time, so that it is possible to provide a highly accurate resistor at low cost.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a trimming system using the trimming method of the present invention, FIG. 2 is an explanatory diagram of a scanning state of a probe electrode, and FIGS. 3 and 4 are explanatory diagrams of a probe electrode scanning position. FIG. 5 is a resistance value change characteristic diagram of a heating resistor by applying a pulse voltage. 1 ... Thermal head, 2 ... DC power supply, 3 ... Drive circuit, 4 ... Probe electrode, 5 ... Stage, 6 ... Pulse generation circuit, 10 ... Resistance measurement circuit, 9 ... Relay section, 8
...... Interface, 7 ...... Control calculation unit, 11 ...... Stage control unit, 21 to 24 are individual electrodes, 31 ...... Substrate, 32 ...... Heating resistor, 33 ...... Common electrode, 34 ...... Individual electrode, 35 ......
Abrasion resistant layer, 36 ... Individual electrode terminal, 37 ... Exposed part of individual electrode for probe electrode contact.

Claims (4)

(57) [Claims] 1. A thermal head in which a heating resistor and an individual electrode group for energizing the resistor are provided on a substrate, and a wear resistant layer is formed so as to cover a part of the resistor and the electrode group. The thermal probe is characterized in that the probe electrode for scanning is pressed against the substrate to scan the individual electrode, and when the probe electrode comes into contact with the individual electrode to be trimmed, a trimming pulse voltage is applied to the heating resistor. Head resistance trimming method. 2. The resistance trimming method for a thermal head according to claim 1, wherein a trimming pulse voltage is applied to the resistor while scanning a plurality of probe electrodes. 3. A thermal head according to claim 1, wherein after the resistance values of all dots of the thermal head are measured in advance, the trimming pulse voltage is applied only to the dots having a resistance value above a certain range. Head resistance trimming method. 4. The resistance trimming method for a thermal head according to claim 1, wherein scanning of the probe electrode is step scanning.