JPH048556A - Thermal head and its resistance value trimming method - Google Patents

Abstract

PURPOSE:To trim the resistance value of a resistor in a short time with high accuracy by applying a trimming pulse voltage to the resistor with the concurrent scan of a probe electrode for trimming over a group of electrodes. CONSTITUTION:To measure each dot resistance value, a stage 5 is moved at a constant speed in a state where the electrode 4 is pressed in contact with a thermal head substrate 1. Subsequently, the probe electrode 4 is allowed to scan over an individual electrode. An output voltage from a DC power supply 2 is set to a specified trimming voltage, and a ratio between the cycle of a trimming pulse signal which is output by a pulse generation circuit 6 and a duty is set to a specified value. Next, one of trimming inhibit signals which corresponds to a resistor to be trimmed is set to a logic 1, while the other is set to a logic 0. Then a trimming pulse is applied to only resistor to be trimmed by entering the logic 1 of a trimming inhibit signal, if the probe electrode 4 comes in contact with an individual electrode for dots to be trimmed, with the concurrent movement of the probe electrode 4.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a thermal head used in a thermal recording device such as a printer or facsimile, and a method for adjusting its resistance value.

Thermal recording devices, such as conventional printers and facsimiles, use conventional thermal heads to perform thermal recording on thermal paper or plain paper overlaid with an ink sheet.The recording density during thermal recording is thermal. This is determined by the amount of heat generated per unit volume of the heating resistor of the head (self-generated Joule heat), and if there is variation in the resistance value of the heating resistor, the amount of heat generated by each resistor will be different, which will lead to uneven printing density. It causes.

Previously, the dot resistance value of thick-film thermal heads that used sintered ruthenium oxide frits as heating resistors
Within the same head, there is a variation of more than 10%. To reduce this variation, the resistance value trimming method generally uses the change in resistance value that occurs when a pulse voltage is supplied to the heating resistor. The so-called current overload trimming method is used. As shown in the figure, the principle is that the resistance value changes by several tens of percent with respect to the applied pulse voltage.

Problems to be Solved by the Invention This conventional current-carrying overload trimming method involves pressing a large number of probe electrodes (8 to 32) against a group of current-carrying electrodes that are in electrical contact with a heat-generating resistor. In this state,
Number of trimmings: 50 total probes with high accuracy
It is difficult to contact the electrode group with a pitch of ~100 μm, and if the contact is insufficient, it is necessary to move the probe position and press it again.This has the disadvantage that it takes too much time to re-probe. An object of the present invention is to provide a method for trimming the resistance value of a resistor in a short time and with high precision, and a thermal head suitable for the method.

Means for Solving the Problems The present invention is characterized in that a probe electrode for horizontal trimming is scanned over the electrode group and a trimming pulse voltage is applied to a resistor. Also, a thermal head suitable for the trimming is provided. It is characterized by:

Effect The above configuration allows quick trimming of the resistance value of the resistor.
It is also realized with high precision, and a high-precision thermal head can be obtained at low cost.

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

A voltage is applied by a DC power supply 2 to the resistor 1 of the thermal head to be adjusted. Each resistor is connected to a force connected to the drive circuit 3 via the probe device (to the drive circuit (by the trimming pulse signal (a) from the pulse generation circuit 6).
The trimming prohibition signal (b) sent from the control calculation unit 7 via the interface 8 is logically multiplied by an AND circuit and added.

The resistance measuring circuit 10 is connected to the thermal head via the relay part 9. The stage control section 11 enables relative scanning of the probe electrodes by moving the thermal head substrate using a pulse motor or the like. Control calculation unit 7 (This is the part that controls the entire trimming system, and the CPL
114, CRT 15, keyboard 16, and memory section 17. 18 is a printer that outputs the trimming results.

The control calculation unit 7 controls each circuit via the interface 8. Measures the resistance of each dot, controls the movement of the stage, sets the output voltage of the DC power supply 2, and controls the output of the trimming pulse signal and control signal of the pulse generation circuit 6. , outputs a trimming prohibition signal to stop application of trimming pulses, etc. In addition, the data measured by the resistance measuring circuit 10 is manually input via an interface to calculate the average resistance value and record each dot resistance value data in the memory.

Next, we will explain the procedure for adjusting the resistance value using this system.

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 probe electrode over the individual electrodes. At this time, the relay part 9 is set on the resistance measuring circuit side, and the resistance value of each dot is sequentially measured in the measuring membrane control calculation part 7, which determines the resistor to which the average resistance value is calculated and which trimming is to be performed. .

Next The force behind trimming ＼ The detailed procedure will be explained below. Set the resistance measurement circuit side to OFF using switch 9 of relay part 2.
The output voltage of the pulse generating circuit 6 is set to a predetermined trimming voltage, and the period and duty ratio of the trimming pulse signal (A) output from the pulse generating circuit 6 are set to predetermined values. Next, for the trimming prohibition signal (b) board, only the signal corresponding to the resistor to be trimmed is 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 is trimmed. Apply trimming pulse. In other words, the position of the plate probe electrode can be controlled by the moving distance of the stage and the pitch between individual electrodes, and by synchronizing the stage control section 11 and the trimming prohibition signal (b) using the same clock signal, a trimming pulse can be applied to any dot. Can be applied.

The timing of this trimming will be explained based on FIG. If the individual electrodes 21 and 24 require trimming of the individual electrodes formed at a pitch of (Ll + L2) as shown in Fig. A trimming pulse voltage of several μsec or less is applied several times during T2 with a delay of TI to trim the heating resistor of the dot electrically connected to the individual electrode 21.

At this time, the relative scanning speed V of the probe electrode is V= (L
1+L2)/T However, it is assumed that L T=(TI+T2+T3+T4), and the condition -i, Vl (TI+T2)<Ll is satisfied.

Here, trimming is completed by simply applying several pulses of a constant voltage, and then the probe electrode 4 automatically scans to the individual electrode 24 that is required for trimming.
A pulse is applied at the same timing with a delay of Tl after contact with . However, the L voltage does not necessarily have to be the same as that of the individual electrodes 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;
2 is preferably 1 to 3 ms. Moreover, the number of trimming operations is basically one, and it is sufficient to perform the trimming sporadically to ensure reliable trimming. The total time required for trimming the thermal head was within 30 sec, so after trimming was completed, the probe was scanned again to measure the resistance value, and a higher voltage than the first time was applied to the dots that required re-trimming. , and may be trimmed again.

By applying a trimming pulse voltage while scanning the probe electrode, the resistance value of the heating resistor can be trimmed more than 10 times faster than conventional methods. To further increase the speed, multiple probe electrodes are provided. , may be trimmed by independent signal processing under simultaneous scanning.

In the above case, the resistance value of all the dots is measured in advance, and then the force length is trimmed based on that data.Another method is to set a certain target resistance value in advance and use the method shown in Figure 2. Of course, it is also possible to measure the dot resistance value within the time period L Tl when scanning the probe electrode as shown in the figure, and to perform trimming within the time period T2 if necessary by comparing the resistance value with the target resistance value. However, it is effective.

T4 is the time for scanning between individual electrodes. It indicates the condition.

Fig. 2(a) is a side view of the thermal head placed on a steller that is driven by a pulse motor.

FIG. 2(b) is a diagram showing the contact positional relationship between the probe electrode and the individual electrodes, where Ll indicates a contact area and L2 indicates a non-contact area. FIG. 2(c) is a diagram showing the application timing of trimming pulses.

Next, regarding the scanning part of the probe electrode, see Figures 3 and 4.
This will be explained in more detail using figures. As shown in Figure 3
A thermal head in which a heating resistor 32, a common electrode 33 for energizing the resistor, and a group of individual electrodes are provided on a substrate 31, and a wear-resistant layer 35 is formed to partially cover the resistor and the electrode group. , an exposed portion 3 for probe electrode contact is provided between the individual electrode terminal 36 of the individual electrode and the heating resistor.
7 is provided. Here, the pitch f of the individual electrode terminals is
It is narrowly designed for IC mounting and TAB mounting. As for the scanning position of the probe electrode, two methods are effective as shown in the figure. One method is method A, in which a specially provided exposed portion 37 for probe electrode contact is scanned. This allows for less precision and more reliable trimming.

For example, in the case of a rt A4 size thermal head with 8 dots/mm dots, the pitch of the probe electrode contacting exposed portions can be secured to 125 μm, and the electrode width Ll>100 μm, making it widely usable.

Another method is Method B, which scans the individual electrode terminals. This method allows for trimming that accurately takes into account the wiring resistance of the individual electrodes, making it possible to more accurately align the resistance values. Length: Scanning accuracy of the probe electrode is required.For example, 8 pieces of rt A4 size/
In the case of a m-dot thermal head, the pitch of the electrode terminals is 50~50 mm depending on IC mounting or TAB mounting.
100μm pitch, 64 dots or 128
It will be divided into blocks of dots.

In addition, as shown in FIG. 4, when the individual electrode terminal group is formed perpendicularly to the heating resistor, high-speed trimming can be achieved by scanning the probe electrode for each block in the C method or D method. Here, C1D may be scanned simultaneously.

The force described above regarding the scanning position of the probe electrode (Next, the relative scanning method of the probe electrode will be described in more detail.Scanning of the probe electrode (scanning at a constant speed while pressing against the front substrate is the fastest trimming method) This is effective in the probe electrode scanning position A and B methods. In the C and D methods (
, t, it is necessary to raise and lower the probe electrode for each block. Furthermore, the step method is a promising scanning method.

In other words, the plate scans at high speed from the exposed part for probe electrode contact that requires trimming to the next exposed part that requires trimming, and can remain stationary on that individual electrode during trimming. This method is more effective when the number of dots to be detected is small.

It goes without saying that the pulse conditions and other values used for trimming the resistance value are not limited to the examples described above, and that various values may be used within the scope of achieving the effects of the present invention.

An example of the trimming device according to the present invention is shown in FIG.

Effects of the Invention According to the present invention, the resistance value of a resistor can be adjusted with high accuracy in a short time, and a low-cost and highly accurate resistor can be provided.

[Brief explanation of the drawing]

FIG. 1 shows a block diagram of an embodiment of a trimming system using the trimming method of the present invention. FIG. 2 shows an explanation of the scanning state of the probe electrode. FIGS. 3 and 4 show an explanation of the scanning position of the probe electrode. The figure is a characteristic diagram of the resistance value change of the heating resistor due to the application of a pulse voltage. 1. Thermal head 2. DC power supply 3. Drive circuit 4. Probe electrode 5. Stage 6. Pulse generation port fu 10. Resistance measurement circuit 9. Relay wide 8. Interface, 7. Control calculation al
l... Stage control K 21 to 24 are individual electrodes 31
...Substrate, 32..Heating resistor 33..Common electric area 34..Individual electric machine 35..Wear resistance 36..Individual electrode end-f-, 37..Probe electrode contact exposure disturbance of individual electrode

Claims (5)

[Claims] (1) In a thermal head in which a heating resistor and a group of electrodes for energizing the resistor are provided on a substrate, and a wear-resistant layer is formed to partially cover the resistor and the electrode group, a probe electrode for trimming is used. A method for trimming a resistance value of a thermal head, characterized in that a trimming pulse voltage is applied to the heating resistor while scanning the electrode group. (2) The method for trimming the resistance value of 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) The thermal head according to claim 1, characterized in that after measuring the resistance values of all dots of the thermal head in advance, the trimming pulse voltage is applied only to the dots having resistance values above a certain range. Resistance trimming method. (4) The method for trimming the resistance value of a thermal head according to claim 1, wherein the scanning of the probe electrode is step scanning. (5) A thermal head in which a heating resistor, a common electrode and a group of individual electrodes for energizing the resistor are provided on a substrate, and a wear-resistant layer is formed to partially cover the resistor and the electrode group, A thermal head characterized in that an exposed portion for contacting a probe electrode is provided at an intermediate portion between the electrode terminal of the individual electrode and the heating resistor.