JPH0673967B2 - Method of trimming resistance value of thermal head heating element - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of trimming a resistance value of a heating element of a thermal head, and an apparatus thereof.

[Description of conventional technology]

Conventionally, the resistance value of the heating element of the thermal head has a variation of several tens of percent in a range among a plurality of heating elements in the same head. A resistance value trimming method for reducing the variation includes a laser method and a cutting method. In the laser method, the accuracy of the laser beam diameter and the relative position of the beam spot and the heating element is different from that of the heating element. It is difficult to sufficiently follow the minute size and high-density arrangement, and it is difficult to make the heat generation characteristics after trimming uniform enough. In addition, the cutting method is also insufficient in cutting accuracy with respect to the accuracy of the heating element, has a large change in the heat generation distribution inside the heating element before and after cutting, and is markedly deteriorated in characteristics such as print quality and the life of the heating element. Further, both of the above methods have the drawbacks that the device is large and the device cost is high.

[Object of the Invention]

An object of the present invention is to provide a method and apparatus for realizing resistance value trimming of a heating element of a thermal head at low cost and without impairing the characteristics of the thermal head. It is an object of the present invention to provide a high-performance thermal head having the same at low cost.

[Explanation of Structure and Operation of Invention]

The feature of the present invention is that, when electric power is supplied to the heating element of the thermal head, the Joule heat generated from the heating element is used,
This is to trim the resistance value of the heating element.

The method of the present invention will be described with reference to the drawings.

FIG. 2 is a general example of changes in the resistance value of the heating element with respect to the number of pulses applied to the heating element of the thermal head, and the resistance value generally tends to increase as the number of applied pulses increases. This tendency is due to thermal oxidation of the constituent material of the heating element.

The trimming procedure of the thermal head having the resistance change characteristic as shown in FIG. 2 will be described below.

(1) First, the resistance values of a plurality of heating elements in one thermal head are measured, and the resistance values are stored in memory.

(2) Next, according to the difference between the maximum resistance value or the target resistance value in the above measurement and the individual resistance values stored in memory,
The number of pulses to be applied is calculated for each heating element.
The calculation calculation is performed based on the resistance value change characteristic shown in FIG.

(3) Next, the calculated number of pulses is applied to each heating element to bring it closer to the target resistance value. The conditions of the pulse to be applied must be the same as the conditions in the experiment in which the resistance value changing characteristic of FIG. 2 was derived.

More specifically, an example will be described. FIG. 3 shows the resistance change characteristics of the heating element of the thin film thermal head used by the inventors. The investigation of the characteristics was carried out without supplying the recording paper.

As a result of 100% measurement of the heating element proximity resistance values R of the thermal heads of the same type as the above thermal heads, which are about to be trimmed, variations of −5% and + 7% with an average value of 630Ω as shown by the broken line in FIG. Had. The maximum resistance value is
It is 675Ω. Based on the above measurement, the trimming resistance amount D of each heating element and the number P of applied pulses are calculated. The target resistance value after trimming is 675Ω.

The function F (D) is a function of the rate of change in resistance versus the number of pulses shown in FIG. The number P of applied pulses calculated by the above procedure is, for example, about 500 for the minimum resistance value of 599Ω.
00.

The resistance value distribution after the trimming performed by the above procedure was within ± 2.5% of the average value as shown by the solid line in FIG.

By the way, in the characteristics shown in FIG. 3, a resistance value change of about 2% appears by 1000 pulses. This is a change caused by the anneal effect in the initial structure of the heating material constituting materials and the structure around the heating element. The resistance value is an unstable region. In the experiments conducted by the inventors, when 1000 pulses were applied to all the heating elements in the thermal head and the trimming was performed by the procedure described above, the variation in the resistance value after trimming was within ± 1%. It has been clarified that the resistance value trimming can be performed with higher precision by removing the unstable region. The resistance value change in the unstable area of the resistance value may decrease not only due to the increase of the resistance value but also due to the structure or the like. The removal operation of the unstable area is effective for both the increase and the decrease. Is.

The inventors also compared the trimming properties before and after formation of the heating element protective layer to be formed on the heating element. The trimming in the above example is performed in the atmosphere before the formation of the protective layer, and is necessary to bring the resistance value of the heating element to the target resistance value as compared with the trimming performed after the formation of the protective layer. The number of pulses is 1/10 to 1/100, and therefore the energy efficiency of trimming is much higher before the formation of the protective layer. Furthermore, when trimming is performed after forming the protective layer, cracks may occur in the protective layer, and in this respect also, it is desirable to perform trimming before forming the protective layer.

The device for trimming the method according to the invention will now be briefly described by way of example.

FIG. 1 (a) is a diagram showing an embodiment of a trimming device according to the present invention. An arithmetic circuit 2 for performing the operation of the function F (R), a presettable subtraction counter 3 for setting the number P of applied pulses by the operation, and a clock circuit 6.
Consists of at least. The resistance value R of the heating element has already been measured, and the resistance value R is input to the arithmetic circuit 2. The arithmetic circuit 2 calculates the number of applied pulses P = F (R) with respect to the resistance value R, and the applied pulse number P is set in the presettable subtraction counter 3 by a trigger,
Subtraction is performed according to the clock pulse. The applied pulse signal synchronized with the clock pulse is output from the terminal 7 until the output of the presettable subtraction counter 3 becomes zero. The heating element 10 is driven by the pulse signal.

FIG. 1 (b) is a trimming device according to another embodiment of the present invention, which is a device for serially generating a binary signal for performing resistance value trimming of a plurality of heating elements. An arithmetic circuit to which the resistance values Ri of the plurality of heating elements are input and which calculates the function F (Ri) for each of the resistance values Ri.
12, and a memory circuit 13 for storing the number of applied pulses Pi of the operation result at individual addresses in association with the plurality of heating elements, a presettable subtraction counter 14 for setting the contents of the memory, and the memory Address counter 15 for designating the address of the address counter, a clock circuit 18 for advancing the count of the address counter 15 and the count of the subtraction counter, and an R gate 16 for determining whether 0 is non-zero in the content of the subtraction counter. And latch circuit 17
Is a device which outputs at least the binary signal for the applied pulse to the plurality of heating elements in order at the terminal 19. By using this device, even in the thermal head 20 equipped with an IC composed of a shift register, a latch, and a driver, the control of the number of pulses to be applied to the heating element of the thermal head is controlled by the output signal of the device described above. It can be realized by inputting to the shift register.

[Explanation of effects]

According to the present invention, it is possible to perform the resistance value trimming at low cost and with high accuracy on the thermal head heating element. Therefore, the thermal head trimmed according to the present invention has a lower cost and higher characteristics.

That is, as is clear from the above description, the resistance value trimming is performed by utilizing the self-heating of the heating element, which is the function of the thermal head. Therefore, trimming scanning over a plurality of heating elements on the same thermal head is performed by laser trimming or the like. As described above, there is no need for mechanical or optical scanning, electrical solid scanning is performed, and in the selectivity of the heating element to be subjected to trimming, there is concern about selection accuracy due to displacement of the beam spot such as laser. Even in a thermal head in which the heating elements are arranged in a high density, the specified heating elements can be trimmed without any problems. Further, as is clear from the above description, the trimming device may be a device having an electric mechanism similar to that of the recording device using the thermal head, and therefore, the trimming device can be downsized and the cost can be reduced. . Further, according to the trimming according to the present invention, one heating element is heated uniformly, so that there is no change in the shape of the heating element or change in the heat generation distribution, and the characteristics of the heating element are not impaired.

Further, since the resistance value of the heating element is uniformized with high accuracy in the thermal head having resistance value trimming according to the present invention, for example, density-type gradation recording performed by controlling the energy of heat generation in the heating element. In, the heat generation energy of each heat generating element can be controlled with high accuracy, and therefore, a multi-value density gradation can be realized with high reproducibility. Also,
Even in binary recording such as black and white, the operation of recording in the saturated coloring area of the thermal paper, which is generally performed in order to suppress the variation in coloring density, is not required, so that the energy consumption is lower. A uniform and high-density clear recording is possible, that is, a thermal head having high printing energy efficiency.

[Brief description of drawings]

FIG. 1 (a) is a block diagram of an embodiment of an apparatus for resistance value trimming of a thermal head heating element according to the present invention.
FIG. 2 (b) is a block diagram of the same embodiment, and FIG. 2 is
FIG. 3 is a diagram showing a general example of the rate of change of the resistance value of the thermal head heating element by pulse application, and FIG. 3 is a diagram showing the rate of change of the resistance value of the thermal head heating element by pulse application in one embodiment of the method according to the present invention. FIG. 4 is a diagram showing changes in the distribution of resistance values of the thermal head heating element in one embodiment of the method according to the present invention. 1,11 ...... Resistance value data input terminal 2,12 …… Arithmetic circuit 3,14 …… Presettable subtraction counter 4,16 …… OR gate 6,18 …… Clock circuit 15 …… Address counter 17 …… Latch circuit 7,19 Output terminal 10 Heating element 20 Thermal head with shift register 8 Trigger signal input terminal 21 Trimming heating element number data input terminal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seiji Kuwahara 6-31-1, Kameido, Koto-ku, Tokyo Seiko Electronics Co., Ltd. (72) Inventor Tomorou Yamamoto 6-31-1, Kameido, Koto-ku, Tokyo Seiko Electronic Industry Co., Ltd. (56) References Japanese Patent Publication Sho 52-8500 (JP, B1)

Claims (2)

[Claims] 1. A method of trimming a resistance value of a heating element by using Joule heat generated in a plurality of heating elements constituting a thermal head by supplying power, wherein the number of pulses to be applied is changed according to the resistance value of the heating element. An arithmetic circuit for calculating, a presettable counter for setting the number of pulses based on the arithmetic result of the arithmetic circuit, and a clock circuit generate a pulse signal applied to the heating element or binary data for the pulse signal, A method for trimming a resistance value of a thermal head heating element, wherein the presettable counter outputs a pulse number corresponding to each heating element according to a trimming amount of each heating element in the thermal head. 2. The method for trimming the resistance value of a thermal head heating element according to claim 1, wherein the resistance value of the heating element is trimmed after aging.