JPH06227016A - Method and apparatus for trimming of thermal head - Google Patents

Abstract

PURPOSE:To improve sensitivity of trimming of a thick film type thermal head in a high image quality printer such as a full color printer and to realize trimming with high sensitivity. CONSTITUTION:The value of resistance of a heat-generating resistive element is measured by means of a measuring device 30 at every bit or every half bit set by a multiplexer relay 40 of the resistive element of a thermal head 70 wherein the dimension of the width is made at most 50mum. The measured value is compared with the value within a specified region of the aimed value of resistance and a short high pressure pulse with 20 nano sec of a voltage in accordance with the difference between the aimed region, is applied on the resistive element to decrease the value of resistance of the heat-generating resistive element. In a high voltage pulse generator, a resistor with a low value of resistance is inserted in parallel with the resistance of the resistive element of the thermal head and when a control apparatus 10 outputs a control signal to a pulse generator 20, the voltage charged in a condenser is discharged through a relay to generate a short pulse of at most 20 nano sec and the sensitivity of trimming is improved and trimming being suitable for the use of high gradation is achieved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thick film type thermal head trimming method and a trimming device for trimming, which are suitable for high image quality printers such as full color printers.

[0002]

2. Description of the Related Art A thermal head is constructed by connecting heating electrodes 5 and 8 between individual electrodes 4 and 7 made of a conductive material and common electrodes 3 and 6 on an insulating substrate 2. A constant voltage is applied between the individual electrodes 4 and 7 made of a material and the common electrodes 3 and 6 for a predetermined time to generate jule heat in the heating resistors 5 and 8, and the heat causes the heating resistors 5 and 8 to generate heat. This is a structure for coloring the thermal recording paper placed in contact with (Fig. 7,
(See FIG. 8). In these thermal heads, for example, heating resistors for 1728 bits are formed per A4 size head, but not all the heating resistors have the same resistance value, and variations occur. . However, if the resistance value of the heating resistor is not uniform, there will be a difference in temperature of the heating resistor when heat is generated, and when printing on thermal transfer paper, etc., uneven density will occur in the printed characters or figures. There was an inconvenience to do. In order to prevent the occurrence of such density unevenness, processing for equalizing the resistance value of each heating resistor is performed.

Conventionally, pulse trimming has been known as a resistance value adjusting (trimming) method for equalizing variations in resistance values of heating resistors of a thermal head. This pulse trimming utilizes the property that the resistance value of the heating resistor decreases according to the strength of the electric field when a predetermined electric field is applied within a range that does not cause resistance breakdown to the heating resistor. The value is made uniform (see, for example, Japanese Patent Laid-Open No. 61-83053), and a recording current is made to flow through a heating resistor having a uniform resistance value so that the amount of heat generated by the bit resistor is made uniform. The generation of uneven density due to the difference in the amount of heat generated by the heating resistors is prevented. The pulse width adopted for this trimming was set to about 1 to several μsec.

By the way, there are various shapes of the heating resistor of the thermal head, and the resistance value is different depending on the shape. For example, the shape and resistance value of the heating resistor 5 corresponding to the 1-bit heating resistor 5a of the strip-shaped heating resistor 5 connecting the alternating lead type electrodes 3 and 4 shown in FIG.
The shapes of the electrodes 6 and 7 of the opposed arrangement type shown in FIG. 8 and the resistance value of the resistor 8 are quite different. That is, alternate reel
The distance between the do-type electrodes 3 and 4 is about 30 μm, and the distance between the facing electrodes 6 and 7 is about 130 μm. And, for example, the alternating lead type heating resistor 5
When trimming, trimming pulse width is 1μsec
In that case, a sufficient rate of resistance change was obtained at an electric field intensity of about 5 × 10 ⁶ V / m. However, when the heating resistor 8 having a large gap between the electrodes 6 and 7 as in the counter arrangement type is trimmed using a trimming pulse having a pulse width of 1 μsec, the electric field strength is 2 × 10 ⁶ V / m. The maximum resistance change rate can be obtained in a certain degree. However, this maximum resistance change rate does not reach -50%, and it may be necessary to reduce the resistance value by 50% or more at the maximum when trimming the heating resistor of the thermal head.

Therefore, in order to increase the maximum resistance change rate during trimming of the heating resistor, the trimming pulse width during trimming is set to 200 nsec or less.
A method for manufacturing a round head is disclosed in Japanese Patent Laid-Open No. 3-261566. When the resistance change rate of the heating resistor is increased in this way and trimming is performed so as to reduce the variation in resistance value, the density unevenness is remarkably improved.
Still, there was a problem that it was not suitable for high gradation applications. As a method of solving this problem, a method of performing thermal annealing in order to suppress a variation in resistance value after trimming (see Japanese Patent Laid-Open No. 3-266650), and trimming every half bit to each bit (pixel) There is proposed a method of making the resistance values of the heating resistors the same and making the resistance values of the entire heating resistor uniform (see JP-A-63-59555 and JP-A-2-72969). Further, full-color transfer multi-gradation recording is performed by using a thermal head having a narrow resistor width (Japanese Patent Laid-Open No. 3-21996).
Japanese Patent Laid-Open No. 9) is also proposed.

[0006]

However, when a thick film type thermal recording head suitable for a high image quality printer is manufactured by a method of narrowing the width of the resistor or / and simultaneously trimming every half bit, There was a problem that the resistance value became larger than that of the conventional thermal head. This phenomenon is a problem caused by the fact that the square of the variation in the resistance value of the thick film resistor is almost inversely proportional to the resistor size. That is, if the width of the resistor is reduced to half the width of the conventional one, the variation in resistance value is about 1.4.
(√2) times increase. Further, when the resistor thinned to half the width is divided and trimmed for each half bit, the resistance value variation further increases by about 1.4 (√2) times. This means that in the conventional thermal head having a resistance value variation of ± 20%, the resistance value variation is about ± 40% when the resistor width is narrowed and trimming is performed for each half bit. Will increase. Then, when the conventional trimming method reduces the resistance value from 120% to 80% by 33%, the resistance value becomes almost uniform, but when the resistor width is narrowed and half-bit trimming is performed, the resistance value is reduced from 140% to 60%. Up to 5%
It is impossible to make all the resistance values uniform without dropping 7%. That is, it is necessary to increase the trimming sensitivity (maximum width of decrease in resistance value) in order to trim a thermal head having a narrow resistor width or to perform half bit trimming. Therefore, the first invention provides a trimming method for improving the trimming sensitivity of a thick film type thermal head in a high image quality printer such as a full color printer. Furthermore, when the effective parameter for the trimming sensitivity was investigated, it was found that shortening the trimming pulse width was the most effective.

FIG. 6 shows a pulse generation circuit using a conventional MOSFET 100. In this circuit, a 680 ohm resistor R ₂ is inserted in parallel with the thermal head resistor R ₁ and D
A circuit that generates a pulse is configured by the C power supply and the MOSFET 100. In the DC power source, a resistor R ₃ of 1360 ohms and a capacitor C ₁ of 50 μF / 250 V are arranged in parallel to form an oscillation circuit. In this circuit,
It is difficult to generate a pulse of 100 nsec or less because a MOSFET having a withstand voltage of several 100 V has a large capacitance. As a means to generate a pulse without using a FET, a transformer method that amplifies the pulse with a transformer, a vacuum tube method that uses a vacuum tube, a mercury reflection method that determines the pulse width by the length of the cable, discharge by a relay by storing an electric charge in a capacitor There is a means such as a capacitor method. Transformer system,
The vacuum tube system requires a large-current power supply, and the large-current power supply requires time to set the voltage, which is not suitable for practical use.
In the capacitor system, a high-speed power supply can be used because charges are stored in a cable or a capacitor and are switched by a relay to generate a pulse. Therefore, a second aspect of the present invention provides a trimming device capable of generating a short pulse width which is optimal for trimming a thermal head in a high image quality printer.

[0008]

A method for trimming a thermal head according to the present invention is a resistance for measuring a resistance value for each bit of a heating resistor having a width of 50 micrometer or less in a double scanning direction. The value measurement step and the pulse of the voltage according to the difference between the measured value and the resistance value of the preset target area are set to 2
A pulse applying step of applying a pulse width of 0 nanosecond or less. Furthermore, the thermal head trimming method of the present invention comprises a resistance value measuring step of measuring a resistance value of each heating resistor for half a bit of the heating resistor and a resistance value of a target area in which the measured value is preset. A pulse applying step of applying a pulse having a pulse width of 20 nanoseconds or less according to the difference to each heating resistor for half a bit.

A trimming device for a thermal head according to the present invention, which applies a voltage pulse to a plurality of heating resistors to align the resistance values of the plurality of heating resistors to values within a predetermined region of a preset target resistance value, By inserting a low resistance resistor in parallel with the prober that connects to the heating resistor of the thermal head and the resistance of the heating resistor of the thermal head, discharge the voltage charged in the capacitor through the relay. , A pulse generator for generating a high voltage pulse of 20 nanoseconds or less, a resistance measuring device for measuring a resistance value of a heating resistor, a prober, and an output terminal of the pulse generator via a changeover switch and Multiplexer relay that is selectively connected to the input terminal of the resistance measuring device, and control that controls the selection of the connection between the prober and the heating resistor and the switching of the changeover switch ; And a location.

[0010]

According to the present invention, a high-speed power source is used to switch the stored charge by a relay controlled by a control device to generate a trimming pulse having a short pulse width, and a high voltage having a short pulse width is applied to the resistor. The trimming performed by applying the voltage can enhance the trimming sensitivity, and can also trim the thermal head having a large variation in the resistance value. This is particularly effective for a thermal head having a narrow resistor width applied to transfer multi-gradation or the like, and / or for trimming every half bit.

[0011]

Embodiments of the present invention will be described with reference to the drawings.
The thermal head of this embodiment shows a case where the width of the resistor is reduced and trimming is performed for each half-bit heating resistor. FIG. 4 shows an electrode structure of a thermal head adopting the present invention. After forming an electrode film made of Au or Cu on the substrate by screen printing and baking at 800 ° C., the electrode pattern formed by photo etching has a shape in which the electrodes 80 and 85 are alternately drawn out. ing. Both electrodes 80 and 85 which are alternately overlapped in the scanning direction X
A resistor 90 made of RuO ₂ is printed on the above and baked to form a lift-off type resistor 90 into a strip-shaped resistor having a width dimension in the double scanning direction Y of 50 μm. After that, the resistance value of the electrode is adjusted (trimming) by applying the pulse voltage.

Next, the configuration of the trimming device will be described with reference to the block diagram shown in FIG. The prober 60 is a probe 61, 62, 63 that contacts the pad of the electrode 85 via the connection terminal.
・ ・ ・ ・ Is equipped. The multiplexer relay 40 is connected to the prober 60, and the prober 6
0 and multiplexer / relay 40 are computer 1
The probe 61, 62, 63 of the prober 60 is controlled to 0.
..., the heating resistor 90 is selected via the individual electrode 85. Multiplexer relay 40
Is selectively connected to an output terminal of the pulse generator 20 or an input terminal of the resistance measuring device 30 via a changeover switch 50 controlled by the computer 10. Then, this trimming device is operated by the computer 10.
By controlling the pulse applied to the heating resistor 90 while measuring the resistance value of the heating resistor for each half bit and lowering the resistance value, the desired resistance value is obtained.

The structure of the pulse generator 20 will be described with reference to the circuit diagram shown in FIG. In this circuit, a 200 kilohm resistor R ₃₀ and a first mercury relay are connected in series with the DC power source.
200 and a second mercury relay 250 are inserted. A resistor R ₂₀ having a low value of 10 ohms is inserted in parallel with the resistor R ₁₀ of the heating resistor of the thermal head. A capacitor C ₁₀ of 2000 pF / 1.5 kV is inserted between the first mercury relay 200 and the second mercury relay 250 and between the arm to form an oscillation circuit. Since this circuit is opened and closed by the mercury relay, it is possible to generate a trimming pulse having a small fluctuation and a short pulse width. The pulse generation circuit is not limited to this configuration, and a transfer relay may be used.

Next, the operation of the trimming device will be described with reference to the flowchart shown in FIG. Start at step S ₀
Then, in step S ₁ , the channel is set by the multiplexer relay. In step S ₂ , the resistance value of the heating resistor is measured, and in step S ₃ , it is determined whether the measured value is the resistance value in the target area. If NO, step S ₄
Then, the applied voltage is set according to the resistance value by voltage calculation, and a high electric field pulse having a pulse width of 20 nsec or less is applied in step S ₅ . In step S ₆ , an annealing pulse having a pulse width of about 1 msec is applied to stabilize the resistance value. Then, returning to step S ₂ , the resistance value of the heating resistor is measured, and in step S ₃ , it is determined whether or not the measured value is the resistance value in the target area. _By proceeding to step ₄ and repeating pulse application, the resistance value of the heating resistor is adjusted to the target resistance value for each half bit. If it is determined that the resistance value of the target area at step S ₃ proceeds to step S _7, and determines whether it has completed all the bits in the case of NO to the next channel set in step S _1. Then, when it is determined that the adjustment of all the bits is completed, the trimming work is completed in step S ₈ .

A method of trimming by applying a pulse voltage using the electrodes shown in FIG. 4 will be described. First, the resistance value of the first resistor 901, which is a heating resistor for half a bit sandwiched between the electrodes 801 and 851, is measured, and the applied voltage for achieving the resistance value in the target region is calculated and calculated. When a voltage pulse is applied between the electrodes 801 and 851,
The resistance value of the first resistor 901 falls within the target area. Next, the resistance value of the second resistor 902, which is a heating resistor for half a bit sandwiched between the electrodes 802 and 851, is measured and the resistance value is adjusted, and the first and second resistors 901, 90 are connected.
The 1-bit heating resistor 90 consisting of 2 is trimmed. By repeating this operation, the resistance values of the third resistor 903, the fourth resistor 904, ... For half a bit are adjusted, and the resistance values of all the resistors of the heating resistor 90 are set within the target region. It becomes possible to arrange. By this trimming method, a trimming experiment was conducted to make the average resistance value of the thermal head uniform, in which the variation in the resistance value of the head was about ± 40%. The pulse width of the pulse voltage is 10 nse
c, 20 nsec, 40 nsec, 100 nsec, the annealing pulse width was 1 μsec, and the number of trimming bits was 960 bits.

The results are shown in FIG. This graph represents the trimming sensitivity (maximum width of decrease in resistance value) corresponding to the applied pulse width. As can be seen from the results of this experiment, the trimming pulse width of 1 μsec shows a decrease of about −40%, but the pulse width of 10 nsec or less gives a decrease of −60% or more. Variation is ± 4
In the case of a thermal head of about 0%, the pulse width is 20ns
If it is ec or less, trimming sensitivity can be -57% or more,
It becomes possible to trim. And 40nse
With the pulse width of c, the resistance value of the high resistance bit does not fall,
Trimming failure occurred. As described above, the trimming of the thermal head in this embodiment has a pulse width of 20.
The trimming sensitivity is improved by applying a high voltage with a short pulse width of nanosecond (nsec).

[0017]

According to the trimming method of the present invention, by shortening the pulse width to 20 nsec or less, the trimming sensitivity is improved, and the resistance width is narrow in the sub-scanning direction, which was not possible due to the large variation in resistance value. -High-sensitivity trimming of round head trimming, half-bit trimming, or narrow-width resistor half-bit trimming is now possible. As a result, the resistance value of the high-resolution thick-film thermal head and the thick-film thermal head for multi-gradation transfer can be improved in accuracy. Furthermore, since the trimming device of the present invention generates a pulse having a short pulse width of 20 nsec or less without noise or bounce, it is possible to reliably apply a high-voltage charge having a short pulse width to a portion to be trimmed.

[Brief description of drawings]

FIG. 1 is a block diagram of a trimming device used in the present invention.

FIG. 2 is a flowchart of trimming used in the present invention.

FIG. 3 is an explanatory diagram showing a pulse generation circuit of the trimming device of the present invention.

FIG. 4 is an explanatory diagram of electrodes of a thermal head and heating resistors.

FIG. 5 is a graph showing the relationship between pulse width and trimming sensitivity.

FIG. 6 is an explanatory diagram showing a conventional pulse generation circuit.

FIG. 7 is a conventional example of a thermal head.

FIG. 8 is a conventional example of a thermal head.

[Explanation of symbols]

10 computer, 20 pulse generator, 30
Resistance meter, 40 multiplexer relay, 50
Switch, 60 prober, 61, 62, 63 probe, 70 thermal head.

Claims (4)

[Claims] 1. A method of trimming a thermal head, wherein a voltage pulse is applied to a plurality of heating resistors to make the resistance values of the plurality of heating resistors equal to a preset target resistance value within a predetermined region. A resistance value measuring step of measuring the resistance value of the heating resistor for one bit, and a pulse applying step of applying a pulse of a voltage according to the difference between the measured value and the resistance value of the preset target area The heating resistor is a heating resistor having a narrow width of 50 μm or less in the double scanning direction and a pulse width of pulse application of 2 in the pulse applying step.
A method for trimming a thermal head, characterized by being set to 0 nanosecond or less. 2. A method of trimming a thermal head, wherein a voltage pulse is applied to a plurality of heating resistors to make the resistance values of the plurality of heating resistors uniform within a predetermined region of a preset target resistance value. , A resistance value measuring step of measuring the resistance value of each heating resistor for half a bit, and applying a pulse of a voltage corresponding to the difference between the measured value and the resistance value of the preset target area to the heating resistor for a half bit. And a pulse applying step for applying each pulse, and the pulse width of the pulse applying in the pulse applying step is 2
A method for trimming a thermal head, characterized by being set to 0 nanosecond or less. 3. The width dimension of the heating resistor in the double scanning direction is 50.
The method for trimming a thermal head according to claim 2, wherein the thickness is equal to or less than a micrometer. 4. A trimming device for a thermal head, which applies a voltage pulse to a plurality of heating resistors to align the resistance values of the plurality of heating resistors to a value within a predetermined region of a preset target resistance value. -A prober connected to the heating resistor of the Maruhead, a pulse generator that generates a high-voltage pulse, a resistance measuring device that measures the resistance value of the heating resistor, and a pulse that is connected to the prober and through a changeover switch. A multiplexer / relay that is selectively connected to the output terminal of the generator and the input terminal of the resistance measuring device, a controller that controls the connection between the prober and the heating resistor, and the switching of the changeover switch. The generator inserts a resistor having a low resistance value in parallel with the resistance of the heating resistor of the thermal head,
A trimming device for a thermal head, which generates a pulse of 20 nanoseconds or less by discharging a voltage charged in a capacitor through a relay when a control device outputs a control signal to a pulse generator.