JP4384313B2 - Thermal head - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thermal head incorporated as a printer mechanism such as a word processor or a facsimile.
[0002]
[Prior art]
For example, as shown in FIG. 4, a conventional thermal head has a head substrate 11 having a large number of heating elements 12 and driver ICs 14 arranged linearly on the upper surface, and a flexible wiring having a plurality of signal wirings and power supply wirings. The substrate 15 is juxtaposed, the flexible wiring substrate 15 and the head substrate 11 are placed on the support plate 16, and the distal end portion extends to the head substrate 11 on the flexible wiring substrate 15. The head cover 17 is attached, and while the recording medium such as thermal paper is conveyed onto the heating element 12, the heating element 12 is selectively joule-heated individually as the driver IC 14 is driven. The generated heat is conducted to the recording medium to form a predetermined print on the recording medium, thereby functioning as a thermal head.
[0003]
The signal wiring of the flexible wiring board 15 is connected to the input terminal of the driver IC 14 via the circuit conductor on the head board 11, and print signals and clock signals from the printer main body are sent to the driver IC 14 on the head board 11. It comes to supply.
[0004]
On the other hand, the power supply wiring of the flexible wiring board 15 is connected to the heat generating element 12 and the ground terminal of the driver IC 14 via the circuit conductor on the head substrate 11, and the switching transistor provided in the driver IC 14 is turned on. The power supply is applied / supplied to the heating element 12.
[0005]
[Problems to be solved by the invention]
However, in the above-described conventional thermal head, when the frequency of the print signal or the clock signal is increased to 8 MHz or more in order to supply the signal to the driver IC 14 at a higher speed, a strong electromagnetic wave is generated from the flexible wiring board 15. . When such a strong electromagnetic wave becomes noise and enters the drive system of another device in the printer, the other device has a drawback of causing a malfunction.
[0006]
Further, when the above-mentioned electromagnetic wave enters the driver IC 14 as noise, the thermal head itself malfunctions, and there is a drawback that it is impossible to form an accurate print corresponding to the print signal.
[0007]
[Means for Solving the Problems]
The present invention has been devised in view of the above disadvantages, and the thermal head of the present invention includes a head substrate having a number of heat generating elements and a driver IC connected to the heat generating elements via circuit conductors on the upper surface, and the driver. arranged side by side and the external circuit board having a ground wiring which is commonly connected via the driver IC to the signal line and the plurality of heat generating elements for supplying a signal to the IC, the external wiring substrate, tip the head In the thermal head formed by attaching a metal head cover that extends to the substrate,
Together to place the plurality of signal lines of the external circuit board between the ground wiring and a head cover, without to hold both the ground wiring and the head cover to a reference potential, and a distal end portion of the head cover The driver IC is in contact with the upper surface of the head substrate on the external wiring substrate side .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
1 is a cross-sectional view of a thermal head according to an embodiment of the present invention, FIG. 2 is an enlarged view of a main part of FIG. 1, FIG. 3 is a plan view showing a state where a head cover is removed from the thermal head of FIG. The head substrate, 2 is a heating element, 4 is a driver IC, 5 is a flexible wiring substrate as an external wiring substrate, 6 is a signal wiring, 7b is a power wiring used as a ground wiring, and 10 is a head cover.
[0010]
The thermal head of this embodiment is generally composed of a head substrate 1, a flexible wiring substrate (hereinafter abbreviated as FPC) 5, a support plate 8, and a head cover 10.
[0011]
The head substrate 1 has a structure in which a large number of heating elements 2 and a large number of circuit conductors 3 are attached to an upper surface of a rectangular ceramic substrate, and a plurality of driver ICs 4 are mounted.
[0012]
The plurality of heating elements 2 are linearly arranged at a dot density of, for example, 300 dpi along the longitudinal direction of the head substrate 1, and each of them is made of an electric resistance material such as TaSiO, TiSiO, TiCSiO, When power is supplied via the circuit conductor 3 or the power wiring 7a, 7b of the FPC 5, etc., Joule heat is generated and the temperature becomes a predetermined temperature necessary for forming a print on a recording medium such as thermal paper.
[0013]
The circuit conductor 3 is for supplying electric power from the outside to the heating element 2 and for supplying signals such as a printing signal and a clock signal from the printer main body to the driver IC 4, such as aluminum or copper. The metal is patterned into a predetermined shape.
[0014]
The heating element 2 and the circuit conductor 3 are deposited and formed on the upper surface of the ceramic substrate 1a by employing a conventionally known thin film technique, specifically, sputtering, photolithography technique, etching technique, and the like.
[0015]
The driver IC 4 is for causing the heating element 2 to selectively generate Joule heat individually based on an external print signal, and a shift register for serially transferring the print signal in synchronization with the clock signal on the lower surface thereof. And an electronic circuit such as a latch for temporarily storing a print signal, a switching transistor for controlling energization to the heating element 2, and terminals such as an output terminal, an input terminal, and a ground terminal.
[0016]
The driver IC 4 is mounted on the head substrate 1 by connecting the terminal to the corresponding circuit conductor 3 via a conductive adhesive such as solder, and so on. As for the terminal of IC4, the output terminal is connected to one end side of the corresponding heating element 2 via the circuit conductor 3, the input terminal is connected to the signal wiring 6 of the FPC 5 via the circuit conductor 3, and the ground terminal is connected to the circuit conductor 3. Thus, it is connected to the power supply wiring (ground wiring) 7b of the FPC5.
[0017]
The driver IC 4 is further covered with an encapsulant R such as an epoxy resin, and the encapsulant R prevents the driver from corrosion due to sliding of the recording medium during printing and contact with moisture contained in the atmosphere. IC4 is protected.
[0018]
Further, the FPC 5 is arranged in parallel on the head substrate 1 described above.
The FPC 5 has a structure in which a pair of power supply wirings 7a, 7b and a plurality of signal wirings 6 are sequentially laminated via an insulating film 5b and sandwiched between a base film 5a made of polyimide resin and a cover film 5c. All signal wirings 6 are arranged directly above the power supply wiring (ground wiring) 7b held at the reference potential GND.
[0019]
The FPC 5 functions as a connecting member for connecting the head substrate 1 to the printer main body. The head substrate side end of the FPC 5 is superimposed on one end of the head substrate 1, and the signal wiring 6 and The signal wiring 6 and the power supply wirings 7a and 7b are electrically connected to the corresponding circuit conductors 3 by soldering the power supply wirings 7a and 7b to the circuit conductors 3 on the head substrate 1.
[0020]
The signal wiring 6 is connected to the input terminal of the driver IC 4 through the circuit conductor 3 and serves to supply signals such as a printing signal and a clock signal to the driver IC 4.
[0021]
The power supply wires 7a and 7b are connected in common to the other end of the heat generating element 2 through the circuit conductor 3 and the other power supply wire 7b is connected to the ground terminal of the driver IC 4 through the circuit conductor 3. Connected to. Here, since the ground terminal is commonly connected to the source side of a large number of switching transistors for controlling energization to the heat generating element 2, the power supply wiring 7b is common to one end side of the large number of heat generating elements 2 via the driver IC4. Will be connected.
[0022]
The signal wiring 6 and the power supply wirings 7a and 7b are electrically connected to the electrical circuit of the printer main body via the connector 9 when incorporated in the printer. At this time, the power supply wiring 7a is, for example, The potential of 24V and the power supply wiring 7b are held at the reference potential GND.
[0023]
Therefore, when the switching transistor in the driver IC 4 is turned on, a predetermined voltage is applied to the heat generating element 2 and the heat generating element 2 generates Joule heat.
[0024]
The head substrate 1 and the FPC 5 are placed and fixed on the support plate 8 in a state where they are arranged side by side.
[0025]
The support plate 8 is made of a metal having good heat conductivity such as aluminum or SUS, and supports the head substrate 1 and the FPC 5 on its upper surface and absorbs a part of the heat of the head substrate 1 in the atmosphere. By diffusing, it acts to effectively prevent the temperature of the head substrate 1 from becoming excessively high.
[0026]
When the support plate 8 is made of aluminum, the support plate 8 is manufactured by processing an aluminum ingot into a predetermined shape by a conventionally known metal processing method, and is formed on the upper surface of the support plate 8 manufactured in this way. The head substrate 1 and the FPC 5 are fixed on the support plate 8 by placing the head substrate 1 and the FPC 5 through an adhesive member (not shown) such as a double-sided tape.
[0027]
A metal head cover 10 is attached on the FPC 5.
The head cover 10 is made of a metal such as aluminum or SUS, and the tip thereof extends to the top of the head substrate 1 so as to cover the connection between the head substrate 1 and the FPC 5.
[0028]
The head cover 10 protects the connection between the head substrate 1 and the FPC 5 from the contact of the recording medium during printing and acts as a guide plate for supporting the running of the recording medium.
[0029]
The head cover 10 is held at the reference potential GND in the same manner as the power supply wiring 7b described above, whereby a plurality of signal wirings 6 of the FPC 5 are connected to the grounded head cover 10 and grounded power supply wiring (ground wiring). It is the shape arranged between 7b.
[0030]
In this way, the plurality of signal wirings 6 of the FPC 5 are arranged between the ground wiring 7b and the head cover 10, and the ground wiring 7b and the head cover 10 are both connected to the reference potential GND, so that the print signal can be transmitted at a higher speed. When the frequency of the print signal or clock signal is increased to 8 MHz or more to supply it to the driver IC 4, even if strong electromagnetic waves are generated from the signal wiring 6 of the FPC 5, such electromagnetic waves are placed on both the upper and lower sides of the signal wiring 6. The ground wiring 7b and the grounded head cover 10 are well shielded and hardly leak to the outside. Therefore, it is possible to effectively prevent other devices in the printer from malfunctioning due to the above-described electromagnetic waves.
[0031]
In this case, the head cover 10 is always disposed between the FPC 5 and the driver IC 4 by bringing the tip of the head cover 10 into contact with the upper surface of the head substrate 1 on the FPC 5 side of the driver IC 4. The above-mentioned electromagnetic wave becomes noise and attempts to enter the driver IC 4 are well shielded by the grounded head cover 10 so that the thermal head can always be operated accurately. Accordingly, it is possible to form an accurate print corresponding to the print signal.
[0032]
Further, in this embodiment, the power supply wiring 7a of the FPC 5 commonly connected to the other end of the heating element 2 is arranged symmetrically and is connected to the connector 9 at the center of the FPC 5, so that the voltage at the power supply wiring 7a The magnitudes of the descent are also substantially equal on the left and right, and thereby the magnitude of the power applied to each heating element 2 is made uniform. Therefore, when all the heating elements 2 are heated simultaneously, the temperature becomes substantially constant, and it is possible to form a good print with little density unevenness.
[0033]
The head cover 10 is manufactured by SUS press molding or aluminum pultrusion molding, and the obtained head cover 10 is fixed on the support plate 8 using screws S or the like, and is attached to the FPC 5.
[0034]
Thus, the thermal head described above applies a power supply to the heating element 2 as the driver IC 4 is driven while conveying a recording medium such as thermal paper on the heating element 2 along the head cover 10, thereby In addition, Joule heat is selectively generated, and the generated heat is conducted to a recording medium to form a predetermined print on the recording medium, thereby functioning as a thermal head.
[0035]
In addition, this invention is not limited to the above-mentioned form, A various change, improvement, etc. are possible in the range which does not deviate from the summary of this invention.
[0036]
For example, in the above-described embodiment, the connector 9 may be divided into two for power supply and signal, and the connector for power supply may be attached to the center of the FPC5 and the signal connector may be attached to both ends or one end of the FPC5.
[0037]
【The invention's effect】
According to the thermal head of the present invention, a plurality of signal wirings of the external wiring board are arranged between the ground wiring and the head cover, and the ground wiring and the head cover are both connected to the reference potential, thereby enabling the print signal to be further transmitted. When the frequency of the print signal or clock signal is increased to 8 MHz or more in order to supply it to the driver IC at high speed, even if a strong electromagnetic wave is generated from the signal wiring on the external wiring board, such electromagnetic waves are generated on both the upper and lower sides of the signal wiring. The ground wiring and the head cover that are arranged are well shielded and hardly leak to the outside. Therefore, it is possible to effectively prevent other devices in the printer from malfunctioning due to the above-described electromagnetic waves.
[0038]
Further, according to the thermal head of the present invention, the tip of the head cover is brought into contact with the upper surface of the head substrate on the side of the external wiring board relative to the driver IC, so that there is always a gap between the external wiring board and the driver IC. Since the head cover is arranged, the above-mentioned electromagnetic wave is noisy and it is well shielded by the grounded head cover that it tries to enter the driver IC, so that the thermal head can always be operated accurately. It becomes like this. Accordingly, it is possible to form an accurate print corresponding to the print signal.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a thermal head according to an embodiment of the present invention.
FIG. 2 is an enlarged view of a main part of FIG.
FIG. 3 is a plan view showing a state in which a head cover is removed from the thermal head of FIG. 1;
FIG. 4 is a cross-sectional view of a conventional thermal head.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Head substrate, 2 ... Heat generating element, 4 ... Driver IC, 5 ... Flexible wiring board as an external wiring board, 6 ... Signal wiring, 7b ... Power supply wiring (Ground wiring) ) 、 10 ・ ・ ・ Head cover

Claims (1)

A head substrate having a connected driver IC large number of heating elements and through the heat generating element and the circuit conductor on the upper surface, through the driver IC to the signal line and the plurality of heat generating elements for supplying a signal to the driver IC arranged side by side and the external circuit board having a ground wiring which is commonly connected to the external wiring substrate, the thermal head formed by attaching a metal cover to the tip portion is extended to the head substrate ,
Together to place the plurality of signal lines of the external circuit board between the ground wiring and a head cover, without to hold both the ground wiring and the head cover to a reference potential, and a distal end portion of the head cover The thermal head is brought into contact with the upper surface of the head substrate on the external wiring substrate side with respect to the driver IC .

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