Typewriting machines – Typing by other than type-face or type-die – Thermal
Patent
1997-07-03
1998-08-11
Burr, Edgar S.
Typewriting machines
Typing by other than type-face or type-die
Thermal
40012018, 347200, 347201, B41J 2315
Patent
active
057917930
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a thermal printhead and a protection cover mounted on the same.
BACKGROUND ART
A typical thermal printhead includes an insulating head substrate formed with a heating resistor and drive ICs for actuating the heating resistor. The head substrate is mounted on a supporting member which is made of aluminum for example and has good thermal conductivity.
Taking a thick film-type thermal printhead for example, a narrow strip-like heating resistor is formed on a substrate by a thick film printing method. The narrow strip-like heating resistor is longitudinally sectionalized into tiny regions to provide heating dots. These heating dots are electrically connected, via a plurality of individual electrodes, to output pads of drive ICs. Further, the heating dots are equally connected to a common electrode. Each output pad of a drive IC is connected to an individual electrode by a bonding wire.
The drive ICs and the bonding wires are enclosed by a hard protection coating made of a thermosetting resin such as an epoxy resin for example. Main functions of the protection coating are to protect the drive ICs and wire-bonded portions from external mechanical forces and to prevent static electricity from destroying the drive ICs. The reason such a preventive measure is necessary to be taken for the drive ICs is that the static electricity, which is generated on the recording paper due to the sliding contact between the recording paper and the heating resistor during printing operation, may be discharged to the drive ICs and destroy them.
In the field of thermal printheads, high-speed printing has been increasingly required. To meet this requirement means to increase the speed of sliding movement of the recording paper relative to the heating resistor. As a result, a greater amount of static electricity will be generated on the recording paper during the printing operation, and the discharge may eventually become unbearable to the protection coating.
To cope with such a problem, conventionally, a protection cover may be additionally provided for covering a protection coating which encloses drive ICs and bonding wires. Such a protection cover prevents the electrostatically charged recording paper from coming into direct contact with the protection coating.
Many conventional protection covers are mounted on thermal printheads by using fixing means such as screws (see U.S. Pat. No. 4,963,886). With such an arrangement, a protection cover is usually attached to a supporting member of the thermal printhead or to a printed circuit board for external connection. To fix the protection cover by fixing means such as screws is a troublesome operation, and it is difficult to locate the protection cover with satisfactory accuracy. Further, the error in attaching the supporting member to the head substrate is additional to the error in attaching the printed circuit board for external connection to the head substrate. Therefore, the positioning accuracy of the protection cover relative to the heating resistor of the head substrate cannot be improved beyond a certain level.
DISCLOSURE OF THE INVENTION
Therefore, it is an object of the present invention to provide a protection cover for a thermal printhead, which is attached to a head substrate with ease and high positional accuracy.
It is another object of the present invention to provide a thermal printhead carrying such a protection cover.
According to a first aspect of the present invention, there is provided a thermal printhead including an insulating head substrate having a first edge and a second edge opposite to the first edge, a heating resistor formed on the head substrate along the first edge, at least one drive IC mounted on the head substrate along the second edge, and a protection cover mounted for covering the drive IC. The protection cover includes a cover member for covering the drive IC and a fixation member formed integrally with the cover member. The fixation member has a positioning wall coming into direct contact wi
REFERENCES:
patent: 4963886 (1990-10-01), Fukuda et al.
patent: 4972205 (1990-11-01), Nagato
patent: 5568174 (1996-10-01), Nagahata et al.
patent: 5568176 (1996-10-01), Moon et al.
patent: 5570123 (1996-10-01), Almonte
Burr Edgar S.
Nguyen Anthony H.
Rohm & Co., Ltd.
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