Electricity: circuit makers and breakers – Solid contact – Membrane type
Reexamination Certificate
1999-11-09
2002-05-14
Gellner, Michael L. (Department: 2832)
Electricity: circuit makers and breakers
Solid contact
Membrane type
C200S517000
Reexamination Certificate
active
06388218
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a cover for a push button switch used as a data input unit or a switch unit for a mobile communication equipment such as a mobile phone, a vehicle-mounted telephone or the like, a measuring instrument, a remote controller, a handy terminal or the like, an input unit in the field of a domestic electric appliance, an electronic equipment, a communication equipment, or the like. More particularly, the present invention relates to a push button switch cover which permits the push button switch to exhibit improved keying characteristics such as reduced stroke characteristics, increased click characteristics and the like.
Now, a conventional push button switch which is used for an input unit for a mobile phone or the like will be described with reference to FIG.
14
. The push button switch includes a cover
100
, which is received in a casing of the equipment or phone while being mounted on a circuit board
102
through dish-shaped springs
104
made of metal such as phosphor bronze, SUS stainless steel or the like, resulting in the push button switch being constituted. The circuit board
102
is provided thereon with contacts
106
. In the push button switch thus constructed, displacement of each of key buttons
108
toward the circuit board
102
permits a corresponding one of pressing projections
110
to displace the dish-shaped metal spring
104
.
Several or tens of such dish-shaped metal springs
104
are arranged in perforated portions of a perforated PET sheet
112
having a pressure-sensitive adhesive or an adhesive coated thereon by means of an aligning unit such as a parts feeder or a robot, a jig, or the like while being kept projected. Then, a pressure-sensitive adhesive sheet
114
is positioned over the dish-shaped metal springs
104
to fix the dish-shaped metal springs
104
between the perforated PET sheet
112
and the pressure-sensitive adhesive sheet
114
, resulting in a dish-shaped metal spring sheet being provided, which is then superposed on the push button switch cover
100
.
However, the conventional push button switch cover
100
thus constructed is provided separately from the dish-shaped metal springs
104
. This causes alignment between each of the pressing projections
110
of the cover
100
and an apex of a corresponding one of the dish-shaped metal springs
104
during superposition of the dish-shaped metal spring sheet on the cover
100
to be highly difficult or troublesome. Also, a procedure for inspecting such alignment has not been established in the art. Thus, the conventional push button switch cover fails to provide the push button switch with satisfactory keying characteristics.
In particular, positioning of the perforated PET sheet
112
mounted thereon with the dish-shaped metal springs
104
with respect to the push button switch cover
100
for superposition of the former on the latter is carried out by inserting positioning pins of an aligning jig through reference holes of the perforated PET sheet
112
and cover
100
. Unfortunately, this causes positional deviation, at the most, between 0.2 mm and 0.5 mm to occur between the PET sheet
112
and the cover
100
due to misregistration between the reference holes and gaps between the reference holes and the positioning pins. Also, the prior art fails to permit accuracy of positioning between the apex of each of the dish-shaped metal springs
104
and each of the projections
110
of the push button switch cover
100
to be confirmed. Thus, the push button switch cover is assembled while keeping positional accuracy between the apex of the dish-shaped metal spring
104
and the projection
110
of the cover
100
from being increased, resulting in the push button switch cover being deteriorated in keying characteristics such as keying load, pressing feeling and the like.
In addition, the prior art requires the PET sheet
112
for holding the dish-shaped metal springs
104
and the pressure-sensitive adhesive sheet
114
fixed on the circuit board
102
are also required, leading to an increase in manufacturing cost.
Moreover, in the conventional push button switch cover, the pressing projections
110
are each compressedly deformed by impact resilience of the dish-shaped metal spring
104
, to thereby cause a stroke generating peak load f
1
(peak stroke s
1
) and a make stroke s
2
generating make load f
2
to be increased as indicated at a thin solid line B in
FIG. 8
, resulting in operation feeling being excessively soft and lacking clearness or distinctness. The ratio of differential load between peak load and make load to peak load will be referred to as “click ratio” hereinafter.
In order to provide operation feeling with increased clearness, it is desired to eliminate compressive deformation of the pressing projections
110
to coincide press load (gf)-stroke (mm) characteristics of the whole cover with ideal characteristics of the dish-shaped metal spring per se as indicated at a broken line C in FIG.
8
. It would be considered that the cover is increased in hardness for elimination of compressive deformation of the pressing projections. However, when the dish-shaped metal spring
104
is deformed through a thin wall portion of the cover
100
of, for example, 0.1 to 0.3 mm in thickness to generate click feeling in the cover shown in
FIG. 1
, an increase in hardness of the cover
100
tends to cause the cover to be broken due to repeated displacement, leading to a deterioration in keying durability of the cover
100
.
In addition, the inventors found that, when the dish-shaped metal springs are bonded to the pressing projections by an elastic adhesive, the push button switch cover causes a stroke with respect to load during keying operation to be increased if the amount of the elastic adhesive is insufficient and causes the stroke to be reduced if the amount is excessive, to thereby reduce a click ratio, leading to a deterioration in bonding durability and functional durability. Also, inclination of the dish-shaped metal spring arranged by means of the adhesive is caused to lead to positional deviation of the dish-shaped metal spring in X-Y directions. For example, peak load is increased above positional deviation of 0.1 mm, resulting in the bonding durability being substantially reduced in association with a reduction in click ratio. A minimum value of inclination of the dish-shaped metal spring which can be visually confirmed is 2.5 degrees.
SUMMARY OF THE INVENTION
The present invention has been made in view of the foregoing disadvantages of the prior art.
Accordingly, it is an object of the present invention to provide a push button switch cover which is capable of increasing positioning accuracy with which a cover substrate and a dish-shaped metal spring are positioned with respect to each other.
It is another object of the present invention to provide a push button switch cover which is capable of exhibiting satisfactory keying load characteristics, to thereby exhibit increased pressing feeling over a long period of time.
It is a further object of the present invention to provide a push button switch cover which is capable of eliminating arrangement of members such as a pressure-sensitive adhesive sheet for fixing dish-shaped metal springs, a perforated PET sheet and the like, to thereby significantly reduce a manufacturing cost.
It is still another object of the present invention to provide a push button switch cover which is capable of minimizing affection of compressive deformation of pressing projections, to thereby provide satisfactory click feeling and clear or distinct keying feeling.
It is yet another object of the present invention to provide a method for manufacturing a push button switch cover which is capable of facilitating inspection of positional accuracy between pressing projections and dish-shaped metal springs.
In accordance with one aspect of the present invention to provide a push button switch cover is provided. The push button switch cover includes a cover substrate, which is provided on a fro
Ando Hitoshi
Kiyosawa Noriyoshi
Ohshima Fumio
Sato Hirohide
Shirasawa Takeo
Gellner Michael L.
Lerner David Littenberg Krumholz & Mentlik LLP
Nguyen Nhung
Shin-Etsu Polymer Co. Ltd.
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