Key top holding structure

A center shaft (2a) for holding a key top (1), and springs (2b) are provided in a casing (2) of a small-sized electronic equipment such as an inter-call receiver. The springs (2b) are provided so as to extend from the peripheral portions toward the center shaft (2a), and holes are formed in the springs (2b) respectively. The key top (1) is provided with a stopper nail (1a), first protrusions 1b and second protrusions 1c. The protrusions (1c) of the key top (1) for pushing switches (3) are inserted through the holes of the springs (2b) respectively, and the stopper nail (1a) of the key top (1) is engaged with the center shaft (2a) acting as a fulcrum during the seesawing operation of the key top (1). Thus, the key top (1) is held in a stable manner. The existence of the center shaft (2a) prevents simultaneous depression of the two switches (3).

BACKGROUND OF THE INVENTION 
The present invention relates to a structure for holding a key top used in 
a small-sized electronic equipment such as an inter-call receiver or the 
like, and particularly relates to a structure for holding a key top, which 
is simple and with which the key top can be attached to a casing easily 
and held stably. 
One or more switches are provided in a small-sized electronic equipment 
such as an inter-call receiver or the like. A key top good and stable in 
manipulability of the switches, and low in manufacturing cost has been 
desired. 
A conventional key top is arranged such that a key top itself is 
constituted by a spring structure or an elastic material, or otherwise, a 
spring, a cushion or the like acting as an elastic member for return 
operation is interposed between a casing and a key top, as disclosed in 
JP-U-2-42292, JP-A-63-254629, JP-A-60-175330, and so on. 
The key top of this type cannot employ a complicated holding structure to 
stabilize the key operation in a case where it is applied to a small-sized 
electronic equipment such as an inter-call receiver or the like, since the 
small-sized electronic equipment generally has switches disposed close to 
each other and thus no sufficient space is provided for installation of 
the holding structure. 
Such a key top is also available, that an elastic material or a spring 
structure was adopted for the key top per se in order to stabilize the key 
operation or in order to prevent abnormal sound or looseness from being 
caused by vibration of a calling vibrator or speaker singing. The key top 
is attached to the inside of a casing. The key top requires an additional 
extra holding mechanism, or the use of an elastic member such as a spring, 
a cushion or the like to possess the returnability of the key top. This 
results in the increased number of component parts, and the complicated 
assembly. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to reduce the number of component 
parts by using a simple structure of a key top with no elastic material or 
spring structure in the key top per se or with no elastic member such as a 
spring, a cushion or the like in the key top per se. 
It is another object of the present invention to stabilize the key 
operation, and to prevent abnormal sound or looseness from being caused by 
vibrations of a calling vibrator or speaker singing. 
It is further another object of the present invention to make it possible 
to easily perform assembling from the outside of a casing, and to prevent 
occurrence of detachment due to external impact such as falling or the 
like. 
To attain the above-noted objects, the present invention provides a key top 
holding structure for holding a key top on a casing to operate a switch. 
The key top holding structure includes a key top and a casing. The key top 
includes a first protrusion, a second protrusion and an elastic stopper 
nail. The casing includes a center shaft and a spring extending from a 
peripheral portion of the casing toward the central shaft. The key top is 
pivotably held on the casing by engagement between the stopper nail and 
the central shaft to depress the spring through the first protrusion and 
the switch through the second protrusion. 
The key top holding structure can reduce the number of component parts by 
providing a spring structure in the casing. The operation and posture of 
the key top can be stabilized. The generation of the abnormal sound and 
looseness caused due to vibrations of a calling vibrator or loudspeaker 
can be surely prevented. Assembly can be also performed easily from the 
outside of the casing. The accidental detachment of the key top by an 
external impact can also be avoided. 
The present disclosure relates to the subject matter contained in Japanese 
patent application No. Hei. 9-274933 (filed on Sep. 24, 1997) which is 
expressly incorporated herein by reference in its entirety.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Next, preferred embodiment of the present invention will be described in 
detail with reference to FIGS. 1 to 6. 
(First Embodiment) 
FIG. 1 is an exploded perspective view of a key top and a casing according 
to a first embodiment of the present invention. FIG. 2 is a sectional view 
showing how to incorporate the key top into the casing. FIG. 3 is a plan 
view of a portion of the casing where the key top is to be incorporated. 
FIG. 4 is a sectional view showing a state in which the key top is 
incorporated in the casing. FIG. 5 is a sectional view showing a state in 
which the key top is pushed. The key top and the casing are, for instance, 
molded from resin. 
The method of assembling the key top will be described with reference to 
FIG. 2. First, a stopper nail 1a of a key top 1 is forced vertically onto 
a center shaft 2a of a casing 2 in the direction of the arrow B. The 
stopper nail 1a of the key top 1 is spread in the direction of the arrow A 
because of its own elasticity. As the stopper nails 1a of the key top 1 
are fitted on the center shaft 2a, protrusion portions 1b for pushing 
springs 2b of the casing 2 abut against heads 2d (see FIG. 3) of the 
springs 2b, respectively. Each of the protrusion portions 1b acts as a 
point of application of the spring. On the other hand, protrusion portions 
1c for pushing switches 3 are respectively inserted into holes 2c (see 
FIG. 3) of the springs 2b of the casing 2, so that the key top 1 can be 
prevented from rotating when the key top is inserted into the casing 2. 
When the stopper nail 1a is entirely fitted onto the center shaft 2a, the 
assembling is completed. Preferably, the upper surface of the center shaft 
2a is formed into a spherical or tapered shape, so that the stopper nail 
1a can be fitted onto the center shaft 2a smoothly. As described above, 
the key top 1 can be assembled easily from the outside of the casing 2. 
Next, the shape of each of the springs 2b of the casing 2 will be described 
with reference to FIG. 3. Each spring 2b of the casing 2 extends toward 
the center shaft 2a from the periphery of a recess portion of the casing 2 
in which the key top 1 is to be set. The spring 2b is formed at its 
central portion with a hole 2c into which the protrusion portion 1c of the 
key top 1 is to be inserted. The spring 2b is strong in structure because 
of its U-shape. Therefore, the spring 2b is substantially free from the 
adverse deformation due to a force when the casing 2 is removed from a 
molding die during resin-molding. In addition, a gradient for improving 
mold releasability during the resin-molding is given to the outer 
circumference of the spring 2b to suppress the adverse deformation of the 
spring. If the spring is not U-shaped and has a structure constituted by 
two thin spring members, the possibility of deformation of the spring 
during molding is high so that there is a fear that the quality lacks 
stability. 
FIG. 4 shows the state in which the key top 1 is incorporated into the 
casing 2. Since the stopper nail 1a of the key top 1 is entirely fitted 
onto the center shaft 2a of the casing 2, the key top 1 cannot be removed 
from the casing 2 unless the stopper nail 1a of the key top 1 is forcibly 
spread in the direction F. That is, since the key top 1 cannot be taken 
off from the outside of the casing 2, it is possible to prevent the key 
top 1 from being detached by an external impact such as falling or the 
like. 
In the state shown in FIG. 4, each spring 2b of the casing 2 is given 
downward tension by the corresponding protrusion 1b of the key top 1, 
whereas the key top 1 is always pushed in the direction E (upward) by the 
elastic force of the springs 2b. That is, the balanced elastic force of 
the two springs holds the key top 1 such that the protrusions 1c are 
spaced slightly from respective switches 3 on printed boards 4. Since the 
key top 1 always receives the tension vertically, it is possible to 
prevent abnormal sound or looseness from being caused by vibrations of a 
calling vibrator or speaker singing. 
As shown in FIG. 5, the key top 1 is operated like a seesaw. When the key 
top 1 is pushed in the direction of the arrow D, the key top 1 rotates 
about the center shaft 2a of the casing 2 as a fulcrum, so that the switch 
3 (left in the drawing) is pushed. In this condition, the tension by the 
right spring 2a in the direction of the arrow G about the central shaft 2a 
is released. When the load to press the key top 1 is released, the key top 
1 is returned to its original state by the balanced elastic force of the 
springs 2b. The action of the springs 2b can keep the stable posture and 
operation of the key top 1. Even if the key top 1 is erroneously pushed at 
its central portion, the key top 1 does not push both the switches 3 
simultaneously because the center shaft 2a acts as a stopper. 
As described above, the key top holding structure according to the first 
embodiment of the present invention has at least the following advantages: 
The stopper nail is engaged with the center shaft of the casing. The key 
top is held to push the springs through the respective first protrusions 
and the switches through the respective second protrusions. The posture 
and operation of the key top is stabilized by the spring action, thereby 
preventing the occurrence of abnormal sound and looseness. The center 
shaft acts as a stopper, thereby preventing the two switches from being 
pushed simultaneously. The number of component parts can be reduced, and 
the assembly can be made easy. 
(Second Embodiment) 
A key top holding structure according to a second embodiment of the present 
invention will be described with reference to FIG. 6. The second 
embodiment of the present invention is different from the first embodiment 
in that the key top holding structure of the present invention is applied 
to a rocking piano-key type arrangement for pushing a single switch. 
A key top 1 has a stopper nail 1a, a protrusion portion 1b and a protrusion 
1c. A casing 2 has a center shaft 2a and a spring 2b. The spring 2b of the 
casing 2 extends toward the center shaft 2a from the periphery of a recess 
portion of the casing 2 in which the key top 1 is to be set. The spring 2b 
is formed at its central portion with a hole 2c through which the 
protrusion 1c of the key top 1 is to be inserted. A switch 3 is provided 
on a printed board 4. 
To incorporate the key top 1 in the casing 2, the stopper nail 1a of the 
key top 1 is forced onto the center shaft 2a of the casing 2 vertically. 
As the stopper nail 1a of the key top 1 is fitted onto the center shaft 
2a, the protrusion portion 1b of the key top 1 abuts against a head 2d of 
the spring 2b. This protrusion portion 1b acts as a point of application 
of the spring 2b. The protrusion portion 1c for pushing the switch 3 is 
inserted through the hole 2c of the spring 2b of the casing 2, so that the 
key top 1 can be prevented from rotating when the key top 1 is assembled. 
The key top 1 can be assembled easily from the outside of the casing 2 in 
this manner. 
When the stopper nail 1a of the key top 1 is entirely fitted onto the 
center shaft 2a of the casing 2, the key top 1 cannot be removed from the 
casing 2 unless the stopper nail 1a of the key top 1 is forcibly spread in 
the direction F. That is, the key top 1 cannot be taken off from the 
outside of the casing 2. Therefore, it is possible to prevent the key top 
1 from being detached by an external impact such as dropping of the 
small-sized electronic equipment, or the like. 
The spring 2b of the casing 2 is given downward tension by the protrusion 
1b of the key top 1, while the key top 1 is always pushed in the direction 
E (upward) by the elastic force of the spring 2b. Since there is no spring 
on the opposite side with respect to the center shaft 2a, the head of the 
key top 1 abuts against the casing 2 so as to bear against the force of 
the spring 2b, thereby holding the top key in a stable manner. Since the 
key top 1 always receives the vertical tension in this manner, there is no 
fear that abnormal sound or looseness is produced in the key top 1 by 
vibrations of a calling vibrator or speaker singing. 
When the key top 1 is pushed in the direction D for key operation, the key 
top 1 rotates about the center shaft 2a as a fulcrum, so that the switch 3 
is pushed. When the load to press the key top 1 is released, the key top 1 
is returned to its original state by the action of the spring 2b. The key 
top 1 is kept in a stable state by the action of the spring 2b. 
As described above, the key top holding structure according to the second 
embodiment of the present invention has at least the following advantages: 
The stopper nail of the key top of a rocking piano-key type is engaged 
with the center shaft of the casing. The key top is held to press the 
spring through the first protrusion and the switch through the second 
protrusion. The center shaft of the casing acts as a fulcrum during the 
operation of the key top. Accordingly, the operation and posture of the 
key top is made stable by the spring action. It is possible to prevent 
abnormal sound or looseness from occurring. The number of component parts 
can be reduced, and the assembly can be made easy.