Keyboard

A keyboard has an upper case, a lower case, and a stacked functional structure formed by stacking and fastening together a membrane switch sheet, a rubber sheet and a housing supporting keys in that order on a curved plate and a flat plate. When assembling the stacked functional structure, the membrane switch sheet and the rubber sheet are placed in that order on the curved plate and the flat plate supported in place on the bottom wall of the lower case and support ribs formed on the inner surface of the bottom wall of the lower case, connecting hooks formed integrally with the housing are inserted through aligned slots formed in the rubber sheet, the membrane switch sheet, the curved plate and the flat plate so that the connecting hooks engage with the lower surfaces of the curved plate and the flat plate with the membrane switch sheet and the rubber sheet are sandwiched firmly between the housing, and the curved plate and the flat plate. The stacked functional structure is sandwiched between the upper and the lower case, and then the upper and the lower case are fastened together to complete the keyboard.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a keyboard to be employed in giving 
signals to an electronic apparatus or the like. 
2. Description of the Related Art 
Keyboards are used widely as input devices for operating personal 
computers, word processors and the like. A conventional keyboard will be 
described with reference to FIGS. 10 to 14. Referring to FIGS. 10 to 12, 
the keyboard has a support plate 1 of a metal having a curved portion 1a, 
a bent portion 1c and a flat portion 1b, a membrane switch sheet 2 having 
an upper membrane provided with electrodes, and a lower membrane closely 
spaced from the upper membrane and provided with electrodes, local 
portions of the upper membrane being depressed to bring the electrodes 
thereof to be in contact with the corresponding electrodes of the lower 
membrane for switching operation, keys 4, a rubber sheet 3 for absorbing 
shocks applied to the keys 4 by operator' fingertips, and a housing 5 of a 
synthetic resin having an upper surface on which the keys 4 are arranged. 
The support plate 1, the membrane switch sheet 2, the rubber sheet 3 and 
the housing 5 are stacked in that order. Those members excluding the 
support plate 1, i.e., the membrane switch sheet 2, the rubber sheet 3 and 
the housing 5, have moderate flexibility that enables those members to 
curve along the curved portion 1a of the support plate 1. 
The keys 4 arranged on the upper surface of the housing 5 are supported by 
key support mechanisms 5a on the housing 5, respectively, so as to be 
vertically movable when depressed. 
Fastening projections 5b project from predetermined positions on the lower 
surface of the housing 5. As shown in FIGS. 11 and 12, the membrane switch 
sheet 2 and the rubber sheet 3 are stacked in that order on the support 
plate 1 having the curved portion 1a, the bent portion 1c and the flat 
portion 1b. The housing 5 is placed on the rubber sheet 3 so that the 
projections 5b are inserted through aligned holes formed in the rubber 
sheet 3, the membrane switch sheet 2 and the support plate 1. End portions 
of the projections 5b project from the lower surface of the support plate 
1. The end portions of the projections 5b are upset to form a stacked 
functional structure 6 consisting of the support plate 1, the membrane 
switch sheet 2, the rubber sheet 3 and the housing 5. In this stacked 
functional structure 6, the membrane switch sheet 2, the rubber sheet 3 
and the housing 5 are curved so as to conform to the shape of the support 
plate 1 having the curved portion 1a and the flat portion 1b. 
In the keyboard provided with the stacked functional structure 6, the 
curved portion 1a of the support plate 1 is seated on the upper surface of 
the bottom wall 9a of a lower case 9 and a rib 9b formed on the bottom 
wall 9a. The flat portion 1b is seated on ribs 9c formed on the bottom 
wall 9a of the lower case 9 as shown in FIG. 10. The stacked functional 
structure 6 is located on the lower case 9 by projections, not shown, 
formed on the lower case 9 and engaging with positioning recesses 1d (FIG. 
14) formed in the support plate 1. An upper case 8 is put on the lower 
case 9, thus supporting the stacked functional structure 6 so that the 
keys 4 project outside through holes formed in the upper case 8. The upper 
case 8 and the lower case 9 sandwiching the stacked functional structure 6 
therebetween are fastened together with screws, not shown, to complete the 
keyboard. 
As shown in FIGS. 10 to 12, an alphanumeric key unit A is disposed on the 
upper surface of the housing 5 with the keys 4 included in the 
alphanumeric key unit A arranged in a curved arrangement along the curved 
portion 1a of the support plate 1, and a function key unit B is disposed 
on the upper surface of the housing 5 with the keys 4 included in the 
function key unit B arranged in a flat arrangement along the flat portion 
1b of the support plate 1. Since the rear end of the curved portion 1a of 
the support plate 1 is seated on the rib 9b, the alphanumeric key unit A 
rises gradually along the curved portion 1a of the support plate 1 toward 
the rear. Since the function key unit B is disposed behind the 
alphanumeric key unit A (on the right-had side, in FIG. 10), as viewed 
from the operator's side and the flat portion 1b of the support plate 1 
corresponding to the function key unit B are supported on the ribs 9c, the 
function key unit B is disposed in a substantially horizontal position on 
a level higher than that of the alphanumeric key unit A. 
In the conventional keyboard illustrated in FIGS. 10 to 14, the membrane 
switch sheet 2 and the rubber sheet 3 are stacked on the upper surface of 
the support plate 1 and holes 1e through which the projections 5b are 
inserted are formed in the support plate 1, the membrane switch sheet and 
the rubber sheet 3 (only the holes 1e formed in the support plate 1 are 
shown) at positions corresponding to the projections 5b of the housing 1. 
The stacked functional structure 6 is fabricated by inserting the 
projections 5b through the holes 1e and upsetting the end portions of the 
projections 5b projecting from the lower surface of the support plate 1 to 
hold the membrane switch sheet 2 and the rubbers sheet 3 between the 
support plate 1 and the housing 5. 
Although the support plate 1 has the curved portion 1a and the flat portion 
1b respectively having different shapes on the opposite sides of the bent 
portion 1c, the housing 5 formed of a flexible synthetic resin is bent 
substantially along the bent portion 1c of the support plate 1 and 
substantially conforms to the shape of the support plate 1 when the 
stacked functional structure 6 is completed. The housing 5 has a linear 
bending portion 5d corresponding to the bent portion 1c of the support 
plate 1 and is capable of being bent along the bending portion 5d when 
fastened to the support plate 1. 
As shown in FIG. 13, housing 5 is fastened to the support plate 1 with its 
first portion A1, in which the alphanumeric key unit A is disposed, in 
conformance to the curved portion 1a and its second portion B1, in which 
the function key unit B is disposed, in conformance to the flat portion 
1b. The keys 4 which are more frequently used among those of the 
alphanumeric key unit A, corresponding to the curved portion 1a of the 
support plate 1, are arranged at positions nearer to the operator in the 
curved first portion A1 than those which are less frequently used to 
facilitate operator's operation for operating the keys and to reduce load 
on the operator. The keys 4 of the function key unit B, which are less 
frequently used than the alphanumeric keys 4, are disposed in the flat 
second portion B1 remote from the operator to form the keyboard in a small 
thickness. 
The support plate 1 having the curved portion 1a and the flat portion 1b of 
the conventional keyboard thus constructed is formed by processing a large 
metal sheet by a pressing process or a roll-bending process. The yield of 
such a process is low and hence the cost of the support plate 1 
manufactured by such a process is high. 
It is very difficult to form the support plate 1 having the curved portion 
1a and the flat portion 1b on the opposite sides of the bent portion 1c in 
a high accuracy by a press or a bending roll because of the springback of 
the metal sheet. If the support plate 1 is not formed accurately is design 
dimensions, the stacked functional structure 6 cannot stably be seated on 
the bottom wall 9a and the ribs 9b and 9c of the lower case 9 and rattles, 
which makes work for assembling the keyboard difficult. 
The stacked functional structure 6 is constructed by stacking the membrane 
switch sheet 2 and the rubber sheet 3 on the support plate 1, the housing 
is put on the rubber sheet 3 so that the projections 5b are inserted 
through the holes formed in the support plate 1, the membrane switch sheet 
2 and the rubber sheet 3, and the end portions of the projections 5b are 
upset. Since the number of the projections 5b is relatively large, it is 
very difficult to upset all the fastening projections 5b uniformly so that 
the curved portion 5a and the flat portion 5b of the housing 5 are 
fastened equally to the support plate 1. Furthermore, an expensive, large 
upsetting machine is necessary to upset the fastening projections 5b so 
that the curved portion 5a and the flat portion 5b are fastened equally to 
the support plate 1. Such problems may be solved by individually upsetting 
the plurality of fastening projections 5b on at a time, which, however, 
takes much time. 
SUMMARY OF THE INVENTION 
According to a first aspect of the present invention, a keyboard comprises 
a case, a plurality of plates supported in place in the case, a membrane 
switch sheet placed on the plurality of plates, and a housing supporting 
keys and mounted on the membrane switch sheet. 
In this keyboard, the plurality of plates may be mounted on the case with a 
space therebetween, the plurality of plates may be extended in different 
planes, respectively, and the membrane switch sheet may be bent in a 
portion thereof corresponding to the space between the plates. 
In this keyboard, some of the plurality of plates may be formed in curved 
shapes and the rest may be formed in flat shapes. 
According to a second aspect of the present invention, a keyboard comprises 
a case, a plurality of plates supported in place in the case and having 
hook retaining portion, a membrane switch sheet put on the plurality of 
plates, a housing supporting keys and mounted on the membrane switch 
sheet, hooks provided on the inner surface of the housing. The hooks are 
brought into engagement with the hook retaining portions of the plurality 
of plates to connect the housing to the plurality of plates.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1 to 9 showing a keyboard in a preferred embodiment 
according to the present invention, the keyboard has a curved plate 10 of 
a metal curved in an arc of a circle with a radius of curvature of 200 mm 
or above and a flat plate 11 of a metal. A stacked functional structure 13 
is formed by stacking a membrane switch sheet 2, a rubber sheet 3, and a 
housing 12 of a synthetic resin supporting a plurality of keys 4 to be 
operated by operator's fingertips for information feeding in that order on 
the plates 10 and 11. The stacked functional structure 13 is held between 
cases 8 and 9. 
The components of the stacked functional structure 13 excluding the plates 
10 and 11, similarly to those of the foregoing conventional keyboard, are 
moderately flexible and can be bent at angles below a certain limit angle. 
The housing 12 is provided on its upper surface with key supports 12a. The 
keys 4 are supported on the key supports 12a so as to be vertically 
movable when depressed by the operator's fingertips. The number of the key 
supports 12a is equal to that of the keys 4. 
As shown in FIG. 7, each key 4 has a key top 4b and a stem 4a and is 
supported on the housing 12. Substantially hemispherical, hollow key 
supports 12a respectively provided with stem guide holes 12f protrude from 
the upper surface of the housing 12. An elastic rubber spring 14 placed in 
the hollow of each key support 12a. The rubber spring 14 has a top wall 
14a, a projection 14b and a domelike side wall 14c. 
The operation of the key 4 will be described hereinafter. The key 4 is 
supported for vertical movement on the key support 12a with the stem 4a 
thereof fitted in the stem guide hole 12f. When depressed by the 
operator's fingertip, the stem 4a depresses the top wall 14a of the rubber 
spring 14. Consequently the side wall 14c is elastically deformed and the 
projection 14b pushes the membrane switch sheet 2 underlying the rubber 
sheet 3 to close a corresponding membrane switch. When the pressure 
applied to the key 4 by the operator's fingertip is removed from the key 
4, the resilience of the elastically deformed side wall 14c pushes up the 
stem 4a and the rubber spring 14 restores its domelike original shape to 
return the key 4 to its initial position. 
The membrane switch sheet 2 has an upper membrane provided with electrodes, 
and a lower membrane closely spaced from the upper membrane and provided 
with electrodes. When a local portion of the upper membrane is depressed, 
the electrode of the upper membrane is brought into contact with the 
corresponding electrode of the lower membrane for switch closing 
operation. The rubber sheet 3 has an elasticity capable of absorbing 
shocks applied to the key 4 by the operator's fingertip. 
A plurality of L-shaped hooks 12b and a plurality of bill-shaped hooks 12c 
are formed on the inner surface of the housing 12 supporting the keys 4 as 
shown in FIG. 3. As shown in FIGS. 3 and 4, the membrane switch sheet 2 
and the rubber sheet 3 are stacked on the curved plate 10 and the flat 
plate 11, and the housing 12 is put on the rubber sheet 3. Slots 11a are 
formed in the flat plate 11, the membrane switch sheet 2 and the rubber 
sheet 3 at positions respectively corresponding to the bill-shaped hooks 
12c,and slots 10a are formed in the curved plate 10, the membrane switch 
sheet 2 and the rubber sheet 3 at positions respectively corresponding to 
the L-shaped hooks 12b. The slots 10a are formed in a size that secures a 
small clearance between the L-shaped hook 12b and the curved plate 10, the 
membrane switch sheet 2 and the rubber sheet 3. 
When connecting the flat plate 11 to the housing 12, the bill-shaped hooks 
12c are inserted through the slots 11a of the rubber sheet 3, the membrane 
switch sheet 2 and the flat plate 11, and are brought into snapping 
engagement with the edges of the slots 11a of the flat plate 11. Thus a 
function key unit B is formed. 
When connecting the curved plate 10 to the housing 12, the L-shaped hooks 
12b are inserted through the slots 10a of the rubber sheet 3, the membrane 
switch sheet 2 and the curved plate 10 as shown in FIG. 8, and then the 
housing 12 is forced to move along the rubber sheet 3 in the direction of 
the arrow X to bring the L-shaped hook 12b into engagement with the edges 
of the slots 10a of the curved plate 10 as shown in FIG. 9. Thus an 
alphanumeric key unit A is formed. When the alphanumeric key unit A and 
the function key unit B are thus formed, a gap 15 is formed between the 
plates 10 and 11 as shown in FIG. 4. 
The stacked functional structure 13 is mounted to the lower case 9 with the 
housing 12 bent along its bending portion 12h corresponding to the gap 15. 
A groove 12g is formed in the bending portion 12h to form the bending 
portion 12h in a small thickness so that the housing 12 can easily be bent 
along the bending portion 12h. 
A method of assembling the keyboard will be described hereinafter. The 
curved plate 10 is seated on the bottom wall 9a of the lower case 9, and a 
rib 9b formed on the bottom wall 9a. The curved plate 10 is located by 
fitting locating lugs, not shown, formed on the lower case 9 in locating 
recesses 10b formed in the curved plate 10 and held temporarily in place 
on the lower case 9. A front portion, i.e., a portion on the side of the 
operator, of the curved plate 10 is placed in contact with the bottom wall 
9a, and a rear portion of the same is seated on the rib 9b. In this stage, 
a space t of a small width, for example, about 3 mm, is formed between a 
portion of the curved plate 10 corresponding to home position keys 4A and 
the bottom wall 9a of the lower case 9. Since the width of the space t is 
small, the home position keys 4A are at a low height, which enables the 
operator to operate the keys 4 in a natural mode. If the curved plate 10 
is extended to the rear end of the lower case 9, the rear portion of the 
curved plate 10 rises high because the space t is small. Therefore the 
flat plate 11 separated from the curved plate 10 is used for forming the 
function key unit B to form the keyboard in a small thickness. 
Subsequently, the flat plate 11 is placed on two ribs 9c formed on the 
bottom wall 9a of the lower case 9. The flat plate 11, similarly to the 
curved plate 10, is located by fitting locating lugs, not shown, formed on 
the lower case 9 in locating recesses 11b formed in the flat plate 11 and 
held temporarily in place on the lower case 9. Then, the membrane switch 
sheet 2 and the rubber sheet 3 are stacked on the plates 10 and 11, and 
the housing 12 supporting the keys 4 is placed on the rubber sheet 3 to 
construct the stacked functional structure 13. The stacked functional 
structure 1 thus mounted on the lower case 9 is bent along a portion 
corresponding to the bending portion 12h of the housing 12. 
When connecting the plates 10 and 11, the key tops 4b of the keys 4 of the 
alphanumeric key unit A are depressed by a jig, not shown, having a curved 
working surface conforming to the shape of the curved plate 10 and, at the 
same time, the key tops 4b of the keys 4 of the function key units B by a 
jig, not shown, having a flat working surface conforming to the shape of 
the flat plate 11. Portions of the housing 12, the membrane switch sheet 2 
and the rubber sheet 3 corresponding to the curved plate 10 are curved 
along the curved plate 10 so that the portion of the membrane switch sheet 
2 is brought into close contact with the curved plate 10. The L-shaped 
hooks 12b are inserted through the slots 10a of the rubber sheet 3, the 
membrane switch sheet 2 and the curved plate 10 as shown in FIG. 8. 
In this state, a stopper 12d formed in a front end portion of the housing 
12 lies on the rubber sheet 3 and the front end portion is warped upward. 
Then, the housing 12 is forced to move in the direction of the arrow X 
relative to the rubber sheet 3. Consequently, the curved plate 10, the 
membrane switch sheet 2 and the rubber sheet 3 are clamped between housing 
12 and the noses 12e of the L-shaped hooks 12b to complete a portion of 
the stacked functional structure 13 corresponding to the alphanumeric key 
unit A. In this state, the stopper 12d of the housing 12 in close contact 
with the front edges of the curved plate 10, the membrane switch sheet 2 
and the rubber sheet 3, so that the curved plate 10 is unable to come off 
the L-shaped hooks 12b. Since the housing 12 has a substantially flat 
original shape and is elastically curved in conformance to the curved 
shape of the curved plate 10, the housing 12 tends to restore its flat 
original shape. Therefore, the L-shaped hooks 12b are kept in firm 
engagement with the curved plate 10 by the resilience of the housing 12 
and hence the curved plate 10 and the housing 12 are never separated from 
each other by vibrations or the like. The bill-shaped hooks 12c are 
inserted through the slots 11a of the rubber sheet 3, the membrane switch 
sheet 2 and the flat plate 11, and are brought into snapping engagement 
with the edges of the slots 11a of the flat plate 11. An upper case 8 is 
put on the lower case 9 so as to sandwich the stacked functional structure 
13 between the cases 8 and 9 with the keys 4 exposed on the surface of the 
upper case 3, and the cases 8 and 9 are fastened together with screws, not 
shown, to complete the keyboard. 
In this keyboard, the plates 10 and 11 are extended in two different 
planes, respectively, in the lower case 9. The alphanumeric key unit A 
corresponding to the curved plate 10 is disposed so as to slope gradually 
up toward the rear, the alphanumeric keys 4 which are more frequently used 
among those of the alphanumeric key unit A are arranged at positions 
nearer to the operator than those which are less frequently used and the 
rear end of the curved plate 10 rests on the rib 9b. The function keys 4 
of the function key unit B corresponding to the flat plate 11, which are 
less frequently used than the alphanumeric keys 4, are arranged on a flat 
plane at positions remote form the operator and the flat plate 11 rests on 
the ribs 9c. The alphanumeric key unit A and the function key unit B may 
be extended in two flat planes or in two curved planes, respectively, in 
stead of in the curved plane and the flat plane. Moreover, the two planes 
may be two stepped horizontal planes instead of the two continuous planes 
forming a plane having a bent portion. 
Since the curved plate 10 and the flat plate 11 are separate members which 
are formed individually and have simple shapes, respectively, the curved 
plate 10 and the flat plate 11 can be accurately formed by a 
mass-production process. 
Since the plates 10 and 11 are separate members and the space 15 is secured 
between the plates 10 and 11 as seated on the ribs 9b and 9c of the lower 
case 9, respectively, and the housing 12, the membrane switch sheet 2 and 
the rubber sheet 3 are flexible, the stacked functional structure 13 can 
easily be mounted on the ribs 9b and 9c even if the ribs 9b and 9c are not 
formed accurately in design height. 
In a modification of the keyboard in this embodiment, the housing 12 may be 
provided with bill-shaped hooks instead of the L-shaped hooks 12b. 
The keyboard of the present invention can easily and quickly be assembled 
without using a large upsetting machine.