Key-holding structure of keyboard with curved operating surface of keys

A keyboard assembly having key-switches, comprising a key holder plate supporting multiple keys in plural rows and movably across the thickness of the plate, and further comprising an upper casing which has a rectangular aperture closed by the key holder plate. The key holder plate has holes through which the keys extend, and integral guide portions concentric with the holes and extend toward the rectangular aperture. Opposite right and left sides of the aperture perpendicular to the rows of the keys are defined by side walls of the upper casing each of which has a downward extension toward the key holder plate. The extension has a convex lower end profile with which the key holder plate is held in pressed contact by fasteners, with elastic deformation thereof following the convex lower end profile of the downward extension, such that a surface generally defined by top faces of the keys is curved in cross section across the rows of the keys.

BACKGROUND OF THE INVENTION 
The present invention relates to a keyboard assembly for providing 
electrical outputs corresponding to multiple keys, to signal utilization 
electronic devices such as typewriters and other data processing 
equipment. 
In such a keyboard for electronic devices, a multiplicity of keys are 
disposed in plural rows to provide electric signals corresponding to the 
keys which have been depressed on their top faces. To improve ease of 
operation of the keys, attempts based on human engineering or ergonomics 
have been made to arrange the keys such that an operating surface 
generally defined by the top faces of the individual keys is curved to a 
downwardly convex shape in cross section across the rows of the keys. 
There have been proposed the following two methods to obtain such a curved 
operating surface of the keyboard: 
The first method uses a curved key holder plate 2 having multiple guide 
holes 1, as shown in FIG. 1. The holder plate 2 is made from a steel plate 
by shaping it to a suitable curvature in the transverse cross section. In 
the guide holes 1, keystem guides 5 are fixedly inserted to slidably guide 
respective keystems 4 which carry at their upper ends keytops 3 having the 
finger-pressed top faces. In this case, the keys 3, 4 are all equally 
sized so that an operating surface 6 defined by the top faces is curved 
substantially to the curvature of the key holder plate 2. 
In this method, however, it is required to fix the individual keystem 
guides 5 in the guide holes 1 formed in the shaped key holder plate 2. 
This assembling procedure is cumbersome and time-consuming, and reduces 
the efficiency of manufacture of the keyboard to an appreciable extent, 
and accordingly pushes up the cost of manufacture. 
While the above method is advantageous in that the key holder plate 2, 
which is shaped under plastic working from a metal sheet, is capable of 
maintaining an initially given curved profile virtually permanently, the 
metal plate is required to be relatively thick for permanency of the 
original shape, and this inherently increases a total weight of the 
keyboard assembly, which may be considered as an undesired factor in the 
recent trend in the art toward providing compact and lightweight 
equipment. 
The second method is illustrated in FIG. 2, wherein an upper casing 7 of a 
keyboard is provided with integrally formed keystem guides 8 which 
slidably support respective keystems 9 having keytops 10 fixed to their 
upper ends. In this method, an operating surface 11 of the keyboard is 
established by forming the keytops 10 in different sizes and shapes, 
depending upon the positions in which they are disposed. For example, the 
keytops 10 carried on the keystems 9 disposed in one of plural rows are 
formed with a top face having a curvature which is different from that of 
the keytops 10 carried on the keystems 9 in another of the plural rows. 
Thus, the above second known method requires different kinds of keytops or 
keytops and keystems to provide different contours of top faces of the 
keys so that the top faces cooperate to form the curved operating surface 
11. This means a need of using different kinds of molds for forming the 
different keys, and consequently an increased cost of manufacture of the 
keyboard assembly. 
SUMMARY OF THE INVENTION 
It is accordingly an object of the present invention to provide an improved 
keyboard simple in construction, easy to operate and economical to 
manufacture, which has a key holder plate for supporting keys with their 
top faces forming a curved operating surface. 
According to the invention, there is provided a keyboard having multiple 
key-switches each comprising a key having a finger-pressed top face, a 
movable electrode and at least two stationary electrodes. The keyboard 
comprises: an upper casing including a portion which has a rectangular 
aperture formed through a thickness of said portion; a key holder plate 
supporting the multiple keys in plural rows perpendicular to the right and 
left sides of the rectangular aperture and movably in a direction 
perpendicular to a plane of the key holder plate; a printed circuit board 
disposed below the key holder plate and having a pattern of the stationary 
electrodes such that the key-switches are operated upon movement of the 
respective multiple keys; and a lower casing disposed below the printed 
circuit board and cooperating with the upper casing to enclose the key 
holder plate and the printed circuit board. The key holder plate has holes 
through which the respective keys extend in said direction, and integral 
guide portions formed concentrically with the holes and extending in said 
direction towards said rectangular aperture. The upper casing includes a 
pair of side walls defining opposite right and left sides of the 
rectangular aperture. Each of the side walls has a downward extension from 
a lower surface of said portion. The downward extension has a convex 
profile at its lower end. The keyboard further comprises retaining means 
for holding the key holder plate curved in cross section across the plural 
rows of the keys, with elastic deformation thereof in pressed contact with 
the convex profile of the downward extension of the side walls, such that 
a surface generally defined by the top faces of the multiple keys is 
curved to the convex end profile of the downward extension in the cross 
section taken along a line perpendicular to the plural rows of the 
multiple keys. 
In the above construction, the downward extensions formed at the right and 
left edges of the rectangular aperture in the upper casing, permit easy 
shaping of the key holder plate to support the keys to that their top 
faces define an operating surface with a desired downwardly-convex 
curvature. This curvature is determined by the lower and profile of the 
downward extensions of the upper casing, without forming the keys in 
different sizes and shapes depending upon their positions on the key 
holder plate. Further, the provision of the guide portions integrally with 
the key holder plate to guide the keys eliminates cost and labor which are 
otherwise required to insert and fix keystem guides in association with 
guide holes as previously discussed in connection with the prior art 
keyboards. Further, the fabrication of a planar key holder plate with 
integral guide portions according to the invention is very much easier 
than the fabrication of a curved key holder plate with integral guide 
portions by plastic working on a metal sheet or by molding of a synthetic 
resin material. In the former method of plastic working, it is difficult 
to shape the metal sheet to a desired curvature because of the presence of 
the guide portions which are formed before the sheet is curved. The latter 
method of synthetic resin molding has a problem of mold release because 
the guide portions are formed radially. Further, the key holder plate of 
the keyboard of the invention is comparatively light in weight because it 
is not made from a relatively thick metal sheet as used in the art. Thus, 
the keyboard constructed according to the present invention is simple in 
construction, easy and economical to manufacture, as well as easy to 
operate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIGS. 3-7, there is illustrated one preferred form of a 
keyboard constructed according to the invention, wherein a keyboard 
housing generally indicated at 20 in FIG. 3 includes an upper casing 21 
and a lower casing 22, both made of synthetic resin. As illustrated in 
FIG. 4, the upper casing 21 includes a generally planar portion 21a which 
has a rectangular opening 23 formed through the thickness of the generally 
planar portion 21a. The planar portion 21a has a pair of side walls 24 and 
25 which define opposite right and left sides of the rectangular aperture 
23. Each of the side walls 24, 25 has a downward extension 24a, 25a from 
the lower surface of the planar portion 21a. The downward extension 24a, 
25a has a convex profile at its lower end. The planar portion 21a is 
further provided with plural downward bosses 26, 27, 28, 29, 30, 31, 32 
and 33 which protrude downwardly from the lower surface of the planar 
portion 21a. 
To the downward bosses 30, 31, 32 and 33, there is fixed a curved retainer 
plate 34 with fixing screws 35, 36, 37 and 38, respectively. This retainer 
plate 34 is formed with a predetermined curvature in cross section taken 
along a line parallel to the right and left sides of the rectangular 
aperture 24, 25. The curved retainer plate 34 is supported at its lower 
surface by three upward extensions in the form of longitudinal ribs 39, 40 
and 41 which extend from an inner surface of the lower casing 24 such that 
upper ends of the ribs 39-41 abut on the lower surface of the curved 
retainer plate 34. The longitudinal ribs 39-41 run in a direction 
perpendicular to the right and left sides of the rectangular aperture 23, 
and are spaced from each other in a direction parallel to these sides. 
A printed circuit board 42 rests on an upper surface of the curved retainer 
plate 34. The printed circuit board 42 and the retainer plate 34 are 
fastened to the lower ends of the downward bosses 26, 27, 28 and 29 of the 
upper casing 21 with fixing screws 43, 44, 45 and 46, respectively, such 
that the printed circuit board 42 backed by the retainer plate 34 is also 
curved following the shape of the retainer plate 34. The circuit board 42 
comprises a substrate which carries on its upper surface a printed pattern 
of conductors, i.e., multiple pairs of stationary electrodes 50 as shown 
in FIG. 5. The substrate (42) further carries, also on its upper surface, 
an elastomeric member 48 which is formed with multiple frusto-conical or 
inverted-cup-shaped elastic housings 47 made of rubber, each of which 
cooperates with the substrate to enclose the corresponding pair of 
stationary electrodes 50, 50. Each frusto-conical housing 47 has a top 
wall 47a which is spaced from and opposite to the stationary electrodes 
50. A sponge member 49 is bonded at one surface thereof to an inner 
surface of the top wall 47a of the frusto-conical housing 47. The sponge 
member 49 carries on the other surface thereof a movable electrode 51 made 
of flexible aluminum foil which is covered with a thin insulating film 51a 
made of flexible synthetic resin, such that the movable electrode 51 faces 
the stationary electrodes 50 via the insulating film 51a. This movable 
electrode 51 cooperates with the pair of stationary electrodes 50, 50 to 
constitute a variable capacitor. 
A key holder plate 52 made from synthetic resin, is supported on the curved 
retainer plate 34. The key holder plate 52 has front and rear legs 53 
which run parallel to opposite front and rear sides 57 and 58 of the 
rectangular aperture 23. These legs 53 protrude downwardly from a lower 
surface of the key holder plate 52 toward the curved retainer plate 34, 
such that the plate 52 encloses the printed circuit board 42 and the 
elastic housings 47. At the same time, the key holder plate 52 closes the 
rectangular aperture 23 formed in the upper casing 21. Thus, the key 
holder plate 52 has dimensions sufficient to cover or close the 
rectangular aperture 23. As indicated in FIGS. 5 and 6, a multiplicity of 
holes 52a are formed in the key holder plate 52 in plural rows parallel to 
the front and rear legs 53, or perpendicular to the right and left sides 
of the rectangular aperture 23. Along the peripheral edge of each of these 
holes 52a, is integrally formed an annular guide portion 52 which are 
concentric with the holes 52a and extends perpendicularly from an upper 
surface of the plate 52 towards the rectangular aperture 23, to support a 
key which consists of a keystem 55 and a keytop 54 fixed to upper end of 
the keystem 55. The keystem 55 is inserted through the hole 52a and the 
annular guide portion 56, such that the key (keystem 55) is slidably 
movable in a direction perpendicular to the plane of the key holder plate 
52. Thus, a multiplicity of keys (54, 55) are supported in plural rows 
parallel to the front and rear legs 53, i.e., perpendicular to the right 
and left sides of the rectangular aperture 23 defined by the side walls 
24, 25. 
The key holder plate 52 has, in its lower surface, four parallel grooves 59 
of generally U-shaped cross section which are formed parallel to the front 
and rear legs 53 and between the adjacent rows of the holes 52a. These 
parallel grooves 59 are provided to facilitate elastic deformation of the 
key holder plate 52 in pressed contact with the convex lower ends of the 
downward extensions 24a, 25a of the side walls 24 and 25, which cooperate 
with the curved retainer plate 34 to provide the key holder plate 52 with 
a suitable curved configuration. As shown in FIGS. 3 and 5, the 
frusto-conical housing 47 of the elastomeric member 48 biases the keystem 
55 toward its upper position in which a lower end 55a of the keystem 55 is 
held in abutting contact with an outer surface of the top wall 47a of the 
housing 47 and forced against the lower surface of the key holder plate 
52, as illustrated in FIG. 5. In this condition wherein the movable 
electrode 51 is spaced from the stationary electrodes 50 on the printed 
circuit board 42, a capacitive switch constituted by the keystem 55, 
keytop 54, movable electrode 51, stationary electrodes 50, etc. is placed 
in its non-operated position. 
As indicated above, the key holder plate 52 is installed such that the 
right and left ends of the upper surface thereof are held in pressed 
contact with the convex lower end profiles of the downward extensions 24a, 
25a of the side walls 24, 25 of the upper casing 21, respectively, with 
the front and rear legs 53 supported on the curved retainer plate 34 which 
is screwed to the upper casing 21. With this arrangement, the key holder 
plate 52 is subject to elastic deformation to a curvature corresponding to 
the convex profile of the downward extensions 24a, 25a, whereby an 
operating surface 60 of the keyboard defined by the top faces of the 
individual keytops 54 is curved to a desired downwardly convex shape 
corresponding to the curvature of the key holder plate 52, in cross 
section taken along a line parallel to the right and left sides of the 
rectangular aperture 23, i.e., perpendicular to the rows of the keys (54, 
55). It is noted, in this connection, that the retainer plate 34 has a 
curvature equal to the curvature of the convex profile of the downward 
extensions 24a, 25a. Stated the other way, the retainer plate 34 is curved 
such that a distance thereof to the lower end of the downward extensions 
24a, 25a is constant over an entire width thereof along the right and left 
sides of the rectangular aperture 23. 
Each of the capacitive switches constructed as described above, is operated 
in the following manner. 
Upon depression of the keytop 54 while it is located at its upper position, 
the keystem 55 is moved downward while being guided by the annular guide 
portion 56, whereby the top wall 47a of the frusto-conical housing 47 is 
forced down by an integral lower end 55a of the keystem 55. As a result, 
the assembly of the sponge member 49 and the movable electrode 51, fixed 
to the inner surface of the top wall 47a of the housing 47, is moved 
toward the printed circuit board 42, and the movable electrode 51 covered 
by the insulating film 51a is brought into contact with the pair of 
stationary electrodes 50, 50, as shown in FIG. 7. Thus, the two stationary 
electrodes 50 are capacitively coupled to each other, and a high frequency 
signal is transferred from one of the electrodes 50 to the other. Since 
the movable electrode 51 is carried by the elastic sponge member 49 bonded 
to the top wall 47a of the elastic housing 47, the movable electrode 51 
covered by the insulating film 51a may be held in close and perfect 
contact with the other surfaces of the stationary electrodes 50, through 
elastic deformation of the sponge member 49, thereby assuring a stable 
transfer of the high frequency signal of sufficiently high level between 
the two stationary electrodes 50. 
When the operator's finger pressure is released from the keytop 54, the 
resilient force of the elastic housing 47 causes the keystem 55 and the 
movable electrode assembly 49, 51, 51a to be moved upward to their 
original upper position, whereby the movable electrode 51 is separated 
from the stationary electrodes 50, and the signal transfer between the two 
stationary electrodes 50 is ceased. 
The keyboard of the present embodiment comprising the components which have 
been discussed above, is assembled in the following way. 
In assembling the keyboard, the printed circuit board 42 is first placed on 
the curved retainer plate 34. Then, the elastomeric member 48 with the 
integrally formed elastic housings 47 is set on the printed circuit board 
42. In the meantime, the keystems 55 with the lower ends 55a are set in 
the key holder plate 52 such that the keystems 55 are slidably movable 
through the holes 52a and annular guide portions 56. The keytops 54 are 
then secured to the keystems 55. The key holder plate 52 is placed on the 
curved retainer plate 34 such that the printed circuit board 42 and the 
elastomeric member 48 are enclosed by the two plates 34 and 52. 
Subsequently, an assembly of these components 34, 42, 48 and 52 superposed 
one on another is secured to the upper casing 21 with the fixing screws 
43, 44, 45 and 46 threaded to the respective downward bosses 26, 27, 28 
and 29, such that the right and left ends of the key holder plate 52 are 
kept in pressed contact with the lower ends of the downward extensions 
24a, 25a of the side walls 24, 25, and such that the keytops 54 project 
out of the rectangular aperture 23. 
Successively, the curved retainer plate 34 is further fastened to the upper 
casing 21 with the fixing screws 35, 36, 37 and 38 threaded to the 
respective downward bosses 30, 31, 32 and 33, in order to assure that the 
key holder plate 52 is held curved, due to elastic deformation thereof, 
exactly to the convex lower end profiles of the downward extensions 24a, 
25a. When the assembly 34, 42, 48 and 52 is secured to the upper casing 21 
with the screws 43-46 and 35-38, the key holder plate 52 is comparatively 
easily curved with the aid of the grooves 59 formed therein, and the 
curved retainer plate 34 serves to hold the printed circuit board 42 and 
the elastomeric member 48 as well as the key holder plte 52, in their 
curved postures. With the key holder plate 52 retained in its curved 
posture as described above, the multiple keys of the same dimension are 
supported by the plate 52 so that the top faces of the keytops 54 define 
an operating surface with is downwardly convexed to a curvature 
substantially identical to that rendered to the key holder plate 52. 
Finally, the lower casing 22 is coupled to the upper casing 21 to form the 
keyboard housing 20. 
As described above in detail, the key holder plate 52 has the annular guide 
portions 56 formed integrally therewith on its upper surface, and the 
plural U-shaped parallel grooves 59 in its lower surface. The integral 
formation of the guide portions 56 eliminates otherwise required cost and 
labor for fixing separate guide portions to a pre-shaped holder plate as 
used in the known keyboard. The provision of the grooves 59 contributes to 
easier shaping of the key holder plate 52 to the convex profile of the 
downward extensions 24a, 25a of the side walls 24, 25, so that the keys 
54, 55 may be disposed with the top faces of the keytops 54 located 
substantially on a surface which is downwardly curved to a convex shape 
corresponding to the curvature of the key holder plate 52, without varying 
the dimensions and/or shapes of the keys according to the rows in which 
they are disposed. Thus, the keyboard constructed according to the 
invention is simple in construction, economical to manufacture and easy to 
operate. 
Further, the use of the sponge member 49 to support the movable electrode 
51 on the inner surface of the top wall 47a of the elastic housing 47, 
undergoes elastic deformation upon depression of the keytop 54, which 
permits perfect contact of the movable electrode 51 with the stationary 
electrodes 50 over the entire areas of their opposite surfaces, even under 
condition that the printed circuit board 42 is curved. Consequently, the 
capacitive switch including the stationary and movable electrodes 50, 51, 
and the keytop and keystem 54, 55, may be operated with increased 
switching reliability. 
While the described embodiment represents the preferred form of a keyboard 
of the present invention, it is to be understood that modifications and 
variations are possible in the light of the foregoing teachings, and 
without departing from the scope of the invention defined in the appended 
claims.