Key switch and keyboard

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a switch mechanism for key-entry operation and, more particularly, to a key-entry switch (hereinafter referred to as a key switch) preferably used for a keyboard incorporated as an input device in electronic equipment. The present invention also relates to a keyboard provided with a plurality of key switches.

2. Description of the Related Art

In the technical field of portable electronic equipment such as notebook-size personal computers or wordprocessors, etc., various techniques have been proposed to facilitate a reduction in height or thickness of the housing of equipment including a keyboard and to improve the portability of the equipment. Particularly, when the height of a keyboard provided with a plurality of key switches is to be reduced, it has been generally required to maintain the stroke of each key switch at a predetermined length to ensure constant operational properties thereof and, simultaneously, to reduce the entire height of the key switch upon both the non-operated (or switched-off) and operated (or pushed-down and switched-on) conditions thereof.

A conventional key switch for use in a relatively thin keyboard with a reduced height generally includes a base, a key top disposed above the base, a pair of link members for supporting the key top above the base and directing the key top in the vertical or up-and-down direction, and a switching mechanism for selectively opening/closing contact points in an electric circuit in accordance with the vertical or up-and-down movement of the key top. The conventional pair of link members has been provided essentially with any one of three types of configurations.

First type pair of link members may be referred to as a gear-link type, wherein the link members are assembled together into a reverse V-shape as seen in a lateral direction and meshed at toothed end regions thereof with each other, each link member being slidably engaged at a first end region thereof with the base and pivotably engaged at the toothed or second end region with the key top (see, e.g., Japanese Unexamined Patent Publication (Kokai) No. 11-3628). Second type pair of link members may be referred to as a pantograph type, wherein the link members are assembled together into an X-shape as seen in a lateral direction and rotatably joined at intersections thereof with each other, each link member being slidably engaged at a first end region thereof with one of the base and the key top and pivotably engaged at a second end region with the other of the base or the key top (see, e.g., Japanese Unexamined Utility Model Publication (Kokai) No. 5-66832). Third type pair of link members may be referred to as a modified pantograph type, wherein the link members are assembled together into an X-shape as seen in a lateral direction and slidably connected at intersections thereof with each other, each link member being slidably engaged at a first end region thereof with the base and pivotably engaged at a second end region with the key top (see, e.g., Japanese Unexamined Patent Publication (Kokai) No. 9-27235).

In the conventional key switch having any one of the above types of link members, the link members are shifted in a mutually interlocked manner, and the key top is thereby allowed to be moved in a parallel displacement in a substantially vertical direction relative to the base, while keeping a predetermined posture of the key top. Once the key top reaches a lowermost position of a vertical or key-entry stroke thereof, the link members are laid in a generally horizontal position under the key top and received inside an opening defined in the base. This arrangement permits the entire height of the key switch to be reduced in both the non-operated and operated conditions while maintaining the key-entry stroke of the key top at a desired length.

In the conventional key switch having the gear-link type pair of link members as described, each link member includes a pair of arms extending generally parallel to each other and a pair of axles formed at the second end region of the link member, i.e., the distal end region of the respective arms, the axles extending outward along the rotation axis of the second end region for pivotable engagement with the key top. Each arm of the link member is further provided with one or more teeth projecting outward from the second end region in a direction generally orthogonal to the rotation axis, the teeth constituting an interlocking element for meshable engagement with the second end region of the counterpart link member.

On the other hand, the key top is provided with two pairs of pivot supports for pivotably supporting the axles of the respective arms of the respective link members. The pivot supports are formed on the inner surface of the key top as separate plate-like projections extending generally parallel to one another. Each pivot support includes a bearing hole for pivotably receiving the axle of each arm of each link member and a slit communicating with the bearing hole. The slit of the pivot support is shaped and dimensioned so as to define an opening smaller than the associated axle of the link member. The slits of four pivot supports extend generally parallel to one another and in a direction generally perpendicular to the inner surface of the key top.

In the assembling process of the abovedescribed key switch, first the link members are arranged so as to engage the first end regions thereof to the base and to mesh the corresponding teeth thereof with each other, and are laid in a generally horizontal position to be received inside the opening of the base. In this state, the link members are positioned at a location substantially identical to a location defined by the lowermost position of key-entry stroke of the key top. Then, the key top is put on the link members so as to bring the respective pivot supports into contact with the associated axles, and is pushed down on the link members. Thereby, the axles are inserted into the slits of the correlate pivot supports under pressure to elastically deform the pivot supports, and are finally press-fitted into the bearing holes in a snap-fit manner. This configuration generally facilitates both the assembling process of the key switch and the construction of a mold used for molding the key top.

In the above conventional structure of the key switch having the gear-link type pair of link members, the base and the link members are typically shaped and dimensioned so that a slight clearance may be defined between the second end region (especially, the distal end of each axle) of each link member and the inner peripheral surface at the opening of the base after the assembling process is completed, so as to ensure the relatively easy press-fitting operation in the assembling process for the respective pivot supports of the key top fitted with the associated axles of the link members. However, such a clearance tends to enable the link members located inside the base opening to be slightly displaced in a horizontal direction, which may result in an incorrect intermesh between the toothed end regions or interlocking elements of the link members located inside the base opening due to an inadvertent mutual horizontal displacement caused between the link members before the key top is fitted to the link members.

If the key top is press-fitted to the incorrectly intermeshed link members as described, problems may arise wherein the tooth or teeth of the toothed end regions of the link members are deformed or damaged, which may affect the key-entry operation or stroke properties of the key switch. Accordingly, it is typically required for the assembling process of the conventional key switch to correct the intermeshed state of the gear-link type pair of link members before the key top is fitted with the link members.

In a typical assembling process of a conventional keyboard including a plurality of key switches having the above-described structure, a large-sized base panel (referred to as, e.g., a switch panel) with a plurality of openings respectively used for the individual key switches is provided, and the plural pairs of link members are inserted into the respective openings in the intermeshed state as described and, in this state, the key tops of the individual key switches are press-fitted to the associated pairs of link members. Therefore, it is necessary to investigate the intermeshed state of the link members of all the key switches and properly correct the probable incorrectly intermeshed state thereof, before the key tops are fitted to the link members. However, such investigation and correction have generally been performed by a manual operation, and thus have required much time and the skill of an operator, which may increase the manufacturing cost of the key switches as well as of the keyboard. Also, a certain careless error in correction may arise when the investigation and correction are repeatedly performed in the assembling process of many keyboards.

Also, in a conventional key switch having any type pair of link members, i.e., the gear-link type pair, the pantograph type pair or the modified pantograph type pair, each link member is pivotably connected through the axles provided on the first or second end region of the link member with either the base or the key top. The axles of each link member are respectively fitted into the bearing holes or grooves of the associated pivot supports provided on the base or the key top. In this structure, the slit communicating with the bearing hole is typically formed in each pivot support so as to ease the press-fitting operation of the axle and simplify the construction of a mold for the key top, as already described. However, the slit may facilitate the generation of backlash of the axle in the bearing hole, which may cause problems of the fluctuation or wobble of the key top and the resultant noise during the key-entry operation. If the pivotable engagement between the axle and the bearing hole is designed to be excessively tight to solve the above problems, the key-entry operation properties may be deteriorated.

Moreover, in the conventional key switch having any type pair of link members, i.e., the gear-link type pair, the pantograph type pair or the modified pantograph type pair, the key top is continuously applied with a biasing force by an elastic member in a vertical upward direction away from the base. In the key-entry operation, the key top is pushed downward against the upward biasing force of the elastic member, whereby the electric contact points of the switching mechanism disposed beneath the key top are closed. Therefore, when a downward pushing force to the key top is released, the key top is moved back to an initial or uppermost position in the key-entry stroke by the biasing force of the elastic member under the guiding action of the link member pair. In this respect, the uppermost position of the key top is determined at the instant when the axles provided to project from the slidable end region of each link member are abutted to and stopped by the walls of the associated slide supports, slidably supporting these axles, formed on the base or the key top. Consequently, at the time when the key top reaches the uppermost position, a collision noise is generated between the axles on the slidable end region of each link member and the walls of the associated slide supports on the base or the key top. It is desired to reduce this type of collision noise generated between some components in the key switch as much as possible, in consideration of the use of the keyboard in situations demanding quietness.

Incidentally, in the assembling process of the conventional keyboard, the key top of each key switch is often printed with desired one or more signs, such as letters or symbols, after the key tops of all the key switches are fitted to the associated link member pairs. In the case where the key switches incorporated in the keyboard include the key tops having various shapes and/or colors, it is necessary to manage the stock of the various types of precursor or non-printed key tops according to the shapes and/or colors thereof, preparing for the assembling process of the keyboard, and to supply the precursor key tops to assembling lines while identifying the required shapes and/or colors thereof. Moreover, in the case where the key tops formed from various materials should be stored, for the purpose of, e.g., allowing respective key tops to be subjected to different printing steps such as laser printing, pad printing, and so on, it is necessary to manage the stock of the precursor key tops according to the materials thereof in addition to the shapes and/or colors. However, it is ordinarily difficult to visually identify the key tops having different materials but identical shapes and colors. If the key tops having different materials but identical shapes and colors are accidentally or carelessly mixed in a storage and/or supply stage, the assembling process of the keyboard may suffer due to, e.g., a poor printing step wherein the key top made of a material suitable for pad printing is subjected to laser printing.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a key switch including a key top adaptable for a key-entry operation, in which, in an assembling process, a gear-link type pair of link members can be relatively easily set in an accurate intermeshed state and the possibility of inaccurate intermeshing can be reduced or eliminated, before the key top is fitted with the link members, so that the assembling process of the key switch and of a keyboard can be simplified and the manufacturing cost thereof can be reduced.

It is another object of the present invention to provide a key switch including a key top adaptable for a key-entry operation, in which the backlash in a pair of link members generated due to a clearance defined between certain components constituting pivotable joints of the link members to a base or the key top can be restrained, without deteriorating key-entry operation properties, so that the fluctuation or wobble of the key top and the resultant noise, which may be generated during the key-entry operation, can be reduced or eliminated.

It is yet another object of the present invention to provide a key switch including a key top adaptable for a key-entry operation, in which, in the key-entry operation of the key top, a collision noise, generated between certain components at the instant when the key top reaches an initial uppermost position in a key-entry stroke, can be reduced or eliminated.

It is a further object of the present invention to provide a key switch including a key top adaptable for a key-entry operation, which can make it possible to precisely and relatively easily identify various key tops made of different materials, so that the productivity of a keyboard incorporating therein a plurality of key switches can be improved.

It is an yet further object of the present invention to provide a keyboard incorporating therein a plurality of key switches, which can provide good assembling properties and superior operability of key switches.

In accordance with the present invention, there is provided a key switch comprising a base; a key top arranged above the base; a pair of link members interlocked with each other to support the key top above the base and direct the key top in a vertical direction, each of the link members including an engagable region engaged with the key top; and a switching mechanism capable of opening and closing an electric circuit in connection with a vertical movement of the key top; wherein the base is provided with an inner peripheral surface defining an opening capable of receiving the pair of link members, and a protruding wall part provided on the inner peripheral surface to locally reduce a clearance defined between the inner peripheral surface and the engagable region of each of the link members when the link members are received in the opening.

In one aspect of the invention, each of the link members may be provided at the engagable region with an axle projecting outward, the axle being pivotably connected with the key top, and the base may be provided with a plurality of protruding wall parts on the inner peripheral surface, each of the protruding wall parts being positioned so as to oppositely and closely face the axle of each link member when the key top is located at a lowermost position of a key-entry stroke.

In this arrangement, each of the protruding wall parts may have a cross-sectional shape smaller than that of the axle of associated one of the link members.

It is preferred that the protruding wall part has a uniform height measured from the inner peripheral surface.

It is also preferred that the protruding wall part has a gradually increased height measured from the inner peripheral surface as seen in a direction away from the key top.

The present invention also provides a key switch comprising: a base; a key top arranged above the base; a pair of link members interlocked to each other to support the key top above the base and direct the key top in a vertical direction, each of the link members including an engagable region engaged with one of the base and the key top; and a switching mechanism capable of opening and closing an electric circuit in connection with a vertical movement of the key top; wherein each of the link members is locally abutted in the engagable region onto one of the base and the key top under an elastic restoring force generated relatively in each link member and the base or the key top with which the link member is engaged.

In one aspect of the invention, the key top may be provided with pivot supports and abutting plates arranged respectively adjacent to the pivot supports, each of the link members may be provided at the engagable region with an axle projecting outward, the axle being pivotably connected with one of the pivot supports of the key top, and the axle may be provided with an end surface including an apex abutted to one of the abutting plates arranged adjacent to one of the pivot supports with which the axle is pivotably connected.

In this arrangement, the axle may be abutted at the apex to one of the abutting plates under a certain pressure caused due to an elastic restoring force generated relatively in one of the link members and an associated one of the abutting plates.

In another aspect of the invention, the base may be provided with slide supports, each of the link members may be provided at the engagable region with an axle projecting outward, the axle being slidably connected with one of the slide supports of the base, and the axle may be provided with an end surface including an apex abutted to one of the slide supports with which the axle is slidably connected.

In a yet another aspect of the invention, the base may be provided with slide supports, each of the link members may be provided at the engagable region with an axle projecting outward, the axle being slidably connected with one of the slide supports of the base, and the axle may be provided with an annular rib circumferentially extending along a part of an axial length of the axle, the annular rib being abutted to one of the slide supports with which the axle is slidably connected.

In a further aspect of the invention, the key top may be provided with pivot supports, each of the link members may be provided at the engagable region with an axle projecting outward, the axle being pivotably connected with one of the pivot supports of the key top, and each of the link members may be provided with a textured surface located around a proximal end of the axle, the textured surface being abutted to one of the pivot supports with which the axle is pivotably connected.

In a yet further aspect of the invention, the key top may be provided with pivot supports, each of the link members may be provided at the engagable region with an axle projecting outward, the axle being pivotably connected with one of the pivot supports of the key top, and each of the link members may be provided with a protuberance located adjacent to a proximal end of the axle, the protuberance being abutted to one of the pivot supports with which the axle is pivotably connected.

The present invention also provides a key switch comprising a base; a key top arranged above the base; a pair of link members interlocked to each other to support the key top above the base and direct the key top in a vertical direction, each of the link members including an engagable region slidably engaged with one of the base and the key top; a switching mechanism capable of opening and closing an electric circuit in connection with a vertical movement of the key top; and a buffering portion for gradually braking a sliding motion of the engagable region of each of the link members relative to one of the base and the key top caused in accordance with the vertical movement of the key top just before the key top reaches an uppermost position of a key-entry stroke.

In one aspect of the invention, the buffering portion may comprise a buffer plate extending from the base, the buffer plate being elastically deflected by one of the link members colliding with the buffer plate just before the key top reaches the uppermost position.

In another aspect of the invention, the buffering portion may comprise a slanted wall surface formed on the base to face the engagable region of one of the link members, the slanted wall surface exerting a contact pressure against one of the link members colliding with the slanted wall surface just before the key top reaches the uppermost position.

In a further aspect of the invention, the key switch may further comprise a sheet member arranged beneath the base, and the buffering portion may comprise a high-friction area formed on the sheet member, the high-friction area exerting a friction force against one of the link members running onto the high-friction area just before the key top reaches the uppermost position.

The present invention also provides a key switch comprising a key top having an operating surface for a key-entry operation and supported to be directed in a vertical direction above a base; the key top being provided with an identifying portion for identification of an attribute of the key top.

In one aspect of the invention, the identifying portion may comprise a plurality of elements having various features including at least one of numbers, locations, shapes and dimensions.

In this arrangement, the key top may further include a brim surface adjacent to the operating surface, and the elements may be formed as recesses on the brim surface.

The present invention also provides a keyboard comprising a plurality of key switches, each of the key switches having any one of the above-described features.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent from the following description of preferred embodiments in connection with the accompanying drawings, in which:

FIG. 1

is an exploded perspective view showing a key switch according to a first embodiment of the present invention;

FIG. 2

is a top plan view of the key switch of

FIG. 1

in a partially assembled state before a key top is fitted;

FIG. 3

is a bottom view of a key top used in the key switch of

FIG. 1

;

FIG. 4

is a vertical sectional view taken along line IV—IV of

FIG. 2

;

FIG. 5A

is a sectional side view showing a projecting wall portion provided in the key switch of

FIG. 1

;

FIG. 5B

is a sectional side view showing a modified projecting wall portion;

FIG. 6

is a partially cut-away perspective view showing a keyboard according to one embodiment of the present invention;

FIG. 7

is a sectional side view showing a key switch according to a second embodiment of the present invention;

FIG. 8

is an enlarged view showing a part of a key top used in the key switch of

FIG. 7

;

FIG. 9

is an enlarged view showing a part of a modified link member usable in the key switch according to the second embodiment;

FIG. 10

is an enlarged view showing a part of another modified link member usable in the key switch according to the second embodiment;

FIG. 11

is an enlarged view showing a part of a further modified link member usable in the key switch according to the second embodiment;

FIG. 12

is an enlarged view showing a part of yet further modified link member and pivot support, usable in the key switch according to the second embodiment;

FIG. 13

is a sectional view showing the link member and the pivot support of

FIG. 12

in an assembled state;

FIG. 14

is a vertical sectional view showing a key switch according to a third embodiment of the present invention in an assembled state;

FIG. 15

is a perspective view showing a base used in the key switch of

FIG. 14

;

FIGS. 16A and 16B

are enlarged partial sectional views respectively showing a function of a buffering portion provided in the key switch of

FIG. 14

at positions corresponding respectively to the lowermost and uppermost positions of a key top in a key-entry stroke;

FIG. 17

is a perspective view showing a part of a modified base usable in the key switch according to the third embodiment as seen from the bottom side;

FIGS. 18A and 18B

are enlarged partial bottom views respectively showing a function of a buffering portion provided in the base of

FIG. 17

at positions corresponding respectively to the lowermost and uppermost positions of a key top in a key-entry stroke;

FIG. 19

is a plan view showing a part of a modified link member usable with the base of

FIG. 17

;

FIG. 20

is a perspective view showing a part of another modified base usable in the key switch according to the third embodiment;

FIGS. 21A and 21B

are enlarged partial sectional views respectively showing a function of a buffering portion provided in the base of

FIG. 20

at positions corresponding respectively to the midway and uppermost positions of a key top in a key-entry stroke;

FIG. 22

is a perspective view showing a part of a further modified base usable in the key switch according to the third embodiment;

FIG. 23

is a perspective view showing a part of a yet further modified base usable in the key switch according to the third embodiment;

FIG. 24

is a perspective view showing a modified sheet member usable in the key switch according to the third embodiment;

FIGS. 25A and 25B

are enlarged partial sectional views respectively showing a function of a buffering portion provided in the sheet member of

FIG. 24

at positions corresponding respectively to the lowermost and uppermost positions of a key top in a key-entry stroke;

FIG. 26

is a bottom view showing a key top used in a key switch according to a fourth embodiment of the present invention;

FIG. 27

is a side view showing a key top of

FIG. 26

;

FIG. 28A

is a side view showing a modified key top having one identifying element;

FIG. 28B

is a side view showing another modified key top having two identifying elements with different depths; and

FIG. 29

is an enlarged partial bottom view showing a further modified key top.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, in which the same or similar components are denoted by common reference numerals,

FIG. 1

is an exploded perspective view showing a key switch

10

according to a first embodiment of the present invention,

FIG. 2

is a top plan view of the key switch

10

shown in a partially assembled state before a key top is fitted, and

FIG. 3

is a bottom view of a key top used in the key switch

10

. The key switch

10

includes a base

12

, a key top

14

disposed movably in a vertical or up-and-down direction on a major surface

12

a

of the base

12

, a pair of link members

16

for supporting the key top

14

above the base

12

and directing or guiding the key top

14

in the vertical direction, and a switching mechanism

18

capable of opening and closing contact points of an electric circuit in accordance with the vertical movement of the key top

14

.

The base

12

is a frame-like member having a generally rectangular center opening

20

arranged to be covered by the key top

14

. The base

12

is provided, along a pair of opposed inner peripheral surfaces

12

b

thereof defining the center opening

20

, with two pairs of slide supports

22

, one pair being spaced from the other pair in a link-slide direction as described later (i.e., leftward and rightward directions in FIG.

2

). Each of the slide supports

22

includes a wall portion extending in an L-shape and projecting from the major surface

12

a

and the inner peripheral surface

12

b

of the base

12

, and a guide groove

22

a

formed inside the wall portion and extending generally parallel to the major surface

12

a.

The slide supports

22

in each pair are positioned on the opposed inner surfaces

12

b

of the base

12

in such a manner that the guide grooves

22

a

of respective slide supports

22

are disposed at locations corresponding to each other. Further, the slide supports

22

in two pairs, disposed on the respective same sides, are aligned with each other in the link-slide direction along the corresponding inner peripheral surfaces

12

b

of the base

12

. Each slide support

22

slidably supports a first end region of each link member

16

, as described later.

The key top

14

is a dish-like member having a generally rectangular profile, and has an operating surface

14

a

adapted to be pressed by an operator's finger. The key top

14

is provided, on an inner surface

14

b

thereof opposite to the operating surface

14

a

, with two pairs of pivot supports

24

, one pair being spaced from the other pair in the link-slide direction (i.e., leftward and rightward directions in FIG.

3

). Each of the pivot supports

24

is formed as a small plate uprightly projecting from the inner surface

14

b

of the key top

14

, and includes a bearing hole

24

a

penetrating through the thickness of the plate and a slit

24

b

extending generally perpendicularly to the inner surface

14

b

to communicate with the bearing hole

24

a.

The pivot supports

24

in each pair are positioned on the inner surface

14

b

of the key top

14

, in such a manner that the pivot supports

24

are spaced from each other at a distance allowing the end regions of arms

26

,

28

of each link member

16

to be interposed therebetween as described later, and that the bearing holes

24

a

of respective pivot supports

24

are axially aligned with each other. Further, the pivot supports

24

in two pairs, disposed on the respective same sides, are aligned with each other in the link-slide direction on the inner surface

14

b

of the key top

14

. Each pivot support

24

pivotably supports a second end region of each link member

16

, as described later.

The link members

16

have shapes and dimensions substantially identical to each other. The link members

16

are assembled together into a reverse V-shape as seen in a lateral direction and meshed at toothed end regions thereof with each other, to form a gear-link type pair. Each of the link members

16

is slidably engaged or connected at a first, engagable end region thereof with the base

12

and pivotably engaged or connected at the toothed or second, engagable end region with the key top

14

.

Each link member

16

includes a pair of arms

26

,

28

extending generally parallel to each other and a connecting portion

30

integrally connecting the arms

26

,

28

with each other. In the illustrated embodiment, the first end region of the link member

16

includes the connecting portion

30

and the thicker proximal end areas of the arms

26

,

28

adjacent to the connecting portion

30

, while the second end region includes the thinner distal end or parallel-length areas of the arms

26

,

28

opposite to the proximal end areas.

A pair of axles

32

are formed in the first end region of each link member

16

in such a manner that the respective axles

32

mutually coaxially project on the opposite sides of the link member

16

and face away from the connecting portion

30

. Also, a pair of axles

34

are formed in the second end region of each link member

16

in such a manner that the respective axles

34

mutually coaxially project on the opposite sides of the link member

16

or arms

26

,

28

and extend parallel to the respective axles

32

in the same directions as the latter. Further, in the second end region of each link member

16

, a single tooth

36

is formed on the first arm

26

near the axle

34

so as to project outward from the distal end face of the arm

26

, while double teeth

38

are formed on the second arm

28

near the axle

34

so as to project outward from the distal end face of the arm

28

.

The axles

32

formed in the first end region of the link member

16

are slidably fitted or received in the respective guide grooves

22

a

of the associated slide supports

22

on the base

12

, and the axles

34

formed in the second end region of the link member

16

are pivotably fitted or received in the respective bearing holes

24

a

of the associated pivot supports

24

on the key top

14

, whereby each link member

16

is arranged between the base

12

and the key top

14

in such a manner as to be pivotable about the axles

34

. In this situation, the link members

16

are joined with each other through an interlocking structure wherein the single tooth

36

of the first arm

26

of each link member

16

is meshed with the double teeth

38

of the second arm

28

of the counterpart link member

16

. As a result, the link members

16

can rotate about pivot axes

40

defined by respective pairs of axles

34

on the arms

26

,

28

in a mutually interlocked manner.

Thus, when the link members

16

synchronously rotate about respective pivot axes

40

in opposite direction and the axles

32

of the link members

16

slide horizontally along the base

12

, the key top

14

is subjected to a parallel displacement in a substantially vertical direction relative to the base

12

, while keeping a predetermined, generally horizontal posture of the key top

14

wherein the operating surface

14

a

is substantially parallel to the major surface

12

a

of the base

12

. The uppermost or initial position of key top

14

in a vertical or key-entry stroke thereof is determined at the instant when the interlocked sliding motion of the axles

32

of the respective link members

16

toward each other is stopped by the walls of the associated slide supports

22

defining the guide grooves

22

a

formed on the base

12

. As the key top

14

moves downward from this uppermost position, the axles

32

of the respective link members

16

slidingly move away from each other in a direction generally perpendicular to the vertical direction. Once the key top

14

reaches a lowermost position of the key-entry stroke, the link members

16

are housed inside the inner surface

14

b

of the key top

14

, and at least partially received in the center opening

20

of the base

12

(FIG.

2

).

As shown in

FIGS. 2 and 4

, the base

12

is provided, on the opposed inner peripheral surfaces

12

b

defining the center opening

20

, with two pairs of protruding wall parts

42

locally projecting from the inner surfaces

12

b

into the center opening

20

with each pair being arranged on each inner surface

12

b

. The protruding wall parts

42

are positioned and dimensioned so as to oppositely and closely face the axial end surfaces of the axles

34

formed in the second end regions of the respective link members

16

, at the time when the key top

14

is located at the lowermost position of the key-entry stroke and the link members

16

are received in the center opening

20

of the base

12

. Thus, a clearance defined between each inner surface

12

b

of the base

12

, defining the center opening

20

, and the axle

34

on each arm

26

,

28

of each link member

16

, opposing the inner surface, is locally reduced at the position of each protruding wall part

42

, during the time when the link members

16

are received in the center opening

20

of the base

12

.

The switching mechanism

18

of the key switch

10

comprises a sheet-like switch

48

(hereinafter referred to as a membrane switch

48

) having a pair of sheet substrate

46

respectively carrying contacts

44

(only one contact

44

is shown in

FIG. 1

) to oppositely face the latter to each other, and an actuating member

50

disposed between the key top

14

and the membrane switch

48

, which operates to close the contacts

44

as the key top

14

moves downward. A spacer

52

(

FIG. 4

) is interposed between the sheet substrates

46

of the membrane switch

48

so as to define a predetermined distance between the sheet substrates

46

and maintain the contacts

44

in an open state.

The sheet substrates

46

of the membrane switch

48

have well-known construction of flexible printed circuit boards, and the contacts

44

capable of contacting with each other are provided on the surface of the film substrates of the circuit boards. The sheet substrates

46

are supported beneath the base

12

on a supporting plate

54

, and the contacts

44

are positioned generally centrally in the center opening

20

of the base

12

. The actuating member

50

is a dome-shaped elastic member integrally formed from a rubber material, and is arranged in the center opening

20

of the base

12

with the dome top

50

a

of the actuating member being oriented toward the key top

14

. When no force is applied, the dome top

50

a

of the actuating member

50

is spaced upward from the upper sheet substrate

46

. The actuating member

50

is provided on the inner surface of the dome top

50

a

with a column-shaped pusher (not shown) extending toward the sheet substrates

46

.

The contacts

44

carried on the sheet substrates

46

are normally held open by the inherent stiffness of each sheet substrate

46

via the spacer

52

, and positioned beneath the pusher of the actuating member

50

. When the external force is applied on the dome top

50

a

of the actuating member

50

in a direction toward the sheet substrates

46

, the actuating member

50

is elastically deformed, and the pusher thereof presses the upper sheet substrate

46

from the outside thereof, so as to close the contacts

44

. In the illustrated embodiment, the actuating member

50

is fixedly connected at the dome bottom open-end

50

b

thereof with a flexible sheet member

56

disposed between the base

12

and the upper sheet substrate

46

. Alternatively, without using the sheet member

56

, the actuating member

50

may be directly connected with the upper sheet substrate

46

.

When no external force is applied to the key top

14

in the key switch

10

, the actuating member

50

of the switching mechanism

18

urges or biases the key top

14

and supports, on the outer surface of the dome top

50

a

, the key top

14

in the uppermost position spaced vertically away from the base

12

. During this condition, the membrane switch

48

is in a state where the contacts

44

are open. When the key top

14

is pushed down by a key-entry operation, the actuating member

50

is deformed while exerting an upward elastic biasing force to the key top

14

, and presses the upper sheet substrate

46

from the out side thereof, just before the key top

14

reaches the lowermost position, so as to close the contacts

44

. When the pushing-down force to the key top

14

is released, the actuating member

50

elastically recovers the initial shape to return the key top

14

to the initial uppermost position, and thereby the upper sheet substrate

46

restores the original shape to open the contacts

44

.

In the assembling process of the key switch

10

having the above-described structure, the membrane switch

48

, the actuating member

50

and the base

12

are first laid or placed on the support plate

54

in the above-described positional correlation. Then, the link members

16

are arranged so as to engage the axles

32

in the first end regions thereof to the associated slide supports

22

of the base

12

and to mesh the tooth

36

and the teeth

38

in the second end regions thereof with the counterpart tooth and teeth, and are laid in a generally horizontal position to be received inside the center opening

20

of the base

12

(FIG.

2

). In this state, the axles

34

in the second end region of each link member

16

closely and oppositely face, at the axial end surfaces thereof, to the protruding wall parts

42

provided on the respective inner peripheral surfaces

12

b

of the base

12

. During this condition, where the link members

16

are located at a position corresponding to the lowermost position of the key-entry stroke of the key top

14

, the key top

14

is put on the link members

16

so as to bring the respective pivot supports

24

into contact with the associated axles

34

, and is pushed down on the link members

16

. Thereby, the axles

34

are inserted into the slits

24

b

of the associated pivot supports

24

under pressure to elastically deform the pivot supports

24

, and are finally press-fitted into the bearing holes

24

a

in a snap-fit manner.

In the key switch

10

, the clearance defined between the axle

34

on each arm

26

,

28

of each link member

16

, laid in a generally horizontal position in the center opening

20

of the base

12

, and each inner surface

12

b

of the base

12

, opposing the axle

34

, is locally reduced at the position of each protruding wall part

42

, as already described. Accordingly, if the tooth

36

and the teeth

38

of the link members

16

, as interlocking elements, are incorrectly intermeshed with each other, the protruding wall parts

42

interfere with the horizontal positioning of the link members

16

in the center opening

20

of the base

12

. On the other hand, once the link members

16

are laid in the horizontal position it the center opening

20

of the base

12

, the link members

16

are restricted in the center opening

20

so as to be hardly displaced in the axial direction of the axles

34

. As a result, the tooth

36

and the teeth

38

of the link members

16

are maintained in a correctly intermeshed state.

Moreover, each protruding wall part

42

is shaped or configured to oppositely face each axle

34

of each link member

16

in a local manner on each inner surface

12

b

of the base

12

, so that the wall part

42

is prevented from being an obstacle to each pivot support

24

of the key top

14

when the pivot support

24

is pushed down on the associated axle

34

. Accordingly, the relatively easy press-fitting operation for fitting the respective pivot supports

24

of the key top

14

with the associated axles

34

of the link members

16

can be obtained, to a certain extent similar to the conventional structure having no protruding wall part

42

. In this manner, the tooth

36

and the teeth

38

of the link members

16

are surely and relatively easily prevented from causing the incorrect intermesh therebetween, before the key top

14

is fitted to the link members

16

. Therefore, it is possible to fit the key top

14

to the link members

16

correctly intermeshed with each other. The key switch

10

thus assembled can achieve good touch during key-entry operation and superior stroke properties of the key top

14

, with a proper interlocking action and a stable guiding function of the link members

16

.

To surely prevent the protruding wall parts

42

of the base

12

from being an obstacle to the pivot supports

24

of the key top

14

, it is desirable to form each protruding wall part

42

in such a manner that the cross-sectional shape of each wall part

42

is smaller than that of each axle

34

as taken along a plane orthogonal to the axis

40

, as shown in FIG.

2

. The protruding wall part

42

may have any shape, such as a prism (FIG.

4

), a cylinder (FIG.

1

), and so on. Also, the protruding wall part

42

may have a uniform height or thickness (

FIG. 5A

) measured from the inner peripheral surface

12

b

. Alternatively, the protruding wall part

42

may have a gradually increased height or thickness (

FIG. 5B

) measured from the inner peripheral surface as seen in a direction away from the key top

14

. The protruding wall part

42

with such a gradually increased height can smoothly guide the pivot support

24

of the key top

14

along the tapered surface

42

a

of the wall part

42

into the center opening

20

. Thus, even if the protruding wall part

42

is formed larger than the axle

34

to be, e.g., entirely on the inner peripheral surface

12

b

, the wall part

42

is surely prevented from being an obstacle to the pivot support

24

.

FIG. 6

shows a keyboard

60

, according to an embodiment of the present invention, that incorporates a plurality of key switches

10

in arrays, each of which has an above-described structure. In the keyboard

60

, the base

12

, the membrane switch

48

, the support plate

54

and the sheet member

56

fixed to the actuating member

50

, provided in each key switch

10

described above, are formed as a large base

12

′ with plural openings

20

′, a large membrane switch

48

′, a large support plate

54

′ and a large sheet member

56

′ fixed to plural actuating members

50

, which are commonly used for all the key switches

10

incorporated in the keyboard

60

. The link members

16

of each key switch

10

are omitted from the drawing. Also, the key switch

10

and the keyboard

60

, according to the present invention, may have various types of switching mechanism

18

, other than the mechanism

18

having the dome-shaped actuating member

50

as described above.

In the assembling process of the keyboard

60

, the link members

16

of the individual key switches

10

are laid in the respective openings

20

′ of the base

12

′ in such a manner as already described, and in this condition, the key tops

14

of all the key switches

10

are put on and press-fitted to the associated pair of link members

16

in a certain order. In this situation, the respective pairs of link members

16

of all the key switches

10

are relatively easily maintained in a correctly intermeshed state without requiring the skill of the operator, as already described. Consequently, it is no longer necessary to investigate and correct the intermeshing state, which can prevent an increase in the manufacturing cost of the keyboard

60

, and therefore, it is possible to provide the keyboard

60

having good assembling properties and superior operability.

FIG. 7

shows a key switch

70

according to a second embodiment of the present invention. The key switch

70

has a structure substantially identical to that of the key switch

10

shown in

FIG. 1

, except for the structure of a key top

72

and link members

74

, so that corresponding components are denoted by the same reference numerals and the description thereof is not repeated. That is, the key switch

70

includes a base

12

, a key top

72

disposed movably in a vertical or up-and-down direction on the major surface

12

a

of the base

12

, a pair of link members

74

(only one link member

74

is shown in

FIG. 7

) for supporting the key top

72

above the base

12

and directing or guiding the key top

72

in the vertical direction, and a switching mechanism

18

capable of opening and closing contact points of an electric circuit in accordance with the vertical movement of the key top

72

.

The key top

72

is a dish-like member having a generally rectangular profile, and has an operating surface

72

a

adapted to be pressed by an operator's finger. The key top

72

is provided, on an inner surface

72

b

thereof opposite to the operating surface