Bistable mechanism for collapsing and elevating a keyboard in a portable computer

A notebook computer is provided with a collapsible keyboard in which a dome sheet with elastomeric key return dome members thereon is horizontally shiftable through elevation and retraction strokes to respectively shift the keys between elevated operating positions in which the domes underlie and support the keys, and retracted positions in which the domes are shifted away from their key-underlying positions. A linkage member interconnected between the computer lid and a drive bar on the dome sheet creates initial triggering movements of the dome sheet through its elevation and retraction strokes in response to opening and closing of the lid. In response to these lid-created triggering movements of the dome sheet, a bistable spring structure connected to the drive bar takes control of the dome sheet and drives it through the balance of the stroke and then releasably retains the fully shifted dome sheet in the resulting stroke end position thereof.

CROSS-REFERENCE TO RELATED APPLICATION 
This application discloses subject matter similar to that illustrated and 
described in U.S. Pat. No. 5,602,715 to Lempicki et al which is hereby 
incorporated by reference herein in its entirety. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to electronic devices and, in a 
preferred embodiment thereof, more particularly relates to keyboard 
structures for portable computers such as notebook computers. 
2. Description of Related Art 
In recent years the notebook computer has made considerable gains in both 
popularity and technical sophistication. One factor contributing to the 
increasing popularity of the notebook computer is its ever decreasing size 
and weight, a factor arising from the ability to fabricate various 
components of the computer in smaller and smaller sizes while, in many 
instances, increasing the power and/or operating speed of such components. 
One continuing challenge in the design of notebook computers, however, is 
the keyboard structure. This design challenge arises from two conflicting 
design goals--the desire to even further reduce the size of the keyboard 
structure, and the desirability of having the notebook computer emulate as 
closely as possible the size and typing "feel" of a desktop computer 
keyboard. 
There are, of course, two dimensional factors which may be varied to reduce 
the size of a notebook computer keyboard structure--its horizontal 
dimensions (i.e., its length and width), and its vertical or thickness 
dimension. The horizontal dimensions of the keyboard are governed by the 
number, size, and relative spacing of the manually depressible key cap 
portions of the keyboard, and various reductions in these three 
dimensional factors may be utilized to reduce the overall length and/or 
width of the keyboard. However, as will be readily appreciated, a 
reduction in these three configurational aspects to gain a keyboard size 
reduction correspondingly lessens the similarity of the notebook computer 
keyboard in appearance, key arrangement and typing feel to its desktop 
counterpart. 
Similar restraints are also presented when attempts are made to reduce the 
overall thickness of a notebook computer keyboard. One possibility which 
has been investigated and attempted is to simply reduce the keystroke 
distance in the notebook computer keyboard compared to its desktop 
counterpart. Using this design technique, the overall thickness of the 
notebook computer in its closed storage and transport orientation may be 
correspondingly reduced. However, this thickness reduction in the overall 
notebook computer, achieved by reducing the keyboard keystroke distance, 
creates what many users consider to be an undesirable typing "feel" 
difference compared to the longer keystroke distance typically found in a 
larger desktop computer keyboard. 
Illustrated and described in U.S. Pat. No. 5,602,715 to Lempicki et al, 
which has been incorporated herein by reference, is a notebook computer 
which provides a useful thickness reduction in the closed computer without 
a corresponding reduction in the operative keystroke distance of the 
keyboard. This very desirable thickness reduction is achieved in the 
notebook computer illustrated and described in this patent by providing 
the computer with a collapsible keyboard. 
The keys in this collapsible keyboard are supported on scissored linkage 
arm assemblies. In response to closing of the computer lid housing, 
resilient key return dome portions of the keyboard are shifted away from 
their normal underlying relationships with the keys, and the scissored 
linkage arm assemblies and keys are forcibly retracted to a storage and 
transport orientation in which the overall thickness of the keyboard 
structure is reduced by an amount essentially equal to the stroke distance 
of the keys. 
When the lid is subsequently opened, the key return domes are horizontally 
shifted back to their normal underlying relationships with the keys, and 
the keys and scissored linkage arm assemblies are forced outwardly by the 
return spring portions to their operating orientations above the resilient 
key return domes. 
The key return domes are carried on the top side of a plastic dome sheet 
which underlies a monoblock structure upon which the keys are movably 
supported by their scissored linkage arm assemblies, with the dome sheet 
defining the top layer of a multi-layer signal pad structure. The dome 
sheet is shifted along the underside of the monoblock structure to cause 
the domes to cammingly engage portions of the scissored linkage arm 
assemblies and elevate the keys from their retracted storage and transport 
positions to their elevated operating positions. 
While the collapsible notebook computer keyboard illustrated and described 
in U.S. Pat. No. 5,602,715 provides a useful reduction in the keyboard 
thickness when the keys are retracted to their storage and transport 
orientations, the keyboard structure carries with it the following three 
disadvantages. 
First, the assembly tolerance compensation between the keyboard and the lid 
structure which creates the requisite shifting of the dome sheet is 
incorporated in the keyboard and requires that the keyboard achieve its 
collapsed or retracted position and hold down the keys within a dome sheet 
translation range of about 5.0 to 6.0 mm. This requirement has proven 
difficult to meet due to the small space available under the key cap 
members. 
Second, an elongated leaf spring member is used to provide the force on the 
dome sheet to elevate the keys when the computer lid is opened. The 
oppositely directed force exerted on the dome sheet to collapse the keys 
is created by two beak-shaped protrusions on the computer lid housing. 
When the computer lid is closed, and the keys are collapsed, these lid 
protrusions keep the sliding dome sheet bar under tension and maintain the 
leaf spring under compression. These forces place plastic parts under 
stress for long periods of time and under the many different environmental 
extremes to which the computer is exposed during transport and storage. 
This situation increases the risk of product reliability problems due to 
spring fatigue and stressed or broken plastic parts. 
Third, in the sliding dome sheet collapsible keyboard design in U.S. Pat. 
No. 5,602,715 the sliding bar attached to the dome sheet must extend above 
the keyboard and under the edge of the computer's lid in order to be 
operatively engaged by the lid drive beaks during closure. This extension 
of the keyboard parts adds size and weight to the keyboard, limits the 
assembly options for securing the keyboard in the computer, and may be 
less appealing from an aesthetic standpoint than a design which more 
discreetly conceals the mechanism which collapses and elevates the keys. 
It can thus be seen from the foregoing that it would be desirable to 
provide a portable computer having incorporated therein an improved 
collapsible keyboard, of the type generally described above, which 
eliminates or at least substantially alleviates these disadvantages. It is 
accordingly an object of the present invention to provide a portable 
computer with such an improved collapsible keyboard incorporated therein. 
SUMMARY OF THE INVENTION 
In carrying out principles of the present invention, in accordance with a 
preferred embodiment thereof, an electronic device, representatively a 
portable notebook type computer, is provided with an improved collapsible 
keyboard in which spring forces exerted on the key shifting portion of the 
keyboard during prolonged storage and use conditions of the computer are 
substantially reduced, with the manual lid opening and closing forces 
being the primary forces utilized to elevate and collapse the keys. 
The portable computer representatively comprises a base housing, and a lid 
portion secured to the base housing for pivotal movement relative thereto 
between open and closed positions. 
In a preferred embodiment thereof the improved collapsible keyboard 
incorporated in the portable computer is carried by the base housing and 
includes a plurality of keys supported for movement between elevated and 
retracted positions, and shifting means operative to (1) shift the keys 
from their retracted positions to their elevated positions and (2) permit 
the keys to move from their elevated positions to their retracted 
positions in response to movement of the shifting means respectively 
through (1) an elevation stroke and (2) a retraction stroke. 
Representatively, the shifting means include a slidably supported dome 
sheet upon one side of which a spaced series of elastomeric key return 
domes are mounted. When the dome sheet is shifted through its elevation 
stroke, the domes are forced into an underlying supporting relationship 
with the retracted keys in a manner moving them to their elevated 
positions. When the dome sheet is shifted through its retraction stroke, 
the domes are shifted horizontally away from their underlying 
relationships with their associated keys to permit the previously elevated 
keys to return to their retracted positions. 
Triggering means are provided and are operative to move the shifting means 
through initial portions of their elevation and retraction strokes in 
respective response to movement of the lid portion toward its open and 
closed positions thereof. The triggering means preferably comprise a 
linkage structure connected to the shifting means and drivably engageable 
by the lid portion only during an initial portion of its opening movement 
and a final portion of its closing movement. 
In a preferred embodiment thereof, the linkage structure includes a striker 
member carried by the computer lid portion, a pivotally supported lever 
member having first and second differently sloped ramped surfaces 
respectively engageable by the striker member as the lid housing is being 
opened and closed to cause pivotal movement of the lever member in 
opposite directions, and a drive member interconnected between the 
shifting means and the lever member and being translatable in response to 
rotation of the lever member. 
The computer base housing has a front side, and the elevation stroke of the 
shifting means may be either (1) forwardly directed, with the retraction 
stroke being rearwardly directed, of (2) rearwardly directed, with the 
retraction stroke being forwardly directed. Two linkage structure versions 
are provided to accommodate these two relative elevation/retraction stroke 
directional relationships. 
The portable computer also comprises final drive means operative to move 
the shifting means through final portions of their elevation and 
retraction strokes in respective response to movement of the shifting 
means by the triggering means through the aforementioned initial portions 
of the elevation and retraction strokes. 
The final drive means preferably include a bistable spring structure 
drivingly connected to the shifting means and operative to move the 
shifting means through final portions of their elevation and retraction 
strokes, and then releasably and resiliently retain the shifting means in 
the resulting stroke end position thereof, in respective response to 
movement of the shifting means through the aforementioned initial portions 
of their elevation and retraction strokes. 
The bistable spring structure is representatively provided in a variety of 
embodiments including: 
(1) a body portion supported for rotation relative to the shifting means 
and drivingly connected thereto, and a spring portion engaging the body 
portion in a manner permitting the body portion to rotate between two 
stable positions through an intermediate unstable position; 
(2) various spring structures having generally V-shaped portions 
resiliently engaging corresponding spaced pairs of oppositely ramped drive 
surfaces operatively disposed on the shifting means; and 
(3) a pair of telescoped, axially spring-biased tie rod assemblies each 
having a first end pivotally connected to the shifting means, and a second 
end pivotally supported external to the shifting means.

DETAILED DESCRIPTION 
Illustrated in simplified, partially cut away side elevational form in FIG. 
1 is an electronic device, representatively a portable, notebook type 
computer 10, which incorporates therein a specially designed collapsible 
keyboard structure 12 embodying principles of the present invention. 
Computer 10 includes a hollow rectangular base housing 14 having a top 
horizontal side wall 16 with an opening 18 therein; a bottom horizontal 
side wall 20; front and rear vertical end walls 22,24; and a pair of 
opposite vertical side walls 26,28. 
A hollow rectangular lid housing 30, having a display screen 32 on its 
front or inner side, is pivotally secured along a hinge joint structure 34 
to a top rear corner portion of the base housing 14. Lid housing 30 may be 
upwardly pivoted to place the computer 10 in an open use orientation (FIG. 
1) in which the top side 16 of the base housing 14 is exposed and the 
display screen 32 forwardly faces the user of the computer, or downwardly 
pivoted to place the computer 10 in a closed storage and transport 
orientation (FIG. 12) in which the lid housing extends across and covers 
the top side of the base housing 14. Suitable latch means (not shown) are 
provided to releasably retain the lid housing 30 in its closed 
orientation. 
With the important exceptions noted below, the collapsible keyboard 
structure 12 is similar to the sliding dome sheet type collapsible 
notebook computer keyboard structure illustrated and described in the 
aforementioned U.S. Pat. No. 5,602,715 which has been incorporated herein 
by reference. Still referring to FIG. 1, collapsible keyboard 12 extends 
across the opening 18 in the top side wall 16 of the base housing 14 and 
occupies only a relatively small upper portion of the interior 36 of the 
base housing 14. The collapsible keyboard 12 basically comprises a 
relatively thin rectangular monoblock support structure 38 that 
horizontally extends across the base housing top side opening 18 and is 
suitably anchored to the base housing 14; and a series of manually 
depressible key cap members 40 each carried by a scissored linkage 
assembly 41 for vertical movement relative to the support structure 38 (as 
indicated by the arrow 42 in FIG. 1) between an elevated solid line use 
orientation, and a downwardly retracted dotted line storage and transport 
orientation. 
Underlying the monoblock support structure 38 is a multilayer signal pad 
structure 44 having a bottom layer defined by a metal backing sheet 46, 
and a top layer defined by a plastic base member or dome sheet 48 which is 
sandwiched between the bottom side of the monoblock support structure 38 
and the balance of the signal pad structure 44. Dome sheet 48 carries on 
its top side a spaced series of resilient key return spring members 
representatively in the form of elastomeric dome members 50, and is 
slidable relative to the stationary monoblock structure 38 and the 
stationary balance of the signal pad structure leftwardly or forwardly 
through a key elevation stroke, and rightwardly or rearwardly through a 
key retraction stroke. 
As more fully described in U.S. Pat. No. 5,602,715, the shifting of the 
dome sheet 48 through its elevation stroke, initiated in response to the 
opening of the lid housing 30, causes the elastomeric domes 50 to be 
cammingly driven under the retracted key caps 40 and raise them from their 
dotted line retracted positions to their solid line elevated operating 
positions. With the key cap members 40 in these elevated operating 
positions they may be manually depressed to operatively activate, via 
their associated domes 50, underlying conventional switch circuitry in the 
signal pad structure 44. A subsequent reverse movement of the dome sheet 
48 through its retraction stroke, initiated by a closing of the lid 
housing 30, shifts the domes 50 away from their underlying supporting 
relationships with the key caps 40 and causes the retraction of the key 
caps 40 to their dotted line storage and transport orientations as more 
fully described in U.S. Pat. No. 5,602,715 incorporated by reference 
herein. 
As will now be described, the present invention provides a substantially 
improved drive structure operative to selectively shift the dome sheet 48 
through its elevation and retraction strokes. More specifically, with 
reference now to FIGS. 1-4, the dome sheet 48 is drivably connected to the 
pivotal lid housing 30 by a specially designed linkage structure 52 (see 
FIGS. 1 and 3). Linkage structure 52, in response to opening the lid 
housing 30, operates to shift the dome sheet 48 through an initial or 
triggering portion of its elevation stroke and, in response to closing the 
lid housing 30, operates to shift the dome sheet 48 through an initial or 
triggering portion of its retraction stroke. 
The linkage structure 52 includes an elongated rectangular plastic slide 
bar 54 suitably anchored to and longitudinally extending along a rear side 
edge portion of the dome sheet 48 and having an elongated central slot 56 
formed therein. The front end of an elongated rectangular drive bar 58 has 
an upwardly projecting boss 60 disposed thereon and extending upwardly 
into the slide bar slot 56. Drive bar 58 is transverse to the slide bar 
54, is suitably supported for driven movement in a front-to-rear direction 
within the base housing 14, and has an elongated slot 62 formed in its 
rear end and having front and rear end surfaces 62a and 62b. 
A downwardly extending lower rectangular tab portion 64 of a rotatable 
lever member 66 (see FIGS. 2 and 3) is downwardly received within the slot 
62, with an upper end portion 68 of the lever member 66 being pivotally 
secured, by pins 70, within a recess 72 in the lid hinge structure 34. As 
best illustrated in FIGS. 2 and 3, the upper end portion 68 of the lever 
member 66 has a pair of mutually angled, generally planar upper and lower 
ramp surfaces 74,76 formed on its front side. The linkage structure 52 
also includes a striker projection 78 formed on a rear side edge portion 
30a of the lid housing 30 and positioned to operatively engage the ramp 
surfaces 74,76 in a manner subsequently described herein in response to 
opening and closing the lid housing 30. 
As best illustrated in FIGS. 4-4B, the overall dome sheet drive structure 
also includes a bistable spring structure 80 interconnected between the 
base housing 14 and the slide bar 54. In a manner subsequently described 
herein, the bistable spring structure 80 functions to drive the dome sheet 
48 through final portions of its elevation and retraction strokes in 
respective response to the dome sheet 48 being driven through initial 
triggering portions of its elevation and retraction strokes by the linkage 
structure 52 caused by opening and closing of the lid housing 30. 
Bistable spring structure 80 includes a generally disc-shaped body portion 
82 positioned above a longitudinally central portion of the slide bar 54 
and having a top side 84 from which a diametrically extending drive 
projection 86 upwardly projects. Drive projection 86 has, along one of its 
opposite sides, a pair of arcuate indentations 88,90 with a curved lobe 
projection 92 positioned therebetween. On the other side of the drive 
projection are a pair of arcuate indentations 94,96 with a curved lobe 
projection 98 positioned therebetween and being directly opposite the lobe 
projection 92. 
A central cylindrical mounting pin 100 projects upwardly from a 
longitudinally central portion of the drive projection 86 and is rotatably 
received in a corresponding opening in the base housing wall structure, 
and a peripheral cylindrical drive pin 102 projects downwardly from the 
bottom side of the body portion 82 and is slidingly received in the slide 
bar slot 56. The bistable spring structure 80 also includes an opposing 
pair of left and right force exerting members 104a,104b (as viewed in 
FIGS. 4A and 4B), with facing rounded outer ends 106, which are 
resiliently biased toward one another by a pair of schematically depicted 
spring members 108 compressed between the force exerting members 104 and 
suitable support structures 110 disposed within the base housing 14. 
When the lid housing 30 is closed, the dome sheet 48 is at the rear end of 
its retraction stroke, the drive bar 58 is at the rear end of its 
front-to-rear stroke, the key caps 40 in their retracted storage and 
transport positions, and the bistable spring structure 80 is in its FIG. 
4A initially stable position with the outer ends 106 of the force exerting 
members 104a,104b being respectively received in the drive projection side 
indentations 90 and 94. As the lid housing 30 is opened (i.e., pivoted in 
a clockwise direction as viewed in FIGS. 1 and 3), the striker projection 
78 (see FIG. 3) forcibly engages and travels across the upper ramp surface 
74, causing the lever member 66 to pivot in a clockwise direction as 
viewed in FIG. 3 to thereby cause the tab portion 64 to forcibly engage 
the slot end surface 62a and forwardly move the drive bar 58 away from its 
rearwardly shifted position. 
In turn, via the engagement of the boss 60 with the slide bar 54, this 
forwardly moves the dome sheet 48 through an initial triggering portion of 
its forward elevation stroke. As the dome sheet 48 moves through this 
initial elevation stroke position, under the mechanically advantages lid 
force being exerted thereon, the forward force exerted on the spring 
structure drive pin 102 by the slide bar 54 begins to rotate the bistable 
spring structure body portion 82 in a counterclockwise direction away from 
its FIG. 4A first or rear stable position. 
Such counterclockwise rotation of the body portion 82 cams the force 
exerting members 104a,104b outwardly away from one another, against the 
resilient resistance of the springs 108, as the body portion 82 
rotationally approaches an unstable intermediate position in which the 
outer tip portions of the oppositely directed central drive projection 
lobes 92,98 respectively engage the outer ends 106 of the force exerting 
members 104a,104b. As the dome sheet 48 continues to be forwardly driven 
by the drive bar 58 (see FIGS. 2 and 3), the bistable spring structure 
body portion 82 is rotationally driven in a counterclockwise direction 
past this intermediate unstable point at which time the springs 108 
rotationally snap the body portion 82 to its second or forward stable 
position shown in FIG. 4B. 
As the body portion 82 rotationally reaches its FIG. 4B second or forward 
stable position, the continuing rotation of its drive pin 102 about the 
axis of the mounting pin 100 forwardly drives the dome sheet 48 through 
the balance of its elevation stroke to elevate the key cap members 40 to 
their solid line use orientations shown in FIG. 1. 
During this driven rotation of the body portion 82 from its central 
unstable position to its second or forward stable position, and the 
corresponding spring-driven forward translation of the dome sheet 48 
through the balance of its forward elevation stroke, the tab portion 64 
(see FIGS. 2 and 3) is disengaged from the front slot end 62a, thereby 
disengaging the lid housing 30 from the dome sheet 48 and permitting the 
lid housing 30 to be pivoted through the rest of its opening stroke. 
Representatively, the mechanically advantaged lid force is exerted on the 
dome sheet 48, to move it through an initial portion of its elevation 
stroke, through only about the first 45 degrees of pivotal opening 
movement of the lid housing 30. After this initial pivotal opening 
movement of the lid housing 30, the now unstable spring structure 80 
"takes over" from the lid housing 30 and drives the dome sheet 48, which 
serves as a base structure for the domes 50, through the balance of its 
forward elevation stroke and then resiliently and releasably "latches" the 
dome sheet in this forwardmost position thereof. 
When the lid housing 30 is subsequently closed, the dome sheet 48 does not 
begin to be rearwardly shifted through its retraction stroke until during 
about the last 45 degrees or so of the lid housing's closing movement. As 
the lid housing 30 begins to pivot in a counterclockwise direction (as 
viewed in FIGS. 1 and 3) through this final pivotal increment, the striker 
projection 78 (FIG. 3) forcibly engages and travels along the lower ramp 
surface 76, thereby displacing the ramp surface 76 down and causing the 
lever member 66 to pivot in a counterclockwise direction about pins 70. 
This counterclockwise pivoting of the lever member 66 causes the tab 
portion 64 to rightwardly engage the rear slot end surface 62b (see FIG. 
3) and rearwardly drive the dome sheet 48, via the drive bar 58, through 
an initial or triggering portion of its rearward retraction stroke. 
Initial rearward movement of the dome sheet 48 through its retraction 
stroke exerts a corresponding rearward force on the drive pin 102 (see 
FIG. 4B) to thereby begin to rotate the bistable spring structure body 
portion 82 in a clockwise direction away from its FIG. 4B stable position 
and through its previously described intermediate unstable position in 
which the lobes 92,98 point in opposite horizontal directions as viewed in 
FIG. 4B. 
When the body portion 82 rotationally passes this intermediate rotational 
unstable position, the springs 108 rotationally snap the body portion 82 
to its FIG. 4A rear stable position to thereby decouple the lid housing 30 
from the dome sheet 48, rearwardly drive the dome sheet 48 through the 
balance of its retraction stroke, retract the key caps 40, and resiliently 
and releasably latch the dome sheet 48 at the rear end of its retraction 
stroke. 
The use of the bistable spring structure 80 to drive the dome sheet 48 
through final portions of its elevation and retraction strokes, in 
respective response to movement of the dome sheet 48 through initial 
triggering portions of its elevation and retraction strokes, and then 
resiliently and releasably latch the dome sheet in its fully shifted 
position to await the next oppositely directed stroke, provides several 
advantages over the sliding dome sheet drive structure illustrated and 
described in U.S. Pat. No. 5,602,715. 
For example, the primary force used to collapse and elevate the key cap 
members 40 is supplied by the user's opening of the computer lid. Thus, 
the maximum available force to elevate and collapse the key cap members is 
substantially higher than could be practically supplied by a spring 
mechanism, due to the large mechanical advantage of the computer lid. 
Additionally, there is no need for overtravel within the keyboard. This 
simplifies keyswitch actuator design and key hold-down design. Moreover, 
this design is more favorable to an assembly method which allows the 
keyboard to be installed as the last part of the computer assembly 
process. 
Another advantage is that there is no large spring force exerted on the 
dome sheet for extended periods of time during operating and storage 
conditions. Substantial force is exerted on the dome sheet 48, via the 
slide bar 54, only during brief moments when the keys are being collapsed 
or elevated. Thus, the risk of plastics bowing, fatiguing, etc. due to 
high stress is substantially eliminated. Of course, spring forces are 
continuously exerted on the shifting mechanism, but only on the relative 
thick and sturdy drive projection portion 86 of the bistable spring 
structure 80 as opposed to being exerted on the slide bar 54 and the dome 
sheet 48. 
Because of the incorporation of the bistable spring structure 80 in the 
dome sheet drive system as described above, problems of limited assembly 
tolerance between the keyboard and the lid housing are substantially 
eliminated. Furthermore, in the configuration of the overall dome sheet 
drive structure described above, the slide bar 54 need not be positioned 
above the keyboard and under the lid housing's edge to be operatively 
engaged by the lid housing. This reduction in volume required for the dome 
sheet drive system advantageously reduces the total size and weight 
requirement for the overall keyboard assembly, thereby providing more 
assembly options for securing the keyboard in the computer, and provides 
the aesthetically desirable option of at least substantially entirely 
concealing the elevation and retraction mechanism for the collapsible 
keyboard. 
Various other forms of the previously described bistable spring structure 
80 may be employed to drive the dome sheet 48 through terminal portions of 
its elevation and retraction strokes, in respective response to forcible 
movement of the dome sheet 48 through initial portions of its elevation 
and retraction strokes. For example, a first alternate embodiment of the 
bistable spring structure 80 is shown in simplified form in FIG. 5 and is 
used in conjunction with a modified version 54a of the previously 
described slide bar 54. 
The modified slide bar 54a secured to a rear edge portion of the dome sheet 
48 has generally V-shaped outer ends 112, and the modified bistable spring 
structure includes a pair of elongated leaf spring members 114 having 
inner end portions embedded in monoblock support structure portions 38a 
positioned adjacent rear side edge portions of the dome sheet 48, and 
generally V-shaped inturned outer end portions 114a positioned to 
resiliently and cammingly engage the oppositely sloped surfaces of the 
slide bar end portions 112 as shown. The unstressed position of one of the 
springs 114 is shown in phantom in FIG. 5. 
In FIG. 5A the slide bar 54a is shown in its rearward limit position 
("rearward" being toward the top in FIGS. 5-5C) in which it is resiliently 
and releasably latched by the springs 114, with bistable spring structure 
being in its rear stable position, and the spring end portions 114a being 
resiliently urged against the forwardmost sloping surfaces of the 
generally V-shaped end portions 112 of the slide bar 54a. FIG. 5B 
illustrates the slide bar 54a having been forwardly moved (by the 
previously described lid housing drive linkage) to correspondingly cam the 
spring ends 114a out to their intermediate unstable position in which the 
apexes of the spring end portions 114a engage the corresponding apexes of 
the slide bar end portions 112. 
As the slide bar 54a is moved further forwardly from its FIG. 5B position, 
the springs 114 snap inwardly toward each other to their FIG. 5C forward 
stable positions to thereby cause the spring end portions 114a to drive 
the slide bar 54a, and thus the dome sheet 48, through the balance of its 
forward retraction stroke. It can be readily seen that by rearwardly 
moving the slide bar 54a from its FIG. 5C stable position through its FIG. 
5B unstable position will cause the springs 114 to automatically drive the 
slide bar 54a, and thus the dome sheet 48, through the balance of its 
rearward retraction stroke in which the springs 114 once again assume 
their FIG. 5A rear stable position. 
Further possible alternate embodiments of the bistable spring structure 80 
are schematically shown in FIGS. 6-11. For example, in FIG. 6, the slide 
bar 54b is generally U-shaped, with inturned, generally V-shaped facing 
lobes 116 formed on the transverse opposite end portions 118 of the slide 
bar 54b. A pair of elongated leaf spring members 120 have inner end 
portions embedded in portions 38b of the monoblock support structure 38, 
and generally V-shaped outer end portions 120a which are positioned 
inwardly of and cammingly engage the lobes 116, exerting oppositely 
directed forces F thereon. As can be seen, forced movement of the slide 
bar lobes 116 forwardly and rearwardly past the spring end portions 120a 
moves the springs 120 from first stable positions through unstable 
intermediate positions to second stable positions. 
A third alternate embodiment of the bistable spring structure 80 is 
schematically illustrated in FIG. 7 and includes a suitably supported, 
generally U-shaped spring member 122 having V-shaped lobes 124 on its free 
outer ends. The spring lobes 124 cammingly engage corresponding lobes 126 
on the slide bar 54c and exert opposite inwardly directed forces F 
thereon. 
A fourth alternate embodiment of the bistable spring structure 80 is 
schematically illustrated in FIG. 8 and includes a suitably anchored 
rectangularly shaped spring member 128 with inturned, generally V-shaped 
lobes 130 on opposite side portions 132 thereof. The spring side portions 
132 are positioned outwardly of corresponding slide bar lobes 134, with 
the spring lobes 130 cammingly engaging the slide bar lobes 134 and 
exerting opposite inwardly directed resilient forces F thereon. 
A fifth alternate embodiment of the bistable spring structure 80 is 
schematically illustrated in FIG. 9 and includes a suitably anchored 
rectangularly shaped spring member 136 with outwardly projecting, 
generally V-shaped lobes 138 on opposite side portions 140 thereof. The 
spring side portions 140 are positioned outwardly of corresponding slide 
bar lobes 142, with the spring lobes 138 cammingly engaging the slide bar 
lobes 142 and exerting opposite outwardly directed resilient forces F 
thereon. 
A sixth alternate embodiment of the bistable spring structure 80 is shown 
in simplified form in FIGS. 10A-11 and includes a pair of spring-loaded 
telescoped tie rod assemblies 144 pivotally interconnected between the 
monoblock support structure 38 and the slide bar 54. Each tie rod assembly 
144 includes an outer tubular member 146 with an outer annular connection 
end section 148, and a smaller diameter inner tubular member 150 with an 
outer annular connection end section 152. The inner tubular member 150 is 
slidingly telescoped within the outer tubular member 146, with the 
telescoped outer and inner members 146,150 being resiliently urged axially 
away from one another by an internal compression spring member 154. The 
connection end section 148 is pivotally retained on a pin 156 on the 
monoblock structure 38 or the metal backing sheet 46, and the connection 
end section 152 is pivotally retained on a pin 158 on the slide bar 54. 
In FIG. 10A the dome sheet 48 is at the rear end of its retraction stroke, 
and the spring-loaded tie rod assemblies 144 are in a rearwardly and 
horizontally inwardly sloped first stable position thereof. As the dome 
sheet 48 is forwardly moved through an initial portion of its elevation 
stroke to its FIG. 10B position (by the previously described lid housing 
drive linkage), the tie rod assemblies 144 are pivoted toward one another 
to a shortened, unstable intermediate position in which they are generally 
parallel to the length of the slide bar 54. A further forward movement of 
the dome sheet 48 past this unstable position causes the tie rod 
assemblies 144 to extend and forwardly pivot to their FIG. 10C second 
stable positions in which the springs 154 have driven the dome sheet 48 
forwardly through the balance of its elevation stroke. 
A subsequent lid housing-driven rearward movement of the dome sheet 48 from 
its FIG. 10C position through an initial portion of its retraction stroke 
pivots the spring-loaded tie rod assemblies 144 through their FIG. 10B 
unstable positions at which point the springs 154 take over from the lid 
housing drive linkage and drive the dome sheet 48 rearwardly through the 
balance of its retraction stroke, thereby pivotally returning the tie rod 
assemblies 144 to their FIG. 10A stable positions. 
An alternate embodiment 52a of the previously described lid housing-to-dome 
sheet linkage structure 52 is illustrated in simplified form in FIG. 12 
and may be utilized in design situations in which it is desirable to 
reverse the previously described directions of the elevation and 
retraction strokes of the dome sheet 48--i.e., to elevate the key cap 
members 40 by moving the dome sheet 48 rearwardly in response to opening 
the lid housing 30, and to retract the key cap members 40 by moving the 
dome sheet 48 forwardly in response to closing the lid housing 30. 
The modified linkage structure 52a includes a striker member 160 which is 
pivotable about the rotational axis 162 of the lid housing 30; an 
elongated, generally T-shaped lever member 164; and a horizontal drive bar 
166 having an upturned front end portion 168 received as shown in the 
slide bar slot 56. The transverse upper end of the lever member 164 has 
mutually angled, upwardly facing front and rear ramp surfaces 170 and 172, 
and the lever member 164 is supported, as at 174, for pivotal movement 
between its solid and dotted line positions about a horizontal axis 
positioned rearwardly of the slide bar 54 and extending parallel to its 
length. The lower end of the lever member 164 is pivoted, as at 176, to 
the rear end of the drive bar 166. 
With the lid housing 30 in its FIG. 12 closed position, the linkage 52a is 
in its solid line position, dome sheet 48 is at the forward end of its 
forward retraction stroke, and the key cap members 40 (not shown in FIG. 
12) are in their retracted storage and transport orientations. As the lid 
housing 30 is opened by pivoting it in a clockwise direction from its FIG. 
12 position, the striker member 160 forcibly engages and travels along the 
front lever member ramp surface 170 to thereby forcibly rotate the lever 
member 164 in a counterclockwise direction, as indicated by the arrow 178 
about pivot point 174 toward the dotted line position of the lever member 
174. 
Via the drive bar 166, this moves the dome sheet 48 through an initial 
triggering portion of its rearwardly directed elevation stroke in a manner 
moving the bistable spring structure 80 (or one of the several alternate 
embodiments thereof as the case may be) from one of its stable positions 
and through its central unstable position as previously described. At this 
point, the striker member 160 disengages from the ramp surface 170, and 
the bistable spring structure 80 takes over, drives the dome sheet to the 
rear end of its rearwardly directed elevation stroke, and causes the 
linkage 52a to finish its pivotal movement to its dotted line position in 
FIG. 12 at which point the key cap members 40 are elevated to their use 
orientations. 
When the lid housing is subsequently closed, the sequence is reversed. With 
the lever member now in its dotted line position, the striker member 
(which is now rotating in a clockwise direction) forcibly engages and 
travels along the ramp surface 172, thereby rotating the lever member 164 
in a clockwise direction about the pivot point 174 and moving the dome 
sheet 48 forwardly through an initial triggering portion of its forwardly 
directed retraction stroke, after which the bistable spring structure 80 
takes over and drives the dome sheet 48 forwardly through the balance of 
its retraction stroke to collapse the key cap members 40 to their storage 
and transport orientations. 
As in the case of the previously described linkage 52, during opening of 
the lid housing 30, the striker member 160 preferably engages the lever 
member 164 only during about the first 45 degrees of pivotal motion of the 
lid housing. Similarly, as the lid housing 30 is being closed, it 
drivingly engages the lever member 164 only during about the last 45 
degrees of pivotal motion of the lid housing. 
The foregoing detailed description is to be clearly understood as being 
given by way of illustration and example only, the spirit and scope of the 
present invention being limited solely by the appended claims.