Keypad

Details Keypad Keypad

1999-12-17

2001-01-30

Friedhofer, Michael (Department: 2832)

Electricity: circuit makers and breakers

Multiple circuit control

Multiple switch

C200S517000, C200S341000, C200S314000

Reexamination Certificate

active

06180895

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a keypad assembly having particular, but not exclusive, application in the field of portable radiotelephones.
Some driving forces behind the design of keypads are mechanical reliability, reliability of operation, reduced cost and efficiency of manufacture.
Keypads are used in the user interfaces of devices such as calculators and radiotelephones (e.g. mobile phones). One design of keypad is shown in cross-section in FIG.
1
. There is a flexible rubber keymat
1
which has key portions
2
surrounded and joined to the main web of the keymat by resilient deformation zones
3
. Each key portion has an upper region
4
which projects through a corresponding hole
5
in an outer housing
6
of the device, and a lower region
7
which terminates in a projection
8
. The upper portion can include in-moulded or printed indicia
9
to allow a user to identify the key. When a user presses the upper region
4
of the key the resilience of the deformation zone surrounding the key allows the key to travel towards a switch assembly
10
associated with the key so that the projection
8
can engage the switch. When the key portion is released the deformation zone urges it to return to its original position as illustrated in FIG.
1
. The switch assembly comprises an upper assembly
11
, including a flexible dome
12
made of sheet material, and a lower assembly
13
comprising a circuit board
14
with exposed conductive tracks
15
. When the key is pressed it urges the dome
12
to deform suddenly to the configuration illustrated at
12
a
or
12
b,
in which it bridges the conductive tracks
15
of the switch assembly and connects them together electrically. This connection is sensed by the device. When the key is released the dome returns to its natural state, disconnecting the tracks from each other. The sudden deformation of the dome provides a user with a pleasant tactile and/or aural feedback when a key is pressed.
Such keypads are widely used, but are expensive, and they suffer from the problem that the printing
9
on the surface of the key is prone to wear and tear and may become unreadable over time.
There has been an increased usage in recent times of so-called in-mould keymats. Specific types of in-mould keymats are termed film-on-plastic and film-on rubber, in reference to their constituent parts. These differ from the keymats described above in that the keymat starts as a planar sheet onto which the final markings of the keys, i.e. the text to appear thereon, is indelibly printed or etched. This has the advantage that the markings do not suffer so greatly from the wear and tear problems associated with more traditional rubber keymats.
The planar sheet is then selectively vacuum or heat formed in parts such that the keys are made to stand proud of the surrounding material. The spaces thus created behind the keys need to be filled with a solid material so that the keys may be used to exert pressure on a key dome
12
, and hence actuate the switch
10
, as in the previously described solution. This can be achieved in a number of ways, but a particularly suitable method uses injection moulding techniques to fill the spaces with a suitable solid material, such as rubber or plastics.
A problem with this solution is that if the rubber keymat is directly replaced by the in-mould variety, the keymat does not benefit from the resilient deformation zones
3
. This is because the in-mould keymat is relatively rigid, and there is not so great a degree of mechanical independence between adjacent keys. This results in a tendency for pressure on a given key to drag down its neighbour, which can result in unwanted key presses. This in turn may lead to incorrectly dialled telephone numbers, for instance.
Another problem with the in-mould keymat is that the keystroke, i.e. the distance travelled by the key from its rest position to the point at which the circuit is completed, is only of the order of 0.2 mm. With traditional rubber keymat solutions, the compression of the rubber material and the resilient deformation zones contribute to a keystroke of approximately 1 mm. This distance feels pleasing to the user, whereas the 0.2 mm for the in-mould keymat gives something of a hair-trigger feel, and does not afford such a good tactile solution.
In addition, the two problems mentioned above can combine such that erroneous key presses can occur through pressure on the casing of the apparatus, particularly the front casing
6
of the apparatus, enclosing the keymat.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided a keypad assembly including: a keymat; a switch assembly; and an intermediate element having at least one aperture positioned between a key of the keymat and a switch of the switch assembly, wherein a resilient member extending from the intermediate element into the aperture is disposed between said key and said switch.
The keypad advantageously affords to a user a greater degree of tactility in its use. This is because the user has to move a key through a greater distance than would be the case if an in-mould type keymat were used to directly actuate a key-dome type switch. This increased keystroke provides feedback to the user, and may help to convince him that he has successfully completed a keying operation.
Advantageously, the intermediate element, known as a C-cover, also assists in providing a greater degree of mechanical independence between neighbouring keys. Raised portions surrounding the apertures in the C-cover coincide with the edges of corresponding apertures in the front cover, or A-cover, of the telephone. These raised portions encircle each aperture, and the bracing therein provided helps to enable individual keys to operate independently of one another.
Further, the C-cover can be constructed to operate as a light-guide. This particular function is achieved by the selection of a material which allows light to be transmitted through it by the process of total internal reflection. One or more LED's are provided, and the light therefrom is channelled through the C-cover to illuminate each key from beneath, thus allowing use of the keypad in conditions of poor lighting.
According to a second aspect of the present invention, there is provided an intermediate element for use in a keypad assembly having a key or array of keys overlying a switch or array of switches of a switch assembly, including: a substantially rigid body having an aperture, or array of apertures, corresponding to the switch, or the array of switches, of the switch assembly, wherein a resiliently flexible member extends into the or each aperture.


REFERENCES:
patent: 4163138 (1979-07-01), Harden
patent: 4323740 (1982-04-01), Balash
patent: 5568367 (1996-10-01), Park
patent: 5570114 (1996-10-01), Fowler
patent: 5747756 (1998-05-01), Boedecker
patent: 5847336 (1998-12-01), Thornton
patent: 5892192 (1999-04-01), Ishiguro et al.
patent: 0500330 (1992-08-01), None
patent: 0503198 (1992-09-01), None

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