Keypads

Details Keypads Keypads

1995-10-19

1998-01-06

Walczak, David J.

Electricity: circuit makers and breakers

Electric switch details

Cases and bases

200512, 200513, H01H 1306

Patent

active

057044678

DESCRIPTION:

BRIEF SUMMARY
The invention relates to keypads and particularly, but not exclusively to keypads for use in hostile environments or keypads likely to be subject to vandalism.
There are two main types of keypad currently in use. In one type, the keys are protected by an overlay of a waterproof flexible elastomeric material which has marked zones identifying the location of the keys beneath the layer. Such keypads can be subject to wear and ripping and thus require frequent replacement.
In a second form of keypad, a key-plate is provided with keyholes through which project individual keys. These keys can be depressed in order to operate circuitry beneath the associated key.
Such keys suffer from the disadvantage that they are generally mounted in such a way that they can move laterally relative to the associated keyhole and engage the associated keyhole. This can cause wear and eventually may prevent the key functioning at all. In addition, such lateral movement can allow a knife or other object to be inserted between the key and the keyhole and the circuitry beneath to be attacked. Further, such an arrangement can often allow the ingress of water, dust or other damaging matter between the key and the keyhole and into the interior of the keypad where damage to the circuit can be caused.
According to the invention there is provided a keypad comprising a housing including at least one key hole and a key located in said hole, there being provided a key mount sealingly engaged with the key hole to prevent the passage between the mount and the key hole of damaging matter, the key mount locating said push-button relative to said key hole.
By providing a key mount which engages the key and the internal surface, ingress of contaminants into the housing through the gap between the key and the housing is prevented and the key is accurately positioned relative to the housing.
Preferably, the key mount includes a peripheral rib sealingly engaging a locating member provided on the housing and extending around the associated key hole. The rib may be provided with a channel sealingly receiving a locating flange provided on the housing. The rib and the flange are preferably rectangular.
The key mount may carry a separately formed key for manual operation. The key is preferably connected to the key mount by an interference fit between a part of the key and a part of the key mount. The key part may be a recess and the key mount part a projection.
The recess and the projection may be of circular cross-section. In this case the recess and the projection may include co-operating formations to prevent rotation of the key relative to the key mount. The formations may comprise a projection in the recess and a depression in the projection. The projection and the depression may be cruciform in shape with the limb of each such shape leading from an edge of the associated part.
The key and the key hole are preferably rectangular in cross-section. The key may be provided with means which, on depression of the key, create a flow of air tending to expel liquid held between the associated key mount and the housing.
The key mount is preferably formed from an elastomeric material with the peripheral rib being connected to a central core forming said key by a flexible web which holds the core normally in an inoperative position, the core being movable to an operative position against the force applied by the web to operate the associated switch.
The core may carry a contact, with the housing including a circuit board having a switch operated by said contact when the core moves to said operative position. Preferably, the switch is operated when the key is below the level of an adjacent surface of the housing.
There are preferably a plurality of keys and key mounts. The key mounts may in this case be formed separately. Alternatively, they may be formed as a single member.
A specific embodiment of the invention will now be described, by way of example only, with reference to and as illustrated by, the accompanying drawings, in which:
FIG. 1 is a plan view from

REFERENCES:
patent: 5144103 (1992-09-01), Suwa
patent: 5172805 (1992-12-01), Gumb
patent: 5203448 (1993-04-01), Osada et al.
patent: 5442152 (1995-08-01), Huang
patent: 5516996 (1996-05-01), Shin

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