FR2669462A1 - US SWITCH STRUCTURE FOR MAKING KEYBOARDS, AND KEYBOARDS USING SUCH STRUCTURE. - Google Patents

Abstract

The structure according to the invention comprises a substrate (10) carrying at least a pair of fixed contacts (C, C '), an elastic membrane (12) covering the substrate (10) and having a hollow boss (13) and an element conductor (14) arranged in the concavity of the boss (13) and integral with the latter. The boss (13) is extended by a transmission part (15), the end of which slides in a bore (16) of a guide part (2) which has a flared orifice (18). The part (2) is covered by a sheet of semi-rigid material (20) which has a conformation (21) in the form of a convex cap serving as a key and on which the part (15) bears. The invention makes it possible to ensure precise guidance of the conductive element (14) which serves as a movable contact bridge and to make the elastic return means and the means used to generate the tactile effect independent.

Description

-1-

  USING SWITCH STRUCTURE FOR REALIZATION

  KEYBOARDS, AND KEYBOARDS USING SUCH A STRUCTURE.

  The present invention relates to a structure

  particularly usable but not exclusive

  for the production of waterproof keypads, low

thickness and tactile effect.

  In general, it is known that many solutions have been proposed for the production of keyboards to

  such keys, the simplest solution is

  both to use a sandwich structure comprising: a relatively flexible plastic sheet whose outer face has a multiplicity of areas serving as keys which bear inscriptions, for example alphanumeric characters, while

  the other side has electrically conductive

trices

  a perforated interlayer on which is applied

  said sheet and which has a multiplicity of through holes arranged opposite said zones; and

  a substrate which may for example consist of a

  rigid printed circuit board (possibly flexible) which has opposite each of the orifices, 2 - at least one pair of fixed contacts which cooperates with a corresponding conductive pad of the aforesaid sheet (this range acting as a bridge of

mobile contact).

  Of course, the mechanical properties of the plastic sheet and the thickness of the insert are determined in such a way that

  the conductive areas of the sheet are

  held away from the contacts of the substrate and that an electrical connection between a pair of fixed contacts is ensured by a corresponding conductive pad only as a result of a pressure exerted voluntarily on

  the zone serving as the corresponding key.

  In a keyboard of this kind, a tactile effect can be obtained by producing the outer sheet of a semi-rigid plastic material and by conforming the aforesaid zones so that they have a curved shape of convexity oriented outwards, the aforesaid conductive pads then coating the concave face of said pads. It is clear that when pressure is applied to one of the aforesaid zones, the convex shape is deformed into

  first exerting a growing resistant force.

  Beyond a determined threshold of deformation, this curved shape undergoes a sudden inversion of concavity, and gives rise to a feeling of relaxation, at the very moment when the conducting range comes to bear on the fixed contacts.

associated with it.

  It turns out that in a large number of industrial applications

  such keyboards are not

sufficient capacity.

  Indeed, because of the deformations of the zones serving as keys, the quality of the contact between these 3 -

  conductive areas and the fixed contact torques cor-

  respondents, is not good and that in addition, the beaches

  Conductors tend to deteriorate in the long run.

  It has also been proposed, in particular in US Pat. No. 3,728,509, a waterproof keyboard involving a waterproof rubber or elastomer-mounted membrane.

  on a substrate such as a printed circuit board.

  This membrane has a multiplicity of bosses pre-

  each feeling the shape of a hollow key In the concavity of each of these bosses, is fixed an elastomeric part electrically conductive This piece, which serves as a movable contact bridge, is arranged opposite

  at least one pair of fixed contacts provided on the sub-

Strat.

  This solution has the disadvantage of

  do not lend themselves to miniaturization and not to

  precise guidance of the elastomer

mobile contact bridge.

  The invention therefore more particularly aims at eliminating

to overcome these disadvantages.

  It proposes, for this purpose, a switch structure in which the mobile equipment, including the movable contact bridge, is correctly guided and comprises

  elastic return means independent of the means

  to create the tactile effect.

  More precisely, this structure comprises, as in the example described in the cited US patent: a substrate carrying at least a pair of fixed contacts;

  an elastic membrane covering at least partial-

  the substrate, this membrane comprising, in a 4-zone situated opposite the fixed contacts, a cap-shaped boss whose concave face, oriented towards

  contacts, wears a piece of electrical material-

  conductor constituting a movable contact bridge capable of providing a connection between the fixed contacts at

  following an elastic deformation of the boss.

  According to the invention, this structure is characterized in that it further comprises a transmission piece integral with the boss, this part being axially movable perpendicularly to the substrate; a guide piece in the form of a plate secured to the substrate and having a bore in which engages and is axially guided the free end of the transmission part, said bore comprising an outwardly oriented flare; a sheet of semi-rigid material that covers the face

  outer surface of the guide plate, this sheet pre-

  sensing opposite said flare, a convex shaped crown-shaped conformation, which serves as a key and against which the free end of the transmission piece bears, said conformation and said recess being designed to obtain a

  touch effect when pressing the key.

  Advantageously, the aforesaid substrate consists of a

  printed circuit board fixed inside

  an electrical or electronic device box.

  In this case, the aforesaid guide piece may consist of a wall of the housing parallel to the printed circuit, the

  sheet of semi-rigid material also serving as a mem-

brane sealing.

  Of course, the invention also relates to a keyboard using the previously described structure In this case the substrate comprises a multiplicity of fixed contact pairs;

  the elastic membrane comprises a multiplicity of

  wise each corresponding to a pair of fixed contacts and each comprising an electrically conductive member;

  the guide piece comprises a multiplicity of

  each of which serves to guide a piece of

  mission integral with a boss of the membrane; the sheet of semi-rigid plastic material is provided with a plurality of cone-shaped conformations on each of which abuts a transmission part. One embodiment of the invention will be described below,

  as a non-limitative example, with reference to the

  1 is a top view of an electrical appliance housing comprising a keyboard made according to the invention; FIG. 2 is a diagrammatic section along A / A 'of FIG. showing more

  especially the keyboard structure.

  In this example, the apparatus includes a 1-parallel housing

  the elepiped whose frontal wall 2 is provided with a viewing area 3 constituted, for example, by a liquid crystal cell, and a keyboard 4 located in 6 - the interval between the area 3 and the front edge of the case 1 This keyboard includes here four keys 6

  9 aligned along an axis parallel to the edge 5.

  Each of the keys 6 to 9 is identified by a functional symbol, here the signs + and -, as well as a

  vertical arrow and a horizontal arrow.

  As can be seen in FIG. 2, this keyboard 4 involves a substrate fixedly mounted inside the casing 1 and which here consists of the printed circuit 10 of the apparatus. This printed circuit 10 comprises, in zones located in the axis of the keys 6 to 9, four pairs of respective conductive pads C, C ', each pair of ranges constituting the fixed contacts of an associated switch.

to the corresponding key.

  On the printed circuit 10 is fixed, by means of rivets 11 or any other means, a rubber or elastomer membrane 12 comprising, in the aforesaid zones,

  bosses 13 in the form of frustoconical caps which delimit

  therefore, above the conductive areas C, C '

free volume.

  This free volume is partially occupied by a piece 14 made of conductive elastomer, the lower face of which extends parallel and at a determined distance from the printed circuit 10, this piece 14, of cylindrical shape, being fixed on the inner surface of the boss 13, at the level

from its bottom.

  In this example, the upper part of the bosses 13 is extended by a coaxial cylindrical portion 15 which

  performs the function of the aforesaid transmission part.

  7 - The end of each of these cylindrical parts 15 engages in a coaxial bore 16 provided in the front wall 2 of the housing 1 and ends with a convex face

  17 slightly above the plane of the outer face.

  2. Each bore 16 comprises outwardly a tapered portion 18, conical in shape, the outside diameter of which

  is substantially equal to the side of a key 6 to 9.

  The outer face of the front wall 2 of the housing 1 is covered (in the part constituting the keyboard) by a sheet of semi-rigid plastic material 20, by

example in polycarbonate.

  At the level of the flared holes of the bores, this sheet comprises bosses 21 in the form of a cap, on the inner faces of which are applied the

  curved ends 17 of the cylindrical portions 15.

  The locations of the keys 6 to 9 as well as the symbols identifying their functions are indicated for example by

print on this sheet 20.

  The operation of the keyboard as previously described

is then the next.

  At rest, the membrane 13 occupies the position indicated in FIG. 2, the elastomeric conductive parts 14 being

  spaced apart from the conductive pads C, C '.

  From this position, if a pressure P is exerted on a key, an axial displacement of the

  cylindrical portion 15, against the resistant stresses

due:

  elastic deformation of the lateral walls of the

  sage 13; The deformation of the boss 21 of the polycarbonate sheet 20. During this action, the resistant force generated by the deformation of the walls of the boss 13 is increasing on

the whole race of the touch.

  On the other hand, the resisting force engendered by deformation

  boss 21 of the sheet 20 is first increasing

  in the first part of the race, then vanishes abruptly

  talement due to the inversion of concavity of the boss

  21, thus producing the desired tactile effect.

  Of course, at the end of the race, the conductive elastomer 14 is applied to the conductive pads C, C 'in

  establishing an electrical contact between these two ranges.

  This contact is of good quality because of the guiding provided by the cylindrical part 15 and thanks to the properties of

  the conductive elastomer of the part 14.

  The return of the key to the rest position is mainly

  provided by the effort exerted by the boss 13, to which is added, only after a new inversion of concavity, the force exerted by the boss 21. It is clear that the means used here for

  tactile effect, are independent of cinematography

  switch and do not affect its operation.

Claims (7)

claims   1 Switch structure of the type comprising   a substrate (10) carrying at least one pair of fixed contacts (C, C ');   an elastic membrane (12) covering at least   the substrate (10), this membrane comprising, in an area facing fixed contacts, a boss (13) in the form of a cap whose concave face, facing towards the contacts (C, C '), carries a piece of electrically conductive material constituting a movable contact bridge capable of providing a connection between   fixed contacts as a result of elastic deformation   boss of the boss, characterized in that it further comprises a transmission part (15) integral with the boss   (13), this part being axially movable perpendicularly   stretching to the substrate (10); a guide piece (2) in the form of a plate secured to the substrate and comprising a bore (16) in which the free end of the transmission piece (15) engages and is axially guided, said piercing (16) comprising an outwardly facing flare (18); a sheet of semi-rigid material (20) which covers the outer face of the guide plate, this sheet having opposite said flare, a conformation (21) in the form of domed cap facing outwards, which serves as a touch and against which the free end of the transmission piece (15) abuts, said conformation (21) and said recess (18) being designed -   in order to achieve a tactile effect when quote from the key.   2 Structure according to claim 1, characterized in that the aforesaid substrate-consists of a printed circuit board fixedly mounted to   inside a device housing (1).   3 Structure according to one of claims 1   and 2, characterized in that the said guide piece consists of a device housing wall (2) in   which is made the aforesaid drilling (16).   4 Structure according to one of the claims   preceding, characterized in that the aforesaid transmission part   (15) is integral with the aforesaid membrane.   5 Structure according to one of the claims preceding,   characterized in that the aforesaid boss (13) of the mem-   brane (12) has a frustoconical shape.   6 Structure according to one of the claims   preceding, characterized in that the aforesaid piece (14) of electrically conductive material is made of a conductive elastomer. 7 Keyboard using structures according to one of the preceding claims,   characterized in that: the substrate comprises a plurality of fixed contact pairs (C, C '); it - the elastic membrane (12) comprises a multiplicity of bosses (13) each corresponding to a pair of fixed contacts (C, C ') and each comprising an electrically conductive part (14); the guide piece (2) comprises a multiplicity of holes (16) each serving to guide a transmission piece (15) integral with a boss (13) of the membrane (12); the sheet of semi-rigid plastic material (20) is provided with a multiplicity of conformations (21) in the form of a cap on each of which is supported by a transmission part (15).