FR2563940A1 - PUSH-BUTTON SWITCH - Google Patents

Abstract

THE INVENTION CONCERNS A PUSH-BUTTON SWITCH INCLUDING AN ELASTIC ELEMENT1 HAVING A CONTACT GRAIN AND APPLIED THROUGH ITS LOWER EDGE2 ON A FLEXIBLE PRINTED CIRCUIT BOARD4 BASED ON AN INDEFORMABLE BASE, THE CONTACT GRAIN ESTABLISHING CONTACT BETWEEN TRACKS5 OF CONDUCTORS THE MAP 4. TO PROVIDE AN ACCOMPANYING STROKE3 FOR SUCH A SWITCH, THE PRINTED CIRCUIT BOARD4 IS EQUIPPED WITH A BOMBAGE4A FACING THE ELASTIC ELEMENT1.

Description

The invention starts from a push-button switch comprising an element

  elastic having the elasticity of a rubber,

  with or without a diver, which is electrically conductive or pos-

  a contact binder solidified at its inner edge, and which rests, by its outer edge, on a flexible printed circuit board, which rests on an indeformable base in bending, and in which the elastic element or the contact grain establishes a contact between the conductive tracks of the printed circuit board. O Push-button switches of the type mentioned above are described in the article entitled "Schaltmatten aus Kautschuk" published in the German-language periodical "Markt &

  Technik ", No. 4, January 28, 1983, page 20.

  Experience shows that an extension of the contact closure time increases functional reliability. According to the German patent application DE-OS 30 32 557, for example, this is

  obtained by the fact that following the establishment of the contact pro-

  actually said the race of the elastic element having the elasticity

  of a rubber has an accompanying race. The elastic dement

  used in this case, however, is relatively expensive to

  brick and has a shape and height that differ from those of the current elastic elements without

accompanying race.

  The present invention therefore aims to achieve a push-button switch with elastic elements of a type

  current, domed, having such an accompanying race.

  According to the invention, this object is achieved by the fact that the flexible printed circuit board has a bending in the region

  of the dome-shaped elastic element.

  This bending of the flexible printed circuit board is advantageously of a height such that said contact bead and the conductive tracks in the region of the bending only touch each other after having exceeded the point of resistance of said dome-shaped elastic member (FIG. "resistance point" designating the point where the resistance to the thrust of the switch ceases to

grow and shrink).

  The advantages achieved by the invention reside in

  the first step in that, due to the bending of the flexible printed circuit board, the establishment of the contact is effected at approximately half the stroke of the push-button, so that a closing time defined contact is assured. In addition, because of the bending effect of the bending of the printed circuit board, the restoring force of the elastic element

  in the depressed condition can be reduced or even deleted.

  The curve of the evolution characteristic of the reaction to depression may be steeper, so that the sudden negative variation of this reaction is more pronounced, hence a better perception.

  that the actuation is actually performed.

  The different objects and characteristics of the invention

  will now be detailed in the description that follows, made

  By way of non-limiting example, referring to the figures

which represent:

  FIG. 1, a diagrammatic representation of a

  conventional mutator, push-button type, seen in section; - Figure 2a, a sectional view of a schematic representation of a pushbutton according to the invention;

  FIGS. 2b and 2c, the push-button according to FIG.

  gure 2a considered at different stages of actuation, and

  FIG. 3, the displacement-reaction diagram of the button

  pusher shown in Figures 2a to 2c.

  FIG. 1 represents a cross-sectional view of a

  push button switch, of a type commonly marketed.

  A dome-shaped elastic element 1 is applied by its outer edge 2, on a flexible printed circuit board 4, which rests flat on a non-deformable bending base 6. The map to

  printed circuit board 4 is provided with conducting tracks 5.

  At the zenith of the dome, the elastic element 1 comprises

  a contact grain 3 made of an electrically conductive material

  duct, for example silicone rubber (synthetic).

  On the elastic element in the form of dMme applies, without being fixed, a plunger 7 guided to slide vertically in a plate

8.

  In this embodiment, the establishment of the contact between the contact grain 3 and the conductive tracks 5 takes place only at the end of the control path SI. This can lead to times

  so short that no reliable detection is ensured.

  Figures 2a to 2c show a touch switch

  using an elastic element 1 identical to that described below.

  Figure 1. The difference lies in the form of

  This is, in the inner region of the dome-shaped elastic element 1,

  domed in Drofil plate. The conductive tracks 5 are arranged

  in the middle of the bending 4a, side up. Thanks to the bending 4a, the control race S1 is subdivided into a contact approach race, S2, and a support race with support

in contact, S3.

  As indicated by the displacement-force diagram according to FIG. 3, the contact approach travel S2 ends beyond the point corresponding to the maximum fk where the force variation becomes

  negative, that is to say that from the point fk the mechanical resistance

  that detectable by the top 7 of the key, by deforming the dome of the elastic element, suddenly becomes weaker. Immediately after this sudden negative variation, felt as an indication of the actuation, the contact grain 3 touches the conductive tracks 5 on the dish-shaped bending 4a. The situation at this time is illustrated in Figure 2b. During the contact holding stroke, S3, to the abutting position in which the center of the dish-shaped profile bending 4a is applied to the base 6, as shown in FIG. 2c, the pressure increasing, maintaining the contact between the grain 3 and

  the conductive tracks is ensured.

  As can be seen from Figure 3, the

  The pressure of the contact pressure results from the fact that the dish-shaped bending 4a is biased in pressure during the contact holding phase S3. The antagonistic force acting on the des = sus 7 of the key evolves as indicated in dotted line and has,

  at the end of the SI command run, the fL value is super-

  the elastic force of the elastic element 1 is applied, decreasing under the effect of the deformation of the dome, the latter elastic force evolving as indicated by the dash, and at the end of the

  control run S1, only has the value fs. From the overlap

  the two force components fL and fs, in the field of the support stroke S3 the result is evolved in the solid line with a restoring force fR at the end of the race. S1 control. This one is noticeably

  beyond what is essential, so that the elastic element

  Figure 1 deformed according to Figure 2c returns itself to the position

  initial configuration according to Figure 2a, when releasing the pressure

  exerted on the top 7 of the key. It is therefore possible to

  proud the elastic characteristic of the elastic element 1 so

  that the resulting restoring force has the value fs. Thus, the

  force characteristic becomes slightly "steeper", which manifests itself advantageously by a strengthening of perception

  touch testifying to the actuation.

  The push-button switch can also be used without the plunger 7. In this case, it is appropriate that the top of

  the elastic element 1 in the form of a dome is rounded.

  It is obvious that the foregoing descriptions have

  given as a non-limitative example and that many variants can be envisaged without departing from the scope

of the invention.

Claims (2)

  1. Switch & pushbutton comprising an elastic element having the elasticity of a rubber, with or without a plunger, which is electrically conductive or has a contact bump secured to its inner side, and which rests, by   its outer edge, on a flexible printed circuit board,   which rests on a base that is indeformable in bending, and in which the elastic element or the contact bump makes contact between the conductive tracks of the printed circuit board, characterized   in that the flexible printed circuit board (4) has a bell   bage (4a) in the region of the demenlike elastic element (1). 2. Switch according to claim 1, wherein the dome-shaped elastic element has a point of resistance   characterized in that the bending (4a) of the printed circuit board   said flexible mound (4) is of a height such that said contact grain (3) and conductive tracks (5) in the region of the hanger (4a)   touching each other only after the resistance point of the said ele- elastically dome-shaped.