The present invention relates to an electrical push button switch, of the normally closed type, in particular intended for use with the keypad of a portable communication device. The invention also relates to the manufacture of a flexible electrical contact keypad of the normally closed type, the corresponding flexible keypad, the key and contact strip.
It should be reminded that a switch may flip between a closed position in which it allows an electric current to pass, and an open position, in which it interrupts the flow or passage of this electric current. A push button switch is said to be of the normally closed type when it is brought back to its closed position in the absence of external stress, and when it passes into its open position when actuated by a user, particularly by means of the push button.
The current membrane keypads that are extremely fine and inexpensive are manufactured by printing silver based conductive ink tracks on plastic substrates in order to create extra fine circuits.
The keys of the keypad thus formed are all executed according to the same principle: at least two tracks are arranged facing one another and are contacted when the key is pressed. These keys are therefore normally open type electrical contact keys.
The electrically conductive member that enables the contacting is, as appropriate, either a metal cup forming a cup contact, or a silver dot printed on the back of the upper circuit or the back of the decorative face placed on the circuit. This type of contact is thus designated as comb contact with flat or thermoformed front face.
The above techniques enable the production of membrane keypads, which have reduced thicknesses of the order of 1 to 1.5 mm, or in the most elaborate cases, even of 0.6 to 0.7 mm.
The development of the aforementioned techniques has made it possible, more recently to integrate extra fine components into membrane keypads, components such as light emitting diodes LED or small resistors, whose thickness of the order of 0.5 mm allows their integration in these fabrications.
However, when the use of more complex components appears to be necessary, it is imperative to change the technology. Larger circuits are then most often bonded on to machined metal plates, which are used to support the integration of buttons, switches, emergency stop buttons or other elements.
When integrators of such circuits or keypads wish to take advantage in this type of circuit or keypad of one or more normally closed type electric contact keys, in which two or more conductive tracks are in permanent contact, the action of an operator on one of the keys serving to open the contact, it is now necessary to either integrate buttons that are bulky and constraining in terms of implementation costs, or to introduce electronic management of this type of contact, which many integrators do not want to or cannot execute.
For example, from the technical state of the art, in particular from EP 0 793 246, an electric push button switch, of the normally closed type is already known. Such a switch conventionally comprises a printed circuit, comprising first and second contact pads, and an electrical conductor for electrically connecting the first and second contact pads.
Such a switch of the normally closed type has numerous elements, and therefore is particularly costly and complex to implement. Moreover, on account of its complexity and size, such a switch is not generally suitable for the keypad of a portable communication device.
The present invention aims to overcome these drawbacks by providing an electric push button switch, of the normally closed type, having a structure that is simple, economical and compact.
Specifically, the invention relates in particular to the implementation of a process for the manufacture of a flexible electrical contact keypad of the normally closed type, of a normally closed type contact key and a keypad having at least one such key, while retaining the advantages inherent in the flexible keypad technology, namely:
maintaining a very thin keypad, its thickness not exceeding 1 to 1.5 mm, according to the construction;
conservation of the operating principle of cup or thermoformed keys that are used in membrane keypads at the present time;
maintaining a manufacturing cost structure that is competitive and compatible with the specifications of existing markets that are seeking quality products at low costs;
obtaining a type of key that can function hundreds of thousands of times, or more, without any reasonably foreseeable problems;
making available a semi finished product that is easy to implement for integrators without additional constraints related to adaptation of their working methods
producing a final product, that is a flexible membrane keypad, durable enough to withstand sometimes difficult conditions of use such as vibration, shock or other conditions.
An object of the present invention is in particular the implementation of a method for the manufacture of a flexible membrane keypad comprising of at least one normally closed type contact key.
This method is remarkable in that it consists at minimum, of equipping the keypad with at least one circuit board printed on both sides comprising of at least one front contact face and one back contact face; of providing in the printed circuit, between the front contact face and the back contact face, an insertion slot; of inserting into the slot one flexible conducting strip forming a normally closed electrical contact between the front contact face and the back contact face, this flexible conducting strip having a pressure point so as to enable the exertion of a force for breaking the normally closed electrical contact.
Advantageously, the flexible conducting strip comprises of a flexible center tab that includes the pressure point, which is electrically and mechanically joined and adjacent to a first side tab and a second side tab by a common point, the first and the second side tabs being placed in one and the same plane and the center tab being arranged in an offset position in an orthogonal direction to said plane so as to form a first and a second insertion space for inserting the flexible strip in the slot, the operation consisting of inserting includes at least one step consisting of inserting said flexible strip into the slot by clipping of the first and second insertion space on the opposite edges of the slot, in a manner so as to bring the flexible center tab to rest and respectively at least one of the first or second side tabs in electrical contact with the back contact face and respectively the front contact face or vice versa.
Preferably, the pressure point provided on the center tab is placed in distant offset position on the center tab in relation to the common point so as to form a cross-force lever between the contact point of the center tab on the back or front contact face and the common point.
Another object of the present invention is the implementation of a flexible contact strip of normally closed type for the double sided printed circuit board.
Such a flexible contact strip is remarkable in that it comprises at least one flexible center tab, and a first side tab and a second side tab that are electrically and mechanically joined to the same common point. The electrically and mechanically joined first side tab and second side tab are substantially placed in the same plane, laterally adjacent to the flexible center tab. The center tab is arranged in offset position in an orthogonal direction to the plane so as to form a first and a second insertion space for inserting the printed circuit board that is provided with one slot and at least one front contact face and one back contact face each disposed in the vicinity of one of the two opposite edges of the slot.
Advantageously, the contact face of the flexible center tab is formed by a boss, and, optionally, the contact faces of the first side tab and the second side tab are also formed by a boss.
Preferably, the flexible center tab is offset at rest in an oblique plane in relation to the plane containing the first flexible side tab and the second flexible side tab to form by opposite constrained rotation of the flexible center tab, the first and second insertion spaces of the printed circuit board between this flexible center tab and the first and second side tabs, respectively.
Advantageously, the strip has been derived from the cutting/stamping of a sheet of conductive material.
Another object of the present invention is the implementation of a contact key for the flexible membrane keypad, such a contact key being remarkable in that it comprises of at least one printed circuit board provided with at least one front contact face and one back contact face, each placed in the vicinity of one of the opposite edges of a slot provided in the printed circuit board, and a flexible contact strip according to the invention inserted into the slot and forming a normally closed electrical contact between the front contact face and the back contact face. The flexible strip includes a pressure point for enabling the exertion of a force for breaking the normally closed electrical contact.
Advantageously, the pressure point can be actuated by pressure on a cup or a touch pad disposed over it.
The invention also relates to a flexible membrane keypad having at least one corresponding key and/or one flexible contact strip of the normally closed type.
The manufacturing process, the corresponding keypad and the normally closed type electrical contact key, objects of the invention, find application in the manufacture of keypads of all sizes, in particular small size keypads for mobile portable phone devices, personal digital assistants (PDAs) and keypads and keyboards of larger dimensions such as keypads and keyboards for laptops or desk top computers, musical instruments or the like.
The invention also relates to an electrical push button switch, of the normally closed type, in particular intended for a portable communication device keypad, comprising of:
a printed circuit board, including first and second contact pads, and
an electrical conductor, designed for electrically connecting the first and second contact pads,
characterised in that:
the printed circuit has at least locally a generally plane shape and comprises of a first face bearing a first contact pad, a second face, opposite the first, bearing a second contact pad, and a through-orifice allowing access between the first face and the second face,
the conductor comprises of a first part, which cooperates with the first contact pad, and
the conductor comprises of a second part, which extends between a first end, fixed to the first part, and a free second end, passing through the orifice, the second part is elastically deformable between a rest position, in which its second end cooperates with the second contact pad, and a stressed position, in which its second end is moved away from the second contact pad.
Such a switch has a particularly simple structure, wherein the conductor cooperates with the two contact pads without any intermediary and for which it is sufficient to apply a force on the second part of the conductor in order to move this second part away from the second contact pad, and thus open the switch.
Such simplicity of structure is possible in particular thanks to the contact pads arranged on the opposite faces of the printed circuit.
In an optional manner, an electric switch according to the invention may include one or more of the following characteristics, taken alone or based on any of the technically feasible combinations:
the switch comprises of a metal cup pusher, accessible from the side of the first face of the printed circuit, and movable between a rest position, in which the second part of the conductor is in its rest position, and an engaged position, in which the metal cup cooperates with the second part of the conductor in order to keep it in its stressed position,
the second part of the conductor has a boss provided between its first and second ends, meant for cooperating with the metal cup when the metal cup is in its engaged position,
the first part of the conductor comprises of two branches and a base, so as to have a U-shape, the two branches being arranged on either side of the orifice of the printed circuit,
the second part of the conductor forms a small strip extending the base of the first part, and extending longitudinally between the two branches of the first part,
the first and second parts are formed integrally, with the conductor for example, being of sheet metal, and
the switch comprises of means for backlighting, arranged on the side the second face of the printed circuit, and
the switch includes sealing means covering at least the metal cup and the conductor.
The invention will be better understood upon reading the description which follows, given solely by way of example and by making reference to the accompanying figures in which:
a to 1d shows the essential steps for implementing a method for manufacturing a flexible keypad according to an exemplary embodiment of the invention;
In the above mentioned figures the relative proportions of the elements have not necessarily been respected, so as not to affect the overall clarity of the illustrations.
The method of manufacturing a flexible membrane keypad according to the object of the present invention is now described in a detailed manner in connection with
In step 1, shown in
The double sided printed circuit board CI can be formed by a printed circuit board of any type, a double faced circuit or otherwise.
Step 1 is followed by a step 2, shown in
Step 2 is followed by a step 3 comprising of a sub step 3 (1), shown in
As further shown in the drawings, the flexible strip LS has a pressure point PA that enables the exertion of a force for breaking the normally closed electrical contact.
Moreover, in sub step 3 (2), represented in
For this purpose, during step 3 (1) shown in
It is thus understood that, in step 3 (1) shown in
Finally it can thus also be observed in
A more detailed description of a normally closed type flexible electric contact strip specially designed for the implementation of the process, of a contact key and a flexible membrane keypad in accordance with the object of the present invention will now be given in connection with
In
The flexible strip LS further consists of the first side tab LL1 and the second side tab LL2 each being electrically and mechanically joined by the common point PC.
The first and the second side tabs are adjacent and parallel to the flexible center tab LC, but are arranged to be offset in position in an orthogonal direction to the plane P so as to form the first insertion space EI1 and the second insertion space EI2 for the printed circuit board CI that is provided with the slot F, and the front contact face and the back contact face disposed in the vicinity of the two opposite edges of this slot. With reference to
With reference to the above mentioned figure, it is clear that the flexible center tab LC is offset at rest in an oblique plane PO in relation to the plane P containing the first flexible side tab LL1 and the second flexible side tab LL2 in order to form, through opposite constrained rotation of this flexible center tab LC, the first insertion space EI1 of the printed circuit board CI between this flexible center tab LC and the first and second side tabs LL1 and LL2. The angle of inclination of the oblique plane PO in relation to the above mentioned plane P may be between 10° and 20°, depending on the elasticity characteristics of the metallic material constituting the flexible strip LS.
In
The flexible strip LS can thus be clipped at its insertion spaces EI2 and EI2 by performing opposite constrained rotation on the flexible center tab LC in order to enable this center tab to pass under the printed circuit CI, the latter entering, by the corresponding edge of the slot F, in the first insertion space EI1; and to enter into electrical contact with the back contact face PV, then, by displacement of the flexible strip LS, towards the opposite edge of the slot F, so as to bring the latter into the second insertion space EI2 and make electrical contact between the front contact face PR and the flexible side tab or tabs LL1, LL2.
Thus, it is to be understood that the center tab LC makes it possible to ensure the function of breaking of the normally closed electrical contact by applying a stress on the pressure point PA in cooperation with the flexible side tabs LLl1 and LL2.
The flexible strip as shown in
In particular the pressure point PA provided on the center tab LC is advantageously formed by a boss, for example. Similarly, the contact face PcC1 of the flexible center tab LC is formed, for example, by a boss. In addition, optionally, the contact faces PcL1, PcL2 respectively of side tabs LL1 are also formed by a boss, according to the present embodiment.
A contact key for flexible membrane keypad, according to the object of the invention is now described in connection with
With reference to the above mentioned figure, the contact key comprises of the printed circuit board CI equipped with the front contact face PR and the back contact face PV each placed in the vicinity of one of the opposite edges of the slot F provided in the printed circuit board. A flexible contact strip LS, as previously described in connection with
Finally, the invention relates to a flexible membrane keypad provided with a contact key forming a normally closed type electrical contact as described in connection with
Shown in
The switch 10 includes a printed circuit 12 of generally plane shape, having a first face 12A and a second face 12B opposite to the first face 12A.
The first face 12A is generally an upper face intended to be turned towards the exterior of the portable communication device. This first face 12A is in particular shown in the
The second face 12B is generally a lower face, intended to be turned towards the inside of the portable communication device. This second face 12B is shown in particular in
The printed circuit 12 has a through orifice 14, allowing access between the first face 12A and the second face 12B. In the example shown, the orifice 14 has a generally rectangular shape in the plane of the printed circuit 12.
As shown in
As is shown in
The switch 10 also includes a conductor 20, in the form of a flexible conducting strip, designed for electrically connecting the first 16 and second contact pads 18.
The conductor 20 comprises a first part 22, such as shown in
The conductor 20 includes, in addition, a second part 24 extending between a first end 24A connected to the first part 22, and a second free end 24B designed to cooperate with the second contact pad 18.
Preferably, the conductor 20 is made of sheet metal, the first 22 and second 24 parts having been formed integrally.
In the example shown, the second part 24 of the conductor forms a strip (or flexible center tab) extending the base 22B of the first part 22, and extending longitudinally between the two branches 22A of this first part 22. This strip 24 passes through the orifice 14 so as to electrically connect the first part 22 with the second contact pad 18.
The second part 24 is elastically deformable between a rest position, shown in
Advantageously, the second part 24 comprises, at its second end 24B, of a boss 25, also called contact face, facilitating contact with the second pad 18.
It should be noted, that due to the elastically deformable structure of the conductor 20, this conductor 20 can be assembled on the printed circuit board 12 by the pinching of the printed circuit 12 between the first 22 and second 24 parts of the conductor 20. This assembly is particularly stable, thanks to the U-shape of the first part 22. This structure thus facilitates the assembly of the switch 10.
The switch 10 also comprises a metal cup 26 of conventional type, forming a pusher/push button, accessible from the side of the first face 12A of the printed circuit 12. This metal cup 26 is arranged above the conductor 20, so that it is capable of cooperating with the second part 24 of the conductor 20. To this end, as shown in
Such a metal cup 26 can be pushed by a user, in a manner so as to be deformed elastically between a rest position as shown in
In its rest position, the metal cup 26 is held away from the second part 24 of the conductor, which is also found in its resting position. The switch 10 is therefore closed. It should be noted that the height of the metal cup 26 in its position of rest is usually about 1 millimeter. Thus, the switch 10 is compact and can be easily integrated into a compact portable communication device.
In its engaged position, the metal cup 26 cooperates with the second part 24 of the conductor to maintain it in its stressed position. The switch 10 is thus opened.
Advantageously, the second part 24 of the conductor 20 includes a boss 28, forming a pressure point, provided between its first 24A and second 24B ends and intended to cooperate with the metal cup 26 when the metal cup 26 is in its engaged position. This boss 28 makes it possible to ensure contact between the metal cup 26 and the second part 24. Alternatively, the metal cup 26 could bear a similar boss meant for cooperating with the second part 24.
It should be noted that when the user releases the metal cup 26, the metal cup 26 and the second part 24 of the conductor 20 return by elasticity to their respective rest positions.
Preferably, the metal cup 26 is designed to form a hard point, in order to provide a tactile sensation to the user when he actuates the switch 10 by pressing the metal cup 26 with a finger.
The switch 10 preferably comprises some sealing means (not shown), for example of plastic material, covering at least the metal cup 26 and the conductor 20. The sealing means may also include, on the user-side, an inscription relating to the operation of the switch 10.
Such sealing means preferably cover the entire keypad of the communication device so that the device can be used in wet and aggressive environments.
On an optional basis, the switch 10 may also include means for back lighting, arranged on the side of the second face 12B of the printed circuit 12. Indeed, thanks to the orifice 14, it is possible to provide the switch 10 with back lighting in a simple and effective manner.
The previously described switch 10 comprises of few elements, and thus it has a low weight, as well as a low cost.
It should be noted that the invention is not limited to the embodiment that has been described above, but may be presented in different variants without departing from the scope of the claims. In particular, the characteristics of each embodiment described above may be implemented in a manner equivalent to the other embodiment described.
Number | Date | Country | Kind |
---|---|---|---|
1002193 | May 2010 | FR | national |
1005040 | Dec 2010 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/FR11/51196 | 5/26/2011 | WO | 00 | 2/6/2013 |