Electrical contact switch

Abstract: Electrical contact switch intended to be mounted, in particular, on a printed circuit board (86) comprising a fixed part and a part which is mobile with respect to the fixed part, characterized in that it comprises a base (10) provided with electrical contacts (20), a cover (12) which is movable with respect to this base and has means of illumination (68), supply connections (36) for these means of illumination, at least one arched resilient ele­ ment (16) arranged substantially transversely to the dir­ ection of movement of the cover (12) in a seating in the base (10) and co-operating with the said movable cover, and a shoe (14) jointed with respect to the cover and co­ operating with a means for guiding and for limiting the base and provided with contacts (50) arranged opposite the electrical contacts (20) of the base along the direction of movement of the cover. The switch according to the invention also compri­ ses a water- and dust-tight membrane (78) which protects the shoe (14) and its contacts (50) during any movement in the base (10) and which prevents any penetration of this base into the upper part (44).

Description: The present invention relates to an electrical contact switch intended to be mounted, in particular, on a printed circuit board. There are numerous applications for which industry seeks switches which might combine reliability, a long life and contacting which is constant with time with a simple design, a low cost price and a small bulk. Moreover, for certain applications it is necessary for the upper face of the switches to be illuminated internally, and putting them in position must also be simple. Another limitation is that of having available a modular switch, that is to say one which can easily be mounted on a previously prepared printed circuit and whose structure makes it autonomous such that the function of the external housing is reduced merely to the function of masking and not the function of guiding. There is known a push-button switch having a resilient element of rapid action, which is described in French Patent No. 2,468,197, in the name of ITT INDUSTRIES, which partially fulfils the abovementioned conditions. Such a switch has a particularly long useful life, thanks to a special arrangement and to the use of a helical spring arranged transversely to the direction of movement of the push button. The switch has a casing in which there slides a pusher, the lower part of which substantially has the shape of a fork so as to ensure guiding of the pusher during its movement. The rod of the pusher has parallel to this a bore in the shape of a diabolo enabling a helical spring to pass, the ends of which are arranged in the bores made in the walls of the casing. A return spring is arranged in the lower part of the pusher between the bottom of the casing and this same pusher in coaxial manner, in order to push the pusher upwards. The transversely arranged spring can thus take on, when pressure is exerted on the pusher, two stable positions, an upper and a lower position. The passage from the lower position to the upper position is effected by exerting a complementary pressure on the return spring, which provides sufficient inertia to the pusher to overcome the resistant force of the transversely arranged spring and leads the latter to pass from its lower position of equilibrium to its first position, in which the pusher is in the upper position. This same push button can also be used without a bistable position, and to this end the bores receiving the ends of the transversely arranged spring are oriented upwards in order to give this spring a curvature towards the top such that actuation of the pusher downwards for a given course is not sufficient to put the transversely arranged spring in a stable position. Although this switch has certain advantages, it does not fulfil all the above-listed criteria. In fact, there is no provision for illumination of the front face of the push button, and furthermore guiding of the pusher is ensured by the cover of the casing and by a fork in its lower part, and the forces exerted on this push button, when they are not perfectly in the axis of the pusher, can bring about premature wear of the guiding means. Furthermore, if the contact is registered, there is no provision for contacts of a particular shape suitable for ensuring operational reliability. Premature wear of the guiding means leads to the introduction of foreign bodies inside the casing in the form of dust, which can lead to poor functioning of this switch. Document GB-A-2.042.271 discloses a switch comprising a fixed part and a movable part, the fixed part comprising a base with electrical contacts, a cover which is movable with respect to the base and has means of illumination with electrical supply connections. The cover is provided with means for exerting a return spring force. These means comprise a great number of components which are successively arranged between the cover and the base and which include a movable insert urged by a return arched spring wich cooperates with a rocking contact guided on a movable shoe which is slidebly guided in one part of the fixed base an don which acts another return spring. Due to this great number of components, it is very difficult to precisely control the actual return spring force which is exerted on the push-button, the control of this return force being critical in the case of a push-button switch providing a trigging action and a tactile sensation of switching to the user. The object of the present invention is thus to propose an electrical contact switch intended to be mounted, in particular, on a printed circuit board, which overcomes the disadvantages of the known switches and fulfils all the above-listed criteria. To this end, the electrical switch according to the invention is characterized in that the return spring means are only comprised of said at least one resilient spring which is arranged in a seating in the base to impart on the cover a single stable position and to tend to move the cover away from the base, and in that the shoe is directly coupled to the cover by means of a pivot pin joint. The invention will be better understood by reading the description which follows, of a particular embodiment, with regard to the attached drawings, in which: Figure 1 shows an exploded perspective view of a switch acording to the invention; Figure 2 shows a sectional view along a longitudinal vertical central plane and Figure 3 shows, on the right-hand side, a sectional view along a transversal central plane and, an the left-hand side, an elevation with some parts removed. Figure 1 shows the three principal subassemblies of the switch according to the invention, namely the base 10, the cover 12 and the shoe 14. The base 10, which is of substantially parallelepipedic shape, has two springs 16 of the helical type which are arched upwards, the ends of which are received in seatings 18 inclined with respect to the plane of the base so as to orient the arching of the spring upwards. This base also has electrical contacts 20 situated on either side of a longitudinal groove 22. Moreover, these same contacts 20 extend outside the base 10 to form pins 24. A complementary groove 26 is made in this base along an orientation which is perpendicular to that of the first groove 22. The longitudinal side walls have a recess 28, substantially in the centre of which there projects a retaining stop 30, this stop being mouided in one piece with the base. The transverse side faces also each have a recess 32 through which pass the helical springs 16, which makes the latter accessible via their upper part. Moreover, this base 10 is provided with four bores 34, through which pass electrical supply connections 36, the upper end of which is in the form of non-contiguous helical spirals 38, while the lower part 40 is bent into a J shape in order to constitute a pin. Finally, this base is completed by a groove 42 made in its upper part 44. The shoe 14 has a U shape, the open side of which is.oriented opposite the base 10, and it has in its centre parallel to its arms a rib 46 of a height greater than that of the arms, thus separating the shoe in a U shape into two seatings 48 also in a U shape. In these seatings 48 there are positioned leaf springs 50 of C-shaped profile, the open side of which is directed opposite the base 10. The central part 52 of these springs is introduced with slight force into the seatings 48, in which they are held, while the curved ends 54 extend past these seatings 48. Each spring consists of a leaf, and notches 56 are made in the curved ends 54 of these springs so as to constitute a double contact. The shoe also has two lateral lugs 58 arranged outside the arms of the shoe 14 and, in its upper part, the male element 60 of a pivot pin which projects above this same shoe. The cover 12 is of parallelepipedic shape, and its dimensions are such that its lateral faces come outside the base 10 and co-operate with it by sliding. This cover has an opening 62 on each of its longitudinal lateral faces, arranged substantially in its central part. This cover 12 also has a support plate 64 intended to receive a printed circuit board 66 on which are arranged light-emitting diodes 68 arranged in two parallel series along the longitudinal axis of the. board 66, this board 66 being provided with notches 70 intended for the passage of the ends of the supply connections 36. Moreover, this cover has a projecting shoulder 72, against which there bears a transparent or at least translucent mask 74, this mask carrying the pictogram 76 of the function which can be executed by means of the switch according to the invention. In this same Figure 1, there is also shown a sealing membrane 78 located between the shoe 14 and the support plate 64 which is integrally formed with the cover 12, the diameter of this membrane being sufficient to cover the upper part of the base 10 and be housed by means of its lower part 80 in the groove 42. In its upper part, this membrane 78 has a bore 82 intended for the passage of the projecting part 60 of the pivot pin. With reference to Figure 2, which is a sectional view along a vertical longitudinal plane, 84 shows the hollow female part which co-operates with the projecting part 60 of the pivot pin. Moreover, in this same section there is shown the board, in particular for a printed circuit, 86 intended to receive the switch according to the invention, the latter being fastened to this board by soldering the pins 24. Similarly, the lower ends of the supply connections 40 are also soldered so as to enable electric current to pass into the diode support plate 66. the ends of these connections being soldered at 88 to this same plate. There is also shown the external covering 90 of the apparatus in which the modular switch according to the invention is arranged. In this same figure, there are seen inside the transverse lateral faces lugs 92 which project inside the cover 12 so as to co-operate via the recesses 32 with the springs 16. The assembly of the switch according to the invention is effected in the following way. The printed circuit 66 provided with the diodes 68 and springs 36 is arranged on the support plate 34. The supply connections 36 are then fastened by soldering at their upper end to the board 66. The contacts 50 are slid into the seatings 48 of the shoe 14 until they latch in. Similarly, the mask 74 is fastened to the upper part of the cover 12. The base 10 is provided with its helical springs 16 and receives in its grooves 22 and 26 the ribs 46 and the lugs 58 of the shoe 14 respectively. The projecting part 60 of the pin is passed through the bore 82 of the sealing membrane 78, and the lower part 80 of this same membrane 78 is housed in the groove 42 of the upper part 44 of the base 10. The base 10 is then introduced into the cover 12 until the projecting element 60 of the pivot pin co-operates with the hollow part 84 simply by means of the resilience of the material until it latches in. Parallel to this, the lower ends 40 of the connection devices 36 are passed through the bores 34 of the base 10 and project at the lower part of this same base. The assembly of the switch according to the invention on the printed circuit board 86 is effected in simple manner by inserting the pins 24 and 40 in this board 86 and by fastening the latter with the aid, for example, of welding spots. The operation of this switch is reliable and simple, as will be demonstrated below. The user exerts a pressure on the upper face of the switch, and more particularly on the mask 74, which brings about a movement Of the cover 12 with respect to the base 10, and the movement of the cover 12 simultaneously drives the movement of the shoe 12 which is mounted jointed to this cover 12, the lugs 92 projecting inside the cover 12 bearing against the springs 16. The user must therefore overcome the resistant force opposed by the spring 16 which, in the example shown, is of the order of 2·45 N (250 gF) per spring. It may also be calibrated to 4·9 N (500 gF). The rigidity of the supply connection 36 is, in contrast, negligible with respect to the rigidity of the helical springs 16, and thus does not play a part in the resistance to depression. The rib 46 and the lugs 58 slide respectively in the grooves 22 and 26 as far as the stop. As can be seen in Figure 2, the distance h separating the lower. part of the rib 46 from the base of the groove 22 is greater than the distance d which separates the lower part of the curved parts 94 of the spring leaves 52 so that, when the rib 46 comes up against the base of the groove 22, the spring leaf 52 exerts a contact pressure proportional to this distance on the contacts 20, which form fixed blocks, in a resilient manner, thus avoiding any plastic deformation which might prejudice the good functioning of the switch. It will also be noted at the same time that the helical part 38 of the supply connections 36 is compressed, since the distance between the printed circuit board 66 to which it is connected and the base 10 has also been reduced. When the rib 46 is up against the base of the groove 22, the helical spring 16 causing the contact has been deformed into a substantially M-shaped profile, but this position of the spring is an unstable position and, as soon as the user releases the pressure exerted on the cover 12 via the mask 74, the spring tends to reassume its initial arch and thus repels the cover 12 upwards and drives the shoe 14, which itself drives the spring leaves 50 and releases the contact between these leaves 50 and the contacts 20 forming the fixed blocks integrally formed with the base 10. The curved parts 54 thus reassume their initial profile because of the very resilience of the material of which they are composed. The cover 12 pushed by the spring 16 moves away from the base 10 until the retaining stop 30 comes into contact with the lower part of the opening 62 made in the cover 12, thus preventing the cover 12 and the base 10 from becoming separated. In this position, the lower end of the rib 46 is always in contact with the groove 22 and the rib remains guided, while the lateral faces of the cover 12 also surround the base 10 at one part of its height. The switch according to the invention thus has numerous advantages, in particular perfect guiding and sliding of the cover 12 with respect to the base 10. In fact, this sliding is independent of the movement of the contacts, since the shoe 14 is jointed to the cover 12. The shoe can thus slide perfectly, since it has its own guiding means and an excellent electrical contact is ensured between the flexible leaf contact 50 and the fixed block contacts 20. Thanks to the jointing, the manufacturing tolerances are thus perfectly compensated. Moreover, the spring 16 produces a clean contact which can be modified as a function of the requirements by modifying the rigidity of this spring. As regards the supply connections, as a result of their helical spiral shape, they can undergo a great many cycles, bringing about a very long life for the switch. The light-emitting diodes 68 enable illumination of one row or the other or of both together, as desired, this illumination moreover being effected with limited emission of heat. Furthermore, the membrane 78 ensures perfect sealing during the movements of the shoe 14 in the base 1 0, thus avoiding any penetration of water, dust or any other element which might prejudice the good functioning of the electrical contacts. The electrical contacts must be kept clean and water may not accumulate in the upper part of the base 10 so that the circuit-breaking ability of the switch is maintained. Such a sealing membrane has an important function in particular in the case where this switch is used in particular atmospheres or in sectors such as aviation where the reliability requirements are high. It is seen that the assembly of this switch is effected in a simple manner by pushing until it latches in, and that the cover 12 is jointed by means of a pivot pin or latched onto the retaining stops 30 of the base 10. The switch according to the invention consists of a single module which, once assembled, is monolithic and can thus be easily installed on printed circuit boards such as 86, and that it is easy to automate this operation. Similarly, the switch according to the invention does not require further adjustment with respect to the covering 90, since it is independent of the latter. This ease of assembly brings about a very low cost price for the assembled switch. The variant which has just been described has two contacts 50, four fixed block contacts 20 and two rows of light-emitting diodes 68. This double input/double output switch can be used to act in a single circuit or in two independent circuits, which correspondingly increases its versatility of use.

Claims: Electrical contact switch of the type comprising a fixed base (10) for mounting on a printed circuit board and provided with fixed electrical contacts (20), a cover (12), in the form of a push-button, which is slidably mounted with respect to the base (10) and which comprises means of illumination (68) and supply connections (36) for these means of illumination, return spring means arranged between the cover (12) and the base (10) and comprising at least one arched resilient spring (16) arranged substantially transversely to the direction of displacement of the cover and cooperating with the cover (12), and a shoe (14) which is joined to the cover (12), which cooperates with means (22) for guiding and limiting the displacement of the cover (12) with respect to the base (3) and which is provided with electrical contacts (50) arranged opposite the electrical contacts (20) of the base, characterized in that the return spring means are only comprised of said at least one resilient spring which is arranged in a seating (18) in the base (10) to impart on the cover a single stable position and to tend to move the cover (12) away from the base, and in that the shoe (14) is directly coupled to the cover (12) by means of a pivot pin joint (60, 84). Switch according to Claim 1, characterized in that the Lower part of the shoe (14) is provided with a rib (46), and in that the means for guiding and for limiting is a groove (22) made in the base (10) with which the said rib cooperates. Switch according to Claim 1 or 2, characterized in that the pivot pin joint comprises a projecting part (60) which is in one piece with the shoe, the hollow part of which (84) being made in the cover (12). Switch according to any one of the preceding claims, characterized in that the electrical contacts (20) of the base are fixed blocks, of which one part projects past the lower part of the base so as to form pins (24). Switch according to any one of the preceding claims, characterized in that the electrical contacts (50) of the shoe are flexible C-shaped leaves of which the open side is oriented opposite fixed blocks. Switch according to Claim 5, characterized in that each C-shaped leaf (50) is arranged in its central part (52) in a seating (48) made in the shoe (14) and is oriented perpendicularly to the direction of movement of the cover. Switch according to any one of the preceding claims, characterized in that the distance d between the curved end part (54) of the leaves (50) of the contacts of the shoe (14) and the fixed blocks (20) of the base is less than the distance h which separates the lower part of the rib (46) and the base of the groove (22) so that the leaf bears against the bloks by resilient deformation. Switch according to any one of the preceding claims, characterized in that the shoe comprises two lateral lugs (58) arranged on either side of the rib (46) along a direction perpendicular to the longitudinal axis of the said rib so as to ensure complementary guiding, cooperating with a groove (26) made in the base (10) and oriented perpendicularly to the longitudinal axis of the base. Switch according to any one of the preceding claims, characterized in that the base (10) comprises a retaining stop (30) which cooperates with an opening (62) made in the lateral walls of the cover (12). Switch according to any one of the preceding claims, characterized in that a flexible sealing membrane (78) is fastened by its periphery (80) in a groove made in the upper part (44) of the base, and in that it has a bore (82) enabling the projecting part (60) of the pivot pin to pass. Switch according to any one of the preceding claims, characterized in that the means of illumination are light-emitting diodes (68) mounted on a printed circuit board (66) which is housed in a seating made in the upper face of the movable cover (12). Switch according to any one of the preceding claims, characterized in that the supply connections (36) are resilient elements of which on end is fastened to the printed circuit board carrying the light-emitting diodes and the other is mounted so as to slide through bores (34) of the base and projects past the lower part of this base so as to form a pin (40). Switch according to any one of the preceding claims, characterized in that the resilient arched spring (16) is an arched helical spring of which one part can be curved in the opposite direction so as to form an M, while the rib (46) of the shoe comes up against the base of the groove (22) of the base, this position being unstable. Switch according to any one of the preceding claims, characterized in that the resilient element is calibrated to 4·9 N (500 gF), and in that the rigidity of the supply connections is negligible with respect to the rigidity of the resilient element

Inventors: JANNIERE ALAIN, JURET BERNARD, JANNIERE, ALAIN, JURET, BERNARD
Applicants: ITT COMPOSANTS INSTR, ITT COMPOSANTS ET INSTRUMENTS
Application year: 1989
Main classification: H01H13
IPC codes: H01H13, H01H1