Push button switch with elastic conductive sheet

Abstract

There is provided a push button switch using an elastic conductive sheet having a spherical protuberance which is adapted to be deformed by a keytop for electrically connecting fixed electrodes formed on a printed circuit board. Spring means for returning the keytop is not required, so that the construction is simplified. Also, excellent switching action, operability and reliability can be ensured.

Description

This invention relates to push button switches using as elastic conductive sheet, and has as an object providing a push button switch suited particularly for use as a keyboard switch for desk-top electronic calculators.

Other objects, features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIGS. 1 and 2 are sectional views showing prior art push button switches using a conductive plastic sheet;

FIG. 3 is an exploded perspective view of a keyboard switch assembly for desk-top electronic calculators using the push button switch according to the invention;

FIGS. 4 and 5 are sectional views showing embodiments of the push button switch according to the invention;

FIGS. 6a and 6b are sectional views showing different forms of the spherical protuberance incorporated in the push button switch according to the invention;

FIGS. 7a to 7d show the way in which the spherical protuberance of the push button switch according to the invention is deformed with pressure;

FIG. 8 is a sectional view showing a further example of the push button switch according to the invention;

FIGS. 9 and 10 are sectional views showing other embodiments of the push button switch according to the invention;

FIGS. 11a to 11c show examples of the spherical protuberance having a nodal character;

FIGS. 12 to 15 are sectional views showing still further embodiments of the push button switch according to the invention;

FIG. 16 is a view showing a conductor pattern on the printed circuit board of a prior art push button switch; and

FIGS. 17 to 19 are views showing electrode patterns on the printed circuit board of the push button switch according to the invention.

The prior art switch in which metal contacts are made and broken is prone to the phenomenon of chattering at the time the contacts are made. Also, if the contact pressure when the contacts are made is unnecessarily high, wear of the contact area becomes high, rendering the contact state unstable. This is of course undesirable from the standpoint of reliability, durability and safety to the switch. Heretofore, various types of switches have been proposed for overcoming the above drawbacks.

For example, push button switches in which the switching action is obtained by bringing a conductive plastic film into contact with electrodes printed on a printed circuit board and normally held underneath the conductive plastic film at a predetermined distance therefrom are roughly classed into two types as shown in FIGS. 1 and 2.

The switch of the type shown in FIG. 1 comprises a printed circuit board 1 having two electrodes 2 and 2' printed thereon, a return spring member such as a coil spring 3, a keytop 5 held in a frame 4 and having a downward integral extension 6, and a conductive plastic sheet piece 7 provided at the lower end of the extension 6 and having an area capable of covering both the electrodes 2 and 2'. The other type of switch shown in FIG. 2 has a construction consisting of a printed circuit board 1 having two electrodes 2 and 2' printed thereon, a return spring member such as a coil spring 3, a keytop 5 held in a frame 4 and having a downward integral extension 6 and a conductive plastic sheet 7' supported on a spacer intervening between printed circuit board 1 and plastic sheet 7' to hold the plastic sheet above and at a slight distance from the electrodes 2 and 2'.

The switches of both of these types are actuated or closed when the electrodes 2 and 2' are contacted by the conductive plastic sheet piece 7 or plastic sheet 7' due to vertical displacement of the plastic film piece toward the electrodes 2 and 2' on the printed circuit board 1 caused by depressing the keytop 5.

In the switches of the above constructions, however, the elasticity of the conductive plastic sheet piece 7 or plastic sheet 7' constituting an element of the switch is not fully utilized. Also, since the plastic sheet piece is displaced in the vertical direction with respect to the electrodes, the closing of the switch is achieved only at the end of the downward stroke of the keytop. In other words, there is provided no play for any extra movement of the keytop after the switch is turned on, and the switch will not be actuated until the keytop is depressed through the full stroke. Therefore, the keytop 5 is subject to excessive depressing force, so that the wear of the contact area is spoiled. Further, since the keytop return spring 3 is used, the spring and the conductive plastic film piece are likely to resonate due to the elasticity of the spring and the complex elasticity of the conductive plastic, so that the possibility of occurrence of chattering is increased. This problem has been fatal in the prior art push button switch, and this type of chattering has direct bearing upon the user's power or skill to operate the keytop and is liable to lead to malfunctioning of the keyboard switch of the desk-top electronic calculators and push botton telephone sets where chattering is particularly undesirable, thus greatly degrading the reliability and durability of these machines.

An object of the invention is to provide a push button switch having a construction effectively utilizing the elasticity of an elastic sheet of a conductive material such as a conductive rubber sheet and conductive plastic sheet for returning the keytop due to the elasticity of the elastic sheet.

Another object of the invention is to prevent chattering by an arrangement wherein the switch is closed at an intermediate point of the full stroke of the keytop.

A further object of the invention is to provide a push button switch which can be reliably closed by lightly depressing the keytop.

A still further object of the invention is to provide simplified construction and improved reliability of the switch by using a conductive plastic sheet.

The push button switch according to the invention will now be described in connection with some embodiments thereof.

FIG. 3 shows a keyboard switch assembly for desk-top electronic calculators using the push button switch according to the invention. In the Figure, reference numeral 30 designates a keytop supported in a frame 31 such that it can be moved vertically. Numeral 32 designates an elastic conductive sheet formed with a plurality of spherical protuberances 33 each formed at a position corresponding to the associated keytop 30. Numeral 34 designates an insulating sheet formed with holes 35 each corresponding in position to the associated spherical protuberance 33. Numeral 36 designates a printed circuit board having conductor patterns 37 printed thereon. It is also formed with small holes 38 each for each switch. Numeral 39 designates a dust filter.

FIGS. 4 and 5 show embodiments of the push button switch according to the invention. In these Figures, like reference numerals refer to corresponding parts.

The embodiment of FIG. 4 comprises a printed circuit board 9 having electrodes 10 and 10' formed thereon. Held over the printed circuit board 9 and supported on a spacer 12 having a diaphragm structure is a conductive plastic sheet having a spherical protuberance 11' extending directly above the electrode 10'. The other electrode 10 is in contact with the conductive plastic sheet 11. Numeral 13 designates a frame having a hole 14, and numeral 15 designates a keytop having an integral downward extension 16. The keytop 15 is mounted in the hole 14 of the frame 13 such that it can be moved vertically.

In operation, by downwardly depressing the keytop 15 the lower end of the extension 16 of the keytop 15 pushes and deforms the spherical protuberance 11' of the conductive plastic sheet 11 to bring the protuberance 11' into contact with the electrode 10', thus electrically connecting the electrodes 10 and 10'. If the conductive plastic sheet 11 formed with the spherical protuberance 11' has elasticity, the spherical protuberance 11' will flex in a quick action. More particularly, when pressure is applied to the keytop 15, it will not flex until a certain predetermined pressure is reached and will undergo sudden flexural deformation as soon as this pressure value is exceeded. When the pressure applied to the keytop 15 is removed, the spherical protuberance is quickly restored to the initial state and separated from the fixed electrode 10', thus opening the associated electric circuit. In this way, the electric circuit is closed and opened. Since this is down in a quick action, reliable operation can be ensured. Also, the coil spring for returning the keytop used in the prior art can be omitted, which is a great advantage in view of the cost.

In the embodiment of FIG. 5, which also uses a conductive plastic sheet having a spherical protuberance, the conductive plastic sheet 11 is normally in contact with neither electrode 10 or 10', and it is brought into contact with both electrodes 10 and 10' on the printed circuit board 9 normally extending below it for closing the switch. Otherwise, the operation and effects are the same as in the preceding embodiment of FIG. 4.

The extent of the quick action and the returnability of the keytop may be suitably preset by appropriately selecting the hardness and thickness of the conductive plastic sheet and the shape and dimensions of the spherical protuberance.

FIGS. 6a and 6b show other possible shapes of the spherical protuberance, and these and other shapes may be appropriately selected to match the design values of the push button switch depressing pressure, stroke and so forth.

FIGS. 7a to 7d show transforming states of movements according to an embodiment of the invention. This switch according to the invention comprises a support consisting of a printed circuit board 9 having electrodes 10 and 10' formed thereon by means of the printed circuit technique, an elastic conductive plastic sheet 11 having a spherical protuberance or dimple 20 having a flexural node for two-step deformation and a spacer 12 having a diaphragm structure for insulating the sheet 11 from the printed circuit on the printed circuit board. In this embodiment, an annular shoulder 20a on the spherical protuberance or dimple 20 of the conductive plastic sheet 11 is brought into contact with the electrodes 10 and 10' due to its flexing for closing the associated electric circuit.

FIG. 7a shows the switch in its "off" state without any pressure exerted on the spherical protuberance 20. When pressure is exerted on the spherical protuberance 20 for turning on the switch, the conductive plastic sheet 11 flexes about the flexural node of the spherical protuberance 20 as shown in FIG. 7b. Then, as the first step in the deforming action the flexural node shoulder 20a are brought into contact with the board 9 as shown in FIG. 7c. As this instant, the flexural node is brought into contact with the electrodes 10 and 10' on the board 9 to turn on the switch. Subsequently, the conductive plastic sheet 11 can undergo the second step deformation wherein the central portion 20b of the dimple 20 is pressed between electrodes 10 and 10' as shown in FIG. 7d. In this way, there is provided a so-called trouble after the closure of the switch.

If the conductive plastic sheet 11 formed with the spherical protuberance 20 has elasticity, the spherical protuberance 20 will flex in quick action. More particularly, when pressure is applied to it, it will not flex until a certain predetermined pressure is reached and will undergo sudden flexural deformation as soon as this pressure level is exceeded.

When the pressure applied is removed, the spherical protuberance 20 is quickly restored to its initial state and separated from the electrodes 10 and 10', thus opening the associated electric circuit. In this way, the electric circuit is closed and opened. Since this is done in quick actions, reliable operation can be ensured. Also, it is possible to suitably preset a point at which the switching action takes place (FIG. 7c) during the total displacement from the state of FIG. 7a to the state of FIG. 7d (corresponding to the full stroke of the push button switch) so as to provide for the so-called trouble for the displacement from the state of FIG. 7c to the state of FIG. 7d. By doing so, an excellent sense of operation may be obtained. Further, since the spherical protuberance 20 can provide a large restoring force, the coil spring for returning the keytop in the prior art can be omitted, which is a great advantage in view of the cost.

FIG. 8 shows a modification of the preceding embodiment. In this modification, the electrode 10 and conductive plastic sheet 11 are always in contact with each other, and only when turning on the switch the flexural node portion of the spherical protuberance 20 of the conductive plastic sheet 11 is brought into contact with the other electrode 10'.

FIGS. 9 and 10 show embodiments of the push button switch using the afore-mentioned switching mechanism. In these embodiments, the keytop 44 made of an insulating material is mounted in a hole formed in the top wall of a switch frame 13 such that it can be moved vertically, and the afore-mentioned switching mechanism is provided below the keytop 44. In the embodiment of FIG. 9, the switching mechanism consists of a printed circuit board 9 having electrodes 10 and 10' provided with leads, a conductive plastic sheet 11 and a spacer 12 for insulating the conductive plastic sheet 11 when the switch is off. In the embodiment of FIG. 10, the electrode 10 is always in contact with the conductive plastic sheet 11, and only when turning on the switch the flexural node portion of the spherical protuberance 20 of the conductive plastic sheet 11 is brought into contact with the other electrode 10'. In the operation of these embodiments, with the downward movement of the keytop 44 of the conductive plastic sheet 11 is flexed and brought into contact with the electrodes 10 and 10' (or only the electrode 10) at the time of the first step deforming action, with the second step deforming action reserved for the so-called trouble after the closure of the switch. In this way, the closing and opening of the associated electric circuit are effected.

The extent of the quick action and the returnability of the keytop may be suitably preset by appropriately selecting the hardness and thickness of the conductive plastic sheet and the shape and dimensions of the flexural node of the spherical protuberance.

FIGS. 11a to 11c show possible shapes of the spherical protuberance having a flexural node for two-step deformation, and these and other shapes may be appropriately selected to match the design values of the push button switch depressing pressure, stroke and so forth. Also, where a plurality of push button switches are assembled into a keyboard switch assembly for desktop electronic calculators, push botton telephone sets and so forth, the productivity may be improved by using a single sheet formed with a plurality of spherical protuberances at a suitable pitch as the conductive plastic sheet 11.

FIGS. 12 and 13 show further embodiments of the push button switch according to the invention. Either of these embodiments comprises a switch frame 51, a keytop 52 of an insulating material mounted for vertical movement in a hole formed in the top wall of the frame 51, a conductive plastic sheet 53 disposed below the keytop 52 and having a spherical protuberance, electrodes 54 and 54' facing the spherical protuberance and formed on a board 56 formed with a small hole 55 and a spacer 57 of a diaphragm structure provided for taking out leads from the electrodes 54 and 54' and insulating the plastic sheet 53.

In operation, when the keytop 52 is downwardly depressed with pressure applied thereto, the spherical protuberance of the conductive plastic sheet 53 undergoes flexural deformation and is brought into contact with the electrodes 54 and 54' to close the associated electric circuit. When the applied pressure is removed the electric circuit is opened due to the effect of the small hole 55 formed in the board 56 and the elastic restoring force of the conductive plastic sheet 53. In this way, the electric circuit is closed and opened.

In the embodiment of FIG. 12, the conductive plastic sheet 53 is adapted to undergo single step deformation, with the switch closed at the end of the full stroke, while in the embodiment of FIG. 13 two-step deformation of the conductive plastic sheet is provided to provide for a so-called trouble after the closure of the switch. In both these embodiments, the function and effects of the small hole 55 formed in the board 56 are the same.

FIGS. 14 and 15 show still further embodiments of the push button switch according to the invention. Either of these embodiments comprises a switch frame, a keytop of an insulating material mounted for vertical movement in a hole formed in the top wall of the frame 51, a conductive plastic sheet 53 disposed below the keytop 52 and having a spherical protuberance, electrodes 54 and 54' facing the spherical protuberance and formed on a board 56 formed with a small hole 55, a spacer 57 of a diaphragm structure provided for taking out leads from the electrodes 54 and 54' and insulating the plastic sheet 53 and a fibrin cloth-like insulator 58 serving as a filter.

In operation, when the keytop 52 is downwardly depressed with pressure applied thereto, the spherical protuberance of the conductive plastic sheet 53 undergoes flexural deformation and is brought into contact with the electrodes 54 and 54' to close the associated electric circuit. When the applied pressure is removed, the electric circuit is opened due to the effect of the small hole 55 formed in the board 56 and the elastic restoring force of the conductive plastic sheet 53. In this way, the electric circuit is closed and opened.

In the embodiment of FIG. 14 the conductive plastic sheet 53 is adapted to undergo single step deformation, with the switch closed at the end of the full stroke, while in the embodiment of FIG. 15 two-step deformation of the conductive plastic sheet is provided to provide for a so-called trouble after the closure of the switch. In both these embodiments, the function and effects of the small hole 55 formed in the board 56 and the filter 58 are the same.

For the fibrin cloth-like insulator 58 which serves as a filter, a porous or net-like material which permits the flow of air but does not transmit the dust in the air may be used. While felt is the best material, formed plastic such as urethane foam having thin continuous pores may also be effectively used. Also, it may extend over the entire back area of the board 56 or only for the portion adjacent the small hole 55.

As has been described, according to the invention with the provision of the spherical protuberance in the conductive plastic sheet and the small hole in the printed circuit board the resonance and bounce phenomena can be eliminated, and also the chattering can be minimized. Further, reliable return action can be ensured. Furthermore, with the provision of the filter means contact failure due to collection of dust can be prevented. Thus, it is possible to provide a push button switch having excellent reliability and stability.

FIGS. 16 to 19 show conductor patterns to be formed on the printed circuit board. FIG. 16 shows a prior art pattern. With such a simple pattern consisting of two separate rectangles it is likely that a steady and stable contact state is not obtained depending upon the shape and structure of the conductive material brought into contact with the electrodes, giving rise to chattering phenomenon at the time of contact. FIGS. 17 to 19 show conductor patterns which can prevent such chattering phenomenon. With combinations of comb-like patterns of the two electrodes printed on the board, reliable and stable contact of these electrodes with the conductive plastic material may be ensured so that it is possible to provide a push button switch of high reliability.

Claims

What we claim is:

1. A push button switch comprising support means; a pair of fixed spaced electrodes located on said support means; and an elastic conductive sheet having a dimple positioned adjacent said electrodes and spaced therefrom by a predetermined distance, said dimple including a central portion and an annular shoulder separated from said central portion by a flexural node, said dimple being deformable with a double snap action when depressed by a force exerted on the central portion thereof, the first snap action of said dimple forcing said annular shoulder into contact with said pair of fixed electrodes thereby making electrical contact therebetween, and the following snap action forcing the central portion of said dimple between said electrodes.

2. A push button switch comprising a printed circuit board; spaced fixed electrode means printed on said printed circuit board; an elastic conductive sheet having a dimple positioned adjacent said electrodes and spaced therefrom by a predetermined distance, said dimple including a central portion and an annular shoulder separated from said central portion by a flexural node, said dimple being deformable with a double snap action when depressed by a force exerted on the central portion thereof; and a keytop slidably supported above said dimple for depressing said dimple, the first snap action of said dimple forcing said annular shoulder into contact with said pair of fixed electrodes thereby making electrical contact therebetween, and the following snap action forcing the central portion of said dimple between said electrodes.

3. The push button switch according to claim 2, which further comprises an insulating member having a hole therein in the position corresponding to said dimple, said insulating member being disposed between said conductive sheet and said printed circuit board.

4. The push button switch according to claim 2, wherein said printed circuit board has a small hole for the escape of air.

5. The push button switch according to claim 2, which further comprises a fibrin filter provided on the underside of said printed circuit board.