GB1558649A - Push button electric switch - Google Patents

Description

(54) PUSH BUTTON ELECTRIC SWITCH (71) We, ISOSTAT, a French body corporate, of 2 Avenue Francois-Godin 62780, Cucq, France. do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a push button switch and more particularly to a miniature electrical switch having an inoperative condition in which the circuit or circuits controlled by the switch are open, and an operative condition in which the push button is depressed and the circuit or circuits are closed.

The invention is applicable, for example, to electronic apparatus such as miniature electronic calculators in which such switches are grouped to form a keyboard.

Previously known switches of this type have comprised a relatively large number of parts, and, moreover, they often have a relatively short life as a result of dirtying of the contacts.

An object of the present invention is to obviate or mitigate these disadvantages by providing a switch which comprises a relatively small number of parts which can be assembled easily and economically on automatic machines, the contacts of which are self-cleaning, and which are adapted for mounting on simple face printed circuits which are much less expensive than double face circuits which often had to be used with previously known switches.

According to the present invention there is provided a pushbutton switch comprising a base having an inner axial recess, a button telescopically mounted on the base and formed with an axially inwardly projecting guide post which is stepped down in diameter to Provide two longitudinally spaced inwardly facing annular shoulders separated by a short intermediate post length portion which terminates in an axial post extension which is a sliding fit in the inner recess of the base, a coil spring surrounding the extension and positioned between an inner surface portion of the base and the lower shoulder of the post to bias the button away from the base, at least two spaced stationary contacts positioned within the base and having portions extending outwardly therefrom, and a movable contact constituted by a flexible, resilient, apertured disc mounted on the intermediate post length portion for bridging the stationary contacts when the button is depressed, the diameter of the disc aperture being greater than the diameter of the intermediate post length portion but smaller than the diameter of the upper annular shoulder and also smaller than the outer diameter of the coil spring.

Preferably, the base carries three stationary contacts.

Good results are obtained with a movable contact disc the thickness of which is in the order of one hundredth of the diameter, for example, eight hundredths of a millimetre for a diameter of 7 mm.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is an axial sectional view of a switch according to the invention in an inoperative condition; Fig. 2 is a sectional view corresponding to Fig. 1, but in the operative condition; Fig. 3 is a plan view corresponding to Fig. 1 from below; Fig. 4 is a plan view corresponding to Fig.

1 from above; Fig. 5 is an elevation of the push button cap; and Fig. 6 is a fragmentary sectional view of the base of the switch, showing the arrange- mtnt of the contacts.

A push button switch according to the invention comprises a base 2 of electrically insulating plastics material. The base carries at least two fixed contacts which in the embodiment shown, are formed by cylindrical wires 4 (see Fig. 6) which pass through the base and are bent back on the upper face of the base in a half-loop 6 which forms the fixed contact on which a movable contact comes to bear so as to establish a bridge between the fixed contacts. The ends of the wires 4 projecting below the base 2 constitute the output terminals of the switch, and are provided for engaging in the holes in a printed circuit which has a plurality of identical switches forming a keyboard.

In the embodiment shown, the base has four holes 8 for reception of the contact wires. In two of the holes 8'-8' (Fig. 3), there can be fitted a single wire 4', bent in the form of a staple, to form, on the upper part of the base, a single fixed contact 6' provided with two output wires 4'. The switch can thus comprise an inner bridge which constitutes a permanent connection between two points in the printed circuit on which the switch is mounted. Such an arrangement can avoid use of double face printed circuits.

The switch can thus comprise three fixed contacts 6-6 and 6' which will be connected when the movable contact engages the fixed contacts.

In the upper face of the base 2, recesses 9 receive the bent-back ends of the wires 4 so as to locate the contacts 6. Preferably, in the contact 4'-6'A' with two outlets and bent to the form of a staple, the upper branch is generally of roof shape so as to ensure more of a point contact than a linear contact. The base 2 is preferably circular, and may have a fiat portion 10 facilitating setting of the orientation of the contactor, and preventing pivoting of the cap, will be seen later.

The base 2 is covered by an insulating cap 12 of which the push button 14 forms an integral part. The cap 12 is in the form of a cup and comprises a skirt 16 which fits and slides on the cylindrical exterior part 18 of the base 2. The skirt 16 also has a flat portion 10' corresponding to the flat portion 10, and this prevents the push button cap pivoting relative to the base.

As will be seen later, and as is conventional in a push button switch, the button 14 is urged to its raised (inoperative) position by a return spring 32. The base 2 has stop means formed by two projecting teeth 20-20' which are abutted by the lower parts 22-22' of the skirt 16 of the cap 12.

Windows (slots) 24-24' provided in the skirt 16 permit free passage of the teeth 20-20' when the cap slides on the base. The bottom of the skirt, especially the parts of the skirt corresponding to the parts 22-22', have a chamfer facilitating resilient ratchet engagement of the cap 12 on the base 2 during assembly.

The single moulded piece in the form of a cup forming the cap and the push button comprises, on the inside of the cup, an axial post 26 of which the end 28 engages in a blind hole 30 provided in the bottom of the base 2.

A return spring 32 fits around the end 28 of the post 26 and presses on the one hand against the bottom 34 of the base 2, and on the other hand against a shoulder 36 on the post 26-28.

On the intermediate part 38 of the axial post 26, there is fitted the movable contact which is preferably in the form of a thin metallic disc 40. The central aperture of the disc 40 has a diameter slightly greater than that of the intermediate part 38 of the post, so that the disc may float on the post.

In the axial direction, the disc is located on the one hand by a shoulder 42 between the parts 26 and 38 of the axial post, and on the other hand by the upper convolution of the return spring 32.

The inoperative condition of the switch is shown in Fig. 1, and the operative condition is shown in Fig. 2.

In the latter position with the push button 14 being held depressed manually, the metallic disc 40 bears on the fixed contacts 6-6-6' so as to close one or more circuits connected to the terminals 4-44'-4'.

The despression of the push button is limited by the end of the post 28 abutting the bottom of the recess 30 in the base.

In this depressed position, the centre of the disc 40 is pressed by the shoulder 42 of the post 26. The floating mounting of the disc 40 on the post permits the disc to engage the fixed contacts in a balanced manner.

In the inoperative condition, the uppermost convolution of the spring does not press on the disc 40 and does not thus impede its floating mounting.

In the preferred embodiment of the invention, the disc 40 is very thin, for example, in the region of one hundredth of its diameter, and it is made of resilient metal. As a result of this arrangement, in the operative position shown in Fig. 2, the disc 40 flexes slightly to a dished shape, and its marginal portions effect a wiping action on the contacts 6-6' which produces a self-cleaning effect between the fixed contacts and the movable contact in each operation. The flexing of the disc 40 is limited to a predetermined amount due to the limitation of the depression of the push button by the abutment of the end 28 of the post against the bottom of the recess 30.

In a miniature switch having an external diameter of about 11.5 mm, the disc forming the movable contact may have a dia meter of about 7 mm, and a thickness of eight hundredths of a millimetre.

Assembly of the members forming a switch according to the invention is extremely simple and quick, as it is sufficient to fit the disc 40 and the spring 32 to the post 2628 of the cap and then to fit the cap on the base previously provided with fixed contacts, until ratchet engagement of the teeth 20-20' of the base occurs beyond the parts 22-22' of the skirt of the cap.

Such an assembly can be effected economically on an automatic machine.

The cylindrical wires serve as output terminals and fixed contacts and the disc forming the movable contact can be of metal plated with silver, tin or rhodium or any other similar protective material.

The switch according to the invention can be fixed directly by its output wires on a printed circuit.

In the event that a large number of contacts have to be assembled to form a keyboard, it is more practicable to fix the switches, grouped as a keyboard, on a suitably apertured plate 44 (Fig. 1), In this case there are provided in the moulding, below the base 2, wedges 46 of which the end is subsequently softened thermically in order to fix each switch to its apertured plate. The apertured plate provided with its switches can then be presented en bloc to the printed circuit to constitute the final keyboard, for example, on a miniature calculator.

Of course, the invention is not limited to the embodiment described and shown it being open to numerous modifications available to one skilled in the art, according to the applications envisaged, and without departing from the scope of the invention.

WHAT WE CLAIM IS: 1. A pushbutton switch comprising a base having an inner axial recess, a button telescopically mounted on the base and formed with an axially inwardly projecting guide post which is stepped down in diameter to provide two longitudinally spaced inwardly facing annular shoulders separated by a short intermediate post length portion which terminates in an axial post extension which is a sliding fit in the inner recess of the base, a coil spring surrounding the extension and positioned between an inner surface portion of the base and the lower shoulder of the post to bias the button away from the base, at least two spaced stationary contacts positioned within the base and having portions extending outwardly therefrom, and a movable contact constituted by a flexible, resilient, apertured disc mounted on the intermediate post length portion for bridging the stationary contacts when the button is depressed, the diameter of the disc aperture being greater than the diameter of the intermediate post length portion but smaller than the diameter of the upper annular shoulder and also smaller than the outer diameter of the coil spring.

2. A switch as claimed in claim 1, in which the base carries three stationary contacts.

3. A switch as claimed in either claim 1 or claim 2, in which the stationary contacts are constituted by cylindrical wires of which the heads are bent back on the base, said wires passing through the base, and their ends, projecting outside the base, forming the connecting terminals of the switch.

B A switch as claimed in any preceding claim in which one of the stationary contacts is formed by an intermediate branch of a cylindrical wire bent in the form of a staple, the two side wires of said staple forming two connecting terminals of said switch.

5. A switch as claimed in any preceding claim in which the thickness of the di is in the region of one hundredth of its outer diameter.

6. A switch as claimed in any one of the preceding claims, in which the base includes ratchet and stop means for the button, and in which the button is provided with cooperating ratchet and stop means.

7. A switch as claimed in any one of the preceding claims, in which the outer face of the base is provided with projecting lugs for mounting the switch on an apertured mounting plate, the lugs consisting of a thermoplastic material.

8. A switch as claimed in any one of the preceding claims, in which the base and the bottom are substantially circular with a flat portion preventing rotation of the button relative to the base.

9. A switch as claimed in any preceding claim in which the bottom of the axial recess of the base limits the depression of the post and thus the movement of the push button.

10. A switch as claimed in any one of the preceding claims, in which the movable contact produces self-cleaning of the fixed contacts.

11. An electrical push button switch substantially as hereinbefore described with reference to the accompanying drawings.

12. An electronic calculator or the like including a switch as claimed in any pre

Claims (1)

1. ceding claim.