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The current invention pertains to a push-button switch, and more particularly to such a switch which is particularly adapted for use in electronic desk calculators.
At present, electronic desk calculators are introduced in great quantities into the market place and there are needs for durable, inexpensive and highly reliable push-button switches for electronic desk calculators. SUMMARY OF THE INVENTION
The principal object of the current invention is to provide a push-button switch particularly well suited for use in electronic desk calculators and which is easy and rugged in structure, stable in electrical performance for long periods of time, easy to assemble, and highly reliable.
In accordance with the present invention, there’s provided an improved push-button switch well suited to be used in electronic desk calculators, which comprises a case formed with a recess for containing therein a snap-action spring disc, a standard fixed terminal having two elongate and substantially parallel contact portions spaced apart and supporting the periphery of the snap-action disc inside the recess and two fixed terminal portions each have contacts arranged throughout the recess at a level below that of the contact portions of the common terminal. The case is molded with the three terminals incorporated integrally in the case such that the respective contact portions of the three terminals are exposed throughout the recess thereof. Preferably, the common terminal is mostly H-shaped and has a bridge portion interconnecting the 2 parallel contact portions and the 2 fixed terminals are arranged symmetrically on opposite sides of the bridge portion. BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings, in which:
FIG. 2 is a top plan view of the contact case during which the respective fixed terminals are incorporated;
FIG. 4 is a perspective view showing the underside of the push button;
FIG. 6 is a perspective view of a hard and fast terminal wherein its contact portion and connection portion are connected in a stepped fashion. DETAILED DESCRIPTION OF THE INVENTION
Referring now the drawings wherein like reference numerals have been used throughout to designate like elements, a push-button switch in line with the present invention features a generally square box-shaped push button formed preferably from a synthetic resin or other suitable insulating material and having a cylindrical projection 2 extending downwardly from the center of the rear surface thereof for pushing the peak of a snap-action spring disc 5. The push button 1 is formed in the inner surfaces of its opposing side walls with a pair of recesses 3 (only considered one of which is shown, see FIG. 4), each recess having a size sufficient for the push button 1 to maneuver with the recesses 3 and 3 held in engagement with projections 9 and 9 provided on opposing surfaces of a contact case 6. The push button 1 is also formed in the other opposing walls with cutouts 4 and 4 for escape of the terminal portions 11b, 12b, and 13b of respective fixed terminals 11, 12, and 13. The snap-action spring disc 5 is formed of a resilient and conductive thin metal plate similar to, for example, a pressed stainless steel plate curved to form part of a spherical surface. The snap-action spring disc 5 serves as a movable contact and as a spring member for returning the push button 1 after it’s depressed back to its initial position. The contact case 6 is formed of a synthetic resin or other suitable insulating material and is covered with the push button 1 such that the push button 1 can slide over the outer surface of the contact case 6. The contact case 6 is formed with a circular recess 7 for containing therein the spring disc 5 and the underside of the recess 7 is formed with a groove 8 wherein the contact portions 12a and 13a of the fixed contacts 12 and 13 are received. The contact case 6 is provided in its opposite side surfaces with a pair of projections 9 and 9 of a triangle cross-section which serve as stoppers to stop the push button 1 from separating from the contact case.
A common fixed contact 11 as well as the 2 fixed contacts 12 and 13 are each formed of a conductive material reminiscent of phosphor bronze and are incorporated integrally in the contact case 6 when the contact case 6 is molded. The common fixed contact 11 has a substantially H-shape and is composed of two parallel contact portions 11a and 11a exposed within the recess 7, terminal portions 11b and 11b extending from the respective contact portions 11a and 11a within the reverse directions to the surface of the contact case 6, and a bridge portion 11c connecting the two contact portions 11a and 11a at the center of the recess 7. The 2 fixed terminals 12 and 13 are respectively composed of contact portions 12a and 13a exposed within the recess 7, terminal portions 12b and 13b extending from the respective contact portions 12a and 13a to the outside of the contact case 6, and connection portions 12c and 13c connecting respectively the contact portions 12a and 13a and the terminal portions 12b and 13b in stepped fashion (see FIG. 6). The fixed terminals 12 and 13 are arranged symmetrically on the other sides of the bridge portion 11c of the common fixed terminal 11 in spaced relation and the contact portions 12a and 13a are received in the groove 8 formed in the bottom of the recess 7 such that the contact portions 12a and 13a are placed able lower than that of the contact portions 11a and 11a of the common fixed terminal 11. In this way, the contact portions 12a and 13a are prevented from coming into contact with the periphery of the snap-action spring disc 5. The portions of the three terminals 11, 12 and 13 aside from their portions exposed throughout the recess 7 and their portions projecting to the skin of the contact case 6, are embedded in the walls of the contact case 6.
FIG. 5 shows a mother plate which is stamped from a single length of conductive sheet material so as to have the three fixed terminals 11, 12 and 13 integrally connected by connection bands 10a and 10b. When the contact case 6 is molded, such a mother plate is incorporated thereinto with a purpose to integrally form the fixed terminals and the contact case 6. Thereafter, the mother plate is cut along the lines A–A’ and B-B’ to remove the connection bands 10a and 10b so that the three fixed terminals are electrically separated.
The push-button switch of the current invention is assembled as follows: The snap-action spring disc 5 is inserted, with its peak facing upward, into the recess 7 of the contact case 6 formed integrally with the three fixed terminals 11, 12 and 13 in such a fashion as described herein. The push button 1 is then attached to the contact case 6 with its recesses 3 and 3 engaged over the projections 9 and 9 formed on opposing surfaces of the contact case 6. Within the attachment of the push button 1, the push button 1 may be depressed against the upper inclined surfaces of the projections 9 and 9 to be expanded outwardly so that the projections 9 and 9 can easily be fitted over and held in engagement with the recesses 3 and 3.
The operation of the push-button switch of the current invention will be described. In a non-operative state as shown in FIG. 1, the snap-action spring disc 5 has its periphery supported on the contact portions 11a and 11a of the common fixed contact and its peak upwardly pushing the projection 2 of the push button 1 by its resilient force in order to carry the push-button switch in its OFF state. At the moment, the projections 9 and 9 abut on the lower surfaces of the recesses 3 and three to stop the push button 1 from moving upwardly.
When the push button 1 is pressed downwardly against the resilient force of the snap-action spring disc 5, the projection 2 thereof pushes the peak of the snap-action spring disc 5 downwards to cause the snap-action of the spring disc 5 so that the lower surface of the spring disc comes into contact with the contacts 14 and 15 on the fixed terminals 12 and 13, thereby changing the push-button switch from the OFF to the ON state.
When the pressure exerted on the push button 1 is released, the resilient force of the spring disc 5 causes its snap-action so that the spring disc 5 snaps back and releases from the contacts 14 and 15 and returns the push button 1 to the initial position, thereby changing the push-button switch into the OFF state.
The push-button switch of the present invention could also be provided on a printed circuit base plate by inserting the terminal portions 11b, 11b, 12b, and 12b into holes formed within the printed circuit base plate and soldering them to the circuit.
The push-button switch of the current invention, through which the fixed terminals 11, 12 and 13 are formed integrally with the contact case 6, is straightforward and rugged in structure, easy to assemble, and highly reliable over extended periods of time. As well as, the current invention can eliminate the need for a printed circuit base plate supporting the fixed contacts thereon to thus improve the wear-resistance of the contact portions and provide a stable contact resistance over a very long time period.
It’s, therefore, apparent that there was provided, in accordance with this invention, an improved push-button switch high in durability and electrical performance and low in cost that fully satisfies the objects set forth above. While the present invention has been described in connection with a selected embodiment thereof, it is evident that many alternatives, modifications and variations will likely be apparent to those skilled within the art. Accordingly, it is meant to embrace all alternatives, modifications and variations that fall throughout the spirit and broad scope of the appended claims.
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