GB2140213A

GB2140213A - Push-button switch

Info

Publication number: GB2140213A
Application number: GB08412936A
Authority: GB
Inventors: Koichi Kato
Original assignee: Alps Electric Co Ltd
Current assignee: Alps Alpine Co Ltd
Priority date: 1983-05-21
Filing date: 1984-05-21
Publication date: 1984-11-21
Also published as: KR890001962Y1; GB8412936D0; DE3418931A1; KR840006411U; JPS59181527U

Abstract

A push-button switch has a case 17, a switch element 11 mounted on a lower portion of the case 17, a stem 20 carried by the case 17 and movable towards and away from a switch pressing portion 25 disposed between the stem 20 and the switch element 11. A pressing spring 28 is disposed between the stem 20 and the pressing portion 25, and the pressing spring 28, when compressed by the movement of the stem 20 to increase its spring load, deflects the pressing member 25 to the actuate switch element 11. The push-button switch further has a stem reset spring 29 disposed around the pressing spring 28 and acting between the stem 20 and a support member 23 for the pressing portion 25. The stem reset spring 29 has an initial load which is greater than that of the pressing spring 28 so that, when the stem 20 is not being pressed, the pressing portion 25 is not subjected to the force of the pressing spring. <IMAGE>

Description

SPECIFICATION Push-Button Switch Background of the Invention The present invention relates to a push-button switch of the type having a pressing member disposed resiliently between a switch element and a stem movable for actuating the switch.

As will be explained in detail with reference to the drawings, the push-button switch of the type stated above has encountered a problem in that the moment the switch element is actuated fluctuates over time because the resilience of the pressing member lessens after long use.

Summary of the Invention Accordingly, an object of the invention is to provide a push-button switch which overcomes the above-described problem of the prior art.

To this end the invention relates to pushbutton switch having a switch element mounted on a lower portion of a case, and a stem carried by the case and movable towards and away from the switch element. A pressing member having a pressing portion disposed between the stem and the switch element is mounted integrally on the case such that the pressing portion is movable in the same direction as the direction of movement of the stem. A pressing spring is disposed between the stem and the pressing portion, and the pressing spring, when compressed by the movement of the stem to increase the spring load, deflects the pressing member to actuate the switch element. To improve such switches, a stem reset spring is disposed outside the pressing spring and acts between the stem and the pressing member.The stem reset spring has an initial load which is greater than that of the pressing spring so that, when the stem is not being pressed, the pressing portion is kept away from the force of the pressing spring.

In this push-button switch, when the stem is not being pressed by manual force, the pressing portion of the pressing member is kept away from the force of the spring, because the stem resetting spring disposed outside this spring has an initial load greater than that of the pressing spring.

The invention will be more fully understood from the following description of the preferred embodiment when the same is read in conjunction with the accompanying drawings.

Brief of the Drawings Fig. 1 is a sectional view of a conventional push-button switch; Fig. 2 is a sectional view of an embodiment of the push button switch in accordance with the invention; Fig. 3 is a plan view showing the relationship between the case and the switch pressing member as shown in Fig. 2; and Fig. 4 is a sectional view of the push-button switch in a position different from that shown in Fig. 2.

Description of the Preferred Embodiment Before turning to the description of the preferred embodiment, a description will be made hereinunder as to a typical conventional pushbutton switch with specific reference to Fig. 1.

The typical conventional push-button switch shown in Fig. 1 has a case 2 carrying a stem 3 for movement towards and away from the switch element 1, which is illustrated by a membrane switch. A flexible pressing member 4 is formed of, for example, polyacetal resin is disposed between the stem 3 and the switch element 1. The pressing member 4 is constructed as a unit with the case 2 and carries an integral pressing portion 5 which moves in the same directior. as the direction of movement of the stem 3. A pressing spring 6 is disposed between the stem 3 and the pressing portion 5 to urge the pressing portion towards the switch.

In the operation of this push-button switch, the pressing force exerted on the stem 3 acts to compress the pressing spring 6 and as the energy or the spring force of the pressing spring 6 is increased, the pressing member 4 is deflected to make the pressing portion 5 actuate the element 1. With this arrangement, it is possible to eliminate undesirable chattering of the switch.

In this known push-button switch, the spring 6 compressed between the stem 3 and the pressing portion 5 of the switch pressing member 4 loses its resiliency after prolonged use. Consequently, the pressing member becomes less stiff during long use to cause a fluctuation in the time the switch element 1 is actuated upon movement of stem 3.

This problem, however, is overcome by the present invention. Namely, in the push-button switch of the invention, a stem reset spring is used in addition to the pressing spring disposed between the pressing portion of the pressing member and the stem. The stem reset spring is disposed outside the pressing spring so as to act between the stem and the pressing member. The initial load of the stem reset spring is selected to be greater than the initial load of the pressing spring, so that the pressing portion of the pressing member is kept away from the force of the pressing spring when the stem is not being pressed.

The invention will become clear from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.

Referring to Figs. 2 to 4 showing an embodiment of the invention a push-button switch has a membrane switch 11 as a switch element. The membrane switch 11 is composed of a stationary contact 1 3 in the form of a thin web, a spacer 14 made of an insulating material, and a movable contact 1 5 formed of a sheet-like flexible web. These switch elements are successiveiy formed on a Bakelite plate 1 2 serving as a carrier. The spacer 14 has a small thickness of about 1 mm and is provided with an aperture 1 4a.The arrangement is such that, as the movable contact 1 5 is deflected by, for example, 0.1 mm or so by being pressed towards the stationary contact 1 3 from the upper side of the aperture 14a, the movable contact 15 contacts the stationary contact 1 3 to actuate the switch. A panel 16 is fixed to the Bakelite plate 12 by means of bolts and a spacer which are not shown. The panel 1 6 is provided with a hole 1 6a which receives a plastic case 1 7.

In order to secure the plastic case 1 7 to the panel 16, the side walls 1 7a and 1 7b of the case are formed with respective clamping members 1 8 and 1 9. Clamping members 18 are formed by flexible tabs extending integrally from lower, central portions of the side walls 1 7a and 1 7b and are each flanked by respective clamping members 1 9 also formed by flexible tabs, as can be seen clearly in Fig. 3. A respective latch projection 1 8a is formed on the upper end of each flexible tab forming a clamping member 18.The flexible tabs 1 9 extend upwardly at a predetermined distance from the side wall 1 7a and are inclined slightly outwardly, while the tabs 18 extend generally parallel to the respective side wall 1 7a or 17b. Downwardly slanted guide surfaces 1 9a, 1 9a are formed on the outer lower side of the flexible tabs 19,19.

The panel 1 6 is clamped between the latch projection 1 8a and the retaining step surfaces 1 9b and 1 9b of the clamping members 18 and 1 9 so that the case 1 7 is detachably secured to the panel 16.

The case 1 7 is opened at its upper and lower sides and receives a stem 20 for movement towards and away from the membrane switch 11.

Vertically extending slots 21 and 22 having opened lower ends are formed in the side walls 17a and 17b of the case 17. These slots 21 and 22 are adapted to receive stopper projections 20a and 20b formed on the stem 20. A pressing member 23 is mounted on the lower end of the case 1 7 so as to contact the membrane switch 11. The pressing member 23 is made of a material having high resistances to fatigue, friction and wear.

The pressing member 23 is partly cut away to leave a circular notch 24 around a pressing tab 25, as shown in Fig. 3. The flexible pressing tab 25 includes a thin-walled flexible connecting portion 25a integral with the thick-walled portion 23a, and a pressing portion 25b formed integrally on the end of the connecting member 25a. The pressing portion 25b is disposed between the membrane switch 11 and the stem 20, and is movable in the same direction as the movement of the stem 20 by deflecting the connecting portion 25a.

The lower surface 26 of the pressing portion 25b has a substantially spherical shape to make a point contact with the movable contact 1 5 to permit easy deflection of the movable contact 1 5.

A cylindrical portion 27 is formed at the upper side of the pressing portion 25b integrally with the latter. A pressing spring 28 disposed between the pressing portion 25b and the stem 20 has its lower end loosely received around the cylinder 27. The pressing spring 28 is compressed as the stem 20 is pressed and displaced downwardly. As the spring force is gradually increased as a result of such compression, the pressing portion 25b is displaced downwardly as the flexible pressing portion 25 of the pressing member 23 is deflected at the connecting portion 25a thereof.

As a result, the pressing portion 25b deflects the movable contact 1 5 into contact with the stationary contact 1 3 to actuate the membrane switch.

A stem reset spring 29 is disposed outside the pressing spring 28 so as to act between the stem 20 and a recess 23b formed in the thick-walled portion 23a of the pressing member 23. Even when the stem reset spring is compressed by a downward pressing of the stem 20, the thickwalled portion 1 3a of the switch pressing member 23 is not deflected so that the force stored in this reset spring is used exclusively for the resetting of the stem 20. In the described embodiment, the initial load and the final load of the stem reset spring 29 are set at the levels of 20 gf and 30 gf, respectively. On the other hand, the initial load and the final load of the pressing spring 28 are selected to be O gf and 40 gf, respectively. Thus, the sum of the final loads of the pressing spring 28 and the stem reset spring 29 are the force for actuating the switch.Namely, in the described embodiment, the switch actuating force is calculated to be 70 gf. The "on" load ranges between 30 and 40 gf. In the drawings, a reference numeral 30 designates a key top attached to the stem 20.

When the key 30 is not depressed, since the initial loads of the pressing spring 28 and the stem reset spring 29 are selected to be 0 gf and 20 gf, respectively, the stem 20 and the key top 30 are kept at the raised position by the force produced by the initial load of the stem reset spring 29. In this case, therefore, the pressing portion 25b is freed from the force of the spring 28 and, therefore, the flexible pressing member 25 is prevented from becoming less stiff.

When the key top 30 is pressed, the pressing spring 28 and the stem reset spring 29 are gradually compressed and loaded to increase the reactional spring force. Despite the increased ioad, the stem reset-spring 29 does not deflect the thick-walled portion 23a of the switch pressing member 23. In addition, since the final load of the stem reset spring is selected to be 30 gf which is smaller than the final load of 40 gf of the pressing spring 28, the flexible pressing member 25 of the switch pressing member 23 is deflected at the connecting portion 25a by the final load of the pressing spring 28, so that the pressing portion 25b is displaced downwardly.

The pressing portion 25b then deflects the movable contact 1 5 by an amount of about 0.1 mm towards the stationary contact 13 to make the same contact the latter, so that the membrane switch 11 is actuated. Thus, in the described embodiment of the invention, the membrane switch 11 is actuated by the deflection of the flexible pressing member caused by the final pressure of the spring 28. Therefore, the timing of generation of the final load or force at which the membrane switch 11 is actuated is made more definite and, hence, fluctuation of the timing of actuation of the switch is diminished as the difference between the initial and final loads of the spring 28 is increased.

As has been described, in the push-button switch of the invention, a stem reset spring is used in addition to the pressing spring which acts between the pressing portion of the pressing member and the stem. The stem reset spring is disposed outside the pressing spring so as to act between the stem and the pressing member. The initial load of the stem reset spring is selected to be greater than the initial load of the pressing spring so that the force of the pressing spring is not applied to the pressing portion when the stem is not being pressed. Therefore, when no manual force is exerted on the key top, i.e. when the stem is not being pressed, the stem is urged to its upper position solely by the initial load or force of the stem reset spring, while the pressing spring does not exert any force on the pressing portion of the pressing member.Consequently, the flexible pressing tab of the pressing member is prevented from becoming less stiff even during a long use, and the undesirable fluctuation of the timing for actuating the switch element is avoided advantageously.

On the other hand, when a manual pressing force is exerted on the key top to press the stem, the force of the stem reset spring does not act on the pressing portion of the pressing member, but the pressing spring acts to deflect the flexible pressing tab by the final load thereof to displace the pressing portion downwardly thereby to actuate the switch element. The switch element is actuated only when the final load is imposed on the pressing spring. An fluctuation of the timing of actuating of the switch element is, therefore, avoided also.

Although the invention has been described through specific terms, it is to be noted here that the described embodiment is not exclusive and various changes and modifications may be imparted thereto without departing from the scope of the invention which is limited solely by the appended claims.

Claims

1. A push-button switch having a case, a switch element mounted on a lower portion of said case, a stem carried by said case movable towards and away from said switch element, a pressing member having a pressing portion disposed between said stem and said switch eiement, means including a pressing spring disposed between said stem and said pressing portion for deflecting said pressing member to actuate said switch element upon pressing said stem within said case, and a stem reset spring disposed around said pressing spring and acting between said stem and said pressing member, said stem reset spring having an initial load which is greater than that of said pressing spring so that, when said stem is not being pressed, said pressing portion is kept away from the force of said pressing spring.

2. A push-button switch according to claim 1, wherein said switch element is a membrane switch.

3. A push-button switch according to claim 1, wherein said switch pressing member is made of polyacetal resin.

4. A push-button switch according to claim 2, wherein said switch pressing member is made of polyacetal resin.

5. A push-button switch according to claim 1, wherein said pressing spring has an initial load and a final load of 0 gf and 40 gf, respectively, while said stem reset spring has an initial load and a final load of 20 gf and 30 gf, respectively.

6. A push-button switch according to claim 2, wherein said pressing spring has an initial load and a final load of O gf and 40 gf respectively, while said stem reset spring has an initial load and a final load of 20 gf and 30 gf, respectively.

7. A push-button switch according to claim 3, wherein said pressing spring has an initial load and a final load of O gf and 40 gf, respectively, while said stem reset spring has an initial load and a final load of 20 gf and 30 gf, respectively.

8. A push-button switch substantially as hereinbefore described with reference to the accompanying drawings.