Abstract:
In a push-button switch, serially connected first, second and third coaxial springs having gradually increasing diameters are disposed between a key top and contact members, a key stem extends through the second and third springs for operating the contact members through the first spring.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a push-button switch. 
     In a push-button switch generally used on a keyboard or the like, in order to decrease the manufacturing cost, it is important to decrease as far as possible the number of component parts so as to simplify the construction, as well as the number of assembling steps. 
     FIG. 1 illustrates a conventional push-button comprising a key stem 2 provided with a top or cap 1 and arranged to be slidable in the vertical direction through a mounting frame 3, a restoring spring 4 inserted between the top 1 and the mounting frame 3 and a spring 5 received in a bottom opening of the stem 2 for pressing contacts 8a and 8b through a film 8, the contacts being supported by a bottom plate 6 through an insulating spacer 7. 
     In another conventional switch shown in FIG. 2, the top 9a and the stem 9b are formed integrally suing a plastic so as to decrease the number of the component parts. In FIG. 2, elements corresponding to those shown in FIG. 1 are designated by the same reference numerals. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of this invention to provide an improved push-button switch capable of decreasing the number of component parts than the prior art. push-button switches thereby decreasing the manufacturing cost. 
     Another object of this invention is to provide a novel push-button switch capable of giving a feeling of switch ON and preventing chattering of the contacts when they are closed and opened. 
     According to this invention, there is provided a push-button switch comprising a key having a top and a stem connected thereto, contact means opened and closed by the stem, a first spring disposed between one end of the stem and the contact means for pressing the contact means, and a second and third springs surrounding the stem and acting to restore the key, the second spring having a diameter larger than the first spring, and the third spring having a diameter larger than the second spring and being formed integral with the first and second springs. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIGS. 1 and 2 are vertical sectional views showing typical prior art push-button switches; 
     FIG. 3 is a vertical sectional view showing one embodiment of the push-button switch according to the invention; and 
     FIGS. 4 and 5 are vertical sectional views showing another embodiments of this invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The first embodiment of the push-button switch shown in FIG. 3 comprises a key 10, a spring assembly 11, a mounting frame 12 and a film contact member 20 mounted on a bottom plate 13. 
     The key 10 is made of a plastic and its top 10a, stem 10b and sliding member 10c are formed integrally. The key 10 is mounted on a mounting frame 12 with the sliding member inserted into an opening 12a of the frame 12 so as to move in the vertical direction between a position at which an engaging member 10d at the lower end of the sliding member 10c engages the lower surface 12b of frame 12 and a position at which an engaging member 10e at the base portion of the sliding member 10c engages the upper surface 13c of a hollow cylindrical member 13 of the frame 12. The cylindrical member 13 is formed with a recess 13a at its upper end. 
     The spring assembly 11 is constituted by serially connected three coaxial springs 11a, 11b and 11c having different diameters of which spring 11a is used to press the film contact member 20, while springs 11b and 11c are formed integrally to return the key 10 to the original position. The lower end of spring 11b is connected to the lower end of stem 10b. 
     The film contact member 20 is constituted by a film 21 carrying a upper contact 21a, a film 22 carrying a lower contact 22a and a spacer 23 interposed between films 21 and 22 for defining a predetermined gap between the contacts 21a and 22a. 
     The push-button switch sown in FIG. 3 operates as follows. 
     In a state shown in FIG. 3 in which the key 10 is not depressed, the key is urged upwardly by the force of spring 11c whereby the switch is open. 
     As the key 10 is depressed gradually, spring 11c is firstly compressed and then the spring 11c is further compressed after the lower end of the stem 11b engages the upper surface of the spring 11a. Then densely wound spring 11b is extended to lower the spring 11a. As a consequence, the film 21 is pressed and deformed to urge upper contact 21a against lower contact 22a to close these contacts. After closing the contacts, when the key is depressed further, spring 11a will be compressed by an amount corresponding to the extent of depression. 
     The pressing force caused by the depression of the key varies stepwisely at the times of compression of only spring 11c, and compression of spring 11c and extension of spring 11b. Such stepwise variations of the pressing force gives a feeling of switch ON to a finger of the operator. Furthermore, as the stroke of the key can be continued after the contacts have been closed, it is possible to prevent chattering at the time of opening and closing the switch. 
     FIG. 4 shows another embodiment of this invention in which elements corresponding to those shown in FIG. 3 are designated by the same reference numerals. 
     This modified embodiment is different form the embodiment shown in FIG. 3 in the construction of spring 30. Thus, the spring assembly 30 is constituted by serially connected springs 30a, 30b and 30c having different diameters of which spring 30a is used to depress contact member 20, spring 30b is used to restore the key 10 to the original position and spring 30c is used to secure the spring assembly 30 to be mounting frame 12. 
     The upper end of spring 30a normally engages with the lower end of the stem 10b, spring 30c is normally arrested by the bottom surface of the recess 13a of the hollow cylindrical member 13 of the mounting frame 12, and spring 30b normally applies upward restoring force to the key 10. 
     As the key 10 is depressed down against the restoring force of spring 30b, key 10 moves down while extending spring 30b so that spring 30a at the lower side of stem 10b presses the contact member 20 to close the switch. 
     Although in this embodiment, the top, stem and sliding portion of the key are formed as an integral unit, these portions may be formed independently and then bonded together to form a key. Furthermore, the contact member is not limited to film contacts and ordinary contacts that can be opened and closed by the vertical movement of the spring can be used. the embodiment in FIG. 4 except that the spring 40b is of conical shape. Since the function and operation are same as the embodiment of FIG. 4, explanation will be omitted. 
     As above described, according to this invention, a contact pressing spring and a key restoring spring which have been formed independingly are formed integrally so that it is possible to decrease the number of component parts and the manufacturing cost.