Push Button Switch

1. Field of the Invention:

The present invention relates to a structure of a pushbutton switch for use in a key board, etc., of electronic equipments.

2. Description of the Related Art:

Many related techniques in such a field employ in general a system including a movable contact fixedly mounted on a flexible member and a fixed contact separated away in a confronting relation from the movable contact for making and breaking a switch by making use of deformation of the flexible member caused by pressing it.

To make useable a contact of this type for those such as a full key board where importance is attached to a feeling of depressing it, the structure thereof should be adapted to have a mechanism to alter a stroke such as a coil spring between a pushbutton and a flexible member for conducting secure make-and-brake operation of the contact while increasing the stroke of depressing the pushbutton and depressing the contact with uniform depression at all times. For such a prior technique, "Word Processor File Keyboards, ESU-22 and ESU-21" available from Matsushita Electric Industrial Co., Ltd. is known for example. A keybord of this type employs as shown in its catalogue a pushbutton switch having compression coil springs of different two diameters doubly structured coaxially. This assures a stroke of the pushbutton switch by permitting a slider part provided on the lower portion of a key top to reciprocate in contact in its outside with the inside of a switch body. The lower portion of the switch body includes a switch part provided thereon. A contact of this switch part is composed of a fixed contact provided on the upper surface of a base plate and of a movable contact formed on the lower surface of the flexible member separated away from the fixed contact relation via a spacer. One end of the inside coil spring adjoins the upper portion of the movable contact in an interval, while the other end thereof is mounted on the lower portion of the key top. Moreover, both ends of the outside coil spring are respectively mounted on the lower parts of the key top and the body. Depressed here the pushbutton switch arranged as such, the larger coil spring is compressed, while the smaller coil spring is brought into contact with the flexible member. Depressed furthermore the key top, both the springs are compressed, whereby the flexible member is depressed and deformed by the smaller coil spring to permit the movable contact to make contact with the fixed contact for closing the contact.

Continued the depression furthermore, the two springs are compressed corresponding to an excess stroke, whereby the key top is brought into contact with the body and stopped.

The contact after being closed is stably depressed by the smaller coil spring, so that chattering, etc., is prevented from being produced.

However, with the arrangement described above, separate two larger and smaller coil springs are needed. Accordingly, the number of parts being needed is increased. In addition, assembly thereof, is performed while compressing the coil spring, so that the cost for the assembly is increased due to troubles such as compression buckling of the coil spring, etc.

In view of the drawbacks of the prior technique, it is an object of the present invention to provide a pushbutton switch having a keyboard improved and simplified in a structure of parts constituting the keyboard.

Another object of the present invention is to reduce the number of parts constituting the pushbutton switch.

Still another object of the present invention is to provide a pushbutton switch having a single coil spring serving as two coil springs: one for returning the push button switch and the other for depressing the contact.

Another object of the present invention is to facilitate assembly of the keyboard and reduce the manhour of the assembly.

Further another object of the present invention is to provide initial tension to the coil spring of the pushbutton switch by pulling the coil spring upon assembling the pushbutton switch and thereby preventing any trouble from being produced.

To achieve the above object, a push button switch according to the present invention has a switch coil spring mounted on the lower portion of the pushbutton body provided slidably in a housing, the coil springs being adapted to return the pushbutton to the original state as well as depress a contact of the pushbutton. Namely, the pushbutton switch has a spring support part provided at the center of a base plate of a body, on the upper end of which support part one end of the coil spring is mounted and on the lower end of which a switch part is disposed adjoining thereto, which switch part has the other end of the coil spring arranged thereon. The coil spring is adapted to be a tension spring from the above one end thereof to a prescribed portion and to be a compression spring from the prescribed portion to the above other end. Accordingly, depressed the pushbutton, the other end of the coil spring mounted on the lower part of the body is brought into contact with the switch part. Depressed furthermore the pushbutton, the coil spring presses the switch part as a compression spring to close the contact. Releasing here the pushbutton as a tension spring to open the contact whereby the pushbutton is returned to the original position.

The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.

FIG. 1 is a cross-sectional view of an embodiment of a pushbutton switch according to the present invention illustrating a state of a pushbutton being released;

FIG. 2 is a cross-sectional view of an embodiment of a pushbutton switch of the present invention illustrating a state of a pushbutton being depressed; and

FIG. 3 is a view illustrating details of a coil spring according to the present invention.

A pushbutton switch according to the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIGS. 1 and 2, an embodiment of a pushbutton switch according to the present invention is shown of a state of a pushbutton being depressed and a state of the same pushbutton being released.

In the same figures, designated at 1 is an insulating base plate comprising synthetic resin, 2 is a flexible printed circuit board comprising synthetic resin provided in the insulating base plate 1, 3 is a fixed contact provided on the upper surface of the printed circuit board 2, 4 is an insulating spacer, 5 is a flexible printed circuit board comprising synthetic resin, 6 is a movable contact provided on the lower surface of the printed circuit board 5. Likewise, designated at 11 is a pushbutton, including a projection part 11a provided on the lower surface of the pushbutton at the center thereof, a support arm 11b projected to the outside of the projection part 11a, a slanted pawl 11c for engagement provided on the tip of the support arm 11b, and a pushbutton 11d. In addition, designated at 12 is a coil spring having, as shown in FIG. 3 illustrating details of a structure of the coil spring, a large diameter base winding part 12a formed on the upper end part of the coil spring, and successively in order an intermediate diameter tension coil spring part 12b, a parallel winding part 12e, a small diameter compression coil spring part 12d, and a small diameter base winding part 12e formed together integrally. Furthermore, designated at 13 is a housing including a button surface 13a, a spring seat casing 13b, a guide part 13c for the support arm 11b of the pushbutton, the guide part forming an inner peripheral edge of the housing 13, a stopper part 13d projecting interiorly of the upper end of the housing 13, a flange 13e, and a locking panel 13f for holding a bracket 10 for mounting the switch between the flange 13e and the locking pawl 13f. Moreover, a gap 1 is provided between the lower end part of the coil spring 12 and the flexible printed circuit board 5.

In succession, a method of assembling the pushbutton switch with the respective parts described above will be described.

First, dropping the coil spring 12 into a through-hole in the spring seat casing 13b provided at the center of the housing 13 while directing the small diameter seat winding part being the lowest end of the coil spring downwardly, the large diameter seat winding part 12a is brought into contact with the upper end stepped part of the spring seat casing 13b to restrict the position of the coil spring 12, whereby a prescribed distance is left behind between the lower end small diameter seat winding part 12e of the coil spring 12 and the flexible printed circuit board 5. Then, to mount the pushbutton, the slanted portion 11e of the tip of the pushbutton 11 support arm 11b is inserted into an insertion hole formed between the housing 13 and the spring seat casing 13b while being guided by the stopper part 13d of the housing 13. Pushing down the pushbutton 11 furthermore, the support arm 11b of the pushbutton is elastically deformed whereby the slanted pawl 11c of the tip of the support arm goes over the stopper part 13d of the housing 13.

Hereupon, the projection part 11a of the pushbutton 11 penetrates the intermediate tension coil spring part 12b and makes contact with the parallel winding part 12c provided at a connecting portion between the tension and compression coil spring parts 12b, 12d of the coil spring 12. While, since the large diameter seat winding part 12a of the coil spring 12 is restricted positionablly by the stepped part provided interiorly of the upper end of the spring seat part 13b of the housing 13, the intermediate diameter tension coil spring part 12b is slightly rendered to tension, and hence elongated. Thus, the pushbutton projection part 11a is subjected to force serving to push it back caused by the coil spring 12, whereby the projection part is brought into contact with the housing stopper part 13b, stopped, and positioned. In addition, an interval 1 is left behind between the tip end 12e of the coil spring 12 and the flexible member 8. Thus the assembly of the pushbutton switch is completed as described above.

Then, operation of the present embodiment assembled as such will be described.

As shown in FIG. 1, depressed the pushbutton body 11d, the pushbutton 11 is lowered following the guide part 13a of the housing 13 parallel thereto to permit the pushbutton projection part 11a to apply force to the parallel winding part 12c of the coil spring 12, whereby the large tension diameter compression coil spring part 12b is elongated. While, since the small diameter coil spring 12d has a desired interval 1 between the flexible member 8 and the small diameter seat winding part 12e, it is never deformed until the end surface of the small diameter seat winding part 12e makes contact with the flexible printed circuit board 5.

Depressed furthermore the pushbutton, the small diameter seat winding part 12e makes contact with the flexible printed circuit board 5 to press the small diameter coil spring part 12d, whereby the small diameter coil spring part starts to be compressed and deformed. Hereupon, the flexible printed circuit board 5 is deformed in response to pressure of depression from the small diameter compression coil spring part 12d, and furthermore depressed the pushbutton, the movable contact 9 is brought into contact with the fixed contact 6 for closing the contacts. Still more the pushbutton 11 is not yet allowed to reach the limit of lowering at the moment the contacts are closed with each other as described above, and furthermore allowed to lower until the pushbutton 11 makes contact with the stopper (not shown) provided in the housing.

Furthermore, although the flexible printed circuit boards 2 and 5 were employed in the present embodiment for the switch part, any wired flexible member may be employed without being limited thereto. Moreover, for the base plate 2, the base plate 1 may be employed instead of it. In addition, for the switch part, an electrostatic capacitance type may be employed without limiting it to a mechanical one.

Although a certain preferred embodiment has been shown and described, it should be understood that many changes and modifications may be made therein without departing from the scope of the appended claims.