The present invention relates to a contact plate for use as a movable contact of a push-button switch, and more particularly to a disk contact plate press-formed into a dome shape, a sheet with the contact plate, and the structure of a switch device using the sheet.

Document US 4 195 210 discloses a device according to the preamble of claim 1.

Known structures of a contact plate for use as the movable contact of a push-button switch include the structures illustrated in Fig. 8 through Fig. 12. Fig. 8 through Fig. 10 are sectional views showing the relationship between a movable contact and a fixed contact, and Figs. 11 and 12 illustrate the relationship between the manipulative force on and the shifted quantity of the movable contact.

Fig. 8 shows a state in which a disk movable contact 51 formed by cupping a thin metallic sheet into a dome shape is mounted over a central fixed contact 53 and a peripheral fixed contact 54, each similarly consisting of an electroconductive metallic sheet, arranged on the inner bottom face of a housing 52 consisting of synthetic resin or the like.

The movable contact 51 is formed of a skirt 51a rising from the outer circumference of a disc at a prescribed angle toward the center of the disc and a dome 51b, which is continuous from the skirt 51a and can be repetitively inverted. These skirt 51a and dome 51b are connected to each other by a smooth bend 51c. An outer peripheral end 51d of the skirt 51a is in contact with the peripheral fixed contact 54 all the time, and the inside of the top of the dome 51b constitutes a contact 51e, which comes into contact with the central fixed contact 53 when the dome 51b is repetitively inverted.

Between the central fixed contact 53 and the peripheral fixed contact 54, there is formed a gap, with the central fixed contact 53 being formed a step below the peripheral fixed contact 54. In this case, as the distance (shifted quantity) L1 between the contact 51e and the central fixed contact 53 when the dome 51b of the movable contact 51 is inverted can be greater by the level difference of the step, the shifted quantity after the inversion of the movable contact 51b can be set greater than otherwise as indicated by A in Fig. 11, resulting in a crispy feeling of click. In the diagram the vertical axis represents the manipulative force F, and the horizontal axis represents the shifted quantity L.

Incidentally, AO in the diagram denotes the feeling (click feeling) curve of the movable contact 51, LA, the point where the reaction force after the inversion of the movable contact 51 is at its minimum, i.e. the settable maximum of the shifted quantity.

Fig. 9 illustrates a state in which the movable contact 51 is mounted over a circuit board 55 on which a circuit pattern is formed of a copper foil or the like. In this case, since a central fixed contact 56 and a peripheral fixed contact 57 are formed of a copper foil or the like in a planar form over the circuit board 55, the distance (the shifted quantity) L2 between the contact 51e and the central fixed contact 56 when the dome 51b of the movable contact 51 is inverted is less than L1.

Fig. 10 shows a movable contact 58 formed in a state in which the rising angle &thgr;c of a skirt 58a is set more nearly upright than &thgr;b shown in Fig. 9 (&thgr;b < &thgr;c) so that the distance (the shifted quantity) L3 between a contact 58e and the central fixed contact 56 when the dome 58b of the movable contact 58 is inverted becomes equal to L1 (L3 = L1). In this case, since the distance (the shifted quantity) L3 between the contact 58e and the central fixed contact 56 when the dome 58b of the movable contact 58 is inverted can be greater, the shifted quantity after the inversion of the movable contact 58 can be set greater than otherwise as indicated by C in Fig. 12, resulting in a crispy feeling of click.

However, in the above-described structure of the movable contact 51 according to the prior art, when it is to be used in the planar circuit board 55, the distance (the shifted quantity) L2 between the contact 51e and the central fixed contact 56 when the dome 51b of the movable contact 51 is inverted is less than L1, the shifted quantity becomes smaller after the inversion of the movable contact 51 as indicated by B in Fig. 11, resulting in a problem of a dull feeling of click.

Further, if the rising angle &thgr;c of the skirt 58a is increased, the point LC at which the reaction force of the feeling curve CO of the movable contact 58 will take on a negative value as shown in Fig. 12, resulting in a problem that the movable contact 58 remains inverted instead of automatically returning to the original state.

An object of the present invention, therefore, is to solve the problems noted above and provide a movable contact structure which, even when used in a planar circuit board, can provide a crispy click feeling and will not fail to return to an original position after being inverted.

In order to solve the problems noted above, according to a first aspect of the invention, there is provided a contact plate according to claim 1.

According to a second aspect of the invention, a projection in contact with a fixed contact is formed on an inner face of the dome.

According to a third aspect of the invention, an external face of the dome of the contact plate according to the first or second aspect of the invention is stuck to an adhesive back face layer of an insulating sheet, and the contact plate and an under face of the insulating sheet are covered with a peelable protective sheet.

According to a fourth aspect of the invention, a spacer sheet having an accommodating hole for accommodating the contact plate is provided between the insulating sheet and the protective sheet.

According to a fifth aspect of the invention, the protective sheet of the sheet with the contact plate according to the third or fourth aspect of the invention is peeled, and the sheet with the contact plate after peeling is stuck to a circuit board, over which a plurality of fixed contacts are arranged, by the adhesive back face layer of the insulating sheet so that the contact plate is opposite the fixed contacts.

According to a sixth aspect of the invention, there is provided a switch device having the contact plate according to the first or second aspect of the invention and an accommodating section, whose inner bottom face is provided with a housing over which a fixed contact is arranged and a suppressing member liftably snapped into the accommodating section, wherein the contact plate is arranged opposite the fixed contact to be suppressible by the suppressing member.

• Fig. 1 is a sectional view showing the relationship between a movable contact, which is a preferred embodiment of the present invention, and a fixed contact.
• Fig. 2 is a partial sectional view illustrating the connection section between the skirt and the dome of the movable contact embodying the invention.
• Fig. 3 illustrates the relationship between the manipulative force on and the shifted quantity of the movable contact embodying the invention.
• Fig. 4 is a sectional view showing a sheet-shaped switch device using the movable contact embodying the invention.
• Fig. 5 is a sectional view of the essential part illustrating the sheet-shaped switch device using the movable contact embodying the invention.
• Fig. 6 is an exploded perspective view of a switch device based on an insulating resin-made housing using the movable contact embodying the invention.
• Fig. 7 is a sectional view of the essential part illustrating the switch device based on the insulating resin-made housing using the movable contact embodying the invention.
• Fig. 8 is a sectional view showing an example of relationship between a movable contact and a fixed contact according to the prior art.
• Fig. 9 is a sectional view showing another example of relationship between a movable contact and a fixed contact according to the prior art.
• Fig. 10 is a sectional view showing still another example of relationship between a movable contact and a fixed contact according to the prior art.
• Fig. 11 illustrates an example of relationship between the manipulative force on and the shifted quantity of the movable contact according to the prior art.
• Fig. 12 illustrates another example of relationship between the manipulative force on and the shifted quantity of the movable contact according to the prior art.

A preferred embodiment of the present invention will be described below with reference to Fig. 1 through Fig. 3. Fig. 1 is a sectional view illustrating the relationship between a movable contact and a fixed contact; Fig. 2 is a partial sectional view illustrating the connection section between the skirt and the dome of the movable contact; and Fig. 3 illustrates the relationship between the manipulative force on and the shifted quantity of the movable contact.

Referring to Fig. 1, a movable contact 1 is a thin metallic plate formed in a disk shape. This movable contact 1 is composed of a skirt 1a rising from the outer circumference of the disc at a prescribed angle toward the center of the disc and a dome 1b, which is continuous from this skirt 1a and can be repetitively inverted, and these skirt 1a and dome 1b are formed in multiple steps via a plurality of bent portions 1c and 1d (two portions in this embodiment).

A circuit board 2 consists of an insulating planar laminate, and over its surface are formed a central fixed contact 2a, and a peripheral fixed contact 2b of an electroconductive circuit pattern made of a copper foil or the like.

The movable contact 1 is mounted to be opposite the central fixed contact 2a and the peripheral fixed contact 2b, and the outer peripheral end 1e of the skirt 1a is in contact with the peripheral fixed contact 2b all the time, and the inner face of the top of the dome 1b constitutes the contact 1f, which goes out of contact with the central fixed contact 2a when the dome is repetitively inverted.

In this case, the rising angle &thgr;d of the skirt 1a of the movable contact 1 is formed to be more nearly upright than &thgr;b according to the prior art shown in Fig. 9 (&thgr;b < &thgr;d), and this &thgr;d is formed to be equal to &thgr;c according to the prior art shown in Fig. 10 (&thgr;c = &thgr;d).

Thus, the configuration is such that (the shifted quantity) L4 between the contact 1f and the central fixed contact 2a when the dome 1b of the movable contact 1 is inverted becomes equal to L1 (L4 = L1) and, as the distance (the shifted quantity) L4 between the contact 1f and the central fixed contact 2a when the dome 1b of the movable contact 1 is inverted is greater, the shifted quantity after the inversion of the movable contact 1 can be set greater than otherwise as indicated by D in Fig. 3, resulting in a crispy feeling of click. In the diagram the vertical axis represents the manipulative force F, and the horizontal axis, the shifted quantity L.

Further, while the rising angle &thgr;d of the skirt 1a of the movable contact 1 is formed more nearly upright, the connecting part of the dome 1b to be connected to this skirt 1a is connected via the two bent portions 1c and 1d, and it is possible to generally reduce the angle formed by the bent portion 1d of the bent portions with the dome 1b. Accordingly, the feeling curve DO formed when the dome 1b is inverted can be brought close to the feeling curve AO according to the prior art shown in Figs. 11 and 12, with the result that the point LD, where the reaction force of the feeling curve DO reaches its minimum, never becomes negative and the movable contact 1 can automatically return to its original position without fail.

Fig. 4 and Fig. 5 illustrate the structure of a sheet-shaped switch device using the movable contact 1.

In the drawings, a circuit board 3 is formed of a laminate of phenol resin or the like, and pluralities of central fixed contacts 4a and peripheral fixed contacts 4b, consisting of electroconductive copper foils or the like, are arranged over the surface of this circuit board 3.

An insulating sheet 5 is formed of a filmy insulating material, and its under face is covered all over with an adhesive layer, to which the dome 1b of the movable contact 1 is stuck to integrate the movable contact 1 with the insulating sheet 5.

A spacer 6 is also formed of a filmy insulating material, and its under face is also covered with an adhesive layer. At its center are provided a plurality of accommodating holes 6a for accommodating the movable contact 1.

The spacer 6 is stuck to the under face of the insulating sheet 5, and the back face of the movable contact 1 stuck to the insulating sheet 5 is covered with a protective sheet 20. This protective sheet 20 consists of a film whose face opposite the adhesive layer on the under face of the spacer 6 is peelably coated, and these elements are stacked to form a sheet with the contact plate.

A sheet-shaped switch device is formed by peeling the protective sheet 20 from this sheet with the contact plate and sticking the insulating sheet 5 and the spacer 6 to the circuit board 3 so that the movable contact 1 be opposite the central fixed contact 4a and the peripheral fixed contact 4b.

Then the movable contact 1 is in such a state that the dome 1b is separate from but opposite the central fixed contact 4a and the outer peripheral end 1e of the skirt 1a is in contact with the peripheral fixed contact 4b all the time.

In this case, in the movable contact 1 are formed a plurality of projections 1g (three in this embodiment) scattered in the contact 1f, which is the inner face of the top of the dome 1b. By providing the contact 1f with the projections 1g in this way, the contact of the contact 1f can be stabilized even if dust or the like invades the contact 1f, resulting in improved dustproofness. Incidentally, while even a single projection 1g would be effective, a plurality of them are even more so.

In this embodiment, if the inner face of the movable contact 1 is provided with the projections 1g, a greater distance (the shifted quantity) can be secured between the projections 1g and the central fixed contact 4a, resulting in a crisp click feeling.

Incidentally, although the spacer 6 for accommodating the movable contact 1 is used in the foregoing embodiment, the configuration is not limited to this, but the spacer 6 can as well be dispensed with to have the insulating sheet 5 directly hold the movable contact 1.

Fig. 6 and Fig. 7 illustrate the structure of a switch device based on an insulating resin-made housing using the movable contact 1.

In the drawing, a housing 7 is formed of an insulator, such as synthetic resin, in a box shape with an opening in the top face. On the inner bottom face of an accommodating section 7a formed in the opening in this housing 7 are arranged a central fixed contact 8a and a peripheral fixed contact 8b consisting of electroconductive metallic plates.

Over the central fixed contact 8a and the peripheral fixed contact 8b is formed the movable contact 1 opposite them. In this case, the dome 1b is separate from but opposite the central fixed contact 8a and the outer peripheral end 1e of the skirt 1a is in contact with the peripheral fixed contact 8b all the time.

A stem 9, similarly formed of an insulator such as synthetic resin, is provided with a suppressive manipulating part 9a protruding from the opening in the housing 7, a flange 9b and an operating projection 9c for suppressing the dome 1b of the movable contact 1.

A cover 10, formed of a planar metallic plate or the like, covers the opening in the housing 7, and prevents the stem 9 from springing out by keeping the flange 9b of the stem 9 in contact with the inner face of the cover 10.

By inserting the movable contact 1 and the stem 9 into the opening in the housing 7, covering the opening in the housing 7 with the cover 10 and fixing it by caulking or otherwise, the switch device based on the insulating resin-made housing is formed. In this case, too, in the movable contact 1 are formed a plurality of projections 1g (three in this embodiment) scattered in the contact 1f, which is the inner face of the top of the dome 1b, resulting in improved dustproofness.

As hitherto described, the contact plate according to the present invention consists of a disc formed into a dome shape by cupping the center of a thin metallic sheet in one direction, provided with a skirt rising from the outer circumference of this disc toward the center of the disc, and a dome which is continuous from this skirt and can be repetitively inverted, the connecting part between the skirt and the dome being formed in multiple steps via a plurality of bent portions. Accordingly it is possible to generally reduce the angle formed by one of these bent portions with the dome, with the result that the point where the reaction force of the feeling curve reaches its zero never becomes negative and the failure of the movable contact to automatically return to its original position can be prevented. Moreover, as the shifted quantity after the inversion of the movable contact can be set greater, resulting in a crispy click feeling.

Also, as on the inner face of the dome are formed projections in contact with the fixed contact, the contacting of the contact can be stabilized even if dust or the like invades the contact, resulting in improved dustproofness.

Also, the external face of the dome of the contact plate is stuck to the adhesive back face layer of an insulating sheet, and the contact plate and the under face of the insulating sheet are covered with a peelable protective sheet to provide a sheet with the contact plate, with the result that fitting to a planar circuit board is facilitated and the protective sheet can prevent dust from sticking to the contact part during the handling.

Also, as a spacer sheet having an accommodating hole for accommodating the contact plate is provided between the insulating sheet and the protective sheet, the contact plate can be securely fixed in a prescribed position of the insulating sheet.

Also, as the protective sheet of the sheet with the contact plate is peeled, and the sheet with the contact plate after peeling is stuck to a circuit board, over which a plurality of fixed contacts are arranged, by the adhesive layer of the insulating sheet so that the contact plate is opposite the fixed contact, the sheet-shaped switch device gives a crispy click feeling and is free from failure to automatically return to the original position after being inverted.

Also, as a switch device has the contact plate and an accommodating section, whose inner bottom face is provided with a housing over which a fixed contact is arranged and a suppressing member liftably snapped into the accommodating section, and the contact plate is arranged opposite the fixed contact to be suppressible by the suppressing member, a switch device based on an insulating resin-made housing free from failure to automatically return to the original position and giving a crispy click feeling can be easily obtained.