Two-position pushbutton switch

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a two-position pushbutton switch suitable for use in a digital camera.

2. Description of the Related Art

A conventional two-position pushbutton switch will be described below with reference to

FIGS. 32

to

35

. First, second, and third switch sections S

3

, S

4

, and S

5

are held in a casing

51

.

The first switch section S

3

is formed of a membrane switch in which an insulating sheet

54

with an opening is interposed in a folded sheet

53

having a fixed contact and a movable contact, as shown in FIG.

34

.

The second switch section S

4

is formed of a membrane switch in which a fixed contact formed on a sheet

52

and a movable contact formed on a sheet

53

are opposed to each other via the opening of the sheet

54

.

In the casing

51

, a platelike support member

55

is also placed, and an operating member

56

is mounted on the support member

55

.

The operating member

56

includes a mounting portion

56

a

mounted on the support member

55

, an elastic portion

56

b

connected to the mounting portion

56

a

, a projection

56

c

formed at one end of the elastic portion

56

b

, an operating portion

56

e

connected to the mounting portion

56

a

via hinge portions

56

d

, a projection

56

f

formed at the end of the operating portion

56

e

, and a projection

56

g

formed at the bottom center of the operating portion

56

e.

The sheet

53

is bent in the shape of the letter U, and the first switch section S

3

at the leading end thereof is placed on the upper surface of the operating portion

56

e

. A dome-shaped click spring

57

having a small working force and a small diameter is laid on the first switch section S

3

.

The second switch section S

4

, composed of three stacked sheets

52

,

53

, and

54

, is placed on the upper surface of the support member

55

, and a dome-shaped click spring.

58

having a great working force and a large diameter is laid on the second switch section S

4

and below the projection

56

g

. The third switch section S

5

is placed below the projection

56

f.

A key top

59

includes an operating portion

59

a

, two projections

59

b

and

59

c

formed on the lower side of the operating portion

59

a

, a support portion

59

d

formed at one end of the operating portion

59

a

, and a retaining portion

59

e

formed at the other end of the operating portion

59

a

. The key top

59

is supported in a cantilevered manner at the support portion

59

d.

When the key top

59

is mounted, the operating portion

59

a

is exposed from an opening portion

51

a

of the casing

51

, the projection

59

b

is in contact with the projection

56

c

of the operating member

56

, and the projection

59

c

is in contact with the click spring

57

. Furthermore, the retaining portion

59

e

is retained on the inner surface of the casing

51

by the resilient force of the elastic portion

56

b

of the operating member

56

.

The operation of the conventional two-position pushbutton switch will now be described. First, when the operating portion

59

a

of the key top

59

is pressed, the key top

59

tilts relative to the support portion

59

d

so as to simultaneously push the projection

56

c

and the click spring

57

.

Then, the click spring

57

with a small working force is first inverted and presses the sheet

53

(folded portion) so that the movable contact is put into contact with the fixed contact thereon, thereby turning on the first switch section S

3

.

In this case, the relationship between the stroke A and the working force B of the key top

59

is represented by a curve C

3

, and the stroke A

3

is short, as shown in FIG.

35

.

When the key top

59

is further pressed in this state, the operating portion

56

e of the operating member

56

is tilted via the hinge portions

56

d

, and therefore, the projection

56

g

of the operating portion

56

e presses the click spring

58

.

Subsequently, the click spring

58

with a large working force is inverted and presses the sheet

53

so that the movable contact is put into contact with the fixed contact of the sheet

52

, thereby turning on the second switch section S

4

.

In this case, the stroke A and the working force B of the key top

59

have a relationship represented by a curve C

4

, as shown in FIG.

35

.

In response to the tilting of the operating portion

56

e

, the projection

56

f

operates the third switch section S

5

so as to switch from the ON state to an OFF state.

When the key top

59

is then released from pressing, it is pushed back by the elastic portion

56

b

, and the operating portion

56

e

is returned to its initial state by-the hinge portions

56

d

. Furthermore, the click springs

57

and

58

are inverted into their initial states because of their own resilient forces. This turns off the first and second switch sections S

3

and S

4

, and returns the third switch section S

5

into an ON state.

In a case in which such a two-position pushbutton switch is adopted-in a digital camera, focusing is performed by operating the first switch section S

3

by a first press, and a shutter is released. by operating the second switch section S

4

by a second press.

In the conventional two-state pushbutton switch, however, since the click spring

57

is pressed and inverted immediately after the key top

59

abuts the click spring

57

, a stroke A

3

of the first press is short, as shown in FIG.

35

.

For this reason, when such a two-position pushbutton switch is adopted in a digital camera, the press stroke for focusing is short and the focusing operation is difficult. This decreases ease of use.

Furthermore, the operating member

56

includes the, mounting portion

56

a

and the operating portion

56

e

supported on the mounting portion

56

a

via the hinge portions

56

d

, and the operating

56

e

is able to move via the hinge portions

56

d

. This requires a large space in the lateral direction and increases the size of the switch.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a two-position pushbutton switch in which operability is improved by extending the stroke of a key top for switching between switch sections.

Another object of the present invention is to provide a compact two-position pushbutton switch which allows smooth operation.

In order to overcome the above problems, according to an aspect of the present invention, there is provided a two-position pushbutton switch including: a first click spring to be inverted by a first working force; a first switch section to be operated by the inversion of the first click spring; a driving member disposed opposed to the first click spring so as to press the first click spring; a second switch section laid on the driving member; a second click spring to be inverted by a second working force, different from the first working force, so as to operate the second switch section; and a key top for pressing the second click spring, wherein a cushioning member is placed on at least one of the first and second click springs and the click spring is pressed via the cushioning member.

This can make a first press stroke long. For this reason, in a case in which such a two-position pushbutton switch is adopted in a digital camera, a press stroke for focusing can be made long, and the focusing operation is easy. This improves ease of use of the pushbutton switch.

The cushioning member may be placed on the second click spring.

This can make the first press stroke long. Moreover, since the key top and the second click spring are not in direct contact with each other, even when the key top rattles, no sound is produced by the contact therebetween.

The cushioning member may be placed on the first click spring.

This can make the first press stroke long. The first press stroke can be further extended by using the cushioning member in combination with a cushioning member placed on the second click spring.

Preferably, the two-position pushbutton switch further includes a casing for holding the key top, an operating portion of the key top is exposed from an opening portion of the casing, and the key top is elastically pressed against the casing and supported therein by the cushioning,member.

In this case, the cushioning member also serves to press the key top and to thereby prevent the key top from rattling. This also reduces the number of components and lowers the cost.

Preferably, the first working force for the first click spring is greater than the second working force for the second click spring.

In this case, after the second click spring at the upper position is inverted, the lower first click spring is inverted. The driving member can be stably supported by the lower click spring with a large working force.

Preferably, the diameter of the first click spring is smaller than that of the second click spring, and the thickness of the first click spring is greater than that of the second click spring.

This makes it possible to reliably make the working force for the first click spring greater than that for the second click spring and to thereby allow reliable operation.

Preferably, the first and second click springs are made of a metal leaf spring and also serve as movable contacts of the first and second switch sections.

This reduces the number of components, improves assembly efficiency, and lowers the cost.

Preferably, the two-position pushbutton switch further includes a flexible insulating substrate having fixed contacts for the first and second switch sections, and the flexible insulating substrate is bent in the shape of the letter S and is placed opposed to the first and second-click springs.

In this case, the fixed contacts can be formed in the same plane of the flexible insulating substrate, and therefore, productivity is increased.

Preferably, the two-position pushbutton switch further includes a support member for supporting the first switch section, the support member has a plurality of guide projections extending in the pressing direction of the key top, and the driving member is slid along the guide projections in the pressing direction.

This makes it possible to reduce the space for supporting the driving member and to thereby reduce the size, and to make the sliding motion of the driving member smooth.

According to another aspect of the present invention, there is provided a two-position pushbutton switch including: a first click spring to be inverted by a first working force; a first switch section to be operated by the inversion of the first click spring; a driving member placed opposed to the first click spring so as to press the first click spring; a second switch section placed on the driving member; a second click spring to be inverted by a second working force, different from the first working force, so as to operate the second switch section; a key top for pressing, the second click spring; and a guide member for guiding the motion of the driving member, wherein the driving member is slid along the guide member in the pressing direction of the key top.

Since the space for holding the driving member can be reduced, the size of the two-position pushbutton switch can also be reduced. Moreover, since the driving member can be moved stably, operability is enhanced.

Preferably, the guide member includes a plurality of guide projections arranged to surround the second switch section, and a support member is further provided so as to support the first switch section.

This reduces the size of the pushbutton switch and allows the driving member to be moved stably.

Preferably, the guide projections are shaped like a bendable column, and hook portions are formed at the leading ends of the guide projections so as to retain the driving member.

In this case, the driving member can be easily assembled and the position thereof can be regulated reliably.

The guide member may have a connecting portion for connecting the guide projections.

This facilitates assembly of the guide member and improves productivity.

Preferably, the first switch section is placed on a flexible insulating substrate, a projection is formed at the bottom of the connecting portion of the guide member, the guide member is mounted on the support member by the projection, and the flexible insulating substrate laid on the support member is sandwiched between the support member and the connecting portion.

In this case, the guide member and the flexible insulating substrate can be mounted simultaneously. This increases productivity and prevents the first switch section from lifting.

Preferably, the driving member has a flat portion for holding the second switch section thereon, and the flat portion has a plurality of guide portions to be guided by the guide projections.

This allows the driving member to be moved stably and smoothly.

Preferably, fixed contacts of the first and second switch sections are formed-on the same flexible insulating substrate, and the flexible insulating substrate is placed in a form bent in the shape of the letter S.

Since the fixed contacts can be formed on the same plane of the flexible insulating substrate, productivity is increased.

Preferably, the driving member has a pair of projecting latch portions, the flexible insulating substrate has a pair of holes, and the second switch section is held on the driving member by latching the latch portions in the holes.

In this case, the position of the second switch section with respect to the driving member can be reliably ensured, and the second switch section can be mounted without lifting.

Preferably, the first and second click springs are made of a metal leaf spring, and also function as movable contacts of the first and second switch sections.

This reduces the number of components, improves assembly efficiency, and lowers the cost.

Further objects. features, and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference-to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a plan view of a two-position pushbutton switch according to the present invention.

FIG. 2

is a cross-sectional view taken along line II—II in FIG.

1

.

FIG. 3

is a cross-sectional view taken along line III—III in FIG.

1

.

FIG. 4

is an exploded perspective view of the two-position pushbutton switch.

FIG. 5

is a plan view of a flexible insulating substrate in the two-position pushbutton switch.

FIG. 6

is a plan view of a guide member in the two-position pushbutton switch.

FIG. 7

is a front view of the guide member.

FIG. 8

is a bottom view of the guide member.

FIG. 9

is a cross-sectional view taken along line IX—IX in FIG.

6

.

FIG. 10

is a cross-sectional view taken along line X—X in FIG.

6

.

FIG. 11

is a plan view of a driving member in the two-position pushbutton switch.

FIG. 12

is a front view of the driving member.

FIG. 13

is a side view of the driving member.

FIG. 14

is a cross-sectional view taken along line XIV—XIV in FIG.

11

.

FIG. 15

is a plan view showing a state in which the guide member and the driving member are combined.

FIG. 16

is a plan view of a key top in the two-position pushbutton switch.

FIG. 17

is a front view of the key top.

FIG. 18

is a bottom view of the key top.

FIG. 19

is a side view of the key top.

FIG. 20

is a cross-sectional view taken along line XX—XX in FIG.

16

.

FIG. 21

is a graph showing the relationship between the stroke and the working force in the two-position pushbutton switch.

FIG. 22

is a plan view of another example of a guide member.

FIG. 23

is a front view of the guide member.

FIG. 24

is a bottom view of the guide member.

FIG. 25

is a side view of the guide member.

FIG. 26

is a cross-sectional view taken along line XXVI—XXVI in FIG.

22

.

FIG. 27

is a cross-sectional view taken along line XXVII—XXVII in FIG.

22

.

FIG. 28

is a plan view of another example of a driving member.

FIG. 29

is a front view of the driving member.

FIG. 30

is a bottom view of the driving member.

FIG. 31

is a cross-sectional view taken along line XXXI—XXXI in FIG.

28

.

FIG. 32

is a cross-sectional view of a conventional two-position pushbutton switch.

FIG. 33

is an exploded perspective view of the conventional two-position pushbutton switch.

FIG. 34

is a cross-sectional view showing the principal part of a first switch section in the conventional two-position pushbutton switch.

FIG. 35

is a graph showing the relationship between the stroke and the working force in the conventional two-position. pushbutton switch.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A two-position pushbutton switch according to an embodiment of the present invention will be described below with reference to the attached drawings.

The configuration of the two-position pushbutton'switch of this embodiment will now be described with reference to

FIGS. 1

to

21

.

A support member

1

made of a metal plate or the like has four mounting holes

1

a

formed on the outer side, and three mounting holes

1

b

formed on the inner side.

A flexible insulating substrate

2

made of a polyester. film includes, particularly shown in

FIG. 5

, a rectangular base portion

2

a

, a band portion

2

c

extending from one side of the base portion

2

a

and having cutouts

2

b

on both sides, and a band-shaped extended portion

2

d

extending from one side of the base portion

2

a

at right angles to the band portion

2

c.

The flexible insulating substrate

2

also has four mounting holes

2

e

formed on the outer periphery of the base portion

2

a

, two mounting holes

2

f

formed inside the mounting holes

2

e

, a circular hole

2

g

formed in the center of the band portion

2

c

, and a pair of rectangular holes

2

h

and

2

j

formed at an interval in the band portion

2

c

offset from the hole

2

g

toward the leading end of the band portion

2

c.

A conductive pattern is formed on the upper surface of the flexible insulating substrate

2

by, for example, printing conductive paste made of silver or the like. A first fixed contact

3

is formed at the center of the base portion

2

a

, and a second fixed contact

4

is formed between the holes

2

h

and

2

j

at the leading end of the band portion

2

c

. These fixed contacts

3

and

4

are led into the extended portion

2

d by lead-out conductors

5

. The upper surface of the flexible insulating substrate

2

, excluding the first and second fixed contacts

3

and

4

and the ends of the lead-out conductors

5

, is covered with an insulating resist layer

6

(hatched in FIG.

5

).

A first click spring

7

, which is shaped like a dome and also serves as a first movable contact, is made of a resilient leaf spring of stainless steel, and, for example, is 0.07 mm in thickness and 5 mm in diameter. The first click spring

7

is laid on the base portion

2

a

of the flexible insulating substrate

2

so that it faces the first fixed contact

3

and so that it is constantly in contact with one contact portion of the first fixed contact

3

disposed on the outer side and is spaced from the other contact portion disposed at the center.

The first click spring

7

is stuck on the flexible insulating substrate

2

with its outer surface being covered with an insulating sheet (not shown) having adhesive on one side.

The first click spring

7

and the first fixed contact

3

constitute a first switch section S

1

. The first click spring

7

is inverted by a substantially great working force so that the center thereof moves into contact with and apart from the center contact portion of the first fixed contact

3

.

A second click spring

8

also serving as a second movable contact is made of a resilient leaf spring of stainless steel, and is shaped like a dome larger than that of the first click spring

7

, for example, having a thickness of 0.05 mm and a diameter of 6 mm. The second click spring

8

is laid at the end of the band portion

2

c

of the flexible insulating substrate

2

so that it faces the second fixed contact

4

and so that it is constantly in contact with one contact portion of the second fixed contact

4

disposed on the outer side and is spaced from the other contact portion disposed at the center.

The second click spring

8

is stuck on the flexible insulating substrate

2

with its outer surface being covered with an insulating sheet (not shown) having adhesive on one side, in a manner similar to that of the first click spring

7

.

The second click spring

8

and the second fixed contact

4

constitute a second switch section S

2

. The second click spring

8

is inverted by a working force less than that of the click spring

7

so that the center thereof moves into contact with and apart from the center contact portion of the second fixed contact

4

.

The base portion

2

a

of the flexible insulating substrate

2

having such a structure is placed on the support member

1

with the mounting holes

2

e

and

2

f

aligned with the mounting holes

1

a

and

1

b

of the support member

1

. The band portion

2

c

is able to bend in the form of the letter S relative to the base portion

2

a

, as shown in

FIGS. 2 and 4

.

A casing

9

molded from synthetic resin includes a cylindrical side wall

9

a

, a flange portion

9

c

formed at the upper end of the side wall

9

a

and having a circular opening

9

b

, and four projections

9

d

projecting downward from the bottom end of the side wall

9

a.

The casing

9

and the base portion

2

a

of the flexible insulating substrate

2

are mounted on the support member

1

by placing the bottom end of the side wall

9

a

on the flexible insulating substrate

2

with the projections

9

d

passed through the holes

1

a

and

2

e

and thermally caulking the leading ends of the projections

9

d

on the lower surface of the support member

1

.

A guide member

10

molded from synthetic resin includes, particularly shown in

FIGS. 6

to

10

, a ring-shaped connecting portion

10

a

, a plurality of (four) bendable guide projections

10

b

projecting upward from the connecting portion

10

a

, hook portions

10

c

projecting from the upper ends of the guide projections

10

b

toward the center, three projections

10

d

projecting downward from the connecting portion

10

a

, an L-shaped support portion

10

f

projecting sideways from the connecting portion

10

a

, and a groove portion

10

e

formed between the connecting portion

10

a

and the support portion

10

f.

The guide member

10

is mounted on the support member

1

by placing the lower side of the connecting portion

10

a

on the flexible insulating substrate

2

with the projections

10

d

passed through the mounting holes

2

f

and

1

b

and thermally caulking the leading ends of the projections

10

d

on the bottom surface of the support member

1

. The base portion

2

a

of the flexible insulating substrate

2

is supported on the support member

1

.

After mounting, the guide member

10

is positioned inside the casing

9

, and the first switch section S

1

is positioned in the center space of the connecting portion

10

a.

Since the flexible insulating substrate

2

is pressed against the support member

1

by the connecting portion

10

a of the guide member

10

, the first switch section S

1

will not lift.

A driving member

11

molded from synthetic resin includes, particularly shown in

FIGS. 11

to

14

, a flat portion

11

a

, a plurality of (four) guide portions

11

b

cut out on the outer periphery of the flat portion

11

a

, an L-shaped latch portion

11

c

formed at one end of the flat portion

11

a

so as to partly project on the upper side, a latch portion

11

d

formed on the side opposite from the latch portion

11

c

so as to project from an end face of the flat portion

11

a

, and a pressing portion lie projecting from the bottom center of the flat portion

11

a.

The latch portion

11

c

of the driving member

11

is latched in the hole

2

h

of the flexible insulating substrate

2

, and the latch portion

11

d

is latched in the hole

2

j

. The second switch section S

2

disposed on the band portion

2

c

is placed on the flat portion

11

a

in a state in which the band portion

2

c

is prevented from becoming slack by the latch portions

11

c

and

11

d.

The band portion

2

c

of the flexible insulating substrate

2

is bent along the lower side of the driving member

11

, and the pressing portion

11

e

is passed through the hole

2

g

. A portion of the band portion

2

c

on the side of the base portion

2

a

is placed in the groove

10

e

of the guide member

10

and is supported by the support portion

10

f.

The driving member

11

, on which the band portion

2

c

of the flexible insulating substrate

2

is latched, is placed between guide projections

10

b

of the guide member

10

b

while the guide projections

10

b

are bent outward, and the guide projections

10

b

are then unbent and are engaged with the guide portions

11

b.

The driving member

11

is thereby allowed to vertically move along the guide projections

10

b

. The driving member

11

is prevented from falling off upward and the position thereof is regulated by the hook portions

10

c at the upper ends of the guide projections

10

b.

When the driving member

11

is mounted, the flexible insulating substrate

2

is bent in the shape of the letter S as a whole, as shown in FIG.

2

.

Since the pressing portion

11

e

of the driving member

11

is passed through the hole

2

g

of the flexible insulating substrate

2

, the resilient force of the S-shaped flexible insulating substrate

2

is well balanced and the flexible insulating substrate

2

is held stably.

First and second cushioning members

12

and

13

are made of a sponge material, such as rubber sponge (soft foam rubber) or foamed polyurethane sponge (polyurethane foam), which is elastically deformed (compression-deformed) by a force less than the working force for the second click spring

8

.

The first cushioning member

12

is stuck on the upper surface of the first click spring

7

(more precisely, the upper surface of the insulating sheet, which is not shown, covering the outer surface of the first click spring

7

) by a double-faced adhesive tape or the like. The driving member

11

is always elastically pressed upward against the hook portions

10

c

by the first cushioning member

12

. Similarly, the second cushioning member

13

is stuck on the upper surface of the second click spring

8

covered with the insulating sheet (not shown) by a double-sided adhesive tape or the like.

A key top

14

molded from synthetic resin includes, as particularly shown in

FIGS. 16

to

20

, an operating portion

14

a

shaped like a circular dome, a ring-shaped flange portion

14

b

projecting on the outer periphery of the operating portion

14

a

, a linear portion

14

c

formed in the flange portion

14

b

, and a pressing portion

14

d

projecting from the bottom center of the operating portion

14

a.

The key top

14

is held inside the casing

9

. The surface of the operating portion

14