Membrane switch and dial operation member equipped therewith

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a membrane switch, which is produced by interposing a spacer between flexible films having conductor circuits formed by the printing or the like. The present invention also relates to a dial operation member, which is equipped with such a membrane switch.

2. Description of the Related Art

Such a membrane switch is used as a switch including electrical circuits, which are formed by printing a conductive paste onto flexible substrates, such as polyester films or the like. The membrane switch is used as a lightweight, thin and flexible switch, and therefore is particularly useful for mass production. These significant features of the membrane switch allow it to be used in a wide application field, for instance, in a keyboard for a computer, a home electrical appliance, a portable communication device, such as a cellar phone, a component for an automobile, a musical instrument, a medical appliance and others.

FIG. 7

is a plan view of a conventional membrane switch.

FIG. 8

is a plan view of a lower contact sheet in the conventional membrane switch.

FIG. 9

is a plan view of an upper contact sheet in the conventional membrane switch.

FIG. 10A

is a sectional view of the conventional membrane switch in the non-conductive state, and

FIG. 10B

is a sectional view of the conventional membrane switch in the conductive state.

Such a conventional membrane switch

110

comprises a lower contact sheet

111

, an upper contact sheet

112

, a spacer

113

, a connector

114

and others, as shown in

FIGS. 7-10

. The lower contact sheet

111

includes a conductor

111

a

and a projection portion

111

b

, as shown in FIG.

8

. The conductor

111

a

includes several sets of paired contact areas

111

c

and

111

d

, each end of which is ramified in the form of an approximately U shape. The upper contact sheet

112

includes circular contact areas

112

a

, which are used to come into contact with the corresponding contact areas

111

c

and

111

d

in the conductive state, as shown in FIG.

9

. In the spacer

113

, there are through holes

113

a

, through which paired contact areas

111

c

and

111

d

on the side of the lower contact sheet

111

and corresponding contact areas

112

a

on the side of the upper contact sheet

112

come into contact with each other in the conductive state, as shown in FIG.

7

. The projection portion

111

b

which is part of the lower contact sheet

111

including part of the conductor

111

a

is inserted into the connector

114

.

In the following, the function of the conventional membrane switch will be described.

When trying to push a projection portion

109

d

to bend the upper contact sheet

112

in the lower direction by pushing a projection portion

109

d

, as shown in

FIG. 10A

, the contact area

112

a

is in contact with the paired contact areas

111

c

and

111

d

, as shown in FIG.

10

B. Accordingly, the contact area

112

a

is directly connected to the paired contact areas

111

c

and

111

d

, so that the membrane switch

110

turns on in the conductive state (the ON state).

In the conventional membrane switch

110

, there is a problem in which a decrease in the press force acting to the upper contact sheet

112

occasionally causes the contact area

112

a

to come in contact with only one of the paired contact areas

111

c

and

111

d

, so that the membrane switch

110

does not turn on in the conductive state. Furthermore, in order to securely connect the contact area

112

a

with both the contact areas

111

c

and

111

d

in the conventional membrane switch

110

, it is necessary that the projection portion

109

d

made of a resilient material, such as gum or the like, presses against the upper contact sheet

112

with a press force greater than a predetermined force. This also provides an increase in the production cost, since the number of the parts constituting the membrane switch

110

is inevitably increased.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a membrane switch capable of turning on even with a very small weight.

It is another object of the present invention to provide a dial operation member, which is equipped with such a membrane switch.

In accordance with a first aspect of the invention, a membrane switch comprises,

(a) a first base element made of an electrical insulation elastic material, the first base element having a first conductor including at least one press contact area and at least one permanent contact area on a surface of the first base element;

(b) a second base element made of an electrical insulation material, the second base element having a second conductor and a third conductor on a surface facing the surface of the first base element,

the second conductor including at least one press contact area in accordance with the arrangement of the at least one press contact area in the first conductor, and

the third conductor including at least one permanent contact area in accordance with the arrangement of the at least one permanent contact area in the first conductor,

the second base element further having a connector section for connecting the second and third conductors to an external circuit; and

(c) a spacer made of an electrical insulation material, the spacer being interposed between the first base element and the second element, the spacer having through holes at positions corresponding to those both in the at least one press contact area and the at least one permanent contact area of the first and second base elements.

In accordance with a second aspect of the invention, a membrane switch comprises,

(a) a first base element made of an electrical insulation elastic material, the first base element having a first conductor including at least one press contact area, a second conductor including at least one permanent contact area and a connector section for connecting the first and second conductors to an external circuit on a surface of the first base element;

(b) a second base element made of an electrical insulation material, the second base element having a third conductor on the surface facing the surface of the first base element, the third conductor including at least one press contact area in accordance with the arrangement of the at least one press contact area disposed in the first conductor and the at least one permanent contact area in accordance with the arrangement of the at least one permanent contact area disposed in the first conductor; and

(c) a spacer made of an electrical insulation material interposed between the first base element and the second base element, the spacer having through holes in accordance with the arrangement of the at least one press contact area and the at least one permanent contact area.

In accordance with a third aspect of the invention, a dial operation member comprises,

(a) a shaft;

(b) a bearing through which the shaft passes;

(c) a dial body fixed to the shaft and rotatably supported around the center axis of the shaft;

(d) a press member for switch disposed so at to face the dial body for switching, the press member having at least one press projection portion for switching; and

(e) one of the above mentioned membrane switches, wherein at least one press portion for switching is disposed so as to face the at least press projection for switching in the press member for switch.

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

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a sectional view of an operation dial onto which a membrane switch according to the invention is mounted.

FIG. 2

is a plan view of the membrane switch according to the invention.

FIG. 3

is a plan view of a lower contact sheet in the membrane switch according to the invention.

FIG. 4

is a plan view of an upper contact sheet in the membrane switch according to the invention.

FIG. 5

is a plan view of a spacer in the membrane switch according to the invention.

FIG. 6A

is a sectional view of the membrane switch according to the invention in the non-conductive state.

FIG. 6B

is a sectional view of the membrane switch according to the invention in the conductive state.

FIG. 6C

is a sectional view of the membrane switch according to the invention in the conductive state.

FIG. 7

is a plan view of a conventional membrane switch.

FIG. 8

is a plan view of a lower contact sheet in the conventional membrane switch.

FIG. 9

is a plan view of an upper contact sheet in the conventional membrane switch.

FIG. 10A

is a sectional view of the conventional membrane switch in the non-conductive state.

FIG. 10B

is a sectional view of the conventional membrane switch in the conductive state.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, an embodiment of the invention will be described in detail.

FIG. 1

is a sectional view of a dial operation member

1

, which is equipped with a membrane switch

10

according to the invention.

The dial operation member

1

is used as a device, which has a touch sensing function and is rotatably operated. The dial operation member

1

is fixed to a chassis

3

of an electric appliance or the like, wherein the chassis

3

is covered by a front panel

2

. The dial operation member

1

is normally used, for instance, in a CD player for DJ, in which case, the dial operation member

1

is operated to temporarily pause the driving of the CD in the playback state. As shown in

FIG. 1

, the dial operation member

1

substantially comprises a dial

4

, a shaft

5

, a bearing

6

, an encoder disk

7

, a photo-interrupter

8

, a force transmission element

9

and the membrane switch

10

.

The dial

4

is used as a disk-shaped element, which is capable of being rotatably manipulated and is made of, for instance, stiff plastic material, aluminum die cast or the like, and the dial

4

has an arch-shaped projection portion

4

a

in the circumferential direction.

The shaft

5

is used as an element for rotatably supporting the dial

4

, in which case, the dial

4

is fixed to an end of the shaft

5

and the encoder disk

7

is fixed to the other end of the shaft

5

.

The bearing

6

is used as an element for rotatably supporting the shaft

5

, in which case, pins

6

a

and

6

b

as well as a projection portion

6

c

are formed on the upper part of the bearing

6

and an adaptation element

6

d

is disposed in the lower portion of the bearing

6

. The bearing

6

is fixed to the bottom surface of the chassis

3

by screws

3

a

and

3

b

. The encoder disk

7

is used as a rotary disk, which has a plurality of slits arranged in the same spacing in the circumferential direction, and is capable of being rotated together with the dial

4

.

The photo-interrupter

8

is used as a device for sensing the speed of revolution and the angular position of the encoder disk

7

, wherein, one of the slits in the encoder disk

7

passes through a space between a light-emitting element and a light-receiving element. The photo-interrupter

8

is fixed to the adaptation element

6

d.

The force transmission element

9

is used as an element for transmitting the press force applied onto the dial

4

to the membrane switch

10

, and is constituted by a material such as stiff plastic material, aluminum die cast, or the like in a disk-shape, as similarly to the dial

4

. The force transmission element

9

includes holes

9

a

and

9

b

for receiving the pins

6

a

and

6

b

, a contact portion

9

c

serving to come into contact with the projection portion

4

a

and a projection portion

9

d

serving to come into contact with the membrane switch

10

.

In

FIG. 1

, a gap having a very small spacing is formed between the dial

4

and the bearing

6

. Similarly, a gap having a very small spacing is formed between the encoder disk

7

and the bearing

6

, thereby enabling the dial

4

and the encoder disk

7

to be moved by a very small amount in the axial direction of the shaft

5

. The gaps are designed such that the encoder disk

7

and the photo-interrupter

8

come into no contact with each other. When the surface of the dial

4

is pushed downward, the press force acts to push down the force transmission element

9

via the projection portion

4

a

. The force transmission element

9

pushes down the membrane switch

10

in response to the movement of the force transmission element

9

. When stopping the pushing of the dial

4

, the force transmission element

9

is pushed upwards due to the resilient force of the membrane switch

10

. In conjunction with this movement, the dial

4

is also pushed upwards.

FIG. 2

is a plan view of the membrane switch according to the invention.

FIG. 3

is a plan view of the lower contact sheet in the membrane switch according to the invention.

FIG. 4

is a plan view of the upper contact sheet in the membrane switch according to the invention.

FIG. 5

is a plan view of the spacer in the membrane switch according to the invention.

The membrane switch

10

is used as a switch, which is formed by interposing a spacer

13

between the lower contact sheet

11

including a conductor

11

a

and the upper contact sheet

12

including a conductor

12

a

, and serves to connect one or more of contact areas

11

g

in the conductor

11

a

to one or more of corresponding contact areas

12

g

in the conductor

12

a

with the aid of the press force. As shown in

FIGS. 2-5

, the membrane switch

10

comprises the lower contact sheet

11

, the upper contact sheet

12

, the spacer

13

and a connector

14

.

The lower contact sheet

11

is a base element including the conductor

11

a

. The lower contact sheet

11

is formed by printing a conductive paste prepared by mixing conductive fine particles of copper, carbon, silver or the like with a binder resin is printed onto a polyester film. As shown in

FIG. 3

, the conductor

11

a

for supplying an electrical current, a projection portion

11

b

inserted into the connector

14

, a through hole

11

c

for receiving the projection portion

6

c

in

FIG. 1

, through holes

11

d

and

11

e

for receiving the corresponding pins

6

a

and

6

b

and a through hole

11

f

for receiving a screw

3

a

are formed on the lower contact sheet

11

.

The conductor

11

a

is constituted in a wiring pattern by conductors formed on the surface of the lower contact sheet

11

. The conductor

11

a

comprises six circular contact areas

11

g

coaxially arranged at a radial distance from the center of the lower contact sheet

11

with the same circumferential spacing; a conductor portion

11

h

formed in the circumferential direction of the lower contact sheet

11

for connecting to the contact areas

11

g

; a connection conductor portion

11

i

projecting from the conductor portion

11

h

toward the projection portion

11

b

; an annular conductive area

11

j

for receiving the screw

3

a

; and another connection conductor portion

11

k

projecting from the annular conductive area

11

j

toward the projection portion

11

b.

The upper contact sheet

12

is used as a base element including conductor

12

a

. The upper contact sheet

12

is formed by printing a conductive paste on a polyester film with a similar procedure to that in the lower contact sheet

11

. As shown in

FIG. 4

, the upper contact sheet

12

comprises a conductor

12

a

for supplying an electric current; a through hole

12

c

for receiving the projection portion

6

c

in

FIG. 1

; through holes

12

d

and

12

e

for receiving the corresponding pins

6

a

and

6

b

; and a through hole

12

f

for receiving the screw

3

a.

The conductor

12

a

is constituted in a wiring pattern by a conductor formed on the surface of the upper contact sheet

12

. The conductor

12

a

comprises six annular contact areas

12

g

coaxially arranged with respect to the center of the upper contact sheet

12

with the same circumferential spacing; a conductor portion

12

h

formed in the circumferential direction of the upper contact sheet

12

for connecting to the contact areas

12

g

; and an annular conductive area

12

j

connected to the conductor portion

12

h

for receiving the screw

3

a

. As show in

FIG. 2

, the contact areas

12

g

are disposed so as to face the contact areas

11

g

, and when the contact areas

11

g

and

12

g

receive a press force, the membrane switch turns on in the conductive state. The conductive area

12

j

is disposed to face the contact area

11

g

, as shown in

FIG. 2

, and is connected to the conductor portion

12

h

, as shown in FIG.

4

. The conductive areas

11

j

and

12

j

are fastened so as to come in contact with each other via the screw

3

a

shown in

FIG. 1

, so that the conductor

11

a

and the conductor

12

a

are always maintained in the conductive state.

The spacer

13

is used as an element for maintaining a predetermined spacing between the conductor

11

a

and the conductor

12

a

. The spacer

13

is interposed between the lower contact sheet

11

and the upper contact sheet

12

and it is made of a polyester film for electrically isolating these contact sheets

11

and

12

from each other. As shown in

FIG. 5

, the spacer

13

includes a through hole

13

c

for connecting the conductor portion

11

j

and conductor portion

12

j

to each other; through holes

13

d

and

13

e

for receiving the pins

6

a

and

6

b

respectively; and six through holes

13

g

for connecting the contact areas

11

g

and the corresponding contact areas

12

g

to each other. The six through holes are disposed with the same circumferential distance in the same radial distance from the center of the spacer

13

.

The connector

14

is used as a connection element for electrically connecting the membrane switch

10

to electric wires, an electrical circuit or an electrical appliance. As shown in

FIGS. 2 and 3

, the connector

14

is connected to the conductor

11

a

by inserting thereinto one end of the projection portion

11

b

in which the conductor portions

11

i

and

11

k

are formed.

In the following, the function of the membrane switch according to the embodiment of the invention will be described.

FIG. 6A

is a sectional view of the membrane switch according to the invention in the non-conductive state.

FIGS. 6B and 6C

are sectional views of the membrane switch according to the invention in the conductive state.

As shown in

FIG. 6A

, when the dial

4

in

FIG. 1

is manipulated in the state in which the upper contact sheet

12

is in contact with the projection portion

9

d

, a load or a press force resulting from the contact with the dial

4

is transmitted from the projection portion

4

a

to the projection portion

9

d

via the force transmission element

9

. As a result, the projection portion

9

d

moves the upper contact sheet

12

downward by the press force applied thereto, as shown in

FIG. 6B

, so that the upper contact sheet

12

is bent and the contact areas

11

g

and the corresponding contact areas

12

g

are into contact with each other. As shown in

FIGS. 2-4

, the conductor

11

a

having the contact area

11

g

and the conductor

12

a

having the contact area

12

g

come into contact with each other via the conductive area

11

j

and conductive area

12

j

. As a result, the conductors

11

a

and

12

a

are always maintained in the conductive state. Hence, the contact of the contact areas

11

g

with the corresponding contact areas

12

g

causes the membrane switch

10

to be in the conductive state (ON).

When a load resulting from the touching of the dial

4

is so small as to provide a restricted contact between the contact areas

11

g

and

12

g

, as shown in

FIG. 6C

, the membrane switch

10

becomes in the conductive state (ON) as similarly to the case in FIG.

6

B.

A decrease in the load or the press force applied to the projection portion

9

d

causes the projection portion

9

d

to be moved upward by the resilient force of the upper contact sheet

12

, and to be returned into the initial position. As a result, the membrane switch

10

is transferred into the non-conductive state (OFF).

The membrane switch according to the embodiment of the invention has the following advantages:

(1) In accordance with the embodiment, the conductive areas

11

j

and

12

j

enable the conductors

11

a

and

12

a

to be in contact with each other and therefore to be always maintained in the conductive state. When a press force is applied to the contact areas

11

g

and

12

g

in the conductors

11

a

and

12

a

in such manner that they come into contact with each other in a small area, the membrane switch

10

turns on into the conductive state. As a result, in the operation of the membrane switch

10

according to the embodiment of the invention, no such large load is needed, as in the conventional membrane switch

110

, where a large load has to be applied between the contact area

112

a

and the ramified contact areas

111

c

and

111

d

, and therefore turns on in the conductive state by applying a very small press force in touch sense, thereby enabling the reliability in the operation to be greatly enhanced. In the membrane switch

10

, moreover, there is no need for firmly applying a resilient projection portion

109

d

to the upper contact sheet

112

in the conventional membrane switch

110

, thereby enabling the number of parts to be reduced as well as the production cost to be reduced.

(2) In accordance with the embodiment, the contact areas

12

g

are always connected to the conductive area

11

j

and, along with this arrangement, the membrane switch turns on, when at least one of the contact areas

11

g

and the contact area

12

g

corresponding thereto come into contact with each other. Due to this arrangement, the connector

14

of the membrane switch

10

is compatible with the connector

114

of the conventional membrane switch

110

shown in FIG.

7

. Accordingly, this arrangement ensures an easy connection of the connector, compared with the arrangement in which two connectors are connected to the conductor

11

a

and

12

a

, respectively. In case of trying to form a connector

14

by extending the conductor portion

11

i

from the contact areas

12

g

, contacts of the connector have to be disposed in both the lower contact sheet

11

and the upper contact sheet

12

, thereby lacking the compatibility with the conventional connector regarding the contacts.

(3) In accordance with the embodiment, the contact areas

11

g

and

12

g

are disposed with the same circumferential spacing on a circle from the centers of the lower contact sheet

11

and the upper contact sheet

12

, respectively. As a result, the membrane switch

10

turns on steadily in the conductive state, if a soft touch of at least one of the contact areas

11

g

is carried out.

In the above-described embodiment, six contact areas

11

g

and

12

g

are disposed on a circle. However, the number of the contact areas and the spacing therebetween can be arbitrarily selected. In the embodiment, an appropriate spacing can be provided between the contact areas

11

g

and the contact areas

12

g

. Therefore, the press force necessary for contacting the contact areas

11

g

with the contact areas

12

g

can be adjusted by appropriately selecting the thickness of the spacer

13

and the inside diameter of the through holes

13

g

. In the embodiment, moreover, the conductive area

11

j

and the conductive area

12

j

are directly in contact with each other. However, the electrical connection between the conductive areas

11

j

and

12

j

can be attained via an appropriate conductive material. In the embodiment, however, the lower contact sheet

11

and the upper contact sheet

12

are formed by the same material (for instance, polyester). Actually, the upper contact sheet

12

can be formed by a flexible material. In this case, however, it is not necessary that the lower contact sheet

11

and the spacer

13

are formed by a flexible material. In particular, the lower contact sheet

11

must be disposed on a flat surface of a stiff material in order to receive the press force applied to the upper contact sheet. Otherwise, the lower contact sheet

11

itself must be made of a stiff material. In the embodiment, furthermore, the conductor portions

11

i

and

11

k

on the side of the lower contact sheet

11

are connected to the connector

14

. However, such conductor portions connected to the connector can be formed on the side of the upper contact sheet. In other words, the geometry of the upper contact sheet

12

and the lower contact sheet

11

can be arranged upside down, such that the contact sheets

11

and

12

are disposed respectively on the upper and lower sides and the contact sheet

12

, in which case the lower contact sheet

11

can be made of a flexible material.

While the preferred embodiment has been shown and described, various modifications and substitutions may be made without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of example, and not by limitation.