Normally open extended travel dual tact switch assembly with sequential actuation of individual switches

BACKGROUND OF THE INVENTION

1. Field of the Invention

This disclosure relates generally to electrical switches and in particular to a more reliable, extended travel, dome-type pushbutton switch having tactile feedback and three states of switching.

2. Description of Related Art

Tactile feedback, push button switches are well known in the art, but for certain applications the life of the switch is not as long as may be desired or necessary. Often in dome switches, the top dome gets very stressed and the switch looses its tactile feel or fails. Also, the limited movement of the activating pushbutton in three-state switches minimizes the feel of the center position.

In U.S. Pat. No. 5,172,114 issued Dec. 15, 1992 to Claude Bedoya and assigned to Sextant Avionique of France, a tactile effect switch used in a keyboard is disclosed. The tactile effect is obtained by combining a snap acting switch and the deformation of an elastomer stud, axially deformable under compression, which is integrally formed on a membrane made from a resilient material disposed on a support plate and which provides a resilient connection between a key and the switch in the manner of a pusher. A resilient blade is deformed when pressure is applied to the stud causing actuation of the switch as the blade makes contact between an inner contact and two outer contacts.

In U.S. Pat. No. 5,228,561 issued Jul. 20, 1993 to Christopher K. Schroeder et al. and assigned to Hewlett-Packard Company of Palo Alto, Calif., a long traveling pushbutton switch with enhanced user tactile feedback is disclosed. The switch comprises a keycap, a keycap plunger, a retaining bezel, an elastomeric dome switch button formed in an elastomeric sheet comprising rubber which rests on a printed circuit board having a conductive pattern. Deformation of the button switch provides tactile feedback, while impact of the keycap top against the retaining bezel provides audible feedback. The pushbutton switch is configured to limit the downward displacement of the keycap plunger to avoid excessive force on the printed circuit board.

In U.S. Pat. No. 5,199,557 issued Apr. 6, 1993 to Gert Brandt et al. and assigned to MEC A/S of Ballerup, Denmark, a key is disclosed comprising a domed metal disc with its dome facing upward, a rubber component arranged on top of the domed metal disc which comprises a membrane part and a stem part. The stem part is a hollow part, which is elastically deformable and serves the purpose of transmitting a mechanical force from a button to which the mechanical force is applied to the domed metal disc, as the metal disc is deformed or allowed to revert to its normally domed shape from its deformed shape by the elastic deformation of the stem. The key has only two states whereby the metal dome makes contact with a central contact pad when the mechanical force is applied to the button (state

1

) and brakes contact when the force is removed (state

2

).

In U.S. Pat. No. 5,345,051, issued Sep. 6, 1994 to Teruhisa Miike and assigned to Alps Electric Company, Ltd., of Tokyo, Japan, a pushbutton switch is disclosed which has a comparatively small height and minimal rattling of a stem upon movement. The pushbutton switch comprises an insulating case, a pair of fixed contacts on the inner bottom of the case, a moveable contact for movement toward and away from the fixed contacts a stem for operating the movable contact and being resiliently biased away from the fixed contacts, the stem having a flat plate and four legs, a click rubber element positioned below the flat plate of the stem, and guide holes formed at the four corners of the insulating case. Thus when the flat plate of the stem is depressed, the top of the click rubber element is pushed down to resiliently deform the click rubber element until the movable contact contacts the fixed contact on the inner bottom face of insulating case to short-circuit the fixed contacts. When the stem is released, the click rubber element pushes up the stem by its own resilient returning force. This switch has only two states.

In U.S. Pat. No. 5,898,147, issued Apr. 27, 1999 to Frank M. Domzalski et al., and assigned to C & K Components, Inc., of Watertown, Mass., a dual action 3 state, convex disc pushbutton switch assembly is described which provided tactile feedback to the operator. Each convex disc contact comprises four tabs, each tab of which is fitted and secured in the base of the switch assembly making the switch easy to assemble and operate reliably. The tabs of a first convex disc contact are positioned forty-five degrees relative to the tabs of a second convex disc contact. The switch is sealed thereby permitting various ways to secure the switch terminals to an electronic board. However, the top disc experiences considerable stress during its operational usage and can loose its tactile feel or fail.

SUMMARY OF THE INVENTION

Accordingly, it is therefore an object of this invention to provide a three-state, tactile feedback pushbutton switch having an upper elastomeric dome with a conductive coated bottom surface contacting a lower metal dome for increased switch reliability.

It is a further object of this invention to provide a three-state, tactile feedback, pushbutton switch having extended travel for improved feel of an intermediate switch state.

It is another object of this invention to provide a semicircular conductor positioned below the elastomeric dome for making electrical contact with the metal dome.

It is another object of this invention to provide a circular conductor positioned below the elastomeric dome having opposite inwardly extending radial tabs for making electrical contact with the lower metal dome.

It is a further object of this invention to provide an alternate embodiment of the three-state tactile feedback, pushbutton switch comprising an extruded elastomeric switch element with a conductive bottom surface for improved reliability and lower cost.

These and other objects are accomplished by a tactile feedback pushbutton switch comprising an insulated housing having an inner bottom surface and a plurality of walls, a conductive contact provided on approximately the center of the inner bottom surface of the housing, an elastomeric dome disposed in the insulated housing having a conductive means attached to a bottom surface of the dome for making an electrical contact when the pushbutton is activated, a switching element, disposed between the conductive contact and the conductive means of said elastomeric dome, having a first state of no electrical contact, having a second state of making electrical contact with the conductive means of the elastomeric dome, and having a third state of the conductive means electrically contacting the switching element which contacts the conductive contact, as a pushbutton is being pressed in a direction toward the bottom surface of the housing, the pushbutton, disposed above the rubber dome, comprises a plurality of legs, for limiting the travel of the pushbutton within the housing, a collar disposed around the elastomeric dome having an opening for a top portion of the dome to extend therethrough, and a frame having an opening for the pushbutton to extend therethrough, the frame comprises at least a pair of sides which snap over tabs on the outside of the housing. The switch comprises at least three external terminals for connecting the switch in a circuit. The conductive means on the bottom of the elastomeric dome comprises a conductive coating. Alternate embodiments of the conductive means include a semicircular conductor, or the conductive means may include a circular conductor with two opposite inwardly extending tabs. The switching element comprises a metal dome.

The objects are further accomplished by a method of providing an extended travel tactile feedback pushbutton switch comprising the steps of providing an insulated housing having an inner bottom surface and a plurality of walls, providing a conductive contact on approximately the center of the inner bottom surface of the housing, disposing an elastomeric dome in the insulated housing having a conductive means attached to a bottom surface of the dome for making an electrical contact when a pushbutton is activated, disposing a switching element between the conductive contact and the elastomeric dome conductive means which provides a first switch state of no contact, pressing the pushbutton a first distance in a direction toward the bottom surface of the housing wherein the conductive means of the elastomeric dome makes electrical contact with the switching element which provides a second switch state, pressing the pushbutton a second distance in the direction of the bottom surface of the housing wherein the conductive means of the elastomeric dome electrically contacts the switching element which contacts the conductive contact, thereby providing a third switch state, providing the pushbutton having a plurality of legs disposed above the elastomeric dome, disposing a collar around the elastomeric dome, the collar having an opening for a top portion of the dome to extend therethrough, and extending the pushbutton through an opening in a frame, the frame having a pair of sides, each side having an opening which snaps over a tab on the outside of the housing. The method comprises the step of providing a plurality of external terminals extending from the housing for connecting the switch in a circuit. The step of providing the conductive means on the bottom of the elastomeric dome comprises the step of providing a silver silicone conductive coating on the bottom. The step of providing the conductive means on the bottom of the elastomeric dome comprises the step of providing a semicircular conductor positioned below the elastomeric dome. The step of providing the conductive means on the bottom of the elastomeric dome comprises the step of providing a circular conductor with two opposite inwardly extending tabs on the bottom positioned below the elastomeric dome. The step of providing the switching element comprises the step of providing a metal dome including silver plated stainless steel.

The objects are further accomplished by a tactile pushbutton switch comprising an insulated housing having an inner bottom surface and a plurality of walls, a pair of opposite walls of the housing, each of the walls having a pair of integral right angle appendages extending inward and disposed a predetermined distance from each other, a first conductive contact disposed on approximately the center of the inner bottom surface of the housing, a first switch element having an upper elastomeric portion and a lower portion comprising conductive means for making an electrical contact when the pushbutton is activated, second conductive contacts on the bottom surface of the housing, each disposed between the right angle appendages for making electrical contact with the lower portion of the first switch element on two opposite sides of the switch, a second switch element, disposed between the first conductive contact on the inner bottom surface of the housing and the conductive means of the first switch element, having a first state of no contact with the first switch element, having a second state of making electrical contact with the conductive means of the first switch element, and having a third state of the conductive means of the first switch element electrically contacting the second switch element which electrically contacts the first conductive contact, as a pushbutton of the switch is being pressed in a direction toward the bottom surface of the housing, the pushbutton, disposed above the elastomeric element, comprises a plurality of legs for limiting the travel of the pushbutton within the housing, retainer means, inserted between each of the right angle appendages on the opposite sides of the switch resting on top of the outer feet of the first switch element, for forcing the lower portion of the first switch element to make electrical contact with the second conductive contacts, and a frame having an opening for the pushbutton to extend therethrough, the frame having a pair of sides which secure the frame to the housing. The switch comprises a plurality of external terminals for connecting the switch in a circuit. The conductive means on the bottom of the elastomeric dome comprises a conductive coating including conductive silicone having a silver fill. The second switch element comprises a metal dome.

Additional objects, features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of the preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended claims particularly point out and distinctly claim the subject matter of this invention. The various objects, advantages and novel features of this invention will be more fully apparent from a reading of the following detailed description in conjunction with the accompanying drawings in which like reference numerals refer to like parts, and in which:

FIG. 1

is a perspective view of a preferred embodiment of a tactile feedback, three-state pushbutton switch;

FIG. 2

is a fragmentary perspective view of the preferred embodiment tactile feedback, three-state pushbutton switch of

FIG. 1

;

FIGS. 3A

,

3

B and

3

C are electrical schematics of the three states of the switch of

FIG. 1

;

FIG. 4

is a plan view of the insulating housing;

FIG. 5

is a simplified perspective view of the electrically conductive components of the three-state pushbutton switch of

FIG. 1

;

FIG. 6

is a compression curve (resistance force versus travel) of a pushbutton according to the invention;

FIG. 7

shows an alternate embodiment of the conductor on the bottom of the upper dome of

FIG. 2

;

FIG. 8

shows a second alternate embodiment of the conductor on the bottom of the upper dome of

FIG. 2

;

FIG. 9

is a perspective view of an alternate embodiment of the tactile feedback, three-state pushbutton switch;

FIG. 10

is a fragmentary perspective view of the alternate embodiment, tactile feedback, three-state pushbutton switch of

FIG. 9

;

FIG. 11

is a plan view of the insulating housing of the alternate embodiment of

FIG. 10

;

FIG. 12

is a perspective view of the alternate embodiment of

FIG. 9

with the surface plate and pushbutton removed showing the extruded elastomeric element and retainers on each side of the elastomeric element; and

FIGS. 13A

,

13

B and

13

C are electrical schematics of the three state switch of FIG.

11

.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENT

Referring to FIG.

1

and

FIG. 2

,

FIG. 1

is a perspective view of the preferred embodiment of the invention of a tactile feedback, three-state, pushbutton switch

10

.

FIG. 2

is an exploded perspective view of the switch

10

of

FIG. 1

showing the individual components of the switch

10

that are enclosed in the housing

12

.

The pushbutton switch

10

comprises a base housing

12

having two terminals

24

,

26

extending from one side and a third terminal

28

extending from an opposite side of the housing

12

.

A stem

20

extends above the housing

12

and acts as a pushbutton which is pushed to activate the switch

10

. The stem

20

comprises four legs

50

-

53

and is secured within the housing

12

by a surface plate or frame

22

having an opening

23

on top for the stem

20

to protrude through. The frame

22

is secured to the housing

12

by tabs

30

,

31

on opposite sides of the housing

12

. Each of the tabs

30

,

31

protrudes into openings

25

,

27

on two sides of the frame

22

for holding the stem

20

within the switch housing

12

.

Referring now to

FIGS. 3A

,

3

B and

3

C, electrical schematics of the three-state pushbutton switch

10

are shown.

FIG. 3A

shows the switch contacts in the normally open position.

FIG. 3B

shows the contacts in a first closed position whereby an electrical signal on terminal

24

is transferred to terminal

26

.

FIG. 3C

shows the contacts in a second closed position whereby the electrical signal on terminal

24

is transferred to both terminals

26

and

28

.

Referring again to

FIG. 2

, the pushbutton switch

10

is designed to have improved reliability over the prior art by providing tactile feedback with a metal dome

14

positioned under an upper elastomeric dome

16

having a conductive bottom surface facing the lower metal dome

14

. The metal dome

14

is retained by the heat-stake posts

38

a

,

38

b

and

38

c

in the base portion of housing

12

. A spacer

18

is positioned in the housing

12

around the upper portion of the elastomeric dome

16

. The spacer

18

, which does not move, provides force for contact between the upper dome

16

and terminal

36

in the base of housing

44

. The spacer

18

essentially applies a pressure to the upper dome

16

to insure that electrical connection is made from metal dome

14

up to the conductive portion

17

of the elastomeric dome

16

, and the elastomeric dome outer portion which makes contact with terminal

36

inside the housing

12

.

The stem

20

comprises four legs

50

-

53

having outwardly protruding feet portions

56

-

59

provided at the ends of the legs

50

-

53

respectively as shown in FIG.

2

. The legs

50

-

53

move along the four inside corners of the housing

12

and by the outside corners of spacer

18

as the pushbutton

20

moves in and out of the switch

10

.

Referring now to

FIG. 4

, a plan view of the insulating housing

12

is shown. The three stake posts

38

a

,

38

b

,

38

c

hold the metal dome

14

. Side supports

40

a

,

40

b

,

40

c

, and

40

d

are provided for the elastomeric dome

16

which rests on surface

42

within the base. Center contact

44

makes electrical contact with the center of the metal dome

14

when the switch is in state

3

. Inside terminal

34

is connected to outside terminal

24

and makes electrical contact with the metal dome

14

. Inside terminal

36

is connected to outside terminal

26

and makes electrical contact with the conductive portion

17

of the elastomeric dome

16

. The inside center terminal

44

is connected to outside terminal

28

and also makes electrical contact with the center of the metal dome

14

when the switch is in state

3

.

Referring now to

FIG. 5

, a simplified perspective view of the electrical conductive components of the three-state pushbutton is shown. When pressure is applied to the top of elastomeric dome

16

, it collapses enabling the conductive bottom surface portion

17

to make electrical contact with the top of the metal dome

14

. When additional pressure is applied the top of the elastomeric dome

16

, the metal dome

14

collapses making electrical contact with the center contact

44

in the base of the housing

12

.

The elastomeric dome

16

is embodied with a material such as silicone. The conductive material on the bottom of the elastomeric dome

16

is a conductive coating such as conductive silver silicone. The elastomeric portion is made by a well known injection molding process and the conductor coating is sprayed on the bottom.

The metal dome

14

is made from stainless steel (silver plated). The curvature is very slight. The metal dome

14

is a commercial item available from many sources. The center conductor

44

is made of brass with silver plating.

Referring now to

FIG. 6

, a compression curve provides a plot of Resistance versus Force as force is applied to activate the pushbutton switch

10

. The first negative slope

60

indicates the collapse of the elastomeric dome

16

and the second negative slope

61

indicates the collapse of the metal dome as more force is applied to the switch pushbutton

20

.

Referring to

FIG. 7

, an alternate embodiment of an elastomeric dome

65

is shown comprising a metallic conductor

66

positioned below the dome

65

. The conductor

66

is made of beryllium copper (silver plated) and is semicircular in shape which satisfies the requirement to make contact with internal terminal

36

and dome

14

. An advantage of using the metallic conductor is that the contact resistance can be lower than that achieved with a conductive elastomeric coating.

Referring to

FIG. 8

, a second alternate embodiment of an elastomeric dome

68

is shown comprising a circular metallic conductor

69

. Positioned below dome

68

, the conductor

69

comprises two opposite inwardly extending radius tabs

70

,

71

for making connection to dome

14

. The circular portion makes contact with internal terminal

36

. The conductor

69

is made of beryllium copper (silver plated).

Referring now to FIG.

9

and

FIG. 10

, an alternate embodiment is shown of a tactile feedback, three-state pushbutton switch

90

.

FIG. 9

is a perspective view of the complete switch

90

.

FIG. 10

is a fragmentary perspective view of the alternate embodiment showing an elastomeric element

96

disposed above a metal dome

94

. The pushbutton switch

90

comprises a base housing

92

having two terminals

110

,

112

extending from one side and two terminals

114

,

116

extending from an opposite side of the housing

92

. A concave-shaped metal disc

94

rests on contacts

124

,

126

on opposite sides of the inside bottom surface of housing

92

.

A pushbutton

100

is positioned above the elastomeric element

96

and the upper portion of pushbutton

100

extends through an opening

104

in a frame

102

which secures the switch components within the switch

90

. The pushbutton

100

activates the three-states of switch

90

when it is pushed inward toward the base. The pushbutton

100

comprises four legs

130

-

133

, each of which slide between the corners of the base housing

92

and the sides of the retainer holders

134

-

137

, when the pushbutton

100

is pushed inward. The legs

130

-

133

of the pushbutton

100

extend away from the horizontal portion

101

so that they can protrude into the inside corners of the housing

92

formed by the retainer holders

134

-

137

. The frame

102

is secured to the housing

92

by tabs

118

,

119

on opposite sides of the housing

92

. Each of the tabs

118

,

119

protrudes into openings

106

,

108

respectively of frame

102

. Retainers

97

,

98

slide into spaces formed by retainer holders

134

,

135

and retainer holders

136

,

137

respectively. The bottom surfaces of retainer

97

,

98

rest on the outer upper surfaces of outer feet

93

,

95

of the elastomeric element

96

.

Referring now to

FIG. 11

, a plan view of the housing

92

for the three-state switch

90

is shown. The switch housing

92

has two terminals

110

,

116

that connect to the elastomeric dome

96

via contacts

120

,

122

respectively. Center contact

128

makes contact with the center of the metal dome

94

when it is depressed and center contact

128

is connected to terminal

114

. Contacts

124

and

126

on the inside base of the housing

92

make constant contact with the outer portion of the metal dome

94

, and they both connect to terminal

112

.

Referring now to

FIG. 12

, a perspective view of the alternate embodiment is shown with the surface plate

102

and pushbutton

100

removed exposing the elastomeric element

96

and the retainers

97

,

98

. The retainers

97

,

98

are shown positioned within housing brackets

134

,

135

and brackets

136

,

147

respectively. Such brackets are formed as part of the housing

92

. The retainers

97

,

98

rest on top of the outer feet

93

,

95

of the elastomeric element

96

.

Referring to

FIGS. 10 and 12

, the elastomeric element

96

comprises a material such as silicone with a conductive material

99

applied to the underside of all portions of the elastomeric element

96

. The conductive material

99

portion is a conductive silicone with silver fill and the element

96

combination of the silicone and conductive material

99

may be produced by an extrusion process for low cost. The conductive material

99

may also be sprayed on the bottom of the elastomeric element. The angle of the sides

140

,

141

relative to the vertical center section

142

is proportional to the force required to push the pushbutton

100

and activate the switch

90

. The greater the angle the less force required to move the elastomeric element

96

downward to contact the metal dome

94

.

Referring to

FIGS. 13A

,

13

B and

13

C, electrical schematics of the three state switch pushbutton switch

90

of

FIG. 11

are shown.

FIG. 13A

shows the switch contacts in the normally open position.

FIG. 13B

shows one of the contacts in a closed position whereby electrical signal on terminal

112

is transferred to terminals

110

and

116

.

FIG. 13C

shows both of the contacts in a closed position whereby the electrical signal on terminal

112

is transformed to not only terminals

110

and

116

but also terminal

114

.

This invention has been disclosed in terms of certain embodiments. It will be apparent that many modifications can be made to the disclosed apparatus without departing from the invention. Therefore, it is the intent of the appended claims to cover all such variations and modifications as come within the true spirit and scope of this invention.