Information
-
Patent Grant
-
6399907
-
Patent Number
6,399,907
-
Date Filed
Wednesday, June 13, 200124 years ago
-
Date Issued
Tuesday, June 4, 200223 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 200 276
- 200 2761
- 200 243
- 200 447
- 200 448
- 200 540
-
International Classifications
-
Abstract
An electrical contact assembly is disclosed comprising a bracket having at least first and second cavities located on opposite ends of the bracket and an opening extending through the bracket between the first and second cavities. A retention member is arranged to be mounted within the bracket opening with a first portion of the retention member extending outward from the first cavity and a second portion of the retention member extending outward from the second cavity. Each first and second portion terminates in a head end. First and second helix-shaped electrical contacts are positioned about a respective retention member first and second portion and are compressively retained between a respective and associated head end and bracket cavity.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to electro-mechanical switch contacts and, more specifically, to an electrical contact assembly having helical coil contact structures.
2. Discussion of the Related Art
Industrial limit switches, such as global limit switches, safety interlocks, safety solenoid interlocks and cable pull limit switches are used in a variety of industrial applications. Limit switches contain switches that are manufactured to suit the particular application.
Typically, switches used in these products are designed and manufactured for a particular contact arrangement. Such switches generally contain two or more circuits having one or more normally closed (NC) contacts and/or one or more normally open (NO) contacts. Conventional arrangements typically include one normally open/one normally closed, also called a “single pole” arrangement, or two normally open/two normally closed, also called a “double pole” arrangement. Conventional industrial limit switches often require additional normally closed contacts for added redundancy. Limit switch applications often require at least three positively driven, normally closed contacts along with one normally open monitor circuit.
U.S. Pat. No. 6,114,639, assigned to the assignee of the present invention, teaches a configurable switch having a configurable base and a configurable plunger, which together permit the adjustable arrangement of contacts into several electrical switching configurations. Within such a switch, one or more movable contacts are mounted to a plunger that is movable between a first position and a second position. In the first position or the second position, the movable contacts make contact and/or break contact with respective stationary contacts, depending upon the arrangements of the stationary contacts and the movable contacts. The movable contacts shown and typically used in such switch configurations are constructed from conductive material with each including two contact pads spaced at a distance from each other and connected by a contact bracket. The contact pads are each preferably composed of a fine silver disk or other suitable conductive material welded or otherwise attached to the movable contact. The contact bracket of each movable contact is mounted within a respective opening of the movable plunger and biased by a spring, thereby positioning the associated contact pads either apart from a respective stationary contact or engaged to the stationary contact, forming either a make or a break switching arrangement.
When such an electro-mechanical switch is used in low energy applications, typically those in the 24 volt, 2-10 milliamp range, other more-conductive materials or contact structures are used in order to enhance continuity and reliability. For example, gold plating may be deposited on a serrated contact, a bifurcated contact can be substituted for the contact pad, or a knife-edge shaped contact using a gold-inlay material substituted for the contact pads.
All of these material and structural substitutions, however, over the course of many switching operations, eventually fail in maintaining continuity, causing the low energy switch to fail. For example, gold-plating, deposited typically at a thickness of 0.0001 to 0.0002 inches, tends to wear off over the life of the contact. Serrated contacts attract contaminants from within the switch, which contaminants become trapped as the serrations degrade. Gold-inlay, which is very soft and ductile, also degrades over many mechanical operations of the contacts due to the “hammering” effect imparted by the mechanical closure of the contacts. Gold-plated bifurcated contacts, even though providing a somewhat more reliable contact, due primarily to its plural points of electrical contact, also eventually suffers from wear imparted by the hammering effect and contact bounce. Contact bounce in such switching contacts can lead to equipment malfunctions due to the fast response time of the industrial equipment being controlled.
Therefore, reliability of operation is important in such low-energy switching devices since these devices are extensively used in safety relay and safety control applications in industry. A marginally-operating or failed switch can have economic as well as catastrophic consequences to an industrial process if the devices fail to operate correctly.
BRIEF SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide an improved electrical switch contact.
It is also an object of the present invention to provide an electrical switch contact assembly that increases the level of continuity in low-energy switch applications.
It is also a further object of the present invention to provide an improved switching contact assembly that minimizes contact bounce.
Therefore, there is provided in a first embodiment of the present invention, an electrical contact assembly comprising a bracket having at least a first and a second cavity located on opposite ends of the bracket and an opening extending through the bracket between the first cavity and said second cavity. The electrical contact assembly further includes an electrically conductive retention member mounted within the bracket opening having a first tubular portion extending outward from the first cavity, terminating in a first annular flange. A second tubular portion extends outward from the second cavity, also terminating in a second annular flange. The said first and said second flanges have a diameter greater than their respective and associated retention member first and second portions. A first coiled electrical contact is positioned about and compressively retained on the retention member first portion between the first annular flange and the bracket first cavity. A second coiled electrical contact is also positioned about and compressively retained on the retention member second portion, between the second annular flange and the bracket second cavity.
In a second embodiment of the present invention there is provided an electrical contact assembly comprising a bracket having at least a first and a second cavity located on opposite ends of the bracket and an opening extending through the bracket between the said first cavity and said second cavity. An electrically conductive retention member is mounted within the bracket opening and includes a first portion having first and second arms, oriented in a parallel and spaced relationship to the other, extending outward from the first cavity. A second portion, also having first and second arms, oriented in a parallel and spaced relationship to the other, extends outward from the second cavity. Each first and second arm of the first and second portions terminates in a wedge-shaped structure that extends perpendicularly from its associated arm, thereby forming a shoulder member having a width greater than the width of the first and second portions respectively. The electrical contact assembly further includes a first coiled electrical contact positioned about and compressively retained on the retention member first portion, between its associated shoulder member and the bracket first cavity and a second coiled electrical contact positioned about and compressively retained on the retention member second portion, between its associated shoulder member and the bracket second cavity.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
Other objects, features, and advantages of the present invention will be apparent from the following description of a preferred embodiment thereof, taken in conjunction with the sheets of drawings, in which:
FIG. 1
is a perspective view of a first embodiment of the helical coil switch contact assembly in accordance to the present invention;
FIG. 2
is an elevational view of a first embodiment of the helical coil switch contact assembly of the present invention;
FIG. 3
is a sectional view taken along line
3
—
3
of
FIG. 2
;
FIG. 4
is a perspective view of a second embodiment of the helical coil switch contact assembly in accordance to the present invention; and
FIG. 5
is a perspective view of a switch plunger having the movable contacts of the present invention mounted thereon.
DETAILED DESCRIPTION OF THE INVENTION
FIGS. 1
,
2
and
3
show the helical coil switch contact assembly according to one preferred embodiment of the present invention. The assembly is comprised of two barrel-shaped helical coil spring contacts
12
and
12
′ held in compression about an electrically conductive retention device
15
between first and second head ends
18
and
20
of the retention device
15
and a contact bracket
22
. Each coil spring contact
12
and
12
′ is composed of a good electrically conductive material. Typically, this material would be copper-based and may also be gold-plated to improve its electrical conductivity.
As was previously mentioned, the helical coil switch contact assembly
10
of the present invention may be used to advantage in the configurable switch assembly of U.S. Pat. No. 6,114,639, assigned to the assignee of the present invention and which is incorporated herein by reference. The helical coil switch contact assembly of the present invention can be used in place of the movable contacts shown in the reference. However, it will be well understood by those skilled in the art that the helical coil switch contact assembly
10
of the present invention can also be used in other electrical contact switching applications and is not limited for use with the configurable switching devices shown by U.S. Pat. No. 6,114,639.
Each coil of each coil spring contact
12
and
12
′ provides a contact surface for engagement with an associated stationary contact surface (not shown). As can be seen in
FIGS. 1-3
, each coil spring contact
12
,
12
′ groups together a contact structure having four contact surfaces or contact points that as a group is disposed to mechanically engage an associated stationary contact. It will be appreciated by those skilled in the art that even though the present invention is shown with each coil spring contact
12
,
12
′ having four coil turns, any number of individual coil turns may be used to form each coil spring contact
12
and
12
′ and, therefore, the invention is not limited thereto.
Further, each coil spring contact
12
,
12
′ is barrel-shaped, that is, the coil turns at the center of each coil spring contact are larger in diameter than the coil turns at each end. This particular form has advantage over a non-barrel or straight coil springs in that it compensates for imperfections and/or lack of flatness with the associated stationary contact (not shown) and also tends to “wipe” across the stationary contact surface upon engagement, thereby minimizing the effects of contact bounce.
As can best be seen in
FIGS. 2 and 3
, each coil spring contact
12
,
12
′ is mounted about separate portions of the retention member
15
. Retention member
15
is comprised of a single monolithic pin member having a tubular body
14
that terminates on a first end in an annular head
18
having a diameter greater than the diameter of the tubular body
14
. A second and opposite end of tubular body
14
terminates in a cavity
16
extending from the second end of tubular body
14
longitudinally within its interior. Retention member
15
is composed of a good electrically conductive material such as any copper-based material or the like and may also be gold-plated to improve its electrical conductivity. The retention member
15
may also be made using a standard commercially available rivet fastener of an appropriate dimension that has good electrical conductivity properties.
The retention member
15
is held within a molded plastic contact bracket
22
. A through-hole
122
extends through the contact bracket
22
and is arranged to receive therethrough and retain therein, tubular body
14
of retention member
15
. As can be best seen in
FIG. 3
, coil spring contact
12
is installed on body
14
and held in slight compression between head end
18
and mating surface
124
of contact bracket
22
. Similarly, coil spring contact
12
′ is installed over body
14
and held in slight compression between head end
20
and a mating surface
125
of the contact bracket
22
. Mating surfaces
124
and
125
are molded at a slight angle with respect to the center plane of each coil spring contact
12
,
12
′, creating a linear imbalance in each coil spring contact. Over continued actuation of a switch mechanism employing the contact assembly
10
each coil spring contact
12
and
12
′ will rotate about retention member
15
, thus presenting a new contact surface throughout the life of the contact assembly
10
.
The contact bracket
22
further includes cutout portions
30
and
32
formed on the front and back surfaces of the contact bracket
22
respectively and a biasing element retainer cavity
40
formed on the contact bracket
22
top surface. These aforementioned structures are used to advantage in the mounting of the contact assembly
10
within a switch plunger, such as switch plunger
50
in FIG.
5
. Cutouts
30
and
32
are arranged to closely engage with opening
52
of switch plunger
50
and thus restrict unwanted movement of the contact assembly
10
within switch plunger
50
. The contact assembly
10
is mounted within opening
52
preferably with a bias element, such as bias spring
55
, positioned within each opening
52
. Spring
55
urges the contact assembly
10
toward a stop or edge surface of plunger
50
adjacent opening
52
. One end of bias spring
55
is arranged to be set within cavity
40
of the contact bracket
22
with a second and opposite end of biasing spring
55
engaging surface
54
of opening
52
. Each contact assembly
10
is displaceable within the limits allowed by cavity
52
and functions in a manner similar to the movable contacts shown in U.S. Pat. No. 6,114,639.
The aforementioned contact assembly
10
of
FIGS. 1-3
is assembled by passing coil spring contact
12
over the second end of tubular body
14
to rest against an inside surface of head end
18
. Next, the second end of tubular body
14
is inserted into through-hole
122
of contact bracket
22
until coil spring contact
12
compresses slightly between head end
18
and mating surface
124
. Next coil spring contact
12
′ is passed over the second end of tubular body
14
until it rests on mating surface
125
of contact bracket
22
. The assembly is completed by cold forming head end
20
. The cold forming is accomplished by the use of a tool (not shown) that includes a bit that is inserted into cavity
16
. Sufficient pressure is applied by the tool to the tubular body cavity
16
to turn aside and slightly outward the peripheral edges of the cavity, thereby permanently forming the structure shown in
FIG. 3
as head end
20
. As can be seen in
FIG. 3
, after the cold forming step, head end
20
forms a generally annular structure having a diameter greater than the tubular body
14
and that slightly compresses coil spring contact
12
′ between head end
20
and mating surface
125
.
Turning now to
FIG. 4
of the included drawings, a second preferred embodiment of the helical coil switch contact assembly
10
of the present invention is shown. As will be appreciated by those skilled in the art, the assembly procedure of the helical coil contact assembly
10
of
FIG. 1
requires an ordered step process in its assembly. The helical coil switch contact
10
of this second preferred embodiment simplifies its assembly.
In this second embodiment of the present invention, the retention member
25
is comprised of a flat, generally rectangular shaped, stamped body
24
that is arranged to be accepted within through-hole
122
of contact bracket
22
. The flat body
24
has a transverse dimension or width that is substantially the same dimension as the diameter of through-hole
122
. As will be appreciated by those skilled in the art, with the flat body width at substantially the same dimension as the diameter of the through-hole
122
, the longitudinal center axis of flat body
24
will be located along and concentric with the center axis of through-hole
122
when the flat body
24
is installed therein. As will also be appreciated, the concentric association between the longitudinal center axis of flat body
24
and the center axis of through-hole
122
is maintained as the flat body
24
is rotated along its longitudinal axis during the operation of the contact assembly
10
.
With renewed reference to
FIG. 4
, the portions of the flat body
24
extending outward from mating surfaces
124
and
125
are formed into two sets of double arms
70
and
80
respectively. Arm-set
70
is comprised of arms
71
and
72
extending from a first end in a spaced and parallel relationship to each other from flat body
24
. A second and opposite end of each arm
71
and
72
terminates in a wedge-shaped head structure
73
and
74
respectively. Coil spring contact
12
is supported by arms
71
and
72
and held in slight compression between mating surface
124
of contact bracket
22
and shoulders
75
,
76
of head structures
73
,
74
respectively. Arm-set
80
includes the same structures described for arm-set
70
and supports and holds coil spring contact
12
′ in the same manner as explained for coil spring contact
12
.
The coil spring contact assembly
10
is assembled in this second embodiment by first installing the retention member
25
flat body
24
within through-hole
122
of the contact bracket
22
. Coil spring contact
12
is installed on the retention member
25
by deflecting arms
71
and
72
toward each other, allowing coil spring contact
12
to be passed over head structures
72
and
73
until a first end of the contact
12
engages mating surface
124
. The coil spring contact
12
is compressed toward contact bracket
22
and arms
71
and
72
are allowed to return to their un-deflected positions. When the compression force is released from coil spring contact
12
, the contact attempts to return to its uncompressed state, however, it is held in slight compression by the engagement of the contact
12
second end with shoulders
75
and
76
of head structures
73
and
74
. Coil spring contact
12
′ is assembled on arm-set
80
in the same manner as previously explained for coil spring contact
12
. The flat body
24
and arm-sets
70
and
80
, forming the retention member
25
of this second embodiment, are constructed as an integral structure from a good electrically conductive material such as any copper-based material or the like and gold-plated to improve its electrical conductivity.
The present invention has been described with particular reference to the preferred embodiments thereof. It will be obvious that various changes and modifications can be made therein without departing from the spirit and scope of the invention as defined in the appended claims.
Claims
- 1. An electrical contact assembly comprising:a bracket having at least first and second surfaces and an opening extending through said bracket between said first and second surfaces; a retention member mounted within said bracket opening having at least a first portion extending outward from said first surface and terminating in a first head end; and at least a first helix-shaped electrical contact positioned about said retention member first portion, compressively retained between said first head end and said bracket first surface.
- 2. The electrical contact assembly as claimed in claim 1 wherein said retention member further includes a second portion extending outward from said bracket second surface and terminating in a second head end, and said electrical contact assembly further includes a second helix-shaped electrical contact positioned about said retention member second portion compressively retained between said second head end and said bracket second surface.
- 3. The electrical contact assembly as claimed in claim 2 wherein said retention member first and second portions are generally tubular in cross section having a diameter that is acceptable within said bracket opening, and said first head end is an annular flange integrally fixed to one end of said first portion, said head end having a diameter greater than the diameter of said first portion.
- 4. The electrical contact assembly as claimed in claim 3 wherein said retention member second portion includes a cavity and an outer peripheral edge surface surrounding said cavity, whereby said second head end is formed by inserting a tool in said cavity and applying pressure to said cavity peripheral edge, thereby deforming said peripheral edge into an annular flange having a diameter greater than said second portion.
- 5. The electrical contact assembly as claimed in claim 4 wherein said retention member is composed of an electrically-conductive material.
- 6. The electrical contact assembly as claimed in claim 5 wherein said retention member is further plated with gold to improve its electrically conductive properties.
- 7. The electrical contact assembly as claimed in claim 2 wherein each of said first and second helix-shaped electrical contacts is comprised of first and second barrel-shaped coil springs, each of said coil springs having a plurality of coil turns with first and second terminating coil turns having a diameter less than the coil turns at the coil springs' center.
- 8. The electrical contact assembly as claimed in claim 7 wherein the diameter of each of said first and second coil springs second terminating coil turn is less than the diameter of said retention members first and second head ends, respectively.
- 9. The electrical contact assembly as claimed in claim 7 wherein said first and second coil springs are composed of an electrically-conductive material.
- 10. The electrical contact assembly as claimed in claim 9 wherein said first and second coil springs are further plated with gold to improve their electrically conductive properties.
- 11. The electrical contact assembly as claimed in claim 7 wherein said brackets first and second surfaces is the floor of a respective first and second circular cavity, wherein said first and second cavity floor accepts thereon said first terminating coil of said first and second coil spring respectively.
- 12. The electrical contact assembly as claimed in claim 11 wherein said floor of each of said first and second cavities is oriented at an angle with respect to the center plane of each respective first and second coil spring.
- 13. The electrical contact assembly as claimed in claim 7 wherein said retention member is generally planar in cross section and includes a center portion having a width that is acceptable within said bracket opening and each of said first and second portions are comprised of first and second arms oriented in a parallel and spaced relationship to the other extending from opposite ends of said center section, each first and second arm of said first and second portion terminating in a wedge-shaped structure that extends perpendicularly from its associated arm, thereby forming a shoulder member having a width greater than the width of said first and second portions respectively.
- 14. The electrical contact assembly as claimed in claim 13 wherein the diameter of each of said first and second coil springs second terminating coil turn is less than the width of said first and second retention member shoulder member respectively.
- 15. The electrical contact assembly as claimed in claim 14 wherein said retention member is composed of an electrically-conductive material.
- 16. The electrical contact assembly as claimed in claim 15 wherein said retention member is further plated with gold to improve its electrically conductive properties.
- 17. An electrical contact assembly comprising:a bracket having at least a first and a second cavity located on opposite ends of said bracket and an opening extending through said bracket between said first cavity and said second cavity; an electrically-conductive retention member mounted within said bracket opening, having a first tubular portion extending outward from said first cavity, terminating in a first annular flange and a second tubular portion extending outward from said second cavity, terminating in a second annular flange, said first and said second flanges having a diameter greater than their respective and associated first and second portions; a first coiled electrical contact positioned about and compressively retained on said retention member first portion between said first annular flange and said bracket first cavity; and a second coiled electrical contact positioned about and compressively retained on said retention member second portion between said second annular flange and said bracket second cavity.
- 18. The electrical contact assembly as claimed in claim 17 wherein each of said first and second coiled electrical contacts is comprised of first and second barrel-shaped coil springs, each of said coil springs having a plurality of coil turns with first and second terminating coil turns having a diameter less than the coil turns at the coil springs' center.
- 19. The electrical contact assembly as claimed in claim 18 wherein the diameter of each of said first and second coil spring's second terminating coil turn is less than the diameter of said retention member first and second head ends respectively.
- 20. The electrical contact assembly as claimed in claim 19 wherein each of said bracket's first and second cavities is circular in cross section and further includes a cavity floor, each first and second cavity floor arranged to accept thereon said first terminating coil of said first and second coil spring, respectively.
- 21. The electrical contact assembly as claimed in claim 20 wherein said floor of each of said first and second cavities is oriented at an angle with respect to the center plane of each respective first and second coil spring.
- 22. The electrical contact assembly as claimed in claim 17 wherein said retention member is further plated with gold to improve its electrically conductive properties.
- 23. The electrical contact assembly as claimed in claim 17 wherein said first and second coil springs are further plated with gold to improve their electrically conductive properties.
- 24. An electrical contact assembly comprising:a bracket having at least a first and a second cavity located on opposite ends of said bracket and an opening extending through said bracket between said first cavity and said second cavity; an electrically conductive retention member mounted within said bracket opening, including a first portion having first and second arms oriented in a parallel and spaced relationship to the other extending outward from said first cavity and a second portion having first and second arms oriented in a parallel and spaced relationship to the other extending outward from said second cavity, each first and second arm of said first and second portions terminating in a wedge-shaped structure that extends perpendicularly from its associated arm, thereby forming a shoulder member having a width greater than the width of said first and second portions respectively; a first coiled electrical contact positioned about and compressively retained on said retention member first portion, between said shoulder member and said bracket first cavity; and a second coiled electrical contact positioned about and compressively retained on said retention member second portion, between said shoulder member and said bracket second cavity.
- 25. The electrical contact assembly as claimed in claim 24 wherein each of said first and second coiled electrical contacts is comprised of first and second barrel-shaped coil springs, each of said coil springs having a plurality of coil turns with first and second terminating coil turns having a diameter less than the coil turns at the coil springs' center.
- 26. The electrical contact assembly as claimed in claim 25 wherein the diameter of each of said first and second coil spring's second terminating coil turn is less than the width of said first and second retention member shoulder members, respectively.
- 27. The electrical contact assembly as claimed in claim 26 wherein each of said bracket's first and second cavities is circular in cross section and further includes a cavity floor, each first and second cavity floor arranged to accept thereon said first terminating coil of said first and second coil spring, respectively.
- 28. The electrical contact assembly as claimed in claim 27 wherein said floor of each of said first and second cavities is oriented at an angle with respect to the center plane of each respective first and second coil spring.
- 29. The electrical contact assembly as claimed in claim 24 wherein said retention member is further plated with gold to improve its electrically-conductive properties.
- 30. The electrical contact assembly as claimed in claim 24 wherein said first and second coil springs are further plated with gold to improve their electrically conductive properties.
US Referenced Citations (5)
Foreign Referenced Citations (1)
Number |
Date |
Country |
2042271 |
Sep 1980 |
GB |