Helical coil switch contact assembly

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)
Number Name Date Kind
RE15152 Krantz Jul 1921 E
1709947 Frantl Apr 1929 A
2487922 DeChant et al. Nov 1949 A
4473727 Beck Sep 1984 A
5569890 Olsen Oct 1996 A
Foreign Referenced Citations (1)
Number Date Country
2042271 Sep 1980 GB