Connector assembly having visual indicator

Information

  • Patent Grant
  • 6561841
  • Patent Number
    6,561,841
  • Date Filed
    Monday, August 27, 2001
    23 years ago
  • Date Issued
    Tuesday, May 13, 2003
    21 years ago
Abstract
An indicator for a mating connector pair provides a visual indication when a plug-side connector is fully engaged with a jack-side connector. The plug-side connector is configured for engagement with the jack-side connector to form an electrical connection. The plug-side connector includes a connector body and a bayonet sleeve rotatably connected to the connector body. The sleeve includes two slots which are configured for engagement with corresponding lugs on the jack-side connector. The indicator is located on the sleeve and aligns with a reference point when the slots in the sleeve are fully engaged with the lugs of the jack-side connector. The indicator may be a substantially V-shaped notch, a dimple, a ridge or a lug.
Description




BACKGROUND OF THE INVENTION




1. Field of the Invention




The present invention relates generally to the field of electrical connectors. In particular, the present invention relates to a mechanism for providing a visual indication of the engagement position of a mating connector pair having a bayonet mechanism.




2. Related Art




Electrical connectors, particularly RF (radio frequency) connectors, provide couplings between electronic elements and/or devices. Many different types of electrical connectors exist and have been used to provide removable electrical connections between electronic elements and devices.




Bayonet mechanisms are one way of securing such removable electrical connectors. One type of removable or separable electrical connector having a bayonet mechanism is known as a BNC or Bayonet Neil-Concelman mating connector pair. BNC mating connector pairs facilitate attachment of coaxial electrical cables to electronic elements or devices. Typical BNC mating connector pairs include a jack-side connector mounted to an electronic device or element and a plug-side connector connected to a cable. The jack-side connector typically includes a tubular cylindrical housing and a socket formed in a central location of the housing. The plug-side connector typically includes a tubular cylindrical connector body having a central contact formed in a central location of the connector body. The central contact of the plug-side connector is inserted into the socket of the jack-side connector and the connector body of the plug-side connector is inserted into the housing of the jack-side connector.




The jack-side connector also includes outwardly extending lugs formed on the outer surface of the housing. The plug-side connector includes a bayonet sleeve rotatably mounted on the outer surface of the connector body. The bayonet sleeve includes slots, which are typically J-shaped (J-slots), to mate with the lugs on the jack-side connector. The J-slots include an initial portion and a terminal portion. To connect the BNC mating connector pair, the slots in the bayonet sleeve first receive the lugs the initial portion of the J-shaped slots, such that the mating connector pair is in a position of partial engagement. The bayonet sleeve is then rotated relative to the jack-side connector until the lugs slide into the terminal portion of the J-shaped slots. The mating connector pair is now in a fully engaged position, where the lugs are held and locked into the terminal portion of the J-shaped slots.




U.S. Pat. No.4,037,909 to Trompeter et al. and U.S. Pat. No. 3,708,781 to Trompeter, which are herein incorporated by reference in their entirety, each disclose known BNC mating connector pairs. Further, BNC mating connector pairs are commercially available from Trompeter Electronics, Inc., Westlake Village, Calif. A common use of the Trompeter 75 Ohm BNC mating connector pair is for telephone company central office DS3 applications. BNC mating connector pairs also see high volume use in the broadcast industry for providing high bandwidth connections between television broadcast equipment.




This twist-lock connection of the bayonet mechanism is a central feature of BNC connector pairs, and provides a convenient and reliable means for electrically connecting various electronic elements and devices. BNC and connector pairs allow a reliable electrical connection to be made without the danger of the jack-side and plug-side connectors gradually working loose or becoming inadvertently unplugged.




The bayonet mechanism of BNC mating connector pairs provides a positive engagement between jack-side connectors and plug-side connectors. This positive engagement allows a user to determine whether a jack-side connector is fully engaged with a plug-side connector by attempting to manually rotate the bayonet sleeve (e.g., using his or her fingers). If substantial resistance is encountered, then the mating connector pair is fully engaged.




However, multiple mating connector pairs are often positioned in close proximity to each other on electronic elements or devices, both horizontally and vertically, such that there is not sufficient space for a user to easily grasp the bayonet sleeve using his or her fingers. Further, it is often not possible for a user to look at the mating connector pairs from a viewpoint that allows visual inspection of the relative positioning between the lug and the J-shaped slot. Consequently, it is often difficult to manually determine whether a jack-side connector is fully engaged with a corresponding plug-side connector. Thus, a need exists for an improved mating connector pair that provides visual indication of the engagement position of the plug-side connector relative to the jack-side connector when the plug-side connector is fully engaged with the jack-side connector.




SUMMARY OF THE INVENTION




The present invention is drawn to a plug-side connector in a mating connector pair, where the plug-side connector is configured for engagement with a jack-side connector to for m an electrical connection. The plug-side connector includes a connector body and a bayonet sleeve rotatably connected to the connector body. The sleeve includes two slots which are configured for engagement with corresponding lugs on the jack-side connector. The sleeve further includes an indicator on the sleeve that aligns with a reference point when the slots in the sleeve are fully engaged with the lugs o f the jack-side connector. The indicator provides a visual indication that the plug-side connector is fully engaged with the jack-side connector. Preferred embodiments of the indicator of the invention include a V-shaped notch, a dimple, a raised ridge and a lug.




Indicators of the present invention allow a user to easily determine by visual inspection whether a jack-side connector is fully engaged with a plug-side connector even when the mating connector pair is located in a crowded area. Further, the indicators, of the present invention allow a user to quickly check the engagement positions of multiple mating connector pairs. Moreover, the indicators of the present invention are straightforward and inexpensive to produce.











BRIEF DESCRIPTION OF THE FIGURES




The foregoing and other features and advantages of the present invention will be apparent from the following, more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings in which:





FIG. 1

is a top view of the mating connector pair of the present invention, including a jack-side connector and a plug-side connector;





FIG. 2

is a perspective front view of a jack-side connector;





FIG. 3

is a cut-away perspective front view of a plug-side connector;





FIG. 4

is a perspective view of a bayonet sleeve of a plug-side connector;





FIG. 5

is a top view of the mating connector pair of the present invention depicting the plug-side connector in partial engagement with the jack-side connector, wherein the lugs of the jack-side connector are positioned in the initial portion of the slots of the plug-side connector; and





FIG. 6

is a top view of the mating connector pair of the present invention depicting the plug-side connector in full engagement with the jack-side connector, wherein the lugs of the jack-side connector are positioned in the terminal portion of the slots of the plug-side connector.





FIGS. 7

,


8


, and


9


are perspective views of a bayonet sleeve of a plug-side connector illustrating additional embodiments of the indicator of the invention.











DETAILED DESCRIPTION OF THE INVENTION




A preferred embodiment of the present invention is now described with reference to the Figures, in which like reference numerals are used to indicate identical or functionally similar elements. Also in the Figures, the left most digit of each reference numeral corresponds to the Figure in which the reference numeral is first used. While specific configurations and arrangements are discussed, it should be understood that this is done for illustrative purposes only. A person skilled in the relevant art will recognize that other configurations and arrangements can be used without departing from the spirit and scope of the invention. It will be apparent to a person skilled in the relevant art that this invention can also be employed in a variety of other devices and applications.




A Miniature-BNC (M-BNC) mating connector pair


100


is shown in FIG.


1


. M-BNC mating connector pairs are commercially available from Trompeter Electronics, Inc., Westlake Village, Calif. M-BNC mating connector pairs are significantly smaller than traditional full-size BNC mating connector pairs while still able to deliver the necessary impedance through a reliable and durable connection. For purposes of this application, the term “BNC” refers to both traditional full-size BNC and M-BNC mating connector pairs, jack-side connectors, and plug-side connectors.




Mating connector pair


100


includes a plug-side connector


102


and a jack-side connector


104


. Plug-side connector


102


is configured for engagement with jack-side connector


104


to form an electrical connection.




As shown in

FIG. 1

, the plug-side connector


102


includes a plug-side connector body


106


, a bayonet sleeve


108


, and a ferrule


110


. Plug-side connector body


106


is configured for mating with a jack-side connector body


112


of jack-side connector


104


along a longitudinal axis


114


. Bayonet sleeve


108


is rotatably mounted on plug-side connector body


106


, and includes at least one slot


116


, which is preferably J-shaped as shown in FIG.


1


. The J-shaped slot (J-slot)


116


includes an initial portion


118


and a terminal portion


120


. Slot


116


is configured and arranged for engagement with a lug


122


of jack-side connector body


112


. Bayonet sleeve


108


further includes an indicator


124


located on bayonet sleeve


108


. Indicator


124


aligns with a reference point when slot


116


of bayonet sleeve


108


is fully engaged with lug


122


of jack-side connector body


112


, that is when lug


122


rests in terminal portion


120


of slot


116


. In the embodiment shown in

FIG. 1

, the reference point is terminal portion


120


.




The jack-side connector


104


includes jack-side connector body


112


with lug


122


disposed on a peripheral surface of jack-side connector body


112


. Jack-side connector


104


is inserted into plug-side connector


102


so that lug


122


is inserted into initial portion


118


of slot


116


. Bayonet sleeve


108


is then rotated until plug-side connector


102


and jack-side connector


104


are fully engaged such that lug


122


rests in terminal portion


120


of slot


116


. Indicator


124


provides a visual indication when plug-side connector


102


is fully engaged with jack-side connector


104


.




Jack-side connector


104


, plug-side connector body


106


and bayonet sleeve


108


are more fully described with reference to

FIGS. 2

,


3


and


4


.





FIG. 2

is a perspective front view of an M-BNC jack-side connector


104


. Jack-side connector


104


includes a jack-side connector housing


202


, jack-side connector body


112


, a lumen


204


, a jack-side conductor


206


, a jack-side connector insulator


205


, and lugs


122


. Jack-side connector body


112


is preferably tubular and cylindrical and formed of a conductive material such as aluminum, beryllium copper, brass, zinc or stainless steel.




Lugs


122


are disposed on a peripheral surface of jack-side connector body


112


. Lugs


122


are preferably cylindrical and extend radially outward from the peripheral surface of jack-side connector body


112


. In a preferred embodiment, jack-side connector


104


includes two lugs


122


positioned on jack-side connector body


112


approximately one hundred eighty degrees apart from one another. Although an M-BNC jack-side connector


104


having two lugs


122


is shown in

FIG. 2

, in alternate embodiments, a jack-side connector


104


having a single lug or three or more lugs could be used, as would be well known to one skilled in the relevant art. For example, in an alternate embodiment, jack-side connector body


112


could include three lugs positioned on jack-side connector body


112


approximately one hundred twenty degrees apart. Further, jack-side connector body


112


could include four lugs positioned on jack-side connector body


112


approximately ninety degrees apart. In alternate embodiments, lugs


122


may be spaced at irregular intervals around jack-side connector body


112


.




Lumen


204


extends longitudinally through jack-side connector body


112


. Jack-side conductor


206


is disposed within lumen


204


, and is configured to mate with a plug-side conductor


302


(discussed below) of plug-side connector


102


to form an electrical connection. In a preferred embodiment, jack-side conductor


206


is a female socket. A jack-side connector insulator


205


is preferably provided within lumen


204


and around jack-side conductor


206


to electrically isolate jack-side conductor


206


from jack-side connector body


112


. In a preferred embodiment, the jack-side connector insulator is formed of polytetrafluoroethylene (PTFE).





FIG. 3

is a cut-away perspective front view of an M-BNC plug-side connector


102


, including bayonet sleeve


108


and plug-side connector body


106


. Plug-side connector body


106


is preferably tubular and cylindrical and formed of a conductive material such as aluminum, beryllium copper, brass, zinc or steel. Plug-side connector body


106


includes spring fingers


304


, a plug-side conductor


302


, and a plug-side connector insulator


303


. Spring fingers


304


act to bias plug-side connector body


106


into engagement within jack-side connector body


112


. Plug-side conductor


302


is configured to mate with jack-side conductor


206


. In a preferred embodiment, plug-side conductor


302


is a male contact which mates with female socket


206


of jack-side connector


104


. Plug-side connector insulator


303


is preferably provided around plug-side conductor


302


to electrically isolate plug-side conductor


302


. In a preferred embodiment, plug-side connector insulator


303


is formed of PTFE.




In an alternate embodiment, plug-side conductor


302


and jack-side conductor


206


may be reversed so that plug-side conductor


302


is a female socket, and jack-side conductor


206


is a male contact. In a preferred embodiment, plug-side connector body


106


mates with jack-side connector body


112


such that spring fingers


304


fit within lumen


204


and plug-side conductor


302


mates with jack-side conductor


206


to form an electrical connection. Bayonet sleeve


108


is discussed in greater detail below with reference to FIG.


4


.





FIG. 4

is a perspective view of an M-BNC bayonet sleeve


108


. Bayonet sleeve


108


is configured to be rotatably mounted on plug-side connector body


106


, and includes a recessed portion


402


, slots


116


and indicators


124


. Sleeve


108


is preferably tubular and cylindrical and formed of a conductive material such as aluminum, beryllium copper, brass, zinc or stainless steel.




Slots


116


are configured and arranged for engagement with lugs


122


of jack-side connector


104


. In a preferred embodiment, sleeve


108


includes two slots


116


positioned on recessed portion


402


approximately one hundred eighty degrees apart from one another, corresponding to two lugs


122


positioned approximately one hundred eighty degrees apart from one another on jack-side connector body


112


. Although an M-BNC bayonet sleeve


108


having two slots


116


is shown in

FIG. 4

, in alternate embodiments, a bayonet sleeve


108


having a single slot or three or more slots corresponding to a single lug or three or more lugs, respectively, could be used, as would be well known to one skilled in the relevant art. For example, in an alternate embodiment, sleeve


108


could include three slots positioned approximately one hundred twenty degrees apart corresponding to three lugs on jack-side connector body


112


positioned approximately one hundred twenty degrees apart. Alternatively, sleeve


108


could include four slots positioned approximately ninety degrees apart corresponding to four lugs on jack-side connector body


112


positioned approximately ninety degrees apart. Further, in alternate embodiments, slots


116


and lugs


122


may be spaced at irregular intervals around sleeve


108


and jack-side connector body


112


, respectively.




As shown in

FIG. 4

, slots


116


are substantially J-shaped. Although J-shaped slots are shown, in alternate embodiments, slots may be any type of suitable shape, as would be apparent to one skilled in the relevant art. J-shaped slots


116


include initial portions


118


and terminal portions


120


, as shown in FIG.


4


. As discussed above, slots


116


are configured and arranged to correspond and engage with lugs


122


.




Bayonet sleeve


108


further includes at least one indicator


124


. Indicator(s)


124


are aligned with a reference point, so that when slots


116


are fully engaged with lugs


122


, indicator(s)


124


provide a visual indication that plug-side connector


102


is fully mated with jack-side connector


104


. In a preferred embodiment, sleeve


108


includes two indicators


124


positioned on sleeve


108


approximately one hundred eighty degrees apart from one another, which correspond to two slots


116


. However, in alternate embodiments having a different number of slots


116


, different, corresponding numbers of indicators


124


can be used at corresponding positions on sleeve


108


.




In a preferred embodiment, indicator


124


is a V-shaped notch, as shown in FIG.


4


A. In alternate embodiments, indicator


124


may be a dimple


700


(

FIG. 7

) on sleeve


108


, or may be any other shape, size, or configuration, as would be known to one skilled in the relevant art. However, an advantage of the V-shaped notch is that it is easily visible from the back of plug-side connector


102


. That is, referring back to

FIG. 1

, when plug-side connector


102


is connected to a jack-side connector


104


, the V-shaped notch is clearly visible when looking toward plug-side connector


102


from a point on axis


114


to the right of plug-side connector


102


. This view point is referred to herein as looking from the “back” of plug-side connector


102


.




When plug-side connector


102


is manufactured, sleeve


108


is mounted on plug-side connector body


106


, and a peripheral edge


404


of sleeve


108


is then bent inward or necked-down to form a lip on sleeve


108


. This lip has an inner diameter that is smaller than an outer diameter of a portion (not shown) of body


106


to allow sleeve


108


to rotate on body


106


but to prevent sleeve


108


from being removed from body


106


. Preferably, the V-shaped notch of indicator


124


which is cut in peripheral edge


404


, is made more visible by the forming of the lip which makes sleeve


108


appear to have a greater wall thickness and exposes a larger surface area of notched sleeve


108


for viewing from the back of plug-side connector


102


.




In yet another embodiment, indicator


124


may be a ridge


800


(

FIG. 8

) or lug


900


(

FIG. 9

) formed on sleeve


108


. An advantage of a raised ridge or lug is that it would be easily visible from the back of plug-side connector


102


. A raised ridge or lug may have the additional advantage of improving a user's grip for rotating sleeve


108


during connection and disconnection of mating connector pair


100


.




The mating and engagement of jack-side connector


104


and lugs


122


to plug-side connector


102


and slots


116


is further discussed with reference to

FIGS. 5 and 6

. As shown in

FIG. 5

, to mate plug-side connector


102


and jack-side connector


104


, lugs


122


are aligned and inserted into corresponding slots


116


. As shown in

FIG. 5

, when jack-side connector


104


is initially inserted into plug-side connector


102


, lugs


122


are inserted into an initial portion


118


of slots


116


. The slots


116


and lugs


122


are said to be partially engaged at this point. Next, plug-side connector


102


is pushed against jack-side connector


104


(depressing on an internal spring member of plug-side connector


102


) and bayonet sleeve


108


is rotated until lugs


122


are at the terminal portion


120


of slots


116


. The slots


116


and lugs


122


are said to be fully engaged at this point, because lugs


122


are now locked into position.




As stated above, indicators


124


are aligned with reference points when each lug


122


is locked into position in a corresponding terminal portion


120


of a slot


116


. In this position, the mating connector pair is fully engaged. In a preferred embodiment, the reference points are the terminal portions


120


of slots


116


. Thus, when the mating connector pair


100


is fully engaged, each indicator


124


of plug-side connector


102


will align with a corresponding lug


122


of jack-side connector


104


. This permits inspection from the back of plug-side connector


102


to determine whether mating connector pair


100


is fully engaged.




Prior to the present invention, a user desiring to confirm full engagement of a mating connector pair including a bayonet mechanism would attempt to visually confirm that the lugs of a jack-side connector were positioned in the terminal portions of J-shape slots on a bayonet sleeve, or manually confirm full engagement by attempting to rotate the bayonet sleeve using their fingers. However, when full-size BNC and/or M-BNC mating connector pairs are used with telecommunications and broadcast equipment, large number of mating connector pairs are often used in close proximity to one another, both horizontally and vertically. This can make it difficult to obtain a viewpoint that will allow visual inspection and makes it difficult to manually rotate the bayonet sleeve. The present invention overcomes this limitation of prior mating connector pairs.




BNC Jack-side connectors are typically mounted on the case panels of electronic equipment. They are typically oriented so that the lugs of all jack-side connectors are aligned. For example, a typical orientation for standard two-lug BNC jack-side connectors has the lugs aligned on a vertical axis (i.e., at 12 o'clock and 6 o'clock on a clock dial). With this orientation, the invention permits visual confirmation that each mating connector pair


100


is fully engaged by simply inspecting from the rear of each plug-side connector


102


to confirm that each indicator


124


is vertically oriented. The invention makes it unnecessary to visually inspect the position of lug


122


in J-slot


116


.




Although the visual indicators have been shown an described with reference to full-size BNC and M-BNC mating connector pairs, in alternate embodiments, the visual indicators of the present invention could be used with any device having a bayonet mechanism that provides a positive engagement.




While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that they have been presented by way of example only, and not limitation, and various changes in form and details can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. Additionally, all references cited herein, including journal articles or abstracts, published or corresponding U.S. or foreign patent applications, issued U.S. or foreign patents, or any other references, are each entirely incorporated by reference herein, including all data, tables, figures, and text presented in the cited references.




The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge within the skill of the art (including the contents of the references cited herein), readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance presented herein, in combination with the knowledge of one of ordinary skill in the art.



Claims
  • 1. A plug-side connector configured for engagement with a jack-side connector to form an electrical connection, comprising:a plug-side connector body; a bayonet sleeve rotatably connected to said connector body, said sleeve having two slots therein for engagement with corresponding lugs on a jack-side connector; and a first indicator located on a peripheral edge of said sleeve, said indicator being visible from a back of said plug side connector and aligned with a reference point when said slots in said sleeve are fully engaged with the lugs of a jack-side connector to provide a visual indication that the plug-side connector is fully engaged with the jack-side connector.
  • 2. The plug-side connector of claim 1, wherein the plug-side connector is a BNC plug-side connector, and the jack-side connector is a BNC jack-side connector.
  • 3. The plug-side connector of claim 1, further comprising:a second indicator, wherein each of said first and second indicators is aligned with a terminal portion of a respective slot so that said visual indication is provided when each indicator is substantially aligned with a respective lug of a mated jack-side connector.
  • 4. The plug-side connector of claim 3, wherein each of said slots in said sleeve comprises a J-shaped slot, and wherein said J-shaped slots are positioned on said sleeve approximately one hundred eighty degrees apart from one another.
  • 5. The plug-side connector of claim 4, wherein each of said indicators comprises a substantially V-shaped notch in said sleeve.
  • 6. The plug-side connector of claim 5, wherein said second indicator is positioned on said sleeve such that it is visible from the back of the plug-side connector.
  • 7. The plug-side connector of claim 4, wherein each of said indicators is selected from the group comprising a dimple on said sleeve, a ridge on said sleeve and a lug on said sleeve.
  • 8. The plug-side connector of claim 7, wherein said second indicator is positioned on said sleeve such that it is visible from the back of the plug-side connector.
  • 9. The plug-side connector of claim 1, wherein said sleeve further comprises:a third slot for engagement with a corresponding lug on the jack-side connector; and a third indicator, wherein each of said first, second and third indicators is aligned with a terminal point of a respective slot so that said visual indication is provided when each indicator is substantially aligned with a respective lug of a mated jack-side connector.
  • 10. The plug-side connector of claim 9, wherein each of said slots in said sleeve comprises a J-shaped slot, and wherein said J-shaped slots are positioned on said sleeve approximately one hundred twenty degrees apart from one another.
  • 11. The plug-side connector of claim 10, wherein each of said indicators comprises a substantially V-shaped notch in said sleeve.
  • 12. A mating connector pair comprising:(a) a jack-side connector comprising a jack-side connector body having two lugs disposed on a peripheral surface thereof, said lugs being positioned on said jack-side connector body approximately one hundred eighty degrees apart from one another, a jack-side conductor disposed within a lumen of said jack-side connector body, and a jack-side connector insulator electrically isolating said jack-side conductor from said jack-side connector body; and (b) a plug-side connector comprising a plug-side connector body configured for mating with said jack-side connector body, a plug-side conductor disposed within a lumen of said plug-side connector body, said plug-side conductor being configured for mating with said jack-side conductor of said jack-side connector, a plug-side connector insulator electrically isolating said plug-side conductor from said plug-side connector body, a bayonet sleeve rotatably connected to said plug-side connector body, said sleeve having two J-shaped slots therein, each slot being configured and arranged for engagement with a corresponding one of said lugs of said jack-side connector body when said jack-side connector is mated with said plug-side connector, and two indicators located on a peripheral edge of said sleeve, each indicator being visible from a back of said plug side connector and aligning with a terminal portion of a corresponding one of said slots to provide a visual indication of full mating of said connector when said slots in said sleeve are fully engaged with said lugs of said jack-side connector body.
  • 13. The mating connector pair of claim 12, wherein each indicator comprises a substantially V-shaped notch in said sleeve.
  • 14. The mating connector pair of claim 12, wherein the mating connector pair is a BNC mating connector pair, said jack-side connector is a BNC jack-side connector, and said plug-side connector is a BNC plug-side connector.
US Referenced Citations (9)
Number Name Date Kind
3609632 Vetter Sep 1971 A
3708781 Trompeter Jan 1973 A
3790915 Dugan et al. Feb 1974 A
4037909 Trompeter et al. Jul 1977 A
4290662 Storcel Sep 1981 A
4702537 Mattingly et al. Oct 1987 A
4703988 Raux et al. Nov 1987 A
5067909 Behning Nov 1991 A
5409398 Chadbourne et al. Apr 1995 A