Method for ultrasonic welding a coaxial cable to a coaxial connector

A coaxial connector for interconnection with a coaxial cable with a solid outer conductor by ultrasonic welding is provided with a monolithic connector body with a bore. An annular flare seat is angled radially outward from the bore toward a connector end of the connector, the annular flare seat open to the connector end of the connector. An inner conductor cap is provided for interconnection with an inner conductor of the coaxial cable by ultrasonic welding. The ultrasonic welding of each of the inner and outer conductor interconnections may be performed via inner conductor and outer conductor sonotrodes which are coaxial with one another, without requiring the cable and or connector to be removed from their fixture.

BACKGROUND

1. Field of the Invention

This invention relates to electrical cable connectors. More particularly, the invention relates to a coaxial connector and method and apparatus for interconnection of such coaxial cable connector with a coaxial cable via ultrasonic welding wherein the interconnection may be performed with a single fixture mounting operation.

2. Description of Related Art

Coaxial cable connectors are used, for example, in communication systems requiring a high level of precision and reliability.

To create a secure mechanical and optimized electrical interconnection between the cable and the connector, it is desirable to have generally uniform, circumferential contact between a leading edge of the coaxial cable outer conductor and the connector body. A flared end of the outer conductor may be clamped against an annular wedge surface of the connector body via a coupling body. Representative of this technology is commonly owned U.S. Pat. No. 6,793,529 issued Sep. 21, 2004 to Buenz. Although this type of connector is typically removable/re-useable, manufacturing and installation is complicated by the multiple separate internal elements required, interconnecting threads and related environmental seals.

Connectors configured for permanent interconnection via solder and/or adhesive interconnection are also well known in the art. Representative of this technology is commonly owned U.S. Pat. No. 5,802,710 issued Sep. 8, 1998 to Bufanda et al. However, solder and/or adhesive interconnections may be difficult to apply with high levels of quality control, resulting in interconnections that may be less than satisfactory, for example when exposed to vibration and/or corrosion over time.

Passive Intermodulation Distortion, also referred to as PIM, is a form of electrical interference/signal transmission degradation that may occur with less than symmetrical interconnections and/or as electro-mechanical interconnections shift or degrade over time, for example due to mechanical stress, vibration, thermal cycling and/or material degradation. PIM is an important interconnection quality characteristic as PIM from a single low quality interconnection may degrade the electrical performance of an entire RF system.

During interconnection procedures, the coaxial connector and/or coaxial connector may be mounted in a fixture which secures the connector and/or cable in a secure pre-determined orientation with respect to one another. Depending upon the type of interconnection, multiple fixtures and/or mounting/remounting may be required to perform separate portions of the interconnection procedure, such as separately forming secure electro-mechanical interconnections with respect to each of the inner and outer conductors of the coaxial cable. However, each mounting/remounting procedure consumes additional time and/or may provide opportunities for the introduction of alignment errors.

Competition in the coaxial cable connector market has focused attention on improving electrical performance and long term reliability of the cable to connector interconnection. Further, reduction of overall costs, including materials, training and installation costs, is a significant factor for commercial success.

Therefore, it is an object of the invention to provide a coaxial connector and method of interconnection that overcomes deficiencies in the prior art.

DETAILED DESCRIPTION

Aluminum has been applied as a cost-effective alternative to copper for the conductors in coaxial cables. However, aluminum oxide surface coatings quickly form upon air-exposed aluminum surfaces. These aluminum oxide surface coatings may degrade traditional mechanical, solder and/or conductive adhesive interconnections.

The inventor has recognized that increasing acceptance of coaxial cable with solid outer and/or inner conductors of aluminum and/or aluminum alloy enables connectors configured for interconnection via ultrasonic welding between the outer and inner conductors and a respective connector body and/or inner conductor cap inner contact which may each also be cost effectively provided, for example, formed from aluminum and/or aluminum alloy.

Further with respect to the inner conductor interconnection, the inventor has identified several difficulties arising from the interconnection of aluminum inner conductor coaxial cable configurations with prior coaxial cable connectors having inner contact configurations. Prior coaxial connector mechanical interconnection inner contact configurations are generally incompatible with aluminum inner conductors due to the creep characteristics of aluminum. Further, galvanic corrosion between the aluminum inner conductor and a dissimilar metal of the inner contact, such as bronze, brass or copper, may contribute to accelerated degradation of the electro-mechanical interconnection.

Utilizing friction welding, such as ultrasonic welding, for both the outer conductor to connector body and inner conductor to inner conductor cap interconnections enables a molecular bond interconnection with inherent resistance to corrosion and/or material creep interconnection degradation. Further, a molecular bond interconnection essentially eliminates the opportunity for PIM generation due to shifting and/or degrading mechanical interconnections.

An ultrasonic weld may be formed by applying ultrasonic vibrations under pressure in a join zone between two parts desired to be welded together, resulting in local heat sufficient to plasticize adjacent surfaces that are then held in contact with one another until the interflowed surfaces cool, completing the weld. An ultrasonic weld may be applied with high precision via a sonotrode and/or simultaneous sonotrode ends to a point and/or extended surface. Where a point ultrasonic weld is applied, successive overlapping point welds may be applied to generate a continuous ultrasonic weld.

Ultrasonic vibrations may be applied, for example, in a linear direction and/or reciprocating along an arc segment, known as torsional vibration.

Because the localized abrasion of the ultrasonic welding process can break up any aluminum oxide surface coatings in the immediate weld area, no additional treatment may be required with respect to removing or otherwise managing the presence of aluminum oxide on the interconnection surfaces.

Exemplary embodiments of an inner and outer conductor ultrasonic weldable coaxial connector2are demonstrated inFIGS. 1-7. As best shown inFIG. 1, a unitary connector body4is provided with a bore6dimensioned to receive the outer conductor8of a coaxial cable9therein. As best shown inFIG. 3, a flare seat10angled radially outward from the bore6toward a connector end18of the connector body4is open to the connector end of the coaxial connector2providing a mating surface to which a leading end flare14of the outer conductor8may be ultrasonically welded by an outer conductor sonotrode16of an ultrasonic welder inserted to contact the leading end flare14from the connector end18.

One skilled in the art will appreciate that connector end18and cable end12are applied herein as identifiers for respective ends of both the coaxial connector2and also of discrete elements of the coaxial connector2and sontotrodes described herein, to identify same and their respective interconnecting surfaces according to their alignment along a longitudinal axis of the connector between a connector end18and a cable end12.

Prior to interconnection via ultrasonic welding, the leading end of the coaxial cable9may be prepared, as best shown inFIG. 1, by cutting the coaxial cable9so that the inner conductor24extends from the outer conductor8. Also, dielectric material26between the inner conductor24and outer conductor8may be stripped back and a length of the outer jacket28removed to expose desired lengths of each.

The inner conductor24extending from the prepared end of the coaxial cable9may be selected to pass through to the connector end18as a portion of the selected connection interface31. If the selected coaxial cable9has an inner conductor24that has a larger diameter than the inner conductor portion of the selected connector interface31, the inner conductor24may be ground at the connector end18to the required diameter.

Although a direct pass through inner conductor24advantageously eliminates interconnections, for example with the spring basket interconnection with a traditional coaxial connector inner contact, such may introduce electrical performance degradation such as PIM. Where the inner conductor24is also aluminum material some applications may require a non-aluminum material connection point at the inner contact/inner conductor of the connection interface31. As shown for example inFIG. 1, an inner conductor cap20, for example formed from a metal such as brass or other desired metal, may be applied to the end of the inner conductor24, also by friction welding such as ultrasonic welding.

The inner conductor cap20may be provided with an inner conductor socket at the cable end12and a desired inner conductor interface22at the connector end4. The inner conductor socket may be dimensioned to mate with a prepared end23of an inner conductor24of a coaxial cable9. To apply the inner conductor cap20, the end of the inner conductor24is ground to provide a pin corresponding to the selected socket geometry of the inner conductor cap20. To allow material inter-flow during welding attachment, the socket geometry of the inner conductor cap20and/or the end of the inner conductor24may be formed to provide a material gap25.

A rotation key27may be provided upon the inner conductor cap20, the rotation key27dimensioned to mate with an inner sonotrode tool15for rotating and/or torsionally reciprocating the inner conductor cap20, for interconnection via ultrasonic friction welding.

The cable end12of the coaxial cable9is inserted through the bore6and an annular flare operation is performed on a leading edge of the outer conductor8. The resulting leading end flare14may be angled to correspond to the angle of the flare seat10with respect to a longitudinal axis of the coaxial connector2. By performing the flare operation against the flare seat10, the resulting leading end flare14can be formed with a direct correspondence to the flare seat angle. The flare operation may be performed utilizing the leading edge of the outer conductor sonotrode16, provided with a conical cylindrical inner lip with a connector end18diameter less than an inner diameter of the outer conductor8, for initially engaging and flaring the leading edge of the outer conductor8against the flare seat10.

An overbody30, as shown for example inFIG. 1, may be applied to the connector body4as an overmolding of polymeric material. The overbody30increases cable to connector torsion and pull resistance.

Depending upon the applied connection interface31, demonstrated in the exemplary embodiments herein as a standard 7/16 DIN male interface, the overbody30may be provided dimensioned with an outer diameter cylindrical support surface34and/or support ridges depending upon the diameter of the selected coaxial cable. Tool flats39(seeFIG. 8) for retaining the coaxial connector2during interconnection with other cables and/or devices may be formed in the cylindrical support surface34by removing surface sections of the cylindrical support surface34.

The coupling nut36is retained upon the support surface34and/or support ridges at the connector end18by an overbody flange32. At the cable end12, the coupling nut36may be retained upon the cylindrical support surface34and/or support ridges of the overbody30by applying one or more retention spurs41(seeFIG. 8) proximate the cable end of the cylindrical support surface34. The retention spurs41are angled with increasing diameter from the cable end12to the connector end18, allowing the coupling nut36to be passed over them from the cable end12to the connector end18, but then retained upon the cylindrical support surface34by a stop face provided at the connector end18of the retention spurs41.

The overbody30may also provide connection interface structure at the connector end18and further reinforcing support at the cable end12, enabling reductions in the size of the connector body4, thereby potentially reducing overall material costs. For example, the overbody30is demonstrated extending from the connector end18of the connector body4to provide portions of the selected connector interface31, an alignment cylinder38of the 7/16 DIN male interface, further reducing metal material requirements of the connector body4.

The overbody flange32may be securely keyed to a connector body flange40of the connector body4and thereby with the connector body4via one or more interlock apertures42such as holes, longitudinal knurls, grooves, notches or the like provided in the connector body flange40and/or outer diameter of the connector body4, as shown for example inFIG. 1. Thereby, as the polymeric material of the overbody30flows into the one or more interlock apertures42during overmolding, upon curing the overbody30is permanently coupled to and rotationally interlocked with the connector body4.

The cable end of the overbody30may be dimensioned with an inner diameter friction surface44proximate that of the coaxial cable jacket28, enabling, for example, an interference fit and/or polymeric friction welding between the overbody30and the jacket28, by rotation of the connector body4with respect to the outer conductor8, thereby eliminating the need for environmental seals at the cable end12of the connector/cable interconnection.

The overbody30may also have an extended cable portion proximate the cable end provided with a plurality of stress relief apertures46. The stress relief apertures46may be formed in a generally elliptical configuration with a major axis of the stress relief apertures46arranged normal to the longitudinal axis of the coaxial connector2. The stress relief apertures46enable a flexible characteristic of the cable end of the overbody30that increases towards the cable end of the overbody30. Thereby, the overbody30supports the interconnection between the coaxial cable9and the coaxial connector2without introducing a rigid end edge along which a connected coaxial cable2subjected to bending forces may otherwise buckle, which may increase both the overall strength and the flexibility characteristics of the interconnection.

Where the overbody30is interconnected with the jacket28via friction welding, friction between the friction surface44and the outer diameter of the jacket28heats the respective surfaces to a point where they begin to soften and intermingle, sealing them against one another. The jacket28and/or the inner diameter of the overbody30may be provided as a series of spaced apart annular peaks of a contour pattern such as a corrugation, or a stepped surface, to provide enhanced friction, allow voids for excess friction weld material flow and/or add key locking for additional strength. Alternatively, the overbody30may be sealed against the outer jacket28with an adhesive/sealant or may be overmolded upon the connector body4after interconnection with the outer conductor8, the heat of the injected polymeric material bonding the overbody30with and/or sealing against the jacket28.

In a method for cable and connector interconnection, the prepared end of the coaxial cable9is inserted through the coupling nut36(the coupling nut36is advanced along the coaxial cable9out of the way until interconnection is completed) and connector body bore6so that the outer conductor8extends past the flare seat10a desired distance. The connector body4and/or cable end of the overbody30may be coated with an adhesive prior to insertion, and/or a spin welding operation may be performed to fuse the overbody30and/or cable end of the connector body4with the jacket28. The connector body4and coaxial cable9are then retained in a fixture37, rigidly securing these elements for the flaring and electrical interconnection friction welding via ultrasonic welding steps. One skilled in the art will appreciate that the fixture may be any manner of releasable retention mechanism into which the coaxial cable and/or coaxial connector2may be easily inserted and then released, for example as demonstrated inFIGS. 8-10.

The flaring operation may be performed with a separate flare tool or via advancing the outer conductor sonotrode16to contact the leading edge of the head of the outer conductor8, as shown for example inFIG. 4, resulting in flaring the leading edge of the outer conductor8against the flare seat10(SeeFIG. 3). Once flared, the outer conductor sonotrode16is advanced (if not already so seated after flaring is completed) upon the leading end flare14and ultrasonic welding may be initiated.

Ultrasonic welding may be performed, for example, utilizing linear and/or torsional vibration. In linear vibration ultrasonic-type friction welding of the leading end flare14to the flare seat10, a linear vibration is applied to a cable end side of the leading end flare14, while the coaxial connector2and flare seat10therewithin are held static within the fixture37. The linear vibration generates a friction heat which plasticizes the contact surfaces between the leading end flare14and the flare seat10. Where linear vibration ultrasonic-type friction welding is utilized, a suitable frequency and linear displacement, such as between 20 and 40 KHz and 20-35 microns, selected for example with respect to a material characteristic, diameter and/or sidewall thickness of the outer conductor8, may be applied.

With the outer conductor interconnection completed, the outer diameter sonotrode head may be advanced into supporting contact against the leading end flare14of the outer conductor8, further improving the immobilization of the coaxial cable9and coaxial connector2.

As shown inFIG. 5, within a bore of the outer conductor sonotrode16, the inner conductor sonotrode15is then advanced to friction weld the inner conductor cap20upon the prepared end23of the inner conductor24. Because the outer conductor sonotrode16and the inner conductor sonotrode15are arranged coaxially, alignment with the desired coaxial elements of the coaxial cable9is ensured, without requiring adjustment of the coaxial cable9and/or coaxial connector2within the fixture37.

The inner conductor cap20may have been pre-inserted upon the prepared end23of the inner conductor24or alternatively may be provided loaded into the cable end of the inner conductor sonotrode15. The inner conductor sonotrode15may include a key feature48configured to receive and engage the rotation key27of the inner conductor cap20. Utilizing the key feature48to drive the inner conductor cap20, torsional vibration ultrasonic-type friction welding may be applied.

In torsional vibration ultrasonic-type friction welding, a torsional vibration is applied to the interconnection via the inner conductor sonotrode15coupled to the inner conductor cap20by the rotation key27, while the coaxial connector2and coaxial cable9with inner conductor24there within are held static within the fixture37. The torsional vibration generates a friction heat which plasticizes the contact surfaces between the prepared end23and the inner conductor cap20. Where torsional vibration ultrasonic-type friction welding is utilized, a suitable frequency and torsional vibration displacement, for example between 20 and 40 KHz and 20-35 microns, may be applied, also selected with respect to material characteristics and/or dimensions of the mating surfaces.

Alternatively, the inner conductor sonotrode15may be applied to interconnect the inner conductor cap20and prepared end23of the inner conductor24and the outer conductor sonotrode16then advanced coaxially around the inner conductor sonotrode15to perform flaring of the outer conductor leading end flare14and/or ultrasonic friction weld interconnection.

Where the outer conductor and inner conductor sonotrodes16,15are independent of one another during operation, a vibration profile comprising a vibration type, frequency and/or amplitude selected according to the requirements of each type of interconnection may be applied. If desired, both the inner conductor and outer conductor sonotrodes15,16may be applied, either with the same vibration profile or separate vibration profiles, simultaneously to further reduce the interconnection time requirements.

As shown for example inFIG. 5, when the interconnection is completed, the inner conductor and outer conductor sonotrodes15,16may be withdrawn and the interconnected coaxial cable9and coaxial connector2released from the fixture37. With the coupling nut36advanced over the overbody30to a ready for interconnection position against the overbody flange32, the interconnection has been completed, as best shown inFIG. 7.

One skilled in the art will appreciate that the coaxial connector2and interconnection method disclosed has significant material cost efficiencies and provides a permanently sealed interconnection with reduced size and/or weight requirements. Because of the coaxial sonotrode configuration, the coaxial cable9and coaxial connector2need to be mounted in the fixture37only once, which simplifies the electrical interconnection procedure. Thereby, the single fixturing feature of the flaring and electrical interconnection method may increase the speed of manufacture and/or improve alignment of the resulting interconnection. Finally, because a molecular bond is established at each electro-mechanical interconnection, PIM resulting from such interconnections may be significantly reduced and/or entirely eliminated.

Where in the foregoing description reference has been made to materials, ratios, integers or components having known equivalents then such equivalents are herein incorporated as if individually set forth.

While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus, methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of applicant's general inventive concept. Further, it is to be appreciated that improvements and/or modifications may be made thereto without departing from the scope or spirit of the present invention as defined by the following claims.