Patent Application
20080081488
Where like parts appear in more than one drawing, it has been attempted to use like reference numerals for clarity.
Exemplary embodiments relate to a three dimensional rotary joint comprising electrically conductive and non-conductive surfaces arranged with respect to one another to provide multiple electrically isolated circuits. According to one embodiment of the invention, the rotary joint comprises plateable and non-plateable resins arranged to provide both plateable and non-plateable surfaces of the rotary joint. By “plateable” and “non-plateable” is meant that the resin generally accepts or does not accept, respectively, plating of an electrically conductive material on its surface. The exposed plateable surfaces attract and adhere to electrically conductive materials, such as metals, to create the electrically conductive surface and thus provides a resin based connector with conductive pathways across various three dimensional surfaces of the rotary joint. The plateable surfaces thus permit creation of circuit trace paths on both external and internal surfaces of the rotary joint that are electrically isolated from other paths by a non-plateable resin to which no electrically conductive material adheres during plating and provides a surface that remains electrically insulating.
In this manner, connectors in accordance with exemplary embodiments of the invention are formed with a geometric arrangement of conductive and non-conductive surfaces that effectively accomplish, preferably in a unitary structure, what other connectors, such as conventional slip rings, accomplish through intricate and time consuming assembly of many separate components.
In some cases, rotation of the rotary joint 5 may advantageously be accomplished during operation by turning an axle (not shown) that is substantially coincidental with the longitudinal axis 11 and extending into and/or through the central channel 12. Thus, any central channel 12 in the core 10 may be sized to receive the axle in addition to, or in lieu of, wires. Alternatively, as shown in
Returning to
As will be discussed in more detail later with respect to
As better seen in
According to one embodiment of the invention, a cross-cut 20 protrudes into the core 10 adjacent at least one groove 16. The depth of the cross-cut 20 into the core 10 generally ranges from about one quarter to about three quarters of the core's radius and more typically is about one half the core's radius. If multiple cross-cuts are included as discussed below, the depths may vary from groove to groove, but preferably are of the same depth. The cross-cut 20 typically extends perpendicular to the longitudinal axis 11 entirely across the core 10. That is, the cross-cut 20 typically forms a chord across the core 10 when viewed in cross-section.
As seen better in the enlarged cross sectional view of
Successive cross-cuts 20 may be present adjacent other grooves 16 and oriented at some angle to the others, thereby creating a rotating pattern of cross-cuts 20 in the core 10. Typically, the cross-cuts 20 are oriented so as to be equally spaced about the circumference of the core 10 according to the formula 360°/n, where n equals the number of circuits. For example, if two circuits are used, the cross-cuts 20 would ordinarily be oriented at 180° from each other, while if three circuits are used, they would ordinarily be oriented at 120°, etc.
The internal passageway 18 extends through the core 10 from the wire trough 14 to connect to a corresponding cross-cut 20. The passageway is generally straight and substantially parallel with the core's longitudinal axis 11 for ease of manufacture, although more complicated internal geometries are possible. The connection between the passageway 18 and its corresponding cross-cut 20 may be achieved by passing into that cross-cut 20 through the second wall 24, or more preferably via the aperture 25 in the floor 23 of the cross-cut 20.
Like the cross-cuts 20, the passageways 18 are also typically oriented with respect to other passageways in such a manner that one passageway 18 does not intersect any other passageway 18 or through any non-corresponding cross-cut 20. This maintains electrical isolation of the conductive path associated with a particular passageway from other circuits of the rotary joint 5. As seen in
It will be appreciated that, as best seen in
As described above, the rotary joint 5 has both electrically conductive and non-conductive surfaces. Preferably, this is achieved by manufacturing the core 10 from a combination of plateable and non-plateable resins. In this manner, surfaces that define the electrically conductive path may be formed with a plateable resin so that an electrically conductive material can be coated to the plateable surface to create the electrically conductive surface of the rotary joint 5. Conversely, the remaining surfaces, i.e., generally all surfaces which are not part of a conductive path, are formed from a non-conductive, non-plateable resin. Thus, surfaces of these materials do not become coated with an electrically conductive material during plating operations and serve to electrically isolate electrical conductive paths from one another to permit multiple circuits in the rotary joint 5. Suitable resins for use with the exemplary embodiments of the present invention include any wholly aromatic polyesters that fall into the category generally referred to as liquid crystal polymers (LCPs). Other suitable resins include ABS, polycarbonate, polysulfone, polyethersulfone, syndiotactic polystyrene and polyphthalamide, by way of example only.
The plateable resins for use with exemplary embodiments of the invention can be any resin that can be plated with a suitably continuous layer of electrically conductive material, typically a metal, to provide a usable electrically conductive path. More preferably, the resins are electrically non-conductive but are plateable using electroless plating techniques as described in more detail below, thus providing an insulative substrate beneath the conductive layer that further serves to maintain electrical isolation between conductive paths.
Plateable resins are commercially available and may be produced using processing techniques that involve adding a catalyzing component such as a silicate filler and/or certain metals dissolved or dispersed in a nonplateable resin. One such technique is described in more detail in U.S. Pat. No. 5,338,567, the entirety of which is hereby incorporated by reference.
The non-conductive surfaces may be formed from any non-plateable material, and is typically of the same family as the plateable resin. That is, for example, where the plateable resin is a liquid crystal polymer, the non-plateable resin is also generally selected to be a liquid crystal polymer. In some cases, the non-plateable resin may be the same base polymer as the plateable resin but which has no additives nor undergone any subsequent processing to make it plateable.
According to one embodiment of the invention, the plateable resin is a plateable LCP resin, such as Zenite® ZE55801 NC010, available from the DuPont Company of Wilmingtone, Del. or CCP 34-94096 available from the RTP Company of Winona, Minn., by way of example only, and the non-plateable resin is a non-plateable LCP resin, such as Zenite® 5130L, for example, also available from DuPont.
Because the core 10 may be formed by injection molding, the plateable and non-plateable resins are generally selected to have compatible melting ranges and molding ranges, as a well as comparable heat deflection temperatures. The melting ranges of the plateable and non-plateable resins may be within about 20° C. of each other. Likewise, the molding ranges of the plateable and non-plateable resins may also be within about 20° C. of each other.
According to one embodiment of the invention, a two-shot molding process is used in which the cylindrical core 10 is initially formed from plateable resin 50, followed by overmolding a shell of non-plateable resin 60 to at least a portion of the external surface of the core 10. The non-plateable resin shell is typically about 0.1 mm or greater in thickness, and more typically is at least about 0.5 mm thick. It will be appreciated, however, that the non-plateable resin may be of any thickness, provided that it sufficiently covers the plateable resin to prevent plating on corresponding surfaces intended to maintain electrical isolation between circuits.
The resulting molded component forms the basic cylindrical geometry of the core 10, and may even be a solid cylinder of plateable resin 50 entirely covered by a shell of non-plateable resin. The final component geometry, such as the internal passageways 18 and any wire troughs 14 may be subsequently bored or otherwise machined into the solid cylinder, breaking through the non-plateable shell 60 to expose underlying plateable surfaces 52. Likewise, the circumferential grooves 16 and the cross-cuts 20 may be machined into the rotary joint 5 by cutting through the outer shell of non-plateable resin 60 overmolded on the plateable resin 50 to expose plateable surfaces 52 of the plateable resin 50.
According to another embodiment, subsequent machining techniques may be reduced or avoided entirely by molding the core 10 into its final geometry in two separate molding steps. In the first molding step, an intermediate core is molded using plateable resin 50 so that the grooves 16, cross-cuts 20 and passageways 18 are all present. In a second molding step, a second mold masks the surfaces 52 of the intermediate core that will remain exposed for subsequent plating. The non-plateable resin 60 is injected to cover the unmasked surfaces of the intermediate core that will not be plated to a desired thickness as already described.
Alternatively, a combination of molding and machining the geometrical features and exposing surfaces of plateable resin at appropriate locations may be used. Molding temperatures generally range from about 270° C. to about 450° C. In embodiments in which the final geometry of the plateable resin is molded directly, with non-plateable resin applied only to unmasked portions, the core 10 is preferably cooled rapidly to maintain dimensional stability in the core's discrete geometrical features.
Once the core 10 has been formed to have plateable and non-plateable resin surfaces 52, 62 in the desired geometry, the core 10 then undergoes a plating process to provide a rotary joint 5 of unitary structure having electrically conductive and non-conductive surfaces. Plating is used to plate the exposed plateable resin surfaces 52 with one or more layers of a conductive material typically a metal, such as tin, copper, nickel, gold, silver, platinum, aluminum, palladium, alloys thereof and combinations thereof, by way of example only.
According to one embodiment of the invention, an electroless plating bath is used to plate the exposed surfaces of plateable resin with three separate conductive layers (
The overall thickness of the conductive material may depend on the number and composition of the layers to be applied; generally about 10 to about 30 microns is sufficient. In accordance with an exemplary tri-layer embodiment shown in
According to yet another embodiment of the invention, the rotary joint 5 may be constructed by a single shot molding of the core 10 to its finally geometry using a plateable resin involving lithography techniques. After molding, the core 10 is submerged in an electroless plating bath to completely coat all surfaces of the core 10 with copper or another electrically conductive material. Following the plating, a lithographic process is used in which a resist is painted over those plated surfaces of the core 10 that will form the conductive surfaces of the finished rotary joint 5. The core 10 is then placed in an etching tank which removes the copper from those surfaces of the core 10 to which the resist was not applied, re-exposing the underlying resin. Finally, the resist is removed from the core 10 to reveal the conductive surfaces of the core 10, from which the copper was protected during etching by the resist, to yield the final rotary joint 5.
As better seen in the cross sectional view shown in
The stator 110 may include a stator core 140 having two equal halves, one half of which is illustrated in
Conversely, by splitting the stator 110 into two halves, it may be possible to use each half as a separate tools to connect the first and second electrical devices directly by orienting the two stator halves opposite one another and disposing the stator contacts 130 for each stator half in the same groove 16 of the rotary joint 5.
The stator attachment plate 120 may advantageously be a plateable resin with an overlying metallic layer as described above with respect to the rotary joint 5. Conversely, the stator core 140 may be a non-plateable resin, electrically isolating attachment plates 120 and contacts 130 of different circuits from one another.
While the foregoing specification illustrates and describes exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
