Abstract:
A rotatable electrical connector has a pair of wiring boards. Each wiring board supports two (or more) concentric conductors that have substantially smooth coplanar surfaces. The coplanar surfaces of the concentric conductors on each wiring board define a contact plane. To provide electrical contact between the two wiring boards, each wiring board is positioned perpendicular to an axis of rotation and is supported so that the respective contact planes of the first and second wiring boards are parallel. A resilient member, such as a spring, urges the wiring boards together to establish electrical contact between the respective surfaces of corresponding conductors on the two wiring boards. The above-described wiring boards are included in a circuit module that also includes a printed circuit board, or other electrical component, sandwiched between a pair of the wiring boards. The concentric conductors of the wiring boards face away from the electrical component so that the circuit modules can be assembled in series, much as batteries are assembled inside a flashlight, to create complex electrical systems.

Description:
BACKGROUND 
     Rotary electrical connectors are used in a variety of applications where one part must mechanically rotate with respect to another part while retaining an electrical connection between the two. Where the required extent of rotation is small, typically less than one complete revolution, hardwired electrical connections can be used. However, hardwired connections can be difficult and expensive to make, especially where such connections must be made at remote locations or in confined spaces. 
     For larger required rotations, on the order of several revolutions, wraparound wire arrangements are available. In other instances, the connector must permit an arbitrarily large extent of rotation. In such a connector, electrical connection must be maintained, and the mode of connection cannot hinder the rotational movement. For these applications, the most common type of connector is a slip ring system. A plurality of slip rings in side-by-side arrangement extend along the length of a rotating shaft. Stationary brushes make contact to the individual slip rings. Unfortunately, such systems are typically expensive, due to the number of parts, and can be too bulky for some applications. 
     Some of the foregoing problems are addressed by Mohi Sobhani in his patent entitled “Rotary Electrical Connector,” U.S. Pat. No. 5,588,843. That patent describes an electrical connector that includes two planar connector members positioned perpendicular to an axis of rotation and supported in rotational facing relation. One of the connector members has a set of concentric tracks, and the other has a corresponding set of protrusions positioned to contact the tracks. The two connector members are urged together by a spring so that the concentric tracts remain in electrical contact with the protrusions. A second patent to Sobhani, U.S. Pat. No. 5,690,498, entitled “Spring Loaded Rotary Connector,” teaches a similar connector in which the protrusions are replaced with dimples. Both of the foregoing Sobhani patents are incorporated herein by reference. 
     The Sobhani connectors work well in many applications. However, the complexity of making the protrusions or dimples increases the cost of making the connectors. Further, such connectors can be sensitive to shock, which can damage the protrusions or dimples. There is therefore a need for a more robust and less expensive means of providing rotational electrical contact. 
     SUMMARY 
     The present invention is directed to a robust, inexpensive and rotatable electrical connector. In accordance with the invention, the connecter is used in conjunction with other parts to create a system of interconnected electrical components in which the individual components are easily removed for repair or to change the functionality of the system. 
     The inventive electrical connector includes a pair of wiring boards (e.g., printed-circuit boards) that each includes, on one side, two or more concentric conductors. The opposite sides of the two wiring boards include contacts that are electrically connected through the respective boards to the concentric conductors. 
     Each wiring board is held in place by a respective connector support. Contact is established between the two wiring boards when the supports are positioned so that the concentric conductors on the wiring boards face one another and are brought into electrical contact. This contact can be direct or through other components. For example, one embodiment includes a conductive elastomeric member between the wiring boards to allow some tolerance to ensure adequate conductive contact between opposing concentric conductors in the event that the wiring boards are not exactly parallel. In other embodiments, a spring or other elastic member urging one wiring board against the other supplies this tolerance. 
     The above-described wiring boards are used to advantage in a novel circuit module. The circuit module includes a printed circuit board, or other electrical component, sandwiched between a pair of wiring boards. The concentric conductors of the wiring boards face away from the electrical component so that the circuit module can be assembled in series with other modules much as batteries are assembled inside a flashlight. This simple configuration allows for easy assembly of systems that include circuit modules configured in accordance with the present invention, and further allows for easy substitution of modules within such systems. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIGS. 1A and 1B are plan views of a wiring board  100 ; 
     FIG. 2 depicts an electrical connector  200  in accordance with one embodiment of the present invention; 
     FIG. 3 depicts a connector support  300  in which a cable  310  is connected to wiring board  100  of FIG. 1; 
     FIG. 4A is a top view of conductive member  400  that may be 
     FIG. 4B is a side view of conductive member  400  of FIG. 4A; disposed between a pair of wiring boards  100 ; 
     FIG. 5 is a cutaway view of a connector support  500 ; and 
     FIG. 6 is an exploded view of a system  600  configured in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIGS. 1A and 1B are plan views of a wiring board  100  configured in accordance with the present invention. FIG. 1A depicts a surface  110  of wiring board  100  that supports four concentric conductors  120 A-D; FIG. 1B depicts the opposite surface  130  of wiring board  100 , which supports four electrical contacts  140 A-D. Finally, wiring board  100  includes four conductive elements  150 A-D, each of which penetrates wiring board  100  to provide electrical contact between corresponding ones of conductive elements  120 A-D and electrical contacts  140 A-D. 
     Wiring board  100  can be formed by any of a number of conventional printed-circuit board manufacturing processes. However, wiring board  100  is not limited to printed-circuit boards. An example of a different but acceptable configuration is described in U.S. Pat. No. 4,590,337, to Engelmore, entitled “Rotatable Electrical Connector For Coiled Telephone Cords,” which is incorporated herein by reference. In some embodiments electrical conductors  120 A-D and electrical contacts  140 A-D are gold plated to prevent oxidation and to reduce contact resistance. 
     FIG. 2 depicts an electrical connector  200  in accordance with one embodiment of the present invention. Connector  200  includes a pair of wiring boards  100 A and  100 B. In the embodiment of FIG. 2, wiring boards  100 A and  100 B are identical to wiring board  100  of FIGS. 1A and 1B, like-numbered elements being the same. The surfaces of concentric conductors  120 A-D of wiring board  100 B form a contact plane  205  opposite a similar contact plane (not shown) defined by the concentric conductors of wiring board  100 A. Wiring boards  100 A and  100 B need not be identical, but may be configured in any manner desired for a given application. Such adaptations are well within the skill of those in the art. 
     Wiring board  100 A is solder-mounted to a connector support  210 , a PC board in the depicted embodiment, via a number of edge-mounted pads  220 A-D, each of which corresponds to a respective one of electrical contacts  140 A-D. In the depicted embodiment, wiring board  100 A is similarly mounted to a second connector support  230  positioned in parallel with connector support  210 . Both connector supports  210  and  230  are substantially orthogonal to wiring board  100 A. 
     Like wiring board  100 A, wiring board  100 B is solder-mounted to a pair of connector supports  240  and  242  via a number of edge-mounted pads (not shown). Also like wiring board  100 A, connector supports  240  and  242  are each mounted orthogonally to wiring board  100 B. The configuration of connector  200  provides physically robust connections between wiring boards  100 A and  100 B and their respective supports. These robust connections allow for significant compressive force between wiring boards  100 A and  100 B to ensure adequate electrical contact between respective concentric conductors. As discussed below in connection with FIG. 6, this configuration allows components, such as the PC boards that make up connector supports  210 ,  230 ,  240 ,  242 , to be stacked end-to-end, much like batteries in a flashlight, to create relatively complex circuits with easily substituted individual components. 
     Soldering wiring boards  100 A and  100 B to their respective connector supports  240  and  242  provides robust, low-impedance electrical connections. However, other types of connections may be used. For example, wiring board  100 A might be equipped with conventional conductive clips that mate with edge-mounted pads  220 A-D. Many other connector configurations will be obvious to those of skill in the art. 
     Conductive elements  150 A-D are typically through holes internally coated with metal. In one embodiment, center conductive element  150 A is configured to receive a corresponding pin extending from the center of the opposite wiring board. This configuration ensures that the opposing wiring boards remain properly aligned along the same rotational axis. In another embodiment, a concentric screw in one wiring board mates with a threaded concentric hole in the opposite wiring board. In still other embodiments, components equipped with connectors configured in accordance with the invention can be threaded onto a concentric rod, much like beads on a string. The threaded components can then be urged against one another to ensure good electrical connections between them. 
     Connector support  210  includes a surface-mounted integrated circuit  250 . For illustrative purposes, one leg  252  of circuit  250  is connected to pad  220 D via a trace  255 . In one embodiment, circuit  250  is a portion of a circuit component such as an amplifier; however, circuit  250  may be any of myriad conventional integrated circuits or components that may be used for selected applications. Connector supports  240  and  242  are shown to include respective integrated circuits  260  and  265  that are mounted using leads that extend through the respective circuit boards. 
     FIG. 3 depicts a connector support  300  in which a cable  310  is connected to surface  130  (see FIG. 1) of wiring board  100 . To assemble connector support  300 , cable  310  is threaded through an end cap  315 , a compression fitting  320 , an  0 -ring  325 , a cable body  330 , and a second  0 -ring  335 . The assembler then ties a knot  340  in cable  310  to secure an end of cable  310  within cable body  330 . Next, the assembler should strip the outer insulation from cable  310  and then the individual insulation off of each of internal wires  350 . Each of internal wires  350  is connected to a respective one of conductive elements  140 A-D (See FIG.  1 ), and wiring board  100  is then snapped in place. Finally, cable  310  is then pulled tight against the necked-down portion of cable body  330  before tightening compression fitting  320  to compress  0 -ring  325  around cable  310 . A dedicated insertion tool  342 , made by modifying a conventional screw driver as shown in FIG. 3, simplifies the process of inserting compression fitting  320 . The end of insertion tool  342  mates with a slot  344  in the end of compression fitting  320 , allowing the assembler to turn compression fitting  320  inside cable body  330 . This action compresses  0 -ring  325  between compression fitting  320  and the seat in cable body  330  to create a watertight seal. 
     A pair of  0 -rings  355  and  360  provide a watertight seal between cable body  330  and a cylindrical housing that will be described in more detail in connection with FIG.  6 . Threads  365  are provided on the outside of cable body  330  to mate with the cylindrical housing. In one embodiment, wiring board  100  includes a peripheral tab that mates with a slot (not shown) in cable body  330  to keep wiring board  100  from rotating inside cable body  330 . Such rotation can also be avoided by employing a wiring board that is not round. 
     FIG. 4 is a top view of a conductive member  400 FIG. 4B is a side view of conductive member  400  of FIG.  4 A. Referring to FIG. 2, conductive member  400  may be disposed between surface  110  of wiring board  110 B and the opposing surface (not shown) of wiring board  100 A. Conductive member  400  includes a dielectric retainer  410  with a slot  420 . A piece of anisotropic elastomeric material  430  is pressed into slot  420 . Material  430  conducts electricity in a direction perpendicular to the flat surfaces of retainer  410  but does not conduct electricity in a direction parallel to the long dimension of slot  420 . Thus, material  430  provides electrical contact between opposite respective concentric conductors when sandwiched between of the contact planes wiring boards  100 A and  100 B Conductive member  400  is configured to maintain electrical contact between opposing surfaces of wiring boards  100 A and  100 B without shorting adjacent concentric conductors on either of wiring boards  100 A and  100 B. Elastomeric material suitable for use in conductive member  400  is available from Fujipoli of Cranford, N. J., under the trademark Zebra™. 
     Conductive member  400  advantageously provides a wiping action when wiring boards  100 A and  100 B are brought into rotational contact. In addition, the resilience of conductive material  430  creates some tolerance that ensures adequate conductive contact between wiring boards  100 A and  100 B in the event that wiring boards  100 A and  100 B are not exactly parallel. Conductive member  400  can be aligned with adjacent wiring boards by encompassing them in a common cylinder or by using a concentric pin, rod, or screw. These and other methods of maintaining the appropriate alignment can easily be implemented by those of skill in the art. 
     FIG. 5 is a cutaway view of a connector support  500 . In accordance with the invention, connector support  500  includes wiring board  100  as described above in connection with FIGS. 1A and 1B. Wiring board  100  is snapped into a connector body  510  and held in place by a lip  520 . A spring  530  within connector body  510  urges wiring board  100  against lip  520 . Wires or components (not shown) can be connected from within connector body  510  to conductive elements  140 A-D of wiring board  100  (FIG.  1 B). In one embodiment, wiring board  100  includes a peripheral tab that mates with a corresponding slot in connector body  510  to keep wiring board  100  from rotating inside connector body  510 . 
     Connector body  510  also includes a slot  540  running parallel to the long dimension of connector body  510 . This slot provides an avenue for a protrusion on the inside of a cylindrical housing that is slipped over connector body  510  during the assembly process. The protrusion mates with threads  550  to join the housing with connector support  500 . A pair of  0 -rings  555  and  560  provide a watertight seal between connector support  500  and the cylindrical housing, which will be described in detail in connection with FIG.  6 . 
     FIG. 6 is an exploded view of a system  600  configured in accordance with the present invention. System  600  includes a pair of circuit modules  610  and  620  disposed between connector supports  300  and  500  of FIGS. 3 and 5, respectively. Conductive member  400  is disposed between wiring boards  100 A and  100 B of respective circuit modules  610  and  620 . System  600  is completed when a component housing  630 , typically a stainless-steel tube, is threaded onto each of connector supports  300  and  500 . A pair of dimples  640  and  645 , pressed into the side of component housing  630 , create corresponding protrusions on the inside surface of component housing  630 . These protrusions mate with threads  550  and  365  to secure connector supports  300  and  500  to component housing  630 . 
     Once system  600  is assembled, spring  530  exerts a compressive force on the stack of circuit components that includes circuit modules  610  and  620  and conductive member  400 . This compressive force ensures excellent electrical contact between opposing wiring boards. Moreover, the radial symmetry of the concentric conductors on the respective wiring boards allows system  600  to be assembled using screw-type couplings, although other types of couplings may also be used. The various wiring boards remain stationary with respect to one another under normal operating conditions. 
     Each circuit module  610  and  620  can be virtually any type of electrical circuit. For example, circuit module  610  might be a preamplifier and circuit module  620  an analog-to-digital converter. Being arranged as they are, components  610  and  620  can be removed and replaced as easily as batteries in a flashlight. Moreover, component housing  630  can be substituted with a longer or shorter housing to accommodate more or fewer electrical components or to accommodate components of different sizes. Dummy components can be inserted to allow room for future additions. For example, a particular system may be adapted for use where no power supply is readily available by substituting a dummy component with a battery pack configured with connectors in accordance with the present invention. 
     System  600  can support a number of applications. In the embodiment of FIG. 6, System  600  includes a sensor  650  that may be attached to connector support  500  using any conventional connection method suitable for a given application. Sensor  600  may be, for example, an ion sensor for monitoring ground water, a thermometer, a microphone, a video camera, or any of a variety of other conventional transducers. In one embodiment, sensor  650  is a pH sensor for monitoring groundwater acidity or alkalinity, circuit module  620  is a differential amplifier configured to amplify an output signal from sensor  650 , and circuit module  610  is a transmitter that accepts signals from the amplifier and transmits those signals through cable  310 . 
     The order and orientation of the various modules can be critical to system function and to avoid damage. Some systems may therefore include modules that can only be installed in a particular orientation, thus ensuring that the systems cannot be assembled improperly. In one embodiment, for example, the wiring board  100 D of system  600  is smaller in diameter than wiring board  100 B so that circuit module  620  cannot contact wiring board  100 E should circuit module  620  be installed backwards. Other keying methods will be readily apparent to those of skill in the art. 
     The types of connections illustrated in FIG. 6 are illustrative and not limiting. For example, while only one conductive member  400  is shown, each pair of opposing wiring boards may be provided with some form of conductive member, or with no conductive member. Further, unless otherwise specified, each of the elements described in the foregoing Figures can be made from various materials and by various methods. For Example, end cap  315 , cable body  330 , and connector body  510  can be machined from a plastic, such as Delrin™. The selections of materials and manufacturing techniques, dictated chiefly by particular applications and economic considerations, are well within the ability of those of skill in the art. 
     While the present invention has been described in connection with specific embodiments, variations of these embodiments will be obvious to those of ordinary skill in the art. For example, 
     1. system  600  is not limited to sensor applications; 
     2. wiring board  100  may include a greater or lesser number of concentric conductors; 
     3. circuit modules, such as circuit modules  610  and  620 , can be made to snap together and to other modules and supports; and 
     4. connector support  300  may be used in conjunction with another similar connector body with or without intermediate electrical components. 
     Still other variations will be readily apparent to those of skill in the art. Therefore, the spirit and scope of the appended claims should not be limited to the foregoing description.