Patent Publication Number: US-6908310-B1

Title: Slip ring assembly with integral position encoder

Description:
FIELD OF THE INVENTION 
   The present invention relates to electromechanical couplers, and more particularly, to slip ring assemblies which are used to maintain multiple electrical connections through a rotating joint. 
   BACKGROUND OF THE INVENTION 
   In constructing various electromechanical devices there is frequently a need to transmit power and/or electrical signals from a stationary structure to a rotating structure. One well known example is a radar antenna that continuously rotates through three hundred and sixty degrees of motion. A special type of electromechanical connection is required in such cases, which is most often referred to as a “slip ring”, but it may also be called a rotary electrical joint, collector or electric swivel. Any electromechanical system that requires unrestrained intermittent or continuous rotation while also transmitting power and/or data can utilize a slip ring to great advantage. Typically in a slip ring a plurality of resilient, elongated metal or carbon conductors contact and slide over corresponding conductive contact rings. See for example U.S. Pat. No. 6,611,661 granted Aug. 26, 2003 of Buck. The design of a slip ring can improve mechanical performance of the system, and improve reliability by eliminating dangling wires that can break or become tangled. Fiber optic rotary joints (FORJ&#39;s) have also been specially designed for high-speed data transfer in EMI sensitive environments. While slip rings have been widely used for decades, little attention has been paid to improving their simplicity and versatility. Therefore, it would be desirable to provide an improved slip ring assembly that is more functional, cost-effective and reliable, and has improved features of use and operation. 
   In accordance with the present invention, a slip ring assembly includes a plurality of contact rings and means for supporting the contact rings in spaced relation about a common axis. A housing is located adjacent the contact rings and is configured to permit relative rotation between the contact rings and the housing about the common axis. A plurality of contact brushes each have a proximal end connected to means mounted to the housing for supporting a circuit. The circuit supporting means may include one or more printed circuit boards (PCBs) or it may be comprised of other circuit supporting structures. A distal end of each of the contact brushes is slidably engaged with a corresponding one of the contact rings. Optionally a signal generating portion of a position encoder may be mounted on the circuit supporting means. The position encoder has a reference portion that is mounted on the contact ring supporting means. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a functional block diagram of a video pipe inspection system incorporating the slip ring assembly of the present invention. 
       FIG. 2  is an exploded isometric view of an embodiment of the slip ring assembly of the present invention. 
       FIG. 3  is an isometric view of the slip ring assembly of  FIG. 2  in its assembled state taken from the front side. 
       FIG. 4  is an isometric view of the slip ring assembly of  FIG. 2  in its assembled state taken from the back side. 
       FIG. 5  is an enlarged longitudinal sectional view of the slip ring assembly of  FIG. 2  in its assembled state but otherwise taken along line  5 — 5  of  FIG. 2 . 
       FIG. 6  is a greatly enlarged side elevation view of one of the contact rings of the slip ring assembly of  FIG. 2  showing the V-shaped groove in its perimeter in which the distal ends of an opposing pair of contact brushes slide. 
       FIG. 7  is an enlarged transverse sectional view of the slip ring assembly of  FIG. 2  in its assembled state but otherwise taken along line  7 — 7  of  FIG. 2 . 
   

   DETAILED DESCRIPTION 
   There are many devices that can take advantage of our novel slip ring assembly. One of these is a video pipe inspection system that is used to provide a real time image of the inside of a buried tubular structure, search for defects, leaks or obstructions in drain pipes, water pipes, well casings, gas pipes, electrical conduits, and so forth. 
   Referring to  FIG. 1 , a video pipe inspection system  10  includes an elongate, resilient and flexible video push cable  12 . Examples of suitable video push cables are disclosed in U.S. Pat. No. 5,457,288 granted Oct. 10, 1995 to Mark S. Olsson and U.S. Pat. No. 5,808,239 granted Sep. 15, 1998 to Mark S. Olsson, the entire disclosures of which are hereby incorporated by reference. Both of said patents are assigned to DeepSea Power &amp; Light, the assignee of the subject application. The forward or distal end of the push cable  12  is operatively connected through an electromechanical termination assembly  14  to a video camera head  16  which includes a rugged generally cylindrical outer stainless steel housing with a hollow interior for enclosing a black and white or color video camera  17 . Further details of the termination assembly  14  are disclosed in the aforementioned U.S. Pat. No. 5,457,288. The video camera  17  includes an optical sensing device such as an array of charge-coupled-devices (CCDs) with adjacent color filter elements. The video camera head  16  further includes a camera circuit which receives the output of the CCD and generates a video image signal representing real time images of scenes viewed by the optical sensing device through a forward end of the video camera head  16 . The video camera head  16  may function with video systems employing EIA, NTSC, CCIR, PAL and other standard video signal formats. 
   A stainless steel coil spring  18  surrounds the push cable  12  and is coupled between the rear end of the video camera head  16  and the termination assembly  14 . The coil spring  18  could also be plastic with armor or some other suitable material. The coil spring  18  provides the desirable amount of flexibility to permit the video camera head  16  to negotiate tight turns in a pipe P being internally inspected. The pipe P is usually buried in the ground and typically includes at least one turn. Two stainless steel aircraft cables  19  or other suitable connecting hardware attach the video camera head  16  to the termination assembly  14 . The connection hardware extends longitudinally within the spring  18  and limits its extension. This facilitates removal of the video camera head  16  from the pipe P if it gets stuck. 
   The video camera head  16  is preferably dimensioned for insertion into pipes having internal diameters as small as two inches. With advancements in video camera miniaturization, the video camera head  16  can be designed to fit within pipes having internal diameters of one inch or less. A light source is mounted in the forward end of the video camera head  16  comprising a plurality of white LEDs (not illustrated). A large number of LEDs provides sufficient illumination for the color video camera  17 . The scene that is illuminated by the LEDs is the interior of the pipe P, including its interior walls and any objects or debris within the pipe. A plurality of red LEDs could be used in connection with red-spectrum sensitive CCDs incorporated in black and white camera systems. In some applications infrared LEDs may be suitable. Preferably the circuit that drives the LEDs has a feedback control so that the power dissipated by the LEDs does not cause excessive heat that would adversely affect the signal-to-noise ratio of the CCDs in the video camera. The video camera head  16  preferably has a fixed focus lens group consisting of lens elements (not illustrated) that provide a wide viewing angle with substantial depth of field, thereby eliminating the need for remote focusing in most applications. Preferably the video camera head  16  is constructed so that it is waterproof to a depth of at least three hundred and thirty feet and is capable of withstanding pressures of at least one hundred and fifty pounds per square inch (PSI). Further details of the video camera head  16  are found in co-pending U.S. patent application Ser. No. 09/506,181 filed Feb. 17, 2000 of Mark S. Olsson, also assigned to DeepSea Power &amp; Light, the entire disclosure of which is hereby incorporated by reference. 
   Optionally deformable plastic fins  24  ( FIG. 1 ) extend radially from the exterior of the video camera head  16  to centrally position and guide the camera head within the pipe P. The fins  24  or a dolly with wheels (not illustrated) are preferably releaseably coupled to the coil spring  18  via a unique C-shaped clamping arrangement disclosed in co-pending U.S. patent application Ser. No. 10/278,549 filed Oct. 22, 2002 of Eric Chapman et al., the entire disclosure of which is hereby incorporated by reference. Said application is also assigned to DeepSea Power &amp; Light. The push cable  12  may extend several hundred feet within the pipe P between the termination assembly  14  and a push reel  26 . The push reel  26  preferably comprises a roto-molded plastic annular body roughly similar in overall shape and size to an automobile tire. The push cable  12  is wound into continuous circular coils or turns inside the push reel  26 . Due to its resilience, the coils of the push cable  12  push radially outwardly and are restrained by the annular cylindrical wall of the push reel  26 . The push reel  26  is manually rotatable about a horizontal axis on a stationary frame (not illustrated) that supports the push reel  26  to pay out the push cable  12  from a circular central opening on one side of the push reel  26 . This forces the video camera head  16  down the pipe P. The push cable  12  must be pulled back out of the pipe P and pushed back inside the push reel  26  to withdraw the camera head  16 . 
   It is important for the video pipe inspection system  10  to be able to accurately measure the amount of push cable  12  that has been payed out or wound back to the push reel  26 . This allows breakages or blockages in the pipe P to be accurately located so that defective segment of pipe can be excavated and repaired or cleared with a snake, for example. An electromagnetic signal transmitter  27  ( FIG. 1 ) is mounted inside the coil spring  18  and powered via the push cable  12 . The transmitter  27  emits electromagnetic signals that can be detected by portable hand-held proximity locating equipment so that the location of the camera head can be tracked. An example of a hand-held portable locator is disclosed in co-pending U.S. patent application Ser. No. 10/308,752 filed Dec. 3, 2002 of Mark S. Olsson et al., the entire disclosure of which is hereby incorporated by reference. Said application is assigned to DeepSea Power &amp; Light. The transmitter  27  preferably includes a flexible bundle of high magnetic permeability material such as low carbon braided steel wire encased in electrical insulation material. This flexible bundle extends through a donut-shaped exciter coil. Further details of the transmitter  27  may be found in co-pending U.S. patent application Ser. No. 10/061,887 filed Jan. 31, 2002 of Mark S. Olsson et al., the entire disclosure of which is hereby incorporated by reference. Said application is assigned to DeepSea Power &amp; Light. 
   A plumber or other workman using the video pipe inspection system  10  may not have a portable hand-held locator available to him or may not be familiar with its operation. Moreover, accurate location of the video camera head  16  using a hand-held portable locator that detects electromagnetic signals emitted by the transmitter  27  may not be as accurate as desired or may be difficult where reception is poor. Therefore, the system  10  includes a position encoder (not illustrated in  FIG. 1 ) that detects the amount and direction of rotation of the push reel  26  relative to the stationary frame that supports the push reel  26 , for example, using quadrature encoding techniques. The amount and direction of rotation of the push reel  26  sensed by the position encoder can be used to calculate the amount of push cable  12  payed out of the push reel  26 . This in turn indicates the precise location of the video camera head  16  within the pipe P and thus the location of the obstruction, leak or defect in the pipe. Further details of the push reel  26 , its axle and support frame are disclosed in U.S. Pat. No. 6,545,704 granted Apr. 8, 2003 to Mark S. Olsson et al., the entire disclosure of which is hereby incorporated by reference. Said patent is also assigned to DeepSea Power &amp; Light. The video signal transmitted over the push cable  12  passes through a slip ring assembly (SLA)  28 , a portion of which rotates with the push reel  26  and another portion of which stays stationary with the frame that supports the push reel  26 . The slip ring assembly  28  allows video, power and ground conductors routed over the stationary frame to be connected through the axle of the push reel  26  to corresponding conductors in the push cable  12  at its proximal end. The slip ring assembly  28  permits these electrical connections to be maintained while the coil of the push cable  12  wound within the push reel  26  rotates around the axis of rotation of the push reel  26 . As hereafter described in detail, the position encoder is integrated into the slip ring assembly  28 . The video signal from the video camera  17 , and a signal generated by the position encoder, are processed by an electronic circuit  30 . Real time video images of the interior of the pipe P are shown on a display  32  with overlaid alphanumeric distance, time and date information, all of which are recorded on a video recorder (“VCR”) or other recording device such as a magnetic or optical disk drive. 
   Referring to  FIGS. 2 and 3 , the slip ring assembly (SRA)  28  includes a plurality of contact rings  34  and a cylindrical plastic slip ring body  36  ( FIGS. 2 ,  5  and  7 ) for supporting the contact rings  34  in spaced relation about a common axis  38 . A housing  40  ( FIG. 2 ) comprising mating shell halves  40   a  and  40   b  is located adjacent the contact rings  34  and is configured to permit relative rotation between the contact rings  34  and the housing about the common axis  38 . A plurality of contact brushes  42  each have an inner or proximal end connected to a printed circuit board (PCB)  44  that provides a means mounted to the housing  40  for supporting a circuit. The circuit supporting means may include one or more PCB or it may be comprised of other circuit supporting structures such as one or more flexible circuit boards, injection molded circuit boards, ceramic circuit boards, frames, dedicated connectors, etc. An outer or distal end of each of the contact brushes  42  is slidably engaged with a corresponding one of the contact rings  34 . The contact brushes may be made out of suitable electrically conductive metal or they can be made out of carbon. 
   Optionally a signal generating portion  46  of a position encoder may be mounted on the PCB  44 . The position encoder has a reference portion  48  that is mounted on the slip ring body  36 . The signal generating portion  46  of the position encoder is preferably a Hall effect sensor mounted on the PCB  44 . The reference portion  48  of the position encoder is preferably a magnetic ring Preferably the magnetic ring is made up of powdered magnetic material molded into the required cylindrical shape and magnetized to provide the needed resolution, for example, sixty-six circumferentially spaced magnetic domain regions. The Hall effect sensor detects the passage of the magnetic domain regions through a window or recess  49  formed in the shell half  40   a . Other forms of position encoder could be utilized such as a well known optical encoder having an emitter-detector pair mounted on the PCB  44  and a slotted disk mounted on the slip ring body  36 . The position encoder could also be provided in the form of a single magnet with a rotating reluctor or it could employ a ratiometric method such as a potentiometer, differential transformer, or optical analog system. However, it is believed at the present time that the combination of the Hall effect sensor and the magnetic ring are best suited for use in the pipe inspection system  10  which encounters substantial physical abuse, dirt, water and other harsh environmental effects. An indexing method can be employed so that the electronic circuit  30  can derive a zero degree position. 
   The shell halves  40   a  and  40   b  enclose the contact rings  34  and the reference portion  48  of the position encoder. The shell halves  40   a  and  40   b  are removably held together by upper and lower metal clips  50  and  52 . This allows the slip ring assembly  28  to be readily disassembled for maintenance or repair. The clasping function of the upper metal clip  50  relative to shell halves  40   a  and  40   b  is visible in  FIGS. 3 and 4 . The contact brushes  42  are arranged on opposite sides of the PCB  44  in two groups as illustrated in  FIG. 2 . The distal ends of opposing pairs of the contact brushes  42  ride in a V-shaped groove  34   a  ( FIG. 6 ) formed in the outer perimeter of a common one of the contact rings  34 . The contact brushes are resilient and apply a spring force to their corresponding contact rings  34 . Thus each contact ring  34  is lightly squeezed between an opposing pair of the contact brushes  42  to ensure a positive electrical connection with the contact ring  34 . The contact rings  34  are preferably made of a material consisting of ninety-five weight percent Silver and five weight percent graphite for improved lubricity. 
   A male portion  54  of an electrical connector is mounted on the PCB  44 . A female portion  56  of the electrical connector can be mated with the male portion  54 . Suitable electrical connectors of the type illustrated are commercially available under the trademarks AMPS, BERG®, MOLLEX® and others. Conductive traces (not illustrated) formed on the PCB  44  electrically interconnect separate corresponding prong conductors in the male portion  54  of the electrical connector to the signal generating portion  46  of the encoder and the proximal ends of each of contact brushes  42 . This allows the power, ground and video signals to be routed through corresponding ones of the contact rings  34  to insulated wire leads  58 ,  60  and  62 . Each of the contact rings  34  has an electrical contact clip  64  soldered or otherwise bonded thereto for electrically connecting the wire leads  58 ,  60  and  62  ( FIG. 2 ) and the connections are protected via shrink tube segments  66 . 
   Wire wings  68  and  70  ( FIGS. 3 and 4 ) have their inner hooked portions  68   a  and  70   a  retained in corresponding recesses molded into the shell halves  40   a  and  40   b . The outer portions  68   b  and  70   b  of the wire wings  68  and  70  are held in molded recesses in the push reel  26  (not illustrated) to cause relative rotation between the contact rings  34  and the contact brushes  42  when the push reel  26  is rotated on its support frame. The engagement of the wire wings  68  and  70  with the push reel  26  similar causes relative rotation of the Hall effect sensor relative to the magnetic ring when the push reel  26  is rotated on its support frame. See  FIGS. 4–6  of U.S. Pat. No. 6,545,704 for illustrations of the configuration of tire-shaped the push reel  26 . A plurality of ring spacers  72  are carried on the slip ring body  36  on opposite sides of the contact rings  34 . The ring spacers  72  are preferably made of dielectric material with good electrical insulating properties and low friction, such as Nylon® plastic. The contact brushes  42  are prevented from touching any other contact rings  34  besides their assigned contact ring by the ring spacers  72  as can best be seen from  FIGS. 5 and 7 . A top ring spacer  74  is mounted about the slip ring body  36  towards one end thereof and a cylindrical end cap  76  is mounted about the slip ring body  36  towards the other end thereof. The top ring spacer  74  and the cylindrical end cap  76  are also made of a suitable dielectric material, such as Teflon® filled acetal sold under the trademark Delrin AF®. 
   While we have described an example of our slip ring assembly  28  in detail, and one suitable system  10  in which it can be used to advantage, it should be apparent to those skilled in the art that our invention can be modified in both arrangement and detail. Therefore the protection afforded our invention should only be limited in accordance with the following claims.