Patent Publication Number: US-6663395-B2

Title: Electrical joint employing conductive slurry

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to electrical circuits. More specifically, the present invention relates systems and methods for coupling electrical signals and current between objects that move relative to one other. 
     2. Description of the Related Art 
     In many devices, electrical signals are coupled between rotating objects, or between objects that move relative to one another. A classic example is the commutator and brush arrangement used in electric motors and generators. Typically, the commutator is formed as plural conductive cylindrical rings insulatively supported about an armature shaft that rotates together with armature windings. The commutator rings are electrically coupled to the armature windings. The brushes are held in a fixed position relative to the motor frame, or stator windings, and are typically urged toward the commutator rings by spring force. The brushes rotatably engage the commutator rings so as to enable the flow of electric current between the fixed position brushes and the rotating commutator rings, which couple the current to the armature windings. Depending on the type of motor or generator involved, the brushes may be electrically coupled to the stator or field windings or the brushes may be coupled to an external circuit, such as a power supply. 
     Of course, those skilled in the art will appreciate that there are a great variety of systems and circuits that require the coupling of electric current, or electrical signals, between movably related objects. The relative movement between objects is frequently rotational, however, linear and other non-linear relative movements are also encountered from time to time. Consider the amusement park bumper car. The floor area is at a first electrical potential and the ceiling area is at another potential. A first “brush” engages the floor surface and second “brush” is coupled to a pole and extends upwardly to engage the ceiling surface. Since the floor and ceiling are at different electrical potentials, the bumper car is enabled to draw electric current to operate its lights and motor. The motion of the bumper car is constrained within a plane parallel to the floor, but is otherwise random in nature. Of course, there are numerous other examples of considerably more sophisticated systems that require the moveable coupling of electric current and signals between objects. 
     An example of a sophisticated system that utilizes the moveable coupling of is electric signals is the airborne radar system deployed in various aircraft. For example, an F-15 fighter aircraft employs a tactical radar system deployed within its nose cone. The radar comprises a phased array antenna that forms a narrow radio beam in both of the transmit and receive modes of operation. In order to enable wide-angle radar coverage, the radar antenna is mounted on gimbals that enable the antenna, and therefore the radar beam, to be mechanically steered by servo-actuators. To enable the coupling of electric signals and power between the moveable antenna and other circuits fixed relative to the F-15 airframe, an electromechanical contact arrangement is employed. In many ways, this contact arrangement is not unlike the classic commutator and brush arrangements discussed above. Basically, two solid conductors are held in physical contact as they move relative to one another so as to maintain electrical continuity therebetween. 
     There are a number of problems associated with the conventional electromechanical coupling of signals through a commutator and brush arrangement. The effect of the brush dragging on the commutator causes friction. The friction produces heat and causes wear of the brush and commutator surfaces. The heat changes the electrical characteristic of the coupling, in particular altering the resistivity of the coupling. The wear implies that maintenance will ultimately be required. The electromechanical coupling is not perfect and thus is a source of electrical noise during operation. The noise results from variations in the quality of the signaling coupling. In extreme cases, arcing and loss of signal coupling can occur. Noise problems tend to increase as the mechanical components wear. This noise degrades the signal to noise ratio of the coupled signal, and can interfere with reliable operation. The noise created by electromechanical couplings can also radiate to interfere with other devices. In some circumstances, the noise power bandwidth may interfere with radio frequency devices causing other system&#39;s reliability of be reduced. 
     Thus there is a need in the art for an apparatus for transferring electrical signals and electrical power between objects moveably related to one another, which improves reliability, reduces noise, minimizes coupling resistance, and allows flexible application in a variety of technologies. 
     SUMMARY OF THE INVENTION 
     The need in the art is addressed by the electrical joint of the present invention. The inventive electrical joint includes a first object that is moveably aligned with a second object. A conductive slurry is deposited upon a first surface of the first object, and a conductor is coupled to the second object and is aligned to maintain conductive coupling with the conductive slurry while the first object and the second object move relative to one other. 
     In a specific embodiment, the conductive slurry may comprise metallic particles suspended in a fluid. The metallic particles may be silver or copper. The first object may be formed from an insulator, such as polymide. 
     In a specific implementation of the foregoing invention, a non-conductive is disposed upon the exposed surface of the conductive slurry, and the conductor extends through the non-conductive gel to maintain the conductive coupling. The non-conductive gel may be hydraulic vacuum oil. In a further refinement, the conductive slurry is disposed within a channel of the first surface, and, the channel is positioned to maintain alignment with the conductor as the objects move relative to one another. The channel may be defined by a groove formed in the first surface or by built-up material extending from the first surface. The coupling of electrical signals is accomplished with a conductive coating disposed upon the first surface at a position to electrically couple the conductive slurry to the conductive coating. The conductive coating may be electroplated to the first surface. 
     In one embodiment, the first surface is substantially planar and the objects are constrained to move parallel to the first surface. In a second embodiment, the first object and the second object are moveably aligned about an axis or rotation, and, the first surface is cylindrical, having a centerline aligned with the axis of rotation. The conductor is a conductive blade that extends radially from the second object to maintain conductive coupling with the conductive slurry as the first object and the second object rotate with respect to one another. The blade may be a conductive disk. In a third embodiment, the first surface is planar and the second object is moveably aligned to rotate about an centerline extending perpendicular from the first surface, and the conductive slurry is disposed along a circular path defined by the movement of the conductor as the first object and the second object rotate with respect to one another. The conductor may be a conductive dowel extending from the second object to engage the circular path of conductive slurry. To improve reliability, the conductor may include a plurality of dowels extending from the second object and located at positions about a circle such that all of the dowels engage the circular path of conductive slurry. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a section view of the outer portion of an axially rotating electrical joint in an illustrative embodiment of the present invention. 
     FIG. 2 is a perspective view of the inner portion of an axially rotating electrical joint in an illustrative embodiment of the present invention. 
     FIG. 3 is a section view of a multiple conductor rotary electrical joint according to an illustrative embodiment of the present invention. 
     FIG. 4 is a detail view of a single conductive blade. 
     FIG. 5 is a section view of a single channel for receiving conductive slurry. 
     FIG. 6 is a section view of a single channel and it corresponding conductive blade with conductive slurry and non-conductive gel in place. 
     FIG. 7 is a perspective view of a planar electrical joint in an illustrative embodiment of the present invention. 
     FIG. 8 is a perspective view of a first mating piece in a planar rotating electrical joint in an illustrative embodiment of the present invention. 
     FIG. 9 is a perspective view of a second mating piece in a planar rotating electrical joint in an illustrative embodiment of the present invention. 
     FIG. 10 is a section detail of a single groove in a planar rotating electrical joint in an illustrative embodiment of the present invention. 
     FIG. 11 is a section view of a planar rotating electrical joint in an illustrative embodiment of the present invention. 
    
    
     DESCRIPTION OF THE INVENTION 
     Illustrative embodiments and exemplary applications will now be described with reference to the accompanying drawings to disclose the advantageous teachings of the present invention. 
     While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility. 
     The present invention teaches a novel apparatus for coupling electrical signals and current between moveably aligned objects. As noted herein before, the relative movement between two conductive circuits is at the center of the problem known in the prior art. The present invention overcomes the problem in the prior art by employing a conductive slurry, a fluid (or semi-fluid), at the point of relative movement between two objects. 
     According to the present invention, each object has a conductor or conductive material in contact with the conductive slurry. A circuit is formed from a conductor aligned with a first object, through the conductive slurry, and to a conductor aligned with the second object. As the objects move relative to one another, the conductive slurry accommodates the movement while continuously maintaining conductivity through the circuit. The conductive slurry employed in the illustrative embodiment is a mixture of solid metal particles in a fluid-carrying agent, which may be oil, for example. The oil is selected to meet operating requirements, which may include temperature swings from minus forty degrees Celsius to plus eighty degrees Celsius. The fluid-carrying agent may have conductive properties in and of itself. The slurry, being a fluid, creates less friction between the two objects moving relative to one another than would two solid objects physically engaging one another. Lessening friction reduces heat generated in the electrical joint, and greatly reduces mechanical wear of the conductive components. In the prior art, when two solid objects where slideably engaged to conduct current across a moveable joint, the objects rubbed together generating heat and causing the materials to deteriorate. By application of the teachings of the present invention, there is a reduction in friction and a corresponding reduction in heat. Thus, the present invention overcomes the friction and heat build-up problems in the prior art and extends the life of the electrical joint. The reduction in friction also results in a reduction in the amount of energy required to move the objects relative to one another and consequently makes the present invention electrical joint system more efficient. 
     The conductive slurry taught in the present invention is comprised of conductive particles suspended in a fluid-carrying agent. Many conductive particle materials can be employed, including metals such as gold, silver, copper, aluminum, iron, other metals, or alloys of such metals. Non-metals may also be employed, such as graphite or semi-conductive materials, for example. Those skilled in the art will appreciate the any particulate material that possesses conductive or semi-conductive properties could be employed in the present invention. The selection of a suitable particulate material is constrained by the circuit conductivity requirements, empirical performance tests, and cost. The ratio of particulate material to carrying agent (called a slurry ratio) is determined in part by the resistivity requirements and current carrying requirements of the circuit application. The slurry ratio may also be varied according to environmental factors, such as heat, humidity, vibration, etc. The carrying agent may be any of a variety of fluids or semi-fluids. In an illustrative embodiment, an oil with wide temperature specifications is employed. 
     It is beneficial to protect the exposed surface of the conductive slurry, as this will extend the useful life of the moveable coupling. Such protection prevents the movement and dissipation of the conductive slurry from its desired position. To achieve this improvement, the present invention teaches that mechanical structure and arrangements in the relative position of objects can be used to retain the conductive slurry. Also, a non-conductive gel is applied to cover and retain the conductive slurry. 
     Reference is directed to FIG.  1  and FIG. 2, which depict first and second objects, respectively, that are combined to form a rotary electrical joint according to an illustrative embodiment of the present invention. FIG. 1 is a section view of the outer cylindrical portion  2  of the rotary electrical joint. The cylinder  2  is fabricated from a non-conductive material. The cylinder has a bore hole  5  aligned with and centered on the axis of the cylinder  2 . The bore hole  5  provides clearance for a shaft, discussed below. An annular channel  3  is formed inside the cylinder  2  as an extension of the bore hole  5  opening. At the outer periphery of the annular channel  3  is an enlarged annular cavity  4 . The aforementioned conductive slurry  10  is disposed within the annular cavity  4 , and may extend somewhat into the annular channel  3 . The conductive slurry  10  has an exposed surface in the area of the annular channel  3 . The exposed surface of the conductive slurry  10  is covered with the aforementioned non-conductive gel  12 , which serves to protect, retain, and isolate the conductive slurry  10 . A portion of the annular cavity  4  surface is plated with a conductive material  16 , which is conductively coupled to a conductor  14 . Since the conductive slurry  10  contacts the plated surface  16 , and the conductor  14  is coupled to plated surface  16 , the conductive surface is effectively coupled to conductive slurry  10 . 
     The second object of the conductive joint is depicted in FIG. 2. A shaft  8 , which is preferably fabricated from a non-conductive material, has a conductive blade  6  affixed thereto. Alternatively, the shaft  8  can be fabricated from a conductive material, but with an insulative connection to the conductive blade  6 . A conductor  18  passes through the shaft  8  and is electrically coupled to conductive blade  6 . The shaft  8  and blade  6  assembly is placed into bore hole  5  of cylinder  2 . The conductive blade is aligned with annular channel  3  and annular cavity  4 . The conductive blade extends far enough along its radial dimension from shaft  8  so that the blade  6  passes through the non-conductive gel  12  to engage the conductive slurry  10  disposed within annual cavity  4 . The assembly of these two objects provides for the conduction of electric current and signals through conductor  14 , through the plated surface  16 , through the conductive slurry  10 , through the conductive blade  6 , and through conductor  18 . As the objects rotate with respect to one another, the continuous conduction of electric current and signals is maintained. 
     Reference is directed to FIG. 3, which is a section view of a multiple conductor rotary electrical joint according in an illustrative embodiment of the present invention. Both objects, or halves of the joint, are depicted in the section view of FIG. 3. A shaft  82  is coupled to two bearing supports  84  and  88 , which are rotatively coupled to tube  80  by ball bearings  86  and  90 . Thus, the shaft  82  is free to rotate with respect to tube  80  by virtue of ball bearings  86  and  90 . Disposed along the length of shaft  82  are six conductive blades  96 . In the illustrative embodiment, the blades  96  are in the shape of disks. The blades  96  are rigidly and insulatively connected to shaft  82 . Within tube  80  is an insulative cylinder  92 , which is supported by tube  80 . The inside cylindrical surface of insulative cylinder  92  has six annular channel recesses  94  formed therein. The annular channel recesses  94  are sized and positioned to encompass, but not to interfere with, the rotational movement of the conductive blades  96 . Each annular recess has a plated portion (not shown) on its inside surface, each of which has a conductor  100  conductively coupled thereto. Each of the conductive blades  96  has a conductor  98  conductively coupled thereto. Conductors  98  are routed through the center of shaft  82 . Each of the annular recesses  94  is filled with a conductive slurry (not shown), which is protected by a non-conductive gel (not shown). The physical arrangement of the slurry and gel, as well as specifics about the configuration of annular channel recesses  94 , are more fully described with respect to FIG.  5  and FIG. 6 below. In FIG. 3, electric signals and current are rotatively coupled by conduction through conductors  98 , through conductive blades  96 , trough the conductive slurry (not shown), through the plated surface portion (not shown), and through conductors  100 . In this fashion, multiple electrical signals can be rotatively coupled through a single axis or rotation by utilization of the teachings of the present invention. 
     FIGS. 4A and 4B are detailed views of a conductive blade as employed in the illustrative embodiment in FIG.  3 . FIG. 4A is a side view of the conductive blade  96 , and FIG. 4B is an end view of conductive blade  96 . The blade  96  is circular and fabricated from a conductive metal, such as copper for example. The blade  96  has a hole  102  formed at its center to allow passage through and coupling of the support shaft (Item  82  in FIG.  3 ). The conductor  98  is conductively coupled to blade  96 . In the illustrative embodiment, the conductor  98  is an insulated copper wire that is soldered to conductive blade  102 . 
     Reference is directed to FIG. 5, which is a section detail of a portion of insulative cylinder  92  at a single annular channel recess  94 , as described with reference to FIG. 3, above. FIG. 5 also serves to illustrate a fabrication approach applicable in the illustrative embodiment for forming the annular channel recess  94 . In particular, the insulative cylinder  92  is comprised of an inner insulative cylinder  104  and an outer insulative cylinder  106 . The outer cylinder  106  has six annular channel recesses  112  formed on its inside surface. The inner cylinder  104  has six annular recesses  110  of material removed through its periphery. The width of annular recess  110  is smaller than the width of annular channel  112 . When the two cylinders  106  and  104  are combined, an annular channel recess  94 , as illustrated, is formed. The outer cylinder  106  has a conductive material  108  plated to the inside surface of annular channel recess  112 . A conductor  100  passes through the outer wall of outer cylinder  106  to allow coupling of electric signals and current to the conductive plating material  108 . 
     FIG. 6 is a section detail of a portion of insulative cylinder  92  at a single annular channel recess  94  with the conductive slurry  114 , the non-conductive gel  116 , and the conductive blade in place  96 . The conductive slurry  114  is disposed within the wider portion  112  of annular channel recess  94 . The conductive blade  96  extends into this area  112  as well. Electric current is coupled from the conductive blade  96 , though the conductive slurry  114 , to the plated surface  108 . The plated surface  108  is conductively coupled to conductor  100 , as was described above. A non-conductive gel  116  is disposed within the narrower portion  110  of annular channel recess  94 . As was described herein before, the non-conductive gel  116  serves to protect, retain, and isolate the conductive slurry  114 , while allowing the conductive blade  96  access to the conductive slurry  14  while the shaft  82  and cylinder  80  rotate with respect to one another. 
     Reference is directed to FIG. 7, which is a perspective view of an electric joint according to an illustrative embodiment of the present invention in which two objects move relative to one another, but are constraint to move within a two dimensional planar area. A first object  22 , that is made of a non-conductive material, has a substantially planar surface  24 . A conductive slurry  26  is disposed upon surface  24  along a path that is defined by the movement through which the planar motion of the joint will occur. For example, this may be the path defined by a cam-follower mechanism. A channel recess may also be formed into surface  24 , and may include a layer of non-conductive gel, as is described with respect to the other embodiments herein. In FIG. 7, a conductive dowel  27  extends from a second object (not shown) and is aligned to make physical contact with the conductive slurry  26 . A conductor  29  is moveably and electrically coupled with the conductive slurry  26  at connection point  28 . A conductor  21  is electrically connected with the dowel  27  at connection point  23 . The alignment is such that with relative movement, the dowel remains in physical contact with the conductive slurry  26 , which in turn provides an electrical joint. Those skilled in the art will appreciate that multiple conductive paths, or circuits, can be laid out in parallel on surface  24 , with corresponding multiple dowels, so that multiple conductor circuits can operate. In a further comprehension, those skilled in the art will appreciate that non-planar motion can also be accommodated through utilization of the teachings herein. In fact, any repetitive circuit of motion can be adapted to the teachings herein. 
     Reference is directed to FIG. 8, FIG. 9, FIG. 10, and FIG. 11, which illustrate components and details of an illustrative embodiment of the present invention as applied to a rotary joint having an axis or rotation substantially perpendicular to two planar surfaces. FIG. 8 depicts, in perspective, a first object  30  that is fabricated from a non-conductive material. The material may be polymide or other suitable printed circuit or printed wire board material as are known to those skilled in the art, for example. Surface  32  is substantially planer and is formed as a circle. Object  30  has a circular opening  36  formed near the center of the surface  32 . Conductive rods extend from surface  32  along several radii from the center of surface  32 . The rods are affixed to the object  30  by soldering each to a plated-through hole (not visible). Plated-through holes are known to those skilled in the art. In particular, four conductive rods  31  are place at ninety-degree increments and at equal distance from the center of object  30 , and the center defines the axis of rotation of the illustrative embodiment rotary joint. As such, each of the four rods  31  follow the same circumferential path as the object  30  rotates about it center. Similarly, each of the four rods  33  are placed at ninety degrees and at equal distance from the center. Each of the four rods  34  are placed at ninety degrees and at equal distance from the center. Each of the four rods  35  are placed at ninety degrees and at equal distance from the center. Thus, four circular paths are defined by the sixteen rods  31 ,  33 ,  34 , and  35 . In the illustrative embodiment, object  30  is fabricated from an insulator. It will be appreciated by those skilled in the art that an insulator is chosen for the purpose of electrically isolating each of the rods from one another. This is done so that they may be utilized as individual conductive elements is circuit. The object  30  could be fabricated from a conductive material, however, this would require that the conductive rods be supported using some other insulative technique. 
     FIG. 9 illustrates, in perspective, the second object  46  that is used in conjunction with the foregoing object  30  to embody a rotary electrical joint in an illustrative embodiment of the present invention. The second object  46  is fabricated from a non-conductive material, such as polymide or other suitable printed circuit or printed wire board material as are known to those skilled in the art, for example. The second object  46  has a surface  48  that is substantially planer. Four circular channels  39 ,  41 ,  43 , and  50  are formed within surface  48 . The center of the circular channels define the axis of rotation of the rotary electrical joint in the illustrative embodiment. A circular opening is formed at the center of the surface  48  through object  46 . The radii of the four circular channels  39 ,  41 ,  43 , and  50  correspond to the four radii defined by the placement of conductive rods  31 ,  33 ,  34 , and  35  respectively. 
     It will be appreciated that four conductive dowels will engage each circular channel when the first object  30  and the second object  46  are aligned by the aforementioned axis of rotation with their respective planar surfaces  32  and  48  in close proximity. As will be discussed more fully below, each circular channel has conductive slurry disposed therein. This arrangement provides that four dowels are electrically coupled to each circular channel that is filled with conductive slurry. This provides multiple paths for the electrical signal or current coupled between the two objects. By using this technique, better performance of the rotary electrical joint is achieved both in terms of reliability and current carrying capability. Those skilled in the art will appreciate that any number of conductive dowels could be paralleled in this fashion to meet design objectives. 
     FIG. 10 is a section view of the second object  46  at circular channel  50  discussed respecting FIG.  9 . In FIG. 10, the second object  46  has circular channel  50  formed therein. Within the circular channel  50  is disposed a conductive slurry  58  of the similar type descried herein before. A non-conductive gel  60  is disposed upon the exposed surface of the conductive slurry  58 . The bottom of circular channel  50  is plated with a conductor  62  that passes through second object  46  and is electrically coupled to printed circuit conductor  64 . Each of the other circular channels  39 ,  41 , and  43  are structured in the same way. 
     FIG. 11 illustrates a section view showing both the first object  30  and the second object  46  when they are aligned about their axis of rotation. The planar surfaces  32 ,  48  in such proximity that the conductive dowels  31 ,  33 ,  34 , and  35  engage the conductive slurry disposed within the circular channels  39 ,  41 ,  43 , and  50  respectively. Further details of the assembly and circuit coupling also appear in FIG.  11 . The first object  30  has a support bearing  61  that allows the first object  30  to rotate about its axis. The plurality of conductive dowels  31 ,  33 ,  24 , and  35  are supported by the first object  30  and extend from the first planar surface  32 . The conductive dowels are electrically coupled to a plurality of printed circuit traces  63  that route electrical signals and current from the conductive dowels to a junction point  70 . The junction point  70  serves to couple the printed circuit traces  63  to a plurality of conductive wires  66 . Such junction points  70  are known to those skilled in the art. The second object  46  comprises the aforementioned circular channels  39 ,  41 ,  43 , and  50  disposed upon the second planar surface  48 . The second object  46  has a support bearing  65  that allows the second object  46  to rotate about its axis. Each of the circular channels are filled with conduct slurry, covered by non-conductive gel, as was described in reference to FIG.  10 . In FIG. 11, a plurality of printed circuit traces  64  coupled the plated bottom of each circular channel to a junction point  72 . The junction point  72  serves to couple the printed circuit traces  64  to a plurality of conductive wires  68 . Such junction points  72  are known to those skilled in the art. 
     When first object  30  and second object  46  oriented in the position illustrated in FIG. 11, and installed on a common shaft (not shown) inserted through opening  36  and opening  52 , the two objects are free to rotate with respect to one another. Surface  48  and surface  32  are positioned together to allow the plurality of conductive dowels to engage the conductive slurry as the two object rotate. The plurality of dowels pass through the non-conductive gel  60  into the conductive slurry  58 . As the objects rotate relative to one another the plurality of dowels remain in contact with the slurry, thereby enabling the conduction of electric signals and current as the object rotate. 
     Thus, the present invention has been described herein with reference to a particular embodiment for a particular application. Those having ordinary skill in the art and access to the present teachings recognizes additional modifications applications and embodiments within the scope thereof. 
     It is therefore intended by the appended claims to cover any and all such applications, modifications and embodiments within the scope of the present invention. 
     Accordingly,