Abstract:
A rotary connector assembly for an electrical apparatus on a rotating component is presented. The rotary connector assembly has a fixed base for mounting the assembly within the rotating component. The rotary connector assembly is rotatable relative to the rotating component. The attachment has an annular flange at the outer periphery and a mechanism that contacts the flange and supports the rotary connector portion. Connections at the base have terminations to attach incoming wiring and at the rotary portion to attach wiring to the electrical apparatus.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS  
       [0001]    This patent application claims the benefit of U.S. Provisional Patent Application No. 60/346,855, filed Jan. 10, 2002. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention pertains to electrical connections, and more particularly relates to electrical rotary connectors.  
         BACKGROUND OF THE INVENTION  
         [0003]    Slip rings are used in a variety of applications to transfer electrical signals, including power signals, between components where one component rotates in relation to another component. One application where slip rings are used is in magnetic chucks to transfer power from the stationary frame of the magnetic chuck to the magnetic chuck rotating assembly. The slip ring is typically composed of a metal ring upon which a graphite material brush (and the like) rubs and transfers the signal. The metal ring or the graphite material brush rotates. FIG. 6 illustrates a typically slip ring assembly  10 . The brush  12  is placed in a sleeve of a brush holder  14 . The brush  10  is in electrical contact with brush connection  16  and a wire assembly  18  is connected to the brush connection  16 . During operation, the brush contacts a conductive metal ring  20 . A connection point  22  is attached to the ring  20  and wire leads  24  are connected to the connection point. As the ring  20  or brush  12  rotates, the brush  12  rubs against the ring  20  and signals are transferred across the brush/ring interface  26 . The ring  20  and/or the brush  12  is connected to a rotating member of a device (not shown).  
           [0004]    The operation of the slip ring is technically simple. However, there are a number of problems with slip rings in magnetic chuck applications. The brush wears down over time, which leads to degradation in the efficiency of transferring power and degradation of signal quality. Additionally, the brush and metal ring typically have high resistance, which results in power loss due to I 2 R heating losses. The resistance varies due to oxidation and other factors, which increases power losses and the fluctuations causes electrical noise. Additionally, the slip rings may need high levels of maintenance to remove the debris causes by the wear of the brushes and to replace the brushes. Other problems include electrical arcs that are produced as the slip ring assembly rotates. The arc, in combination with other factors, can lead to demagnetization problems with the magnetic chuck.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    The invention provides brushless rotary connector for use in magnetic chuck applications and the like. The rotary connector uses a housing having a sealed metal fluid with sliding contacts capable of handling high current levels. During rotation, the fluid maintains the electrical connection between the contacts without any wear, and the use of the liquid metal as a conduction path offers an extremely low resistance connection that is constant.  
           [0006]    The housing is mounted in a base that serves as a support for the housing and for connections to the stationary component. The rotating member of the rotary connector is connected to a ring that is attached to the rotating member of the magnetic chuck. This connector is a simple, low cost and highly reliable connector. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    While the appended claims set forth the features of the present invention with particularity, the invention, together with its objects and advantages, may be best understood from the following detailed description taken in conjunction with the accompanying drawings of which:  
         [0008]    [0008]FIG. 1 is a block level diagram illustrating the rotary connector of the present invention;  
         [0009]    [0009]FIG. 2 is an isometric view of the rotary connector of the present invention with the yoke removed;  
         [0010]    [0010]FIG. 3 is an isometric view of the rotary connector of the present invention inserted onto the yoke;  
         [0011]    [0011]FIG. 4 is an exploded isometric view of the rotary connector of the present invention;  
         [0012]    [0012]FIG. 5 is an isometric view of the rotary connector of the present invention installed in a rotary table housing; and  
         [0013]    [0013]FIG. 6 is a view illustrating a simplified slip ring assembly.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    Turning to the drawings, wherein like reference numerals refer to like elements, the invention will be described in an environment of a magnetic chuck such as those used in grinding operations. The rotary connector eliminates the “wear and replace” cycle of slip rings. FIG. 1 is a simplified schematic illustrating the elimination of brushes. The rotary connector  100  provides a connection through a conductive liquid film between contacts that rotate with respect to each other. One contact is in the top portion  102  of the rotary connector  100  and the other contact is in the bottom portion  104  of the rotary connector. Connection points  106 ,  108  provide one or more connections to wires, bus bars, etc.  
         [0015]    Turning now to FIGS.  2 - 5 , the rotary connector of the present invention is a brushless design incorporating sealed liquid contacts capable of handling high current levels in a superior manner to the traditional brush and slip ring method. The base  120  is a fixed or stationary support for the rotary connector main body  122  located in the center cavity  124  that is concentric to the rotary table housing  200  and associated electrical apparatus. The base in made of a hard plastic in one embodiment. The rotary connector main body  122  may be press fit or held in place via a set screw  125 . The electrical apparatus in this case are conductors  202 ,  204  comprised to make a magnetic chuck. The base  120  also supports wire terminals  126 ,  128  for a power source (not shown) to provide power to the rotary connector  100 . Wires or bus work  130 ,  132  connect the wire terminals  126 ,  128  to connection points  134 ,  136  of the rotary connector main body  122 . The connection points  134 ,  136  are connected to the contact within the bottom portion of the rotary connector main body  122 .  
         [0016]    A rotating base  138  fits over the rotating portion of the rotary connector main body  122 . The rotating base  138  has a hole  140  in which the rotating portion of the rotary connector main body  122  fits within. Wires  142 ,  144  are used to connect the electrical apparatus (e.g., conductors  202 ,  204 ) to the connections  146 ,  148  on the rotation portion of the rotary connector main body  122 . Bus bars may also be used. The connection points  146 ,  148  are connected to the contact within the top portion of the rotary connector main body  122 . Any type of wire connection may be used. For example, wire crimp lugs, self-contained splices, twist-locks, etc. The rotating base  138  supports legs  150 ,  152 , which are used to provide support and orient the rotating base  138  with respect to a yolk  154  (e.g., annular flange). While FIGS.  2 - 5  illustrate the rotating base  138  covering the connections  146 ,  148 , those skilled in the art will recognize that the rotating base  138  may be smaller than the height of the rotating portion of the rotary connector main body  122 . This provides easy access to the connections  146 ,  148 .  
         [0017]    The yolk  154  attaches to the collector ring or table housing of the rotating component such as the magnetic chuck. The set of legs  150 ,  152  are attached to the rotating base  138  and extend out into access holes  156 ,  158  to engage the yolk  154 . It should be recognized that a plurality of sets of legs may be used. The rotating base  138  is made of plastic or other types of soft or hard material that provide support for the legs  150 ,  152  and wire/bus bars  142 ,  144 . The legs  150 ,  152  may be bar stock, hard plastic, bolts, etc. The yolk  154  may be plastic, fiberglass, a mold, etc. The yolk  154  is connected and enable the connector to table rotation. Set screws  160 ,  162  are used to secure the yolk  154  to the collector ring  206  (e.g., housing of the rotating component) of the rotating component  200  via threaded holes  164 ,  166  in the yolk  154 . Bolts (now shown) are used to connect the base  120  to a fixed support in the stationary component (e.g., fixed table support of a magnetic chuck). The bolts are placed within bored holes  170 ,  172  to mount the base  120  to the fixed support. The bored holes  170 ,  172  have a seat for bolt head.  
         [0018]    During operation, as the rotating component moves, the yolk  154  moves. The set of legs  150 ,  152  rotate as a result of the yolk  154  rotating. As a result, the rotating portion of the rotary connector main body  122  moves, thereby moving one of the contacts within the rotary connector main body  122 . The conductive liquid film between the contacts in the rotary connector main body  122  maintains electrical connection as the contacts rotate with respect to each other.  
         [0019]    In a preferred embodiment, the rotary connector  122  is manufactured by Mercotac, Inc. of Carlsbad, Calif. The connection in the Mercotac connector is made through a pool of liquid metal molecularly bonded to the contacts, and it provides a low resistance, stable connection. When there is rotation the fluid maintains the electrical connection between the contacts during rotation of either the upper portion or lower portion of the connector.  
         [0020]    It can be seen that the rotary connector assembly of the present invention provides an economical way to provide power and/or electrical signals to a rotating component without having to use brushes. This eliminates the wear and replace cycle of brushes. The use of the legs and annular flange allows the rotary connector assembly to be used in rotating elements that has opening significantly larger than the size of the rotary connector. All that is needed to go from one size opening to another size opening with the same power rating and/or signal rating is to use a longer leg and larger annular flange. The further reduce cost, the legs may come in a standard size and cut to fit the application. The use of the legs also allows the base to be offset (i.e., non-concentric) from the center of the opening of the rotating component by adjusting the length of individual legs. This allows the rotary connector assembly to be used in situations where the mounting surface for the base is offset from the center of the opening of the rotating element.  
         [0021]    All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.  
         [0022]    The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.  
         [0023]    Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.