Patent Publication Number: US-2012043850-A1

Title: Electrical rotary joint

Description:
This application claims priority of U.S. Provisional Patent Application No. 61/376,081 filed date: Aug. 23, 2010. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to an electrical rotary joint, or electrical slip ring, and more particularly to an apparatus having a plurality of conductive gears to transfer electrical power, and/or signal(s) between relatively rotatable objects. 
     BACKGROUND OF THE INVENTION 
     Electrical rotary joints, or electrical slip rings are electromechanical devices that consist of rotational (rotors) and stationary (stators) members. They allow the transmission of electrical signals and power from their rotors to stators or vise verse. 
     A conventional electrical slip ring consists of conductive rings mounted on a rotor and insulated from it. Fixed brushes run in contact with the rings, rubbing against the peripheral surfaces of the rings, transferring electrical power or signals to the stator. 
     The sliding contact between the rings and brushes during this continuous rotation of the rotor causes the wear on the slip rings and generate heat, even noise in the system. Therefore, even properly operating slip rings require frequent maintenance at significant cost. Sometimes the debris of slip rings causes an electrical insulation breakdown between adjacent circuits. 
     One of the objectives in the current invention is to eliminate the sliding contacts between brushes and rings. reduce the friction and wear, as well as to minimize the need for maintenance so that the electrical rotary joint not only can work at much higher speed and last much longer, but also it could be used in any harsh environments such as extreme temperatures, vibration, and shock. 
     Gears are used in a variety of mechanical devices. Gears are toothed members which transmit power/motion between two shafts by meshing without any slippage. If the gears are made of conductive material, they can also transmit electrical signal/power, during their rotational motion. Although there is friction in the gear meshing, the efficiency related to tooth friction losses for single tooth mesh is usually as high as 98˜99.5%. So it is ideal to replace brushes and rings in electrical slip ring with conductive gear meshing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of a simple planetary gear mechanism in current invention; 
         FIG. 2  is a cross section view of the first preferred embodiment of the current invention; 
         FIG. 3  shows the cycloidal pin-wheel mechanism of the second preferred embodiment in the current invention; 
         FIG. 4  is a schematic illustration of the pin-wheel the second preferred embodiment in the current invention. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     A simple planetary or epicyclic gear mechanism consists of a sun gear in the center. an internal or ring gear with a common axis with sun gear, and at least one planet gear. The planet gear is located between the sun gear and ring gear, and meshes with both the sun gear and the ring gear. If the ring gear is stationary, when sun gear rotates, the planet gear not only rotates about its axis, its axis also rotate around the axis of sun gear. 
     In stead of employing the sliding motion between the ring and the brush in electrical slip ring, the current invention makes use of a plurality of conductive gears, particularly a planetary gear mechanism, to transfer electrical power, and/or signal(s) between relatively rotatable objects. 
     In  FIG. 1 , a ring gear  01 , and a sun gear  03  have a common axis  21 . At least one planet gear  02  meshes with both sun gear  03  and ring gear  01 . For the illustration purpose. only one planet gear is showed. All the gears are made of conductive material. Circle  05  is the orbit of the planet gear  02 . 
     As shown in  FIG. 2 , a preferred embodiment of the present invention comprises a rotor  31 , stator  32   a  and  32   b.  A plurality of bolts  32  are used to connect stator  32   a  and  32   b.  A pair of bearings  35   a  and  35   b  are mounted in the bore of the stator  32   a  and  32   b  on the common axis  21  of rotor and stator so that the rotor  31  is able to rotate around the axis  21 . This invention can be a multi-channel electrical rotary joint, e.g., multiple sets of ring gear, planetary gear, and sun gear assemblies are stacked in axial direction, layer by layer, to further increase the number of channels provided in the electrical rotary joint. For the illustration purpose, only one channel is marked. The sun gear  03  is attached to the rotor  31  through insulating spacers  07  and insulating cylinder  06 . The ring gear  01  is fixed to stator  32   a  and  32   b  through insulating spacers  08  and bolts  33 . The planet gear  02  is hold in axial position by insulating spacers  07  on both sides. For anti-backlash purpose, the ring gear  01 , the sun gear  03  and/or the planet gear  02  is a flex gear. For the purposes of this patent a flex gear shall he considered any gear that shows some degree of flexibility without permanent distortion. 
     There is a variety of gear tooth profiles available in gear industry. Examples of explanation in current invention include, but are not limited to: involute tooth profile, cycloid tooth profile, and Novikov, Wildhaber or Circular Arc Tooth Profile. 
     The involute gear profile is the most commonly used in gear industry today. In involute gears, the profiles of the teeth are involutes of a circle. The kinematics of a gear meshing pair with involute profile is best described as rolling/sliding contact with pure rolling at the pitch line. Although there is friction in the gear meshing, the efficiency related to tooth friction losses for single tooth mesh is usually as high as 98˜99%. 
     In cycloidal gears, the contact takes place between a convex flank and concave surface. This condition results in the mostly rolling contact, larger contact area, and less wear in cycloidal gears. So cycloidal teeth have longer life and it is a better option for electrical rotary joint. 
     The Novikov gears have circular tooth surfaces. For a meshed gear pair, normally one of the gears has a convex tooth profile and another gear tooth has a concave tooth profile, thus leading to pure rolling action at the contact for these gears. The efficiency for Circular Arc Tooth Profile is as high as 99.5%. 
     There is another embodiment, illustrated in  FIG. 3 , of the present invention, wherein a planetary cycloidal pin-wheel mechanism replace the simple planetary gear mechanism in the first embodiment of the invention. Specifically, the plurality of planet gears are substituted by the plurality of conductive pin-wheels  51 . As shown in  FIG. 4 , the pin-wheel  52  consists of two plates connected by a couple of paralleled positioned pins. The planetary cycloidal pin-wheel mechanism consists of the cycloidal sun gear  53  in the center, an internal or ring cycloidal gear  51  with a common axis with sun gear  53 , and at least one pin-wheel  52 . For illustration purpose, only one pin-wheel is showed. Like the planet gear  02  in  FIG. 1 , the pin wheel  52  revolves both around the sun gear  53  and on its own axis.  55  is its orbit. All the cycloidal gears and pin-wheels are made of conductive materials. 
     While two preferred embodiments of the invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the claims.