Abstract:
An eccentric magnetic, non-contacting gear system which can affect shaft speed and torque while minimizing mechanical friction and wear has bi-axial shafts. This efficient, non-contacting gear system can be produced by the interaction of circular arrays (or pitch circles) of permanent magnets with eccentric engagement. Coupling is provided by magnetic field repulsion. Input torque is applied to a circular array of permanent magnets representing a first gear, which then through magnetic fields, not physical contact, transfers the torque to another circular array of permanent magnets representing a second gear having an offset output shaft. Gearing may be done in one step or in stages.

Description:
RELATED APPLICATIONS 
     This application is related to and claims priority under 35 U.S.C. 119(e) to U.S. provisional application Ser. No. 61/449,134, entitled “Eccentric Magnetic Gear System,” filed on Mar. 4, 2011, with inventor Allen G. Storaasli of Federal Way, Wash., which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention pertains generally to gear systems and more specifically to an eccentric, magnetic, non-contacting gear system which can affect shaft speed and torque while minimizing mechanical friction and wear. 
     BACKGROUND OF THE FIELD 
     Traditional gear systems are used to reduce or increase rotational shaft speed, along with resulting effect on shaft torque. A typical application for such a gear system is to a weak electrical motor in order to increase shaft torque. However, with a traditional gear system, there are often mechanical limitations due to, e.g., friction, wear, and temperature sensibility. Temperature changes can degrade gear mesh geometry and lubrication properties. These problems could be minimized, if not eliminated entirely, by using non-contacting, magnet elements in the gear system. Another benefit could be reduced mechanical and torque noise. 
     Biaxial gear systems have been previously patented, such as in U.S. Pat. Nos. 3,523,204 (to Rand Aug. 4, 1970) and 6,047,456 (to Yao et al. Apr. 11, 2000). The biaxial gear systems in these patents are inefficient and also likely have torque cogging problems when torque transmission loads are low. 
     In other applications, internal gear topology causes a higher number of magnet interactions between the drive and driven gears, which aids torque capability. Frank Jorgensen, in his article “The Cycloid Permanent Magnetic Gear,” IEEE Transaction on Industry Applications, November 2008, shows effectiveness of such magnetic gearing with cycloidal arrangement. The magnets are arranged such that at the region of closest approach, non-contacting, strong magnetic attractive forces are developed. As a result, there is a strong rotation transmission torque along with high torsional stiffness. The article details the analysis used to estimate the torque transmission characteristics; however, it does not address the high radial forces which must be reacted by the support bearing sets. It is apparent to those skilled in the art that the high bearing loads, which are constant at all speeds, can have serious effects on torque efficiency. In addition, highly loaded bearings are subject to wear-out. 
     SUMMARY OF THE INVENTION 
     The present invention solves the above-mentioned problems by providing an efficient, non-contacting gear system produced by the interaction of circular arrays (pitch circles) of permanent magnets with eccentric (also called cyloidal) arrangement. Unlike prior art, coupling is provided by magnetic field repulsion. Torque may be inputted into the system from a motor, such as a weak electrical motor, through idler links, an input shaft or some other appropriate method. The torque is applied to a circular array of permanent magnets representing a first gear, which then through magnetic fields, not physical contact, transfers the torque to another circular array of permanent magnets representing a second gear having an offset output shaft. Gearing may be done in one step or in stages. 
     Unlike in the prior art, the present invention may comprise generally cylindrical, axially polarized magnets which are spaced apart from each other with significant gaps. All magnet fields in both, or all, arrays have the same axial orientation (conventionally referred to as N and S). When the pitch circles of the two arrays are brought into tangential, non-touching intersection (called the tangential mesh area), the magnet-to-magnet repulsion establishes a condition tending to avoid magnet-to-magnet contact, thereby enabling torque transmission in the tangential direction. This “magnetic meshing engagement” of the two arrays may be compared to traditional gear mechanical engagement, except there is no mechanical contact. Some radial forces also result which must be reacted by the support bearings. These radial forces are much less than in the prior art. Because the resultant bearing torques are much lower, the system efficiency is improved. This should be most noticeable at low rotational speeds and low torque transmission levels. Low speed aggravates prior art because bearing lubrication film thickness is reduced, allowing metal-to- metal contact between the balls and races. 
     Motorized spacecraft positioners operate at low speeds and reversing directions. The term ‘direct drive’ has always signified a simple motor on an axis with no gearing. The present invention enables the use of a motor with amplified torque using simple, reliable, non-contacting gearing and may be considered as nearly equivalent to a direct drive, but now with increased torque output for the same weight. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a front view of a first embodiment having an eccentric arrangement of magnetic elements with offset (parallel but non-coaxial) axes; 
         FIG. 1B  is a sectional side view of two adjacent magnets (from different pitch circles) from  FIG. 1 ; 
         FIG. 1C  is a front view of another embodiment having an eccentric arrangement of magnetic elements with offset (parallel but non-coaxial) axes with equal number of magnetic elements in the first and second magnet sets. 
         FIG. 2  is a perspective view of  FIG. 1 ; 
         FIG. 3A  is a side view of a second embodiment using a compound planetary arrangement with a small number of magnets for achieving higher gear ratios; 
         FIG. 3B  is a partial sectional front view showing the non-touching meshing engagement of one gearing stage of said second embodiment; 
         FIG. 4A  is a side view of a third embodiment; and 
         FIG. 4B  is a front sectional view of this third embodiment taken at the tangential intersection plane. 
     
    
    
     DETAILED DESCRIPTION 
     The objects, features, and advantages of the present invention will be apparent to one skilled in the art from reading the following description in which: 
       FIG. 1A  shows a first embodiment of the invention of the eccentric magnetic gear system  10  that may comprise a first generally circular input magnet set (first pitch circle)  12  interdigitally meshed with a second generally circular output magnet set (second pitch circle)  14 . The pitch circles have different diameters to provide for precessing of the tangential mesh area  40 . In this embodiment, the input magnet set  12  has seven magnets evenly spaced around the circumference of and attached to input carrier plate  16  and represents a first (input) gear. (As can be seen in  FIGS. 1B and 2 , these magnets are typically offset axially from the carrier plate  16 .) The output magnet set  14  represents a second gear and is spaced evenly around and attached to output carrier plate  18  which itself is arranged around and linked to output shaft  22  that is laterally offset (generally parallel but non-coaxial) from the input axis  20  of the input carrier plate  16 . In this embodiment there are  6  magnets in the output magnet set  14 . 
     On the input carrier plate  16  is mounted the first set of magnets  12 , and the carrier plate  16  is itself constrained to move in orbital cycloidal motion (not rotational) by the linkage nature of the three idler links  30 ,  32 ,  34 . The three links  30 ,  32 ,  34  are mounted on three fixed posts  31 ,  33 ,  35 , and the imaginary longitudinal input axis  20  passes axially through the geometric center of the circle described by magnet set  12 . The motor torque is input to the carrier plate  16  by an input motor  36  through an input shaft  31  that attaches to motor link  30  (one of the idler links) from an odd number of points, e.g., through the single point  30  or also through the idler cranks  32 ,  34  if they are affixed to the motor  36 . The carrier plate  16  translates in an orbital, cycloidal fashion and causes the closest gap (tangential mesh area  40 ) between the two meshed magnet sets  12 ,  14  to advance, thereby spinning the second gear  18  (output carrier plate  18 ) and the output shaft  22 . 
     The differential between the number of magnets in the input magnet set  12  and the output magnet set  14  set determines the gear ratio of the overall system  10 . If the number of inner magnets were equal to the number of outer magnets, the gear ratio would be 1:1, and the system would represent simply a magnetic direct drive coupling. Varying the number of magnets in one magnet set results in a fairly large gear ratio. In the embodiment shown, seven input magnets linked to the input carrier plate  16  and six output magnets linked to the output carrier plate  18 —and thus the output shaft  22 —result in a gear ratio of 6:1. 
     As has been previously mentioned, motor function can be added to links  32  and  34 , if desired, to increase input torque and/or improve system reliability relative to motor drive failure or motor open winding. All magnets in this system are polarized axially with like poles (conventionally labeled as N and S) in a common direction, as is illustrated in  FIG. 1B .  FIG. 1B  also shows the gap between magnets from different sets ( 12  and  14 ). There must be a gap to ensure non-touching, but the magnets must be within the magnetic field of one another to benefit from repulsion.  FIG. 1B  illustrates the tangential mesh area of the magnets of the two pitch circles-both input and output. As the input carrier plate  16  moves cycloidally, this tangential mesh area  40  precesses around the pitch circles. When properly indexed, the two pitch circles can be generally co-planar, and there still will be no metal-to- metal contact. 
       FIG. 2  shows the basic system of  FIG. 1  in a perspective view. It can easily be seen in this figure that the motor link  30  and idler links  32 ,  34  are generally coplanar (but slightly offset) with the carrier plate  16 . In variations on this embodiment, the links could be further offset from the carrier plate to accommodate different configurations. The input magnets  12  are arranged around the carrier plate  16  and are spaced from the face of the carrier plate to provide clearances for the physical components while keeping the magnets of both input and output sets within the magnetic fields of each other. Likewise the magnets of the output set  14  are spaced axially from the end of the output carrier plate and output shaft. 
       FIG. 3A  shows a second embodiment  60  that can be used to achieve even higher gear ratios. This embodiment also eliminates the use of idler linkages (such as  32  and  34  in the first embodiment). This second embodiment has two stages of interdigitally meshed gearing in a compound epicyclic arrangement, similar to conventional gearing but having no mechanical contact. This second embodiment also makes use of a stepped input shaft having a standing portion which is generally coaxial with the output shaft. The stepped portion of the input shaft passes through the center of the input carrier plate  66  using conventional bearings  68 . The orbiting magnet sets  62  and  64  are mounted on carrier plate  66 —the first generally circular orbiting magnet set  62  mounted on a first face of said carrier plate, defining the first gearing stage, and the second generally circular orbiting magnet set  64  mounted on the opposing face of said carrier plate, defining the second gearing stage. The carrier plate  66  is the input to the overall system and is constrained to move in a cycloidal fashion by the stepped input shaft  78  and the fixed magnets  74 . The mesh areas shown as  70  and  72  (better seen in the sectional view of  FIG. 3B ) denote areas where the magnet sets are interdigitally meshed (i.e., orbiting set  62  with generally circular fixed set  74  and orbiting set  64  with generally circular rotational set  76 ); meshing (but non-touching) gear sets use the same repulsive forces described in the first embodiment to spin the output plate  84  and thereby the output shaft  80 . Also as in the first embodiment, the speed of the output shaft  80  is increased or reduced greatly by proper choice of magnet ratios. 
     In  FIG. 3A , the fixed magnet set  74  defines a geometric center, and the standing part of the input shaft  78  passes through this geometric center. The input shaft  78  then steps through a prescribed offset  82 , and the stepped portion of the shaft passes through the center of the input carrier plate  66 . The offset  82  (between the longitudinal axes of the standing part of the input shaft  78  and the output shaft  80 ) is sized to cause proper interdigital engagement of meshing magnet sets. The interdigital (or tangential) meshing of two magnet circles (pitch circles) of different diameters allows torque transmission at the mesh area of magnetic engagement. As the mesh area/engagement region precesses with carrier rotation there is a relative angle change between the magnet sets. The magnet complement shown in  FIG. 3A  results in 35:1 speed reduction from input shaft  78  to output shaft  80 . One advantage of this system may be that a motor gearhead designed with a low torque motor can have that torque multiplied 35 times for the same input power. 
       FIG. 4A  shows a third embodiment  40  that can be used to achieve a moderate gear ratio using less axial space. This embodiment has a stepped input shaft as in the previous embodiment but only one gearing stage. As in the previous embodiment, the standing portion of the input shaft lies along the longitudinal axis of the overall system and then steps through a prescribed offset so that the stepped portion passes through the center of the input carrier plate. In this third embodiment, all magnets are interdigitally meshed in one common plane (as represented in  FIG. 4A  as section cut  4 B), including input magnet set  42 , which is linked to input shaft  46 , and output magnet set  44 , which is linked to output shaft  50 . Note that in the first embodiment of  FIGS. 1A, 1B, and 2 , idlers  32  and  34  are required to constrain orbital motion of the input carrier plate. In this third embodiment  40 , the intermediate fixed magnet set  48 , having the same number of magnets as the input magnet set  42 , provides rotational constraint of the input carrier plate  52  and causes it to move in a cycloidal motion. 
     Input magnet set  42  (sometimes referred to as the input pitch circle), consisting of seven magnets mounted on input carrier plate  52 , follows input motion; the center of the pitch circle translating in a circle due to the step  54  in the input shaft  46 . Intermediate fixed pitch circle  48  consisting of seven magnets, interacts magnetically with input pitch circle  42  (best seen in  FIG. 4B ). The repulsion among the orbiting magnets of input pitch circle  42  and the fixed magnets of intermediate pitch circle  48  causes input pitch circle  42  to orbit cycloidally without rotating, thereby eliminating the need for idler cranks that were used in the first embodiment. The input shaft  46  supplies input torque to the input carrier plate of the magnetic system. 
     The orbiting path of input pitch circle  42  now causes output pitch circle  44  to rotate as output, rotating output carrier plate  56  (on which output magnet set  44  is mounted) and output shaft  50 . Again, as in the second embodiment, the tangentially meshed area will precess around the system with input. Output pitch circle  44  has eight magnets and is linked to output shaft  50 . Therefore speed is reduced, and mechanical advantage is gained. The three pitch circles all have different diameters to allow for the precessing of tangential mesh areas.