Abstract:
A harmonic drive motor includes a first annular member, concentric second and third members, and a device for flexing the first annular member. The first annular member has a longitudinal axis and is flexible. The second member is relatively rigid and is substantially coaxially aligned externally of the first annular member, and the third member is relatively rigid and is substantially coaxially aligned internally of the first annular member. One of the second and third members is rotatable about the longitudinal axis and the other is relatively non-rotatable. The flexing device flexes the first annular member into at least two spaced-apart points of contact with the inner diameter surface of the second member and into at least two spaced-apart points of contact with the outer diameter surface of the third member. The flexing device sequentially flexes the first annular member to rotate both sets of at least two points of contact about the longitudinal axis which effects relative rotation between the second and third members.

Description:
RELATED PATENT APPLICATIONS  
       [0001]     This application claims priority to U.S. provisional patent application Ser. No. 60/691,144 filed 16 Jun. 2005, entitled “Harmonic Linear Actuator and Flexing Splined Interlock for Harmonic Motor or Linear Actuator”. This application is also related to U.S. application Ser. No. 11/412,057 filed 26 Apr. 2006, entitled “Harmonic Drive Linear Actuator”, the specification of which is expressly incorporated herein by reference. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates generally to motors, and more particularly to motors employing harmonic drives.  
       BACKGROUND OF THE INVENTION  
       [0003]     Motors include harmonic motors. One type of harmonic motor has a rotatable rotor and a surrounding nonrotatable stator. The rotor makes a single point of contact with the inner circumference of the stator. The single point of contact rotates around (i.e. rolls around) the inner circumference of the stator. The rotor rotates a few degrees about its longitudinal axis for each complete rotation of the single point of contact about the inner circumference of the stator. In one modification, the outer circumference of the rotor and the inner circumference of the stator have gear teeth. Such motors find use in high torque, low speed motor applications. In one known variation, the rotatable rotor is above a nonrotatable stator, and the rotatable rotor flexes or wobbles downward to make a single point of contact with the stator, the single point of contact rotates around an “inner circumference” of the stator, and the rotor rotates a few degrees about its longitudinal axis for each complete rotation of the single point of contact. In another type of harmonic motor, a shaft is surrounded by a shaft-driving member, which is brought into a single point of contact with the shaft by electro-restrictive devices, wherein the rotor rotates a few degrees for each complete rotation of the single point of contact around an inner circumference of the shaft-driving member.  
         [0004]     Harmonic motors are generally used to impart rotary motion, and may be of the type described in, for example, U.S. Pat. No. 6,664,711 B2 entitled “Harmonic Motor”, the disclosure of which is expressly incorporated herein by reference. Such motors employ a first, flexible annular member provided with gear teeth that are engagable with gear teeth of a second member surrounding or surrounded by the first annular member, the first annular member actually being cup-shaped as described herein below, and also referred to as a flex-tube.  
         [0005]     Harmonic drive gear trains are known. In one known design, a motor rotates a “wave generator” which is an egg-shaped member, which flexes diametrically opposite portions of the surrounding flex-spline gear, which is inside an outer gear. As the diametrically opposite teeth of the flex-spline gear contact the teeth on the outer gear, the rotatable one of the gears rotates with respect to the nonrotating one of the gears.  
         [0006]     Currently, the only method of preventing rotation of the annular flexible member in a harmonic motor or actuator is to configure the member to have a generally cylindrical body with opposite open and closed ends, where the rim and a base are respectively located. That is, existing flex-tubes in such devices are cup-shaped rather than truly tubular. This cup configuration allows the wall at and near the rim of the first, annular flex tube member to be moved into operative engagement with the second annular member and still be fixed at its base against rotation.  
         [0007]     However, to bring the rim of the flex-tube and the second member into operative engagement requires additional work and power to bend the cup-shaped flex-tube&#39;s base and flex its cylindrical wall near the base.  
         [0008]     What is needed is a new type of harmonic motor or actuator device having a flexible member which does not rotate, requires less power to operate, and simultaneously reduces the effective gear ratio between the rotor and stator.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention provides a harmonic drive device such as a harmonic motor or harmonic actuator having a flex-tube that is tubular rather than cup-shaped, and yet is prevented from rotating during operation of the device. The first tubular, flexible member of the inventive device is provided with inner and outer generally cylindrical surfaces, one of which is provided with gears or threads that respectively inter-engage with gears or threads on the second member to induce linear or rotational movement or the second member, as the case may be. The other of the first member&#39;s inner and outer generally cylindrical surfaces is provided with gear teeth or splines that are engaged with identical mating gear teeth or splines on a stationary third member or armature in a circumferentially moving manner. The inter-engagement of the armature, flexible first member and movable second member prevent rotation of the first member during operation of the harmonic motor or harmonic actuator.  
         [0010]     In the preferred embodiment of the invention, a harmonic motor includes a first annular member, second and third members, and a device for flexing the first annular member. The first annular member has a longitudinal axis, lies on a plane perpendicular to the longitudinal axis, and is flexible in a direction, which lies in the plane. The second and third members are substantially coaxially aligned with the first annular member and lay in the plane. One of the second and third members is rotatable about the longitudinal axis, and the other or the first and second members is non-rotatable about the longitudinal axis. The flexing device flexes the first annular member to rotate the at least two spaced-apart points of contact with the second member and an additional at least two spaced-apart points of contact with the third member, and sequentially flexes the first annular member to rotate the points of contact with said second and third members about the longitudinal axis which rotates the rotatable one of said second and third members about the longitudinal axis.  
         [0011]     Several benefits and advantages are derived from the preferred embodiment of the invention. By using at least two points of contact between the first annular and second members as well as the first annular and third members, the rotatable one (i.e. the rotor) of the second and third members is being driven by at least two points of contact by the non-rotatable one (i.e. the rotor driving member or stator) of the second and third members. Driving the motor with at least two points of contact provides a more robust and more smoothly operating motor than is provided in the prior art, as can be appreciated by the artisan. In addition, mechanical interconnection torque input/output interconnection means directly to the flexible member is avoided.  
         [0012]     In another aspect of the preferred embodiment, the first annular member assumes a substantially cylindrical configuration due to its inherent resiliency when the flexing means is not active. This results in mechanical disengagement between the second and third members, preventing any undesirable load back-drive.  
         [0013]     These and other features and advantages of this invention will become apparent upon reading the following specification, which, along with the drawings, describes preferred and alternative embodiments of the invention in detail. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0015]      FIG. 1A , is a top view of a prior art, cup-shaped flex-spline member for a harmonic device;  
         [0016]      FIG. 1B , is a cross-sectional view, taken on lines  1 B- 1 B of  FIG. 1A ;  
         [0017]      FIG. 2 , is a schematic diagram of the preferred embodiment of the harmonic motor of the present invention; and  
         [0018]      FIG. 3 , is a schematic diagram similar to that of  FIG. 2 , but where the harmonic motor is de-activated.  
     
    
       [0019]     Although the drawings represent embodiments of the present invention, the drawings are not necessarily to scale and certain features may be exaggerated in order to illustrate and explain the present invention. The exemplification set forth herein illustrates an embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.  
       DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]     The present invention is intended for application in varied automotive vehicle applications and will be described in that context. It is to be understood, however, that the present invention could be successfully applied in many other applications. Accordingly, the claims herein should not be deemed limited to the specifics of the preferred embodiment of the invention described hereunder.  
         [0021]     Known harmonic motors and gear systems typically have a cup-shaped flex-spline that, in application, is mechanically coupled to an associated input or output member to transmit forces created by the associated gear system. Referring to  FIGS. 1A and 1B , a known cup-shaped flex-spline  10  is illustrated. Flex-spline  10  comprises a cylindrical sidewall  12  and a bottom wall  14  integrally formed therewith. A nominally right angle corner, indicated generally at  16 , continuously circumscribes the bottom wall  14 . The open upper portion of side wall  12  defines a rim  18  which is thickened to form radially outwardly facing gear teeth  20  extending continuously circumferentially thereabout for engagement with opposed teeth of a mating gear (not illustrated).  
         [0022]     Flex-spline  10  is formed with the sidewall  12  assuming a circular configuration when in the unloaded condition. In application, the upper portion of the sidewall  12 , including the rim  18  and gear teeth  20 , is loaded into an ellipsoid configuration, illustrated in phantom, wherein the rim alternately flexes inwardly and outwardly during rotation of flex-spline  10 . Additionally, the bottom wall  14  tends to “oil can” axially inwardly and outwardly at the same time. In addition to imposing high parasitic losses and inefficiencies, the reciprocal “tilting” or bending of the upper portion of the side wall  12  inwardly and outwardly creates stress risers at corner  16  which can work-harden the material, leading to fracture and failure of the mechanism. The only practical design implementation to address this shortcoming is to increase the axial length of the flex-spline  10 . Although this partially mitigates the flexing problem, there remains a limit to the axial length of the gear teeth  20 , resulting in relatively high force loads and moments which must be reinforced by increasing package size and material costs. Furthermore, the cyclical tilting of the side wall  18  and gear teeth  20  results in rotational misalignment of gear teeth  20  with any mating teeth (not illustrated), thereby increasing unit loading and wear. This rotational misalignment is illustrated as offset angle θ in  FIG. 1B .  
         [0023]     Referring now to  FIG. 2 , a preferred embodiment of the presently inventive harmonic drive motor  22  is illustrated. The harmonic drive motor  22  includes a first annular member  24 , a second member  26 , a third member  28  and means  30  for flexing the first annular member  24 . The first annular member  24  has a longitudinal axis  32  (seen as a point in  FIG. 2 ). The first annular member  24  lies on a plane  34  corresponding to the plane of the drawing sheet and normal to the longitudinal axis  32 .  
         [0024]     The first annular member  24  is cylindrically tube-shaped, defining radial inner and outer surfaces  36  and  38 , respectively. Both ends of first annular member  24  are parallel to plane  34  and are open in both axial directions. Inner surface  36  forms a plurality of radially inwardly extending gear teeth  40  which are substantially equally circumferentially spaced. Outer surface  38  forms a plurality of radially outwardly extending gear teeth  42  which are substantially equally circumferentially spaced. Gear teeth  40  and  42  are similarly shaped and dimensioned, are mutually parallel and extend the entire axial length of the first annular member  24 . First annular member  24  is formed of material, which allows it to be easily flexed radially inwardly and outwardly from its normal or relaxed round configuration illustrated in  FIG. 3 . For example, first annular member  24  can be a molded composite of hard rubber or reinforced Nylon combined with particles of ferromagnetic material in sufficient quantity to enable localized magnetic attraction/repulsion of regions or circumferential segments of the first annular member  24  to effect deflection thereof as illustrated in  FIG. 2 . Although flexible radially, the first annular member is relatively rigid in the circumferential direction.  
         [0025]     The second member  26  is a nominally round and relatively rigid cylinder having an inwardly facing circumferential surface  44  forming a plurality of radially inwardly extending gear teeth  46  which are substantially equally circumferentially spaced. Gear teeth  46  of second member  26  are shaped and dimensioned to selectively cooperatively engage gear teeth  42  of first annular member  24  as is described herein below. The second member  26  is preferably constructed of aluminum, reinforced Nylon, or other suitable non-ferrous material. The second member  26  is arranged concentrically with first annular member  24  for rotation about longitudinal axis  32 . Gear teeth  46  extend the entire axial length of the second member  26  to maximize the operating contact surfaces between cooperating adjacent gears  42  and  46 . As is best illustrated in  FIG. 3 , first annular member  24  and second member  26  are dimensioned to permit radial clearance between the tips of gears  42  and  46 , respectively, wherever the first annular member  24  is in the relaxed position.  
         [0026]     The third member  28  is a nominally round and relatively rigid cylinder having an outwardly facing circumferential surface  48  forming a plurality of radially outwardly extending gear teeth  50  which are substantially equally circumferentially spaced. Gear teeth  50  of third member  28  are shaped and dimensioned to selectively cooperatively engage gear teeth  40  of first annular member  24  as is described herein below. The third member  28  is preferably constructed of aluminum, reinforced Nylon, or other suitable non-ferrous material. The third member  28  is arranged concentrically with the first annular member  24  about the longitudinal axis  32 . Gear teeth  50  extend the entire axial length of the third member  28  to maximize the operating contact surfaces between cooperating adjacent gear teeth  40  and  50 . As is best illustrated in  FIG. 3 , first annular member  24  and third member  28  are dimensioned to permit radial clearance between the tips of gear teeth  40  and  50 , respectively, whenever the first annular member  24  is in the relaxed position.  
         [0027]     The means  30  for flexing the first annular member  24  is preferably constructed as an electromagnetic actuator assembly, and herein after, is identified as such. Electromagnetic actuator assembly  30  includes a generally cylindrical armature body  52  fixedly mounted to a splined end of an axially elongated support member  54 . In application, support member  54  could extend axially in one or both directions beyond the axial ends of the first annular member  24  as well as the second member  26  to fix the electromagnetic stator assembly from displacement or rotation about longitudinal axis. Furthermore, support member can be employed to affix end closure members, seals, output shaft bearings and the like (all non-illustrated), depending upon the particular application intended.  
         [0028]     Armature body  52  is generally spool-shaped, including axially leading and trailing outwardly extending flange portions (not illustrated). A plurality of electrical coils or windings  56  are insulatively disposed within armature body  52  and are each electrically in-circuit with a control system via electrical conductors to define a discrete number of circumferentially arranged magnetic poles. Armature body  52  is formed of ferrous material such as laminated or sintered steel or other suitable material. Although eight electrical coils  56  are illustrated, more or fewer can be applied, as the intended application dictates.  
         [0029]     The third member  28  has an inwardly facing cylindrical surface  58  which forms an interference fit with an outwardly facing cylindrical surface  60  of armature body  52 . Thus, the third member  28  and the electromagnetic actuator assembly  30  are affixed in-assembly as a stator for relative non-rotation with respect to the first annular member  24  and the second member  26 .  
         [0030]     As best viewed in  FIG. 3  where the first annular member  24  is in the relaxed position, i.e. when none of the electrical coils  56  are electrically energized, first annular member assumes a substantially round configuration. Insodoing, radial spaces are established between opposed gear teeth  42  and  46  of first annular member  24  and second member  26 , respectively, as well as between gear teeth  40  and  50  of first annular member  24  and third member  28 , respectively. In this condition the second member  26  (motor rotor) is entirely mechanically de-coupled from the third member  28  and electromagnetic actuator assembly  30  (motor stator), as well as the first annular member  24 .  
         [0031]     Referring to  FIG. 2 , the harmonic motor functions by selectively energizing opposed coil pairs within the actuator assembly  30 . For example, if an opposed pair of coils  56 C and  56 D are energized, they create a magnetic field, which attracts 90° offset portions of the flexible first annular member  24 , causing it to distend into an elliptical or egg-shaped configuration. The portions of the first annual member  24  adjacent coils  56 A and  56  B are drawn radially inwardly into intimate contact with the outer peripheral surface  48  of third member  28 , wherein gear teeth  50  of third member  28  engage gear teeth  40  of first annular member  24 . Such points-of-contact or engagement are designated by brackets  62  and  64 . Simultaneously, opposed (by 90°) portions of the first annular member  24  are forced radially outwardly into intimate contact with inner surface  44  of second member  26 , wherein gear teeth  42  of first annular member engage gear teeth  46  of second member  26 . Such points-of-contact or engagement are designated by brackets  66  and  68 . This engagement can be supplemented by magnetic repulsion of adjacent reverse polarized coils  56 C and  56 D.  
         [0032]     As illustrated in  FIG. 2 , second member  26  is interconnected with third member  28  for non-rotation by the first annular member or flex-spline interlock  24 . When the electrical coils are sequentially (ex.: circumferentially) energized, the localized points of contact  62  &amp;  64  and  66  &amp;  68  of the cooperating engaged gear teeth “walks around” the circumference of the harmonic motor  22 , thereby effecting relative rotation between the second member  26  and the third member  28 .  
         [0033]     The electrical control of harmonic motors and actuators is well known. For example, U.S. Pat. No. 6,664,711 B2 and U.S. patent Application 2005/0253675 A1 describe harmonic motors and controllers therefore which can be adopted for use in the present invention. U.S. Pat. No. 6,664,711 B2 and U.S. 2005/0253675 A1 are hereby incorporated herein by reference as an exemplary teaching of one possible approach. It is to be understood that they reflect only one of many possible control strategies. Furthermore, other methodologies for sequentially flexing the first annular member such as mechanical, electrical or electromagnetic could be implemented without departing from the spirit of the invention.  
         [0034]     In the present harmonic motor, the gear teeth are parallel to the motor axis. This will result in the flex-spline rotating in the same direction as the outer gear since the flex-spline inside gear teeth would have more teeth than the matching armature gear teeth. The overall effect will be an approximate doubling of the motor output torque for the same actuation.  
         [0035]     It is to be understood that the invention has been described with reference to specific embodiments and variations to provide the features and advantages previously described and that the embodiments are susceptible of modification as will be apparent to those skilled in the art.  
         [0036]     Furthermore, it is contemplated that many alternative, common inexpensive materials can be employed to construct the basis constituent components. Accordingly, the forgoing is not to be construed in a limiting sense.  
         [0037]     The invention has been described in an illustrative manner, and it is to be understood that the terminology, which has been used is intended to be in the nature of words of description rather than of limitation.  
         [0038]     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. For example, . . . It is, therefore, to be understood that within the scope of the appended claims, wherein reference numerals are merely for illustrative purposes and convenience and are not in any way limiting, the invention, which is defined by the following claims as interpreted according to the principles of patent law, including the Doctrine of Equivalents, may be practiced otherwise than is specifically described.