Abstract:
A method and system providing a flex spline for a compound harmonic generator having a harmonic wave generator, a primary ring gear, and a secondary ring gear, includes a primary flex spline with a first number of primary teeth, the primary flex spline driven by the harmonic wave generator and in meshed contact with the primary ring gear, and at least one secondary flex spline with a second number of secondary teeth, the at least one secondary flex spline driven by the harmonic wave generator and in meshed contact with the secondary ring gear, wherein the at least one secondary flex spline rotates independently from the primary flex spline.

Description:
BACKGROUND 
       [0001]    The subject matter disclosed herein relates to flex splines, and more particularly, to a system and a method for providing a flex spline for use with a compound harmonic generator. 
         [0002]    Typically, flight control surfaces on aircraft wing structures utilize actuators that are coupled to the flight control surfaces to control and guide the movement of the flight control surfaces between positions. Certain actuator applications, such as actuators for use with thin wing designs may utilize a compound harmonic generator to provide suitable gear reduction. The use of flex splines that can reduce stress and fatigue for a compound harmonic generator is desired. 
       BRIEF SUMMARY 
       [0003]    According to an embodiment, a flex spline for a compound harmonic generator having a harmonic wave generator, a primary ring gear, and a secondary ring gear, includes a primary flex spline with a first number of primary teeth, the primary flex spline driven by the harmonic wave generator and in meshed contact with the primary ring gear, and at least one secondary flex spline with a second number of secondary teeth, the at least one secondary flex spline driven by the harmonic wave generator and in meshed contact with the secondary ring gear, wherein the at least one secondary flex spline rotates independently from the primary flex spline. 
         [0004]    According to an embodiment, a method for operating a compound harmonic generator having a harmonic wave generator, a primary ring gear, and a secondary ring gear, includes providing a primary flex spline with a first number of primary teeth, providing at least one secondary flex spline with a second number of secondary teeth, engaging the primary flex spline in meshed contact with the primary ring gear, engaging the at least one secondary flex spline in meshed contact with the secondary ring gear, driving the primary flex spline via the harmonic wave generator, driving the at least one secondary flex spline via the harmonic wave generator, and rotating the primary flex spline independently from the at least one secondary flex spline. 
         [0005]    According to an embodiment, a compound harmonic generator includes a harmonic wave generator, a motor to drive the harmonic wave generator, a primary ring gear, a secondary ring gear, and a flex spline including a primary flex spline with a first number of primary teeth, the primary flex spline driven by the harmonic wave generator and in meshed contact with the primary ring gear, and at least one secondary flex spline with a second number of secondary teeth, the at least one secondary flex spline driven by the harmonic wave generator and in meshed contact with the secondary ring gear, wherein the at least one secondary flex spline rotates independently from the primary flex spline. 
         [0006]    Technical function of the embodiments described above includes that the at least one secondary flex spline rotates independently from the primary flex spline. 
         [0007]    Other aspects, features, and techniques of the embodiments will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The subject matter is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the embodiments are apparent from the following detailed description taken in conjunction with the accompanying drawings in which like elements are numbered alike in the FIGURES: 
           [0009]      FIG. 1  is a plan view of one embodiment of a compound harmonic generator for use with a flex spline; 
           [0010]      FIG. 2  is a cross sectional view of the compound harmonic generator of  FIG. 1  along line  2 - 2  of  FIG. 1 ; 
           [0011]      FIG. 3  is an isometric view of one embodiment of a harmonic wave generator assembly with a flex spline for use with a compound harmonic generator; 
           [0012]      FIG. 4  is a schematic view of the harmonic wave generator assembly with the flex spline of  FIG. 3 ; 
           [0013]      FIG. 5  is a detail view of the harmonic wave generator assembly with the flex spline of  FIG. 3 ; 
           [0014]      FIG. 6  is an isometric view of another embodiment of a harmonic wave generator assembly with a flex spline for use with a compound harmonic generator; 
           [0015]      FIG. 7  is a schematic view of the harmonic wave generator assembly with the flex spline of  FIG. 6 ; and 
           [0016]      FIG. 8  is a detail view of the harmonic wave generator assembly with the flex spline of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Referring now to the drawings,  FIGS. 1-3  show a compound harmonic generator  100  and the harmonic wave generator assembly  110 . In the illustrated embodiment, the compound harmonic generator  100  includes a ground arm  102  with a secondary ring gear  103 , an output arm  104  with a primary ring gear  105 , a motor  106  and a harmonic wave generator assembly  110  which includes a harmonic wave generator  112 , a primary flex spline  120  and secondary flex splines  130 . 
         [0018]    As an overview, in the illustrated embodiment, the compound harmonic generator  100  (also called a strain wave gear assembly) utilizes the primary flex (flexible) spline  120  and at least one secondary flex (flexible) spline  130  that are rotationally independent. The primary flex spline  120  meshes with the primary ring gear  105  and the secondary flex splines  130  mesh with the secondary ring gear  103 . In the illustrated embodiment, the harmonic wave generator  112  can rotate both the primary flex spline  120  and the secondary flex splines  130  independently. In the illustrated embodiment, the harmonic wave generator  112  is connected to a rotational input, such as the motor  106 , or any other suitable rotational input. In the illustrated embodiment, the secondary ring gear  103  is coupled to the ground arm  102  and the primary ring gear  105  is coupled to the output arm  104 . During operation, the primary flex spline  120  and the secondary flex splines  130  work together along with the primary ring gear  105  and the secondary ring gear  103  as a compact compounded gear drive to step down the rotational input of the motor  106 . Advantageously, the compound harmonic generator  100  is simple and compact, yet maintains a relatively high gear ratio and relatively high torque-to-weight ratio. In certain embodiments, the compound harmonic generator  100  can be utilized in space limited applications such as control surface actuation in thin wing design aircrafts. 
         [0019]    In the illustrated embodiment, the compound harmonic generator  100  includes at least one secondary ring gear  103  to mesh with the secondary flex splines  130 . In certain embodiments, the compound harmonic generator  100  can include multiple secondary ring gears  103  corresponding to multiple secondary flex splines  130 . In certain embodiments, the compound harmonic generator  100  can include multiple primary ring gears  105  corresponding to multiple primary flex splines  120 . In the illustrated embodiment, the compound harmonic generator  100  can include two secondary ring gears  103  corresponding and meshing with the two secondary flex splines  130  and one primary ring gear  150  corresponding and meshing with one primary flex spline  120 . In the illustrated embodiment, the secondary ring gears  103  are connected to a ground via the ground arm  102  which remains stationary relative to the harmonic wave generator assembly  110 . 
         [0020]    In the illustrated embodiment, the compound harmonic generator  100  includes a primary ring gear  105  to mesh with the primary flex spline  120 . In the illustrated embodiment, the primary ring gear  105  is coupled to the output arm  104  to provide the rotational output of the compound harmonic generator  100 . 
         [0021]    In the illustrated embodiment, the motor  106  can be any suitable motor, including, but not limited to an electric motor, hydraulic motor, etc. In certain embodiments, the motor  106  may not provide the desired torque required for certain operations, requiring the use of the compound harmonic generator  100  to provide adequate gear reduction and torque multiplication. Advantageously, the use of the compound harmonic generator  100  allows for a low torque motor  106  to be utilized, while minimizing space needed. In the illustrated embodiment, the motor  106  rotates the harmonic wave generator assembly  110 . 
         [0022]    Referring to  FIG. 3 , the harmonic wave generator assembly  110  is shown. In the illustrated embodiment, the harmonic wave generator assembly  110  includes a harmonic wave generator  112 , rolling elements  114 , the primary flex spline  120 , and at least one secondary flex spline  130 . In the illustrated embodiment, the harmonic wave generator  110  is drive by the motor  106  to rotate. 
         [0023]    In the illustrated embodiment, the harmonic wave generator  112  is rotated by the motor  106 . In the illustrated embodiment, the harmonic wave generator  112  has an eccentric outer profile or other non-circular outer profile to facilitate the harmonic operation of the compound harmonic generator  100 . 
         [0024]    In the illustrated embodiment, rolling elements  114  are disposed between the harmonic wave generator  112  and the primary flex spline  120  and the secondary flex splines  130 . As the harmonic wave generator  112  rotates, the rolling elements  114  provide radial support of the primary flex spline  120  and the secondary flex splines  130  while allowing rotation of the primary flex spline  120  and the secondary flex splines  130  independently of each other and of the harmonic wave generator  112 . In certain embodiments, the primary flex spline  120  and the secondary flex splines  130  can rotate in a direction opposite to the direction of rotation of the harmonic wave generator  112 . In the illustrated embodiment, the rolling elements  114  reduce rolling friction. The rolling elements  114  may be any suitable element, such as ball bearings, etc. 
         [0025]    In the illustrated embodiment, the primary flex spline  120  is disposed between two secondary flex splines  130 . In the illustrated embodiment, the primary flex spline  120  is a flexible gear. In certain embodiments, the primary flex spline  120  is made from spring steel or any other suitable material that is relatively thin, flexible and elastic. In the illustrated embodiment, the primary flex spline  120  has a generally hoop shape to allow for uniform deformation of the primary flex spline  120 . The primary flex spline  120  is driven by the harmonic wave generator  112 . 
         [0026]    In the illustrated embodiment, the harmonic wave generator assembly  110  includes at least one secondary flex spline  130 . The secondary flex splines  130  can be flexible gears. In the illustrated embodiment, the harmonic wave generator  110  can include two secondary flex splines  130  each disposed on each side of the primary flex spline  120 . In certain embodiments, the secondary flex splines  130  are made from spring steel or any other suitable material that is relatively thin, flexible and elastic. In the illustrated embodiment, the secondary flex splines  130  have a generally hoop shape to allow for uniform deformation of the secondary flex splines  130 . The secondary flex splines  130  can be driven by the harmonic wave generator  112 . In the illustrated embodiment, the secondary flex splines  130  are rotationally independent from each other and from the primary flex spline  120 . 
         [0027]    In  FIGS. 4 and 5 , the primary flex spline  120  and the secondary flex splines  130  are shown meshed with the primary ring gear  105  and the secondary ring gears  103 . During operation, the harmonic wave generator  112  rotates the primary flex spline  120  and the secondary flex splines  130 . In the illustrated embodiment, the harmonic wave generator  112  rotates the secondary flex splines  130  at a rate slower than the rotation rate of the harmonic wave generator  112 . Similarly, the harmonic wave generator  112  rotates the primary flex spline  120  at a rate slower than the rotation rate of the harmonic wave generator  112 , and slower than the rotation rate of the secondary flex splines  130 . In the illustrated embodiment, the primary flex spline  120  has more teeth than the secondary flex splines  130 , causing the difference in rotational speed. The secondary flex splines  130  are connected to the ground arm  102  via the secondary ring gears  103 . The output from the primary ring gear  105  is output via the output arm  104 . In addition to stepping down the rate of rotation of the motor  106 , the compound harmonic generator  100  approximately steps up the torque from the motor  106  in an inverse relationship to the step down in rate. 
         [0028]    In the illustrated embodiment, the primary flex spline  120  has a first number of teeth greater than the second number of teeth of the secondary flex splines  130  but an equal pitch diameter to that of the secondary flex splines  130 , as best shown in  FIG. 4 . Accordingly, to maintain the same pitch diameter, the primary flex spline  120  can have a different gear tooth thickness compared to the secondary flex splines  130 . In certain embodiments, the primary flex spline  120  can have a thicker gear tooth thickness than the gear teeth of the secondary flex splines  130 . In other embodiments, the primary flex spline  120  can have a thinner gear tooth thickness than the gear teeth of the secondary flex splines  130 . As best shown in  FIGS. 4 and 5 , since the primary flex spline  120  and the secondary flex splines  130  have equal pitch diameters, the corresponding ground arm  102 , secondary ring gear  103 , output arm  104 , and primary ring gear  105  have corresponding dimensions. 
         [0029]    In the illustrated embodiment, the primary flex spline  120  and the secondary flex splines  130  are rotationally independent. Advantageously, the construction of the primary flex spline  120  and the secondary flex splines  130  can prevent stress risers and failure due to fatigue. Advantageously, the construction of the primary flex spline  120  and the secondary flex splines  130  can prevent stress risers and failure due to fatigue. 
         [0030]    Referring to  FIGS. 6-8 , an alternative primary flex spline  120   a  is illustrated. In the illustrated embodiment, the primary flex spline  120   a  has a larger pitch diameter than the pitch diameter of the secondary flex splines  130 . In certain embodiments, the primary flex spline  120   a  can have a smaller pitch diameter than the pitch diameter of the secondary flex splines  130 . In the illustrated embodiment, the primary flex spline  120   a  has a greater number of teeth than the secondary flex splines  130 . In certain embodiments, the primary flex spline  120   a  has a fewer number of teeth than the secondary flex splines  130 . In certain embodiments, the primary flex spline  120   a  can have a teeth thickness that is the same as the secondary flex splines  130 . In certain embodiments, the primary flex spline  120  can have teeth thickness that is thinner than the teeth thickness of the secondary flex splines  130 . 
         [0031]    As shown in  FIG. 7 , the pitch diameter of primary flex spline  120   a  may differ from the secondary flex splines  130 . Therefore, in certain embodiments, the primary ring gear  105   a  and the output arm  104   a  are sized appropriately according to the pitch diameter of the primary flex spline  120   a . As shown in  FIGS. 7 and 8 , if the primary flex spline  120   a  has a pitch diameter greater than the pitch diameter of secondary flex splines  130 , the primary ring gear  105   a  and the output arm  104   a  are recessed relative to the secondary ring gears  103  and the ground arm  102 . 
         [0032]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the embodiments. While the description of the present embodiments has been presented for purposes of illustration and description, it is not intended to be exhaustive or limited to the embodiments in the form disclosed. Many modifications, variations, alterations, substitutions or equivalent arrangement not hereto described will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the embodiments. Additionally, while various embodiments have been described, it is to be understood that aspects may include only some of the described embodiments. Accordingly, the embodiments are not to be seen as limited by the foregoing description, but are only limited by the scope of the appended claims.