Patent Publication Number: US-2023140554-A1

Title: Strain wave gearing

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Japanese Patent Application No. 2019-222917, filed on Dec. 10, 2019, the entire disclosure of which is incorporated by reference herein. 
     FIELD 
     The present disclosure relates generally to a strain wave gearing. 
     BACKGROUND 
     In the related art, there are reduction drives that use strain wave gearings. For example, Japanese Unexamined Patent Application Publication No. 2012-72912 describes a strain wave gearing that includes a circular spline as an internal gear, a flex spline as an external gear, and a wave generator having an elliptical cam. The flex spline is flexed in an elliptical shape by the cam of the wave generator, and partially engages with the circular spline. Then, when the cam of the wave generator rotates in accordance with a rotation input, the engagement positions between the two gears move in the circumferential direction, thereby producing, between the two gears, relative rotational motion corresponding to the difference in the number of teeth of the two gears. The device according to Japanese Unexamined Patent Application Publication No. 2012-72912 has a structure in which the output shaft is attached to a diaphragm that forms the bottom of the cup-like flex spline. 
     Herein, a plurality of imaginary points arranged in a circumferential direction centered on a rotational axis (hereinafter referred to as “axis”) of the output shaft is considered to be the transmitting points of force from the rotating flex spline to the output shaft. The vector of the force applied to each imaginary point from the rotating flex spline is not uniformly directed in the circumferential direction. That is, shifts occur in the phase depending on the point due to the flexibility of the flex spline, the cam shape of the wave generator, and the like. 
     With the flex spline according to Japanese Unexamined Patent Application Publication No. 2012-72912, the output shaft is fixed to the diaphragm that closes one end of the cylinder portion. As such, this flex spline has a structure that transmits rotational force to the output shaft around the entire circumference of the cylinder portion. In this structure, a large number of vectors of force in which the flex spline has caused phase shifts such as described above exist. As such, unnecessary stress that does not contribute to the torque for rotating the output shaft is generated in, and unnecessary twisting force is applied to, the cylinder portion of the flex spline. In addition to this unnecessary twisting force being applied, there is a problem in that the flex spline is more likely to break due to the cylinder portion being formed extremely thin (for example, the thickness is about 0.1 mm). 
     Additionally, with the flex spline according to Japanese Unexamined. Patent Application Publication No. 2012-72912, the position of the output shaft is separated from the rotating body on the input side (for example, the cam of the wave generator) by an amount corresponding to the height (length along the axis) of the cylinder portion of the flex spline. Consequently, there is a problem in that the size of the device in the direction along the axis increases. 
     An objective of the present disclosure is to provide a strain wave gearing that is less likely to break and that can suppress increases in the size of the device. 
     SUMMARY 
     A strain wave gearing according to the present disclosure that achieves the objective described above includes: 
     an internal gear including an inner gear formed along an inner circumferential surface; 
     a wave generator including a cam that rotates around an axis in accordance with a rotation input; 
     a flex gear including (i) a ring-shaped outer gear that is formed along an outer peripheral surface with a smaller number of teeth than the inner gear and that has an inner circumferential side fitted to the wave generator and (ii) an adjacent member adjacent to the outer gear in a direction along the axis; 
     an outputter that includes an opposing portion facing the adjacent member in a radial direction centered on the axis and that rotates together with the flex gear with respect to the internal gear; and 
     a transmitter that extends along the radial direction and that transmits motive power of the flex gear to the outputter, wherein 
     the cam has N poles positioned at equal intervals in a circumferential direction centered on the axis, and causes the outer gear to engage with the inner gear at N locations, N being an integer of 2 or greater, 
     the transmitter is fixed to one of the opposing portion and the adjacent member, and an insertion portion into which the transmitter is inserted is provided in another of the opposing portion and the adjacent member, 
     the insertion portion has a width along the circumferential direction that is wider than the transmitter, and allows relative displacement in the circumferential direction of the flex gear and the outputter, and 
     a plurality of transmission pairs is arranged in the circumferential direction, the transmission pairs being pairs of the transmitter and the insertion portion. 
     According to the present disclosure it is possible to provide a strain wave gearing that is less likely to break and that can suppress increases in the size of the device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of this application can be obtained when the following detailed description is considered in conjunction with the following drawings, in which: 
         FIG.  1    is a schematic cross-sectional view of the main configuration of a strain wave gearing according to an embodiment of the present disclosure; 
         FIG.  2 A  is a drawing in which the main configuration of the strain wave gearing according to the embodiment is viewed from an axial direction, illustrating a case in which a number of poles of a cam is 2; 
         FIG.  2 B  is a drawing illustrating a portion of an outer peripheral surface of a flex gear; 
         FIG.  3    is drawing for explaining the arrangement and features of a transmitter according to the embodiment; 
         FIG.  4 A  is a drawing in which a cam for which the number of poles is 3 and the flex gear are viewed from the axial direction; 
         FIG.  4 B  is a drawing in which a cam for which the number of poles is 4 and the flex gear are viewed from the axial direction; 
         FIG.  5    is a drawing illustrating Modified Example 1, in which the part of the configuration of the strain wave gearing according to the embodiment is modified; 
         FIG.  6 A  is a drawing illustrating Modified Example 2, in which the part of the configuration of the strain wave gearing according to the embodiment is modified; and 
         FIG.  6 B  is a drawing illustrating Modified Example 3, in which the part of the configuration of the strain wave gearing according to the embodiment is modified. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure are described while referencing the drawings. 
     As illustrated in  FIG.  1   , a strain wave gearing  100  is incorporated into an industrial robot  200 . In one example, the robot  200  is constituted from a vertical articulated robot. The robot  200  includes a first arm  211 , a second arm  212  connected to the first arm  211  via the strain wave gearing  100 , a motor  213 , and a non-illustrated controller. The motor  213  consists of a servo motor or the like, and operates on the basis of control of the controller. The controller rotates/drives the second arm  212  via the motor  213  installed in the first arm  211  and the strain wave gearing  100  to carry out positioning control, angle control, and rotation speed control of the second arm  212  with respect to the first arm  211 . 
     The strain wave gearing  100  includes a wave generator  10 , a flex gear  20 , an internal gear  30 , an outputter  40 , a supporter  50 , and a transmitter  6   a.    
     Note that, in  FIG.  1   , to make the drawing easier to view, a part of the hatching indicating the cross-section of the configuration is omitted. In the following, when explaining the configuration of the strain wave gearing  100 , the right side in  FIG.  1    is referred to as the input side (indicated as “Si”) and the left side is referred to as the output side (indicated as “So”). The same is true for  FIG.  9   , described later. 
     The wave generator  10  includes a cylindrical shaft  11 , a cam  12  that is formed integrally with the cylindrical shaft  11 , and a wave bearing  13 . 
     An input-side end of the cylindrical shaft  11  is rotatably supported by a bearing B 1 , and an output-side end of the cylindrical shaft  11  is rotatably supported by a bearing B 2 . The bearing B 1  is provided on an immovable part  211   a  that is immovable with respect to the first arm  211 . The bearing B 2  is provided on an inner circumferential surface of the outputter  40 . In one example, the bearings B 1 , B 2  are implemented as ball bearings. Due to this configuration, the cylindrical shaft  11  is supported rotatably around an axis AX with respect to the first arm  211 . The rotational motive power of the motor  213  is transmitted to the cylindrical shaft  11  by a known transmission mechanism. It is sufficient that this transmission mechanism is a gear mechanism, a belt mechanism using a timing belt and a pulley, or the like. 
     The cam  12  is provided protruding in an outer diameter direction from the outer peripheral surface of the cylindrical shaft  11 . The cam  12  is provided at a position adjacent to the bearing B 1  in a direction along the axis AX (hereinafter referred to as the “axial direction”). The cam  12  has N poles (where N is an integer of 2 or greater) positioned at equal intervals in a circumferential direction centered on the axis AX. In the following, the number of poles of the cam  12  is referred to as the “number of poles.” For example, as illustrated in  FIG.  2 A  a cam  12  for which the number of poles N=2 has an elliptical shape when viewed from the axial direction. 
     As illustrated in  FIGS.  1  and  2 A , the wave bearing  13  includes an inner ring  13   i  fixed to the outer peripheral surface of the cam  12 , a flexible outer ring  13   o , and a plurality of balls  13   b  inserted in a rollable state between the inner ring  13   i  and the outer ring  13   o . Note that the inner ring  13   i  may be formed from a portion including the outer peripheral surface of the cam  12 . 
     The flex gear  20  is provided with flexibility due to a metal material such as a special steel or the like and, in one example, is formed in a cylindrical shape along the axial direction. The flex gear  20  includes an outer gear  21 , and an adjacent member  22  that is formed integrally with the outer gear  21 . 
     The outer gear  21  includes a plurality of teeth  21   a  formed along the outer peripheral surface, is formed in a ring shape, and has an inner circumferential side fitted to the outer ring  13   o  of the wave generator  10 . The plurality of teeth  21   a  of the outer gear  21  are arranged along the circumferential direction at a set pitch. A number of teeth t that is the number of the teeth  21   a  of the outer gear  21  is less than a number of teeth T that is the number of the teeth  31   a  of an inner gear  31  (described later). In one example, when the number of poles of the cam  12  is N, the relationship between the number of teeth t and the number of teeth T is set so that T=t+N is established. For example, when N=2, the relationship of T=t+2 is established. 
     The adjacent member  22  is adjacent to the outer gear  21  in the axial direction, and pushes out more to the output side than the outer gear  21 . As illustrated in  FIGS.  2 A and  2 B , the adjacent member  22  includes an insertion portion  6   b  into which the transmitter  6   a  is inserted. The motive power of the flex gear  20  is transmitted to the outputter  40  via the transmitter  6   a  that is inserted into the insertion portion  6   b . A plurality of insertion portions  6   b  is provided along the circumferential direction centered on the axis AX. The number of insertion portions  6   b  is the same as the number of transmitters  6   a . The transmitter  6   a  and the insertion portion  6   b  are described later. 
     Note that, in  FIGS.  2 A and  2 B , the adjacent member  22  of the flex gear  20  is partially illustrated.  FIG.  2 B  is a drawing of a portion of the outer peripheral surface of the flex gear  20 , viewed from the 0° direction illustrated in  FIG.  2 A . 
     The adjacent member  22  may have any shape. For example, the entire circumference of the adjacent member  22  may push out more than the outer gear  21  in a ring-like manner, or the adjacent member  22  may push out more to the output side than the outer gear  21  at each portion where the insertion portion  6   b  is provided. 
     The internal gear  30  is formed with rigidity due to the metal material, and is fixed to an inner side of the first arm  211 . The internal gear  30  includes an inner gear  31  that partially engages with the outer gear  21  of the flex gear  20  flexed by the cam  12 . The inner gear  31  includes a plurality of teeth  31   a  formed along the inner circumferential surface, and is formed in a ring shape. The plurality of teeth  31   a  of the inner gear  31  is arranged along the circumferential direction at a set pitch. 
     The outputter  40  rotates together with the flex gear  20  with respect to the internal gear  30 . The outputter  40  is supported, by the supporter  50 , rotatably around the axis AX with respect to the internal gear  30 . In one example, the outputter  40  is formed in a ring shape, with rigidity due to the metal material. 
     The outputter  40  includes an opposing portion  41  that faces the adjacent member  22  of the flex gear  20  in a radial direction centered on the axis AX (hereinafter referred to simply as the “radial direction”), and a supported portion  42  that is a portion positioned more to the output side that the opposing portion  41  and supported by the supporter  50 . A fixing hole  41   a  for fixing the transmitter  6   a  to the outputter  40  is formed in the opposing portion  41 . As illustrated in  FIG.  1   , the opposing portion  41  of the outputter  40  is positioned on the inner circumferential side of the adjacent member  22  of the flex gear  20 . 
     In one example, the supporter  50  is constituted from a cross roller bearing, and includes an outer ring  51  fixed to the internal gear  30 , and an inner ring  52  fixed to the supported portion  42  of the outputter  40 . 
     In this embodiment, the outputter  40  is connected to the second arm  212  that is the load of the strain wave gearing  100 , via the inner ring  52  of the supporter  50 . As a result of this configuration, the second arm  212  rotates around the axis AX due to the rotation of the outputter  40 . Note that the mode of supporting the outputter  40  by the supporter  50  and the method of connecting the outputter  40  to the load can be changed as desired. 
     As illustrated in  FIG.  1   , the adjacent member  22  of the flex gear  20  and the opposing portion  41  of the outputter  40  are positioned between the supporter  50  and the cam  12  in the axial direction. The transmitter  6   a  fixed to the outputter  40  is pressed, by the flex gear  20 , in the circumferential direction centered on the axis AX (hereinafter referred to simply as the “circumferential direction”) and, as a result, the outputter  40  rotates together with the flex gear  20 . 
     The transmitter  6   a  transmits the motive power of the flex gear  20  to the outputter  40 , and is fixed to the opposing portion  41  of the outputter  40 . In one example, the transmitter  6   a  is constituted by a cylindrical pin. The transmitter  6   a  is inserted into the fixing hole  41   a  of the opposing portion  41 , and is fixed by a known method such as screwing, fitting, sticking, welding, or the like. The transmitter  6   a  extends along the radial direction centered on the axis AX and toward the adjacent member  22  of the flex gear  20 , and is inserted into the insertion portion  6   b  of provided on the adjacent member  22 . 
     As illustrated in  FIGS.  2 A and  2 B , the transmitter  6   a  is inserted in the insertion portion  6   b . The insertion portion  6   b  is an elongated hole having an opening diameter in the circumferential direction (indicated by “C” in the drawings) that is longer than the outer diameter (diameter) of the pin constituting the transmitter  6   a . Due to this configuration, the insertion portion  6   b  allows relative displacement in the circumferential direction of the flex gear  20  and the transmitter  6   a  (that is, relative displacement in the circumferential direction of the flex gear  20  and the outputter  40 ). The elongated hole serving as the insertion portion  6   b  is a through-hole that penetrates the adjacent member  22  in the radial direction centered on the axis AX. Accordingly, the insertion portion  6   b  also allows relative displacement in the radial direction of the flex gear  20  and the transmitter  6   a  (that is, relative displacement in the radial direction of the flex gear  20  and the outputter  40 ). It is sufficient that the length in the circumferential direction of the insertion portion  6   b  is set such that a first pair  61  and a second pair  62  (described later) can appear as pairs of the transmitter  6   a  and the insertion portion  6   b . Additionally, it is sufficient that the width in the axial direction of the insertion portion  6   b  is slightly greater than the outer diameter of the pin constituting the transmitter  6   a , and is a size that does not obstruct movement in the circumferential direction and the radial direction of the transmitter  6   a  in the insertion portion  6   b . As illustrated in  FIG.  3   , a plurality of transmission pairs, each of which is a pair of a transmitter  6   a  and an insertion portion  6   b , is provided along the circumferential direction, and is arranged at equal intervals in the circumferential direction. 
     Deceleration Operations 
     Next, the deceleration operations of the strain wave gearing  100  are described. 
     Provided that the number of poles N of the cam  12  is 2 or greater, the number of poles N can be set as desired according to an objective. Here, a case is described of a cam  12  in which N=2 and an elliptical shape is formed. 
     When the motor  213  operates due to control by the controller of the robot  200 , the rotational motive power of the motor  213  is transmitted to the cam  12  of the wave generator  10  via the non-illustrated transmission mechanism, and the cam  12  rotates at a comparatively high speed around the axis AX. 
     Here, to facilitate comprehension, it is assumed that the cam  12  prior to rotation start is, as illustrated in  FIG.  2 A , at an initial position where the long axis of the elliptical shape of the cam  12  is aligned with an axis that passes through 0° and 180°. The cam  12  that is at the initial position causes the outer gear  21  of the flex gear  20  to engage with the inner gear  31  of the internal gear  30  at two engagement positions, namely 0° and 180°, which correspond to the two poles. Note that the illustrated angles are angles centered on the axis AX. The twelve o&#39;clock direction is 0°, and angles increase in the clockwise direction. It is assumed that the cam  12  rotates in the clockwise direction. 
     In a case in which θ is the angle that the flex gear  20  rotates in the counter-clockwise direction with respect to the internal gear  30  when the cam  12  rotates an angle α in the clockwise direction from the initial position, θ={360°×(T−t)/T}×α/360°=(α/T)×N is established. When using a cam  12  in which the number of poles N=2, the difference between the numbers of teeth of the inner gear  31  and the outer gear  21  is T−t=N=2 and, as such, θ=(α/T)×2 is established. For example, when this cam  12  rotates 90°, the flex gear  20  rotates in the counter-clockwise direction the angle θ=(90°/T)×2, which corresponds to the amount of ½ tooth, which is ¼ (90°/360°) the difference between the numbers of teeth of 2. 
     Thus, the flex gear  20  elastically deforms in accordance with the rotation of the cam  12 , and the engagement positions with the internal gear  30  sequentially move. Moreover, when the cam  12  rotates 360°, the flex gear  20  rotates in the counter-clockwise direction the angle θ=(360°/T)×2, which corresponds to the amount of the difference between the numbers of teeth of 2. Thus, the outputter  40  that rotates/moves together with the flex gear  20  is decelerated by a reduction ratio i=(T−t)/t with respect to the rotation speed of the cam  12 . That is, according to the strain wave gearing  100 , it is possible to rotate/control, with high accuracy, the load (in this example, the second arm  212 ) connected to the outputter  40  with output decelerated by the reduction ratio i described above. Note that any reduction ratio i can be used. For example, the reduction ratio i can be set to about 1/30 to 1/320. 
     In the description given above, a case is described in which the number of poles N=2, but the concept is the same for cases in which N≥3 and, as such, such cases are described collectively. When then number of poles N≥3, the shape of the cam  12  when viewed from the axial direction forms a regular N-sided shape and, in one example, each pole and the space between adjacent poles has a curved surface shape that gently expands in the outer peripheral direction.  FIG.  4 A  illustrates a case in which the number of poles N is 3, and  FIG.  4 B  illustrates a case in which the number of poles N is 4. Note that, while not illustrated in the drawings, the same effects can be realized for cases in which N≥5. 
     The outer gear  21  of the flex gear  20  is flexed by the cam  12  having the N poles via the wave bearing  13 , and engages with the inner gear  31  of the internal gear  30  at the N locations. When the number of poles of the cam  12  is N, the relationship between the number of teeth t of the outer gear  21  (hereinafter referred to as the “number of teeth t of the flex gear  20 ”) and the number of teeth T of the inner gear  31  (hereinafter referred to as the “number of teeth T of the internal gear  30 ”) is set such that T=t+N is established. 
     Moreover, when, for example, the cam  12  rotates 360° in the clockwise direction, the flex gear  20  moves an amount corresponding to N teeth in the counter-clockwise direction. Specifically, when the number of poles of the cam  12  is N, when the cam  12  rotates the angle (360°/N), the flex gear  20  moves an amount corresponding to one tooth with respect to the internal gear  30 . When the number of poles of the cam  12  is N, the outputter  40  fixed to the flex gear  20  is decelerated by the reduction ratio i=(T−t)/t=N/t with respect to the rotation speed of the cam  12 . 
     As described above, with the strain wave gearing  100 , when the number of poles N of the cam  12  is set to 2, and even when N≥3, when the cam  12  of the wave generator  10  rotates in accordance with rotation input from the motor  213 , the engagement positions of the gears of the flex gear  20  and the internal gear  30  move in the circumferential direction, and the flex gear  20  rotates in the opposite direction of the cam  12  with respect to the internal gear  30 , in accordance with the difference between the numbers of teeth of the two gears. 
     Transmitter  6   a  and insertion portion  6   b  Next, the transmitter  6   a  and the insertion portion  6   b  are described.  FIG.  3    illustrates a preferred arrangement example of the transmitter  6   a  and the insertion portion  6   b  in which the number of poles N of the cam  12  is 4 (that is, the shape illustrated in  FIG.  4 B ). 
     Note that, in  FIG.  3   , the portion of drawing located outward from the illustration of the flex gear  20  and the outputter  40  viewed from the axial direction illustrates the relative displacement of the transmitter  6   a  and the insertion portion  6   b  in the illustrated 0° to 90° range, in a case in which a cam  12  in which the number of poles N is 4 is rotating around the axis AX in accordance with the operations of the motor  213  (hereinafter referred to as “relative displacement drawing”). 
     Viewing the relative displacement drawing of  FIG.  3   , it is understood that the position of the transmitter  6   a  with respect to the insertion portion  6   b  is not uniform at each position where the transmitter  6   a  is provided. This is caused by the phase shifting described above in the summary. The strain wave gearing  100  according to the present embodiment uses the hereinafter described effects of the transmitter  6   a  and the insertion portion  6   b  to reduce the unnecessary stress that is caused by the phase shift and that does not contribute to the rotation of the outputter  40 , and rotates the outputter  40  with excellent transmission efficiency. 
     In the example illustrated in  FIG.  3 ,  16    transmitters  6   a  arranged at equal intervals in the circumferential direction are fixed to the opposing portion  41  of the outputter  40 . Additionally, 16 of the insertion portions  6   b  are provided on the adjacent member  22  of the flex gear  20 . Each of 16 of the transmitters  6   a  is inserted into each of the insertion portions  6   b . Specifically, the transmission pairs that are pairs of a transmitter  6   a  and an insertion portion  6   b  are arranged in the circumferential direction every 360°/16 (=22.5°). 
     As illustrated in the relative displacement drawing of  FIG.  3   , in the transmission pair positioned in the 0° direction, in a state in which the transmitter  6   a  is positioned in the center in the circumferential direction of the insertion portion  6   b , the transmitter  6   a  positioned in the 45° direction and the transmitter  6   a  positioned in the 90° direction are positioned in the center in the circumferential direction of the insertion portion  6   b  corresponding to each transmitter  6   a . The transmitters  6   a  positioned in the 0°, 45°, and 90° directions do not contact the insertion portion  6   b  corresponding to each transmitter  6   a  in the circumferential direction and, as such do not contribute to the rotation of the outputter  40 . 
     In the following, transmission pairs in which the transmitter  6   a  is positioned at the center of the insertion portion  6   b  in the circumferential direction, such as the transmission pairs positioned in the 0°, 45°, and 90° directions of  FIG.  3   , are referred to as “first state transmission pairs.” That is, the first state transmission pairs do not contribute to the rotation of the outputter  40 . 
     Meanwhile, in a state in which the first state transmission pairs are positioned in the 0°, 45°, and 90° directions, the transmitter  6   a  positioned in the 22.5° direction is positioned at one end (the end in the clockwise direction in the drawing) of the insertion portion  6   b  in which that transmitter  6   a  is inserted. Additionally, the transmitter  6   a  positioned in the 67.5° direction is positioned at the other end (the end in the counter-clockwise direction in the drawing) of the insertion portion  6   b  in which that transmitter  6   a  is inserted. The transmitter  6   a  positioned in the 22.5° direction contacts, in the circumferential direction, the insertion portion  6   b  of the flex gear  20  that moves in the counter-clockwise direction when the cam  12  is rotating in the clockwise direction and, as such, contributes to the rotation of the outputter  40 . The transmitter  6   a  positioned in the 67.5° direction contacts, in the circumferential direction, the insertion portion  6   b  of the flex gear  20  that moves in the clockwise direction when the cam  12  is rotating in the counter-clockwise direction and, as such, contributes to the rotation of the outputter  40 . 
     In the following, transmission pairs in which the transmitter  6   a  contacts the insertion portion  6   b  in the circumferential direction, such as the transmission pairs positioned in the 22.5° and 67.5° directions of  FIG.  3   , are referred to as “second state transmission pairs.” That is, the second state transmission pairs contribute to the rotation of the outputter  40 . 
     Note that the behavior of the transmitters  6   a  and the insertion portions  6   b  in each of the 90° to 180°, 180° to 270°, and 270° to 360° ranges is the same as the transmitters  6   a  and the insertion portions  6   b  in the 0° to 90° range. That is, the first state transmission pairs and the second state transmission pairs alternately appear every position where the center angle with respect to the axis AX is 22.5°. Additionally, although the relative displacement drawing of  FIG.  3    is illustrated in a static manner, the first state transmission pairs transition to second state transmission pairs via an intermediate state in accordance with the rotation of the flex gear  20 . Conversely, the second state transmission pairs transition to first state transmission pairs via the intermediate state. Specifically, in a process in which the outputter  40  rotates 22.5°, the transmitters  6   a  that are not contributing to the rotation of the outputter  40  are displaced with respect to the insertion portions  6   b , thereby contacting the flex gear  20  in the circumferential direction and becoming transmitters  6   a  that contribute to the rotation of the outputter  40 . Conversely, the transmitters  6   a  that contact the flex gear  20  in the circumferential direction and are contributing to the rotation of the outputter  40  are displaced with respect to the insertion portions  6   b , thereby becoming transmitters  6   a  that do not contribute to the rotation of the outputter  40 . 
     Next, an overview of the transmission pairs illustrated in  FIG.  3    is given. 
     When the number of poles N of the cam  12  is 4, when the cam  12  rotates the angle (360°/ 4 ), the flex gear  20  moves an amount corresponding to one tooth with respect to the internal gear  30 . Thus, in the 90° range that is the rotation angle of the cam  12  for moving the flex gear  20  an amount corresponding to one tooth with respect to the internal gear  30 , the first state transmission pairs and the second state transmission pairs alternately appear every 90°/4=22.5°. The transmission pairs in the 90° range include a first pair  61  in which the transmitter  6   a  is positioned at one end in the circumferential direction of the insertion portion  6   b , and a second pair  62  in which the transmitter  6   a  is positioned at the other end in the circumferential direction of the insertion portion  6   b.    
     In the relative displacement drawing of  FIG.  3   , the first pair  61  is positioned in the 22.5° direction, and the second pair  62  is positioned in the 67.5° direction. Extending this to the 360° range, the 16 transmission pairs include four of the first pairs  61  arranged at equal intervals in the circumferential direction and four of the second pairs  62  arranged at equal intervals in the circumferential direction. The first pairs  61  and the second pairs  62  alternately exist every 45° in the 360° range. 
     The concept described above is not limited to cases in which N=4, and can be generalized. Accordingly, a case in which the number of poles of the cam  12  is N (an integer of 2 or greater) and there are (4×N) transmission pairs is described. The transmission pairs are arranged at equal intervals in the circumferential direction. 
     When the cam  12  in which the number of poles is N rotates the angle (360°/N), the flex gear  20  moves an amount corresponding to one tooth with respect to the internal gear  30 . Thus, in the (360°/N) range that is the rotation angle of the cam  12  for moving the flex gear  20  an amount corresponding to one tooth with respect to the internal gear  30 , the first state transmission pairs and the second state transmission pairs alternately appear every 360°/(4×N). The transmission pairs in the (360°/N) range include the first pair  61  and the second pair  62 . Extending this to the 360° range, the (4×N) transmission pairs include N of the first pairs arranged at equal intervals in the circumferential direction and N of the second pairs arranged at equal intervals in the circumferential direction. Furthermore, the first pairs  61  and the second pairs  62  alternately exist every 360° (2×N). 
     Note that, when the number of poles of the cam  12  is N, (4×N) or more transmission pairs may be provided. In such a case, the plurality of transmission pairs includes first state transmission pairs, second state transmission pairs, and intermediate state transmission pairs that are transitioning from one of the first state and the second state to the other of the first state and the second state. The transmitters Ga of the intermediate state transmission pairs do not contact the insertion portions  6   b  in the circumferential direction and, as such, the intermediate state transmission pairs do not contribute to the rotation of the outputter  40 . However, as with the first state transmission pairs, the intermediate state transmission pairs transition, in accordance with the rotation of the flex gear  20 , to second state transmission pairs that contribute to the rotation of the outputter  40 . 
     As described above, the first state transmission pairs and the second state transmission pairs appear alternately and, as such, the relative displacement of the transmitter  6   a  and the insertion portion  6   b  in the circumferential direction can be absorbed by the so-called cam method. Therefore, according to the strain wave gearing  100 , the occurrence of unnecessary stress, that does not contribute to the torque for rotating the outputter  40 , in each of the flex gear  20  and the outputter  40  can be reduced and the application of unnecessary twisting force to the flex gear  20  can be reduced. 
     When the flex gear  20  flexed by the cam  12  rotates/moves with respect to the internal gear  30 , the two gears of the flex gear  20  and the internal gear  30  engage and move. As such, pulsation in the radial direction is generated. The insertion portion  6   b  according to the present embodiment also allows relative displacement of the flex gear  20  and the transmitter  6   a  in the radial direction. As such, relative displacement of the transmitter  6   a  and the insertion portion  6   b  in the radial direction can also be absorbed. This also leads to a reduction in the unnecessary stress described above. 
     The second state transmission pairs include the first pair  61  and the second pair  62  that are arranged at equal intervals in the circumferential direction. Due to this, force in the circumferential direction can be efficiently transmitted from the flex gear  20  to the outputter  40 . 
     As a result, according to the strain wave gearing  100  of the present embodiment, the mechanical loss caused when the flex gear  20  is completely fixed to the outputter  40  can be significantly reduced, and excellent transmission efficiency can be realized. Additionally, breaking of the flex gear  20  can be suppressed. 
     Since the output points (that is, the positions where the transmitter  6   a  is provided) at which the force from the flex gear  20  is transmitted to the outputter  40  are uniformly distributed in the circumferential direction, the load per engagement location between the flex gear  20  and the internal gear  30  is reduced and, as a result, the outputter  40  can be rotated with high torque. 
     Note that the number of transmission pairs is not limited to (4×N). The number of transmission pairs can be changed as desired depending on the number of N. 
     For example, in a case in which the number of poles N of the cam  12  is 8, when there are (4×N)=32 transmission pairs, in the (360°/N)=45° range that is the rotation angle of the cam  12  for moving the flex gear  20  an amount corresponding to one tooth with respect to the internal gear  30 , the first state transmission pairs and the second state transmission pairs alternately appear every {360°/(4×N)}=11.25°. Extending this to the 360° range, the 32 transmission pairs include eight of the first pairs  61  arranged at equal intervals in the circumferential direction and eight of the second pairs  62  arranged at equal intervals in the circumferential direction. 
     However, providing four of each of the first pair and the second pair is thought to be sufficient to stably rotate the outputter  40  and, as such, (2×N)=16 transmission pairs may be provided. In addition to cases where N=8, it is thought it is possible to configure so that all of the transmitters  6   a  contribute to the rotation of the outputter  40  by setting the transmission pairs to (2×N) and providing N each of the first pairs  61  and the second pairs  62 . Furthermore, the number of transmission pairs may be set regardless of the number of N. For example, provided that 16 transmission pairs are arranged at equal intervals in the circumferential direction and at least four or more of each of the first pairs  61  and the second pairs  62  are provided, the outputter  40  can be stably rotated, regardless of the number of N. Thus, the outputter  40  to which the transmitter  6   a  is fixed can be shared regardless of the number of poles N of the cam  12  and, as such, manufacturing efficiency can be improved. 
     As described above, even in the case of a strain wave gearing  100  in which the number of transmission pairs is set to (2×N) or is set to a fixed value (for example, 16) independent of the number of N, the unnecessary stress can be reduced and excellent transmission efficiency can be realized due to the same effects as described above. 
     Note that, in the first pairs  61 , it is sufficient that “the transmitter  6   a  is positioned on one end in the circumferential direction of the insertion portion  6   b ” is a mode in which the transmitter  6   a  contacts or is proximal to the one end in the circumferential direction of the insertion portion  6   b.    
     Likewise, in the second pairs  62 , it is sufficient that “the transmitter  6   a  is positioned on the other end in the circumferential direction of the insertion portion  6   b ” is a mode in which the transmitter  6   a  contacts or is proximal to the other end in the circumferential direction of the insertion portion  6   b . That is, in a case in which the flex gear  20  moves toward the transmitter  6   a , it is sufficient that first pairs  61  and the second pairs  62  are in a mode in which the transmitter  6   a  can immediately be pushed in the circumferential direction by the insertion portion  6   b.    
     It is sufficient that the plurality of transmission pairs “is arranged at equal intervals in the circumferential direction” is a state in which the plurality of transmitters  6   a  arranged at equal intervals in the circumferential direction is inserted into the plurality of insertion portions  6   b  corresponding to the plurality of transmitters  6   a . For example, the “transmission pairs positioned in each of the 0°, 45°, and 90° directions” refers to transmission pairs in which the transmitters  6   a  are positioned in each of the 0°, 45°, and 90° directions. This relationship is true for other angles as well. Note that, since the insertion portion  6   b  is provided in the flex gear  20  that has flexibility, depending on the state of the transmission pairs, a shift in a range of −2 degrees to +2 degrees with respect to the corresponding transmitter  6   a  occurs. 
     Provided that the first pairs  61  and the second pairs  62  can be created, the plurality of transmission pairs need not be arranged at equal intervals in the circumferential direction. In such a case, from the perspective of stably rotating the outputter  40 , it is preferable that the overall center of gravity of the outputter  40  and the plurality of transmitters  6   a  fixed to the outputter  40  match the axis AX, and that the moment of inertia around the axis AX is minimized. 
     In the strain wave gearing  100 , the adjacent member  22  of the flex gear  20  and the opposing portion  41  of the outputter  40  are positioned between the supporter  50  and the cam  12 . Due to this, the distance in the axial direction from the rotation input element to the output element can be shortened. As a result, each component can be made compact in the axial direction, and a size of the strain wave gearing  100  can be reduced. Additionally, when the distance in the axial direction from the rotation input element to the output element is short, stress in a diagonal direction with respect to the axis AX is less likely to be applied to the flex gear  20  and the internal gear  30  that engage with each other. As a result, tooth crests of one of the flex gear  20  and the internal gear  30  and tooth bottoms of the other of the flex gear  20  and the internal gear  30  can be made to contact along the axial direction, and friction between the gears can be suppressed. 
     In the strain wave gearing  100 , in addition to the cam  12 , the flex gear  20  and the outputter  40  are also hollow shapes that form a ring shape when viewed from the axial direction. As such, it is possible to secure space inside the device for routing wiring or the like. Additionally, since the output side end of the flex gear  20  is not closed, the flexibility of the flex gear  20  can be maintained while securing a certain degree of thickness of the flex gear  20 . Accordingly, resistance to buckling of the flex gear  20  can be made excellent and the flex gear  20  is less likely to break. Note that the thickness of the flex gear  20  is not limited but, for example, can be set to about 0.5 mm to 1 mm. Additionally, the flex gear  20  has a bottomless cylinder shape and, as such, is easy to machine. Note that, according to the strain wave gearing  100 , it goes without saying that backlash can, in principle, be eliminated and lost motion can be minimized. 
     According to the strain wave gearing  100 , in addition to cases in which the number of poles N of the cam  12  is 2, variations in which N≥3 can be provided. As such, the following benefits are obtained. Firstly, a case is considered in which an elliptical shape (N=2) is set for the cam  12  of the wave generator  10 . When D is the pitch circle diameter of the internal gear  30 , and d is the pitch circle diameter of the flex gear  20 , it can be considered that the reduction ratio i is i=(T−t)/t=2/t or i=(D−d)/d. As such, to reduce the value of the reduction ratio i (to obtain decelerated rotation output), it is necessary to increase the number of teeth t or increase the ratio of the diameter d of the flex gear  20  to the diameter D of the internal gear  30 . Meanwhile, to increase the value of the reduction ratio i (to suppress the degree of deceleration of the rotation output), it is necessary to decrease the number of teeth t or decrease the ratio of the diameter d of the flex gear  20  to the diameter D of the internal gear  30 . Thus, relying solely on an elliptical cam  12  gives rise to various constraints on the size and conditions of the device, and makes it difficult to realize all reduction ratios. 
     However, in a variation in which the number of poles of the cam  12  is N≥3, even if at least one of the number of teeth T of the internal gear  30  and the number of teeth t of the flex gear  20  is maintained constantly, as understood from reduction ratio i=N/t, the value of the reduction ratio can be increased by increasing the number of poles, and the value of the reduction ratio can be decreased by decreasing the number of poles. In addition to variations of the number of poles, it is possible to realize a substantially innumerable number of variations of the reduction ratio by changing the settings of the number of teeth T or the number of teeth t, and changing the diameter of the flex gear  20  or the internal gear  30 . 
     Note that the present disclosure is not limited by the embodiment and drawings described above, and modifications (including the omission of constituents) and the like can be made, as appropriate, without departing from the scope of the present disclosure. In the following, modified examples in which a part of the configuration of the strain wave gearing  100  is modified are described. 
     Modified Example 1 
     As in Modified Example 1 illustrated in  FIG.  5   , a configuration is possible in which the outputter  40  is positioned on the outer peripheral side of the flex gear  20 . In such a case, the opposing portion  41  of the outputter  40  is positioned on the outer peripheral side of the adjacent member  22  of the flex gear  20 . Additionally, the transmitter  6   a  fixed to the opposing portion  41  extends toward the axis AX and is inserted in the insertion portion  6   b  provided in the adjacent member  22 . Note that, in  FIG.  5   , the portion of the drawing located outward from the illustration of the flex gear  20  and the outputter  40  viewed from the axial direction illustrates the relative displacement of the transmitter  6   a  and the insertion portion  6   b  in the illustrated 0° to 90° range, in a case in which a cam  12  in which the number of poles N is 4 is rotating around the axis AX in accordance with the operations of the motor  213 . In Modified Example 1 as well, the number and functions of the transmission pairs that are pairs of the transmitter  6   a  and the insertion portion  6   b  are considered to be the same as in the embodiment described above. 
     Modified Examples 2 and 3 
     As illustrated in  FIGS.  6 A and  6 B , a configuration is possible in which the transmitter  6   a  is fixed to the flex gear  20 , and the insertion portion  6   b  is provided in the outputter  40 . In such a case, a configuration is possible in which the outputter  40  is positioned on the inner circumferential side of the flex gear  20  as in Modified Example 2 illustrated in  FIG.  6 A  and, a configuration is possible in which the outputter  40  is positioned on the outer peripheral side of the flex gear  20  as in Modified Example 3 illustrated in  FIG.  6 B . 
     The transmitter  6   a  according to Modified Examples 2 and 3 is fixed to the adjacent member  22  of the flex gear  20 . This transmitter  6   a  extends along the radial direction centered on the axis AX and toward the opposing portion  41  of the outputter  40 , and is inserted into the insertion portion  6   b  provided in the opposing portion  41 . 
     The insertion portion  6   b  according to Modified Examples 2 and 3 is constituted by an elongated hole into which the transmitter  6   a  is inserted and that has an opening diameter that is longer than the outer diameter (diameter) of the pin constituting the transmitter  6   a . Due to this configuration, the insertion portion  6   b  allows relative displacement in the circumferential direction of the outputter  40  and the transmitter  6   a  (that is, relative displacement in the circumferential direction of the outputter  40  and the flex gear  20 ). Additionally, provided that the insertion portion  6   b  can allow relative displacement in the radial direction of the outputter  40  and the transmitter  6   a  (that is, relative displacement in the radial direction of the outputter  40  and the flex gear  20 ), a configuration is possible in which the insertion portion  6   b  is the bottomed hole illustrated in  FIGS.  6 A and  6 B , and a configuration is possible in which the insertion portion  6   b  is a non-illustrated through-hole. In Modified Examples 2 and 3 as well, the number and functions of the transmission pairs are considered to be the same as in the embodiment described above. In Modified Examples 2 and 3, it is sufficient that the plurality of transmission pairs “is arranged at equal intervals in the circumferential direction” is, for example, a state in which the corresponding plurality of transmitters  6   a  is inserted into the plurality of insertion portions  6   b  arranged at equal intervals in the circumferential direction. 
     Other Modified Examples 
     In the foregoing, an example is described in which the strain wave gearing  100  is incorporated into the robot  200  constituted by a vertical articulated robot. However, the present disclosure is not limited thereto. The strain wave gearing  100  can be incorporated into a variety of robots such as a horizontal articulated robot, a delta-type robot, and the like. Additionally, the device that the strain wave gearing  100  is incorporated into is not limited to a robot, and the strain wave gearing  100  may be incorporated into any device that has an objective of obtaining rotation output decelerated by a desired reduction ratio with respect to the rotation input. For example, in addition to a robot, the strain wave gearing  100  may be incorporated into precision machines, hobby supplies, home electronics, vehicle-mounted components, and the like. 
     Provided that T&gt;t, any values may be used for the number of teeth t of the flex gear  20  and the number of teeth T of the internal gear  30 . However, when the number of poles of the cam  12  is N, it is preferable that the relationship between the number of teeth t and the number of teeth T is set to T=t+N. 
     In the foregoing, an example is described in which one transmitter  6   a  is constituted from one pin, but a configuration is possible in which one transmitter  6   a  is constituted from a plurality of pins arranged in the axial direction. In such a case, it is sufficient that the insertion portion  6   b  corresponding to the transmitter  6   a  is provided with a size that enables the insertion of the plurality of pins constituting the transmitter  6   a . It is sufficient that the insertion portion  6   b  can allow relative displacement of the flex gear  20  and the outputter  40  in the circumferential direction and the radial direction. 
     Any materials may be used for the materials of the members of the strain wave gearing  100 , and are not limited to metal. For example, the materials of the members of the strain wave gearing  100  can be appropriately selected from engineering plastics, resins, ceramics, and the like in accordance with the purpose of the strain wave gearing  100 . 
     The strain wave gearing  100  described above includes, as the configuration that transmits the motive power of the flex gear  20  to the outputter  40 , transmission pairs that are pairs of the transmitter  6   a  and the insertion portion  6   b . The transmitter  6   a  is fixed to one of the opposing portion  41  and the adjacent member  22 , and the insertion portion  6   b  into which the transmitter  6   a  is inserted is provided in the other of the opposing portion  41  and the adjacent member  22 . Moreover, the width in the circumferential direction of the insertion portion  6   b  is greater than that of the transmitter  6   a , and the insertion portion  6   b  allows relative displacement in the circumferential direction of the flex gear  20  and the outputter  40 . According to this configuration, as described above, it is possible to suppress unnecessary stress from being applied to mainly the flex gear  20  and, as such, the strain wave gearing  100  is less likely to break. 
     In the strain wave gearing  100 , the adjacent member  22  that is adjacent to the outer gear  21  is the component that transmits force from the flex gear  20  to the outputter  40 . Due to this, it is possible to suppress increases in the size in mainly the axial direction of the strain wave gearing  100 . Additionally, various reduction ratios can be realized with simple configurations by setting the number of poles N to a desired value. 
     A configuration is possible in which the plurality of transmission pairs is arranged at equal intervals in the circumferential direction. According to such a configuration, since the output points that transmit the force from the flex gear  20  to the outputter  40  are uniformly distributed in the circumferential direction, the outputter  40  can be rotated with high torque. 
     The plurality of transmission pairs includes transmission pairs that satisfy the conditions of the first pair  61  and the second pair  62  when the cam  12  is rotating around the axis AX. Due to this configuration, as described above, the force in the circumferential direction can be efficiently transmitted from the flex gear  20  to the outputter  40 . 
     It is preferable that there are 2×N of the transmission pairs. Additionally, it is preferable that there are N of the first pairs  61  and N of the second pairs  62 . Moreover, it is preferable that the first pairs  61  and the second pairs  62  alternately exist every 360°/(2×N) at angles centered on the axis AX. Note that a configuration is possible in which there are 4×N of the transmission pairs, and a configuration is possible in which there is a fixed number (for example, 16) of the transmission pairs regardless of the number of poles N. 
     The insertion portion  6   b  allows relative displacement of the flex gear  20  and the outputter  40  in the radial direction. According to this configuration, relative displacement of the flex gear  20  and the outputter  40  in the radial direction can also be absorbed and, as such, the unnecessary stress described above can be reduced even more. 
     In the strain wave gearing  100 , the adjacent member  22  and the opposing portion  41  are positioned between the supporter  50  and the cam  12 . According to this configuration, as described above, the length in the axial direction from the cam  12  to the output point of the flex gear  20  can be reduced, each component can be made compact in the axial direction, and a smaller configuration of the strain wave gearing  100  can be achieved. When the length to the output point can be suppressed in this manner, the tooth crests of one of the flex gear  20  and the internal gear  30  and the tooth bottoms of the other of the flex gear  20  and the internal gear  30  can be made to contact along the axial direction, and friction between the gears can also be suppressed. Note that the supporter  50  is not limited to a cross roller bearing, and may be a ball bearing, a bearing that slidably/rotatably supports the outputter  40 , or the like. 
     It is preferable that the transmitter  6   a  is constituted by a column-shaped pin, and the insertion portion  6   b  is constituted by an elongated hole that has an opening diameter in the circumferential direction that is longer than the outer diameter of the pin. 
     As illustrated in  FIGS.  1 ,  3 , and  6 A , with a configuration in which the opposing portion  41  is positioned on the inner circumferential side of the adjacent member  22 , it is possible to suppress increases in the size of the strain wave gearing  100  in the radial direction. 
     As illustrated in  FIGS.  5  and  6 B , with a configuration in which the opposing portion  41  is positioned on the outer peripheral side of the adjacent member  22 , space inside the strain wave gearing  100  for routing wiring and the like can be secured, near the axis AX of the strain wave gearing  100 . 
     In the foregoing, descriptions of known technical matters are omitted facilitate comprehension of the present disclosure. 
     The foregoing describes some example embodiments for explanatory purposes. Although the foregoing discussion has presented specific embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the broader spirit and scope of the invention. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. This detailed description, therefore, is not to be taken in a limiting sense, and the scope of the invention is defined only by the included claims, along with the full range of equivalents to which such claims are entitled.