Patent Publication Number: US-2022226985-A1

Title: Robot and its servo motor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present disclosure is based on and claims priority to Chinese Patent Application No. 202120117227.X, filed Jan. 15, 2021, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to the field of robot technologies, and in particular, to a servo motor and a robot having the servo motor. 
     BACKGROUND 
     Servo motors are commonly used drive devices for footed robots (also known as legged robots) and used to drive a leg assembly of the robot so that the footed robot can move. In related art, in order to control the movement of the leg assembly, a position sensor and a magnet are usually utilized to detect a relative position of a stator and a rotor, but an absolute position of the motor output cannot be detected. Consequently, robot control accuracy is relatively low in the art. 
     SUMMARY 
     A servo motor according to embodiments of the present disclosure includes: a housing; a rotor arranged in the housing and having a rotor support and a rotor shaft; a stator arranged in the housing; a planetary reduction mechanism arranged in the housing and including a sun gear, a planetary carrier, and a plurality of planetary gears, a reduction ratio of the planetary reduction mechanism being N:1, where N is a positive integer; a first Hall magnet arranged on the planetary carrier; a plurality of Hall switches corresponding to the first Hall magnet and arranged in the housing at even intervals around a rotation axis of the rotor shaft, wherein a number of Hall switches is N; a second Hall magnet arranged on the rotor; and a position sensor arranged in the housing and opposite the second Hall magnet. 
     A robot according to embodiments of the present disclosure includes a body assembly; and a leg assembly rotatably connected to the body assembly. The leg assembly including a first leg, a second leg, a servo motor, an output flange and a transmission component. The servo motor includes a housing; a rotor arranged in the housing and having a rotor support and a rotor shaft; a stator arranged in the housing; a planetary reduction mechanism arranged in the housing and including a sun gear, a planetary carrier, and a plurality of planetary gears, a reduction ratio of the planetary reduction mechanism being N:1, where N is a positive integer; a first Hall magnet arranged on the planetary carrier; a plurality of Hall switches corresponding to the first Hall magnet and arranged in the housing at even intervals around a rotation axis of the rotor shaft, wherein a number of Hall switches is N; a second Hall magnet arranged on the rotor; and a position sensor arranged in the housing and opposite the second Hall magnet. The servo motor is arranged at a first end of the first leg, and the motor output shaft of the servo motor is connected to the output flange to drive the output flange to rotate, the first leg is pivotally connected to the second leg, the transmission component is connected to the output flange and the second leg to drive the second leg to rotate relative to the first leg, the output flange is provided with a first limit portion, the first leg is provided with a first stop portion and a second stop portion, and the first stop portion and the second stop portion are spaced apart to limit a rotation angle of the output flange by stopping the first limit portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a robot according to an embodiment of the present disclosure. 
         FIG. 2A  is a schematic diagram of a servo motor according to an embodiment of the present disclosure. 
         FIG. 2B  is a schematic diagram of a servo motor according to another embodiment of the present disclosure. 
         FIG. 3  is a cross-sectional view of a servo motor according to an embodiment of the present disclosure. 
         FIG. 4  is a schematic diagram of installation of a planetary reduction mechanism of a servo motor and a first Hall magnet according to an embodiment of the present disclosure. 
         FIG. 5  is a schematic diagram of installation of a Hall switch board and Hall switches of a servo motor according to an embodiment of the present disclosure. 
         FIG. 6  is a cross-sectional view of a servo motor according to another embodiment of the present disclosure. 
         FIG. 7  is a cross-sectional view of a servo motor according to yet another embodiment of the present disclosure. 
         FIG. 8  is a cross-sectional view of a servo motor according to still another embodiment of the present disclosure. 
         FIG. 9  is an exploded view of a leg assembly of a robot according to an embodiment of the present disclosure. 
         FIG. 10  is a schematic diagram of a leg assembly of a robot according to an embodiment of the present disclosure. 
         FIG. 11  is a schematic diagram of a leg assembly of a robot according to an embodiment of the present disclosure, where a second leg is in a folding limit position. 
         FIG. 12  is a schematic diagram of a leg assembly of a robot according to an embodiment of the present disclosure, where a second leg is in an unfolding limit position. 
         FIG. 13  is a schematic diagram of a first leg and an output flange of a leg assembly of a robot according to an embodiment of the present disclosure. 
         FIG. 14  is a schematic diagram of a second leg of a leg assembly of a robot according to an embodiment of the present disclosure. 
         FIG. 15  is a schematic diagram of connection between an output flange and a connecting rod in a leg assembly of a robot according to another embodiment of the present disclosure. 
         FIG. 16  is a schematic diagram of a leg assembly of a robot according to yet another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure are described in detail below and examples of the embodiments are illustrated in the accompanying drawings. The embodiments described below with reference to the drawings are exemplary, and are intended to explain the present disclosure, but should not be understood as a limitation on the present disclosure. 
     A servo motor and a robot having the servo motor according to embodiments of the present disclosure will be described below with reference to the accompanying drawings. 
     According to the servo motor of embodiments of the present disclosure, the first Hall magnet rotates with the planetary carrier to activate the Hall switch in a corresponding position, so that a rotation position of the rotor can be detected. In addition, the rotation of the rotor can drive the second Hall magnet on the rotor to rotate, and a rotation angle of the second Hall magnet can be obtained by the position sensor and then a rotation angle of the motor can be obtained, improving the detection accuracy of the servo motor. 
     First, the servo motor according to embodiments of the present disclosure will be described with reference to the accompanying drawings. As illustrated in  FIGS. 1 to 5 , the servo motor  5  according to the embodiments of the present disclosure includes a housing  51 , a rotor  52 , a stator  53 , a planetary reduction mechanism  58 , a first Hall magnet  54 , a Hall switch  551 , a second Hall magnet  56 , and a position sensor  571 . The rotor  52  is arranged in the housing  51  and has a rotor support  521  and a rotor shaft  522 . The planetary reduction mechanism  58  is arranged in the housing  51  and includes a sun gear  581 , a planetary carrier  583 , and a plurality of planetary gears  585 . A reduction ratio of the planetary reduction mechanism  58  is N:1, where N is a positive integer. 
     As illustrated in  FIG. 3 , the first Hall magnet  54  is arranged on the planetary carrier  583 , and a plurality of Hall switches  551  are provided. The plurality of Hall switches  551  correspond to the first Hall magnet  54  and are arranged in the housing  51  at even intervals around a rotation axis of the rotor shaft  522 , and a number of the Hall switches  551  is N. The second hall magnet  56  is arranged on the rotor  52 , the position sensor  571  is arranged in the housing  51 , and the position sensor  571  faces the second hall magnet  56 ; one first hall magnet  54  may be provided. 
     According to the research of inventors of the present disclosure, the reduction ratio of the planetary reduction mechanism  58  is N and the number of Hall switches  551  is N too. That is, when the number of the Hall switches  551  is the same as the value of the reduction ratio of the planetary reduction mechanism  58 , the detection accuracy of the servo motor  5  can be improved. When the first Hall magnet  54  rotates with the planetary carrier  583  to a certain position, the first Hall magnet  54  will activate the Hall switch  551  in a corresponding position, so that the rotation position of the rotor  52  can be detected. In addition, the rotation of the rotor  52  can drive the second Hall magnet  56  on the rotor  52  to rotate, and a rotation angle of the second Hall magnet  56  can be obtained by the position sensor  571  to obtain a position of the rotor  52  and a rotation angle of the rotor  52 . 
     In some embodiments, in the embodiment illustrated in  FIG. 3 , three planetary gears  585  are provided. The planetary gears  585  mesh with the sun gear  581  and an inner gear ring  582 , and the sun gear  581  is coaxially connected with the rotor shaft  522 , for example, the sun gear  581  is fitter over the rotor shaft  522 . Planetary shafts  586  of the plurality of planetary gears  585  are connected to the planetary carrier  583  and a motor output shaft  584 . It can be understood that when the servo motor  5  works, the rotor  52  drives the sun gear  581  to rotate, the sun gear  581  drives the planetary gears  585  and the planetary shafts  586  to rotate, and the planetary shafts  586  drive the planetary carrier  583  and the motor output shaft  584  to rotate. 
     In some embodiments, as illustrated in  FIG. 3 , the servo motor  5  further includes a Hall switch board  55  and a support frame  552 , the support frame  552  is arranged in the housing  51 , the Hall switch board  55  is mounted on the support frame  552 , and the plurality of Hall switches  551  are arranged on the Hall switch board  55 . The support frame  552  is configured to support the Hall switch board  55  so that the Hall switch board  55  and the housing  51  are relatively fixed. 
     In at least one embodiment, as illustrated in  FIGS. 3 and 5 , the Hall switch board  55  is annular, and a center hole of the Hall switch board  55  is in clearance fit with the rotor  52 , that is, the rotor  52  and the Hall switch board  55  are not in contact. The plurality of Hall switches  551  are evenly arranged on the Hall switch board  55  along its circumferential direction, and the Hall switches  551  are located on a side of the Hall switch board  55  close to the planetary carrier  583 . 
     For example, as illustrated in  FIGS. 3 and 5 , the reduction ratio of the planetary reduction mechanism  58  is 6:1, and six Hall switches  551  are provided and evenly arranged on the Hall switch board  55  along its circumferential direction. One first Hall magnet  54  is provided and arranged on an end of the planetary carrier  583  close to the Hall switch board  55 . When the first Hall magnet  54  rotates to be right above a corresponding Hall switch  551 , the Hall switch  551  at the corresponding position will be activated, obtaining a rotation position of the rotor  52 . 
     In some embodiments, as illustrated in  FIGS. 3 to 5 , an inner radius of the planetary carrier  583  is r, and a radius of the sun gear  581  is R 1 , where R 1 +2 mm r R 1 +5 mm. The plurality of Hall switches  551  are arranged in a circle around the rotor shaft  522 , and R refers to a radius of a circle where the centers of the plurality of Hall switches  551  are located, where R 1 +5 mm t R 1 +12 mm. According to the research of the inventors of the present disclosure, by limiting the sizes of the planetary carrier  583  and the sun gear  581  and the positions of the Hall switches  551  to the above numerical ranges, the detection accuracy of the servo motor  5  can be further improved, and the servo motor  5  can operate more stably. 
     In at least one embodiment, as illustrated in  FIG. 4 , the first Hall magnet  54  and the Hall switch  551  are both substantially rectangular, and a length direction of the first Hall magnet  54  (e.g., a left-right direction of the first Hall magnet  54  in  FIG. 4 ) is orthogonal to a radial direction of the planetary carrier  583 , a length of the first Hall magnet  54  is L 1 , a width of the first Hall magnet  54  is W 1 , and a length of the Hall switch  551  is L 2 , where (2πR/N) L 1   1.5(2πR/N) and L 2   W 1   2L 2 . According to the research of the inventors of the present disclosure, by limiting the sizes of the first Hall magnet  54  and the Hall switch  551  to the above-mentioned numerical ranges, the first Hall magnet  54  can activate one to two Hall switches  511  while rotating, improving the reliability of detection. 
     In some embodiments, as illustrated in  FIG. 3 , S 1  refers to a distance between the first Hall magnet  54  and the Hall switch  551 , and 2 mm≤S 1 ≤6 mm. According to the research of the inventors of the present disclosure, setting the distance S 1  between the first Hall magnet  54  and the Hall switch  551  within the range of 2 mm to 6 mm can not only ensure the detection accuracy, but also improve the utilization rate of space inside the servo motor  5 , to reduce the size of the servo motor  5 . According to the experimental research of the inventors, if S 1  is less than 2 mm, the detection accuracy is reduced; and if S 1  is greater than 6 mm, the distance between the first Hall magnet  54  and the Hall switch  551  becomes too large, which increases the space required inside the servo motor  5 . 
     Further, as illustrated in  FIG. 3 , S 2  refers to a distance between the second Hall magnet  56  and the position sensor  571 , and 1 mm≤S 2 ≤3 mm. According to the research of the inventors, setting the distance S 2  between the second Hall magnet  56  and the position sensor  571  within the range of 1 mm to 3 mm can not only ensure the detection accuracy, but also improve the utilization rate of space inside the servo motor  5 , to reduce the size of the servo motor  5 . According to the experimental research of the inventors, if S 2  is less than 1 mm, the detection accuracy is reduced; and if S 2  is greater than 3 mm, the distance between the second Hall magnet  56  and the position sensor  571  becomes too large, which increases the space required inside the servo motor  5 . 
     In some embodiments, as illustrated in  FIG. 3 , the servo motor  5  further includes a printed circuit board  57 , the printed circuit board  57  is arranged in the housing  51 , and the position sensor  571  is arranged on the printed circuit board  57 . Since the servo motor  5  includes one printed circuit board  57 , electronic components such as the position sensor  571  are integrated on the one printed circuit board  57 , to improve the utilization rate of space inside the servo motor  5 , reduce the size of the servo motor  5 , and facilitate the miniaturization of the motor. 
     In some embodiments, as illustrated in  FIG. 3 , the printed circuit board  57  is arranged at a rear part in the housing  51 ; S 3  refers to a minimum distance between the printed circuit board  57  and a rear end cover  511  of the housing  51 , and 4 mm S 3   8 mm. Here, it should be understood that the minimum distance refers to a distance between the rear end cover  511  and a part or element on the printed circuit board  57  closest to the rear end cover  511 . 
     As illustrated in  FIG. 3 , the printed circuit board  57  is arranged between the rear end cover  511  of the housing  51  and the rotor support  521 , and the minimum distance between the printed circuit board  57  and the rear end cover  511  of the housing  51  is S 3 . By setting the minimum distance S 3  within the above range, the risk of collision with and damage to the electronic components on the printed circuit board  57  due to the deformation of the rear end cover  511  can be reduced and the overall size of the servo motor  5  is reduced, which further facilitates the miniaturization of the servo motor  5 ; in the meanwhile, the space between the rear end cover  511  and the printed circuit board  57  can also serve as heat dissipation space, which is beneficial to the heat dissipation of the printed circuit board  57 . If S 3  is too small, the components on the printed circuit board  57  are prone to damage and heat dissipation is affected. If S 3  is too large, it is adverse to the miniaturization of the servo motor  5 . 
     In some embodiments, a surface of the printed circuit board  57  facing the stator  53  and a surface of the printed circuit board  57  away from the stator  53  are each provided with an electronic component, and the position sensor  571  is arranged on the surface of the printed circuit board  57  facing the stator  53 . The electronic component arranged on the surface of the printed circuit board  57  facing the stator  53  generates less heat than the electronic component arranged on the surface of the printed circuit board  57  away from the stator  53 . 
     As illustrated in  FIG. 3 , the electronic component arranged on the upper end face of the printed circuit board  57  generates less heat than the electronic component arranged on the lower end face of the printed circuit board  57 , and most of the heat can be led out toward the rear end cover  511 , to avoid affecting the position sensor  571 , improve the detection accuracy of the position sensor  571 , and improve the overall heat dissipation performance of the servo motor  5 . 
     In some embodiments, as illustrated in  FIG. 3 , the second Hall magnet  56  may be arranged at an end of the rotor shaft  522  facing the position sensor  571 . In at least one embodiment, the second Hall magnet  56  may be arranged at a position on the rotor support  521  facing the position sensor  571 . 
     In some embodiments, as illustrated in  FIG. 3 , the rotor support  521  is coaxially fitted over the rotor shaft  522 , and the rotor support  521  and the rotor shaft  522  rotate together. The second Hall magnet  56  is mounted on an end of the rotor support  521  close to the printed circuit board  57 , and the second Hall magnet  56  is arranged to face the position sensor  571 . 
     In at least one embodiment, as illustrated in  FIG. 3 , the second Hall magnet  56  is cylindrical or annular, the rotor support  521  is provided with a mounting groove  5211 , and the second Hall magnet  56  is arranged in the mounting groove  5211 . An outer surface of the second Hall magnet  56  is lower than or flush with an outer surface of the mounting groove  5211 . For example, the second Hall magnet  56  can be fixed in the mounting groove  5211  by gluing. 
     In some embodiments, as illustrated in  FIGS. 6 and 8 , the rotor shaft  522  and the sun gear  581  are integrally formed. It can be understood that the rotor shaft  522  and the sun gear  581  are of a gear-shaft structure. In the servo motor  5  of the present disclosure, since the rotor shaft  522  and the sun gear  581  are made into an integral structure, the outer diameter of the sun gear  581  can be reduced while ensuring its strength, to reduce the size of the servo motor  5 , facilitate the miniaturization design of the servo motor  5 , and improve the applicability of the servo motor  5 . 
     In some embodiments, as illustrated in  FIGS. 3, 6 and 7 , the planetary reduction mechanism  58  further includes a rotor bearing  587 ; an end of the motor output shaft  584  (e.g., a lower end of the motor output shaft  584  in  FIG. 3 ) is provided with a bearing mounting groove  5841 , the rotor shaft  522  is provided with a flange  5221 , the rotor bearing  587  is fitted over the rotor shaft  522 , an end of the rotor bearing  587  (e.g., a lower end of the rotor bearing  587  in  FIG. 3 ) abuts against the flange  5221 , and the other end of the rotor bearing  587  (e.g., an upper end of the rotor bearing  587  in  FIG. 3 ) abuts against an inner wall of the bearing mounting groove  5841 . It can be understood that since an inner ring of the rotor bearing  587  abuts against the flange  5221 , the rotor bearing  587  can be axially positioned; and since an outer ring of the rotor bearing  587  abuts against the inner wall of the bearing mounting groove  5841 , the rotor bearing  587  can be further positioned radially, improving the positioning accuracy of the rotor bearing  587 . In addition, since the bearing mounting groove  5841  does not penetrate through the motor output shaft  584 , the possibility of external dust or sewage entering the servo motor  5  can be reduced to a certain extent, and the waterproof performance of the servo motor  5  is improved. 
     In at least one embodiment, as illustrated in  FIGS. 3 and 7 , the rotor shaft  522  and the sun gear  581  are detachably connected, and the sun gear  581  abuts against the flange  5221 . It can be understood that the rotor shaft  522  is in an interference fit with the sun gear  581 , and an upper end of the sun gear  581  abuts against the flange  5221  to position the sun gear  581  in both axial and radial directions and facilitate the assembly and disassembly of the servo motor  5 . 
     In other embodiments, as illustrated in  FIG. 8 , the planetary reduction mechanism  58  further includes a rotor bearing  587 , a bearing mounting hole  5842  is defined in the motor output shaft  584 , the rotor bearing  587  is fitted in the bearing mounting hole  5842 , and an end of the rotor shaft  522  (e.g., an upper end of the rotor shaft  522  in  FIG. 8 ) protrudes from the rotor bearing  587  and is engaged by a circlip  588 . It can be understood that the bearing mounting hole  5842  penetrates through the motor output shaft  584  along the axial direction of the motor output shaft  584 . The bearing mounting hole  5842  is configured as a stepped hole. The outer ring of the rotor bearing  587  abuts against the bearing mounting hole  5842  and is in an interference fit with the bearing mounting hole  5842 . The rotor shaft  522  is in an interference fit with the rotor bearing  587 , and the upper end of the rotor shaft  522  protrudes upward from the inner ring of the rotor bearing  587 . The upper end of the rotor shaft  522  has a snap groove in which the circlip  588  is engaged for positioning the rotor shaft  522 , avoiding axial displacement between the rotor shaft  522  and the rotor bearing  587 . 
     In some embodiments, as illustrated in  FIGS. 3, 6 and 8 , a plurality of fitting holes  5843  penetrate through the motor output shaft  584 , the plurality of fitting holes  5843  are in one-to-one correspondence with the plurality of planetary shafts  586 , and ends of at least part of the planetary shafts  586  protrude through the fitting holes  5843 . For example, three planetary shafts  586  and three fitting holes  5843  are provided. The three planetary shafts  586  are spaced apart along the circumferential direction of the sun gear  581 , and the upper ends of the three planetary shafts  586  respectively protrude through the three fitting holes  5843 . It can be understood that the portion of the planetary shaft  586  protruding through the fitting hole  5843  constitutes a positioning portion  5845  to perform positioning when other components are assembled with the servo motor  5 , thus improving the assembly efficiency. 
     In other embodiments, as illustrated in  FIG. 7 , an end of the motor output shaft  584  (e.g., a lower end of the motor output shaft  584  in  FIG. 7 ) is provided with a plurality of fitting grooves  5844 , the plurality of fitting grooves  5844  are in one-to-one correspondence with the plurality of planetary shafts  586 , and an end of the planetary shaft  586  (e.g., an upper end of the planetary shaft  586  in  FIG. 7 ) is fitted in the fitting groove  5844 . For example, three planetary shafts  586  and three fitting grooves  5844  are provided. The three planetary shafts  586  are spaced apart along a circumferential direction of the sun gear  581 . The upper ends of the three planetary shafts  586  are respectively mounted in the three fitting grooves  5844 . It is understood that since the fitting grooves  5844  do not penetrate through the motor output shaft  584 , the possibility of external dust or sewage entering the servo motor  5  can be reduced to a certain extent, improving the waterproof performance of the servo motor  5 . In at least one embodiment, the planetary shafts  586  are in clearance fit with the fitting grooves  5844  to facilitate the assembly of the planetary shafts  586  and the motor output shaft  584 . 
     Further, as illustrated in  FIGS. 2B and 7 , the other end of the motor output shaft  584  (e.g., an upper end of the motor output shaft  584  in  FIG. 7 ) is provided with a positioning portion  5845 . The positioning portion  5845  includes a first positioning portion  58451  and a second positioning portion  58452 . The first positioning portion  58451  and the second positioning portion  58452  are spaced apart in the radial direction of the motor output shaft  584 , and the first positioning portion  58451  is arranged coaxially with the motor output shaft  584 . For example, the first positioning portion  58451  is configured as a positioning groove, and the second positioning portion  58452  is configured as a positioning post. It can be understood that when the motor output shaft  584  of the servo motor  5  is assembled with other components, the components can be positioned radially and axially through the first positioning portion  58451  and the second positioning portion  58452 , improving assembly efficiency. 
     A robot according to embodiments of the present disclosure will be described below with reference to the accompanying drawings. 
     The robot according to embodiments of the present disclosure can control the rotation of the leg assembly through the servo motor, and then can detect the rotation angle and the moving position of the leg assembly, improving the movement accuracy of the robot. 
     As illustrated in  FIG. 1 , the robot according to embodiments of the present disclosure includes a body assembly  200  and a plurality of leg assemblies  100 . In the embodiment illustrated in  FIG. 1 , four leg assemblies  100  are provided. Therefore, the robot can be called a four-footed robot or a four-legged robot. It can be understood that the present disclosure is not limited to this. For example, the robot may also include two leg assemblies  100 , and accordingly the robot may be called a two-footed robot or a two-legged robot. In the embodiment illustrated in  FIG. 1 , the four leg assemblies  100  are connected to the body assembly  200  to support the body assembly  200 . When the leg assembly  100  works, the robot&#39;s walking and other actions can be realized. 
     The leg assembly  100  is rotatably connected to the body assembly  200 , and the leg assembly  100  includes a first leg  1 , a second leg  2 , a servo motor  5 , an output flange  4  and a transmission component  3 . It can be understood that the first leg  1  can also be referred to as a thigh, and the second leg  2  can also be referred to as a calf. The first leg  1  may be pivotally connected to the body assembly  200  of the robot. 
     The servo motor  5  is arranged at a first end of the first leg  1  (e.g., an upper end of the first leg  1  in  FIG. 1 ). The motor output shaft  584  of the servo motor  5  is connected to the output flange  4  to drive the output flange  4  to rotate. The leg  1  and the second leg  2  are pivotally connected, and the transmission component  3  is connected with the output flange  4  and the second leg  2  to drive the second leg  2  to rotate relative to the first leg  1 . 
     As illustrated in  FIGS. 9 to 11 , the output flange  4  is provided with a first limit portion  41 . The first leg  1  is provided with a first stop portion  11  and a second stop portion  12 , and the first stop portion  11  and the second stop portion  12  are spaced apart along a circumferential direction of the output flange  4 . The first stop portion  11  and the second stop portion  12  can limit a rotation angle of the output flange  4  by stopping the first limit portion  41 , to limit a rotation range of the second leg  2  relative to the first leg  1  and an unfolding limit position and a folding limit position of the second leg  2 . 
     In other words, the first stop portion  11  and the second stop portion  12  respectively define rotation limit positions of the first limit portion  41 . When the first limit portion  41  is stopped by the first stop portion  11  or the second stop portion  12 , further rotation of the output flange  4  is stopped, that is, further rotation of the servo motor  5  is stopped. 
     For example, as illustrated in  FIGS. 10 to 12 , when the output flange  4  rotates clockwise from a position illustrated in  FIG. 10 , after the first limit portion  41  comes into contact with the second stop portion  12  on the first leg  1 , the second stop portion  12  stops the output flange  4  from further rotating clockwise, as illustrated in  FIG. 12 , that is, the output flange  4  reaches a clockwise rotation limit position, so that the second leg  2  rotates to the unfolding limit position. Conversely, when the output flange  4  rotates counterclockwise from a position illustrated in  FIG. 10 , after the first limit portion  41  comes into contact with the first stop portion  11  on the first leg  1 , the first stop portion  11  stops the output flange  4  from further rotating counterclockwise, as illustrated in  FIG. 11 , that is, the output flange  4  reaches a counterclockwise rotation limit position, so that the second leg  2  rotates to the folding limit position. 
     A second limit portion  13  is arranged on the first leg  1  and configured to stop the second leg  2  to limit the rotation of the second leg  2 . As illustrated in  FIG. 11 , when the second leg  2  moves to the folding limit position, the second limit portion  13  stops the second leg  2 , and at the same time, the first stop portion  11  stops the first limit portion  41 . 
     In the robot according to the embodiment of the present disclosure, by arranging the first stop portion  11  and the second stop portion  12  on the first leg  1 , the rotation angle range of the output flange  4  can be conveniently limited, facilitating the control over the rotation range of the second leg  2 , i.e., the unfolding limit position and the closing limit position, and further accurately controlling the operation of the second leg  2 . Moreover, since the second limit portion  13  is arranged on the first leg  1 , when the first limit portion  41  is stopped by the first stop portion  11 , the second leg  2  that moves to the folding limit position is stopped by the second limit portion  13 , preventing the second leg  2  from colliding with the first leg  1 . As a result, the rotation of the output flange  4  can be conveniently limited within a predetermined angle range, and at the same time, the second leg  2  that moves to the folding limit position is limited by the second limit portion  13 , improving the limit reliability; moreover, stress and impact on various members of the leg assembly  100  are reduced, which reduces noise and facilitates accurate control of the leg assembly  100 . 
     As illustrated in  FIGS. 10 to 12 , the output flange  4  is configured as a disc and coaxially connected with the motor output shaft  584  of the servo motor  5 . The first limit portion  41  is arranged on an outer peripheral wall of the output flange  4 , and the first stop portion  11  and the second stop portion  12  are arranged at the upper end of the first leg  1  along the circumferential direction of the output flange  4 . 
     In the embodiments illustrated in  FIGS. 10 to 12 , the first limit portion  41 , the first stop portion  11  and the second stop portion  12  are all rectangular blocks, so that the first limit portion  41  is in surface contact with the first stop portion  11  and the second stop portion  12 , thus achieving more even stress and smaller compact. In at least one embodiment, a surface of the first stop portion  11  and a surface of the second stop portion  12  and/or a surface of the first limit portion  41  are covered with a buffer layer, such as an elastic rubber layer, to further reduce the impact when the first limit portion  41  comes into contact with the first stop portion  11  and the second stop portion  12 . Further in at least one embodiment, tapered grooves may be defined in the surfaces of the first stop portion  11  and the second stop portion  12  in contact with the first limit portion  41 , and the first limit portion  41  is provided with a tapered protrusion. In this way, when the first limit portion  41  comes into contact with the first stop portion  11  or the second stop portion  12 , the tapered protrusion gradually enters the tapered groove, further increasing the smoothness of the contact and reducing the impact. More advantageously, a surface of the tapered groove and/or a surface of the tapered protrusion may be covered with an elastic material layer to further reduce the impact. 
     In some embodiments, as illustrated in  FIGS. 10 to 12 , the second limit portion  13  is configured as a limit block suitable for surface contact with the second leg  2 . In at least one embodiment, the second limit portion  13  may also be configured as a limit post suitable for line contact with the second leg  2 , as illustrated in  FIG. 16 . 
     In some embodiments, the second limit portion  13  is configured as a limit block suitable for surface contact with the second leg  2 , which can further reduce the stress and impact on the leg assembly  100  and increase the service life of the leg assembly  100 . 
     In some embodiments, as illustrated in  FIG. 11 , the second limit portion  13  can limit the counterclockwise rotation of the second leg  2  and the height of the leg assembly  100  is further limited when the robot stands up, improving the applicability of the leg assembly  100  and facilitating the design of the robot. 
     In some embodiments, as illustrated in  FIGS. 10 to 12 , a third limit portion  42  is arranged on the output flange  4  and configured to stop the transmission component  3  to limit the rotation of the second leg  2 . 
     In at least one embodiment, as illustrated in  FIGS. 11 and 12 , the third limit portion  42  is configured as a protrusion  421  arranged on the surface of the output flange  4 . As illustrated in  FIG. 12 , when the output flange  4  rotates clockwise and the second leg  2  rotates clockwise to the unfolding limit position, the transmission component  3  comes into contact with the third limit portion  42  to stop the movement of the transmission component  3 , limiting the rotation of the output flange  4 , the servo motor  5  and the second leg  2 ; the protrusion  421  rotates clockwise together with the output flange  4  and stops the transmission component  3  and the movement of the second leg  2  is further limited, thus further improving the limit reliability of the leg assembly  100 . Therefore, when the second leg  2  moves to the unfolding limit position and the folding limit position, double limit is realized, which improves the limit reliability. 
     In some embodiments, as illustrated in  FIGS. 9 to 12 , the transmission component  3  includes a connecting rod  31 , a first end of the connecting rod  31  is pivotally connected to the output flange  4  by a first pivot  3111 , a second end of the connecting rod  31  is pivotally connected to a first end of the second leg  2  by a second pivot  312 , and a second end of the first leg  1  and the first end of the second leg  2  are pivotally connected by a third pivot  22 . 
     After the servo motor  5  is started, the output flange  4  is driven to rotate, for example, swing, around a center axis of the motor output shaft  584  through the motor output shaft  584  of the servo motor  5 . Since the first pivot  311  is eccentrically arranged with respect to the center axis of the motor output shaft  584 , the first pivot  311  revolves around the central axis of the motor output shaft  584 , and then the first end of the connecting rod  3  is driven to revolve around the central axis of the motor output shaft  584 , thus driving the connecting rod  3  to move. Since the second end of the connecting rod  3  is pivotally connected to the first end of the second leg  2  through the second pivot and the first end of the second leg  2  is pivotally connected through the third pivot  22 , the connecting rod  3  drives the second leg  2  to rotate around the third pivot  22  relative to the first leg  1 . 
     In some embodiments, in  FIG. 10 , the third pivot  22  is located between the second pivot  312  and a second end of the second leg  2 , that is, the third pivot  22  is closer to the second end (a right end in  FIG. 10 ) of the second leg  2  than the second pivot  312 . When the output flange  4  rotates clockwise, the connecting rod  3  moves upward and drives the second pivot  312  to move upward, and then the second leg  2  is driven to swing clockwise around the third pivot  22 , thus unfolding the second leg  2  relative to the first leg  1 . Conversely, when the output flange  4  rotates counterclockwise, the connecting rod  3  moves downward and drives the second pivot  312  to move downward, and then the second leg  2  is driven to swing counterclockwise around the third pivot  22 , thus folding the second leg  2  up relative to the first leg  1 . 
     Alternatively, the second pivot  312  may also be located between the third pivot  22  and the second end of the second leg  2 , that is, the second pivot  312  is closer to the second end (the right end in  FIG. 10 ) of the second leg  2  than the third pivot  22 . In this way, when the output flange  4  rotates clockwise, the second leg  2  is driven to fold up relative to the first leg  1 ; and when the output flange  4  rotates counterclockwise, the second leg  2  is driven to unfold relative to the first leg  1 . 
     In some embodiments, as illustrated in  FIG. 15 , the output flange  4  is provided with a recessed portion  422 , an end of the recessed portion  422  is provided with a U-shaped fitting groove  43 , the first end of the connecting rod  31  is pivotally fitted in the U-shaped fitting groove  43 , and a surface of the recessed portion  422  constitutes a third limit portion  42 . As illustrated in  FIG. 15 , when the connecting rod  31  moves, a side wall of the connecting rod  31  can abut against the surface of the recessed portion  422 , limiting the rotation of the connecting rod  31 , and further limiting the rotation of the output flange  4 , the servo motor  5  and the second leg  2 ; in this way, the limit reliability can be improved, the stress and impact on various members can be reduced, and the movement of the second leg  2  can be accurately controlled. 
     Further, as illustrated in  FIGS. 10, 13 and 14 , L 1  refers to a first connecting line between the first stop portion  11  and a center of the motor output shaft  584 , L 2  refers to a second connecting line between the second stop portion  12  and the center of the motor output shaft  584 , and  0  refers to an angle between L 1  and L 2  and 110 degrees θ 160 degrees. In other words, L 1  refers to a connecting line between the center of the output flange  4  and a contact surface of the first stop portion  11  for contact with the first limit portion  41 , and L 2  refers to a connecting line between the center of the output flange  4  and a contact surface of the second stop portion  12  for contact with the first limit portion  41 . According to the research of the inventors of the present disclosure, by setting a swing angle of the first limit portion  41  between 110 degrees and 160 degrees, the stress and impact on the leg assembly  100  can be further reduced, and the rotation of the second leg  2  is more stable. 
     In some embodiments, as illustrated in  FIGS. 10, 13 and 14 , a refers to an angle between the first connecting line L 1  and a third connecting line L 3  (between the center of the third pivot  22  and the center of the motor output shaft  584 ), and 0≤a≤40 degrees. b refers to an angle between the second connecting line L 2  and a direction perpendicular to the third connecting line L 3 , and 10 degrees b 50 degrees. 
     As illustrated in  FIGS. 11 and 12 , the sum of the angle a between the first connecting line L 1  and the third connecting line L 3  (between the center of the third pivot  22  and the center of the motor output shaft  584 ) and the angle b between the second connecting line L 2  and the direction perpendicular to the third connecting line L 3  plus 90 degrees is equal to the angle θ between the first connecting line L 1  (between the first stop portion  11  and the center of the motor output shaft  584 ) and the second connecting line L 2  (between the second stop portion  12  and the center of the motor output shaft  584 ). According to the research of the inventors of the present disclosure, by limiting the angle a and the angle b within the above ranges, the stress on various members can be further reduced, the impact is smaller, the operation is more stable, and the operation of the second leg  2  can be controlled more accurately. 
     In some embodiments, as illustrated in  FIGS. 10, 13 and 14 , c refers to an angle between a length direction of the second end of the first leg  1  and the third connecting line L 3 , and 130 degrees c 170 degrees. Further, d refers to an angle between a fourth connecting line L 4  (between a center of the second pivot  312  and a center of the third pivot  22 ) and a fifth connecting line L 5  (between the center of the third pivot  22  and the center of the second end (e.g., the lower end of the second leg  2  in  FIG. 13 ) of the second leg  2 ), and 140 degrees≤d≤180 degrees. 
     According to the present disclosure, by setting the angle c in the first leg  1  and/or the angle d in the second leg  2  as above, the movement ranges of the first leg and the second leg are relatively wide, their degrees of freedom are good used, interference is avoided, and the first leg  1 , the second leg  2  and the connecting rod  3  can move stably. 
     Further, as illustrated in  FIGS. 10, 13 and 14 , a distance between the center of the first pivot  3111  and the center of the motor output shaft  584  is less than a distance between the center of the second pivot  312  and the center of the third pivot  22 . Based on this design, a swing path of the second leg  2  can be controlled more conveniently, the movement performance of the second leg can be improved, and the movement characteristics of the leg assembly and the robot can be controlled more accurately. 
     In some embodiments, as illustrated in  FIG. 16 , the transmission component  3  includes a first wheel  32 , a second wheel  33 , and a flexible transmission member  34  wound on the first wheel  32  and the second wheel  33 . The first wheel  32  is mounted on the output flange  4 , the second wheel  33  is rotatably mounted on the second end of the first leg  1 , and the first end of the second leg  2  is connected to the second wheel  33 . 
     As illustrated in  FIG. 16 , the first wheel  32  and the second wheel  33  are configured as pulleys and the flexible transmission member  34  is configured as a transmission belt. In at least one embodiment, the first wheel  32  and the second wheel  33  may be configured as sprockets, and the flexible transmission member  34  may be configured as a chain. The servo motor  5  can drive the first wheel  32  to rotate, the first wheel  32  drives the second wheel  33  to rotate through the flexible transmission member  34 , and the second wheel  33  can drive the second leg  2  to rotate. 
     Further, as illustrated in  FIG. 16 , the second limit portion  13  includes a left second limit portion  132  and a right second limit portion  133  spaced apart along a width direction of the first leg  1  (e.g., the left-right direction of the first leg  1  in  FIG. 11 ); and the left second limit portion  132  and the right second limit portion  133  are configured to limit the rotation angle of the second leg  2 . In some embodiments, the flexible transmission member  34  is located between the left second limit portion  132  and the right second limit portion  133 , and the left second limit portion  132  and the right second limit portion  133  are symmetrically arranged relative to a length direction of the first leg  1 . 
     In some embodiments, as illustrated in  FIG. 16 , the first end of the second leg  2  is provided with a U-shaped groove  21 , and a part of the second wheel  33  is located in the U-shaped groove  21 . It can be understood that the second wheel  33  is mounted at an upper end of the second leg  2 , and the upper end of the second leg  2  is connected with the second wheel  33  by bolts or rivets, so that the second wheel  33  can drive the second leg  2  to rotate. 
     As illustrated in  FIG. 9 , the output flange  4  is connected to the motor output shaft  584  through a plurality of pin shafts  44 . For example, three pin shafts  44  are provided, and the output flange  4  is fixed to the motor output shaft  584  through the three pin shafts  44 , improving the connection strength between the output flange  4  and the motor output shaft  584 . 
     As illustrated in  FIG. 1 , the robot according to the embodiment of the present disclosure has four leg assemblies  100 , and the four leg assemblies  100  are connected to the body assembly  200 . It can be understood that the first leg  1  of the leg assembly  100  can be driven by another servo motor to rotate relative to the body assembly  200 , and the servo motor  5  drives the second leg  2  to rotate relative to the first leg  1 , thus realizing the walking and other actions of the robot. In the robot according to the embodiment of the present disclosure, the limit of the leg assembly  100  is reliable, the stress on various members is small, the impact is small, the noise is low, the operation is stable, and the control accuracy is high. 
     In the description of the present disclosure, it should be understood that the orientations or positional relationships, indicated by the terms “central”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “on”, “under”, “front”, “rear”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, and the like, are based on the orientations or positional relationships shown in the drawings and are only for the purpose of facilitating and simplifying the description of the present disclosure, rather than indicating or implying that the described device or element must have a particular orientation or must be constructed and operated in a particular orientation, and therefore they cannot to be construed as limiting the present disclosure. 
     Moreover, the terms “first” and “second” are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, features defined by the term “first” or “second” may include at least one of the features, either explicitly or implicitly. In the description of the present disclosure, the meaning of “a plurality of” is at least two, such as two, three, etc., unless specifically defined otherwise. 
     In the present disclosure, unless explicitly stated and defined otherwise, the terms “mounted”, “connected with”, “connected”, “fixed” and the like shall be understood broadly; for example, it may be either a fixed connection or a detachable connection, or in one piece; it may be a mechanical connection, or it may be an electrical connection or a mutual communication; it may be a direct connection or indirect connection through an intermediate medium, and may be an internal communication of two components or an interaction relationship between two components, unless otherwise expressly defined. It will be apparent to those skilled in the art that the specific meanings of the above terms in the utility model can be understood according to the specific conditions. 
     In the present disclosure, the first feature being “on” or “under” the second feature may mean that the first feature and the second feature are in a direct contact, or the first and second features may be in an indirect contract through an intermediate medium, unless otherwise explicitly stated and defined. Moreover, the first feature being “at the top of”, “above” and “on” the second feature may mean that the first feature is right above or above and to one side of the second feature, or may merely mean that the first feature is horizontally higher than the second feature. The first feature being “at the bottom of”, “below” and “under” the second feature may mean that the first feature is below or below and to one side of the second feature, or may merely mean that the first feature is horizontally lower than the second feature. 
     In the description of the present disclosure, the terms “one embodiment”, “some embodiments”, “example”, “specific example”, or “some examples” and the like means specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present disclosure. In the present specification, the schematic representation of the above terms is not necessarily directed to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can integrate and combine various embodiments or examples described in the present specification, as well as features of various embodiments or examples, without contradicting each other 
     Although the embodiments of the present disclosure have been shown and described, it would be understood that the above-described embodiments are illustrative and are not to be construed as limiting the scope of the present disclosure. Changes, modifications, substitutions and variations of the above-described embodiments may be made by those skilled in the art within the scope of the present disclosure.