Patent Publication Number: US-2022231581-A1

Title: Servo motor and robot having same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present disclosure is based on and claims priority to Chinese Patent Application No. 202120117218.0, filed Jan. 15, 2021, the entire contents of which are incorporated herein by reference. 
     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 order to improve control accuracy, it is required to detect the relative position of a stator and a rotor of a motor. Servo motors in related art have certain disadvantages due to their large size, low utilization of internal space, and low relative position detection accuracy. 
     SUMMARY 
     The 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 Hall magnet arranged on the rotor; and a printed circuit board arranged in the housing and provided with a position sensor facing the 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 Hall magnet arranged on the rotor; and a printed circuit board arranged in the housing and provided with a position sensor facing the Hall magnet. The servo motor is arranged at a first end of the first leg, a 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, and 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. 
    
    
     
       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 cross-sectional view of a servo motor according to another embodiment of the present disclosure. 
         FIG. 5  is a cross-sectional view of a servo motor according to yet another embodiment of the present disclosure. 
         FIG. 6  is a cross-sectional view of a servo motor according to still another embodiment of the present disclosure. 
         FIG. 7  is an exploded view of a leg assembly of a robot according to an embodiment of the present disclosure. 
         FIG. 8  is a schematic diagram of a leg assembly of a robot according to an embodiment of the present disclosure. 
         FIG. 9  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. 10  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. 11  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. 12  is a schematic diagram of a second leg of a leg assembly of a robot according to an embodiment of the present disclosure. 
         FIG. 13  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. 14  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 shown 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. 
     First, the servo motor according to the embodiments of the present disclosure will be described with reference to the accompanying drawings. As illustrated in  FIGS. 1 to 3 , the servo motor  5  according to the embodiments of the present disclosure includes a housing  51 , a rotor  52 , a stator  53 , a Hall magnet  54 , and one printed circuit board  55 . The rotor  52  is arranged in the housing  51  and has a rotor support  521  and a rotor shaft  522 . The stator  53  is arranged in the housing  51 , the Hall magnet  54  is arranged on the rotor  52 , the printed circuit board  55  is arranged in the housing  51 , and the printed circuit board  55  is provided with a position sensor  551  facing the Hall magnet  54 . 
     In the servo motor according to embodiments of the present disclosure, the rotor  52  of the servo motor  5  drives the hall magnet  54  to rotate, and a rotation angle of the hall magnet  54  can be obtained by the position sensor  551  on the printed circuit board  55 , to obtain a rotation angle of the rotor  52 . Since the servo motor  5  only includes one printed circuit board  55 , electronic components such as the position sensor  551  are integrated on the one printed circuit board, improving the utilization of space inside the servo motor  5 , reducing the size of the servo motor  5 , and contributing to the miniaturization of the motor. 
     The Hall magnet  54  may be arranged at an end of the rotor shaft  522  facing the position sensor  551 . In at least one embodiment, the Hall magnet  54  may be arranged at a position on the rotor support  521  facing the position sensor  551 . 
     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 Hall magnet  54  is mounted on an end of the rotor support  521  close to the printed circuit board  55 , and the Hall magnet  54  is arranged in a way of facing the position sensor  551 . 
     S1 refers to a distance between the Hall magnet  54  and the position sensor  551 , and 1 mm S1 3 mm. According to the research of the inventors, setting the distance S1 between the Hall magnet  54  and the position sensor  551  within the range of 1 mm to 3 mm can not only ensure the detection accuracy, but also improve the utilization 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 S1 is less than 1 mm, the detection accuracy is reduced; and if S1 is greater than 3 mm, the distance between the Hall magnet  54  and the position sensor  551  becomes too large, which increases the space required inside the servo motor. 
     In at least one embodiment, the printed circuit board  55  is arranged at a rear part in the housing  51 ; S2 refers to a minimum distance between the printed circuit board  55  and a rear end cover  511  of the housing  51 , and 4 mm≤S2≤8 mm. Here, it should be understood that the minimum distance refers to a distance between the rear end cover and a part or element on the printed circuit board closest to the rear end cover. As illustrated in  FIG. 3 , the printed circuit board  55  is arranged between the rear end cover of the housing  51  and the rotor support  521 , and the minimum distance between the printed circuit board  55  and the rear end cover of the housing  51  is S2. By setting the minimum distance S2 within the above range, the risk of collision with and damage to the electronic components on the printed circuit board  55  due to the deformation of the rear end cover  511  can be reduced and the overall size of the servo motor 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  55  can also serve as heat dissipation space, which is beneficial to the heat dissipation of the printed circuit board  55 . If S2 is too small, the components on the printed circuit board  55  are prone to damage and heat dissipation is affected. If S2 is too large, it is adverse to the miniaturization of the servo motor. 
     In some embodiments, the electronic component arranged on the surface of the printed circuit board  55  facing the stator  53  generates less heat than the electronic component arranged on the surface of the printed circuit board  55  away from the stator  53 . As illustrated in  FIG. 3 , the electronic component arranged on the upper end face of the printed circuit board  55  generates less heat than the electronic component arranged on the lower end face of the printed circuit board  55 , so most of the heat can be led out toward the rear end cover  511 , to avoid affecting the position sensor  551 , improve the detection accuracy of the position sensor  551 , and improve the overall heat dissipation performance of the servo motor. 
     In some embodiments, the servo motor  5  further includes a planetary reduction mechanism  56 , and the planetary reduction mechanism  56  includes a sun gear  561 , an inner gear ring  562 , a planetary carrier  563 , a motor output shaft  564 , and a plurality of planetary gears  565 . In the embodiment illustrated in  FIG. 3 , three planetary gears  565  are provided. The planetary gears  565  mesh with the sun gear  561  and the inner gear ring  562 , and the sun gear  561  is coaxially connected with the rotor shaft  522 . The planetary gears  565  are fitted over planetary shafts  566 , and the planetary shafts  566  are connected to the planetary carrier  563  and the motor output shaft  564 . When the servo motor  5  works, the rotor  52  drives the sun gear  561  to rotate, the sun gear  561  drives the planetary gears  565  and the planetary shafts  566  to rotate, and the planetary shafts  566  drive the planetary carrier  563  and the motor output shaft  564  to rotate. 
     In at least one embodiment, as illustrated in  FIGS. 4 and 6 , the rotor shaft  522  and the sun gear  561  are integrally formed. It can be understood that the rotor shaft  522  and the sun gear  561  are of a gear-shaft structure. In the servo motor  5  of the present disclosure, since the rotor shaft  522  and the sun gear  561  are made into an integral structure, the outer diameter of the sun gear  561  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 to 5 , the planetary reduction mechanism  56  further includes a rotor bearing  567 ; an end of the motor output shaft  564  (e.g., a lower end of the motor output shaft  564  in  FIG. 3 ) is provided with a bearing mounting groove  5641 , the rotor shaft  522  is provided with a flange  5221 , the rotor bearing  567  is fitted over the rotor shaft  522 , an end of the rotor bearing  567  (e.g., a lower end of the rotor bearing  567  in  FIG. 3 ) abuts against the flange  5221 , and the other end of the rotor bearing  567  (e.g., an upper end of the rotor bearing  567  in  FIG. 3 ) abuts against an inner wall of the bearing mounting groove  5641 . It can be understood that since an inner ring of the rotor bearing  567  abuts against the flange  5221 , the rotor bearing  567  can be axially positioned; since an outer ring of the rotor bearing  567  abuts against the inner wall of the bearing mounting groove  5641 , the rotor bearing  567  can be further positioned radially, to improve the positioning accuracy of the rotor bearing  567 . In addition, since the bearing mounting groove  5641  does not penetrate through the motor output shaft  564 , 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 5 , the rotor shaft  522  and the sun gear  561  are detachably connected, and the sun gear  561  abuts against the flange  5221 . It can be understood that the rotor shaft  522  is in an interference fit with the sun gear  561 , and an upper end of the sun gear  561  abuts against the flange  5221  to position the sun gear  561  in both axial and radial directions and facilitate the assembly and disassembly of the servo motor  5 . 
     In other embodiments, as illustrated in  FIG. 6 , the planetary reduction mechanism  56  further includes a rotor bearing  567 , a bearing mounting hole  5642  is defined in the motor output shaft  564 , the rotor bearing  567  is fitted in the bearing mounting hole  5642 , and an end of the rotor shaft  522  (e.g., an upper end of the rotor shaft  522  in  FIG. 6 ) protrudes from the rotor bearing  567  and is engaged by a circlip  568 . It can be understood that the bearing mounting hole  5642  penetrates through the motor output shaft  564  along the axial direction of the motor output shaft  564 . The bearing mounting hole  5642  is configured as a stepped hole. The outer ring of the rotor bearing  567  abuts against the bearing mounting hole  5642  and is in an interference fit with the bearing mounting hole  5642 . The rotor shaft  522  is in an interference fit with the rotor bearing  567 , and the upper end of the rotor shaft  522  protrudes upward from the inner ring of the rotor bearing  567 . The upper end of the rotor shaft  522  has a snap groove in which the circlip  568  is engaged for positioning the rotor shaft  522 , avoiding axial displacement between the rotor shaft  522  and the rotor bearing  567 . 
     In some embodiments, as illustrated in  FIGS. 3, 4 and 6 , a plurality of fitting holes  5643  penetrate through the motor output shaft  564 , the plurality of fitting holes  5643  are in one-to-one correspondence with the plurality of planetary shafts  566 , and ends of at least part of the planetary shafts  566  protrude from the fitting holes  5643 . For example, three planetary shafts  566  and three fitting holes  5643  are provided. The three planetary shafts  566  are spaced apart along the circumferential direction of the sun gear  561 , and the upper ends of the three planetary shafts  566  respectively protrude through the three fitting holes  5643 . It can be understood that the portion of the planetary shaft  566  protruding through the fitting hole  5643  constitutes a positioning portion  5645  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. 5 , an end of the motor output shaft  564  (e.g., a lower end of the motor output shaft  564  in  FIG. 5 ) is provided with a plurality of fitting grooves  5644 , the plurality of fitting grooves  5644  are in one-to-one correspondence with the plurality of planetary shafts  566 , and an end of the planetary shaft  566  (e.g., an upper end of the planetary shaft  566  in  FIG. 5 ) is fitted in the fitting groove  5644 . For example, three planetary shafts  566  and three fitting grooves  5644  are provided. The three planetary shafts  566  are spaced apart along a circumferential direction of the sun gear  561 . The upper ends of the three planetary shafts  566  are respectively mounted in the three fitting grooves  5644 . It is understood that since the fitting grooves  5644  do not penetrate through the motor output shaft  564 , the possibility of external dust or sewage entering the servo motor  5  can be reduced to a certain extent, to improve the waterproof performance of the servo motor  5 . In at least one embodiment, the planetary shafts  566  are in clearance fit with the fitting grooves  5644  to facilitate the assembly of the planetary shafts  566  and the motor output shaft  564 . 
     Further, as illustrated in  FIGS. 2B and 5 , the other end of the motor output shaft  564  (e.g., the upper end of the motor output shaft  564  in  FIG. 5 ) is provided with a positioning portion  5645 . The positioning portion  5645  includes a first positioning portion  56451  and a second positioning portion  56452 . The first positioning portion  56451  and the second positioning portion  56452  are spaced apart in the radial direction of the motor output shaft  564 , and the first positioning portion  56451  is arranged coaxially with the motor output shaft  564 . For example, the first positioning portion  56451  is configured as a positioning groove, and the second positioning portion  56452  is configured as a positioning post. It can be understood that when the motor output shaft  564  of the servo motor  5  is assembled with other components, the components can be positioned radially and axially through the first positioning portion  56451  and the second positioning portion  56452 , improving assembly efficiency. 
     A robot according to embodiments of the present disclosure will be described below with reference to the accompanying drawings. 
     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. 
     As illustrated in  FIGS. 1 to 14 , 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  8  in  FIG. 8 ). The motor output shaft  564  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. 7 to 10 , 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 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. 8 to 10 , when the output flange  4  rotates clockwise from a position illustrated in  FIG. 8 , after the first limit portion  41  comes into contact with the second stop portion  12  on the first leg  1 , the second stop portion  10  stops the output flange  4  from further rotating clockwise, as illustrated in  FIG. 10 , 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. 8 , after the first limit portion  41  comes into contact with the first stop portion  11  on the first leg  1 , the first stop portion  9  stops the output flange  4  from further rotating counterclockwise, as illustrated in  FIG. 9 , 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. 9 , 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 embodiments 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 of the leg assembly  100 ; 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. 8 to 10 , the output flange  4  is configured as a disc and coaxially connected with the motor output shaft 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. 8 to 10 , 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 impact. 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. 8 to 10 , 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. 14 . 
     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. 9 , 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. 8 to 10 , 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. 9 and 10 , the third limit portion  42  is configured as a protrusion  421  arranged on the surface of the output flange  4 . As illustrated in  FIG. 10 , 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 , further 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, 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 always realized, which improves the limit reliability. 
     In some embodiments, as illustrated in  FIGS. 7 to 10 , the transmission component  3  includes a connecting rod  31 , a first end of the connecting rod  31  (e.g., an upper end of the connecting rod  31  in  FIG. 8 ) is pivotally connected to the output flange  4  by a first pivot  3111 , a second end of the connecting rod  31  (e.g., a lower end of the connecting rod  31  in  FIG. 8 ) is pivotally connected to a first end of the second leg  2  (e.g., a left end of the second leg  2  in  FIG. 8 ) by a second pivot  312 , and a second end of the first leg  1  (e.g., a lower end of the first leg  1  in  FIG. 8 ) 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  564  through the motor output shaft  564  of the servo motor  5 . Since the first pivot  311  is eccentrically arranged with respect to the center axis of the motor output shaft  564 , the first pivot  311  revolves around the central axis of the motor output shaft  564 , and then the first end of the connecting rod  3  is driven to revolve around the central axis of the motor output shaft  564 , 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. 8 , 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. 8 ) 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. 8 ) 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. 13 , 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. 13 , when the connecting rod  31  moves, a side wall of the connecting rod  31  can abut against a surface of the recessed portion  422 , to limit the rotation of the connecting rod  31 , and further limit 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. 8, 11 and 12 , L1 refers to a first connecting line between the first stop portion  11  and a center of the motor output shaft  564 , L2 refers to a second connecting line between the second stop portion  12  and the center of the motor output shaft  564 , and θ refers to an angle between L1 and L2, where 110 degrees≤θ≤160 degrees. In other words, L1 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 L2 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 can be further reduced, and the rotation of the second leg  2  is more stable. 
     In some embodiments, as illustrated in  FIGS. 8, 11 and 12 , a refers to an angle between the first connecting line L1 and a third connecting line L3 (between the center of the third pivot  22  and the center of the motor output shaft  564 ), and 0 a 40 degrees. b refers to an angle between the second connecting line L2 and a direction perpendicular to the third connecting line L3, and 10 degrees≤b≤50 degrees. 
     As illustrated in  FIG. 8 , the sum of the angle a between the first connecting line L1 and the third connecting line L3 (between the center of the third pivot  22  and the center of the motor output shaft  564 ) and the angle b between the second connecting line L2 and the direction perpendicular to the third connecting line L3 plus 90 degrees is equal to the angle θ between the first connecting line L1 (between the first stop portion  11  and the center of the motor output shaft  564 ) and the second connecting line L2 (between the second stop portion  12  and the center of the motor output shaft  564 ). 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. 8, 11 and 12 , c refers to an angle between a length direction of the second end of the first leg  1  and the third connecting line L3, and 130 degrees≤c≤170 degrees. Further, d refers to an angle between a fourth connecting line L4 (between a center of the second pivot  312  and a center of the third pivot  22 ) and a fifth connecting line L5 (between the center of the third pivot  22  and the center of the second end (e.g., a lower end of the second leg  2  in  FIG. 12 ) of the second leg  2 ), and 140 degrees≤d≤180 degrees. 
     According to the research of the inventors of 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  FIG. 8 , a distance between the center of the first pivot  3111  and the center of the motor output shaft 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. 14 , 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. 14 , 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. 14 , 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., a left-right direction of the first leg  1  in  FIG. 14 ); 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. 14 , 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  FIGS. 2A, 2B and 7 , the output flange  4  is connected to the motor output shaft  564  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  564  through the three pin shafts  44 , improving the connection strength between the output flange  4  and the motor output shaft  564 . 
     As illustrated in  FIG. 1 , the robot according to embodiments of the present disclosure has four leg assemblies  100 , and the four leg assemblies  100  are connected to the body assembly  200 . 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 embodiments of the present disclosure, the limit reliability of the leg assembly  100  is high, 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.