JP4811821B2 - Linear actuator - Google Patents

Description

  The present invention relates to a linear actuator that includes an electric motor, a nut member that is rotationally driven by the electric motor, and a screw shaft that is screwed into the nut member via a ball held by the nut member.

  In this type of linear motion actuator, the nut member is pivotally supported in a cylindrical nut case via a pair of angular bearings, and the thrust reaction force acting on the nut member as the screw shaft advances and retreats is received by the angular bearing. I am trying to do it. Conventionally, the nut member is configured to have a nut main body that holds the ball and shafts at both ends in the axial direction whose outer diameter is smaller than that of the nut main body, and both shafts are pivotally supported by a pair of angular bearings. What was made to do is known (for example, refer patent document 1).

  In this configuration, when the angular bearing on one axial end side is tightened toward the angular bearing on the other axial end side during assembly, a tightening force is applied to the nut body via the inner ring of the angular bearing. When the outer diameter of the nut main body is the minimum dimension necessary for holding the ball, the ball does not move smoothly due to compressive deformation of the nut main body, and the friction loss increases. Therefore, in the above conventional example, the nut body portion is formed to have a large outer diameter with a surplus on the outside of the ball holding portion so that the tightening force acts only on the surplus portion of the nut body portion.

Here, if the outer diameter of the shaft portion at both ends of the nut member is smaller than the ball holding portion of the nut body portion, the tightening force also acts on the ball holding portion, so the outer diameter of the shaft portion is the ball holding portion. It is necessary to form a larger diameter. As a result, the angular bearing also has a large diameter, and the nut case that inevitably accommodates the angular bearing also has a large diameter, making it difficult to reduce the size and weight of the linear actuator.
JP-A-11-198828 (FIG. 4)

  This invention makes it the subject to provide the linear actuator which devised the nut member and its support structure, and was able to achieve size reduction and weight reduction in view of the above point.

  In order to solve the above problems, a linear motion actuator comprising an electric motor, a nut member that is rotationally driven by the electric motor, and a screw shaft that is screwed into the nut member via a ball held by the nut member. The nut member is pivotally supported in the cylindrical nut case via a pair of angular bearings. The nut member includes a nut main body portion that holds the ball and both axial ends having a smaller outer diameter than the nut main body portion. The first collar is interposed between the inner rings of the angular bearings, and the first collar is attached to the nut main body. Inserted between the cylindrical part to be inserted and the axially opposite ends of the cylindrical part, and enters between the step between the nut main body part and each shaft part and the inner ring of each angular bearing to contact the inner ring. And having a pair of annular plate portion.

  According to the present invention, when the angular bearing at one end in the axial direction is tightened toward the angular bearing at the other end in the axial direction during assembly, the tightening force is applied to the annular plate portion, the cylindrical portion, and the other end of the first collar. It is transmitted to the angular bearing on the other axial end side through the annular plate portion, and no tightening force acts on the nut body portion. Therefore, even if the outer diameter of the nut body is set to the minimum necessary size necessary for holding the ball, and the outer diameter of the shaft is made smaller than this, the smoothness of the movement of the ball is impaired by the tightening force, There is no problem that the friction loss increases. Further, the diameter of the angular bearing can be reduced by reducing the diameter of the shaft portion. As a result, it is possible to reduce the diameter of the nut case and reduce the size and weight of the direct acting actuator.

  If both the annular plate portions of the first collar are integral with the cylindrical portion, the first collar cannot be attached to the nut member. Therefore, at least one of the annular plate portions of the first collar is separable from the cylindrical portion.

  By the way, when the outer ring of the angular bearing at one axial end is excessively tightened in the axial direction, the amount of pressure applied to the angular bearing becomes excessive, and the friction torque increases. Therefore, in the present invention, it is desirable to provide a cylindrical second collar having the same axial length as the first collar between the outer rings of both angular bearings. According to this, the second collar can prevent the outer ring of the angular bearing on the one end side in the axial direction from being excessively tightened in the axial direction.

  Even if a slight difference occurs between the axial length of the first collar and the axial length of the second collar, the amount of pressure applied to the angular bearing is greatly affected. Therefore, it is necessary to set both the first and second collars on the jig, and simultaneously grind the end portions of both collars so that the axial lengths of both collars coincide with each other accurately. In this case, a tapered portion that is inclined inward in the axial direction toward the radially inward is formed on the inner peripheral portion of the surface facing the axially outward of at least one of the annular plate portions of the first collar. If so, the tapered portion becomes the engaging portion of the jig, and simultaneous surface grinding of the first collar and the second collar becomes possible.

  1 to 4 show a biped walking robot including a linear actuator according to an embodiment of the present invention. This biped walking robot includes a body part 1 and a pair of left and right leg parts 2 and 2. The body portion 1 includes a body frame 3, and a control box 4 is mounted on the body frame 1. The body frame 3 is provided with a pair of left and right swivel frames 5 and 5 that can swivel about a vertical axis (Z axis), and the left and right leg portions 2 are connected to the swivel frames 5. Yes.

  Each leg 2 includes a thigh link 7 connected to the lower end of each revolving frame 5 of the body 1 via a hip joint 6, and a crus link 9 connected to the lower end of the thigh link 7 via a knee joint 8. And a foot portion 11 connected to the lower end of the lower leg link 9 via an ankle joint portion 10.

  The hip joint portion 6 is composed of a biaxial joint having a degree of freedom of rotation about two axes, a horizontal axis (Y1 axis) perpendicular to the Z axis and a front and rear axis (X1 axis). Therefore, the thigh link 7 is swingable in the front-rear direction about the Y1 axis with respect to the revolving frame 5, and is swingable in the lateral direction about the X1 axis. The hip joint portion 6 is provided with encoders 6a and 6b that detect the swing angles of the thigh link 7 about the Y1 axis and the X1 axis.

  The knee joint portion 8 is constituted by a uniaxial joint having a degree of freedom of rotation about a horizontal axis (Y2 axis). Accordingly, the crus link 9 is swingable in the front-rear direction with respect to the thigh link 7 about the Y2 axis. The knee joint portion 8 is provided with an encoder 8a that detects a swing angle of the crus link 9 around the Y2 axis.

  The ankle joint portion 10 is composed of a biaxial joint having a degree of freedom of rotation about two axes, a lateral axis (Y3 axis) and a longitudinal axis (X3 axis) orthogonal thereto. Therefore, the foot portion 11 is swingable in the vertical direction around the Y3 axis with respect to the crus link 9, and swings in the lateral direction around the X3 axis. The ankle joint 10 is provided with encoders 10a and 10b that detect the swing angle of the foot 11 around the Y3 axis and the X3 axis.

Further, the two-legged walking robot of this embodiment, the fuselage frame 3 and the pivot frame 5 and the first linear actuator 12 ₁ connected by a portion apart from the Z axis, the pivot frame 5 and the leg 2 The pair of left and right second linear motion actuators 12 ₂ , 12 ₂ that connect the thigh link 7 at a portion away from the hip joint portion 6, and the thigh link 7 and the crus link 9 of each leg portion 2 from the knee joint portion 8. A pair of left and right fourth linear actuators 12 that connect the third leg actuator 12 ₃ connected at a distant part, and the leg link 9 and the foot part 11 of each leg 2 at a part away from the ankle joint part 10. ₄ and 12 ₄ are provided.

Pivoting frame 5 is pivoted operating the Z-axis direction by the first linear actuator 12 ₁ of the telescopic operation. The thigh link 7 is swung in the front-rear direction around the Y1 axis of the hip joint portion 6 by extending or contracting the pair of second linear actuators 12 ₂ , 12 ₂ together. By swinging one of ₂ and 12 ₂ and contracting the other, the hip joint 6 is swung laterally about the X1 axis. Lower link 9 is swung in the front-rear direction about the Y2 axis of the knee joint 8 by expansion and contraction of the third linear actuator 12 _3. The foot portion 11 is swung in the vertical direction about the Y3 axis of the ankle joint portion 10 by extending or contracting the pair of fourth linear motion actuators 12 ₄ and 12 ₄ together, and both fourth linear motions. When one of the actuators 12 ₄ and 12 ₄ is extended and contracted, the other is oscillated laterally about the X3 axis of the ankle joint 10.

As shown in FIG. 5, each of the first to fourth linear actuators 12 ₁ , 12 ₂ , 12 ₃ , and 12 ₄ includes an electric motor 13 and a drive unit 15 that includes a nut member 14 that is rotationally driven by the electric motor 13. And a ball screw mechanism including a screw shaft 16 screwed into the nut member 14 via a ball 14a held by the nut member 14. The linear actuators 12 ₁ , 12 ₂ , 12 ₃ , and 12 ₄ expand and contract by the axial movement of the screw shaft 16 accompanying the rotation of the nut member 14. The screw shaft 16 includes a main body portion 16a having a thread groove formed on the outer peripheral surface, and a rod portion 16c connected to one axial end of the main body portion 16a via a joint portion 16b. Incidentally, FIG. 5 is shown a fourth linear actuator 12 _4, and the other linear actuator _{12 1,} 12 2, 12 ₃ also becomes similar structure.

  The drive unit 15 includes a mount frame 17 on which the electric motor 13 is mounted. A cylindrical nut case 18 that rotatably accommodates the nut member 14 is provided in parallel with the electric motor 13 on the mount frame 17. . The nut member 14 is pivotally supported in the nut case 18 via a pair of angular bearings 19, 19. The drive pulley 13b is coupled to the output shaft 13a of the electric motor 13 projecting from the mount frame 17, and the driven pulley 14b is coupled to the end of the nut member 14 projecting from the mount frame 17, and both pulleys 13b and 14b are coupled. The belt 13c is wound around and the nut member 14 is driven to rotate by the electric motor 13 through the belt 13c.

  Further, the nut case 18 is formed with a hole 18 a having a hole axis perpendicular to the central axis of the nut member 14. The nut case 18 is pivotally supported by a bearing 18b mounted in the hole 18a in a swingable manner on a support shaft 18c described later.

The first linear actuator 12 ₁ of the drive unit 15, parallel to the swing axis in the Z-axis in the nut case 18 to the fuselage frame 3 (Za axis) is pivotally connected around. That is, a support shaft 18c located on the Za axis is attached to the body frame 3, and a nut case 18 is supported on the support shaft 18c so as to be swingable through a bearing 18b. In this case, the Za axis is orthogonal to the central axis of the nut member 14. The first linear actuator 12 ₁ of the screw shaft 16 is swingably connected to the parallel pivot axis (Zb axis) in Z axis in the rod section 16c on the pivot frame 5.

Each second linear actuator 12 _{and second} drive unit 15, pivot frame 5 parallel swing axis in the Y1 axis hip joint 6 in the nut case 18 (Y1a axis) and the swing axis orthogonal thereto (X1a axis) Are pivotably connected around two axes. Specifically, a joint member 12 ₂ a that is rotatable about the Y1a axis is attached to the revolving frame 5, and a support shaft 18 c located on the X1 a axis is attached to the joint member 12 ₂ a, and this support shaft 18 c is attached. A nut case 18 is pivotally supported via a bearing 18b. In this case, the X1a axis is orthogonal to the central axis of the nut member 18, and the Y1a axis is also orthogonal to the central axis of the nut member 18. Further, each of the second linear actuator 12 ₂ of the screw shaft 16, parallel to the swing axis in the Y1 axis in the rod section 16c on the upper end of the thigh link 7 located behind the hip 6 (Y1b axis) and to It is connected so as to be swingable around two axis lines with an orthogonal swing axis line (X1b axis). Specifically, the rod portion 16c is connected to the upper end of the thigh link 7 through the two-axis joint 12 2 _b with two axes of rotation freedom between Y1b axis and X1b axis.

The third linear actuator 12 ₃ of the drive unit 15 is swingably connected to the nut case 18 in the upper portion of the thigh link 7 parallel swing axis to Y2 axis of the knee joint 8 (Y2a axis) around. Specifically, a support shaft 18c positioned on the Y2a axis is attached to the upper portion of the thigh link 7, and a nut case 18 is supported on the support shaft 18c in a swingable manner via a bearing 18b. In this case, the Y2a axis is orthogonal to the central axis of the nut member 14. The third screw shaft 16 of the linear actuator 12 _3, parallel swing axis to Y2 axis in the rod section 16c on the upper end of the lower link 9 extending above the knee joint 8 (Y2b axis) around It is swingably connected. Specifically, it is connected to an upper end portion of the lower leg link 9 via a uniaxial joint 12 3 _b of the rod portion 16c has a rotation degree of freedom Y2b axis.

Each fourth linear actuator 12 ₄ of the drive unit 15, parallel to the swing axis to Y3 axis of the ankle joint portion 10 in the nut case 18 in the upper part of the shank link 9 (Y3a axis) and the swing axis orthogonal thereto ( X3a axis) and are swingably connected around two axes. Specifically, to attach the support shaft 18c which is pivotally attached a rotatable joint member 12 4 _a to Y3a axis on top of the lower leg link 9, located on X3a axis to the joint member 12 4 _a, the supporting A nut case 18 is pivotally supported on the shaft 18c via a bearing 18b. In this case, the X3a axis is orthogonal to the central axis of the nut member 18, and the Y3a axis is also orthogonal to the central axis of the nut member 18. Further, the screw shaft 16 of the fourth linear actuator 12 _4, parallel swing axis to Y3 axis is fixed on a rod portion 16c to the foot 11 and (Y3b axis) and the swing axis orthogonal thereto (X3b axis) Are pivotably coupled around the two axes. Specifically, the rod portion 16c is connected to the foot 11 through the two-axis joint 12 ₄ b with rotational freedom of the two axes of Y3b axis and X3b axis.

Each fourth linear actuator 12 _4, stretching force of the respective fourth linear actuator 12 ₄ is tilted backward relative to connection L1 connecting the Y3 axis Y2 axis and the ankle joint portion 10 of the knee joint 8 It arrange | positions so that it may act on the line L2. Specifically, the Y3a shaft is coupled portion with respect to the lower link 9 of the fourth linear actuator 12 ₄ is positioned behind the connection L1, connecting portion for foot 11 of the fourth linear actuator 12 ₄ The Y3b axis is positioned in front of the connection L1. Here, since the stretching force of the fourth linear actuator 12 ₄ acts on a line connecting the Y3a shaft and Y3b axis in the sagittal plane, the Y3a shaft and Y3b axis by positioning as above, the fourth straight action line L2 of the stretching force of the dynamic actuator 12 ₄ is tilted backward relative to the connection L1.

The fourth linear actuator 12 ₄ of the drive unit 15 disposed laterally outward of the lower leg link 10, of the pair of leg portions 2 fourth linear actuator ₁₂ 4, 12 _4, next to the nut case 18 Although the electric motor 13 is in the position located outward, the fourth linear actuator 12 ₄ of the drive unit 15 disposed laterally inward of the lower link 9, the other leg 2 of the crus link 9 to avoid interference with the fourth driving unit 15 of the linear actuator 12 ₄ disposed laterally inward, the electric motor 13 to the front side of the nut case 18 is in the position to position.

Meanwhile, a drive unit and a fourth linear actuator 12 ₄ of the third linear actuator 12 ₃ and foot driving for crus driving, respectively, and a screw shaft which is rotated by the electric motor and the motor, A ball screw mechanism including a slider having a nut member screwed onto the screw shaft may be considered. However, this requires a heavy vertical guide frame with a guide rail attached to guide the slider, and the center of gravity position of the linear actuator from the upper end of the drive unit is affected by this guide frame. It leaves far below. Therefore, even if the drive unit is connected to the thigh link 7 or the crus link 9 so that the upper end of the drive unit has the same height as the joints (the hip joint part 6 and the knee joint part 8) of each link 7, 9, the drive unit is driven. The distance between the center of gravity of the unit and the joints at the upper ends of the links 7 and 9 becomes longer. Moreover, since the weight of the linear actuator becomes heavy due to the influence of the guide frame, the inertia moment around the hip joint portion 6 of the thigh link 7 and the inertia moment around the knee joint portion 8 of the crus link 9 become large.

On the other hand, in this embodiment, a nut member 14 that is rotationally driven by the electric motor 13 is provided in the drive unit 15 of each of the linear motion actuators 12 ₃ and 12 ₄ , and a screw shaft that is screwed into this by rotation of the nut member 14. Since 16 is advanced and retracted, a heavy guide frame having a heavy weight in the vertical direction to which the above-described guide rail for guiding the slider is attached becomes unnecessary. As a result, the center of gravity of each of the linear motion actuators 12 ₃ and 12 ₄ approaches the upper end of the drive unit 15, and the joints (the hip joint portion 6 and the knee joint portion 8) of the upper end of the thigh link 7 and the lower leg link 9 and the respective linear motions. The distance between the center of gravity of the actuators 12 ₃ and 12 ₄ can be shortened. Moreover, since the weight of each linear motion actuator 12 _3, 12 ₄ is lightly by heavy serving guide frame is not required, reducing the joint moment of inertia about the upper end of the thigh link 7 and lower link 9 In addition, the movement performance of the biped walking robot such as walking speed and responsiveness is improved.

When the nut member 14 is provided in the drive unit 15 of each of the linear motion actuators 12 ₃ and 12 ₄ , the swing axis of the drive unit 15 with respect to the thigh link 7 and the crus link 9 is from a line perpendicular to the central axis of the nut member 14. When offset, the drive unit 15 swings around the swing axis offset from the axis of the screw shaft 16 as the screw shaft 16 advances and retracts, and a bending load acts on the screw shaft 16. In order to absorb the bending load, the nut member 14 needs to be floating supported by the linear guide. On the other hand, in the present embodiment, the swing axes (Y2a axis, Y3a axis, X3a axis) of the drive units 15 of the linear motion actuators 12 ₃ and 12 ₄ with respect to the thigh link 7 and the crus link 9 are the centers of the nut members 14. Since it is orthogonal to the axis, no bending load is applied to the screw shaft 16, and no linear guide is required. Accordingly, the linear motion actuators 12 ₃ and 12 ₄ are lightened accordingly, and the moment of inertia of the thigh link 7 and the crus link 9 is reduced.

Further, when the nut member 14 is provided in the drive unit 15 of each of the linear actuators 12 ₃ and 12 ₄ , a nut case is disposed immediately below the electric motor 13 and the nut member is rotatably accommodated in the nut case. Is also possible. However, this increases the length of the drive unit 15 in the vertical direction, and accordingly, the position of the center of gravity of each of the linear motion actuators 12 ₃ and 12 ₄ decreases. On the other hand, when the nut case 18 is arranged in parallel with the electric motor 13 as in the present embodiment, the vertical length of the drive unit 15 is shortened, and the center of gravity of each of the linear actuators 12 ₃ and 12 ₄ is increased accordingly. Become. Thereby, the moment of inertia of the thigh link 7 and the lower leg link 9 can be further reduced.

By the way, when walking on the stairs, as shown in FIG. 6, the bending angle of the knee joint portion 8 increases, and the crus link 9 tilts greatly forward with respect to the foot portion 11 that contacts the staircase surface. In order ranks, it is necessary to impart a greater moment of the fourth front-down in which the ankle joint 10 about the foot 11 by the linear actuator 12 ₄ (downhill) direction.

Here, to contribute to the imparting of the moment in the foot 11 is only the direction of the component perpendicular to the foot 11 (ground plane) of the stretching force of the fourth linear actuator 12 _4. In this case, than allowed to act on a line parallel to the connection L1 to the stretching force of the fourth linear actuator 12 ₄ connecting the knee joint 8 and the ankle joint portion 10, the connection L1 during down stairs, i.e., stretching force in order to effect line is inclined forward greatly to the foot 11, component in a direction perpendicular to the foot 11 of the stretching force of the fourth linear actuator 12 ₄ becomes slightly. Therefore, it becomes impossible imparted efficiently moment in the fourth linear actuator 12 ₄ to the foot 11. As a result, to grant the required moment required climbing stairs is forced to not give so a fourth linear actuator 12 ₄ to that of the high output large.

On the other hand, in the present embodiment, even if the connection line L1 connecting the knee joint part 8 and the ankle joint part 10 is greatly inclined forward with respect to the foot part 11 at the time of stair walking, the line L2 inclined backward with respect to the connection line L1. since the stretching force of the fourth linear actuator 12 ₄ is applied to the upper, the angle formed between the direction perpendicular to the action line L2 and the foot 11 of the stretching force is at right angles close. Therefore, the direction of the component perpendicular to the foot 11 of the stretching force of the fourth linear actuator 12 ₄ is increased, efficiently moment is imparted to the foot 11. As a result, even without the fourth linear actuator 12 ₄ to that of the high output large, it becomes possible to impart the required moment required climbing stairs to the foot 11. Therefore, the fourth linear actuator 12 ₄ smaller and lighter, the moment of inertia of the shank link 9 can further reduce, can be reduced even further power saving.

Incidentally, the connecting portion serving Y3a shaft for the fourth linear actuator 12 ₄ of the lower link 9 with is positioned in front of the connection L1, connection to a fourth linear actuator 12 ₄ of the foot 11 in front of Y3a axis positions the part serving Y3b axis or the a Y3b shaft with is positioned behind the connection L1, by positioning the Y3a axis behind the Y3b axis, the fourth stretching force line of action of the linear actuator 12 ₄ It is also possible to tilt backward with respect to the connection line L1. However, this is a fourth linear actuator 12 ₄ will projects largely to the front and rear side of the crus link 9, the smart of the leg 2 is impaired.

On the other hand, if the Y3a axis is positioned rearward of the connection L1 and the Y3b axis is positioned forward of the connection L1 as in the present embodiment, the fourth linear motion actuator forward and backward of the crus link 9 12 overhang of ₄ is reduced, the leg 2 is smart. Thereby, the leg part 2 can be brought close to a humanoid profile.

In this embodiment, the nut member 14 and its support structure are also devised in order to reduce the size and weight of the drive unit 15 of each of the linear actuators 12 ₁ , 12 ₂ , 12 ₃ , and 12 ₄ . Hereinafter, this point will be described in detail.

  As shown in FIG. 5, the nut member 14 includes a nut main body portion 141 that holds the ball 14 a and shaft portions 142 and 143 at both axial ends having a smaller outer diameter than the nut main body portion 141. 142 and 143 are supported by a pair of angular bearings 19 and 19, and a driven pulley 14 b is connected to a shaft portion 142 at one end in the axial direction. The shaft portion 142 is connected to the nut main body portion 141 via a dog portion, and is separate from the nut main body portion 141. However, the shaft portion 142 can be integrally formed with the nut main body portion 141.

  By the way, each angular bearing 19 can be arranged such that the end surface of the inner ring 19a abuts on the step between the nut main body 141 and the shafts 142 and 143, but this causes the following problems. Arise. That is, at the time of assembly, when the angular bearing 19 on one axial end side is tightened toward the angular bearing 19 on the other axial end side, a tightening force is applied to the nut main body 141. Then, the ball 14a does not move smoothly due to the compression deformation of the nut main body 141, and the friction loss increases.

  In this case, it is also conceivable that a surplus portion is attached to the outside of the nut main body portion 141 of the present embodiment so that a tightening force acts on the surplus portion. Here, if the outer diameters of the shaft portions 142 and 143 are the same as those of the present embodiment, the tightening force also acts on the portion of the nut main body 141 that holds the ball 14a. The diameter needs to be equal to or larger than the outer diameter of the nut main body 141 of the present embodiment. As a result, the angular bearing 19 also has a large diameter, and the nut case 18 that accommodates the angular bearing 19 necessarily has a large diameter, making it difficult to reduce the size and weight of the drive unit 15.

  Therefore, in the present embodiment, as described above, the shaft portions 142 and 143 at both ends of the nut member 14 that are pivotally supported by the pair of angular bearings 19 and 19 are made smaller in diameter than the nut main body portion 141, and the both angular bearings 19 and 19. A first collar 20 having a special shape is interposed between the inner rings 19a and 19a to prevent a tightening force from acting on the nut main body 141. That is, the first collar 20 is provided on the cylindrical body 20a that is extrapolated to the nut main body 141, and at both ends in the axial direction of the cylindrical portion 20a, and the steps between the nut main body 141 and the shafts 142 and 143 It has a pair of annular plate portions 20b and 20b that enter between the inner ring 19a of the angular bearing 19 and abut against the inner ring. A slight clearance is generated between the step between the nut main body 141 and the shafts 142 and 143 and the annular plate 20b. If both the annular plate portions 20b and 20b are integral with the cylindrical portion 20a, the first collar 20 cannot be attached to the nut member 14, so that at least one annular plate portion 20b is separable from the cylindrical portion 20a. In the present embodiment, both the annular plate portions 20b and 20b are separable from the cylindrical portion 20a.

Here, the outer ring 19 b of the angular bearing 19 on one axial end side (mount frame 17 side) is fastened to the other axial end side by the mount frame 17 by bolting the mount frame 17 to the nut case 18. At this time, the tightening force is axially transmitted through the bearing ball 19c of the bearing 19, the inner ring 19a, the annular plate portion 20b at one axial end of the first collar 20, the cylindrical portion 20a, and the annular plate portion 20b at the other axial end. It is transmitted to the inner ring 19a of the angular bearing 19 on the other end side. Then, the outer ring 19b of the angular bearing 19 on the other axial end side is pressed against the shoulder 18d on the other axial end of the nut case 18 by the pressing force transmitted from the inner ring 19a of the bearing 19 through the bearing ball 19c. It is pressed through. As a result, the angular bearings 19 and 19 are held in the nut case 18 immovably in the axial direction, and the thrust reaction force acting on the nut member 14 by the expansion and contraction operations of the respective linear motion actuators 12 ₁ , 12 ₂ , 12 ₃ , and 12 _4. Can be received by both the angular bearings 19, 19.

  Further, the tightening force applied to the angular bearing 19 on one axial end side during assembly is transmitted to the angular bearing 19 on the other axial end side through the first collar 20 as described above, and therefore the tightening force is applied to the nut main body 141. Does not work. Therefore, even if the outer diameter of the nut main body 141 is set to the minimum necessary size required for holding the ball 14a, and the outer diameters of the shaft portions 142 and 143 are made smaller than this, the movement of the ball 14a is caused by the tightening force. There is no problem that smoothness is lost and friction loss increases. And the diameter of the angular bearing 19 can also be reduced by reducing the diameter of the shaft portions 142 and 143. As a result, the diameter of the nut case 18 can be reduced, and the drive unit 15 can be reduced in size and weight.

  In addition, before the outer ring 19b of the angular bearing 19 on the other axial end side is pressed against the shoulder 18d on the other axial end of the nut case 18, the mount frame 17 comes into contact with one axial end of the nut case 18 and cannot be tightened. In order to prevent this, in consideration of dimensional tolerances, a slight clearance is generated between the axial end of the nut case 18 and the mount frame 17 in the assembled state. For this reason, the outer ring 19b of the angular bearing 19 at one end in the axial direction can be tightened in any amount in the axial direction, the amount of pressure applied to the angular bearing 19 becomes excessive, and the friction torque may increase.

  Therefore, in the present embodiment, a cylindrical second collar 21 having the same axial length as that of the first collar 20 is interposed between the outer rings 19b, 19b of the angular bearings 19, 19. According to this, it is possible to prevent the second collar 21 from excessively tightening the outer ring 19b of the angular bearing 19 on one axial end side in the axial direction.

  However, even if a difference of micron order occurs between the axial length of the first collar 20 and the axial length of the second collar 21, the amount of pressure applied to the angular bearing 19 is greatly affected. Therefore, as shown in FIG. 7, the first and second collars 20 and 21 are set on the jig 100, both the collars 20 and 21 are ground simultaneously, and the axial lengths of both the collars 20 and 21 are accurately determined. Try to match.

  Here, a tapered portion 20c that is inclined inward in the axial direction toward the radially inward is formed on the inner peripheral portion of the surface facing the axially outward of each annular plate portion 20b of the first collar 20. . The jig 100 includes a jig body 101 and a holding jig 102 that can be attached to the jig body 101 with a magnet chuck or the like. The holding jig 102 includes a lower half portion 103 having a female screw portion 103a and an upper half portion 104 having a male screw portion 104a. Tapered portions 103b and 104b corresponding to the tapered portions 20c of the annular plate portions 20b of the first collar 20 are formed on the outer periphery of the end portions of the upper and lower half portions 103 and 104, respectively.

  During the surface grinding, one annular plate portion 20b of the first collar 20 is placed on the jig body 101 so that the tapered portion 20c engages with the tapered portion 103b of the lower half 103 of the holding jig 102, The cylindrical portion 20a of the first collar 20 and the other annular plate portion 20b are placed thereon. Next, the upper half 104 of the holding jig 102 is screwed into the lower half 103. Thereby, the tapered portion 104b of the upper half 104 is engaged with the tapered portion 20c of the other annular plate portion 20b, and the first annular plate portion 20b, the cylindrical portion 20a, and the other annular plate portion 20b are formed. The collar 20 is fixed on the jig body 101 with the collar 20 sandwiched between the lower half 103 and the upper half 104. Next, the second collar 21 is placed on the jig body 101 so as to surround the first collar 20, and the upper surface of the annular plate portion 20 b above the first collar 20 and the upper end surface of the second collar 21 are placed. Surface grinding at the same time.

  By forming the tapered portion 20c on the annular plate portion 20b in this way, the tapered portion 20c becomes an engaging portion of the holding jig 102, and simultaneous surface grinding of the first collar 20 and the second collar 21 becomes possible. In the present embodiment, the tapered portion 20c is formed on both the annular plate portions 20b and 20b of the first collar 20, but the lower half 103 of the holding jig 102 is firmly fixed to the jig body 101. If present, the tapered portions 20c and 104b may be formed only on the upper annular plate portion 20b to be ground and the upper half portion 104 of the holding jig 102.

  Although the embodiment in which the present invention is applied to the linear motion actuator for the biped walking robot has been described above, the present invention can be similarly applied to the linear motion actuator for uses other than the biped robot.

The perspective view seen from the slanting back of the biped walking robot which comprises the linear motion actuator of embodiment of this invention. The front view of a biped walking robot. The rear view of a biped walking robot. The side view of a biped robot. The VV line expanded sectional view of FIG. The side view which shows the state of the leg part at the time of stair walk of a biped walking robot. Sectional drawing which shows the state at the time of surface grinding of the 1st and 2nd color | collar provided in the nut case which the linear motion actuator of embodiment comprises.

Explanation of symbols

12 ₁ , 12 ₂ , 12 ₃ , 12 ₄ ... linear motion actuator, 13 ... electric motor, 14 ... nut member, 14a ... ball, 141 ... nut body part, 142, 143 ... shaft part, 16 ... screw shaft, 18 ... Nut case, 19 ... angular bearing, 19a ... inner ring, 19b ... outer ring, 20 ... first collar, 20a ... cylindrical part, 20b ... annular plate part, 20c ... taper part, 21 ... second collar.

Claims (4)

A linear motion actuator comprising an electric motor, a nut member that is rotationally driven by the electric motor, and a screw shaft that is screwed into the nut member via a ball held by the nut member, the nut member having a cylindrical shape In what is pivotally supported in the nut case via a pair of angular bearings,
The nut member has a nut main body portion that holds the ball, and shaft portions at both axial ends having a smaller outer diameter than the nut main body portion, and is configured to pivotally support both shaft portions by a pair of angular bearings.
The first collar is interposed between the inner rings of both angular bearings,
The first collar is provided on a cylindrical portion that is extrapolated to the nut main body portion, and on both axial ends of the cylindrical portion, and enters between a step between the nut main body portion and each shaft portion and an inner ring of each angular bearing. A linear motion actuator comprising a pair of annular plate portions in contact with an inner ring.   The linear actuator according to claim 1, wherein at least one of the annular plate portions of the first collar is separable from the cylindrical portion.   3. The linear actuator according to claim 1, wherein a cylindrical second collar having an axial length identical to that of the first collar is interposed between outer rings of the angular bearings.   A tapered portion that is inclined inward in the axial direction toward the radially inward is formed on the inner peripheral portion of the surface facing the axially outward of at least one of the annular plate portions of the first collar. The linear motion actuator according to claim 3, wherein the linear motion actuator is provided.