Transmission with integrated overload protection for a legged robot

1. A robot comprising:

a motor disposed at a joint of a leg of the robot, the motor configured to control motion of the leg of the robot;

a transmission comprising an input member coupled to and configured to rotate with the motor, an output member, and a fixed intermediate member that engages the output member, the input member configured to engage the fixed intermediate member and rotate within an open annular space defined by the fixed intermediate member, and when the input member rotates, the output member rotates at a different speed;

a pad frictionally coupled to a side surface of the output member of the transmission and coupled to the leg of the robot;

a spring configured to apply an axial preload on the pad, the axial preload defining a torque limit that indicates a torque load on the leg of the robot that causes the output member of the transmission to slip relative to the pad; and

an output flexure member disposed between, and interfacing with, the pad and the spring, wherein the output flexure member is torsionally stiff and axially flexible, and wherein the output flexure member is coupled to the leg of the robot.

2. The robot of claim 1 , wherein the joint corresponds to a hip joint of the leg of the robot.

3. The robot of claim 2 , further comprising a housing at the hip joint of the leg of the robot, wherein the motor is disposed within the housing.

4. The robot of claim 1 , wherein the robot comprises a quadruped robot.

5. The robot of claim 1 , wherein the robot comprises a biped robot.

6. The robot of claim 1 , further comprising a second pad frictionally coupled to a proximate side surface of the output member, and wherein the pad is frictionally coupled to a distal side surface of the output member of the transmission.

7. The robot of claim 6 , wherein the second pad is coupled to a presser plate, the presser plate coupled to the leg of the robot.

8. The robot of claim 1 , further comprising a constraint ring coupled to the leg of the robot, the constraint ring defining the open annular space where the output member of the transmission is mounted.

9. The robot claim 8 , further comprising a constraint bushing mounted between the constraint ring and the output member of the transmission, the constraint bushing comprising an exterior peripheral surface interfacing with an interior peripheral surface of the constraint ring and an interior peripheral surface interfacing with an exterior peripheral surface of the output member of the transmission.

10. The robot of claim 1 , further comprising an O-ring mounted within a second annular space defined by the pad.

11. The robot of claim 1 , wherein:

the input member is elliptically shaped and configured to cause the intermediate member to deform as the input member rotates;

the fixed intermediate member comprises external teeth disposed on an external peripheral surface of the intermediate member; and

the output member comprises internal teeth disposed on an interior peripheral surface of the output member, the internal teeth configured to engage the external teeth of the intermediate member.

12. An assembly comprising:

a motor disposed at a hip joint of a leg of a robot, the motor configured to control motion of the leg of the robot;

a harmonic drive comprising a wave generator coupled to and configured to rotate with the motor, a flexspline, and a circular spline, and when the wave generator rotates, the flexspline is fixed while the circular spline rotates with the wave generator at a different speed;

a first pad frictionally coupled to both a distal side surface of the circular spline and the leg of the robot;

a second pad frictionally coupled to a proximal side surface of the circular spline;

a compliant member configured to apply an axial preload on the first and second pads, the axial preload defining a torque limit, and when a torque load on the leg of the robot satisfies the torque limit, the circular spline slips relative to at least one of the first or second pads; and

an output flexure member disposed between and interfacing with the first pad and the compliant member, the output flexure member coupled to the leg of the robot.

13. The assembly of claim 12 , wherein the robot comprises a quadruped robot having four legs, and wherein the leg comprises one leg of the four legs of the quadruped robot.

14. The assembly of claim 12 , wherein the robot comprises a biped robot having two legs, and wherein the leg comprises one leg of the two legs of the biped robot.

15. The assembly of claim 12 , wherein the second pad is coupled to a presser plate, the presser plate coupled to the leg of the robot.

16. The assembly of claim 15 , further comprising a constraint ring coupled to the leg of the robot, the constraint ring defining an open annular space, the circular spline and the first and second pads frictionally coupled to the circular spline mounted within the open annular space, the presser plate coupled to the leg of the robot by a radial array of bolts that couple the presser plate to the constraint ring.

17. The assembly of claim 16 , further comprising a cross-roller bearing mounted between an exterior peripheral surface of the constraint ring and an interior surface of a housing of the motor.

18. The assembly claim 12 , further comprising a constraint bushing mounted between the constraint ring and the circular spline, the constraint bushing comprising an exterior peripheral surface interfacing with an interior peripheral surface of the constraint ring and an interior peripheral surface interfacing with an exterior peripheral surface of the circular spline.

19. The assembly of claim 12 , wherein the first pad defines a first open annular space and the second pad defines a second open annular space, the assembly further comprising:

a first O-ring mounted within the first open annular space defined by the first pad; and

a second O-ring mounted within the second open annular space defined by the second pad.

20. The assembly of claim 12 , wherein the flexspline comprises a thin-walled cylinder with external teeth formed circumferentially on a portion of an outer surface of the thin-walled cylinder, and the assembly further comprises a torque sensor mounted on a housing of the motor and coupled to a portion of the thin-walled cylinder.

21. The assembly of claim 12 , wherein the compliant member comprises a Belleville spring.

22. An assembly comprising:

a motor disposed at a hip joint of a leg of a robot, the motor configured to control motion of the leg of the robot;

a harmonic drive comprising: a wave generator coupled to and configured to rotate with the motor; a flexspline; and a circular spline, and when the wave generator rotates, the flexspline is fixed while the circular spline rotates with the wave generator at a different speed, wherein the flexspline comprises a thin-walled cylinder with external teeth formed circumferentially on a portion of an outer surface of the thin-walled cylinder;

a torque sensor mounted on a housing of the motor and coupled to a portion of the thin-walled cylinder;

a first pad frictionally coupled to both a distal side surface of the circular spline and the leg of the robot;

a second pad frictionally coupled to a proximal side surface of the circular spline; and

a compliant member configured to apply an axial preload on the first and second pads, the axial preload defining a torque limit, and when a torque load on the leg of the robot satisfies the torque limit, the circular spline slips relative to at least one of the first or second pads.