Transmission with integrated overload protection for a legged robot
An example robot includes: a motor disposed at a joint configured to control motion of a member of the robot; a transmission including an input member coupled to and configured to rotate with the motor, an intermediate member, and an output member, where the intermediate member is fixed such that as the input member rotates, the output member rotates therewith at a different speed; a pad frictionally coupled to a side surface of the output member of the transmission and coupled to the member of the robot; and a spring configured to apply an axial preload on the pad, wherein the axial preload defines a torque limit that, when exceeded by a torque load on the member of the robot, the output member of the transmission slips relative to the pad.
1. A method for operating a robot, the method comprising:
driving rotation of a leg member of the robot with a motor, wherein the motor is coupled to the leg member through a transmission system that comprises an input member coupled to an output of the motor, and an output member, the transmission system configured such that the output member rotates at a different speed than the input member, wherein the output member of the transmission system is engaged with the leg member of the robot through a clutch member comprising a clutch surface that contacts a surface of the output member; and
providing overload protection for the motor or the transmission system by applying, with a compliant member, a preload force on the clutch member to contact the clutch surface of the clutch member with the surface of an output member of the transmission system, wherein the preload force provides a torque limit such that:
when a torque load on the transmission system is less than the torque limit, the surface of the output member and the clutch surface of the clutch member are frictionally engaged and rotate together, and
when the torque load on the transmission system is greater than the torque limit, the surface of the output member slips relative to the clutch surface of the clutch member.
2. The method of claim 1 , wherein the torque load on the transmission system results from a force acting on the leg member of the robot.
3. The method of claim 2 , wherein the force results from contact between the leg member and an object or a ground surface.
4. The method of claim 1 , wherein the input member and the output member of the transmission system are configured to rotate about an axis, and wherein the compliant member applies the preload force in a direction parallel to the axis.
5. The method of claim 1 , wherein:
the surface of the output member comprises a first surface and the output member further comprises a second surface opposite the first surface; and
the clutch surface of the clutch member comprises a first clutch surface contacting the first surface of the output member and a second clutch surface contacting the second surface of the output member.
6. The method of claim 5 , wherein at least a portion of the output member is positioned between the first clutch surface and the second clutch surface.
7. The method of claim 1 , further comprising adjusting the preload force by positioning one or more shims between the compliant member and the output.
8. The method of claim 1 , wherein the transmission system comprises a harmonic drive, and wherein harmonic drive comprises a wave generator, a flexspline, and a circular spline.
9. The method of claim 8 , wherein the input member of the transmission system comprises the wave generator, and the output member of the transmission system comprises the circular spline.
10. The method of claim 8 , wherein the input member of the transmission system comprises the wave generator, and the output member of the transmission system comprises the flexspline.
11. The method of claim 1 , wherein the compliant member comprises a Belleville spring.
12. The method of claim 11 , wherein the torque limit is based on a spring rate of the Belleville spring.
13. The method of claim 1 , further comprising measuring a rotary position of the output of the motor using a hall effect sensor positioned on a printed circuit board of a motor controller and a magnet positioned on or in the output of the motor.
14. The method of claim 1 , further comprising dissipating heat from the motor and a motor controller through a thermal interfacial material positioned between and contacting both a surface of the motor and a surface of the motor controller.
15. A method for providing overload protection for a transmission system, the method comprising:
applying, with a compliant member, a preload force on a clutch member to contact a clutch surface of the clutch member with a surface of an output member of the transmission system, wherein the transmission system comprises an input member configured to be driven by a motor, and the output member;
wherein the preload force provides a torque limit such that:
when a torque load on the transmission system is less than the torque limit, the surface of the output member and the clutch surface of the clutch member are frictionally engaged and rotate together; and
when the torque load on the transmission system is greater than the torque limit, the surface of the output member slips relative to the clutch surface of the clutch member.
16. The method of claim 15 , wherein the clutch member is coupled to an output, and wherein the torque load of the transmission system results from a force imparted on the output.
17. The method of claim 16 , wherein the output comprises a leg member of a robot.
18. The method of claim 17 , wherein the force imparted on the leg member of the robot results from contact between the leg member and a ground surface.
19. The method of claim 15 , further comprising measuring a rotary position of a shaft of the motor using a hall effect sensor positioned on a printed circuit board of a motor controller and a magnet positioned on or in the shaft of the motor.
20. The method of claim 15 , further comprising dissipating heat from the motor and a motor controller through a thermal interfacial material positioned between and contacting both a surface of the motor and a surface of the motor controller.