Biomimetic joint actuators
View Patent ↗In a powered actuator for supplying torque, joint equilibrium, and/or impedance to a joint, a motor is directly coupled to a low-reduction ratio transmission, e.g., a transmission having a gear ratio less than about 80 to 1. The motor has a low dissipation constant, e.g., less than about 50 W/(Nm) 2 . The transmission is serially connected to an elastic element that is also coupled to the joint, thereby supplying torque, joint equilibrium, and/or impedance to the joint while minimizing the power consumption and/or acoustic noise of the actuator.
1. A powered actuator for supplying to a joint augmented by a powered human augmentation device at least one of an augmentation torque, joint equilibrium, and an impedance, the powered actuator comprising:
a motor having a dissipation constant less than about 50 W/(Nm) 2 , wherein the dissipation constant is given by R/k t 2 , where R refers to stator winding resistance and k t refers to motor torque constant;
a transmission coupled directly to the motor; and
an elastic element coupled to the joint and coupled, in series, to the transmission,
to generate a normalized joint torque in a range from about −2.8 to about 2.8 Nm/kg.
2. The powered actuator of claim 1 , wherein the motor comprises a high-torque motor supplying motor torque of at least about 0.06 Nm/kg.
3. The powered actuator of claim 1 , wherein the motor comprises a low revolutions per minute (RPM) motor having an RPM less than about 1500.
4. The powered actuator of claim 1 , wherein the motor comprises a transverse-flux motor.
5. The powered actuator of claim 1 , wherein the actuator is adapted to be backdrivable.
6. The powered actuator of claim 1 , wherein the transmission has a gear ratio less than about 80:1.
7. The powered actuator of claim 1 , wherein the transmission comprises a ball-screw transmission having a ball nut coupled to the elastic element.
8. The powered actuator of claim 7 , wherein the ball-screw transmission comprises a screw having a pitch in a range of about 2 mm up to about 10 mm, thereby resulting in the gear ratio of less than about 80:1.
9. The powered actuator of claim 7 , wherein the elastic element comprises a spring, the powered actuator further comprising a cable and a joint output pulley, the cable being coupled to both the spring and the joint output pulley.
10. The powered actuator of claim 1 , wherein the transmission comprises a ball-screw transmission having a ball nut coupled to the motor rotor and the screw coupled to the elastic element.
11. The powered actuator of claim 1 , wherein:
the motor comprises a motor having an external rotor; and
the transmission comprises a cable and a joint output pulley, the cable coupling the external rotor and the joint output pulley.
12. The powered actuator of claim 11 , wherein the cable is selected from the group consisting of a synthetic cable, a steel cable, a belt, and a chain.
13. The powered actuator of claim 1 , further comprising:
a motor encoder adapted to measure angular displacement of a rotor of the motor with respect to a stator of the motor; and
a joint encoder adapted to measure angular displacement of the joint about a joint pivot.
14. The powered actuator of claim 13 , wherein at least one of the motor encoder and the joint encoder comprises an absolute encoder.
15. The powered actuator of claim 13 , wherein at least one of the motor encoder and the joint encoder comprises a magnetic encoder having at least 13-bit resolution.
16. A powered human augmentation device, comprising:
an artificial joint;
a motor constructed and arranged to supply torque to the artificial joint, the motor having a dissipation constant of less than about 50 W/(Nm) 2 , wherein the dissipation constant is given by R/k t 2 , where R refers to stator winding resistance and k t refers to motor torque constant;
a transmission coupled directly to the motor; and
an elastic element coupled to the joint and coupled, in series, to the transmission, to generate a normalized joint torque in a range from about −2.8 to about 2.8 Nm/kg.
17. The device of claim 16 , wherein the motor comprises a transverse-flux motor.
18. The powered actuator of claim 16 , wherein the motor comprises a high-torque motor supplying motor torque of at least about 0.06 Nm/kg.
19. The powered actuator of claim 16 , wherein the motor comprises a low revolutions per minute (RPM) motor having an RPM less than about 1500.
20. The powered actuator of claim 16 , wherein the actuator is adapted to be backdrivable.
21. The powered actuator of claim 16 , wherein the transmission has a gear ratio less than about 80:1.