Compound harmonic gear

1. A compound harmonic actuator, comprising:

a motor;

a flex spline disposed about the motor; and

a wave generator radially interposable between the motor and the flex spline and rotatably drivable by the motor and shaped to form the flex spline into an elliptical shape with an axis such that wave generator rotations drive rotations of the axis of the ellipse of the flex spline,

the wave generator comprising a scalloped outer surface and roller bearings arranged circumferentially about the scalloped outer surface,

wherein the flex spline comprises a ground flex spline configured to interface with the wave generator and having a first number of external teeth, an output flex spline configured to interface with an output gear and having a second number of external teeth which is different from the first number and a coupling configured to interface with the respective first and second numbers of external teeth of the ground and output flex splines.

2. The compound harmonic actuator according to claim 1 , further comprising:

a ground arm in which the motor is supportively disposable; and

an output arm which is drivable by the flex spline to pivot within a predefined range of angles relative to the ground arm.

3. The compound harmonic actuator according to claim 1 , wherein the wave generator is shaped to form the flex spline into an irregular elliptical shape with multiple major axes.

4. The compound harmonic actuator according to claim 1 , wherein the scalloped outer surface comprises sequential ridges and lands.

5. The compound harmonic actuator according to claim 4 , wherein a distal edge of each ridge is sharp.

6. The compound harmonic actuator according to claim 4 , wherein a distal edge of each ridge is radially aligned with or terminal within respective central longitudinal axes of adjacent roller bearings.

7. The compound harmonic actuator according to claim 1 , wherein the flex spline is formed as only a single unitary piece.

8. A compound harmonic actuator, comprising:

a motor;

a flex spline disposed about the motor and formed as only a single unitary piece; and

a wave generator radially interposable between the motor and the flex spline,

the wave generator being rotatably drivable by the motor and shaped to form the flex spline into an elliptical shape with an axis such that wave generator rotations drive rotations of the axis of the ellipse of the flex spline,

wherein the flex spline comprises a ground flex spline configured to interface with the wave generator and having a first number of external teeth, an output flex spline configured to interface with an output gear and having a second number of external teeth which is different from the first number and a coupling configured to interface with the respective first and second numbers of external teeth of the ground and output flex splines.

9. The compound harmonic actuator according to claim 8 , further comprising:

a ground arm in which the motor is supportively disposable; and

an output arm which is drivable by the flex spline to pivot within a predefined range of angles relative to the ground arm.

10. The compound harmonic actuator according to claim 8 , wherein the wave generator is shaped to form the flex spline into an irregular elliptical shape with multiple major axes.

11. The compound harmonic actuator according to claim 8 , wherein the wave generator comprises a scalloped outer surface and roller bearings arranged circumferentially about the scalloped outer surface, wherein:

the scalloped outer surface comprises sequential ridges and lands,

each roller bearing rolls about a central longitudinal axis thereof in a corresponding land.

12. The compound harmonic actuator according to claim 8 , wherein the single unitary piece of the flex spline comprises a body integrally formed with a smooth interior diameter and external teeth.

13. A compound harmonic actuator, comprising:

a motor;

a flex spline disposed about the motor; and

a wave generator radially interposable between the motor and the flex spline and rotatably drivable by the motor and shaped to form the flex spline into an elliptical shape with an axis such that wave generator rotations drive rotations of the axis of the ellipse of the flex spline,

the flex spline comprising:

a ground flex spline configured to interface with the wave generator and having a first number of external teeth;

an output flex spline configured to interface with an output gear and having a second number of external teeth which is different from the first number; and

a coupling configured to interface with the respective first and second numbers of external teeth of the ground and output flex splines.

14. The compound harmonic actuator according to claim 13 , further comprising:

a ground arm in which the motor is supportively disposable; and

an output arm which is drivable by the output flex spline to pivot within a predefined range of angles relative to the ground arm.

15. The compound harmonic actuator according to claim 13 , wherein the wave generator is shaped to form the flex spline into an irregular elliptical shape with multiple major axes.

16. The compound harmonic actuator according to claim 13 , wherein the wave generator comprises a scalloped outer surface and roller bearings arranged circumferentially about the scalloped outer surface, wherein:

the scalloped outer surface comprises sequential ridges and lands,

each roller bearing rolls about a central longitudinal axis thereof in a corresponding land.

17. The compound harmonic actuator according to claim 13 , wherein the coupling comprises:

a first ring gear having internal teeth to interface with the first number of external teeth of the ground flex spline;

a second ring gear having internal teeth to interface with the second number of external teeth of the output flex spline; and

coupling pins disposed to secure the first and second ring gears.

18. The compound harmonic actuator according to claim 13 , wherein the ground flex spline is provided as first and second ground flex splines on either side of the output flex spline.

19. The compound harmonic actuator according to claim 18 , wherein the coupling comprises:

first ring gears that each have internal teeth to interface with the first number of external teeth of each of the first and second ground flex splines;

second ring gears that each have internal teeth to interface with the second number of external teeth of the output flex spline; and

first and second sets of coupling pins disposed to secure each of the first ring gears to one of the second ring gears.