Powered lower extremity orthotic and method of operation

1. A method of controlling a powered lower extremity orthotic having at least one leg with at least two actuators configured to be controlled by a signal processor and coupled to the lower limb of a person, comprising:

controlling a trajectory of a reference point on the at least one leg of said orthotic when the at least one leg is not touching a ground surface to follow a predetermined trajectory that is defined by at least one Cartesian coordinate; and

switching coordinates used to define said trajectory within a single gait cycle.

2. The method of claim 1 wherein the Cartesian coordinate is measured in a horizontal axis.

3. The method of claim 1 wherein the Cartesian coordinate is measured in a vertical axis.

4. The method of claim 1 wherein the Cartesian coordinate is measured in an axis that is not purely horizontal or vertical.

5. The method of claim 1 wherein the trajectory is defined by a vertical Cartesian coordinate and a knee angle coordinate.

6. The method of claim 1 wherein the trajectory is defined by a vertical Cartesian coordinate and a hip angle coordinate.

7. The method of claim 1 wherein the trajectory is defined by a horizontal Cartesian coordinate and a knee angle coordinate.

8. The method of claim 1 wherein the trajectory is defined by a horizontal Cartesian coordinate and a hip angle coordinate.

9. The method of claim 1 further comprising: measuring the trajectory of said reference point with respect to a torso link configured to couple said orthotic to a pelvis or torso region of the person.

10. The method of claim 1 wherein the trajectory of said reference point is measured with respect to an absolute frame of reference.

11. The method of claim 1 wherein the trajectory of said reference point is measured with respect to the ground.

12. The method of claim 11 further comprising: estimating a position of said reference point from an orientation of a second leg of the orthotic that is in contact with the ground surface.

13. The method of claim 11 directly measuring a height of said reference point from the ground surface with a non-contact sensor.

14. The method of claim 1 further including maintaining a state machine to switch between the coordinates.

15. An artificial leg device, configured to be coupled to the lower limb of a person, comprising:

an artificial foot having a toe and a heel;

a shank link coupled to the artificial foot;

a thigh link configured to be attached to a person;

a knee mechanism interconnecting said thigh link and said shank link, said knee mechanism allowing flexion and extension movements of said thigh link and said shank link relative to each other;

a torque generator configured to generate torque between said shank link and said thigh link;

a knee angle sensor creating a knee angle signal representing an angle between said shank link and said thigh link;

a stance sensor configured to identify which part of said artificial foot is in contact with a ground surface;

a power source configured to provide electric power; and

a signal processor connected to the power source, the torque generator, the knee angle sensor and the stance sensor, wherein said signal processor receives signals from the knee and stance sensors, determines that the artificial foot is in a swing state and controls the angle between said shank link and said thigh link through the torque generator such that said artificial foot follows a predetermined trajectory.

16. The artificial leg device of claim 15 , wherein the predetermined trajectory is generally parallel to the ground.

17. An artificial leg device, configured to be coupled to the lower limb of a person, comprising:

a shank link configured to be attached to a person;

a thigh link configured to be attached to a person;

a torso link configured to be attached to a person;

a knee mechanism interconnecting said thigh link and said shank link, said knee mechanism allowing flexion and extension movements of said thigh link and said shank link relative to each other;

a knee torque generator configured to generate torque between said shank link and said thigh link;

a knee angle sensor creating a knee angle signal representing an angle between said shank link and said thigh link;

a hip mechanism interconnecting said thigh link and said torso link, said hip mechanism allowing flexion and extension movements of said thigh link and said torso link relative to each other;

a hip torque generator configured to generate torque between said shank link and said torso link;

a hip angle sensor creating a hip angle signal representing an angle between said torso link and said thigh link;

a power source configured to provide electric power; and

a signal processor connected to the power source, the knee torque generator, the hip torque generator, the knee angle sensor and the hip angle sensor, wherein said signal processor receives signals from the knee and hip sensors, and controls the angles between said shank link and said thigh link and between said thigh link and said torso link through the knee torque and hip torque generators respectively such that a reference point on the artificial leg device follows a predetermined trajectory that is defined by at least one Cartesian coordinate.

18. The artificial leg device of claim 17 , wherein the Cartesian coordinate is the height of the reference point from a ground surface.

19. An artificial leg device, configured to be coupled to the lower limb of a person, comprising:

an artificial foot having a toe and a heel;

a shank link coupled to the artificial foot;

a thigh link;

a torso link configured to be attached to the person;

a knee mechanism interconnecting said thigh link and said shank link, said knee mechanism allowing flexion and extension movements of said thigh link and said shank link relative to each other;

a knee torque generator configured to generate torque between said shank link and said thigh link;

a knee angle sensor creating a knee angle signal representing an angle between said shank link and said thigh link;

a hip mechanism interconnecting said torso link and said thigh link, said hip mechanism allowing flexion and extension movements of said torso link and said thigh link relative to each other;

a hip torque generator configured to generate torque between said thigh link and said torso link;

a hip angle sensor creating a hip angle signal representing an angle between said thigh link and said torso link;

a stance sensor configured to identify which part of said artificial foot is in contact with a ground surface;

a power source configured to provide electric power; and

a signal processor connected to the power source, the knee torque generator, the hip torque generator, and each of the knee angle, hip angle and stance sensors, wherein said signal processor receives signals from the knee, hip and stance sensors, determines that the artificial leg is in a swing state and controls the angles between said shank link and said thigh link and between the thigh link and the torso link through the knee and hip torque generators respectively such that said artificial foot follows a predetermined trajectory.

20. The artificial leg device of claim 19 , wherein the predetermined trajectory is generally parallel to the ground surface.