Elastic motor-spring actuator

1. An actuator, comprising:

a fixed member;

a free member operatively engaged with said fixed member so that said free member is moveable with respect to said fixed member;

a connector member, said connector member engaging said fixed member and said free member so that said connector member is moveable with respect to said fixed member and said free member;

an elastic element operatively associated with said connector member and said free member, said elastic element having a variable compliance; and

means for moving operatively associated with said connector member and said fixed member so that said means for moving moves said connector member with respect to said fixed member, said actuator being operable to store energy in said elastic element without a change in an overall length of said actuator, wherein said means for moving comprises a motor mounted to said fixed member; a lead screw mounted for rotation to said fixed member and operatively connected to said motor so that said motor can rotate said lead screw; and a nut mounted to said connector member and operatively engaged with said lead screw, rotation of said lead screw causing said connector member to move with respect to said fixed member.

2. The actuator of claim 1 , wherein changes in the compliance of said elastic element changes a compliance of said actuator.

3. The actuator of claim 2 , wherein said elastic element increases a compliance of said actuator with a decrease in a contraction force and wherein said elastic element decreases a compliance of said actuator with an increase in the contraction force.

4. The actuator of claim 1 , wherein said means for moving does work on said elastic element.

5. The actuator of claim 1 , wherein said elastic element does work on said means for moving.

6. The actuator of claim 1 , further comprising a take-up system operatively connected to said elastic element, said take-up system lengthening and shortening an operating length of said elastic element to change a compliance of said elastic element.

7. The actuator of claim 6 , wherein said take-up system comprises a spool and a motor operatively associated with said spool.

8. The actuator of claim 7 , further comprising a strain sensor operatively associated with said actuator, said strain sensor sensing a strain in said actuator.

9. The actuator of claim 6 , wherein said take-up system lengthens or shortens said elastic element during operation of said actuator so that a compliance of said elastic element is changed without halting operation of said actuator.

10. The actuator of claim 1 , wherein said free member is moveable with respect to said fixed member along an axis so that said actuator is operable along the axis.

11. An actuator, comprising:

a fixed member;

a connector member operatively engaged with said fixed member so that said connector member can move with respect to said fixed member;

a free member operatively engaged with said connector member so that said free member can move with respect to said fixed member;

a drive system operatively associated with said fixed member and said connector member, said drive system operable to move said connector member with respect to said fixed member, wherein said drive system comprises a motor mounted to said fixed member; a lead screw mounted for rotation to said fixed member and operatively connected to said motor so that said motor can rotate said lead screw; and a nut mounted to said connector member and operatively engaged with said lead screw, rotation of said lead screw causing said connector member to move with respect to said fixed member; and

an elastic element having a first end and a second end, the first end of said elastic element being connected to said free member, the second end being connected to said connector member.

12. The actuator of claim 11 ,

wherein said fixed member comprises a tubular structure and wherein said connector member comprises generally elongate structure sized to be slidably received by the tubular structure of said fixed member.

13. The actuator of claim 12 , wherein said free member comprises a tubular structure sized to slidably receive said connector member.

14. The actuator of claim 13 , wherein said tubular structures of said fixed member and said free members comprise generally hollow, cylindrically-shaped structures.

15. The actuator of claim 14 , wherein said fixed member comprises a slot provided therein and wherein said free member comprises at least one slot provided therein, and wherein said connector member comprises a plurality of pins sized to be slidably received by slots provided in said fixed and free members.

16. An actuator, comprising:

a fixed member;

a free member operatively engaged with said fixed member so that said free member is moveable with respect to said fixed member;

a connector member operatively associated with said fixed member and said free member;

an elastic element operatively associated with said free member and said connector member, said elastic element having a variable compliance; and

a drive system operatively connected to said fixed member, said connector member, and said elastic element, said drive system changing a length of said elastic element during operation both in contraction and in extension of said actuator to store energy in said elastic element, said drive system and said elastic element applying a total force to said free member during operation both in contraction and in extension of said actuator that is a sum of a force produced by said drive system and a force produced by said elastic element, wherein said drive system comprises a motor mounted to said fixed member; a lead screw mounted for rotation to said fixed member and operatively connected to said motor so that said motor can rotate said lead screw; and a nut mounted to said connector member and operatively engaged with said lead screw, rotation of said lead screw causing said connector member to move with respect to said fixed member.

17. The actuator of claim 16 , wherein the compliance of said elastic element changes during operation of said actuator so that a compliance of said actuator is changed without halting operation.

18. The actuator of claim 17 , wherein said elastic element is non-linearly elastic.