Well lift frame

1. A clamping assembly, comprising:

a linkage assembly;

an actuator coupled to said linkage assembly so as to selectively position said linkage assembly; and

a shoe carried by said linkage assembly, said shoe defining a face;

wherein said clamping assembly is arranged so that when mounted to a side of a well lift frame in proximity to a vertical slot having an opening formed in said side, said clamping assembly is operable to travel along an arcuate path between a disengaged position, in which said clamping assembly is substantially clear of said opening, and an engaged position in which said clamping assembly at least substantially covers a horizontal extent of said opening;

wherein said linkage assembly is arranged to maintain said face of said shoe parallel said side of said well lift frame while said clamping assembly travels along said arcuate path.

2. The clamping assembly of claim 1 , wherein:

said linkage assembly defines a four-bar linkage mechanism.

3. The clamping assembly of claim 2 wherein said linkage assembly further comprises:

a ground link fixed in relation to said lift frame;

a master leg driven by said actuator;

a slave leg pivotally coupled to said lift frame; and

a foot pivotally coupled to said master leg and said slave leg, said foot carrying said shoe.

4. The clamping assembly of claim 3 wherein:

said ground link is defined by said actuator.

5. The clamping assembly of claim 4 wherein said actuator further comprises:

a prime mover; and

a transmission operatively coupled between said prime mover and said master leg.

6. The clamping assembly of claim 5 wherein:

said prime mover includes a rotary motor; and

said transmission includes a gear train.

7. The clamping assembly of claim 5 further comprising:

a locking assembly disposed between said linkage assembly and said side of said lift frame and arranged for selectively locking said shoe in said engaged position.

8. A well lift frame comprising: a frame;

a vertical slot forming an opening in a side of said frame; and

a clamping assembly mounted to said side of said frame in proximity to said opening, said clamping assembly including a linkage assembly arranged so as to travel along an arcuate path between a disengaged position, in which said clamping assembly is substantially clear of said opening, and an engaged position in which said clamping assembly at least substantially covers a horizontal extent of said opening, and an actuator coupled to said linkage assembly so as to selectively position said linkage assembly; wherein said linkage assembly comprises:

a ground link fixed in relation to said lift frame, said ground link defined by said actuator;

a master leg driven by said actuator; a slave leg pivotally coupled to said lift frame; and

a foot directly pivotally coupled to said master leg and said slave leg, said foot carrying a shoe.

9. The lift frame of claim 8 further comprising:

said shoe carried by said linkage assembly, said shoe defining a face; wherein

said linkage assembly is arranged to maintain said face of said shoe parallel to said side of said lift frame.

10. The lift frame of claim 9 wherein said actuator further comprises:

a prime mover; and

a transmission operatively coupled between said prime mover and said master leg.

11. The lift frame of claim 8 further comprising:

a locking assembly disposed between said linkage assembly and said side of said frame and arranged for selectively locking said clamping assembly in said engaged position.

12. The lift frame of claim 8 wherein:

said frame includes an upper section translatably coupled to a lower section;

said vertical slot is formed in said lower section;

said clamping assembly mounted to a side of said lower section; and

said lift frame further comprises a compensating cylinder operatively coupled between said upper section and said lower section.

13. A clamping assembly on a well lift frame, comprising: a linkage assembly comprising:

a ground link fixed in relation to said lift frame; a master leg driven by an actuator; a slave leg pivotally coupled to said lift frame; and

a foot directly pivotally coupled to said master leg and said slave leg, said foot carrying a shoe; and

the actuator coupled to said linkage assembly so as to selectively position said linkage assembly;

wherein said clamping assembly is arranged so that when mounted to a side of the well lift frame in proximity to a vertical slot having an opening formed in said side, said clamping assembly is operable to travel along an arcuate path between a disengaged position, in which said clamping assembly is substantially clear of said opening, and an engaged position in which said clamping assembly at least substantially covers a horizontal extent of said opening.

14. The clamping assembly of claim 13 further comprising:

said shoe carried by said linkage assembly, said shoe defining a face; wherein

said linkage assembly is arranged to maintain said face of said shoe parallel to said side of said lift frame.

15. The clamping assembly of claim 14 wherein:

said ground link is defined by said actuator.

16. The clamping assembly of claim 15 wherein said actuator further comprises:

a prime mover; and

a transmission operatively coupled between said prime mover and said master leg.

17. The clamping assembly of claim 16 wherein:

said prime mover includes a rotary motor; and

said transmission includes a gear train.

18. The clamping assembly of claim 17 further comprising:

a locking assembly disposed between said linkage assembly and said side of said lift frame and arranged for selectively locking said shoe in said engaged position.