Gripper assembly for downhole tools
A gripper assembly for anchoring a tool within a downhole passage and for possibly assisting movement of the tool within the passage. The gripper assembly includes an elongated mandrel and flexible toes that can be radially displaced to grip onto the surface of the passage. The toes are displaced by the interaction of a driver slidable on the mandrel and a driver interaction element on the toes. In one embodiment, the toes are displaced by the interaction of rollers and ramps that are longitudinally movable with respect to one another. In another embodiment, the toes are displaced by the interaction of toggles that rotate with respect to the toes.
1. An elongated tool for use within an elongated passage, comprising a gripper assembly for anchoring the tool within the passage, the gripper assembly comprising:
a tool body;
a plurality of grippers, each including a first end, a second end and a gripping portion between said first end and said second end, each of said plurality of grippers rotatable with respect to the tool body;
a piston movable with respect to the body, the piston connected to at least one of said plurality of grippers, such that movement of said piston in a first longitudinal direction causes the radially outward movement of said at least one of said plurality of grippers relative said body;
a first actuator selectively exerting force on said piston in a second longitudinal direction wherein movement of said first piston in said second longitudinal direction causes radially inward movement of said at least one of said plurality of grippers relative said body; and
a second actuator selectively exerting force on said piston in a second longitudinal direction wherein movement of said first piston in said second longitudinal direction causes radially inward movement of said at least one of said plurality of grippers relative said body,
wherein the gripper assembly has a movement-limiting mode configured to substantially prevent relative longitudinal movement between the gripper portions and the passage, the gripper assembly also having a movement-permissive mode configured to permit relative longitudinal movement between the gripper portions and the passage.
2. The tool of claim 1 , said first actuator comprising a spring that exerts a spring force onto the piston in the second longitudinal direction.
3. The tool of claim 1 , said second actuator comprising a valve assembly for directing fluid to exert a pressure force onto the piston in the second longitudinal direction.
4. The tool of claim 3 , wherein said valve assembly moves from a first position to a second position in response to pressure above a predetermined operating pressure.
5. The tool of claim 4 , wherein once said valve assembly moves from said first position to said second position in response to pressure above a normal operating pressure, it will not move from said second position to said first position if said operating pressure falls to said predetermined operating pressure or below.
6. The tool of claim 1 , wherein at least a section of each of the gripper portions has a substantially fixed radial position with respect to said tool body.
7. The tool of claim 6 , said first actuator comprising a spring that exerts a spring force onto the piston in the second longitudinal direction.
8. The tool of claim 7 , said second actuator comprising a valve assembly for directing fluid to exert a pressure force onto the piston in the second longitudinal direction.
9. The tool of claim 8 , wherein said valve assembly moves from a first position to a second position in response to pressure above a predetermined operating pressure.
10. The tool of claim 9 , wherein once said valve assembly moves from said first position to said second position in response to pressure above a normal operating pressure, it will not move from said second position to said first position if said operating pressure falls to said predetermined operating pressure or below.