Patent ID: 7174974

Claim:
A tractor for moving within a passage, comprising: an elongate tractor body configured to pull equipment within the passage; a first gripper assembly having an actuated position in which the first gripper assembly limits movement of the first gripper assembly with respect to an inner surface of the passage and a retracted position in which the first gripper assembly permits substantially free relative movement between the first gripper assembly and the passage, the first gripper assembly comprising: at least one gripper defining a gripping surface, said gripper having a first end, a second end, a first connection location, and a second connection location, said at least one gripper supported by the tractor body at the first connection location and the second connection location; and an actuator operatively coupled to the gripper, the actuator movable between a first position in which the first gripper assembly is in the actuated position and a second position in which the first gripper assembly is in the retracted position, wherein application of an expansion force by the actuator to the gripper between the first connection location and the second connection location expands the first gripper assembly toward the actuated position.