Patent ID: 8028766

Claim:
A tractor for moving within a passage, comprising: a body portion positioned along a longitudinal axis of the tractor; a gripper assembly comprising: a gripper motor having an output shaft adapted to rotate about a gripper motor axis during activation of the gripper motor; a first gripper interface portion oriented substantially along the gripper motor axis; a second gripper interface portion in engagement with the first gripper interface portion, wherein one of the first and second gripper interface portions comprises a gripper rotating element configured to rotate about the gripper motor axis during rotation of the output shaft relative to the gripper motor, the other of the first and second gripper interface portions comprising a gripper extension element being configured to move longitudinally with respect to the gripper motor during rotation of the output shaft relative to the gripper motor, due to said engagement between the first and second gripper interface portions; and at least two elongated gripping elements engaged with respect to the body portion, the gripping elements having a movement-limiting mode in which the gripping elements limit relative movement between the gripping elements and an inner surface of a passage, and a movement-permissive mode in which the gripping elements permit substantially free relative longitudinal movement between the gripping elements and the inner surface of the passage; wherein the gripper extension element comprises part of a gripper expansion assembly for converting longitudinal motion of the gripper extension element into movement of the gripping elements between said movement-limiting mode and said movement-permissive mode of the gripping elements, the gripper assembly being configured to limit longitudinal movement of the body portion relative to the passage when the gripping elements are in said movement-limiting mode; and a gripper brake configured to lock the gripper assembly in its movement-limiting mode and to release the gripper assembly from its movement-limiting mode if electrical power to the gripper motor is interrupted; wherein each of the gripping elements comprises: an aft link having an aft portion that is rotatably connected to an aft toe anchor of the tractor, so that the aft portion of the aft link is substantially radially fixed with respect to the longitudinal axis of the tractor; a passage-engaging link having an aft portion rotatably connected to a forward portion of the aft link; and a forward link having an aft portion that is rotatably connected to a forward portion of the passage-engaging link, the forward link having a forward portion that is rotatably connected to a forward toe anchor of the tractor, so that the forward portion of the forward link is substantially radially fixed with respect to the longitudinal axis of the tractor.