Preventing Buckling For Downhole Linear Actuator

Abstract

A linear actuator having a power rod supported by movable supports is disclosed. The movable supports can provide support to the power rod to avoid buckling of the power rod under large compressive forces. The movable supports are designed to move towards (e.g., by a biasing mechanism) a first position that minimizes the unsupported length of the power rod, but are capable of being displaced by the power rod during extension of the power rod. Examples of movable supports include slidable bearings (e.g., axially slidable) or rotating braces (e.g., rotatable form a supporting position to an out-of-the-way position). Examples of suitable biasing mechanisms include springs and spring members. In some embodiments, hydraulic force is used to move the movable supports.

What is claimed is: 
     
         1 . An assembly, comprising:
 a housing;   a power rod at least partially contained within the housing, the power rod being retractable and extendable; and   a movable support within the housing, the movable support being movable to a first position in response to the power rod retracting for displacing radial force from the power rod into the housing, and being movable to a second position in response to the power rod extending.   
     
     
         2 . The assembly of  claim 1 , wherein the movable support includes a spring member for biasing the movable support towards the first position, and wherein the power rod includes a feature for displacing the movable support into the second position in response to the power rod extending. 
     
     
         3 . The assembly of  claim 2 , wherein the movable support further includes a slidable bearing for receiving the power rod therethrough, the slidable bearing being axially slidable between the first position and the second position, and wherein the spring member is positioned for biasing the slidable bearing towards the first position. 
     
     
         4 . The assembly of  claim 2 , wherein the movable support further includes a brace rotatably coupled to the housing, wherein the brace is perpendicular to the power rod when in the first position and not perpendicular to the power rod when in the second position. 
     
     
         5 . The assembly of  claim 4 , wherein the spring member is positioned for biasing the brace to rotate in a first direction; and wherein the brace includes a step for contacting the housing when the brace is in a first position and for blocking the brace from rotating further in the first direction. 
     
     
         6 . The assembly of  claim 4 , wherein the movable support further includes a second brace and a third brace, each rotationally spaced about the power rod 120° apart from the brace. 
     
     
         7 . The assembly of  claim 1 , wherein the movable support is movable to the first position in response to pressure of a fluid within the housing, and wherein the power rod is axially movable for changing the pressure of the fluid within the housing. 
     
     
         8 . The assembly of  claim 1 , wherein the power rod is retractable at least partially into the housing. 
     
     
         9 . A method, comprising:
 extending a power rod of a linear actuator by axially moving the power rod from a retracted position to an extended position;   displacing a movable support from a first position to a second position in response to extending the power rod;   retracting the power rod by axially moving the power rod from the extended position to the retracted position;   moving the movable support from the second position to the first position in response to retracting the power rod; and   displacing radial force from the power rod into a housing of the linear actuator by the movable support in the first position.   
     
     
         10 . The method of  claim 9 , wherein the moving the movable support from the second position to the first position includes a biasing element of the movable support moving the movable support towards the first position. 
     
     
         11 . The method of  claim 9 , wherein displacing the movable support includes sliding a slidable bearing from the first position to the second position; wherein the power rod passes through the slidable bearing; and wherein moving the movable support includes a spring member moving the slidable bearing from the second position to the first position. 
     
     
         12 . The method of  claim 9 , wherein displacing the movable support includes rotating a brace from the first position to the second position, wherein the brace is perpendicular to the power rod when in the first position; and wherein moving the movable support includes a spring member rotating the brace from the second position to the first position. 
     
     
         13 . A linear actuator, comprising:
 a housing;   a power rod at least partially contained within the housing;   a motor;   a lead screw coupled to the motor and the power rod for retracting and extending the power rod;   a movable support within the housing, the movable support being movable to a first position in response to the power rod retracting for displacing radial force from the power rod into the housing, and being movable to a second position in response to the power rod extending.   
     
     
         14 . The linear actuator of  claim 13 , wherein the movable support includes a biasing member for biasing the movable support towards the first position, and wherein the power rod includes a feature for displacing the movable support into the second position in response to the power rod extending. 
     
     
         15 . The linear actuator of  claim 14 , wherein the movable support further includes a slidable bearing for receiving the power rod therethrough, the slidable bearing being axially slidable between the first position and the second position, and wherein the biasing member is positioned for biasing the slidable bearing towards the first position. 
     
     
         16 . The linear actuator of  claim 14 , wherein the movable support further includes a brace rotatably coupled to the housing, wherein the brace is perpendicular to the power rod when in the first position and not perpendicular to the power rod when in the second position. 
     
     
         17 . The linear actuator of  claim 16 , wherein the biasing member biases the brace to rotate in a first direction; and wherein the brace includes a step for contacting the housing when the brace is in a first position and for blocking the brace from rotating further in the first direction. 
     
     
         18 . The linear actuator of  claim 16 , wherein the movable support further includes a second brace and a third brace, each rotationally spaced about the power rod 120° apart from the brace. 
     
     
         19 . The linear actuator of  claim 13 , wherein the movable support is movable between the first position and the second position in response to pressure of a fluid within the housing, and wherein the power rod is axially movable for changing the pressure of the fluid within the housing. 
     
     
         20 . The linear actuator of  claim 13 , wherein the power rod is retractable at least partially into the housing.