Patent Publication Number: US-2018038163-A1

Title: Preventing Buckling For Downhole Linear Actuator

Description:
TECHNICAL FIELD 
     The present disclosure relates to oilfield operations generally and more specifically to downhole linear actuators. 
     BACKGROUND 
     Downhole linear actuators are used inside wellbores to provide push and pull forces to accommodate different mechanical tasks. These tools can contain a power rod that is pushed and pulled by various systems, such as electro-mechanical or hydraulic systems. The pushing strength of these rods can be limited due to buckling for a given rod size (e.g., diameter and length). The force able to be applied through a power rod before it buckles changes with respect to the diameter of the power rod and the unsupported length of the power rod. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The specification makes reference to the following appended figures, in which use of like reference numerals in different figures is intended to illustrate like or analogous components 
         FIG. 1  is a schematic diagram of a wellbore including a linear actuator according to certain aspects of the present disclosure. 
         FIG. 2A  is a partial cross-sectional diagram depicting a linear actuator in a retracted position according to certain aspects of the present disclosure. 
         FIG. 2B  is a partial cross-sectional diagram depicting a linear actuator in an extended position according to certain aspects of the present disclosure. 
         FIG. 3A  is a partial cross-sectional diagram depicting a linear actuator with slidable bearings in a retracted position according to certain aspects of the present disclosure. 
         FIG. 3B  is a partial cross-sectional diagram depicting a linear actuator with slidable bearings in an extended position according to certain aspects of the present disclosure. 
         FIG. 4A  is a partial cross-sectional diagram depicting a linear actuator with hydraulically-motivated slidable bearings in a retracted position according to certain aspects of the present disclosure. 
         FIG. 4B  is a partial cross-sectional diagram depicting a linear actuator with hydraulically-motivated slidable bearings in an extended position according to certain aspects of the present disclosure. 
         FIG. 5A  is a partial cross-sectional diagram depicting a linear actuator with rotatable braces in a retracted position according to certain aspects of the present disclosure. 
         FIG. 5B  is a partial cross-sectional diagram depicting a linear actuator with rotatable braces in an extended position according to certain aspects of the present disclosure. 
         FIG. 6  is a cross-sectional view of a linear actuator having four rotatable braces according to certain aspects of the present disclosure. 
         FIG. 7  is a cross-sectional view of a linear actuator having three rotatable braces according to certain aspects of the present disclosure. 
         FIG. 8  is a cross-sectional view of a linear actuator having multiple sets of rotatable braces according to certain aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Certain aspects and features of the present disclosure relate to a linear actuator having a power rod supported by movable supports. The movable supports are designed to provide support to the power rod to avoid buckling of the power rod when large compressive forces are imparted on the power rod. 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. 
     A linear actuator for use in downhole environments is disclosed herein. The linear actuator includes a power rod that interacts with a downhole tool. An example linear actuator includes a motor that drives a lead screw, which axially moves the power rod. In other embodiments, a hydraulic piston can be used. Other types of linear actuating mechanisms can be used to axially drive the power rod. In many downhole environments, it can be desirable to use a small-diameter power rod for various reasons, such as space limitations and pressure considerations. For example, a non-pressure compensated linear actuator, the power rod exiting the actuator housing would be pushed back into the actuator by the surrounding high-pressure environment, and thus a small diameter power rod may be desirable to lower the force of the pressure that is effectively pushing the rod back into the actuator. However, as the diameter of a power rod lessens, the amount of force necessary to cause buckling (“buckling load”) decreases, meaning less force can be pushed through that power rod. 
     Additionally, the buckling load decreases as the unsupported span of the power rod increases. The unsupported span includes any distance of the power rod that is not supported, such as by bearings that displace radial forces to a housing. Therefore, it may be desirable to decrease the unsupported span of a power rod in order to increase the amount of compressive force that can be applied to the power rod without the power rod buckling. However, the use of internal supports can reduce the stroke length of the power rod. Additionally, in downwell environments, it can be necessary for a power rod to have a smooth surface finish for sealing purposes. Therefore, any supports used cannot be attached to the power rod itself. 
     Various aspects of the present disclosure relate to movable supports that are capable of returning to a supporting position that minimizes the unsupported span of the power rod after being displaced by the power rod in order to maximize the stroke length of the power rod. The movable supports can be biased back to the supporting position by biasing mechanisms such as springs and spring members. In some embodiments, the movable supports can be moved into the supporting position through the use of pressurized fluids. Examples of suitable movable supports include slidable bearings and rotatable braces, while other movable supports can be used. Multiple movable supports can be used in a single linear actuator. The movable supports can be located entirely within the housing of the linear actuator. 
     In an example, a movable support can be a slidable bearing. The bearing can be positioned within the housing of the linear actuator and the power rod can pass through the bearing. The bearing does not need to be rotationally or axially fixed and can pass radial forces from the power rod to the housing, thus preventing buckling. The bearing can be coupled to other bearings and the housing through biasing mechanisms that are springs or spring members. Example biasing members can include elastomeric bellows or springs. As the power rod extends, features of the power rod, such as a rear flange, can contact the slidable bearings and push them towards the distal end of the housing where they collected together (e.g., thus maximizing the stroke length of the power rod). However, as the power rod retracts, the biasing mechanisms can push or pull the slidable bearings back to their first position (supporting position). The biasing mechanisms can be selected to have lengths that would position the slidable bearings equally within the housing to minimize the lengths of the unsupported spans of the power rod. 
     In another example, the slidable bearings are moved using pressurized fluid. The housing can be filled with a fluid (e.g., hydraulic fluid) and the slidable bearings can form seals with the housing and the power rod, thus separating the housing into two or more chambers, depending on the number of slidable bearings. A valve or piston can provide the distal-most chamber with high pressure from the surrounding high-pressure environment. As the power rod extends, the slidable bearing can be pushed to the distal end of the housing. As the power rod retracts, the high pressure from the surrounding high-pressure environment can push the slidable bearing back into its supporting position. A mechanical stop (e.g., a flange or track of the housing that engages the slidable bearing) can stop the slidable bearing from being pushed beyond its supporting position. 
     In another example, the movable support can be a brace that is rotatably coupled to the housing. Multiple braces can be used to provide support to the power rod from various directions. For example, two or more braces can be used and spaced equally around the power rod (e.g., spaced at 120° when three braces are used, or spaced at 90° when four braces are used). Each brace can be hinged to move from a supporting position where the brace is perpendicular to the power rod and provides support to carry radial forces from the power rod to the housing, to an out-of-the-way position where the brace is no longer perpendicular to the power rod. In some embodiments, the out-of-the-way position can be generally parallel to the power rod. The brace can be biased (e.g., through a spring or spring mechanism) to rotate in a first direction and the brace can include a step that engages the housing to stop the brace from rotating in the first direction once the brace is in the supporting position. The brace can then be displaced into the out-of-the-way position by the power rod as the power rod extends. 
     Various linear actuators as described herein can provide increased force (e.g., load) and increased stroke length over linear actuators without movable supports. The increased force and increased stroke length can allow a single linear actuator to perform more actions in a single run than a linear actuator without movable supports, thus decreasing the number of runs necessary to perform certain actions for a particular wellbore. The movable supports disclosed herein do not require the use of complicated latches or rails. The movable supports disclosed herein can be easily adaptable to multiple rod sizes. 
     These illustrative examples are given to introduce the reader to the general subject matter discussed here and are not intended to limit the scope of the disclosed concepts. The following sections describe various additional features and examples with reference to the drawings in which like numerals indicate like elements, and directional descriptions are used to describe the illustrative embodiments but, like the illustrative embodiments, should not be used to limit the present disclosure. The elements included in the illustrations herein may be drawn not to scale. 
       FIG. 1  is a schematic diagram of a wellbore  102  including a linear actuator  106  according to certain aspects of the present disclosure. The wellbore  102  can penetrate a subterranean formation  104  for the purpose of recovering hydrocarbons, storing hydrocarbons, disposing of carbon dioxide, or the like. The wellbore  102  can be drilled into the subterranean formation  104  using any suitable drilling technique. While shown as extending vertically from the surface in  FIG. 1 , in other examples the wellbore  102  can be deviated, horizontal, or curved over at least some portions of the wellbore  102 . Portions of the wellbore  102  can be cased, open hole, contain tubing, and can include a hole in the ground having a variety of shapes or geometries. 
     A service rig, such as a drilling rig, a completion rig, a workover rig, or other mast structure or combination thereof can support a workstring  108  in the wellbore  102 , but in other examples a different structure can support the workstring  108 . For example, an injector head of a coiled tubing rigup can support the workstring  108 . In some aspects, a service rig can include a derrick with a rig floor through which the workstring  108  extends downward from the service rig into the wellbore  102 . The servicing rig can be supported by piers extending downwards to a seabed in some implementations. Alternatively, the service rig can be supported by columns sitting on hulls or pontoons (or both) that are ballasted below the water surface, which may be referred to as a semi-submersible platform or rig. In an off-shore location, a casing may extend from the service rig to exclude sea water and contain drilling fluid returns. Other mechanical mechanisms that are not shown may control the run-in and withdrawal of the workstring  108  in the wellbore  102 . Examples of these other mechanical mechanisms include a draw works coupled to a hoisting apparatus, a slickline unit or a wireline unit including a winching apparatus, another servicing vehicle, and a coiled tubing unit. 
     The workstring  108  can include a tubular attached to a linear actuator  106 . In some embodiments, the linear actuator  106  can be supported by a wireline or can be otherwise embodied in a downhole tool supported by a wireline or a tubular. The linear actuator  106  can be coupled to a downhole tool  110  that is operable through linear motion. The linear actuator  106  can extend and retract its power rod. As the power rod is extended and retracted, different operations of the downhole tool  110  can be actuated. 
     In an example the downhole tool  110  can include components that need to be shifted, set, or latched. A user from the surface can send an actuation signal (e.g., an electrical signal or a pressure signal or other) to the linear actuator  106 . Upon receiving the actuation signal, the linear actuator  106  can extend its power rod to a first, extended position to perform one of the shifting, setting, or latching tasks of the downhole tool  110 . A second actuation signal can be sent from the surface and then received by the linear actuator  106 , which causes the linear actuator  106  to extend the power rod to a second extended position to perform another of the shifting, setting, or latching tasks of the downhole tool  110 . A third actuation signal can be sent from the surface and then received by the linear actuator  106 , which causes the linear actuator  106  to retract the power rod to a refracted position. In some embodiments, retraction of the power rod can perform yet another of the shifting, setting, or latching tasks of the downhole tool  110 . In other embodiments, any number of extended positions and retracted positions can be used. In other embodiments, any suitable tasks can be performed by the downhole tool  110  in response to axial movement of the power rod. 
       FIGS. 2A-2B  are partial cross-sectional diagrams depicting a linear actuator  200  without movable supports.  FIG. 2A  depicts the linear actuator  200  when retracted and  FIG. 2B  depicts the linear actuator  200  when extended. The linear actuator  200  includes a housing  202  and a driving mechanism for axially moving the power rod  212  from the retracted position, as seen in  FIG. 2A , to the extended position, as seen in  FIG. 2B . The driving mechanism can be electric, hydraulic, or other.  FIGS. 2A-2B  depict a simple version of an electric driving mechanism, having a motor  204  that drives a screw  206 . Rotation of the screw  206  causes the sleeve  208  to extend or retract. Other driving mechanisms can be used. 
     The housing  202  can include a stationary support  210 , which can support the power rod  212  or sleeve  208 . As seen in  FIGS. 2A-2B , the stationary support  210  supports the sleeve  208 . The power rod  212  can be coupled to the sleeve  208 , such that movement of the sleeve  208  in an axial direction (e.g., left-to-right or right-to-left as seen in  FIGS. 2A-2B ) causes movement of the power rod  212  in the axial direction. The sleeve  208  can include a flange  214 . The power rod  212  can be supported (e.g., radially supported) by a seal or other feature of the housing  202  where the power rod  212  exits the housing. The length where the power rod  212  is not supported (e.g., radially supported, such as by a stationary support  210  or the housing  202 ) can be known as the unsupported span  218 . The largest unsupported span  218  is the first likely place where buckling can occur as increased compression forces are applied to the power rod  212 . As the largest unsupported span  218  decreases in length, the amount of force necessary for buckling of the power rod  212  (e.g., buckling load) increases. In other words, with shorter unsupported spans  218 , more compressive force can be applied through the power rod  212  without the power rod  212  buckling. 
     The power rod  212  can be extended from a refracted position (e.g., as seen in  FIG. 2A ) to an extended position (e.g., as seen in  FIG. 2B ). The distance the distal end of the power rod  212  (e.g., that end towards the right of the figure as seen in  FIGS. 2A-2B ) travels between the furthest retracted position and the furthest extended position can be known as the stroke length  216 . As described above, long stroke lengths can be desirable, such as to enable a downhole tool to perform more functions on a single run in the well. Additionally, long stroke lengths  216  may be necessary to operate certain downhole tools. 
       FIGS. 3A-3B  are partial cross-sectional diagrams depicting a linear actuator  300  with slidable bearings  326  according to certain aspects of the present disclosure.  FIG. 3A  depicts the linear actuator  300  when retracted and  FIG. 3B  depicts the linear actuator  300  when extended. Slidable bearings  326  are located within the housing to provide support to the power rod  312 . The slidable bearings  326  are able to move between a first position (e.g., a supporting position, as seen in  FIG. 4A ) and a second position (e.g., an out-of-the-way position, as seen in  FIG. 4B ). The slidable bearings  326  may still supply some support to the power rod  412  when in the out-of-the-way position. The power rod  312  can pass through a central aperture of each slidable bearing  326 . In some embodiments, a slidable bearing  326  is round in shape, similar to a washer or a round spacer. As seen in  FIGS. 3A-3B , the slidable bearings  326  are located between the stationary support  310  and the distal wall of the housing  302  (e.g., the wall to the right of the figure as seen in  FIGS. 3A-3B ). However, the slidable bearings  326  can be located anywhere within the housing  302  where they may provide support to the power rod  312 , irrespective of whether or not a stationary support  310  is used. 
     The slidable bearings  326  provide radial support to the power rod  312 . The slidable bearings  326  can be rotationally free within the housing  302 , or can be keyed or otherwise rotationally fixed. When the power rod  312  is in a retracted position (e.g., as seen in  FIG. 3A ), biasing mechanisms cause the slidable bearings  326  to be positioned at certain locations between the distal wall of the housing  302  and the stationary support  310 . More specifically, connecting members  328  can be located between adjacent slidable bearings  326 , between a slidable bearing  326  and the housing  302 , between a slidable bearing  326  and the sleeve  308 , or between any combination thereof. 
     In some embodiments, the connecting member  328  are elastomeric bellows or other connectors that are collapsible, but that are capable of pulling the slidable bearings  326  into a supporting position (e.g., as seen in  FIG. 3A ) upon refraction of the sleeve  308 . Refraction of the sleeve  308  can pull on the proximal-most slidable bearing  326  via the connecting member  328 , which can then pull on the next most proximal slidable bearing  326 , until all slidable bearings  326  are pulled into the appropriate position, which can be dictated by the length of the connecting members  328 . The connecting members  328  can be coupled to other features (e.g., the flange  314 ) that move along with the power rod  312  during retraction or extension of the power rod  312 . 
     In other embodiments, the connecting members  328  are spring members, which are capable of being compressed, but which then expand to provide a biasing force on the slidable bearings  326 . Such connecting members  328  can be loose or can be coupled to the slidable bearings  326  or housing  302 . When the connecting member  328  are spring members, there is no need for a connecting member  328  to couple a slidable bearing  326  to the sleeve  308 , as retraction of the sleeve  308  will necessarily allow the slidable bearings  326  to move into the supporting position (e.g., as seen in  FIG. 3A ) due to expansion of the spring members. The connecting members  328  provide a biasing force to the slidable bearings  326  to separate the slidable bearings  326  to a certain extent. The extent to which the slidable bearings  326  are separated can depend on the length of the connecting members  328 . 
     Connecting members  328  cause the slidable bearings  326  to be spaced out between the stationary support  310  and the distal wall of the housing  302 . In some embodiments, the slidable bearings  326  are spaced equidistant from one another. The presence of movable supports results in several unsupported spans  318 ,  320 ,  322 ,  324 . The connecting members  328  can be selected to position the slidable bearings  326  at distances from one another, from the stationary support  310 , and from the distal wall of the housing  302 , such that each of the unsupported spans  318 ,  320 ,  322 ,  324  is minimized. Other arrangements can be used. 
     As the power rod  312  is extended towards the extended position, the flange  314  or other feature can interact with the slidable bearings  326  and begin to compress them towards the distal end of the housing  302 . When the power rod  312  is in an extended position (e.g., as seen in  FIG. 3B ), the slidable bearings  326  can be compressed towards the distal end of the housing  302 , thus compressing the connecting members  328 . As the power rod  312  is retracted towards the retracted position, the connecting members  328  will cause the slidable bearings  326  to separate from one another and provide support to the power rod  312  to reduce the length of unsupported spans  318 ,  320 ,  322 ,  324 . 
     The power rod  312  is able achieve a long stroke length  316  since the slidable bearings  326  can collect at the distal end of the housing  302 , as opposed to using additional stationary bearings, which would reduce the stroke length  316 , as additional stationary bearing would act as a stop for the flange  314 . 
     In some embodiments, additional slidable bearings  326  can be located around the sleeve  308 , such as between the stationary support  310  and the flange  314 , in order to provide additional radial support to the sleeve  308 . 
       FIGS. 4A-4B  are partial cross-sectional diagrams depicting a linear actuator  400  with a hydraulically-motivated slidable bearing  420  according to certain aspects of the present disclosure.  FIG. 4A  depicts the linear actuator  400  when retracted and  FIG. 4B  depicts the linear actuator  400  when extended. Slidable bearing  420  is located within the housing  402  to provide support to the power rod  412 . The slidable bearing  420  is able to move between a first position (e.g., a supporting position, as seen in  FIG. 4A ) and a second position (e.g., an out-of-the-way position, as seen in  FIG. 4B ). The slidable bearing  420  may still supply some support to the power rod  412  when in the out-of-the-way position. The power rod  412  can pass through central apertures of the slidable bearing  420 . The slidable bearing  420  can separate a subset of the housing  402  into a first chamber  424  (e.g., between the stationary support  410  and slidable bearing  420 ) and a second chamber  428  (e.g., between the slidable bearing  420  and the distal end of the housing  402 ). A seal can be included in the central aperture of the slidable bearing  420  to limit the flow of fluid across the slidable bearing  420  (e.g., from one chamber  424 ,  428  to another). In some embodiments, fewer or more slidable bearings can be used, thus separating a portion of the housing  402  into fewer or more fluidly-isolated chambers. 
     The slidable bearing  420  provides radial support to the power rod  412 . The slidable bearing  420  can be rotationally free within the housing  402 , or can be keyed or otherwise rotationally fixed. When the power rod  412  is in a retracted position (e.g., as seen in  FIG. 4A ), differences in fluid pressure between the chambers  424 ,  428  can bias the slidable bearing  420  towards the proximal end of the housing  402  (e.g., left, as seen in  FIGS. 4A-4B ). The slidable bearing  420  can engage a stop  430  to retain the slidable bearing  420  in an appropriate locations (e.g., to minimize the unsupported spans  418 ). In some embodiments, instead of using a stop  430 , other features can be used to stop the travel of the slidable bearing  420  at the appropriate locations. In an example, a compressible material (e.g., a flexible ribbon) or structure (e.g., two struts connected to one another with a hinge) can be used to couple the slidable bearing  420  to the housing  402  or to another slidable bearing to limit travel of the slidable bearing  420 . When the power rod  412  is in a retracted position, the compressible material or structure keeps the slidable bearing  420  from moving too far towards the proximal end of the housing  402 , and when the power rod  412  is in the extended position (e.g., as seen in  FIG. 4B ), the compressible material or structure compresses or folds adjacent the slidable bearing  420 , allowing the slidable bearing  420  to collect near the distal end of the housing  402 . 
     As the power rod  412  moves from a retracted position (e.g., as seen in  FIG. 4A ) to an extended position, the flange  414  can interact with the slidable bearing  420 , causing it to be forced towards the distal end of the housing  402 . As slidable bearing  420  moves, the pressure in the first chamber  424  may drop, as the pressure in the second chamber  428  may rise. Continued movement of slidable bearing  420  can cause pressure in the second chamber  428  to be released through valve  434 . Valve  434  can be an opening or aperture in the housing that is in fluid communication with the surrounding environment  440 . In some embodiments, valve  434  is a piston that retains fluid isolation between the second chamber  428  and the surrounding environment  440 , but allows pressure equalization between the second chamber  428  and the surrounding environment  440 . Eventually, slidable bearing  420  is able to collect at the distal end of the housing  402 , in an out-of-the-way position, as seen in  FIG. 4B . 
     During retraction of the power rod  412 , the flange  414  moves towards the proximal end of the housing  402 , thus allowing slidable bearing  420  to move in the same direction because of the relatively low pressure in the first chamber  424 , as compared to the relatively high pressures in the second chamber  428  and surrounding environment  440 . The slidable bearing  420  can continue to move towards the proximal end of the housing, being biased in that direction due to the relatively low pressure of the first chamber  424  and the relatively high pressure of the surrounding environment  440 . Eventually, the slidable bearing  420  will be pressed up against stop  430 , or otherwise held at their appropriate locations, as described above. 
     The power rod  412  is able achieve a long stroke length  416  since the slidable bearing  420  can collect at the distal end of the housing  402 , as opposed to using additional stationary bearings, which would reduce the stroke length  416 , as additional stationary bearing would act as a stop for the flange  414 . 
     In some embodiments, additional slidable bearings can be located around the sleeve  408 , such as between the stationary support  410  and the flange  414 , in order to provide additional radial support to the sleeve  408 . 
     In embodiments where multiple slidable bearings are used, some slidable bearing may contain check valves to regulate pressure build-up in chambers between adjacent slidable bearings. When multiple slidable bearings are used, all but the most proximal (e.g., towards the left as seen in  FIGS. 4A-4B ) slidable bearing may require a set of check valves. 
       FIGS. 5A-5B  are partial cross-sectional diagrams depicting a linear actuator  500  with braces  530 ,  532 ,  534  supporting a dual-diameter power rod  512  according to certain aspects of the present disclosure.  FIG. 5A  depicts the linear actuator  500  when retracted and  FIG. 5B  depicts the linear actuator  500  when extended. Braces  530 ,  532 ,  534  are located within the housing to provide support to the power rod  512 . The power rod  512  is a dual-diameter power rod  512 , having a larger diameter section  526  within the housing  502  and a smaller diameter section  528  that exits the housing. Such power rods  512  can be useful in certain applications. 
     Braces  530 ,  532 ,  534  are able to rotate between a first position (e.g., a supporting position, as seen in  FIG. 4A ) and a second position (e.g., an out-of-the-way position, as seen in  FIG. 4B ). The braces  530 ,  532 ,  534  may still supply some minimal support to the power rod  412  when in the out-of-the-way position. In some embodiments, the pivot point  538 , size of a brace  530 ,  532 ,  534 , or both can be used provide support to both the smaller diameter section  528  and larger diameter section  526 , depending on how far extended the power rod  512  may be. As seen in  FIGS. 5A-5B , the braces  530 ,  532 ,  534  are located between the stationary support  510  and the distal wall of the housing  502  (e.g., the wall to the right of the figure as seen in  FIGS. 5A-5B ). However, the braces  530 ,  532 ,  534  can be located anywhere within the housing  502  where they may provide support to the power rod  512 , irrespective of whether or not a stationary support  510  is used. In some embodiments, braces  530 ,  532 ,  534  can be located in recesses of the housing  502  and can be rotated into recesses of the housing  502 . 
     The braces  530 ,  532 ,  534  provide radial support to the power rod  512 . Each brace  530 ,  532 ,  534  can be coupled to the housing  502  at a pivot point  538 . When the power rod  512  is in a retracted position (e.g., as seen in  FIG. 5A ), biasing mechanisms cause the braces  530 ,  532 ,  534  to rotate to a supporting position (e.g., the brace being perpendicular to the power rod  512 ). More specifically, spring members  536  can be located between each brace  530 ,  532 ,  534  and the housing  502 . The spring members  536  can bias each brace  530 ,  532 ,  534  to rotate in a first direction (e.g., from the position depicted in  FIG. 5B  towards the position depicted in  FIG. 5A ). The housing  502  can include recesses into which the braces  530 ,  532 ,  534  can rotate. The housing  502  can include stops  542  that act to halt rotation of the braces  530 ,  532 ,  534 , due to the biasing forces of the spring members  536 , past the supporting position (e.g., perpendicular with the power rod  512 ). In alternate embodiments, other biasing mechanisms can be used to cause rotation of the braces  530 ,  532 ,  534 , such as hydraulic pistons. 
     The braces  530 ,  532 ,  534  can be installed in the housing  502  to create desirable or optimal unsupported spans  518 ,  520 ,  522 ,  523 . A set of braces can be positioned, in a single lateral plane, around the power rod  512  in various configurations, as described in further detail herein. 
     As the power rod  512  is extended towards the extended position, the flange  514 , larger diameter section  526  or other feature can interact with braces  530 ,  532 ,  534  and displace each brace  530 ,  532 ,  534  to rotate about its respective pivot point  538  to compress its respective spring member  536 . As the power rod  512  is retracted back towards the retracted position, the spring members  536  cause their respective braces  530 ,  532 ,  534  to pivot back to the supporting positions. 
     The power rod  512  is able achieve a long stroke length  516  since the braces  530 ,  532 ,  534  can rotate to an out-of-the-way position, as opposed to using additional stationary bearings, which would reduce the stroke length  516 , as additional stationary bearing would act as a stop for the flange  514  or the larger diameter section  526  of the power rod  512 . 
     In some embodiments, additional braces can be located around the sleeve  508 , such as between the stationary support  510  and the flange  514 , in order to provide additional radial support to the sleeve  508 . Such braces may rotate in a direction opposite the rotational direction of braces  530 ,  532 ,  534 . 
       FIG. 6  is a cross-sectional view of a linear actuator  600  having four rotatable braces  606  according to certain aspects of the present disclosure. The cross-sectional view is taken from a plane located adjacent the distal end of the housing  604  of the linear actuator  600 . The power rod  602  is supported by four movable supports that are rotatable braces  606 . Each brace  606  is positioned directly across a diameter of the power rod  602  from another brace  606 . Each brace  606  is positioned 90° offset from one another. 
       FIG. 7  is a cross-sectional view of a linear actuator  700  having three rotatable braces  706  according to certain aspects of the present disclosure. The cross-sectional view is taken from a plane located adjacent the distal end of the housing  704  of the linear actuator  700 . The power rod  702  is supported by three movable supports that are rotatable braces  706 . Each brace  706  is positioned equidistant around the power rod  702  from one another. Each brace  606  is positioned 120° offset from one another. 
     Any number of braces can be used and with any spacing. 
       FIG. 8  is a cross-sectional view of a linear actuator  800  having multiple sets of rotatable braces  806 ,  808  according to certain aspects of the present disclosure. The cross-sectional view is taken from a plane located adjacent the distal end of the housing  804  of the linear actuator  800 . The cross-sectional view depicts a first set of rotatable braces  806  in the plan of the page. The first set of rotatable braces  806  can include three braces that are each positioned 120° offset from one another. The cross-sectional view also depicts a second set of rotatable braces  808  that lies in a plane below the page (e.g., is axially offset from the first set of rotatable braces  806  along an axis of the power rod  802 ). The second set of rotatable braces  808  can also include three braces that are each positioned 120° offset from one another. The first set of rotatable braces  806  and the second set of rotatable braces  808  can be rotationally offset from one another (e.g., out of phase from one another). As seen in  FIG. 8 , the first set of rotatable braces  806  is 180° offset from the second set of rotatable braces  808 . This rotational offset between axially displaced, but adjacent sets of braces can provide beneficial support to the power rod  802 . Other suitable rotational offsets and numbers of braces per set can be used. 
     The foregoing description of the embodiments, including illustrated embodiments, has been presented only for the purpose of illustration and description and is not intended to be exhaustive or limiting to the precise forms disclosed. Numerous modifications, adaptations, combinations and uses thereof will be apparent to those skilled in the art. 
     As used below, any reference to a series of examples is to be understood as a reference to each of those examples disjunctively (e.g., “Examples 1-4” is to be understood as “Examples 1, 2, 3, or 4”). 
     Example 1 is 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. 
     Example 2 is the assembly of example 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. 
     Example 3 is the assembly of example 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. 
     Example 4 is the assembly of examples 2 or 3, 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. 
     Example 5 is the assembly of example 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. 
     Example 6 is the assembly of examples 4 or 5, 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. 
     Example 7 is the assembly of examples 1-6, 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. 
     Example 8 is the assembly of examples 1-7, wherein the power rod is retractable at least partially into the housing. 
     Example 9 is a method comprising extending a power rod of a linear actuator by axially moving the power rod from a refracted 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 refracting 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. 
     Example 10 is the method of example 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. 
     Example 11 is the method of examples 9 or 10, 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. 
     Example 12 is the method of examples 9-11, 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. 
     Example 13 is 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. 
     Example 14 is the linear actuator of example 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. 
     Example 15 is the linear actuator of example 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. 
     Example 16 is the linear actuator of examples 14 or 15, 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. 
     Example 17 is the linear actuator of example 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. 
     Example 18 is the linear actuator of examples 16 or 17, 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. 
     Example 19 is the linear actuator of examples 13-18, 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. 
     Example 20 is the linear actuator of examples 13-19, wherein the power rod is retractable at least partially into the housing.