Abstract:
The subject matter of this specification can be embodied in, among other things, a locking apparatus for a rotary actuator includes an outer housing comprising a cylindrical interior surface having a recess. A rotor is disposed within the outer housing. The rotor has an interior cavity and a port extending radially from the interior cavity to the cylindrical exterior surface. A piston is disposed for reciprocal movement within the interior cavity between a first position and a second position and includes a first portion having a first thickness, a second portion having a second thickness larger than the first thickness. A key is disposed for radially reciprocal movement within the port and includes a radially proximal end and a radially distal end. The radially proximal end contacts the first portion and the radially distal end does not extend into the recess when the piston is in the first position.

Description:
TECHNICAL FIELD 
     This instant specification relates to rotary actuators with locking mechanisms. 
     BACKGROUND 
     Rotary hydraulic actuators of various forms are currently used in industrial mechanical power conversion applications. This industrial usage is commonly for applications where continuous inertial loading is desired without the need for load holding for long durations, e.g. hours, without the use of an external fluid power supply. Aircraft flight control applications generally implement loaded positional holding, for example, in a failure mitigation mode, using the blocked fluid column to hold position. 
     In certain applications, such as primary flight controls used for aircraft operation, positional accuracy in load holding by rotary actuators is desired. Positional accuracy can be improved by minimizing internal leakage characteristics inherent to the design of rotary actuators. However, it can be difficult to provide leak-free performance in typical rotary hydraulic actuators, e.g., rotary “vane” or rotary “piston” type configurations as it requires substantially perfect sealing of the blocked hydraulic fluid in order to maintain the angular position of the actuator. Furthermore, any single failure of a seal will result in a complete loss of locking capability of the actuator. 
     SUMMARY 
     In general, this document rotary actuators with locking mechanisms. 
     In a first aspect, a locking apparatus for a rotary actuator includes an outer housing comprising a cylindrical interior surface having a radial recess having at least one circumferential end formed therein. A rotor is disposed within the outer housing and includes a cylindrical exterior surface rotatable within the cylindrical interior surface. The rotor has an axial interior cavity and a port disposed to be capable of rotational alignment with the radial recess and extending radially from the axial interior cavity to the cylindrical exterior surface. A piston is disposed for axially reciprocal movement within the axial interior cavity between a first position and a second position and includes a first portion having a first thickness, a second portion having a second thickness larger than the first thickness, and a piston bevel extending axially from the first portion to the second portion. A key is disposed for radially reciprocal movement within the port and includes a radially proximal end having a first key bevel complementary to the piston bevel, and a radially distal end. A body extends from the radially proximal end to the radially distal end such that the radially proximal end contacts the second portion and the radially distal end extends into the radial recess when the piston is in the second position, and the radially proximal end contacts the first portion and the radially distal end does not extend into the radial recess when the piston is in the first position. 
     Various embodiments can include some, all, or none of the following features. The circumferential end can have a housing bevel extending circumferentially from the radial recess to the cylindrical interior surface, and the radially distal end has at least one second key bevel complementary to the housing bevel. The rotary actuator can also include an axial spring in biasing contact with the piston. The axial spring can be configured to urge the piston into the first position or the second position. The piston can also include at least one seal between at least one of the first portion and a radially interior wall of the axial interior cavity, and the second portion and the radially interior wall of axial interior cavity. The rotary actuator can include a pressure chamber defined by the axial interior cavity, the piston, and the seal, the pressure chamber being configured to selectably apply fluid pressure to the piston to urge reciprocal axial movement of the piston within the axial interior cavity. 
     In a second aspect, a method for selectively locking a rotary actuator includes providing a rotary actuator having an outer housing comprising a cylindrical interior surface having a radial recess having at least one circumferential end formed therein, a rotor disposed within the outer housing and comprising, a cylindrical exterior surface rotatable within the cylindrical interior surface, an axial interior cavity, and a port disposed to be capable of rotational alignment with the radial recess and extending radially from the axial interior cavity to the cylindrical exterior surface. The rotary actuator also includes a piston disposed for axially reciprocal movement within the axial interior cavity between a first position and a second position and includes a first portion having a first thickness, a second portion having a second thickness larger than the first thickness, and a piston bevel extending axially from the first portion to the second portion. The rotary actuator includes a key disposed for radially reciprocal movement within the port and includes a radially proximal end having a first key bevel complementary to the piston bevel, a radially distal end, and a body extending from the radially proximal end to the radially distal end such that the radially proximal end contacts the second portion and the radially distal end extends into the radial recess when the piston is in the second position, and the radially proximal end contacts the first portion and the radially distal end does not extend into the radial recess when the piston is in the first position. The method also includes contacting the first portion with the radially proximal end, moving by an external force the piston from the first position toward the second position, contacting the piston bevel with the key bevel, urging by movement of the piston and contact between the first key bevel and the piston bevel partial radial extension of the key through the port and partial extension of the radially distal end into the radial recess, contacting the second portion with the radially proximal end, preventing radial retraction of the key through the port and escapement of the radially distal end from the radial recess, and contacting by the radially distal end the circumferential end. 
     Various implementations can include some, all, or none of the following features. The method can also include contacting the second portion with the radially proximal end, urging by an external force the piston from the second position toward the first position, allowing radial retraction of the key through the port and escapement of the radially distal end from the radial recess, and contacting the first portion with the radially proximal end. The at least one of the circumferential ends can have a housing bevel extending circumferentially from the radial recess to the cylindrical interior surface, and the radially distal end can have at least one second key bevel complimentary to the housing bevel, and the method can also include rotating the housing relative to the rotor, the key, and the piston, contacting one of the circumferential ends to a complementary one of the second key bevels, urging by the contact between the circumferential end to the complimentary one of the second key bevels radial retraction of the key through the port and ejection of the radially distal end from the radial recess, contacting the piston bevel with the key bevel, and urging by contact between the key bevel and the piston bevel movement of the piston from the second position to the first position. The rotary actuator can also include an axial spring in biasing contact with the piston. The axial spring can be configured to urge the piston into the first position or the second position. The piston can include at least one seal between at least one of the first portion and the axial interior cavity, and the second portion and the axial interior cavity. The rotary actuator can include a pressure chamber defined by the axial interior cavity, the piston, and the seal, the pressure chamber being configured to selectably apply fluid pressure to the piston to urge reciprocal axial movement of the piston within the axial interior cavity. Moving the piston from the first position toward the second position can include applying a fluid pressure to the pressure chamber. Moving the piston from the first position toward the second position can include relieving a fluid pressure within the pressure chamber. 
     The systems and techniques described here may provide one or more of the following advantages. First, a system as disclosed herein can provide improved position-holding capability. Second, the system can provide a fail-safe mechanism that can provide position-holding capability in event of loss of actuation fluid pressure or external or internal leakage failures. Furthermore, the techniques shown provide a robust mechanical lock that has high external load (torque) carrying capability. The system has an additional advantage in that visual or electrical means of indication of lock position may easily be incorporated for safety critical applications. 
     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIGS. 1A and 1B  are cross-section side and end diagrams that show an example of a locking rotary actuator in an unlocked configuration. 
         FIGS. 2A and 2B  are cross-section side and end diagrams that show an example of the locking rotary actuator in a locked configuration. 
         FIG. 3  is flow chart that shows an example of a process for locking a locking rotary actuator. 
         FIG. 4  is flow chart that shows an example of a process for unlocking a locking rotary actuator. 
     
    
    
     DETAILED DESCRIPTION 
     This document describes systems and techniques for locking rotary actuators. In general, the rotary actuators described herein include a rotor that rotates relative to an outer housing. The rotor includes a mechanism that can be actuated to cause one or more keys to extend radially from the rotor. The keys extend into axial grooves (non-circumferential recesses) formed in the inner diameter of the outer housing. The extended keys become reversibly trapped within the recesses and mechanically limit or prevent rotation of the rotor relative to the outer housing. In an example aircraft application, the rotor may be configured to control the position of a control surface (e.g., a flap, rudder, or aileron) relative to a wing to which the outer housing is attached, and in the locked configuration the locking rotary actuator can maintain a relative position between the control surface and the wing. 
       FIGS. 1A and 1B  are axial cross-section side and radial end diagrams that show an example of a locking rotary actuator  100  in a first configuration (e.g., an unlocked configuration). In some embodiments, the actuator  100  can be configured to actuate components of an aircraft, spacecraft, marine craft, land vehicle, or any other appropriate form of vehicle. 
     The example locking rotary actuator  100  includes an outer housing  112 . The outer housing  112  includes a cylindrical interior surface  114 . A radial recess with an axial length  116  is formed in a portion of the cylindrical interior surface  114 . Referring now to  FIG. 1B , the radial recess  116  has at least one radially angled circumferential end  118  forming an axial end with respect to the circumferential orientation of the cylindrical interior surface  114 . In some embodiments, the outer housing  112  may include multiple ones of the radial recess  116  arranged radially along the cylindrical interior surface  114 . 
     Referring again to  FIGS. 1A and 1B , the example locking rotary actuator  100  includes a rotor  120 . The rotor  120  is disposed within the outer housing  112 , and includes a cylindrical exterior surface  122 . The cylindrical exterior surface  122  is rotatable within the cylindrical interior surface  114 . In some embodiments, the rotor  120  may be a moving part, e.g., the outer housing  112  may be affixed to an external platform or surface, or may otherwise provide a relative frame of reference for motion of the rotor  120 . In some embodiments, the rotor  120  may be a stator or other relatively non-moving part, e.g., the rotor  120  may be affixed to an external platform or surface, or may otherwise provide a relative frame of reference for motion of the outer housing  112 . For example, the rotor may be held substantially still, and the actuator  100  may be actuated to cause the outer housing  112  to at least partly rotate about the rotor  120 . 
     The rotor  120  of example locking rotary actuator  100  also includes an axial interior cavity  124  and a port  126 . The port  126  is disposed to be capable of rotational alignment with the radial recess  116  and extends radially from the axial interior cavity  124  to the cylindrical exterior surface  122 . For example, the rotor  120  may be rotated within the outer housing  112  to bring the port  126  into alignment with the radial recess  116 . 
     The example locking rotary actuator  100  also includes a piston  130 . The piston  130  is disposed for axially reciprocal movement within the axial interior cavity  124 . For example, the cylindrical exterior surface  122  may have a generally cylindrical shape about an axis  128 . The piston  130  can be configured for motion substantially parallel to the axis  128 . The piston  130  is configured for motion between a first position, depicted in  FIGS. 1A and 1B , and a second position that will be discussed further in the descriptions of  FIGS. 2A and 2B . 
     The piston  130  of the example locking rotary actuator  100  includes a first portion  132  having a first thickness  133 , a second portion  134  having a second thickness  135 , and a piston bevel  136  extending axially from the first portion  132  to the second portion  134 . The second thickness  135  is greater than the first thickness  133 . As such, the piston bevel  136  forms a ramp from the first portion  132  to the second portion  134  along the axis  128 . 
     The example locking rotary actuator  100  also includes a key  140  disposed for radially reciprocal movement, relative to the axis  128 , within the port  126 . The key  140  includes a radially proximal end  142  proximal relative to the axis  128  and the axial interior cavity  124 , and a radially distal end  143  proximal to the exterior surface  122  and the outer housing  112 . In some embodiments, multiple keys  140  may be included as necessary for increased actuator load carrying capability. 
     The radially proximal end  142  of the key  140  includes a first key bevel  144  that is complementary to the piston bevel  136 . For example, the piston bevel  136  may extend from the first portion  132  to the second portion  134  at approximately a 45-degree (e.g., 30-60 degree) angle relative to the axis  128 , and the key bevel  144  may be formed and oriented at an approximately 45 degree angle (e.g., 30-60 degrees relative to the axis  128 ) that approximately parallels (e.g., +/−10 degrees) the piston bevel  136 . 
     Referring to  FIG. 1B , the radially distal end  143  of the key  140  includes a pair of key bevels  145 . The key bevels  145  are complementary to a pair of housing bevels  119  formed at the circumferential ends  118  of the radial recess  112 . For example, the housing bevels  119  may be formed and oriented at an approximately 65 (e.g., 30-80) degree angle relative to the cylindrical interior surface  114 , and the key bevels  145  may be formed and oriented at an approximately 65 (e.g., 30-80) degree angle (e.g., relative to the cylindrical interior surface  114 ) that approximately parallels (e.g., +/−10 degrees) the housing bevels  119 . 
     Referring again to  FIGS. 1A and 1B , the key  140  includes a body  148  extending from the radially proximal end  142  to the radially distal end  143 . The radially proximal end  142  contacts the second portion  132 , and as will be discussed further in the descriptions of  FIGS. 2A and 2B , the radially distal end  143  is configured to not extend into the radial recess  116  when the piston  130  is in the first position, such that the radially proximal end  142  is able to contact the first portion  132 . 
     The example locking rotary actuator  100  includes a seal  150  between the first portion  132  and a radially interior wall  129  of the axial interior cavity  124 , and a seal  152  between the second portion  134  and a radially interior wall  129  of the axial interior cavity  124 . The axial interior cavity  124 , the first portion  132  of the piston  130 , and the seal  150  partly define a pressure chamber  154 , and the axial interior cavity  124 , the second portion  134  of the piston  130 , and the seal  152  partly define a pressure chamber  156 . In some embodiments, either or both of the pressure chambers  154  and  156  can be configured to selectably apply fluid pressure to the piston  130  to urge reciprocal axial movement of the piston  130  within the axial interior cavity  124 . For example, the pressure chamber  154  may be pressurized to urge the piston  130  toward the second position shown in  FIGS. 2A and 2B , and/or the pressure chamber  156  may be pressurized to urge the piston  130  toward the first position shown in  FIGS. 1A and 1B . 
     The example locking rotary actuator  100  includes an axial spring  160  in biasing contact with the piston  130 . In some embodiments, the axial spring  160  can be configured to urge the piston  130  from the second position to the first position. For example, as shown in  FIGS. 1A and 1B , the spring  160  is in biasing contact with the second portion  134 . Fluid pressure applied to the pressure chamber  154  may be sufficient to urge the piston  130  to compress the spring  160 , and when the fluid pressure is relieved the spring  160  may urge the piston back toward the first position. In some embodiments, the axial spring  160  can be configured to urge the piston  130  from the first position, shown in  FIGS. 1A and 1B , to the second position, shown in  FIGS. 2A and 2B . For example, the locking rotary actuator  100  may be configured with the spring  160  in biasing contact with the first portion  132  of the piston  130 . Fluid pressure applied to the pressure chamber  156  may be sufficient to urge the piston  130  to compress the spring  160 , and when the fluid pressure is relieved the spring  160  may urge the piston back toward the second position. 
     Referring to  FIG. 1B , in which the piston  130  is substantially in the first position, the key  140  is able to rest substantially within the port  126 . With the radially distal end  143  being below the cylindrical exterior surface  122 , the rotor  120  is free to rotate substantially without mechanical interference with the outer housing  112 . 
       FIGS. 2A and 2B  are cross-section side and end diagrams that show an example of the locking rotary actuator  100  in the second configuration (e.g., a locked configuration). In the second configuration, the piston  130  is positioned at a second position (e.g., different from the first position shown in  FIGS. 1A and 1B ) within the axial interior cavity  124 , such that the radially proximal end  142  of the key  140  is able to contact the second portion  134  of the piston  130 . 
     As the piston  130  is urged from the first position to the second position, complementary sliding contact between the key bevel  144  and the piston bevel  136  urges the key  140  radially away from the axis  128  though the port  126 . As the key  140  moves radially along the port  126 , the radially distal end  145  of the key  140  extends into the radial recess  116 . With the radially distal end  145  extended into the radial recess  116 , sufficient clearance is provided for the piston  130  to move substantially into the second position in which the radially proximal end  142  of the key  140  can contact the second portion  134  of the piston  130 . With the piston  130  in the second position, the key  140  can be maintained in an extended position with the radially distal end  145  of the key  140  extended into the radial recess  116 . 
     Referring to  FIG. 2B , in which the piston  130  is substantially in the second position, rotation of the rotor  120  relative to the outer housing  112  causes the radially distal end  143  of the key  140  to contact and mechanically interfere with the circumferential ends  118  of the outer housing  112 . The interference between the circumferential ends  118  and the radially distal end  143  of the key  140 , which in turn is positioned within the port  126 , substantially prevents rotation of the rotor  120  relative to the outer housing  112 , reversibly “locking” the rotor  120  relative to the outer housing  112  and structures to which the outer housing  112  may be mounted. For example, the outer housing  112  may be mounted to an aircraft wing, and the rotor  120  may be connected to an aircraft control surface such as a flap. In such an example, the piston  130  may be moved to the first position to allow movement of the flap relative to the wing, and the piston  130  may be moved to the second position to substantially lock the flap into a selected position relative to the wing. 
     The locking rotary actuator  100  is unlocked by moving the piston  130  from the second position as shown in  FIGS. 2A and 2B , back to the first position as shown in  FIGS. 1A and 1B . As the piston  130  moves from the second position to the first position, the second portion  134  of the piston  130  is moved away from contact with the radially proximal end  142  of the key  140 . 
     As discussed previously, rotation of the rotor  130  relative to the outer housing  112  causes mechanical contact between the distal end  143  of the key  140  and the radial recess  116 . Referring mainly now to  FIG. 2B , rotation of the rotor  130  urges at least one of the key bevels  145  into contact with the housing bevels  119 . Contact between the complimentary angles of the key bevels  145  and the housing bevels  119  urges the key  140  radially inward toward the piston  130 . In some implementations in which the piston  130  is in a position approximately halfway between the first position and the second position (e.g., proximal the midpoint of total travel of the piston  130 ), in which the piston bevel  136  can be contacted by the radially proximal end  142 , rotation of the rotor  120  relative to the outer housing  112  can urge the key  140  into contact with the piston bevel. In such an example, contact between the complimentary angles of the key bevel  144  and the piston bevel  136  can urge the piston  130  axially toward the first position. 
     In some implementations, rotation of the rotor  120  relative to the outer housing  112  can provide mechanical energy to assist in the unlocking process, by providing at least some of the energy used to move the piston  130  from the second position to the first position. For example, rotation of the rotor  120  and the interference between the key bevels  145  and the housing bevels  119  can provide energy to urge the distal end  143  of the key  140  out of the radial recess  116 . In turn, radially inward movement of the key  140  and the mechanical cooperation between the key bevel  114  and the piston bevel  136  can provide energy to urge the piston from the second position to the first position. 
     In some embodiments, the locking rotary actuator  100  may initially be in the second configuration until fluid pressure within the pressure chamber  154 , or another appropriate force, urges the piston  130  toward the first position. In some embodiments, the locking rotary actuator  100  may initially be in the first configuration until fluid pressure is applied to the pressure chamber  156 , or another appropriate force, urges the piston  130  toward the first position. For example, the spring  160  may be located proximal to the first portion  132  of the piston  130  to urge the piston toward the second position, while fluid pressure in the pressure chamber  156  may be sufficient to overcome the force of the spring  160  and urge the piston  130  toward the first position. 
     In some embodiments, the locking rotary actuator  100  may initially be in the first configuration until fluid pressure within the pressure chamber  154  is relieved. In some embodiments, the locking rotary actuator  100  may initially be in the second configuration until fluid pressure applied to the pressure chamber  156  is relieved, allowing the piston  130  to move toward the first position. For example, the spring  160  may be located proximal to the first portion  132  of the piston  130  and compressed by the piston  130  due to fluid pressure in the pressure chamber  156 , and when that pressure is relieved the spring  160  may move the piston toward the first position. 
       FIG. 3  is flow chart that shows an example of a process  300  for locking a locking rotary actuator. In some implementations, the process  300  can be used with the locking rotary actuator  100  of  FIGS. 1A-2B . 
     At  302 , a locking rotary actuator is provided. For example, the locking rotary actuator  100  can be provided. 
     At  304 , the first portion is contacted with the radially proximal end. For example, the first portion  132  of piston  130  can be contacted with the radially proximal end  142  of key  140 . 
     At  306 , the piston is moved by an external force from the first position toward the second position. For example, fluid pressure can be applied to the pressure chamber  154  to urge the piston  130  from the first position shown in  FIGS. 1A and 1B  toward the second position shown in  FIGS. 2A and 2B . 
     At  308 , the piston bevel is contacted with the key bevel. For example the piston bevel  136  can be contacted by the key bevel  144 . 
     At  310  movement of the piston and contact between the first key bevel and the piston bevel urges partial radial extension of the key through the port and partial extension of the radially distal end into the radial recess. For example, as the piston  130  is moved from the first position toward the second position, the piston bevel  136  contacts the key bevel  144 , urging the key  140  to extend radially away from the piston  130 . As the key  140  extends radially, the radially distal end  143  of the key  140  extends into the radially recess  116 . 
     At  312 , the second portion is contacted with the radially proximal end, preventing radial retraction of the key through the port and escapement of the radially distal end from the radial recess. For example, when the radially proximal end  142  of the key  140  is in contact with the second portion  134  of the piston  130 , the key  140  is substantially unable to move radially inward to allow the radially distal end  143  of the key  140  from escaping the radial recess  116 . 
     At  314 , the circumferential end is contacted by the radially distal end. For example, the rotor  120  can be fractionally rotated relative to the outer housing  112 , causing the radially distal end  143  of the key  140  to contact one of the circumferential ends  118 . Mechanical interference between the radially distal end  143  of the key  140  and the circumferential ends  118  can prevent further rotation of the rotor  120  relative to the outer housing  112 , substantially “locking” the rotor  120  in place relative to the outer housing  112 . 
       FIG. 4  is flow chart that shows an example of a process  400  for unlocking a locking rotary actuator. In some implementations, the process  400  can be used with the locking rotary actuator  100  of  FIGS. 1A-2B . 
     At  402 , the second portion is contacted with the radially proximal end. For example, the second portion  134  of the piston  130  can be contacted by the radially proximal end  142  of the key  140 . 
     At  404 , the piston is urged by an external force from the second position toward the first position, allowing radial retraction of the key through the port and escapement of the radially distal end from the radial recess. For example, fluid pressure applied to the pressure chamber  154  can urge the piston  130  to move toward the first position. In other examples, the spring  154  may be located proximal to the first portion to provide a force that can move the piston from the second position toward the first position. As the piston  130  moves toward the first position, the key  140  can move radially inward within the port  126  and allow the radially distal end  143  of the key  140  to escape the radial recess  116 . 
     In some implementations, the housing can be rotated relative to the rotor, the key, and the piston, and one of the circumferential ends can be contacted to a complementary one of the second key bevels. For example, the one of the key bevels  145  can be brought into contact with a corresponding one of the housing bevels  119 . In some implementations, contact between the circumferential end to the complimentary one of the second key bevels can urge radial retraction of the key through the port and ejection of the radially distal end from the radial recess. For example, relative rotary motion between the key and the outer housing can cause the complimentary angles of the housing bevel  119  and the key bevel  145  to transform some of the rotary force into radial force that can urge the key radially inward such that the radially distal end  143  of the key  140  is ejected from the radial recess  116 . In some implementations, the piston bevel can be contacted with the key bevel, and contact between the key bevel and the piston bevel can urge movement of the piston from the second position to the first position. For example, inwardly radial movement of the key  140  can be transformed into axial movement of the piston  130  by contact between the complimentary angles of the key bevel  144  and the piston bevel  136 . 
     At  406 , the first portion  132  is contacted with the radially proximal end  142 . For example, the radially proximal end  142  of the key  140  can contact the second portion  132  of the piston  130  when the piston  130  is in the first position, as shown in  FIGS. 1A and 1B . 
     Although a few implementations have been described in detail above, other modifications are possible. For example, the logic flows depicted in the figures do not require the particular order shown, or sequential order, to achieve desirable results. In addition, other steps may be provided, or steps may be eliminated, from the described flows, and other components may be added to, or removed from, the described systems. Accordingly, other implementations are within the scope of the following claims.