Patent Publication Number: US-11035320-B2

Title: Over-center thrust reverser primary lock

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application is a divisional of and claims the benefit of priority to U.S. patent application Ser. No. 15/409,240, filed Jan. 18, 2017, the contents of which are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     This instant specification relates to lock mechanisms for thrust reverser actuation systems. 
     BACKGROUND 
     Thrust Reverser Actuation Systems (TRAS) power and control the deployment of aircraft thrust reversers. Thrust reversal, also called reverse thrust, involves the temporary diversion of a jet aircraft&#39;s exhaust so that it acts against the forward travel of the aircraft, providing deceleration, for example, to help slow an aircraft after touch-down. Such devices are considered important for safe operations by airlines. 
     However, such devices can also negatively affect the operation of an aircraft if they are misused or malfunction. A number of aircraft accidents have been traced back to accidental TRAS deployments. As such, many TRAS designs include locking mechanisms to ensure that the TRAS remains stowed until needed. Many of these systems utilize large bias springs to bias locks toward the locked position and to overcome vibration and air load forces, and use hydraulic linear actuators with high power densities to overcome the bias springs in order to release the lock. Such systems add weight and consume space, both of which can be limited, especially in aircraft applications. 
     SUMMARY 
     In general, this document describes lock mechanisms for thrust reverser actuation systems. 
     In a first aspect, a lock apparatus includes a latch hook having a catch at a first latch end, a first pivotal mount at a second latch end opposite the first latch end, and a second pivotal mount, a rotary actuator configured to selectably rotate a rotor shaft in a first rotary direction and in a second rotary direction opposite the first rotary direction, a rotor arm coupled to the rotor shaft at a first arm end and extending radially outward from the rotor shaft to a second arm end opposite the first arm end, and a link arm pivotably connected to the second arm end at a first link end, and pivotably connected to the second pivotal mount at a second link end opposite the first link end. 
     Various embodiments can include some, all, or none of the following features. The apparatus can include a bias member configured to bias the rotor shaft in the first rotary direction. The apparatus can include a stop configured to prevent rotation of the rotor shaft past a first rotary position in the first rotary direction. The apparatus can include a receiver configured to engage the catch. The latch hook, the rotor arm, and the link arm can form a bistable over-center mechanism configurable to at least a first configuration in which the rotary actuator is rotated in the first direction to a first rotary position such that the receiver is engaged with the catch, and a second configuration in which the rotary actuator is rotated in the second rotary direction to a second position such that the receiver is disengaged from the catch. The apparatus can include a second link arm pivotally connected to the rotor arm at the second shaft end and pivotally connected to the link arm at the first link end. The apparatus can include a guide configured to constrain angular movement of the link arm and permit guided linear movement of the link arm. The apparatus can include a moveable stop configured to prevent rotation of the rotor shaft past a second rotary position in the second rotary direction in a first stop configuration, and permit rotation of the rotor shaft past the second rotary position in the second rotary direction in a second stop configuration. The apparatus can include a moveable stop configured to prevent movement of at least one of the rotor arm and the link arm in a first stop configuration, and permit movement of the rotor arm or the link arm in a second stop configuration. The second pivotal mount can be between the first latch end and the second latch end. 
     In a second aspect, a method for reversible locking includes providing a lock apparatus having a latch hook having a catch at a first latch end, a first pivotal mount at a second latch end opposite the first latch end, and a second pivotal mount, a rotary actuator configured to selectably rotate a rotor shaft in a first rotary direction and in a second rotary direction opposite the first rotary direction, a rotor arm coupled to the rotor shaft at a first arm end and extending radially outward from the rotor shaft to a second arm end opposite the first arm end, and a link arm pivotably connected to the second arm end at a first link end, and pivotably connected to the second pivotal mount at a second link end opposite the first link end, rotating the rotary actuator in a first direction to a first rotary position, engaging, during the rotating, the catch with a receiver, rotating the rotary actuator in a second direction opposite the first direction to a second rotary position, and disengaging the catch from the receiver. 
     Various implementations can include some, all, or none of the following features. The method can include contacting a stop at the first rotary position, and stopping, by the stop, rotation of the rotary actuator in the first rotary direction at the first rotary position. The method can include applying a back force to the catch while rotary actuator is proximal the first rotary position, urging rotation of the rotary actuator in the first rotary direction, resisting, by the stop, the back force, and maintaining engagement of the catch and the receiver. The method can include urging, by a bias member, the rotary actuator in the first rotary direction. The method can include configuring a moveable stop in a first configuration, urging rotation of the rotary actuator in the second rotary direction, contacting the moveable stop at a second rotary position, stopping, by the moveable stop in the first configuration, rotation of the rotary actuator in the second rotary direction at the second rotary position, configuring the moveable stop in a second configuration, urging rotation of the rotary actuator in the second rotary direction, and rotating the rotary actuator in the second rotary direction past the second position. The method can include configuring a moveable stop in a first configuration, urging movement of the link arm, stopping, by the moveable stop in the first configuration, movement of the link arm, configuring the moveable stop in a second configuration, urging movement of the link arm, and permitting, by the moveable stop in the second configuration, movement of the link arm. The lock apparatus can include a second link arm pivotally connected to the rotor arm at the second shaft end and pivotally connected to the link arm at the first link end, and the method can include constraining, by a guide, angular movement of the link arm, and moving the link arm linearly through the guide. 
     The systems and techniques described here may provide one or more of the following advantages. First, a system can provide a robust locking action. Second, the system can be implemented with actuators having reduced space and weight requirements. Third, the system can be driven electrically rather than hydraulically or pneumatically. Fourth, the system can be implemented without the additional use of gearboxes or stroke amplifiers. 
     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 schematic diagrams that show an example of a system for locking a thrust reverser actuation system (TRAS). 
         FIGS. 2A and 2B  are schematic diagrams that show another example of a system for locking a TRAS. 
         FIGS. 3A and 3B  are schematic diagrams that show another example of a system for locking a TRAS. 
         FIGS. 4A and 4B  are schematic diagrams that show another example of a system for locking a TRAS. 
         FIGS. 5A and 5B  are schematic diagrams that show another example of a system for locking a TRAS. 
         FIGS. 6A and 6B  are schematic diagrams that show another example of a system for locking a TRAS. 
         FIG. 7  is flow chart that shows an example of a process for locking a TRAS. 
     
    
    
     DETAILED DESCRIPTION 
     This document describes systems and techniques for locking a thrust reverser actuation system (TRAS). Many TRAS systems include locking mechanisms to keep jet engine reverser cowl sections from deploying accidentally. Some existing TRAS locking mechanisms systems utilize large bias springs to bias locks toward the locked position and to overcome vibration and air load forces, and use hydraulic linear actuators with high power densities to overcome the bias springs in order to release the locks. Such systems add weight and consume space, both of which can be limited especially in aircraft applications. 
     Electric actuation generally has a lower power density and range of motion when compared to hydraulic actuation, which limits the use of electric systems as replacements for hydraulics. For example, electric motor-driven locks sometimes require the use of gearing, control systems, limit switches, and other components in order to replicate the power and range of a hydraulic system, but such components add weight, add cost, and consume space. In other examples, electric linear solenoids can be used, but solenoids generally have strokes that are too short (e.g., 80 to 100 thousands of an inch) to use as a replacement for hydraulics without stroke amplification. However, mechanisms for stroke amplification also consume space, add cost and weight, and also generally trade solenoid force in exchange for stroke length thereby reducing overall robustness of the system. 
     Generally speaking, the systems and techniques described in this document use rotary electric actuation, rather than linear hydraulic or pneumatic actuation, to lock a TRAS. The rotary actuators are used to actuate over-center mechanisms to lock and unlock the TRAS, rather than lock and unlock the TRAS directly. The over-center mechanisms can provide the desired robustness needed to keep a TRAS secured, and actuation of the over-center mechanisms can be performed with a relatively low amount of mechanical power (e.g., when compared to the amount of power needed to secure a TRAS lock directly). 
       FIGS. 1A and 1B  are schematic diagrams that show an example of a system  100  for locking a thrust reverser actuation system (TRAS). In the illustrated example, the TRAS is not shown in its entirety; a receiver  101  (e.g., catch, latch) of a TRAS reverser door (not shown) is included for purposes of describing the operation of the system  100 . 
     The system  100  includes a latch hook  110  having a catch  112  at a first latch end  113 , a first pivotal mount  114  at a second latch end  115  opposite the first latch end  113 , and a second pivotal mount  116  at a midpoint of the latch hook  110 . A rotary actuator  120  is configured to selectably rotate a rotor shaft  122  in a first rotary direction (e.g., counterclockwise in the current example), represented by the arrow  102   a  in  FIG. 1A , and in a second rotary direction, represented by the arrow  102   b  in  FIG. 1B , opposite the first rotary direction  102   a  (e.g., clockwise in the current example). In some embodiments, the rotary actuator  120  can be an electric motor or a rotary electric solenoid. In some embodiments, the rotary actuator  120  can be a rotary fluid actuator (e.g., pneumatic, hydraulic). 
     A rotor arm  130  is coupled to the rotor shaft  122  at a first arm end  132  and extends radially outward from the rotor shaft  122  to a second arm end  134  opposite the first arm end  132 . A link arm  140  (e.g., an idler link) is pivotably connected to the second arm end  134  by a third pivotal mount  141  at a first link end  142 , and is pivotably connected to the second pivotal mount  116  at a second link end  144  opposite the first link end  142 . 
     The system  100  also includes a stop  150  (e.g., an over-center stop). The stop  150  is configured to prevent rotation of the rotor arm  130  and the rotor shaft  122  past a first rotary position in the first rotary direction  102   a . For example, in  FIG. 1A , the rotor arm  130  is rotated counterclockwise by the rotor shaft  122  to contact the stop  150  at a rotary position that is slightly less than 90 degrees (e.g., a bit less than the three o&#39;clock position) from top dead center (e.g., the twelve o&#39;clock position). 
     Referring to  FIG. 1A , the catch  112  is engaged with the receiver  101 . The receiver  101  is confined to move linearly, substantially perpendicular to the latch hook  110 , as illustrated by arrows  160 . The rotor arm  130  and the link arm  140  form a linkage in which pivotal movement of the latch hook  110  can urge rotation of the rotary actuator  120 . In general, clockwise motion of the latch arm  110  will create tension along the rotor arm  130  and urge rotation of the rotary actuator  120  such that the third pivotal mount  141  is drawn into substantially direct alignment between the rotor shaft  122  and the second pivotal mount  116 , as represented by line  164 . Such a configuration is substantially stable in tension, but is mechanically unstable in compression. Counterclockwise motion of the latch arm  110  will compress the rotor arm  130 , cause the rotor arm  130  to pivot relative to the link arm  140  about the third pivotal mount  141 , and in turn urge rotation of the rotary actuator  120 . 
     The direction of rotation of the rotary actuator  120  is generally determined by the rotational side (e.g., clockwise or counterclockwise) of the line  164  the third pivotal mount  141  is already on. For example, if the third pivotal mount  141  is positioned counterclockwise relative to the line  164 , then compression of the rotor arm  130  will generally urge further counterclockwise rotation of the rotary actuator  120 . In another example if the third pivotal mount  141  is positioned clockwise relative to the line  164 , then compression of the rotor arm  130  will generally urge further clockwise rotation of the rotary actuator  120 . 
     Stability of the system  100  in compression is provided by the stop  150 . The stop  150 , the rotor shaft  122 , the rotor arm  130 , the third pivotal mount  141 , and the link arm  140  form an over center linkage that prevents back-driving of the system  100 . 
     In the illustrated example, the rotor shaft  122  is rotated such that the rotor arm  130  is rotated past direct alignment with the line  164 , such that the third pivotal mount  141  is not positioned along the line  164 . The third pivotal mount  141  and the rotor arm  130  are positioned counterclockwise relative to the line  164 . As such, counterclockwise motion of the latch hook  110  (e.g., caused by leftward, back-driving movement of the receiver toward the system  100 ) can urge counterclockwise rotation of the rotary actuator  120 . Counterclockwise rotation of the rotor arm  130  is limited by the stop  150 . As such, the stop  150  resists further counterclockwise rotation of the rotor arm  130 , and by resisting such further rotation the stop  150  resists the counterclockwise motion of the latch arm  110  caused by the leftward, back-driving movement of the receiver  101 . With the back-driving forces being resisted, the catch  122  is kept in engagement with the receiver  101 . 
     In the illustrated configuration, movement of the receiver  101  away from the system  100  (e.g., to the right) urges contact between the catch  112  and the receiver  101 , which in turn urges clockwise pivotal motion, represented by arrow  162   a , of the latch hook  110 . Such pivotal motion draws the catch  112  into more forceful engagement with the receiver  101 , resisting disengagement of the receiver  101  from the system  100 . 
     Referring now to  FIG. 1B , the system  100  is shown in a disengaged configuration. In the illustrated example, the rotary actuator  120  is actuated to rotate the rotor arm  130  clockwise, away from the stop  150 , past the line  164 . Such rotary motion urges counterclockwise motion  162   b  of the latch hook  110 , causing the catch  112  to disengage from the receiver  101 . 
       FIGS. 2A and 2B  are schematic diagrams that show an example of another system  200  for locking a TRAS. In general, the system  200  is substantially similar to the system  100 , with the addition of a protective housing  201  (e.g., a de-icing boot) configured to protect various moving components of the system  200  (e.g., parts that could become jammed or short-circuited by debris, such as ice or de-icing agents). In the illustrated example, the TRAS is not shown in its entirety; the receiver  101  (e.g., a catch or latch) of a TRAS reverser door (not shown) is included for purposes of describing the operation of the system  200 . 
     The system  200  includes the latch hook  110 . The rotary actuator  120  is configured to selectably rotate the rotor shaft  122  in the first rotary direction (e.g., counterclockwise in the current example), represented by the arrow  102   a  in  FIG. 2A , and in the second rotary direction, represented by the arrow  102   b  in  FIG. 2B , opposite the first rotary direction  102   a  (e.g., clockwise in the current example). 
     The rotor arm  130  is coupled to the rotor shaft  122  at a first arm end  132  and extends radially outward from the rotor shaft  122  to the second arm end  134 . A first link arm  240  (e.g., an idler link) is pivotably connected to the second arm end  134  by a third pivotal mount  241  at a first link end  242 , and is pivotably connected to a second link arm  250  (e.g., a guided rod) by a fourth pivotal mount  251  at a second link end  244  opposite the first link end  242 . The second link arm  250  extends from the fourth pivotal mount  251  at a third link end  252  to a fourth link end  254  opposite the third link end  252 . The second link arm  250  is pivotably connected to the latch hook  110  by the second pivotal mount  116 . 
     The second link arm  250  is configured to extend through and retract from the protective housing  201 . Motion of the second link arm  250  is directed by a guide  202  (e.g., to constrain the section link arm  250  to move reciprocally along a linear, axial path of motion). Referring now to  FIG. 2B , the motion of the second link arm  250  is substantially linear, represented by the arrow  261 . In some embodiments, a seal or compliant boot may be included between the protective housing  201  and the second link arm  250  to permit movement of the second link arm  250  relative to the protective housing  201  while also resisting intrusion of outside debris and contaminants into the protective housing  201 . 
     Returning to  FIG. 2A , the system  200  also includes the stop  150 . The stop  150  is configured to prevent rotation of the rotor arm  130  and the rotor shaft  122  past a first rotary position in the first rotary direction  102   a . For example, in  FIG. 2A , the rotor arm  130  is rotated counterclockwise by the rotor shaft  122  to contact the stop  150  at a rotary position that is slightly less than 90 degrees (e.g., a bit less than the three o&#39;clock position) from top dead center (e.g., the twelve o&#39;clock position). 
     Still referring to  FIG. 2A , the catch  112  is engaged with the receiver  101 . The receiver  101  is confined to move linearly, substantially perpendicular to the latch hook  110 , as illustrated by arrows  160 . The rotor arm  130 , the first link arm  240 , and the second link arm  250  form a linkage in which pivotal movement of the latch hook  110  can urge rotation of the rotary actuator  120 . In general, clockwise motion of the latch arm  110  will create tension along the rotor arm  130  and urge rotation of the rotary actuator  120  such that the third pivotal mount  241  is drawn into substantially direct alignment between the rotor shaft  122  and the fourth pivotal mount  251 , as represented by line  264 . Such a configuration is substantially stable in tension, but is mechanically unstable in compression. Counterclockwise motion of the latch arm  110  will compress the second link arm  250 , compress the first link arm  240 , compress the rotor arm  130 , cause the rotor arm  130  to pivot relative to the first link arm  240  about the third pivotal mount  241 , and in turn urge rotation of the rotary actuator  120 . 
     The direction of rotation of the rotary actuator  120  is generally determined by what rotational side (e.g., clockwise or counterclockwise) of the line  264  the third pivotal mount  241  is already on. For example, if the third pivotal mount  241  is positioned counterclockwise relative to the line  264 , then compression of the rotor arm  130  will generally urge further counterclockwise rotation of the rotary actuator  120 . In another example if the third pivotal mount  241  is positioned clockwise relative to the line  264 , then compression of the rotor arm  130  will generally urge further clockwise rotation of the rotary actuator  120 . 
     Stability of the system  200  in compression is provided by the stop  150 . The stop  150 , the rotor shaft  122 , the rotor arm  130 , the third pivotal mount  241 , the link arm  140 , the second link arm  250 , and the fourth pivotal mount  251  form an over center linkage that prevents back-driving of the system  200 . 
     In the illustrated example, the rotor shaft  122  is rotated such that the rotor arm  130  is rotated past direct alignment with the line  264 , such that the third pivotal mount  241  is not positioned along the line  264 . The third pivotal mount  241  and the rotor arm  130  are positioned counterclockwise relative to the line  264 . As such, counterclockwise motion of the latch hook  110  (e.g., caused by leftward, back-driving movement of the receiver toward from the system  200 ) can urge counterclockwise rotation of the rotary actuator  120 . Counterclockwise rotation of the rotor arm  130  is limited by the stop  150 . As such, the stop  150  resists further counterclockwise rotation of the rotor arm  130 , and by resisting such further rotation the stop  150  resists the counterclockwise motion of the latch arm  110  caused by the leftward, back-driving movement of the receiver  101 . With the back-driving forces being resisted, the catch  112  is kept in engagement with the receiver  101 . 
     In the illustrated configuration, movement of the receiver  101  away from the system  200  (e.g., to the right) urges contact between the catch  112  and the receiver  101 , which in turn urges clockwise pivotal motion, represented by arrow  162   a , of the latch hook  110 . Such pivotal motion draws the catch  112  into more forceful engagement with the receiver  101 , resisting disengagement of the receiver  101  from the system  200 . 
     Referring now to  FIG. 2B , the system  200  is shown in a disengaged configuration. In the illustrated example, the rotary actuator  120  is actuated to rotate the rotor arm  130  clockwise, away from the stop  150 , past the line  264 . Such rotary motion urges counterclockwise motion  162   b  of the latch hook  110 , causing the catch  112  to disengage from the receiver  101 . 
       FIGS. 3A and 3B  are schematic diagrams that show an example of another system  300  for locking a TRAS. In general, the system  300  is the system  200  of  FIGS. 2A and 2B , with the addition of a compliant member  301  (e.g., a spring) between the receiver  101  and a component to be latched, such as a TRAS reverser door (not shown). In some embodiments, the compliant member  301  can be added to the system  100  of  FIGS. 1A and 1B  as well. 
     In  FIG. 3B , the system  300  is shown in an unlatched configuration in which the catch  112  of the latch arm  110  is disengaged from the receiver  101 . In  FIG. 3A , the system  300  is shown in a latched configuration in which the catch  112  of the latch arm  110  is engaged with the receiver  101 . To drive the system  300  from the unlatched configuration shown in  FIG. 3B  to the latched configuration shown in  FIG. 3A , the rotary actuator  120  rotates the rotor arm  130  counterclockwise to urge the catch  112  toward, and eventually into contact with the receiver  101 . 
     As the rotor arm  130  approaches alignment with the line  264  in the counterclockwise direction  102   a , the catch  112  is urged into compression with the receiver  101 , compressing the compliant member  310 . As the rotor arm  130  is rotated over center, past the line  264 , expansion of the compliant member  301  back-drives the system  300  to urge the rotor arm  130  away from the line  264  in the direction  102   a  and into contact with the stop  150 . 
     The addition of the compliant member  301  provides additional functionality to the system  200 . In the example of the system  200 , the rotary actuator  120  may be kept energized in order to maintain the rotor arm in a position between the line  164  and the stop  150 , such that any back-driving of the linkage will be resisted by contact between the rotor arm  130  and the stop  150 . In the example of the system  300 , once latched (e.g., as depicted in  FIG. 3A ) the rotor arm  130  is continually urged past the line  264  and into contact with the stop  150  by the back-driving force provided by the compliant member  301 . In such examples, the catch  112  will remain engaged with the receiver  101  even if latching (e.g., counterclockwise rotational) power is removed from the rotary actuator  120  intentionally (e.g., to conserve power) or unintentionally (e.g., a power outage). 
       FIGS. 4A and 4B  are schematic diagrams that show an example of another system  400  for locking a TRAS. In general, the system  400  is the system  200  of  FIGS. 2A and 2B , with the addition of a second stop  450 . In some embodiments, the stop  450  can be added to the system  100  of  FIGS. 1A and 1B  as well. 
     As in the example systems  100 ,  200 , and  300  of  FIGS. 1A-3B , the stop  150  limits rotation of the rotor arm  130 , by the rotary actuator  120 , in the counterclockwise direction  102   a . However, in the example of the system  400 , the stop  450  is also present in the rotational path of the rotor arm  130 . The stop  450  is spaced apart from the stop  150  far enough to provide space for the rotor arm  130  (or some portion thereof) to be rotationally constrained between the stop  150  in the counterclockwise direction  102   a  and the stop  450  in the clockwise direction  102   b  when the rotor arm  130  is in the over-center, latched configuration shown in  FIG. 4A . 
     The stop  450  is moveable to selectively block (baulk) or permit (unbaulk) movement of the rotor arm  130 , in the clockwise direction  102   b , away from the latched configuration. An actuator  452  is controllable to actuate the movement of the stop  450 . For example, the stop  450  can be mounted on a piston that is configured to extend and retract the stop  450  into and out of the path of rotation of the rotor arm  130  (e.g., into an out of the plane of the views shown in  FIGS. 4A and 4B ), and the actuator  452  can provide fluid (e.g., hydraulic, pneumatic) to drive the motion of the piston. In another example, the stop  450  can be mounted on a solenoid (e.g., a baulking solenoid) or other linear or rotary actuator that is configured to move the stop  450  into and out of the path of rotation of the rotor arm  130 , and the actuator  452  can provide electrical power (e.g., a switch, a motor driver) to drive the motion of the stop  450 . 
     Referring now to  FIG. 4A , the rotor arm  130  is in the over-center, latched configuration. Rotation of the rotor arm  130  is constrained in the counterclockwise direction  102   a  by the stop  150 , providing resistance against back-driving of the system  400  through the latch arm  110 . Rotation of the rotor arm  130  is constrained in the clockwise direction  102   b  by the stop  450 , preventing the rotor arm  130  from moving out of the over-center, latched configuration. In such examples, the catch  112  will remain engaged with the receiver  101  even if latching (e.g., counterclockwise rotational) power is removed from the rotary actuator  120  intentionally (e.g., to conserve power) or unintentionally (e.g., a power outage). 
     Referring now to  FIG. 4B , the actuator  452  can actuated the stop  450  such that the stop  450  is moved (as represented by the dotted lines in  FIG. 4B ) out of the path of rotation of the rotor arm  130 . As such, the rotary actuator  120  can be actuated to rotate the rotor arm  130  in the clockwise direction  102   b , out of the latched configuration and disengage the catch  112  from contact with the receiver  101 . 
     In some embodiments, other forms of the stop  450  can be implemented. For example, instead of mechanically interfering with the motion of the rotor arm  130 , a stop can be configured to interfere with rotation of the rotary actuator (e.g., a clutch, a stop pin, escapement). 
       FIGS. 5A and 5B  are schematic diagrams that show an example of another system  500  for locking a TRAS. In general, the system  500  is the system  200  of  FIGS. 2A and 2B , with the addition of a second stop  550 . In some embodiments, the stop  550  can be added to the system  100  of  FIGS. 1A and 1B  as well. 
     The stop  550  is engageable to selectively block (baulk) or permit (unbaulk) linear movement of the second link arm  250  away from the latched configuration, as shown in  FIG. 5A . An actuator  552  is controllable to actuate the movement of the stop  550 . For example, the stop  550  can be mounted on a piston that is configured to extend and retract the stop  550  into and out of the path of motion of the second link arm  250 , and the actuator  552  can provide fluid (e.g., hydraulic, pneumatic) to drive the motion of the piston. In another example, the stop  550  can be mounted on a solenoid (e.g., a baulking solenoid) or other linear or rotary actuator that is configured to move the stop  550  into and out of the path of motion of the second link arm  250 , and the actuator  552  can provide electrical power (e.g., a switch, a motor driver) to drive the motion of the stop  550 . 
     In the illustrated example, the stop  550  is extended so as to interfere with rightward (as illustrated) movement of a stop member  554  affixed to the second link arm  250 . In the extended configuration, the back-driving forces applied to the latch hook  110  by the receiver  101  are resisted, and the rotor arm  130  is held in the latched, over-center position illustrated by  FIG. 5A . With the back-driving forces being resisted, the catch  112  is kept in engagement with the receiver  101 . 
     Referring now to  FIG. 5B , the actuator  552  can actuated the stop  550  such that the stop  550  is moved out of the path of the stop member  554 . As such, the catch  112  can be disengaged from contact with the receiver  101 . 
       FIGS. 6A and 6B  are schematic diagrams that show an example of another system  600  for locking a TRAS. In general, the system  600  is a re-arrangement of the system  200  of  FIGS. 2A and 2B , such that the axes of the rotor shaft  122  and the first pivotal mount  116  are close or share a common axis. In some embodiments, the system  600  can be a more compact version of the system  200 . 
     The system  600  includes the latch hook  110 . A rotary actuator  620  is configured to selectably rotate a rotor shaft  622  in the first rotary direction (e.g., counterclockwise in the current example), represented by the arrow  602   a  in  FIG. 6A , and in the second rotary direction, represented by the arrow  602   b  in  FIG. 6B , opposite the first rotary direction  602   a  (e.g., clockwise in the current example). 
     A rotor arm  630  is coupled to the rotor shaft  622  at a first arm end  632  and extends radially outward from the rotor shaft  622  to the second arm end  634 . A first link arm  640  (e.g., idler link) is pivotably connected to the second arm end  634  by a third pivotal mount  641  at a first link end  642 , and is pivotably connected to a second link arm  650  by a fourth pivotal mount  651  at a second link end  644  opposite the first link end  642 . The second link arm  650  extends from the fourth pivotal mount  651  at a third link end  652  to a fourth link end  654  opposite the third link end  652 . The second link arm  650  is pivotably connected to the latch hook  110  by the second pivotal mount  116 . The motion of the second link arm  650  is substantially linear, represented by the arrow  661  in  FIG. 6B . 
     Returning to  FIG. 6A , the system  600  also includes a stop  650 . The stop  650  is configured to prevent rotation of the rotor arm  630  and the rotor shaft  622  past a first rotary position in the first rotary direction  602   a . For example, in  FIG. 6A , the rotor arm  630  is rotated counterclockwise by the rotor shaft  622  to contact the stop  650  at a rotary position that is slightly greater than 90 degrees (e.g., a bit less than the nine o&#39;clock position) from top dead center (e.g., the twelve o&#39;clock position). 
     Still referring to  FIG. 6A , the catch  112  is engaged with the receiver  101 . The receiver  101  is confined to move linearly, substantially perpendicular to the latch hook  110 , as illustrated by arrows  660 . The rotor arm  630 , the first link arm  640 , and the second link arm  650  form a linkage in which pivotal movement of the latch hook  110  can urge rotation of the rotary actuator  620 . Counterclockwise motion of the latch arm  110  will compress the second link arm  650 , tension the first link arm  640 , tension the rotor arm  630 , cause the rotor arm  630  to pivot relative to the first link arm  640  about the third pivotal mount  641 , and in turn urge rotation of the rotary actuator  620 . 
     Stability of the system  600  is provided in part by the stop  650 . The stop  650 , the rotor shaft  622 , the rotor arm  630 , the third pivotal mount  641 , the link arm  640 , the second link arm  650 , and the fourth pivotal mount  651  form an over center linkage that prevents back-driving of the system  600 . 
     In the illustrated example, the rotor shaft  622  is rotated such that the rotor arm  630  is rotated past direct alignment between the rotor shaft  622  and the fourth pivotal mount  651 , as represented by line  264 , such that the third pivotal mount  641  is not positioned along the line  664 . The third pivotal mount  641  and the rotor arm  630  are positioned counterclockwise relative to the line  664 . As such, counterclockwise motion of the latch hook  110  (e.g., caused by leftward, back-driving movement of the receiver toward from the system  200 ) can urge counterclockwise rotation of the rotary actuator  620 . Counterclockwise rotation of the rotor arm  630  is limited by the stop  650 . As such, the stop  650  resists further counterclockwise rotation of the rotor arm  630 , and by resisting such further rotation the stop  650  resists the counterclockwise motion of the latch arm  110  caused by the leftward, back-driving movement of the receiver  101 . With the back-driving forces being resisted, the catch  112  is kept in engagement with the receiver  101 . 
     In the illustrated configuration, movement of the receiver  101  away from the system  600  (e.g., to the right) urges contact between the catch  112  and the receiver  101 , which in turn urges clockwise pivotal motion, represented by arrow  662   a , of the latch hook  110 . Such pivotal motion draws the catch  112  into more forceful engagement with the receiver  101 , resisting disengagement of the receiver  101  from the system  600 . 
     Referring now to  FIG. 6B , the system  600  is shown in a disengaged configuration. In the illustrated example, the rotary actuator  620  is actuated to rotate the rotor arm  630  clockwise, away from the stop  650 , closer to the line  664 . Such rotary motion urges counterclockwise motion  662   b  of the latch hook  110 , causing the catch  112  to disengage from the receiver  101 . 
       FIG. 7  is flow chart that shows an example of a process  700  for locking a TRAS. In some implementations, the process  700  can be performed using the example systems  100 ,  200 ,  300 ,  400 ,  500 , and/or  600  of  FIGS. 1A-6B . 
     At  710 , a lock apparatus is provided. The lock apparatus includes a latch hook having a catch at a first latch end, a first pivotal mount at a second latch end opposite the first latch end, and a second pivotal mount, a rotary actuator configured to selectably rotate a rotor shaft in a first rotary direction and in a second rotary direction opposite the first rotary direction, a rotor arm coupled to the rotor shaft at a first arm end and extending radially outward from the rotor shaft to a second arm end opposite the first arm end, and a link arm pivotably connected to the second arm end at a first link end, and pivotably connected to the second pivotal mount at a second link end opposite the first link end. For example, the example system  100  can be provided. 
     In some implementations, the lock apparatus can also include a second link arm pivotally connected to the rotor arm at the second shaft end and pivotally connected to the link arm at the first link end, and the process  700  can also include constraining, by a guide, angular movement of the link arm, and moving the link arm linearly through the guide. For example, the system  200  includes the second link arm  250  and the guide  202 , and the second link arm  250  can be moved linearly through the guide  202 . 
     At  720 , the rotary actuator is rotated in a first direction to a first rotary position. For example, the rotary actuator  120  can be rotated in the direction  102   a  from the configuration shown in  FIG. 1B  to the configuration shown in  FIG. 1A . 
     At  730  the catch is engaged with a receiver during the rotating. For example, as the rotary actuator  120  is rotated in the direction  102   a  from the configuration shown in  FIG. 1B , in which the catch  112  is disengaged from the receiver  101 , to the configuration shown in  FIG. 1A , the catch  112  is moved into engaging contact with the receiver  101 . 
     In some implementations, the process  700  can include contacting a stop at the first rotary position, and stopping, by the stop, rotation of the rotary actuator in the first rotary direction at the first rotary position. For example, the rotor arm  130  can rotated into contact with the stop  150  by the rotary actuator  120 . When the rotor arm  130  contacts the stop  150 , rotation of the rotary actuator  120  in the direction  102   a  is stopped. 
     In some implementations, the process  700  can include applying a back force to the catch while rotary actuator is proximal the first rotary position, urging rotation of the rotary actuator in the first rotary direction, resisting, by the stop, the back force, and maintaining engagement of the catch and the receiver. For example, the receiver  101  can back-load the system  100  (e.g., by moving leftward in the view shown in  FIG. 1A ). Such back-loading can urge counterclockwise rotation (e.g., in direction  102   a ) of the rotor arm  130  and the rotary actuator  120 . Such rotation can cause the rotor arm  130  to contact the stop  150 , and the stop  150  can resist further rotation in the direction  102   a  and keep the catch  112  in latching contact with the receiver  101  (e.g., through the linkage of the rotor arm  130 , the link arm  140 , and the latch hook  110 ). 
     The method of claim  10 , further comprising urging, by a bias member, the rotary actuator in the first rotary direction. 
     At  740 , the rotary actuator is rotated in a second direction opposite the first direction to a second rotary position. For example, the rotary actuator  120  can be rotated in the direction  102   b  from the configuration shown in  FIG. 1A  to the configuration shown in  FIG. 1B . 
     At  750 , the catch is disengaged from the receiver. For example, as the rotary actuator  120  is rotated in the direction  102   b  from the configuration shown in  FIG. 1A , in which the catch  112  is engaged in contact with the receiver  101 , to the configuration shown in  FIG. 1B , the catch  112  is moved out of engaging contact with the receiver  101 . 
     In some implementations, the process  700  can include configuring a moveable stop in a first configuration, urging rotation of the rotary actuator in the second rotary direction, contacting the moveable stop at a second rotary position, stopping, by the moveable stop in the first configuration, rotation of the rotary actuator in the second rotary direction at the second rotary position, configuring the moveable stop in a second configuration, urging rotation of the rotary actuator in the second rotary direction, and rotating the rotary actuator in the second rotary direction past the second position. For example, the system  400  includes the stop  450 . The stop  450  can controlled (e.g., actuated) to prevent and permit movement of the rotor arm  130  away from the latched position shown in  FIG. 4A . With the rotary actuator  120  and the rotor arm  130  in the latched configuration and the stop  450  engaged, the rotor arm  130  is substantially maintained in the latched position. If the rotary actuator  120  is rotated in the clockwise direction  102   b , then the motion will be resisted by the contact between the rotor arm  130  and the stop  450 , and the system  400  will be held in the latched configuration. If the stop  450  is disengaged and the rotary actuator  120  is rotated in the clockwise direction  102   b , then the stop  450  will not interfere with the motion of the rotor arm  130  as it moves toward the unlatched configuration shown in  FIG. 4B . 
     In some implementations, the process  700  can include configuring a moveable stop in a first configuration, urging movement of the link arm, stopping, by the moveable stop in the first configuration, movement of the link arm, configuring the moveable stop in a second configuration, urging movement of the link arm, and permitting, by the moveable stop in the second configuration, movement of the link arm. For example, the system  500  includes the stop  550 . The stop  550  can controlled (e.g., actuated) to prevent and permit movement of the second link arm  250  away from the latched position shown in  FIG. 5A . With the rotary actuator  120  and the second link arm  250  in the latched configuration and the stop  550  engaged, the second link arm  250  is substantially maintained in the latched position. If the rotary actuator  120  is rotated in the clockwise direction  102   b , then the motion will be resisted by the contact between the second link arm  250  and the stop member  554 , and the system  500  will be held in the latched configuration. If the stop  550  is disengaged and the rotary actuator  120  is rotated in the clockwise direction  102   b , then the stop  550  will not interfere with the stop member  554  and motion of the second link arm  250  as they move toward the unlatched configuration shown in  FIG. 5B . 
     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.