Linear actuators

Abstract

A linear actuator comprises rotary motion producing means ( 1,2,3,4,5 ); linear motion producing means ( 6,7,10,11,12 ) coupled with the rotary motion producing means for converting rotary motion to linear motion; a driven member ( 18 ) movable linearly by the linear motion providing means from a first position to a second position; and back-drive means ( 22 ) for returning the driven member to the first position. The arrangement is such that the linear motion producing means includes torque reaction means ( 13,15,16,17 ) which, in normal operation, is in an activated condition and provides a torque reaction path to enable the driven member to be moved from the first to the second position but which, in the event of a fault, is in a de-activated condition so that it no longer provides the torque reaction path and the back-drive means can move the driven member to the first position, without disengaging the rotary motion producing means from the linear motion producing means.

1 . A linear actuator comprising: 
 a rotary motion producing device for causing rotation in first and second directions;    a linear motion producing means device coupled with said rotary motion producing device for converting said rotary motion to linear motion, said linear motion producing device comprising a threaded shaft and nut arrangement;    a driven member movable linearly by said linear motion producing device between a first position and a second position, said driven member being coupled to one of said shaft and nut arrangement; and    a back-drive member for returning said driven member to said first position in the event of a fault;    characterized in that:    said linear motion producing device includes a torque reaction assembly which, in normal operation, is in an activated condition and provides a torque reaction path to enable the driven member to be reversibly moved from said first to said second position by rotating said rotary motion producing device in the first direction, and from said second position to said first position by rotating said rotary motion producing device in said second direction, the driven member being restrained from rotating, but which, in the event of a fault, is in a de-activated condition so that the torque reaction assembly no longer provides said torque reaction path and said back-drive member can move the driven member to said first position, without rotating the rotary motion producing device in said second direction.    
   
   
       2 - 5 . (canceled)  
   
   
       6 . A linear actuator according to  claim 1 , wherein, said shaft is rotatable by a worm and wheel arrangement and said nut arrangement is coupled to said driven member.  
   
   
       7 . A linear actuator according to  claim 6 , wherein said shaft is coupled to said worm and wheel arrangement via clutch means, said clutch means being part of said torque reaction path.  
   
   
       8 . A linear actuator according to  claim 1 , wherein said driven member is moved from said first to said second position against the action of said back-drive member.  
   
   
       9 . A linear actuator according to  claim 1 , wherein said back-drive member comprises a spring.  
   
   
       10 . A linear actuator according to  claim 1  wherein when said torque reaction assembly is in a de-activated condition, said back-drive member can move the driven member to said first position, without disengaging the rotary motion producing device from the linear motion producing device.  
   
   
       11 . A linear actuator comprising: 
 an electrical motor;    a gear train connected to said electrical motor and having an output member that is rotated by said electrical motor;    a motion converter coupled with said output member of said gear train for converting rotary motion of said output member of said gear train to linear motion, said motion converter comprising a linearly stationary rotatable first member in threaded engagement with a linearly movable second member, said first member being coupled to said output member of said gear train for being rotatably driven, said second member being nonrotatable and moving linearly when said first member rotates;    a spring that is biased against said second member for opposing forward linear motion of said second member;    a clutch connected between said output member and said first member, such that when said clutch and said electrical motor are activated, said output member rotates said first member, and when said clutch and said motor are de-activated, said spring moves said second member rearward, causing said first member to rotate independently of said output member.    
   
   
       12 . A linear actuator according to  claim 11 , wherein said first member comprises a shaft and said second member comprises a nut arrangement.  
   
   
       13 . A linear actuator according to  claim 11 , wherein rotation of said motor in a first direction causes said first member to rotate in one direction to cause said second member to move in a forward direction, and rotation of said motor in a second direction causes said shaft to rotate in another direction to cause said second member to move in a rearward direction.  
   
   
       14 . A linear actuator according to  claim 11 , wherein said gear train comprises a worm and wheel arrangement.