Fault tolerant linear actuator

Abstract

In varying embodiments, the fault tolerant linear actuator of the present invention is a new and improved linear actuator with fault tolerance and positional control that may incorporate velocity summing, force summing, or a combination of the two. In one embodiment, the invention offers a velocity summing arrangement with a differential gear between two prime movers driving a cage, which then drives a linear spindle screw transmission. Other embodiments feature two prime movers driving separate linear spindle screw transmissions, one internal and one external, in a totally concentric and compact integrated module.

1 . A linear actuator comprising: 
 a substantially-cylindrical actuator frame having a principal axis;    a linear output screw having threads disposed thereon, the linear output screw disposed at least partly within the actuator frame along the principal axis;    a planetary spindle screw set, having threads mated to the threads of the linear output screw, disposed in a spindle screw carrier about the linear output screw;    a first armature disposed within the actuator frame about the principal axis;    a second armature disposed within the actuator frame about the principal axis;    a differential gearset disposed in the spindle screw carrier, and connected to the first and second armature in such manner to provide a differential action between the first and second armature.    
   
   
       2 . The actuator of  claim 1  further comprising a first field coil cylinder disposed around the first armature and a second field coil cylinder disposed around the second armature.  
   
   
       3 . The actuator of  claim 1  wherein the first armature is rotationally fixed to a first gear on one end of the first armature meshed to the differential gearset and the second armature is rotationally fixed to a second gear on one end of the second armature meshed to the differential gearset.  
   
   
       4 . The actuator of  claim 1  wherein the differential gearset comprises four central differential planetary gears.  
   
   
       5 . The actuator of  claim 1  further comprising a set of sensors for constantly monitoring the torque output of each armature.  
   
   
       6 . The actuator of  claim 1  wherein the differential gearset is supported by a differential cage.  
   
   
       7 . The actuator of  claim 1  wherein the set of planetary spindle screws comprises a first set of planetary spindle screws at a first axial location along the linear output screw and a second set of planetary spindle screws at a second axial location along the linear output screw.  
   
   
       8 . The actuator of  claim 1  wherein the actuator frame further comprises a trunnion extending radially from the principal axis of the actuator frame.  
   
   
       9 . The actuator of  claim 1  further comprising a first brake to lock the radial position of the first armature with respect to the actuator frame and a second brake to lock the radial position of the second armature with respect to the actuator frame.  
   
   
       10 - 19 . (canceled)  
   
   
       20 . A linear actuator comprising: 
 an actuator frame having a central reference frame fixed thereto;    a first rotary actuator having a fixed portion that is fixed to the central reference frame, and a radially-movable portion;    a second rotary actuator having a fixed portion that is fixed to the central reference frame, and a radially-movable portion;    a first cylinder threadably engaged with the radially-movable portion of the first rotary actuator; and    a second cylinder threadably engaged with the radially-movable portion of the second rotary actuator.    
   
   
       21 . The actuator of  claim 20  wherein the first and second cylinders interact with the radially-movable portions of the rotary actuators through acme threads.  
   
   
       22 . The actuator of  claim 20  wherein the first and second cylinders interact with the radially-movable portions of the rotary actuators through ball screws.  
   
   
       23 . The actuator of  claim 20  wherein the first and second cylinders interact with the radially-movable portions of the rotary actuators through roller screws.  
   
   
       24 . The actuator of  claim 20  wherein the central reference frame has a first side and a second side opposite the first side, and wherein the first actuator is disposed on the first side and the second actuator is disposed on the second side.  
   
   
       25 . The actuator of  claim 23  wherein the first cylinder is disposed on the first side and the second cylinder is disposed on the second side.  
   
   
       26 . The actuator of  claim 20  wherein the first and second cylinders have a rectangular outer cross-section.  
   
   
       27 . The actuator of  claim 20  wherein the first and second cylinders are axially-movable and radially-fixed with respect to the central reference frame.  
   
   
       28 . The actuator of  claim 20  further comprising an external rectangular frame fixed to the central reference frame.  
   
   
       29 . The actuator of  claim 28  wherein the first and second cylinders are suspended in the external rectangular frame by a set of roller bearings.  
   
   
       30 - 39 . (canceled)  
   
   
       40 . A linear actuator comprising: 
 a substantially-cylindrical actuator frame having a principal axis, an electromagnetic field therein, and an internal surface having a thread disposed thereon;    a linear output screw having threads disposed thereon, the linear output screw disposed at least partly within the actuator frame along the principal axis;    a first armature disposed within the actuator frame about the principal axis;    a first spindle screw set, having threads mated to the threads of the linear output screw, disposed in a first carrier about the linear output screw;    a first geartrain, disposed between the first armature and the first carrier, connecting the first armature and the first carrier in such a manner as to maintain a fixed ratio between the angular velocity of the first armature with respect to the actuator frame and the angular velocity of the first carrier with respect to the actuator frame;    a second armature disposed within the actuator frame about the principal axis; and    a second spindle screw set, having threads mated to the internal threads of the actuator frame, disposed in a second carrier about the linear output screw; and    a second geartrain, disposed between the second armature and the second carrier, connecting the second armature and the second carrier in such a manner as to maintain a fixed ratio between the angular velocity of the second armature with respect to the actuator frame and the angular velocity of the second carrier with respect to the actuator frame.    
   
   
       41 . The actuator of  claim 40  further comprising a first field coil cylinder axially aligned with the first armature and a second field coil cylinder axially aligned with the second armature.  
   
   
       42 . The actuator of  claim 41  wherein the first and second field coil cylinders are disposed in a movable carriage.  
   
   
       43 . The actuator of  claim 42  wherein the movable carriage is axially-movable with respect to the actuator frame, but is radially-fixed with respect to the actuator frame.  
   
   
       44 . The actuator of  claim 43  wherein the movable carriage comprises a set of bearings for supporting the first and second geartrains.  
   
   
       45 . The actuator of  claim 44  further comprising a movable carriage axially-movable with respect to the actuator frame, but radially-fixed with respect to the actuator frame.  
   
   
       46 . The actuator of  claim 45  wherein the first planetary spindle screw set is axially-fixed within the first carrier but radially-movable, and wherein the second planetary spindle screw set is axially-fixed within the second carrier but radially-movable.  
   
   
       47 . The actuator of  claim 40  further comprising a set of sensors for constantly monitoring the torque output of each armature.  
   
   
       48 . The actuator of  claim 40  wherein the first set of planetary spindle screws are disposed at a first axial location along the linear output screw and the second set of planetary spindle screws are disposed at a second axial location along the linear output screw.  
   
   
       49 . The actuator of  claim 40  further comprising a first brake to lock the radial position of the first armature with respect to the carriage and a second brake to lock the radial position of the second armature with respect to the carriage.