Abstract:
A linear actuation system has two linear actuator channels acting in tandem and a gear housing connecting the two actuator channels and providing an output for the actuation system. The gear housing has multiples gears with at least one gear connected to each actuator and is movable.

Description:
BACKGROUND 
       [0001]    The present application is directed toward a linear actuation system and more specifically toward a velocity summing linear actuator. 
         [0002]    Linear actuation systems are used in a variety of applications requiring pushing or pulling. In a simple linear actuation system, a rotary motion is generated using an electric or hydraulic motor, and the rotary motion is then converted into linear motion via the use of a screw assembly. Various technologies exist for the screw assembly including Acme or lead screws, ball screws, and roller screws. The present application can be applied using any of these technologies; for simplicity “screw assembly” will be used to describe the application of one of these technologies. In such a system, linear translation is achieved when relative rotation is generated between the screw shaft and nut of the screw assembly. The threads force the nut to move along the screw assembly in a direction depending on the direction of rotation and the direction of the threading. 
         [0003]    In certain applications it can be critical to have a linear actuator remain functional after a component failure. In these applications, it is known to use a redundant linear actuation system where the system includes redundant components. Often the redundancy is focused on the motor, sensors, and brake (when used). 
       SUMMARY 
       [0004]    Disclosed is a redundant linear actuation system with a primary and a secondary channel. Each of the channels has a motor which is connected to a first output component. The first output components of each channel are further connected to a second output component. Each channel additionally has a brake which is operable to prevent rotational movement of the motors. Each of the second output components is connected to a sleeve. Each of the sleeves is connected into a movable gear housing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The disclosure can be further understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
           [0006]      FIG. 1  is a schematic illustration of a prior art, single channel, linear actuator. 
           [0007]      FIG. 2  is another schematic illustration of a prior art, dual channel, linear actuator. 
           [0008]      FIG. 3  is another schematic illustration of a prior art, dual channel, velocity summing linear actuator. 
           [0009]      FIG. 4  is a schematic illustration of a first example of a dual channel velocity summing linear actuator. 
           [0010]      FIG. 5  is a schematic illustration of a second example of a dual channel velocity summing linear actuator. 
           [0011]      FIG. 6  is a schematic illustration of a third example of a dual channel velocity summing linear actuator. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]      FIG. 1  illustrates a prior art linear actuator  10 . The prior art linear actuator has an electric motor  12  coupled magnetically to a motor shaft  40 , which is attached to a screw shaft  16 . The screw shaft  16  has a threaded nut  14  connected to it. A brake  26 , is coupled to the motor shaft  40 . The nut  14  is movable along the screw shaft  16 . The nut  14  is also attached to a sleeve  28  which is incapable of rotation due to an anti-rotation device  22 . The sleeve  28  transfers motion of the nut  14  to an output  20  which can be connected to a component  30  which needs to be precisely pushed or pulled. 
         [0013]    The linear actuator  10  operates such that when the motor  12  is energized it rotates the motor shaft  40  and causes the screw shaft  16  to rotate. This arrangement causes the nut  14  and the attached sleeve  28  to move along the screw shaft  14  either extending or retracting the output  20  depending on the direction of motor rotation. A brake  26  may be operated to lock the motor shaft  40  in place, thereby preventing screw shaft  16 , the nut  14  and sleeve  28  from moving when the motor is unpowered. The brake  26  and the motor  12  are controlled by an external controller (not pictured). 
         [0014]    Certain linear actuation applications require the actuator to be able to move at all times, even with the failure of certain components. One prior art linear actuation system  100  used to address this condition is illustrated in  FIG. 2 . The linear actuator  100  employs an electrically redundant two channel actuator. The actuator  100  operates such that when either the primary motor  112  or secondary motor  113  are powered it causes a common motor shaft  140  to rotate. The rotation of the motor shaft  140  causes the screw shaft  116  to rotate. This arrangement causes the nut  114  and the attached sleeve  128  to move along the screw shaft  114  either extending or retracting the output  120  depending on the direction of motor rotation. A brake  126  may be operated to lock the motor shaft  140  in place, thereby preventing screw shaft  116 , the nut  114  and sleeve  128  from moving when the motor is unpowered. The brake  126  and the motor  112  are controlled by an external controller (not pictured). 
         [0015]    In the system of  FIG. 2 , if the primary motor  112  fails, the secondary motor  113  is power instead and the actuator continues functioning normally. The non-powered motor will still be rotating causing the motor  112  to act as a generator and generate electrical power which is transmitted back into a control system. The generated electrical power is undesirable. 
         [0016]      FIG. 3  illustrates a prior art dual channel velocity summing linear actuation system  200 . The actuator  200  has a primary motor  212  coupled with primary motor shaft  240 . A primary brake  226  is coupled to the primary motor shaft  240 . The actuator  200  also has a secondary motor magnetic  213  coupled with secondary motor shaft  241 . A secondary brake  227  is coupled to the secondary motor shaft  241 . The primary motor shaft  240  and secondary motor shaft  242  are both coupled to a velocity summing gearbox  250 . The velocity summing gearbox is also coupled to a screw shaft  216  such that the screw shaft  216  is rotated at a speed equal to the speed of the primary motor shaft  240  plus the speed of the secondary motor shaft  242 . The rotation of the screw shaft  216  causes the nut  214  and the attached sleeve  228  to move along the screw shaft  216  either extending or retracting the output  220  depending on the of sum of the primary motor shaft  240  and secondary motor shaft  241  rotation. The primary motor  212 , primary brake  226 , secondary motor  213  and secondary brake  227  brake are controlled by an external controller (not pictured). 
         [0017]    Under normal operation of the system in  FIG. 3  the primary brake  226  is released and the primary motor  212  is energized, causing the primary motor shaft  240  to rotate. The secondary brake  227  is engaged and the secondary motor  213  is unpowered causing the secondary motor shaft  241  to remain zero speed. The state of the primary motor shaft  240  and secondary motor shaft  242  cause the velocity summing gearbox  250  to rotate the screw shaft  216  at a speed equal to the speed of the primary motor shaft  240 . If the primary motor  212  fails the primary brake  226  is engaged preventing the primary motor  240  from spinning. The secondary brake  227  is then released and the secondary motor  213  is energized causing the secondary motor shaft  241  to rotate. The state of the primary motor shaft  240  and secondary motor shaft  242  causes the velocity summing gearbox  250  to rotate the screw shaft  216  at a speed equal to the speed of the secondary motor shaft  250 , allowing the actuator  200  to continue operation with the failed primary motor  212 . The actuator  200  still requires use of an anti-rotation feature  222 , which reduces performance of the system. The reduction in performance is undesirable. 
         [0018]      FIG. 4  illustrates a dual channel velocity summing linear actuation system  300 . A primary and secondary channel exist each with a motor  312 ,  313 , brake  326 ,  327 , motor shaft  340 ,  341 , screw shaft  316 ,  317 , nut  314 ,  315 , and sleeve  328 ,  329  arranged in a similar configuration as in the prior art example of  FIG. 1 . In the example of  FIG. 4 , however, the sleeve  328 ,  329  is not held in place with an anti-rotation device and is capable of rotating. Additionally the nuts  314 ,  315  are connected to the sleeves  328 ,  329  and can rotate. Also included in the example of  FIG. 3  is a gear housing  350  connecting the two sleeves  328 ,  329  and the output  320 . Each of the sleeves  328 ,  329  is coupled to a gear  352 ,  353  within the gear housing  350  and allows rotation of one sleeve  328  to be translated to the other sleeve  329  and visa-versa under specific conditions. An idler gear  356  connects the gears  352 ,  353  together to allow for the translation of rotation between sleeves  328 ,  329 . The primary screw assembly (screw shaft  316  and nut  314 ) and secondary screw assembly (screw shaft  317  and nut  315 ) are threaded in opposite directions. 
         [0019]    When both channels are functioning and the primary and secondary motor shafts  340 ,  341  are rotating at the same speed, the gears  352 ,  353 ,  356  in the gear housing  350  allow axial movement of the sleeves  328 ,  329  without rotating. Thus the nuts  314 ,  315  do not rotate either. This allows the full rotation of the screw shafts  316 ,  317  to be translated into linear movement of the nuts  314 ,  315 , sleeves,  328 ,  329 , gear housing  350 , and output  320  along the screw shafts  316 ,  317 . Output  320  can be connected to an object  330  which needs to be precisely pushed or pulled, thereby allowing the actuation system  300  to fully control the motion of the object. 
         [0020]    In the example linear actuation system  300  illustrated in  FIG. 4  when one of the channels fails, the actuator can remain functional. If the primary motor magnetic  312  fails then the corresponding brake  326  is applied, thereby preventing the motor shaft  340  and screw shaft  316  from rotating. When the screw shaft  316  on the non-functioning channel stops rotating, the gears  352 ,  353  and  356  allow both nuts  314 ,  315  to rotate due to the rotation of the secondary screw shaft  317 . The nut  315  on the secondary channel will begin rotating with the threads of the corresponding screw shaft  317  at half the speed of the screw shaft  317  rotation. The rotation of the nut  315  and the sleeve  329  is then transmitted through the gear housing  350  to the sleeve  328  corresponding to the non-functioning channel. By driving the secondary motor shaft  341  at twice the speed it was running before the failure, the actuator can operate with the failed motor  312 . 
         [0021]    The sleeve  328  and the nut  314  of the primary channel are caused by the gearing  352 ,  353 ,  356  to rotate in the same direction as the sleeve  329  and nut  315  at the same rotational speed. The primary screw assembly (screw shaft  316  and nut  314 ) and secondary screw assembly (screw shaft  317  and nut  315 ) are threaded in opposite directions, which results in the nut  314  and sleeve  328  of the primary channel moving along the screw shaft  316  at the same rate of speed, in the same direction, and with the same force as the secondary channel. A failure of the secondary motor  313  instead of the primary motor  312  results in similar operation 
         [0022]      FIG. 5  illustrates another example linear actuation system. The example of  FIG. 5  utilizes a similar configuration to the example of  FIG. 4  with two differences. First, the primary screw assembly (screw shaft  416  and nut  414 ) and secondary screw assembly (screw shaft  417  and nut  415 ) are threaded in the same direction. The second difference is the gearing  452 ,  453  contained within the gear housing  450 . The gearing  452 ,  453  of the example of  FIG. 5 , does not include an idler gear, and is configured in such a way that when the nut  414  or  415  on the functioning channel rotates, the nut  415  or  414  on the non-functioning channel is rotated as well, but in the opposite direction. Since the primary screw assembly (screw shaft  416  and nut  414 ) and secondary screw assembly (screw shaft  417  and nut  415 ) are threaded in the same direction the gearing  452 ,  453  is configured to translate rotational movement of the nut  414  or  415  on the functioning channel into rotational movement of the nut  415  or  414  on the non-functioning channel in the opposite direction. This achieves the same affect as described above with regards to the rotation of the nuts  414  and  415  in  FIG. 4  when one channel is in a failed state. 
         [0023]      FIG. 6  illustrates another example actuation system  500 . The motor shafts  540 ,  541  are connected to the screw shafts  516 ,  517  through a gear set  560 ,  561 . The gear set  560 ,  561  allows the linear actuation system  500  to have different physical dimensions, while retaining all the functionality described above with regards to the example of  FIG. 4 . The example of  FIG. 6  can be used in any application where the length of the actuation system is a factor or where specific dimensions are required. 
         [0024]    Although preferred embodiments have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.