Abstract:
A fault-tolerant actuator module, in a single containment shell, containing two actuator subsystems that are either asymmetrically or symmetrically laid out is provided. Fault tolerance in the actuators of the present invention is achieved by the employment of dual sets of equal resources. Dual resources are integrated into single modules, with each having the external appearance and functionality of a single set of resources.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/411,979, filed Sep. 19, 2002. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002] The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of DE-FG04-94EW37966 awarded by the U.S. Department of Energy and N00014-01-10864 awarded by the Office of Naval Research. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0003]    The present invention relates generally to rotary actuators and more specifically to rotary actuators having improved fault-tolerance.  
           [0004]    Rotary actuators are the most common drivers of our machines. The partial or complete failure of an actuator can cause a life threatening accident, result in costly downtime, or prevent the continuation of a critical long-duration process, such as micro-surgery. In certain applications, it is crucial that the actuator continue to function even in the event of a fault or failure in the system. Such a fault might occur, for example, in the electronics, wiring, sensors, prime mover, or gear train of the system.  
           [0005]    Continued operation under a fault is especially desirable where long-duration missions are involved, where human life is at stake, or where a large economic loss would occur. Fault-tolerant designs have been developed incorporating excess actuators into the system in order to create an excess of inputs, thereby creating a redundant system. In such systems, this redundancy then necessitates that a huge number of decisions must be made in real time at the system level in order to get the whole system to reliably produce a desired output motion or force. Owing to inherent resulting output uncertainty, this approach is still largely a laboratory approach that is rarely used in industrial production systems.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention solves many problems associated with current fault-tolerant designs and overcomes problems associated with current approaches, development of redundant systems and output uncertainties.  
           [0007]    In certain embodiments, the present invention is a fully integrated actuator module, in a completely concentric arrangement in a single containment shell, containing two equal actuator subsystems that are either asymmetrically or symmetrically laid out. Both symmetric and asymmetric embodiments are described in detail herein.  
           [0008]    Fault tolerance in the actuators of the present invention is achieved by the employment of dual sets of equal resources. In the embodiments described herein, dual resources are integrated into single modules, with each having the external appearance and functionality of a single set of resources.  
           [0009]    In certain embodiments disclosed herein, the actuators employ a force-summing architecture wherein the dual output velocities are the same but the dual equal forces are summed to double the output load capacity. Should one side completely fail, then a clutch on that side would be disengaged to take that side out of action, leaving the other side to operate to return the system to home base in a ‘limp home’ mode, after which maintenance by module replacement can occur.  
           [0010]    In other embodiments, the actuators employ a velocity-summing architecture wherein the velocities are summed, but the maximum torque output is limited to the torque output from each individual actuator. In these embodiments, should one side completely fail, then a clutch would be engaged on that side to lock that side in place and take that side out of action, leaving the other side to operate the system.  
           [0011]    In one embodiment, the present invention is a rotary actuator having a fixed structure, with first and second prime movers attached to the fixed structure. The first prime mover has a first portion fixed to the fixed structure, and a second portion rotationally movable with respect to the first portion. The second prime mover has a first portion fixed to the fixed structure, and a second portion rotationally movable with respect to the first portion. The actuator incorporates a first gearset having an input portion connected to the second portion of the first prime mover and an output portion, as well as a second gearset having an input connected to the second portion of the second prime mover and an output portion. The actuator incorporates a first clutch having an input portion connected to the output portion of the first gearset and an output portion, and a second clutch having an input portion connected to the output portion of the second gearset and an output portion. The actuator incorporates dual equal outputs. A first actuator output is rotationally fixed to the output portion of the first clutch, and a second actuator output is rotationally fixed to the output portion of the second clutch.  
           [0012]    In a second embodiment, the present invention is a rotary actuator having a fixed structure having first and second prime movers attached thereto. The first prime mover has a first portion fixed to the fixed structure, and a second portion rotationally movable with respect to the first portion. The second prime mover also has a first portion fixed to the fixed structure, and a second portion rotationally movable with respect to the first portion. A first gearset has an input portion connected to the second portion of the first prime mover and an output portion. A second gearset has an input connected to the second portion of the second prime mover and an output portion. A first clutch has an input portion connected to the output portion of the first gearset and an output portion. A second clutch has an input portion connected to the output portion of the second gearset and an output portion. An actuator output is rotationally fixed to the output portion of the first clutch and the output portion of the second clutch.  
           [0013]    Those skilled in the art will further appreciate the above-noted features and advantages of the invention together with other important aspects thereof. Upon reading the detailed description which follows in conjunction with the drawings.  
       
    
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS  
       [0014]    For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which:  
         [0015]    [0015]FIG. 1A is a three-dimensional section view of a first embodiment of a rotary actuator in accordance with the present invention;  
         [0016]    [0016]FIG. 1B is a three-dimensional section view of the prime mover section of the rotary actuator of FIG. 1A;  
         [0017]    [0017]FIG. 1C is a three-dimensional section view of the gear train section of the rotary actuator of FIG. 1A;  
         [0018]    [0018]FIG. 1D is a three-dimensional section view of the output section of the rotary actuator of FIG. 1A;  
         [0019]    [0019]FIG. 2A is a three-dimensional section view of a second embodiment of a rotary actuator in accordance with the present invention;  
         [0020]    [0020]FIG. 2B is a three-dimensional section view of the first prime mover section of the rotary actuator of FIG. 2A;  
         [0021]    [0021]FIG. 2C is a three-dimensional section view of the second prime mover section of the rotary actuator of FIG. 2A; and  
         [0022]    [0022]FIG. 3 is another view of a rotary actuator in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    Although making and using various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many inventive concepts that may be embodied in a wide variety of contexts. The specific aspects and embodiments discussed herein are merely illustrative of ways to make and use the invention, and do not limit the scope of the invention.  
         [0024]    In the description which follows like parts are marked throughout the specification and drawing with the same reference numerals, respectively. The drawing figures are not necessarily to scale and certain features may be shown exaggerated in scale or in somewhat generalized or schematic form in the interest of clarity and conciseness.  
         [0025]    [0025]FIG. 1A is a three-dimensional section view of a first embodiment of a rotary actuator  100  in accordance with the present invention. FIG. 1B is a three-dimensional section view of the prime mover section of the rotary actuator  100  of FIG. 1A. FIG. 1C is a three-dimensional section view of a representative gear train section of the rotary actuator  100  of FIG. 1A. FIG. 1D is a three-dimensional section view of the output section of the rotary actuator  100  of FIG. 1A.  
         [0026]    In actuator  100 , duality is achieved by summing the equal prime mover forces against output plate  106  through a pair of geared transmissions. Prime mover  110  drives gear train  104  to create a torque on the output attachment plate through clutch  114 . Similarly, prime mover  102  drives gear train  112  to create a torque on the output attachment plate  106  through clutch  108 . Should the subsystem incorporating prime mover  102  and gear train  112  fail, then clutch  108  would be energized to take that subsystem out of service. In this case, the remaining subsystem would either carry 50% of the required output, which may be entirely adequate for most operations, or it could be peaked up past its normal performance level for a short period until the system could be taken down for maintenance. In certain embodiments, prime movers  102  and  110  exhibit substantially identical performance characteristics. In other words, prime movers  102  and  110  are able to generate substantially identical torque output, and operate across a similar range of speeds.  
         [0027]    Output plate  106  contains a torque sensor  116 . Output plate  106  is separated from the input attachment  118  by principal bearing  120 . As described above, output plate  106  is connected to the input drive systems by clutches  108  and  114 . Clutch  114  is driven by sun gear  122 , supported by bearings  124  and bull gear  126 . Bull gear  126  is meshed with planet gear set  128  supported by bearings  124  and held in place by planet cage  132 . Planet cage  132  is driven by armature  134  and supported by bearings  136 .  
         [0028]    The fixed motor field  138  operates on armature  134 . Fields  138  and  140  are fixed to the rigid fixed structure  142  attached to the outer shell  146  of the actuator  100  through end cap screws  144 . Rigid fixed structure  142  also employs screws  148  to fix the stationary shaft  150 , which supports bearings  152  for armature  154 . Armature  154  is also supported by bearing  156  and planet cage  158 , using bearings  160  to support planet gear set  162 . Planet gear set  162 , in turn, meshes with the stationary bull gear  164  and sun gear  166 , supported by bearings  170 . Sun gear  166  then drives the output plate  106  through clutch  108 .  
         [0029]    Auxiliary bearing  172  gives further support to the output plate  106  from the stationary shaft  150 . A similar set of auxiliary bearings  174  are used to provide mutual support between the planet gear cages  158  and  132 . The result is that two prime mover-transmission subsystems create independent torques on output plate  106  through clutches  108  and  114 .  
         [0030]    This system incorporates no single point failure, since it can still operate even under a total, or partial, failure of 50% of the actuator&#39;s resources. This system can be described as being reconfigurable in the level of force to be supplied by each prime mover to the output. Where force balancing between the two equal subsystems may be achieved in real time, this actuator may perform at an even higher level of performance.  
         [0031]    Actuator  100  employs a certain geartrain architecture, but it will be understood by those of skill in the art that a number of geartrain geometries and architectures would be operable in the present invention without departing from the spirit and scope of the present invention. Additionally, while actuator  100  employs a pair of fixed fields and rotating armatures in concentric arrangement, nothing within the spirit and scope of the present invention requires this geometry. In alternate embodiments, the armatures could be fixed, or could be disposed adjacent to the fields in a pancake arrangement.  
         [0032]    Actuator  100  described above provides a high level of performance in a short, space-efficient package having a relatively small outer diameter. Certain rotary actuator applications may occur where there is a need for the diameter of the actuator to be minimized while the length of the actuator is not critical. This is the case, for example, for trim tabs for water vanes on ships or ailerons on aircraft.  
         [0033]    Since length is not critical, then two symmetrically placed mirror image actuators, or prime mover transmissions, can be combined in a long cylindrical shell. FIG. 2A is a three-dimensional section view of a second embodiment of a rotary actuator  200  having a symmetrical geometry in accordance with the present invention. FIG. 2B is a three-dimensional section view of the first prime mover and gear train section of the rotary actuator  200  of FIG. 2A. FIG. 2C is a three-dimensional section view of the second prime mover and gear train section of the rotary actuator  200  of FIG. 2A.  
         [0034]    FIGS.  2 A- 2 C provide a detailed graphical representation of a dual symmetric torque summing fault tolerant rotary actuator  200 . FIG. 2A shows the general layout of rotary actuator  200  wherein two prime movers each drive a gear train, each of which drives an output attachment plate through a torque sensor and a clutch.  
         [0035]    As seen in FIGS.  2 A- 2 D, motor fields  202  and  204  interact with armatures  206  and  208  to drive planet gear cages  210  and  212 . Planet gear cages  210  and  212  are supported by needle bearings  214  and  216 , and carry planet gear sets  218  and  220  in bearings  222  and  224  on shafts  226  and  228 .  
         [0036]    The planet gear sets  218  and  220  mesh with the stationary bull gears  230  and  232  and rotating sun gears  234  and  236 . The bull gears  230  and  232  are rigidly attached to the outer shells  238  and  240  of the actuator  200 . The sun gears  234  and  236  are rigidly attached to the output attachment plates  242  and  244 . The bull gears  230  and  232  and sun gears  234  and  236  are separated by the principal bearings  246  and  248 , which also act as the bearings of the joint of which this actuator  200  is a part.  
         [0037]    The output attachment plates  242  and  244  incorporate torque sensors  250  and  252  and release clutches  254  and  256 . The shell is assembled in two halves using assembly screws  258  with a fixed structure  260  in the center that also holds the centering shaft  266  of the actuator  200 , holding support bearings  262  and  264 .  
         [0038]    The output attachments shown are configured for yokes. Other geometries are possible wherein attachments are molded into the shell or as axial extensions to the face of the output plates. This latter arrangement would make the assembly longer and slimmer, which is useful as an actuator for a water vane trim tab for a ship or an aileron for an airplane. The yoke arrangement shown would be useful as an elbow in a robot manipulator or similar device.  
         [0039]    A third embodiment of a rotary actuator  300  according to the present invention is shown in FIG. 3. The central axis of actuator  300  is the center line of the output shaft  302 . The two independent prime movers are permanent magnet disks  304  and  306  that rotate about the center line supported by bearings  308  and  310  supported directly by the actuator shell  312 . The stationary magnetic fields  314  are rigidly held by the outer walls of the actuator  300  and are independently controlled by a power supply module. In one embodiment, actuator  300  may employ a power supply module provided by Silicon Power Corporation of Eaton, Pa. Another suitable power supply module is manufactured by ARM Automation, Inc. of Austin, Tex.  
         [0040]    Each of the prime mover magnet disks  304  and  306  drives a radial gear  316 , which is meshed with differential gears  318  supported by bearings  320  and  322  in cage  324 , which rotates about the major center line of the actuator module  300 . The differential gears  318  will be stationary relative to magnet disks  304  and  306  if they rotate at the same speed, or produce the same torque. Otherwise, just as in an automobile drive train, the differential gears  318  will rotate to accommodate this difference in velocity.  
         [0041]    Where there is a speed difference between magnet disk  304  and magnet disk  306 , the differential gears  318  will drive the cage  324  at the average of the angular velocities of disks  304  and  306 . Cage  324  contains the planet gears  326  and  328 , which are rigidly connected to each other and supported on the ends by bearing  10  all held by the cage  324 . Cage  324  is the central structural element in actuator  300 .  
         [0042]    The section holding the race for bearing  330  and bearings  332  is assembled from machined sections. There may be four differential gears and up to eight planetary gears  326  and  328  held by the cage  324  which is supported by bearings  334  as well as bearing  330 .  
         [0043]    The planet gears  328  drive a sun gear  336 , which is machined into shaft  302 . Planet gears  326  roll over a stationary bull gear  338 . This stationary bull gear  338  is rigidly bolted to the actuator shell  312  with benefit of a centering boss to accurately locate it on the main center line of actuator  300 .  
         [0044]    Additional objects, advantages and novel features of the invention as set forth in the description, will be apparent to one skilled in the art after reading the foregoing detailed description or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instruments and combinations particularly pointed out here.