Abstract:
Improved circular force generator devices ( 100 ), systems, and methods for use in an active vibration control system are disclosed. The present subject matter can include improved rotary actuator devices, systems, and methods in which a center shaft ( 120 ) is positioned in a fixed relationship with respect to a component housing ( 114 ). At least one movable body can be positioned in the component housing and rotatably coupled to the center shaft by a radial bearing ( 130 ), the at least one movable body comprising a motor ( 110 ) and at least one eccentric mass ( 150 ). With this configuration, the motor can be configured to cause rotation of the movable body about the center shaft to produce a rotating force with a controllable rotating force magnitude and a controllable rotating force phase.

Description:
PRIORITY CLAIM 
       [0001]    The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/173,148, filed Dec. 12, 2012, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The subject matter disclosed herein relates to devices, systems, and methods for controlling problematic vehicle vibrations. More particularly, the subject matter disclosed herein relates to methods and systems for controlling helicopter and/or fixed wing vehicle vibrations and/or noise, particularly methods and systems for canceling problematic rotating helicopter vibrations. 
       BACKGROUND 
       [0003]    Helicopter vibrations are particularly troublesome in that they can cause fatigue and wear on the equipment and occupants in the aircraft. In vehicles such as helicopters, vibrations are particularly problematic in that they can damage the actual structure and components that make up the vehicle in addition to the contents of the vehicle. 
         [0004]    There is a need for a system and method of accurately and economically canceling rotating vehicle vibrations, accurately controlling rotary wing vibrations in a weight efficient manner, controlling vibrations in a helicopter hub so that the vibrations are efficiently minimized, and/or controlling problematic helicopter vibrations. 
       SUMMARY 
       [0005]    In accordance with this disclosure, improved rotary actuator devices, systems, and methods are provided in which a center shaft is positioned in a fixed relationship with respect to a component housing. At least one movable body can be positioned in the component housing and rotatably coupled to the center shaft by a bearing, the at least one movable body comprising a motor rotor and at least one eccentric mass. With this configuration, the motor can be configured to cause rotation of the movable body about the center shaft to produce a rotating force with a rotating force magnitude and a controllable rotating force phase. 
         [0006]    In another aspect, a method of active vibration control can comprise rotating at least one movable body about a center shaft positioned in a fixed relationship with respect to a component housing, the at least one movable body being rotatably coupled to the center shaft by a bearing, and the at least one movable body comprising at least one eccentric mass, wherein rotating the at least one movable body produces a rotating force. The method can further comprise controlling at least one of a rotating force magnitude and a rotating force phase of the rotating force. 
         [0007]    Although some of the aspects of the subject matter disclosed herein have been stated hereinabove, and which are achieved in whole or in part by the presently disclosed subject matter, other aspects will become evident as the description proceeds when taken in connection with the accompanying drawings as best described hereinbelow. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1A  is a graph illustrating a relationship between the bore diameter of a bearing of a circular force generator and the power required for operation of the circular force generator. 
           [0009]      FIG. 1B  is a graph illustrating a relationship between the frequency of operation of a circular force generator and the power required for operation. 
           [0010]      FIG. 2  is a sectional side view illustrating a circular force generator according to an embodiment of the presently disclosed subject matter. 
           [0011]      FIG. 3  is an exploded perspective view illustrating a circular force generator according to an embodiment of the presently disclosed subject matter. 
           [0012]      FIG. 4  is a partially-exploded perspective view illustrating a motor of a circular force generator according to an embodiment of the presently disclosed subject matter. 
           [0013]      FIG. 5A  is a graph illustrating the position control error of a conventional circular force generator that uses an encoder. 
           [0014]      FIG. 5B  is a graph illustrating the position control error of a circular force generator using a Hall-effect servo control system according to an embodiment of the presently disclosed subject matter. 
           [0015]      FIGS. 6A-6D  are perspective views illustrating various form factors for circular force generators according to embodiments of the presently disclosed subject matter. 
           [0016]      FIG. 7  is a sectional side view illustrating a circular force generator having integrated control electronics according to an embodiment of the presently disclosed subject matter. 
           [0017]      FIG. 8  is a schematic view illustrating an active vibration control system according to an embodiment of the presently disclosed subject matter. 
           [0018]      FIG. 9  is a schematic model illustrating two masses rotating about a common axis. 
           [0019]      FIG. 10  is a graph illustrating the bi-axial force output of 2 circular force generators (e.g.,  4  rotating masses). 
           [0020]      FIGS. 11A and 11B  are force diagrams for circular force generators having two rotating masses according to embodiments of the presently disclosed subject matter. 
           [0021]      FIG. 12  is a graph illustrating a relationship between force output and moment output for a circular force generator having plural rotating masses according to an embodiment of the presently disclosed subject matter. 
           [0022]      FIG. 13A  is a graph illustrating a relationship between maximum N/rev force and maximum 2nd harmonic force for a circular force generator according to an embodiment of the presently disclosed subject matter. 
           [0023]      FIG. 13B  is a graph illustrating a relationship between maximum N/rev force and maximum residual moment for a circular force generator according to an embodiment of the presently disclosed subject matter. 
           [0024]      FIGS. 14A to 14C  are illustrations of a weight-optimized mass for a circular force generator according to an embodiment of the presently disclosed subject matter. 
           [0025]      FIGS. 15A to 15C  are illustrations of a moment-optimized mass for a circular force generator according to an embodiment of the presently disclosed subject matter. 
           [0026]      FIG. 16  shows a block diagram of a motor control gravity compensation that uses the vertical acceleration at the base of the circular force generator to reduce the force distortion at the second harmonic according to an embodiment of the presently disclosed subject matter. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    The present subject matter provides improvement in circular force generators (CFGs) for use in an active vibration control system, such as is used to control vibration in a helicopter. The disclosed devices, systems, and methods can entail modifications to both software and hardware to control the CFG and/or to minimize force distortion created by the CFG. These devices, systems, and methods can be implemented in the CFG and can be particularly useful under low force operating conditions where the residual vibration created by the CFG can be larger than the vibration created by the main rotor of the helicopter, which can be undesirable to the customer. Low force is typically less than 30% of the maximum force output of the CFG and on a helicopter active vibration control system can occur during conditions such as hover or at mid-speed flight ranges (e.g. 80-100 kias). 
         [0028]    In a first aspect, the disclosed devices, systems, and methods can involve the use of a CFG having a bearing (e.g., a ball bearing or other rolling-element bearing) with a diameter that can be comparatively smaller than that of a conventional CFG. Large diameter bearings were used in the past partially due to the sensing technology (centerline encoder), which did not allow for a center shaft with small diameter bearing. Specifically, for example, whereas conventional CFGs can have a bearing diameter of about 150 mm, a CFG according to the present subject matter can be configured to have a bearing diameter of about 15 mm. The reduced bearing diameter can result in a reduced ball speed during operation at a given rotational speed compared to conventional systems, thereby lowering power requirements. (See, e.g.,  FIG. 1A ) Furthermore, as shown in  FIG. 1B , even when the frequency of operation is increased, the power required for such operation can be maintained at a comparatively lower level. 
         [0029]    In a particular configuration shown in  FIGS. 2 and 3 , for example, a CFG, generally designated  100 , includes a pair of motors  110  each having a stator  112  mounted to endplates  114 . A rotor  116  of each motor  110  is coupled for rotation about a stationary center shaft  120  by a bearing  130  mounted inside the motor  110 . A rotating mass  150  is eccentrically connected to each rotor  116  such that rotation of the rotor  116  about the shaft  120  can generate a “circular” force. 
         [0030]    Each of these elements of such a configuration allows for a comparatively lower profile design. In particular, the size of the bearing  130  provides a number of advantages over conventional CFG configurations. In some aspects, such novel bearings can be press fit on or about portions of a shaft and/or rotor frames to reduce any differential in thermal expansion. Moreover, the shaft, rotor, bearings, and/or portions thereof can be fabricated out of materials having a same or similar coefficient of thermal expansion (CTE). This can be advantageous for both improving wear and reducing fatigue. Such components can each be fabricated from a similar steel material or alloy, a similar aluminum (Al) material or alloy, or any other similar materials or metals having similar CTEs. Bearings, which can be press fit on steel shaft or rotors, improves wear fatigue and allows for smaller internal clearances. The improved bearings can be disposed on or about a centerline shaft. This results in a lowered drag torque, which results in reduced power requirements and a reduced motor size. For example, the CFG  100  having such a configuration operates at a much lower power level as discussed above. In addition, the bearing  130  generates less heat as a result, allowing the CFG  100  to operate in an extended temperature range (e.g., between about −54 to 70° C.). The press fit of bearing onto shaft also produces less noise than current bearings. The increased ratio of the size of the balls within the bearing  130  with respect to the cross sectional dimension further enables a longer operating life for the CFG  100  compared to traditional designs. 
         [0031]    In another aspect, the improved CFG devices, systems, and methods include a high accuracy servo controller  200  that uses a plurality of rotating mass sensors to monitor the rotational position of the rotating mass  150  on the rotor  116  being driven by the motor  110  such that the controller  200  knows the rotational phase position of the rotating mass  150 . For example, the rotating mass sensors can comprise Hall-effect sensors configured for sensing the rotation of a magnetic rotating mass sensor target to provide out through a circuit board  202  to the system controller the rotational position of the rotating mass  150 . In one particular configuration shown in  FIG. 4 , and in addition to one or more standard commutation Hall sensors (e.g., embedded within stator  112 ), an additional 1/rev Hall sensor  160   b  (e.g., mounted on a printed circuit board on top of stator  112 ) can be used for servo control of the CFG  100 . Specifically, 1/rev Hall sensor  160   b  can be configured to precisely monitor the position of rotor  116  based on the position of one or more target magnets  160   a . The configuration shown in  FIG. 4  is but one exemplary arrangement, and the particular number and positioning of the rotating mass sensors can be modified based on a variety of design considerations of the system. 
         [0032]    The accuracy of such a control configuration can be comparable to an encoder or resolver servo controller. As shown in  FIGS. 5A and 5B , the position control error realized when using an encoder (See  FIG. 5A ) is only marginally better than the hall-effect sensor position control error (See  FIG. 5B ). By eliminating the need for an encoder or resolver, however, even if there is a small increase in position control error, that small detriment is offset by the great simplification in the design (e.g., reduce size/cost) and electronics. Furthermore, as discussed above with reference to  FIG. 4 , such a configuration only requires one additional hall sensor (i.e., 1/rev Hall sensor  160   b ), which can be built into the existing motor circuitry. 
         [0033]    A further feature of the disclosed devices, systems, and methods is that, rather than being oil-lubricated, the bearing  130  can be a substantially sealed greased bearing. This feature simplifies lubrication requirements and allows the CFG  100  to be mounted in any orientation, thereby improving flexibility of the system and its ability to match the complex vibration field in the helicopter in an optimal manner. In this regard, as shown in  FIGS. 6A-6D , a modular CFG according to the presently-disclosed subject matter is easily implemented in any of a variety of different form factors. For instance,  FIG. 6A  shows the CFG  100  and the controller  200  being arranged in a stacked configuration with a connector  210  (e.g., a D-sub connector or a D38999 connector) being connected to the controller  200  for communication with the system controller. In this configuration, both a length d 1  (e.g., about 5.4 inches) and a width d 2  (e.g., about 5.4 inches) of the CFG  100  are minimized. This small footprint comes at the expense of a relatively increased height d 3  (e.g., about 4.7 inches) of the CFG  100 , but even in this arrangement, the integrated package is still relatively compact when compared to conventional systems. 
         [0034]    Alternatively,  FIGS. 6B-6C  each show various side-by-side configurations in which the CFG  100  and the controller  200  can be arranged. Each of these exemplary configurations results in a relatively lower-profile design having a reduced height d 3  (e.g., between about 2.5 to 3 inches) compared to the stacked configuration shown in  FIG. 6A , although this reduction in height is offset by an increased length d 1  (e.g., between about 7.1 and 10.5 inches). Those having skill in the art will recognize that the different form factors shown in  FIGS. 6A-6D  can be considered advantageous depending on the specific constraints of a particular mounting location (e.g., size, orientation, access). Furthermore, those having skill in the art will recognize that these exemplary configurations only illustrate four possible implementations, and other configurations can be used depending on these or other particular design considerations. By way of example, controller  200  may be remotely attached to CFG  100  by a cable or conduit. Additionally, controller  200  and CFG  100  may have a modular configuration where controller  200  may be detachable from CFG  100  via a plug, such as aviation quick-connect plugs. The use and positioning of the plug on the CFG is compatible with all configuration discussed herein. 
         [0035]    Taken together, all of the improvements in the presently-disclosed CFG  100  results in a simpler mechanical assembly. For example, whereas previous CFG designs can constitute  18  machined parts, the improved CFG  100  disclosed herein (See, e.g.,  FIG. 3 ) uses significantly fewer machined parts (e.g., as few as 7 parts or fewer). As a result, the compact design allows motor mounting features to be incorporated into the CFG  100 , thereby eliminating the need for separate motor retainers and/or bearing retainers. Further in this regard, the presently disclosed subject CFG  100  has a significantly lower manufacturing cost than previous designs. 
         [0036]    Referring to  FIG. 7 , the design can be made further compact and modular by integrating the drive electronics into the CFG  100 , which can be enabled, at least partially, as a result of the reduced heat generation of the relatively low-power CFG. For example, the controller  200  can be a highly-integrated micro-controller that includes a signal board  202  and a power board  204  that occupy an electronics volume that protrudes only a small distance h e  (e.g., about 1.765 inches or less) from the CFG  100 . Such a configuration allows the controller  200  to operate as a completely stand-alone module, with the module configured to receive high-level digital commands from a small central controller. This modularity of co-located drive electronics enables any number of CFGs to be efficiently implemented. 
         [0037]    Regardless of the specific configuration of the CFG  100 , one or more of CFG  100  can be operated together as part of an active vibration control system.  FIG. 8  illustrates an exemplary configuration for such an active vibration control system having a plurality of CFGs  100  connected to a small central controller  300 . In addition, one or more input devices can further be connected to the central controller  300  to help determine the vibration being experienced. For example, a tachometer  310  that measures the rotor speed of the aircraft in which it is used and one or more accelerometers  320  provide inputs to the central controller  300 . Based on these inputs, each CFG can be controlled to reduce the effect of the measured vibrations on the system. 
         [0038]    The present systems can be configured such that operating power for each CFG  100  can be provided by an unregulated aircraft power source (e.g., about 28 VDC). This low power design enables both the central controller  300  and the CFG drive electronics (i.e., controller  200 ) to run off of an unregulated 28 VDC aircraft supply, which provides a wide range of advantages, such as simplifying design, saving cost, and saving the weight and space that would be required for a separate generator on a smaller aircraft. This low-power capability is helpful in active vibration control systems for smaller aircraft which only have 28 VDC aircraft power available and not the high-voltage systems (e.g., 115 VAC or 270 VAC) that are conventionally required to power the operation of force actuators. 
         [0039]    As a result of the more compact size and modular nature of the improved CFG devices, systems, and methods disclosed herein, multiples of the CFG  100  can be arranged in pairs/arrays and specifically controlled to minimize or otherwise control force distortion created by the CFGs. For example, each CFG can be selectively operated to produce a circular force of varying magnitude and phase. The force of each rotor  116  can be determined by a size (m) of the rotating mass  150 , a distance (r) to a center of the rotating mass  150 , and its angular speed (ω): 
         [0000]        F   0   =mrω   2 , 
         [0040]    With the configuration shown in  FIG. 9 , the total CFG force of two masses (e.g., a first rotating mass  150   a  and a second rotating mass  150   b ) rotating about a common axis are determined by the force of each rotor and their relative phase angles: 
         [0000]    
       
         
           
             
               F 
               CFG 
             
             = 
             
               2 
                
               
                   
               
                
               
                 F 
                 0 
               
                
               
                 cos 
                  
                 
                   ( 
                   
                     
                       
                         ϕ 
                         1 
                       
                       - 
                       
                         ϕ 
                         2 
                       
                     
                     2 
                   
                   ) 
                 
               
             
           
         
       
     
         [0041]    Based on such known relationships, the two imbalanced masses  150   a  and  150   b  can be configured to co-rotate such that the combination of the two generates circular forces acting radially outward. In this way, whereas one CFG produces a circular force, two counter-rotating CFGs mounted side-by-side or back-to-back are configured to produce a bi-linear force. (See, e.g.,  FIG. 10 ). The controlled combination of circular forces from multiple CFGs is used to achieve higher degrees of vibration control. 
         [0042]    Referring to  FIG. 11A , when CFGs are arranged in pairs, the imbalanced masses revolve in distinct parallel planes that are separated by a distance (e.g., r 2 -r 1 ), whereby the opposing force components produce a residual moment (M r ). This residual moment varies inversely with the force output: 
         [0000]    
       
         
           
             
               M 
               r 
             
             = 
             
               
                 
                   r 
                   2 
                 
                 · 
                 
                   F 
                   0 
                 
               
                
               
                 sin 
                  
                 
                   ( 
                   
                     
                       
                         ϕ 
                         1 
                       
                       - 
                       
                         ϕ 
                         2 
                       
                     
                     2 
                   
                   ) 
                 
               
             
           
         
       
     
         [0043]    As illustrated in  FIG. 11B , because the imbalanced masses each typically revolve in planes some distance from a mounting bracket, the total force of the CFGs produces moment about the mounting bracket. This force moment varies linearly with the force output: 
         [0000]    
       
         
           
             
               M 
               f 
             
             = 
             
               
                 ( 
                 
                   
                     r 
                     1 
                   
                   + 
                   
                     
                       1 
                       2 
                     
                      
                     
                       r 
                       2 
                     
                   
                 
                 ) 
               
               · 
               
                 F 
                 CFG 
               
             
           
         
       
     
         [0044]    The residual moment and force moment are perpendicular, and the total moment of the CFGs is the vector sum of residual and force moment as shown in  FIG. 12 : 
         [0000]        M   CFG =√{square root over ( M   r   2   +M   f   2 )}
 
         [0045]    Residual moments can further be minimized by reducing the distance (e.g., r 2 ) between the center of mass of the two imbalanced masses. Another approach to reduce the residual moment is to change the inertia (J) of the rotating (movable) imbalance. By increasing the inertia (J), the residual moment is decreased. 
         [0046]    In another exemplary implementation, when a CFG is mounted vertically, gravity accelerates and decelerates the imbalanced masses as they revolve: 
         [0000]    
       
         
           
             ω 
             = 
             
               
                 
                   ( 
                   
                     mrg 
                     
                       J 
                        
                       
                           
                       
                        
                       
                         ω 
                         0 
                       
                     
                   
                   ) 
                 
                  
                 
                   sin 
                    
                   
                     ( 
                     
                       
                         
                           ω 
                           0 
                         
                          
                         t 
                       
                       + 
                       ϕ 
                     
                     ) 
                   
                 
               
               + 
               
                 ω 
                 0 
               
             
           
         
       
     
         [0047]    This fluctuation in speed due to gravity creates a force distortion at the second harmonic, which is inversely proportional to angular speed (ω) and rotor inertia (J), proportional to the imbalance authority (mr), and varies with the relative phase angle (φ). The 2nd harmonic distortion can be much more pronounced at low force outputs such that total harmonic distortion (THD) is predominantly due to the 2nd harmonic. 
         [0048]    Referring to  FIG. 13A , the second harmonic force distortion can also be reduced by increasing the inertia of the imbalanced mass, which results in a decrease in the residual moment as well (See, e.g.,  FIG. 13B ). 
         [0049]    In another embodiment, measurement of the acceleration at the base of the CFG is used in the motor control feedback to reduce the second harmonic distortion. For example, one of the one or more accelerometers  320  can be incorporated onto co-located electronics (e.g., integrated with the controller  200 ). As discussed above, this CFG-positioned accelerometer can also be used to control vibration by providing an input to the central controller  300  for determining the vibration to be controlled.  FIG. 16  shows a block diagram of the accelerometer in the motor control. The gravity compensation term for motor control is calculated from the following general equation: 
         [0000]        V   GC   =f (φ, F   cmd   ,a   z )
 
         [0000]    where
       V GC =Gravity compensation for motor control   φ=Rotor position   F cmd =Force command   a z =Vertical acceleration       
 
         [0054]    V GC  can be implemented as analytical function or table look-up. One exemplary form of the above function for voltage motor control is as follows. 
         [0000]        V   GC   =A   GC  sin(φ+ P   GC )· C   F ( F   cmd )· C   a ( a   z )
 
         [0055]    A GC  and P GC  are amplitude gain and phase, respectively, to take dynamics of motor circuit into account. C F (F cmd ) and C a (a z ) are variable coefficients to change the gravity compensation amount with respect to force command and vertical acceleration. C F (F cmd ) and C a (a z ) can be implemented as analytical function or table look-up. Exemplary implementation of C F (F cmd ) and C a (a z ) are presented in the below. 
         [0000]        C   F ( F   cmd )− A   F   F   cmd   +B   F  
 
         [0000]        C   a ( a   z )= A   a   a   z    
         [0000]    where A F , B F , and A a  are tuning parameters. Note that the accelerometer can have additional functionality. 
         [0056]      FIGS. 14A-14C  and  15 A- 15 C show various configurations for the rotating mass  150 . Specifically,  FIGS. 14A-14C  depict the rotating mass  150  in a “weight optimized” configuration in which a center of mass of the rotating mass  150  is spaced at a greatest radius possible relative to the axis of rotation for a given set of system constraints. In this configuration, a substantially equivalent inertia is produced using a rotating mass  150  having a relatively small size. In contrast,  FIGS. 15A-15C  depict the rotating mass  150  in a “moment optimized” or “performance optimized” configuration in which a height h of the rotating mass  150  is reduced (e.g., about 50% of the thickness of the weight optimized mass) such that adjacent CFGs are positioned closer to one another, thereby allowing the distance (e.g., r 2 ) between the center of mass of adjacent imbalanced masses to be minimized as discussed above to help reduce the residual moment. The “moment optimized” mass can have an inertia that is approximately twice that of the “weight optimized” mass even though the CFG with a “moment optimized” mass may only be about 10% heavier than the CFG with a “weight optimized” mass. 
         [0057]    The present subject matter can be embodied in other forms without departure from the spirit and essential characteristics thereof. The embodiments described therefore are to be considered in all respects as illustrative and not restrictive. Although the present subject matter has been described in terms of certain preferred embodiments, other embodiments that are apparent to those of ordinary skill in the art are also within the scope of the present subject matter.