Abstract:
An active vibration control system provides a mass which is movable through a large excursion while minimizing the system size in two of three dimensions to compensate for sensed vibrations. A first rotating member is rotatable about a first axis and a second rotating member is rotatable about a second axis to drive a belt mounting a mass. The first axis is offset from the second axis such that as the members are rotated, the belt is driven about an elongated path. This arrangement generates an impulsive vibratory force as the mass passes over each of the rotating members and quickly changes direction. A belt including a sinusoidal mass distribution generates a vibratory force that is a smooth sinusoidal output. Multiple systems are suitably usable in conjunction with one another to provide a wide range of vibratory outputs.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present application claims priority to U.S. Provisional Patent Application Serial No. 60/271,560, filed Feb. 27, 2001.  
           [0002]    The present invention relates to producing large, controllable, vibratory forces to compensate for sensed noise or vibrations, and more particularly to an active vibration control (AVC) system for an aircraft.  
           [0003]    The dominant source of vibration in a helicopter in forward flight is that generated by the main rotor system rotating at the blade passing frequency. Forces and moments are transmitted usually through the transmission via fuselage attachments, to produce vibration in the fuselage.  
           [0004]    One conventional approach to reducing such vibration involves replacing a rigid gearbox mounting strut with a compliant strut and parallel hydraulic actuator. A control computer commands the actuators such that the gearbox is selectively vibrated to produce inertial forces which minimize fuselage vibrations. Although effective, this approach is inadequate in a vehicle having a gearbox which is directly attached to the airframe i.e., without struts.  
           [0005]    Another conventional approach utilizes counter-rotating eccentric masses that rotate at the frequency of the primary aircraft vibration and generate a fixed magnitude vibration force. A second pair of eccentric masses is phased relative to the first pair to yield any force magnitude from zero to maximum force. This system, although effective for direct gearbox mounting, requires a parasitic mass of considerable magnitude which results in an unacceptable weight penalty. Moreover, this approach does not provide an acceptable reduction in size as the diameter of the circular shaped device is difficult to fit in the confined spaces available in an aircraft.  
           [0006]    Accordingly, it is desirable to provide an active vibration control system which generates relatively large controllable vibratory forces with a lower weight and smaller size than conventional systems.  
         SUMMARY OF THE INVENTION  
         [0007]    The active vibration control (AVC) system according to the present invention provides a mass which is movable through a large excursion while minimizing the system size in two of three dimensions to compensate for sensed vibrations.  
           [0008]    An AVC system according to the present invention includes a first rotating member such as a first pulley which is rotatable about a first axis and a second rotating member such as a second pulley which is rotatable about a second axis. The first axis is offset from the second axis such that as the pulleys are rotated, a belt having a discrete mass attached thereto is driven about an elongated path defined by the pulleys. This arrangement generates an impulsive vibratory force as the mass passes over each of the pulleys and quickly changes direction.  
           [0009]    In another AVC system, a belt includes a sinusoidal mass distribution. This arrangement generates a vibratory force that is a smooth sinusoidal output.  
           [0010]    In another AVC system, a fixed track guides one or more movable mass units about a path defined by a first and second radius. The first radius is defined about a first axis and a second radius is defined about a second axis to form an elongated path. The mass units are movable along the track and relative to each other. Movement of the mass units along the single track generate a desired force output magnitude and phase.  
           [0011]    Adjustable masses such as magneto-rheological fluids may additionally or alternatively be provided to adjust the vibratory output in real time. Moreover, the various AVC systems are suitably usable in conjunction with one another to provide a wide range of force output magnitudes and phases.  
           [0012]    The present invention therefore provides an active vibration control system which generates relatively large controllable vibratory forces while providing weight and size advantages particularly applicable to aircraft. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:  
         [0014]    [0014]FIG. 1 is a general perspective view an exemplary rotary wing aircraft embodiment for use with the present invention;  
         [0015]    [0015]FIG. 2A is a general perspective view of an active vibration control system according to the present invention;  
         [0016]    [0016]FIG. 2B is a graphical representation of a mass distribution for the active vibration control system of FIG. 2A;  
         [0017]    [0017]FIG. 2C is a graphical representation of a force output for the active vibration control system of FIG. 2A;  
         [0018]    [0018]FIG. 2D is a side view of an active vibration control system of FIG. 2A;  
         [0019]    [0019]FIG. 3A is a general perspective view of an active vibration control system according to the present invention;  
         [0020]    [0020]FIG. 3B is a graphical representation of a mass distribution for the active vibration control system of FIG. 3A;  
         [0021]    [0021]FIG. 3C is a graphical representation of a force output for the active vibration control system of FIG. 3A;  
         [0022]    [0022]FIG. 4 is a general perspective view of another active vibration control system according to the present invention;  
         [0023]    [0023]FIG. 5 is a general perspective view of another active vibration control system according to the present invention;  
         [0024]    [0024]FIG. 6A is a general perspective view of another active vibration control system according to the present invention;  
         [0025]    [0025]FIG. 6B is a sectional view taken along the line  6 B- 6 B of FIG. 6A; and  
         [0026]    [0026]FIG. 7 is a general perspective view of another active vibration control system according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0027]    [0027]FIG. 1 schematically illustrates an aircraft  10  having a main rotor assembly  12 . The aircraft  10  includes a fuselage  14  having an extending tail  16  which mounts an anti-torque rotor  18 . Although a particular helicopter configuration is illustrated in the disclosed embodiment, other machines will also benefit from the present invention. The main rotor assembly  12  is driven through a transmission (illustrated schematically at  20 ) by one or more engines  22 . Vibrations from the rotating main rotor assembly  12 , transmission  20 , and the engines  22  are thus transmitted to the helicopter fuselage  14 . This vibration transmission is particularly manifest in rigid gearbox mounted systems.  
         [0028]    An active vibration control (AVC) system  24  is mounted within the fuselage  14  and preferably within a fuselage sidewall. For example, there are several places in an aircraft sidewall that have relatively large heights (waterline) but relatively narrow widths (buttline) and lengths (station) which are particularly appropriate for locating the AVC system  24 .  
         [0029]    A plurality of sensors  26  are mounted at various locations and communicate with a processor  28 . The sensors  26  are preferably mounted in the cockpit or cabin areas adjacent crew or passenger stations. The sensors  26  are preferably accelerometers which generate signals representative of dynamic changes at selected locations as the main rotor assembly  12  rotates. The processor  28  generates output signals to drive a power source  30  which controls the phase and magnitude characteristics of the AVC system  24 .  
         [0030]    In operation, vibratory forces are produced by the main rotor assembly  12  due, for example, to asymmetric air flow in forward flight. Such vibratory forces arising as the main rotor assembly  12  rotates are, in the absence of any compensating systems, transmitted from the rotor  12  to the fuselage  14 . Operation of the AVC system  24  is continuously varied by the processor  28  to cater to changing dynamic characteristics such that vibratory forces are reduced or eliminated.  
         [0031]    Referring to FIG. 2A, an AVC system  24   a  is illustrated. A first rotating member such as a first pulley  32  is rotatable about a first axis  34 . A second rotating member such as a second pulley  36  is rotatable about a second axis  38 . Preferably the power source  30  (also illustrated in FIG. 1) includes an AC or DC power supply or other vehicle power source with sufficient output to rotate pulleys  32 , 36  in a desired manner as directed by the processor  28  (FIG. 1).  
         [0032]    The first axis  34  is offset from the second axis  38  such that an elongated path  40  is formed about the pulleys  32 , 36 . Preferably, a belt  42  or the like is driven by the pulleys  32  and  36 . The belt  42  is rotated when the pulleys  32 , 36  rotate. It should be understood that other elongated members such as chains, hoses, and the like that move the mass along a path will benefit from the present invention. It will be further understood that a fixed track having movable mass members will also benefit from the present invention.  
         [0033]    A discrete mass  44  is mounted to the otherwise uniform belt  42 . The mass distribution is represented by a step function (FIG. 2B). As the pulleys are rotated, the mass  44  travels with the belt  42  along the elongated path  40 . Applying torque to one of the pulleys  32 , 36  propels the belt  42 . This arrangement generates a vibratory force that is impulsive (FIG. 2C). This impulsive force results when the single concentrated mass  44  passes over each of the pulleys  32 , 36  thereby quickly changing direction. During the time the mass  44  traverses between pulleys  32 , 36  the mass  44  is moving with a substantially constant velocity and does not produce a force. It should be understood that by adjusting the radius of the pulleys, the length of the path and the velocity, various forces and phases are achieved.  
         [0034]    A radial guide  46  extends from the pulleys  32 , 36 . Preferably, the guide  46  is a radial extending flange on each side of the pulleys  32 , 36  (FIG. 2D). The guide  46  supports the belt  42  to reduce undesired lateral motion.  
         [0035]    Referring to FIG. 3A, another AVC system  24   b  is illustrated. The FIG. 3A system  24   b  is similar to the FIG. 2A system but produces a sinusoidal output. Pulleys  48 , 50  rotate about a respective first axis  52  and second axis  54  drive a belt  56  along an elongated path  58 . The belt  56  is rotated when the pulleys  48 , 50  rotate as described above. The belt  56  includes a sinusoidal mass distribution (FIG. 3B). The sinusoidal mass distribution is preferably provided by weighting the belt along its length or may additionally or alternatively include a plurality of discrete masses attached to the belt to provide the desired mass distribution (FIG. 3B).  
         [0036]    Applying torque to one of the pulleys  48 , 50  propels the belt  56 . This arrangement generates a vibratory force that is a smooth sinusoidal output (FIG. 3C). Another way to understand the dynamics is to visualize the center of gravity of the belt moving up and down as the belt progresses around the pulleys  48 , 50 . Such a smooth sinusoidal vibratory force output is particularly suitable for the compensation of main rotor rotation vibrations.  
         [0037]    Referring to FIG. 4, another AVC system  24   c  is illustrated. As illustrated in FIG. 4, two of the FIG. 2A systems can be phased relative to each other to produce a variable unidirectional force amplitude and phase. A first system  60  provides a discrete mass  62  affixed to a belt  64 . A first pulley  66  is rotatable about a first axis  68  and a second pulley  70  is rotatable about a second axis  72 . A second system  74  provides a second discrete mass  76  affixed to a second belt  78 . A third pulley  80  is rotatable about a third axis  82  and a fourth pulley  84  is rotatable about a fourth axis  86 . It should be understood that the first axis  68  and third axis  82  and the second axis  72  and fourth axis  86  maybe coaxial. That is, the first system  60  and second system  74  operate about common axes (FIG. 4A). Preferably, the systems  60 , 74  rotate in opposite directions to cancel small off-axis forces.  
         [0038]    Referring to FIG. 5, another AVC system  24   d  is illustrated. As illustrated in FIG. 5, two of the FIG. 3A system can be phased relative to each other to produce a variable unidirectional sinusoidal force amplitude and phase. A first system  88  provides a belt  90  having a sinusoidal mass distribution. A first pulley  92  is rotatable about a first axis  94  and a second pulley  96  is rotatable about a second axis  98 . A second system  100  provides a second belt  102  having a sinusoidal mass distribution. A third pulley  104  is rotatable about a third axis  106  and a fourth pulley  108  is rotatable about a fourth axis  110 . It should be understood that the first axis  94  and third axis  106  and the second axis  98  and fourth axis  110  maybe coaxial. That is, the first system  88  and second system  100  operate about common axes. Preferably, the systems  88 , 100  rotate in opposite directions to cancel small off-axis forces.  
         [0039]    Referring to FIG. 6A, another AVC system  24   e  is illustrated. A first rotating member such as a first pulley  112  is rotatable about a first axis  114 . A second rotating member such as a second pulley  116  is rotatable about a second axis  118 . The first axis  114  is offset from the second axis  118  such that an elongated path  120  is formed about the pulleys  112 ,  116 .  
         [0040]    A belt  122  or the like is driven by the pulleys  112 , 116  along the elongated path  120 . Preferably, corresponding belt teeth  124  along the inner surface of the belt  122  engage pulley teeth  126  on the outer diameter of the pulleys  112 ,  116  to prevent slipping therebetween.  
         [0041]    The belt  122  is rotated within a housing  128 . The belt  122  includes a plurality of fins  130  extending about the outer surface of the belt  122  and in engagement with the housing  128  to form a multiple of cavities  132 . The fins  130  preferably extend past the width of the pulleys  112 ,  116  (FIG. 6B) in sealing relationship with the housing  128 .  
         [0042]    An output  134  in the housing  128  communicates with a magneto-rheological fluid return passage  136  and a magneto-rheological fluid source  138 . Preferably, the output  134  is located in a low portion of the housing  128 . The magneto-rheological fluid passage  136  communicates with an input  140  to the housing  128 . The input  140  is located in a higher portion of the housing  128 . A pump  142  or the like transfers fluid from the source  138  through the input  140  and into the housing  128 .  
         [0043]    The magneto-rheological fluid preferably includes a relatively high iron content. An electromagnetic valve  142  adjacent the output  124  operates to seal the housing  128  such that a cavity  132 ′ adjacent the output  134  may be filled with fluid. That is, the actuated electromagnetic valve  142  solidified the fluid in the passage  136  and seals the output  134 . Fluid is trapped in a lower portion of the housing  128  as the fins  130  pass thereby. Under normal conditions, the magneto-rheological fluid is a free-flowing liquid. Actuation of the electromagnetic valve  142  selectively transforms the fluid into a near-solid in milliseconds such that the fluid in the lower portion of the housing  128  will not drain through the output  124 . Just as quickly, the fluid can be returned to its liquid state with the removal of the field.  
         [0044]    A fluid filled cavity  132 ″ formed between the fins  130  and housing  128  is thereby formed which selectively creates a mass distribution which weights the belt  122  along its length and creates a vibratory force as the filled cavity  132 ″ passes each pulley  114 ,  116  as described above. One or more filled cavities  132 ″ may thereby be formed to alter the weight distribution along the belt  122  and the controlled force output of the AVC system  24   e.  Centrifugal force entraps the fluid between opposed fins  130  and the housing  128  during rotation of the belt  122 . Once filled, control of vibratory forces may be further controlled by varying the speed of the pulleys  114 ,  116  as described above. Operation of the AVC system  24   e  is then controlled as described above to cater to changing dynamic characteristics such that vibratory forces are reduced or eliminated. It should be understood that the cavities  132  may also be partially filled to further vary the compensation for vibratory forces. Essentially any vibratory force output may thereby be provided by the controlled filling of a desired number and portion of one or more cavities.  
         [0045]    When the electromagnetic valve  142  is deactivated, the magneto-rheological fluid is returned to its liquid state and flows through the output  124 . The fluid from the filled cavity  132 ″ drains into the source  138  such that the weight distribution of belt  122  is returned to equilibrium (no filled cavities) and no vibratory force is generated. The processor  28  preferably controls the phase and magnitude characteristics of the AVC system  24   e  by filling one or more cavities.  
         [0046]    Referring to FIG. 7, another AVC system  24   f  is illustrated. A track  144  is defined about a first radius R 1  about a first axis  146  and a second radius R 2  defined about a second axis  148  to form an elongated path  150 . The first axis  146  is offset from the second axis  148  such that one or more independent masses  152 ( a ) . . . ( n ) (where n is any desired number) are independently movable along the track  144 . That is, the track  144  remains stationary and the masses  152  move relative to the track  144 . Adjustable masses  152 ( a ) . . . ( n ) are preferably electromagnetically movable along the track  144  and relative to each in a manner as described above. It should be understood that other drive mechanisms will benefit according to the present invention. By moving the masses  152  relative to each other, the vibratory forces are controlled to cancel each other out, or provide a desired vibratory force.  
         [0047]    The AVC systems described herein are suitably used in conjunction with one another. For example only, the discrete mass system may be used in conjunction with one or more of the sinusoidal mass systems, adjustable mass systems, or the passageway system depending on the application. Furthermore, the present invention is not limited to a microprocessor based control system. The system may be implemented in a non-microprocessor based electronic system (either digital or analog).  
         [0048]    The foregoing description is exemplary rather than defined by the limitations within. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.