WO2015031826A1

WO2015031826A1 - Circular force generator (cfg) devices, systems, and methods having dual acting vibration cancelling

Info

Publication number: WO2015031826A1
Application number: PCT/US2014/053530
Authority: WO
Inventors: Russell E. Altieri; Daniel E. KAKALEY; Mark R. Jolly
Original assignee: Lord Corp
Current assignee: Lord Corp
Priority date: 2013-08-29
Filing date: 2014-08-29
Publication date: 2015-03-05
Anticipated expiration: 2016-02-29
Also published as: WO2015031768A1; US10364865B2; US20160195161A1

Abstract

Force generation devices, systems, and methods can include at least one set of imbalanced rotors, each set including two or more imbalanced rotors (12) disposed about a center point (Cp), and the at least one set of imbalanced rotors being selectively operable in both an active vibration mode and a passive absorber mode. When in the active vibration mode, the two or more imbalanced rotors (12) in each of the at least one set of imbalanced rotors are configured to co-rotate synchronously about the center point (Cp) to create a controllable rotating force vector having a controllable magnitude and phase about the center point. Alternatively, when in the passive absorber mode, the two or more imbalanced rotors are freely rotatable about respective individual imbalance radiuses for operation as independent pendulum absorbers.

Description

DESCRIPTION

CIRCULAR FORCE GENERATOR (CFG) DEVICES, SYSTEMS, AND

METHODS HAVING DUAL ACTING VIBRATION CANCELLING

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001 ] This application relates and claims priority to U.S. Provisional Patent Application Serial No. 61/871 ,620, filed August 29, 2013, and to U.S. Provisional Patent Application Serial No. 61/871 ,646, filed August 29, 2013, the disclosures of which is fully incorporated herein by reference, in their entireties.

TECHNICAL FIELD

[0002] The present subject matter relates generally to force generator devices, systems, and methods. More particularly the present subject matter relates to circular force generator (CFG) devices, systems, and methods in which imbalanced rotors are used for generating vibrations and/or imparting vibration control.

BACKGROUND

[0003] Various types of structures or platforms, not limited to vehicles, aircraft, helicopters, machinery, equipment, buildings, bridges, etc., experience vibration during operation. Over time, vibration may damage or induce damage to the structure and/or components thereof, including contents or occupants disposed therein. This increases costs associated with maintaining and providing the structures, such as costs associated with inspecting and replacing parts that may become damaged during vibration. Many varieties of solutions to these problems have been developed, but each has notable disadvantages. For example, many helicopters have passive vibration absorbers mounted to the hub of the helicopter. Although these passive absorbers are known to have high reliability, they can be large and add substantial weight to the system and/or their effectiveness in controlling vibrations can be limited. In contrast, active devices (e.g., hub mounted vibration systems) offer large weight savings, but are complex devices, and potentially may not be as reliable as passive devices. In addition, active devices having electric motors are also only as reliable as the power system driving them. In any form, current solutions in the field of vibration control are expensive to produce, manufacture, and must be customized and/or custom designed for use in different applications.

[0004] In view of these problems, a need exists for vibration control devices, such as force generator devices, systems, and methods, for providing lower cost vibration control solutions, in which a common design may be suitable for use in different applications and/or be scalable to different vibrating structures not limited to buildings, structures, machinery, equipment, vehicles, aircraft, etc. A need also exists for controlling vibration in industrial machinery, by using or inducing controlled vibration profiles.

SUMMARY

[0005] In accordance with the disclosure provided herein, novel and improved circular force generator (CFG) devices, systems, and methods having dual acting vibration cancelling are provided.

[0006] In one embodiment, a CFG device is provided. A CFG device includes at least one set of imbalanced rotors, each set comprising two or more imbalanced rotors disposed about a center point, the at least one set of imbalanced rotors being selectively operable in both an active vibration mode and a passive absorber mode. With this configuration, when in the active vibration mode, the two or more imbalanced rotors in each of the at least one set of imbalanced rotors are configured to co-rotate synchronously about the center point to create a controllable rotating force vector having a controllable magnitude and phase about the center point. In contrast, when in the passive absorber mode, the two or more imbalanced rotors are freely rotatable about respective individual imbalance radiuses for operation as independent pendulum absorbers.

[0007] In another embodiment, a CFG device includes a spindle configured to be rotatably coupled to a hub associated with a moving machine, wherein when the hub is rotated at a first rotation speed about a center point, the spindle is configured to have a second rotation speed having an equal and opposite direction to the first rotation speed. In this embodiment, at least one set of imbalanced rotors are rotatably mounted to the spindle, each set comprising two or more imbalanced rotors disposed about the center point, and the at least one set of imbalanced rotors being selectively operable in both an active vibration mode and a passive absorber mode. When in the active vibration mode, the two or more imbalanced rotors in each of the at least one set of imbalanced rotors are configured to co-rotate synchronously about the center point to create a controllable rotating force vector having a controllable magnitude and phase about the center point. When in the passive absorber mode, the two or more imbalanced rotors are freely rotatable about respective individual imbalance radiuses for operation as independent pendulum absorbers.

[0008] In yet another embodiment, a method for operating an active vibration generating device as a passive vibration absorber includes co-rotating two or more imbalanced rotors synchronously in at least one set of imbalanced rotors about a center point to create a controllable rotating force vector having a controllable magnitude and phase about the center point. Upon identification of a failure condition, the two or more imbalanced rotors are freely rotated about respective individual imbalance radiuses for operation as independent pendulum absorbers.

[0009] These and other objects of the present disclosure as may become apparent from the disclosure herein are achieved, at least in whole or in part, by the subject matter disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIGS. 1 through 3 illustrate perspective views of embodiments of a circular force generator (CFG) device according to aspects of the disclosure herein.

[0011] FIGS. 4A to 4C illustrate perspective, plan, and sectional views, respectively, of another embodiment of a CFG device according to aspects of the disclosure herein.

[0012] FIGS. 5A and 5B illustrate perspective views of another embodiment of a CFG device according to aspects of the disclosure herein. [0013] FIGS. 6A and 6B illustrate perspective and sectional views of directly and indirectly driven units of the CFG device illustrated in FIGS. 3A and 3B, according to aspects of the disclosure herein.

[0014] FIGS. 7A and 7B illustrate schematic representations of a CFG device being operated in either an active vibration mode or a passive absorber mode according to aspects of the disclosure herein.

[0015] FIGS. 8 through 10 schematically illustrate further embodiments of CFG devices according to aspects of the disclosure herein.

[0016] FIG. 1 1 illustrates a CFG system according to aspects of the disclosure herein.

[0017] FIGS. 12A and 12B illustrate further embodiments of a CFG device according to aspects of the disclosure herein.

[0018] FIG. 13 illustrates an embodiment of a CFG device mounted on a helicopter rotor hub according to aspects of the disclosure herein.

[0019] FIG. 14 illustrates a further embodiment of a CFG device according to aspects of the disclosure herein.

[0020] FIG. 15 schematically illustrates a CFG system according to aspects of the disclosure herein.

[0021] FIG. 16 illustrates generating a force via a CFG device or system according to aspects of the disclosure herein.

DETAILED DESCRIPTION

[0022] The subject matter described herein is directed to improved force generator (FG) devices, systems, and methods. Improved FG devices, systems, and methods described herein include circular force generator (CFG) devices, systems, and methods configured for providing a rotating force vector of a controllable magnitude and phase about a center point of the device or system. The force is used to impart a vibration to a structure (i.e., for use in industrial vibratory equipment, e.g., Fig. 1 1) or to actively control vibration of or within a structure (i.e., cancelling vibration imparted by a helicopter main/tail rotor). CFG devices, systems, and methods herein include non-coaxial and/or indirectly driven imbalanced rotors and/or masses (i.e., masses configured to have the center of mass offset from the center of rotation), which both lowers the cost of providing vibration control and provides a simplified, scalable FG design thereby enabling vibration of and/or vibration control for a variety of different applications.

[0023] Figures (also "FIGS.") 1 to 16 illustrate various views and/or features associated with CFG devices, systems, and related methods for controlling vibration of and/or within various structures, vehicles, aircraft, helicopters, machinery, equipment, buildings, bridges, etc., which experience vibration during operation. CFG devices, systems, and related methods described herein may also impart vibration to a structure where desired, for example, in industrial machinery or equipment.

[0024] CFG devices and systems herein may include a common design and/or a design having common structure in which one or more sets of imbalanced rotors are configured to rotate, synchronously and/or coupled via a power transmission scheme, and in a same direction to minimize, cancel, and/or eliminate vibration on/within a vibrating structure or platform. CFG devices, systems, and related methods described herein are scalable (e.g., scaled larger or smaller) for attachment to various sized and/or shaped vibrating structures. Thus, CFG devices, systems, and methods described herein utilize common designs having non-coaxial imbalanced rotors for use in controlling vibration in a wide variety of applications.

[0025] Figure 1 is a front perspective view of a first embodiment of a CFG device, generally designated 1 0, for use in inducing or controlling vibration of a structure, equipment, vehicle, or platform. Device 1 0 includes one or more imbalanced rotors, generally designated 1 2, including imbalanced mass concentrations for co-rotating in sets or groups synchronously, thereby creating a rotating force having a fixed magnitude at a center point Cp for inducing or controlling vibration on and/or within the structure, equipment, vehicle, and/or platform. In some aspects, force vector F is in a horizontal/radial plane. Center point C_P of device 1 0 is disposed along a central axis CA of device 10. A plurality of imbalanced rotors 12 is disposed about center point C_P. In some embodiments, rotors 12 are disposed in an annular ring or "donut" shape about center point C_P. Rotors 12 may be provided in one or more groups, sets, or pairs of imbalanced rotors. Any number of imbalanced rotors 12 may be provided in a given set or group, for example, two or more imbalanced rotors 12 may be included in a first set S_{1 (} three or more imbalanced rotors 12 may be included in first set S-i , or more than four imbalanced rotors 2 may be included in first set S-i .

[0026] In the embodiment shown in Figure 1 , for example, four imbalanced masses are mounted on a spindle 13 that can rotate about the center of a hub of a moving machine (e.g., a helicopter). If the spindle 13 moves at the hub speed, then the centripetal torque required to spin imbalanced rotors 12 is very large, If the spindle 13 is rotated backward at the hub speed (i.e., at an equal speed but in an opposite direction), however, then imbalanced rotors 12 are essentially stationary, and the centripetal load is zero. Imbalanced rotors 12 can then be spun up to a harmonic of the hub speed to generate vibration cancelling forces. The number of masses can be altered to change the vibration profile created on the hub. The direction of some masses can also be in an opposite direction to give the vibration profile an elliptical characteristic.

[0001] Alternatively, Figure 2 illustrates another embodiment of device 10 in which a plurality of off-center imbalanced rotors 12 are again provided. Motors are used to drive the rotation of the imbalanced rotors 12 and are sized to spin the imbalanced rotors 12 in the presence of the centripetal field. Once imbalanced rotors 12 are spinning, the power loss is only due to the friction in the system. As a result, if motors associated with opposing imbalanced rotors 12 are driven with electronic servo drives, and their power source is a common DC bus, then the net energy between the opposing motors is zero. Accordingly, imbalanced rotors 12 are motored at their resonance frequency, which helps spin the motors in the presence of a high centripetal field. In addition, the motors may have to oscillate imbalanced rotors 12 back and forth in order to get the masses spinning initially.

[0002] In either configuration, the ratio of the mass radius to the imbalance radius creates pendulum mass absorbers. Specifically, each of imbalanced rotors 12 is placed at a mounting radius from center point C_P such that a ratio of an imbalance radius r of each of imbalanced rotors 12 to the mounting radius R is with a range in which imbalanced rotors 12 are tuned to be operable as pendulum absorbers for a given vibrating system. To achieve such a ratio, imbalanced rotors 12 are designed and positioned to satisfy the following relationship:

(W_n/W)² = R/r (1)

where W_n is a harmonic of a frequency W of the rotation of the hub, wherein vibrations are occurring at this same frequency and its harmonics. With respect to the vibrations generated by a helicopter, for example, this relationship can be restated in terms of parameters of the helicopter system:

(N-1)² = R/r (2)

Where N is the number of blades of the helicopter.

[0027] In yet a further alternative, in some embodiments, each of the imbalanced rotors 12 within a group or set is mechanically linked via a mechanical coupler or coupling device 14. In this way, when on a spindle rotating at a frequency W, the centripetal torque on the masses is then neutralized because the torque is equal and opposite. Coupler device 14 may include a belt, gear, pulley, wheel, axle, sprocket, or any other type of device configured to physically and/or mechanically link imbalanced rotors 12 such that movement of one imbalanced rotor imparts movement to other imbalanced rotors in the same set or group.

[0028] In any configuration, device 10 may include a second group of two or more imbalanced rotors, generally designated S₂. Imbalanced rotors 12 of first and second groups Si and S₂, respectively, may alternate (e.g., 360 °) about center point C_P, and may co-rotate about independent axes thereby providing or generating a vibration cancelling force at or about center point C_P. For example, as shown in Figure 3, the vibration cancelling force can be characterized as a force vector F having a magnitude and phase, which may be controlled by phasing the rotation of imbalanced rotors in first and second sets Si and S₂. In each of the embodiments, a rotating force F is generated when imbalanced rotors 12 in first set Si spin in a same direction as imbalanced rotors 12 in second set S₂. In the alternative, a linear force with a controllable phase may be created when rotors 12 in first set Si spin in the opposite direction as rotors 12 in second set S₂.

[0029] Each group or set (i.e., Si , S₂) of imbalanced rotors 12 includes at least two imbalanced rotors in the form of imbalanced sprockets, pulleys, or gears (i.e., a first and a second imbalanced rotor 12 per set Si and/or S₂), where at least one of the rotors 12 is directly driven by a motor 16. In some embodiments where imbalanced rotors 12 within a given one of first or second set S-i, or S₂ are mechanically coupled, one of rotors 12 is directly driven, while the remaining rotor(s) 12 in each set is/are mechanically linked to the motor driven imbalanced rotor. Thus, in such embodiments the motor driven rotor induces rotation of the non-motor driven rotor or rotors in each set S-i and S₂. Indirectly driven rotors are referred to as "followers".

[0030] In any configuration, imbalanced rotors 12 associated with each of first and second sets Si and S₂ are non-coaxial with respect to each other and center point C_P. For example, the two rotors 12 in set S₂ rotate about individual axes Ai and A₂, etc. That being said, respective imbalanced rotors 12 associated with each set Si and S₂ of rotors are configured to co- rotate in a given direction (e.g., clockwise or counterclockwise) for generating a rotating force vector having a fixed magnitude at or about center point C_P. The imbalanced rotors 12 of each set ST and S₂ collectively generate a controllable rotating force vector (i.e., F) at center point Cp. This rotating force vector F essentially allows the two or more groups of two or more imbalanced rotors 12 to act as a single pair of co-rotating imbalanced rotors centered at Cp. The first set S-i of imbalanced rotors 12 and the second set S₂ of imbalanced rotors 12 may be individually phased to provide a controllable rotating force vector. In some embodiments, individual imbalanced masses or rotors 12 within a set or group are oriented so that a twist moment about center point Cp is equal to or approximately zero.

[0031 ] Still referring to Figure 3 and in some embodiments, imbalanced masses 12 are integrally built into gears and/or sprockets disposed within a CFG housing 18. Housing 18 is illustrated in broken lines, as it may include any size and/or shape which is scalable for use in a variety of vibrating and/or vibration control applications. Motors 16 are typically configured to directly drive at least some of the imbalanced rotors 12 comprised of gears or sprockets, while other imbalanced rotors 12 comprising gears or sprockets are indirectly driven via the mechanical link or coupling device 14. In configurations where rotors 12 of a given one of first or second set S-i, or S₂ are mechanically coupled, mechanical coupling devices 14 may include one or more belts (e.g., a timing belt), one or more gears (e.g., spur gears), one or more chains, and/or additional, intervening sprockets.

[0032] In some embodiments, device 0 includes two pairs of imbalanced sprockets (i.e., rotors 12), which are interconnected with a timing belt (i.e., 14). Two motors 16 are directly connected to at least two of the sprockets (i.e., 12), one in first set Si and one in second set S₂. One motor 16 may co- rotate at least two non-coaxial sprockets (i.e., 12) simultaneously via movements transferred using belt or coupler device 14. The sprockets on a common timing belt have imbalanced masses that are "clocked" or oriented identically about center point C_P so that the moment about the centerline axis CA for each pair or set S-|/S₂ is approximately zero.

[0033] This configuration enables device 10 to incorporate and/or include a central opening, aperture or through-hole, generally designated H, having an inner diameter D. Through-hole H is open for receiving and/or attaching to portions of vibrating machinery, equipment, vehicles, etc., thereby obviating the need for large diameter bearings and/or costly ring motors. Thus, device 10 includes a low cost and low weight option for imparting/controlling vibration to/of a plurality of different types of machines, vehicles, equipment, etc., while maintaining the through hole H unobstructed. Devices described herein may rotate as a whole (e.g., the entire device 10 spins/rotates) or devices described herein may be entirely stationary, but for the rotating imbalance rotors.

[0034] Figures 4A to 4C illustrate further embodiments of a CFG device, generally designated 20. Referring to Figures 4A to 4C collectively, device 20 includes a housing 22 configured to house and/or support one or more imbalanced masses or rotors 24 including imbalanced masses within device 20. Housing 22 is again illustrated in broken lines so that portions disposed inside of housing are visible in Figure 4A, which otherwise may not be visible from the outside of device 20. [0035] Device 20 may be configured for attachment to and/or over vibrating machinery, equipment, vehicles, structures, platforms, etc., and/or portions or components thereof. Imbalanced rotors 24 may be provided in one or more sets, or groups which are mechanically linked via a mechanical coupler or coupling device 26. Typically, at least a first imbalanced rotor per set of imbalanced rotors is directly driven via a motor, generally designated 28. At least a second imbalanced rotor per set of imbalanced rotors is indirectly driven via motor 28 upon receiving motion imparted thereto via coupling device 26. Each set of imbalanced rotors is configured to synchronously co-rotate about non-coaxial axes.

[0036] As Figure 4A illustrates, imbalanced rotors 24 include imbalanced sprockets or gears disposed between one or more bearings. A first set of imbalanced rotors 24 may include upper faces linearly aligned along and/or be located in a same plane, such as a first plane Pi, and a second set of imbalanced rotors 24 may include upper faces linearly aligned along and/or be located within a same plane, such as a second plane P₂, that is different from first plane P-i. First and second planes Pi and P₂ may be vertically disposed with respect to each other, such that at least some of the imbalanced rotors 24 are located or disposed on a plane above some of the other imbalanced rotors 24.

[0037] Imbalanced rotors 24 of a given set may be positioned opposite each other about a center point Cp of device 20, and configured to co-rotate in a same direction at a same time. Imbalanced rotors 24 in each set simultaneously rotate in a same direction in a synchronized movement, such that the movements of the similarly shaped/aligned imbalanced rotors 24 are synchronized. Several sets of imbalanced rotors 24 may collectively rotate for generating a controllable rotating force vector (e.g., F, Fig. 3) having a controllable magnitude and phase at center point C_P for reducing or creating vibration within a machine, equipment, vehicle, structure, etc.

[0038] In some embodiments, the speed and direction at which imbalanced rotors 24 rotate is controllable via an electronic control unit or component (e.g., 156, Figure 15), which is configured to detect a vibration level of the component or structure to which device 20 is attached. In some embodiments, device 20 imparts vibration to a structure for performing a function (i.e., conveying as described in reference to Fig. 1 1). In other embodiments, device 20 generates an equal and opposing force for cancelling vibration of the component or structure to which device 20 is attached.

[0039] Figure 4B is a top plan view of device 20. As Figure 4B illustrates, opposing imbalanced rotors 24 are configured into one set by coupling device 26. One rotor per set is directly driven or rotated by motor 28 (Fig. 4A), while the other rotor or rotors per set is/are indirectly driven or rotated by motor 28, and is/are configured to rotate upon movement imparted by coupling device 26. Each rotor 24 per set rotate co-rotate in a same direction (e.g., clockwise or counterclockwise) and at a same speed. Each rotor 24 per set is also aligned or oriented directly for minimizing a moment about the centerline axis C_A.

[0040] As Figure 4B illustrates, each imbalanced rotor 24 includes a first side, generally designated 30A and a second, more heavily weighted side, generally designated 30B. The difference in weight or mass between first and second sides 30A and 30B, respectively, generates an imbalance, thereby providing imbalanced masses, which rotate in the form of imbalanced rotors 24. Each set of rotors 24, which are connected via coupling device 26, is oriented identically (e.g., "clocked" or "synced") with respect to first and second sides 30A and 30B, respectively. That is, the more heavily weighted sides (i.e., second sides 30B) of opposing rotors 24 are aligned and disposed directly across from each and about opposing sides of center point Cp. Together, the two sets of imbalanced rotors 24 act as two rotating imbalanced rotors centered at C_P for generating a controllable rotating force vector at or about center point C_P, the magnitude and phase of which may be controlled by phasing the rotation of first and second sets of imbalanced rotors 24 with respect to each other.

[0041] Device housing 22 includes center point Cp_, which may include a through hole or opening having an inner diameter D adapted for placement over a stationary or rotating structure, machine, vehicle, etc., or portions thereof. Housing 22 and/or center point Cp may be stationary (i.e., non- spinning) or non-stationary (i.e., rotating or spinning). For example and as described in detail below, device 20 is configured for provision over and/or attachment to a stationary piece of equipment or machinery (See, e.g., Fig. 1 1 ), such as a material vibrator. In some embodiments, device 20 is configured for provision over and/or attachment to a rotating or spinning structure or vehicle, such as a spinning or rotating rotor head, hub, or shaft of a rotary wing aircraft (e.g., a helicopter main/tail or tandem rotor). When device 20 attaches to a rotating or spinning structure, housing 22 also spins about center point C_P. Thus, movement of rotors 24 via belts or coupler devices 26 cancels out centrifugal forces on the imbalanced rotors 24. Imbalanced rotors 24 rotate in synchronized movements about non-coaxial axes with respect to each other and center point C_P. The non-coaxial rotation generates a force at or about center point Cp.

[0042] Figure 4C is a sectional view of device 20 along the lines 4C-4C indicated in Figure 4B. As Figure 4C illustrates, imbalanced rotors 24 may be disposed along different planes (e.g., a first plane P and a second plane P₂) of and/or with respect to device housing 22. Pairs, sets, or groups of co- rotating imbalanced rotors 24 are mechanically coupled or linked along the different planes via coupling devices 26. The coupled imbalances rotors 24 co-rotate about non-coaxial shafts 32 including non-coaxial axes (i.e., Ai, A₂) for generating vibration cancelling forces. Two or more sets of imbalanced rotors 24 collectively generate a force having a force vector F at or about center point C_P of device 20, where the force vector F rotates in plane.

[0043] At least one imbalanced mass 24 per mechanically coupled set of rotors, and in some embodiments, only one imbalanced rotor 24 per mechanically coupled set of rotors, is directly driven via motor 28. Motor 28 may include a brushed or a brushless motor configured to directly rotate one imbalanced rotor 24 about a first axis Ai , and indirectly rotate additional imbalanced rotors 24 about at least one other axis (e.g., A₂), or multiple axes, by virtue of being coupled or linked with the directly driven rotor 24 which rotates about first axis Ai. Motors 28 may be disposed directly above one or more imbalanced rotors (e.g., per Fig. 3) or directly below imbalanced rotors 24 as illustrated in Figures 4A to 4C. Any configuration, position, and/or placement design of motors 28 and rotors 24 is contemplated, and may be provided.

[0044] Figures 5A and 5B illustrate a further embodiment of a CFG device, generally designated 40, for vibrating a structure, such as industrial equipment. Device 40 includes a housing, generally designated 42 and one or more individual units, generally designated 44, disposed and/or bolted therein. Housing 42 may include a first portion 42A and a second portion 42B disposed inside the first portion 42A. First portion 42A may include an attachment portion adapted to mount or attach to a vibrating structure. Second portion 42B may include a force generating portion disposed above and/or below first portion 42A. In some embodiments, first portion 42A is held stationary over a vibrating structure, and second portion 42B rotates or spins relative to first portion. In other embodiments, first and second portions 42A and 42B both spin and/or rotate over or with a vibrating structure. In yet further embodiments, first and second portions 42A and 42B are both held stationary over a vibrating structure.

[0045] Units 44 may include both directly driven units 44A and indirectly driven (i.e. "follower") units 44B, which are described in detail below with regards to Figures 6A and 6B. Directly driven units 44A include a motor (58, Fig. 6A) for directly driving one or more imbalanced rotors disposed therein. Follower units 44B are devoid of a motor, but synchronously and simultaneously co-rotate with directly driven units by virtue of being mechanically coupled or linked thereto via a belt, chain, gear, sprocket, wheel, pulley, axle, or any other coupler, coupling member or device.

[0046] In some embodiments, housing 42 includes a centrally disposed aperture, through hole, or opening 46. Opening 46 allows housing 42 to be disposed over, straddle, and/or otherwise connect to a portion of a rotating structure, vehicle, equipment, etc. Opening 46 and housing 42 designs may be scaled up or down, thereby allowing device 40 to be connected to multiple different types of vibrating structures at a low cost. Sets of separate, co-rotating imbalanced rotors rotating about different axes (i.e., non-coaxial rotors) generates vibration forces and/or vibration cancelling forces about a central axis CL or center point C_P. The magnitude and phase of the resultant force is controllable via phasing the sets of imbalanced rotors differently. Opposing modules or units in each set (e.g. , 44A and 44B in S-i) maintain a fixed phase relationship via the use of a timing belt, chain, sprocket, etc.

[0047] In some embodiments, housing 42, and/or portions thereof, is configured to spin or rotate with a vibrating structure, or a portion or component thereof. For example, housing 42 may attach to and rotate with a rotor head of a helicopter. In other embodiments, housing 42 is held stationary over a vibrating structure, or portion thereof. For example, housing 42 may be mounted over a stationary industrial equipment such as a vibratory conveyor feeder. Any centrifugal torque acting on individual imbalanced rotors associated with a spinning housing 42 is cancelled out via mechanically linked imbalanced rotators connected via a timing belt.

[0048] In some embodiments, individual imbalanced rotor modules or units 44 are configured to bolt into and/or otherwise join or mate with housing 42. In some embodiments, units 44 are coupled to housing 42 via mechanical fasteners or fastening members M, such as bolts, screws, pins, clips, etc. In some embodiments, units 44 are welded or otherwise structurally/physically joined with housing 42.

[0049] Each unit 44 includes at least one imbalanced rotor (50, Figs. 6A and 6B) forming, including, supporting, and/or otherwise providing an imbalanced mass or imbalanced mass concentration. Imbalanced rotors 50 (Figs. 6A and 6B) are configured to co-rotate in groups or pairs for generating vibration cancelling forces. For example and referring to Figure 5B, device 40 includes a first set Si of imbalanced rotors disposed in a set of units 44 mechanically coupled via a timing belt 52 and a second set S₂ of imbalanced rotors disposed in a set of units 44 mechanically coupled via a second, additional timing belt 52. At least two opposing imbalanced rotors housed and/or disposed in opposing units 44 are configured in a single set via belt 52, although more than two imbalanced rotors may also be coupled via a belt, chain, axle, wheel, pulley, sprocket, gear, or any other suitable coupler.

[0050] In some embodiments, timing belt 52 mechanically connects to a support or support portion 54 of each module or unit 44. Support portion 54 may include a pulley, sprocket, chain, axle, wheel, or other structures about which belt 52 may be provided and moved (e.g. , translated/rotated between opposing support portions 54) for indirectly driving at least one other imbalanced rotor disposed, for example, in one or more follower units 44B. In some embodiments, a set of directly driven units 44A and follower units 44B are disposed 180 ⁰ from each other about center point Cp.

[0051 ] Figures 6A and 6B are cut-away perspective views of individual units 44, namely of a directly driven unit 44A (Fig. 6A) and an indirectly driven follower unit 44B (Fig. 6B). Referring to Figure 6A, directly driven unit 44A includes an outermost housing, generally designated 56, which may include one or more housing portions 56A and 56B. Housing portions 56A and 56B may be disposed about at least one imbalanced rotor, generally designated 50, and a motor, generally designated 58, for directly driving or rotating imbalanced rotor 50. Imbalanced rotor 50 is configured to rotate about and/or by a rotation shaft 60. Shaft 60 may physically and/or mechanically connect, link, join, and/or extend through portions of imbalanced rotor 50 and support portion 54, such that support portion 54 rotates in sync with imbalanced rotor 50. As imbalanced rotor 50 rotates, a belt (52, Fig. 5B) disposed in or about support portion 54 induces movement of a non-coaxial imbalanced rotor 50 disposed within an indirectly driven, follower unit 44B (Fig. 6B). That is, a belt (i.e. , 52, Fig. 5B) connects support portions 54 of a respective directly driven unit 44A and a follower unit 44B (see Fig. 5B) disposed in a physically joined (i.e., coupled or linked) set, such that follower unit 44B co-rotates in sync with directly driven unit 44A.

[0052] In some embodiments, motor 58 includes a brushless motor. Motor 58 includes a motor winding assembly 62. Motor winding assembly 62 is disposed about a centrally disposed motor rotor 64. Device 40 includes at least one annular shaped motor assembly 62 for rotating and directly driving imbalanced rotor 50 about shaft 60. A plurality of permanent magnets 66 is disposed about motor rotor 64. Permanent magnets 66 may interface with electromagnets provided on the motor winding assembly 62 causing rotation of imbalanced rotor 50 extending therefrom. Imbalanced rotor 50 includes an integrally formed imbalanced mass 68 or a separately formed imbalanced mass. Imbalances rotors 50 of units 44A and 44B include or support imbalanced masses 68 for synchronized rotation about non-coaxial axes to provide a rotating force proximate center point Cp (Fig. 5A) of device 40. Permanent magnets 66 interface with electromagnets for controlling a direction, a rotational speed, a rotational position, and/or a rotational phase of the imbalanced rotor 50 and respective masses 68, according to commands received within a circuitry component or electrical unit, generally designated 70.

[0053] Electrical unit 70 may include a plurality of hardware electrical and circuitry components disposed over a circuit carrying substrate 72, such as a circuit board. Electrical unit 70 may include sensors (e.g., a rotary encoder, accelerometer(s), and/or temperature sensor(s)), one or more processors (e.g., a power chip or other hardware processing component), and a memory (e.g., a memory chip or other hardware memory component). A processor disposed on and/or in electrical communication with in electrical unit 70 is configured to control electric signals received at motor 58 thereby controlling a rotation speed and/or a rotation frequency of the plurality of linked imbalanced rotors 50 for generating and imparting vibrating forces and/or vibration cancelling forces to the structure, machinery, equipment, vehicle, etc., to which device 40 is attached.

[0054] Figure 6B illustrates follower unit 44B. Follower unit 44B is devoid of a motor or direct driving component. Follower unit 44B includes an outermost housing 74 adapted to bolt or otherwise attaching to housing 42 of device 40 (Fig. 5A). Housing 74 is held stationary within housing 42 of device (Fig. 5A) and housing 42 of device may be held stationary or spin, depending upon the type of machine to which it is attached. [0055] Follower unit 44B includes an imbalanced rotor 50 configured to rotate about a shaft 76 via rotation of a timing belt (e.g., 52, Fig. 5B) and support portion 54. Imbalanced mass 50 rotates about shaft 76 within an enclosure or spacing, generally designated 78, disposed within and/or between portions of housing 72. The speed, rotation, and position of imbalanced rotor 50 of follower unit 44B is synchronized in regards to the speed, rotation, and position of imbalanced rotor 50 of directly driven unit 44A Fig. 6A). Co-rotation of imbalanced rotors 50 within directly driven and follower units 44A and 44B, respectively, generates a rotating force proximate center point Cp of device 40 (see Fig. 5A) for imparting forces to vibrate or control vibration of the structure to which it is attached.

[0056] In any particular implementation of the CFG devices and systems disclosed herein, the at least one set of imbalanced rotors can be designed such that they are operable in both an active vibration mode discussed hereinabove and in a passive absorber mode. For example, in all applications for which the housing is rotating, the CFG devices disclosed herein are operable at imparting and/or cancelling vibration even during instances where imbalanced rotors in a given set become decoupled or disengaged (e.g., with reference to Figure 5B, in the event belt 52 becomes broken or disengaged). In this regard, in one failure mode where masses or rotors (i.e., 50, Figs. 6A/6B) become decoupled (e.g., via broken or defective timing belt 52), the imbalanced rotors (i.e., 50, Figs. 6A 6B) become tuned pendulum absorbers (e.g., tuned to a harmonic of an expected frequency of vibration of a vibrating system as discussed above) to attenuate in-plane vibration at or near center point C_P. Thus, where rotors or masses decouple, the disclosed devices and systems are configured to absorb vibration as opposed to generate vibration cancelling force. In-plane vibrations in rotating machinery or equipment may be suppressed via identically oriented decoupled imbalanced rotors within opposing units, as the rotors transition into absorbers, which remain tuned to the in-plane vibration of the vibrating equipment to which the devices are attached. In this regard, upon decoupling of the power transmission to the imbalanced rotors, opposing rotors balance each other to create a net force vector of zero,

[0057] Alternatively, the CFG devices and systems disclosed herein can be configured to intentionally decouple the rotation of the imbalanced rotors from one another in a failure condition so that the device operates as a passive vibration absorber in such a scenario. Specifically, for example, as shown in Figure 7A, for a CFG device 10, when in an active vibration mode, two or more imbalanced rotors 12 in a first set Si are operable to co-rotate synchronously about center point C_P, and two or more imbalanced rotors 12 in a second set S₂ are similarly operable to co-rotate synchronously about center point Cp to create a controllable rotating force vector having a controllable magnitude and phase about the center point.

[0058] If any fault is detected, however, or there is a loss of power, and CFG device 10 is operable in a passive absorber mode shown in Figure 7B. In configurations in which each of imbalanced rotors 12 is independently driven (See, e.g., the embodiments of Figs. 1 and 2), identification of a failure condition triggers the power to each of imbalanced rotors 12 to be shut off. In configurations where imbalanced rotors 12 are mounted on a spindle 13 that is rotated backward at the hub speed (See, e.g., the embodiment of Fig. 1), a passive mode is achieved by stopping the counter-rotation of spindle 13. Alternatively, where imbalanced rotors 12 are mechanically coupled for operation together (See, e.g., the embodiments of Figs. 3 to 5B), a passive mode is achieved by disengaging the mechanical coupling. In any configuration, when in the passive mode and the transmission of power to imbalanced rotors 12 is disengaged, the masses will then be exposed to the centripetal torque of the rotating system, and if the ratio of the mass radius to the imbalance radius is correct, then the masses will become pendulum mass absorbers. This disengagement can be achieved by reversible or irreversible means. Specifically, for example, reversible engagement can be achieved by selectively engaging or disengaging the respective coupler element with one of a clutch mechanism, a belt engagement, a centrifugal clutch, or similar mechanisms understood by those having skill in the art. Alternatively, irreversible engagement can be implemented using one or more of cutting or exploding a belt, or breaking a mechanical fuse. In any configuration, when in the passive absorber mode, while rotating about the center point C_P, the two or more imbalanced rotors 12 are freely rotatable about respective individual imbalance radiuses for operation as independent pendulum absorbers.

[0059] Figures 8 to 10 schematically illustrate various exemplary imbalanced mass groupings, placement, positioning, and/or rotation scenarios associated with CFG devices, systems, and methods described herein. Figures 8 to 10 schematically illustrate exemplary CFG devices including a plurality of imbalanced rotors R and mass concentrations M that are non-coaxially disposed for rotating about non-coaxial axes with respect to a center point C_P of each device. Referring to Figure 8, in some embodiments a CFG device, generally designated 80, includes multiple sets or groups of imbalanced rotors R and respective imbalanced masses M. In some embodiments, a set or group of imbalanced rotors R may include three imbalanced sprockets interconnected by a timing belt B. For example, Figure 8 includes provision of a first set, generally designated Si , of imbalanced rotors R (also designated in hatched lines) and a second set, generally designated S₂, of imbalanced rotors R or sprockets (designated in white). Each set of rotors R includes one motor 82 for driving at least three imbalanced sprockets or rotors R about individual non-coaxial axes as belts B move about center point C_P. Masses M may be symmetrically disposed and/or symmetrically oriented about center point C_P.

[0060] Each motor 82 directly drives or rotates a single imbalanced sprocket of each group, and indirectly drives at least two other imbalanced sprockets of the respective group. Motors 82 of opposing groups or sets may be oriented 180 degrees (°) apart providing a static mass balance. Opposing rotors R, which are oriented 180 ⁰ apart, are configured to rotate in a same direction, which allows the overall CFG authority to be distributed amongst more than two imbalanced rotors R and consequently bearing stresses are better distributed over more bearings. This enables the use of smaller, less expensive, and lower weight bearings. The "keep out zone" illustrated in Figure 8 refers to an area of the device that should remain devoid of couplers, such as belts B, so as not to negatively interfere with an underlying vibrating structure or machine. Sets of rotors R may be coupled via gears, belts, chains, pulleys, axles, or any other suitable coupling device.

[0061 ] Figure 9 illustrates a CFG device, generally designated 90, which also includes multiple sets of imbalanced rotors R having imbalanced mass concentrations M configured to co-rotate about non-coaxial axes. Sets of rotors R are mechanically coupled via couplers, such as belts B. One or more idler gears G or sprockets prevent belts B from overlapping portions of the keep out zone. Motors 92 rotate one rotor R directly, and at least one other rotor R indirectly. Rotors R in each set co-rotate in a same direction (e.g., either counter clockwise or clockwise) as indicated by the arrows. The masses M within a given set are, again, clocked or co-oriented in such a way as to prevent torsional moments about center point C_P.

[0062] Figure 10 illustrates a CFG device, generally designated 100, which also includes multiple sets of imbalanced rotors R having imbalanced mass concentrations M configured to co-rotate about non-coaxial axes. Sets of rotors R are mechanically coupled via couplers, such as gears G. That is, in some embodiments, rotors R are mechanically coupled or linked via couplers other than belts, and may be devoid of belts altogether. Motors 102 rotate one rotor R directly, and at least one other rotor R indirectly. Rotors R in each set co-rotate in a same direction (e.g., either counter clockwise or clockwise) as indicated by the arrows. The masses M within a given set are, again, clocked or co-oriented in such a way as to prevent torsional moments about a center point.

[0063] Figures 9 and 10 are adapted for provision about or around a rotating shaft or machinery component without requirement machinery disassembly. This prevents creating a moment about the center line of the keep-out area due to mass orientation, as shown. The motors 92, 102 may be oriented approximately 80 ⁰ apart to provide static mass balance. If the entire assembly is rotating (e.g., as on a rotor hub), the centrifugal force loading on the masses will balance through belt loading so that there is no direct centrifugal force impact on motor torque. If the entire assembly is rotating and a belt breaks, then the centrifugal force will send all masses to an outer diameter, which will produce zero net force on the rotating shaft. The broken belt scenario can thus reproduce the passive vibration absorber effect of a pendulum absorber. If the belt remains intact and a motor fails, the masses M in Figure 8 can be designed to allow both sets of belted masses designated in groups S1 and S2 to produce zero net force on the rotating shaft. For example if a single mass M in each group S1 and S2 is slightly more massive than the other belted masses in the respective groups (the center of mass is offset from the center of rotation) and the larger masses are 180° apart, the system will produce zero net force on the rotating shaft in the event of a motor failure. In other words, in some embodiments, one of masses M in first set S1 is weighted slightly more than the others within first set Si to create a first preferred angle of rest for first set Si , and one of masses M in second set S₂ is weighted slightly more than the others within second set S₂ to create a second preferred angle of rest for second set S₂. In this configuration, where the first preferred angle of rest is substantially opposite from the second preferred angle of rest, the net force vector is substantially zero, and thus first set Si and second set S₂ balance each other.

[0064] Furthermore, as discussed above, CFG devices 80, 90, and 100 are also operable such that, upon identification of a failure condition, belts B, gears G, or other coupling device are controllable to decouple rotors R from one another (e.g., using a clutch mechanism) and thereby allow rotors R to freely rotate about respective individual imbalance radiuses for operation as independent pendulum absorbers.

[0065] Figure 1 1 illustrates a CFG system, generally designated 1 10, incorporating at least one CFG device. System 1 10 includes a CFG device 40 (i.e., previously described above in Figures 1 to 6B) and a vibrating structure 1 12. Structure 1 12 may include industrial equipment or a vibrating machine adapted to convey material by imparting vibration thereto. For illustration purposes, structure 1 12 is generically and schematically depicted as a cylinder, but can take on any size, shape, form and/or include any type of machine or industrial equipment. In some embodiments, CFG device 40 is disposed directly over, on, and/or above vibrating structure 1 12. CFG device 40 is configured to generate vibrations allowing structure 1 12 to function, or vibration cancelling forces for reducing or mitigating vibrations before such impart damage and/or fatigue stresses to the structure 1 12 and/or components thereof.

[0066] Vibrating structures 12 are not limited to industrial equipment, but may include any machine, platform, vehicle, aircraft, and/or any other structure in need of a vibrating force and/or a vibration cancelling force.

[0067] Figures 12A and 12B are embodiments of an additional CFG device, generally designated 120. Device 120 includes a housing 122 for housing rotating components, and a central opening, generally designated 124. Figure 12B illustrates the inner portions of device 120, which are disposed within housing 122.

[0068] Device 120 includes a plurality of imbalanced masses 126 supported by a plurality of rotors. Rotors and respective masses 126 may be grouped into one or more co-rotating sets which rotate in a same direction and have a synchronized orientation about different (i.e., non- coaxial) axes. Rotational movement of imbalances masses 126 is induced via rotation of one or more centralized gears.

[0069] In some embodiments, a first centrally disposed gear 128 rotates a first set of rotors 132 supporting respective imbalanced masses 126. A second centrally disposed gear 130 rotates a second set of rotors 134 supporting respective imbalanced masses 126. In some embodiments, first and second centralized gears 128 and 130, respectively, are vertically disposed with respect to each other. First and second sets of rotors 132 and 134, respectively, are also vertically disposed within device 120.

[0070] In some embodiments, first and second sets of rotors 132 and 134, respectively, rotate masses thereby generating a rotating centralized force having a force vector F rotating about a center point C_P of device 120. In some embodiments, opening 124 is disposed about a rotating shaft (not shown), such as a component of a rotor head or main rotor hub, generally designated 135, of a helicopter as shown in Figure 13. At least two of the rotors 132 and 134 are disposed 180° apart and have motors therein. The motors rotate (e.g., directly or indirectly) rotors in each of the sets. This is similar to the embodiment illustrated schematically in Figure 8, but here spur gears are used in the place of a timing belt.

[0071] Figure 14 is a further embodiment of a CFG device, generally designated 140. Device 140 includes two side-by-side (i.e., adjacent) sets of imbalanced rotors and respective imbalanced masses M. Rotors and masses R and M, respectively, co-rotate at a same time, speed, and in sync via gears G. This is similar to the embodiment illustrated schematically in Figure 9, but here spur gears are used in the place of a timing belt.

[0072] Figure 15 is a schematic block diagram illustrating an exemplary CFG system, generally designated 145. CFG system 145 includes a structure 150. Structure 150 includes any suitable structure, machine, platform, equipment, vehicle (including fixed and rotary winged aircraft), or components thereof, either in need of vibrating forces imparted thereto and/or generation of vibration cancelling forces. Structure 150 may include a building, a bridge, industrial equipment, vehicular components such as a rotor hub of a helicopter, a tail rotor, an engine structure, or any other suitable structure either in need of vibratory forces imparted thereto (e.g., a structure 1 12, Fig. 1 1 ) or a structure in need of vibration control (e.g., a rotor hub). System 145 enables a low cost CFG on such machinery or equipment, and is useful in applications where a CFG needs to straddle a support structure or a material inlet or outlet port. In these applications, CFG system 145 creates prescribed vibration profiles for industrial equipment.

[0073] Structure 150 includes a CFG device 152 disposed thereon, mounted thereto, or otherwise physically connected to one or more portions of structure 150 for imparting vibration control or for imparting vibration thereto. CFG device 152 includes structural features of any of the previously described devices previously (e.g., devices 10, 20, 40, 80, 90, 100, 120, 140). [0074] CFG device 152 may include at least one or more hardware processors 154. Processor 154 is adapted to control an amount of electrical current, power, or electrical signal transmitted to drive motors or other driving components of CFG device 154. In some embodiments, processor is configured to receive and execute (i.e., process) software stored in a memory thereof for executing force commands communicated from a controller 156. In some embodiments, software may be implemented via a non-transitory computer readable medium having stored thereon computer executable instructions that when executed by processor 154 allow device 152 to generate a force as communicated via a force command or commands from controller 156. The force or forces generated by one or more devices 152 may apply vibration to a machine or equipment alone and/or for actively controlling complex vibration occurring within a structure or vehicle (e.g., an aircraft) due to rotating components thereof. Controller 156 may be configured to generate and send force commands to one or more CFG devices 152. Any number of CFG devices may be provided in system 145.

[0075] Controller 156 is illustrated as being disposed in and/or co-located with structure 150, but controller may be disposed external from and/or located away from structure 150, as the vibrations can be controlled remotely. Controller 156 can be disposed at any given location on or away from structure 150.

[0076] In some embodiments, system 145 is configured to monitor vibrations within structure 150 via a plurality of sensors 158 for generating forces to actively control vibration. In some embodiments, sensor 158 may actively test for structural responses to vibration control implemented via CFG device 152 over time. Sensors 158 may be active in that as device 152 creates active forces for cancelling vibrations, changes may be detected via sensors 158 and actively responded to via generation of force commands at controller 156, and implementation of force commands at device 152. That is, in some embodiments, controller 156 may monitor vibrations via sensors 158 and send force commands to CFG device 152 for generating vibration forces or vibration cancelling forces. In some embodiments, sensors 158 are also included and/or disposed within CFG device 152. [0077] Figure 16 is an exemplary block diagram of a method, generally designated 160, for operating and/or generating a force via CFG devices and/or systems described herein. The generated force can either impart operability to a structure, equipment, or device or impart vibration control to a vibrating structure. In block 162, a force command is received. The force command may be received at a CFG device of a CFG system. A controller may generate and send the force command to CFG device according to information received at one or more sensors.

[0078] In block 164, a force is generated via co-rotation of one or more sets of non-coaxial imbalanced rotors either including imbalanced masses or supporting imbalanced mass concentrations. In some embodiments, a plurality of sets of imbalanced rotors are provided, there each set includes two, three, or more than three imbalanced rotors. In some embodiments, imbalanced rotors co-rotate about different (i.e., non-coaxial) axes. Block 166 provides a passive absorber mode for the CFG devices and/or systems, wherein the one or more sets of non-coaxial imbalanced rotors are disengaged from one another in a failure condition.

[0079] Exemplary application to which CFG devices and/or systems may be useful include using two CFGs about a vertical centerline of the equipment around both an input port and an output port for providing four degrees of freedom of vibratory control (two lateral, two rocking) to enable a controllable orbital motion. CFG devices and system are also applicable to vibratory conveyors and other industrial vibratory machines.

[0080] CFG devices and/or systems may also be used on main/tail/tandem rotor hubs such as helicopter rotor heads. In particular, CFG devices and/or systems herein create in-plane vibration cancelling forces. Such forces are sometimes created by pendulum absorbers, and more recently by a hub mounted vibration control system (HMVS) including CFG devices. CFG devices and systems herein may be attached to two different rotor heads. A slip ring and deice system often reside at the center line of the hub. Thus, annular ring or donut shaped CFG devices/systems are useful in accommodating such equipment. CFG device and systems described herein are devoid of expensive thin, ring shaped motors and bearings.

[0081 ] Embodiments as described herein may provide one or more of the following beneficial technical effects: reduced production cost; improved ease of installation; scalability for use a wide variety of applications requiring vibration control; reduced weight; and/or improved vibration control. Other embodiments of the instant subject matter will be apparent to those skilled in the art from a consideration of this specification or practice of the invention disclosed herein. Thus, the foregoing specification is considered merely exemplary of the current invention with the true scope thereof being defined by the following claims.

Claims

CLAIMS What is claimed is:

1 . A force generating device comprising:

at least one set of imbalanced rotors, each set comprising two or more imbalanced rotors disposed about a center point, the at least one set of imbalanced rotors being selectively operable in both an active vibration mode and a passive absorber mode;

wherein, when in the active vibration mode, the two or more imbalanced rotors in each of the at least one set of imbalanced rotors are configured to co- rotate synchronously about the center point to create a controllable rotating force vector having a controllable magnitude and phase about the center point; and

wherein, when in the passive absorber mode, the two or more imbalanced rotors are freely rotatable about respective individual imbalance radiuses for operation as independent pendulum absorbers.

2. The force generating device of claim 1 , wherein a ratio of an imbalance radius of each of the two or more imbalanced rotors to a mounting radius of the two or more imbalanced rotors about the center point is tuned to a harmonic of an expected frequency of vibration of a vibrating system.

3. The force generating device of claim 2, wherein the ratio of the imbalance radius of each of the two or more imbalanced rotors to the mounting radius of the two or more imbalanced rotors about the center point has a relationship:

R/r = (W_n/W)²

where R is the mounting radius, r is the imbalance radius, W is a rotational frequency of a rotating hub to which the at least one set of imbalanced rotors is mounted, and W_n is a harmonic of the rotational frequency W, wherein vibrations are occurring at the rotational frequency W and at the harmonic frequency W_n.

4. The force generating device of claim 1 , wherein the at least one set of imbalanced rotors comprises:

a first set of imbalanced rotors disposed about the center point, the first set of imbalanced rotors comprising two or more imbalanced rotors that are configured to co-rotate synchronously about the center point when in the active vibration mode; and

a second set of imbalanced rotors disposed about the center point, the second set of imbalanced rotors comprising two or more imbalanced rotors that are configured to co-rotate synchronously about the center point when in the active vibration mode;

wherein the first set of imbalanced rotors and the second set of imbalanced rotors are controllable in combination to create the rotating force vector.

5. The force generating device of claim 1 , comprising a coupler device associated with one of the at least one set of imbalanced rotors, wherein the coupler device mechanically couples the rotation of the respective two or more imbalanced rotors to achieve synchronous co-rotation about the center point.

6. The force generating device of claim 5, wherein the coupler device is selected from the group consisting of a belt, a chain, a gear, a sprocket, a wheel, a pulley, and an axle.

7. The force generating device of claim 1 , comprising one or more motors connected to each of the at least one set of imbalanced rotors, the one or more motors being configured to selectively drive rotation of the respective two or more imbalanced rotors when in the active vibration mode.

8. The force generating device of claim 1 , comprising a controller in communication with each of the at least one set of imbalanced rotors and configured for selectively driving the rotation of the two or more imbalanced rotors.

9. A force generating device comprising: a spindle configured to be rotatably coupled to a hub associated with a moving machine, wherein when the hub is rotated at a first rotation speed about a center point, the spindle is configured to have a second rotation speed that is equal to the first rotation speed but in an opposite direction; and

at least one set of imbalanced rotors rotatably mounted to the spindle, each set comprising two or more imbalanced rotors disposed about the center point, the at least one set of imbalanced rotors being selectively operable in both an active vibration mode and a passive absorber mode;

10. The force generating device of claim 9, wherein the at least one set of imbalanced rotors comprises:

11 . A method for operating an active vibration generating device as a passive vibration absorber, the method comprising: co-rotating two or more imbalanced rotors synchronously in at least one set of imbalanced rotors about a center point to create a controllable rotating force vector having a controllable magnitude and phase about the center point; and

upon identification of a failure condition, freely rotating the two or more imbalanced rotors about respective individual imbalance radiuses for operation as independent pendulum absorbers.

12. The method of claim 11 , wherein co-rotating the two or more imbalanced rotors synchronously comprises mechanically coupling the two or more imbalanced rotors for rotation together.

13. The method of claim 12, wherein freely rotating the two or more imbalanced rotors comprises disengaging the mechanical coupling.

14. The method of claim 12, wherein mechanically coupling the two or more imbalanced rotors for rotation together comprises coupling the coupling the two or more imbalanced rotors together with a coupler element selected from the group consisting of a belt, a chain, a gear, a sprocket, a wheel, a pulley, and an axle.

15. The method of claim 11 , wherein co-rotating two or more imbalanced rotors synchronously comprises:

co-rotating two or more imbalanced rotors synchronously in a first set of imbalanced rotors disposed about the center point; and

co-rotating two or more imbalanced rotors synchronously in a second set of imbalanced rotors disposed about the center point;

wherein co-rotation of the two or more imbalanced rotors synchronously in a first set of imbalanced rotors and co-rotation of the two or more imbalanced rotors synchronously in a second set of imbalanced rotors comprises is controlled in combination to create the rotating force vector.