WO2000049309A2

WO2000049309A2 - Apparatus for vibrations attenuation using electronic and electromagnetic actuation

Info

Publication number: WO2000049309A2
Application number: PCT/US2000/040034
Authority: WO
Inventors: Rahmat A. Shoureshi; Mark J. Bell; R. Bruce Deroo
Original assignee: Cooper Tire and Rubber Co
Current assignee: Cooper Tire and Rubber Co
Priority date: 1999-02-22
Filing date: 2000-02-22
Publication date: 2000-08-24
Anticipated expiration: 2001-08-22
Also published as: JP2003530522A; BR0008384A; WO2000049309A3; EP1210529A2

Abstract

A vibration and noise canceling system includes an electromagnetic vibration canceling actuator (21) and an electronic control system (16). The vibration canceling actuator (21) includes a permanent magnet (6) in proximity with a flux collector (4, 10). The flux collector has a gap between through which the magnet magnetic field of the magnet is directed. Current directed to flow through a coil or set of coils (8) wound on a coil form (9) within the gap generates a magnetic field that is used to move the actuator mass comprise of the flux collector and the magnet so as to create vibration or noise canceling destructive interference. The driving current is provided by the electronic control system (16) and amplifier. The electronic control system receives input from a variety of sensors (14, 19, 22) which could include noise (19) and vibration sensors (14). The sensors may provide feedforward and feedback information. The controller may include adaptive control algorithms.

Description

APPARATUS FOR VIBRATIONS ATTENUATION USING ELECTRONIC AND ELECTROMAGNETIC ACTUATION

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an integrated electromagnetic and electronic device to be mechanically attached to a vibrating body for the purpose of attenuating such vibrations from that body at multiple points or throughout that body. Objects where the device can be applied include, for example, structures composed of several substructures and vibrating bodies such as an engine, chassis, or body of a vehicle. One or more actuators as disclosed herein can be attached to optimally defined points on, for example, a chassis, for the purpose of attenuating vibration and structure-borne noise within the interior of the vehicle.

Discussion of the Art

A vibration control system is composed of three major elements: a sensor or sensors that provides information about the vibration, a controller/amplifier that utilizes sensor signals and determines the required control effort, and an actuator that takes the control signal and generates appropriate force that nullifies the vibration force. This invention relates to integrated electronics and an electromagnetic actuator for attenuation of vibrations of a structure, or noise within an interior of an enclosure, caused by structural vibrations .

Several active vibration dampers and vibration absorbers have been introduced in the prior art. U.S. Patents 5,427,362, 5,718,418, 4,493,599 5,297,781,

5,810,336, and 5,520,375 cover basic ideas of the prior art. However, in terms of actuators feasible for applications where cost, design simplicity, manufacturability, linearity of operation, performance, small size, etc. are of great importance, available vibration control actuators have demonstrated significant shortcomings. These shortcomings of the prior art have created a major bottleneck in the realization of low cost, high performance active vibration control systems for such applications as automotive vehicles, appliances, and industrial machinery.

Two major shortcomings are present in the prior art: a presence of significant harmonic distortions; a non-flat or peaky transfer function of actuators developed in the prior art. Mechanical surface sliding is the major cause of harmonic distortion. A key component of the prior art, that introduces such a mechanical contact friction, and thus distortion, is a through shaft and guide way.

Accordingly, it has been considered desirable to develop a new and improved active vibration damping system that would overcome the foregoing difficulties and others . BRIEF SUMMARY OF THE INVENTION

An underlying objective of the present invention is to provide a device that can be easily attached at optimally and strategically defined points or locations of a structure which utilizes electronics to derive an appropriate signal that drives an electromagnetic circuit which, in turn, creates interference forces to attenuate vibrations at apriori defined locations of that structure or other structures in mechanical communication with the first structure. Therefore, unlike the prior art, the embodiment of this invention does not need to reside between the source of excitation and the structure of interest, namely between the engine and chassis of a vehicle, rather it can be attached anywhere on the structure that is deemed appropriate based on the dynamic analysis of the whole system.

A vibration control system according to the present invention is characterized by its magneto-mechanical or mechanical stiffness and its mass to operate in a narrow-band within the frequency of vibration excitation to utilize the concept of resonance for its mechanical benefits, or utilize its electronics to move its operating frequencies outside of the excitation frequency and thus produce a flat wide-band actuation spectrum and large bandwidth. Thus, when the active vibration control according to the present invention is used, the source of excitation can be from a multiplicity of sources, namely, in the case of automotive vehicles: road excitations, engine vibrations, vibrations of transmission, generator, exhaust, air moving machinery, etc. One or more units of the embodiment of the present invention can compensate for all of these sources.

In accordance with the foregoing, and objects of this invention, a smart and adaptive active vibration control system is developed comprising:

a low cost permanent magnet that is in proximity to ferrous flux collectors, thus increasing the magnetic flux collection within an electromagnetic circuit;

a coil wound on a coil former that resides in the flux collector and thus exposed to a very high magnetic flux density, which can be made into a single coil or parallel sets of coils according to the types of available power sources, namely it has the ability to operate with low or high currents;

a very unique design of an actuator having double supports or spiders that can be conical or flat- shaped and used at the top and bottom, one attached between an upper portion of the upper flux collector and a top lid, the other attached between a lower portion of the lower flux collector and a bottom plate. The spiders having very large radial stiffness and very small axial stiffness that enables the actuator to maintain a uniformly constant gap width between the coil and magnetic flux collectors which results in linear operating characteristics for the embodiment with reduced mechanical distortion; mechanical, elastomeric, or other types of compliant elements can be added between the upper portion of the upper flux collector and the top lid, and the lower portion of the lower flux collector and the bottom plate to limit the excursion of the moving parts, as well as defining the operating frequency band of the actuator;

to better control the required stiffness and excursion of moving parts with limited mechanical friction that results in distortion, the top lid and bottom plate can have thin film permanent magnets of the same polarities with the thin film permanent magnets attached to the upper and lower flux collectors, thus creating electro-magneto stiffness, rather than mechanical stiffness which could eliminate the need for any compliant element at the top and bottom.

In accordance with features of this invention, there are no bearings, no through shafts, no guide bolts or sliding between moving parts, thus unlike the prior art, reduced distortion is experienced.

In accordance with additional features of the invention, an inner electronic circuit controls the shape of the force output spectrum, thus without using mechanical parts, this actuator can be used for both narrow-band and broad-band applications, namely, in the case of automotive vehicles, it can be used for both engine vibration attenuation as low as the idle frequency through high frequency noise attenuation. BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating preferred embodiments and are not to scale. The drawings are not to be construed as limiting the invention.

FIG. 1 is a schematic diagram of an exemplary embodiment of the vibration attenuation system using electronic and electromagnetic actuator, in accordance with the invention.

FIG. 2 shows a cross-sectional view of the actuator and its unique components that is also in accordance with the invention.

FIG. 3 describes the preferred embodiment of the electromagnetic actuator of the invention when mechanical springs are used in place of the magnetic-film springs .

FIGS. 4A and 4B describe a top plan view and cross-sectional view respectively of the conical spider made of fabric molded into the nylon with special top and bottom edges for attachment to a top lid and bottom plate .

FIG. 5 presents harmonic distortion that is experienced based on operating prior art electromagnetic actuators, a major shortcoming that is reduced by this invention. FIG. 6 shows a peaky transfer function exhibited by the prior art, which is not ideal for different applications, this shortcoming is also reduced by this invention.

FIG. 7 shows mechanical communication and vibration energy transfer between an electromagnetic actuator and the structure.

FIG. 8 describes the concept of combined pseudo-feedforward and feedback control used to represent mathematical and computational logic imbedded in 16.

FIG. 9 presents a block diagram for adaptive pseudo feedforward feedback control system.

FIG. 10 describes an internal feedback control for this invention embodiment around the actuator which provides virtual damping.

FIG. 11 illustrates internal block diagram for automatic sensing to create electronic damping in the actuator of embodiment of this invention.

DETAILED DESCRIPTION OF THE PREFERED EMBODIMENTS

Referring to Figs. 1, 2, 3, 4A and 4B for a general overview, a preferred embodiment of the invention includes a new vibration attenuation actuator 21 that exhibits reduced harmonic distortion. This vast improvement in harmonic properties is achieved through the frictionless design of the actuator. Furthermore, the preferred embodiment of the vibration attenuation system has a control system 16 and inner loop electronics 15 that incorporates an adjustable, active, non-mechanical, damping using internal feedback. This provides an ability to electronically tune the system and allows it to have a flat transfer function in one application, and as peaky a frequency response as is needed in certain other applications, and/or operating conditions.

Efficiency and linearity of electromagnetic actuators are directly related to the quality and efficiency of flux collection and steering used and to the symmetry of the resulting magnetic field. By using a first or magnetic flux collector 10 and a second or magnetic flux collector 4 in a complementary double-cupping design in conjunction with a magnet 6, the preferred embodiment of this invention generates a symmetric magnetic field around and through a drive coil or coils 8 and provides an effective actuator with linear characteristics .

Reduced friction operation is achieved by utilizing symmetrically angled supports or spiders, which in a preferred design (Figs 4A and 4B) are akin to conical bellows 7 that have very large radial rigidity with very low axial stiffness. This unique characteristic of the spiders provides central rigidity. That rigidity, combined with the magnet and flux collector design, enables the actuator to maintain a more uniformly constant radial gap width between the flux collectors 4, 10 and coil 8. The high radial stiffness of the spiders 7 maintains a more constant gap width. The low axial stiffness of the spiders allows the actuator mass to move freely along its intended direction of motion.

To provide a great deal of flexibility in the design and operation of the actuator 21 for different applications, axial magnetic stiffeners 2 (Fig. 2) and/or helical springs 25 (Fig. 3) , or optionally elastomeric springs (not shown) are included in the preferred embodiment. This unique combination for creating axial stiffness for resonant actuators is introduced for the first time with the present invention.

Now describing the preferred embodiment in greater detail, FIG. 1 shows an overall schematic of a vibration attenuation system installed in an example of a typical application. The application includes excitation source 20, e.g. engine or other rotating machines. The excitation source 20 is attached to a structure 13 through a mounting device 17. The excitation source 20 causes structure 13 to vibrate and transfers this vibration to a variety of substructures 18, which could cause both vibrations sensed by sensor 14 or structure-borne noise sensed by sensor 19. A predetermined combination of sensors, such as for example vibration sensors 14, noise sensors 19 and feedforward sensors 22, are strategically located throughout the subject object and/or environment. A control system 16, such as designed according to our patent numbers 5,418,858; 5,564,537; 5,629,986, and other pending patent applications, that uses feedforward, feedback and combined feedforward/ feedback control schemes, receives sensor information from, for example, vibration sensor 14 and noise sensor 19. The control system 16 then, in real time, calculates appropriate signals to send to inner loop electronics 15, if used. Inner loop electronics 15 then, derives a drive signal for electromagnetic actuator 21.

FIG. 2 illustrates an embodiment of the electromagnetic actuator 21. In this embodiment, a permanent magnet 6 is attached by bonding, encapsulation, fasteners, or other attachment means, within a first or upper flux collector 10 and a second, or lower flux collector 4. This combination of flux directing collectors 10, 4 and magnet 6 form an inertial mass 24 of the actuator 21. The upper and lower flux collectors 10, 4 each have a base wall 26 and a sidewall 28 extending outwardly therefrom. Therefore, the flux collectors 10,4 are in the shape of large cups or bowls and, as indicated above, are formed from a ferrous material. The lower flux collector 4 fits within the sidewall of the cup formed by the upper flux collector 10. The magnet 6 preferably fits within both of the cups formed by both upper and lower flux collectors 10, 4.

The magnet 6 is centered or axially aligned within, and attached to, an inner surface of the base of both flux collectors 10, 4. In this embodiment the cup formed by the flux collector 10 is installed upside down and the cup formed by the lower flux collector 4 is installed right side up. Since the magnet 6 is centered or axially aligned within and attached to inner surfaces of both flux collectors 10,4, the lower flux collector 4 is also centered or received in an axially aligned manner within the upper flux collector 10. An annular or radial gap 26 is formed between the sidewalls of the upper and lower flux collectors 10, 4. The upper flux collector 10 collects and redirects the magnetic flux associated with one pole of the magnet 6 and the lower flux collector 4 collects and redirects the flux associated with the other pole of the magnet 6. The two flux collectors 10, 4 cooperate to direct the flux in an even and symmetric manner across the annular gap 26.

The upper flux collector 10 and therefore the entire inertial mass 24 is suspended from a support surface, such as, for example lid 11. The lower flux collector is similarly attached to a second support surface, such as, for example, bottom plate 5. The flux collectors 10, 4 are attached to and thereby suspended from their respective support surfaces 11, 5 by support members or conical spiders 7.

Referring now to Figs. 4A and 4B, in the preferred embodiment, each spider 7 is formed from a conical bellows 42. An inner attachment ring 46 is used to secure the spider to one of the flux collectors 10, 4. An outer attachment ring 44 is used to secure or attach the spider to a support surface, such as for example lid 11 or bottom plate 5. It is possible to use other spider designs that achieve the objectives of high radial stiffness and low axial stiffness, for example, using a planar shape design, and still remain within the scope of invention. The illustrated spider design provides a beneficial flexibility in a direction of inertial mass 24 motion (up and down in Fig. 4B) , while providing a beneficially high degree of stiffness in a direction perpendicular to the direction of inertial mass 24 motion. This stiffness limits the inertial mass 24 from moving side to side and therefore maintains a substantially constant separation distance between the flux collectors 10, 4 and coils 8. This fixed gap or substantially constant separation, in turn, has a beneficial impact on actuator harmonics, linearity, and other operational characteristics.

Referring once again to Fig. 2, a coil former 9 is attached to a support surface such as, for example, the bottom plate 5. The coil former 9 can hold a single or multiple coils 8 depending on the intended power source and power requirements of the application. The coil 8 and therefore at least part of coil former 9 are positioned within the annular or radial gap 26 that is formed between the upper and lower flux collectors 10. 4. The coil 8, magnet 6, and flux collectors 10, 4 form an efficient electromagnetic circuit.

Any kind of permanent magnet 6 can be used, as long as it is well suited to the operating environment of the actuator. Preferably, the magnet 6 is inexpensive and unaffected by temperature extremes, shock, and vibration. The preferred embodiment of the invention uses thin, solid, ceramic cylindrical magnets. These magnets are relatively immune to environmental extremes, are available in high volume, and are therefore relatively inexpensive.

The first support surface (for example lid 11), a second support surface (for example bottom plate 5), and a separator (for example shell 3), combine to frame or house the actuator. An attachment means, such as bolt 1 can be used to mechanically attach the actuator to the structure 13. Ribs 12 are used to provide the necessary strength and rigidity to the lid 11 for attachment to the structure 13 without increasing the passive weight of the actuator .

Although not as preferred as using a spring, magnetic films 2 can provide magneto-stiffness characteristics and limit the excursion of the upper and lower cups. Particularly, the magnetic films are repelled by magnetic films secured to the flux collectors. Like poles are disposed in proximal relation to magnetically suspend the magnet and the flux collectors between the lid and the bottom plate. These magnetic films can be used in conjunction with or be replaced by other biasing members such as, mechanical, elastomeric or pneumatic springs, which can also be used to alter the actuators frequency response characteristics.

In the preferred embodiment of Fig. 3 an actuator is shown that uses mechanical coil springs 25 to apply axial restoring forces, instead of the magnetic films 2 of Fig. 2. As in the case of the magnetic films, the springs 25 keep the inertial mass centered in the housing. Any kind of suitable low friction or preferably low friction compliant element, including elastomeric elements, can be used in addition to or instead of coil springs 25. The elements are selected, in part, on the operating characteristics of the actuator 21 such as the frequency response of the actuator 21. For example, stiffer elements produce peaks or resonances at higher frequencies .

In substantially all other respects, the preferred embodiment of Figure 3 is similar to that described above in Figure 2. Accordingly like numerals refer to like elements and new components are identified by new numerals. The housing receives the permanent magnet and the flux collectors 4, 10 and the springs 25 interposed between the lid and the upper flux collector, and the bottom plate and the lower flux collector, respectively, suspend the assembly in the housing. The coil 8 is secured to the housing and positioned in the radial gap between the flux collectors. It will be appreciated, however, that the embodiments of Figures 2 and 3 illustrate first and second flux collectors, although a single flux collector in proximity or operative relation with the permanent magnet could be used without departing from the scope and intent of the present invention. The spiders 7 still provide the desired radial stiffness and axial flexibility in this actuator assembly.

James Clark Maxwell established the fundamental equations of electromagnetic theory that describe operational principles of all electromagnetic actuators and shakers in 1873. These include:

V E (/ /) + — B (r, = 0 Faraday' s Induction Law dt

V xH (r, t) + — D (r,t)= j(r,t) Ampere' s Circuit Law dt

V - B (r, t) = 0 Gauss' Law for Magnetic Field

V - -D (r, t) -P(r, t) Gauss' Law for Electric Field

When a charged particle, q, travels with a velocity v and is subjected to a magnetic field B, it would experience a force F expressed by the following relationship : F = q v x B

If an electric field is also added, then the force experienced by the particle is:

F=q(E+ιxB)

When a wire with a length of 1 is placed in a magnetic field, there will be a force on the wire as current flows through it. This is the principle of operation of every electric motor. The resulting force is:

F= (lxB)

Assuming electric and magnetic fields are perpendicular and the wire is circular coil with radius r, and n turns, then the resulting force is:

F=2πrnIB

This is the principal equation relating current, magnetic field and force generation. As shown in FIG. 7, the preferred embodiment of the electromagnetic actuator 21, can be represented by a lumped parameter system which is rigidly attached to the structure. Where mass M represents the inertial mass 24 of the combined mass of magnet 6, and upper and lower flux collectors 10, 4. The combined effects of magnetic films or springs 2 or mechanical springs 25 can be lumped into the K of FIG. 7. If the spider 7 introduces any damping, then C in FIG. 7 represents it.

Vibrations from structure 13 would be transmitted to the actuator shell 3 causing coil former 9 and coil 8 while carrying electrical current provided by inner loop electronics 15 to be moved through the magnetic field which in turn will generate a magnetic force. Based on the Newton's law of motion, the following is resulted:

-_c- , d²x _ dx _T/r f =M — - + C — + Kx dt² dt

In order to completely cancel the vibration of the structure 13 at the attachment point of the actuator, appropriate current should be sent to the actuator coil, such that the resulting electromagnetic force is equal and 180 degrees out of phase with that of f m. Thus, the following is resulted:

d²x dx M^+C— + Kx = 2πrnBl(t) dt² dt

Thus the transfer function between the required current and displacement of mass M is :

X(s) 2πrnB 2πrnB /M

I(s) MS² + Cs + K s² + 2 ξ ω_nS + ω_n ²

or in the frequency domain we obtain

X(jω) _ 2πrnBM

!(jω) (ω_N ² - ω²) + j2 ξ ωω_n

and for acceleration we obtain: ω

2πrn B / M

X (j ω ) ω I(jω ) ω

+ J2 ξ ω

Therefore, for a given structural vibration expressed in terms of acceleration of the structure at the attachment, the required current through the coil of actuator is obtained from the following:

Zl(jω)= ZX(jω)= Tan - 180^c

Either in frequency domain or S-domain, I(s) is the desired current required to cancel vibrations. However, because vibration attenuation at certain locations on the structure or substructures is more important than others, this invention incorporates feedback sensors 14 and/or 19 located at strategic locations and utilizes control logic, presented in FIG. 8, embedded within controller 16. As shown, to be able to attenuate both repetitive and random vibration excitations of the structure 13 both pseudo feedforward and feedback control signals are used. The feedforward sensor 22 provides advance information about the incoming vibration excitations, thus software running in the controller 16 anticipates what needs to be done ahead of time. Feedback or performance sensors 14, 19, describe how well the system is attenuating vibrations at the desired locations. Since exact advance information about the excitation source is not always accessible, controller 16 can use pseudo feedforward control software to predict and approximate feedforward type information. The goal of combined pseudo feedforward and feedback is to minimize:

where, Qi represents ith desired location, w represents frequency range of interest and Qi is the ith spectrum order of the excitation that needs to be emphasized more in the optimization. If there are significant variations in the characteristics of transmission paths, then feedforward control, feedback control or both can be made adaptive, as shown in FIG. 9.

In order to identify the optimal location for actuators, using predefined performance sensor locations, operational deflection shape analysis is used, where the amount of power in a given structure response spectrum due to the excitations is determined.

Assuming m response points are identified, then let x be the linear spectrum for each m measurements of x(t) with length N.

By calculating cross power spectrum, the following matrix is obtained:

[G _XX ] = [X ]^* [X ]

Where * denotes complex conjugate transpose operation. Performing the eigenvalue problem on the cross spectrum Gxx frequency by frequency, yields the eigenvalues [Gxx] and the eigenvectors [ v] which take on distinct values at each frequency.

[^GχxHΦxχ]M^*

From this analysis, mode shapes, modal participation with respect to the input excitations can be used to identify best locations for positioning actuators .

In order to avoid the distortion shown m FIG. 5 and 6 that plagues prior art actuators, the actuator 21 is designed to avoid mechanical friction or damping. Therefore, the actuator's 21 transfer function relating force and displacement is :

This means the actuator 21, if driven without the special features of the control system 16 and inner loop or internal feedback 15, will have a very peaky response and it will resonate at its natural frequency. To eliminate this problem while not introducing any mechanical friction, internal feedback loop 15 uses active electronics, to provide virtual damping, thus a flat actuator response can be developed. FIG. 10 shows the actuator with internal feedback. The resulting transfer function is:

X 1/M

₂ B 2 s H s+ω„

M

Thus, to add this virtual damping, a measure of velocity is needed. This invention does not use a velocity sensor; rather it takes advantage of the inverse problem, namely,

X I υ s

Ms"+K Ms'+K

or

Thus for a given actuator design where all parameters n, r, B, M, are determined apriori, by measuring current one determines velocity. To measure current, a known resistor can be in series with the actuator, the voltage across that resistor will be proportional to the current. Thus, an embodiment may include inner loop electronics 15, as shown in FIGURES 1 and 11, which introduces virtual damping and thus the ability to provide a variety of actuator frequency response spectra, namely narrow band, flat broad band, etc.

The invention has been described with reference to an exemplary embodiment. Obviously, modifications and alterations will occur to others upon a reading and understanding of this specification. It is intended to include all such modifications and alterations in so far as they come within the scope of the appended claims or the equivalents thereof.

Claims

WHAT IS CLAIMED IS:

1. A vibration attenuation actuator comprising: a housing receiving a magnet therein; a flux collector mounted in the housing for limited movement relative thereto in response to a control signal and operatively housing the magnet; a coil assembly secured in the housing and having a portion cooperating with the flux collector to generate an appropriate force to nullify the vibration; and a flexible mounting member for securing the flux collector to the housing.

2. The vibration attenuation actuator of claim 1 wherein the flux collector is cup-shaped.

3. The vibration attenuation actuator of claim 1 wherein the flux collector includes first and second flux collectors .

4. The vibration attenuation actuator of claim 3 wherein sidewalls of the first and second flux collectors are disposed in an axially overlapping, radially spaced relation that defines a gap that receives the coil assembly.

5. The vibration attenuation actuator of claim 4 further comprising a second flexible mounting member for securing the second flux collector to the housing.

6. The vibration attenuation actuator of claim 4 further comprising a first biasing member interposed between the housing and the flux collectors to limit excursions of the flux collectors relative to the housing.

7. The vibration attenuation actuator of claim 6 wherein the first biasing member is a spring interposed between the housing and one of the flux collectors.

8. The vibration attenuation actuator of claim 6 wherein the first biasing member is a magnetic film on the housing.

9. The vibration attenuation actuator of claim 6 further comprising a second biasing member interposed between the housing and one of the flux collectors.

10. The vibration attenuation system of claim 4 wherein the flexible mounting member has a conical shape.

11. The vibration attenuation system of claim 4 wherein the flexible mounting member has a planar shape.

12. The vibration attenuation system of claim 1 wherein the flux collector has a base wall and a sidewall extending outwardly therefrom and a gap that receives the coil assembly.

13. The vibration attenuation actuator of claim 4 wherein the flexible mounting member further comprising: a first conical bellows; and a second conical bellows.

14. The vibration attenuation actuator of claim 1 included in a vibration control system for reducing the vibration or noise of an environment, the vibration control system comprising: at least one sensor strategically mounted in the associated environment; and a control system receiving signals from the sensor and generating a set of control signals.

15. The vibration control system of claim 14 wherein the at least one sensor includes: a vibration sensor; a noise sensor, and a feedforward sensor.

16. The vibration control system of claim 15 wherein the at least one feedforward sensor includes at least one pseudo-feed forward sensor.

17. The vibration control system of claim 15 wherein the control system includes both feedback and feedforward control for attenuating both random and repetitive vibrations.

18. The vibration control system of claim 17 wherein at least one of the feedback control and the feed forward control is adaptive.